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CEMENT AND CONCRETE
BY
LOUIS CARLTON SABIN, B. S., C. E.
Assistant Engineer, Engineer Department, U. S. Army ; Member of thk
Ambuioan Society of Civil Engineebs
SECOND EDITION, BE VISED AND ENLARGED
NEW YORK
McGRAW PUBLISHING COMPANY
1907
COPYHIOHTED, 1904, 1907
BY
L. C. SABIN
Stanbope prece
r. H. O/LSON COMPAN\
■ OS roN, U.S.A.
PREFACE
That the use of cement has outstripped the literature on
the subject is evidenced by the number and character of the
inquiries addressed to technical journals concerning it. This
volume is not designed to fill the proverbial "long felt want,"
for until within a few years the number of engineers using
cement in large quantities was quite limited. These American
pioneers in cement engineering, under one of whom the author
received his first practical training in this line, needed no formal
introduction to the use and properties of cement; their knowl-
edge was born and nurtured through intimate association and
careful observation.
To-day the young engineer frequently finds a good working
knowledge of cement one of the essentials of success, and the
gaining of this knowledge by experience alone is likely to be
too slow and expensive, judged by twentieth century standards.
In fact, the variety and extent of the uses to which cement is
applied, and the knowledge concerning its properties, have of
late increased so rapidly that even the older engineer, whose
practice may have directed his special attention along other
channels for a few years, finds it difficult to follow its progress.
One who wishes only a catechetical reply to any question
that may arise concerning cement and its use will be somewhat
disappointed in these pages; on the other hand, he who would
devote special attention to the subject must, of course, go far
beyond them. The author has attempted to take a middle
course, avoiding on the one hand a dogmatic statement of facts,
and on the other too detailed and extended series of tests, but
giving, where practicable, sufficient tests to support the state-
ments made, and endeavoring to show the connection between
theory and practice, the laboratory and the field.
The original investigations forming the basis of the work
were made in connection with the construction of the Poe
Lock at St. Marys Falls Canal, Michigan, under the direction
iv PREFACE
of the Corps of Engineers, U. S. Army. To the late General
O. M. Poe, the Engineer officer in charge of the district at that
time, and to Mr. E. S. Wheeler, his chief assistant engineer,
may be credited a very large share of the value of the results
obtained, .since the accomplishment of a series of experiments
of so comprehensive a character was made possible only through
the broad views held by them as to the value of thorough tests
of cement.
The author wishes to express his appreciation of the courtesy
of General G. L. Gillespie, Chief of Engineers, U. S. A., in grant-
ing permission to use the data collected, and of the kindness
of Major W. H. Bixby in presenting a request for this per-
mission.
When not otherwise stated, the tables in the work are con-
densed from the results of the above mentioned investigations.
In supplementing this original matter, much use has been made
of the experiments of others as published in society transac-
tions, technical journals, etc., to all of whom credit has been
given in the body of the work.
If this attempt to place in one volume a connected story of
the properties and use of cement serves to make the road to
this knowledge a little less devious than that followed by the
writer, the latter will be rewarded.
L. C. S.
Sault Ste. Marie, Mich.
January 3, 1905.
CONTENTS
PART I. CEMENT: CLASSIFICATION AND
MANUFACTURE
CHAPTER I. DEFINITIONS AND CONSTITUENTS
Paob
Art. 1. General Classification of Hydraulic Products .... 1
Art. 2. Lime: Common and Hydraulic 3
Art. 3. Portland Cement 4
Art. 4. Slag Cement 7
Art. 5. Natural Cement 10
CHAPTER II. MANUFACTURE
Art. 6. Manufacture op Portland Cement 12
Materials. — Wet Process. — Dry Process. — Semi-dry Process. —
Details of the Manufacture: Burning, Grinding. — Sand-Cement.
Art. 7. Other Methods of Manufacture of Portland .... 35
Art. 8. Manufacture of Slag Ce.ment 36
Art. 9, Manufacture op Natural Cement 37
PART 11. PROPERTIES OF CEMENT AND
METHODS OF TESTING
CHAPTER III. INTRODUCTORY
Desirable Qualities. — Uniform Methods of Testing 42
CHAPTER IV. CHEMICAL TESTS
Art. 10. Composition and Chemical Analysis 45
CHAPTER V. THE SIMPLER PHYSICAL TESTS
Art. 11. Microscopical Tests. — Color 50
Art. 12. Weight per Cubic Foot, or Apparent Density .... 51
Art. 13, Specific Gravity, or True Density 53
vi • CONTENTS
CHAPTER VI. SIFTING AND FINE GRINDING
Paqb
Art. 14. Fineness 59
Importance of Fineness. — Sieves. — Methods. — Specifications.
Art. 15. Coarse Particles in Cement 66
Effect on Weight, Time of Setting and Tensile Strength.
Art. 16. Fine Grinding 72
Effect on Weight, Time of Setting and Tensile Strength.
CHAPTER VII. TIME OF SETTING AND SOUNDNESS
Art. 17. Setting of Cement 79
Process of Setting. — Rate. -.— Variations in Rate.
Art. 18. Constancy of Volume 90
Causes of Unsoundness. — Tests. — Discussion of Methods. — Hot
Tests for Natural Cements. — Conclusions.
CHAPTER VIII. TESTS OF THE STRENGTH OF CEMENT
IN COMPRESSION, ADHESION, ETC.
Art. 19. Tests in Compression and Shear 103
Art. 20. Tests of Transverse Strength 104
Art. 21. Tests of Adhesion and Abrasion 106
CHAPTER IX. TENSILE TESTS OF COHESION
Art. 22. Sand for Tests 109
Value of Tests of Sand Mortars. — Uniformity in Sand. — Com-
parison of DiflEerent Kinds. — Tests with Natural Sand. — Fineness.
Art. 23. Making Briquets Ill
Proportions. — Consistency. — Temperature. —Gaging: Hand and
Machine. — Methods. — Amount of Gaging. — Form of Briquets.
— Molds. — Molding. — Briquet Machines. — Approved Methods
of Hand Molding. — Marking the Briquets.
Art. 24. Storing Briquets 131
Time in Air before Immersion. — Moist Closet. — Water of Im-
mersion. — Storing in Air; in Damp Sand.
Art. 25. Breaking the Briquets 137
Testing Machines. — Clips. — CIij>-breaks. — Comparative Tests of
Clip>s. — Requirements for a Perfect Clip. — Form Recommended.
— Rate of Applying Tensile Stress. — Treatment of Results.
Art. 26. Interpretation of Tensile Tests of Cohesion .... 151
CHAPTER X. RECEPTION OF CEMENT AND RECORDS
OF TESTS
Art. 27. Storing and Sampling 158
Storage Houses. — Percentage of Barrels to Sample. — Method of
Taking and Storing the Sample.
CONTENTS vu
Paob
Art. 28. Records of Tests 160
Value of Records. — Marking Specimens. — Records at St. Marys
Falls Canal.
PART III. THE PREPARATION AND PROP-
ERTIES OF MORTAR AND CONCRETE
CHAPTER XI. SAND FOR MORTAR
Art. 29. Character of the Sand 168
Shape and Hardness of the Graias. — Siliceous vs. Calcareous
Sands. — Slag Sand. — Sand for Use in Sea Water.
Art. 30. Fineness of Sand 173
Relation Volume and Superficial Area. — Effect of Fineness.
Art.- 31. Voids in Sand 176
Conditions Affecting Voids: Shape of Grains; Granulometric Com-
position. — Effect on Tensile Strength of Mortar. — Moist Sand.
Art. 32. Impurities in Sand 182
Art. 33. Conclusions. — Weight and Cost of Sand 184
CHAPTER XII. MORTAR: MAKING AND COST
Art. 34. Proportions of the Ingredients 186
Capacity of Cement Barrels. — Equivalent Proportions by Weight
and Volume. — Richness of Mortars. — Effect of Pebbles. — Con-
sistency.
Art. 35. Mixing the Mortar 191
Hand Mixing. — Machine Mixing.
Art. 36. Cost of Mortars 193
Ingredients Required. — Tables of Quantities. — Estimates of
Cost. — Tables of Cost of Portland and Natural Cement Mortars.
CHAPTER XIII. CONCRETE: AGGREGATES
Art. 37. Character of Aggregates 200
Proper Materials. — Screenings in Broken Stone. — - Foreign
Ingredients.
Art. 38. Size and Shape of Fragments and Volume of Voids . 202
Conditions Affecting Voida. — Effect on Strength of Concrete. —
Gravel vs. Broken Stone.
Art. 39. Stone Crushing and Cost of Aoorexjate 208
Breaking Stone by Hand. — Stone Crushers. — Cost of Aggregate.
— Examples.
viii CONTENTS
CHAPTER XIV. CONCRETE MAKING: METHODS
AND COST
Paob
Art. 40. Phopoktions of the Ingredients 214
Theory of Proportions. — Determination of Amount of Mortar
Required. — Aggregates Containing Sand. — Required Strength.
Art. 41. Mixing Coitcrete by Hand 217
Hand vs. Machine Mixing. — Method of Hand Mixing; Number of
Men and Output; Examples.
Art. 42. Concrete Mixing Machines 221
General Classification. — Description of Machines. — Basis of
Comparison.
Art, 43. Concrete Mixing Plants and Cost of Machine Mixing 226
Art. 44. Cost of Concrete 232
Ingredients Required for a Cubic Yard, — Examples of Actual Cost.
CHAPITER XV. THE TENSILE AND ADHESIVE STRENGTH
OF CEMENT MORTARS AND THE EFFECT OF VARIA-
TIONS IN TREATMENT
Art. 45. Tensile Strength op Mortars op Various Compositions
AND Ages 241
Art. 46. Consistency of Mortar and Aeration of Cement . . 246
Art. 47. Regaging of Cement Mortar 250
Art. 48. Mixtures of Cement with Lime, Plaster Paris, etc. . 257
Mixtures of Portland and Natural. — "Improved" Cement. —
Ground Quicklime with Cement ; Slaked Lime ; Plaster of Paris. —
Conclusions,
Art. 49. Mixtures of Clay and Other Materials with Cement 267
Effect of Powdered Limestone, Brick, etc.; Sawdust; Terra Cotta.
Art, 50, Use of Cement Mortars in Freezing Weather .... 274
Effect of Frost on Set Mortars. — Effect of Salt; Heating Materials;
Consistency; Fineness of Sand. — Conclusions.
Art. 51. The Adhesion of Cement 284
Adhesion between Portland and Natural. — Adhesion to Stone and
Other Materials, — Effect of Consistency ; Regaging ; Character of
Surface of Stone, — Effect of Plaster of Paris. — Adhesion to Biick;
Effect of Lime Paste. — Adhesion to Rods of Iron and Steel,
CHAPTER XVI, COMPRESSIVE STRENGTH AND MODULUS
OF ELASTICITY OF MORTAR AND CONCRETE
Art, 52, Compressive Strength op Mortars 302
Ratio of Compressive to Tensile Strength.
Art. 53. Concretes with Various Proportions of Ingredients . 305
Effect of Consistency; Amount and Richness of Mortar; Methods
of Storage.
CONTENTS be
Page
Art. 54. Concretes with Various Kinds and Sizes of Agoregates 312
Art. 55. Cinder Concrete and Effect of Clay 316
Art. 56. Modulus of Elasticity of Cement Mortar and Concrete 320
CHAPTER XVII. THE TRANSVERSE STRENGTH AND
OTHER PROPERTIES OF MORTAR AND CONCRETE
Art. 57. Transverse Strength 327
Transverse Strength of Mortars Compared to Tensile and Com-
pressive Strength. — Richness of Mortar; Consistency. — Transverse
Tests of Concrete Bars: Variations in Mortar Used; Consistency;
Mixing ; Aggregate ; Screenings. — Deposition in Running Water.
— Use in Freezing Weather.
Art. 58. Resistance to Shear and Abrasion 342
Art. 59. Expansion and Contraction of Cement Mortar, and
the Resistance of Concrete to Fire 345
Change in Volume during Setting. — Coefficient of Expansion of
Mortar and Concrete. — Fire-Resisting Quahties of Concrete. —
Aggregate for Fireproof Work.
Art. 60. Preservation of Iron and Steel by Mortar and Concrete 350
Action of Corrosion. — Tests of Effect of Concrete.
Art. 61. Porosity, Permeability, etc 354
Porosity. — Permeability. — Waterproof Mortars and Concretes. —
Washes for Exteriors of Walls. — Efflorescence. — Pointing Mortar.
— Cements in Sea Water.
PART IV. USE OF MORTAR AND CONCRETE
CHAPTER XVIII. CONCRETE: DEPOSITION
Art. 62. Timber Forms or Molds 365
Sheathing. — Lining. — Posts and Braces.
Art. 63. Deposition of Concrete in Air 372
Transporting, Depositing, Ramming. — Rubble Concrete. — Fin-
ish; Plastering ; Facing; Bushhammering ; Colors for Concrete Finish.
Art. 64, Placing Concrete under Water 383
Laitance. — Tremie, Skip, etc. — Depositing in Bags ; Cost. —
Block System: Molds; Cost.
CHAPTER XIX. CONCRETE-STEEL
Art. 65. Monier System 395
Art. 66. Wi'nsch, Melan, .\nd Thacher Systems 397
Art. 67. Other Systems of Concrete-Steel 399
Hennebique, Kahn, Ransome, Roebling, Expanded Metal.
Art. 68. The Strength of Combi.vations of Concrete and Steel 401
X CONTENTS
Paob
Art. 69. Beiams with Single Reinforcement 404
Formulas for Ck)nstant Modulus Elasticity; for Varying Modulus.
— Excessive Reinforcement. — Tables of Strength.
Art. 70, Beams with Double Reinforcement 417
Art. 71. Shear in Concrete-Steel Beams 419
CHAPl'ER XX. SPECIAL USES OF CONCRETE: BUILD-
INGS, WALKS, FLOORS, AND PAVEMENTS
Art. 72. Buildings 424
Roof ; Floor System ; Columns. — Building Forms. — N. Y. Build-
ing Regulations.
Art. 73. Walks 434
Foundation; Base; Wearing Surface; Construction; Cost.
Art. 74. Floors of Basements, Stables, and Factories .... 440
Art. 75. Pavements and Driveways 442
Pavement Foundations. — Concrete Wearing Surface. — Construc-
tion. — Example.
Art. 76. Curbs and Gutters 445
Art. 77. Street Railway Foundations 447
CHAPTER XXI. SPECIAL USES OF CONCRETE (Continued):
SEWERS, SUBWAYS, AND RESERVOIRS
Art. 78. Sewers 450
Methods and Cost. — Forms.
Art. 79. Subways and Tunnel Lining 457
Waterproofing. — Subways. — Tunnels in Firm Earth ; in Soft
Ground; in Rock. — Examples; Methods; Cost.
Art. 80. Reservoirs: Linings and Roofs 467
Details of Construction. — Groined Arch. — Forms. — Examples ;
Cost.
CHAPTER XXII. SPECIAL USES OF CONCRETE (Continued):
BRIDGES, DAMS, LOCKS, AND BREAKWATERS
Art. 81. Bridge Piers and Abutments and Retaining Walls . 478
Bridge Piers ; Steel Shells. — Repair of Stone Piers. — Retaining
Walls and Abutments: Coping; Rules for Use of Concrete.
Art. 82. Concrete Piles 485
Building in Place. — Concrete-Steel Piles: Molding; Driving.
Art. 83. Arches * 488
Design ; Centers ; Construction ; Finish and Drain^e. — Examples
and Cost.
Art. 84. Dams 498
Concrete vs. Rubble. — Quality of Concrete. — Construction. -
Examples.
Art. 85. Locks 502
Methods of Building. — Examples.
Art. 86. Breakwaters 507
CONTENTS xi
CHAPTER XXIII. CONCRETE BUILDING BLOCKS: THEIR
MANUFACTURE AND USE
Paok
Art. 87. General Methods op Manufacture 512
Tamped Blocks; Machine; Curing. — Pressed Blocks. — Poured
Blocks.
Art. 88 Materials and Finish 520
Proportions. — Special Forms. — Freezing. — Waterproofing.
Art. 89. Cost and Laying 526
Volume. — Weight. — Cost. — Laying. — Comparison of Concrete
Block and Brick.
Art. 90. Strength of Concrete Blocks and Building Regula-
tions 533
APPENDIX I.
Uniform Methods of Testing suggested by the Am. Soc. C. E. Committee.
APPENDIX II.
Standard Specifications for Cement adopted by the American Society for
Testing Materials.
APPENDIX III.
Methods of Analysis suggested by the New York Section of the American
Chemical Society.
PART I
CEMENT
CLASSIFICATION AND MANUFACTURE
CHAPTER I
DEFINITIONS AND CONSTITUENTS
Art. 1. General Classification of Hydraulic Products
1. The use of a cementitious substance for binding together
fragments of stone is older than history, and it is known that the
ancient Romans prepared a mortar which would set under
water. So far as our present knowledge of cement manufac-
ture is concerned, however, the credit of demonstrating that a
limestone containing clay possessed, when burned and ground,
the property of hardening under water, is due to Mr. John
Smeaton, who announced this as the result of his experiments
made in 1756 in seeking a material with which to build the
Eddystone Lighthouse. After this discovery by Smeaton nearly
sixty years elapsed before M. Vicat gave the true explanation
of this action, namely, that the lime during burning combined
with the silica to form silicate of lime, the essential ingredient
of hydraulic limes and cements.
In 1796, Parker, of London, obtained a patent for the manu-
facture of a cement from septaria nodules, and aptly named his
product "Roman Cement." In 1824, Joseph Aspdin of Leeds,
England, patented a process of manufacture of "Portland
Cement."
2. The cements in general use in the United States to-day
are of two kinds, Portland cements and natural cements, and in
what follows our attention will be directed almost entirely to
these two products.
Common limes were formerly used largely in engineering
construction, but have of late been almost entirely superseded,
2 CEAfENT AND CONCRETE
for this purpose, by cements. Since the hardening of lime
mortar depends on the absorption of carbonic acid from the
atmosphere, these limes are sometimes called "air limes," while
the hydraulic products which set under water are. for a similar
reason, styled "water limes." Hydraulic limes, though playing
an important role in foreign countries, are not manufactured or
used to any extent in the United States. The European prod-
uct known as "Roman" or "Vassy" cement, somewhat re-
sembles our natural cement, but is usually inferior to the Ameri-
can article. Our chief interest in these products, which are used
only abroad, is to know what relation they bear to the cements
with which we are familiar. The following classifications are
selected as being authoritative:
3. The conferences of Dresden (1886) and Munich (1884) on
Uniform Methods of Testing for Materials of Construction, clas-
sified the hydraulic products as follows: —
(1) Hydraulic limes: made by roasting either argillaceous or
siliceous limestones. They slake partially or wholly on the ad-
dition of water.
(2) Roman cements: made from argillaceous limestones hav-
ing a large proportion of clay. They do not slake by the addi-
tion of water and hence must be mechanically ground to powder.
(3) Portland cements: obtained by burning to the point of
insipient vitrification either hydraulic limestones or mixtures of
argillaceous materials and limestones, and afterward grinding
the product to fine powder.
(4) Hydraulic gangues: natural or artificial materials which
do not harden alone, but which furnish hydraulic mortars when
mixed with quicklime.
(5) Pozzolana cements produced by an intimate mixture
of powdered hydrate of lime and finely pulverized hydraulic
gangues.
(6) Mixed cements: the products of intimate mixtures of
manufactured cement with certain materials proper for such a
purpose. Mixed cements should always be designated as such
and the materials entering into the composition should be stated,
but it may be added parenthetically that- these things are
seldom done.
4. MM. Durand-Claye and Debray divide cements into six
classes, namely, ( 1 ), Grappier cements — obtained by grinding
LIME 3
the pieces of hydraulic lime which do not slake; (2), quick-set-
ting (Vassy) cements — formed by burning very argillaceous
limestones at a low temperature; (3), natural Portland cements,
or those cements made from natural rock which correspond to
artificial Portland in character; (4), mixed cements; (5), arti-
ficial Portlands; and (6), slag cements.
M. H. LeChatelier, an eminent French authority, divides
hydraulic products into four classes, namely : ^ — Portland ce-
ments, hydraulic limes, natural cements, and mixed cements. He
subdivides the third class, natural cements, into quick-setting,
slow-setting and grappier cements, and includes natural Port-
lands among the slow-setting natural cements. Slag cements,
which are put in a separate class by MM. Durand-Claye and
Debray, are included in "mixed cements" by M. LeChatelier.
5. Prof. I. 0. Baker gives a classification that is better
adapted for use in this country than any of the above.* He
divides the products obtained by burning limestone, either pure
or impure, into lime, hydraulic lime and hydraulic cements. He
then sub-divides cement into Portland, Rosendale (preferably
called natural) and Pozzolana.
Art. 2. Lime; Common and Hydraulic
6. Common lime is the product obtained by burning a pure,
or nearly pure, carbonate of lime. On being treated with water
it slakes rapidly, evolving much heat and increasing greatly in
volume. It is now seldom used in engineering construction and
will not be considered further.
7. Prof. M. Tetmajer has thus defined hydraulic limes: Hy-
draulic limes are the products obtained by the burning of argil-
laceous or siliceous limestones, which, when showered with water,
slake completely or partially without sensibly increasing in
volume. According to local circumstances, hydraulic limes may
be placed on the market either in lumps, or hydrated and pul-
verized. The following table gives a classification of hydraulic
limes according to M. E. Candlot ' who states that the first
' "Tests of Hydraulic Materials," by H. LeChatelier. Trans. Am. Inst.
Mining Engrs., 1893.
* "Masonry Construction," p. 48.
' "Ciments et Chaux Hydrauliques," par E. Candlot.
4 CEMENT AND CONCRETE
class is seldom used for important work and that the fourth
class is quite rare.
TABLE 1
Classification of Hydraulic Limes. E. Candlot
Class.
Per Cent,
of Clay In
Limestone.
Per Cent,
of Silica
and Alumi-
na in Fin-
ished Prod-
uct.
Hydraulic
Index, or
Ratio of
Silica and
Alumina to
Lime.
Approx.
Time to
Set,
Days.
Feebly Hydraulic Lime
Ordinary " *'
Real " "
Eminently " "
5 to 8
8 to 15
16 to 19
19 to 22
9 to 14
14 to 24
24 to 30
30 to 33
.10 to .16
.16 to .31
.31 to .42
.42 to .50
16 to 30
10 to 16
6 to 9
2 to 4
Hydraulic limes should be burned slowly, and at such a tem-
perature that sintering does not take place. The best hydraulic
limes have a composition very similar to that of Portland cement.
The comparatively low temperature at which they are burned
permits them to slake on the addition of water. They gain
strength much more slowly than cements.
Having considered the classification of hydraulic products as
a whole, we may proceed to the discussion of Portland and nat-
ural cements, the hydraulic products which have by far the
greatest importance here, and the only varieties which will be
taken up in detail in the present work.
Art. 3. Portland Cement
8. Definition. — Although questions may still arise as
to whether a given product is entitled to the name Portland
cement, yet ideas are now pretty well crystallized as to what
shall be included under that title. All authorities agree that
the proportion of the constituents must be confined within
comparatively narrow limits, that certain ingredients must be
present only in small quantities, if at all, that the calcination
must be carried to a point just short of vitrification, and that
the resulting product must be ground to a fine powder.
Two definitions recently adopted are worthy of special men-
tion: That of the Association of German Portland Cement
Manufacturers specifies that the raw materials shall be inti-
mately ground, then calcined at a clinkering temperature and
reduced to proper fineness; the product is to contain not less
PORTLAND CEMENT 5
than 1.7 parts lime by weight to each part silica + alumina +
iron oxide, and its specific gravity is to be not less than 3.10.
The definition adopted by the Board of Engineer Officers of
the United States Army in 1901 is as follows : "By a Portland
cement is meant the product obtained from the heating or cal-
cining up to incipient fusion of intimate mixtures, either natural
or artificial, of argillaceous with calcareous substances, the
calcined product to contain at least 1.7 times as much lime,
by weight, as of the materials which give the lime its hydraulic
properties, and to be finely pulverized after said calcination,
and thereafter additions or substitutions for the purpose only
of regulating certain properties of technical importance to be
allowable to not exceeding 2 per cent, of the calcined product."
It is noticed that neither definition attempts to specify the
kind of raw materials which shall be used in the manufacture.
The first definition requires the raw materials to be ground
before calcination, while the second does not. The question is
sometimes raised as to whether a product prepared from a
rock which, as it occurs in nature, contains the proper propor-
tions of silica and lime shall be designated Portland cement.
In the United States, cements are made from rocks having so
nearly the correct proportions of ingredients that one part of a
ledge may require addition of lime and another part may need
more clay to correct the mix. If some of the rock is found to
be correct in composition without addition of either lime or
silica it is preeminently suited to the manufacture of Portland
cement. To insure uniform composition and burning, however,
preliminary grinding is a wise precaution if not absolutely essen-
tial. A definite understanding of what is meant by the term
Portland cement will prove a very great convenience, and may
save law suits, but the engineer must not neglect to ascertain
whether a given product has the properties he desires under
whatever name it may appear on the market, and if imposed
upon he should not blame the definition.
9. COMPOSITION. — As a result of an extended series of
experiments M. Le Chatelier first published in 1887* his conclu-
sion that the essential composition of Portland cement consists
of (1) tricalcium silicate, 3CaO, SiO,; (2) tricalcium aluminate,
' Annales des Mines, 1887 and 1893. Jour. Soc. Chem. Ind., Mar. 31,
1891, p. 256.
6 CEMENT AND CONCRETE
3CaO, Alj Oa; and (3) "a fusible calcium silico-aluminate whose
chief function is that of a flux during burning to promote the
necessary chemical reactions." It is generally agreed that the
first component named is the real cementitious ingredient in
Portland cement, while Le Chatelier states that the tricalcium
aluminate is "mainly active during setting, contributing some-
what to the subsequent hardening." In accordance with this
theory he considered that the basic constituents should not
exceed three equivalents of the acid constituents, and proposed
the following formulas:
CaO + MgO <
= 6,
and
CaO + MgO > _
SiO^ - {Al,03 + Fe,03)
in each case the quantities in the formulas being the chemical
equivalents of the substances, not weights.
If weights be substituted for equivalents in the first equation
it is found that the silica and alumina should not be less than
.56 the lime and magnesia. This ratio of the acid and basic
constituents is known as the hydraulic index. In the light of
recent investigations, however, this index is of limited value.
One reason for this is that in the above formulas magnesia is
considered of equal basic value with lime, while Dr. Erdmenger
and other authorities have shown that magnesia does not
replace lime in Portland cement mixtures. Later researches, and
notably those of Messrs. Newberry, * have also shown that the
lime and alumina probably combine to form the dicalcite alumi-
nate, 2CaO,Al208, their conclusions being stated as follows: —
"First — Lime may be combined with silica in the propor-
tion of 3 molecules to 1, and still give a product of practically
constant volume and good hardening properties, though harden-
ing very slowly. With 3^ molecules of lime to 1 of silica the
product is not sound, and cracks in water.
"Second. — Lime may be combined with alumina in the
proportion of 2 molecules to 1, giving a product which sets
quickly, but shows constant volume and good hardening prop-
erties. With 2^ molecules of lime to 1 of alumina the product
is not sound."
» Jour. Soc. Chem. Ind., Nov., 1897.
SLAG CEMENT 7
Since to produce a sound cement all the lime must be com-
bined, it follows from the above that the total lime must be
sufficient only to furnish 3 molecules to each molecule of silica
and 2 molecules to each molecule of alumina. As the mole-
cular weights of lime, silica, and alumina are 56.1, 60.4, and
102.2 respectively, the maximum permissible amount of lime
by weight would be 2.78 times the silica, plus 1.1 times the
alumina. This does not take account of the ferric oxide, FegOg,
present. The action of the latter has not been determined
with certainty, but Professor Newberry considers it should be
omitted from the calculation.
Expressing the above statement as a formula we shall have
<
per cent lime = 2.78 (% silica) + 1.1 (% aJumina),
or,
»u 1 t ,u 1- -A *• per cent lime
the value of the hme-acid ratio = ^ -^ ~ — rrf .. . ,^ — ; : — r »
2.78 (% sihca) + 1.1 (% alumina) /
must not exceed one.
The mean value of this ratio for twenty representative Ameri-
can brands is found to be .915. Values of .76 and .99 respec-
tively were given by two well-known German brands.
The above discussion is based upon the theory evolved by sev-
eral authorities from the results of experiment. Much doubt has
been thrown upon this theory, however, by the recent investiga-
tions of Messrs. Day and Shepard in the Geo-physical Laboratory
of the Carnegie Institution. In the Journal of the American
Chemical Society for September, 1906, Messrs. Day and Shepard
presented their results, showing that the only definite compounds
of lime and silica are the metasilicate CaOSiO, and the orthosih-
cate CajSiO^. This discovery will necessitate the modification of
present accepted theories, but as yet the investigations have not
been carried far enowgh to lead to definite conclusions.
10. The analyses of thirty-two brands of Portland cement,
most of them of American manufacture, given in Table 2, are
selected from various sources and illustrate the proportions
obtaining in commercial products.
CEMENT AND CONCRETE
TABLE 2
Analyses of Portland Cement
Raw Materials.
1 Limestone and Shale . . .
2 Cement Rock and Limestone
3 Chalk and Clay
4 Cement Rock and Limestone
5 Marl and Clay . . .
6 Marl and Clay . . .
7 Cement Rock . . .
8 Limestone and Clay .
9 Limestone and Clay .
jQ ( Limestone and Clay
I Limestone and Marl
1 1 Cement Rock and Limestone
12 Marl and Clay
13 Marl and Clay
14 Cement Roclc and Limestone
15 Limestone and Clay ....
16 Limestone and Clav ....
17 Chalk and Clay .......
18 Cement Rock and Limestone
19 Marl and Clay
20 Marl and Clay
21 Cement Rock and Limestone
22 Cement Rock and Limestone
23 Limestone and Clay ....
24 Marl and Clay
25 Marl and Clay
26 Cement Rock
27 Cement Rock and Limestone
28 Slag and Limestone . .
29 Cement Rock and Limestone
30 Marl and Clay
31 Clay and Waste Limestone
32 Chalk and Clay
Pro-
CICSS.
s
D
W
D
W
S
D
D
D
D I
Wf
D
S
w
D
D
D
W
D
W
W
D
D
D
W
W
D
D
D
D
W
W
W
Brand.
Alpena
Alpha
Alsens
Atlas
Brunson
Buckeye
Buckhorn
Catskill
Diamond
Dyckerhoff
Edison
Empire
Germania
Giant
Hudson
Iron Clad
K. B. & S.
Lehigh
Medusa
Medusa
Nazareth
Northampton
Old Dominion
Omega
Peerless
Red Diamond
Saylors
Universal
Vulcanite
Wolverine
Wyandotte '
Yankton
Location.
Alpena, Mich.
Alpha, N. J.
Itzehoe, Germany.
Northampton and Cop-
lay, Pa.
Bronson, Mich.
Harper, Ohio.
Manheim, W. Va.
Smiths Landing, N. Y
Middle Branch, Ohio.
Amoeneburg, Ger.
New, Village, N. J.
Warners, N. Y.
Lehrte, Germany
Egypt, Pa.
Hudson, N. Y.
Glens FaUs, N. Y.
England.
Allentown, Pa.
Bay Bridge, Ohio.
Syracuse, Ind.
Nazareth, Pa.
Stockertown, Pa.
Craigsville, Va.
Jonesville, Mich.
Union City, Mich.
Demopolis, Ala.
Coplay, Pa.
Chicago, 111.
Vulcanite, N. J.
Cold water, Mich.
Wyandotte, Mich.
Yankton, S. Dak.
Note. — Wet process is indicated by W ; dry, by D ; and semi-wet,
byS.
Art. 4. Slag Cement
11. Slag cement is manufactured to a considerable extent
in Europe and is beginning to assume some importance in the
United States. It is a pozzolana cement in which the silica
ingredient is supplied by blast furnace slag. Pozzolana
cements have been defined as "products obtained by intimately
and mechanically mixing, without subsequent calcination, pow-
dered hydrates of lime with natural or artificial materials which
generally do not harden under water when alone, but do so
SLAG CEMENT
TABLE 2 (continued)
Analyses of Portland Cement
No.
SiO,.
AUO3.
FejO,.
CaO.
MgO.
Na,0,
K,0.
SO3.
H,0&
L088.
1
20.26
8.62
2.71
63.22
2.34
1.34
0.76
2
22.62
8.76
2.66
61.46
2.92
1.52
3
24.90
8.00
3.22
59.38
0.38
0.50
0.98
2.16
4
21.30
7.65
2.85
60.95
2.95
1.15
1.81
1.41
5
22.90
6.80
3.60
63.90
0.70
1.10
0.40
0.60
6
21.30
6.95
2.00
62.30
1.20
0.98
4.62
7
23.72
6.85
3.41
61.54
1.44
1.72
0.90
8
23.44
6.35
3.99
63.21
1.15
1.22
9
21.24
7.85
4.14
63.22
0.28
0.68
1.11
1.32
10
19.35
7.00
4.50
63.75
5.40
11
20.14
7.51
3.33
62.71
2.34
1.64
12
22.04
6.45
3.41
60.92
3.53
2.25
13
21.14
6.30
2.50
66.04
1.11
2.91
14
23.36
8.07
4.83
58.93
1.00
6.50
0.50
2.46
15
21.60
9.27
3.80
61.78
1.27
1.53
16
21.50
10.
50
63.50
1.80
0.40
1.50
0.80
17
19.75
7.48
5.01
60.71
1.28
0.75
0.97
3.38
18
22.26
9.
49
62.46
2.65
1.56
19
23.20
7.03
2.41
64.19
0.97
2^20
20
22.06
4.80
1.66
65.44
3.82
0^90
21
19.06
7.47
2.29
61.23
2.83
1.41
1.34
4.52
22
21.18
7.03
2.41
63.06
2.05
23
21.20
7.90
2.82
63.14
2.40
l'37
24
22.24
7.26
2.54
64.96
2.26
0.41
0.33
25
20.30
7.60
3.40
62.60
1.70
1.70
1.30
1.10
26
20.54
8.55
3.84
63.85
0.66
1.34
27
21.25
8.25
4.21
61.25
1.50
2.00
1.38
28
23.62
8.21
2.71
61.92
1.78
1.32
0.52
29
21.08
7.86
2.48
63.68
2.62
1.25
30
21.22
7.51
3.83
63.75
0.82
1.58
1.02
31
23.20
8.00
2.40
62.10
2.00
0.90
0.80
32
22.00
7.74
4.61
59.50
0.90
1^20
0.80
when mixed with hydrates of lime (such materials being pozzo-
lana, Santorin earth, trass obtained from volcanic tufa, furnace
slag, burnt clay, etc.), the mixed product being ground to ex-
treme fineness."*
Slag cement somewhat resembles Portland in its properties,
but is more like some of the natural cements in its constituents,
while in the manner of occurrence of these constituents and in
the method of manufacture it is quite different from either of
these classes.
' "Report of Board of Engineers on Steel Portland Cement," Washing-
ton, 1900.
10 CEMENT AND CONCRETE
12. As this cement is a mixture of lime and pozzolanic
materials, its value depends largely upon its extreme fineness
and the intimate mixture of the ingredients. Its specific gravity
is low, about 2.7 to 2.8, and it sets very slowly, although the
setting may be hastened by the addition of certain substances
such as caustic soda. On account of the sulphide present,
most slag cements are not suited to use in air, as they crack
and soften in this medium; neither are they suitable for use in
sea water, nor in freezing weather, but when mixed with two
or three parts of sand and kept constantly wet with fresh water,
they give quite satisfactory results.
Slag cement has an approximate composition of silica, 20 to
30 per cent., alumina, 10 to 20 per cent., and lime, 40 to 50 per
cent. It usually contains calcium sulphide, the amount some-
times reaching three or four per cent. The characteristic green-
ish tint which slag cements exhibit when they harden in water
is due to this ingredient, as is the odor of hydrogen sulphide
sometimes given off by a briquet when broken, especially if it
has hardened in sea water. Some slag cements have also quite
a percentage of magnesia.^
Art. 5. Natural Cement
13. Natural cement, as its name implies, is made from rock
as it occurs in nature. Argillaceous limestones or argillo-
magnesian limestones, having the proper proportion of clay,
magnesia and lime, may be used for the production of natural
cement. The burning is not carried so far as in the manufac-
ture of Portland cement, and the resulting product is of lighter
weight and usually quicker setting, though some natural ce-
ments are quite slow setting. The properties of these cements,
coming from different localities, vary greatly. In fact, it is
difficult to distinguish some natural cements from Portland,
and they may be considered to grade into the natural Portlands.
Light burning in manufacture, light weight per cubic foot, and
slower rate of acquiring strength, may be considered the dis-
tinguishing characteristics from a physical point of view.
' For an excellent resume of the qualities and distinguishing character-
sties of slag cements, the reader is referred to "Report of Board of Engi-
neers on Steel Portland Cement as used in United States Lock at Plaque-
mine, La." Washington, 1900.
NATURAL CEMENT
11
14. Analyses. — Table 3 gives the results of a number of
analyses of natural cement, compiled from various sources.
TABLE 3
Analyses of Natural Cements
Bnuid.
Bonneville Improved
Round Top ....
Cumberland ....
Double Star ....
Black Diamond . .
Fern Leaf ....
Hulme
Star
Norton
Rosendale ....
Brooklyn Bridge . .
Hoffman
Lawrence
Newark & Rosendale
Clarks Utica . . .
Milwaukee ....
Mankato
James River . . .
Howard
Union Akron . . .
Akron Star ....
Buffalo
30.
28.
28
23.
22.
26.
25.
23.
27.
26.
30.
27.
22.
28.
34.
23.
27.
49.
22.
17.
20.
16.
10.36
10.20
10.12
6.99
8.24
6.28
7.85
5.96
7.28
5.
7.75
7.14
10.
5.88
5.10
6.33
7.06
11.
7.23
7.61
6.22
4.40
Iron
Oxide.
2.60
8.80
4.42
5.97
2.14
1.00
1.43
2.16
1.70
89
2.11
1.80
43
3.60
1.00
1.71
1.86
29
3.35
2.00
2.56
2.00
Lime.
52.12
44.48
49.60
53.96
42.31
45.22
44.65
41.28
37.59
45.30
34.49
35.98
34.54
27.00
30.24
36.08
37.00
25.15
48.18
36.83
40.64
39.20
0.21
1.00
3.76
7.76
5.39
9.00
9.50
15.39
15.00
17.06
17.77
18.00
21.85
30.00
18.00
20.38
22.63
13.77
15.00
25.09
25.80
26.52
0.50
2.82
4.24
4.25
1.98
7.96
4.00
6.80
3.63
6.16
5.27
3.64
1.85
"a o I
='.07
7.00
2.66
7^86
7.04
2.49
3.64
2.98
4.43
3.52
4.84
7.07
2.46
0.26
3.66
1.47
6.80
The localities indicated by letters are as follows : —
A, Siegfried, Pa. ; B, Hancock, Md. ; C, Cumberland, Md. ; D, Fort Scott,
Kan. ; E, F, and G, Louisville, Ky. ; H, Speeds, Ind. ; I, K, L, M, and N, Ulster
Co., N. Y.; J, Howes Cove, N. Y.; O, Utica, 111.; P, Milwaukee, Wis.; Q, Man-
kato, Minn.; R, Locker, Virginia; S, Cement, Ga. ; T and U, Akron, N. Y.;
V, Buffalo, N. Y.
Comparing these analyses with those given for Portland
cement in Table 2, it is seen that natural cements have a higher
percentage of silica, about the same amount of alumina, and a
much smaller content of lime, than have Portlands. Many natu-
ral cements have a large percentage of magnesia, but the mag-
nesia and lime together of natural cements usually do not equal
the percentage of lime in Portlands. In other words, the
hydraulic index is usually higher than in Portland cements.
CHAPTER II.
MANUFACTURE
Art. 6. The Manufacture of Portland Cement
15. HISTORICAL. — It is said that as early as 1810 a patent
was obtained in England for the manufacture of an artificial
product by calcining a mixture of carbonate "of lime and clay.
This, however, was not called cement, and it was not until 1824
that Joseph Aspdin, of Leeds, England, in obtaining a patent
for the manufacture of a similar material, called his product
"Portland Cement." This name was probably suggested by
the fact that the color of the hardened product resembled that
of a Hmestone quarried on the Island of Portland. The industry
was introduced into Germany about thirty years later, and has
since grown to very substantial proportions in both of these
countries, as well as in France, Austria, and Russia.
David O. Saylor was the first to manufacture Portland
cement in the United States, at Coplay, Pa., about 1872, and
works were established at that point in 1875. These were
soon followed by other factories in Pennsylvania and Indiana,
and at present cement is successfully manufactured in nearly
half of the states of the Union, the production having steadily
increased.
16. MATERIALS REQUIRED. — The materials requisite for the
manufacture of Portland cement are carbonate of lime and
silica. The former may be in the form of limestone, chalk or
calcareous marl, while the latter may be in the form of clay or
shale, or it may occur as an impurity in the limestone, as in
the so-called "cement rock" of the Lehigh Valley region. The
proportions required for ordinary materials are 25 per cent,
clay or shale to 75 per cent, carbonate of lime. The cement
rock worked in the Lehigh Valley region usually requires the
addition of 10 to 20 per cent, of purer limestone, though in
some deposits a small percentage of clay must be added. Some
of the chief requisites for all Portland cement materials are
12
PORTLAND CEMENT 13
that they shall be of uniform composition, and that they shall
not contain such proportions of sulphur and magnesia as to
give injurious percentages of these ingredients in the finished
product. (§§ 50 and 52.) Formerly authorities did not agree
as to whether the alumina in the clay or shale was an unwel-
come constituent for Portland cement manufacture, but it is
now generally agreed that the alumina, as well as the iron
oxide, is useful as a flux in burning and that the dicalcic alumi-
nate formed plays a role in the setting of the cement, and
probably also in the subsequent hardening. If the ratio of
silica to alumina and iron oxide falls below 2.5, however, the
cement is likely to be too quick setting, while if this ratio
exceeds 3 the mix is likely to be too refractory.
In regard to physical characteristics neither material should
contain flinty nodules, difficult to crush and of a different com-
position from the main body of the rock. Marl should be as
free as possible from hard shells, since their presence necessi-
tates more careful preliminary grinding. Clay should not
contain any considerable amount of coarse sand, for although
silica is the most useful constituent of the clay it must not be
in this insoluble form. In the highly argillaceous limestone
known as cement rock, the mixing of the proper materials has
been partially accomplished in nature, and with this material
there is somewhat less danger from poorly proportioned mix-
tures than in dealing with practically pure carbonate of lime
and clay or shale. The soft materials, marl and clay, have an
advantage because they are usually of fine grain and easily
reduced and mixed, but since they are so hygroscopic the ex-
pense of drying them may easily offset this advantage.
A few analyses of materials suitable for Portland cement
manufacture are given in Table 4.
17. The materials for Portland cement manufacture, lime-
stone, marl, clay, shale, etc., are widely disseminated, but the
suitability of a certain locality for successful commercial manu-
facture depends upon the manner of occurrence of these requi-
sites. In England the clay is dug from the old beds of the
Thames and Medway Rivers, and chalk, which occurs in abun-
dance, furnishes the carbonate of lime in most cases, though
limestone is sometimes used. In Germany both chalk and
marl are used; the chalk being a soft white marl similar to the
14
CEMENT AND CONCRETE
deposits in this country, and the marl a "more or less hard
limestone rock containing clay." In the United States both
limestones and marls are used. The most important cement
producing region in the United States is in the Lehigh Valley,
where an argillaceous limestone is employed. The factories
using marl are situated in New York, Ohio, Indiana, Michigan,
etc., where the marl is found overlying or in the vicinity of beds
of clay or shale suitable for cement making. In the Lehigh
Valley region many advantages are combined. The cement
rock of that locality has nearly the correct composition for
Portland cement manufacture, requiring usually a small admix-
ture of pure limestone. The supply of this rock is almost
inexhaustible, the managers of the works have had long
experience in the production of cement from these materials,
and a market for the product is near at hand.
TABLE 4
Analyses of Portland Cement Materials
Portland
q
o
d
H2O
Material.
Cement
State.
SiO,.
CaO.
^
d
CO2.
and
Company.
^
fe
S
CO
43.3
Loss
Limestone . .
Atlas
Mo.
0.4
0.4
54.9
0.2
Limestone . .
Hudson
N. Y.
1.0
1.0
54.3
Tr
42.7
Limestone . .
Alpena
Mich.
3.1
L2
52.1
1.1
42.1
Limestone . .
Northampton
Penn.
5.6
2.4
50.5
1.0
39.6
Limestone . .
Diamond
Ohio
9.5
2.512.7
45.7
1.0
1
4
37.0
White Marl
Newaygo
Mich.
0.8
0.1
53.6
0.9
43.1
White Marl
Peninsular
Mich.
0.2
0.8
51.6
1.3
40.5
5.7
White Marl .
Sandusky
Ind.
1.8
1.2
49.6
1.3
0
9
40.4
4.2
Chalk ....
Western
Sci. Dak.
4.1
4.5
51.0
0
5
40.0
Cement Rock .
Penn.
Penn.
9.5
15.7
4 J
7.9
45.2
39.6
2.3
1.7
38.1
33.2
Cement Rock .
Northampton
Cement Rock .
Penn
Ind.
22.2
55.3
7.2 0.9
10.2 3.4
35.5
9.1
2.2
5.7
30.3
7.1
Clay ....
Sandusky
Clay ....
Peninsular
Mich.
61.4
25.1
1.4
6.6
Shale ....
Alpena
Mich.
57.4
23.3
4.3
3.2
0
4
8.2
Shale ....
Western
So. Dak.
58.0
22.8
1.8
1.8
1
3
12.1
Shale ....
Lehigh
Ind.
59.6
19.1|7.6
0.3
2.3
4.7
Shale ....
Hudson
N. Y.
62.4
27.6
0.3
1.5
8.0
Information collected from following sources : —
Cement Materials and Industry, Bulletin 243 U. S. Geol. Survey, by E. C.
Eckel; Annual Reports, State Geological Surveys; and direct from com-
panies.
Deposits of cement materials are of value only when the
limestone or marl, and clay or shale, are found in large quanti-
PORTLAND CEMENT 15
ties and near together, when the physical character of the
materials is such as to render them easy of comminution and
mixture, when coal or other suitable fuel may be had at low
prices, and when the market is not too far removed.
The following estimate of the relative quantities of cement
made in the United States in 1903 from the several classes of
materials has been made by Mr. E. C. Eckel :^
Argillaceous limestone and pure limestone 56 f)er cent.
Marl and clay . 14 "
Soft limestone and clay 3 "
Hard limestone and clay 28 "
18. GENERAL DESCRIPTION OF PROCESSES. — The essen-
tials of any method of Portland cement manufacture are that the
materials shall be correctly proportioned, very finely comminuted
and thoroughly mixed; that the mixture shall be carefully
burned to just the proper degree of calcination, and the result-
ing clinker ground to extreme fineness. How these essentials
can be best accomplished depends upon the character of the
raw materials and the cost of fuel and labor, so that the de-
tails of the method vary with the materials used and with the
local conditions.
In order that the proportions may be accurately determined,
it is usually necessary to dry one or both of the raw materials.
The ingredients may be ground separately and afterward mixed,
though with certain materials the grinding and mixing may be
done at the same time. In this mixing, a large amount of
water may be used, giving a thin slurry, as in the wet process;
a moderate amount of water may be employed, as in the semi-
dry process, giving a mix of the consistency of puddled clay; or
the dry process may be employed, in which after the materials
are once dried no water is added before the burning of the
clinker. The burning may be accomplished in any one of
several styles of kilns, although the advantages of the rotary
kiln are so great that it has nearly superseded all other styles
in this country. The grinding is a simple mechanical problem,
to secure the required degree of fineness with least cost.
19. THE DRY PROCESS. — This method of manufacture is
especially adapted to such materials as cement rock, lime-
* "Cements, Limes and Plasters," Wiley and Sons, New York, 1905.
16 CEMENT AND CONCRETE
stone, and shale, that must be ground before they can be mixed,
although it is occasionally employed for marl and clay. In
order that the proper chemical combinations shall take place
in the kiln it is essential that the material shall be finely ground
as well as thoroughly mixed. The rock is obtained by the
ordinary quarry methods and is usually conveyed to the plant
in cars which dump into the hoppers of large rock crushers.
From these the crushed rock is passed to driers, usually of the
rotary type. The drying of the raw materials serves two pur-
poses— it prepares the rock for further reduction in mills in which
wet material would tend to clog, and it facilitates the proper
weighing of the two ingredients to form the mixture.
After drying, the two raw materials may be combined, and
the continuation of the process is on the mix so formed. This,
however, is not the universal practice; some manufacturers com-
bine the two ingredients even before crushing, others mix them
before they pass to the drier, while others keep them separate
until after the second or third stage of the preliminary grind-
ing. The second stage of the grinding is frequently accom-
plished in ball mills or in kominuters, although rolls and grind-
ers of the impact type are also employed. The final mixing and
grinding preliminary to burning is usually done in tube mills,
this type being considered most efficient for fine materials.
From the tube mills the mix passes directly to the rotary
kilns for burning. As the clinker falls from the lower end of
the rotary, a small stream of water is allowed to trickle over it.
This partially cools the clinker, renders it somewhat easier of
reduction, and probably makes the cement somewhat slower
setting. After further cooling, either in coolers or in sheds,
the clinker is ground, usually by two or more stages, ball mills
or rolls being frequently used for the first reduction, and tube
mills or Griffin mills for the final grinding. Before the grind-
ing is completed a proportion of calcium sulphate is added to
regulate the rate of setting of the cement. The ground cement
is stored in large bins and packed as desired in cloth or paper
sacks, or in barrels, for shipment.
20. THE WET PROCESS. — Although water may be used to
facilitate the mixing of materials that require previous grind-
ing, the wet process is particularly adapted to such raw mate-
rials as are easily acted upon by water. The present types of
PORTLAND CEMENT 17
grinding machinery are such that it is no longer necessary to
add water to assist in the mixing and grinding, and the use
of the wet process is now confined almost entirely to the treat-
ment of the softer raw materials, marl and clay, which, as
they occur in nature, contain a considerable percentage of
water. This contained water constitutes, from an economic
standpoint, one of the serious problems in treating this class of
materials, because of the expense involved in evaporating it
at some stage of the process; it is, however, not without its
advantages. Aside from the fact that the mixing is more
readily accomplished in the wet state, the grinding is compar-
atively easy, the slurry may be pumped from point to point
instead of being carried and elevated, and the correction of the
mix, by adding the desired amount of over-clayed or over-
limed slurry, is more readily accomplished than is the case with
the dry process.
The marl and clay are commonly loaded in cars by dredges
or steam shovels and drawn to the works by locomotive, cable
or horses. The stones and sticks are removed from the marl
by separators if necessary, and as a first step the clay is usually
dried and ground to facilitate the calculation of the mix. The
marl is sometimes passed through a pug mill before mixing with
the clay, though more frequently the weighed amount of dried
clay is added during the first pugging. Here sufficient water
is added so that the slurry may be pumped to tube mills in
which the final grinding of the raw materials is usually accom-
plished. Either just before or just after passing the tube mill
the slurry is caught in vats where it is kept agitated either by
compressed air or mechanical agitators. Here the mix is
analyzed and corrected if need be by adding the proper amount
of an over-clayed or over-limed slurry kept in separate tanks
for this purpose. As the slurry is pumped to the rotaries it
usually contains as much as fifty per cent, water, which must
be evaporated in the upper end of the kiln by the gases from
the burning which is taking place in the lower half.
It may be remarked here that in the older form of the wet
process, developed in England and formerly used here to some
extent, the thin slurry was run into "backs" or shallow reser-
voirs to settle, the clear liquid was run off, and the slurry, after
further drying, was cut into bricks to be artificially dried and
18 CEMENT AND CONCRETE
then burned in dome kilns. The adaptation of the rotary kiln
to the burning of wet materials has put the original form of
the wet process out of use in this country.
The fuel consumption in the wet process is appreciably
greater than in the case of a dry mixture. The cooling and
grinding of the clinker do not necessarily differ from the corre-
sponding operations in the dry process.
21. THE SEMI-DRY PROCESS. — During the first thirty
years of Portland cement production in the United States this
process of manufacture was prominent, but the successful
development of the rotary kiln has rendered it almost obsolete,
and the modern cement mill is designed to use one of the pro-
cesses already outlined with such minor modifications as the
designer may consider advantageous.
With wet materials the semi-dry process consists in forming
the mix into bricks after it has passed a pug mill, drying the
bricks artificially either in drying ovens or in a portion of the
burning kilns, and then burning the bricks in a stationary kiln.
With dry materials, sufficient water is added after the prelimi-
nary grinding to permit pugging the mixture and making the
bricks. The method is not only expensive in labor account,
but considerable loss results from imperfect burning, and the
uniform results attainable by the methods already described
are not usually realized with this process.
22. DETAILS OF THE MANUFACTURE: Preparation and Mix-
ing of the Raw Materials. — The main points in the prepara-
tion of the raw material for burning are: First, the proper
amount of each ingredient must enter the mixture; second, the
materials must be reduced to an extremely fine state of divi-
sion; and third, the mechanical mixing must be as perfect as
possible. Unless the ingredients are dried, the first require-
ment is not easy to fulfill, especially with marl and clay, as the
absorptive power of the materials renders it difficult to properly
apportion them. The wet process, which thus offers the greatest
difficulty in the first proportioning, furnishes a ready oppor-
tunity for correction of the mix before burning. With the dry
process the variation in the analysis of the materials is the
most frequent cause of variations in the mix, and should be
carefully watched. A slight error in proportions is apparently
less dangerous with argillaceous limestone, such as cement rock.
PORTLAND CEMENT 19
than with pure limestone and clay, and for this reason some of
the works producing cement from this material are prone to
become careless in proportioning and correcting the mix.
Referring to §9 we have seen that the per cent, of lime
must not exceed 2,78% silica +1.1% alumina. In practice,
however, the percentage of lime in the mix seldom exceeds 2.7 x
percent, silica -t{per cent, alumina; and the percentage of lime
in the finished cement is still less, because of the loss of some
volatile products and the addition of a small amount of ash
and kiln lining in the process of burning.
To illustrate the method of calculating a cement mixture
let us consider that we have a Lehigh cement-rock of composi-
tion Ume 37.5; silica 17.0; alumina 7.0, and purer limestone
of composition lime 51.5; silica 4.5; alumina 0.5, and desire to
determine the proper proportions in which to mix them.
Using the above formula as fixing the proper proportion of
lime we have.
For 100 parts Cement Rock:
FABTS
Lime required by Silica 17.0 x 2.7 = 45.9
Lime required by Alumina = 7.0
Total Lime required for 100 parts rock = 52.9
Lime in rock 37. 5
Lime to be added 15.4
In one part of Limestone:
PABTS
Lime required by Silica . 045 X 1 . 7 = . 0765
Lime required by Alumina = . 0050
Total Lime required for 1 part limestone . 0815
Lime contained in 1 part limestone .515
Excess of Lime in 1 part limestone . 4335
15 4
Then to 100 parts cement rock we must add ' = 35.5 parts limestone.
. ^ooo
More than three-fourths of the Portland cement manufac-
tured in the United States is made from limestones, either pure
or argillaceous. These must be ground before they can receive
the required addition of clay, or of purer limestone, as the case
may be, and they are usually dried to facilitate the grinding
as well as to permit of determining the correct proportions of
the ingredients for the mix. The first step in the process with
20
CEMENT AND CONCRETE
hard materials is to pass them through ordinary rock crushers.
These are commonly of the gyratory type and of large size.
Rolls and "dry pans" are also sometimes employed for the
softer limestones and shales. Rolls and ordinary rock crushers
are too familiar to need description here. A "dry pan" con-
sists of a cylinder 6 to 12 feet in diameter in which revolve two
heavy rollers. The rollers, being on opposite ends of a hori-
zontal shaft attached to a vertical axis, turn about the shaft
as well as revolve about the axis, the crushing being done
between the edges of the rollers and the floor of the pan. This
style of mill is also called an edge runner. The rock works to
the outside and is discharged through perforated plates. Edge
runners are not suited to reducing coarse lumps of very hard
material, but work well on clay and soft rock. A similar grinder
used on wet materials is called a "wet pan."
In the dry process the material passes from the rock crushers
to the driers. The rotary drier, the style in most common use,
resembles the rotary kiln; it is a cylinder about four or five
feet in diameter and about forty feet long, lined with brick,
and is set slightly inclined to the horizontal and revolves slowly
on rollers. The drier may be heated by the gases from the
burning kilns or by a separate furnace, the hot gases entering
at one end and escaping into the stack. The material is intro-
duced at the higher or stack end and works slowly to the lower
or furnace end. One style of drier, the Ruggles-Coles, has an
RUGGLES-COLES DRIER
inner cylinder, and the materials pass through the annular space
between the two, the products of combustion being forced first
through the inner cylinder and then back through the raw
material. The stack drier has also been used, in which the
CEMENT KILNS 21
material is fed at the top and is deflected by baffle plates as it
falls through the hot gases.
The logical time for mixing the ingredients would seem to be
immediately after they pass the driers, and this is usually done,
though in some cases the materials are not mixed until after
further reduction, while in a few mills the mixing precedes the
drying. The further grinding of the raw materials is usually
accomplished in two stages, a typical combination being ball
mills and tube mills, though Kominuters, Griffin, Kent, Wil-
liams, and Huntington mills are also employed. The thorough
grinding of the raw materials is of the greatest importance, not
only because of its effect on the quality of the product, but
because an extremely fine mix may be burned at a smaller
expense for coal. As the same styles of grinding machinery
are used in pulverizing the clinker they will be briefly described
under that head.
In the wet process, which is seldom used for materials other
than marl and clay, only the clay is dried. The grinding of
the clay may be accomplished in one of the forms of disinte-
grators, such as the Williams or Stedman mill, or in a dry pan
or edge runner, described elsewhere. After the addition of the
clay to the marl the further grinding or mixing is done in ordi-
nary pug mills, in wet pans, or in wet Griffin, ball and tube
mills. These mills are described under the head of grinding
(§§ 28 and 29). After thorough grinding the material is run
into tanks for correcting the proportions and here the thorough
mixing is completed by revolving paddles working in the tanks,
or by agitation caused by jets of compressed air allowed to
escape into the slurry.
23. STYLES OF KILNS. — The various styles of kilns in use
may be divided into four classes, namely: (1) Common dome
kilns, (2) Continuous kilns, (3) Chamber and ring kilns, and (4)
Rotary kilns. The Dome Kiln is the simplest type. The cham-
ber is usually egg-shaped. Cement-brick and coke are piled in
alternate layers, the use of the proper amount of the latter
requiring much skill, as it is a matter of experience. As the
draft in the kiln varies with the weather, this method of burn-
ing is more or less at the mercy of the winds. When the burn-
ing is complete, the kiln is allowed to cool before removing the
clinker, and thus much heat is lost, and the lining of the kiln
22 CEMENT AND CONCRETE
is destroyed by alternate heating and cooling. The amount of
underburned and overburned clinker is likely to be large. The
output is small, and fuel expense high. This style of kiln was
formerly used for Portland cement, but is now confined almost
entirely to burning natural cement and is then used as a con-
tinuous kiln, material being charged at the top as the clinker is
withdrawn at the bottom.
The Dietsch Kiln is one of the best examples of the second
type, or continuous kiln. The slurry, in the form of bricks, is
introduced at the base of the stack, into what may be called
the heating chamber. Below this there is a right angle with a
short horizontal section, over which the hot slurry is raked,
to fall into the burning chamber. The t^linker in the lower
part of the latter is cooled by the air entering through the grates,
while the slurry in the upper chamber is heated by the gases
from the burning zone. At intervals a portion of the clinker,
partially cooled, is removed at the bottom; this causes a general
settlement in the kiln and leaves a space at the top of the burn-
ing chamber, into which the dried clinker from above is raked,
and more fuel added. This kiln uses small coal for fuel and is
more economical than the dome type.
The distinguishing feature of the Schofer kiln is the con-
traction of the dome at the point where combustion takes
place, concentrating the draft at this point. The air entering
the shaft at the bottom cools the clinker already burned, while
the gases from the clinker burning in the central section serve
to dry the raw bricks above. Several kilns of this type are in
successful operation in this country.
24. Chamber Kilns are used largely in England with coke as
fuel. The gases from the kiln are made to pass over the slurry
spread on brick floors, the kiln proper being at one end of this
chamber and the stack at the other. These kilns are inter-
mittent, have a comparatively small output, and require con-
siderable labor.
The Hoffman Ring Kiln consists of a series of compartments
built around a large central stack. The chambers communicate
by means of flues in such a way that the smoke and hot gases
from one may be passed through other chambers before reach-
ing the chimney. The kiln may be either "up draft" or "down
draft," according to the direction in which the heat is drawn
ROTARY KILNS 23
through the chamber. The compartments are charged from
the sides, and when the moisture has been driven off from the
material in the chamber first fired, the gases from this chamber
are passed through the adjacent chambers, which have in the
meantime been filled with raw materials. Although this kiln
is economical of fuel if run continuously, much labor is re-
quired to charge and empty it. This type is not used in the
United States, though it has been employed to some extent
in Germany.
25. Rotary Kilns. — Although rotary kilns for other purposes
had been in use for some time, the first patent for a process of
manufacture of cement by their use was issued in 1877 to Mr.
T. R. Crampton. The method, apparently, did not pass beyond
the stage of laboratory experiment until 1885, when Frederick
THE BONNOT COMPANY ROTARY KILN
Ransome, of England, patented a rotary kiln, which, how-
ever, required many important modifications to make it a
success.
About 1888 Mr. J. G. Sanderson and Dr. Geo. Duryee made
some successful experiments with the rotary kiln for wet mix-
tures, and in the following year experiments were begun at the
works of the Atlas Portland Cement Co. under Mr. P. Giron,
which resulted in the construction of a practical kiln for burning
dry mixtures. Prof. Spencer B. Newberry, at about the same
time, perfected the rotary process for wet materials at Warners,
N. Y., and Sandusky, Ohio.
A rotary kiln as used for the burning of cement consists of
a steel cylinder from five to seven feet in diameter and sixty
feet or more in length. This cylinder rests on two sets of rol-
lers with its axis inclined to the horizontal about one foot in
twenty, and is revolved slowly by gearing. (See cut.) The
mixture to be burned is introduced at the upper or stack end
24 CEMENT AND CONCRETE
of the cylinder, while a jet of powdered coal, or sometimes of
fuel gas or oil, is injected at the lower end through a special
burner. As the cylinder revolves, the material works slowly
towards the lower end, the clinkering temperature being main-
tained, roughly speaking, throughout the lower twenty feet of
the kiln. This portion of the kiln must be lined with the most
fire-resisting brick; as the clinker acts upon fire brick lining
to form a fusible compound at the high temperatures required
in the burning, a coating of fused cement clinker is sometimes
beaten down upon the lining while it is still plastic; this adheres
to the brick and protects them somewhat from further injury.
The clinker as discharged from the lower end is in rough, green-
ish black, balls varying in size from a quarter inch to an inch
in diameter.
The dried and pulverized coal is fed through a special burner
supplied with a blast, the greater part of the air necessary for
combustion entering through openings in and around the hood
of the kiln. The burning may be controlled by the rate of
feeding the mix, the rate of revolution of the kiln, or the amount
of coal and air supply, the temperature being determined by
the appearance of the molten mass. The crowding of a kiln
to increase the output increases considerably the fuel cost per
barrel on account of the great quantity of air introduced which
must be heated.
While until recently the ordinary length of a rotary kiln
was 60 feet, it was realized that, especially for wet mixtures, a
greater length was economical, and recently a much advertised
plant has installed, among several other innovations, kilns
150 feet long, and these have shown such results that just now
a period of evolution to kilns of greater length seems to be
fairly inaugurated. While the results at different mills vary
greatly, and it is not easy to give a correct estimate of output
and ^uel consumption, since these vary with the character of
the raw materials and fuel as well as with the details of the
kiln, it may be said that with the dry process using cement
rock and limestone a 60-foot kiln will give an output of
about 200 barrels per day with a fuel consumption of 100 pounds
of coal per barrel, while a kiln 150 feet long may give 300 barrels
per day with only about 75 pounds of coal per barrel. With
wet mixtures an output of 100 barrels per day may require as
ROTARY KILNS
25
much as 200 pounds of coal per barrel with a 60-foot kiln, more
than half of the coal being required to evaporate the water
in the mix. The advantage of the longer kiln in this case
would probably be still greater. Dr. Richards found from
tests of a 60-foot kiln in a dry process plant that of the 110
pounds of coal required to burn a barrel of cement the heat
from about 80 pounds was carried in the waste gases, half of
which was due to excess of air introduced, while the heat from
12 pounds remained in the hot clinker issuing from the kiln,
and the equivalent of 14 pounds of fuel was lost in radiation.
The keen competition in cement making, and the occasional
low prices prevailing, have led to efforts to utilize the heat
contained in the waste gases. With a longer kiln the waste
gases are expelled at a much lower temperature.
26. ADVANTAGES OF THE ROTARY KILN. — A comparison
of the average output of the several styles of kilns described
above, and the approximate fuel consumption, are given in
the following table. Where it is necessary to dry the materials
before introducing them into the burning kiln, the fuel required
in drying is not included.
FUEL REQUIRED FOR VARIOUS KILNS
Style of KUn.
Barrels per Day.
Pounds of Coal
per Barrel of
Cement.
Intermittent dome
30
25
50 to 75
30
80 to 120
130 to 200
175 to 250
300 to 500
80 to 120
60 to 80
60 to 80
160 to 200
140 to 200
100 to 140
95 to 120
75 to 100
Hoffman (per chamber)
Dietsch and Schofer
Chamber
Rotary, wet process, 60-foot kibi. '. . . .
Rotary, wet process, 110-foot kiln
Rotary, dry process, 60-foot kiln
Rotary, dry process, 150-foot kiln
Although, as seen from the above table, the burning of
cement in a rotary kiln of the ordinary length requires a larger
fuel consumption than with some other types, the ability to
use a cheaper form of fuel and the saving in the amount of
labor required, much more than offset this disadvantage. Since
either wet or dry materials may be fed into the kiln, the neces-
sity of forming the slurry into bricks, drying and stacking
them in the kiln, is eliminated, and it is possible to so arrange
26 CEMENT AND CONCRETE
a plant that the material is handled entirely by machinery
from the raw state to the finished product. In fact, the con-
veying and elevating devices in a cement plant form a most
important part of its equipment, and the mechanical problems
in cement manufacture are given, in one sense, more careful
attention than the chemical questions. The control possible
in burning with the rotary is much better than with fixed
kilns, since the clinker may be watched while burning and the
temperature may be gaged according to its appearance. The
fact that the pieces of clinker are much smaller with the rotary
process also contributes to uniform burning as well as to greater
ease in grinding. The remarkable development of the Port-
land cement industry in the United States is due in no small
measure to the adoption and perfection of the rotary kiln, for
the labor expense in manufacture is so reduced thereby that
we are able to successfully compete with cements made abroad
where lower wages prevail.
27. GRINDING. — In grinding it is not sufficient that the
cement be so reduced that a certain percentage of it will pass
a sieve having, say, 10,000 holes per square inch; but it is de-
sired that as large a proportion as possible shall be of the finest
floury nature. To accomplish this result it has been claimed
that French buhr millstones are the best, but their great con-
sumption of power has led to the introduction of other forms
of grinding machinery, so that at present millstones find their
<5hief use in natural cement manufacture.
It is usually considered that the greatest economy results
from a gradual reduction of the clinker as it passes from one
form of grinder to another, each machine being supplied with
the size of pieces it is best adapted to handle. Large pieces of
clinker are first passed through an ordinary rock crusher, such
as the Gates or Blake. Where rotary kilns are in use, this step
in the process may be omitted, as the clinker comes from the
kiln in small, nut-like pieces, and the grinding is completed in
two stages. The first reduction may be accomplished in ball
mills, Kominuters. Kent mills. Disintegrators or rolls, while
the final grinding may be done in tube mills. Griffin mills,
rolls or Huntington mills.
28. BALL AND TUBE MILLS. — The ball mill is perhaps in
most common use for the first reduction. It consists of a short
GRINDING
27
cylinder of large diameter partially filled with flint or steel
balls. (See cut.) The grinding plates arranged about the
inner circumference overlap one another and form a series of
steps. The material is fed to the mill through one axis, and
as the mill revolves the balls drop down the steps formed by
the plates and roll over one another, pulverizing the clinker
between them. The grinding plates are perforated, and as the
clinker is pulverized it passes through the perforations and
drops on a screen, and finally on a second finer screen. The
particles too coarse to pass the screens are returned to the
nprnfiiiini
KllUPP BALL MILL
grinding chamber through the openings between the steps
formed by the grinding plates, while the material passing the
screens is discharged to the conveyor. A ball mill working
on ordinary rotary kiln clinker will grind from 15 to 24 barrels
per hour to pass a 20-mesh screen and will require from 30 to
50 H.P.
The Kominuter is a modification of the ball mill, the prin-
cipal point of difference being that the grinding plates are
not perforated, but the material must travel the full length
of the drum, escaping to the screens outside the plates through
openings at the end opposite the inlet. It then travels back
28
CEMENT AND CONCRETE
across the screens surrounding the plates, the material re-
jected being returned to the grinding chamber when it reaches
the inlet end. (See cut.) The machine is said to grind 40
to 50 barrels per hour, giving a product passing 20-mesh
screen.
The Tube Mill is another style of pulverizer depending upon
the action of balls for the grinding. It is usually employed for
the final reduction either of clinker or raw material, and from
THE LINDHARD KOMINUTER, F. L. SMIDTH & CO.
its very general adoption for this duty must be considered a
very satisfactory machine. It consists of a steel cylinder 15
to 30 feet long and about 5 feet in diameter, lined with chilled
iron or with stone, and mounted on trunnion bearings about
which it is slowly revolved. (See cut.)
The tube is at least half full of flint or steel balls, the former
being a natural product imported from Europe, while the
latter are made in this country. As the tube revolves the balls
are carried up the rising side, but before reaching the highest
point of revolution they drop to the bottom of the tube, im-
pinging upon each other and crushing the product between
them. The material is fed in at one end and gradually works
toward the other; the fineness of grinding is regulated by the
rate of feed, and no sieving is necessary. The capacity of a
tube mill 5 feet by 22 feet is said to be from 8 to 20 barrels per
hour when working on the product of a ball mill, and the power
GRINDING
29
consumed is variously stated at 30 to 70 H.P. The renewing
of the flint pebbles forms one of the heaviest repair items, and
THE DAVIDSEN TUBE MILL. F. L. SMIDTH & CO.
the cost of these has been estimated as high as one-half cent
per barrel of cement.
29. The Griffin Mill is an American invention that has
found much favor for grinding clinker. A heavy steel crush-
ing roller is rigidly attached to the lower end of a steel shaft
which is suspended by ball and socket joint at its upper end.
The shaft is thus free to swing in any direction within a case
which incloses a ring or die surrounding the crushing roller.
When the shaft is revolved rapidly by means of a horizontal
pulley at the top, the roller presses by centrifugal force against
the inner surface of the ring where the grinding takes place, and
thus runs around the ring in a direction opposite to that
in which the pulley is revolved. The material which drops
below the roller is thrown up again by steel blades attached
to the bottom of the shaft, and above the roller are fans which
create a draft, forcing the finished product through the screens
above the ring whence it falls into a hopper. Although the
repair expenses of a Griffin mill. are high, it has proved a very
satisfactory machine and is extensively used, especially for the
final reduction of clinker. The size of mill is designated by
the diameter of the ring or die. A 36-inch mill, with roller 24
inches in diameter, 6-inch face, and weighing 175 pounds,
consumes 25 to 35 H.P. and grinds 8 to 10 barrels of cement
per hour when working on clinker not coarser than one-half
inch. The manufacturers of the Griffin mill now make a 3-roll
mill of somewhat similar construction.
30
CEMENT AND CONCRETE
30-INCU GKLFFIN MILL ARRANu.
LVERIZING
GRINDING
31
The Huntington Mill is very similar to the Griffin mill, the
single roller of the latter being replaced by three rolls suspended
from a revolving head. As the head is revolved, the rolls press
against the steel ring surrounding them, and by reason of this
contact the rolls revolve upon their shafts. The output and
power consumption are said to be about the same as in the
Griffin mill.
The FuUer-Lehigh Pulverizer Mill is a more recent style of
grinder, said to be suitable for Portland cement clinker as well
as raw material and coal. The machine consists of an up-
right horizontal ring or die with a circular groove or track in
which travel four balls. The balls rest upon a horizontal
annular plate the revolution of which causes the balls to revolve
and press against the circular track. The die, plate and balls
are of Swedish iron. The balls are 9J inches in diameter and
weigh 112 pounds each, and as they revolve at the rate of
about 210 revolutions per minute the pressure against the
surrounding track is estimated to be about 1,600 pounds. The
material entering the center of the mill falls into a pan below
the balls and is thrown
up between the balls and
track. The ground mate-
rial is driven upward by
fans and through a screen,
the rejected portion return-
ing for further grinding.'
The Kent Mill resem-
bles the Griffin mill in that
the crushing is done be-
tween rolls and die, but the
arrangement is quite dif-
erent. There are three rolls,
one of which is driven
while the others revolve
only because of their con-
tact with the exterior ring which is revolved rapidly by the
contact of the driven roll upon its inner face. (See cut.) The
material is held upon the revolving ring by centrifugal force
AOJUSTINa-
SCREW
fEEO ««*«•
I SROUND OS FLOM
INTERIOR OF KENT MILL
' For cut and detailed description see Engineering News, June 21, 1906.
32 CEMENT AND CONCRETE
and passes under the three rolls in succession. The rolls are
held against the concave surface of the ring by springs which
permit some yielding, to pass lumps.
This mill was at first used only as a preliminary grinder or as a
feeder for a tube mill, but it has been found that by screening
the material, either with an inclined screen or with an air
separator, it may be used economically as a fine grinder. When
working on rotary kiln clinker this mill has given 40 to 50
barrels per hour of 20-mesh material with a power consumption
of 24 H.P.; in grinding the same clinker to pass a 100-mesh
screen, with 88 to 90 per cent, passing 200-mesh, it has given
10 to 12 barrels per hour.
30. Rolls. — Although rolls have not as yet been exten-
sively employed for cement grinding, one mill has recently
been equipped entirely with rolls for both coarse and fine grind-
ing, and in other mills rolls are employed for a first reduction
of the clinker. The rolls are 24 to 30 inches in diameter with
16 to 18 inch face. The shells may be of forged steel, chrome
steel, or chilled cast iron, with beveled edges to prevent break-
ing the corners. The distance between the rolls varies with
the fineness of the clinker and of the finished product; the
feed is regulated by an automatic device. The rolls are sonie-
times mounted in sets of three for double passage of the material,
only one roll being actuated, the others being driven by fric-
tion, a peripheric speed of about six feet per second being
maintained. The three-roll fine grinders in the Edison Port-
land Cement Mill at New Village, N. J., have rolls 28 inches
diameter and 8-inch face. The rolls are held together with a
pressure of about 9 tons per square inch, this pressure being
obtained by an endless rope passing over loose sheaves on the
ends of the outer rolls at each side of the machine; a sheave in
the bight of this endless rope is attached to a piston working
in a cylinder to which compressed air may be admitted. This
relieves the bearings of all pressure except the weight of the
rolls. These machines have a large power consumption, but
give a correspondingly large output.
31. Disintegrators. — This class, including all the machines
which crush the material by impact, may be briefly described
here, although seldom employed in the manufacture of Port-
land cement. Under this head may be mentioned the Williams
GRINDING 33
Crusher, the Raymond Pulverizers, and the Stedman Disinte-
grator. The Williams Mill consists of a series of hammers
hinged to a horizontal rotating shaft, the whole being inclosed
in a case. The grinding is accomplished by the rapid blows of
the hammers upon the material fed into the case.
In the Raymond Automatic Pulverizer large square blades
are attached to discs keyed to a horizontal shaft that is re-
volved rapidly. The blades are set at such an angle with the
shaft that the material is thrown alternately to right and left,
the pulverizing being the result of the impact of the particles
against each other and against the walls of the inclosing
chamber.
The Stedman Disintegrator consists of a series of circular
cages composed of steel bars, and fitting one within another.
The cages are mounted on a horizontal shaft, and are arranged
to revolve, two right-handed and two left-handed. The mate-
rial being fed to the inside of the central cage is thrown out to
the bars of the second cage moving in the opposite direction,
and so on through the series. This mill is especially adapted
to materials not so hard as Portland cement clinker.
32. The grinding of the clinker, being an important and
expensive part of the process of cement making, has been the
subject of much experimentation on the part of the manufac-
turers. That they have not all arrived at the same conclusion
is partly due to variations in the character of the material. A
high-limed hard-burned clinker is harder to grind than one of
higher silica and alumina content which is burned at a some-
what lower temperature. The fineness requirements in cement
specifications have been constantly increasing, and manufac-
turers are vying with eacn other to produce a finely ground
product without incurring prohibitory expenses in the grinding.
While the reduction from clinker to finished cement was form-
erly sometimes accomplished in one machine, the one-stage
reduction process, nearly all plants now pass the material
through two mills, usually of different styles. Ball mills for
first reduction and tube mills for final reduction probably now
form the most common combination. The user of cement is
interested chiefly in having a large percentage of the finest
material present, and it has been found that in this regard
there is little to choose between several of the best types.
34 CEMENT AND CONCRETE
33. SAND-CEMENT. — This product, which is also called silica
cement, is composed of Portland cement and silicious sand mixed
in any desired proportion and then ground to extreme fineness.
This product is placed on the market by dealers, but rights to-
use the process may be purchased. In the construction of Lock
and Dam No. 2, Mississippi River, between Minneapolis and
St. Paul, Major F. V. Abbot ^ used the process ; grinding with-
a tube mill one part of Portland cement with one part fine
sand. The cost, exclusive of plant, is estimated as follows: —
J barrel of Portland cement at $2.85 $1.42
i " " sand at . 05 03
Cost of grinding .50
Cost of royalty .05
Cost of one barrel Silica cement $2 . 00
This cement has given remarkably high tests considering the
adulteration with sand, and is claimed to be specially useful in
making impervious mortar and concrete.
Art. 7. Other Methods of Manufacture, of Portland
Cement
34. Portland Cement from Blast Furnace Slag. — The prep-
aration of a true Portland cement from blast furnace slag has
been followed in Germany and elsewhere in Europe for several
years, and recently has been introduced in the United States.
As this process utilizes a waste product, its popularity is likely
to increase. Whereas, for the manufacture of slag cement only
the slag from gray pig iron is available, it is found that in most
cases the slag from white pig iron may be used for the produc-
tion of Portland cement from slag.
The method of manufacture is briefly as follows: The slag
as it comes from the blast furnace is subjected to the action of
a stream of water, which granulates it and changes it chemi-
cally, the water combining with the calcium sulphide, which is
injurious to cement, to form lime and sulphuretted hydrogen.
' Report of Mr. A. O. Powell, Asst. Engineer, Report Chief of Engineers,
U.S. A., 1900, p. 2779.
SLAG CEMENT 35
The granulated slag is then dried, mixed with the correct pro-
portion of dried limestone, and ground to extreme fineness.
The mixture is next burned in rotary kilns, the remainder of the
process being the same as that employed when ordinary raw
materials are used. While a cement made from slag by this
method may have some peculiarities due to the nature of the
raw materials used, and should be very carefully tested before
it is used in important work, it should not be confounded with
slag cement, which is a mixture of granulated slag and hydrated
lime subsequently ground, but not burned together.
35. Portland Cement from By-Products of Soda Manufacture.
— The Michigan Alkali Company has installed at Wyandotte,
Mich., a cement plant to utilize the large amount of limestone
which they have as waste in the manufacture of soda products.
The limestone which has served its purpose in the soda manu-
facture is in a finely divided and semi-fluid state; to this is
added the proper percentage of clay, which has been dried and
pulverized. The two are then very thoroughly mixed and
ground by pug mills and tube mills, the mix corrected by proper
combination of over-clayed and over-limed slurry, and finally
burned in rotary kilns.
Art. 8. The Manufacture of Slag Cement
36. Slag Cement is made by adding calcium hydrate to a
granulated basic slag resulting from the manufacture of gray
pig iron. The slag must be carefully selected as to its chemical
composition ; Professor Tetmajer having found by extended
experiments that slags containing silica, alumina, and lime in
the ratio 30 to 16 to 40 are best adapted to the purpose. As the
molten slag runs from the blast furnace it is suddenly chilled
by being run into water, or is partially disintegrated by being
treated with a strong current of water, air, or steam. It is thus
reduced to coarse particles resembling sand, or to a spongy or
fibrous mass which, after drying, is readily ground to a fine
powder. The process of chilling results in a certain chemico-
physical change that renders the powder capable of combining
more readily with the slaked lime which is subsequently added.
Slag which has been allowed to cool slowly will not form an
hydraulic product when mixed with the lime, although the
36 CEMENT AND CONCRETE
chemical composition of the slag may be identical in the two
cases. The lime is dipped into water, or treated with steam,
until slaked to a fine dry powder, and is then added to the
powdered slag in proportions of about one part of the former
to three parts of the latter, this proportion depending upon the
composition of the slag used. The powdered slag and lime are
sifted, then mixed and reground together to an extreme fine-
ness, thus insuring an intimate incorporation of the ingredients.
Since there is no burning in the process, it is evident that the
finished product is merely a mixture, not a chemical compound
as is the case with Portland cement.
37. One of the largest mills for the manufacture of slag
cement in the United States is conducted by the Illinois Steel
Company, and the following description of the process is con-
densed from a statement of Mr. Jasper Whiting,* manager of
the cement department, and patentee of the process: Slag of
the proper composition is chilled as it comes from the furnace
by the action of a large stream of cold water under high pres-
sure. The slag is thereby broken up, about one-third of its
sulphur is eliminated, and it is otherwise changed chemically.
A sample of the slag thus granulated is mixed with a proportion
of prepared lime, and ground in a small mill whereby actual
slag cement is produced. If the tests upon this trial cement
are satisfactory, the slag is dried and then ground, first in a
Griffin mill and then in a tube mill, where it is mixed with the
proper amount of prepared lime and the two materials ground
and intimately mixed together. The resulting product is said
to be so fine that but 4 per cent, is retained on a sieve having
200 meshes per linear inch. The lime is burned from a very
pure limestone and stored in bins, beneath which are two
screens of different mesh, the coarser at the top. A quantity
of lime being drawn on the upper screen is slaked by the addi-
tion of water containing a small percentage of caustic soda.
The lime passes through the two screens as it slakes and is
then heated in a drier; the slaking being thus completed, the
lime may be incorporated with the slag. The purpose of the
caustic soda added in the above process is to render the cement
quicker setting.
» " Report of Board of Engineers on Steel Portland Cement," Appendix I.
NATURAL CEMENT 37
Art 9. The Manufacture of Natural Cement
38. History. — The American product called natural cement
was first manufactured at Fayette ville, Onondaga County,
N. Y,, in 1818, and used in the construction of the Erie Canal.
Other early dates of manufacture are given as 1823, near Rosen-
dale, N. Y., and 1824 at Williamsville, Erie County, N. Y., the
products being used in the construction of the Erie and the
Delaware & Hudson Canals. Factories were soon started in
other states, and at present nearly every State in the Union has
one or more natural cement factories, the total annual produc-
tion being now about nine million barrels.
39. Materials Required. — The composition of rock from
which natural cement may be made varies within wide limits.
Natural cement is essentially a combination of acid constituents,
silica, alumina, and iron oxide, with the basic constituents, lime
and magnesia, but the proportions in which the several mate-
rials shall occur in the natural cement rock is not confined to
the narrow limits we have seen were necessary in Portland
cement manufacture. When argillaceous limestone is used
the product is sometimes referred to as aluminous natural
cement, its essential ingredient being a bisilicate of alumina
and lime, while the product made from argillo-magnesian lime-
stone is called magnesian cement, and is probably composed
of a triple silicate of lime, magnesia, and alumina. The Mary-
land cements are typical of the former or aluminous variety,
containing only one to five per cent, of magnesia, while the
Rosendale and Milwaukee are magnesian cements containing
15 to 25 per cent, magnesia. (See Table 3, page 11.)
Rocks suitable for the manufacture of natural cement are
widely distributed throughout the United States. If this
were not so the use of natural cement would be very much
curtailed, for if it must be transported long distances it cannot
successfully compete with Portland cement, since the cost of
transportation makes a much greater proportionate increase
in the price of the product than is the case with Portland.
In the following table are given a number of analyses of
raw cement rock quoted by Mr. Eckel in his report on Cement
Materials and Industry of the United States.*
» Bulletin No. 243, U. S. Geological Survey.
38
CEMENT AND CONCRETE
ANALTSES OF NATURAL CEMENT ROCK
Authority.
Locality.
8iO».
AljOa
FejO^
CaO.
MgO.
CO,.
Mineral Industry
Coplay, Pa.
18.34
7.49
37.60
1.38
31. 0€
C. Richardson .
Hancock, Md.
19.81
7.35
2.41
35.76
2.18
C. Richardson
Fort Scott, Kan.
21.80
3.70
3.10
35.00
3.50
33. OC
W. A. Noyers . .
Louisville, Ky.
18.33
4.98
1.67
30.41
8.04
32.76
W. A. Noyers . .
L. C. Beck . . .
Louisville, Ky.
9.80
2.03
1.40
29.40
16.70
41. 4f
Howes Cave, N. Y.
11.50
1..50
31.75
14.91
40.34
C. Richardson
Lawrenceville, N.Y.
21.41
10.09
25.80
10.09
F. W. Clarke . .
Utica, Ills.
12.22
9.39
3.90
24.40
10.43
Mineral Industry
Milwaukee, Wis.
17.00
4.25
1.25
24.64
11.90
32.46
C. Richardson .
Maukato, Minn.
12.14
4.62
1.84
22.66
16.84
39.07
G. Steiger . . .
Akron, N. Y.
9.03
2.25
0.85
26.84
18.37
40.33
The materials found at any locality may vary considerably
as to chemical composition, especially among the several strata.
In some cases the different strata are utilized to make two or
more brands, which differ somewhat in their characteristics as
to time of setting, etc. It is common also to mix two or
more layers together in the manufacture, with the idea that
the ingredients lacking in one stratum will be supplied by the
others.
40. DESCRIPTION OF PROCESS. — As the ingredients have
been incorporated by nature in such proportions as to yield a
natural cement, much of that portion of the process of Portland
cement manufacture preliminary to the burning is unnecessary.
The rock occurs in strata and is quarried in open cut where
near the surface, or is mined in case the stripping is heavy.
In open cut a face of 20 feet or more is sometimes worked. As
has already been stated, the strata vary in chemical composi-
tion, and while two or more brands are sometimes made at the
same mill, the rock from several strata are frequently mixed
in the production of one brand, the idea being that if one layer
has an excess of acid constituents it may be corrected by
another containing too much lime or magnesia. As the rock
is not finely pulverized before it enters the kiln, each lump
bums by itself and makes a certain cement; the piece of cement
next it must make as distinct a product as though burned in a
separate kiln. What is obtained, then, by this method is a
mixture of several cements, and it would seem that the mere
NATURAL CEMENT 39
mechanical mixing of an over-limed and an over-clayed cement
can not produce a well-balanced product, but that whatever
advantage may be gained by this process is due to the pozzo-
lanic reaction which plays a part in the hydration of natural
cements. Moreover, the fact that wide variations in com-
position must call for similar variations in the temperature of
burning precludes the probability that the best results are
obtained in this way. This practice undoubtedly accounts,
in a great degree, for the large variations that occur in the
cement from a single mill, variations which are often, however,
more noticeable in short-time tests than in longer ones.
41. Burning. — As the rock is quarried it is broken into
pieces varying in size up to six inches. To secure uniformity
in burning, the pieces should be approximately of the same
size, and to this end the rock should be passed through the
ordinary rock crusher. It is then conveyed to the kilns, usually
by tramway.
The style of kiln almost universally used in burning natural
cement is the cylindrical dome kiln, briefly described under
Portland cement manufacture (§ 23). These kilns are from
20 to 50 feet high and 8 to 16 feet in diameter, built of masonry
or steel lined with brick, and are operated as continuous kilns.
The coal used for fuel is about pea size, either bituminous or
anthracite being used, according to the locality. The rock and
fuel are spread on the top of the kiln in alternate layers, the pro-
portion of fuel being usually regulated by the man in charge,
though a machine is sometimes employed to govern automat-
ically the amount of coal used.
The temperature reached in the burning varies quite widely
according to the character of the rock. Materials high in
alumina, iron oxide, and silica, that is, with a loW lime-acid
ratio (§ 9), are most readily broken up. The carbon dioxide
is first driven off, then takes place the combination of the lime
and magnesia with alumina and iron oxide, and finally with
the silica. Such rocks may be burned at a temperature of
about 1000° to 1200° C, while those having a high hme-acid
ratio may require 1200° to 1400°.
There is little question that the cement rock used in most
natural cement plants is capable of producing a much better
and more uniform quality of product than is actually obtained..
40 CEMENT AND CONCRETE
Many plants depend largely upon a local market, and there
has not been the incentive to improvement that comes from
sharp competition in a broader field, and consequently the rule
of thumb methods, handed down from the early operation of
the plant, are still employed. To select the rock with great
care and burn each stratum at the temperature required to
develop the best results, as determined by experiinents on a
practical scale, would undoubtedly improve the product. As
this would call for the installation of rotary kilns and a higher
cost of production throughout, it is usually considered that it
would not be profitable, but this has not been established.
42. Grinding. — The calcined rock is conveyed first to some
sort of stone crusher; a common form is known as a "pot-
cracker," and consists of a corrugated conical shell in which
works a cast iron core, also corrugated. The elements of the
shell and core have a smaller angle to the vertical in the lower
part of the mill, providing for gradual reduction and greater
power on the smaller particles. The Berthelet and McEntre
crackers are mills of this general type. A small cracker, about
15 inches diameter and 18 inches high, working as a coarse
grinder only, will pass 250 to 300 barrels per day.
The ordinary buhr millstones have been used from the
inception of the natural cement industry and are still very
generally employed. The "rock-emery" mill, a stone in which a
layer of harder composition is set about the exterior face, has
replaced the older buhr mills in some plants, as it requires less
frequent dressing. While ball mills, Williams crushers, Sted-
man disintegrators, and dry pans have been introduced to
some extent in natural cement plants, tube mills have, perhaps,
proved the most efficient for this work of any of the modem
types of reducers. These are described in Article 6 under
Portland cement manufacture. When, as is now common
practice, the reduction is accompHshed in several stages, the
fine material or finished product is separated after each stage,
the power consumption for a given output being reduced
thereby, although the proportion of extremely fine dust is
probably also diminished. Mr. Berthelet of the Milwaukee
Cement Company has perfected a screening system for this
purpose that has proved very successful, and has been installed
in other cement plants.
NATURAL CEMENT 41
After passing the grinding mills the product is sometimes
conveyed to "mixers" by means of which the cement is thor-
oughly mixed to promote uniformity. It is now ready for
packing, and may be placed in bins or sent direct to the chute
from which the bags or barrels are filled. Most natural cement
is packed in paper or cloth sacks, as barrels add too large a
proportionate cost to the product.
It is seen that the manufacture of natural cement is very
similar to that portion of Portland cement manufacture suc-
ceeding the preparation of the raw material for burning. In
general, less care is requisite with natural cement, the burning
is carried on at a lower temperature, and the calcined rock is
softer, so that less expense is incurred in grinding.
PART II
THE PROPERTIES OF CEMENT AND
METHODS OF TESTING
CHAPTER III
INTRODUCTORY
43. In the tests of such structural materials as wood and
steel it will not usually be difficult to determine the suitabiUty
of the material for the intended purpose, provided the test
pieces truthfully represent the members to be used. It is known
that so long as these members are protected from oxidation and
over-loading they will retain their qualities, and there is always
a reasonably clear understanding of what these qualities should
be. On the other hand, in the testing of cement, one may be
perfectly sure that from the moment the cement is manufac-
tured until long after it has been in service in the structure its
properties will be ever changing; and, further, the quahties
which it is desirable the cement should possess are not always
clearly in mind.
44. Desirable Qualities in Cement. — The desirable elements
in a cement may be stated as follows: 1st, That when treated in
the proposed manner it shall develop a certain strength at the
end of a given period. 2d, That it shall contain no compounds
within itself which may, at any future time, cause it to change
its form or volume, or lose any of its previously acquired strength.
3d, That it shall be able to withstand the action of any exterior
agency to which it may be subjected that would tend to decrease
its strength or change its form or volume. When it is deter-
mined that a cement has these three qualities, it is certain that
it is safe to use it, but it is further desirable to know that the
42
UNIFORM METHODS 43
cement in question will accomplish the given object as cheaply
as any other cement.
The cohesive and adhesive strengths of cement are not usu-
ally considered in the design of the structure into which cement
enters. The design of a masonry arch does not comprehend any
adhesive strength in the cement, except as it may be recognized
as an additional factor of safety, and a masonry dam is so de-
signed that there shall be no tension at the heel. These facts
are due in a large measure to the very imperfect knowledge we
have of the behavior of cements in various contingencies. With
the increasing use of concrete, as in arches, locks, floors, roofs,
etc., the tensile and transverse strengths of cement are coming
to be relied on to a certain extent; and as its properties become
better known, and as means of recognizing these properties
become more certain and widespread in their application, ce-
ment will be more extensively employed in a scientific and eco-
nomical manner.
Cement may be compared in one sense to timber and cast
iron. A large factor of safety is employed when dealing with
these materials because of hidden defects that may exist. The
defects which lie hidden in cement may be even greater than
these in proportion to its possible strength, and defects in ce-
ment are often more treacherous because their development
may be deferred for some time. The importance of knowing
whether the cement fulfills the second and third requirements
noted above is therefore evident.
45. Having considered the qualities a cement should have,
we may proceed to the detailed consideration of the various
tests employed to disclose the presence or absence of these qual-
ities. The strength a given cement will develop is investigated
by chemical analysis, by obtaining the specific gravity and fine-
ness, and by actual rupture tests, whether they be tensile, com-
pressive, transverse, or shearing. By tests for change of volume
and by chemical analysis, it is sought to determine whether a
cement has within itself elements of destruction. For the power
to withstand external agencies there are no adequate tests,
though chemical analysis is considered an aid. The methods
of use, the proportions of the materials, their incorporation and
deposition are of great importance in insuring against external
causes of injury.
44 CEMENT AND CONCRETE
46. Uniform Methods of Cement Testing. — In order that
uniformity should prevail in the methods employed in testing
cements, various societies have discussed the subject in detail,
usually through committees, and much valuable work has been
done along this line. The engineers of public works in many
European countries have adopted specifications and laid down
more or less detailed rules for testing. The Corps of Engineers,
U. S. A., has recently adopted a similar code of rules.
The International Society for Testing Materials, with which
the American Society for Testing Materials is affiliated, has con-
sidered the subject and still has committees at work upon it.
The New York section of the Society of Chemical Industry has
recently formulated a method for analysis of materials for the
Portland cement industry. The American Society of Civil En-
gineers received a report in 1885 from a committee appointed
to consider methods of cement testing, and in order to keep the
subject abreast of the latest developments in the manufacture
and use of cement, a second committee was appointed several
j'^ears ago, which has been making a thorough discussion of the
subject, and has submitted a preliminary or progress report.
47. Notwithstanding that so much has been done toward
unification of methods, it may never be possible to determine
accurately the value of one cement as compared with another
tested in a different laboratory; though in tests of iron and
steel no such difficulty is experienced. Certainly, as at present
carried out, strength tests of cement are purely relative tests
and do not show the absolute strength which may be developed
in the structures; nor can the results be compared with the re-
sults obtained in other laboratories and any fine distinctions of
quality drawn. To attempt to carry out acceptance tests in
such a way as to show directly the strength which v/ill be de-
veloped in actual construction, is only to introduce causes of
irregularity in the tests.
CHAPTER IV
CHEMICAL TESTS
Art. 10. Composition and Chemical Analysis
48. Value of Chemical Tests. — The definite aid which chem-
ical analysis may render in determining the quality of a cement
is limited by the following considerations. It is not definitely
known just what part is played by each of the compounds that
go to make up commercial cement, and chemical analysis does
not tell the manner of the occurrence of these compounds. A
cement may have a chemical composition that is thought to be
perfect, but if the burning has not been properly accomplished,
it may be a dangerous product and analysis would show no de-
fect. Some of the best authorities say that chemical analysis
is useful principally in tracing the cause of defects which, by
other tests, have been found to exist. However, there are some
constituents which it is fairly well known a cement should not
contain in any considerable quantities. An analysis may be of
value in estimating quantitatively such constituents, while it
may also be of service in detecting adulterations. It is not im-
possible, then, that chemical tests may yet play a more impor-
tant role in cement testing, especially if the method of analysis
can be made more simple and rapid, without too great a sacri-
fice of accuracy.
49. Lime. — The proportion of lime in Portland cement may
vary from 59 to 67 per cent. A much greater range than this
is allowable in natural cement, the percentage usually being
from 30 to 45, according to the amount. and character of the
other active constituents. An analysis of Portland cement which
shows a percentage of lime far outside of the limits mentioned
above, should be regarded with suspicion and submitted to very
thorough tests before acceptance. As already stated, the ratio
of the silica and alumina to the lime in a cement is called the
hydraulic index. The value of this ratio is usually between .42
and .48 for Portland cement.
45
46 CEMENT AND CONCRETE
Cement mixtures containing a large percentage of lime re-
quire a high temperature for calcination, are difficult to grind,
and yield a slow-setting product. The danger in highly limed
cements is that they will not be properly calcined and a por-
tion of the lime will be left in a free state. The demand for
high strength in short-time tests has led manufacturers to
make a heavily limed product, and in some cases the limits of
safety have probably been overstepped. The introduction of the
rotary kiln, however, has so improved the facilities for burning
cement that a higher percentage of lime is now possible.
There is no method known at present for determining quanti-
tatively the amount of free lime in a cement, and it seems doubt-
ful whether its presence can be detected with certainty by chemi-
cal analysis. The method usually employed for this purpose
depends on the hydration of the lime and subsequent absorption
of carbonic acid.
50. Magnesia. — The detection of magnesia in several con-
crete structures that had failed, led to the conclusion that mag-
nesia, in quantities exceeding two or three per cent., was a
dangerous element in Portland cement. In 1886-87 Mr. Har-
rison Hayter^ mentioned several failures of masonry and con-
crete which he considered were due to magnesia, and concluded
that cement should not contain more than one per cent. Later
investigations, however, indicated that such failures could be
explained in other ways, and that the magnesia found in the
failing structure had come from the sea water and replaced the
lime in the cement. Mr. A. E. Carey^ has considered that "an
excess of caustic lime or magnesia causes first, disintegration
by expansion due to hydration, and second, being soluble, when
conditions permit of their washing out, leave the concrete in a
honeycombed state." Notice that this refers to causiic mag-
nesia, and Prof. S. B. Newberry' has stated that "it is doubtful
if magnesia is ever combined in Portland cement. Our own
experiments tend to confirm the opinion of many German
authorities that magnesia remains free in cement and does
not combine with the constituents of clay after the manner
of lime."
' Proc. Inst. C. E., Part 1, Session of 1886-87.
« Ibid., 1891-92.
' Municipal Engineering, October, 1896.
COMPOSITION AND ANALYSIS 47
On the other hand, M. H. LeChatelier ^ says that the "acci-
dents occasioned by certain magnesian elements, and the similar
results obtained in laboratory experiments, have been due to
the employment of badly proportioned cements, containing free
uncombined magnesia and too small a quantity of clay. Cor-
responding mixtures containing lime instead of magnesia would
have caused still more serious accidents, yet it would not be con-
cluded that there must be no lime in cement." Again, Dr.
Erdmenger characterizes magnesia as an adulterant only, and
considers that its effect is nil if a greater percentage of lime is
added in the manufacture.
Some authoritative information on the amount of magnesia
allowable in Portland cement is contained in the report of the
magnesia commission of the Association of German Cement
Makers, 1895: Three members of this committee, Messrs. Schott,
Meyer and Arendt concluded that ''the presence of magnesia
up to ten per cent, causes no harmful expansion or cracking of
the cement, even after several years." Mr. Dyckprhoff, how-
ever, presented a minority report, in which he pointed out that
while a large amount of magnesia, not sintered, may not have
an injurious effect, yet a content of more than four per cent, of
sintered magnesia, whether added or substituted for part of the
lime, has an injurious effect after long periods. The committee
continued the ruling of 1893 that "a magnesia content of five
per cent, in burnt cement is harmless," but held the question
open for further investigation, indicating that this limit might
be raised.
In view of the disagreement among such eminent authori-
ties it is impossible to arrive at a satisfactory conclusion, but if
the effect of magnesia depends upon the manner of its occur-
rence, whether free or combined, sintered or unsintered, then
chemical analysis can be of but limited value as a test of quality
in this regard. Natural cements frequently contain large pro-
portions of magnesia replacing lime, and in this case an analysis
is of the same value as an analysis for lime.
51. Alumina and Iron Oxide. — The amount of alumina
which a cement should contain is not well established. Its
presence tends to facilitate the burning, and it renders the prod-
* Trans. Amer. Inst. Mining Engrs., 1893.
48 CEMENT AND CONCRETE
uct quicker setting. Cements containing large percentages of
alumina are inferior for use in air or sea water, and it is probable
that the percentage of alumina should not exceed eight or ten
to obtain the best results in all media. A slag cement may be
detected by its large content of alumina. Oxide of iron acts
as a flux in burning, but in the finished product is little more
than an adulterant.
52. Sulphuric Acid. — French specifications say that Port-
land cements shall not contain more than one per cent, of sul-
phuric acid or sulphides in determinable proportions. This is
doubtless intended for cement to be used in sea water. Adul-
terations with blast-furnace slag may sometimes be detected
by the amount of sulphides present, but small quantities of sul-
phuric acid in the cement may be derived from the coke used
in burning and have no injurious effect for use in fresh water.
A content of 1.75 per cent, of sulphuric anhydride, SOs, is now con-
sidered the maximum permissible. Sulphates mixed with the
raw materials and burned with the cement may be harmless,
while the same amount added after burning would not be per-
missible. [For tests on the effect of adding sulphate of lime to
cement, see Art. 48.]
53. Water and Carbonic Acid. — The determination of these
may give some idea of the deterioration of a product by storage,
and they may also indicate defective burning. M. Candlot con-
siders that in the case of Portland cement, a loss on ignition
(water and carbon dioxide) exceeding three per cent, "indicates
that the cement has undergone sufficient alteration to appre-
ciably diminish its strength." Natural cements may, however,
contain considerable proportions of these ingredients and still
give good results.
54. Conclusions. — Finally, then, the determination of silica,
alumina, magnesia and lime may be of value, first, in classify-
ing a product, and second, as indicating whether the proportions
contained in it are sucji that if properly manufactured it is
capable of giving good results. What these proportions should
be for Portland cement has already been stated, § 9. The de-
termination of certain injurious ingredients is also of some
value, but it must be remembered that the dangerous elements
most commonly occurring, namely, free lime and magnesia, are
not determinable by chemical analysis. It has been stated by
COMPOSITION AND ANALYSIS 49
M. LeChatelier that "neither complete nor partial chemical
analysis of the constituents of hydraulic materials can be ranked
among normal tests. But chemical analysis may render real
service in controlling the classification of a product concerning
which there is reason to doubt the declaration of the manufac-
turer. Thus, a slag cement can be distinguished from a Port-
land by its tenor in alumina and water; certain natural cements,
by their contents of sulphuric acid, etc." ^
The methods of analysis for Portland cement are given in
considerable detail in a Httle book, "The Chemical and Physical
Examination of Portland Cement," by Richard K. Meade. The
method of analysis suggested by the New York Section of the
Society of Chemical Industry is published in the Engineering
Record of July 11, 1903, and in Engineering News of July 16,
1903.
"Tests of Hydraulic Materials," H. LeChatelier.
CHAPTER V
THE SIMPLER PHYSICAL TESTS
Art. 11. Microscopical Tests. Color
55. Microscopical examinations are of some interest and
value to those who are thoroughly versed in the chemistry of
the burning and hardening of cements, as an aid in determining
the part played by each compound in the hardening.
Examinations may be made either of the dry powder, or of
thin sections of hardened cement, or clinker. Dry powder of
Portland cement appears to be made up of scaly particles, many
of which are clearly defined and semi-transparent, while natural
cement particles are more nearly opaque and less angular. Thin
sections of Portland cement clinker have been found to exhibit
colorless crystals somewhat cubical in structure, which are
thought to form the essential hardening constituent; thin sec-
tions of hardened Portland cement show a clear crystalline
structure. Prof. Hayter Lewis found that the particles in good
Portland cement were angular in form, consisting of scales and
splinters, while the particles of cement of poor quality were
rounded or nodular.
Microscopic examinations have no place at present in ordi-
nary tests of quality.
56. Significance of Color. — The color of cement is chiefly
derived from its impurities, such as oxides of iron and manga-
nese, rather than from its essential ingredients, and the color is
therefore of minor importance. Other things being equal, a
hard burned Portland cement will be darker in color than an
underburned product. An excess of lime may be indicated by
a bluish cast, and excess of clay or underburning may give a
brownish shade. Gray or greenish gray is usually considered
to be indicative of a good Portland.
57. The colors of natural cements have a wide range, vary-
ing from a light yellow to a very dark brown, without reference
to quality. Owing to a popular idea that dark color indicated
50
WEIGHT PER CUBIC FOOT 51
strength, some manufacturers have been said to add coloring
matter to their product, but although this may have been true
at one time, the correction of this false idea has doubtless ren-
dered such a practice quite unnecessary now. Variations in
shade in different samples of the same brand of natural cement
may indicate differences in burning or in the composition of the
rock; but the interpretation of color for any given brand must
be the result of close study, for some cements become lighter
on burning and others become darker, while in some cases no
variation in shade can be detected for different degrees of
burning.
Art. 12. Weight per Cubic Foot or Apparent Density
58. Significance. — Since a hard burned Portland cement
will usually be heavier than a Ught burned one, a test of the
weight per cubic foot was once thought to be of great value in
judging of the degree of burning. But it has been shown re-
peatedly that the weight per cubic foot depends quite as much
on the fineness as on the burning. It also depends on the age
of the cement, and its chemical composition. As a test for
quality, the determination of the apparent density has therefore
been discarded. However, it is an aid in classifying a product,
since Portland cements weigh from 70 to 90 pounds per cubic
foot when loosely filled in a measure, while natural cements
weigh from 45 to 65 pounds. A knowledge of the weight per
cubic foot is also useful in reducing proportions given by weight
to equivalent volumetric proportions, and vice versa.
59. Method. — This test may be made with a very simple
apparatus, and the results obtained, though not strictly accu-
rate, are sufficient for all practical purposes. A metal tube,
2 feet 4 inches long, about 6 inches in diameter at the top, and
3 or 4 inches at the bottom, is supported by a frame resting on
four legs. A metal cyHnder, 6 inches in diameter and 6^^
inches deep, holding one-tenth cubic foot, is placed on the floor
below the tube. A coarse sieve, through which all of the ce-
ment will pass, is placed on top of the tube and three feet above
the bottom of the measure. The cement passes through the
sieve, falling freely to the cylinder below, which is struck off
level when full. The cement must not be heaped too much,
and great care must be taken that the measure is not jarred
52 CEMENT AND CONCRETE
while it is being filled or struck off. The cement is in such a
light condition that a very slight jar is sufficient to cause it to
settle.
The above apparatus is on the same plan as that used by
Mr. E. C. Clarke on the Boston Main Drainage Works, and is
described here for general use when it is desired to compare
the results obtained by operators at different points. Should
one wish simply to obtain a series of results on different cements
which are to be compared among themselves, it is quite suf-
ficient to sift each sample through a coarse sieve, and then with
an ordinary scoop carefully fill a measure of any known capac-
ity, without other apparatus.
Mr. Henry Faija has described an apparatus consisting of a
funnel with a screw at the mouth which carries the cement
horizontally to the point where it falls freely into the measure.
Various other devices have been employed, but none seems to
have met with universal favor.
60. To determine the relative accuracy obtainable with the
. simple form of apparatus first described, the author made a
series of tests which may be summarized as follows: —
1st Method. — Cement passed a wire mesh sieve, holes .033
inch square and fell freely two feet through a 6-inch tube into
a measure holding ^ cu. ft. Five trials Avith a sample of Dycker-
hoff Portland, highest weight per cubic foot, 81 lbs. 4 oz.,
lowest, 79 lbs. 2 oz., difference, 2 lbs. 2 oz. Three trials with
Alsen's Portland, highest weight, 73 lbs., lowest, 72 lbs., dif-
ference, 1 lb.
2d Method. — Measure same size filled with scoop without
other apparatus, and cement not shaken or jarred in measure.
Five trials with Alsen's Portland, highest result, 73 lbs. 8 oz.
per cu. ft., lowest result, 72 lbs. 12 oz., difference, 12 oz. Five
trials with different sample of same cement, highest, 72 lbs.
4 oz., lowest, 72 lbs., difference, 4 oz.
3d Method. — Measure filled with scoop, and cement well
shaken down as filling proceeded. Five trials with Alsen's
Portland, highest result, 100 lbs. 8 oz., lowest, 97 lbs. 14 oz.,
difference, 2 lbs. 10 oz.
It appears from these tests that when the measure is filled
with the scoop, the results are about as uniform as when the
apparatus is used, provided the filling is always done by the
SPECIFIC GRAVITY 63
same person. But the results obtained by different operators
with the same sample of cement would probably vary less, one
from the other, when the apparatus is employed. In other
words, the personal factor is more nearly eliminated when the
cement is passed through a sieve and allowed to fall freely
from a given height.
61. As to the effect of age on the weight per cubic foot, it
was found in one case that cement which weighed 93^ pounds
per cubic foot when freshly ground, weighed but 88 pounds
when a few days old, and 78 and 74 pounds after six months
and one year, respectively.*
Many experiments have been made to show the effect of
fineness on the weight per cubic foot, but as this subject will
be taken up again under "fineness," it will suffice to quote one
series of tests made by Mr. E. C. Clarke,^ giving the "weight
per cubic foot of the same sample of German Portland cement
containing different percentages of coarse particles as deter-
mined by sifting through the No. 120 sieve."
Samples containing 0, 10, 20, 30, and 40 per cent, of coarse
particles retained on No. 120 sieve gave the following weights
per cubic foot: 75, 79, 82, 86 and 90 pounds, respectively.
It may be repeated that the weight per cubic foot is no
longer considered an indication of quality, but should it be
desired to specify a given weight, the method by which the
test is to be made should also be stated.
Art. 13. Specific Gravity or True Density
62. The apparent density or weight per cubic foot is in-
fluenced to such an extent by the degree of fineness of the
cement that this test has been almost superseded by the test
for specific gravity. Although the true density, or specific
gravity, is not affected by the fineness, it is influenced by the
composition, the degree of burning, and the age, or amount of
aeration of the sample.
The method commonly employed in this test consists in de-
termining the absolute volume of a given weight of the cement
' "Cement for Users," by H. Faija, p. 54.
* " Record of Tests of Cements for Boston Main Dnjunage Works," Trans.
A. S. C. E., Vol. xiv, p. 144.
54 CEMENT AND CONCRETE
powder by measuring the amount of liquid which it will dis-
place. A simple form of apparatus may be constructed in
any laboratory as follows: In a wide mouth bottle, having
straight sides and holding 200 c.c. or more, fit a perforated
cork. Through the cork slip a burette graduated in cubic
centimeters from 0 to 50, placing the zero end down. Fill the
bottle and the tube up to the zero mark, with some liquid such
as turpentine, benzine or kerosene oil, but preferably benzine
(62° Baum6 naptha). By means of a funnel in the top of the
burette, add slowly 100 grams of cement; then jar the bottle to
remove air bubbles and read the burette. This reading, x,
represents the volume of 100 grams of cement; and 100, the
volume of 100 grams of water, divided by x gives the specific
gravity of the sample.
63. Among other forms of apparatus which are also of sim-
ple construction and tend to facilitate the test, may be men-
tioned the following: —
M. Candlot^ devised an apparatus consisting of a graduated
tube terminating in a bulb at the upper end, the lower end of
the tube being ground to fit the neck of a flask. The tube and
flask being disconnected, sufficient liquid is placed in the bulb
so that when connected with the flask and placed upright, the
level of the liquid will be at or near the zero mark on the tube.
The actual level of the liquid is read after standing a few minutes;
the apparatus is again inverted and the flask disconnected to
allow of the introduction of 100 grams of cement. ' The flask is
then replaced and the contents of the apparatus well shaken to
expel air-bubbles. When the latter have been completely ex-
pelled, the flask is placed upright, and after standing a short
time the level of the liquid is again read, the difference between
the two readings indicating the absolute volume of 100 grams
of the cement powder.
The apparatus devised by M. H. LeChatelier ^ consists of a
flask of a capacity of about 120 c.c, and having a neck some
20 c. in length, halfway up which is a bulb having a capacity
* "Ciments et Chaux Hydrauliques," par. E. Candlot.
' "Report of Commission des Methode d'Essai des Maieriaux de Con-
struction," The Engineer (London); Illustrated also in Meade's "Examina-
tion of Portland Cemeuit," Spaulding's "Hydraulic Cement," and Engineer-
ing News, January 29, 1903.
SPECIFIC GRAVITY
55
S
-4^
b^
-31-
-30-
/ns*tf« c/ia.3mm^
of 20 c.c. Near the bottom of the tube, or flask, is the zero
mark, and above the bulb the tube is graduated for a length
corresponding to a capacity of 3 c.c, each graduation repre-
senting .1 c.c. The diameter of the tube is about 9 mm. The
zero mark on the tube is below the bulb. The method of opera-
tion is similar to that described
above.
64. The following style of
apparatus (see Fig. 1) is sug-
gested as a very convenient
form, and one which may be
used for another test soon to
be described. In this form, the
flask, of a capacity of about
200 c.c, has straight sides and
a flat bottom. The lower part
of the burette is of large diame-
ter, about 15 mm., to allow the
cement to pass readily, while
the upper portion is made
smaller, about 8 mm., to per-
mit more accurate reading, and
is graduated from 30 c.c. to 40
c.c, the divisions being 0.1 c.c.
Half divisions may be esti-
. mated. The zero mark is in the
larger part of the burette, but it
is less difficult to make an ac-
curate reading at the zero mark,
since at the time of taking this
reading the liquid is clear; this
mark should entirely surround
the burette. The mouth of the
bottle and the lower end of the
burette should be ground to fit,
and a ground glass stopper should form a part of the apparatus.
A long pipette will be found convenient for adjusting the level
of the liquid to the zero mark.
65. Turpentine is frequently employed for this test, but it
is somewhat inconvenient to use, since its volume is so sensi-
J-— o — \tns/de «5w. tSmtfi^
t i
c
BoUk ZOO Cu. Cent. ^
Fig.
1. — SPECIFIC GRAVITY APPA-
UATUS
56 CEMENT AND CONCRETE
tive to changes in temperature. This sensitiveness renders it
imperative that the temperature at the time of taking the final
reading be the same as when the initial reading is taken, or
that a correction be applied. To assure this condition the ap-
paratus should be immersed in a water bath, and the tempera-
ture of the cement should be the same as that of the turpentine.
The use of water in the apparatus does not offer this inconven-
ience, but it is possible that the hydration of the cement during
the experiment might be sufficient to so affect the volume as
to change the result, especially with quick-setting cements.
Light oils, such as benzine and kerosene, are rather volatile,
but the former (62° Baume naptha) is recommended in the
preliminary report of the Committee of the American Society
of Civil Engineers. With the precautions mentioned above,
turpentine may be used with good results; that which has
been dried by standing over cement or quicklime is to be
preferred.
66. This test may be extended to give interesting and valu-
able results, in the following manner: When the cement has
settled in the bottle, leaving the liquid clear, pour off a portion
of the latter and replace the burette by a glass stopper. Thor-
oughly agitate the remaining liquid and cement until the latter
is in suspension; allow the cement to settle again without dis-
turbance, and it will be found that it is graded in the bottle
according to its fineness, the coarsest particles being at the
bottom. With Portland cement, if a portion of the sample is
underburned it will appear as the top layer, and be indicated
by its yellow color. It will also be interesting to note what
proportion of the cement is so fine that the separate grains
are indistinguishable. That the bottle should have straight
sides and a flat bottom is to accommodate this part of the
test, which also dictates the use of some other liquid than
water.
67. Effect of Composition, Aeration, Etc. — It has been said
above that the composition of a cement affects its specific
gravity, a highly limed cement having a higher density. On
this account an analysis for lime is valuable in connection with
this test, in order to determine whether a high specific gravity
is due to a high percentage of lime or to hard burning.
The age, or aeration of a sample affects its specific gravity
SPECIFIC GRAVITY 57
because of the absorption of water from the atmosphere. The
absorption of two per cent, of water is sufficient to lower the
specific gravity from 3.125 to 3.000. The following may be
given as illustrating this point: a certain sample of natural
cement when taken from the barrel had a specific gravity of
3.106; after it had been spread out in the air for two months its
specific gravity was 3.000. A quantity of this aerated cement
weighing 120 grams was placed in an iron vessel and heated
over an oil stove for about one hour; at the end of this time
the cement had lost two grams in weight. The specific gravity
of the fresh cement being 3.106, 118 grams would have an ab-
solute volume of 38 c.c; two grams of water would occupy 2
c.c, hence 120 grams of the aerated cement would occupy 40
c.c, and 120 -r- 40 = 3.00, the specific gravity of the aerated
cement as found above. It is not always possible to thus
drive off all of the water absorbed, since a portion of it may
enter into combination with the cement; but a sample should
always be heated for at least thirty minutes at a temperature
of 100° C. before making the test for specific gravity, and
should any appreciable loss of weight occur, it is an indication
of aeration.
68. A determination of the specific gravity is primarily a
test for burning, but it may also be of much value in detecting
adulterations, as with blast furnace slag or ground limestone.
An admixture of 10 per cent, of either of these substances would
suffice to lower the specific gravity from 3.15 to about 3.10.
The specific gravity of Portland cement ranges from 2.90 to
3.25, but a first-class product should not show a lower specific
gravity than 3.05. If fresh Portland gives a result below this
it is probably either underburned or underlimed, or, perhaps,
has been adulterated.
The specific gravity of natural cements has been found to
vary from 2.82 to 3.25. The specific gravity of one sample of
underburned natural cement was found to be lower than a
sample of the same brand which was overburned, but it seems
very doubtful whether this is true of other brands made from
rock of a different character. It was also found that the spe-
cific gravity of the coarse particles of some natural cements is
lower than that of the fine particles (see Table 10, Art, 15)^
while the opposite is true in the case of Portland cements.
58 CEMENT AND CONCRETE
No general rules can be given at present for the interpreta-
tion of this test that are applicable to all natural cements; it is
thought that the test will be of value in comparing samples
of the same brand, though it seems doubtful whether it will
prove of value in comparing one brand of natural cement with
another, since it is quite probable that the interpretation may
vary with the variety of rock used in the manufacture. The
value of the test for Portland cements is, however, well
established.
CHAPTER VI
SIFTING AND FINE GRINDING
Art. 14. Fineness
69. Importance of Fineness. — The fineness of cement is al-
ways conceded to be one of its most important qualities, and
the determination of fineness is omitted in none but the very
crudest tests. Unfortunately, however, sieves that are so coarse
as to give delusive results are usually employed. It is very easy
to show that grains of cement as large as one-fiftieth of an inch
in diameter are practically valueless, but much more difficult
to determine the point of fineness at which the particles begin
to have cementitious value.
70. A moderately coarse sieve is easier to operate than a
very fine one, less time being consumed in sifting. The impres-
sion seems to be quite general also that there is a fixed relation
between the proportions of the different sized grains in different
samples. Many specifications require that a certain percentage
"shall pass a sieve having 2,500 holes per square inch." Now,
there is little doubt that grains of cement larger than .005 inch
in one dimension have very little cementitious value, and hence
a cement, all of which would pass holes .015 inch square, while
but 50 per cent, of it would pass holes .005 inch square, is little
better than one which leaves a larger residue on the coarser
sieve but the same residue on the finer.
In America and Germany it is the usual practice in the pro-
cess of manufacture to pass the cement through a screen which
will reject particles larger than about .015 inch in diameter; the
futility in attempting to determine, with a sieve no finer than
this, the proportion of the particles which are fine enough to be
of value, is therefore apparent. Since the English cement
makers have not been so progressive in the practice of screen-
ing, they have obtained the reputation of producing a coarse
product. In many cases this reputation is probably a just one,
but when tested with a very fine meshed sieve, some of the
59
60 CEMENT AND CONCRETE
English cements do not compare so unfavorably with those of
German manufacture. It is a curious fact in this connection
that the English are the most conservative in holding to the
use of the coarse sieve in testing, which makes their cement
appear so very much coarser than the American or German
product.
71. Sieves. — Sieves for cement testing may be made either
of wire or silk gauze, set in metal or wood frames. Sieves of
perforated metal plate are sometimes employed for sifting sand,
but seldom for cement. It is with considerable difficulty that
accurate gauze sieves are obtained. They are usually desig-
nated by numbers corresponding to the number of meshes per
linear inch; this is in some respects an unsatisfactory method,
for the size of the wire, which is quite as important as the
number of meshes, is frequently not given at all, or stated
in terms of some wire gage which is capable of various
interpretations.
As usually supplied by different manufacturers, sieves pur-
porting to have the same number of meshes per linear inch may
vary in this regard as much as 10 or 15 per cent. Likewise the
size of wire used by different makers, in sieves having the same
number of meshes per inch, may vary quite as much. Again,
on account of irregularities in the gauze, the holes in a given
sieve vary one from another; in some cases an opening may be
but 60 or 70 per cent, as large in one dimension as an adjacent
one.
An ideal sieve should conform to the following requirements:
(1) holes to be of uniform size and shape throughout, (2) sides
of the holes to be very smooth, and (3) the spaces between the
holes to be of such size and shape that particles will not easily
rest there.
It is evident that the largest holes determine the character
of the sieve. For example, a sieve having half its holes 0.01
inch square and the other half 0.02 inch square, would, if used
long enough, separate the cement exactly as it would if all
the holes had been 0.02 inch square. Hence, if a very small
percentage of the holes are larger than the normal, it seriously
impairs the accuracy of the sieve by introducing an- indeter-
mination; but holes smaller than the normal have no greater
objection than that, as the sifting proceeds, they become spaces
FINENESS
61
between the real or larger holes, and as such do not fulfill the
third requirement mentioned above. The shape of the holes,
whether round, square or hexagonal, seems of minor importance
so long as uniformity is maintained. The second requirement
is necessary, because, should particles adhere to the sides of
the hole, the size of the latter would be decreased to that ex-
tent. The third requirement is for convenience, but would
require consideration if the style of the sieve were changed to a
punched metal plate.
72. The Committee of the American Society of Civil Engi-
neers, in their report on "A Uniform System for Tests of Cement "
in 1885, recommended three sizes of sieves for cement: No. 50
(2,500 meshes to the square inch) wire to be of No. 35 Stubbs'
wire gage ; No. 74 (5,476 meshes to the square inch) wire to
be of No. 37 Stubbs' wire gage; No. 100 (10,000 meshes to the
square inch) wire to be of No. 40 Stubbs' wire gage. For sand,
two sieves were recommended. No. 20 and No. 30 (400 and 900
meshes per square inch) wire to be of No. 28 and No. 31 Stubbs'
TABLE 5
Sieves : — Number of Meshes per Iiinear Inch eind Sizes of
Openings, as Found by Measurement
Pi
O
a u
'A
No. OF
Meshes
PER
Linear
Inch.
DiAKETEB OF WiKE
IN Decimals op
AN Inch.
Mean Size of Opening in Decikals
OF AN Inch.
(0
Si
<
h
Web.
Woof.
i
i
o
a
1
5
1-
3
Remarks.
Diam-
eter.
Diam-
eter.
a
b
c
d
e
/
9
h
♦
1
2
3
4
5
6
7
8
9
10
11
1
20
20
30
30
30
40
60
74
100
120
200
20
20
30
30
30
40
60
80
101
120
210
19
28i
30
29.V
36'
47
80
88^
120
170
.0185
,01«5
.0119
.0118
.0116
.0095
.0082
.0054
.0040
.0037
.0022
.0169
.0168
.0119
.0118
.0122
.0095
.0083
.0054
.0040
.0037
.0022
.0016
.0003
.0000
.0000
.0006
.0000
.0001
.0000
.0000
.0000
.0000
.0315
.0335
.0214
.0215
.0217
.0155
.0118
.0071
.0059
.0046
.0026
.0337
.0358
.0229
.0215
.0217
.0183
.0130
.0071
.0073
.0046
.0037
.0022
.0023
.0016
.0000
.0000
.0028
.0012
.0000
.0014
.0000
.0013
.93
.93
.93
1.00
1.00
.85
.90
1.00
.80
1.00
.70
Approx.
62
CEMENT AND CONCRETE
wire gage, respectively. It seems to be impracticable to com-
ply with these sizes of wires, because neither manufacturers nor
engineers appear to agree as to what diameters of wire corre-
spond to No. 37 and No. 40 Stubbs' wire gage.
73. The conferences of Dresden and Munich decided that
fineness should be determined by sieves of 900 and 4,900 meshes
per sq. cm., respectively, for Portland cement, and 900 and
2,500, respectively, for other hydraulic products, the size of the
wires being as follows: for 4,900, .05 mm.; for 2,500, .07 mm.;
and for 900, .10 mm. These sieves would have respectively
31,600 (178 X 178), 16,000 (127 X 127), and 5,800 (76 X 76)
meshes per square inch, and the sizes of the holes would be
approximately .0037 inch square, .005 inch square and .009 inch
square, respectively. It was also decided that for sifting sand,
punched metal plates were preferable to wire cloth sieves.
74. In Table 5 are given some of the results obtained by the
writer which will serve to show what variations may exist in
sieves which have been selected from a considerable number
offered for use.
Table 6 gives the data available concerning certain sieves
that have been used or recommended in this country and else-
where.
TABLE 6
Sizes of Openings in Sieves Recommended or in Use
Ref.
TTpEj
Size
Hole,
Inch
Square.
Rehabks.
1
2
3
4
6
6
7
8
9
10
11
12
13
14
a
178
127
76
76
76
176
103
170
80
60
30
20
200
100
6
C
.00197
.00276
.00394
.00437
.00691
.00162
.0022
.00279
.00651
.00881
.01214
.01899
.0024
.0045
.00366
.00512
.00920
.00875
.00721
.004
.0075
.00309
.00699
.01119
.02119
.03101
.0026
.0065
Established by Conferences, Dresden & Munich.
(( (( 1.1. (( ((
«( (1 {.1. (( i(
Present German Standard.
Recommended by H. LeChatelier.
Silk mesh — Vyrnwy Reservoir.
Cornell University, Marx & Mosscrop, 1887.
(( (( (( t( ((
11 (1 11 (( ((
11 11 11 (( (1
(1 11 (1 (( ((
Progress Report, A. S. C. E. Committee, 1903.
11 11 11 i( 11 t(
SIFTING AND GRINDING
63
75. The time sifting should be continued will depend on the
fineness of the meshes, the diameter of the sieve, the amount
of cement taken, and the manner of sifting ; it will also depend
upon the fineness of the cement, as well as its nature, and its
condition as to dryness. But, although some care is necessary
concerning these points, very large variations in results due to
variations in the time the sifting is continued may easily be
avoided. The diameter of the sieve is usually made greater
for the finer meshes, but this is not always the case. It is a
common practice in America to use one-tenth of a pound of
cement in testing the fineness, using a scale weighing in ten-
thousandths of a pound. Where the metric system is in use
{and it may well be adopted in a cement laboratory), 100 grams
of cement are usually taken.
76. M. H. LeChatelier recommends a sieve having 900 meshes
per sq. cm., of wire 0.15 mm. diameter, giving holes 0.18 mm.
(.0072 inch) square. He prefers machine screening, but says
that for current tests it might be sufficient to screen by hand
for ten minutes with a sieve three decimeters (about 12 inches)
in diameter.
Table 7 is taken from experiments made by M. Durand-
Claye and M. Candlot, and shows what differences may arise
from varying the length of time that a sample is screened. The
cements used were not the same in the two cases, but the sieves
had each 5,000 meshes per sq. cm. (about 180 per Unear inch),
and 100 grams of cement were taken in each case. Had a coarse
sieve been used, the differences would have been much less
after the same lengths of time.
Fineness : -
TABLE 7
-Mechainiceil and Hand Sifting Compsired
M. Duband-Claye.
Mechanical Sieve Making 200
Revolutions pkb Mindtk.
M. Candlot.
Hand Sieve, 12 Inches in
DiAMETBB.
No.
Revolutions.
Per Cent.
Retained.
Ditf.
After
Minutes.
Per Cent.
Retained.
Diff.
600
1,000
1,600
2,000
2,600
41.2
39.4
38.6
38.0
37.6
Y.8
.8
.6
.4
6
10
20
30
40
29.6
29.1
28.4
28.0
27.7
ois
0.7
0.4
0.3
64
CEMENT AND CONCRETE
77. Table 8 gives the results obtained by the author in
sifting several samples. The No. 80 sieve was about 6^ inches
in diameter, and Nos. 120 and 200 about 5^ inches. One hun-
dred grams of cement were taken in each case, and the sieve
was shaken vigorously by hand. It is seen that coarse samples
require less time for sifting than fine samples, and that natural
cements require a longer time than Portlands. With the No.
80 sieve, five minutes usually suffices to obtain the fineness,
TABLE 8
Effect of Time of Sifting on the Result Obtained in Testing
Fineness
PS
Sieve.
Cement.
Per Cent, by Weight that had
Passed Sieve afteh Sifting.
5|
Kind.
Brand.
Sam-
ple.
6
a
V.
a
a
iS
i
■3
1
1
3
a
1
1
4)
3
1
3
s
0
3
a
^
0.6 ^
Sa
^^
n
■0
t-
0
3
k
s
m
a
b
c
d
e
f
9
h
i
1
80 J
.0071
by
.0071
Port.
X
685
91
92
93
93
2
3
4
5
6
7
8
.0046
K
Nat.
11
Y
S
z
Bn
An
In
Gn
42 s
34 s
43 s
27 s
G
28 s
108 T
82
95
100
68
78
85
75
85
96
86
96
71
80
89
89
71
82
90
90
82
90
91
91
9
120 1
by
.0046
Port.
X
685
45
78
82
84
84
10
11
12
13
14
15
11
11
11
Nat.
11
11
Y
S
z
Bn
An
In
42 s
34 s
43 s
27 s
G
28 s
41
72
54
27
45
13
73
89
94
62
73
42
77
90
96
65
76
64
78
91
97
66
78
82
78
91
98
66
78
83
16
''
.0036
It
Gn
108 T
5
16
27
64
82
85
86
17
200 J
by
.0037
Port.
X
685
68
65
68
70
71
18
11
Y
42 s
65
68
71
72
72
19
11
S
34 s
72
76
78
80
81
20
11
z
43 s
74
78
81
82
83
21
Nat.
Bn
27 s
57
59
60
60
22
11
An
G
67
69
70
72
72
2;^
It
In
28 s
41
53
69
75
77
78
24
"
Gn
108 T
40
49
64
76
79
FINENESS
65
and with the No. 120 sieve, but little cement usually passed after
the sifting had continued ten minutes, though with one brand
of natural, Gn, it appears that the true fineness would not be in-
dicated by sifting less than 20 minutes. With the No. 200
sieve 20 minutes is usually required, and in the case of two samples
of natural cement, a still longer time appears to be necessary.
78. Conclusions. — Until there is a proper standard in the
United States concerning sieves and methods of sifting, the best
that can be done is to select, from the sieves that manufacturers
have to offer, those which appear to be most nearly uniform in
size of mesh, and then actually determine the size of the holes.
This may be done by counting, under the magnifying glass, the
number of meshes per inch each way, and determining the size
of wire with a micrometer wire gage.
As to the time sifting should be continued, one can easily
find by trial the time required in using a given sieve in order to
confine the error within given limits. A fine natural cement
should be selected to determine this, as such a cement requires
the longest sifting. Care should be taken that the cement is
well dried before making the test for fineness. It will be found
that for sieves having holes between .003 inch and .004 inch
square (sieves approximating 170 to 200 meshes per linear
inch) 20 to 30 minutes are required, while for sieves having
holes .007 to .009' inch square (approximately 70 to 100 meshes
per hnear inch) from five to ten minutes will usually suffice.
79. Specifications for Fineness. — The following table has
been compiled to show what are considered reasonable require-
ments for fineness. In most specifications there is the usual
indetermination concerning the sizes of holes in the sieves.
TABLE 9
Requirements as to Fineness
Spbcification.
Date.
Pek Cent. Required to Pasu
Sieve Having 10,000
Holes peb Squaue Inch.
Portland.
Natural.
U. S. Army Engineers .
U. S. Navy Department
City Pittsburg, Pa. .
1901
1900
1897
1896
1895
92
95
90
90
96
85
80
77'
'so'
New East River Bridge
Topeka, Kan., Bridge
Master Builders' Exchange
, Phila.
66
CEMENT AND CONCRETE
Art. 15. Coarse Particles in Cement
80. The Effect of Coarse Particles on the Weight of Cement.
— To remove the coarse particles by sifting will reduce the
specific gravity of a sample of Portland cement, as the un-
ground particles are from the harder burned and denser por-
tion of the clinker, and to remove these denser particles will,
of course, decrease the average density of the sample. This is
not always the case with natural cements, as is shown by the
following tests: —
TABLE 10
The Relative Specific Gravity of Coarse and Fine Particles of
Cement
Cement.
Specific Gravity.
Kind.
Brand.
Fineness.
Portland
Natural
R
X
Gn
An
As received
50-100 . .
Pass 50 .
Ret. on 50
Pass 100 .
Ret. on 50
Pass 50 .
Ret. on 50
3.086
3.145
3.039
3.125
2.874
2.817
2.945
2.817
The apparent density or weight per cubic foot of Portland
will be reduced more than the specific gravity by the removal
of the coarse particles; because not only will the true density
be decreased, but the packing, which is facilitated by a wide
range in the sizes of the particles, will be less perfect than when
the coarse particles are present. In § 89 a table is given show-
ing the changes in specific gravity and weight per bushel oc-
casioned by removing the coarse particles by sifting.
81. Effect of Coarse Particles on the Time of Setting. —
Table 11 gives the results of a number of tests on Portland and
natural cements to determine the relative time of setting of
samples from which the coarse particles had been removed by
the No. 200 sieve, while Table 12 gives results obtained with
a sample of natural cement of varying fineness.
In Table 11, 30 per cent, of water was used for all Portland
cements, and 36 per cent, for all naturals, but the consistency
COARSE PARTICLES
67
varied as stated in the table. It is seen that in nearly every
case the setting was hastened by removing the coarse particles,
though this may have been due in part to the fact that with the
same percentage of water the finer cement gave a stiffer paste.
For the tests in Table 12, the attempt was made to make all
of the mortars of the same consistency by varying the percent^
age of water. As would be expected, the coarse particles are very
slow setting. In fact, what hardness they attained was prob-
ably due largely to the fine dust that adhered to the grains.
These coarse particles may be considered as practically inert,
and their presence in a sample would naturally make it slow
setting. To show this by actual test, however, is very diflScult,
TABLE 11
Effect of Coarse Particles on the Time of Setting
Cement.
Cement Passing No. 20
Sieve.
Cement Passing No. 200
Sieve.
Kind.
Brand.
Time to bear
J lb. wire.
Minutes.
Consistency.
Time to bear
J lb. wire.
Minutes.
Consistency.
Portland
Y
39
Trifle moist
13
Trifle dry
"
X
9
Moist
4
0. K.
♦'
Z
432
Trifle moist
354
Trifle dry
it
s
566
It tt
341
It tt
Natural
Gn
31
. . .
29
.
«>
Bn
143
Trifle moist
151
Trifle dry
u
In
397
It tt
256
•
"
Hn
256
• • •
233
Note: — 30 per cent, water used for all Portlands.
36 per cent, water used for all natural cements.
TABLE 12
Effect of Coarse Particles on Time of Setting
Natural Cement, Brand Gn — All pastes appeared same consistency.
Fineness.
Water Used as
Per Cent, of
Cement.
Time to Beak
i LB. Wire.
Minutes.
Time toBe.\r
1 LB. Wire.
Minutes.
Pass No. 20 sieve
33
14
169
" 50 "
36
29
219
100 "
38
24
214
Retained on 60,
reground to pass 100
Pass No. 50. retained
28
73
670
on No. 100
34
206
8!K)
68 CEMENT AND CONCRETE
as the amount of water required to bring the mortars to the
same consistency varies with the amount of coarse particles
present, and as there is no very satisfactory method of testing
the consistency, the tests for time of setting have in them this
indetermination.
82. Effect of Coarse Particles on the Tensile Strength. — A
cement having a certain quantity of coarse particles will fre-
quently give a higher tensile strength when tested neat than a
cement from which the coarse particles have been removed by
screening. The reason for this may be found in the fact that
a wide range in the sizes of grain of the powder facilitates pack-
ing, both when dry and when mixed with water to form a paste.
Another reason is that the unground particles are stronger
than the hardened mortar, and, considering the broken section
of a briquet, the break does not take place through these par-
ticles, but they are pulled out of their bed; this virtually in-
creases the area of section. Were the same sample of cement
reground, so that a certain proportion of the coarse particles
was rendered active, it might then give a higher strength, neat,
than at first. If so, the reason would be found in the fact that
the coarse particles, being the hardest burned, were really from
the best part of the cement clinker, and rendering these parti-
cles active by fine grinding increased the cohesive properties of
the cement so much as to overcome the physical effect of the
coarse particles, which, when judged by neat tests, appear to be
beneficial. The above serves to illustrate the difference be-
tween sifting and fine grinding which are so frequently con-
fused in treating this subject.
83. Among the many tests that have been made to show
the effect of sifting on the cohesive and adhesive strength of
cements, a few may be given as follows: —
Mr. Maclay^ gives a few experiments to show that the pres-
ence of coarse particles increases the cohesive strength, neat,
seven days.
Lieut. W. Innes^ gives two tables of results obtained by ex-
perimenting on very coarse cements. The tables show that
removing the particles that would not pass through sieves of
» Trans. Am. Soc. C. E., Vol. vi.
* Minutes Proc. Inst. C. E., Vol. xxv.
COARSE PARTICLES 69
1,296 meshes and 2,500 meshes per square inch, decreased the
strength when tested neat at the ages of three months and six
months; but increased the strength when sand mortars were
used. The differences at six months were relatively somewhat
less than at three months. By separating a sample of cement
into two parts, that passing a sieve having 2,500 meshes per
square inch and that retained on the same sieve, and then
remixing the screenings with the fine portion, he found
that the highest strength, neat, six months, was given by the
mixture containing the largest amount tried (70 per cent.) of
screenings.
84. In the tests of cement for the Cairo Bridge^ a series of
experiments was made to determine the effect of coarse parti-
cles on the value of both Portland and natural cements. The
cement was separated into two parts, by a sieve having 10,000
meshes per square inch. Briquets were made both neat and
with sand, the cement used being made of 100, 90, 80, 70 and
60 volumes of sifted cement to 0, 10, 20, 30, and 40 volumes,
respectively, of cement screenings. The briquets were broken
when six months old.
It was found that in the case of Portland cement, neat, the
highest result was obtained with the largest (40) per cent, of
screenings, but with one and two parts sand, the strength
steadily fell as larger amounts of screenings were used. With
Louisville natural cement the presence of screenings seemed to
have little effect on neat tests; and with one part of sand to one
of cement, the use of as much as 30 per cent, of screenings to
70 per cent, of sifted cement did not appear to decrease the
strength. With two parts sand to one cement, the results were
slowly diminished by successive additions of larger percentages
of screenings.
85. M. R. Feret is said to have replaced with sand the grains
of cement retained on sieves having 5,800 and 32,300 meshes
per square inch, and found that, except in the case of neat ce-
ment mortars, the substitution of sand for coarse particles of
cement did not decrease the strength. In experimenting on
this subject Mr, Eliot C. Clarke ' found that the coarse particles
' Jour. Assn. Engr. Soc, 1890, and Engineering News, Jan. 31, 1891.
» Trans. A. S. C. E., Vol. xiv, pp. 158-162.
70
CEMENT AND CONCRETE
TABLE 13
Effect of Removing Coarse Particles from Natural Cement
No. Parts
Sand TO
Water as
Per
Cent, of
Tensio! Strength, Pounds
per Square Inch.
Cement.
One
Cement
BY
Weight.
Weight
Dry
Ingredi-
ents.
7 da.
28 da.
3 mo.
6 mo.
2 years.
A
None
33.3
120
276
B
((
35.7
100
266
C
(1
38.6
83
263
B
ti
28.3
202
264
E
n
36.0
127
143
A
One
19.0
121
263
330
380
B
^i
19.6
104
261
344
398
C
, "
20.0
94
261
331
385
D
u
16.0
286
360
396
385
A
Two
16.1
168
216
223
210
B
t(
16.1
203
246
267
302
C
(1
16.1
218
297
317
368
D
tt
13.9
227
230
246
262
E
n
15.8-16.1
. . .
71
40
67
50
A
Three
14.6
127
128
B
u
14.6
. . .
. . .
167
164
C
((
146
205
234
D
(1
12.1
125
118
Fineness of Cement
Cement A
Cement B
Cement C
Per Cent. Passing Sieve No.
50
82
100
100
70
85
100
120
64
78
91
Note: — All cement from same barrel, Brand Bn, Sample 27s.
Sand, crushed quartz 20-30.
All briquets made by one molder and stored in one tank.
AH results, mean of 5 briquets, except two which are means of
ten and two briquets, respectively.
A — Cement passing No. 20 sieve, holes .033 inch square.
B— " " " 50 " " .012 "
C— " " " 100 " " .0065 "
D — " retained on No. 50, reground to pass No. 100.
E — " passing No. 50, retained on No. 100.
COARSE PARTICLES
71
of cement were somewhat better, for use in mortar, than fine
sand, but very little better than coarse sand.
86. The tests given in Table 13 were made under the au-
thor's direction to determine the effect of sifting and the value
of coarse particles. It is seen that in neat tests the strength is
slightly diminished by sifting out the coarse particles; in the
tests of mortars containing equal parts by weight of sand and
cement, there is little difference in the strength of the three
samples, though the coarser cement appears to gain its strength
a little more rapidly. With two parts sand to one of cement,,
the greater value of the fine particles is very noticeable, and
with one-to-three mortars the difference is still more marked,
the sifted cement giving 80 per cent, greater strength than the
unsifted.
87. In Table 14 these results are arranged in a different
way. If we assume that the particles that will not pass the
No. 120 sieve are not cement at all, but equivalent to sand,
TABLE 14
Effect on Tensile Strength of Removing Ccarse Particles from
Natural Cement
Cemext.
Per Cent.
Passing Sieve
No. 120.
Parts Sand
TO
One Cement.
Parts Sand and
Coarse Par-
ticles TO One
Part
Fine Particles.
Strength
OF Mortar after
Two yEARS.
A
64
3
5.2
128
B
78
3
4.1
164
A
64
2
3.7
210
C
91
3
3.4
234
B
78
2
2.8
302
G
91
2
2.3
358
A
64
1
2.1
380
B
78
1
1.6
398
C
91
1
1.2
385
and that all particles passing this sieve are cement, we obtain
a new set of proportions of sand to cement. Thus the sample
of cement passing No. 20 sieve, sample A, would be composed
of 64 parts cement and 36 parts sand, and the 1 to 3 mortar
would have in reality the proportion 64 cement to 336 sand, or
1 to 5.2, It is seen that the tensile strength bears a closer
relation to the richness of the mortar when considered in this
way. There is, of course, no abrupt division in size such that
72
CEMENT AND CONCRETE
TABLE 15
Value of Coarse Particles of Cement, Natural and Portland
03
Tbssile Strength, Pounds
PER Square Inc
a.
Neat Cement.
1 Part Standard
Sand to 1 Cement.
3 Parts Standard
Sand to 1 Cement.
3 Parts Limestone
Screenings,
(}g) to 1 Cement.
3mos.
4 m08.
lyr.
3mo6.
lyr.
3mo8.
lyr.
3mos.
lyr.
d
e
/
9
h
i
J
it
I
1
330
390
108
139
160
2.34
2
259
336
193
217
269
332
3
295
334
203
224
251
319
4
306
370
102
106
137
170
6
309
343
92
96
1.S9
155
6
630
706
786
812
378
395
472
589
7
550
553
755
838
423
463
538
677
8
621
665
745
891
455
469
561
676
9
615
651
746
841
357
399
425
568
10
591
764
765
837
362
354
405
506
Ref. No. 1. Natural cement passing No. 20 sieve.
" " 2. Natural cement passing No. 80 sieve.
" " 3. Natural cement reground before sifting, until all passed
No. 80 sieve.
" " 4. Natural cement, 64| per cent, of cement passing No. 80
sieve mixed with 35i per cent, of limestone screen-
ings retained between Nos. 20 and 80 sieves.
" " . 5. Natural cement, 64f per cent, of cement passing No. 80
sieve mixed with 35^ per cent, of crushed quartz
retained between Nos. 20 and 80 sieves.
" " 6. Portland cement passing No. 40 sieve.
" " 7. Portland cement passing No. 80 sieve.
" " 8. Portland cement reground (before sifting) until all passed
No. 80 sieve.
" " 9. 81 § per cent, of cement pas.sing No. 80 sieve mixed with
18J per cent, limestone screenings retained between
Nos. 40 and 80 sieves.
" " 10. 81§ per cent, of cement passing No. 80 sieve mixed with
18J per cent, crushed quartz retained between Nos.
40 and 80 sieves.
Of the natural cement passing No. 20 sieve, 35^ per cent, was retained
on sieve No. 80, while 645 per cent, passed the No. 80 sieve. In lines 4 and
5 the coarse particles of cement (20-80) were removed and replaced by an
equal weight of sand grains, retained between sieves 20 and 80.
Of the Portland cement passing No. 40 sieve, 18J per cent, was retained
on sieve No. 80, while 81 § p>er cent, passed sieve No. 80. In lines 9 and 10
the coarse particles of cement (40-80) were removed and replaced by an equal
weight of sand grains retained between sieves 40 and 80.
All briquets made by same molder, each result mean of five specimens.
FINE GRINDING 73
coarser particles act only as sand, while finer ones enter into
combination as cement; part of the coarse particles will have
some cementitious value, while some of the finer particles will
have somewhat the effect of sand.
As to the sample composed of coarse particles reground, it
must be considered that although this sample was passed through
the No. 100 sieve, yet it was in reality much coarser than sam-
ple C, because the particles were harder, and the grinding
in the mortar less thorough than the original grinding. Since
this sample of reground cement gives so high a strength neat
and with one part sand, it appears that the hard particles from
which it was made are of excellent quality if ground fine enough,
and the relatively lower results with larger proportions of sand
must be attributed to imperfect grinding.
The coarse particles retained between sieves 50 and 100 gave
a higher strength neat than was expected, but much of this
strength may be due to the floury portion of the cement that
doubtless adhered to the coarse particles instead of passing
through the sieve.
88. The tests in Table 15 were made to determine whether
the coarse particles of cement are of greater value in mortar
than the same quantity of fine sand. The coarse particles of
the cement were sifted out and replaced with sand grains of
about the same size. The conclusion drawn from the preced-
ing tests would indicate that some of the coarse particles of
cement might be replaced by sand without diminishing the
tensile strength; but the tests given in this table indicate that
this is not the case when it is a question of substituting sand
grains of the same size. Although such a substitution has
little effect on the strength of rich mortars, it results in a de-
creased strength with mortars containing as much as three
parts sand to one of cement by weight. (See § 85 in this con-
nection.)
Art. 16. Fine Grinding
89. Effect of Fine Grinding on the Weight of Cement. — Fine
grinding will decrease the weight per cubic foot, the fine ce-
ment not packing as closely as the coarser product. In "Ce-
ment for Users," by Mr. Henry Faija, the following results are
given, showing the relation between fineness, weight, and spe-
74
CEMENT AND CONCRETE
TABLE 16
Relation of Fineness to Specific Oravity and Weight per Bushel
From " Ceiuent for Users "
Specific Gravity.
Weight pkb Bushel.
Sam-
ple.
a
b
c
a
b
c
d
e
1
3.00
2.97
3.07
116.5
107.5
121.0
112.0
115
2
3.03
2.94
3.04
116.0
104.0
130.5
109.0
115
3
3.02
2.91
3.035
114.0
100.0
128.0
104.5
109
cific gravity: (a), cement as delivered; (b), siftings that passed
through sieve with 2,500 holes per sq. in.; (c), coarse, retained
on above sieve ; (d), cement all ground to pass above sieve; (e),
coarse particles reground to pass above sieve.
90. Effect of Fine Grinding on Time of Setting. — Since the
coarse particles of cement are practically inert, there is every
reason to believe that finer grinding will increase the activity
of a sample, since it will render some inert particles active.
For the reason mentioned in § 81, however, it is difficult to show
this difference in time of setting by actual tests.
Tests reported by Mr. David B. Butler ^ showed that several
Portland cements which took an initial set in 20 to 30 minutes
and hard set in 45 to 120 minutes would, when reground to pass
a sieve having 180 meshes per linear inch, begin to set in from
1 to 7 minutes and set hard in 5 to 15 minutes. These may be
considered extreme results; the rise in temperature of these
cements during setting was so great as to indicate they were
not normal cements, and variations in consistency of the pastes
may have influenced the time of setting.
91. EFFECT OF FINE GRINDING ON STRENGTH. — Since the
best burned clinker of Portland cement is the hardest, it follows
that the unground particles would, if ground fine enough to
become active, form the best portion of the cement. This is
not, a priori, true of natural cements, because burning renders
some varieties of cement rock softer at first, but when the burn-
ing is carried beyond a certain point they become harder again.
The coarse particles in a natural cement may thus be either
^ Proceedings Inst. C. E., 1898.
FINE GRINDING
75
from underburned or overburned rock; hence it is possible that
in some cases it might be better to leave the hardest particles
in an unground state. Thus, while it has been generally ac-
cepted that fine grinding improves Portland in a twofold de-
gree, — by bringing into action the best burned clinker, as well
as by rendering a given weight of cement capable of coating a
larger number of sand grains, — a similar conclusion concern-
ing natural cement is not well established.
TABLE 17
Effect of Fine Grinding of Natural Cement on the Tensile
Strength of Mortar
Tensile Stbenoth, Pockds peb Squabe Inch.
Neat
1 Part Stand-
ard Sand
to 1 Cement.
2 Parts Standard Sand
3 Parts
Standard
4 Parts
Standard
Cement.
to 1 Cement.
Sand to 1 Ce-
ment.
Sand to 1 Ce-
ment.
7 da.
6} mo.
7 da.
28 da.
28 da.
3 mo.
6 mo.
2yr.
6 mo.
2yr.
6 mo.
2 yr.
a
6
c
d
e
/
9
h
i
J
k
I
1
268
538
224
381
207
354
291
70
202
48
156
49
2
283
473
230
350
245
433
426
102
302
65
212
78
3
278
638
307
433
292
469
406
92
305
61
240
65
4
392
592
368
538
271
344
369
160
274
110
205
90
5
21
73
45
Befebekce.
Fineness of Cement,
Peb Cent. Passing
Sieve Number.
100
120
1. Cement as received passed through Up. 20
2. Cement as received passed through No. 100
3. Reground in mortar, not sifted ....
76.5
100.0
95.8
72.4
94.6
91.6
Cement; Natural, Brand Jn.
No. 1. Passing No. 20 sieve.
" 2. Passing No. 100 sieve.
" 3. Reground before sifting.
" 4. Particles retained on No. 50 sieve, reground to pass No. 100 sieve,
" 5. Particles retained on No. 50 sieve, reground to pass No. 50 sieve,
but retained on No. 100 sieve.
All briquets made by one molder and immersed in one tank. In general,
each result is mean of five 3p>ecimeQS.
76 CEMENT AND CONCRETE
92. Some tests bearing upon the value of fine grinding have
already been given in Table 15. Samples 3 and 8 were reground
with mortar and pestle before being sifted. If we compare the
results given by sample 3 with those obtained with samples 1
and 2, not reground, it appears that the regrinding diminishes
the strength in neat mortars but increases it in mortars con-
taining three parts sand to one of cement. Regrinding ap-
pears to be no better, however, than sifting. Comparing sam-
ple 8 with samples 6 and 7, it is seen that regrinding Portland
cement does not diminish the strength in neat mortars to the
same extent as sifting does, and in sand mortars regrinding
generally results in a greater increase in strength than sifting.
93. The results in Table 17 were obtained with another
sample of natural cement and are of greater practical value as
indicating the importance of fine grinding, since in these tests
a sample is included obtained by regrinding the original cement
without previous sifting. The conclusions concerning the ce-
ment retained on No. 50 sieve reground to pass No. 100, and
the coarse particles alone retained between sieves 50 and 100,
are practically the same as those drawn from Table 13.
As to the other three samples, the No. 20 sieve removed only
a very few coarse particles, and that passing this sieve may be
considered to represent the cement as received The No. 100
sieve removed about 24 per cent, by weight from the original
cement, and the cement that was reground contained but about
4 per cent, of particles which would not have passed the No.
100 sieve. The third sample, reground cement, may be com-
pared with the first to indicate the improvement obtained by
finer grinding, and it may be compared with the second to de-
termine the difference between removing the coarse particles by
sifting and reducing them by fiuer grinding. In considering
these results it will be best to neglect the two-year tests, since
all of the samples failed at this age. A comparison of the re-
sults obtained with these three samples indicates that while the
advantage of finer grinding is not apparent in neat tests, in
sand mortars the value of finer grinding is more marked the
larger proportion of sand used, so that with three or four parts
sand, the strength with the fine samples is about 50 per cent,
greater than with the cement as received. It also appears that
the reground sample gains its strength more rapidly than the
FINE GRINDING 77
sifted sample, though at six months it seems to make little dif-
ference whether the coarse particles are removed by sifting or
reduced by grinding.
94. Conclusions as to the Effect of Fine Grinding and Sifting
on Tensile Strength. — The general conclusions to be drawn
concerning fine grinding and sifting may be summarized as fol-
lows: According to the tests given, it appears that to remove
the coarse particles from a sample of natural cement by sifting,
or to reduce them by finer grinding, generally diminishes the
strength obtained in tests of neat cement mortars. In one-to-
one mortars, the strength of the finer samples is not much
greater than when the coarse particles are present; but in mor-
tars containing greater proportions of sand, the advantage ob-
tained by eliminating the coarse particles is very marked
in the case of natural cement, the strength given by the
finer samples sometimes exceeding that of the original cement
by more than 60 per cent. While the advantages of sifting
and finer grinding are also important for Portland cements,
there does not result such a large proportionate increase in
strength.
Reground samples of natural cement gain strength more
rapidly than resifted samples, but eventually the strength
attained is about the same. In Portland cements regrinding
seems to be of greater value than resifting. A sample of natural
cement made from coarse particles reground gains strength
rapidly, and for mortars with small proportions of sand, gives
good results. The fact that such samples do not give a high
strength with large proportions of sand is doubtless due to the
fact that the grinding is not thorough, and the indications are
that the material of which such coarse particles are composed
would form a valuable part of the cement if ground fine
enough.
The coarse particles of either natural or Portland cement
may be replaced by grains of sand of the same size without
materially affecting the strength attained by neat and one-to-
one mortars, but for mortars containing larger proportions of
sand, such a substitution results in a decreased strength.
95. Finally, it may be said that the process of manufacture
and the character of the materials from which cement is made
have such an influence on the relative proportions of fine and
78 CEMENT AND CONCRETE
coarse particles that the percentage of finest particles cannot
be determined by testing with a coarse sieve. While it is not
known at what point of fineness grains of cement begin to have
cementitious value, or what proportion of the cement should be
the finest flocculent matter, it is certain that a cement should
leave as small a percentage as possible on a sieve having holes
.004 inch square, in order to have the greatest sand carrying
capacity.
There is, however, a reason for using a comparatively coarse
sieve in connection with the fine one. Overburned lime, which
is likely to occur in Portland cements, is more dangerous in the
form of coarse particles than an equal quantity in a fine condi-
tion, because coarse particles slake more slowly and it is better
that expansion should occur early in the process of hardening
if it is to occur at all. For the same reason a cement that would
be unsound normally may be rendered less dangerous by re-
grinding.
As fine grinding is expensive, it is only a question as to when
the increased strength obtained is offset by the extra expense
incurred in grinding. There is now little trouble in obtaining
either natural or Portland cement of which from 70 to 85 per
cent, will pass holes .004 inch square. (See § 77.)
CHAPTER VII
TIME OF SETTING AND SOUNDNESS
Art. 17. Setting of Cement
96. Process of Setting. — When cement is gaged with suffi-
cient water to bring it to a paste, and is then left undisturbed,
it soon begins to lose its plasticity and finally reaches such a
condition that its form can no longer be changed without pro-
ducing rupture. This change of condition is known as the
^'setting" of cement and is considered to be, in a measure, dis-
tinct from "hardening." Setting usually takes place within a
few hours, or perhaps minutes, while the hardening is continu-
ous for months or years.
The precise chemical changes that take place in the setting
and hardening of cements are not thoroughly understood. The
chief cementitious ingredient in Portland cement is considered
to be a tricalcium silicate, 3 CaO, Si02; in contact with water it
forms hydrated monocalcic silicate and calcium hydrate. This
process is believed to contribute more to the final hardening of
the mortar than to the setting, though the hydration of the
finer particles of this important compound also contributes to
the first setting. It is considered that the calcium aluminates
play an important role in the first setting of cement, as they set
rapidly in contact with water, and it has been suggested that
they form the chief active constituents of natural cement.^
These chemical changes cause the formation of crystals
which by their interlocking and adhesion give strength to the
new compounds. For a scientific and detailed treatment of
this subject, the reader is referred to the articles of M. H. Le
ChateUer in Annates des Mines, 11, pp. 413-465, Trans. Am.
Inst. Mining Engineers, August, 1893; to the conclusions of
S. B. and W. B. Newberry, Cement and Engineering News,
1898; and to " The Constitution of Portland Cement from a
> S. B. Newberry, " Mineral Resources of the United States," 1892.
79
80 CEMENT AND CONCRETE
Physico-Chemical Standpoint," a paper by Mr. Clifford Richard-
son read before the Association of Portland Cement Manufac-
turers at Atlantic City, June 15, 1904, Engineering Record,
August 13 and 20, 1904, Engineering News, August 11, 1904.
97. THE RATE OF SETTING AND ITS DETERMINATION. — The
setting of cement being a gradual and continuous process with-
out well-defined points of change, it is necessary, in order to com-
pare the rates of change in condition of different samples, to
adopt an arbitrary standard. The method usually adopted is
to determine the resistance of the mortar to the penetration of a
wire or needle. The wires used by General Tottcn and rec-
ommended by General Gilmore for this purpose are now in
general use in this country. One of the wires is xV ii^ch in diame-
ter and is loaded to weigh ^ pound; the other is i^^ of an inch
in diameter and loaded to weigh one pound. The paste is said
to have reached "initial set" and "end of set" when these two
wires, respectively, fail to make an impression on the surface.
98. M. Vicat also suggested a needle test as follows: The
cement paste is placed in a conical ring, 4 cm. in height and 7
cm. in diameter at the base. The consistency should be such
that a rod 1 cm. in diameter and weighing 300 grams does not
entirely pierce the mass. This consistency having been ob-
tained by trial, a needle of circular cross-section having an area
of 1 sq. mm. and loaded to weigh 300 grams, is gently lowered
on the paste. The moment when this needle no longer pene-
trates the mass is called the beginning of the set, and the time
in which it fails to make an impression upon it is called the end
of setting. It may be mentioned in passing, that, according to
a few comparative tests made by the author, when a cement
paste has "set" by Gilmore's "heavy" wire, ^ inch weighing
one pound, it requires about 1,100 grams weight on the Vicat
1 sq. mm. needle to make an impression on the paste. Vicat's
method was indorsed by the Munich Conference and was sug-
gested in the recent progress report of the Committee of the
American Society of Civil Engineers.
99. M. LeChateher has suggested a modification of this
method by substituting for the rod 1 cm. in diameter a disc of the
same diameter carried by a slender rod, the disc being loaded
to weigh 50 grams, the normal consistency being such that the
disc will stop midway in the ring, or "vase." The beginning
SETTING OF CEMENT 81
and end of setting he would define by the penetration of the
needle (1 sq. mm. in section) to mid-depth in the ring, the
weights being 50 grams and 3,000 grams, respectively.
100. An approximate method of determining time of setting
is also in Use as follows: After mixing the cement paste to the
proper consistency, place enough of it on a glass plate to form
a thin cake, or "pat," about three inches in diameter and one-
half inch thick at the center, thinning toward the edges. When
the pat is sufficiently hard to bear a gentle pressure of the fin-
ger nail, the cement is considered to have begun to set, and
when it is not indented by' a considerable pressure of the thumb
nail, it may be said to have set.
101. Mr. Henry Faija objected to all methods which are
based upon the rates of acquiring hardness, on the ground that
there are periods in the early stages of hardening that may be
more rationally defined. He considers that the time at which
the water leaves the surface of the pat, depriving it of its glossy
appearance, is really the beginning of setting, and that this
time may or may not correspond to the result obtained by the
use of the needle.
102. Variations in the Rate of Setting. — Some of the quali-
ties which determine the actual rate of setting of a cement
are, its composition, degree of burning, age and fineness. Aside
from these qualities of the cement itself, the addition of certain
salts subsequent to the manufacture also influences the rate.
The observed rate of setting will be influenced by the details
of the test, such as the quantity, temperature and composition
of the water used in gaging, the amount of gaging, the tem-
perature of the cement, and the temperature and character of
the medium in which the pat is placed after molding.
103. An over-limed or highly limed cement is usually slower
setting than an over-clayed one. Among natural cements, those
of the aluminous variety are usually quick setting. Other
things being equal, a well-burned Portland cement will be slower
setting than an underburned sample. It is not certain that
such is the case for all natural cements, though it probably is
true of most of them. It has been said that underburned ce-
ments owe their quick setting to their porosity, but the forma-
tion of different compounds in the higher temperature may also
account for the difference.
82
CEMENT AND CONCRETE
104. The effect of the age of cement on its time of setting
is very marked, but varies widely with different samples. The
idea that cements invariably become slower setting by storage
is a false one. The origin of this error may be found in the
fact that by the time cement has reached its destination, it
has usually passed through the earlier and more rapid changes
in characteristics. Dr. Erdmenger ^ has stated that some Port-
land cements become slower setting, while some set more rapidly
as a result of storage. Dr. Tomei made experiments on several
Portland cements ^ which show that they generally become
quicker setting at first (from one to four months after grind-
ing), and then become gradually slower setting, until at the
end of a year they set in about the same length of time as
when fresh. The writer has seen this trait exhibited very
TABLE 18
Time of Setting of Five Samples of Natural Cement as Affected by-
Aeration
Time Setting
Time Setting
Water.
X
Cement
Cement Aerated
H
FBOM Package.
19 Days.
. n
<0
<c
6
«
Ed
Ok
■w "^
is
«3
■ u
u
.^
S3
H
h
<
u
Cut*
<i
^
£■
Dlff.
f-e.
^
^
.0
Diff.
i-h.
Remarks.
m
^'
s
^
•**
^
Mm.
Min.
Min.
Min.
Min.
Min.
a
b
c
d
e
/
9
h
i
J
1
84 R
32.0
65°
67-73°
62
110
68
64
173
119
Five sample?,
2
83 R
ii
50
100
60
61
164
113
game brand.
U, and Oj re-
quired more
o
82 R
t(
44
100
66
48
166
118
4
\U
34.7
60
280
220
100
326
226
and less wa-
5
0,
29.3
101
349
248
147
306
159
ter respect-
ively than
the others to
6
84 R
40.0
87
1200
1110
130
1241
nil
7
mn
<t
80
1178
1098
122
1233
1111
make same
8
82 R
"
72
1202
1130
125
1227
1102
consistency.
9
TIv
42.7
109
1266
1147
202
1221
1019
10
O2
37.3
192
1247
1045
234
1216
982
plainly by samples of Portland cement of American manufacture,
but has not noticed it in natural cements. Table 18 gives the
results of some tests on the effect of aeration on the time of
' "Notes on Concrete," by John Newman, p. 11.
» Trans. A. S. C. E.. Vol. xxx, p. 12.
SETTING OF CEMENT
83
setting of five samples of natural cement from the same
factory.
105. The coarse particles in a cement retard the setting be-
cause they are inert. Either fine grinding or sifting will doubt-
less hasten the rate of setting, but, as has been stated above,
the detection of changes in the rate is difficult. Table 11,
§ 81, gives the results of a few tests on this subject.
106. Addition of Salts. — The time of setting of a cement is
sometimes regulated at the factory by addition of sulphate of
lime to the finished product. Such additions are admitted to
the extent of two per cent, by the regulations of the Asso-
ciation of German Portland Cement Makers, and are now quite
generally made by American Portland cement manufacturers.
Table 19 gives the results of a few experiments on the effect
of plaster of Paris on the time of setting of several cements.
TABLE 19
Effect of Plaster Paris on Time of Setting
Cement.
Time to Bear } lb.
Wire, Minutes, with Plaster
Paris as Certain Percent-
age of Cement and
Plaster Paris.
Time to Bear 1 lb.
Wire, Minutes, with Plaster
Paris as Certain Percent-
age of Cement and
Plaster Paris.
Kiud.
Brand.
0%
1%
2%
3%
6%
0%
1%
2%
3%
6%
Portland
Natural
S
R
X
Gn
An
24
24
26
34
34
232
96
4
38
93
477
375
258
106
179
460
381
287
107
302
425
358
268
86
295
40
75
84
42
93
498
345
305
543
193
917
745
625
414
439
910
776
725
527
592
860
778
668
671
725
832
750
694
632
698
It is seen that small oercentages retard the initial setting in
a marked degree, the maximum effect usually being given by
2 per cent, of the plaster. Larger percentages tend to make
the cement quicker setting again, so that with 6 to 10 per cent,
added, the cement may begin to set quicker than without the
addition of plaster. The final set (time to bear one pound
wire) does not appear to be thus hastened by large percentages.
This might be considered to indicate that the hastening of the
initial set is caused by plaster of Paris taking up the water from
the cement and obtaining sufficient hardness to bear the light
wire.
The probable explanation of the action of a small amount of
84 CEMENT AND CONCRETE
sulphate of lime in retarding the setting is that suggested by
M. Candlot, ^ namely, that the aluminate of lime, to which is
due the initial setting, dissolves less readily in a solution of
sulphate of lime than in pure water. If the aluminate does
not commence to hydrate until the silicate of lime has set, the
subsequent combination of the sulphate and aluminate may
cause the mortar to disintegrate.
107. Solutions of common salt have been found to retard
the setting, but when a large percentage of salt is used, it some-
times forms a crust on the top which may resist a light wire and
thus make the paste appear to be quicker setting. Sea water
generally retards the setting somewhat more than solutions of
common salt, probably on account of the magnesian salts pres-
ent, but M, Candlot says that cements to which sulphate of
lime has been added set more rapidly when gaged with sea water
than when gaged with fresh water.
The effect of calcium chloride on the setting of cements is
entered into in detail in M. Candlot's treatise on "Cements and
Hydraulic Limes," and may be summarized as follows: A weak
solution of calcium chloride renders Portland cement slower
setting because the aluminate of lime dissolves more slowly in
such a solution than in pure water. On the other hand, the
aluminate dissolves rapidly in a concentrated solution of calcium
chloride, and therefore such a solution hastens the setting of
Portland cement. Aluminous cements, i.e., cements containing
a very high percentage of alumina, are not appreciably affected
by gaging with a comparatively weak solution of calcium chlo-
ride on account of the large excess of aluminate of lime present;
and on the other hand, cements containing no alumina are not
affected, as in such cements the hardening is due to the siUcate
of lime. A weak solution of the chloride hastens the ?iydration
of the free lime, and therefore a cement which contains a dan-
gerous percentage of the latter may be made sound by gaging
with such a solution, as the lime may thus be hydrated before
the cement sets. The chloride of calcium test for soundness is
based on the supposition that the free lime may be hydrated by
the action of the chloride soon after the setting of the cement,
and thus the expansive action be hastened.
"Ciments et Chaux Hydrauliques ," par E. Candlot.
SETTING OF CEMENT
85
The effect of sugar on the time of setting does not seem to
be well known, but it is said ^ that the presence of saccharine
matter may either accelerate or retard the setting of the cement,
depending on the amount of sugar present, the character of the
cement and the amount of water used.
108. The quantity of water used in gaging has a most impor-
tant influence on the test for time of setting, an increased quan-
tity of water retarding the setting. This may be seen from
Table 20.
TABLE 20
Effect of Consistency of Mortar on the Time of Setting
Natural
Ckment.
A
' Water as per cent, of
cement by weight , .
26.7
28.6
30.8
33.3 36.4
40.0
Minutes to bear ^J^ inch
wire weighing | pound.
Minutes to bear ^^^ inch
wire weighing 1 pound
20
28
23
41
30
57
42
76
46
78
55
85
a
Water as per cent, of
cement by weight . .
24
26
28
30
32
34
36
Minutes to bear yi2inch
^ pound wire . . .
Minutes to bear ^^^ inch
1 pound wire . .
2
160
2
188
3
279
7
289
21
371
28
403
38
583
As might be supposed, this influence varies with different
samples, and M. H. LeChatelier ^ has given the following table
which illustrates this point.
TABLE 21
Effect of Consistency of Mortar on Time of Setting
Cement.
Per Cent.
Water.
Time Setting,
Minutes.
Portland A j
Portland B |
Quick setting Vassy <
24
34
25
35
50
58
20
85
7
46
10
' "Masonry Construction," I. O. Baker, p. 98.
' "Tests of Hydr. Materials," p. 33.
86
CEMENT AND CONCRETE
109. It is necessary, then, in writing specifications and in
making tests, where the time of setting is at all carefully con-
sidered, to note the consistency of the paste used in the test.
Practically, it is preferable to use a paste rather thinner than
that usually employed for briquets.
The consistency is sometimes defined by M. Vicat's apparatus
of a rod 1 cm. in diameter, or by M. LeChatelier's modification
of the same mentioned above, or by the requirement that it
shall be at the point of ceasing to adhere to the trowel. Another
definition is that it shall, when placed on a glass plate, flow
toward the edges only on repeated jarring of the plate. This
last is a very fair approximate method, though giving a rather
thin paste.
That mortars set more slowly than neat cement paste is
largely due to the increased amount of water present in the
former, this excess of water being required to moisten the
grains of sand. The relation between the time of setting of mor-
tars and neat cement paste is not definite. M. Candlot found
the time of setting of one-to-three mortars to be from two to
twenty times as great as that of the paste of neat cement of
normal composition.
110. The temperature of the cement and water also has an
important bearing on the observed time of setting. As the
temperature of the materials is increased, the time of setting
diminishes in about the same proportion. The following table
gives a few of the results obtained by M. Candlot ^ with Port-
land cements.
TABLE 22
Effect of Temperature of Materials on Time of Setting
Cement No. 1
Cement No. 2
Tkmpebatube,
Degrees C.
15
25
7
20
30
TiM?5 OF Skttinc;
Minutee.
60
25
4
350
205
190
Table 23 gives the results of similar tests made under the
author's direction. The temperatures of cement and water
'Ciments et Chaux Hydrauliques," par E. Candlot.
SETTING OF CEMENT
87
were varied while the temperature of the room iii which ithe*
tests were made remained nearly constant, or from 63° to 67°
Fahr.
TABLE 23
Effect of Temperatures of Cement and Water on the Time of
Setting of Paste
Temp, cement and water, j
Degrees, Fahr. . . . j
40
50
60
'0
80
90
100
110
Minutes to bear y'j ^
inch wire weigli- > Portland
ing i pound. ) jjj^^^^,.^i
270
102
247
90
225
84
196
72
175
60
158
54
135
55
43
111. Amount of Gaging. — If a cement paste containing a
moderate amount of water be insufficiently gaged, it will appear
dry, when a more thorough working might make it plastic.
Thus an insufficient gaging may make a cement appear quicker
setting. It is also the case that when a cement is regaged after
having begun to set, the second setting will take place more
slowly; this, however, is a somewhat different matter.
112. The temperature and character of the medium in which
the pat is kept during the setting process will have a decided
influence on the rate of setting.
This is clearly shown ,by the following table, given by M.
TABLE 24
Time of Setting as Affected by Temperature of the Water and
of the Medium in vrhich Cement Sets
Tempera-Ture
Time Kequibed to
Sample.
Of water at time
of gaging.
Of air during
setting.
Begin to set.
Set.
Degrees C.
Degrees C.
Hr. Min.
Hr. Min.
0
16
0
16
0
15
6
15
1
16
1
KJ
3
15
.3.5
17
6 47
0 20
5 30
0 52
12 0
0 43
0 24
0 20
11 0
2 23
8 8
5 13
20 0
3 3
1 3
0 45
88 CEMENT AND CONCRETE
Paul Alexandre/ from which it appears that different samples
are affected in very different degrees. It is seen that the
higher the temperature, the more rapid the setting.
113. At temperatures below 32° F. (0° C), setting seems
to be entirely suspended. If a cement paste, which has been
submitted to such low temperatures since gaging, is brought
into a warm room, the setting process begins as though the
mortar had just been gaged. It must not be concluded,
however, that freezing has no evil effect on mortars. (See
Art. 50.)
114. Setting in Air and Water. — A cement paste sets much
quicker in air than in water. This is due to the percolation of
water to the interior of the pat, when it is immersed as soon as
made, being analogous to using an excess of water in gaging.
When a pat sets in dry air, the evaporation of water from the
surface hastens the hardening of that portion. If immersed
directly after it has set in air, it re-softens, and this is also
true of some briquets immersed when twenty-four hours old.
The time of setting of cements that are to be deposited under
water may well be tested in that medium, when they should
be protected by a mold of some form to retain their shape.
Ordinarily the time of setting should be tested in moist air.
Cements are said to set more quickly in compressed air than
in free air; this may be partially due to the higher temperature
usually existing in the former.
115. Requirements as to Time of Setting. — What is desir-
able as to time of setting will, of course, depend on the work
in hand; certain purposes requiring that the cement shall be
able to retain its shape soon after deposition, while in other
cases ability to mix large quantities at a time, without fear of
the cement setting before it is in place, may be very convenient.
An extremely quick setting cement should be regarded with
suspicion until it has proved itself of good quality. It is some-
times stated that where a quick setting mortar is desired, nat-
ural cement must be used, but this is not true; either Portland
or natural may be found with almost any rate of setting de-
sired. • As a general rule, however, among cements that have
been stored several months, the Portlands are slower setting.
' " Recherches Experimentales sur les Mortiers Hydrauliques ," par Paul
Alexandre.
SETTING OF CEMENT 89
Portland cement will ordinarily begin to set in from twenty
minutes to six hours, and natural cement in from ten minutes to
two hours, though there are many cements the time of setting of
which is outside of these limits.
116. Conclusions. — The purpose aimed at in the test for
time of setting will, to a certain extent, regulate the method
to be employed. The pressure of the finger nail will be suf-
ficient to determine (after a little experience) whether a cement
will answer a certain purpose in this regard. But, if one is
working to rigid specifications, or pursuing investigations as to
the effect of different treatment on time of setting, it becomes
very desirable to have a method of determining and defining
the consistency of the mortar, and an accurate method of de-
termining the rate of setting.
In the author's experience, the Vicat consistency apparatus
as modified by M. LeChatelier (see § 99) has proved unsatisfac-
tory except for thin pastes of neat cement or mortars contain-
ing less than two parts of sand. If the paste is not of such a
consistency as to run freely into the ring, or "vase," an error
may be introduced in the method of filling the latter. In oper-
ating with a natural cement it was found that a neat paste, in
which the water used was 32 per cent, of the dry cement, re-
quired a gross weight of 640 grams to make the disc (1cm. diam-
eter) penetrate midway in the vase; %vith 33 per cent, water,
a weight of 410 grams was required; 34 per cent., about 250
grams; 35 per cent., 175 grams; 37 per cent., 155 grams. It
would seem that some modification of this apparatus might be
made which would not only indicate when a thin, neat cement
paste has the assumed "normal" consistency, but which would
also define the consistency of a given mortar, whether of neat
cement or of sand mixture.
General Gilmore's wires are very simple, and will perhaps
answer the purpose of obtaining the time of setting as well as
any method in use. They can be used somewhat more accu-
rately if the wires are made to slide vertically in a frame, than
when held in the hand.
The necessity of care in all of the details of this test, tem-
perature and amount of water, amount of gaging, character
of medium, etc., has been suflUciently emphasized in the preced-
ing paragraphs.
90 CEMENT AND CONCRETE
Art. 18. Constancy of Volume
117. That a cement should not contain within itself ele-
ments which may lead to its destruction, is evidently a most
important quality. It is probable that nearly all cements un-
dergo a slight change in volume during induration, contracting
in air and expanding in water. But it is the detection of those
larger changes, which result from bad proportions or defective
manufacture, and which cause deterioration or even complete
disintegration, that is the object of the tests for soundness.
118. Causes of Unsoundness. — The most frequent cause of
unsoundness is considered to be the presence of free lime or
magnesia. (See §§49 and 50.) Any one of the following causes
may account for the presence of free lime in cement: (1) An
.excessive percentage of lime may have been used in proportion-
ing the raw materials; (2) the raw materials may not have been
sufficiently mixed to render the mass homogeneous; (3) hard
particles of lime, such as shells, may not have been ground fine
enough in making the mix to permit them to enter into com-
bination with the other ingredients during burning; or (4) the
cement may have been underburned, so that part of the lime
did not enter into combination.
The particles of free lime which occur in cements are nat-
urally rather difficult to slake on account of their impurity and
the high temperature at which they have been calcined, and
the same thing is probably true of magnesia. It may thus
require weeks or months of exposure to the atmosphere to cor-
rect tendencies to expand due to the presence of free lime or
magnesia. Likewise when such defective cements are immersed
in water of ordinary temperature, the expansion may not occur
for a considerable period. This fact has led to the use of hot
tests of various kinds to detect such faults, but before touch-
ing on these so-called "accelerated tests," the ordinary cold-
water test will be described.
119. TESTS FOR SOUNDNESS.— The Committee of the Amer-
ican Society of Civil Engineers on a "Uniform System for
Tests of Cement" recommended, in 1885, the following test for
•soundness: "Make two cakes of neat cement two or three inches
in diameter, about one-half inch thick, with thin edges. One
of these cakes, when hard enough, should be put in water and
CONSTANCY OF VOLUME 91
examined from day to day to see if it becomes contorted, or if
cracks show themselves at the edges, such contortions or cracks
indicating that the cement is unfit for use at that time. In
some cases the tendency to crack, if caused by the presence of
too much unslaked lime, will disappear with age. The re-
maining cake should be kept in air and its color observed, which
for a good cement should be uniform throughout, yellowish
blotches indicating a poor quality; the Portland cements being
of a bluish-gray, and the natural cements being light or; dark,
according to the character of the rock of which they are made."
For the ordinary cold test this method will probably give as
valuable results as any of the forms that are suggested.
120. The German regulations require a very similar test,
except that in the case of slow setting cements the pat is not
immersed until twenty-four hours old. While a cement that is
decidedly bad may show its defects in from one day to one week
by this cold water test, it may be the case that cracks will ap-
pear only after several months' immersion. It has therefore
been proposed to hasten the destructive action of the free
lime or magnesia by submitting the cakes of cement to steam,
hot water, or dry heat.
121. The Kiln Test, recommended by Prof. Tetmajer in 1890,
consists in placing in an air bath, pats which have been kept
in moist air for twenty-four hours; and then gradually raising
the temperature of the air bath to 120° C. This temperature
is maintained for at least one-half hour after the disengage-
ment of steam has ceased. The pats should show no tendency
to expand under this treatment, but if cements fail to pass the
test, the results of the ordinary cold water treatment are to be
awaited. This test is intended for cements that are to be
used in air.
122. The Boiling Test, which was also recommended by Prof.
Tetmajer, consists in placing the pats, twenty-four hours after
made, in water of ordinary temperature, and gradually heating
the water to bring it to the boiling point in about an hour;
five or six hours in the boiling water should develop no defects.
This is a severe test, and has been objected to on the ground
that cements which have been well proportioned, but which
are a trifle underburned, will fail to pass this test while giving
good results in mortars to be used in the air. This test, how-
92 CEMENT AND CONCRETE
ever, is steadily gaining in favor, and is used in many cement
works as a test of quality.
123. The Warm Water Test. — Mr. H. Faija was an early
experimenter in accelerated tests for soundness, and about 1882
he began the use of a ''steamer," using a temperature of about
110° Fahr. After eleven years' use he still believed this tem-
perature to be high enough to detect tendencies to expand in
faulty cements. The apparatus^ "consists of two vessels, one
within the other, a water space being thus maintained between
them, which assists in equalizing the temperature of the inner
or working vessel." The latter is partially filled with water
and is provided with a rack or shelf near the top. A ther-
mometer is inserted through the cover of the inner vessel, and
the water within is kept constantly at 110° Fahr. As soon as
the pat is gaged, it is placed on the rack in the vapor, which
will be at about 100° Fahr. After six or seven hours in this
moist heat, the pat is immersed in the warm water. "In the
course of twenty-four hours it is taken out and examined, and if
then found to be quite hard and firmly attached to the glass, the
cement may at once be pronounced sound and perfectly safe
to use; if, however, the pat has come off the glass and shows
cracks or friability on the edges, or is much curved on the
under side, it may at once be decided that the cement in its
present condition is not fit for use." Mr. Faija also recom-
mended, in case of failure in the first test, that the cement be
spread out in a thin layer for a few days and a second test
made. If the cement passes this second test, it is pronounced
sound and fit for use after being stored a sufficient length of
time.
124. The Hot Water Test. — The temperature to be used in
accelerated tests for soundness is a point which has received
much attention and is still under discussion. In 1890 M. Deval
described a series of experiments he had made, in which he
employed a temperature of 80° C. While this is much more
severe than the temperature used by Mr. Faija, it is still mild
in comparison to some temperatures that have been advocated.
125. Mr. W. W. Maclay, who was probably the first engi-
neer in this country to introduce a hot test requirement in
* "Portland Cement Testing," by H. Faija, Trans. A. S. C. E., Vol. xvii,
p. 222.
CONSTANCY OF VOLUME 93
specifications, gave the results of his experiments in a paper
presented to the American Society of Civil Engineers in 1892.
The method used "consists in molding six pats of pure cement
and water, about one-half inch thick and about three inches in
diameter, on thin glass plates, and of the same consistency as
for the briquets for tensile strength." The treatment to which
these pats are submitted is as follows: —
No. ], in steam (vapor) bath, temperature 195° to 200° F.,
as soon as made.
No. 2, in same vapor bath when set hard (bear ^:f inch wire
weighing one pound).
No. 3, ditto, after twice the length of time in air allowed the
second pat.
No. 4, ditto, after 24 hours.
No. 5, in water of temperature about 60° F. when set hard.
No. 6, kept in moist air at temperature of about 60° F.
"The first four pats are each kept in the steam bath three
hours, then immersed in water of a temperature of about 200°
Fahr. for twenty-one hours each, when they are taken out and
examined. To pass this test perfectly, all four pats, after being
twenty-one hours in hot water, should, upon examination, show
no swelling, cracks, nor distortions, and should adhere to the
glass plates. The latter requirement, while it obtains with
some cements nearly free from uncombined lime, is not insisted
upon; the cracking, swelling and distortion of the pats being
much the more important features of this test. The cracking
or swelling of No. 1 pat alone can generally be disregarded."
126. Deval's Method. — Making tests of mortar briquets,
which have been kept in hot water, seems to be the most rational
accelerated test for soundness. This method was used in Ger-
many several years ago, when it was claimed that a definite
relation existed between the results thus obtained and the longer
time cold water tests. This theory being disproved, threw dis-
credit on the hot test, but M. Deval ^ has since made many
experiments showing that it is of much value in detecting
bad products.
The method consists in making briquets with three parts
sand to one of cement, and after twenty-four to seventy-two
* "Hot Tests for Hydraulic Cements," M. Deval, Bull. Soc. cC Encourage
ment, etc., 1890, pp. 560-583.
94
CEMENT AND CONCRETE
hours in moist air, according to the rate of setting, immersing
them in water maintained at 80° C, the briquets being broken
after an immersion of from two to seven days. These hot
water briquets are to be compared with briquets stored in
water of the ordinary temperature and broken at seven and
twenty-eight days after immersion,
127. Among other tests M. Deval compared the results ob-
tained with six samples of Portland cement as follows: —
No. 1. Good finely ground cement of modern make.
No. 2. Coarsely ground cement of good quality, but partially
aerated.
No. 3. Quick setting cement with low per cent, lime and
lighter burn.
No. 4. Made from clinker having property of disintegrating
spontaneously while cooling; large proportion of inert
material.
No. 5. Under-burnt cement; contains free lime.
No. 6. Over-limed cement.
The results of the tests are given in the following table: —
TABLE 25
Cold and Hot Tests on Six Samples of Portland Cement
(M. Deval)
Cement.
Tensile Stbength in Kilos per Sq. Cm.
Cold.
Hot.
7 days.
28 days.
2 days.
7 days.
1
15.0
23.3
17.2
24.3
2
6.7
13.7
7.6
11.0
3
6.2
16.5
7.3
16.2
4
2.9
3.9
•\
5
6.1
12.2
> Disintegrated.
6
7.6
20.2
^
No. 4, when allowed forty-eight hours to set, gave 3.2 kijos
at two days, and 4.3 kilos at seven days, when tested hot.
Among the cements which disintegrated in the hot water, the
only one that gave a high result cold was No. 6, and this sam-
ple, it is stated, would crack and swell badly even in cold water
CONSTANCY OF VOLUME 95
if mixed neat. It is quite possible, however, that a sample
might be found which, not having quite as flagrant defects as
No. 6, would pass all the cold tests but be condemned by the
hot test.
128. The conclusions drawn from these experiments have
been stated as follows: —
"(1) Tests made cold do not indicate the quality of the
cement, inasmuch as cement containing excess of Ume, and, in
consequence, deplorably bad, may give excellent results."
"(2) Portland cement of good quality, mixed with normal
sand in the proportion of one to three, resists water at 80° C.
Its strength at two and seven days after setting is about equal
to that which it would have at seven and twenty-eight days
in the cold."
"(3) Poor cement containing much inert material does not
resist the action of water at 80° C. unless the setting be allowed
to proceed for some days before immersion."
"(4) Cements containing free lime do not withstand the ac-
tion of water at 80° C. if immersed twenty-four hours after
setting." Comparison of the strength hot and cold will suffice
for the detection of even small quantities of free lime.
129. Before passing to the comparison of the tests for sound-
ness already outlined, a few other tests which have been sug-
gested for use may be briefly mentioned.
The Chloride of Calcium Test depends on the fact that slak-
ing of free lime is hastened by feeble solution of chloride of
calcium. (See § 107.) Concerning this test, Prof. F. P. Spald-
ing^ says he "has found it to give true indications in a number
of cases, including some unsound magnesian cements. It con-
sists in mixing the mortar for the cakes with a solution of 40
grammes chloride of calcium to one liter of water, allowing
them to set, immersing them in the same solution for twenty-
four hours, and then examining them for checking and soften-
ing as in other tests."
130. M. H. LeChatelier's Method. — The method recom-
mended by M. H. LeChatelier for testing soundness requires
the use of a cylindrical mold, about 1^ inches in diameter and
of about the same height, which is made of thin metal and
* " Notes on the Testing and Use of Hydraulic Cement, " by Fred. P.
Spalding.
96 CEMENT AND CONCRETE
slit along a generatrix. The mortar is to be placed in the
mold as soon as made, and immersed at once in cold water;
the mold is held firmly by a clamp, and a flat plate at either
end of the mold retains the mortar in shape until set. When
setting has taken place, the mold is undamped and the widen-
ing of the slit indicates the expansion of the mortar. If de-
sired, the swelling may be increased and hastened by transfer-
ring the mold and its contents to hot water as soon as the ce-
ment is set. The same writer has suggested a modification of
the hot test by placing briquets in cold water and gradually
heating to near the boiling point, this temperature being main-
tained for six hours.
Various other tests have been suggested, such as the effect
of regaging; withstanding immersion as soon as gaged; allow-
ing large thin cakes to harden in air and striking them to obtain
a musical sound. Most of these tests, however, are worthy of
passing notice only.
131. Discussion. — There are but few experiments to show
that a cement which will actually fail and disintegrate when
properly used, may still pass the cold water neat pat test; yet
there is no doubt that inferior cements may pass this test per-
fectly, "inferior cements" being those which will not give the
best results in practice, though they do not disintegrate.
Cement is at present used in a very crude way, and it is only
in exceptional cases that a poor quality of material may be
detected in the completed structure. This is sufficient reason
why so few failures can be found in cement work which may
be attributed to a poor quality of cement. But in the more
economical manner in which this material is, even now, begin-
ning to be used, it is absolutely essential to know what its fu-
ture behavior will be. That the cement will never be exposed
to hot water in actual use, is a weak argument against hot
water tests. It must be remembered that the chief object of
testing cement is to arrange the various products in their true
order of merit, and any system which will effect this result is
perfectly legitimate. On the other hand, it is due to the man-
ufacturers that a test which will occasionally reject perfect
cements should not be adopted when it is possible in any other
way to detect poor products with certainty.
132. It is possible that the temperature used and recom-
CONSTANCY OF VOLUME 97
mended by Mr. Faija is sufficiently high to detect unsoundness
or a tendency to "blow." It has never been clearly proved
that it is not, but the higher temperature of 70° to 100° C. has
appeared to meet with greater favor. The writer made a few
experiments to compare results obtained with mixtures of
Portland cement and lime when using the temperature of 110°
Fahr. (43° C.) with those obtained in water at 190° Fahr. (88°
C), and in water at the ordinary temperature of 60° to 65° Fahr.
{16° to 18° C). Quicklime, in proportions varying from one
to ten per cent., was added to the cement, and seven pats were
made from each mixture of cement and lime.
These pats were subjected to the following treatment : —
Pat No. 1, placed in vapor of water at 110° F. when made.
2, " " " 110° F. when set.
3, " " " 110° F. after 24 hours.
4, " " " 190° F. when made.
5, " " " 190° F. when set.
6, " " " 190° F. after 24 hours.
Above six pats immersed in the hot water after three hours in
vapor.
Pat No. 7, placed in cool water when set.
When no lime was added, pats 1, 2 and 3 revealed no defects;
pats 4 and 5 showed small cracks in two days, but pat No. 6
still adhered to the glass after eight days. Pat No. 7 was perfect
after two months. With 2 per cent, lime added to the cement,
pat No. 1 was slightly warped and cracked, and Nos. 2 and 3
were off glass; Nos. 4 and 5 were cracked and warped; No. 6
was off glass, and No. 7 became detached from glass after two
months, but was otherwise perfect. With 4 per cent, lime, all
the pats failed, the one in cool water being off glass, cracked
and warped after one day.
It must be remembered that the free lime occurring in cement
is of a different character from the quicklime added in these
tests, because the former contains impurities and has been cal-
cined at a very high temperature, and would therefore slake
more slowly. It has been said that as small an amount as 1
per cent of free lime in cement is dangerous. If this is true,
and it probably is, the temperature of 110° Fahr. would seem
to be inadequate to quickly indicate a tendency to "blow."
98
CEMENT AND CONCRETE
133. Some of the results obtained by M. Deval hav3 already
been given (§ 127). Mr. Maclay made similar tests on several
samples of Portland cement, using a temperature of 200° Fahr,,
but these tests only permit of comparing the strength acquired
in cold water in seven and twenty-eight days with the strength
in hot water at ages of from two to seven days. Long time
tests, showing that the cements which give low results in hot
water and normal results in cold water on short time tests,
give in reality a low strength at the end of six months or more,
have been almost entirely lacking until very recently.
Table 40, § 226, gives some of the results obtained by the
author in hot tests and long time cold tests on Portland cement.
It is seen that the hot test at 80° C. indicated, in seven days^,
TABLE 26
Cold and Hot Tests on Samples of One Brand of Portland Cement
Cemkkt.
Pakts.
Sand
Date
Made.
1894.
Age.
Tensile
Strength.
Bkiquets Stored.
Mo. Da.
Moist air.
Water.
B'
2
4 16
5 da.
8
1 da.
80° C. 4 da.
A
2
7 2
5 da.
235
4 u
B'
2
4 16
7 da.
13
u Q a
A
2
7 2
7 da.
229
" 6 "
B
.3
7 2
7 da.
197
15 to 18° C. 6 da.
A
3
7 2
7 da.
108
6 "
B
3
7 2
28 da.
298
" 27 "
A
3
7 2
28 da.
198
" 27 "
B'
2
4 16
7 mo.
411
" 7 mo.
A
2
7 2
6 mo.
465
6 "
Behavior of Pats Made July 2, 1894
nmersed in wate
hours in vapor.
No. 1 in vapor, when held |if wire. J Immersed in water 80° C. after three
No. 2 in vapor, when held 1# wire. ) '
No. 3 in tank, when held 1# wire.
No. 4 in tank ; two hours after held 1# wire.
Cement: A, No. 1 off glass in two days; No. 2 warped some in two days.
" A, No. 3 O.K. after twenty-one days; off glass and warped in
fifty-two days.
" A, No. 4 loose on glass in twenty-one days; off glass and warped
in fifty-two days.
" B, No. 1 off glass and warped some in two days; No. 2 entirely
disintegrated in two days; No. 3 loose on glass in twenty-
one days; off glass and warped in fifty-two days; No. 4 loose
on glass in twenty-one days; off glass and warped in fifty-two
days.
CONSTANCY OF VOLUME 99
the inferior quality of sample W, although it gave normal re-
sults in cold water up to twenty-eight days; the two year tests
with mortars containing two parts or more sand, show it to be
inferior. If we attempt to carry the analogy too far, however,
we fall into the error which placed the hot test in disrepute for
several years, that is, we must not expect that the strength in
cold water after a long time will be exactly proportional to the
strength developed in hot water in a few days.
134. In Table 26 are given the results of tests by the author,
on samples of a single brand of Portland cement. The por-
tion marked "A" had been spread out in open air for seventy-
seven days in a thin layer. The portion marked "B" was
taken directly from the barrel July 2d, and B ' was taken
from the same barrel April 16th. Samples B and B' are not
identical, because the cement had undergone some change,
though stored in the barrel. Each result is the mean of five
briquets.
In the short time cold tests there was nothing to indicate that
the cement directly from the barrel was not good, except the
very small evidence in the fact that pat No. 3 was loose on glass
plate after twenty-one days. In fact, the cold water briquet
tests at seven and twenty-eight days unmistakably declare in
favor of the sample B. On the other hand, how sharply did
the hot tests bring out the defects, two days in hot water being
sufficient to entirely disintegrate one of the pats. Although
sample B' showed a considerable tensile strength at seven
months with two parts sand, yet the pats of neat cement failed,
even in cold water, after two months, altogether too late a date
to be of any value in preventing the use of the cement.
135. In a paper read before the American Society for Testing
Materials, July, 1903,^ Mr. W. P. Taylor of the City Testing
Laboratory, Philadelphia, gives some very interesting data con-
cerning the behavior of cements that failed to pass the boiling
test. The method employed was to make cakes of cement in
the form of a small egg, keep them in moist air for twenty-four
hours, then place them in cold water which is gradually raised
to the boiling point and maintained at that temperature for
three hours. The results cited show that some unsound ce-
* Proceedings Amer. Soc. for Testing Materials, 1903.
100 CEMENT AND CONCRETE
ments may be much improved by sifting out the coarse parti-
cles, and that a cement failing in the boiling test when fresh
may pass it satisfactorily after four or five weeks.
Examination of the results showed that 96 per cent, of a
large number of specimens which did not pass the hot water
test failed within three hours, and 99 per cent, in four hours.
This fixes a practical limit to the time necessary to continue
the test. Some very valuable tests are cited to show the
ultimate failure in cold water of samples that failed in the
hot tests. Ten cements which passed the cold water pat test
of twenty-eight days' duration, but which failed in the boiling
test above described, gave normal results in one-to-three mor-
tars at twenty-eight days, showing a tensile strength of 217 to
252 pounds per square inch, but gave only 47 to 147 lbs. per
square inch at four months.
Another valuable comparison is given by Mr. Taylor: A
compilation of data, covering over a thousand tests on many
varieties of cements, showed that "of those samples that failed
in the boiling test but remained sound at twenty-eight days (in
cold water), 3 per cent, of the normal pats showed checking or
abnormal curvature in two months; 7 per cent, in three months;
10 per cent, in four months; 26 per cent, in six months and 48
per cent, in one year; and of these same samples, 37 per cent,
showed a falling off in tensile strength in two months; 39 per
cent, in three months; 52 per cent, in four months; 63 per cent,
in six months and 71 per cent, in one year."
136. It may be of interest to introduce here some of the
opinions that have been expressed concerning hot tests. M.
Candlot ^ says that cements of normal composition, the burning
of which has not been carried to the point of vitrification, would
be condemned by the hot test of neat cement, although mor-
tars made with them show no signs of alteration in sea water,
and, when preserved in air, give entirely satisfactory results.
Referring to the tests of one-to-three mortar briquets in water
at 80° C, he considers that "cements containing free lime give
in hot water, lower resistances than in cold water ; cements of
good quality give resistances at least equal and nearly always
greater in hot water than in cold. Cements well proportioned
'Ciments et Chaux Hydrauliques," -par M. Candlot, pp. 144r-145.
CONSTANCY OF VOLUME 101
and homogeneous, but not having obtained the maximum burn-
ing, give satisfactory results with this test."
In using the sUt cylinders mentioned in § 130, M. H. Le
Chatelier found ^ that the addition of 5 per cent, of lime could
be detected by cold tests in a few hours, while 5 per cent, of
magnesia could not be detected in twenty-eight days. The
cement containing 5 per cent, lime disintegrated almost at
once in hot water, while the sample to which 5 per cent, of mag-
nesia had been added, swelled considerably in one day.
Mr. A. MarichaP found that "the percentage of water en-
tered in combination, after ten days in hot water, was the same
as for six months in cold water, and that the strength of the
cement was increasing with the amount of water entered in
combination. It was discovered incidentally, that cement con-
taining over 5 per cent, of magnesia, or 3 per cent, of uncom-
bined lime, would not stand the boiling test."
137. Hot Tests for Natural Cements. — All that has pre-
ceded concerning hot tests refers to their use for testing Port-
land cements. Very little is known concerning the value of hot
tests for natural cements. There are comparatively few natural
cements that are absolutely bad, but to distinguish between the
first and second quality of this variety of products is much more
difficult than to make a similar distinction with Portlands. One
point is certain, natural cements must not be expected to with-
stand boiling water. Mr. de Smedt experimented with fifteen
brands of natural cement, and found that thirteen of them
went to pieces in boiling water in two hours, although none of
them was thought to contain caustic lime. Prof. Tetmajer
has stated that for Roman cements, boiUng water, or even 75° C,
is not at all conclusive, and recommends 50° C. for trial, but our
natural cements are not strictly comparable with Roman ce-
ments.
138. The author has experimented with three temperatures,
namely, 50°, 60°, and 80° C, and is inchned to consider that
80° C. is likely to give the most useful information for sand
mortar briquets but not for neat cement pastes. Table 41,
§ 227, gives the results of hot briquet tests on six brands of
> " Tests Hydr. Materials," by H. LeChatelier.
» Trans. Amer. Soc. C. E., Vol. xxvii, p. 438.
102 CEMENT AND CONCRETE
natural cement. It is seen that, with two parts sand, brands
Jn, Hn, and Bn, give very low results at 80° C, and these brands
are really inferior cements as shown by the two-year cold tests.
Brand Jn is the only one that gave a lower result at seven days
than at five days when tested at 80° C, and this brand failed
entirely at two years, though it gives normal results in cold
water up to six months. Neat cement pats of this brand, after
being stored in cold water for nearly one year, were found to be
cracked, although they had been perfect after one month in
cold water. It was also found that neat cement pats of this
brand warped and cracked in two days when placed in water of
60° C. when set.
139. CONCLUSIONS. — It may be said that although the
limits within which the hot tests are reliable have not been well
established, and although a strict adherence to them may at
times reject a usable product, yet it is believed that sufficient
experiments have been made to indicate that they are of much
value, and should be made in all cases where the quality of the
cement is of high importance.
The present indications seem to be that Portland cements
may well be tested in the form of neat cement pats and sand
mortar briquets at a temperature of about 80° C. Natural ce-
ments in the form of neat paste should not be called upon to
resist a temperature above 60° C, but 80° C. will probably give
the most useful information with sand mortars. In either case,
the mortar should be allowed to set in moist air of ordinary
temperature, then transferred to the vapor, to remain two or
three hours before immersion in the hot water. It is not rec-
ommended that these hot tests should replace the ordinary
cold tests, but simply that in cases where the extra work in-
volved is not prohibitive, the hot tests should be made in con-
nection with the cold tests.
CHAPTER VIII
TESTS OF THE STRENGTH OF CEMENT IN COMPRES-
SION,. ADHESION, ETC.
140. In testing the strength of cement the object is three-
fold : 1st, to obtain an idea of the strength that may be ex-
pected from the cement as used in the structure; 2d, to obtain a
basis for comparing the value of different cements in this regard;
and 3d, to determine the ability of the cement to withstand
destructive agencies, whether these agencies be due to exterior
causes or emanate from the character of the cement itself. To
illustrate the last point it is only necessary to mention such de-
stroying agents as free lime (interior) and frost (exterior). It is
evident that the stronger the cement the more effectually will
these agencies be resisted.
The strength of cement may be tested by compression,
shearing, bending, adhesion, abrasion and tension. The tensile
test is the one most frequently used, but the tests will be con-
sidered in the order named.
Art. 19. Tests in Compression and Shearing
141. Value of Test. — In practically all forms of masonry
construction, cement is called upon to resist compression. In
consequence of this fact, the opinion is somewhat general that
the greatest amount of information would be obtained by com-
pressive tests. But the compressive strength of cement is so
much greater than its tensile strength, that when failures occur,
they are likely to be due to other forms of stress. In short, the
ratio of the compressive strength to the crushing force it is
likely to be called upon to resist, is usually much greater than
the corresponding ratio in tensile strength.
1^. There is no doubt that compressive tests are of much
interest and value, especially so since the use of concrete and
steel in combination has become general, but as yet the facili-
ties for making the test are not available without considerable
expense. This is on account of the larger force required (the
103
104 CEMENT AND CONCRETE
compressive strength being six to ten times the tensile) and be-
cause the uniform distribution of the stress over the surface of
the specimen, and the accurate recording of the force exerted,
are even more difficult than the corresponding operations in
tensile tests. Prof. Sondericker,^ in a paper read before the
Boston Society of Civil Engineers, describes an apparatus in
which he seems to have overcome a part of these difficulties.
A convenient specimen for compressive tests is a cube meas-
uring two inches on a side. The specimens are prepared and
treated in the same way as briquets for tensile tests. Before
testing, two opposite faces of the cubes are usually ground so as
to be true planes, parallel to each other, or the opposite sides
may be faced with plaster of Paris, though this is not recom-
mended. Grinding two surfaces to true planes increases very
much the work involved in testing, so that several tensile tests
may be made in the time required to make one compressive test.
143. Conclusions. — Although tests of compressive strength
are of interest from a scientific point of view, it is not considered
that they would give much greater information concerning the
relative qualities of cements than is given by tensile tests, and
therefore they need not be included in an ordinary series of
acceptance tests.
144. Tests of Shearing Strength. — Although cement is fre-
quently called upon to withstand a shearing stress, tests of this
kind are very seldom made. Some of the difficulties encoun-
tered in compressive tests are also present in tests of shearing.
Prof. Cecil B. Smith made quite an extended series of shearing
tests by cementing together three bricks, the middle one pro-
jecting above the other two, and the pressure being so applied
as to avoid any transverse stress. It is evident that by this
method the adhesive strength is also brought into play. Shear-
ing tests need not be included in normal tests of quality.
Art. 20. Tests of Transverse Strength
145. It is probable that the earliest rupture tests of cement
were made by submitting rectangular prisms to a' bending
stress; but such tests have long held a place subordinate to
trials of tensile strength. A mass of masonry, taken as a whole,
is very apt to be subjected to a bending stress, but it is a ques-
* Jour. Assoc. Engr. Soc, Vol. vii, p. 212.
TRANSVERSE TESTS 105
tion whether a transverse test on a small specimen gives any
better idea of the ability of a large beam to carry its load, than
do simple tensile and compressive tests.
In Engineering News of December 14, 1893, appeared an
article giving the comparative results obtained in tensile and
transverse tests. The tensile specimens had an area of one
square inch at the smallest place, and the transverse specimens
also had an area of cross-section of one square inch. It was
found that the modulus of rupture computed by the common
SW I
formula/ = , , ^ was from 1.1 to 3.8 times the tensile strength
developed by the briquets. Some comparative tests made at
St. Mary's Falls Canal are discussed in Art. 56.
146. The objections to transverse tests are: 1st, if the speci-
mens are made but one inch in cross-section, it is difficult to
handle them without injuring them, and if the section is made
much larger than one inch square, a much greater amount of
cement is required to make the specimens and more room re-
quired to store them; 2d, it would seem that the results ob-
tained might be less trustworthy than those in tensile tests
because of the greater influence of the outside layers, which are
subjected to the greatest accidental variations, on the apparent
strength of the specimen. On the other hand, it may be said
that, when no testing machine is at hand, the apparatus requi-
site to make a crude test may easily be improvised. All that is
required is a rectangular wooden mold, three knife edges, and a
pail with a quantity of sand or water.
147. When it is a question of making tests of transverse
strength accurately and rapidly, the apparatus required is no
more simple than the apparatus for tensile tests. In the con-
struction of metal molds in large quantities it makes little dif-
ference whether the form requires curved or straight lines. As
far as breaking is concerned, there is a certain force to be applied,
and a machine that will answer for one test may also be used
for the other. In the matter of clips, there may be a slight
advantage as to simplicity in a cUp designed for transverse
breaking.
In making transverse tests the author has used a form two
inches square and eight inches long. By placing the end sup-
ports five and one-third inches apart, the modulus of rupture
106 CEMENT AND CONCRETE
SWl
by the formula / = , .3 becomes equal to W, the center load
applied.
148. Finally, it may be said that there is little objection to
substituting transverse tests for tensile tests, although no evi-
dent advantage would be gained. It would also seem that
there is no object in making tests for quality by both trans-
verse and tensile tests, though from a scientific standpoint
comparative tests of transverse and tensile strength are of great
interest.
Art. 21. Tests of Adhesion and Abrasion
149. Adhesion. — The test for adhesion is also one of long
standing, being used during that time when engineers were con-
tent with an approximate idea of what might be expected of an
hydraulic product. It has been stated above that when failure
occurs in a mass of masonry, it is more frequently a failure in
tension than in compression; it may be added, that it is also
more likely to fail in adhesion than in cohesion. Hence, an
adhesive test is a very proper one to make, and will give most
valuable results. In fact, it is perhaps the most rational rup-
ture test, and were it not for the difficulties involved in its ap-
plication, it would doubtless come into general use.
150. One of the greatest difficulties experienced in making
adhesive tests is the preparation of the specimens of stone or
other material to which the mortar is to adhere. In early ex-
periments common brick were used, or pieces of stone were cut
to the same shape as brick, and two or more pieces cemented
together. In later methods the flat surfaces of two specimens
are sometimes joined with their axes at right angles, thus mak-
ing the cemented surface square. The upper brick being held
on two supports, a load is applied to the lower brick.
151. Mr. I. J. Mann, in a paper presented to the Institution
of Civil Engineers,^ described a method of testing adhesion in
which are used test pieces 1^ inches long by 1 inch wide by I to
I inch thick. These are cemented together in a cruciform shape,
and a simple spring balance machine with properly arranged
levers pulls them apart. The upper block is supported at its
ends and an inverted U-shaped piece bears upon the ends of
' Proc. Inst. C. E., Vol. Ixxi, p. 251.
TRANSVERSE TESTS 107
the lower block. The stress is applied through a conical shaped
pivot bearing on the U-shaped saddle. Mr. Mann states that
test pieces may be made either of plate glass or close grained
limestone, the latter being sawn into pieces of the right size.
152. Another method is to make test pieces to fit one end
of the mold used for tensile tests, and after placing the piece of
stone in the mold, to fill the other end with the mortar to be
tested. The objection to this method is the expense of pre-
paring pieces of this form. It has been suggested to substitute
artificial stone for the cut stone samples. Thus, suppose it is
required to test the adhesion of a certain mortar to granite:
mold half briquets of a mixture of ground granite with cement,
and after these have well hardened, replace them in the mold
and fill the other end of the mold with the mortar to be used.
It is quite certain that the same result would not be obtained
in this way as though the specimens were cut from a piece of
solid granite.
153. One of the simplest methods of applying this test is
one which the author has used for some time. The test pieces
are in the form of flat plates one inch square and one-fourth
inch or less in thickness. These plates being placed in the
center of a briquet mold, the ends of the mold are filled with
mortar. The plates may be improved by cutting shallow
grooves in two opposite sides to make a more perfect fit with
the sides of the mold. This may easily be done with a round
file. Besides the simple form of the test pieces and consequent
ease of making them, this method has the further advantage
that a test may be made almost as readily and accurately as a
tensile test of cohesion. AJso, since the adhesive area is one
square inch, the results may be compared with cohesive tests
on specimens having the same area of cross-section.
154. The experiments on adhesive strength made by Mr.
Mann were probably more extensive than any others published.
His results are useful mainly as showing the lack of cementitious
properties in the coarser grains of cement, and this point he
proves very clearly by quite a large number of experiments.
It was also developed that cement that had been rendered slow
setting by aeration or "cooling" gave a lower adhesive strength
than samples directly from the makers, which set more rapidly.
But the method followed by Mr. Mann, of immersing the speci-
108 CEMENT AND CONCRETE
mens as soon as cemented together, may have had something to
do with this result; the quicker setting samples would earUer
resist the injurious action which is likely to follow the immer-
sion of such small quantities of mortar before they have set.
155. All of the things which influence the results in testing
the cohesive strength must also be considered as affecting the
adhesive test. The consistency of the mortar, the method of
gaging, the pressure applied in cementing the specimens, and
the conditions of storage until the time of breaking, will all
have an influence on the result obtained. In addition to these,
the character of the samples as to the kind of stone used, its
structure, the physical condition of the surfaces, etc., must all
be considered. It is therefore clear that many difficulties must
be met before the test for adhesion can ever be included in
standard tests.
156. Special tests directed toward ascertaining the compara-
tive adhesion of cement to different varieties of stone, the effect
of the various differences in manipulation, the comparative ad-
hesion of mortars containing various proportions of sand, etc.,
are of undoubted value. But, before the adhesive test can be
considered a normal one for cement, much of this experimental
work will be required.
The results of a number of adhesive tests made under the
author's direction are given in Art. 51.
157. TESTS OF Abrasion. — Abrasion tests of cement are
not at all common, and for the ordinary uses to which cement
is put, its resistance to such action is of little interest except as
it may imply other kinds of strength. Occasionally, however,
it may be desired to have a mortar which will withstand wear,
as, for instance, in making concrete walk. In such cases, tests
for resistance to abrasion have some interest and value.
The test is usually made on a sample prepared as for tensile
or compressive tests, by submitting it to the wearing action of
an emery or grindstone, or a cast iron disc covered with sand.
The number of revolutions of the stone or disc is recorded,
automatically if possible, and the loss of weight is determined
after a given number of revolutions.
A few tests of this kind made at St. Mary's Falls Canal are
given in Art. 58.
CHAPTER IX
TENSILE TESTS OF COHESION
158. The testing of cement by applying tensile stress to a
previously prepared briquet, containing definite proportions of
cement and water, or of cement, sand and water, is the strength
test which is now in most general use. The value of this method
in comparison with that of other forms of rupture tests has al-
ready been briefly discussed.
That cement fails oftener in tension than in compression is
one reason for preferring the tensile test. Its ready applica-
bility is a still more important point in its favor.
Art. 22. Sand for Tests
159. Whether the tensile test should be applied to neat ce-
ment briquets or to those prepared from sand mortars has been
a disputed point, but there are now but few authorities who
recommend the use of the neat test exclusively. When tests
for soundness are not carefully made, the behavior of the cement
in neat briquets gives, perhaps, a better idea as to the reliability
of the cement than do sand tests, but otherwise the sand test is
a better index of the value of the cement. The principal ob-
jection to the sand test is that the use of sand introduces another
cause of variation in the results obtained by different experi-
menters. This objection has considerable weight, because it is
impracticable to find sand in widely separated localities which
is absolutely the same in composition and physical properties;
but two cements which appear to be of equal value when tested
neat may exhibit quite different characteristics when used with
sand, and it is believed that this fact far outweighs the objec-
tion noted. As soon as regularity in sieves is established, the
size of the sand grains may be regulated. The chemical and
physical properties of the sand and the shape of the grains is a
more difficult matter. The crushed quartz that is used in the
manufacture of sandpaper was recommended by the Committee
109
110
CEMENT AND CONCRETE
of the American Society of Civil Engineers of 1885, and if some
care is taken to select that which is clean and made from pure
quartz, there is little difficulty in obtaining a uniform product
of this kind.
160. The German Normal Sand is obtained by washing and
drying a natural quartz sand. In various parts of Germany
sand answering the purpose may be found. Some tests made
in this country to compare the "normal" German sand with
American crushed quartz have shown the sand to give a some-
what higher strength, while other tests have shown an opposite
result.* A few of these tests are given in Table 27.
TABLE 27
Results Obtained 'with German "Normal" and American
ard " Sand in Three Laboratories
' Stand-
Saitd.
Age.
Days.
Strength of Mobtar,
1 Cement, 3 Sand, Obtained at
Laboratory Number
3
4
5
Normal
Standard
Normal
Standard
Normal
7
7
28
28
218
263
317
334
173
219
341
300
201
211
281
283
Per Cent, of Water Used. 1
8
9
9
10
. . .
Standard
Mr. Max Gary has stated that "the Russian standard sand
gives markedly lower, and the Swiss sand considerably higher,
strength than the German."
161. Tests with Natural Sand. — It is not to be concluded
from what has preceded that one must make mortar tests with
a "standard" sand only. On the contrary, one may obtain
valuable results by using in tests the sand which it is proposed
to use on the work. The only point to be insisted upon is that
a cement shall not be rejected on account of the poor quality
of the sand used in testing. It is thus very desirable that a
certain proportion of the tests be made with a pure quartz
sand, and by making parallel tests with the natural sands, the
* Article by Clifford Richardson, Engineering Record, Aug. 4, 1894.
MAKING BRIQUETS 111
coefficient of the latter may be obtained. In any case it is
necessary, in order to obtain comparable results, to sift the
sand used for tests.
162. Fineness of Sand for Tests. — The American practice in
using crushed quartz is to reject the coarser particles by a sieve
having 20 meshes per linear inch (holes about .03 inch square)
and to reject the finer particles by a sieve of 30 meshes per linear
inch (holes about .02 inch square). The size of grain of German
normal sand is practically the same. In using a natural sand
it is not necessary to use this size of grain, but it is better to do
so, or at least to use some definite size or definite combination
of sizes; as, for instance, one-half of 20 to 30 (passing holes .03
inch square and not passing holes .02 inch square) and one-half
30 to 50 (passing holes .02 inch square and failing to pass holes
.012 inch square). Such a method will permit of duplicating a
given size of grain at any time, while if the sand is used as it
occurs in nature, considerable variations will be found. The
effect of the quality of sand on the strength obtained is dis-
cussed in Chapter XL
Art. 23. Making Briquets
163. Proportions. — The proportions of the ingredients should
always be determined by weight rather than by measure. It
will be found more convenient to use metric weights for the
dry ingredients. The water should then be measured in cubic
centimeters, which is equivalent to weighing it in grams. The
proportion of sand to be used for mortar briquets will depend
upon circumstances, but for short time (seven day) tests good
results are not usually obtained with natural cement if more
than two parts of sand by weight are added to one part of ce-
ment. Portland cement may be tested at seven days with
three parts of sand to one of cement. If too large a proportion
of sand is used, the briquets are liable to be injured in handling,
and very low strengths are not as accurately recorded by the
testing machine.
164. CONSISTENCY: DETERMINATION. — The consistency of
the mortar has such a marked influence on the strength obtained
that its importance can hardly be overestimated. The difficul-
ties attendant upon specifying the consistency of a given mortar
have already been touched upon in § 116. The Committee of
112 CEMENT AND CONCRETE
the American Society of Civil Engineers of 1885 recommended
the use of a "stiff plastic" mortar, but this phrase has had va-
rious interpretations.
The present Committee in its progress report ^ recommended
the use of the Vicat apparatus: "In making the determination,
500 gr. (17.64 oz.) of cement are kneaded into a paste, and
quickly formed into a ball with the hands, completing the oper-
ation by tossing it six times from one hand to the other, main-
tained six inches apart; the ball is then pressed into the rubber
ring (§ 98) through the larger opening, smoothed off, and placed
(on its large end) on a glass plate, and the smaller end smoothed
off with a trowel; the paste, confined in the ring resting on the
plate, is placed under the rod bearing the cylinder, which is
brought in contact with the surface and quickly released. The
paste is of normal consistency when the cylinder (1 cm. in di-
ameter and loaded to weigh 300 grams) penetrates to a point in
the mass 10 mm. (0.39 in.) below the top of the ring. Great
care must be taken to fill the ring exactly to the top."
The following simple test taken from French specifications
will determine a good consistency of mortar to use for briquets.
It should be capable of being easily molded into a ball in the
hands, and when dropped from a height of one and a half feet
on a hard slab, this ball should retain its rounded form without
cracking. The mortar should also leave the trowel clean when
allowed to drop from it. Were a smaller quantity of water
used, the mortar would be crumbly and the ball would crack
when dropped on the slab, while a larger amount of water would
cause the mortar to adhere to the trowel and the ball would be
flattened by striking the slab.
165. Another method of determining the proper consistency,
which the author believes will prove very satisfactory, is to
make several batches of mortar containing the same weights of
cement and sand, but having different percentages of water.
As each batch is mixed, the volume of the resulting mortar is
measured by pressing it lightly into a metal cylinder (a small
tin pail will answer the purpose), taking pains to fill the cylinder
in the same manner each time. That batch of mortar which
' Proc. Amer. Soc. C. E., Jan. 1903; also Engineering News, Jan. 29,
1903, and Engineering Record, Jan. 31, 1903.
CONSISTENCY OF MORTAR
113
occupies the least volume, when thus lightly packed, is the one
in which the amount of water used is most nearly correct.
Should either the mortar which, contained the least water or
that which contained the most water chance to have the least
measured volume, then more trials must be made until such a
consistency is obtained that either more or less water will in-
crease the bulk of the mortar. This method will give a con-
sistency somewhat more moist than that which gives the highest
results on short time cohesive tests, but it is believed that where
briquets are made by hand, more uniform results will be ob-
tained when the mortar is a trifle moist. This method is not
suited to daily use, as it requires too much time, but is valuable
as a check on one's ideas of proper consistency.
166. EFFECT OF CONSISTENCY ON TENSILE STRENGTH.—
Tables 28 and 29 give a few of the results obtained by the author
TABLE 28
Variations in Consistency of Mortar. — Effect on Tensile Strength,
Neat Natural Cement
Tensile Strength
, Pounds ]
PER Square Inch. 1
Cemkst.
Water Used Expressed as
1
Age of
Per Ce
NT. OF Dry Ingredients by Weight. |
Briquets.
Brand.
Sample.
25%
30%
35%
40%
45%
Gn
83 R
7 days
1136
205d
122/
72sr
61h
Gn
84R
11
926
72d
58/
54g
S9h
An
G
((
162c
165e
108/
75sr
54A
An
N
((
1626
194c
204e
134/
79flr
Hn
26 S
((
226d
176/
99gf
56A
35i
Gn
83 R
28 days
1896
244d
211/
182flr
135A
Gn
84R
((
1496
168d
114/
107sf
108h
An
G
t(
210c
228e
165/
102gr
80h
An
N
(I
1736
286c
254e
208/
150^
Hn
26 S
ii
333d
309/
2ng
12U
89i
Ln
31 S
Iday
162c
148e
97/
63flr
mh
Ln
((
7 days
178c
177e
124/
1^9
45A
Ln
((
28 days
207c
257e
202/
UOg
88A
Ln
((
3 mos.
300c
389e
333/
264g
197A
Significance of Letters
a — barely damp.
6 — very dry; no moisture shown on surface briquets. '
e — dry; slight moisture shown on surface briquets.
d — trifle dry.
e — about right consistency.
/ — trifle moist.
g — moist.
ft — very moist ; would just hold shape.
i — extremely moist ; would not hold shape.
114 CEMENT AND CONCRETE
in tests to determine the effect of consistency on the tensile
strength of natural cement mortars. All of the briquets were
made in the usual manner and stored in fresh water until time
of breaking. Each result given is the mean of from two to ten
briquets. The letters affixed to each result indicate the degree
of moisture which the mortar appeared to have when mixed,
varying from "a," barely damp, to "i," so wet that the mortar
could not hold its shape when laid on a glass slab.
The results in Table 28 were obtained with neat cement mor-
tars of several brands of natural cement. The first point to be
noted is the variation in the amount of water required by dif-
ferent samples to give the same consistency; thus, Brand An,
sample N, when mixed with 35 per cent, water, appeared to
have about the same consistency as did sample G of the same
brand mixed with 30 per cent. It is also apparent that the
strength of all samples is not affected alike by given variations
in the amount of water used in mixing; comparing the results
obtained when 45 per cent, water is used with that given when
25 per cent, water is used, it is seen that at seven days the wet
mortar gives 42 per cent, of the strength obtained with dry mor-
tar for sample 84 R, Brand Gn, while with the sample of Brand
Hn the strength of the wet mortar briquet is but 16 per cent,
of that given by the dry mortar. Of the six samples tested at
seven days and twenty-eight days, three gave the highest
strength at seven days when mixed with 25 per cent, water,
and five gave the highest strength at twenty-eight days when
30 per cent, water was used. The results on Brand Ln show
the greater proportionate gain with age of the wet briquets.
Table 29 shows similar results for mortars made with one,
two and three parts sand. With one part sand the wet mortar
made from Gn, 21 R, which gave but 22 pounds per square
inch at seven days, gave 429 pounds, or nearly the highest
strength, at six months. A similar result is shown for sample
15 R of the same brand when mixed with two parts sand, the
highest strength at one year and two years being given by the
mortar containing the greatest per cent, of water. That mor-
tars containing three parts sand to one cement may be more
easily damaged by an excess of water, is indicated by the re-
sults on Brand Ln in this table.
167. The effect on the strength of Portland cement mortars,
CONSISTENCY OF MORTAR
115
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116
CEMENT AND CONCRETE
of variations in consistency, has been investigated by Mr. Eliot
C. Clarke/ M. Am. Soc. C. E., and by M. Paul Alexandre,^ Chief
Engineer, Fonts et Chauss^es. The results of one series of ex-
periments made by M. Alexandre are given in Table 30. The
mortars were mixed with fresh water and the samples immersed
in sea water.
TABLE 30
Variations in Consistency of Mortar
Effect on Tensile Strength, Portland Cement Mortar.
25 pounds cement to 1 cu. ft. sand (about 1 to 4 by weight).
Consistency,
Water
Per
Cent, of
Sand.
Resistance, Lbs. per Sq. In. at Age of 1
1
at
0
1
S
CO
Dry . .
Ordinaiy .
Wet . .
14
22
30
31
26
16
56
46
35
73
74
55
77
116
89
69
153
126
67
170
136
88
162
180
Disintegrated
190
189
From " Recherches Experimentales sur Les Mortiers Hydrauliques,"
par M. Paul Alexandre, Annales des Fonts et Chauss4es, Sept., 1890
It is seen that the highest strength at three days and seven
days is given by the dry est mortar, at twenty-eight days to two
years by that of the ordinary consistency, and at three years by
that containing the highest per cent, of water. All of the sam-
ples exhibited white spots in the broken section at three years,
and at four years the dry mortar briquets had lost their cohe-
rence on account of their porosity permitting the sea-water to
permeate them.
168. Conclusions. — It may be concluded, then, that the
consistency of the mortar has a very marked effect on the ten-
sile strength obtained; that different samples of cement are not
affected in the same degree by given variations in consistency ;
that the effect of consistency is usually shown most plainly in
short time tests; and that while the dryer or stiff er mortars give
the highest results on short time tests, the moist mortars attain
a greater strength after a certain time.
* "Records of Tests of Cement made for Boston Main Drainage Works."
Trans. A. S. C. E., Vol. xiv.
' Annales des Fonts et Chatiss^es, Sept., 1890.
TEMPERATURE 117
169. Temperature of the Ingredients and of the Air where the
Briquets are Made. — The temperature of the mortar and of
the air in which the briquets are prepared is a matter of some
moment. In 1877, Mr. Maclay * reported a series of experi-
ments on Portland cements from which conclusions may be
drawn concerning the effects of the temperature of the mortar.
These experiments indicate that mortar having a temperature
of 40° Fahr. when gaged, will attain greater strength in from
seven days to three weeks than a mortar having an initial
temperature of 70° Fahr. One is most likely to work some-
where between these two temperatures, but it may be mentioned
that according to Mr. Maclay's experiments, it appears that
mortars gaged at a temperature of 90° or 100° Fahr. also at-
tain a higher strength than those gaged at 70° Fahr.
Similar experiments made by M. Candlot ^ indicate that mor-
tars gaged with cold water give but feeble resistance at first,
but in from two weeks to one month, such mortars surpass in
strength those gaged with warm water. M. P. Alexandre ^ im-
mersed some briquets at a temperature of about 90° C. (194°
Fahr.) for forty-eight hours and then at 15° to 18° C. (60° to
65° Fahr.) until broken, while other briquets were maintained
at the latter temperature from the time of molding. The bri-
quets that were broken at the age of four days showed that
the highest strength had been obtained by the briquets which
had been kept hot for forty-eight hours, but at twenty-eight
days and three months those briquets which had not been sub-
jected to this high temperature gave the highest strength.
170. Table 31 gives a few of the many experiments on this
point made under the author's direction. It appears that the
briquets made in a low temperature (34° to 37° Fahr.) are usu-
ally stronger than those made in the ordinary temperature of
65° to 68° Fahr. In some cases the difference was not very
great, and in some of the tests the briquets made in the ordi-
nary temperature gave higher results at one day and seven
days than those made in the cold; but at twenty-eight days the
cold-made briquets were nearly always in the lead, and in many
* "Notes and Experiments on the Use and Testing of Portland Cement,"
Trans. A. S. C. E., Vol. vi, p. 311.
' "Ciments et Chaux Hydrauliques"
* "Les Mortiers Hydrauliques."
118
CEMENT AND CONCRETE
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MORTAR MIXING 119
cases this difference held good at three months and six months.
Some of the results indicated that if the briquets were allowed
to remain twenty-four hours or more in the cold air, it tended
to counteract the beneficial effects of cold molding, but this
point was not satisfactorily established.
171. From the foregoing the following; conclusions may be
drawn: To make briquets of cold materials and allow them
to remain some hours in cold air, retards the hardening of the
briquets; but when briquets so treated are, after a few hours,
placed in a medium of ordinary temperature, they gain strength
more rapidly than briquets made of warm materials and kept
continuously at the ordinary temperature of 60° to 70° Fahr.
After being placed in a warmer medium, the briquets made
with cold materials in cold air frequently gain strength at such
a rate as to surpass in strength the warm-made briquets at seven
days; the former almost invariably surpass the latter at twenty-
eight days. In some cases it appears that this superiority of
cold-made briquets is maintained up to six months, but in other
cases the difference seems to disappear after three months.
Although these variations in temperature have not as marked
an effect on tensile strength as have many other variations in
manipulation, yet in carefully conducted experiments one should
always operate in a constant temperature. As a matter of
convenience, 65° to 70° Fahr. will commend itself, and this
temperature may well be taken.
172, GAGING BY HAND. — The objects to be attained in
gaging are to thoroughly incorporate the cement and sand, to
evenly distribute the water throughout the mass, and, if pos-
sible, to give the mortar a certain tenacity resembling that of
putty. This last object is not always possible of attainment
with mortars containing a large dose of sand.
The ordinary method of preparing mortars in the laboratory
is to gage with a trowel on a glass, slate, or marble slab. In
gaging mortars, the cement and sand are first mixed dry; the
materials are then drawn away from the center, leaving a crater
to receive the water, which is all added at one time. The dry
material is then gradually turned from the edges toward the
center until all of the water is absorbed, after which the mass
is thoroughly worked with the trowel in such a way as to rub
the material between the trowel and plate until the consistency
120 CEMENT AND CONCRETE
is uniform throughout. A batch of mortar sufficient for five
briquets cannot usually be properiy gaged by this method in
less than five minutes.
The Committee of the American Society of Civil Engineers,
in their prehminary report on methods of manipulation, sug-
gested that "as soon as the water has been absorbed, which
should not require more than one minute," the mortar should
be kneaded with the hands for one and one-half minutes, the
process being similar to that used in kneading dough.
173. HOE AND BOX METHOD. — Mr. Alfred Noble used for
many years a form of gaging apparatus, consisting of a box
with sloping bottom, in which the mortar is worked by means
of a hoe. The author has used an iron box made on this prin-
ciple (Fig. 2), which has given excellent results. The box is
2 feet 7^ inches long, 6 inches wide at the bottom, and at the
1 1* — 6^--»i!
»* 2 S' -^— ^ ^ — 7'—JA
Side Etevation £nef-
Fig. 2.— mixing BOX.
center is 6 inches deep. The level part of the bottom is 3 inches
by 6 inches, and from this level part the incUned portions of
the bottom slope up toward the ends at an inclination of about
22^ degrees. The sides of the box extend below these in-
clined planes to give a level bearing for the box when in use.
It is also well to have the sides flare enough to give a width
of 6^ inches at the top to prevent the hoe from becoming
wedged. A " German clod hoe," which is strong and heavy,
yet a trifle flexible in the blade, is used in connection with the
box.
The weighed quantities of the dry ingredients being put in
the box and well mixed, the measured volume of water is added.
Two minutes of hard work, in which the operator may put all
his strength, is sufficient to bring the mass to plasticity if the
amount of water added is correct, A return to the trowel and
MORTAR MIXING 121
slab method of mixing is not likely after a trial of this simple
device.
174. Machine for Mortar Mixing. — As the mixing by
hand is a rather slow and tedious method, and the hoe and box
method are not very generally known, several machines have
been devised to do the work. None of them, however, has
given such satisfactory results as to bring it into general use.
One of the machines is called a "jig," or "milk shake"
machine,^ and consists of a cup which moves rapidly up and
down, this motion being imparted by means of a hand wheels
crank and connecting rod. The dry cement and water being
placed in the cup and tightly covered, a few rapid turns of the
wheel are sufficient to reduce the cement to a paste. This
form is only applicable to neat cement mortars, and has been
said to give unsatisfactory results even for these, though in
some laboratories this machine has been used for all neat
mortars.
Other forms have been made in which the mortar is thoroughly
stirred by means of forks or blades projecting into the mortar
from a horizontal arm above. The gager devised by Mr. Faija
is constructed on this principle, and similar machines may be
obtained from manufacturers of testing apparatus.
175. Steinbriich's Mortar Mixer is a German machine oper-
ating on a different principle. It consists of a circular shell
having on its upper side and near its outer edge a circular groove,
or trough, to receive the mortar to be mixed. In this trough
rests a wheel on a fixed horizontal axis, which is above the pan
and normal to the axis of the pan. A cross-section of the rim
of the wheel is a semicircle fitting the groove in the pan. The
gearing is such that the pan is made to revolve about its vertical
axis, and the wheel about its horizontal axis, the inner surface
of the trough and the under side of the periphery of the wheel
.where the two are in contact moving in the same direction at
a given instant. The mortar is thus rubbed between the two.
Small blades, or plows, scrape the sides of the trough as the latter
revolves, thus keeping the mortar in the bottom of the trough.
The wheel and the plows are mounted on hinged axes, or sup-
ports, so that they may be raised from the pan when the mortar
* S. Bent Ruseell, Engineering News, Jan. 3, 1891.
122
CEMENT AND CONCRETE
is to be cleaned out. The mixing requires about two and one-
half minutes. The price of the machine is about $130,
176. The amount of gaging which a mortar receives has an
important effect on its consistency and the strength it will
attain. This was found to be the case in several experiments
where mortar gaged eight minutes in the box described above,
gave from 15 to 35 per cent, greater strength at one year than
that which was gaged but two minutes, the amount of water
used being the same in the two cases. Experiments on this
point are given in Table 78, § 364. It is therefore important to
eliminate, if possible, the variations which must follow hand
mixing, but as yet no apparatus has seemed to meet with gen-
Pio. 3. — FORM OF BRIQUET
USED ON THE CONTI-
NENT OF EUROPE.
Fig. 4. — FORM OF BRIQUET
USED IN THE UNITED
STATES.
eral approval, though among machine mixers those similar to
that used by Mr. Faija seem to have given the best results.
The hoe and box method described in § 173 partially eliminates
the personal equation, and for facility of operation and thor-
oughness of mixing leaves little to be desired.
177. Form of Briquet. — The shape and size of the briquet
have been the subject of much discussion and experiment.
Mr. John Grant, a pioneer in tensile tests, tried many forms
before finally adopting one quite similar to the form afterward
recommended by the Committee of the Amer. Soc. C. E. in
1885. Mr. Alfred Noble also made a series of experiments on
FORM OF BRIQUET 123
different styles of molds and clips, and presented the results
in a paper* read before the American Society of Civil Engineers.^
There are two forms of mold that are now in quite general
use. On the continent of Europe the form most generally used
is that shown in Fig. 3. It has a cross-sectional area of five
square centimeters (.775 sq. in.) at the smallest place, and the
heads of the briquet are elliptical in form, the major axes being
transverse to the briquet axis. The curve forming the side of
the briquet in the central portion is of very short radius, giving
the effect of a semicircular notch on either side of the briquet
at the smallest section. These notches have the effect of con-
fining the break to this place.
The other form of mold is the one mentioned above as recom-
mended by the Amer. Soc. C. E. Committee, and used in America
and England. A briquet of this form is shown in Fig. 4. The
cross-sectional area at the center is one square inch, and the
increase of section toward the ends is gradual, the radius of the
curve at the side of the briquet being | inch.
178. Area of the Breaking Section. — Formerly a section of
2j square inches was more commonly used here and in England,
while an area of 16 square centimeters (2.48 sq. in.) was com-
mon in France and other continental countries. The larger
the area of the breaking section, the smaller will be the com-
puted strength per square inch; this point seems fairly well
established, although the experiments recorded in a very ex-
cellent paper by Mr. Eliot C. Clarke ^ indicate no apparent dif-
ference in strength between briquets 1 square inch and 2\
square inches in section.
M. Durand-Claye found that the tensile strength of a briquet
varied more nearly as the perimeter than as the area of the
section. The experiments of M. Candlot do not point to this
conclusion, though they clearly show that the indicated strength
per square centimeter is very much greater for a briquet hav-
ing an area of five square centimeters at the small section than
for a briquet of 16 square centimeters area.
Mr. D. J. Whittemore ' experimented with briquets that were
* Trans. Amer Soc. C. E., Vol. ix, p. 186.
» Trans. Amer. Soc. C. E., Vol. xiv, p. 141.
« "Tensile Tests of Cements," etc. Trans. A. S. C. E., Vol. ix, p. 329.
124 CEMENT AND CONCRETE
circular in cross-section. He found that while the ultimate
strength of a briquet was about proportional to the periphery
of the breaking section for the ordinary solid briquet, yet if a
core were inserted in the mold, giving the cross-section an annu-
lar form, this proportion was not maintained. It was con-
cluded from this that the apparent peripheric strength could
not be explained by saying that the surface of the briquet had
gained a greater strength than the interior, but that the expla-
nation must rather be sought in the method of applying the
stress in breaking the briquet. The force being communicated
to the surface of the briquet, the stress is not uniformly dis-
tributed throughout the breaking section, because of the low
elasticity of the mortar.
M. Paul Alexandre showed that the difference in strength
per unit area decreased with age, although it did not entirely
disappear at one year. It would therefore seem that the expla-
nation of this phenomenon may be found in a combination of
these two causes; more rapid hardening of the smaller speci-
mens, and greater inequality of stress in breaking the briquets
of larger section.
179. Form of Briquet Suggested. — As a result of experi-
ments which will be described under the head of " Clips," ^
(Art. 25) the following conclusions were drawn as to the desir-
able features for a briquet:
1st. The smallest section should not have an area much less
than one square inch. Probably an area of five square centi-
meters would represent a minimum.
2d. The area of the section of the briquet between opposite
gripping points should be about one and three-fourths times
the area of the smallest section.
3d. The distribution of stress over the smallest section
should be as nearly uniform as possible.
4th. The curve of the sides at the breaking section should
not be very sharp; one-half inch might be taken as a minimum
radius.
5th. The area of the vertical section from the gripping point
to the plane of the end of the briquet — the section subjected
' These experiments were described by the writer in detail in "Munid'pal
Engineering," Dec, 1896, Jan. and Feb. 1897.
FORM OF BRIQUET
125
to shear when the stress is applied — should be ilearly as great
as the area of the neck of the briquet.
6th. The face and back of the briquet should be parallel
planes, to permit of easy storage.
7th. The total volume should be kept as small as is consis-
tent with the other conditions.
Fig. 5 represents a form of briquet which will, it is thought,
satisfactorily fulfill the above requirements, and in which it is
believed the full strength of the smallest section may be more
nearly developed than with present forms. The curve at the
central section has a radius of one inch, and the line of the
side of the briquet is con-
tinued in a tangent one- ic Gr^aiest ty/c/th£3i--—^
half inch in length, having
an inclination of nearly
45 degrees with the axis
of the briquet. The total
length of the briquet is
four inches, the ends be-
ing formed by straight
lines tangent to the curves
forming the corners. If
the clip is so formed that
the gripping points bear
at the centers of the one-
half inch tangents form-
ing the sides of the briquet,
the distance between op-
posite gripping points will
be 1^ inches.
180. Comparison with
other Forms. — Compar-
ing this briquet with the forms in common use, the German and
the form shown in Fig. 5 both have an area between opposite
gripping points about If times the area of the smallest section,
but in the form shown in Fig. 4 this ratio is too small to fulfill
the second specification.
The unequal distribution of stress over the breaking section
of the briquet has already been mentioned as a probable partial
cause why briquets of small cross-section show a greater strength
FlO. 6. — FORM OF BRIQUET SUGGESTED
FOR USE
126 CEMENT AND CONCRETE
per unit area than those having a larger area of cross-section.
In Johnson'i "Materials of Engineering" is given the theory of
the distribution of stress over the breaking section of a briquet,
as developed by M. Durand-Claye, and published in Annales des
Fonts et Chaussees of June, 1895. Applying the formulas there
given to three styles of briquet, the A. S. C. E. form of 1885,
the German standard, and the form shown in Fig. 5, it is found
that the ratios of the maximum stress to the mean stress are,
for the three forms respectively, 1.54, 1.52 and 1.22. From a
theoretical point of view, this means that with a total pull of
100 pounds on each briquet, the outer fiber of the briquet
shown in Fig. 4 would be subjected to a stress of 154 pounds
per square inch, while with the form suggested above, the
stress on the outer fiber would be but 122 pounds per square
inch ; briquets of the latter form should, therefore, theoretically,
show a breaking strength 1.27 times the strength given by
briquets of the same mortar made in the A. S. C. E. form of
1885.
The German form has too sharp a curve at the sides to fulfill
the fourth requirement given above. All of the forms comply
with the first, fifth and sixth requirements.
As to the volume of the briquet, the author's form having a
total length of four inches, has about 50 per cent, greater volume
than the A. S. C. E. form of 1885.
181. Molds. — In the early tests of cement, wooden molds
were employed, but they absorb water from the mortar and
soon warp out of shape. Iron molds have also been used to a
considerable extent, but these are apt to become rusted if not
in constant use. Brass, bronze or some similar metal not easily
corroded should be used, and molds of this character can be
obtained of dealers in testing apparatus.
The molds may be made single, or in "nests" or "gangs"
of three to five. The two halves of the mold may be entirely
separable, or may be hinged at one end and fastened by a clip
at the other end. The gang molds are somewhat cheaper than
the single ones. The hinged molds and those held with patent
clip are rather difficult to clean, while the gang molds, if made
heavy enough to prevent spreading, are unwieldy, and briquets
are removed from them with greater difficulty than from the
single molds. It is considered, therefore, that the most con-
MOLDING BRIQUETS 127
venient form is the single mold, in which the two halves are
held together by a screw clamp of simple design.
182. To clean these molds, place ten in a row with clamps
removed ; scrape the upper faces with a piece of zinc, brush
with a stiff "horse-brush," and wipe with oily waste. Turn
them over and repeat the process. Then separate the two
halves of each mold, place the twenty halves in line with inner
surfaces up, forming a trough twenty inches long. Wipe this
trough thoroughly with oily waste, finishing with some that is
only slightly oiled.
183. Molding. — Methods of molding briquets vary widely
and have a considerable effect on the results obtained by differ-
ent operators. The mold may be placed on a glass or marble
slab, or on a porous bed. This difference in treatment will
affect the results chiefly because a porous bed will extract
moisture from the briquet, and, unless it is already mixed very
dry, will make it give a higher result on a short time test. The
use of a porous bed probably originated with a desire to more
closely imitate the use of mortar in actual work, but it intro-
duces another source of variation in results and should not be
followed.
184. In hand work the whole mold may be filled at once,
or small amounts of mortar may be added at a time, and each
layer packed; the mortar may be tamped into the mold with a
rod, in which case the pressure used may vary widely; or the
mortar may be pressed in with the fingers, or with the point of
a small trowel; and, finally, the pressure applied on the top of
the whole briquet may be light or heavy. It is evident that it
is almost impossible to so describe all these details of manipula-
tion that another operator may follow the same system and
obtain the same results. The practice of ramming the mortar
into the mold by means of a metal rod or a stick faced with
zinc is objectionable, because of the possible wide variation in
the force thus applied. This method is sometimes used by
manufacturers, since by making the mortar quite dry and ram-
ming it into the molds very hard, a high initial strength is
obtained. But the foremost cement makers are now eschewing
such methods and are aiming to make fair tests. Some experi-
ments made under the author's direction indicate that the
pressure applied to the top of the briquet is the salient point in
128
CEMENT AND CONCRETE
the process of molding, and that the other details are of minor
importance.
In Germany a heavy trowel or iron plate weighing about
250 grams, and provided with a handle, is used in making one-
to-three mortar briquets. The mortar is made rather dry
(about 10 per cent, water), and after the mold is filled and
heaped, the mortar is beaten with the trowel until it becomes
elastic, and water appears on the surface. The excess of mor-
tar is then scraped off with an ordinary trowel or spatula.
185. Several machines have been devised for making bri-
quets, some of which are said to give good results. Among
these the most prominent is the Bohme hammer apparatus,
which is much used in Germany, although not employed to any
extent in the United States. It consists of a plunger which
fits the mold and upon which a given number of blows are
struck by a hammer. The mortar is first gaged as for hand
molding, and placed in the form. A pinion, turned by a hand
crank, is geared to a wheel provided with ten cams. These
cams operating on the wrought iron handle of the hammer
cause a certain number of blows to be delivered to the plunger.
The mechanism is automatically shut off after the proper number
of blows has been delivered. The following results were ob-
tained by Professor Bohme with his apparatus: —
TABLE 32
Comparison of Hand Made Briquets V7ith Those Made by Bohme
Hammer
No.
Method.
Weight op
Briquets.
Mean Tensile
Strength at
7 Days in Kgs.
per Sq. Cm.
1
2
3
4
5
By hand
Hammer, 76 blows
100 "
125 "
150 "
160.0
1.58.0
159.5
159.5
169.0
16.06
12.75
13.25
14.56
15.56
186. Several American engineers have devised machines for
briquet-making, but none of them has been generally adopted.
An apparatus designed by Prof. Charles Jameson, of Iowa
University, is said to work very rapidly. The mortar is packed
in the mold by a plunger of the form of the briquet. This.
MOLDING BRIQUETS 129
plunger works in a chamber of the same shape as the briquet
mold. The mortar is placed in a hopper at the side of this
chamber, and is delivered to the mold automatically when the
plunger is raised. The force is applied to the plunger by hand,
but it should be so arranged that this be done by a weight, to
prevent variations in pressure. In this method the briquet is
removed from the mold as soon as made, and this would appear
to be an objectionable feature.
Professor Spalding, of Cornell University, in his excellent
little book on "Hydraulic Cement," states that he has found
that "a pressure of about 500 pounds upon the surface of the
briquet is sufficient to produce a compact and homogeneous
briquet, and a crude appliance consisting of a lever arranged to
bring a pressure upon the mortar in the mold by means of a
weight suspended at the end of the lever, has been found to
increase both the rapidity and the regularity of the work, and
especially to diminish the variations in results obtained by dif-
ferent men."
A machine which would give more uniform results and work
more rapidly than hand molding, would commend itself for
general use.
187. Method Recommended. — In making briquets by hand,
the mortar may well be packed into the molds by the fingers,
which should be protected by rubber tips. When the mold is
filled and slightly heaped, the trowel should be placed on top,
and the molder put about 60 pounds pressure on the trowel.
The excess mortar is then cut off by the trowel and the top of
the briquet is smoothed by drawing the trowel across the face.
The results obtained by four molders using this method in the
same laboratory are given in Table 33.
188. The recent progress report of the Committee of the
American Society of Civil Engineers on uniform tests of cement
contains the following, under "Molding": —
"Having worked the paste or mortar to the proper consist-
ency, it is at once placed in the molds by hand.
"The Committee has been unable to secure satisfactory re-
sults with the present molding machines; the operation of
machine-molding is very slow, and the present types permit of
molding but one briquet at a time, and are not practicable with
the pastes or mortars herein recommended.
130
CEMENT AND CONCRETE
TABLE 33
Results Obtained by Different Molders when Using Similar Mortar
o
MS"
§g
Mean Tensile
Stbength.
H
Ah
go
H Ed
■<«
Date.
n
AOE.
Q
a
«
u
a
OS
^ 1
O
o
S
o
a
6
c
d
e
/
9
A
i
1
0
31.6
62-65
7 days
8
1 92
89
5
10-22
Clear
2
0
n
"
28 "
19
7 213
220
5
3
1
18.7
67-62
7 "
7
9 91
89
5
4
1
((
"
28 "
23
5 257
259
6
6
1
((
63-68
3 mo.
51
5 541
519
5
6
1
i(
"
1 year
55
8 569
555
5
7
2
16.2
70-65
28 days
19
6 186
197
5
8
2
((
u
3 mo.
42
3 383
406
6
9
3
13.3
65-61
3 mo.
25
^ 263
239
5
10
3
"
(1
1 year
26
0 232
236
5
11
Su
m of M
eans
e
J79
7 2827
Holder
S.
2809
Molder
T.
12
0
31.6
62-65
7 days
60
60
5
10-28
Cloudy
13
0
"
«'
28 "
145
167
5
14
1
18.7
65
7 "
67
71
5
15
1
"
"
28 "
223
211
5
16
1
n
i(
3 mo.
435
449
5
17
1
((
"
1 year
504
491
5
18
2
15.2
67
28 days
182
179'
5
19
Su
m of M
eans
1616
1628
Cement, Brand Gn, Sample 21 R. Sand, Crushed Quartz 20 to 40.
,\11 briquets in same line received same treatment after made and were
immersed in same tank until broken.
' Mean of ten specimens.
"Method. The molds should be filled at once, the material
pressed in firmly with the fingers and smoothed off with a
trowel without ramming; the material should be heaped up on
the upper surface of the mold, and, in smoothing off, the trowel
should be drawn over the mold in such a manner as to exert a
moderate pressure on the excess material. The mold should be
turned over and the operation repeated.
"A check upon the uniformity of the mixing and molding is
afforded by weighing the briquets just prior to immersion, or
STORING BRIQUETS
131
upon removal from the moist closet. Briquets which vary in
weight more than 3 per cent, from the average should not be
tested."
189. Marking the Briquets. — The briquets made in a given
laboratory should be numbered consecutively, so that no con-
fusion can arise, and this one number is all that should be placed
on the briquet. The record of the brand of cement, the pro-
portions used, etc., should be placed in a book opposite the
briquet number. The briquets should be numbered on the
face, near the end. Steel stamps furnish a ready means of
numbering, and when mortar contains more than two parts of
sand to one of cement a thin strip of neat cement paste plastered
across one end of the briquet will aid in making the numbers
legible.
Art. 24. Storing Briquets
190. The Time in Air before Immersion. — As soon as the
briquets are molded they should be covered with a damp cloth
TABLE 34
Variations in Length of Time Briquets are Left in Moist Air before
Immersion — Natural Cement
Tensile Strength, Pounds i-ek I
Sq. Inch. 1
Cement.
Parts Crushed
Quartz, 20-30°
TO
1 Cement.
Age
When
Broken.
1
Hours in Moist Air before
Immersion.
8
12
(
72
168
Brand.
Sample.
24
48
Gn
15 R
0
7 days
123
139
151
161
237
It
i(
1
7 days
91
106
114
114
182
11
16 R
0
28 days
110
106
109
89
113
t(
"
1
28 days
142
138
139
152
175
"
n
2
28 days
102
103
112
113
115
An
G
0
7 days
• • .
168
181
194
185
238
n
tt
0
28 days
200
210
224
241
243
ti
It
1
7 days
108
137
141
157
160
it
((
1
28 days
278
283
297
297
301
n
tt
3
28 days
120
130
137
139
152
Note : — All briquets made by same molder. Each result is mean of ten
specimens.
until they are ready to be removed from the molds, when they
should be transferred to a "damp closet," lined with zinc or
other non-corroding metal. It was formerly the practice to
immerse the briquets as soon as they were considered to be
132
CEMENT AND CONCRETE
sufficiently set; but for the sake of uniformity, they are now
left in moist air for twenty-four hours before immersion, whether
the cement is quick or slow setting. Briquets which are to be
broken at twenty-four hours, however, are usually immersed
as soon as set hard.
Table 34 gives the results obtained by allowing natural
cement briquets to remain in moist air different lengths of time
before immersion. In general, the strength is greater for seven
and twenty-eight day tests the longer the briquets are allowed
to remain in the moist air. It appears that, while the time in
moist air should be made as nearly uniform as possible, a varia-
tion of a few hours will not cause an important difference in
strength.
TABLE 35
Gain or Loss in Strength of Natural Cement Briquets by Immersion
Tensile Stki
:noth, Pounds
Time in
Moist Aie.
Age When
Broken.
pee Sq
. Inch.
Time in Tank.
One Part Stand-
Neat Cement.
ard Sand to
One Cement.
20 hours
20 hours
151
94
18 hours
6\ days
7 days
147
153
2 days
.
2 days
192
126
2 days
5 days
7 days
160
158
3 days
3 days
205
141
3 days
4 days
7 days
177
155
4 days
4 days
218
165
4 days
3 days
7 days
191
166
5 days
5 days
230
176
5 days
2 days
7 days
192
169
Note : — All briquets made by same molder. Each result is mean of
five specimens.
Table 35 shows the early action of the water on the briquets.
These tests were made in sets of ten; five briquets of a set were
immersed after twenty hours, forty-eight hours, etc., while the
other five of the same set were broken at the time the first five
were immersed. With this sample of natural cement, it appears
that the briquets lose part of their strength by immersion, and
that some time is required to regain this lost strength. Thus,
with neat cement mortar the briquets broken at twenty hours
without immersion were as strong as those broken at seven
days which had been immersed the last six and one-fourth days.
With briquets of one-to-one mortar, it appears that if immersed
STORING BRIQUETS 133
at the end of four days, the gain in strength during the last
three days (in water) is about equal to the loss of strength due
to immersion. If immersed earlier than this, the gain is greater
than the loss, but if immersed later, the loss is greater than
the gain.
191. For storing briquets the required twenty-four hours
before immersion a moist closet is very convenient, tends to
promote uniformity of treatment, and may be very easily
made. The use of a damp cloth for covering briquets is incon-
venient, as the cloth may dry out. If it is used, the end of
the cloth should rest in a pail of water, so it will keep wet by
capillarity; it should also be kept from touching the briquets by
a wire screen or by wooden slats.
A moist closet may be made of slate, glass or soapstone, or
of wood lined with metal. In the bottom of the box is a pan of
water, or a sponge kept constantly wet. The shelves may well
be of glass, and should be so arranged that any shelf may be
removed without disturbing the others.
192. Water of Immersion. — When the briquets are ready to
be immersed, i.e., usually, twenty-four hours after made, they are
placed in a tank, containing water that is kept fresh by frequent
renewals. The water in the tank should also be maintained at
a nearly constant temperature. It is sometimes the case that
briquets are subjected to considerable variations of temperature
while in storage. It also frequently occurs that the water is
allowed to become stale. " A few of the many experiments
made at St. Marys Falls Canal to show the effect, on the tensile
strength of natural cement briquets, of variations in the tem-
perature of the water of immersion, are given in Table 36. The
details of these experiments, as well as other tests on the same
point, may be found in the Annual Report, Chief of Engineers,
U. S. A., for 1894, page 2314.
The very marked effect which the temperature of the water
may have on the rate of hardening of natural cements is clearly
shown. When broken at the age of one day or seven days,
the effect on the strength may not be evident, or the briquets
stored in cold water may develop a greater strength, but the
more rapid hardening of the briquets stored in warm water is
usually very evident at twenty-eight days, and increases up to
two or three months. Some samples of cement are affected
134
CEMENT AND CONCRETE
less than others, and a few experiments indicated that the
differences in strength due to the temperature of water of im-
mersion decrease after three months and become almost nil at
one year.
193. The conclusion drawn from these tests may be briefly
stated as follows: Between certain Hmits tl;ie early strength of
natural cement mortars is usually developed faster in cool
TABLE 36
Variations in Temperature of Water in vrhich Briquets are
Immersed
6
Q
Tensile Strength, Pounds per Square
"A
Natural
M
M
Inch, When Immer.seo in
»
Cement.
§o^=?
««i
Water of Approximate Temperature,
Degrees Fahr.
S
Brand.
Sample.
<
38°
146
40°
60°
137
55°
125
co°
65°
70°
80°
1
Gn
16 R
0
7 days
126
154
2
11
11
0
14 days
144
131
125
131
150
168
208
3
11
11
0
28 days
166
178
184
247
280
4
"
"
1
7 days
83
88
84
89
98
97
121
5
It
11
1
14 days
84
111
123
150
191
6
11
It
1
28 days
9(J
156
187
221
243
288
7
Ln
31 S
0
1 day
143
124
120
109
109
8
"
"
0
7 days
204
201
183
193
186
9
"
11
0
14 days
184
203
204
229
245
10
11
"
0
28 days
221
245
254
281
303
11
11
11
0
2 mos.
261
292
348
382
429
12
An
G
1
7 days
134
140
160
154
158
13
11
11
1
14 days
149
162
189
182
216
14
"
"
1
28 days
198
223
250
281
296
15
11
It
1
2 mos.
251
286
337
386
403
16
11
11
3
14 days
.
50
58
69
73
100
17
11
11
3
28 days
67
87
100
102
157
18
11
11
3
2 mos.
104
127
147
194
231
water, but after the first seven days, and sometimes after a
shorter time, the strength is developed more rapidly in warm
water, and the strength at any time between seven days and
three months is approximately proportional to the temperature.
After three months, the effect of the temperature seems to
diminish, and may entirely disappear in time,
M. Paul Alexandre * made quite a number of experiments
on this point with Portland cement. In these experiments the
' " Recherches Experimentales sur les Mortiers Hydrauliquea."
STORING BRIQUETS 136
gaging was done in about the same temperature as that at which
the water of immersion was maintained, so that a double cause
of variation was present. However, it was found that in all
cases the higher strength was attained at seven days by the
briquets made and stored in the higher temperature (15° to
18° C, 60° to 65° Fahr.) while at twenty-eight days the briquets
of the lower temperature (0° to 5° C, 32° to 40° Fahr.) were
ahead in the case of neat cement, and nearly as high as the
warm briquets in the case of mortar. At three months the
differences seemed to disappear.
194. Stale Water. — Some experiments made to compare the
strength of briquets which were alike in all other respects, but
were immersed in different tanks in which the water had not
been frequently renewed, showed very clearly the possible varia-
tions from this source. Natural cement briquets, neat, and with
one and two parts sand, gave, when immersed in one of the
tanks, only from 40 to 60 per cent, of the strength attained
in another tank by briquets entirely similar.
To store briquets in running water is going to the other
extreme; this appears to be the best method, at least for short-
time acceptance tests, provided the temperature can be regu-
lated. However, in some cases where this has been adopted,
the strength of the briquets is said to have fallen off very much
after four or five years. Whether this is due to the action of
running water is a very interesting point, and a valuable one
from the practical standpoint of the use of cement, but it has
not yet been thoroughly investigated.
195. It appears from the foregoing that variations in the
temperature and freshness of the water in which the briquets
are immersed is an uncertain contingent, and therefore that all
such variations should be carefully avoided. As a matter of
convenience, the tanks may well be maintained at 60° to 70°
Fahr., but if one does not care for a comparison of his results
with those obtained in other laboratories, then any other con-
stant temperature between 40° and 75° may be adopted. The
water in the tanks should be renewed at least once a month,
and preferably once a week.
196. Storing Briquets in Sea Water. — When the cement
under test is to be used for constructions in the sea, some of
the briquets should be stored in sea water to indicate the be-
136 CEMENT AND CONCRETE
havior in this medium. Many tests have been made in this
way by several experimenters, but the varied results obtained
only indicate the different effects of such treatment on different
samples of cement. One of the effects of storing in sea water
has been touched upon under the head of consistency of mortar,
where it is shown that porous briquets may disintegrate in this
medium. A small specimen like a briquet will of course be
more quickly affected than a large mass of concrete, but on the
other hand, the concrete in work is likely to be more porous
than the briquet. The effect of sea water upon cement will be
taken up in another place.
197. Other Methods of Storing Briquets. — It has been
thought that briquets, made to test cement that is to be used
in air, should be hardened in the same medium in order that
the tests should more nearly approach the conditions of use.
Several points, however, should be borne in mind in interpret-
ing the results obtained with air-hardened specimens. In actual
work the mortar is usually in a large mass, or is protected from
the influence of a warm, dry atmosphere, so that it remains
moist for a long time, whereas a briquet placed in the open
air is much more affected by changes in atmospheric condi-
tions. If the briquets are allowed to harden in a room, such a
small quantity of mortar may become quite dry in a few days,
and, unless the amount of moisture in the air is regulated, an-
other source of variation is introduced in the tests.
It has been found impossible to obtain uniform results from
briquets made as nearly alike as possible and stored side by
side in the air of the laboratory. The regular acceptance tests
should, therefore, it is thought, be made in the ordinary man-
ner, but if cement is to be used in locations where it is likely
to become very dry, a few special tests should be made to assure
one that the brand of cement in question is one that will yield
good results in such exposure. It may be found that certain
kinds or brands should be entirely avoided for use in such lo-
cations. A few tests of this character are given in Tables 72
and 73, §§ 359, 360. The results in any given line of the table
are from briquets made the same way but treated differently
in the method of storing. It is seen that these brands harden
well in dry air. The effect of the amount of water used in
gaging appears to follow somewhat the same law, whether the
briquets are stored in air or water.
BREAKING THE BRIQUETS 137
A method more nearly approaching conditions that fre-
quently prevail in practice is to bury the briquets in damp
sand. Table 120, §409, gives the results obtained with a large
number of briquets stored in this way. While the results are
somewhat more irregular than those for water-hardened speci-
mens, since the conditions cannot be made so nearly uniform,
yet this method gives better results than dry air storage.
Art. 25. Breaking the Briquets
198. THE TESTING Machine. — The function of the testing
machine is simply to furnish a means of applying the tensile
stress, and of measuring the amount of force required to break
the briquet. Aside from the clips, which hold the briquet,
any contrivance which may be conveniently operated, and
which will accurately measure the force applied, may be used
for this purpose.
There are several forms of testing machines on the market,
all designed on the lever principle, though differing slightly in
the method of application. The force is applied either by al-
lowing water or shot to run into or out of a vessel suspended
at the end of the longer arm of a lever, or a weight is made to
run along the lever arm, which is graduated so that the force
applied may be read from the beam.
199. In machines of the first class the delivery of shot is
cut off automatically the instant the briquet breaks. The ad-
vantage of this style is that the flow of shot may be so adjusted
as to approximately regulate the rate of applying the stress;
but little skill is required to operate it, and, since in its best
form two levers are used, the shorter arm of one acting on the
longer arm of the other, the machine occupies but little space.
This machine does not permit rapid operation, since the shot
must be weighed each time a briquet is broken. One of the
main disadvantages of this form has been that in the case of
strong briquets, a certain initial strain had to be applied in
order that the stretch of the briquet and the slipping of the
clips should not allow the shot to be cut off before the briquet
broke. This objection, however, has recently been met by the
makers, who have provided means of taking up this slip by a
hand crank.
200. Another objection urged against the short-lever shot
138 CEMENT AND CONCRETE
machines is the fact that as the stream of shot flowing into the
scale pan is cut off by the breaking of the briquet, a certain
amount of shot on its way to the pan falls into the pan after
the briquet breaks, and is weighed, although not acting on the
briquet at the time of the break. A form of shot machine is
now on the market, however, in which this objection has been
overcome. The load is applied by means of a weight hanging
from one end of a lever. This weight is at first counterbalanced
by a pail of shot at the other end of the lever, but as the shot
is allowed to run out of the vessel, the unbalanced portion of
the weight acts, through suitable levers, upon the briquet.
The flow of shot is shut off automatically by the breaking of
the briquet, and the shot that has escaped is weighed on a
special scale to determine the load acting on the briquet.
201. In the other form of machine the weight is made to
move along the arm by means of a cord and hand-wheel. This
style may be operated much more rapidly, but some skill is
required to use it properly, and as now made it occupies too
much space. These machines are preferable for laboratories,
while the shot machines may well be used in cement factories
and small works where a foreman does the testing.
202. It would seem that a machine could easily be made
which would combine the desirable features of both of these
forms, by placing a heavy weight provided with rollers upon
the upper lever arm of the shot machine, and using it in the
same way that the hand power machine is now used. This
would involve placing a hand wheel and cord upon the machine
to operate the moving weight, the shot attachment being re-
moved. Such a machine would combine the compactness of
the shot machine, with the accuracy and speed of the single
lever machine; the graduations on the beam could represent
five pounds each, instead of two pounds, the value of the grad-
uations now on the single lever machines.
203. Forms of Clip. — Since cement has been tested by
tensile strain, it has ever been a problem to obtain a clip which
would give a perfectly true axial pull on the briquet. Various
forms of clips have been used from time to time, but none of
them has proved satisfactory in all respects. To trace the his-
tory of the development of the clip is not warranted by its
interest, but it may be said that in some of the early forms the
BREAKING THE BRIQUETS
139
head of the briquet was held between two plates and clamped
tight enough to develop sufficient friction to transmit the stress.
The later forms of briquets are made with a shoulder or with
wedge-shaped ends to allow the clip to grasp them. Mr, John
Grant, Mr. Alfred Noble, General Gilmore, Mr. J. Sondericker
and Mr. D. J. Whittemore have each designed or adapted dif-
ferent forms, and more recently Mr. S. Bent Russell and Mr.
liiliiliilirE
3
I" ^4 Vi W 0 I 2 3i/f.
Fig. 6. — RIEHLE "ENGINEERS' STANDARD" CLIP
W. R. Cock have each devised a clip which will be mentioned
below.
204. Form in Most General Use. — The clip in most general
use in the United States is of the general style shown in Fig. 6.
It differs only in detail from the form recommended by the
Amer. Soc. C. E. Committee of 1885, which has been called
140 CEMENT AND CONCRETE
the "Engineers' Standard." The general form is pear shaped;
the briquet is grasped at the points of reverse curve at the side
of the briquet, giving an area between opposite gripping points
of about one and a quarter square inches. The gripping points
are rather too sharp, when new, as they have a tendency to
crush the briquet locally. The width of the bearing increases
with the amount of wear the clip sustains. The clip is provided
with a conical pivot, which rests in a cone-shaped cavity at-
tached to the machine, so that the two parts of the clip are
free to swing. In a form which was previously used to a con-
siderable extent, each bearing surface was designed to be about
an inch square, the jaw being made to conform to the outline
of the briquet. This form, however, did not give satisfactory
results; a particle of sand between the briquet and the bearing
surface of the clip would give an eccentric pull, and strong
briquets would sometimes break in the head of the briquet
transverse to the axis, in several curved layers joining opposite
gripping surfaces.
205. Clip-BREAKS. — When a briquet is inserted in the or-
dinary clip, the gripping points will not, in general, grasp the
briquet symmetrically. The gripping points have a tendency
to slide on the surface of the briquet in order to assume a sym-
metrical position; there is friction to resist this sliding, and
when this resistance overcomes the tendency to motion, the two
clips and the briquet become a rigid system, and bending strains
may be introduced. Again, if the briquet is not too badly ad-
justed in the clips, it is apt to break in a line joining two op-
posite gripping points, instead of at the smallest section; this
is called a " clip-break." The tendency to form clip-breaks is
greater if the gripping points are very narrow or have sharp
edges; neat cement briquets exhibit this tendency much more
than briquets from sand mortars, and some samples of cement
are much more likely to give clip-breaks than others.
206. Cause of Clip-breaks. — When a briquet breaks in this
manner, the broken section is usually about normal to the side
of the briquet at the point where the jaw was in contact. This
indicates that a clip-break is caused by compression at that
place: there is evidently compression along the plane joining
the two opposite gripping points, and tension at right angles
to that plane, and the briquet fails here as a result of the two
BREAKING THE BRIQUETS 141
stresses. If the briquet is not properly adjusted in the clips,
but is so placed that its longest axis is at one side of the line
joining the points of application of the forces (in the "Engi-
neers' Standard" clip, the line joining the pivot points), then
the bending strain that is introduced is greatest at the central
section of the briquet; this may cause the briquet to break at
the smallest section, when if it were properly adjusted in the
clips it would develop a clip-break. The bearing surfaces of
the clip should not be too small, as this increases the intensity
of pressure, but on the other hand there appears to be no prac-
tical advantage in making this area more than ^^ to J inch
wide (the length being limited by the thickness of the briquet,
one inch).
207. Prevention of Clip-breaks. — The method most fre-
quently adopted to prevent clip-breaks is to cushion the grip-
ping points with some compressible material, such as thin rub-
ber or blotting-paper. This device prevents clip-breaks, but
the result of about three hundred tests made under the author's
direction showed clearly that it also lowered the apparent
strength very materially.^ Briquets broken with the bare clips
showed a mean strength of 606 pounds per square inch, while
the cushioned clips gave an apparent strength of but 521 pounds,
or 86 per cent, of the strength without the cushion; of the bri-
quets broken with the bare clips, 33 per cent, were clip-breaks;
with the cushioned clips no clip-breaks occurred. The rubber
was applied by slipping two rubber bands over each end of the
briquet, giving cushions about xV inch thick.
208. Strength of Briquets that Develop Clip-breaks. — It was
also found in breaking 277 briquets with two styles of clips
without cushions that 129 of them that gave clip-breaks aver-
aged 611 pounds per square inch, while 148 which did not de-
velop clip-breaks had a mean strength of 590 pounds. This
result is easily accounted for by saying that some of the bri-
quets that broke in the small section were made to do so by the
cross-strain introduced by imperfect adjustment in the clips.
When a briquet breaks at other than the smallest section, it
is certain that the smallest section has a greater strength per
* For a report of these tests in detail, see Annual Report Chief of Engi-
neers, U. S. A., 1895, p. 2913. Also "Municipal Engineering," Dec, 1896,
Jan., Feb., 1897.
142
CEMENT AND CONCRETE
square inch than is shown by the result obtained ; how much
greater cannot be told. But it follows that if clip-breaks could
be eliminated in a proper way, one which would not cause center
breaks by the introduction of cross-strains or other undesirable
conditions, the strengths thus obtained would be greater than
when clip-breaks occur. The fact that the use of a rubber
cushion gives lower strengths, shows that this is not the proper
method of preventing clip-breaks.
209. Mr. W. R. Cock has devised a clip, with rubber-covered
gripping points, which has attracted some attention. It has
I ' ' ' ' ' I ' ■ I ■ ' I
r ^M '/i. *A 0
I 2
Fig. 7.— RUSSELL CLIP
3 in.
sometimes been assumed that because this clip eliminated clip-
breaks it must give a higher apparent strength than the rigid
form. No extensive series of experiments have been published
which permit of comparing this clip with other forms, but
from the results obtained above, in using rubber cushions, it
would appear that the Cock clip may give lower apparent
strengths.
BREAKING THE BRIQUETS
143
210. The form of clip designed by Mr. S. Bent Russell is
constructed on the "evener" principle, each clip having free-
dom of motion imparted by four pin-connected joints (see Fig.
7). It is sought to prevent any but an axial pull being ap-
plied to the briquet. On account of details of construction,
into which it is not necessary to enter here, the clip must be
in its normal position when the briquet is inserted, in order
that the possibility of cross-strain shall be effectually removed.
As a result of many tests vnth. this form and the ordinary "En-
'" ^
r ^ >t )* o
3 in.
Fig. 8. — single GIMBAL CLIP
gineers' Standard," it was found that they gave very nearly
the same strength. But that the evener motion itself was of
some value was shown by a series of experiments in which part
of the briquets were broken by this form of clip without modi-
fication, while part were broken by the same clip when it had
been changed to a rigid form by means of a clamp that elimi-
nated the evener motion. It is believed that with some modifi-
cations this clip will give good results, and it may be used al-
most as rapidly as the ordinary rigid form.
144 CEMENT AND CONCRETE
211. Several experiments were made with a clip in which
the gimbal principle was applied, the stress passing from the
machine to the gripping points through knife edges placed in
the line joining opposite gripping points and midway between
them ^ (Fig- 8). Higher results were obtained with this form,
the " Single Gimbal," than with any of the styles with which it
was compared, but it was made only for experimental purposes,
and unless modified is not convenient enough to be recom-
mended for general use.
212. In the course of these experiments it was shown that to
increase the distance between gripping points, grasping the bri-
quet nearer the head, increased the apparent strength and
diminished the number of clip-breaks. With the Russell clip,
increasing this distance from IfV inches to l^V inches gave an
increase of about six per cent, in the apparent strength; and a
similar increase in the width between jaws of the Gimbal clip,
from IfV to lx*V inches, gave an increase in apparent strength
of about five per cent. It was found later that Mr. J. Son-
dericker had previously arrived at similar results,^ and as the
form of briquet used by the latter had permitted extending
the experiment, he found that when the points were about If
inches apart (making the area of the briquet about If square
inches between opposite gripping points), nearly all the frac-
tures occurred at the smallest section.
213. Effect of Improper Adjustment. — The effect of not
properly adjusting the briquets in the clip was also investigated.
In some cases the briquets were placed in the proper position
as nearly as possible. In the other cases they were in a de-
cidedly distorted position, much worse than they would be
placed with the most careless manipulation. It was found that
if the briquet was so placed in the "Engineers' Standard"
clip that the gripping points on one side of the briquet were
farther apart than those on the other side, the decrease in break-
ing strength was very marked (about 35 per cent.), while if the
planes determined by the lines of contact of the gripping points
of each clip were parallel, there appeared to be no efifect. The
' This clip was devised by the author at the suggestion of Mr. E, S.
Wheeler, M. Am. Soc. C. E.
' Jour. Assoc. Eng. Soc, Vol. vii, p. 212.
BREAKING THE BRIQUETS 145
reason of this is evident: in the former case the Hne of force,
joining the two pivot points, does not pass through the center
of the smallest section of the briquet, and transverse stresses
are introduced, while in the latter case the line of force does
pass through the center of the smallest section, though not at
right angles to its plane. With the Russell and Gimbal clips
the distortion seemed to have little effect, provided, that in
the case of the former, the clip was itself in its normal position
when the briquet was inserted.
214. Conclusions Derived from Tests of Several Styles of
Clips. — From the tests described above,* the following conclu-
sions may be drawn: —
1st. When using the ordinary form of clips with metal
gripping points, the briquets which break at the places of con-
tact of the jaws give higher apparent strengths than those
which break at the smaller sections.
2d. A rubber cushion between the briquet and the jaw of
the clip prevents clip-breaks, but materially lowers the stress
required to break the briquet.
3d. The form of clip designed by Mr. S. Bent Russell gives
somewhat less irregular results than are obtained with the
Riehle "Engineers' Standard" rigid clip. Although the results
given by the Russell clip in its present form are a trifle lower
than those given by the Riehle, it seems probable that these
lower results are due to defects in detail which may readily
be eliminated.
4th. By the application of the gimbal principle to cement
testing clips, higher, as well as more nearly uniform, results
may be obtained.
5th. In using the rigid form of clip, careless manipulation
in adjusting the briquet may result in serious error due to the
introduction of cross-strains, while with either the Single Gim-
bal or Russell clip slight deviations in adjustment are not im-
portant.
6th. With the form of briquet recommended by the commit-
tee of the American Society of Civil Engineers in 1885, the break-
ing stress may be somewhat increased, and the number of clip-
' Theae tests were described in greater detail and discussed by the
writer in "Municipal Engineering," Dec, 1896, Jan. and Feb., 1897.
146
CEMENT AND CONCRETE
breaks may be very materially decreased, by such a modifica-
tion of the clip as to allow grasping the briquet nearer the head.
215. Requirements for a Perfect Clip. — As a logical result
of these conclusions, the ideal clip should fulfill the following
requirements: —
1st. It should impart a true axial pull to the briquet with-
out subjecting it either to cross-strains or to compressive forces
ll ll II I lltTTl"
r 'A >i W 0
3//».
Fig. 9. — FORM OF ARTICULATED CLIP SUGGESTED FOR USE
sufficient to cause it to break at other than the smallest section.
2d. The bearing surfaces of the gripping points should not
be more than about one-fourth of an inch wide, since this is
sufficient to prevent crushing the briquet at these places, and
too wide a jaw will not usually bear uniformly over its whole
surface.
BREAKING THE BRIQUETS
147
3d. Its parts should have sufficient strength and stiffness,
so that they will not bend appreciably when in use.
4th. It should permit rapid operations, and
5th. It should be as light as consistent with the above
requirements.
216. Form Suggested. — Fig. 9 shows a style of clip which
closely conforms to the above specifications. The evener
form devised by Mr. Russell has been selected for modification.
The S. G. clip would more nearly meet some of the requirements,
and, so far as the principle is concerned, this form is. considered
quite the equal of the evener clip. But no method of applying
the gimbal principle has commended itself as affording such
rapid manipulation as does the evener motion, and since it is
thought that either form will obviate cross-strains in a plane
parallel to the face of the briquet, the evener form has been
adopted on account of convenience.
The defects in detail of the Russell clip which have already
been mentioned have been obviated in the present form. The
gripping points are made one-fourth of an inch wide, and a little
more material has been used between the gripping points and
the first pin to stiffen the clip. This form is designed for use
with the briquet shown in Fig. 5 (see § 179).
217. Rate of Applying the Tensile Stress. — Table 37
gives the results of several hundred experiments made by Mr.
TABLE 37
Relation of Apparent Tensile Strength to Rate of Applying Stress
Rate of Applying
Tensile Strength
Stress,
Obtained,
Pounds per Minute.
Pounds per Sq. Inch.
60
400
100
415
200
430
400
450
6,000
493
Henry Faija * to show the effect on tensile strength of varying
the rate of applying the stress.
A few of the results obtained from nearly 900 tests, made
'Cement for Users," by Mr. Henry Faija.
148
CEMENT AND CONCRETE
under the author's direction to illustrate this point, are given
in Table 38. Some of these results accord very well with those
given in Table 37, but the results in the latter table were doubt-
less obtained from neat Portland briquets only, while the ex-
periments given in Table 38 were made with briquets neat
and with two parts sand, and on natural as well as Portland
cement mortars.
TABLE 38
Relation of Apparent Tensile Strength to the Rate of Applying the
Stress
Cehent.
Propobtions.
Age of
Briquets.
TEXSILE STEENGTH, PODNDS FEB
Square Inch, fob Stress Applied at
Rate of Pounds peb Minute.
100
300
500
700
900
Portland
(<
((
Natural
((
Neat cement
Neat cement
1-2
Neat cement
Neat cement
1-2
7 and 14 days
3 months
3 months
7 days
3 months
3 months
453
445
150
309
255
485
590
467
169 .
351
299
521
617
487
186
363
327
520
622
607
378
329
528
640
510
202
390
354
218. It appears from all these results that the increase in
the breaking strength due to increasing the rate of applying
the stress is considerable in the case of low rates of speed, but
when a rate of 500 or 600 pounds per minute has been reached,
a further increase in rapidity does not make a material increase
in the apparent strength. Since certain variations in rate are
sure to occur, until some device is used to automatically regu-
late it, a rate should be adopted which would allow of slight
variations without materially changing the result of the test.
A rate of 600 pounds per minute would fulfill this requirement,
and, with certain machines at least, would be still more con-
venient than the rate of 400 pounds per minute which has here-
tofore been quite generally used.
An analysis of the experiments made to determine the de-
gree of uniformity obtained by using each of the given rates,
showed there was but Httle difference in this regard, but if
any choice could be made on this basis it seemed to lie with
the more rapid rate.
219. With the shot machines it is not difficult to approxi-
BREAKING THE BRIQUETS 149
mately regulate the rate at which the stress is applied. In
operating a machine in which a handwheel moves a weight
along the graduated beam, it must be remembered that the rate
at which the weight moves is the controlling factor, and not
the movement of the lower wheel, which simply serves to take
up lost motion, the stretch of the briquet under strain, and
the slipping of the briquet in the jaws of the clip. A mistaken
idea concerning this matter has sometimes led to the adoption
of a device to regulate the motion of this lower wheel. Until
one is accustomed to applying the stress at a given uniform
rate, he will find it an aid to hang near the machine a pendulum
of such a length that a certain number of vibrations correspond
to a complete revolution of the handwheel.
220. Treatment of the Results. — The number of briquets
which are made to test the strength of a given sample of cement
will depend on the accuracy which it is desired to attain. If
but two briquets are made, neither of the results may be re-
jected; however widely they may differ one from the other,
the mean of the two must be considered the result of the experi-
ment when nothing is known as to their comparative value.
But if several briquets are made from the same sample, and
they vary one from another, the final result is sometimes ob-
tained by rejecting certain of the observations. In some cases
if five or six specimens are made, the highest and the lowest
ones are omitted, while sometimes the two lowest are rejected,
and the mean of the three or four highest is taken.
221. While the absolute mean of all of the observations will
ordinarily be quite sufficient, and should usually be considered
the result of the test, yet where tests are very carefully made
to compare two samples, or two methods of manipulation, it
may be desired to reject certain observations that appear to
be abnormal. The beginner in cement testing, unfamiliar with
observations of this character, may not feel confidence in his
own judgment as to what observations may be rejected, and the
criteria sometimes used in more accurate work are entirely too
complicated for this purpose. To serve as a guide in such
cases, the writer would suggest the following simple method
which, though entirely arbitrary, is more justifiable than either
of the methods mentioned above. As the experimenter be-
comes more familiar with the work, he will doubtless prefer to
150
CEMENT AND CONCRETE
depend on his own judgment in the rejection of observations,
taking into account the general accuracy of the work.
First obtain the absolute mean and the difference between
this mean and each individual result; let us call this difference
the "error" for each result. Reject any observations whose
error is, say, ten per cent, of the absolute mean, and obtain the
mean of the remaining observations as the true result.
222. For example, suppose that we have broken ten bri-
quets obtaining the strengths given below, and wish to deter-
mine the result of the test. The absolute mean is found to be
213.9 pounds, or, the nearest whole number, 214 pounds.
TABLE 39
Rejection of Observations
Number
OF
Briquets.
Obsekykd
Strength.
Error.
Obskrved
Strenoth.
New
Error.
1
2
3
4
5
6
7
8
9
10
209
226
227
184
217
262
200
195
193
2.36
6
12
13
30
3
88
14
19
21
22
209
226
227
'217
260'
195
193
1
16
17
' 7'
'lb'
15
17
Sum . . .
2,139
177
1,467
83
Mean . .
213.9
17.7
209.6
11.9
The "errors" are given in the third column, and it is seen
that three of them are greater than ten per cent, of the mean.
Omitting the results having these large errors, we obtain a new
mean of 209.6 pounds, which is to be considered the result of
the test. An inspection of the first column of errors shows that
the mean of the errors is 17.7 pounds; if we divide this by the
mean of the tensile strengths, we obtain 17.7 -?- 213.9 = .0827.
Expressing this as a percentage, we may call 8.27 per cent,
the "average error." The same result is, of course, obtained
by dividing the sum of errors by the sum of the strengths.
Now if we consider column five, we see that the new average
error will be but 83 -^ 1467 = 5.66 per cent.
INTERPRETATION OF TESTS 151
223. In giving the results of a series of tests, it is a common
practice to state only the absolute mean, but it is of considerable
interest to know the variations that occurred in breaking in
order that one may judge of the reliability of the results, or,
in other words, to make a rough approximation as to the prob-
able error. For this purpose the highest and lowest result may
be given, but a much better index to reliabiUty would be tc
give the "average error" as explained above. However, in
reporting a large number of tests, the extra labor involved in
obtaining this "average error" is usually considered too great
to be attempted, and in such cases the absolute mean and the
highest and lowest results must serve the purpose.
224. Accuracy Obtainable. — When an operator has become
expert and is working under good conditions, he may expect
to obtain results within the following limits: The extreme varia-
tions between the results in a set of ten briquets (the difference
between the highest and lowest) not exceeding 20 per cent, of
the mean strength of the set, the maximum variation from the
mean not exceeding 12 per cent, of the mean, and the "aver-
age error," as explained above, not exceeding 8 per cent.
Art. 26. The Interpretation of Tensile Tests of
Cohesion
225. One of the problems presented in the inspection of
cement is to foretell the ultimate relative strengths of two
samples from the results of short time tests. Formulas have
been presented purporting to solve this problem, such formulas
being based on the assumption that the strength gained at the
end of months or years is a function of that developed in a few
days. In fact, the raison d'etre of tensile or other short-time
strength tests for the acceptance of cement, rests, in a sense,
upon this same assumption.
The value of strength tests as one of the guides in determin-
ing in a short time the probable quaUty of a cement is unques-
tioned. One is apt, however, to seek too close an agreement
between the results of such tests and the actual quaUty of the
cement. It would be easy to select examples illustrating the
harmony between short and long time tests; but it will be of
greater value to show, rather, some of the many exceptions to
such a rule, and thereby emphasize the fact that it is only by
152
CEMENT AND CONCRETE
a close analysis of all of the information obtainable concerning
a sample, and a general knowledge of the behavior of the dif-
ferent grades of cement, that one may hope to arrive at a tol-
erably accurate opinion.
226. Comparative Tests of Portland Cements. — In Table
40 are given the results of tests on four brands of Portland
cement at seven days, twenty-eight days and two years. From
the tests at two years it appears that T and U are the best
cements, V is nearly as good, but W gives a much lower result.
Turning now to the seven and twenty-eight day tests of bri-
quets maintained at the ordinary temperature, it is seen that
W gave in every case higher results than T, and nearly as high
as U or V. Among the short time tests it is only the results
of briquets maintained at 80° C. that indicate the inferiority
of Brand W.
TABLE 40
Interpretation of Short Time Tests of Portland Cement, Several
Brands
Tensile Strength. Pounds I
Pabts
Sand to 1
Cement
BY
Tempera-
tube Water
OF
Immersion.
Age of
Briquets.
per Square Inch.
Brand.
Weight.
•
T
U
V
w
2
Hot, 80° C.
7 days
339
278
284
222
3
ti 11
(1
221
191
180
134
3
" 60° C.
u
144
142
169
144
0
Ordinary
"
426
510
487
565
1
"
327
425
400
396
2
11
172
275
256
236
3
"
73
150
160
150
1
28 days
526
577
567
556
2
11
312
394
387
332
3
K
142
241
223
247
1
2 years
719
753
763
654
2
11
564
653
513
407
3
(1
386
373
340
287
227. Comparative Tests of Natural Cements. — From the
nature of natural cements a much greater variation in strength
among different brands, and even among different samples of
the same brand, is to be expected. With Portland cements
made in accordance with ordinary methods, the variations in
strength among ten or twenty brands will usually be compara-
tively small. One of them may possibly prove unsound, and
INTERPRETATION OF TESTS
153
one or two others may give inferior strength, but the variations
in strength among three-fourths of the samples will not gener-
ally exceed 20 per cent. With the same number of brands of
natural cements, variations of 50 to 200 per cent, may be
expected.
TABLE 41
Interpretation of Short Time Tests of Natural Cement, Several
Brands
Tensile. Strength, Pounds
1
PER Square Inch.
1
Pasts
Sand to 1
Cement.
Tempera-
TUEE Water
OF
Immersion.
Age of
Briquets.
1
Brand.
Jn
Hn
Bn
Mn
Nn
Kn
2
Hot, 50° C.
7 days
152
192
84
133
160
277
2
Hot, 60° C.
a
170
270
79
154
164
254
2
Hot, 80° C.
u
58
136
128
179
166 .
221
0
Ordinary
n
174
203
130
189
210
189
1
(1
125
198
103
164
169
164
0
28 days
208
344
293
203
316
289
1
li
237
342
247
247
252
385
2
K
132
223
148
158
184
217
3
•'
64
113
85
93
104
101
1
2 years
177
271
358
631
665
582
2
(1
106
157
195
515
550
661
3
u
99
130
117
340
328
372
In Table 41 six brands of natural cement are compared by
tests at seven days, twenty-eight days and two years. These
six brands have been arranged in the table according to their
value as shown by the two year tests, and it is seen that the
first three, Jn, Hn and Bn, are especially poor, while the last
three, Mn, Nn and Kn, are exceptionally good. In the short
time tests of briquets maintained at ordinary temperature, Jn
and Bn gave low results and Nn and Kn gave fairly high results,
in harmony with the long time tests; but Hn, which proved to
be one of the poorest samples, gave in every case the highest,
or next to the highest, result in seven and twenty-eight day
cold tests. In this table we find again that the results of the
briquets maintained at 80° C. for seven days gave, in a general
way, the best indication of the relative values of the six brands.
228. Several Samples of One Brand. — To show that short
time tests do not always indicate the relative values of several
samples of cement, even when all of the samples are of the
154
CEMENT AND CONCRETE
same brand, Tables 42 and 43 are given. All of the results in
these tables are from samples of the one brand of natural ce-
ment.
TABLE 42
Comparison of Short and Long Time Tests of Samples of One
Brand of Natural Cement
s
M
SI
Sand.
Age.
T DO
Kind.
Parts to
1 Cement.
PEB Squabe Inch.
A
0
0
28 days
6-7 months
Number
of Samples
Tested.
3
7
2
3
5
• •
84
121
123
186
177
241
220
301
297
381
B
Std.
1
1
7 days
6 months
Number
Samples.
17
20
17
16
62
462
74
468
86
442
146
367
C
P.P.
1
1 and 2
2
7 days
6 months '
7 days «
Number
Samples.
50
50
19
19
49
473
273
54
426
249
73
381
265
128
321
283
D
P.P.
0
2
2
7 days
1 year
7 days ^
Number
Samples.
13
48
38
18
66
473
257
80
422
234
95
377
277
147
325
215
, ,
E
0
2
7 days
6 months
Number
Samples.
12
21
18
9
74
535
83
477
120
424
167
373
F
( Cr.Qtz! )
t 20 to 40)
0
2
28 days
( 6 months )
I and 1 year )
Number
Samples.
287
170
41
• •
135
565
191
454
235
367
Mean one-to-one and one-to-two mortars.
Briquets immersed six days in water maintained at 60" C.
INTERPRETATION OF TESTS ' 155
In Table 42 the results are selected from a large number of
tests of this brand, and are arranged in groups according to the
strength shown at a certain age. For instance, in Series A
the results of twenty samples are given, arranged according to
the strength at twenty-eight days. Three of the samples gave
less than 100 pounds per square inch, neat, at twenty-eight
days; the same three samples gave a mean strength of 121
pounds per square inch, neat, six to seven months. Seven
samples, the strength of which fell between 100 and 150 pounds
at twenty-eight days, gave a mean strength of 186 pounds at
six to seven months. The results of this series show the
harmony between short and long time tests when it is a question
of comparing neat cement mortars.
In Series D of this table the samples are arranged in order
according to the strength developed by one-to-two mortars
one year old. Thirteen samples had a strength at this age of
between 450 and 500 pounds, average 473 pounds. The same
samples gave but 66 pounds, neat, seven days. Forty-eight
samples, giving between 400 and 450 pounds, average 422
pounds, gave but 80 pounds, neat, seven days, while eighteen
samples that developed only 300 to 350 pounds mean, 325
pounds at one year, showed a mean strength of 147 pounds, neat,
seven days.
A little study of this table will show that the samples which
were comparatively weak in seven and twenty-eight day tests,
either neat or with sand, gave the best results in the long time
tests of sand mortars. Series A shows that the neat tests at
seven days and at six months are consistent, but in all cases
where sand mortars are tested at six months to one year, the
highest results are given by the samples showing the lowest
strength in the short time tests in cool water. It is very sel-
dom that this conclusion has not been indicated by the author's
tests of this brand. It is not invariably true, however, for
some samples which were selected as being defective in burn,
gave low results both in short and long time tests. The con-
clusion stated above must therefore be understood to have
limits even for this brand, and may not apply at all to many
brands.
As to the results of short time tests of briquets stored in hot
water, Series C and D indicate that such results are more nearly
156
CEMENT AND CONCRETE
consistent with the long time tests, yet it is evident that even
with hot tests one could not readily and accurately differen-
tiate the best from the mediocre samples.
TABLE 43
Natural Cement: Rate of Increase in Strength, Hardening in Water
and Dry Air
Sand, Parts
TO One
Age of
BllIQUKTS
Tensile Strength per Sq. In., ok Samples.
Hardened in Water.
Hardened in Air of
Room.
Cement.
When Broken.
84
U'
0'
84
U'
0'
7 days.
74
63
103
107
68
187
28 days.
228
189
228
188
95
256
3 mos.
416
346
331
158
100
248
6 mos.
506
381
307
425
161
359
2 years.
446
383
209
151
147
403
3
28 days.
99
97
64
112
61
180
3
3 mos.
244
241
129
153
81
194
3
6 mos.
255
232
162
92
69
173
3
1 year.
274
264
186
229
70
144
3
2 years.
258
268
167
274
152
228
Sample 84 U' O'
Fineness : Per cent, passing Sieve No. 120, Holes
.0046 inch square 80.5 87.8 89.7
TimeSetting— to bear^y^lb. Wire, min. . . . 54 23 97
Specific Gravity 3.012 2.950 3.145
U', underburned, O', overburned. All samples same brand, Gn.
229. The results in Table 43 will serve to illustrate the same
point by showing the very different rates of Increase in strength
of three samples when the briquets are stored in water and in
dry air. One of these samples, 84, was taken at random from a
shipment, while U' and O' were supposed to be defective in
burn. Of the water-hardened specimens. No. 84 gained in
strength up to six months or one year and then suffered only
a slight falling off. The underburned sample showed a con-
tinuous gain, but the overburned cement showed a marked
decrease in strength after six months or one year. The air-
hardened specimens were very irregular in strength, but the
underburned sample gave very low results throughout.
Table 44 gives similar results obtained with several samples,
the briquets being hardened in water as usual. 16 R is a fair
INTERPRETATION OF TESTS
157
sample of the best cement of this brand, and its rate of increase
in strength with one to three parts sand is shown. Samples
M and L were tested together, as were CC and DD. M and
CC are of the class giving comparatively high results at seven
days, while L and DD give high results at seven days, but
develop only a moderate ultimate strength.
TABLE 44
Natural Cement: Difference in Rates of Increase in Strength of
Several Samples of the Same Brand
K
US
Cement.
Saxd.
Texsile Strength, Pounds per Sq. Jn.
AT AUE OF
•6
Kind.
i
CO
03
a
09
o
S
i
S
i
«
«
OS
t-
?{
<N
CO
<s
"
N
m
1
Gn
16 R
Crushed Qtz. 20-30
1
94
142
334
399
430
500
445
2
It
"
2
59
101
289
341
335
386
354
3
it
n
3
73
204
243
252
268
262
248
4
M
.
0
118
199
256
248
300
5
6
7
L
M
L
Point aux Pins
11
0
2
2
40
63
30
88
155
150
•
148
216
296
146
241
415
167
252
369
8
CC
i(
1
123
232
276
269
317
9
DD
((
1
77
218
327
337
474
10
CC
"
2
185
268
242
279
279
11
DD
((
2
189
326
303
373
359
230. Conclusions. — From the above tables one should not
draw the conclusion that all strength tests are valueless be-
cause likely to be misleading. Some lessons, however, seem to
be plain; conclusions drawn from the results of short time tests
of strength alone are likely to be far from infallible. This is
especially true of natural cements. The correctness of one's
conclusions concerning the value of a sample is likely to de-
pend very much upon his knowledge of the behavior of that
particular brand, and the beginner in cement testing should
not have too great confidence in his early conclusions. Samples
under inspection should be tested in comparison with other
samples of known quality, and the results of the strength tests
studied in connection with all the information obtainable from
the other tests of quality already outlined.
CHAPTER X
THE RECEPTION OF CEMENT AND RECORDS OF TESTS
Art. 27. Storing and Sampling
231. Storage. — The storage houses provided for the ce-
ment should be such as will effectually preserve it from damp-
ness, the floor being dry and strongly built. A circulation of
air under the floor will insure dryness.
In building houses for storage, due regard should be given
to the ease of getting the cement in and out, and facilities pro-
vided for the use of block and tackle in tiering.
When the cement is received, whether in sacks or barrels, it
should, if possible, be so tiered in the warehouse that any pack-
age is accessible for sampling. In the case of barrels this may
readily be attained by tiering in double rows, the barrels lying
on the side. It has been found that ordinary cement barrels
will withstand the pressure if tiered five high with a "binder"
row on top; and when so piled, a warehouse 32 feet wide and
100 feet long will readily hold 2,200 barrels, an allowance of
about one hundred fifty square feet of floor space for one hun-
dred barrels.
232. Where storage space is limited, the barrels may be
numbered and sampled before they are placed in the warehouse,
and they may then be piled solid, but this should be avoided
if practicable. Sacks cannot be quite so neatly stored, and
since a smaller quantity is contained in a sack, they may be
tiered so that every third or fourth sack is accessible. It is
desirable where work is executed with the greatest care that
every package be numbered for future identification, but this
may sometimes prove impracticable, especially when the ce-
ment is in sacks, and in such cases the sampled packages only
may receive numbers.
233. Percentage of Barrels to Sample. — The amount of ce-
ment which shall be accepted on the test of a single sample
must be determined by each user of cement according to his
158
STORING AND SAMPLING 159
knowledge as to the uniformity and reliability of the brand in
use, and according to the character of the work in which the
cement is to be used. In a few isolated cases every barrel is
tested, while sometimes several tons of cement are accepted on
a single test. As the improvements in methods have decreased
the work involved in ma,king the simpler tests, the tendency
has been to test a larger percentage of the packages.*
The report of the committee of the Amer. Hoc. C. E. in
1885, contains the following concerning sampling: "There is no
uniformity of practice among engineers as to the sampling
of the cement to be tested, some testing every tenth barrel,
others every fifth, and others still every barrel delivered. Usu-
ally, where cement has a good reputation, and is used in large
masses, such as concrete in heavy foundations, or in the back-
ing or hearting of thick walls, the testing of every fifth barrel
seems to be sufficient; but in very important work, where the
strength of each barrel may in great measure determine the
strength of that portion of the work where it is used, or in
the thin walls of sewers, etc., every barrel should be tested,
one briquet being made from it."
234. Taking the Sample. — The sample should be taken in
such a manner as to fairly represent the package, and for this
purpose a "sugar trier" may be used, by which is obtained a
core of cement about one inch in diameter and eighteen inches
long. As any tool used for boring cement barrels soon becomes
dull, and as a sugar trier is somewhat difficult' to sharpen, the
author prefers to use an ordinary bit and brace to penetrate
the barrel head, and then extract the sample with a "trier,"
or a long, slender scoop of similar form provided with a handle.
For storing the sample until it is tested, it has been found
convenient to use covered tin cans holding about one pint,
the cover of the can being labeled with the number of the pack-
age from which the sample is taken.
* In a paper read before the Institution of Civil Engineers in 1865-66, Mr.
John Grant states that "after using, during the last six years, more than
70,000 tons of Portland cement, which has been submitted to about 15,000
tests, it can be confidently asserted that none of an inferior or dangerous
character has been employed in any part of the work in question. " (The
Metropolitan Main Drainage, London.) This is an average of one test to
twenty-five barrels.
160 CEMENT AND CONCRETE
Art. 28. Records of Tests
235. Value of Records. — In conducting work in which the
use of cement enters as a prominent factor, it is not only neces-
sary to know that the cement used is of a good quality, but also
to be able to show at any future time what tests were made to
establish its value. This fact, as well as the convenience of
the work, demands that a record shall be kept of all the tests
made. These records may be more or less elaborate, according
to the kind and amount of the work in hand, but in any case,
enough detail should be given to make them intelligible to other
engineers.
236. Marking Specimens. — There is sometimes a tempta-
tion, in making tensile specimens, to stamp upon them many
details of the test, and for this purpose an elaborate cipher
system has sometimes been used. But this method is to be
strongly deprecated. Each briquet should receive its proper
consecutive number, as mentioned in §189, and the details
concerning it should be placed in the record book.
237. Records Kept at St. Marys Falls Canal.— In the
tests of cement at St. Marys Falls Canal, during the construc-
tion of the Poe Lock, a system of records was used that gave
entire satisfaction. At the time the largest amount of cement
was being used three molders were employed, each making
fifty briquets per day of eight hours. Over one hundred thou-
sand briquets were made in five and one-half years. Although
the system of records used at this point may be more elaborate
than is often necessary, yet the system will be described, and
certain modifications will be suggested for places requiring less
complete records.
238. Barrel Records. — The barrels receive consecutive num-
bers after they are tiered up in the warehouse. The "receiv-
ing book" is a simple transit book in which are entered the
date of the receipt of each cargo, the name of the boat (or the
car number, if shipped by rail), the brand of cement, the num-
ber of barrels, the first and last barrel number of the cargo and
the warehouse in which the cement is placed. The next book
to be used is the "barrel book," in which the numbers of the
barrels are entered consecutively in a column at the left, each
barrel being given one line. This book is also of transit size,
but might well be larger. The headings are given below.
RECORDS OF TESTS
161
SAMPLE PAGE OF "BARREL RECORD"
No.
Bbl.
Samplkd.
Defects.
Ac-
cepted.
Re-
jected.
ISStTED.
IlEMAKKS.
88251
2
3
4
5
6
7
8
9
88260
1
2
3
4
5
M. D.
5 16
M.D.
6 5
S7 = 4Si
M. D.
6 13
M. D.
July 25
July 25
July 25
Sept. 27
July 25
July 25
July 25
July 25
July 25
July 25
July 25
July 25
Sept. 28
July 25
July 25
6-7 = 65f
S7 = io2i
( Removei by
I Contractor
' S7'= io5i
( Removed by
\ Contractor
5 19
6 6
6 5
is7'=3'2ii)
\ S7= 35i S
6 13
6 12
5 19
5 26
5 19
5 26
. . .
5 19
6 6
6 5
(S7^ 40i \
\ S7= 324 S
6 13
6 12
When the barrels are sampled and briquets made, the date
sampled is entered in the second column of the barrel record
book. The other columns will be explained later.
239. Molders' Records. — Separate sheets of paper ruled and
headed as shown on page 148 are used by the molders to record
the details concerning the making of briquets.
Separate sheets properly ruled and headed are also given to
the assistants who test time of setting and fineness. These
record sheets, when filled in by the assistants, are copied the
following day by the bookkeeper, into the permanent "record
book." At the end of the month these separate sheets, con-
taining original records of work done, are folded and filed for
future reference.
240. Briquet Record. — The briquets are made in sets of
ten for convenience. Each set is given a page in the "record
book," as is indicated on page 149 where the form for this book
is given. The size of page is 9 by 12 inches. Paper having the
same ruling and column headings is convenient for reporting
tests to the chief engineer.
241. Summary Book. — The data for each set of briquets
are copied from the record book, in a condensed form, into the
"summary book," one line of the latter containing a page of
the former. In the summary book each brand is given a few
162
CEMENT AND CONCRETE
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RECORDS OF TESTS
163
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164
CEMENT AND CONCRETE
CO
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•SKOiiVOMiaadS
JO 8XN3H3Hiat>
<ac><2i<2i'«s»?0^^
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RECORDS OF TESTS
165
pages by itself, so that this book corresponds to a ledger in form.
By this means a large number of tests on the same brand may
be looked over at once. The summary book might be omitted
where a smaller number of tests are to be made, or it might
be slightly modified and take the place of the record book. A
sample page is given below.
242. Records of Fineness, Time of Setting and Soundness. —
Although provision is made in the record book for recording
time of setting and fineness, it has been found that where a
large amount of cement is being tested it is more convenient
to have separate books for each test. Especially is this true
as it has been judged necessary to test but a very small per-
centage of the barrels for fineness, while a larger percentage of
the barrels are tested for time of setting and soundness. The
"fineness book" is as simple as possible and need not be illus-
trated. A sample page of the "pat book" is given below.
Sample Page of "Pat Book" or Record of Time of Setting and
Soundness
Lagerdorfer Portland Cement Pats, Two from Every Third Barrel
No.
Bbl.
CD
» .
^^
« O
a
a.
CO
4
aw
om
o w"
t-l
1^
Treatment
OF Pats.
Examined.
Removed.
Re-
MABKS.
Stmr.
Tank.
Date.
Condi-
tion.
Date.
Condi-
tion.
1j
to
Z74
7
80
3
6
9
92
95
98
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
9:23
9:'28
9:32
9:34
9:41
9:50
9:5S
9:57
10:28
10:32
117
37
15
143
15
'l2
123
97
103
337
232
268
383
259
250
247
363
367
365
Is
0 .-
&|
1
"1
-S
1
Mo.D.
8 1
V 1
V 1
8 1
V 1
V 1
V 1
8' 1
V 1
8' 1
O.K.
O.K.
O.K.
O.K.
O.K.
O.K.
O.K.
O.K.
O.K.
O.K.
Mo.D.
7 15
8 17
7 15
8 17
7 15
8 17
7 15
8 17
7 15
8 17
7 15
8 17
7 15
8 17
7 15
8 17
7 15
8 17
7 15
8 17
O.K.
((
((
((
((
C Surface
< cracked
K& scaled.
O.K.
((
((
((
((
((
i(
u
((
((
(1
Water
24%.
166
CEMENT AND CONCRETE
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RECORDS OF TESTS 167
243. The Diary. — When the bookkeeper has copied the
data contained on the record blanks into the record book and
summary book, he turns to the proper page in the diary and
records the briquets to be broken. Thus, if briquets made
May 17th are to be broken at three months, he enters the num-
bers of these briquets and the tank in which they have been
placed under the date Aug. 17th. This leaves no chance of
allowing briquets to go beyond the proper time of breaking.
244. Acceptance or Rejection. — If all of the tests on a given
sample are satisfactory, the date of acceptance is placed in the
proper column of the barrel book. It only remains then to
mark the barrels "O. K.," and issue them when needed, placing
the date of issue in the column indicated. If, however, some
of the tests have given unsatisfactory results, the failure is
noted in the "defects" column of the barrel book, and the
barrel is resampled to determine whether the failure was due to
faulty manipulation. If finally rejected, the barrel is promi-
nently marked to prevent its being issued for use.
It is seen from the above that the history of each barrel is
given in the barrel book, and the record of any brand is given
in a condensed form in the summary book.
245. Special Tests. — When special tests are made to inves-
tigate the effects of variations in manipulation, or for any
other special purpose, such as to test the value of certain kinds
of sand, it becomes convenient to have still another form which
may be called a "series book." In this the results are so ar-
ranged that they may be studied for conclusions, and tables
for reports may be copied directly from it. A sample form is
given on preceding page. Should extra rulings be needed,
they may be placed at the right in the "remarks" column.
PART III
PREPAKATION AND PROPERTIES OF
MORTAR AND CONCRETE
CHAPTER XI
SAND FOR MORTAR
246. Mortar. — When cement is mixed with sand and water,
the resulting paste is called mortar. The term "neat cement
mortar" is sometimes used to designate a cement paste with-
out sand, but when the term mortar is not qualified, it refers
to the mixture containing sand. The primary function of mor-
tar is to bind together pieces of stone of greater or less size,
though it is sometimes used alone to prevent the percolation of
water, to make a smooth exterior finish, or in places too confined
to permit of placing concrete.
There are comparatively few cases in which it is judicious
to use cement without the addition of sand, fbr such an ad-
mixture not only cheapens the mortar, but actually improves
it for nearly all purposes. The quality of sand used is only
second in importance to the quality of the cement. Indeed, if
one does not know how to select either a good cement or a good
sand, he is in greater danger of going amiss in the selection of
the latter than the former; for the cement has been placed upon
the market by a manufacturer who has a reputation to estab-
lish or maintain.
Art. 29. Character of the Sand.
247. Various kinds of rock are capable of producing sand of
good quality. The natural sands are usually siliceous in char-
acter, but calcareous sands are also met with and may give
excellent results in mortar. Good artificial sand may be made
from almost any kind of rock that is not liable to chemical
168
CHARACTER OF SAND
169
decay, even though it be only moderately hard. One of the
most essential features of a good sand is that the grains should
be perfectly sound. Evidences that chemical decay is going
on in the grains would indicate that the sand is of very inferior
quality.
248. SHAPE AND HARDNESS OF THE GRAINS.— It is gener-
ally believed that the grains of sand should be angular in order
to give the best results; this is probably true, although in test-
ing three varieties of calcareous sand, M. Paul Alexandre ^ ob-
tained results which seemed to indicate that if rounded grains
are disadvantageous, the other properties of the sand may
readily counterbalance this disadvantage.
M. Alexandre used three sands which were reduced to the
same fineness by sifting into different sizes and then remixing
them in fixed proportions (equal parts of five sizes). The three
sands were, 1st, white marble, very hard with sharp corners;
2d, moderately hard limestone; and 3d, chalk, very soft with
rounded grains. The proportions used were 400 kg. of cement
to one cubic meter of sand, the amount of water varying from
twenty-five to thirty per cent, of the sand, according to the
amount required to produce plasticity. The tensile strength of
the mortars, in pounds per square inch, is given in Table 45.
TABLE 45
Results Obtained -with Three Varieties of Calcareous Sand
Cha&actek of Sand.
Tensile Stkexgth, Pounds
Pek Sqdare Inch at
7 da.
28 da.
6 mo.
IJyrs.
1. Marble
2. Limestone . , . ...
3. Chalk
45
72
86
107
148
129
171
222
205
220
266
252
As these sands varied in the structure and hardness as well
as in the shape of the grains, it cannot be concluded that rounded
grains are as good as sharp and angular ones for mortar-making.
There is little question that if two samples of pure quartz sand,
' ''Recherches Experimentales sur Les Mortiers Hydrauliques.^^
170
CEMENT AND CONCRETE
differing in sharpness but alike in all other respects, including
the percentage of voids, were tested side by side, the rounded
grains would be found inferior. (See also § 253.)
M. Alexandre also made tests on sands differing both in
chemical and physical characteristics, but having the same fine-
ness, namely, twenty per cent, each of five sizes of grain. Some
of the results are given in Table 46.
TABLE 46
Results Obtained vrith Various Sands
Sand.
Water
Per
Cent, of
Volume
OF Saxd.
Tensile Strength, in Lbs. per
Sq. In., of Mortars Contain-
ing 400 Kg. of Cement to 1 Cu.
Meter Sand, at Ages of
7 da.
lyr.
Syrs.
Sea Sand
21
28-
21
20
20
28
69
78-
65
63
TO-
SS
165
198-
168
174
178
99
245
267-
201
215
244
132
Calcareous (Kenville stone) . . .
Granitic
Siliceous (cliff quartz)
Siliceous (Cherbourg Quartzites) .
Coke
249. Siliceous vs. Calcareous Sands. — The above tests
would seem to show that sand to be used in mortar need not be
siliceous. In experimenting on different varieties of sand, both
natural and artificial, the author has obtained results that
point to a similar conclusion. Some of these tests are given in
Tables 47 to 50.
Table 47 gives the results obtained with four varieties of
siliceous sand. The first was an artificial sand made by crush-
ing sandstone, the second and third were natural sands con-
taining a large percentage of quartz grains, and the fourth
appeared to be almost pure quartz. Only the fine particles of
the sands were used in the tests given in this table. The dif-
ferences in strength at the end of two years are not great, but
the two natural sands appear to give somewhat lower results.
In Table 48 the two natural sands were again compared,
but this time in connection with a calcareous sand formed by
crushing limestone. The latter gave the best results. Only
the finer grains were used in these tests.
250. Tables 49 and 50 are more valuable in this connection,
CHARACTER OF SAND
171
TABLE 47
Values of Different Varieties of Fine Siliceous Sand for Use in
Portland Cement Mortar
Two Pabts Sand to One Cement by Wbioht
N
y
Sand.
Fineness.
Watek,
Per
Cent.
Tensile
Stkength, Lbs.
PEK Sq. In. at
6 Mo.
2Yr.
a
b
c
d
e
1
2
3
4
5
( Screenings from (
} crushing Pots- <
( dam sandstone (
Bank sand, siliceous
River sand, siliceous
Clean quartz . .
Pass 40 sieve .
Pass 40 sieve,
retained on 100
Pass 40 sieve .
Pass 40 sieve .
Pass 40 sieve .
18.5
17.5
13.3
12.1
13.3
388
478-
433
382
398
470
539"
445
437
506
Note. — Holes in No. 40 sieve 0.015 inch square, holes in No. 100 sieve
about 0.0065 inch square.
TABLE 48
Different Varieties of Fine Sand for Portland Cement Mortar
Tensile Strength, Pounds
per Square Inch.
Pkb Cent.
Wateb.
Sand.
Fineness.
I Part Sand to 1
2 Parts Sand to
Cement by Wt.
Cement by Wt.
Itol
1 to 2
6 mo.
13
mo.
3yr.
6 mo.
18
mo.
3yr.
a
b
c
d
e
/
9
A
i
J
1
River aand, sili-
ceous . . .
Pass 40 sieve
14.0
12.4
715
725
776
491
575
581
2
Bank sand, sili-
ceous . . .
Pass 40 sieve
14.5
12.6
664-
699
759
442
502
524
3
Calcareous sand
from crushing
limestone . .
Pass 40 sieve
18.2
17.7
721
770
788
531
632
680
4
Calcareous sand
from crushing
limestone . .
Pass 40, re-
tained on 100
17.5
17.0
753-
783-
844-
597-
659-
t27
since the coarser particles of the sand were used with the fine.
The sand was separated into four sizes by sifting, and then
remixed in equal proportions. Table 49 gives the results ob-
172
CEMENT AND CONCRETE
tained with natural cement, and Table 50 refers to Portland.
The superiority of the screenings is very clearly shown, the
limestone giving especially good results. Indeed, the strength
obtained with three parts limestone screenings to one part of
either Portland or natural cement is remarkably high. The
mortar made from such sand is peculiarly plastic when fresh,
and soon gains a high strength which it appears to maintain.
TABLE 49
Values of Different Varieties of Sand for Natural Cement Mortar
fi
^
Saxd.
H
^3
Tensile Stbengtu, Lbs.
PER Sq. In., 3 Parts Saxd
TO 1 Cement by Wt.
28 Da.
6Mo8.
lYr.
2 Yr8.
a
b
c
d
e
/
9
1
2
3
4
5
Clean crushed quartz . . .
River sand, siliceous ^. . .
Limestone screenings \ . .
Potsdam sandstone screenings
Clean crushed quartz . . .
Mx.
Mx.
Mx.
Mx.
20-30
15.4
13.3
16.7
18.2
12.5
117*^
93*3^
143N
113-
118 V
344^^
2971
467^
316^>
330^
356 'i
339:
526 N
416^
342^
332*^
308^
601\
462v
324o
* 13.6 per cent, water, trifle dry.
Note. — Fineness Mx. means 25 per cent, each of 20-30, 30-40, 40-50
and 50-80.
Expression 20-30 means passing No, 20 sieve and retained on
No. 30 sieve.
TABLE 50
Values of Different Varieties of Sand for Portland Cement Mortar
%>
^
Sand.
Tensile Strength, Lbs.
PER Sq. In., 3 Parts Sand
TO 1 Cement by Wt.
28 Da.
6Mo8.
ITr.
2Yr8.
a
b
c
d
e
/
g
1
2
3
4
5
-J
Clean crushed quartz ^. . .
River sand, siliceous '" . . .
Limestone sc^eening8^ . . .
Sandstone screenings •.( . .
Clean crushed quartz,.. . .
Mx.
Mx.
Mx.
Mx.
20-30
12.5
11.1
12.51
12.51
11.1
265'
206'
407 ^
321v
259 i
327
284
574v
438
344-
359'
329
667
495
369-
335
324
665' V
4923 .V
335 ^
' Trifle dry, plastic. ' 13.3 per cent, water. ' 14.3 per cent, water.
Note. — Fineness Mx. means 25 per cent, each of 20-30, 80-40, 40-50
and 50-80.
FINENESS OF SAND 173
251. Slag Sand. — To turn to good account some of the
immense (luantities of blast furnace slag produced yearly, the
use of granulated slag in place of ordinary sand has been ad-
vocated. In a paper read before the Engineers' Society of
Western Pennsylvania, in March, 1904, Mr. Joseph A. Shinn
described some experiments he had made, in which it was shown
that "slag sand," with Portland cement, natural cement, or
common lime, gave a higher strength than the sample of river
sand used in the comparison.
The "slag sand" is produced by projecting two fiat jets of
water into the stream of molten slag, the resulting sand being
heavier, finer and more nearly uniform in size of grain than the
ordinary slag granulate.
252. Sand for Use in Sea Water. — It has been said that
granitic sands when used in sea water do not give good results
on account of the felspar of the granite being attacked by the
cement when the concrete is impregnated with sea water. M.
Paul Alexandre would proscribe the use of argillaceous sands
in sea water, but he found that sands containing calcareous
marl gave excellent results in the sea, and others have stated
that the mixture of crushed limestone with concrete has been
known to hinder the action of sea water upon it. Since porous
and permeable mortars are most liable to disintegration by
sea water, it is evident that it is especially desirable to employ
a sand in which the proportion of voids is small.
Art. 30. Fineness of Sand
253. The size and shape of the grains are important ele-
ments in the quality of sand. Considering grains of the same
shape but differing in size, the larger grain will have a smaller f
surface area in proportion to the volume than the smaller grain,
since the volume varies approximately as the cube of one di-
mension while the surface varies as the square. Since, in order
to obtain the best results in mortar, each grain of sand must be
coated with cement, it follows that, other things being equal,
the coarser grained sands will give the best results, because
they will be more thoroughly coated; this will be especially true
when the amount of sand in the mortar is relatively large.
Following the same reasoning given above as to the relative
volume and superficial area of sand grains, it would appear
174
CEMENT AND CONCRETE
that spherical grains would be better than cubical or angular
ones (see § 248). This, however, is not thought to be the case,
for the better bond obtained with angular grains seems to coun-
terbalance the advantage which the small superficial area would
appear to give to the spherical grains. For this reason a len-
ticular shaped grain, while having a very large area relative to
its volume, will give excellent results in mortar if otherwise
suited to the purpose.
It is usually desirable to have all of the voids in the sand
filled by the cement paste, as this renders the mortar less por-
ous, and makes it more certain that all the grains are coated
with cement. On this account a mixture of fine and coarse
particles is excellent.
TABLE 51
Effect on Tensile Strength of Varying Fineness of Limestone *
Screenings Used vrith Portland Cement
Age
Tensile Strength, Pounds per Squabk Inch
Fineness of Screenings.
Bbiqcets when
Bboken.
10-20.
20-30.
30-40.
40-50.
40-80.
Pass 50.
6 months . .
718
657.
633
516
403
2 years . . .
812
754
656
516
488
4 years . . .
845
782
714
571
516
Significance of Fineness
Designation.
Sieve Number.
Approximate
Mean Size of
Grain.
Passing.
Retained on.
10-20
20-80
30-40
40-60
40-80
Pass 50
10
20
30
40
40
60
20
30
40
50
80
Inch.
.067
.028
.020
.015
.012
.008
Notes. — Three parts screenings to one cement by weight.
All briquets made by one molder and immersed in one tank.
Variations in consistency were slight, the largest percentage of
water being used for the finest particles.
FINENESS OF SAND
175
254. TESTS ON EFFECT OF FINENESS OF SAWD. — Many of
the experiments made to show the effect of the fineness of sand
on the strength of the mortar are defective, because the sand
used varies in the shape of the grains and in chemical charac-
teristics as well as in fineness. The experiments given in Table
51 were made with screenings obtained in crushing limestone,
and thus all causes of variation aside from the fineness of the
sand were absent, except the differences in consistency of the
mortar, the uniformity in consistency depending on the judg-
ment of the operator. The results show quite clearly the su-
periority of the coarser sand.
255. The Relative Effect of Fine Sand on Portland and Nat-
ural Cement. — The tests in Table 52 were made to determine
TABLi: 52
Coarse and Fine Sand, — Relative Effects -with Portland and
Natural Cement
Age OF
Briquets
when
Broken.
■< .
o
Tensile
Strength,
Pounds per
Sq. In. when
Sand is
Percentage
Strength,
Fine
TO Coarse.
a
1
* oS
o
tensile
Strength,
Pounds per
Sq. In. when
Sand IS
H . .
■< H 5
HOS3
>5 >5 >? ■«!
«S g
20-30
40-80
20-30
40-«)
28 days . . |
6 months . . |
2 years . .
Bn
In
Bn
In
Bn
In
197
89
216
364
256
450
145
57
188
267
260
419
74
64
87
73
98
93
A
U
A
U
A
U
406
352
620
499
646
567
337
276
446
415
461
496
83
78
86
83
83
89
Notes. — Sand, limestone screenings ; three parts to one cement by
weight.
20-30 means sand passing sieve with 20 meshes per linear
inch, and retained on sieve with 30 meshes per linear
inch.
Columns 5 and 9 show percentage that strength with finer
sand is of the strength with coarser sand.
the relative effects of fine sand on Portland and natural cements.
Limestone screenings of two sizes of grain were used in con-
nection with two brands of each kind of cement. At twenty-
eight days the natural cement shows the decrease in strength
due to the use of fine sand more than Portland cement does.
176 CEMENT AND CONCRETE
At six months the fine sand seems to have about the same
effect on Portland and natural, but the two-year results in-
dicate that the ultimate effect is less on the natural cement
than on the Portland; the mean ratio of the strength obtained
with fine sand to that given by coarse sand being ninety-six
in the case of natural, and only eighty-six in the case of Port-
land. The effect of fine sand appears to decrease with age,
especially with natural cement.
The fineness of sand will be treated further in the following
article relating to voids.
Art. 31. Voids in Sand
256. Conditions Affecting Voids. — The voids present in a
given mass of sand will depend upon the shape of the grains,
the degree of uniformity in size of grains, the amount of moisture
present, and the amount of compacting to which the mass has
been subjected. If all of the grains in a given mass of sand are
of uniform size, the percentage of voids will be independent of
what that size may be. In other words, the percentage of
voids in a cubic foot of buckshot will be the same as in a cubic
foot of bird shot; but if we take a cubic foot of a mixture of
buck and bird shot we will find that the voids are much
less.
257. Effect of Shape of Grain. — M. Feret has published in
France the results of a large number of experiments made by
him as to the voids in sand and broken stone.^ Table 53 gives
the results he obtained concerning the effect of the shape of
the grains on the percentage of voids- present. He first divided
each sand into three parts by means of three sieves, which we
will call A, B and C. Sieve A had four meshes per sq. cm.
(about five meshes per linear inch), sieve B had 36 meshes per
sq. cm. (about fifteen meshes per linear inch), and sieve C had
324 meshes per sq. cm. (about forty-five meshes per linear
inch). The grains that passed A and were retained on B were
designated G, the grains that passed B and were retained on C
were designated M, and the grains that passed C were desig-
nated F. These different sizes were then recombined by tak-
ing five parts of G, three parts of M and two parts of F, and
^ Abstracted in Engineering News, Vol. XXVII, p. 310.
VOIDS IN SAND
177
the resulting sand was designated G^ M' F^. Thus, all of the
sands tested had the same "granulometric" composition.
TABLE 53
Voids in Sands Having Different Shaped Grains
From M. Feret
Nature of Sand.
Volume of Voids Hkmaimno in
One Liter of Sand.
Unshaken.
CO.
Shaken to Refusal.
CO.
Natural sand with rounded grains.
Cherbourg quartzite, angular grains.
Crushed shells, flat grains.
Residue of Cherbourg quartzite crushed
between jaws, laminated grains.
359
421
443
475
256
274
318
346
It is seen that the rounded grains have the smallest percent-
age of voids, or about thirty-six per cent, unshaken, while the
laminated grains gave the largest percentage. It may also be
noticed that the angular grains were compacted more by shak-
ing than any of the others.
258. Effect of Granulometric Composition of Sand on the
Percentage of Voids. — To determine the effect of uniformity of
size of grain upon the percentage of voids and the strength of
mortars, the author has experimented with an artificial sand
formed by crushing limestone. That portion of the product
that passed the coarse screen of the crusher varied in fine-
ness from particles three-eighths of an inch in one dimension to
a very fine powder, the particles of which were less than .0065
inch in one dimension. Such material admits of division into
parts that differ widely in fineness, but which are essentially
of the same composition, and it is therefore excellent for an
experiment of this kind.
The four sieves used in first separating the material into
parts had, respectively, 10, 20, 40 and 80 meshes per linear inch,
the sizes of the holes being, respectively, about as follows: 0.08
inch, 0.033 inch, 0.017 inch, and 0.007 inch square. The sev-
'eral sizes of grain are designated as follows : —
"C," Coarse, passing No. 10, retained on No. 20.
"M," Medium, " " 20, " " 40.
"F," Fine, " " 40, " " 80.
"V," Very fine, " " 80.
178
CEMENT AND CONCRETE
M. Feret's method of designating the granulometric compo-
sition, namely, to represent by exponents the number of parts
of each size of grain, has been adopted.
259. The voids were obtained by first weighing a given
volume of the sand; dividing the weight by the specific gravity
of the limestone, as previously determined, gives the amount
of solid material in the measure, and this subtracted from the
volume of the measure, gives the voids. This method is con-
sidered more nearly accurate than the usual one of measuring
the amount of water required to fill the voids in a measure of
sand, especially so for a sand of uniform character and one
which absorbs water quite freely.
TABLE 54
Voids in Limestone Screenings, Showing Effect of Variations in
Granulometric Composition
Fineness of
Gbanulometkic
Composition.
Weight of
ONE Litek of
Sand, Dkv,
Gkams.
Volume Solid
Sand in
One Liter
(Sp. Gb. = 2.667)
Cu. Cent.
Peb Cent.
Voids
IN Sand.
Loose.
Shaken.
Loose.
Shaken.
Loose.
Shaken.
a
b
c
d
e
/
g
C = Coarse 10 to 20
M = Medium 20 to 40
F = Fine 40 to 80
V = Very fine, pass 80
C
M
F
V
C^, M25, Fl^ V6
C*o, M*), F20, Vio
C26, M25, F25, V28
C«>, M28, F>6, V30
C«>, MO, i^, V80
11
11
11
11
2(
4(
5(
i
)
)
1358
1362
1392
1609
1395
1439
1459
1656
1606
1732
1912
1860
1991
4
4
4
4
22
28
31
37
509
611
622
603
623
640
647
621
602
649
717
694
746
57.
57.
66.
56.
8
2
9
3
49.1
48.9
47.8
39.7
47.7
46.0
45.3
37.9
39.8
36.1
28.3
30.6
25.4
The results obtained are given in Table 54. Comparing the
voids in C, M, F and V, it is seen that the first three have nearly
the same percentage, but V has less voids than the others.
This is explained by the fact that this sample was made up of >
all sizes smaller than the holes in No. 80 sieve, down to the
fine powder. Comparing the mixed sands, it is seen that the
sample made up of equal parts of coarse and very fine had
VOIDS IN SAND
179
the least voids, the percentage being only a little more than
half of that obtained with coarse particles alone. The next
lowest percentage was given by the sample having equal parts
of four sizes.
It is apparent that the granulometric composition has a
very important effect on the percentage of voids. When one
desires to make a compact mortar with as small a quantity of
cement as possible, similar tests might well be made with the
materials available for use.
260. Effect on Strength of Mortars of Varying the Granulo-
metric Composition of Sand. — Table 55 gives the results of
tensile tests of mortars made with limestone screenings of vari-
ous granulometric compositions. The differences in strength
are not very great, but it appears that with one-to-three mor-
tars the highest strength is developed at six months, with the
coarse grains alone, but when poorer mortars are in question
the result is afifected by the percentage of voids in the sand.
TABL^ 55
Iiimestone Screenings vrith Portland Cement. Ziffect on Tensile
Strength of Variations in Granulometric Composition of Sand
GRANtTIiOMETBIC COMPOSITIOS
OF Sand. Per
Cent, of each Size Gbain.
Voids.
%
Tensile Strength at
6 Mo8. Pounds per
Sq. In. with Parts Sand
TO One Cement by
Weight.
Weight of
Briquets in
Grams.
C
M
F
V
3
5
3
5
0
40
25
30
50
100
30
25
25
0
0
20
25
15
0
0
10
25
30
50
46
35
31
28
25
509
505
470
496
487
324
392
356
391
349
1465
1466
1445
1448
1455
1438
1480
1455
1470
1460
Cement. — Portland, Brand R. For significance of composition of sand,
261. Table 56 gives the results of similar tests of both Port-
land and natural cement with Point aux Pins sand dredged
from St. Marys River and containing a very large percentage
of quartz grains. The sand was divided into but three parts
by sifting, and was then remixed, the proportion of each size
being indicated in the table. The results verify the conclusions
180
CEMENT AND CONCRETE
already drawn that the coarser sands give the higher strength.
It appears that not more than one-half of the grains should be
very fine if the best results are desired.
TABLE 56
Varying the Granulometric Composition of River Sand. Effect on
Value of, for Use in Cement Mortar
Composition of Sand as
TO Fineness.
Tensile Strength, Pounds per Square Inch.
Parts Used
that Passed
No. 20 Sieve
and Re-
tained on
No. 30.
Parts
Used,
30-M)
Parts
Used that
Passed
No. 40
Sieve.
Portland Cement with
Two Parts Sand to One
Cement by Weight, at
age of
Natural Cement with
Three Parts Sand to One
Cement by Weight, at
age of
M
F
V
28 da.
6 mo.
lyr.
2yr.
28 da.
6 mo.
lyr.
2yr.
10
4
2
1
1
0
1
4
3
2
0
5
4
6
7
342-
300>-
290
246
271
471'
448- •
425
384
366
560-
51 5' •
494
455
456
591-
607"
503
442
438
77
77
79
46
67
267
237
278
222
226
348
304
291
234
247
341
319
325
251
251
Note. — River sand, mostly quartz, obtained at Point aux Pins. Each
result mean of five briquets, all made by one molder.
262. Effect of Moisture. — The effect of a small amount of
moisture on the bulk of a given weight of sand is not usually
appreciated, but it may easily be shown that it is very marked.
The results in Table 57 were obtained by adding small amounts
of water to a given bulk of dry sand. Each time, after the
water was added, the sand was stirred up and the weight of a
given volume of the moist sand was obtained. It appears that
the finer sands are affected more than coarse ones.
In the case of the limestone screenings 40-80, if we add but
3.7 per cent, water to a given quantity of dry sand, the bulk
of the sand is so increased that if we take 1,000 c.c. of the moist
sand it will contain but 720 c.c. of dry sand. The voids are,
of course, correspondingly increased from 54.5 per cent, to
67.2 per cent.
The cause of this increase in bulk is that each grain of sand
is surrounded by a film of water which prevents the grains
from lying close together after they have been disturbed. A
large amount of air is also imprisoned in the mass. It may be
noticed that the difference in bulk between moist and dry sand
is greater when the measurements are made "loose."
VOIDS IN SAND
181
TABLE 57
Volume of Sand and Voids as Affected by the Addition of VTater
Sand.
a
Wkight of
DkySandin
One Liter
Volume of
Dby Sand
IN One
LiTEK OF
Percent.
Voids in
Sand by
of Moist
Sand.
Moist
Sand.
Volume.
Kind.
i
p
si
£3
5 u
§1
4^
1
i
1
Jrj
xi-^
■J 3
.C 3
ceo
"^
a
b
c
d
e
/
ff
h
i
Crushed
1
Limestone.
10-20
0.0
1288
1489
1000
1000
, ,
2
a
4.8
1094
1367
849
919
3
n
7.7
1023
1295
794
869
4
^l
11.9
996
1276
773
857
6
40-80
0.0
1214
1481
1000
1000
bi'.b
U.o
6
((
0.85
1124
1489
926
1005
57.9
44.2
7
u
1.6
1059
1470
872
993
60.3
44.9
8
a
2.2
950
1383
782
934
64.4
48.2
9
((
3.7
875
1298
720
877
67.2
51.4
10
((
6.3
824
1274
679
860
69.1
62.3
11
i(
7.8
799
1266
658
855
70.0
52.6
12
((
12.3
817
1280
672
864
69.4
52.0
13
u
16.8
829
1306
683
881
69.0
51.1
14
(1
20.2
836
1274
689
860
68.6
52.3
16
((
25.3
891
1357
783
916
66.6
49.1
16
it
30.3
1049
1270*
864
858*
17
Pass 80
0.0
1186
1500
1000
1000
18
li
2.4
1038
1394
873
929
19
(I
6.1
835
1281
704
854
, ,
20
((
12.2t
806
1310
680
873
21
Point aux
((
17.7t
806
1260
680
840
22
Pins.
r
0.0
1726
1000
, .
23
2.0
1405
815
24
4.0
1400
810
26
t^
6.0
1400
810
26
10.0
1415
820
27
11.6
1425
825
28
'
18.4
1485
860
Water rose to surface.
t Fineness of Point
aux Pins Sand
30 40 50
• Not jarred down in measure as much as usual
t Sand ci'umbled like damp earth.
r Sieves No. 20
J Approx. size
] holes - .033
l_ Per cent, passing 96.0
Note. — 10-20 = passing No. 10 sieve (holes about .08 in. sq.) and retained
on No. 20 sieve.
.022
82.3
.017
46.6
.012
6.7
80
007
1.2
182 CEMENT AND CONCRETE
263. This subject is of great importance in proportioning
mortars, because, in construction, the amounts of cement and
sand are usually measured. Suppose it ife desired to use a mix-
ture of one hundred pounds of cement to four hundred pounds
of sand, and for convenience we will suppose the packed cement
and dry sand each weigh one hundred pounds per cubic foot.
If now we use damp sand, containing about 3.5 per cent, water,
instead of dry sand, and measure the materials, we would have
four cubic feet of damp sand to one cubic foot of cement; but
damp sand would contain only about 4 X 75 = 300 pounds of
dry sand, and we would really have a one-to-three mixture
instead of a one-to-four.
Art. 32. Impurities in Sand
264. The usual specification for sand is that it shall be
"clean, sharp and siliceous." We have shown that it need not
be siliceous, and we have also noted that one authority con-
siders that it need not be sharp, though this latter does not
appear to be proven; let us see what interpretation should be
given to the word "clean" if it must be retained in all speci-
fications for sand.
Mr. E. C. Clarke, in the tests for the Boston Main Drainage
Works, showed that "clay in moderate amounts" (ten per
cent, to thirty per cent, of the sand) "does not weaken cement
mortars." Calcareous marl might be considered an impurity,
but we have seen that M. Alexandre found that sands contain-
ing this material gave excellent results. On the other hand,
there seems to be no doubt that loam, peaty matter or humus
will very materially decrease the strength of mortars, or even
destroy them entirely. Likewise, decayed particles of some
kinds of stone, or grains which readily break up into thin scales,
should be strenuously avoided.
265. Detection of Impurities. — Clean sand when rubbed in
the hand will not leave fine particles adhering to it, but should
the sand not prove to be clean, the character of the impurities
should be investigated before finally rejecting it. When there
is not time for making proper tests, it will, of course, be safest
to use only such sand as has no foreign matter whatever; but
when strictly pure sand can only be obtained at great cost, tests
may show that a small percentage of impurities may be tolerated.
IMPURITIES IN SAND 183
Another simple test, beside the one of rubbing in the hand^
is to place a little of the sand in a test tube filled with water;
if any impurities are present, they may separate from the sand
on account of their Ughter weight, or if in a very fine state of
division, the water may be rendered murky in appearance.
This test is not absolute, however, especially for calcareous
sand, as the fine particles of limestone will give the murky
appearance to the water, although not objectionable except on
account of their extreme fineness.
The use of poor sand will result in a larger proportionate
decrease in strength for a mortar containing a large amount
of sand than for one made with a small amount. The effect of
incorporating various foreign substances in cement mortar is
treated in Art. 49. As some of these substances may occur
in sand, the article referred to should be read in connection
with this subject.
266. SAND WASHING. — When impurities occur, they may
sometimes be removed by washing, but such work must be
carefully inspected if the foreign matter be of a really danger-
ous character.
In the construction of the Canal at the Cascades, Columbia
River, Oregon, quite an elaborate concrete plant was estab-
lished, which had in connection a sand and gravel washer and
separator.^ This consisted of a tube about two and one-half
feet in diameter and seventeen feet long, made of one-quarter-
inch boiler iron and revolving about an axis slightly inclined to
the horizontal. Angle irons were riveted on the inside of the
tube to carry the material up on the side and drop it again,
while a spray of water issued from a perforated pipe inside the
tube. The materials were separated by screens near the lower
end of the tube. The material contained considerable earthy
matter and is said to have been fairly well washed by this pro-
cess.
Another style of sand washer was designed by the contract-
ors for the construction of Lock No. 3, improvement of Alle-
ghany River.^ The sand contained earthy matter and some
coal, the latter being hard to remove by ordinary processes. A
' Report of Lt. Edw. Burr, Report Chief of Engineers, 1891, p. 3334,
' W. H. Rober, Engineering News, Feb. 16, 1899.
:184 CEMENT AND CONCRETE
large barrel or tank, nine feet in diameter and seven feet high,
was provided with double floor, the upper one being pierced
with one-inch holes. Paddles were attached to a vertical shaft
in the axis of the tank and revolved by suitable gearing, while
water was forced into the space between the two floors. The
water finding its way through the holes in the upper floor, passed
up through the sand and overflowed at the top, carrying with
it the coal and sediment. The cost of washing is said to have
been about seven cents per cubic yard, but it is evident that
methods of handling would have to be quite perfect to keep the
cost at so low a figure.
Art. 33. Conclusions. Weight. Cost
267. REQUIREMENTS FOR GOOD SAND. — In conclusion, then,
we may say that good sand may consist of grains of almost
any moderately hard rock that is not liable to future alteration
in the work. The grains may be of any shape, but preferably
should be sharp and angular or lenticular in form, not rounded
and smooth. The sand should not contain such impurities as
loam or humus, but for most purposes a small percentage of
clay or fine rock dust is not objectionable. Clay should not,
however, be permitted in sand for use in sea water.
Coarse grained sands are better than fine grained ones, but
a mixture of fine and coarse is excellent, especially where but
a small amount of cement is used, because such a mixture con-
tains less voids and will make a less permeable mortar, while giv-
ing a good strength. As might be expected, the deleterious effect
of poor sand is more apparent the larger the dose of sand used.
268. Weight of Sand. — It is evident from what has pre-
ceded that the weight of sand per cubic foot will vary greatly,
not only with the character of the rock from which it came,
but also with its physical condition. Natural sand, as it or-
dinarily occurs, will weigh about as follows, according to its
condition : —
Moist and loose 70 to 90 pounds per cu. ft.
Moist and shaken 75 to 100 " "
Dry and loose 75 to 105 " "
Dry and shaken 90 to 125 " «
When settled in water, weight of wet
sand, voids full 100 to 140 " **
WEIGHT AND COST OF SAND 185
If the rock from which the sand is made weighs, say, one
hundred sixty pounds per cubic foot soUd (specific gravity,
2.56), then the sand will weigh per cubic foot 120, 100, and
80 pounds, for voids of 25; 37.5 and 50 per cent., respectively.
269. Cost of Sand. — The cost of sand will, of course, vary
with the locality. In exceptional cases where it is found di-
rectly at the works, it may not cost more than twenty to thirty
cents per cubic yard to deliver it on the mixing platform. If
it has to be pumped from the bed of a river or lake and can be
conveyed to the work in scows with a tow of not more than
ten miles, it may be delivered at the work for from forty to
sixty cents per cubic yard. If it must be hauled in wagons for
some distance, it may cost from fifty cents to one dollar per
yard; and again, if sand is so difficult to obtain that it must be
made by crushing rock, it may cost from one dollar to three
dollars per yard. Usually from sixty cents to a dollar is a fair
price for sand. Several examples of cost of sand will be given
in connection with the subject of cost of concrete.
CHAPTER XII
MORTAR: MAKING AND COST
Art. 34. Proportions of the Ingredients
270. CAPACITY OF CEMENT BARRELS. — Since there is no
standard size for cement barrels, the capacities vary consider-
ably, Portland cement barrels ranging from 3.1 to 3.6 cu. ft., while
natural cement barrels contain from 3.4 to 3.8 cu. ft. In Ger-
many cement is packed to weigh three hundred ninety-six
pounds per barrel, gross, the net weight being about three hun-
dred seventy-five pounds. American Portland usually weighs
four hundred pounds gross or about three hundred eighty
pounds net.
In 1896 the Boston Transit Commission had a number of
measurements made of the capacity of Portland cement bar-
rels, and these have been compiled by Mr. Sanford E. Thompson.*
Table 58 presents some of the averages obtained from this series
of tests. It is seen that the capacity of the barrels varied from
3.12 to 3.50 cu. ft., the mean volume being 3.29 cu. ft. The
difiference between the capacity of the barrel and the volume
of the packed cement contained is due to the fact that there
is usually a small space beneath the head not filled with cement.
A barrel of packed cement makes about 1.25 barrels, measured
loose.
271. Natural cements made in the East are packed to
weigh three hundred pounds net, while some of the Western
natural cements weigh but two hundred sixty-five pounds per
barrel net. Any of the natural cement factories will doubtless
pack their cement to suit customers on large orders, and there
seems to be little reason for this variation in weight between
the West and the East. There would perhaps be some trouble
in getting three hundred pounds of a very light, finely ground,
natural cement in the ordinary sized barrel, but two hundred
^ Engineering News, Oct. 4, 1900.
186
PROPORTIONS IN MORTAR
187
TABLE 58
Capacity of Portland Cement Barrels
Height of barrel between heads, feet ....
Capacity between heads, cubic feet
Volume of packed cement in barrel, cubic feet .
Volume of loose cement in barrel, cubic feet . .
Net weight of cement in barrel, pounds . . .
Weight per cubic foot of cement as packed in
barrel, pounds
Weight per cubic foot, loose, pounds ....
Highest. Lowest. Mean
2.19
3.50
3.48
4.19
387.0
123.16
100.49
2.01
3.12
3.03
3.75
370.7
113.81
88.52
2.09
3.29
3.18
4.07
377.4
118.79
92.63
Note. — Results are averages of thirty-one tests with seven brands, four
of which were American. The above data compiled by Sanford E. Thomp-
son and published in Engineering News of Oct. 4, 1900.
eighty pounds may be put in a barrel without difficulty, and it
would seem that a compromise might be made on this weight.
272. Quantity of Sand. — The amount of sand to be used
in mortar will depend entirely on the character of the work
and the quality of the cement and sand. If it is merely a
matter of strength to be developed, no special care need be
taken to have the voids in the sand filled with cement, but if
an impervious mortar is desired, the mortar must not be too
poor in cement, even though only a moderate strength is re-
quired.
In France the proportions of cement and sand are usually
given in terms of kilograms of cement to one cubic meter of
sand. In England and America the proportions are usually
given by volume, as so many parts of cement to one of sand,
while in Germany the proportions are given by weight. The
bulk of cement varies so much according to the degree of pack-
ing, and the volume of sand is so varied by the amount of mois-
ture contained, that the German method of stating proportions
by weight seems to be the most logical one to adopt.
273. Proportions by Volume. — It has been shown that the
volume of a given quantity of cement may vary twenty-five
per cent, according as it is measured packed or loose, and that
likewise the volume of sand may vary twenty per cent, accord-
ing to the amount of moisture contained. This makes it ne-
cessary to take great precaution in proportioning mortars by
188 CEMENT AND CONCRETE
volume if the desired richness of the mortar is to be assured.
Nevertheless, mortars for use in actual construction are usually
proportioned by volume. The usual method is to state the
proportions as one part of packed cement (as it comes in the
barrel or bag) to so many parts of loose sand, but proportions
are sometimes stated as volumes of loose sand to one volume
of loose cement.
274. Equivalent Proportions by Weight and Volume. — As
cement is now so frequently sold in sacks of one-fourth barrel
each, in which the cement is not so compact as in a barrel, we
have assumed the contents of a barrel to be 3.45 cu. ft. for
Portland, and 3.75 cu. ft. for natural, which are somewhat
higher than the mean actual capacities of stave barrels as
shown by tests. At three hundred eighty pounds and two
hundred eighty pounds net weight respectively for Portland
and natural, this is equivalent to one hundred ten pounds per
cubic foot and seventy-five pounds per cubic foot packed. If
we also assume that loose cement weighs eighty-five pounds per
cubic foot for Portland and sixty pounds per cubic foot for
natural; and that loose, dry sand weighs one hundred pounds
per cubic foot, while loose, damp sand weighs eighty pounds per
cubic foot, we may obtain the following comparisons. Table 59.
275. It is evident that in all specifications and in reports
of tests, as well as in the use of cement, the method of stating
proportions should be made clear, and in interpreting the re-
sults of tests this must be borne in mind. For instance, in
tests to compare the value of limestone screenings with quartz
sand, proportions by weight will favor the quartz, while pro-
portions by volume will favor the screenings, since the latter
are lighter.
276. Richness of Mortar. — Mortars containing small amounts
of sand are often stronger than neat cement mortars. Es-
pecially is this true of most natural cements. Some of these
will give as high strengths when mixed with two parts sand by
weight as when neat, and usually the one-to-one mortars are
stronger than the neat mortars. These remarks refer to tensile
tests where a good quality of sand is used and the mortars are
three months old or more. The neat cement mortars gain
their strength more rapidly, short time tests usually not show-
ing the results mentioned, Portland cements of good quality
PROPORTIONS IN MORTAR
,189
TABLE 59
Comparison of Proportions by "Weight and Volume
Pabts Dry
Sand
Equivalent
Parts Sand, Pboporxions Stated
BY Volume. |
Portland Cement. 1
Natural Cehent. 1
»2 1
<D& a
o «
^j. i
?S|
<B° a
TO One
Ckment by
Weight.
„ *> S
oO ®
Parts Loos
Damp Sand
One of
Packed Cem
Parts Loos
Dry Sand
One of
Loose Ceme
Parts Looe
Damp Sand
One of
Loose Ceme
So|
o o'^
sit
Parts Loo
Damp Sane
One of
Packed Cem
0 oO
III
Parts Loo
Damp Sane
One of
Loose Cem
1
1.10
1.38
0.85
1.06
0.75
0.94
0.60
0.75
2
2.20
2.75
1.70
2.12
1.50
1.88
1.20
1.50
3
3.30
4 12
2.55
3.19
2.25
2.81
180
2.25
4
4.40
5.60
3.40
4.25
3.00
3.75
2.40
3.00
5
5.50
6.88
4.25
5.31
3.75
4.69
3.00
3.75
6
6.60
8.25
5.10
6.38
4.50
5.62
3.60
4.50
In preparing the above table the following assumptions ai-e made :
Material.
Weight
IN A
Babbel.
Volume
OF A
Babbel.
Weight peb Cubic Foot. 1
Packed.
Jjoose
Dry.
Loose
Damp.
Portland cement .
Natural cement .
Sand . ...
380
280
3.45 cu. ft.
3.75 cu. ft.
110
75
85
60
100
80"
usually give about the same tensile strength neat and with
one part sand by weight. Tests showing the rate of decrease
of strength with added sand are discussed in §§363 to 365.
Portland cements are usually mixed with from one to three
parts sand by weight, and natural cements are mixed with
from one to four parts by weight (or three-fourths part to
three parts by measure). For certain special purposes poorer
mortars are sometimes employed. To arrive at the proper
proportion to use in mortar for a given purpose, the tables of
strength given in Chapter XV will be of value.
277. Effect of Pebbles. — If the sand contains pebbles, the
proportions should be considered in a little different way.
Suppose we make a one-to-three mortar with sand that con-
tains ten per cent, of pebbles. We have in reality, then, 3 X .90
= 2.7 parts of sand to one of cement, and .3 part pebbles em-
bedded in this richer mortar. This point is of special signifi-
cance in making concrete from gravel containing some sand, or
190 CEMENT AND CONCRETE
from broken stone from which the fine particles or screenings
have not been removed. Such fine particles serve to weaken
the mortar by increasing the dose of sand, while the pro-
portion of aggregate is diminished. In using aggregates con-
taining some fine material, then, or in using sand containing
pebbles or fine gravel, one should not permit himself to be de-
ceived as to the actual richness of the resulting mortar or
concrete.
278. AMOUNT OF WATER FOR MORTAR. — The amount of
water required for mortar will vary with the proportion of sand
to cement, the character and condition of the ingredients, the
weather, and the purpose which the mortar is to serve. If the
water is stated as such a percentage of the combined weight
of cement and sand, the amount required for a rich mortar
will be greater than for a poor one, since the cement requires
more water than the sand. Fine cement will require more
water than coarse; the same is true of sand. Sand from ab-
sorbent rock will require a larger amount of water. On a hot,
dry day, more water must be used to allow for evaporation;
and again, if the mortar is to be placed in contact with brick
or porous stone, the mortar must be more moist than when
used in connection with metal, or with hard rocks such as
granite. All of these points must be borne in mind when
determining the proper consistency for a given purpose.
279. We may arrive at the approximate amount of water
required in the following manner: find what proportion of
water is required for the neat cement. This will vary among
different samples, and especially between Portland and natural
cements; the former requiring twenty to twenty-eight per cent,
of water (by weight), and the latter thirty to forty per cent.
Then find the amount of water required to bring the sand alone
to the consistency of mortar. This will vary considerably, fine
sand requiring much more water than coarse, etc., as men-
tioned above. Having these two quantities, we may find the
amount of water required for a mortar having any given pro-
portions of these samples of cement and sand. Thus, suppose
we find that the neat cement requires twenty-five per cent,
water and the sand ten per cent, water to bring them to the
proper consistency. If we wish to make a one-to-three mortar
from these ingredients, using one hundred pounds of cement, the
MIXING MORTAR 191
required amount of water is (100 X .25) + (100 X 3 X .10)
= 25 + 30 = 55 pounds.
280. However, it will usually be better to experiment di-
rectly upon the mixture which it is proposed to use, and for
this purpose the following rule will be found of value. For
ordinary purposes, that amount of water should be used which
for given weights of the dry ingredients will give the least
volume of mortar with a moderate amount of packing. In the
actual use of mortars it is not practicable to state that a cer-
tain definite amount of water shall always be used with given
quantities of the dry materials. It is the resulting consistency
of the mortar that must be specified and insisted upon, while
the amount of water required to produce this consistency will
vary from day to day and must be left to the discretion of the
inspector or foreman. For a discussion of the relation of con-
sistency to the tensile strength of the mortar, see Art. 46.
Art. 35. Mixing the Mortar
281. Having decided upon the proportions of cement, sand
and water, it remains to incorporate these into a plastic, homo-
geneous mass. The size of the batch should be so adjusted, if
possible, that a full barrel of cement shall be used, and for
careful work the amount of sand should be weighed instead of
measured. Where this is impracticable, the condition of the
sand from day to day, as regards the amount of moisture con-
tained, should be taken into account (see §§ 262 and 263).
Mortar is usually mixed by hand, but where large amounts
are to be used, machine mixers may profitably be introduced.
282. Hard Mixing. — For hand mixing, a water tight plat-
form or shallow box should be used, of such a size that the given
batch will not cover the bottom more than four inches deep.
If the sand is measured, a bottomless box, provided with
two handles at each end, will be found more convenient than
the bottomless barrel which is often employed for this purpose.
When the sand is delivered on the mixing platform in barrows,
the latter may be fitted with rectangular boxes to avoid re-
measuring. A two-wheel cart, the box of which may be in-
verted to discharge the contents on the mixing platform, will
also be found very serviceable when the runway is suited to
such a vehicle.
192 CEMENT AND CONCRETE
The proper amount of sand is evenly spread on the plat-
form, the cement is then dumped on top of the sand and spread
out over it to an even thickness. With either hoes or shovels
the dry materials are then thoroughly mixed, until, when a
small amount is taken in the hand, it will appear of uniform
color throughout. From two to five turnings of the materials,
according to the expertness of the workmen, will be required to
produce this result. The dry mixture is then drawn to the
edges of the platform to form a ring, and the requisite amount
of water is added at one time in the center. The mixture is
then gradually incorporated with the water, and the mass is
thoroughly worked until plastic and homogeneous. Should it
be found that too little water has been used, a small amount
may be added from a sprinkling pot or rose nozzle, but the
mass should always be worked over again after such addition.
Four shovels may be used at one platform, but if the mixing is
done by hoes, not more than two can be used to advantage
with a batch of ordinary size.
Some engineers prefer one method and some the other, but
in whatever manner done, the mixing should not be stinted.
From two to four turnings of the mass are usually considered
sufficient, but as a general rule it will be found that further
mixing, beyond that required to just give the mass a uniform
appearance, will be amply repaid in the strength of the result-
ing mortar. (See Art. 47.)
283. Machine mixing. — Where large quantities of mortar
are required, machine mixers are sometimes used. A very
complete plant for mortar-making was used in building the
Titicus Dam.^ In this case machinery was used in measuring
the proportions of cement and sand as well as in making the
mortar. The measuring apparatus consisted of two cylindrical
troughs, one for cement and one for sand. Each trough was
divided, by means of six radial vanes and four discs, into eigh-
teen equal compartments. These cylinders revolved in cast
iron boxes which were so constructed as to serve as hoppers
for filling the compartments. Three compartments were pre-
sented to the hoppers at once, and slides were provided by
which any of the hoppers could be cut off at will. The cylin-
Engineering Record, August 3, 1895.
INGREDIENTS REQUIRED 193
ders being geared to the same pinion, it was possible, by means
of the sUdes, to make any desired proportion of cement and sand
from neat cement, to three parts sand to one cement.
The mixing machine "consisted essentially of a semi-cylindri-
cal wrought-iron trough with extended flaring sides, with ele-
ments slightly inclined to the horizontal, and in its axis a re-
volving shaft with oblique radial blades set at an incline of
ninety degrees to each other and of a length to just clear the
bottom of the trough."
284. Another form of machine that is sometimes employed
consists of a semi-cylindrical trough in which rotates an axis
carrying a blade in the form of a screw. The materials are
fed to the mixer at one end and the screw mixes them while
working the mass toward the other end.
Art. 36. Cost of Mortar*
285. INGREDIENTS REQUIRED FOR ONE CUBIC YARD OF
Mortar. — The character of the ingredients used in making cement
mortar varies so much that it is difficult to accurately deter-
mine the quantities of materials required for a proposed mortar
except by experimenting with the materials that are to be
employed. It has been shown that the weights per cubic foot
of both cement and sand vary greatly according to the condi-
tions of packing, the moisture, etc. The percentage of voids
in the sand is one of the most important variations affecting
the amount of mortar made with certain materials mixed in
given proportions. The consistency of the mortar also has a
marked effect, and different cements show a considerable varia-
tion in the volume of mortar that a given weight will yield.
In any general treatment of the question, then, we may expect
only approximate results, and the tables given in this connec-
tion must be considered in this light.
286. Results of Experiments. — The tests froni which Tables
60 and 61 were derived, were made with a natural sand weigh-
ing about one hundred pounds to the cubic foot, dry, and having
about three-eighths of the bulk voids. The grains varied in
size from 0.01 in. to 0.1 in. in diameter with a few grains out-
• Portions of this article were contributed to " Municipal Engineering,"
and appeared m that magazine, Feb., 1899,
194
CEMENT AND CONCRETE
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196 CEMENT AND CONCRETE
side of these limits. The consistency of the mortar was such
that when struck with the shovel blade the moisture would
glisten on the smooth surface thus formed. In the experiments
the proportions were determined by weight, and the results for
proportions by volume were deduced from them. The results
for neat natural cement mortar and for the natural cement
mortars containing more than four parts sand by weight were
derived by analogy.
287. Explanation of Tables. — The first section of Table 60
gives the amount of materials required for Portland cement
mortar when the proportions are stated by weight; the second
and third sections refer to proportions by volume of loose sand
to packed cement when the size of the cement barrel is as-
sumed at 3.65 cu. ft. and 3.33 cu. ft., respectively. The fourth
section gives the materials required when the proportions are
given in terms of loose sand to loose cement. Likewise, the
first section of Table 61 for natural cement refers to proportions
by weight; the second, third and fourth sections, to propor-
tions by volume of loose sand to packed cement when the
cement weighs 265 pounds, 280 pounds and 300 pounds, net,,
per barrel, respectively; while the fifth section refers to propor-
tions of loose sand to loose cement.
As has been shown, the method of stating proportions by
weight is the most accurate, but when the sand does not ap-
proximate the weight of 100 pounds per cubic foot when shoveled
dry into a measure, the sections of the tables referring to weight
proportions may require a correction, and it may be simpler
to use the sections giving proportions by volume of loose sand
to packed cement. The method of stating proportions by vol-
umes of loose sand to loose cement is to be deprecated, but since
it is occasionally used, provision is made for it in the tables.
In using those portions of the tables where the proportions
are stated by volume, it should be borne in mind that if the
sand is damp when used it will weigh less per cubic foot, and
hence more, by measure, will be required to make a cubic yard
of mortar.
288. Estimating Cost of Mortar. — With the data given in
Tables 60 and 61 and a knowledge of unit prices of the mate-
rials used in the mortar, one may estimate the cost of the ma-
terials in a given quantity of mortar. The cost of the mixing
COST OF MORTAR
197
will, of course, depend upon the cost of labor, the method em-
ployed, etc., and may vary from fifty cents to a dollar and
fifty cents per cubic yard. If we assume, for illustration, that
natural cement can be delivered on the mixing platform for
$1.10 per barrel of 280 pounds net, that sand costs 60 cents
per cubic yard, and the mixing costs $1.00 per yard of mortar,
then we have for the cost of a mortar composed of one part
cement to two parts sand by weight : —
3.46 bbls. cement at $1.10 $3.80
0.72 cu. yd. dry sand at .60 43
Cost of mixing per cu. yd 1.00
Total cost of one cu. yd. of mortar $5.23
289. For approximate results, Tables 62 and 63 give the
cost of the materials used in a cubic yard of mortar for different
prices of cement. In Table 62 the proportions by weight only
are indicated, since for Portland the proportions by volume of
loose sand to packed cement vary so little from proportions
by weight.
TABLE 62
Cost of Portland Cement Mortar
Cost of Cbmevt and Sand in One Cubic Yard of Portland Cement
MoRTAK. Sand, 75 Cents per Cubic Yard
Cost of Port-
Cost of Ingredients in Mortar, in Dollars.
land
Cement per
Proportions in Mortar by Weight, — Parts Sand to One of Cement. |
Barrel
OF 380 Pounds
Net.
0
1
2
3
4
5
6
$1.20
8.90
5.38
3.89
3.03
2.56
2.23
2.02
1.30
9.62
6.73
4.17
3.23
2.72
2.36
2.13
1.40
10.36
6.14
4.44
3.43
2.88
2.49
2.24
1.50
11.10
6.55
4.72
3.63
3.03
2.62
2.35
1.60
11.84
6.96
5.00
3.83
3.19
2.75
2.46
1.70
12.68
7.37
5.27
4.03
3.35
2.88
2.67
1.80
13.32
7.77
5.55
4.23
3.51
3.01
2.68
1.90
14.06
8.18
5.82
4.43
3.67
3.13
2.79
2.00
14.80
8.59
6.10
4.63
3.82
3.26
2.90
2.10
15.54
9.00
6.38
4.83
3.98
3.39
3.01
2.20
16.28
9.41
6.65
5.03
4.14
3.52
3.12
2.30
17.02
9.81
6.93
5.23
4.30
3.66
3.23
2.40
17.76
10.22
7.20
5.43
4.46
3.78
3.34
2.60
18.50
10.63
7.48
6.63
4.61
3.91
3.46
2.60
19.24
11.04
7.76
5.83
4.77
4.04
3.66
2.70
19.98
11.46
8.03
6.03
4.93
4.17
3.67
2.80
20.72
11.86
8.31
6.23
5.09
4.30
3.78
2.90
21.46
12.26
8.68
6.43
5.25
4.42
3.89
3.00
22 20
12.67
8.86
6.63
5.40
4.56
4.00
198
CEMENT AND CONCRETE
TABLE 63
Cost of Natural Cement Mortar
Cost of Cement and Sand in One Cubic Yabd of Natural Cehbnt
MoKTAR. Sand, 75 Cents peb Cubic Yabd
Method of Stating
o
Cost of C£ment peb Babbel, Dollabs.
Pbopobtions, and
-<a
Weight of Cement in
One Bahrrl.
CO H
1
0.60
0.70
0.80
0.90
1.00
1.10
1.20
1.30
1.40
1.60
/
0
5.07
5.92
6.76
7.60
8.45
9.30
10.14
10.98
11.83
12.68
1
3.50
4.02
4.54
5.06
5.59
6.11
6.63
7.15
7.67
8.19
Proportions by weight.
Rsirrpl 9i^ Ihs ript
2
2.74
3.10
3.47
3.83
4.20
4.57
4.93
5.30
6.66
6.03
XJAl i CI iAJO llfOt JiCIf,
3
2.23
2.50
2.78
3.05
3.32
3.59
3.86
4.14
4.41
4.68
.
4
1.90
2.12
2.33
2.54
2.76
2.98
3.19
3.41
3.62
3.83
/
0
4.48
5.23
5.98
6.72
7.47
8.22
8.96
9.71
10.46
11.20
1
3.14
3.60
4.06
4.52
4.98
5.44
5.90
6.36
6.82
7.28
Proportions by weight.
'R».rrf>1 .^lOn Ihs npt
2
2.48
2.80
3.12
3.45
3.77
4.09
4.42
4.74
5.06
5.38
JLJcUiCX O^A^^lliO. Ht3l/.
3
2.04
2.28
2.52
2.76
3.00
3.24
3.48
3.72
3.96
4.20
.
4
1.75
1.94
2.13
2.32
2.61
2.70
2.89
3.08
3.27
3.46
By volume; parts dry
loose sand to packed
0
5.07
5.92
6.76
7.60
8.45
9.30
10.14
10.98
11.83
12.68
1
3.13
3.58
4.02
4.46
4.91
5.36
6.80
6.24
6.69
7.14
cement. Oeraent as--
2
2.29
2.57
2.85
3.14
.3.42
3.70
3.99
4.27
4.56
4.84
sumed 265 lbs. per bbl.
3
1.83
2.04
2.24
2.45
2.65
2.86
3.06
3.26
3.47
3.67
of 3.75 cu. ft.
4
1.63
1.79
1.95
2.11
2.27
2.43
2.59
2.75
2.91
3.07
By volume; parts dry
loose sand to packed
cement. Cement as-
sumed 300 lbs. per bbl.
1
2.94
3.36
3.77
4.19
4.61
5.03
5.44
5.86
6.28
6.70
2
3
2.22
1.82
2.50
2.02
2.77
2.22
3.05
2.42
3.32
2.62
3.60
2.82
3.87
3.02
4.15
3.22
4.42
3.42
4.70
3.60
of 3.75 cu. ft.
4
1.59
1.75
1.91
2.06
2.22
2.38
2.53
2.69
2.85
3.00
In Table 63 the cost of materials in one cubic yard of natural
cement mortar is given, 1st, for various parts of sand to one
of cement by weight when the cost of cement refers to a barrel
of 265 pounds; 2d, when this cost is for a barrel of 300 pounds
net; 3d, for various parts sand to one cement when the propor-
tions are expressed as parts by volume, dry loose sand to one
volume of packed cement weighing 265 pounds per barrel; and
4th, when the proportions are expressed as parts of dry loose
sand to one volume of packed cement weighing 300 pounds per
barrel. The quantities in the table are based upon the as-
sumption that the sand used is similar to that used in the ex-
periments from which Tables 60 and 61 were derived, and that
the cost of sand is seventy-five cents per cubic yard.
COST OF MORTAR 199
290. Example. — To indicate the use of these tables, let us
determine the cost per cubic yard of natural cement mortar
composed of one volume of packed cement to three volumes of
loose dry sand when the cement weighs 300 pounds per barrel,
net, and costs $1.25 per barrel, while sand costs $1.00 per cubic
yard. In the fourth section of Table 63, opposite three parts
sand and under $1.20 and $1.30, we find, respectively, $3.02 and
$3.22; then with cement costing $1.25 and sand $0.75, we should
have cost of mortar per cubic yard $3.12. But in our example
sand is assumed to cost $1.00 per cubic yard, or twenty-five
cents more than the price for which the tables are computed^
and from Table 61 we find that for this mortar 0.83 cubic yard
of sand is required. We must therefore add to $3.12, .83 X 25
= 21 cents, giving $3.33 as cost of materials in one cubic yard
of the mortar. The cost of mixing the mortar must be added
to obtain the total cost per cubic yard.
CHAPTER XIII
CONCRETE : AGGREGATE
291. Cement concrete is cbmposed of a mixture of cement
mortar and fragments of stone, brick or other moderately hard
substances to which the mortar may adhere. Put in place while
plastic, it soon obtains a strength and hardness equal to good
building stone. This property, combined with its cheapness
and adaptability to monolithic construction, renders it one of
the most useful of engineering materials.
Art. 37. Character of Aggregate
292. MATERIAL FOR AGGREGATE. — Many of the points men-
tioned concerning the selection of a good sand are also applicable
to broken stone. The latter may be produced from almost
any moderately hard rock, provided it is not subject to decay.
The best material for broken stone is a rather hard and tough
rock, which breaks into angular fragments with surfaces that
are not too smooth.
Gravel makes a good aggregate, although its surfaces are too
smooth and rounding to give the best results. Coarse gravel
may be improved by running it through a rock crusher to render
some of the fragments angular and rough. A mixture of gravel
and broken stone gives excellent results (see § 454). The gravel
assists the compacting of the mass, and the fragments of broken
stone furnish a good bond. A mixture of this kind also leaves
but a small percentage of voids in the mass, and this decreases
the amount of mortar required.
293. Sandstones are sometimes said to be better than lime-
stones, but this will depend on their relative hardness and
structure, and the use to which the concrete is to be put; no
general rule will apply. Some limestones seem to be particu-
larly adapted to concrete-making, as the cement adheres to the
surface so firmly. Granite, syanite and trap are excellent for
the purpose. Fragments of brick and of other burnt clay
200
CHARACTER OF AGGREGATE 201
products give good results up to the limit of the strength of the
pieces, but this limit is not high. Table 155 gives the results
of transverse tests of concrete bars made under the author's
direction, to show the comparative value of different kinds of
stone. The results of these tests are discussed in § 454.
Mr. E. L. Ransome * has pointed out that "for fireproof
work, care should be taken to avoid such aggregates as contain
feldspar," and that limestone should not be used if the con-
crete is likely to be subjected to a long continued red heat.
The same writer mentions the fact that finely crushed granite
may be inferior to finely crushed limestone for use in concrete;
one reason for this being that, "owing to the brittle quality of
granite, in crushing it is not only broken into small pieces, but
many of these pieces are so bruised or contused that upon a
little pressure being exerted upon them, such, for instance, as
can be appUed by the finger or thumb, they will crumble."
294. The care required in the selection of a proper quality
of broken stone or gravel will depend upon the required strength
of the concrete. If a strong concrete is required, rich mortar will
not be able to make up a deficiency in the strength of the stone ;
but if a low strength is sufficient, and consequently a poor mor-
tar is to be used, but little will be gained by having a very
strong rock from which to obtain broken stone. In this case
a rock which presents a good surface to which mortar may
adhere is the principal requirement, and a very hard rock need
not be insisted upon.
295. PRESENCE OF SCREENINGS IN BROKEN STONE. — It is
frequently required that the broken stone shall be freed from
all fine material, resulting from the crushing of the stone, before
the mortar is added to form concrete. The wisdom of this
requirement is not always clear and depends upon the kind of
stone. It has already been stated that some forms of crusher
dust or screenings give, if not too fine, most excellent results
in mortar; this is especially true of limestone screenings. Again,
to retain in the broken stone all of the screenings, will result in
diminishing the percentage of voids in the aggregate, and thus
decrease the amount of mortar necessary.
On the other hand, if a stone is covered with a layer of
* Engineering Record, Nov. 17, 1894.
202 CEMENT AND CONCRETE
moistened, floury dust, it cannot be so readily brought in direct
contact with the mortar, and if the mortar does reach the
stone it is made less rich by the dust, which acts as so much
fine sand. It must be said, however, that so far as our ex-
periments go, they do not confirm this latter theory when a
moderate amount of fine material is in question, especially with
crushed limestone. There is a reason, however, in some cases
why the very fine material which acts as sand should be screened
out of broken stone, even if it is again used in the mortar for
the concrete; the fine material collects in certain parts of the
bin or pile, making the proportions irregular, so that one batch
of concrete may have a rich mortar with a comparatively large
amount of stone, while another may have a poor mortar with
but little stone. If, therefore, all of that portion of the broken
stone finer than, say, one-eighth of an inch, be screened out
and used as so much sand in making the mortar, the resulting
concrete will be better and more nearly uniform in quality.
296. Impurities. — Material that is really foreign, such as
vegetable mold or loam, will be detrimental to the strength of
the concrete. Even clay is not permissible here if it adheres to
the stone, because if the surface of a piece of stone is smeared
with clay, the mortar will not be able to adhere as well to that
surface. Clay in a granulated form and not adhering to the
stone may be permitted, however, in small amounts, possibly
as much as ten per cent., without seriously injuring the concrete
for many uses.
When old masonry is torn down, the stones are sometimes
crushed for use in concrete, but such stones, having particles
of mortar adhering to the surfaces, will not be of first quality
for the purpose; their cheapness, however, will frequently out-
weigh such objections.
Art. 38. Size and Shape of the Fragments and the
Volume of Voids
297. As in the case of sand, the shape of the fragments and
the degree of uniformity in size have an important effect on
the proportion of voids in the mass, and all of these elements
affect the value of broken stone for use in concrete. As in
mortar each grain of sand should be completely covered with
cement, so in concrete should each piece of stone be completely
SIZE OF AGGREGATE
203
covered with mortar. As the pieces in a given volume of broken
stone will have a smaller total superficial area when the frag-
ments are large than when they are small, we should conclude
that the larger fragments will require less mortar or be more
thoroughly coated with a Hmited amount. From the same point
of view we should expect that round fragments would require
less mortar than those of irregular shape.
It is found however, in practice, that these theoretical con-
siderations must be modified to correspond with the facts.
TABLE 64
Voids in Broken Stone and Gravel Varying in Granulometric
Composition
Weight of
Ghabacteb Stone.
Granulometric Composition.
Broken
Stone, Lbs.
PER
Cu. Ft.
Per Cent.
Voids.
Limestone . . .
K
83
47
t(
V
89 •
44
11
F
90
43
"
M
91
42
^^
C
85
46
<■!■
F30, MTO
91
42
((
F*', C*>
94
40
((
RaJ, F20, M50
102
35J
(4
Kao, V20, F20, M2\ C^
104
34
((
C, 120i lbs., K, 33i lbs.
llli
29
Potsdam sandstone
V
86
45
(t ti
M
84
44
(( k(
yas p67
88
43
(i (i
V38 F*8 M**
92
40
(( a
K26^ yas^ jH»^ j^as
97i
36^
Gravel ....
V
110
32
n
F
108
33
((
M
106
34
((
V83, F3«, M88
112
30
((
V«>, M«>
114
29
f
P. 6 cu. ft. on i in. screen (
G. 2 " " i in. to Jin. " f
100
39
Potsdam sandstone
and gravel . .""
P. 4 cu. ft. on ^ in. screen )
G.4 " " i in. to i in. " |
109
33
'
Note. — Stone jarred down in measure for all trials.
K passed holes i inch square, failed to pass holes ^ inch square.
V " I " " i "
p "1 " " X "
M "2 " " 1 "
C " 3 " " 2 "
204
CEMENT AND CONCRETE
When the pieces of broken stone are too large, they do not
bed themselves well in the matrix of mortar, but become wedged
one against another, leaving voids in the concrete. While
round fragments have a small superficial area in relation to
their volume, have a small percentage of voids, and pack to-
gether readily, yet they are lacking in ability to form a good
bond, and hence do not give the best results.
298. Relation of Size of Stone to Volume of Voids. — As illus-
trating the effect of the size of fragments and granulometric com-
position of stone on the volume of voids, Table 64 gives a number
of results obtained at St. Marys Falls Canal.
Table 65 gives some of the results obtained by M. Feret in
-similar tests.*
TABLE 65
Size of Stone and Volume of Voids
CoMPOSiTioif, BY Weight, of Small Stone.
Peb cent, of Voids by Volume.
Fragments Passing a Ring of
Rounded Pebbles.
Broken Stone.
90 mm.
60 mm.
40 mm.
20 mm.
and Retained on a Ring of
60 mm.
40 mm.
20 mm.
10 mm.
1
0
0
0
0
1
1
0
1
0
0
1
4
1
0
0
1
0
0
1
1
0
0
0
1
1
1
4
41.4
40.0
38.8
41.7
35.6
33.5
36.6
52.1
53.4
61.7
62.1
47.1
48.8
46.4
The percentage of voids in a mass of broken stone of uniform
size should be independent of what the size may be, and the
first few lines in Table 65 show this to be nearly the case with
the four samples tested. It is seen from both tables that the
more complex mixtures give smaller percentages of voids, and
that for all sizes the voids are much less in the gravel than in
the broken stone.
* " Sand and Stone Used for Cement Mortar and Concrete, " by M. Feret.
Abstracted in Engineering News, March 26, 1892.
SIZE OF AGGREGATE
205
299. M. Feret's Experiments. — To show the effect of the
variation in sizes of fragments on the strength of the concrete
made, M. Feret experimented with four mixtures of three sizes.
The proportions used in the mortar were one part by weight of
Portland cement to three parts of Boulogne gravel, gaged with
an amount of water equal to seventeen per cent, of the total
weight of cement and sand. The volume of mortar used in
each case was made equal to the volume of the voids in the
stone. The concrete was thor6ughly mixed and then rammed
into a large cylindrical mold. After four months' exposure to
the air, twelve cubes were cut from the cylindrical block, four
cubes being cut from each of three consecutive horizontal
layers. These cubes were placed in sea water and crushed
after one month, being then five months old. The results of
the tests are given in Table 66.
TABLE 66
Strength of Concrete. Var3ring Size Stone
Vol. of
Voids peb
Cu.Meter.
Vol. of
Mobtab
PEB Cu.
Meteb of
Stone.
Weight
of Con-
CEETK
PEB Cu.
Meteb.
Mean Resistance in Kg.
per Sq. Cm.
GRANDLiOHETBIC
compositiox of
Bboken Stone.
Of 4 Cubes fbom
8S
si"
OOOo
i
6
i
%
o
n
G
M
F
Cu. Meter.
Cu. Meter.
Kg.
4
1
1
2
1
4
1
2
1
1
4
2
0.492
0.494
0.486
0.478
0.492
0.494
0.486
0.478
2296
2272
2276
2264
144
141
106
115
143
141
121
132
173
154
133
151
158
145
120
133
Size "G" of broken stone passed a ring 60 mm. (2.4 inches)
in diameter and was held by a ring 40 mm. (1.6 inches) in
diameter; "M" passed 40 mm. (1.6 inches) ring and was held
by a ring 20 mm. (0.8 inch) in diameter; while "F" passed
the 20 mm. (0.8 inch) ring and would not pass a ring 10 mm.
(0.4 inch) in diameter.
The following conclusions are drawn from this table: (1) In
each block the lower layers, which had been submitted to
longer continued ramming than the upper layers, offered a
206 CEMENT AND CONCRETE
greater resistance. (2) The mean resistance varied according
to the granulometric composition of stone used, and was greater
with the increasing proportion of large stone in each block.
Since the amount of mortar used was in all cases equal to the
volume of voids in the stone, the effect of voids on the strength
was not noticeable.
300. Further Experiments. — Tables 153 and 155 give the
results of some experiments made under the author's direction
to test the effect of size and character of broken stone. In
these tests the proportions are generally 35 pounds of cement
to 105 pounds of sand and 3.75 cubic feet of broken stone, the
stone being measured after jarring it down in the vessel. The
amount of mortar made was sufficient to fill the voids in the
stone when the latter did not exceed about thirty-three per
cent (§§ 452, 454).
It is seen that, in general, a higher result was given by mix-
tures of various sizes than by any one size alone, and the fine
stone gave higher results than the coarse. In these tests the
effect of voids is shown, since in some cases there was not suf-
ficient mortar to fill the voids.
301. GRAVEL VS. BROKEN STONE AS AGGREGATE. — The ele-
ments entering into the analysis of the superiority of one kind
of aggregate over another are given above, but since the ques-
tion of the relative merits of gravel and broken stone is so
frequently discussed, a word may be added here to show the
special points involved in sucTi a comparison.
Gravel is composed of hard, rounded pebbles, the surfaces
of which are usually quite smooth. On account of the manner
of its formation and occurrence, the sizes of the pebbles are
usually graded from coarse to fine. Occasional beds of gravel
are found, however, in which the sizes of the several fragments
are nearly the same. In broken stone the fragments are angular
and usually have rough surfaces, though the degree of rough-
ness depends upon the kind of stone. The sizes of the frag-
ments as they come from the stone crusher vary from coarse
to fine, but by regulating the crusher jaws and by screening,
any desired size may be obtained.
302. In determining the value of a certain material for
aggregate, at least six characteristics are to be considered, — the
strength and durability of the stone, the size and shape of the
GRAVEL VS. BROKEN STONE 207
fragments, the volume of the voids, and the character of the sur-
face to which the cement must adhere. As gravel is usually from
the igneous rocks, its strength and durability are not often open to
question. This may or may not be so in the case of broken
stone, but the question of relative value of gravel and broken
stone, which is so frequently conclusively settled either one way
or another, seldom hinges on this point. As to the average size
•of the fragments, it is evident that as a general proposition it
must be allowed that by proper screening either broken stone
or gravel may be obtained of any desired size.
Of the three remaining characteristics, the shape of the
fragments, volume of voids, and character of surface, the first
is probably the least important and the third of the greatest
moment. The round pebbles of the gravel slide readily one on
Another, and do not interlock to give a good bond. The angular
fragments of broken stone give a better bond, but on the other
hand, if not thoroughly tamped, are likely to bridge, or arch,
and thus leave holes in the mass. On account of the shapes of
the fragments and because the sizes are usually more varied in
gravel, the latter has generally a smaller percentage of voids;
thirty to thirty-seven per cent, voids in gravel, and forty to
fifty per cent, in broken stone, may be considered to give, in
a general way, some comparative figures. Coming now to the
character of surface, cement will not usually adhere so firmly
to the smooth surface of the gravel as to the freshly broken
surface of the fragments of stone, but this cannot be con-
sidered a universal rule, for the strength in adhesion is not
simply a matter of smoothness or roughness as it appears to
the eye or the touch. The adhesion to limestone may be
very much stronger than to a sandstone which has a rougher
appearance.
303. Summing up the relative advantages, we find that the
gravel is suitable for concrete because, first, it is not likely to
bridge and leave holes in the concrete; if mixed rather wet, very
little tamping is required to compact it; and second, the usual
smaller percentage of voids makes it possible to secure a com-
pact concrete with a smaller amount of mortar than would be
required for broken stone. On the other hand, the angular
fragments of broken stone will knit together, as it were, to form
a strong concrete if properly tamped, and the very important
208 CEMENT AND CONCRETE
question of a suitable surface for adhesion is usually in favor
of the broken stone. It is evident, then, that this matter must
resolve itself into a question of relative cost and suitabil-
ity, and a general statement that either gravel or broken stone
is superior, is not tenable. One experimenter using a small
percentage of mortar in the concrete, so that the voids in the
broken stone are not nearly filled, may conclude that gravel is
the better, while another experimenter using a larger amount
of mortar, filling the voids in the broken stone but giving a
large excess of mortar for the gravel, will conclude that broken
stone is much to be preferred.
Art. 39. Stone Crushing and Cost of Aggregate
304. Breaking Stone by Hand. — When but a small quantity
of concrete is to be made, and broken stone cannot be pur-
chased in the vicinity, the stone for concrete may be broken by
hand. This is an extremely tedious process, however, and is
generally avoided, since broken stone prepared in this way will
cost from two dollars and a half to four dollars per cubic yard.
In the reconstruction of the breakwater at Buffalo, the cost of
breaking stone by hand was two dollars and eighty-six cents
per cubic yard, and loading on boat cost thirty-nine cents,
making total cost about three dollars and twenty-five cents per
cubic yard.^
305. Stone Crushers. — The most common forms of rock
crushers are the gyratory and the movable jaw types. The
jaw breaker, or Blake crusher, consists of one fixed plate or
jaw and one movable one. The latter is hinged at the upper
end and the lower end is moved backward and forward through
a short space by means of a toggle joint or other mechanism.
The jaws are several inches apart at the upper end, depending
on the size of the machine, and converge toward the bottom.
The distance between the jaws at the bottom regulates the size
of fragments delivered, and this distance may be adjusted at
will.
The Gates crusher is of the gyratory type and consists of
a corrugated cone of chilled iron, called the breaking head,
* Report of Capt. F. A. Mahan in Report Chief of Engineers, U. S. A.,
1888, p. 2034. -
STONE CRUSHING 209
within a larger inverted cone, or shell, which is lined with chilled
iron pieces. The vertical shaft bearing the breaking head is
pivoted at the upper end while the lower end travels in a small
circle ; an eccentric motion is then imparted to the head, so that
it approaches successively each element of the shell. The size of
opening can be regulated by raising or lowering the breaking head.
Stone crushers are made of various sizes having capacities
up to one hundred tons per hour. The cost of running a stone
crusher is not great, the principal expense being incurred in
breaking the stone into pieces of proper size to feed the crusher,
the delivery of the stone to the crusher, and taking it away
when broken.
Crushing plants are usually provided with revolving screens
into which the broken stone is delivered from the crusher.
These screens are usually made of perforated steel plate,
the holes being such as to separate the material into the sizes
desired.
Where large amounts of concrete are required, and the stone
is to be crushed on the work, the arrangement of the crusher
plant should receive careful study to facilitate the transporta-
tion of the rock to and from the crusher. The broken stone
should be discharged from the crusher into bins, from wliich
the carts or cars may be filled by gravity, or from which the
material may be led directly to the mixer through a chute or
other form of conveyor. In quarries preparing aggregate for
sale, and on important works, very complete stone crushing
plants are erected.*
306. COST OF AGGREGATE. — The cost of aggregate varies'
greatly according to the proximity of the stone to the crusher,
the character of the stone, and the amount required. In ex-
ceptional cases gravel suitable for use in concrete is so near
at hand that it may be delivered on the mixing platform for
from twenty-five to forty cents per cubic yard. When it must
be brought from a distance, the cost is correspondingly in-
creased. Where a considerable quantity of stone is to be broken,
the cost of crushing, aside from transportation of the materials
* The stone crushing and sand and gravel washing plant used in the con-
struction of the Canal at the Cascades of the Columbia, Ore., is described
and illustrated in Report of Chief of Engineers, 1891, p. 3332.
210 CEMENT AND CONCRETE
to and from the site of the work, would usually be from thirty
to forty cents per cubic yard.
In one case where the stone was delivered to the crusher in
carts after having been sorted from spoil banks containing
much poor stone that had to be handled over, the cost per
cubic yard of crushed stone was approximately as follows for
about six thousand cubic yards crushed in one season: *
Labor, including sorting and delivering to crusher, per cubic
yard of crushed stone $.67
Rent of power plant 04
Fuel 05
Tools, supplies, breakages, etc 12
Interest and depreciation of plant 12
Total cost per cubic yard $1.00
307. The following data concerning the cost of breaking a
large amount of stone for road material are given by Messrs.
Spielman and Brush.* "The stone was broken by a ten-inch
Blake stone crusher at the rate of about twenty cubic yards in
ten hours. The size of the stones as they came from the crusher
was: fifty per cent., two inches size; twenty-five per cent., one
and one-half to one inch size; twenty-five per cent., screenings
and pea dust. The cost of the crusher, engine, boiler, etc.,
set up complete, was about twenty-five hundred dollars. The
cost of working per day independent of the original cost of the
machinery and interest thereon, and also independent of any
royalty on the stone, was found by the contractor to be as
follows: —
Repairs, lubricants, wear and tear on crusher and engine, about $6.00
1 engineman, $2.50; 1 feeder, $1.50; 1 screener, $1.50; 5 laborers
quarrying and breaking up stone at $1.00 10.50
1 team hauling stone 5.00
J ton coal 2.50
Cost of preparing and crushing 20 cu. yds. of stone, $24.00
Cost of one cubic yard, $1.20.
308. The cost of breaking trap on the Palisades is given as
follows:* "Two crushers deliver thirty-five cubic yards of two-
» Trans. Am. Soc. C. E., April, 1879.
' "Construction and Maintenance of Roads," by Mr. Edward P. North,
M. Am. Soc. C. E., Trans. A. S. C. E., April 16, 1879.
COST OF CRUSHING STONE 211
inch stone per day, when working well, the stone being sledged
to go into the jaws readily; fifteen per cent, of the time is lost
by breakdowns: —
1 engineman and fireman $2.50
2 laborers feeding, at $1.25 2.50
2 laborers screening, at $1.25 2.50
Coal, 1 ton 3.50
Oil and waste 1.00
Breakages . 5.00
$17.00
or about fifty-seven cents per cubic yard.
"On Snake Island, three crushers were arranged in a row,
and the broken stone was carried by an endless belt to the
revolving screen, whence it fell into the bins, so that no screen-
ers were employed. The engine had one cylinder^ eight inches
by twenty-four inches, and was running with eighty pounds of
steam. The product was said to be one hundred eighty cubic
yards per day when there was no breakdown." The cost was
as follows : ^ —
1 engineman and fireman $2.50
3 laborers feeding, at $1.25 3.75
2i tons coal, at $3.50 8.75
Oil, etc 2.00
Breakages 15.00
$32.00
"Allowing for the fifteen per cent, lost by breakdowns, the
cost would be about twenty-one cents per cubic yard."
At another place on the Hudson, two crushers, set face to
face, nine-inch by fifteen-inch jaws, could deliver at the rate of
one hundred twenty cubic yards per day when no trouble
occurred, but one hundred cubic yards was a fair average.
Cost.
1 engineman and fireman $2.50
3 feeders 3.75
2 screeners 2.50
li tons coal, at $4.00 6.00
Oil, etc 2.50
Repairs 10.00
$27.00
or twenty-seven cents per cubic yard."
' "Construction and Maintenance of Roads," by Mr. Edward P. North,
M. Am. Soc. C. E. Trans. A. S. C. E., April 16, 1879.
212
CEMENT AND CONCRETE
It is noticeable that in all the above cases the item for
repairs is very large. The wages paid are lower than at
present.
309. The following data concerning the cost of quarrying
and crushing about five thousand six hundred yards of broken
stone at Baraboo, Wis., is taken from an article by Mr. W. G.
Kirchoffer, C. E.^
Cost per Cubic Yard of Crushed Rock
Items.
1901.
1902.
Stone in quarry
Dynamite, at 24 to 27 cents pound . . ,
Tools, repairs, depreciation, supplies and
improvements • .
Labor, quarrying and tending crusher .
Fuel, at f4.60 per ton, and oil ... .
Rent of engine
Superintendence, including livery . . .
Hauling stone to city
$ .040
.066
.200
.714
.078
.085
.086
.500
$ .027
.110
.218
.544
.053
.066
.165
.500
Total cost per cubic yard . . .
$1.76
$1.68
The cost of common labor was fifteen cents an hour, quarry-
men and drill runners, seventeen and one-half to twenty cents,
engineers and engine, thirty-five cents, and team and driver,
thirty cents.
310. The cost of crushing cobble stone with a rented plant
at Port Huron, Mich., is given by Mr. Frank F. Rogers, C. E.,
from which the following data have been derived.^
JrLY AND
October
August.
November.
Hours run
171.5
1145.
94
522.0
Stone crushed, cubic yards
Average cubic yards crushed per hour . .
6.67
5.65
Average rental cost per cubic yard . . .
11.6 cents
16.1 cents
Average fuel cost per cubic yard ....
3.7 "
7.1 "
Average labor co.st per cubic yard . . .
22.2 "
27.9 "
Average total cost of crushing i)er cu. yd.
37.5 "
51.1 "
' Engineering News, Jan. 15, 1903.
* Michigan Engineers' Annual, 1902, abstracted in Engineering News,
March 6, 1902.
COST OF CRUSHING STONE 213
In the construction of the defenses at Portland, Me.,^ a No.
5 Champion Crusher was used, driven by a thirty horse-power
portable engine. Granite was purchased at one dollar per ton
on the wharf. Hauling to crusher cost thirteen cents per ton.
Cost of crushing, twenty cents per cubic yard of crushed stone,
making total cost of crushed stone in bin at crusher one dollar
eighty-three cents per cu. yd.
' Report of Charles P. Williams; Officer in charge, Maj. Solomon W.
Roessler, Corps of Engineers,U.S.A.; Report Chief of Engineers, 1900, p. 767.
CHAPTER XIV
CONCRETE MAKING: METHODS AND COST
Art. 40. Proportions of the Ingredients*
311. Concrete is simply a class of masonry in which the
stones are small and of irregular shape. The strength of the
concrete largely depends upon the strength of the mortar; in
fact, this dependence will be much closer than in the case of
other classes of masonry, since it may be stated as a general
rule, that the larger and more perfectly cut are the stone, the
less will the strength of the masonry depend upon the strength
of the mortar.
In deciding, then, upon the proportions of ingredients to use
in a given case, the quality of the mortar should first be con-
sidered. If the concrete is to be subject to but a moderate
compressive stress, the mortar may be comparatively poor in
cement; but if great strength is required, the mortar must be
of sufficient richness; while if imperviousness is desired, the
mortar must also possess this quality and be sufficient to thor-
oughly fill the voids in the stone.
312. Theory of Proportions. — The usual method of stat-
ing proportions in concrete is to give the number of parts of
sand and aggregate to one of cement. These parts usually
refer to volumes of sand and stone, measured loose, to one vol-
ume of packed cement. However, there is no established prac-
tice in regard to this and a "1-2-5 concrete" may mean five
volumes of loose stone to two volumes loose sand to one volume
loose cement, or any one of several combinations.
This method of stating proportions leads to confusion unless
one is careful to explain what is meant by such an expres-
sion as " 1-3-6 concrete." The evils of similar methods of
stating proportions in mortars, and the desirability of fixing
upon some standard system of weight or volume, have already
' Portions of this article were contributed to Municipal Engineering by
the author and appeared in that magazine, May, 1899.
214
PROPORTIONS OF THE INGREDIENTS 215
been pointed out. The only circumstances under which such
expressions as the above may be used with propriety are when
one wishes to give only an approximate idea of the character
of concrete used.
From tests of strength it is known that to obtain the strong-
est concrete with a given quality of mortar the quantity of the
latter should be just sufficient to fill the voids in the aggregate.
The strength is notably diminished if the mortar is deficient,
and is also impaired by a large excess of mortar. This last
statement is subject to one exception: if the mortar is stronger
than the stone, then an excess of mortar does not weaken the
concrete. This case, however, should never be allowed to occur,
since it is evident that the strength of the stone should be at
least equal to the required strength of the concrete. Further,
the ordinary uses of concrete are generally best served by a
compact mixture containing as few -voids as possible.
For these reasons, then, one should consider concrete not as
a mixture of cement, sand and stone, but rather as a volume
of aggregate bound together by a mortar of the proper strength.
The volume of voids in the aggregate, the per cent, of this
volume filled with mortar, and the strength of this mortar be-
come then the important considerations in proportioning con-
crete. When thus considered, it is an easy matter to determine
the required volume of mortar for a given volume of stone,
and the amount of cement and sand required for a given volume
of mortar has already been considered.
313. Determination of Amount of Mortar to Use. — The bulk
of a given quantity of broken stone is not so variable as the
volume of sand. The volume of the stone, and consequently
the voids, will vary with the degree of packing, but the packing
is not influenced appreciably by the amount of moisture present.
The proportion of voids in the broken stone may be obtained
as follows: Find the weight per cubic foot of the broken stone
in the condition in which the volume of voids is sought, being
careful to use a measure holding not less than two or three cubic
feet. Also obtain the specific gravity, and hence the weight
per cubic foot of the solid stone. Then one, less the quotient
obtained by dividing the weight per cubic foot of the broken
stone by the weight per cubic foot of the solid stone, will be
the proportion of voids in the aggregate.
216 CEMENT AND CONCRETE
For example, suppose the weight per cubic foot of the broken
stone is 102 pounds. The specific gravity of the soUd stone
determined in the ordinary manner is found to be 2.724. Then
weight per cubic foot of soUd stone is 62.4 X 2.724 = 170
pounds and 1 — ^jn — -^O, voids in stone.
Another method is to fill a vessel of known capacity with
the stone to be used, and to pour in a measured quantity of
water until the vessel is entirely filled. The volume of water
required indicates the necessary amount of mortar to use. The
stone should be moistened before placing in the vessel, to approxi-
mate more nearly its condition when used for concrete, and to
avoid an error from absorption of the water used to measure voids.
314. As to the degree of jarring or packing to which the
stone should be subjected in filling the measure, if the stone
is filled in loose, and it is proposed to ram the concrete in place,
the amount of mortar indicated will be a little more than the
required quantity. If the concrete is to be placed without
ramming (as in submarine construction), the amount of mortar
indicated will not be too great. On the other hand, if the stone
is shaken down in the vessel to refusal, the voids obtained will
be less than the amount of mortar which should be used, be-
cause it is not possible to obtain a perfect distribution of mor-
tar in a mass of concrete, and because the concrete will usually
occupy a greater space than did the stone when shaken down.
And again, for perfect concrete, pieces of stone should be sepa-
rated one from another by a thin film of mortar, and hence the
volume of the concrete will be greater than the volume of the
stone measured in a compact condition without mortar. A
deficiency of mortar is usually more detrimental than an excess.
It is safer, therefore, to measure the voids in the stone loose,
or when but slightly packed, and make the amount of mortar
equal to, or a trifle in excess of, the voids so obtained.
315. Aggregates Containing Sand. — If in the case of broken
stone all of the fine particles are used, or if gravel which con-
tains a considerable amount of sand is employed, then this
fine material or sand must be considered as forming a part of
the mortar. This will not change the method of obtaining the
amount of mortar required for such broken stone or gravel,
but it will change the composition of the mortar used. Thus,
MIXING BY HAND 217
suppose we have a gravel ten per cent, of which is sand (grains
smaller than one-tenth inch in diameter) and we find the voids
to be thirty-three and one-third per cent. To three cubic yards
of this gravel we will add one cubic yard of a one-to-three
mortar. The voids will be filled, but instead of having three
cubic yards of stone imbedded in one cubic yard of a one-to-
three mortar, we will in reality have a little less than that
amount of stone imbedded in a mortar composed of one part
of cement to about three and three-tenths parts sand.
316. Required Strength. — In the paragraphs just preced-
ing, an attempt has been made to indicate the general principles
to be applied in proportioning the materials in concrete. To
decide on the actual proportions of the ingredients to use for a
given purpose, one must have clearly in mind the strength that
will be demanded and any special condition to which the con-
crete is to be subjected. A reference to Art. 57 concerning the
strength of concrete, will be of service in deciding on the proper
proportions to use in a given case.
Art. 41. Mixing Concrete by Hand
317. Necessity of Thorough Mixing. — Too much stress can
hardly be laid upon the necessity of thoroughly mixing the
concrete if the best results are to be attained. It has already
been shown that thoroughness in mixing mortar is repaid by
greatly increased strength, and the result is even more marked
in the case of concrete. Every grain of sand should be coated
with cement, and every piece of stone should be covered with
mortar. In general, the cost of mixing is from one-tenth to
one-fifth of the total cost of the concrete in place. If by doub-
ling the cost of mixing we can increase its strength more than
one-tenth or one-fifth in these respective cases, or permit a
corresponding decrease in the amount of cement necessary for
a given result, the additional labor in mixing is justified.
318. Concrete may be mixed by hand or by machine. Opin-
ions vary as to the comparative merits of the two systems, but
as a machine properly installed usually furnishes much the
cheaper method of mixing, it is usually employed. The saving
by this method, however, will evidently depend upon the cost
of labor, the total amount of work to be done, and the degree
of concentration of the work, or facilities for distributing the
218 CEMENT AND CONCRETE
concrete. In certain sections where cheap labor is abundant,
the cost of hand mixing may be as low as machine mixing.
With proper supervision, hand mixing may be thorough, and
the chief argument against it, aside from its cost, is that such
hard work is likely to be slighted. The best forms of mixers
now on the market, however, give results quite equal to the best
hand work.
319. Method of Hand Mixing. — We will assume that the
materials have been brought within easy reach of the mixing
place. If the concrete is to be mixed near the point where it
is to be deposited, the mixing platform must be made portable.
Three platforms, each 8 by 14 feet, built of two-inch plank or
of two layers of one-inch boards, nailed to four 2x6 inch longi-
tudinal scantlings laid flat, will be suitable for such a case.
The platforms should be made without vertical sides, though if
desired a narrow piece of one-inch board may be laid flat around
the edges and nailed. A short piece of rope attached to each
corner of the platforms, or to the ends of the longitudinal scant-
lings, will be found convenient in moving them. These mixing
boards are placed side by side.
The sand, which may be delivered to the mixing platform
in wheelbarrows, is first dumped on the board and spread
evenly over the surface. If the sand is measured, the barrows
should be so arranged as to hold the required amount after
"striking" with a straight edge. This will make the measure-
ment independent of the judgment of the shoveler. If the sand
is delivered in cars, bottomless boxes of two or three barrels
capacity, according to the proportions used, will be found
more convenient for measuring than barrels. If the sand is
determined by weight, which as has been shown is the more
accurate method, the scales should be set at a weight which is
a factor of the total weight, and but little time will be required
to bring the scales to a balance for each barrow.
If it is possible, the batch should be of such a size as to
take either one or two full barrels, or a certain number of full
sacks of cement. This will obviate the necessity of measuring
or weighing the cement. The sand having been spread over the
surface of the mixing board, the cement is dumped upon it and
^read evenly over the sand. These ingredients are then mixed
<ky, the required amount of water is added at one time in the
MIXING BY HAND 219
center of a ring formed of the dry materials, and the whole is
thoroughly mixed as described under the head of mortar-making.
320. The mortar having been spread evenly over the board,
the broken stone is dumped upon it and evenly distributed
over the surface. Four shovelers then mix the concrete. Each
shoveler starts at a corner of the board and turns each shovel-
ful completely over, casting toward the end and spreading the
mortar a Uttle as he draws the shovel toward him. The two
shovelers at each end work toward each other, and meeting at
the axis of the platform, return to the side and repeat. When
the four shovelers meet at the center of the board, they turn the
mass again by casting toward the center in a similar manner.
If in mixing the concrete it is found that sufficient water has
not been used, more may be added from a rose nozzle, or sprink-
ling pot, previous to the last turning of the mass. The shovel
should always be used at right angles to either the side or the
end of the board, never diagonally; and it should always scrape
the mass clean from the board, never cut it at mid-depth. From
three to five turnings are required to thoroughly mix the concrete.
The mode of mixing has been thus minutely described, be-
cause if a gang of men are started properly they will soon be-
come expert, working in unison; whereas if each man is allowed
to mix according to his notion, confusion is sure to result. It
is sometimes preferred to spread the stone on a separate board
and cast the mortar upon it, but this necessitates one handling
of the mortar which does not appear to contribute much to the
incorporation of the ingredients.
While the shovelers are engaged in mixing the concrete on
one platform, the mortar mixers have proceeded to the next
platform to mix another batch of mortar, and the cement and
sand are being placed upon the third platform. Thus the work
proceeds in regular progression without delays. The shoveling
of concrete is hard work, and it will be found necessary not
only to pick good men for this duty, but to cull them until the
evolution results in the proper men for the work. An extra
compensation for men who perform satisfactory service in the
mixing of concrete will usually be repaid in the character and
quantity of the output.
321. With the method described above, a working gang
would consist of the following men under ordinary conditions : —
220 CEMENT AND CONCRETE
Measuring and supplying cement and sand 1
Mixing mortar 2
Delivering stone from bin, one man with horse and cart, or two
men with barrows 2
Shovellers to mix concrete and cast or wheel to place .... 4
Water boy 1
Spreading and tamping concrete 1
Total men required 11
If it is found impracticable to mix the concrete near the
place of deposition, it may be necessary to put on two or more
extra men to wheel the concrete to place. This gang of eleven
men may be doubled and still work on the same three platforms
when so desired.
With a moderate length of wheel for the materials and the
finished concrete, a gang of eleven picked men, working ac-
cording to system, will be able to make from twenty-five to
thirty cubic yards per day of ten hours, or about two and a
half yards per man. The double gang of twenty-two men may
not work to quite as good advantage, and will probably not
put in more than from forty to fifty cubic yards per day. It
would therefore be somewhat more economical to work two
gangs of eleven men each on separate sets of platforms, espe-
cially as in this way a rivalry is created. Lack of room, however,
will frequently preclude this arrangement.
322. Cost of Mixing by Hand. — The amount of concrete
stated above, two and a half yards per man, may be taken as
a maximum. With wages at $1.75 per day this would corre-
spond to a cost of about seventy cents per yard, exclusive of
the wages of a foreman. Numerous examples might be cited
where the mixing costs more. Colonel Mendell, in writing of
the fortifications at Fort Point, California,* states that a fore-
man .(at $4 per day) and twenty laborers (at $2 per day) made
forty-five cubic yards per day of eight hours, the cost of mixing
being thus about $1 per cubic yard. It is stated that "the
circumstances were exceptionally favorable."
As an instance where hand mixing was done at a very low
cost, the Lonesome Valley Viaduct ^ may be mentioned. At
• Jour. Assn. of Engr. Soc, March, 1895.
' Construction of Substructure for Lonesome Valley Viaduct, Gustave R.
Tuska, Trans. A. S. C. E., Vol. xxxiv, p. 247.
CONCRETE MIXERS 221
this point colored labor was used at a cost of $1 for eleven hours'
work. A gang of men, distributed as follows, would mix and
lay forty cubic yards of concrete per day : —
Filling sand barrows and handling water 1
Filling rock barrows 2
Mixing sand and cement 4
Mixing stone and mortar 4
Wheeling concrete 2
Spreading concrete in the molds 1
Tamping concrete in the molds 1
Foremen 1
Total l6
Fifteen men at $1 per day, and foreman at $2.50 per day,
makes a cost of $17.50 for forty yards of concrete, or at the
rate of forty-four cents a yard for mixing. Had the laborers
received $1.75 per day, however, the cost would have been 72
cents per yard.
323. In the construction of the Forbes Hill Reservoir and
standpipe at Quincy, Mass.,^ all concrete was mixed and placed
by hand. "The ordinary concrete gang was made up of a
sub-foreman, two men gaging materials, two" men mixing mor-
tar, three men turning the concrete, three men wheeling con-
crete, one man placing, and two men ramming. Two gangs
were ordinarily employed, placing about twenty cubic yards
per day each, or about 1.43 cubic yards per man. The con-
crete was turned at least three times before placing." With
labor at $1.75 per day, this would give the cost of mixing and
placing $1.22 per cubic yard. The actual cost of mixing and
placing varied from $0.97 to $1.53, according to the character
of the work.
Art. 42. Concrete Mixing Machines
324. General Classification. — Concrete mixing machines may
be divided into two general classes, batch mixers and continu-
ous mixers. In the former, sufficient materials are proportioned
to make a convenient sized batch for the mixer. They are then
charged into the machine at once, given a certain amount of
mixing, and then discharged at once. In the continuous mixers
• Described by C. M. Savilie, M. Am. Soc. C. E., Engineering News, Mar.
13, 1902.
222 CEMENT AND CONCRETE
the materials are dumped on a platform, and after being prop-
erly proportioned, are delivered gradually to the mixer, and if
fed uniformly, the concrete is discharged continuously by the
machine. In the latter method care must be taken to feed
the cement, sand and stone together and at a uniform rate.
If one man shovels cement, two men shovel sand and four men
handle the stone, and the cement man stops to fill his pipe,
there is likely to be a poor streak of concrete. It is therefore
desirable in feeding a continuous mixer to spread the measured
quantity of stone on the platform, and on top of this place the
weighed quantities of sand and cement. Then if each shoveler
gets his shovel blade under the whole mass, he will have some
of each ingredient.
325. There are many styles of concrete mixers of both classes
on the market. One of the oldest, as well as one of the best,
is the cubical box mixer which consists of a box four or five
feet on a side, supported by trunnions at opposite corners, and
made to revolve about this axis. A hinged door is provided
near one corner of the box by which the latter is charged and
emptied. The dry materials may be first charged and mixed
and the water added later, either through the door or through
a perforated pipe in the axis, or the water may be added with
the dry materials; after from ten to thirty revolutions of the
box, the mixed concrete is discharged into a skip or on a car,
to be conveyed to the place of deposition.
The great merit of this mixer is that the materials are thrown
back and forth from one side of the cube to another and a
thorough commingling results. The chief disadvantage is the
difference in elevation between the receiving hopper and point
of delivery, making it necessary to elevate the materials; one
other defect is that the batch is not in view while being mixed,
so that the amount of water cannot be regulated according to
slight variations that may occur in the moisture of the sand and
stone when charged.
326. To obviate this latter difficulty as well as to facilitate
to some extent the charging and dumping of the batch, a form
of box mixer is made in which the corners of the box in the axis
of revolution are truncated, and the trunnions are replaced by
collars which support the box, and through which the materials
may be fed and discharged. The collars are supported in a
CONCRETE MIXERS 223
tilting cradle which permits the dehvery end to be depressed
after the batch is mixed. This style of mixer with truncated
comers and tilting cradle is known as the Chicago Improved
Cube}
Mixers working on the same principle are sometimes made
in other forms than the cube. One of these is the cylindrical
mixer, which is made of boiler plate and may be four or five feet
in diameter and five or six feet long. This is rotated about a
diagonal axis. It is said to be more easily and cheaply made
than the cubical mixer, and dumps more quickly and cleanly,
while the cost of operation is about the same, and the mixing
is as satisfactorily done as in the cubical form.
327. The so-called " Dromedary Mixer " ' is a batch mixer
specially designed for use on street work. The mixing chamber
is a cylindrical steel drum with closed ends, mounted between
two wheels. It is hinged along an element of the cylinder so
that it opens into two halves like a clam shell bucket, to dis-
charge. A trap door is provided for filling. The cart is drawn
by a horse, and the chamber may be thrown in or out of gear
with the cart wheels. The cement and sand being first added
and the trap door closed, the horse draws the cart to the stone
pile. The stone and water are here added and the cart is drawn
to the work; the concrete, mixed on the way, is dumped by the
driver, who merely raises a lever which not only separates the
two halves of the mixer, but throws it out of gear so that it
stops revolving. The chamber may be thrown out of gear at
any time without dumping if desired.
328. The Ransome Concrete Mixer' "consists of a hollow
rotary dome, having upon the inner surface of its periphery
directing guides or flanges, and hinged shelves, by means of
which the materials are thrown together and perfectly com-
mingled. A discharge chute, or spout, is arranged to deliver the
material into the barrow or cart when properly mixed." The
mixer is also provided with an automatic device for proportion-
ing the materials, and a conveyor to carry them to the mixer.
Water is supplied to the mixer through a pipe with facilities
for regulating the supply.
' Municipal Engineering and Contracting Co., Railway Exch., Chicago, 111.
' Manufacture now discontinued.
' Ransome Concrete Machinery Co., 11 Broadway, N. Y.
224 CEMENT AND CONCRETE
329. The Smith Mixer * is a batch machine made of two
truncated cones placed base to base, and provided on the in-
terior with deflecting plates designed to throw the materials
from one end of the mixer to the other as the machine is re-
volved. At the junction of the two cones, on the outer cir-
cumference, is a spur gear by which the chamber is actuated.
The latter rests upon rollers in a swinging frame, so arranged
that the machine may be tilted for dumping while the drum is
revolving. In operating this mixer it has been found advanta-
geous to charge the broken stone or gravel first, and give one or
two revolutions before adding the cement and sand, as this cleans
the mortar from the corners. This form seems to be particularly
adapted for a portable machine. They may be had mounted
on trucks, with or without an engine, as desired.
330. The McKelvey Mixers^ are made in two styles, con-
tinuous and batch. Both styles are cylinders revolving on
friction rollers, and having, on the interior, deflecting blades
and a patent "gravity shovel" which lies against the rising
side of the drum and casts the materials downward when the
cyHnder has revolved far enough to overturn the blade. The
batch mixer has a shorter cylinder and can be discharged at
will. These mixers may be fed by shovels, or they may be
provided with a hopper into which the materials may be dumped
from carts or barrows. They discharge directly into wheel-
barrows. The mixer, and an engine and boiler to run it, are
mounted compactly on a truck, or the mixer is furnished on a
steel frame without an engine.
331. The pan mixer ^ consists of a large shallow pan into
which may be lowered a framework carrying a series of plovirs.
The materials are spread in the pan in layers, the plows are
lowered into it, and the pan is revolved about its vertical axis,
the plows remaining stationary. The plows are so arranged as
to move the materials radially toward and away from the cen-
ter of the pan. The water may be added from a rose nozzle.
For dumping, an opening is made in the bottom of the pan by
withdrawing a shde. Were the plows made to revolve in a
> Contractors' Supply Co., 232 Fifth Ave., Chicago.
* McKelvey Concrete Machinery Co., N. Y. Life Bldg., Chicago.
' Clyde Iron Works, Duluth, Minn.
CONCRETE MIXERS 225
stationary pan, the concrete would be more conveniently
dumped in a pile, or in a car, instead of being scattered about
under the pan.
332. The Cockbum,* a continuous mixer, is in the form of a
long box square in cross-section, surrounded at either end by
circular rings supported on friction rollers. By suitable gear-
ing the mixer is revolved about its longest axis, which has a
slight inclination toward the discharge end. The materials are
added through a hopper at one end, and fall from one side of
the box to the adjacent side as the machine revolves, working
gradually toward the delivery end, which is open. The water
is added through a pipe at about one-third of the length of the
box from the feed end. While this machine has no complicated
system of blades to become clogged, the mortar has a tendency
to stick in the corners of the mixer, making the interior cylin-
drical, and thus much less effective in mixing. Striking the
sides of the box with a heavy hammer will detach the mortar,
and this requires occasional attention.
333. A common form of continuous mixer consists of a screw
working in a cylinder. The materials are fed to the cylinder
near one end and are mixed while being gradually worked toward
the other end by the screw. The water is added through a
fixed perforated pipe at a point about one-third of the distance
from the feed end of the cylinder, and the mixed concrete falls
from the outlet at the other end. This style is frequently
made in a light form and mounted on wheels, and is then con-
venient in the laying of concrete for pavements.
A modification of the screw mixer consists of a semi-cylin-
drical trough, in which revolves a shaft carrying blades set at
right angles to the shaft and to each other. The trough is
sometimes given a slight incKnation to the horizontal, and the
blades are so shaped as to assist in working the materials toward
the delivery end.
334. The Drake Mixer ^ is of the general form just described.
One of the machines made by this company is a semi-cyHndrical
trough in which revolve in opposite directions two shafts, each
carrying some thirty blades. Most of the blades are straight,
Cockbum Barrow and Machine Co., Jersey City, X. J.
Drake Standard Machine Works, 298-302 W. Jackson Boul., Chicago.
226 CEMENT AND CONCRETE
but some of them are curved to work the material toward the
delivery end.
335. Gravity Mixer. — An appliance recently devised, which
is called a concrete mixer, consists of a steel trough provided
with staggered pins and deflecting plates. The trough is sup-
ported in an inclined position and has a hopper at its upper
end. Water is supplied through spray pipes at the side of the
trough. The materials, stone, sand and cement, are spread in
layers on the mixing platform, with the stone at the bottom.
The materials are then thrown into the hopper; they are mixed
as they descend through the pins, and the product is caught in
barrows or carts at the bottom.
336. In a very able article on concrete mixers,^ Mr. Clarence
Coleman, M. Am. Soc. C. E., makes an analytical discussion of
the relative efficiencies of the several forms. In this analysis
he gives the following weights to the several requirements for
a perfect mixer. That the entire mass of concrete shall be so
commingled that the cement shall be uniformly distributed
throughout the batch is given a weight of forty ; that the amount
of water shall be subject to control is given a weight of twenty-
five; perfect dry mixing and relative time of mixing, each ten;
and receiving materials, discharging concrete and self-cleaning,
are each given a weight of five.
The first three requirements, with a combined weight of
seventy-five, relate to the production of good concrete, while
the remaining requirements, with a combined weight of twenty-
five, pertain to economy in use. In short, the first requisite
is that a machine shall be capable of producing a perfect mix-
ture; then the machine that accomplishes this result at the
lowest cost per cubic yard is the best. The choice of a machine
will depend frequently on the character of the work to be done,
as some machines can only be used economically where large
quantities of concrete are to be used in a restricted area, while
others are particularly adapted for portable plants.
Art. 43. Concrete Mixing Plants and Cost of Machine
Mixing
337. Coosa River Improvement. — The concrete plant used
at Lock No. 31, Coosa River Improvement,* was erected in a
' Engineering News, Aiig. 27, 1903.
* Major F. A. Mahan, Corps of Engineers, U. S. A., in charge.
CONCRETE PLANTS 227
three-story shed. The top story served as a cement storage
room and two hoppers were arranged in the floor to receive
the cement for the mixers below. Level with the floor of the
second story were two other hoppers immediately below the
cement hoppers, to receive the sand and broken stone, while in
the first story or basement the mixers were suspended at a
height sufficient to allow concrete cars to pass under them.
The following description is from the report of the designer,
Mr. Charles Firth, U. S. Asst. Engineer: ^
"The cars used in handling the sand and broken stone are
of the side dump pattern and are brought into the charging
room on either side of the hoppers. The cement is drawn from
the cement room overhead in proper quantities, through verti-
cal chutes arranged somewhat on the principle of the old-
fashioned powder flask.
"The water is added to the materials as they enter the mix-
ers, and the quantity, which will probably be variable with
the temperature, is controlled by valves on the mixing floor,
the operators being governed by indicators, which show the
quantity used. The mixers are cubical boxes four feet on each
side, inside measurement, made of steel plate five-sixteenths of
an inch thick, with 2^ by 2^-inch angle irons. Each mixer is
provided with a door in one corner, twenty-two inches square,
fastened with a tempered steel spring catch, and held open
when required with a hinged screw bolt. The shaft which
revolves the mixers is three inches square. It is securely
fastened to them by trunnion castings at diagonally opposite
corners. The whole is driven by a 10 by 16 inch horizontal
engine, and thrown in and out of gear by ordinary friction
gearing with friction and brake levers.
"After a sufficient number of revolutions in the mixers, the
concrete is dumped into the concrete cars below, which are of
the center dump pattern."
The method given of measuring the cement is not recom-
mended, as the charge of cement, if not a full barrel, should
always be weighed. The three-story arrangement by which
the materials were handled almost entirely by gravity was
made possible by the high bank at the side of the lock pit.
' Annual Report, Chief of Engineers, U. S.A., 1894, p. 1292.
228 CEMENT AND CONCRETE
The total cost of the plant, exclusive of the boilers, is stated
to have been about $8,000, and the average output about two
hundred cubic yards of concrete per day of eight hours. The
cost of mixing, depositing and ramming 8,710 cubic yards of
concrete in the construction of lock walls was at the rate of
$0,884 per cubic yard.
338. Portland, Maine, Defenses. — In the construction of the
defenses at Portland, Maine,^ a five-foot cubical mixer was
used. Sand and stone were delivered, by bucket conveyors,
in bins directly over the mixer. "Immediately under these
bins were two measuring hoppers for stone and sand, respec-
tively, and an additional hopper for cement. From these meas-
uring hoppers the charge was dumped into the mixer and
thence, when mixed, into a car immediately under it. This car
delivered the mixed batch by means of a hoisting engine and
an inclined track to the site of the battery under a fifty-five
foot derrick, which placed it in the work at the point required.
Two barrels of cement, sixteen cubic feet of sand, and thirty-
two cubic feet of stone constituted a batch. * * * The usual
number of men engaged in the operation of mixing and placing
was as follows: — Two master laborers, three steam engineers,
two stokers and twenty-five laborers." It is said that 200
barrels of cement, or 100 batches, could be mixed and placed in
a day of eight hours. This would make the labor cost of this
portion of the work 50 or 60 cents per cubic yard. The cost
stated, however, varies greatly according to the amount of detail
in construction, and the lowest cost given for " labor of mixing
and placing" is $1.15 per cubic yard.
339. San Francisco Defenses. — A cubical mixer used in the
construction of the defenses at San Francisco ^ mixed 250 cubic
yards per day with seven men, engineer, fireman, and five men
to feed and dump mixer, at a labor cost of $14.67 per day, or
about six cents per cubic yard, exclusive of cost of transporta-
tion and ramming. The materials and concrete were handled
on cars run almost entirely by gravity.
340. Buffalo Breakwater. — In the construction of the Buf-
* Report of Charles P. Williams to Maj. Solomon W. Roessler, Corps of
Engrs., U. S. A., in charge. Report Chief of Engineers, 1900, p. 745.
- Maj. Charles E. L. B. Davis, Corps of Engineers, U. S. A., Report Chief of
Engrs., 1900, p. 980.
CONCRETE PLANTS
229
falo Breakwater/ the mixing plant, consisting of a cubical
mixer with necessary engines and boilers and two derricks, was
mounted on a dismantled lake schooner which could be placed
beside the section of the breakwater under construction. The
broken stone was delivered in a canal boat which could be tied
up alongside the schooner, and outside of the canal boat lay the
material scow. The latter was made from an old dump scow,
the decked pockets serving as bins for cement, sand and gravel.
Into a steel bucket on the scow were loaded, by wheelbarrows,
the following materials:
5.4 cu. ft. (H bbls.) cement.
10.8 cu. ft. sand.
5.4 cu. ft. gravel.
21.6 cu. ft. total.
Into a similar bucket on the canal boat 21.6 cubic feet of
broken stone were shoveled. As these buckets were filled, they
were hoisted by one of the derricks and dumped into the cubical
mixer. The latter discharged the mixed concrete into a skip
and a derrick deposited the concrete in place. The cost of labor
per cubic yard of concrete is as follows:
Items.
No.
Men.
Cost
PER
HouB.
Cu. Yds.
PEB
HOUB.
Cost of
Labob
PEB
Cu. Yd.
Loading material into buckets from scows
Mixing, including engine men and derrick
men
18
11
13
.^3.17^
2.35
2.65
18.2
18.2
18.2
$0,174
0.129
0.146
Placing, including foreman
Total labor
42
$8.17^
182
$0,449
The above does not include cost of fuel, nor of transporting
materials from the storehouses or yards to the site of the work.
341. Quebec Bridge. — The plant used in the construction
of the Quebec Cantilever Bridge ' consists of a No. 5 rotary
stone crusher, with a maximum capacity of thirty cubic yards
per hour, discharging into a bucket conveyor which delivered
the crushed stone in a small storage bin directly over the con-
crete mixer. The latter was of the cubical form, five feet on ^
side, with a capacity of two cubic yards of concrete per batch.
' Emile Low, U. S. Aast. Engr., Engineering News, Oct. 8, 1903.
' Engineering News, Jan. 29, 1903.
230 CEMENT AND CONCRETE
The cement warehouse and the sand supply were near the
mixer. Cement and sand were hoisted to the top of the ma-
chine in boxes, with bottoms incHned at forty-five degrees,
each holding a batch, and dumped into the charging hopper of
the mixer as required. The mixer was elevated sufficiently to
permit dumping the concrete directly in a skip on a car, the
latter being run to the work. The skip was handled by guy
derricks. This plant made the remarkable record of two hun-
dred eighty-five batches in ten hours, and on one occasion
turned out one hundred fifty batches in five hours, or, if all
were two-yard batches, at the rate of sixty yards per hour.
342. Galveston. — For the construction of the Galveston sea
wall two concrete mixing and handling machines were designed,^
each consisting of a double-deck car, on eight wheels, with two
revolving derricks, one on either side for handling materials
and concrete, respectively. The materials are delivered on
tracks beside the mixer car track which is parallel to the sea
wall. One derrick hoists the loaded skips from the material
cars and deposits them on the upper deck of the mixer car,
whence they are delivered in measured quantities to the Smith
Rotary Mixer located on the lower deck. When mixed, the
concrete is dumped into a skip, which is handled by the second
derrick and dumped into the forms.
343. For work having similar requirements to that just
described, namely, for retaining walls on track elevation, Chicago
& Western Indiana R. R. at Chicago, the problem was met in
a somewhat different manner.^ An ordinary flat car was double
decked and the space between decks inclosed to protect the
machinery, including the Drake Concrete Mixer. Cars contain-
ing cement, sand and stone were coupled in the rear of the mixer
car. These material cars were fitted with removable wheeling
platforms, making a complete runway along the sides of the
cars. The materials were delivered at the mixer car in wheel-
barrows and (lumped into measuring boxes, and thence fed to
the mixer. The concrete was delivered on a belt conveyor
mounted on a boom with turntable permitting nearly half of a
revolution. The outer end of the conveyor could be raised or
lowered as desired, and the concrete was thus deposited where
' Engineering News, Jan. 15, 1903.
' Ibid., Feb. 28. 1901.
COST OF CONCRETE
231
needed in the work. To permit the mixer train to move along
the track, the two ends of a cable were made fast to anchorages
placed about a thousand feet apart, one in front of, and the
other behind, the train. As this cable had about eight turns
around a winding drum on the mixer car, the train could be
propelled forward or backward at will.
A somewhat similar form has been used for street work,
where the mixer and electric motor are mounted on a truck
with a swinging conveyor for the delivery of concrete anywhere
between the curbs. A pair of wheels in the rear serve to carry
an inclined runway for wheelbarrows by which the materials
are delivered to the mixer.
344. The data for the following items concerning the cost of
mixing concrete for culverts on railroad work are taken from
an article in Engineering News}
"The plant is located on a hillside with the crusher bins
above the loading floor or platform that extends over the top
of the mixer, so that crushed stone can be drawn directly from
the chutes of the bins and wheeled to the mixer. The sand is
hauled up an incline in one-horse carts and dumped on the
floor, and is also wheeled in barrows to the mixer." The capa-
city of the cubical mixer used was seven-eighths cubic yard. The
cost of mixing and placing was as follows:
lTEM!<
Cost
PBB
Day.
Cost
PER
Cu.Yu,
One foreman assumed at §2.50 per day .
Three men supplying mixer at SI. 50 per day
One engineman assumed at S2.00 per day .
Fuel and supplies assumed ac ....
.§2.50
450
2.00
200
Cost of mixing 40 cu. yds.
§11.00
§0.275
Two men loading wheelbarrows at §1.60
Four men wheeling wheelbarrows at §1.50
$3.00
6.00
Cost of wheeling 40 cu. yds. 100 feet
Four men ramming at §1.50
Four men wheeling in and bedding large stone in concrete at
$1.50
$9.00
§6.00
6.00
0.225
0.150
0.150
Total cost mixing and placing
§0.800
' Location and Construction of the Ohio Residency, Pittsburg, Carnegie
& Western R.R., Engineering News, May 21, 1903.
232 CEMENT AND CONCRETE
It is not explained why six men are required to load and
wheel forty cubic yards one hundred feet in ten hours, but it
may be that these men assisted in other operations.
Another contractor on the same work used a different form
of mixer with much lower loading platform and handled the
mixed concrete with skips and derrick. The cost is estimated
as follows:
1 man feeding mixer $1.50
1 engineman assumed at 2.50
1 derrick man assumed at 2.50
2 tagmen swinging boom and dumping 3.00
6 barrowmen supplying mixer 9.00
2 men tamping 3.00
Fuel, supplies, etc • 1.50
Cost of mixing and placing 50 cu. yds. . . $23.00
Cost per cu. yd., 46 cents.
Art. 44. Cost of Concrete
345. Quantities of Ingredients in a Cubic Yard.— As
has already been indicated, the rational method of proportion-
ing concrete is to use just sufficient mortar to fill the voids in
the stone, or possibly a very small excess to allow for imperfect
mixing; and in ordinary practice this rule should not be de-
parted from unless it be for some special reason. When so pro-
portioned, a cubic yard of concrete will contain approximately
a cubic yard of stone, depending on the method of measure-
ment. If we know the percentage of voids in the broken stone
or gravel, and consequently the percentage of mortar which
should be found in a cubic yard of the finished concrete, we
may readily obtain the approximate cost per cubic yard of the
latter for a given quality of mortar and given unit prices.
Thus, suppose we have stone in which the voids are such
that the mortar will amount to forty per cent, of the finished
concrete, and we wish to have the mortar composed of three
volumes of loose sand to one volume packed natural cement,
unit prices being as follows:
Cement, $1.25 per barrel of 300 pounds net, 3.75 cubic feet.
Sand, $1.00 per cubic yard.
Stone, $1.75 per cubic yard.
As in § 290, we find the ingredients in one cubic yard of
COST OF CONCRETE 233
mortar to cost $3.33. Since forty per cent, of the concrete is
to be composed of mortar, the mortar in one cubic yard of
concrete will cost forty per cent, of $3.33, or $1.33, and one
yard of stone at $1.75 will make the total cost of the materials
in the concrete $3.08 per cubic yard.
The diagram herewith may be used to get the approximate
cost of the concrete after having obtained the cost of the mortar
as before. Thus, if we enter the diagram with the cost of mor-
tar $3.33, and follow it to the diagonal line marked forty per
cent., we find this is on the ordinate $2.33, the cost of the in-
gredients in one cubic yard of concrete when the stone costs
one dollar per cubic yard. Hence, $2.33 plus $0.75 equals
$3.08, the approximate cost of the materials in a cubic yard of
the concrete as desired.
346. The usual method, however, of stating proportions in
concrete is to give the volumes of sand and stone to one volume
of cement. Thus, one of cement, three of sand and six of stone
would usually mean one volume of packed cement, three vol-
umes of loose sand and six volumes of loose broken stone. To
arrive at the cost of concrete when proportions are thus ar-
bitrarily stated, involves a greater amount of work. From the
tables already given (Art. 36), we can determine the amount of
mortar which a given quantity of dry ingredients will make,
and the consequent cost of the mortar per cubic yard. Then a
knowledge of the voids in the broken stone will permit of a
close estimate of the amount of concrete made, whence we can
determine the cost of the latter.
For example, suppose it is desired to determine the cost of
the materials in a cubic yard of natural cement concrete under
the following conditions:
1 bbl. cement containing 280 pounds net, at $1.00 per bbl,
3 bbls. sand weighing 100 pounds per cu. ft., at $.75 per cu. yd.
6 bbls. loose broken stone, having 45 per cent, voids, at $1.25 per cu. yd.
1 bbl. cement = 3.75 cu. ft. = .139 cu. yd., cost $1,000
3 bbls. sand = 11.25 cu. ft. = .417 cu. yd., cost .313
6 bbls. stone = 22.50 cu. ft. = .833 cu. yd., cost 1.041
Total cost $2,354
From Table 61, § 286, we find that it requires 2.03 barrels of
cement to make one cubic yard of one-to-three mortar, when
234
CEMENT AND CONCRETE
CONCRETE MAKING
Cost of Concrete, Dollars per Cu. Td.
Stone Assumed to Cost $1.00 per Cu. Yd.
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EXAMPLES OF COST 235
proportions are stated as above; then one barrel of cement
would make ^-^ = .493 cu. yd. As forty-five per cent, of the
stone is voids, the amount of solid stone in six barrels would
be — x=-^ — X .55 = .458 cu. yd. Then the mortar plus solid
stone would be .493 + .458 = .951 cu. yd. It has been found
by experiment that the amount of concrete will exceed the sum
of the mortar and solid stone by from two to five per cent.;
hence we may assume in this case that the amount of concrete
made with the above materials would be .95 + .03 = .98 cu.
yd., and 2.354 -r- .98 = $2.40, the cost of materials in one cubic
yard of finished concrete. To obtain the actual cost of con-
crete in place, the cost of mixing and deposition must be added
(see Arts. 41 and 43). When the volume of mortar used is not
greater than the voids in the loose stone, then the amount of
rammed concrete made may be less than the volume of loose
broken stone.
347. EXAMPLES OF ACTUAL COST OF CONCRETE. — The fol-
lowing data are given concerning the cost of concrete on several
works where sufficient details have been pubUshed to be of
value.
Defenses Stolen Island} Cubical box mixer ; proportions by vol-
ume, 1 cement, 3 sand, 5 broken stone; 5,609 cu. yds. of concrete.
Items.
Cost peb Cu. Yd.
concbete in
Place.
Cement, Portland, at §1.98 per bbl
Broken trap rock
$2,546
1.041
0.225
0.149
0.879
0.477
0.190
Sand drawn from beach
Receiving and storing ma,terial8
Mixing, placing and ramming
Forms, lumber and labor .
Superintendence and miscellaneous ....
Total cost per cu. yd
$5,507
It is stated that hand mixing for a portion of the concrete
used in another emplacement cost fifty-six cents more per
cubic yard than machine mixing.
' Major M. B. Adams in charge. Report Chief of Engineers, U.S.A.,
1900, p. 837.
236 CEMENT AND CONCRETE
348. Defenses Tampa Bay, Florida} — Cockburn-Barrow
mixer, with cableway for placing concrete. Shell concrete
made up of 1 cement, 3^ sand and 5^ shell.
1.31 bbls. cement, at $2.42 per bbl $3.17
.71 cu. yd. sand, at 21 cents per cu. yd .15
1.08 cu. yd. shell, at 50 cents per cu. yd 5.4
$3.86
Labor mixing ' $0.28
Labor placing and tamping .33
Labor on forms .155 .765
Total cost per cubic yard $4,625
The above does not appear to include costs of running ma-
chinery, fuel, repairs, and depreciation of plant.
At the same battery ^ in the following year the cost of broken
stone and shell concrete was as follows:
.9 bbl. cement at $2.46 (including $0.59 per bbl.
storage) $2,214
.28 cu. yd. shell, at $0.45 per cu. yd 128
.47 " sand, at 0.12 " " 056
.80 " stone, at 2.95 " " 2.360
Total materials $4,758
Mixing and placing $0,623
Forms 370
Total .993
Total cost per cubic yard $5,751
349. Defenses San Francisco, Cal? — Cubical mixer; ma-
terials drawn from bins into measuring cars, hoisted by elevator
and dumped into hopper of mixer. Mixer given twelve to four-
teen turns and concrete dumped into cars, pushed by hand out
on trestles, and dumped in place. Average capacity plant, 280
cubic yards per day of eight hours. Itemized cost of 8,328
cubic yards of concrete in place was as follows:
' Report Lieut. Robert P. Johnson, Corps of Engineers, U. S. A., Report
Chief of Engineers, 1899, p. 906.
' Report Lieut. Frank C. Boggs, Corps of Engineers, U. S. A., Report
Chief of Engineers, 1900, p. 931.
^ Maj. Charles E. L. B. Davis, Corps of Engineers, in charge. Report
Chief of Engineers, 1900, p. 980.
EXAMPLES OF COST 237
.758 bbl. Portland cement, at $3.03 per bbl . . . $2,298
.887 cu. yd. rock, at $1.80 per cu. yd 1.597
.41 cu. yd. sand, at 0.73 per cu. yd .299
Water .016
Cost of materials $4,210
Concrete plant, erection per cu. yd. concrete . . $0,269
Concrete plant, running expenses per cu. yd. . . .022
Concrete plant, taking down .020
Cost for plant, exclusive of purchase
price .311
Forms — materials $0,272
Forms — labor in erecting .346
Forms — labor taking down .079
Cost forms .697
Labor mixing, placing and ramming .626
Total cost per cubic yard $5,844
350. In the building of a concrete dam for the enlargement
of the head of the Louisville and Portland Canal/ comparison
of cost of hand and machine mixing is given by Asst. Engr. J.
H. Casey.
1.63 bbls. natural cement, at $0,635 per bbl. . . $1,034
2 volumes sand, .47 cu. yd., at .87 per cu. yd. . . .408
5 volumes broken stone, .89, cu. yd. at $.84 . . .756
Cost of testing cement .081
Forms, material for .107
Forms, labor making and setting up .168
Cost materials and forms $2,554
Hand mixed concrete:
Cost of mixing . .' $1,917
Cost of placing and tamping .791
Cost of mixing and placing $2,708
Total cost hand mixed concrete per cu.
yd. in place $5,262
Machine mixed concrete:
Charging and running mixer $0,864
Placing and tamping .585
Cost mixing and placing $1,449
Total cost machine mixed concrete per
cu. yd. in place $4,003
Difference in favor machine mixing $1.26
' Capt. George A. Zinn, Corps of Engineers, U. S. A., in charge. Report
Chief of Engineers, 1900, p. 3467.
238
CEMENT AND CONCRETE
Since the above concrete was placed in large masses, the
costs of labor are considered high, and it is probable the work
was done with exceptional care.
351. In the construction of the lock at the Cascades CanaP
the concrete plant was so arranged that the materials did not
have to be elevated, but much of the work of transportation
was done by gravity. The mixing of about eighteen hundred
yards by hand permits a comparison to be made with machine
mixing by which method about seven thousand eight hundred
yards were made. The costs were as follows:
Items.
,805 bbl. Portland cement at
$4.08
.450 cu. yd. sand at .f 1.04 . .
.579 cu. yd. gravel at §1.04 . .
.317 cu. yd. broken stone at
$1.70
Cost materials in concrete .
Timbering
Testing cement and general
repairs .
Forms and tests
Mixing, labor
" repairs and fuel . . ,
Total cost mixing
Placing, labor
" fuel, tramways, etc.
Total cost placing ....
Total cost concrete per cu. yd.
Cost peu Cu. Xu. of Concuete.
Hand Mixed and
Placed by Derrick.
Amopnts. Total
$.3.29
.47
.60
.54
.15
.22
1.07
.02
.60
.19
.$4.00
..37
1.09
.79
$7.1")
Machine Mixed and
Placed by Chute.
Amounts.
$3.29
.47
60
54
15
Total.
$4.90
.37
.43
.46
$6.16
352. In the construction of the retaining walls for the
Chicago Drainage Canal,* a special plant was designed for the
work on account of the large quantities of concrete required,
and this, combined with the low cost of materials and the char-
acter of the work, resulted in a very low cost concrete. On
' Maj. Thomas H. Handbury, Corps of Engineers, U. S .A., in charge.
Report Lieut. Edward Burr, Report Chief of Engineers, 1891, Vol. v. Ab-
stracted, Engineering News, June 2, 1892.
* " Construction of Retaining Walls for the Sanitary District of Chicago,"
by Mr. James W. Beardsley, and discussion by Mr. Charles L. Harrison.
Jour. W. Soc. Engrs., Dec, 1898.
EXAMPLES OF COST 239
Section 14 the stone was selected from the spoil banks along the
canal and could usually be obtained within one hundred feet.
This stone, which was delivered to the crusher by wheelbarrows,
required some sledging to reduce it to crusher size. An Austin
jaw crusher was mounted on a flat car with the Sooysmith
mixer. "The cement, sand and stone were raised from their
respective bins by means of belt conveyors running at the
same rate of speed, but carrying buckets spaced proportional to
the required ingredients." "The cost of a second hand plant
used on this section was estimated at $9,600, including two
crushers and two mixers at $1,500 for each machine. Common
labor cost $1.50 per day; firemen, enginemen, and carpenters
from $2.00 to $3.00 per day. The itemized cost is as follows:
Itkms.
Cost, Cents
pkbCd.Yd.
General, including superintendent, blacksmith, water boys, etc.
Quarrying, i. e., delivering stone to crusher
Crushing
Transportation, delivering sand and cement to mixer by teams
Forms, exclusive of lumber
Mixing
Placing and tamping
Total
Cost of plant (no salvage allowance)
Cost of cement and sand
Total cost concrete per cubic yard
7.8
30.3
7.3
14.2
16.0
12.1
10.8
97.5
40.7
168.3
$3,015
The amount of concrete used on this section was 23,568 cu. yds.
353. On Section 15 of the same work the conditions were
somewhat different. The stone had to be quarried within about
a thousand feet of the crusher. The stone, after being broken
to crusher size, was delivered on the tipping platform of the
No. 7 Gates crusher in cars drawn by a cable hoist. "The
average output of the crusher for a day of ten hours was about
210 cubic yards." The materials were transported to the
mixer in four and one-half yard dump cars drawn by a light
locomotive. The mixer was of the spiral screw type and de-
posited the materials on a rubber belt conveyor. The mixer
and operating machinery were mounted on a car which pro-
pelled itself by means of rope and winch. The plant for this
section was new and estimated to cost $25,420, including $12,000
for one crusher.
240 CEMENT AND CONCRETE
The detailed cost is as follows:
Items.
General, including superintendent, blacksmith, teams, etc.
Quarrying (exclusive of 8.3 cents for explosives)
Crushing
Transportation, delivering cement, sand and stone on a
platform beside the mixer
Forms, exclusive of timber
Mixing, including shoveling materials from platform to
mixer
Placing and tamping
Total
Cost of plant (no salvage allowance)
Powder for quarrying ....
Cement and sand
Total cost concrete per cu. yd $3,227
Cost
PKB Cu. Yd. of
Concrete,
Cents.
8.2
19.2
12.8
8.1
14.2
25.0
11.6
99.1
56.7
8.3
158.6
The amount of concrete used on this section was 44,811
cubic yards.
CHAPTER XV
THE TENSILE AND ADHESIVE STRENGTH OF CEMENT
MORTARS AND THE EFFECT OF VARIATIONS
IN TREATMENT
Art. 45. The Tensile Strength of Mortars of Various
Compositions and Ages
354. The Proportion of Sand. — The rate of change in
the strength of mortars as the proportion of sand is increased
varies greatly for different cements. The fineness and chemical
composition of the cement, and the quaUty of the sand, are the
most important factors influencing this rate of change upon
which the question of the relative economies of different mor-
tars is so largely dependent.
Table 67 gives the results of tests with two brands of Port-
land cement mixed with from two to ten parts of river sand,
the age of briquets being six months and two years. It is of
interest to notice that the strengths of the mixtures are ap-
proximately in the inverse ratio of the number of parts of sand
used. Thus the strength with six parts sand is approximately
two-sixths of the strength with two parts, while with ten parts
sand, the strength is nearly two-tenths of that with mortar
containing two parts.
TABLE 67
Rate of Decrease in Strength with Addition of Sand
Portland Cement; River Sand, " Point aux Pins "
Parts Sand
TO 1
Cement by
Weight.
Tensile Stsenoth, lbs. per Sq. In.
Proportionate
Strength,
Two Years, if
1 to 2= 100.
6 Months.
2 Tears.
H
R
H
B
Mean.
2
3
4.09
6
8
10
512
390
295
175
113
64
504
335
261
144
96
74
534
363
296
191
132
104
648
355
288
174
132
116
641
359
292
182
132
110
100
66
54
35
24
20
241
242
CEMENT AND CONCRETE
355. In Table 68 similar results are given for two samples
of Portland cement and two kinds of sand, neat cement speci-
mens being included in the comparison. The one-to-one mor-
tars give a higher strength than neat cement, and even the-
mortar containing two parts of the limestone screenings ia
stronger than the neat specimens. From the one-to-one mor-
tars the strengths decrease rapidly as more sand is added, until
five parts sand are used, but the strengths then decrease less
rapidly as larger additions of sand are made.
TABLE 68
Rate of Decrease in Strength -with Addition of Sand
Portland Cement, Brand R; Sand, Crushed Quartz and Limestone
Screenings
Parts Sand
TO 1
Cement by
Weight.
Tensile Strength, Pounds
I'ER Sq. In.
Proportionate
Strength if Strength
1 TO 1 Mortar = 100.
Sample
Cement H H,
Crushed Quartz
Sand, 20-30.
Age Briquets,
6J Months.
Sample
Cement II,
Limestone
Screenings, 20-30.
Age Briquets,
6 Months.
Crushed
Quartz.
Limestone
Screenings.
0
689
686
82
78
1
840
881
100
100
2
521
703
62
80
3
368
508
44
58
4
236
336
28
38
6
203
267
24
30
6
156
178
19
20
8
104
138
12
15
10
78
98
9
11
356. In Table 69 two samples of natural cement are treated
in a similar manner, from one to eight parts river sand being
used in the mortars. With Sample II the strength is dimin-
ished rapidly until five parts sand have been added, but with
further additions of sand, the strength is decreased more slowly.
Sample 18 S gives quite a different curve, as the one-to-two
mortar is stronger, and the one-to-three mortar is but little
weaker than the one-to-one. With four parts sand the mortar
shows a marked falling off in strength, but further additions of
sand diminish the strength more slowly.
357. Increase in Tensile Strength with Time. — In
Table 70 are given the results obtained in tests of tensile strength
STRENGTH OF MORTARS
243
TABLE 69
Rate of Decrease in Strength w^ith Addition of Sand. Natural
Cement, Brand On ; River Sand, " Point auz Pins "
Parts
Sand to 1
Ckmext
BY Weight.
Tensilb Stbength, Pounds per Squabb Inch.
Age.
6 Months.
2 Yeabs.
Proportionate
Strength, Two
Years if 1 to 2
=^100.
Sample
Ceiiieut
II.
18 S.
18 S.
0
1
2
3
4
5
6
7
8
380
297
260
183
128
81
69
56
53
308
314
280
193
161
142
119
101
'280
324
294
187
165
172
156
114
86
100
91
58
51
53
48
35
with twelve samples of Portland cement, illustrating the rates
of .increase in strength from seven days to three years. It is
seen that rich mortars gain strength rapidly, neat and one-to-
one mortars showing usually eighty to ninety per cent, of their
ultimate strength in twenty-eight days. Mortars containing
not more than four parts sand to one cement give practically
their ultimate strength at six months. It is also of interest to
notice that the variations in strength among the several sam-
ples are not very great. The lowest strength at the end of
two to three years is seventy-five to eighty per cent, of the
highest.
358. In the case of natural cements, results for ten brands
of which are given in Table 71, only fifty to seventy per cent,
of the ultimate strength is gained in the first twenty-eight
days; with mortars containing three parts sand to one cement
the average result at twenty-eight days is less than forty per
cent, of the strength at two years. Most of the samples gain
some strength after six months, but two samples fail at two
years which had given a fair result at six months. The varia-
tions in strength among the several samples are very much
greater than with Portland cements; even omitting the two
samples that failed, the strength of the highest is two or three
times the strength of the weakest sample at two years.
244
CEMENT AND CONCRETE
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246
CEMENT AND CONCRETE
359. Table 72 shows in some detail the rate of increase in
strength of a sample of natural cement when the specimens
are maintained in air and in water. This table has several
points of interest. When hardened in water, the cement gained
steadily in strength up to six months, when it began to fall
off, and at two years this cement failed, as is shown in Table
71. The neat cement specimens hardened in air are very
irregular, as usual. These specimens showed high strength at
three months, suffered a marked falling off at six months and
one year, but showed a remarkable strength, equal to neat
Portland cement, at two years. The strength developed at
one year by specimens of this sample containing two parts
sand to one cement and hardened in air, is also equal to that
shown by similar mortars of Portland cement.
TABLE 72
Rate of Increase in Strength in "Water and Air
Age of Briquets.
Tensile Stbexgth, Pounds peh Squabe Inch.
Neat Cement.
Mortar Two Parts Saxb
UY Weight to Oxe
Cement.
Water.
Air.
Water.
Air.
1 day . . . . . .
7 days
14 days
28 days
3 mos
6 mos
1 year
2 years
81
192
232
306
390
437
432
395
152
254
316
473
551
372
314
731
135
142
232
367
409
249
271
459
475
537
All cement, Brand Hn, Sample 26 S, which fails in water after two years,
see Table 71.
Art. 46. Consistency of Mortar and Aeration of Cement
360. EFFECT OF Consistency of Mortar on Tensile
STRENGTH. — The results in Table 73 are from briquets of
Portland cement with two parts "Standard" crushed quartz.
The consistency of the mortars varied from a "trifle dry," in
which water rose to the surface only after continued tamping,
to a wet mortar which would just hold its shape when placed
in a heap on the slab. Half of the briquets were immersed,
CONSISTENCY OF MORTAR
247
while the remainder were stored in the air of the laboratory.
The air hardened specimens gave higher results in all cases
than those hardened in water. The highest strength was given
in general by the dryest mortar, but the differences in strength
decrease as the age of the specimen increases.
TABLE 73
Effect of Consistency on the Strength of Portland Cement Mortar
Hardened in Water and Air
Age of Briquets.
Tensile Strength, Pounds per Square Inch.
Consistency of Mortar.
Briquets Hardenetl in Fresh
Water.
Briquets Hardened in Air
of Laboratory.
a
b
c
d
e
a b
c
d
e
7 days . . .
28 days . . ,
3 months . .
340
383
515
310
378
53o
226
314
514
191
291
429
158
249
411
407
606
665
341
463
593
263
345
638
230
393
697
202
302
451
Cement: Brand R, Sample 18 R, with two parts "Standard" sand.
Consistency: a, trifle dry; b, O.K.; c, moist; d, very moist; e, would just
hold shape.
361. Tables 74 and 75 give similar results for Portland and
natural cement mortars, respectively, all specimens having
hardened in water for three months. The amount of water
used in gaging had a wide range, giving mortars of all consis-
tencies from very dry to very moist. The richness of the mor-
tar was also varied, from neat cement to five parts sand. A
comparison of the results in these two tables indicates that the
highest strength is usually given by mortars a trifle dryer than
that considered right for briquets; that an excess of water is
less deleterious to rich mortars than to lean ones, and to Port-
land cement than to natural cement.
362. Conclusions. — Although all of these tests indicate the
superiority of dry mortars, in considering the effect of consis-
tency from a practical standpoint, one must not fail to consider
the difference between the conditions existing in the actual use
of mortars and in laboratory tests. When mortar is used in
248
CEMENT AND CONCRETE
TABLE 74
Variations in Consistency of Mortar
Effect os Strength of Portland Mortab at Three Months
Parts Sand to
1 Ckment
BY Weight.
Tensile Strength, Pounds per Square Inch, for
Consistency Number.
1
2
3
4
6
6
7
8
9
0
1
2
3
5
608
513
635
543
289
208
763
618
429
744
588
322
230
708
594
447
329
201
707
613
398
'310
189
729
566
393
C85
566
382
279
167
538*
Consistency —
Significance of numbers :
Increasing per cent, water
used for higher numbers.
1 — Very dry ; little or no moisture appeared on
surface of briquets.
5 — About proper consistency for briquets.
9 — Very moist ; mortar would barely hold shape
and shrank in molds in hardening.
TABLE 75
Variations in Consistency of Mortar
Effect on Strength of Natural Cement Mortar at Three Months
Parts Sand to
1 Cement
BY Weight.
Tensile Strength, Pounds per Square Inch kor
Consistency Number.
1
2
3
4
5
6
7
8
9
0
1
2
3
5
372
312
255
217
150
373
314
283
208
155
277'
206
125
305
286
258
183
101
281'
242
268
241
204
139
74
263
207
176
239
Consistency — Significance of numbers:
1 — Very dry ; little or no moisture appeared on surface briquets.
5 — About proper consistency for briquets.
9 — Very moist ; mortar would barely hold shape and shrank in
hardening.
masonry, the stones or bricks, even though they be dipped,
or sprayed with a hose before setting, are very likely to press
out or absorb considerable moisture from the mortar. To
realize this one has only to raise a heavy stone just after it has
been bedded; and the greater ease of setting either stone or
AERATION OF CEMENT
249
brick, and obtaining a full mortar bed, with a rather wet mor-
tar, is appreciated by all masons. In the laying of concrete,
the difficulties of obtaining a compact mass with a dry mortar are
also not to be overlooked, but this point is discussed elsewhere.
363. Effect of Aeration on the Tensile Strength of Cement. —
Portland cements that are not perfect in composition and
burning, and that therefore contain free lime, may sometimes
be rendered sound by exposing them to air, and such exposure
was at one time considered almost essential in Portland cement
manufacture.
Fresh Portland cements that are slightly defective may have
their properties quite radically changed by such treatment;
their rate of setting becoming first more rapid, and then, by
further aeration, slower, and their tendency to expand over-
come or ameliorated. Portland cements that are perfectly
sound suffer some loss in specific gravity by the absorption of
carbonic acid and water from the atmosphere, but moderate
aeration has no radical effect upon their strength, and Port-
lands deteriorate but very slowly by storage, provided the
cement is kept dry and does not cake in the package.
Natural cements, however, usually suffer by aeration, and
this is illustrated by tests on several samples of one brand
given in Tables 76 and 77. Of the four samples in Table 76,
TABLE 76
Effect of Aeration on Four Samples of Same Brand Natural Cement
Tensile Strength, Pounds per Square Inch. [
Number
Weeks
Cement
Age of Briquets, 6 Months to 7 Months.
Age Briquets, 2 Years.
A:erated.
Sample QQ
ss
- NN
00
NN
00
0
242
183
343
340
316
306
2
2:37
269
357
506
368
432
5 .
256
403
.
7
268
368
...
10
226
212
246
284
11
313
'279
. .
.
13
213
218
'260
258
Cement: Brand Gn; Sand, two parts crushed quartz to one cement.
All briquets of one sample were made by one molder and same percentage
water used.
250
CEMENT AND CONCRETE
NN and 00 showed an improvement by two weeks' exposure
to air, spread out in a thin layer, but longer exposure resulted
in a serious loss of strength. Of the other two samples, SS was
greatly improved by five weeks' aeration, but longer exposure
was detrimental, while sample QQ showed a continuous im-
provement up to the limit of eleven weeks' exposure to air.
In Table 77 the effect of aeration on five samples of the same
brand is shown. One of these samples was overburned and
was rendered practically worthless by fourteen weeks' exposure
to air. Nearly all of the samples in this table were seriously
affected by six weeks' aeration.
TABLE 77
Natural Cement. Effect of Aeration
Cement.
Pabts
Sand
TO 1
Ce-
ment.
Age of
Bbi-
qcets.
Tensile Strength, Pounds
PER Square Inch, Cement
Aerated.
a
b
Specific
Qeavitv of
Fresh
Cement.
Brand.
Sam-
ple.
4 to 6
days.
11 to 12
days.
45 to 61
days.
99
days.
Gn
(I
84
83
82
U'
0'
2
6 inc.
14
11
414
463
445
383
263
321
392
350
354
293
208
211
217
273
277
216
235
266
274
52
80.6
85.9
85.6
87.8
89.7
54
41
34
23
97
3.01
3.11
3.09
2.95
3.14
a — Fineness expressed as per cent, passing holes .0046 inch square.
b — Time setting fresh cement, time to bear ^V inch \ lb. wire.
Art. 47. Regaging Cement Mortar
364. The Effect of Thorough Gaging. — The value of thor-
ough gaging is a point frequently overlooked in the preparation
of mortars and concretes. Table 78 gives a few of the results
obtained in experiments to determine the effect of thorough
work in mixing. The tests are made with two brands of natural
and one of Portland, with two parts sand to one cement by
weight. The two minutes' mixing with hoe and box method
gave a more thorough gaging than could have been accom-
plished in the same time with a trowel, and represented
about the amount of work put on mortars for testing. We are
not, therefore, comparing well mixed and poorly mixed mortars,
but rather well gaged and better gaged. The effect of the
additional work is shown in all cases; to double the time spent
REGAGING MORTAR
251
in gaging, increases the strength of the resulting mortar about
five per cent., while to quadruple the time adds twenty-six
per cent, to the strength.
TABLE 78
Effect of Thorough Gaging
Ref.
Cement.
Sand, Two Parts
TO One Cement.
Tensile Stkenoth, Lbs.
PKK Sq. In., fob Moktab
Oaoed,
Kind.
Brand.
Kind of Sand.
2Min.
4Min.
8Min.
1
2
3
4
Natural
n .
Portland
Gn
An
R
( Pt. aux Pins )
I Pass #10 Sieve J
Standard
) Pt. aux Pins )
1 Pass #10 Sieve J
i Pt. aux Pins i
\ Pass #10 Sieve J
352
418
525
356
469
376
564
482
572
421
616
Meai
1
416
100
436
105
523
126
Prop
ortional , : .
365. . REGAGING. — When mpre mortar is mixed at one
time than is required for immediate use, there is always a
temptation to retemper the mass and use it, even though it
may have been standing for some time. The practice is
usually prohibited by specifications and strenuously opposed
by engineers. The tests recorded in Tables 79 to 83 were
made to determine the effect of regaging on the resulting
strength of the mortar.
366. The results obtained with two brands of Portland ce-
ment are given in Table 79. The first result in each line of the
table is the strength attained by the mortar when treated as
usual. The severity of the treatment of the mortar as regards
regaging is shown by the letters heading the columns and the
corresponding foot notes. The first general statement to be
made concerning the results in this table is that in no case is
the effect of regaging Portland mortars containing sand shown
to be seriously deleterious to the tensile strength. Neat cement
mortar is not improved by regaging, and if allowed to stand
more than one hour, and then made into briquets without any
further addition of water, the strength is considerably decreased.
If water is added and the mortar frequently regaged, however.
252
CEMENT AND CONCRETE
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REGAGING MORTAR
253
even neat cement mortar does not suffer a great decrease in
strength by three to six hours standing. Rich mortars, con-
taining one part sand, are not seriously affected by standing
three hours if regaged frequently. Poorer mortars, with two
to four parts sand, show an actual increase in strength as the
effect of such severe treatment as standing five hours, if re-
tempered with more water once an hour. These two brands
wore slow setting Portlands, beginning to set in forty minutes
to two hours. The increase in strength of the regaged mortars
is doubtless due, at least in part, to the more thorough gaging
which they received.
Table 80 gives similar results of briquets one year old made
at another time with two parts river sand. The fact that dur-
ing the delay between the making and use of the mortar it
should be frequently retempered with water to make up for
the loss by evaporation, is plainly shown.
TABLE 80
, Regaging Portland Cement Mortar
Tensile Stkength, Poinds per Squabe Inch, fob Varying Treatment.
a
c
d e
/
h
i
J
579
654
565
579
569
570
508
627
624
560
Cement: Portland, Brand R, Sample 42 M. Sand: 2 parts "Point aux
Pins," passing No. 10 sieve. Age of briquets, 1 year.
Treatment: — a — I.Iolded as soon as gaged.
c — Mortar let stand 1 hour, regaged and briquets made.
d — Mortar let stand 3 hours, regaged each hour.
h — Mortar let stand 3 hours, regaged each hour and water
added to restore original consistency.
e — Mortar let stand 6 hours, regaged each hour.
i — Mortar let stand 5 hours, regaged each hour and water
added to restore original consistency.
/ — Mortar let stand 5 hours, regaged and briquets made.
j — Mortar let stand 5 hours, regaged and briquets made ;
water added to restore original consistency.
367. Similar tests with natural cements are shown in Table
81, and it appears that cements of this class, especially if mixed
neat, will not stand the same severe treatments without injury.
254
CEMENT AND CONCRETE
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REGAGING MORTAR
255
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I I I I I I I I I
256
CEMENT AND CONCRETE
Neat cement mortars of these two brands appeared more plastic
when they were retempered with more water after standing one
hour (column /), but if allowed to stand three hours (column
t), they had then become quite hard set. Mortars containing
two parts sand that had stood sixty to ninety minutes with
intermediate retempering, showed a shght increase in tensile
strength, but more severe treatment was deleterious.
In Table 82 the mortars all contain two parts sand to one
of cement by weight. The only cases of any serious results of
retempering are for mortars standing four hours and regaged,
at intervals of one-half hour or one hour, with no water added
to the original mortar. Briquets made from mortar that had
been gaged every half hour, and was molded two honrs after
first mixed, showed a somewhat higher strength than briquets
made of fresh mortar.
Table 83 shows that the behavior of regaged natural cement
mortars, as shown in the preceding tables, is not an eccentricity
of one or two brands. Mortars containing two parts sand do
not appear to suffer in tensile strength by being allowed to
stand two hours if regaged hourly.
TABLE 83
Effect of Regaging on Tensile Strength, Five Brands Natural
Cement
o
H
ft
Age
Bbiquets.
Time
Elapsed
BETWEEN
PiKST Gag-
ing AND
Molding.
Sod
So
Interval
Between
Suc-
cessive
Gagings.
Tensile Strength, Pounds
Square Inch.
PER
Brands.
<
H
En
An
Dn
Kn
Hn
2
28 days
1
58
171
231
178
174
2
ii
2 hours
3
1 hour
109
168
310
178
190
2
6 months
1
228
328
306
361
273
2
"
2 hours
3
1 hour
284
382
307
416
347
4
28 days
1
39
49
149
23
58
4
<(
2 hours
3
1 hour
33
70
146
56
4
6 months
1
104
146
188
216
129
4
it
2 hours
3
1 hour
97
147
184
227 •
137
Notes: — Sand, Point aux Pins, passing No. 10 sieve.
In general, each result mean of five briquets.
All briquets made by one molder and stored in one tank.
All mortars appeared about same consistency when molded.
No water added in regaging except Brand Kn, 1 to 2 mortar,
standing two hours.
MIXING CEMENTS 257
368. Conclusions. — The conclusions to be drawn from these
tests appear to be as follows: The cohesive strength of mortars
of neat cement is appreciably diminished if they are allowed to
stand a considerable length of time after gaging before they
are used. Sand mortars, especially of Portland cement, usually
develop a higher tensile strength under moderate treatment of
this kind; and if regaged frequently, with sufficient water added
to keep them plastic, mortars of slow setting cements may be
used several hours after made without serious detriment to the
tensile strength. Portland cements withstand severe treatment
better than natural cements.
The effect of regaging on the adhesive strength is shown in
Table 117, § 405. These tests were quite severe and pointed to
the conclusion that the adhesive strength is diminished by stand-
ing and regaging, rich mortars and natural cement mortars
being most affected.
The effect of regaging on a given sample should be investi-
gated before it is permitted to any great extent, or in the most
careful work. Regaged mortars are said not to give good re-
sults in sea water, and it may be expected that quick setting
cement will be injured by regaging.
Art. 48. Mixture of Cement with Lime, Etc.
369. Mixture of Portland and Natural Cements. — For cer-
tain uses mortar is sometimes made from a mixture of Portland
and natural cement, with the idea of retaining some of the
properties of the Portland without involving the expense of
using a clear Portland mortar. Several tests have been made
to determine the rate of hardening and the ultimate strength
of such mixtures.
The mortars used in the tests given in Table 84 contained two
parts sand to one of cement, and the cement was composed of
one-eighth, one-quarter and one-half Portland to seven-eighths,
three-quarters, and one-half natural. Mortars made with Port-
land alone and with natural alone are included for comparison.
It is seen that the mortars containing some Portland harden
more rapidly than the natural cement mortar, so that the in-
creased strength developed at short periods is more than pro-
portional to the per cent, of Portland used. The results ob-
258
CEMENT AND CONCRETE
tained at two and three years, however, indicate that mortars
containing only a small proportion of Portland, as one-eighth
or one-quarter, do not give a higher ultimate strength than is
obtained with clear natural cement mortar.
TAKLE 84
Tensile Strength of Mortars Made 'with Mixture of Portland and
Natural
Age
Tensile Strength, Pounds per Square Inch.
M
g
Briquets.
Per ( Portland
100
60
25
12.6
0
^
Cent. ( Natural
00
50
75
87.5
100
1
7 days
291
206
108
76
24
2
28 days
367
264
219
190
123
3
6 months
560
425
378
300
322
4
1 year
674
441
360
336
291
6
2 years
543
449
375
343
393
6
3 years
592
501
428
370
429
Notes. — Portland cement, Brand R, Sample 42 M.
Natural cement. Brand Gn, Sample 54 R.
Sand, two parts of '' Point anx Pins," pass No. 10 sieve, to. one
part cement by weight.
AH briquets made by one molder and immersed in one tank.
Each result, mean of ten briquets.
370. In Table 85 four ki*nds or mixtures of cement are
used, Portland, natural, an "Improved cement" or a cement
TABLE 85
Comparisons of Portland, Natural, and " Improved " Cements
Ref.
Parts
Standard
Sand to
1 Cement by
Weight.
Age of
Briquets
when
Broken.
Tensile Strength, Pounds per Square Inch.
Portland,
Brand U.
" Improved,"
Brand Nn.
Portland,20%,
Natural, 80%.
Natural,
Brand, Mn.
1
2
3
4
5
6
7
B
9
10
11
None
(1
One
u
Two
Three
It
7 days
28 "
7 "
28 "
7 months
2 years
2 "
7 days
28 "
6§ months
2 years
547
586
468
669
702
677
522
176
272
389
371
206
293
169
263
660
663
610
52
122
301
346
250
341
200
331
578
634
573
80
143
282
356
199
270
166
234
517
497
529
49
114
256
342
12
Mean
2 years
490
473
488
456
LIME WITH CEMENT 259
sold as a mixed cement, and a sample made by mixing twenty
per cent, of the Portland with eighty per cent, of the natural.
The first point noticed is that the "Improved" cement does
not exhibit the early hardening properties due to the Portland
cement in its composition (if any), as strongly as the sample
containing twenty per cent. Portland. In only two tests did
the "Improved" cement give a higher strength then the clear
natural. The results of the two-year tests are of interest as
showing how nearly the same ultimate strength is shown by
the four samples. The sample of natural cement is of excep-
tional quality.
371. Conclusions. — It appears from these tests on the effect
of mixing Portland and natural cements that, in general, the
full strength of both cements is developed in the mixture; that
in the early stages of hardening, the mixture sometimes ex-
hibits more nearly the properties of the Portland, gaining
strength quite rapidly, but that the ultimate strength of mix-
tures containing small amounts of Portland are sometimes as
low as mortars made with natural cement alone. It cannot be
stated that all samples of Portland and natural cement will
give as good results in combination as those obtained in the
above tests, and any extended use of such mixtures should be
based on full tests of mixtures of the brands that are to be used
in combination.
372. Free Lime in Cement. — The presence of free lime in
cement is known to be a serious defect. Table 86 gives the
results obtained by adding ground quicklime to Portland cement
in one- to- two mortars. It appears that eight per cent, quick-
lime reduces the strength at six months about twenty-five per
cent., and smaller amounts of lime produce approximately
proportional decrements. The seven-day results, both hot
and cold, show greater proportional effects. The free lime
occurring in cements as a result of defects of manufacture is
likely to be much more dangerous in character than the lime
used in these tests.
373. The Use of Slaked Lime with Cement. — A small
quantity of Portland cement is frequently added to lime mortar
to hasten the hardening and improve the strength. The ad-
dition of a small amount of slaked lime to Portland cement
mortar is also practiced. This not only cheapens the mortar
260
CEMENT AND CONCRETE
TABLE 86
Mixture of Ground Quicklime with Portland Cement
Briquets Stored
IN Water.
Age of
Briqubtb.
Tensile Strength of Mortars in
Pounds per Square Inch.
Lime as Per Cent, of Total Lime and Cement.
0
2
4
6
8
Hot 80° C
Hot 80° C
Ordinary tank . .
Ordinary tank . .
3 days
7 days
7 days
6 months
269
367
348
604
223
297
321
545
207
266
273
489
194
223
241
496
159
191
220
464
Notes. — Cement: Portland, Brand R, Sample 83 T.
Lime: Quicklime ground to pass No. 100 sieve (holes .0066
in. eq.).
Sand: Standard crushed quartz, 600 grams, to 300 grams of
cement plus lime.
Per cent, of lime given replaced the same weight of cement;
thus: for "4 per cent, lime " the mortar contained 288 grams
cement, 12 grams lime and 600 grams sand.
All briquets made by one molder; each result, mean of five
briquets.
but renders it much more plastic, or less "brash," in mason's
parlance. It is very difficult to lay bricks in a full mortar bed
with Portland cement mortar containing two or three parts
sand to one cement, and to use a richer mortar is usually too
expensive. The work is very much facilitated by mixing a
little slaked lime paste or powder with the mortar.
374. The tensile strength of such mixtures is shown by the
tests in Tables 87 to 89. In the mortars of Table 87 a sample
of Portland cement is mixed with slaked lime in two forms,
paste and powder. When the briquets are hardened in open
air the addition of ten to twenty per cent, of CaO in the form
of lime paste decreases the strength about twenty-five per cent. ;
seven per cent, of lime in the form of slaked, dry powder has,
however, no deleterious effect, and even twenty-eight per cent,
gives no serious decrease in strength. For water-hardened
specimens the addition of twenty to thirty per cent, of lime in
the form of paste appears to increase the strength twenty per
cent, and no deleterious effect is shown by the addition of
forty per cent. Also for water-hardened specimens, seven to
LIME WITH CEMENT
261
twenty-eight per cent, of CaO in the form of slaked powder in-
creases the strength nearly twenty per cent. It thus appears
that the addition of lime gives better results in mortars that are
to harden in water, and that for air-hardened mortars lime
powder should be used in preference to Ume paste. Similar
tests of seven-day briquets showed the lime paste to retard
the hardening of the mortar.
TABLE 87
Slaked Lime in Portland Cement Mortars
Pkopobtions
Tensile Strength,
Pounds per
Square Inch., Sample
Stored in
Ref.
Limb in Fokm
OF
Cement,
Grams.
CaO in Lime
• Paste or
Powder,
Grams.
Sand,
Grams.
Open Air.
Water
Laboratory.
1
Paste
200
0
600
404
382
2
"
200
20
600
308
426
3
((
200
40
600
292
450
4
((
200
60
600
224
462
5
"
200
80
600
219
384
6
Powder
200
0
600
382
371
7
((
200
14.3
600
386
443
8
((
200
28.6
600
316
451
9
it
200
42.8
600
338
431
10
a
200
67.1
600
326
440
Cement : Portland, Brand R. Sand : Crushed Quartz, 20-30, or " Standard."
Age of briquets, 6 months.
375. In Table 88 only lime paste is used, but both Portland
and natural cement are tested, and the specimens are hardened
in dry air and damp sand. In the first column of results
are given the strengths attained by Portland cement mortar
containing three parts sand to one of cement without lime.
In the second column, ten per cent. CaO in form of paste is
added to the cement. In the third, fourth and fifth columns,
respectively, ten, twenty-five and fifty per cent, of the cement
is replaced by CaO.
It appears that ten per cent, of the cement in a one-to-
three Portland mortar may be replaced by lime made into paste
without diminishing the strength, if the mortar hardens in
damp sand. Even in dry air exposure, it is only at one year
262
CEMENT AND CONCRETE
that the lime shows any deleterious effect. To replace twenty-
five per cent, or more of the cement with lime, however, dimin-
ishes the strength of the mortar in a marked degree.
In the case of natural cement, replacing ten per cent, of the
cement with lime is decidedly beneficial, and even twenty-
five per cent, lime gives enhanced strength, except for speci-
mens hardened in dry air.
Table 89 gives similar results for one-to-four mortars and
different percentages of lime, the briquets being hardened in
dry air and damp sand.
TABLE 88
Use of Lime Paste in Cement Mortars Containing Three Parts
Sand
Briquets
Stoked.
KM
Tensile Strength, Lbs. per Sq. In.
Cement.
Cement, gm.
200
200
180
150
100
Lime Paste, "
0
60
60
150
300
CaO in Lime 1
Paste, gm. (
0
20
20
50
100
Amt. CaO ex-^
pressed as % 1
of Cement j
plus Lime. J
0
9
10
26
50
Kind.
Brand.
Sand, gm.
600
600
GOO
600
600
1
Port.
X
Dry air
28 da.
201
242
238
168
57
2
tt
u
Damp sand
u
294
330
309
238
95
3
ti
"
Dry air
3 mo.
236
265
264
IV 1
70
4
((
"
Damp sand
n
350
410
398
309
125
6
n
((
Dry air
1 yr.
384
377
317
215
98
6
t(
li,
Damp sand
u
430
445
442
332
171
7
Nat.
An
Dry air
3 mo.
310
338
359
251
69
8
((
t(
Damp sand
(i
267
344
327
318
93
9
((
<(
Water
"
222
301
319
293
79
J
In all of the above tests the mortars containing much lime
paste were not only more plastic, but somewhat wetter than
the corresponding mortars of cement and sand alone, on ac-
count of the water contained in the paste.
376. The conclusion to be drawn from these tests appears
to be that the addition of a small amount, ten to twenty per
cent., of slaked lime to cement mortars containing as much as
three parts sand, not only renders them more plastic, but
actually increases the tensile strength, especially if the mortars
are kept damp during the hardening. It also appears that for
PLASTER PARIS WITH CEMENT
263
TABLE 89
Use of liime Paste in Cement Mortars Containing Four Parts
Sand to One Cement
Composition of Mortar.
Tensile Strength of Mortar,
Pounds per Square Inch.
Cement.
Lime
Paste,
Grams.
Lime
in
Paste,
Grams.
Sand,
Grams.
Stored in Damp
Sand.
Stored in Dry
Air.
Kind.
Grams.
Fresh
Lime
Paste.
Old
Lime
Paste.
Fresh
Lime
Paste.
Old
Lime
Paste.
Portland, f
Brand X, J
Sample ]
41 S I
Natural,
BrandAn, -s
Sample L
240
240
200
180
240
240
200
180
00
80
120
180
00
80
120
180
00
27
40
60
00
27
40
60
960
960
960
960
960
960
960
960
176
212
198
204
160
160
166
140
180
200
212
194
133
154
173
166
254
280
227
232
127
162
131
124
244
250
237
184
142
150
170
154
Note. — All briquets three months old when broken.
mortars exposed to the open air the lime should be in the form
of slaked powder rather than paste. It may be added, that in
all cases care should be taken that the lime is thoroughly slaked
before use, and' all lumps should be removed by straining or
sifting. Further results on this subject are given in connection
with the tests on adhesion of cement mortar to brick (Art. 5).
377. EFFECT OF PLASTER OF PARIS ON THE COHESIVE
STRENGTH OF MORTARS.
The use of plaster of Paris, or calcium sulphate, in the man-
ufacture of cement to regulate the time of setting, has already
been mentioned. The amount of such additions at the factory
are usually small, the German Cement Makers' Association limit-
ing it to two per cent.
Tests on three brands of Portland cement, showing the effect
of small additions of plaster Paris, are given in Table 90. All
of these mortars hardened in water. It is not known whether
any of the cements had received additions of plaster Paris be-
fore leaving the factory. It is probable that brands R and X
had been so treated, since they are German cements, but it is
not probable that the other brands of Portland had received
any addition of plaster.
It appears that with these brands the addition of from one
264
CEMENT AND CONCRETE
to three per cent, of plaster Paris hastens the hardening and
increases the strength of the mortar at ages of six months to
two years. Six per cent, plaster sensibly retards the hardening,
but, in all cases except one, Brand S, neat, six months, the
mortars containing six per cent, plaster, gave higher results
on long time tests than did the corresponding mortars to which
no plaster had been added.
TABLE 90
Plaster of Paris in Portland Cement Mortars, Hardening in Water
So
o
CO
Tempeka-
TUKE WaTEE
IX WHICH
Briquets
Stoked.
n
Tensile Strength, Pounds per Sq.
In., with Per Cent, of Cement
Keplaced by Plaster
OF Paris.
0
1
2
3
6
1
s
0
60°to65°Fahr.
7 da.
487
626
600
519
380
2
0
6 mos.
743
746
764
742
660
3
2
7 da.
323
388
360
289
182
4
2
6 mos.
492
530
547
607
663
6
2
1 yr.
487
515
610
588
647
6
2
2 yrs.
533
586
612
669
684
7
R
0
7 da.
562
608
726
709
432
8
0
6 mos.
745
751
799
804
795
9
2
7 da.
288
347
372
362
166
10
2
6 mos.
532
538
624
638
642
11
2
lyr.
591
595
643
645
duo
Odd
12
2
2 yrs.
590
623
680
673
666
13
X
0
7 da.
351
368
406
460
204
14
0
6 mos.
660
606
680
645
797
15
2
7 da.
227
258
261
282
96
16
2
6 mos.
494
546
691
574
663
17
2
1 yr.
•572
680
686
583
662
18
2
2 yrs.
592
575
692
692
667
19
s
2
ITe" Fahr.
5 da.
296
307
362
391
422
20
R
2
140° "
5 da.
403
440
416
495
442
21
X
2
140° "
5 da.
361
334
390
452
474
Notes. — Sand, Point aux Pins (river sand) passing No. 10 sieve, except
for hot tests, where standard sand was used. Cement and
plaster of Paris passed through No. 50 sieve before using.
Plaster Paris had no apparent effect on consistency mor-
tar at first, but after making first three briquets of batch
of five, the mortar containing plaster Paris dried out
somewhat.
Each result, mean of five briquets.
Similar tests of natural cement mortars hardening in water
are given in Table 91. One of the brands is not much affected
PLASTER PARIS WITH CEMENT
265
TABLE 91
Plaster of Paris in Natural Cement Mortars, Hardening in 'Water
Temper-
Tensile Stbenqth, Pounds peb
SyuABE Inch, with Peb Cent.
Cement,
Sakd,
Age of
OF
Cement Replaced by
Rkf.
Natubal
Bbamd.
Pabts to
One
ATUUE
Water
Where
Briquets
When
Plasteb of Pabis.
Cement.
Stored.
Broken.
0
1
2
3
6
Degrees F.
1
An
0
60-65
7 da.
233
225
213
235
a
2
0
"
6 mo.
422
449
438
441
324
3
2
7 da.
111
109
97
144
a
4
2
6 mo.
418
416
435
409
133c
5
2
1 yr.
415
451
430
454
6
2
2 yrs.
478
476
489
514
7
Gil
0
7 da.
146
156
115c
a
o
8
0
6 mo.
383
3986
323
312e
234/
9
2
7 da.
62
80
94
a
a
10
2
6 mo.
374
312
355
86/
151/
11
2
1 yr.
448
395
408
ISlf
107/
12
2
2 yrs.
456
437
397
172/
a
13
An
2
140
5 da.
310
365
405
402
203
14
Gn
2
* *
' '
359
.351
189
Vi8
100
Note. — "^ id, Point aux Pins (river sand) passing Xo. 10 sieve, ex-
cept for hot tests, where standard sand was used.
a — Found badly swelled and nearly disintegrated after a few
days in tank.
6 — Surface cracks, 1 inch section swelled to 1 ^ inches.
c — Surface cracks, 1 inch section swelled to 1 y'j inches. Had
nearly disintegrated after 2 days.
d — Surface cracks.
e — Badly cracked on surface.
/ — Badly cracked on surface, and 1 inch section swelled to
about 1^ inches.
by additions of one to three per cent., but the other brand is
practically ruined by the addition of more than one or two per
cent., and both brands are rendered quite unsound by six
per cent, plaster.
378. The briquets reported in the preceding tables were
hardened in water, as usual. Table 92 gives some of the results
obtained by adding plaster Paris to mortars that are hardened
in dry air. The effects on the two samples of the same brand
of Portland, one quick setting and one slow setting, are quite
different. The strength of the quick setting sample is increased,
two per cent, giving the best results, while that of the slow
266
CEMENT AND CONCRETE
setting .sample is diminished by the addition of plaster. Both
brands of natural cement appear to be notably improved by
the plaster, the best result being given by three per cent. Such
an addition to one brand results in a remarkable increase in
strength of 250 per cent.
TABLE 92
Plaster of Paris in Cement Mortars, Hardening in Dry Air.
on Different Samples, Portland and Natural
Effect
Ref.
Cement.
pa
Tensile Strength Pounds pee
Square Inch, with
Per Cent, of Cement Replaced by
Plaster of Paris.
Kind.
Brand.
Sample.
0
1
2
3
6
1
2
3
4
Port.
u
Nat.
R
R
An
In
26 R
23 R
L
28 S
6 mo.
443
559
162
76
443
483
220
110
560
419
282
151
529
436
286
269
493
337
272
240
Notes. — Sample 26 R, Portland, quick setting, bears ^j inch wire in 18
minutes.
Sample 23 R, Portland, slow setting, bears yV inch wire in 244
minutes.
Sand, two parts Point aux Pins (river sand) to one cement.
All briquets stored in air of laboratory until broken.
Each result, mean of five briquets.
For the effect of plaster of Paris on the adhesive strength of
mortar, see § 407.
379. Conclusions. — It is evident from the above tests that
the addition of small amounts of plaster Paris affects different
samples of cement in quite different ways, and it is necessary
to bear this in mind in the application of general conclusions
to special cases. The indications are that the addition to
cement of from one to three per cent, of plaster of Paris or
sulphate of lime generally hastens the hardening and will not
usually result in decreased strength; that some natural cements,
however, are sensibly injured by more than one per cent.,
especially if used neat. The presence of as much as six per
cent, plaster of Paris retards the hardening (although hastening
the initial set) and is quite apt to ruin either Portland or natural
cements. The addition of plaster Paris usually gives better
results in air hardened than in water hardened specimens.
CLAY WITH CEMENT 267
Art. 49. Mixtures of Clay and Other Materials with
Cement
380. Effect of Clay on Cement Mortar and Concrete.
— Clay may occur in cement mortar or concrete due to the
use of sand or aggregate that is not clean. As the plasticity of
cement mortar is increased by the presence of clay, small
amounts are sometimes added to produce this effect, and clay
is also sometimes used to render mortar stiff enough to with-
stand immediate immersion in water. In the case of concrete,
the presence of a certain percentage of clay renders it easier to
compact the mass by tamping, though if too much clay is pres-
ent, the mass becomes sticky.
A number of tests have been made to determine the behavior
of such mixtures of clay and cement. In all of these tests the
clay was first dried, pulverized and sifted, and then a weighed
quantity equal to a given per cent, of the weight of the cement
was added to the latter. In the writer's first tests of this kind
small percentages of clay were used, less than ten per cent., but
it was found that with lean mortars much larger percentages must
be used to determine the point where clay began to be injurious.
381. Table 93 shows the effect of clay on the time of setting
and soundness of neat cement. The effect of small percentages
of clay on the time of setting of Portland cement is not very
marked, but with natural cement even ten per cent, of clay
retards the setting in a marked degree. As to the effect on
soundness, Portland cement pats disintegrate with more than
twenty-five per cent, of clay added, while the natural cement
is affected if more than ten per cent, of clay is present.
382. Table 94 shows the tensile strength of neat cement
mortars to which clay to the amount of 10 to 100 per cent, of
the cement has been added. Some of the Portland briquets
were immersed as soon as molded, while others were left the
customary twenty-four hours in moist air before immersion.
It is seen that to mix clay with neat Portland cement results
in a decided decrease in strength, the results obtained with
twenty-five per cent, clay being only about sixty or seventy
per cent, of the strength of the mortar without clay. With
natural cement the presence of clay seriously retards the hard-
ening and results in decreased strength, though it does not
268
CEMENT AND CONCRETE
TABLE 93
Xiffect of Pulverized Clay on the Time of Setting and Soundness
of Cement
8
z
m
K
H
Cement.
Clay.
Time to Bear A Inch Wire in Minutes,
AND THE Condition
OP Pats after Five Months.
Clay as Per Cent, of Cement.
Kind.
Brand.
Sam-
ple.
Kind.
0
10
25
60
100
1
1
2
2
3
3
4
4
Portland
((
Natural
K
X
Gn
41S
(I
n
KK
u
11
Red
11
Blue
11
Red
(1
Blue
(1
286
Good
288
Good
69
Fair
98
Poor
318
Fair
286
Fair
123
Fair
173
Poor
328
Good
300
Good
195
Bad
215
Bad
328
Bad a
305
Bad
345
Bad
350
Bad
460
Bado
306
Bad a
445
Bad a
415
Bad a
Note. — Results marked a, pats cracked badly in air and were not im-
mersed.
TABLE 94
Effect of Clay on Tensile Strength; Neat Cement Paste
—z —
s •< «
Tensile Strength, Lbs. per
Square Inch.
Ref.
Cement
Kind
OF
Clat.
Pi
f S; S
m
Clay Expressed as Per Cent, of
Cement.
Kind.
Brand.
Sample.
0
10
25
50
100
1
Port.
X
41S
Red
24
3 mo.
658
535
474
336
253
2
11
11
«i
(1
0
"
660
587
476
318
255
3
Nat.
An
D
11
24
28 da.
389
280
138
60
22
4
11
An
D
"
24
3 mo.
376
365
323
219
176
have as deleterious an effect as it does with Portland. The mix-
ing of clay with neat cement is of course very severe treatment.
In Table 95 the mortars contain equal parts cement and sand,
and the clay is from 50 per cent, to 200 per cent, of the weight
of cement. It appears from this table that clay in as large
amounts as 50 per cent, of the cement is injurious to one-to-
one mortars of either Portland or natural cement.
383. The mortars in Table 96 are all of Portland, and con-
tain three parts sand to one cement. Smaller percentages of
CLAY WITH CEMENT
269
TABLE 95
Effect of Large Amounts of Clay in Mortars Containing Equal
Parts Cement and Sand
Cement.
Kind
OF
Clay.
Hours
Elapsed
BETWEEN
Molding
and Im-
g
It
Tensile Strength, Lbs.
PER Square Inch.
Clay Expressed as Per
Cent, of Cement.
1
Kind.
Brand.
Sample.
mersing.
0Q
0
50
100
160
200
Port.
X
41 S
Red
24
3i mos.
747
512
337
239
193
2
n
(i
"
0
t(
720
549
321
242
189
3
Nat.
Gn
KK
24
3 mos.
464
241
212
183
140
4
»'
"
"
0
t(
413
231
206
157
128
6
t(
An
D
24
((
442
259
194
167
152
6
^i
"
(I
0
(k
440
274
184
141
125
7
>i
i(
ii
24
6 mos.
488
335
268
217
184
clay are used, namely, 10 to 40 per cent. The mortars harden-
ing in water show a decided improvement due to the presence
of clay, but the briquets hardening in the open air indicate that
TABLE 96
Effect of Clay in Portland Cement Mortar Conteuning Three Farts
Sand to One Cement
z
1
Briquets Storsd.
Age of
Briquets.
Tensile Strength, Lbs. per Square
Inch.
Clay Added as Per Cent, of Cement.
0
10
20
40
1
2
3
4
Tank, Laboratory
Open Air
1 1 (I
6 months.
2 years.
6 months.
2 years.
385
376
381
660
435
412
403
624
489
478
394
631
533
593
418
670
Notes. — Cement, Portland, Brand R, Sample 83 T.
Sand, three parts crushed quartz \% to one cement by weight.
Clay, red clay dried, pulverized, and passed through No. 100
sieve.
Clay added to mortar, amount cement and sand remaining
constant.
270
CEMENT AND CONCRETE
at two years the mortar without clay is stronger. It may be
noted in passing that these results, obtained at two years, with
one-to-three mortars hardened in open air, are very high.
The effect of clay on mortars containing four parts sand to,
one cement is shown in Table 97. In this case the addition of
clay equal to the weight of the cement almost invariably re-
sults in increasing the strength of the mortar. Briquets im-
mersed as soon as made were especially benefited by the pres-
ence of clay, except in one case, the red clay did not appear to
increase the ability of the natural cement Gn to withstand
early immersion. The red clay appears to give better results
than the blue with Portland, while the reverse is true with at
least one brand of natural. Whether this difference is a chemi-
cal or physical one is not known; the red clay is a good pud-
dling clay, while the blue clay is not, but appears to contain
some very fine sand.
TABLE 97
Effect of Large Amounts of Clay in Cement Mortars Containing
Four Parts Sand to One Cement
Tensile Strength, Lbs.
H
Cement.
Hours
PER Square Inch.
u
Kind
Elapsed
US <^
OF
Clay.
BETWEEN
Molding
AND Im-
0 6. p
»
Clat as Per CEirr. of
Cement.
tf
Kind.
Brand.
Sample.
mersing.
m
0
50
100
150
200
1
Port.
X
41 S
Red
24
3 mos.
271
348
305
239
193
2
(1
ii
u
Blue
'24
K
227
304
250
179
145
3
u
a
a
Red
00
a
156a
320
324
200
192
4
"
"
n
Blue
00
t(
149a
270
215
148
114
5
Nat.
Gn
KK
Red
24
3 mos.
138
155
146
164
133
6
ii
"
t(
Blue
24
((
118
167
200
167
134
7
u
((
(>
Red
00
((
83
87
39
86
72
8
u
ii
t4
Blue
00
t(
49
127
147
136
106
9
n
a
(1
Red
24
2yr8.
194
348
306
266
190
10
a
An
D
Red
24
3 mos.
138
218
174
174
190
Notes. — Sand, crushed quartz f^, ("Standard"), four parts to one
cement by weight.
Clay, dried, pulverized and passed through sieve before using.
All briquets immersed in tank in laboratory as usual.
Each result, mean of five briquets.
Results marked "a," briquets disintegrated some on face from
early immersion.
CLAY WITH CEMENT
271
384. Table 98 gives the results of tests by other experimenters,
showing the effect of clay on one-to-three mortars of Portland
and natural cement.^ The amount of clay used in these tests
Appears to be stated as percentage of the total ingredients in-
stead of as a percentage of the cement as in the preceding
tables. The mortars were mixed quite dry for these experi-
ments. The Portland cement mortar seems to be improved by
the addition of clay to the amount of twelve per cent, of the
mortar. The hardening of natural cement mortar is some-
what slower with twelve per cent, clay than with three to six
per cent., but at the age of twelve weeks the mortars containing
clay were all stronger than that without clay.
TABLE 98
Effect of Clay on the Tensile Strength of One-to-Three Mortars
Cement.
Parts
Sand to
One
Cement.
Age of
Briquets
When
Broken.
Tensile Strength, Pounds
PER Square Inch. Clay Expressed as
Per Cent, of Mortar.
0
3
6
9
12
Portia ud
u
Natural
n
3
3
3
2
2
2
2 weeks
4 weeks
12 weeks
1 week
4 weeks
12 weeks
202
362
451
68
152
170
267
301
506
117
199
214
280
334
521
101
219
252
318
381
522
99
170
230
333
353
547
66
146
211
Note. — Tests by Messrs. J. J. Richey and B. H. Prater.
385. Conclusions. — Always keeping in mind the limitatiqns
to be observed in drawing general conclusions from experi-
ments having a limited range, it may be said that the indications
are as follows: Neat cement and rich mortars are injured by the
addition of clay, the rate of hardening and the ultimate strength
being diminished. Lean mortars containing three to four parts
sand to one cement are usually improved by the addition of
clay to the amount of 40 to 100 per cent, of the cement, or
10 to 25 per cent, of the combined weight of cement and sand,
and the ability of such mortars to withstand early immersion
may be greatly enhanced by such additions. It is evident
from the above tests that the expense which should be incurred
in washing sand to remove a small percentage of clay is limited,
' Messrs. J. J. Richey and B. H. Prater, Technograph, 1902-3.
••^72 CEMENT AND CONCRETE
and for certain uses there is no question that mortar may be
improved by the addition of clay.
(For the effect of clay on the compressive strength of con-
crete, see Art. 55.)
386. Powdered Limestone, Brick, etc. — Various foreign sub-
stances are sometimes used with cement, either in lieu of sand;
or to make the mortar more plastic. Such foreign ingredients
may also occur in mortar as impurities in the sand used. Pow-
dered limestone, slaked lime, powdered brick and clay are some
of the materials experimented with in this connection. A few
tests of the effects of such mixtures on the setting time of ce-
TABLE 99
Foreign Substances in Cement Mortar
Cement.
«s
Tensile Strength, Pounds per
Square Inch.
u
2 z a
Age op
z
N
OS
Briquets
When
Composition of Mortar.
Kind.
Brand.
Sam-
ple.
So H
Broken.
«
a
b
c
d
e
f
1
Port.
R
JJ
None
3 months
705
674
583
615
667
2
(t
((
<■<■
3.75
6 days, H
152
217
164
175
240
198
3
((
"
n
3.75
3 months
259
367
297
284
311
304
4
((
u
u
3.75
1 year
.309
365
367
333
438
438
6
Nat.
An
G
None
3 months
286
203
307
154
203
6
n.
((
((
4
5 days, h
86
105
94
132
164
7
u
((
u
4
3 months
185
214
157
239
215
8
((
((
u
4
1 year
210
2.34
238
263
264
Notes. — Sand, "Standard." Materials added to mortar were first pul-
verized and passed through No. 80 sieve, holes .007 inch
square.
( 5-day results, H = immersed in hot water, 80° C.
» 5-day results, h = immersed in hot water, 60° C.
Composition of mortars: —
a — No foreign substa&ee.
b — No foreign substance, but additional amount cement added,
making mortar 1 to 3 instead of Ito 3.75.
c — Kelleys Isd. Limestone, equal to 25 per cent, weight of ce-
ment added to mortar.
d — Slaked lime powder, equal to 25 per cent, weight of cement
added to mortar.
e — Red clay, equal to 25 per cent, weight of cement added to
mortar.
/ — Red brick, equal to 26 per cent, weight of cement added
to mortar.
FOREIGN SUBSTANCES WITH CEMENT
273
ment indicated that the rate of setting of Portland cement was
not appreciably affected by the addition of twenty-five per
cent, of any of these substances, but the setting time of natural
cement appeared to be sensibly hastened by such additions.
None of these materials had any appreciable effect on the
soundness of either Portland or natural.
Table 99 shows the effect on the tensile strength of mortar
of adding twenty-five per cent, of each of the four substances
mentioned. It appears that the strength of neat cement mor-
tar, either Portland or natural, is usually diminished by the
presence of such materials, but in almost every case mortars
containing about four parts sand to one cement are improved
by the addition of the substances in question to an amount
equal to twenty-five per cent, of the cement. Pulverized clay
and brick give the best results, the increased strength amounting
to from twenty to forty per cent.
387. Sawdust. — Where a very light and porous mortar is
desired for use in floors and similar purposes, the incorporation
of sawdust in the mortar is suggested by a similar use in clay
building materials. The results in Table 100 show that the
use of sufficient sawdust to materially diminish the weight
practically ruins the cohesion of the mortar, even ten per cent,
of sawdust materially diminishing the strength.
TABLi: 100
Sawdust in Cement Mortsu*
2^
z
Tensile Strength PonNoa per
H
1:
X
Square Inch.
U
<=>a
° -, «
2
Briquets
Stored.
Sawdust as Per Cent, of Cement.
H
Kind.
Brand.
^2«
S
n
0
. 10
20
25
50
100
1
Port.
X
0
Tank
lyr.
799
409
169
44
31
2
(i
i(
0
Dry air
674
492
. . .
103
28
a
3
"
((
2
Tank
602
. . .
. • •
32
32
4
i(
t(
2
Dry air
452
129
. . .
14
a
6
Nat.
An
0
Tank
433
253
104
38
b
6
"
ti
2
Tank
313
108
58
20
Notes. — Sand, crushed quartz, |J. Sawdust from white pine, passed
through sieve with one-quarter inch meshes,
o — Briquets broken in applying initial strain.
6 — Briquets disintegrated in tank.
274
CEMENT AND CONCRETE
388. Use of Ground Terra Cotta as Sand. — A light weight
mortar may also be made by using as sand or aggregate, ma-
terials of burned clay, such as brick or terra cotta. The tests
in Table 101 were made to determine the value of ground terra
cotta for use in place of sand, and it appears that this material
gives excellent results. The strength given with one of the
brands of natural cement is especially high.
TABLE 101
Use of Ground Terra Cotta as Sand in Cement Mortar
Tensile Strength, Lbs. per Sq. In.
Z
Ceme>t.
u
Age of
Parts Ground Terra Cotta to One Cement. |
m
csi
Briquets.
by Weight.
Kind.
Brand.
1
2
3
4
6
1
Portland
X
3 months
523
406
332
257
174
2
"
a
1 year
604
518
429
337
266
3
Natural
An
3 months
284
338
346
347
224
4
"
11
1 year
262
360
351
361
186
5
"
En
3 months
291
303
184
136
6
'*
(1
1 year
340
4.34
284
161
Notes. — Terra Cotta tile, of medium bum, ground and passed through
No. 20 sieve, and used in place of sand.
Art. 50. The Use of Cement Mortars in Freezing
Weather
389. It is frequently desirable to use cement in freezing
weather, but to ensure good work under these circumstances it
is necessary to take certain precautions. If mortar is frozen
immediately after mixing, setting cannot take place until it
has again thawed. In the practical use of cement it is always
gaged with a larger quantity of water than is required for the
chemical combination, and if this excess water is frozen after
the setting is somewhat progressed, the consequent expansion
may be suflEicient to disrupt the partially set mortar. By warm-
ing the materials or by lowering the freezing point of the water
by the addition of salt, glycerine, or some other substance hav-
ing this effect, it is sought to prevent the mortar freezing until
the work is protected by another layer of mortar, or otherwise,
and thus to avoid the expansion. Salt is generally used much
EXPOSURE TO FROST 275
too sparingly to prevent freezing. The freezing point of water
is lowered about one and a half degrees Fahr. for each per cent.
of common salt added; thus a twenty per cent, solution would
freeze at about two degrees Fahr.
390. The following tests are selected as showing typical re-
sults of a large number of experiments made under the author's
direction to determine the effect of exposing cement mortars to
frost, and to indicate what treatment will alleviate the delete-
rious effects of low temperature. In making tests with small
specimens, it is difficult to approach the conditions existing in
the actual use of mortars in freezing weather. A small mass
of mortar exposed to the air on all sides sets more quickly than
the interior of a large mass; and on the other hand, the effect
of frost on a small specimen must be more severe and more
quickly apparent. Many of the results are more or less contra-
dictory, and the conclusions that have been drawn are such as
appear to be indicated by the majority of the tests. The
treatment of the briquets, and the conditions existing, are given
in some detail, that the limits of applicability of such conclu-
sions may be seen.
391. Exposure to Frost of Mortars Already Set. — In the
tests recorded in Tables 102 to 104 the briquets were allowed to
remain one or two days in the laboratory. It is evident that
these results are of but limited practical importance, since it
lis seldom that mortars which are made in winter can be allowed
I to set in a warm place before exposure; they are given, how-
ever, for what they are worth. Tables 102 and. 103 give the
; results obtained with Portland cement briquets exposed to a
severe temperature twenty-four to forty-eight hours after made.
JThe most important deduction, and the one most clearly indi-
cated by these tables, is that Portland cement mortar made with
fresh water may be subjected to very low temperatures twenty-
four to forty-eight hours after molded, without seriously de-
creasing the tensile strength given at six months to two years.
It also appears that solutions containing as much as fifteen
per cent, salt are deleterious, and smaller percentages are not
advantageous under these conditions.
Table 104, giving the results of similar tests with natural
cement mortar, indicates that this brand gives good results if
allowed to -set in warm air before exposure to frost. Solutions
276
CEMENT AND CONCRETE
TABLE 102
Exposure of Portland Cement Mortars to Low Temperatures after
Twenty-four Hours in Laboratory
Sand, Kind.
Date
Made.
Age
Whex
Bboken.
Texsile Strength, Pounds per Sq. In.
a
b
c
d
e
/
9
Standard . . .
Standard . . .
Vt. aux Pins, |
pass, sieve ^10 )
1-15
1-15
1-18
1-18
6 mo.
21 mo.
6 mo.
21 mo.
772
790
651
760
960
882
680
780
816
766
769
711
463
543
524
443
443
447
607
642
Notes. — Cement, Portland, Brand R. One part sand to one cement.
Briquets made in laboratory, temp., 64° to 66° Fahr. ; materials
about 65° Fahr.
Temperature, open air, Jan. 16 to Jan. 19, 4° to 15° Fahr.
Treatment of briquets: —
o — Fresh water, briquets stored in water in laboratory.
b — Fresh water, briquets stored in open air after 24 hours,
c — Fresh water, briquets alternated, two days in open air
and then two days in air laboratory, for fifty-two
days, then left in open air.
d — Water 5 per cent, salt; briquets stored in open air.
e — Water 15 per cent salt; briquets stored in ojjen air.
/ — Water 25 per cent, salt; briquets stored in open air.
g — Water 25 per cent, salt; briquets stored in water in lab.
TABLE 103
Exposure of Portland Cement Mortars to Low Temperatures,
Twenty-four to Forty-eight Hours after Made
Sand,
Kind.
Date
Briquet
Made.
Age
When
Broken.
Tensile Strength, Pounds per Sq. In. |
a
b
c
d
e
/
9
h
i
J
Std. .
Std. .
P.P.
P.P.
1-16
1-16
1-19
1-19
6 mo.
21 mo.
6 mo.
21 mo.
415
602
372
372
401
262
384
202
326
381
638
394
430
360
418
371
375
233
344
Noi'ES. — Cement, Portland, Brand R. Three parts sand to one cement.
Briquets made in laboratory. * Temp . : Air and materials, 64° to
67° Fahr. Open air, Jan. 10 to 20,-15° to +18° Fahr.
Treatment of briquets: a, b, c, d and e mixed with water con-
taining 0, 10, 15, 20 and 25 per cent, salt, respectively;
a to d, inclusive, air laboratory 24 hours, water laboratory
16 hours, air laboratory 12 hours, then in open air.
/, g, h, i and /, mixed with water containing 0, 10, 15, 20 and
25 per cent, salt, respectively.
e to /, inclusive, put in open air after about 24 hours in
air of laboratory.
EXPOSURE TO FROST
277
TABLE 104
Exposure of Natural Cement Mortars to Low Temperatures,
Twenty-four Hours after Made
Parts
Sand to
One
Cement.
Date Made.
Age When
Broken.
Tensile Sthkngth, Founds per Sq. In.
a
b
c
d
e
/
2
2
4
4
1-20
1-20
1-20
1-20
6 mo.
lyr.
6 mo.
1 yr.
297
30-5
222
223
404
390
318
269
319
343
319
339
'344"
205
297
273
176
217
114
150
Notes. — Cement, Natural, Brand Gn. Sand, " Pt. aux. Pins" (river
sand).
Temp, materials and air of laboratory where briquets were
molded, 65° to 68° Fahr. Temp, open air Jan. 21 to 23,
= - 1° to +29°.
Treatment of briquets: a, briquets stored in water in labora-
tory, b to /, inclusive, briquets stored in open air after
twenty-four hours in air of laboratory.
a and b, fresh water used for gaging mortar.
c, d, e and /, water used in gaging had 5, 10, 15 and 25 per
cent, salt, respectively.
containing more than ten per cent, salt are deleterious for such
treatment. Briquets of another brand of natural cement, a
one-to-one mortar of which gave about 450 pounds tensile
strength at one year, failed entirely when placed, one hour
after made, in open air for three days, and then immersed in a
tank in the laboratory. A 7.4 per cent, solution of salt used
for gaging assisted very materially in preserving the mortar
under the same severe treatment, although this amount of salt
was not sufficient to lower the freezing point of the water below
the temperature to which the briquets were subjected.
392. Effect of Salt in Mortars Hardened in Water and Air. —
In the tests recorded in Table 105 the materials used were at a
temperature of forty degrees Fahr., and the briquets were
molded in an open warehouse where the temperature was usually
below twenty-three degrees Fahr., though for a few of the
tests the temperature of the air at time of molding was as high
as twenty-seven degrees. The temperature of the mortar
when briquets were finished was usually but little above thirty-
two degrees Fahr. The briquets were left in a warehouse for
three days, when part of them were immersed in cold water
278
CEMENT AND CONCRETE
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EXPOSURE TO FROST
279
(under ice), and the remainder stored in open air on a shelf
covered by a rough board roof, but with front left open to the
weather. All mortars contained two parts river sand to one of
cement by weight. The water used in gaging varied from
tresh to a twenty-five per cent, solution.
The results indicate that Portland mortars made in low
temperatures, to be immersed in cold water, are improved by
fifteen to twenty per cent, salt in the water of gaging, but that
more than five per cent, salt is deleterious for mortars exposed .
to the air only. The very high results given by the air-hardened
specimens are worthy of notice.
A similar series of tests of natural cement gave results from
which no definite general conclusions could be drawn. The
effect of freezing and of the use of salt varied greatly for dif-
ferent samples. For any given sample the treatment, as re-
gards the use of salt, giving good results in open air, was usually
the reverse of that giving good results in cold water. The
conclusions indicated for rich mortars were sometimes the re-
verse of those shown by lean mortars. '
393. The results obtained with five brands of natural ce-
TABLE 106
Effect of Lov^r Temperatures on Five Brands of Natural Cement
h
a
K S
H
O
Z
H
K
a
<
u
a
z
<
50
i
OQ K
1
U 2
iz h (K
2S-K
Mean Tensile Strength,
Brand.
tf
Q
Pk
H ^
es. "
H £
Gn.
An.
Kn.
Hn.
Jn.
a
b
C
d
f.
f
9
h
i
J
k
I
Mo. Da.
Deg.
Days
1
2 20
N
9-11
18
Canal
234
322
285
423
284
2
2 22
N
16-19
0
"
201
327
326
302
219
3
2 20
S
9-11
18
Open air
0
344
416
412
321
292
4
2 22
S
16-19
0
ii
0
367
305
480
360
311
5
2 20
s
9-11
18
ti
7
274
306
413
244
304
6
2 22
s
16-19
0
ti
7
292
338
426
311
304
7
2 21
N
2
7-14
19
Canal
161
318
829
348
238
8
2 23
N
2
9-9
0
ii
160
217
355
2r)8
186
9
2 21
S
2
9-14
19
Open air
0
288
289
382
282
319
10
2 23
S
2
9-9
0
ii
0
338
275
422
423
867
11
2 21
s
2
9-14
19
"
8
268
271
340
240
295
12
2 23
s
2
9-9
0
>i
7
317
333
414
346
368
Note. — All briquets broken when six and a half months old.
280
CEMENT AND CONCRETE
ment are given in Table 106. The briquets were made in a
temperature of nine to nineteen degrees Fahr. Half of the
briquets were made with fresh water, and half with water con-
taining enough salt to lower its freezing point below that of the
TABLE 107
Portland Cement Mortar in Low Temperatures
Effect of Heating Materials
H
H
Temperature
Degrees Fahr.
Air Where
Molded.
Ph
Where
Stored.
>•
is
2o
b Z
0 U
Tensile Strength, Pounds
per Square Inch.
Cold
Ma-
terials,
40°.
Warm
Ma-
terials,
110°.
Cold
Ma-
terials,
40°.
Warm
Ma-
terials,
110°.
Mo.
1
1
1-6
23
Canal
Wet
6
582
598
2
1
8-9
0
u
590
693
3
1
1-5
23
m
7ii
734
4
1
8-9
0
"
((
770
737
5
2
14-16
14
6^
542
650
6
2
23-24
0
((
460
476
7
2
14-16
14
m
549
597
8
Means
9
10
2
23-24
0
((
467
541
572
Vii'
587
'724'
596
469
' 620
450
1
1
4-6
9-10
23
0
Open air
Dry
^
a
11
1
4-6
23
Wet
n
487
470
12
1
9-10
0
(i
((
628
614
13
2
15-18
14
Dry
n
507
542
14
2
24-25
0
"
ti
673
657
15
2
15-18
14
Wet
li
422
'453
16
Means
Grand
2
24-25
0
u
i(
543
495
639
605
622
606
471
534
479
549
Means
'
Notes. — Cement, Portland. Sand, " Point aux Pins."
When warm materials used, the temperature mortar after briquets
finished, 63° to 71° Fahr.
When cold materials used, the temperature mortar after briquets
finished, 32° to 39° Fahr.
When salt water used for mixing, water was 23 f)er cent, salt for
1 to 1 mortars and 14 per cent, salt for 1 to 2 mortars.
Briquets stored in canal were left in cold air three days before
immersion.
Part of briquets stored in open air were immersed in tank in labo-
ratory one week just before breaking, while others were broken
dry as indicated.
In general, each result is mean of five briquets.
EXPOSURE TO FROST
281
air where the briquets were made. The results are chiefly of
interest as showing the strength that may be attained by natural
cement mortars under these severe conditions.
Higher results are usually given by the air-hardened speci-
mens than by those immersed in cold water, though this de-
pends somewhat upon the brand. Salt is usually beneficial if
the briquets are immersed, and detrimental for open air ex-
posure.
394. Effect of Heating the Materials. — The tests in Table
107 were made to determine the effect of heating the materials
when working in low temperatures, and thus delaying for a
time the freezing of the mortars. The -details of the tests are
fully given in the table. The conclusion indicated is that the
ingredients may be used cold or warm indifferently. A gain of
only four per cent, is indicated for warm materials in mortars
mixed with salt water and hardened in cold fresh water. In
practical work, however, the use of warm materials may so delay
the freezing as to permit thorough tamping before the mortar
freezes. Table 108 gives similar results with one brand of natural
cement, from which it appears that warm materials have a shght
advantage for either cold water or cold air hardening.
TABLE 108
Natural Cement Mortars in Freezing Weather
Effect of Heating Materials
U
z
m
X
H
bi
a
Bi
Tempera-
ture Air
Where
Briquets
Molded.
o u
a*
Tensile Strength, Pounds per Sq. In.
Stored in Canal.
Stored in Open Air.
Materials.
32° F.
Materials.
100° F.
Materials.
32° F.
Materials.
100° F.
1
2
3
3
3
2
Deg. Fahr.
15 to 16
15 to 19
22 to 24
6 mos.
9 "
9 "
140
175
167
151
203
204
311
355
372
361
Notes. — Cement, Brand Gn, Natural. All mortars made with fresh water.
Briquets made with warm materials were frozen in from 15 to 24
minutes after made.
Each result, mean of ten briquets.
282
CEMENT AND CONCRETE
395. Consistency of Mortars to Withstand Frost. — Since the
injury due to frost is caused by the expansion of the water
used in gaging, it would be expected that mortars mixed wet
would suffer most. This conclusion is confirmed by the tests
in Table 109. The superiority of dry mortars is especially
shown in mortars that harden in the air. The treatment to
which these briquets were subjected was very severe, yet the
results are excellent.
TABLE 109
Consistency of Mortars as Affecting Ability to Withstand Low-
Temperatures
Age of
Briquets
When
Broken.
Tensile Strength, Pounds per Square Inch.
Stoked in Canal.
Stored in Open Air.
a
b
c
d
e
/
ff
A
6 mos.
9 mos.
414
474
414
468
372
431
501
527
601
727
671
622
521
525
674
563
Notes. — Cement, Portland, Brand R; sand, " Point aux Pins," passing holes
.08 inch sq. Two parts sand to one cement by weight. Each
result, mean of five briquets.
Teniperature, air where briquets were molded, 13° to 14° Fahr.;
materials used, 40° Fahr.
Temperature mortar when molding completed 32° to 36° Fahr.
Briquets made with fresh water had frozen after 30 minutes.
Treatment briquets: — a to rf, stored in canal (under ici).
e to h, stored in open air, January, North-
em Michigan.
Water used: — a and e, 10.4 p)er cent, fresh water.
b and /, 11.9 per cent, fresh water.
c and g, 13.3 per cent, fresh water.
d and h, 11.9 f>er cent, water containing 15 per
cent. salt.
396. Fineness of Sand and Effect of Frost. — The briquets
reported in Table 110 were made from mortar containing one
and two parts limestone screenings to one cement, the screen-
ings varying from coarse to fine. In general, the results follow
the rule appUcable to mortars used in ordinary temperatures,
namely, that the coarse sands give the best results; but it
appears that the briquets made with fresh water and exposed
EXPOSURE TO FROST
283
^
o
o
a
o
O
a ^
o o
03
60
O
Q
S
Briquets Broken
Dry. or Im-
mersed Some Hours
Just Before
Breaking.
Broken dry.
Immersed 19 hrs.
Broken dry.
Immersed 48 hrs.
Broken dry.
Immersed 19 hrs.
Broken dry.
Immersed 48 hrs.
Broken wet.
41 11
8
»
00
a
P .
S o'
H
i
H
Eh
&
d
■3 8
%>
z «
« Q
ft
gi
::§
«
a
d
i
cm
Oi »« 00 CO ^ '-O W --1 X 00 >-0 -N
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6
T3
s
■»j<r-ooiaoco,-isoooO'>!ft>o
oscoect--*£-(Ncooo«o-^ao
Open air
Canal
44
14
C"— < i-i "—I I— 1 1— ll— ii-i.— (
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NX aasQ uaiv/
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J3
c
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a
t^
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c
SI
p
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Tt
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1
n1
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03
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s >^
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b
«
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(fl
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tf
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12 ^
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-5 ^
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H
H
0
^;
284 CEMENT AND CONCRETE
in open air reverse this rule, either the finest sand, |g, or the
1^ giving the best result,
397. Conclusions. — The following conclusions concerning
the use of cement mortars in freezing weather appear to be indi-
cated by the foregoing tests:
1st, Mortars should not be mixed wet for use in low tem-
peratures.
2d, Portland cement mortars made in cold weather usually
develop a good tensile strength, especially when exposed to the
open air.
3d, Portland cement mortars for open air exposure may be
benefited by the use of from three to seven per cent, salt in
the water used in gaging, and from ten to twenty per cent,
salt in the gaging water may prove beneficial for mortars hard-
ening in cold water.
4th, Warming the materials for Portland cement mortar
appears to have but little effect on its frost resisting qualities.
5th, Coarse sand usually gives the best results in Portland
mortars made in cold weather, but fresh water briquets ex-
posed in open air appear to give better results with fine sand.
6th, Some natural cements give fairly good results in freez-
ing weather, while others are practically destroyed by severe
exposure. The effect of variations in treatment on different
brands of natural cement is so varied that no general conclu-
sions can be drawn from the above tests, but the indications
are that salt water for gaging is beneficial if the mortar hardens
in cold water, but detrimental for mortars exposed to the open
air.
Art. 51. The Adhesion of Cements
398. The Adhesion between Portland and Natural
Cements. — The question sometimes arises as to whether Port-
land cement will adhere to natural cement already set, and
whether fresh natural and Portland cement mortars may be
used together, as in the case of a Portland facing mortar used
with natural cement concrete. Tests bearing on these points
are given in Tables 111, 112 and 113.
* In the tests in Table 111 fresh Portland cement mortar was
applied to natural cement mortar that had set seven days.
Natural cement briquets, made neat and with one to four
parts sand, as seen in the headings of the columns of the table,
ADHESION PORTLAND AND NATURAL
285
were broken at the age of seven days. The fresh Portland
mortar was applied to the half briquets on the same day that
the latter were broken, by placing the half briquet in one end
of the mold, and filling the other half of the mold with fresh
Portland mortar of the composition shown in the second column.
TABLE 111
The Adhesion of Portland Cement to Hardened Natural Cement
Mortar
Ref.
Parts Sand to
One Part
Portland
Cement in
Fresh Mortar.
Adhesion of Portland Mortar to Half Briquets of
Hardened Natural Cement Containing Parts Sand.
0 1
2
3
4
1
2
3
0
1
2
246
185
63
255
210
75
197
186
00
194
152
84
161
120
85
NoTBS. — Briquets of natural cement, containing parts sand indicated at top
of columns, were broken at seven days. The half briquets
were then placed in one end of briquet mold and the other
end of mold was filled with fresh Portland mortar.
Fresh mortar made of Portland cement, Brand R.
Sand, " Point aux Pins," passing No. 10 sieve.
In general, each result is mean of ten briquets.
Nearly all briquets broke at jimcture of Portland and natural
mortars.
It is seen that the neat Portland gave the highest results in
adhesion, the one-to-one mortar giving a comparatively low ad-
hesive strength. It is also seen that the neat and one-to-one-
mortars adhered best to the richer natural cement briquets,
but the one-to-two Portland gave the greatest adhesi ve strength
with the poorer natural cement mortars. All of the tests gave
very irregular results.
399. To make the briquets the results of which are recorded
in Table 112, a plate was placed in the center of the mold, one-
half of the mold was filled with fresh natural cement mortar,
the plate was then withdrawn and the other half of the mold
filled with fresh Portland mortar. Briquets in line 1 were
made with Portland cement alone, while those in line 2 con-
tained only natural cement, these briquets being made for pur-
poses of comparison. The briquets containing both Portland
286
CEMENT AND CONCRETE
and natural were made neat and with from one to three parts
sand. By noting the number of briquets that broke at the
juncture between Portland and natural, it was found that, in
general, the adhesion of rich Portland mortar to rich natural
cement mortar is greater than the strength of the natural, but
that with the poorer mortars the adhesion is less than the
strength of the natural.
TABLE 112
Adhesion between Fresh Mortars of Portland and Natural Cement
Parts Sand to One of
Adhesive
OR Cohesive Strenoth, Pounds 1
Ref.
Cement.
PER Square Inch.
In Po rtland
Mortar.
In Natural
Mortar.
28 days.
3 months.
6 months.
1 year.
1
2
278
372
410
464
2
2
164
243
268
308
3
0
0
318
358
323
380
4
1
1
252
326
376
383
5
0
1
229
331
356
357
6
2
1
226
196
339
298
7
2
2
128
235
265
285
8
1
2
145
213
259
271
9
1
3
103
160
185
206
10
2
3
95
176
206
197
11
3
3
63
162
197
193
Notes. — Portland Cement, Brand R. *-
Natural Cement, Brand An.
Sand, " Point aux Pins," passing No. 10 sieve.
Both mortars mixed fresh and filled in opposite ends of mold.
400. In Table 113 the natural cement mortar contained
three parts sand to one of cement, while the richness of the
Portland mortars varied from neat to four parts sand. Four
combinations of different brands were used. Brand R, Port-
land, and brand An, natural, appear to give the best results
together. It is also seen from this table that the adhesion of
the rich Portland mortar is greater than the cohesive strength
of the natural cement, but when the Portland mortar contains
three or four parts sand to one cement, the adhesion is less
than the strength of the natural cement mortar.
401. The Adhesion to Stone and Other Materials.—
Since cement mortars are usually employed to bind other ma-
terials together, it follows that the adhesive strength is of the
ADHESION TO VARIOUS MATERIALS
287
greatest importance. On account of the difficulty of making
tests of adhesive strength, however, the data concerning it are
very meager. Two methods have been employed by the au-
thor in making such tests. One method, used for brick, is
to cement two bricks together in a cruciform shape. The other
method consists in placing small blocks of the substance to be
used in the center of a briquet mold, and filling the ends of
the mold with the desired mortar.
TABLE 113
Adhesion between Fresh Mortars of Portland and Natural Cement
a
m
1 i
«2 "
Natural Cement
Mortar.
p
a
S
0
<
Adhesive Strenqth Pounds per
Square Inch.
Parts Sand to One Cement in Portland
Mortar.
Brand
Cement.
Parts
Sand to
One
Cement.
0
1
2
3
4
1
R
An
3
3 mo.
162 N
173 N
177 N
162 J
127 J
2
R
Gn
3
i(
147 N
175 N
167 N
156
151
S
A
En
3
"
156 N
157 N
143 N
136 N
134
4
G
Bn
8
(1
88 N
106 N
115 N
94
91.1
5
R
An
3
lyr.
214
206 N
206 N
201 N
183 J
6
R
Gn
3
kl
167 N
165 N
180 N
175 N
169
7
A
En
3
((
157 N
158 N
173 N
166 N
160
8
G
Bn
3
(t
108 J
127 J
126 J
130 J
114 J
Notes: — In general, each result is mean of ten briquets.
Results marked N, briquets broke through the natural cement.
Results marked J, briquets broke at juncture of Portland and
natural.
The small blocks were made one inch square and about
one-fourth inch thick, two opposite edges of each piece being
very slightly hollowed to fit, approximately, the side of the
mold. These blocks being placed transversely in the center of
the mold, and the ends of the latter filled with the mortar to
.be tested, formed two joints between the mortar and the block.
402. Table 114 shows the adhesion of a rich Portland ce-
ment mortar to various materials. The mortar adheres moat,
strongly to brick, the adhesion exceeding the strength of the
brick itself. A very high result is also obtained with terra
cotta, and the adhesion to Kelleys Island limestone is high.
The latter is a dolomitic limestone of the corniferous group,
which is soft enough to be worked quite easily. The adhesion
288
CEMENT AND CONCRETE
to Drummond Island limestone, which is a much harder stone
belonging to the Niagara group, is considerably less, and the
adhesion to the Potsdam sandstone is very low. A higher re-
sult than would be expected is obtained with ground plate
glass, but the hammered bar iron gives the lowest result of any
of the substances tried.
TABLE 114
Adhesion of Portland Cement Mortar to Various Materials
U
2
K
H
ft.
H
Kind
OF
Sand.
Age
OF
Speci-
mens.
0 .
0 g
Adhesion, Pounds per Square Inch,
TO Materials.
a
h
c
d
«
/
9
1
2
Cr. Qtz. 20-30
11 (1
1
1
28 days
6mos
742
775
91
103
78
122
211
201
100
252
241
284
223
310
290
395
Notes: — Cement, Portland, Brand R.
Adhesion Blocks, 1 in. x 1 in. X \ in. inserted in center mold.
Materials: — a — Hammered bar iron.
h — Potsdam sandstone, cleavage surface.
c — Drummond Id. limestone, cleavage surface.
d — Ground plate glass.
e — Kelleys Id. limestone, sawn surface.
/ — Soft terra cotta, filed surface.
g — Soft red building brick, sawn surface.
403. The Adhesion of Neat and Sand Mortars. —Table 115
shows the cohesive and adhesive strengths of different mortars,
the adhesion blocks being all of the same material, Kelleys
Island limestone. The Portland mortar giving the highest ad-
hesive strength at six months is that containing one-half part
sand to one part cement, though the greatest cohesive strength
is given by the one-to-one mortar. With natural cement the
one-to-one mortar gives the highest strength, both in adhesion
and cohesion. The ratio of the adhesive strength to the co-
hesive strength is greater for natural than for Portland. It
also appears that between twenty-eight days and six months
the adhesive strength increases more than the cohesive strength.
404. Effect of Consistency on Adhesion. — Table 116 gives
the results of tests to show the relative effects of the consis-
tency of the mortar on the adhesive and cohesive strength. It
EFFECT OF CONSISTENCY
289
TABLE 115
Adhesion of Mortars Containing Different Amounts of Sand
1
a
(A
Cement.
Agb
OF
Speci-
mens.
Cohesion
OR
Adhesion.
Cohesive or Adhesive Strength, Lbs.
per Square Inch, op Mortars with
Sand, Parts by Weight.
Kone.
One-
Half Part
Sand.
One Part.
Two
ParU.
Kind.
Branfl.
1
2
3
4
5
6
7
8
Port.
it
Nat.
ti
n
R
it
An
t;
28 days
6 mos.
28 days
t(
6 mos.
Cohesion
Adhesion
Cohesion
Adhesion
Cohesion
Adhesion
Cohesion
Adhesion
686
270
631
335
183
94
263
228
710
233
787
346
198
104
334
222
747
221
816
287
218
116
383
233
467
169
551
209
186
66
376
171
Notes : — Sand, crushed quartz, 20 to 30.
Adhesion blocks, 1 in. x 1 in. x i in., Kelleys Id. limestone, sawn
surface, saturated before used.
is seen that the effect of consistency on the adhesive strength
is less than on the cohesive strength, but that the best results
in adhesion are given by a mortar that is considerably more
moist than that which gives the highest strength in cohesion.
The practical bearing of this point on the use of mortars is evi-
dent.
TABLE 116
Adhesion of Mortars. Varying Consistency
Cohesive or Adhesive Strength, Lbs.
i
Cement.
Age
Cohesion
per Square Inch, Mortar of
Consistency :
Speci-
mens.
or
Adhesion.
Trifle
Trifle
Quite
Very
Pi
Kind.
Brand.
Dry.
Moist.
Moist.
Moist.
1
Port.
R
28 days
Cohesion
541
502
443
372
2
li
It
"
Adhesion
148
160
145
136
3
n
"
6 mos.
Cohesion
697
660
616
539
4
It
tt
tt
Adhesion
191
209
228
192
5
Nat.
An
28 days
Cohesion
239
212
151
112
6
n
tt
It
Adhesion
96
96
87
70
7
tl
tt
6 mos.
Cohesion
397
385
814
286
8
(I
1 1
tt
Adhesion
146
165
164
1-26
Notes: — Sand," Point aux Pins," pass No.lO sieve, one part to one cement
by weight.
Adhesion blocks, 1 in. X 1 in. X \ in., Kelleys Id. limestone,
surfaces filed smooth, saturated with water before used.
290
CEMENT AND CONCRETE
^)5. Effect of Regaging on Adhesive Strength. — The tests
given in Table 117 were designed to show the effect of regaging
on the adhesion of cement mortar to stone. A comparison is
made between mortars used fresh and those that were allowed
to stand three hours and gaged once an hour. There are but
few tests from which to draw conclusions and the treatment is
very severe, but it appears that while the regaging to which
these mortars were subjected usually resulted in a slight in-
crease in cohesive strength, the adhesive strength was consid-
erably impaired. The decrease in adhesive strength was greater
for natural cement than for Portland, and greater for rich than
for poor mortars. The effect of regaging on the cohesive strength
is treated in Art. 47.
TABLE 117
Effect of Regaging on Adhesive Strength
Adhesion or
Adhesion or Cohesion, Lbs. per Sq. In. 1
One Part Sand to One
Three Parts Sand to
Cement.
Cohesion.
Cement.
One Cement.
Fresh.
Regaged.
Fresh,
Begaged.
Portland, Brand X
Adhesion
178
141
62
41
11 (1 u
11
202
170
59
61
a ii ((
Cohesion
718
764
327
343
Natural, " An
Adhesion
142
90
17
K (( 11
11
180
120
31
28
U 11 11
Cohesion
362
361
235
227
Notes: — Sand, crushed quartz, |g. Each result, mean of two to five speci-
mens, broken at age of six months.
In adhesive tests, pieces Kelleys Id. limestone, 1 in. X 1 in. x \ in.,
placed in center mold and two ends mold filled with mortar.
Results in columns headed "Fresh" from mortar treated as usual.
Results in columns headed "Regaged" mortar allowed to stand
three hours before use, mortar being regaged each hour.
406. Character of Surface of Stone. — In the tests recorded
in Table 118 all of the adhesion blocks were of Kelleys Island
limestone, but part of them were finished with smooth filed
surfaces, while the others were grooved with a coarse rasp. In
the twenty-eight-day tests there is but little difference in the
adhesion to the different surfaces, but at six months the adhe-
sion to the smooth surfaces appears to be slightly greater, ex-
cept in the case of one-to-two natural cement mortar.
EFFECT OF PLASTER PARIS
291
TABLE 118
Adhesion of Mortars. Effect of Character of Surface of Stone
Cohesion or Adhesion
and
Chabacteb of Sdbfacb.
Age of
Specimens^
Adhesion or Cohesion,
Lbs. per Sq. In.
Portland Brand R.j Natural Brand D.
Parts Sand to One Cement.
1
2
1
2
Cohesion
Adhesion, smooth surface . .
" grooved surface
Cohesion
Adhesion, smooth surface . .
" grooved surface
28 days
6 mos.
it
639
151
152
714
238
223
377
85
116
503
176
164
343
138
129
387
141
115
289
113
98
304
68
96
407. The Effect of Plaster of Paris on the Adhesion of Mortar
to Stone. — The results in Table 119 show the effect on the
adhesive strength of adding small percentages of plaster of
Paris to cement mortars of Portland and natural cement. The
Portland cement used was a quick setting sample, neat cement
pats of which began to set in eighteen minutes. The effect of
plaster of Paris on the cohesive strength of mortars from these
samples hardened in dry air, is shown in Table 92, § 378. It is
seen that the addition of from one to three per cent, plaster
TABLE 119
Effect of Plaster of Paris on the Adhesive Strength of Cement
Mortars
Rkf.
Cement.
Parts P.P.
Sand to
• One
Cement.
Age of
Specimens.
Adhesive Strength, Lbs. pek
Sq. In., of Mortars in which
Per Cent, of Cement Replaced
BY Pi..iflTER OF Paris.
Kind.
Brand.
Sample.
0
1
2
3
6
1
2
8
4
Port.
Nat.
R
R
An
An
26 R
L
0
2
0
2
1 year
263
130
88
64
311
107,
97
74
376
144
87
89
291
157
133
82
89
34
a
93
Notes: — Adhesion pieces between two halves of briquet were of Kelleys Id.
limestone, sawn surfaces, saturated with water before used.
Cement and plaster Paris passed through No. 50 sieve.
All briquets stored in tank in laboratory'.
Each result, mean of four to ten briquets.
a Found badly cracked and separated from limestone prisms after
three days.
292 CEMENT AND CONCRETE
has no deleterious effect on the adhesive strength of these
samples at one year. Six per cent, plaster, however, ruins the
Portland and the neat natural cement.
408. The Adhesion of Cement Mortar to Brick. —
Tests of the adhesion of cement mortar to brick were made by
cementing pairs of brick in a cruciform shape, with a one-fourth
inch joint of mortar. The brick were placed together flatwise,
with the bed down, so that in the case of stock brick, one
stock mark, or depression in one side, was filled with mortar.
The mortar was made more moist than was ordinarily used for
briquets, but not so moist as would be used in brickwork. The
top brick of each pair was slightly tapped to place with the
handle of a pointing trowel, and the excess mortar cut away.
About forty-eight hours after cemented, the pairs of brick were
packed in damp sand in a large box prepared for the purpose,
and the sand was kept in a moist condition by a thorough daily
sprinkling. For pulling the bricks apart, a special clip was de-
vised to equalize the pull on the two ends of each brick, and a
simple lever machine was used to measure the force required.
409. Tensile tests were made of briquets from mortars
similar to those used in the adhesive tests and stored in damp
sand, and the results are used for comparison with the adhesive
tests. The cohesive strength given by the briquets is not
strictly comparable with the adhesive strength shown in the
tests with brick, because of the great difference in the area of
the breaking sections in the two cases. It has been well estab-
lished in tensile tests of cohesion that briquets of large cross-
section break at a lower strength than those of small section.
It is quite possible also that even with the special clip devised,
cross-strains were more likely to occur in the adhesive tests
than in the briquet tests. An opportunity was furnished of
comparing the tensile strength of neat natural cement mortar
under the two conditions, for in one case six joints broke di-
rectly through the mortar, the adhesion being greater than the
cohesion. It was found that the strength per square inch
given by the briquets was at least six times that given by the
large joint. This difference should be kept in mind in making
comparisons in the tables between the cohesion and adhesion
as given. It should also be noted that some of the highest
results of adhesive strength represent in reality the strength
ADHESION TO BRICK
293
of the brick rather than the adhesive strength of the mortar, as
chips were pulled from the brick, leaving the mortar joint
undisturbed. The brick were of a rather poor quality, but
selected with a view to obtaining those of a uniform degree of
burning.
TABLE 120
Adhesion of Cement Mortar to Brick.
of Mortar
Variations in Richness
Cement.
Age of
Mortar.
Adhesion
OR
Cohesion.
Tensile Stkength, Pounds per
Square Inch, of Mortars Containing
Parts Sand to One Cement.
None.
k
1
2
3
Portland, X, 41 S
l( (( ((
(; (1 (1
Natural, Gn, KK
U U (I
(( (i u
28 days
3 months
6 months
3 months
6 months
Cohesion
Adhesion
Cohesion
Adhesion
Cohesion
Adhesion
Cohesion
Adhesion
Cohesion
Adhesion
632
48
676
64
723
50
180
46
276
44
596
42
728
62
764
56
240
52
444
52
589
24
694
41
679
39
317
42
388
50
409
20
423
24
524
20
279
28
331
38
270
11
325
12
374
14
181
15
236
18
Notes : — Bricks were cemented together in pairs in cruciform shape and
kept in damp sand until time of test. Briquets for cohesion
tests stored in same manner.
Each result in cohesion, mean of five briquets.
Each result in adhesion is in general mean of six results, three
with common die cut brick and three with sand molded stock
brick.
When adhesion exceeded 50 pounds per square inch, bricks were
about as likely to break as the joint between brick and mortar.
410. Adhesion of Neat and Sand Mortars of Portland and
Natural. — Some of the results of these tests are given in Table
120. The most noteworthy point developed is that for mor-
tars containing more than one-half part of sand to one part
cement, the adhesion of the natural cement is greater than
that of the Portland with the same proportion of sand, al-
though the Portland mortar was much the stronger in cohesion.
The mortars giving the highest adhesive strength are those
containing not more than one-half part sand to one part cement.
The addition of sand lowers the adhesive strength more
rapidly than it does the cohesive strength. This point would
294
CEMENT AND CONCRETE
be shown still more clearly if the true adhesive strength of the
richest mortars was obtained, as we may be certain that the
adhesion of these mortars would be shown to be considerably
greater if the brick were strong enough to allow this strength
to be developed. With natural cement mortars containing not
more than two parts sand to one cement, the adhesion is one-
sixth to one-ninth the cohesion, and with Portland mortars
containing not more than one part sand, the adhesion is about
one-fifteenth the cohesion. (But see § 409 in this connection.)
411. Effect of Lime Paste on Adhesive Strength of Cement
Mortars. — A number of tests were made to determine the
effect, on the adhesive and cohesive strength of mortars, of
mixing lime paste with the cement. Tables 121 and 122 give
the results of a few preliminary tests on this subject.
For the tests recorded in Table 121 the mortars were al-
lowed to harden in dry air. From the cohesive tests it is seen
that lime in form of paste to the amount of ten per cent, of
TABLE 121
Adhesion of Cement Mortar to Brick. Effect of Lime Paste in
Mortar Hardened in Dry Air
Cement.
Age
OF
Mortar.
Cohesion
or
Adhesion.
Tensile Strength, Pounds per
Square Inch.
Composition of Mortar.
A
B
C
D
E
Portland, X, 41 S
i( 11 11
11 (1 ti
Natural, Gn, LL
11 11 u
tl 11 11
3 months
4 "
6 "
3 "
4 "
6 "
Cohesion
Adhesion
11
Cohesion
Adhesion
(1
97
18
18
89
26
99
29
24
38
101
20
20
21
36
25
46
22
19
22
28
27
59
13
11
68
11
Notes: — Brick, sand molded stock.
All briquets and brick stored in dry air.
Composition of mortars:
Grams P. P. river sand,
Grams cement,
Grams lime paste.
Grams lime contained in lime paste.
Lime in paste expressed as per cent.
of cement plus lime, 0
Consistency about same as mason's mortar.
A
B
C
D
E
480
480
480
480
480
120
120
90
60
0
0
40
30
60
120
0
14
10
20
41
10 10 25 100
EFFECT OF LIME PASTE
295
the cement had little effect on one-to-four Portland mortars,
but that a larger amount of lime was very deleterious for dry
, air exposure. The sample of natural cement used did not harden
well in dry air, and the highest result is given by the lime mor-
tar without cement. It appears that the adhesive strength of
the Portland mortar was slightly increased by the addition of a
small amount of lime paste, but the adhesive strength of natural
was not greatly affected. The adhesive strength of the natural
cement is, in general, higher than the Portland. The nat-
ural cement appeared to harden better in the joints than in the
briquets, and we have, as a peculiar result, the adhesive strength
exceeding the cohesion. This illustrates a statement already
made, that to store briquets in dry air does not approach very
nearly the ordinary conditions of use.
412. In Table 122 are given a few tests of mixtures of Port-
TABLE 122
Adhesion of Cement Mortar to Brick. Effect of Iiime Paste in
Portland Cement
Mortar Hardened in
Cohesion
OR
Adhesion.
Tensile Strength, Pounds per Square Inch.
Composition of Mortar.
A
B
C
£>
E
Tank in Laboratory
Dry air,
Damp sand, "
Dry air, "
Damp sand, "
Coh*n.
it
Adh-u.
177
167
173
15
16
203
180
198
36
33
183
167
171
40
36
168
150
164
33
32
82
81
88
26
27
Notes: — Bricks cemented together in pairs in cruciform shape.
Age of all mortars when tested, three months.
Cement, Portland, Brand R, Sample 14 R. Sand, " Point &xxx I*ins."
Lime paste slaked about six months before use.
Each result in cohesion, mean of five to ten briquets.
Each result in adhesion, mean of eight to sixteen pairs of bricks.
Half of pairs were hard burned brick and half soft burned.
Composition of mortars: A
Grams P. P. (river) sand, 960
Grams cement, * 240
Grams lime paste, 0
Grams lime contained in paste, 0
Lime as per cent, lime plus cement, 0
B
C
D
E
960
960
960
960
240
200
180
120
80
120
180
360
27
40
60
120
10
16.7
25
50
29G CEMENT AND CONCRETE
land cement and lime paste, the mortars being hardened in dry-
air and in damp sand. Cohesive tests are also given of briquets
hardened in damp sand, water and dry air. It appears that
the addition of ten per cent, of lime in the form of paste to
mortars of this sample of Portland increases the tensile strength,
the effect being least when the mortars harden in dry air. The
substitution of lime for one-sixth of the cement in a one-to-four
mortar has little effect on the tensile strength. _ Larger propor-
tions of lime result in decreased strength, and if one-half of the
cement is replaced by lime, the resulting strength is only about
one-half that given by the cement mortar without lime. The
results of the adhesive tests show that if half of the cement in
the mortar is replaced by an equal weight of lime in the form
of paste, the resulting strength is increased by nearly 100
per cent., and that if smaller amounts of lime are used, the
adhesive strength is increased by about 150 per cent, over
that given by the cement mortar without lime.
413. The results of a more complete set of tests on this sub-
ject are given in Table 123. The mortars used included one
made with four parts sand to one of cement by weight; one in
which about ten per cent, of lime by weight, which had pre-
viously been made into lime paste, was added to the mortar; a
third in which lime, in the form of paste, was substituted for
one-sixth of the weight of the cement used in the first mortar;
a fourth, in which Ume was substituted for one-fourth of the
cement; and finally, a mortar composed of lime paste and sand
only.
The adhesive strengths of the mortars are given in the
table. The difference in the adhesion of Portland cement
mortar to hard brick and to soft brick is not clearly brought
out. Neither is the strength of air-hardened specimens much
different from that of the mortars stored in damp sand. The
use of lime paste with Portland cement in the amounts tried
here more than doubles the adhesive strength of the "mortar.
The first point to notice in the case of natural cement is
that the adhesive strength of this mortar without lime is nearly
double the adhesive strength of Portland mortar without lime.
The adhesive strength of mortars hardened in damp sand is
somewhat greater than the strength of similar mortars hard-
•ened in dry air. The addition of a small amount of lime paste
EFFECT OF LIME PASTE
2.97
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298 CEMENT AND CONCRETE
increases the adhesive strength somewhat, and when as much
as twenty-five per cent, of the cement is replaced by lime in
the form of paste, the adhesive strength of the natural cement
mortar is not usually diminished. The effect of lime paste,
however, on the adhesive strength is not nearly so great as it
is in the case of Portland mortars.
The following conclusions may be briefly stated: The ratio
of adhesive to cohesive strength is much greater with natural
cement than with Portland. If a high adhesive strength is
desired, Portland cement should not be mixed with more than
two parts sand unless lime paste is added to the mortar, as
the use of lime paste materially increases the adhesive strength
of lean mortars. Tests of cohesion of similar mortars contain-
ing lime paste are given in Art. 48.
414. THE ADHESION OF CEMENT TO RODS OF STEEL AND
Iron. — The tests recorded in Tables 124 and 125 were made
to determine the adhesion of cement mortar to iron rods, or
the strength of a bolt anchorage secured with cement mortar,
and the style of rod and kind of mortar which would give the
best results. The bars were made in an ordinary concrete
mold, ten inches by ten inches by four and one-half feet. The
rods or bolts were placed in a row along the center of the box,
being spaced about nine inches apart, and the mortar was
rammed about them. After being allowed to set in a warm
room for twenty-eight days, the rods were pulled by means of
two hydraulic jacks, a special grip being used to grasp the free
end of the rod, and an hydraulic weighing machine serving to
measure the pull required to start it. The supports against
which the hydraulic jacks were braced bore at points on the
concrete bar about three or four inches from the center of the
rod which was being tested.
415. The rods given in Table 124 were imbedded in mortar
composed of one part of Portland cement to two parts lime-
stone screenings. The rods were cut from bar iron and were
perfectly plain, without nuts or fox wedges. The results in-
dicate that the force required is proportional to the area of
contact. Comparing the different styles and sizes of plain rods,
no difference in favor of one style or size can be determined;
the apparent higher resistance per square inch offered by one-
inch rods would probably disappear in a large number of tests.
ADHESION TO STEEL RODS
299
TABLE 124
Resistance to Pulling of Iron Rods of Various Forms Imbedded
in Mortar
ft
Pounds Pull. |
Perim-
Depth
Rw.
n 0
D
Mortar,
Bar No.
Description of Rod.
eter
of Rod,
Inches.
Im-
bedded,
Inches.
Per In.
Depth
Im-
Per Sq.
In. Area
in Cou-
bedded.
tact.
1
3
2,6, 7
Plain, Y' diameter
1.67
8 to 10
700
447
2
3
"
tt \" n
3.14
1750
566
3
3
"
" 14-" "
3.93
2060
524
4
3
u
*' i" square
2.00
1085
643
5
4
2, 6, 6, 7
4.00
2250
562
6
3
2,6,7
u 1 // u
5.00
2170
434
7
3
4,6
( Twisted 1" square,
J 1 turn in 8" lengtli
i
4.3»
9±
2595
608
8
3
<(
( Twisted 1" square,
1 2 turns in 8" length
!
4.31
9±
2215
516
9
3
t(
j Twisted 1" square,
( 3 turns in 8" length
}
4.31
9-9.5
2405
661
Notes: — Cement, Portland, Brand R.
Sand, limestone screenings passing f inch slits, two parts by
weight to one cement.
Mortar one month old when tension was applied to rods.
The rods given in lines seven to nine were made by twisting
a piece of one inch square bar iron. The twisted portion was
eight inches in length. Comparing the plain one inch square
bolts with the twisted bolts, it appears that the former offered
a resistance of 2,245 pounds per inch depth while the latter
gave 2,405 pounds, an increase of less than eight per cent.
416. In the tests recorded in Table 125, the ordinary river
sand used in construction was employed. The mortar was
made neat and with two and four parts sand to one of cement.
The depth the rods were imbedded varied from two inches to
ten inches. The one-to-two mortar gave nearly as good results
as neat cement, but the one-to-four mortar gave much lower
results. The resistance seems to vary directly as the area of
contact without reference to the depth imbedded, except as
' In computing adhesion, or shear, or pounds pull per square inch of area
in contact, perimeter considered circumference of a circle of diameter equal
to the distance between opposite edges of rod after twisting. A core of mor-
tar of this diameter, was torn from bar in pulling.
To perceive e£Fect twisting, compare pounds pull per inch depth imbedded.
300
CEMENT AND CONCRETE
this enters in obtaining the said area. The results obtained in
this table do not compare favorably with those obtained in
Table 124, where limestone screenings were used.
TABLE 125
Resistance to Fulling of Iron Rods Imbedded in Mortar. Variations
in Depth Imbedded and in Richness of Mortar
Parts
Sand to
One
Cexent.
Adhesion,
Pounds peb Souare Inch op Surface in Contact fob Diffkreni
Depths Imbedded.
Depths )
Imbed-}
ded.In )
1.9-2.2
3.2
4
4.5-4.8
6.8-6
7.8-8
8.8
9.6-10
No.
Re-
sults.
Mean.
0
2
4
840
272
74
294
346
270
119
'262
313
255
117
'247"
100
228
340
275
142
5
15
10
313
264
111
Notes: — Cement, Portland, Brand R.
Sand, "Point aux Pins," river sand.
Mortar one month old when rods pulled.
Rods, round, 1 inch diameter.
417. Tables 126 and 127 are from similar tests made by
Messrs. Peabody and Emerson.^ The rods in Table 126 were
of various shapes and included some having rivets through
them. The i inch by 1 inch bars gave lower adhesion per
square inch than the square and round rods. When two rods
are twisted together and imbedded in a small specimen, the
tendency is to split the specimen. The bars containing rivets
broke before the adhesion was overcome, although the depth
imbedded was but six inches.
In Table 127 neat cement paste and concretes of several
compositions are tried. These results are of interest as show-
ing that concretes show as great adhesion to steel rods as do
mortars. The very low result obtained with neat cement in
this table is not explained and is in opposition to the results
in Table 125.
* Engineering News, March 10, 1904.
ADHESION TO STEEL RODS
301
TABLE 126
Adhesion of Mortar to Steel Rods of Various Shapes, Imbedded
about Six Inches
No.
OF
Tests.
Dbscription of Rod.
Periiteter
of Rod,
Inches.
PoDNDS Pull.
Per Inch
Depth
Imbedded.
Per Square
Inch .\rea
in Contact.
4
3
4
4
4
4
4
Plain, J" square.
Plain, Y' square.
Plain, 1" round.
Twisted, ^" square.
\" by 1 ".
Two y rods twisted
together.
i" by 1" with f " rivets
through.
1.0
2.0
1.57
2.5
369
864
804
1259
744
309
432
612
293
Three specimens split.
One rod broke at 8,000 lbs., or when
adhesion was 1,250 lbs. per inch
depth.
One specimen split.
Three rods broke at first rivet with
9,800 to 10,500 pounds, or when
adhesion was 1,500 to 1,660 lbs.
per inch depth.
Notes: — Tests by Messrs. George A. Peabody and Samuel W. Emerson.
Mortar composed of one part cement (Portland) to three parts sand.
Specimens approximately 6 inch cubes. One rod imbedded in
each, 6 to 6J inches.
Rods pulled forty and eighty days after mortar was made.
TABLE 127
Adhesion of Mortars and Concretes of Various Compositions to
One Inch Square Steel Rods Imbedded about Ten Inches
No.
OF
Tests.
Composition of Mortar
Concrete.
OR
Pounds Pull.
Per Inch
Depth
Imbedded.
Per Square
Inch .\.rea
in Contact.
Cement.
Sand.
Stone.
Gravel.
0
3
3
3
2
2
0
0
6
0
4
0
0
0
0
6
0
4
1112
1644
1912
2062
2348
2187
278
411
478
616
587
647
Note: — Tests by Messrs. George A. Peabody and Samuel W. Emerson.
\
CHAPTER XVI
THE COMPRESSIVE STRENGTH AND MODULUS OF
ELASTICITY OF MORTAR AND CONCRETE
Art. 52. Compressive Strength of Mortar
418. The compressive strength of cement mortar is from
five to ten times the tensile strength. As the result obtained
in tests of either compression or tension depends upon the shape
and size of the specimen, no definite value can be assigned to
the ratio of compression to tension. Comparative tests have
indicated in a general way that the cements giving the best
results in tension show also the highest compressive strength;
but with variations in treatment, different kinds and brands of
cement do not give the same variations in the ratios of the two
kinds of strength.
Mortar is not usually employed alone in large masses. It
more frequently forms the binding medium between fragments
of other substances, such as brick and stone. The dependence
of the strength of masonry upon the strength of the mortar
increases with the roughness of the stone or brick, and the
thickness of the bed joints. In fine ashlar masonry this depend-
ence is comparatively small, in brickwork it is important, and
in concrete any increase in the strength of the mortar increases
the strength of the concrete in nearly the same ratio.
Piers of brickwork may give a crushing resistance either
greater or less than the strength of cubes made from mortar
of the same composition as that used in building the piers.
Thin beds of mortar between strong materials resist high com-
pressive stresses, while in walls or piers built with weak blocks,
the mortar is destroyed by the cracking of the blocks at a lower
stress than the mortar would withstand in a cube pressed
between steel plates. Since in brick and stone masonry the
mortar forms but a small part of the structure, it is not econom-
ical to use a poor quality of mortar with good brick and stone.
302
COMPRESSIVE STRENGTH MORTAR
303
419. Ratio of Compressive to Tensile Strength. — M. E.
Candlot has made many experiments showing the effect of
certain variations in the preparation of mortars upon the com-
pressive and tensile strength. A few of the results of one
series are presented in Table 128. The reduction from the
metric system has been made, and a column added giving
Approximately the number of parts of sand to one of cement by
weight, the accurate proportions appearing in the form of
weight of cement to one cubic yard of sand. These results in-
dicate that the ratio of the strength in compression to that in
tension increases with the age of the mortar and also with its
richness.
TABLE 128
Resistance of Cement Mortars to Tension euid Compression, with
Varying Proportions of Normal Sand
Specimens Hardened in Fresh Water
[From Ciments et Chaux Hydrauliques, par M. E. Candlot.]
0 •<< 0 a
?; Q J
u b; <
Resistance in Pounds per Square Inch in Tension and
Compression.
c 5
7 days.
28 days.
1 year-
2 years.
3 years.
T.
C.
T.
C.
T.
C.
T.
C.
T. C.
< o
10.8
250
27
266
38
408
70
507
74
572
108
738
6.8
6.4
420
128
643
143
1164
212
1730
209
1630
219
1775
8.1
4.6
590
139
1040
234
1940
337
2980
284
2930
341
3080
9.0
3.5
760
233
1520
393
3080
436
4020
400
4400
462
4590
9.9
2.9
930
251
2110
462
3690
490
5580
490
5680
557
6060
10.9
2.5
1100
349
2630
551
5020
594
5820
557
6060
616
6480
10.5
2.0
1350
308
;i360
550
5020
713
7750
805
7860
784
8710
11.1
1.6
1690
443
3310
561
5070
767
7670
907
8800
815
9180
11.8
From a study of the results of nearly three thousand tests
made by Professor Tetmajer, the late Professor J. B. Johnson
concluded that for mortars containing three parts sand to one
cement the ratio of the compressive strength to the tensile
strength is equal to 8.64 -1-1.8 log. A, where A is the age of
the mortar in months. It is shown above that the ratio in-
creases with increasing proportions of sand.
420. Table 129 gives some results obtained at the Water-
town Arsenal in tests of cement mortar cubes.* The mortars
* Prepared by Mr. Geoi^e W. Rafter for the State Engineer of New York.
304
CEMENT AND CONCRETE
TABLE 129
Compressive Strength of Cement Mortar. — Portland and Natural
Tests of 12 Inch Cubes, Twenty Months Old, Made at Watertown
AasENAL Fon State Engineer of New York
Method of Storage of
Cubes.
Cement.
Crushing Strength, Lbs. per
Square Inch, for Mortars
Containing Parts Sand to One
Ckment by Volume:
Kind.
Brand.
d
1
2
3
4
Mean
Water 3 to 4 mo.,
then buried in sand.
Nat.
Buffalo
' Dry
Plastic
Excess
. Mean
3479
■2795
2161
2812
2200
1783
1698
1894
1154
1000
776
977
2278
1859
1545
1894
Covered with burlap;
kept wet for several
weeks, then exposed
to weather. . .
Nat.
Buffalo
r Dry
J Plastic
1 Excess
1^ Mean
3347
2476
2070
2631
2000'
1294
1358
1551
961
(,92
7.38
797
2103
1487
1.389
1660
In cool cellar . .
Nat.
Buffalo
' Dry
Plastic
1 Excess
L Mean
2844
2514
2159
2504
2051
1256
1386
1564
987
F83
678
849
1961
1561
1408
1640
Fully exposed to
weather . . .
Nat.
Buffalo
' Dry
Plastic
Excess
. Mean
3272
2667
1996
2645
1879
1356
1311
1513
10.54
822
669
848
2068
1615
1.325
1669
Means .....
r Bry
X Plastic
[ Excess
3236
2613
2097
2032 2
1421
1438
1039
849
715
2102
1628
1417
Grand mean . .
2649
1630
868
1716
Water 3 to 4 mo.,
then buried in sand
Port.
Empire
/ Dry
\ Plastic
3897
3642
2494
2168
1782
1717
Covered with burlap;
kept wet for several
weeks, then exposed
to weather. . .
Port.
Empire
r Dry
]^ Plastic
3880
3672
2492
2168
1489
1726
In cool cellar . .
Fully exposed to
weather . . .
Port.
Port.
Empire
Empire
r I>ry
1 Plastic
J Dry
1 Plastic
3397
3313
4059
3589
2132
2164
24.50
2270
1614
1679
1715
1465
Means
J Dry
1 Plastic
3808
3554
2392
2193
1650
1647
contained one, two and three volumes of sand to one of natural
cement, and two to four parts sand to one volume of Portland.
Result interpolated.
2,043 omitting interpolated result.
COMPRESSIVE STRENGTH CONCRETE 305
The proportions of water used were such as to give mortars of
different consistency, "dry," Uke damp earth, "plastic," of the
consistency usually employed by masons, and "excess," quak-
ing like liver with slight tamping. The specimens were twelve
inch cubes and four methods of storage were used, as indicated.
Comparing the results with similar tests of tensile strength,
it appears that the strength in compression decreases more
rapidly as sand is added than does the tensile strength. The
same conclusion was drawn from Table 128.
The strength of the Portland mortar with four parts sand
is about equal to the strength of the natural with two parts.
The dry mortar gives the highest strength with natural cement,
but with Portland the "dry" and "plastic" give about the
same result.
Concerning the consistency, it has already been pointed out
that the conditions of the actual employment of mortar are
such as to favor, in general, the use of a wetter mixture than
that which gives the best results in laboratory tests of mortars.
As to storage, the specimens kept in water for three or four
months after made, give the highest results with natural ce-
ment. There seems to be no choice between the other three
methods of storage.
Art. 53. Compressive Strength of Concrete with Various
Proportions of Ingredients
421. With the increasing use of concrete in arch bridges,
in foundation piers and in columns of buildings, and especially
in connection with steel in beams, etc., the compressive strength
of the material becomes of the greatest importance. Moreover,
the composition of concrete may vary so much, the range of
available aggregates is so wide, and the methods of manipula-
tion are so diverse, that many tests must be studied before
one can judge of the probable strength of a given mixture.
For any very extended work, it may be found economical
to make a series of tests using the materials available, and
combining them as nearly as possible in the manner proposed
in actual construction. This practice has been followed in
several important works, and the data thus accumulated have
added much to our hitherto somewhat vague notions of the
probable strength of different mixtures under varying condi-
306
CEMENT AND CONCRETE
tions of use. It is possible here to abstract but a few of the
more reliable and complete tests of this kind, selecting those
which indicate the value of certain special kinds of aggregate
or the effect of certain variations in manipulation.
422. In connection with the design of the Boston Elevated
R. R., Mr. George A. Kimball, Chief Engineer, prepared a series
of concrete cubes of mixtures usually employed in practice,
and with the materials available for the work in hand, and these
cubes were tested at the Watertown Arsenal in 1899. A por
tion of the results of these experiments are given in Table 130,
where the details concerning character of the materials and
the preparation of the specimens are shown. As each result
in the table is the mean of at least twenty specimens, the ir-
regularities frequently appearing in compressive tests have
been largely eliminated, and the results are worthy of much
confidence.
TABLE 130
Compressive Strength of Concrete
Tests of 12 Inch Concrete Cubes for Boston Elevated Railroad.
Composition of Concrete by
Volume.
Crushing Strength, Pounds per Square Inch,
AT Age,
Cement.
Sand.
Stone.
7 days.
1 month.
3 mouths.
6 months.
1
1
1
2
3
6
4
6
12
1525
1232
583
2440
2063
1042
2944
2432
1066
3904
2969
1313
Notes: —
Materials: — Cement, mean results with four brands Portland, two Ameri-
can, two German.
Sand, coarse, clean, sharp, voids 33 per cent, loose.
Broken stone, conglomerate passing 2^ inch ring, voids 49J
per cent, loose.
Mixing : — Sand and cement turned twice, mortar and stone turned twice.
Storage: — Cubes removed from molds three or four days after made and
buried in wet ground until about a week before testing.
Each result, mean of twenty or more tests.
Tests made at Watertown Arsenal, for George A. Kimball, Chief Engineer,
Boston Elevated R.R. "Tests of Metals," 1899.
At the time of making these tests some cubes were crushed
with a die having a smaller area than the face of the cube.
COMPRESSIVE STRENGTH CONCRETE 307
With a die 8 by 8^ inches on one compression face, the area of
the die being thus about .46 of the area of the cube face, the
strength per square inch under the die was about twenty-five
per cent, higher than when the entire face of the cube was
pressed. This is in Une with the behavior of all brittle sub-
stances under compression, as shown by Professor Bauschinger
in testing sandstone specimens.
423. Tables 131 and 132 give a summary of a part of a very
valuable series of tests of concrete cubes prepared by Mr. George
W. Rafter and tested at the Watertown Arsenal for the State
Engineer of New York.*
The results summarized in Table 131 are those obtained with
four brands of Portland cement made in the State of New
York, namely, Wayland, Genessee, Empire and Ironclad. Tests
were also made with a sand-cement, and with one brand of
natural, but these results are not included in the table. The
aggregate was sandstone of the Portage group, broken by hand
to pass a two inch ring.
The mortars used in making the cubes were of three degrees
of consistency: (a) In the dry est blocks the mortar was only a
little more moist than damp earth, and much ramming was
required to flush water to the surface. (6) In another set the
mortar was about the consistency of ordinary mason's mortar,
(c) In the third set, the mortar was wet enough to quake like
liver under moderate ramming.
424. The mortar was composed of one volume of loose ce-
ment to two, three or four volumes of loose sand. Other pro-
portions were also employed, but in this table only those re-
sults are included in which the series of tests was complete as
to variations in consistency and storage.
The voids in the stone were about forty-three per cent,
when the measure was slightly shaken, and thirty-seven and
a half per cent, when rammed without mortar. The amount
of mortar used was made either thirty-three per cent, or forty
per cent, of the volume of the loose stone.
Four methods of storage were used as follows: 1st, blocks
immersed in water as soon as they were removed from the
molds, and after three or four months they were buried in sand ;
> Report of State Engineer of New York, 1897.
308
CEMENT AND CONCRETE
TABLE 131
Compressive Strength of Concrete
Mean Results with Four Brands Portland Cement, Illustrating Effects
OF Proportions, Consistency, and Methods of Storage. Tests of
Concrete Cubes, about Twenty Months Old, Made for
State Eno inker of New York
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COMPRESSIVE STRENGTH CONCRETE 309
2d, blocks covered with burlap and wet frequently for several
weeks, after which they were exposed to the weather; 3d, kept
in a cool cellar from the time of fabrication until shipped for
testing, and 4th, fully exposed to the weather throughout.
425. In Table 131 each result is the mean of four cubes, one
of each brand. The mean results are so arranged as to show
the effects of variations in the amount, the richness, and the
consistency of the mortar, and of the different methods of storage.
Taking up first the question of consistency, it appears from
column "j" that the use of plastic mortar, marked "mason's,"
gave from 92 to 97 per cent, of the strength given by the dry
mortar of about the consistency of "moist earth;" and that
the "quaking" concrete gave from 89 to 95 per cent, of the
strength of that marked "moist earth." From the three Unes
at the bottom of the table it is seen that in the poor concrete,
one-to-four mortar, the wettest mortar gave nearly as good
results as the dryest, while in the rich concrete, one-to-two
mortar, the strength of the wet was but 89 per cent, of the dry.
The explanation of this may be found in the fact that in the
poor concrete the mortar was "brash," and the concrete did
not ram well with a dry mortar, while the rich mortar was
"fuller" and more plastic, so that the excess of water was not
needed to make a compact mass.
426. Turning to the question of the amount of mortar, it is
plainly shown that the concrete containing forty per cent, is
but little better than that containing thirty-three per cent.
This is in hne with what has been said elsewhere, that an excess
of mortar, as well as a deficiency, may be an actual detriment
to the strength of the concrete. In this case the thirty-three
per cent, mortar was not quite sufficient to fill the voids in
the stone, and forty per cent, was a very slight excess.
Some interesting conclusions are indicated by the results in
the line marked "ratios," near the bottom of the table. The
ratios of the strength of the concrete containing thirty-three
per cent, mortar to the strength of that containing forty per
cent, are 91.6 per cent., 98.5 per cent, and 102.6 per cent., re-
spectively, for one-to-two, one-to-three, and one-to-four mor-
tars. That is, with a rich mortar forty per cent, may be used
to advantage, but if the mortar is of poor quality, the strength
of the concrete is not increased" by an excess of mortar.
310
CEMENT AND CONCRETE
Finally, as to the strength developed under different con-
ditions of storage, column "k" shows that for these cements the
highest strengths are attained by immersing the concrete in
water. In comparison, the strength developed by the concrete
covered with wet burlap is 84 per cent. ; in cool cellar, 82 per cent. ;
and in the open air fully exposed to the weather, 81 per cent.
427. The results given in Table 132 are the mean crushing
strengths obtained in the same series of tests as described above,
so arranged as to bring out the effect of the richness of the
mortar. Although several brands were tested, only the results
obtained with a single brand of Portland, namely, Milieu's
"Wayland," are included here, since the series was not com-
pleted with other brands. From similar tests with concretes
containing one-to-two and one-to-three mortars only, it was
found that three other brands of Portland gave from 91 to 102
per cent, of the strength obtained with the Wayland, and a
brand of sand-cement gave 66 per cent.
TABLE 132
Compressive Strength of Concrete. Effect of Richness of Mortar
Mean Resllts, Four Methods of Storage
Volume Mor-
tar AS
Per Cent, of
Volume of
Aggregate.
Consistency
of
Concrete.
Mortar, Proportions Cement to Sand. 1
1-1
1-2 1-3
1-4
1-5
Crushing Strength, Lbs. per Sq. In.
33 j
40 }
Moist Earth .
Mason's . . .
Quaking . . .
Moist Earth .
Mason's . . .
Quaking . . .
4267
4072
3764
3966
4123
3256
2888
2777
2847
3404
2960
3168
2056
2207
1723
2179
2027
2016
1810
1600
1767
1671
1750
1670
1537
1568
1441
1569
1466
1400
Mean
3908
3007
2035
1711
1495
Proportional .
100
77
62
44
88
Notes: — One brand Portland cement.
Aggregate, Portage sandstone, broken to pass two-inch ring.
Age of cubes about twentj' months.
Each result, mean of four cubes.
COMPRESSIVE STRENGTH CONCRETE
311
Each result in the table is the mean of four cubes, each
stored in a different manner. Tests with four brands (Table
131) where the concretes were made with one-to-two, one-to-
three and one-to-four mortars, indicated that the percentages of
the mean strength developed in the several methods of storage
were as follows: If stored in water, the cubes developed 115 per
cent, of the mean result; covered with burlap kept wet, the
cubes developed 97 per cent.; stored in a cool cellar, 95 per
cent.; and fully exposed to weather, 93 per tent, of the mean
strength.
The mean results given at the bottom of the table represent
each a mean of twenty-four cubes made with two different
amounts of mortar, three degrees of consistency, and four
methods of storage. By applying the percentages given above
the probable corresponding result for any set of conditions
may be obtained. The last line of the table shows the propor-
tions that the strength of the concretes made with poorer mor-
tars, bear to the strength obtained with one-to-one mortar.
428. Table 133 gives the results of a series of tests made by
J. W. Sussex at the University of Illinois.^ The materials used
were "Chicago A A Portland cement, sand containing a small
TABLE 133
Compressive Strength of Concrete. Relative Strength of Dry,
Medium, and Wet Mixtures
Tensilk
Strkngth,
Pounds per
Square Inch, at Age of
Propor-
Consistency.
Tamping.
tional Value
AT 3 Mo8.
7 days.
1 mouth.
3 months.
Dry
Light
1200
17.30
2500
82
Medium . . .
22JK)
2200
2150
71
Wet
it
1040
2230
3040
100
Dry
Hard
1:^40
1960.
2000
86
Medium . . .
1330
250.J
2580
85
Notes: — Concrete composition:
Cement, Portland, one volume.
Sand, containing some fine gravel, three volumes.
Six volumes broken limestone passing one-inch mesh.
Specimens, six-inch cubes.
Results by J. W. Sussex, Univ. of 111.
Technograph, 1902-03.
312 CEMENT AND CONCRETE
percentage of fine gravel, and crushed limestone which would
pass through a sieve with one-inch mesh." The proportions
were three parts sand and six of broken stone to one volume of
loose cement. The cubes were six inches on a side. The
treatment during storage is not stated. The consistency of
the concrete was as follows: "Dry," water 6.0 per cent., as
moist as damp earth, no free water flushed to surface in ram-
ming. "Medium," 7.8 per cent, water; water flushed to surface
and concrete quaked only after being well rammed. "Wet,"
water 9.4 per cent., concrete quaked in handling and could be
tamped but lightly.
Each result in the table is the mean of three cubes. The
concrete was tamped in layers about one inch thick with a
rammer weighing 11^ pounds and dropped six inches. Ten
blows of the rammer constituted "light" tamping and twenty
blows "hard" tamping. The results show that the "medium"
concrete gains its strength more rapidly than the "wet," but
that at one month the "wet" concrete has a higher strength
than the dry, and that at three months the wet surpasses in
strength both the dry and the medium.
Art. 54. Concretes with Various Kinds and Sizes op
Aggregates
429. It has already been stated that the character of the
aggregates is second only to the quality of the mortar in its
effect on the strength of concrete. The materials available for
aggregate in different localities are so varied that only a general
idea of their relative values may be obtained from a limited
number of tests.
The results given in Table 134 are from tests made at the
Watertown Arsenal,^ and show the compressive strengths of
concretes made with broken trap and gravel of different sizes.
The concretes are all very rich, and the strengths correspond-
ingly high, although the oldest specimens have hardened less
than three months. The results are somewhat irregular, and
the conclusion to be drawn concerning the best size for the
aggregate is not very clearly brought out. The one-inch trap
gives uniformly good results, as do the mixtures of two or
'Tests of Metals," 1898.
COMPRESSIVE STRENGTH CONCRETE
313
more sizes. The trap rock gives a higher result than the gravel,
the mortar being sufficient to fill the voids in the trap, and in
excess for the gravel.
TABLE 134
Compressive Strengths of Rich Concretes at Different Ages
Tests of Twelve-inch Cubes
CHAKA.CTER OF AqQREQATE.
Wt. per
Cu. Ft. of
Concrete
When
Abodt 1
Mo. Old,
IN Lbs.
Compressive Strkngth, Pounds per
Square Inch, at Age, Days,
7-8
19-23
29-34
61-76
Trap Y'
" r
"1"
" ir
" 2r
" r-i. 2r-2. . .
- Y'-i, r'-i, 2Y'-i
148.6
148.5
169.8
159.2
160.2
168.4
159.8
1391
1900
3390
3189
2400
2800
2800
2220
2769
4254
4006
4143
3786
4156
2800
3200
4917
4562
4140
4349
4800
5021
5272
2583
4523
4544»
5542
Mean results, trap rock alone
2653
3619
4110
4581
Pebbles 1"
" ^"
" r-1, i'-i, ir-i
148.2
151.0
150..3
147.8
1298
2276
1994
1486
2600
3186
3023
2676
2992
3817
3800
3000
3870
4018
3490
3800
Mean, pebbles alone . . .
1764
2871
3402
3794
Notes: — Tests made at Watertown Arsenal, "Tests of Metals," 1898.
AH concretes composed of one cubic foot of Alpha Portland cement,
weight 96| to 106 lbs. per cu. ft., one cu. ft. of bank sand,
weight 93| to 104 lbs. per cu. ft., and 3 cu. ft. of aggregate,
weighing from 93 to 106 lbs. per cu. ft.
The size of aggregate indicated gives the larger of the two screens
used in separating it into different sizes; thus, " f inch "■
means passing f inch mesh and retained on \ inch mesh.
The compressive strength of twelve inch cubes of one-to-one mor-
tar alone was 3,833 lbs. per sq. in. at seven days, and 4,800
lbs. per sq. in. at seventy-five days.
430. In 1896-97 Mr. A. W. Dow'^ prepared a number of
twelve-inch cubes of concrete for the Engineer Commissioner
* Not fractured.
' Report Operations, Engineer Department, District of Columbia, 1897»
Also Baker's "Masonry Construction," p. 112 r.
314
CEMENT AND CONCRETE
of the District of Columbia. These cubes are of interest as
showing the strength of natural cement concrete as well as
Portland, and the results are abstracted in Table 135.
TABLE 135
Compressive Strength of Concrete
Tests of Twelve-inch Cubes for the Engineer Commissioner of the
District of Columbia
Ref.
Composition of Concretes.
Per
Cent.
Voids in
Aggre-
gate.
Crushing
Strength, Lbs.
PER Square
Inch at One
Year.
Cement.
Sand.
Broken Stone.
Gravel.
Port-
land.
Natural.
Coarse.
Average.
Average.
Small.
1
2
3
4
5
6
2
2
2
2
2
2
(
5
6'
' 3' '
4
' d '
3
2
45.3
45.3
39.5
29.3
36.5
36.7
1850
3060
2700
2820
2750
2840
829
916
800
763
841
915
NoTE.s: — Materials:
Cement, Portland, "Atlas" (American), 104 lbs. per cu. ft.; Natural, .
"Round Top," 70 lbs. per cu. ft.
Sand, 15 per cent, retained on No. 8 mesh, 75 per cent, between 8 and
40 mesh, 10 per cent, passing 40 mesh. Sand was used damp, and
weighed in that condition 90 lbs. per cu. ft.
Stone, Bluestone, "Average," 93 per cent, between J inch and 2 inches.
"Coarse," 89 per cent, between 1^ inches and 2\ inches.
Gravel, "Average," 90 per cent, between ^ inch and IJ inches.
"Small," 90 per cent, between \ inch and } inch.
Granolithic, 92 per cent, between -^ inch and \ inch.
Mixing, thorough by experienced man.
Tamping, light, in 4 inch layers, just sufficient to bring mortar to surface.
Storage, cubes thoroughly wet twice a day.
Age of specimens when broken, one year.
The concretes all contained two parts sand and six parts
aggregate to one cement, but the character of the aggregate
varied as shown. The natural cement concrete gave from one-
quarter to one-third the strength of the Portland concrete.
The best result seems to be given by the average size broken
stone, which was in reality a mixture of various sizes, ninety-
* Mixture of one part granolithic size to one of concrete stone.
COMPRESSIVE STRENGTH CONCRETE
315
three per cent, of it being retained on a one-third inch mesh
and passing a two-irtch mesh. The mortar was probably in-
sufficient to fill the voids in the stone for the first three cubes
in the table, and under these conditions the gravel, with its
smaller percentage of voids, makes a good showing. This illus-
trates what we have already said, that the relative value of
broken stone and gravel for aggregate depends upon the pro-
portion of mortar used.
TABLE 136
Compressive Strength of Concrete. Portland Cement
Tests of Six-inch Cubes of Vakiol'S Mixtitkks
U
PS
Parts by Volume to
One Cement.
Crushing Strength, Pounds per Square
Inch, at Age of,
Sand.
Gravel.
Broken
Stone.
7 days.
30 dayg.
90 days.
1
2
3
4
5
6
7
8
9
10
0
0
1
2
2
^
2i
3
0
31
2
2
3
5
0
?*
3
0
0
2i
3
4
0
5
2i
0
4
3412
1077
1430
420
640
666
739
792
767
714
5318
1908
2215
2117a
1199
1385
2033
1482
1345
1028
6140
2517
2903
1324
1290
1609
1783
2014
1409
. 1848
Means, Actual
Means, Per Cent
1056
46
2003
88
2284
100
Note: — Results of Messrs. Ketchum and Honcns.
4S1. The results in Table 136 were obtained by Messrs. R.
B. Ketchum and F. W. Honens at the laboratory of the Uni-
versity of Illinois,' and illustrate the rate of gain in strength
of several mixtures. The cement used was Saylor's Portland,
fine and of good quality. The sand and gravel were composed
principally of silica, with 10 to 30 per cent, of limestone. About
60 per cent, of the sand passed a "number thirty" sieve. The
unscreened gravel had about 42 per cent, caught on a "num-
ber five" sieve and eighteen per cent, of it passed a "number
* Unscreened.
* Result irregular.
' Technograph, 1897-98.
316 CEMENT AND CONCRETE
thirty." Except in one mixture, however, the gravel and
broken stone were screened, and only that portion passing a
two-inch ring and retained on a "number five" sieve was used.
The stone was a magnesian limestone.
The concrete was mixed dry, so that considerable tamping
was required to bring water to the surface. The cubes were
first kept under a damp cloth for one day, immersed six days,
and then stored in air in a room until broken. In crushing,
"the direction of the force applied was parallel to the tamped
surface."
432. Each result in the table is the mean of six specimens.
Comparing number 2 with number 9 indicates that the strength
obtained with one part cement to three parts unscreened gravel
is much higher than with mortar of one part cement to three
parts sand. Comparing 9 and 10 indicates that seven parts
gravel and stone may be mixed with one-to-three mortar and
give higher strength than the mortar alone. A comparison of
6, 7, and 8 shows that in case there is sufficient mortar to fill
the voids in the aggregate, angular fragments give a somewhat
higher strength than rounded ones, but that a mixture of broken
stone and gravel is better than either alone. One of the most
important points brought out by the tests is that the strength
at seven days is 46 per cent., and at thirty days is 88 per cent.,
of the strength attained at three months.
Art. 55. Cinder Concrete, etc.
433. For such purposes as floors for buildings, cinders are
used in concrete to a considerable extent on account of their
light weight. Cinder concrete weighs only from two-thirds to
three-fourths as much as broken stone or gravel concrete.
The strength, however, is correspondingly less, and whether for
a given strength a floor may be made lighter by the use of
cinders will depend upon the conditions of use and the charac-
ter of the reinforcement.
Table 137 gives the results of the tests of eight-inch cyhnders,
fifteen inches high, made by Mr. George Hill.* In these cylin-
ders, cinders, broken stone, and gravel were used as aggregates.
The character of the materials is shown in the foot-note of the
> Trans. Am. Soc. C. E., Vol. xxxix, p. 632.
STRENGTH CINDER CONCRETE
317
table. As the specimens were but one month old when tested,
the results are low, but since in the construction of floor arches
the centers are usually removed in less than one month, the
strength developed in a short time has a special interest.
TABLE 137
Compressive Strength of Concrete about One Month Old
Tb8T8 of Cylinders, Eight Inches Diameter, Fifteen Inches High
Agqreqate.
Proportions bt Volume.
Age,
Compressive
Lbs. per
Strength,
Sq In.
American
Slag
Cement.
Cement.
Sand.
Aggregate.
Days.
Portland
Cement.
Cinders.
3
6
33
246
((
3
6
18
292
(t
2
5
33
305
(t
2
5
33
464
((
2
5
32
490
It
f ^
2.4
6
32
590
<(
1.7
4.2
30
342
t(
1.6
4
30
330
(t
1.6
4
31
766
((
1.6
4
31
765
Stone.
3
6
30
398
(t
2.4
4.1
30
603
<t
2.4
4
33
645
t(
2.4
4
30
730
Gravel.
3
6
30
'9i7
618
((
2.4
4.8
30
660
t(
2
7
25
880
((
1.6
6.5
31
730
Stone and gravel, )
graded . . . . )
1
2
10
30
625
Notes: —
Cement, American Portland, tensile strength 624 lbs. per sq. in., neat, seven
days.
Slag cement, a little less than 400 lbs. per sq. in., neat, seven days.
Sand, clean, sharp, bank sand of mixed sizes, from moderately fine up to
some pebbles size of bean.
Cinders, ordinary steam, dust to f inch size.
Stone, broken trap, nearly uniform size passing 1^ inch ring.
Gravel, clean, washed, J in. to IJ in.
Abstract of tests by Mr. George Hill, M. Am. Soc. C. E., Vol. xxxix, p. 632.
It is evident that cinder concrete should not be loaded very
heavily within a month after made. The gravel gives a better
result than broken stone.
318
CEMENT AND CONCRETE
434. Ill Table 138 are given the results of some tests of
twelve-inch cubes of cinder concrete made at the Watertown
Arsenal for the Eastern Expanded Metal Companies. Steam
cinders were used, practically as they came from the furnace,
only the larger clinkers being broken. Two proportions were
used and the specimens were broken at one month and three
months. It is seen that the one-one-three mixture is about
twice as strong as the one-two-five with all brands. The varia-
tions between the several brands are also very great.
TABLE 138
Crushing Strength of Cinder Concrete. Portland Cement
Tests of Twelve-inch Cubes at Watertown Arsenal
Brand
OF
Cement.
Strength, Pounds per Square Inch.
Mixture A, 1-1-3.
Mixture B, 1-2-5.
Age of Specimens.
Age of Specimens.
1 month.
3 months.
1 month.
3 months.
A
B
C
D
2329
1602
14.38
1032
2834
2414
1890
1393
940
696
744
471
1600
1223
880
685
Notes: —
Concretes mixed rather dry, 10 to 12 J pounds of water per cubic foot of
concrete.
Mixture "A," one part cement, one part sand, three parts cinders.
Mixture "B," one part cement, two parts sand, five parts cinders.
Weight of concrete, 104 to 116 pounds per cubic foot.
Tests for Eastern Expanded Metal Companies. Data from "Tests of
Metals," 1898.
435. Table 139 gives the results of other tests in the same
series, using a single brand of cement and five mixtures, the
richest containing three parts cinders and one part sand to one
volume cement, and the poorest six parts cinders and three
parts sand to one cement. The weight per cubic foot of the
several concretes is also given.
Tests of cinder concrete prisms made by the late Prof. J. B.
Johnson at Washington University ^ indicated that the mixture
• "Materials of Construction," p. 628.
CONCRETE WITH CLAY
319
containing one part sand and three parts cinders to one volume
cement gave the highest strength, or about twelve hundred
pounds per square inch, at one month. The same mixture gave
the highest values for the ratios of strength to cost, and of
strength to weight per cubic foot.
TABLE 139
Crushing Strength of Cinder Concrete. Various Proportions 'with
Germania Portland Cement
Tests of Twelvk-inch Cubes at Watertown Arsenal
Propobtions in Concrete.
Weight per
Cu. Ft. at 98
TO 102
Days, Pounds.
Crushing Strength,
Pounds per Square Inch,
AT Age,
Cement.
Sand.
Cinders.
29 to 39 days.
98 to 102 days.
1
2
2
2
3
3
3
4
5
6
110.4
112.8
107.9
105.3
103.5
1466
1098
904
769
529
2001
1634
1325
1084
788
Note:
1898.
-Tests for Eastern Expanded Metal Companies, "Tests of Metals,"
436. Clay in Concrete. — The effect of clay on the tensile
strength of mortars has already been shown (Art. 49). Aggre-
gates available for concrete frequently contain a certain amount
of clay, and the question arises whether such aggregate must
be washed, or whether certain small percentages may be per-
mitted in the concrete, using, perhaps, a trifle richer mortar.
The results in Table 140 were made to determine the effect of
clay on the crushing strength of concrete.'
The test specimens were six-inch cubes, and were broken
when one week to twelve weeks old in an Olsen machine. The
proportions were two parts sand and six parts gravel by weight
to one of Portland cement, or two parts sand and four parts
gravel by weight to one of natural cement. The clay is ap-
parently expressed as the per cent, of total aggregates. It is
seen that while six or twelve per cent, clay retards the harden-
ing of both Portland and natural cement concrete, the strength
of the Portland concrete after four weeks is increased by six per
* Tests by Messrs. J. J Richey and B. H. Prater, Technograph, 1902-03.
320
CEMENT AND CONCRETE
cent, clay, while at the same age the strength of the natural
cement concrete is not greatly affected. The ramming of con-
crete is facilitated by the presence of a small amount of clay,
but larger amounts may render the mass sticky and difficult
to ram.
TABLE 140
Effect of Clay on Crushing Strength of Concrete
Six-inch Cubes
Cement.
Proportions by
Weight, No. Parts
TO One Cement.
Age of Cubes
When
Broken.
Crushing Strength, Pounds per Sq.
In.; Clay as Per Cent, of Concrete,
Sand.
Gravel.
0
6
12
Port.
((
it
Nat.
2
2
2
2
2
2
6
6
6
4
4
4
1 week
4 weeks
12 "
1 week
4 weeks
12 "
1030
1398
2110
208
428
786
1001
1626
2760
131
364
722
692
1287
1865
81
283
480
Art. 56. The Modulus of Elasticity of Cement Mortar
AND Concrete
437. With the increasing use of concrete and steel in com-
bination, the modulus of elasticity of cement mortar and con-
crete assumes a new importance, since the ratio of the stresses
in the two materials depends upon the relative moduli of elas-
ticity. Some of the earlier determinations of the modulus of
mortar gave very high values. This may have been due to the
use of richer mixtures, and the exercise of greater care in the
manipulation, than are employed in actual construction, and
also to the fact that the determinations were based upon the
deformations resulting from the application of very limited
loads.
It is now considered that the ratio of stress to strain is not
constant, even for moderate loads, but that the modulus of
elasticity decreases with increasing stress, and this fact is brought
out in the following tables. The tests cited bring out a wide
range of values for concretes and mortars made from a variety
of sand and aggregate and of various compositions and ages.
438. Modulus of Elasticity of Natural and Portland Cement
Mortars. — Table 141 gives the modulus of elasticity of mortars
as determined by tests of twelve-inch cubes at the Watertown
MODULUS OF ELASTICITY
321
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322
CEMENT AND CONCRETE
Arsenal.* These specimens were a portion of those prepared
by Mr. Rafter, the compressive strength being given in Table
129. As each value is the result of but one determination, the
results are not as regular as might be desired. In general the
strength and the modulus decrease together as the amount of
water used in mixing is increased. The modulus also decreases
with the strength as the proportion of sand increases.
439. Modulus of Concretes One Month to Six Months Old. —
In the compressive tests of twelve-inch concrete cubes made
for Mr. George A. Kimball and abstracted in Table 130, many
of the specimens were also gaged for compression under load to
determine the modulus of elasticity, and a part of the results
are presented in Table 142.
TABLE 142
Modulus of Elasticity of Concrete
Tksts Made on Twelve-inch Cubes of Portland Cement Concrete at
Watertown Arsenal for Boston Elevated Railroad
Age
OF Cubes
When
Crushed.
Concrete 1-2-4. j Concrete 1-3-6.
CONCRKTB 1-6-12.
Modulus of Elasticity in Thousands, between Loads,
in Pounds per Square Inch, of
100-GOO
100-1000
1000-2000
lOO-GOO
100-1000
1000-2000
100-600
100-1000
7 days
1 month
3 months
6 months
2592c
2662c
3670
3646
2053c
2444c
3170
3567
1351a
1462c
2157
2581
1869c
2438
2976
3608
15296
21.35
2656
3503
121901
1805
1868
"l376'
1642
1820
1363
1522
Notes: — Results marked "a" are means of five or more tests of one brand.
Results marked "b" are means of five or more tests on each of
two brands.
Results marked "c" are means of five or more tests on each of
three brands.
Results not marked are means of five or more tests on each of
four brands, two American, two German.
For compressive strengths of similar cubes, see Table 130.
It is seen that the modulus increases with the age and rich-
ness of the specimens, and decreases as the load increases. For
one-two-four concrete the modulus at one month, for loads
between a hundred and a thousand pounds, is about two and
* "Tests of Metals," 1899.
MODULUS OF ELASTICITY 323
one-half million, and for six months, three and a half million.
The corresponding values for the one-three-six concrete are two
million and three and one-half million. When the ultimate
strength is approached, the modulus of elasticity decreases
rapidly, and between loads of one thousand and two thousand
pounds per square inch, the richest concrete gives only about
one and one-half and two and one-half million at one month
and six months, respectively.
440. Modulus of Concrete Dependent on Richness of Mortar.
— The results in Table 143 are abstracted from the extensive
tests made at the Watertown Arsenal for the State Engineer
of New York. Although several brands were tested, the results
in the table are from one brand only, namely, "Wayland"
Portland. These cubes were all stored in the same manner,
namely, in water three to four months, and then buried in damp
sand until broken at the age of twenty months. The mean
ultimate strengths of similar cubes stored according to four
methods are given in Table 132.
Since in all of these mixtures the quantity of mortar was a
given percentage, either thirty-three or forty, of the volume of
aggregate, the effect of the richness of the mortar may be studied.
While the proportional strengths of the concretes made with
mortars containing from one to five parts sand are 100, 77, 52,
44, and 38, the corresponding proportional moduli of elasticity
are 100, 92, 77, 60, and 55, the modulus decreasing less rapidly
than the strength, with the addition of sand.
441. Gravel and Trap Aggregates. — Table 144 gives the re-
sults of the determinations of the modulus of elasticity of con-
crete specimens made and tested at the Watertown Arsenal,*
the strength of which was given in Table 134. As these are all
rich concretes, the moduli and the strengths are high. The
values of the modulus for the gravel concretes are about 70
per cent, of those for the trap, but the strengths of the gravel
concretes are in general about 80 per cent, of those obtained
with concretes having trap aggregate. In a general way, how-
ever, the modulus and strength vary together.
442. Modulus of Cinder Concrete. — The modulus of elas-
ticity of cinder concrete prepared for the Eastern Expanded
'Tests of Metals," 1898.
324
CEMENT AND CONCRETE
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t^ CD 00
aq to I-
(M rH rH
00 t^ CO
t- CO I^
1^ rH (M
(N ■>* (M
a
O es rj
O cS 3
8
axvoaaooy SHaqo^
Bv uvxuo}^ awaaOj\
MODULUS OF ELASTICITY
325
TABLZ! 144
Modnlns of Elasticity of Rich Concretes with Gravel and
Trap as Aggregates
Tests of Twelve-inch Cubes at Watbrtown Arsenal.
Cement
1--1-3. Alpha
Character of Aooreoate.
Modulus of Elasticity in Thousands, be-
tween Loads of 100 and 1,000
PouxDS PER Square Inch, at Age, Days,
7-8
19-23
29-34
61-76
Trap \"
" *"
"1"
" ir
" ■^"
" J"-l, 2V'-2 . .
" \"-l, 1"-1, 2i"-l
1875
3214
4091
4500
3214
5000
8461
2500
2368
6429
5625
5625
4500
4500
3750
5625
6625
5000
4500
7500
5625
3750
' 5625 "
4091
7500
5625
7500
Mean Results, trap rock aloue
3622
4507
5375
5682
Pebbles f"
1800
3750
2812
1800
3750
4091
3461
3214
3461
3750
4091
8461
3214
3000
4500
3214
" 1\"
'• f"-l, lJ"-2 . .
" i"-l, i"-l, li"-l
Mean Results, pebbles alone
2540
3629
3691
3482
Notes: —
Tests at Watertown Arsenal, "Tests of Metals," 1898.
For crushing strength of these concretes, see Table 134.
The modulus of elasticity of twelve-inch mortar cubes, one volume cement
to one volume sand, was, for loads between five hundred and one thou-
sand pounds per square inch, 3,461,000 at seven days and 5,000,000 at
seventy-five days.
Metal Companies is given in Table 145. The results are seen
to be low, as is the crushing strength. The permanent set in
five-inch gaged length for a load of six hundred pounds per
square inch is also shown in the table.
326
CEMENT AND CONCRETE
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CHAPTER XVII
THE TRANSVERSE STRENGTH AND OTHER PROPERTIES OF
MORTAR AND CONCRETE
Art. 57. Transverse Strength
443. TENSILE, TRANSVERSE AND COMPRESSIVE STRENGTHS
OF MORTAR COMPARED. — The tests given in Tables 146 and
147 were designed to compare the strengths of cement mortars
in tension, bending and compression, and to show the relative
effect on the three kinds of strength of certain variations in
manipulation.
The tensile specimens were briquets of the ordinary form,
made in brass molds. The transverse and compressive speci-
mens were made in wooden molds, the bars for transverse tests
being two by two by eight inches and molded horizontally,
while the specimens for compressive tests were two-inch cubes.
Specimens of the three forms were made from the same batch
of mortar to obviate, as far as possible, variations due to differ-
ence in gaging. Two cubes, two briquets and one bar were
usually made from one gaging of mortar.
The briquets were broken in the usual manner on a Riehl^
cement testing machine. The bars were broken on a home-
made lever machine. Two fixed knife edges were placed five
and one-third inches apart, and the breaking stress was applied
through a third knife edge at mid-span. The lengths of the
lever arms of the testing machine were in the ratio of one to
twenty-five, and water was allowed to run gently into a vessel
at the end of the longer arm. The span of five and one-third
inches was chosen because at this length the modulus of rup-
ture, for a two inch square specimen, has the same numerical
value as the center load applied.
The cubes were crushed in a crude machine, improvised for
the purpose, consisting of two iron plates, two hydraulic jacks,
with hydraulic weighing gage and proper framework. The
upper plate was fastened to the base of the framework by
327
328 CEMENT AND CONCRETE
means of two bolts which worked freely in the lower plate, and
the latter was connected to the weighing gage at the top of the
framework by two bolts which worked freely in the upper
plate. An hydraulic jack was placed under either end of a
yoke, at the middle of which was supported the weighing gage.
While the tensile and transverse tests are doubtless good, the
compressive tests are lacking in accuracy because of the crude
method of crushing.
444. Table 146 shows the comparative tensile, transverse
and compressive strengths of two samples of cement, one of
Portland and one of natural, with different proportions of sand.
It is seen that the modulus of rupture, or stress on the extreme
fiber in transverse tests, computed by the ordinary formula, is
considerably greater than the strength obtained in direct tensile
tests. The ratio of the transverse to the tensile strength varies
from 1,25 to 1.90 for Portland and from 0.95 to 2.19 for natural.
These tests indicate that the ratio of the compressive strength
to the tensile strength diminishes with the addition of sand,
but the reverse has been found to be true in other series of
tests where the facilities for making compressive tests were
better. The result obtained here may be attributed to the fact
that richer mixtures gave cubes with smoother and more regular
faces, and thus less subject to eccentric loading. The com-
pressive strength increases between three months and one year
much more than the tensile and transverse strengths. Tests on
ten brands of Portland and ten brands of natural showed that
in general the brands giving the highest strength in tension
gave also the highest strength in transverse and compressive
tests.
445. A few results to show the effect of consistency of the
mortar on the three kinds of strength are given in Table 147.
With Portland cement the highest strength in transverse and
compressive tests is given by a wetter mortar than that giving
the highest strength in tension, but with natural cement the
compressive strength is lowered more than the tensile strength
by an excess of water. All oi the specimens were one year
•old when broken.
446. TRANSVERSE TESTS OF CONCRETE BARS. — The effect
on the strength of concrete of variations in manipulation and
treatment is most satisfactorily investigated by tests of large
TRANSVERSE STRENGTH
329
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330
CEMENT AND CONCRETE
sized specimens either in compression or bending. In the prep-
aration of such large specimens the conditions of actual con-
struction may be closely reproduced, and the results, although
likely to be quite irregular, as the strength of concrete in struc-
tures is not uniform throughout, are nevertheless very valu-
able On account of the expense connected with such tests,
the number of specimens is usually so limited that the natui'al
irregularities in strength mask the true conclusions.
TABLE 147
Comparative Tensile, Transverse and Compressive Tests,
of Varying Consistency of Mortar
Effect
Ref.
Cement.
Water
AS Per
Cent, of
Dry
Ingre-
dients.
Mean Strength, Pounds per
Square Inch.
Transverse and
Compressive
Strength as Per
Cent, op Tensile.
Tensile.
Trans.
Comp.
Trans.
Comp.
1
P
9
616
837
1731
162
335
2
P
12
533
987
2173
185
408
3
P
15
467
850
2498
180
633
4
P
18
461
966
2823
209
612
5
P
21
430
1022
2487
239
578
6
N
12
272
447
2270
164
835
7
N
14
325
516
2141
158
669
8
N
16
319
619
1481
163
464
9
N .
20
304
509
1612
167
497
10
N
24
315
462
1317
147
418
Notes: — Cement, P = Portland, Brand R; N = Natural, Brand In;
Sand, "Point aux Pins," pass No. 10 sieve. Age of specimens,
one year. Two parts sand to one cement by weight.
In Tables 148 to 156 are given some of the results obtained
in testing over two hundred concrete bars at St. Marys Falls
Canal. The molds for making the concrete bars were ten
inches square by four and one-half feet long inside. The con-
crete was rammed into the mold with a light wooden rammer.
The bars were, in general, covered with moist earth soon after
completed, to await the time of breaking. To break them they
were supported on knife edges placed four feet apart, and the
load was applied at mid-span through an iron bolt laid across
the bar. In the earlier tests a direct load was imposed by means
of a platform which was gradually loaded with one-man stone,
but in the later tests the load was applied by means of hydraulic
TRANSVERSE STRENGTH CONCRETE
331
jacks, an, hydraulic gage being used to measure the force. In
many cases the half bars were again broken at a later date
with a twenty-inch span, as shown in the tables.
447. Variations in Richness of Mortar. — In Table 148 sev-
eral concretes made with mortars having different proportions
of sand are compared, and the results of briquet tests on similar
mortars are also given. Although the briquets were not broken
at the same age as the bars, the tests on the latter at the differ-
ent ages show that they were not gaining strength rapidly,
and the results may therefore be compared without serious
error.
TABLE 148
Transverse Tests of Concrete. Variations in Richness of Mortar
No.
Bars.
Date
Made.
Cem-
ent.
Strength
OF Mortar Bri-
quets in Tension
AT Age of
3 Yrs. and 1 Mo.
Modulus of Rupture.
Four Foot Span.
Twenty Inch Span.
No.
Tests.
Age.
Mean.
No.
Tests.
Age.
Mean.
Mo. Da.
Yr. Mo.
Yr. Mo.
76-77
11-2
Port.
0
717
2
1 7
593
4
2 9
600
78-79
t(
i;
1
790
2
689
4
698
80-81
((
u
2
595
2
538
4
577
82-83
u
u
3
432
2
489
3
415
84-85
11-3
((
4
335
2
379
4
385
86-87
"
"
5
252
2
284
4
316
88-89
((
"
6
218
2
262
4
279
90-91
11-4
Nat.
1
483
2
420
4
450
92-93
u
(1
2
396
2
332
4
387
94-95
il
(1
3
330
2
240
4
224
96-97
n
u
4
237
2
186
4
205
Notes: —
Portland, Brand R, Sample 82 M.
Natural, Brand Gn, Sample 83 T.
Sand, from *' Point aux Pins" (river sand).
Stone, Potsdam sandstone, retained on f inch square mesh, and no pieces
larger than 3 inches in one dimension.
Amount mortar used in each case equal to voids in stone measured loose,
except in case 1-2 natural, when mortar exceeded voids by seven per
cent.
The fracture showed concrete very compact in nearly all cases.
The results obtained with natural cement show that the
tensile strength of the mortar in pounds per square inch was
greater than the modulus of rupture obtained for the concrete.
332
CEMENT AND CONCRETE
This is also the case with rich mortars of Portland cement,
but for Portland mortars containing more than three parts sand
to one of cement the concrete gives the higher result. The
strength of the concrete with one-to-four mortar is fifty-five per
cent, of the strength with one-to-one mortar for Portland, and
forty-five per cent, for natural. The decrease in strength due
to larger proportions of sand in the mortar is usually greater
than the decrease in cost.
TABLE 149
Transverse Tests of Concrete. Variations in Quantity of Mortar
No.
Bar.
Date
Made.
Am't Rammed
Concrete Madk
AS Per Cent.
OF Loose Stonk.
Modulus of Rupture.
Four Foot Span.
Twenty Inch Span.
No.
Tests.
Age.
Mean,
No.
Tests.
Age.
Mean.
42
37-40
38-41
39-43
Mo. Da,
7 3
7 1
7 1
7 1,3
31
38
47
60
88
92
104
U2
1
2
2
2
lyr.
n
u
247
284
350
346
2
3
4
4
Yr. Mo.
1 10
it
363
.447
596
589
Notes: —
Cement, Portland, Brand R, Sample 64 T.
Sand, " Point aux Pins," three parts by weight dry to one cement.
Stone, Drummond Island limestone, passing 1 inch slits and retained on
f inch slits.
448. Variations in Amount of Mortar Used. — Bars 37 to
43, Table 149, were all made with the same kind and quality
of stone and the same quality of mortar, three parts sand to one
cement by weight, but the amount of mortar varied; thus, in
bars 41 and 38 sufficient mortar was used to fill the voids in
the stone, while the bars above were deficient in mortar, and
those below contained an excess. It is seen that the highest
result is given by the bars in which the mortar was just suf-
ficient to fill the voids in the stone, though the bars containing
an excess of mortar gave practically the same result, while a
deficiency of mortar resulted in decreased strength.
449. Variations in the Amount of Sand for Fixed Quantities
of Cement and Stone. — In Table 150, bars 68 to 75 were all
made with the same kind and quantity of cement and stone,
but the amount of sand, and consequently the quantity and
TRANSVERSE STRENGTH CONCRETE
333
quality of the mortar, varied. The highest strength is given by
the concrete in which the weight of the sand was three times
the weight of the cement; this quantity of sand gave sufficient
mortar to fill the voids in the stone. The richer mortars,
though stronger, were deficient in quantity, while four parts
sand made an excess of mortar having a lower strength.
TABLE 150
Transverse Tests of Concrete. Variations in Quantity of Sand for
Fixed Quantities of Cement and Stone
i
6
S
z
p
a
o
1^'
0
^^
a z
oc a
^a
(do
Amount of Mor-
tar Made as
Per Cent, of Com-
pacted Stone.
Amount Rammed
Concrete as Per
Cent. Compacted
Stone.
Modulus of Rupture.
<
a
a
Pi
a
b
c
d
Four Foot Span.
Twenty Inch Span.
No.
Tests.
Age.
Mean.
No.
Tests.
Age.
Mean.
74-75
72-73
70-71
6&-69
65
65
65
65
65
130
195
260
1
2
3
4
16
24
32
42
95
101
104
110
2
2
2
2
Yr.Mo.
1 8
(( u
(( u
u u
299
•335
324
322
4
4
4
4
Yr.Mo.
2 10
i( it
U ((
295
303
354
321
Notes: —
Cement, Portland, Brand R, Sample 768.
Sand, " Point aux Pins."
Stone, Potsdam sandstone, screened with f inch mesh, and all pieces larger
than 3 inches in one dimension rejected.
Appearance of fracture: a, very porous; 6, many voids; c, some voids;
d, few voids.
450, Consistency of Concrete. — The bars, the results of
which are given in Table 151, were made to show the effect of
the consistency of the concrete on the strength obtained. It is
seen that the highest strength is given when the consistency
is such that a little moisture is shown when ramming is com-
pleted ; the decrease in strength from an excess of water is much
less than thp.t caused by a corresponding deficiency. The re-
sults of briquet tests on similar mortar are also given in the
table, and it appears that the highest result is given by the
mortar containing the least water, which shows the familiar
fact that the mortar for concrete should be more moist than
that which gives the best results in briquet tests.
451. Value of Thorough Mixing. — Bars 182 to 189, Table
152, were made to show the effect of thorough mixing of the
334 CEMENT AND CONCRETE
TABLE 151
Transverse Tests of Concrete. Variations in Consistency
Bar.
Cem-
ent,
Kind.
Pro-
D
So .
lis
D U o
Modulus of Rupture.
i
z
u
f-
Z
d
1
z
u
1
H
Z
u
portions.
4 Foot Span,
13 Months
20 In. Span,
2 Years.
Cem-
ent,
Lb8.
Sand,
Lbs.
No.
Tests.
Mean.
No.
Tests.
Mean.
138-139
Port.
120
237
0.61
7.31
2
354
2
289
a
509
136-137
tt
120
237
0.83
7.12
2
450
3
482
b
404
140-141
((
120
237
1.03
7.00
2
450
4
442
c
416
142-143
((
120
240
1.16
7.12
2
385
4
417
d
400
146-147
Nat.
115
230
0.83
7.64
2
180
4
156
a
267
144-145
((
115
230
1.03
7.31
2
223
4
282
b
187
148-149
(,i
116
230
1.16
7.12
2
234
4
266
c
146
150-151
((
115
230
1.35
7.12
2
202
4
177
d
127
152-153
u
115
230
1.51
7.12
2
155
3
170
e
116
Notes: — Portland cement, Brand R, Sample M.
Natural cement, Brand Gn, Sample 88 T.
Sand, " Point aux Pins" (river sand).
Stone, Potsdam sandstone, 7 cubic feet to each batch.
Results in last column give tensile strength at one year of briquets
made from similar mortar.
Consistency : — a, very dry ; no moisture shown on ramming.
b, slight moisture appeared at surface after continued
ramming.
c, quaked somewhat.
d, quaked and water rose to surface in ramming,
e, too wet to ram.
TABLE 152
Transverse Tests of Concrete Bars. Value of Thorough Mixing
No. Bar.
Mixing of Concrete.
Modulus of Rupture.
Four Foot Span.
Twenty Inch Span.
No.
Tests.
Age.
Mean.
No.
Tests.
• Age.
Mean.
182-186
183-187
184-188
185-189
Turned once and back
" twice " "
" 3 times " "
2
2
2
2
1 yr.
290
294
306
328
4
4
4
4
21J mo.
378
363
444
474
Notes: —Cement, Portland, Brand X, 200 lbs.
Sand, " Point aux Pins," 600 lbs.
Stone, Potsdam sandstone, 15 cubic feet.
TRANSVERSE STRENGTH CONCRETE
335
concrete. Comparing the concrete turned once or twice, and
back, with that turned three or four times, and back, it is seen
that the mean strength of twelve tests with the former is 328
pounds per square inch, while the mean strength of the same
number of tests with the more thoroughly mixed concrete is
388 pounds per square inch, an increase of eighteen per cent.
TABLE 153
Transverse Tests of Concrete. Variation in Size of Aggregate
No.
Bar.
K
Si
<!
03
a
a
o
Stone.
0
1 H
0.
Amount
Rammed Con-
crete Made,
Cubic Feet.
MoDuLrUS OF Rupture.
Lbs. pbrSq. In.
Kind.
Sizes.
Per
Cent.
Voids
IN
Com-
pact.
One Bar, 4
Ft. Span,
Age 1 Yr.
Half Bar,
20 In.
Span, Age,
21 Mo.
202
199
201
200
198
196
195
197
194
XR6
<c
XM3
a
a
a
«{
«{
d
d
d
V
iV, §F
M
J each,
V, F, & M
j each,
K, V,F,&M
V
F
M
J each,
V, F, & M
45
48
44
Uo
32
33
34
J30
3.75
3.75
3.75
3.75
3.75
3.75
3.75
3.75
3.75
3.75
3.75
3.75
3.75
3.86
3.75
259
259
216
245
288
216
186
131
207
367
347
269
292
390
311
302
208
302
Notes: —
All mortar, three parts sand to one part Portland cement by weight.
Quantity of mortar about one-third volume of compact stone.
Stone: — a — Potsdam sandstone; d = gravel.
Size : — K = ^ j inch to \ inch.
F = i " i "
F = i " 1 "
M = \ " 2 "
452. Variations in Size of Stone and Volume of Voids. — The
bars given in Table 153 were all made with mortar composed
of three parts sand to one of Portland cement by weight. The
stone for these bars was sorted into different sizes, and these
were recombined in the proportions indicated in the table.
The sizes are denoted as follows: that passing one-half inch
mesh and retained on one-quarter inch mesh, is called V; one-
half inch to one inch is called F; one inch to two inches, M;
two inches to three inches, C; and coarse sand, one-tenth inch
to one-quarter inch, is called K.
336 CEMENT AND CONCRETE
The first five bars were made with broken sandstone, and it
is seen that the coarsest stone, size one inch to two inches,
gave the lowest result. The size V, one-quarter inch to one-
half inch, although containing no smaller percentage of voids,
gave a much higher strength. The highest result was given
by the bar made with a mixture of four sizes, the voids in this
mixture being only thirty-six per cent.
The bars containing gravel as aggregate indicate that the
strength decreases as the size of stone and volume of voids
increase, but a mixture of three sizes gives nearly as good a
result as the fine grave? alone. Comparing the results with
similar sizes of the two kinds of aggregate, it appears that the
broken sandstone gives somewhat better results than gravel,
notwithstanding that the proportion of voids in the former
exceeds that in the latter.
453. Sandstone and Bowlder Stone Compared. — The results
given in Table 154 are from a series of tests made for the Mich-
igan Lake Superior Power Company by Mr. H. von Schon,
Chief Engineer,^ and show the strength of concretes made with
two kinds of aggregate available at Sault Ste. Marie. Two
samples of Portland cement, one made from marl and one from
limestone, a slag cement, and a natural cement, are used in
these tests.
The two samples of Portland cement give nearly the same
result, the slag less than half the strength, and the natural
quite weak. The ratio of the strength obtained with crushed
bowlders to that made with sandstone is about 1.6 with
Portland, and the superiority of the former is shown with all
cements.
454. Various Kinds of Aggregate. — Table 155 gives the re-
sults obtained at St. Marys Falls Canal in using various kinds
of stone. In bars 25 to 30, three kinds of stone are compared.
The superiority of the Kelleys Island Limestone " shavings "
from the stone planers is evident. The shape of the pieces may
have had a considerable influence on this result, the planer
shavings being flat, or lenticular in form. Bar 34 was made
with a hard limestone from Drummond Island, 33 with gravel,
and 31 and 32 with gravel and stone mixed in equal propor-
' Tests reported by H. von Schon in Trans. A. S. C. E., Vol. xlii, p. 135.
TRANSVERSE STRENGTH CONCRETE
337
TABLE 154
Transverse Strength of Concrete vrith Crushed Sandstone and
Bowlders
Aggregate.
MixTtrRB No.
MODUI^US OF RUPTDRB, PoUNDS PER SQUARE InCH.
Portland.
(Marl.)
Portland.
(Bock.)
Slag.
Natural.
Sandstone , . .
1
2
3
4
5
328
283
220
178
106
312
265
178
173
18(>
122
161
118
74
131
43
34
40
'35'
Mean, Sandstone
223
223
121
38
Bowlder Stone .
it n
41 11
1
2
8
4
5
407
377
332
327
333
397
395
374
351
325
145
167
176
146
.123
36
67
55
52
60
Mean, Bowlder Stone ....
355
368
151
54
Ratio of j Bowlder Stone j
Moduli} Sandstone )
1.59
1.65
1.25
1.42
Notes: — Cross breaking tests of 6 in. by 6 in. by 24 in. bars made for
Michigan, Lake Superior Power Co.
Materials: — Cement, representative brands of each of four classes.
Sand, river sand, " Point aux Pins," mostly quartz, 96^ lbs. per cubic foot.
Voids, 41.7 per cent. Fineness, 96 per cent, passing No. 20 sieve,
39 per cent, passing No. 40 sieve.
Stone, Sandstone, broken Potsdam 1 to IJ inch size.
Bowlder stone, broken gneiss and granite bowlders,
1 to IJ inch size.
Proportion in mortar, 1 part cement to 2.4 parts sand by volume.
Mixing: — Consistency, plastic; cement and sand mixed dry, then wet and
mixed; mortar added to wet aggregate and concrete mixed by hand.
Storage: — Bars stored in shed, protected from rain, fully exposed to air.
Age of specimens when broken, sixty days.
Mixture: — 1. Mortar 16 per cent, m excess of quantity required to fill voids.
2. Mortar 10 per cent, in excess of quantity required to fill voids.
3. Mortar 5 per cent, in excess of quantity required to fill voids.
4. Mortar just sufficient to fill voids in stone.
6, Mortar 15 per cent, in excess of amoimt required to fill voids in
stone, but this 16 per cent, excess made with lime instead of
cement.
338
CEMENT AND CONCRETE
60
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TRANSVERSE STRENGTH CONCRETE
339
tions The gravel and hard limestone gave about the same
result, but it is seen that the mixture gave a higher strength.
Bars 154 to 159 were made to test the value of broken brick for
use in concrete. It is seen that the strength obtained with
brick is considerably lower than that obtained with the soft
limestone. Had a poorer mortar been used, the brick would
doubtless have given a better comparative result, since with
the one-to-two mortar, the brick are not strong enough in them-
selves to utilize the full adhesive strength of the mortar.
TABLE 156
Transverse Tests of Concrete. Use of Screenings 'vtrith Broken
Stone
Sand and
Stone.
Stone
TO 80 Lbs.
Cement.
Modulus of Rupture.
No.
Bar.
t-t O
OH
go
Four Foot
Span.
Age, 11 Mos.
Twenty Inch
Span.
Age, 2 Yrs.
(In B
■s5
at
No.
Tests.
Mean.
No.
Tests.
Mean.
114-115
a
49
.240
7.0
3.43
3.05
2
233
4
237
124-125
b
48.4
243
7.0
3.39
3.05
2
196
4
210
112-113
c
44
240
7.0
3.08
2
194
3
236
116-117
d
44
138
7.8
3.43
2.16
2
227
3
311
118-119
e
40.5
243
7.0
2.83
3.10
2
201
4
219
120-121
f
38.8
243
7.0
2.72
3.05
2
122
4
164
122
9
243
7.0
3.05
1
130
2
141
Notes: —
Cement: Natural, Brand Gn, Sample 92 T, 80 lbs.
Stone: — a = Drummond Island limestone, screened.
6 = 10 parts screenings to 100 parts stone.
c = 17 parts screenings to 100 parts stone.
d = 17 parts screenings to 100 parts stone. Screenings replacing
equal amount sand.
e = 50 parts screenings to 100 parts stone.
/ = 100 parts screenings to 100 parts stone.
g = Screenings only, no broken stone.
455. Use of Screenings with Broken Stone. — Table 156 gives
the results of a number of tests made to show the effect of
mixing screenings with the broken stone. A smaller amount
of mortar is required to fill the voids in a given volume of stone
and screenings mixed than is required for the same volume of
340 CEMENT AND CONCRETE
stone. It is seen that, with natural cement, when the same
volume of mortar is used in the two cases, the presence of
screenings to the amount of one-third of the total aggregate
does not (make a material change in the strength of the result-
ing concrete, but when the screenings are allowed to take the
place of a part of the sand in the mortar, as in bars 116 and
117, a much stronger concrete results. Natural cement mixed
with sand and screenings alone, bar 122, does not make a strong
concrete, but Portland cement with screenings without sand
was found to give excellent results.
456. Deposition in Running Water. — A few tests were made
to show the effect of depositing concrete in rapidly running
water. The molds were placed in the stream and weighted
down in twelve inches of water. The concrete for two bars
was deposited as soon as mixed, that for two other bars was
allowed to stand in the air three hours before deposition, until
it should have acquired an initial set, and two bars were made
after the mortar had been allowed to stand five hours and
twenty minutes before deposition; by this time the mortar had
set quite hard. No attempt was made to ram the concrete,
which was deposited by lowering it carefully into the water
with shovels, the molds being filled as rapidly as possible. A
very large amount of the cement was washed out by the current
in all cases. After a few months the bars were removed from
the stream and covered with earth as usual. The tests at eleven
months did not appear to show any advantage in allowing the
mortar to stand some time before deposition, but the tests at
two years showed a distinct advantage in this treatment. ■
457. Use of Concrete in Freezing Weather. — Table 157 gives
the results obtained with Portland cement concrete made in
the open air during cold weather. The conditions as to tem-
peratures and the character of the materials are fully given in
the table. The experiments are too limited to permit of draw-
ing definite conclusions, but the following points are indicated
by the results obtained. The use of warm water, 100° to 156"
Fahr., in freezing weather appears to give somewhat better
results than cold water. Salt should not be used unless the
temperature is below the freezing point, but in very cold weather
the use of enough salt in the water to lower its freezing point
below the temperature of the air seems to hasten the harden-
TRANSVERSE STRENGTH CONCRETE
341
TABLE 157
Transverse Tests of Concrete Bars. Use of Concrete in Low-
Temperatures
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a, Concrete frozen after 10 to 20 min.; b, frozen in 46 min.; c, began to
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Notes: — Cement. Portland, Br. R. Sand, "Point aux Pins." Stone.
Potsdam sandstone.
342
CEMENT AND CONCRETE
ing as well as to increase the ultimate strength,
mortars in freezing weather, see Art. 50.)
(For tests of
Art. 58. Resistance to Shear and Abrasion
458. Shearing Strength. — The shearing strength of mortars
and concretes is of importance not only because of its intimate
relation to the compressive strength, but because of the shear-
ing stresses to which these materials are subjected in structures
reinforced with steel. But few tests of shearing strength have
been made, however, partly because of the lack of appreciation
of their value, and partly because it is difficult to subject a
specimen to a purely shearing stress. It is frequently stated
that the shearing strength is somewhat in excess of the tensile
strength, perhaps as much as twenty per cent.
Table 158 gives the results of a series of tests made by Prof.
Bauschinger in 1878.* The values in shear are very closely
twenty per cent, in excess of the tensile strengths of similar
mortars tested at the same time.
TABLE 158
Shearing Strength of Portland Cement Mortar Cubes Hardened
in Air
Cement.
Shearing Strength, Pounds per
Square Inch.
Tensile
Strength
OF Similar
Mortars
AT Eight
Weeks.
Age of Mortar.
1 week.
2 weeks.
4 weeks.
8 weeks.
Quick setting Port- (
land, mean results <
of four brands. (
Slow setting Portland, (
mean results of four )
brands. (
None
3
5
None
3
5
225
108
67
301
124
78
. 270
128
94
323
164
122
257
154
112
341
199
138
259
196
168
377
237
199
210
169
139
256
181
169
Note : — Cement, each result mean of four brands. Sand, medium grain,
clean. Mortars hardened in dry air.
Tests by Professor Bauschinger, 1878.
459. A distinction should be drawn between the resistance
offered by a thin mortar bed to the sliding of one stone or brick
on another and to shear of the mortar itself. The forme** re-
Quoted by Mr. Emil Knichling in a Report on Cement Mortars.
SHEAR AND ABRASION 343
sistance involves the adhesion of the mortar to the surface of
the brick or stone, and the values for this resistance are usually
much less than the shearing strength, and not greatly in excess
of the adhesive strength. The one is of importance in the de-
termination of the stabiUty of masonry dams, retaining walls,
etc., but the latter is the resistance in question in the design
of monolithic concrete structures.
460. Resistance to Abrasion. — The resistance of cement
mortar to abrasion depends on the quality of the sand as well
as the cement. The abraiding surface wears away the cement
or pulls the particles of sand out of their beds in the cement
matrix. If the adhesion to the sand grains is strong, the sand
particles receive the wear and withstand it until nearly worn
away. With hard sand particles, therefore, the resistance to
abrasion should increase as the proportion of sand increases,
until the volume of the cement matrix becomes relatively too
small to thoroughly bind the sand grains together. This limit is
reached, however, when the mortar contains not more than two
parts sand. With soft sand grains, the neat cement will usually
give the highest resistance to abrasion, at least in the case of
Portland. It has been found that specimens hardened in the air
are brittle and wear more rapidly than those hardened in water.
461. Table 159 gives the results of several tests made to
determine the relative wearing qualities of different mortars for
such uses as sidewalk construction. The specimens were two-
inch cubes, hardened in water and dried for a few hours just
before grinding. An emery plate, set horizontally, was used
in most of the tests. The results in any given line of the table
are comparable, but, owing to changes in the grinding plate
and in the methods used, the results in different lines are not
all intercomparable. It is seen that when soft sand is used,
such as limestone screenings, the greatest resistance to abrasion
is offered by the neat cement mortar, and the resistance de-
creases constantly as the amount of sand is increased. When
hard sand, such as the siliceous river sand, from Point aux
Pins ("P.P." in the table) is employed, the greatest resistance
is offered by mortars containing about equal parts of sand and
cement. A comparison of lines 5 and 10 indicates that rich
natural cement mortars lose about twice as much as similar
mortars of Portland, but natural cement mortars containing
344
CEMENT AND CONCRETE
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A
EXPANSION AND CONTRACTION 345
more than two parts by weight of sand do not give relatively
as good results.
Art. 59. The Expansion and Contraction of Cement Mor-
tar, AND THE Resistance of Concrete to Fire
462. Change in Volume during Setting. — Cement mixtures
shrink somewhat when hardened in air, while specimens stored
in water expand a trifle during hardening. Although several
experiments have been made on this subject the specimens used
have been so small that the results obtained by various author-
ities do not agree, and the effect of variations in the character of
the mixtures has not been thoroughly investigated. The impor-
tance of the question is found in the necessity of providing ex-
pansion joints in long walls or sheets, and in the effect of such
changes in volume in producing initial stresses in concrete or
steel where these materials are used in combination.
Certain general conclusions are well established and may be
stated as follows: 1st. The shrinkage of mortar and concrete
hardening in air is considerably greater than the expansion of
similar specimens hardening in water; 2d. The amount of
change in volume increases with the proportion of cement used
in the mixture; 3d. The change in volume is continuous up to
one year, but about one half of the change occurs in the first
week, and it is very slow after 3 to 6 months.
The following values of the change in linear dimensions are
derived from the results of several experimenters, and show in a
general way what changes are to be expected at the end of three
months.* Variations in the character of the cement and the
consistency of the mortar will affect the result.
Composition: Pabts Sand
TO One Portland
Cement.
Shbinkaqe of Mobtabs
Habdbnbd in Aib.
Expansion of Mobtabs
Habdened in Watbb.
Chanob in Lineab Dimensions, One Unit in
Neat cement ....
One part sand ....
Three parts sand . . .
300 to 800
600 to 1200
700 to 1200
600 to 2000
1200 to 3000
3000 to 5000
* For more detailed results the reader is referred to the following authors
ties: — Dr. Tomei, Trans. A. S. C. E., Vol. xxx, p. 16. Mr. John Grant,
Proc. Inst. C. E., Vol. Ixii, p. 108. Prof. Bauschinger, Trans. A. S. C. E.
Vol. XV, p. 722.
346 CEMENT AND CONCRETE
463. The Coefficient of Expansion of Cement and Concrete. —
Concerning the coefficient of expansion of cement mortars of
various compositions, we know but Uttle. The result obtained
by M. Bonniceau, giving the coefficient of neat Portland cement
as about .000006 per degree Fahr., is frequently quoted. This
is very nearly the value for iron and steel, and has formed a the-
oretical basis for combining these materials. In the case of
cement mortars and concretes, however, it is highly probable
that the coefficient follows quite closely the behavior of the sand
and stone used in the mixture, and is much less dependent upon
the coefficient of the cement. This was indicated by the results
of M. Bonniceau who obtained a value of about .000008 for con-
crete.
464. A number of experiments to determine the coefficient
of expansion of cement concretes were carried out under the
direction of Prof. Wm. D. Pence by students of Purdue Uni-
versity.^ As a mean of seven tests with one-two-four concrete
of Bedford oolitic and Kankakee limestones combined with
Portland cements of two well-known brands, the mean result
for the coefficient was .0000055, the lowest result being .0000052,
and the highest result .0000057. The coefficient of a bar cut
from the Kankakee limestone was .0000056, the same result as
obtained from the mean of three tests of concrete containing
broken stone of this variety.
The average result of four tests of gravel concrete composed
of one part Portland cement, two parts sand and four parts
screened gravel, or one part Portland cement to five parts un-
screened gravel, gave .0000054 as the coefficient of expansion.
These values differ from the coefficient of steel enough to
indicate that in positions where the range in temperature is
great, the resulting stresses in the concrete and steel may be
considerable, and worthy of attention.
465. The Fire-Resisting Qualities of Concrete. — The
value of concrete as a material to be used in the construc-
tion of the walls and floors of buildings, is largely dependent
on its fire-resisting quaUties. That its use for such purposes
is rapidly extending, is some evidence that these qualities are
* Paper read before the Western Society of. Engineers, Engineering News,
Nov. 21, 1901.
RESISTANCE TO FIRE 347
as satisfactory as in other classes of materials devoted to the
same use.
Under favorable circumstances, a fire in a building filled with
combustible materials may reach a temperature of 2,000° to
2,300° Fahr. If a small specimen of cement mortar or concrete
is subjected to a temperature approaching this intensity, the
cement loses its water of crystallization and becomes friable.
If cooled suddenly in water, the specimen cracks and disinte-
grates. If cooled gradually, the outer edge of the specimen
crumbles away. From such tests on small specimens some very
erroneous conclusions have been drawn as to the value of con-
crete as a fire-resisting material. Such conclusions have done
much to prejudice the public mind against concrete, and to re-
tard its introduction in buildings designed to be fireproof.
466. Conductivity. — The great value of concrete as a fire
resistant is due to its low conductivity of heat, and while the
surface of a mass of concrete exposed to an intense flame for
some time is ruined, and may be flaked off by the application
of a strong stream of water from a fire hose, the depth to which
the heat penetrates is very limited. Steel is said to lose ten
per cent, of its strength at about 600° Fahr. and fifty per cent,
at about 750° Fahr. The importance of protecting the steel
framework of a building, not only from warping and complete
destruction due to flames, but from loss of strength from over-
heating, is therefore evident.
Among engineers and architects it is recognized that the
term "fireproof construction" is only relative, although the
lay mind is apt to give a definite and literal meaning to the
term. It is well known that fireproofing tile, whether hard or
porous, will fall to pieces if subjected to a temperature above
that employed in its manufacture. The practical question then
is, what type of const^-uction will withstand long continued
intense flame, and subsequent quenching with water, with the
least injury to the strength of the structure. The results of
fire tests that have been conducted in several places, and no-
tably those made by the Department of Buildings of New York
City, have shown that floor arches properly constructed of
concrete-steel are equal to any style of floor with which they
come in competition.
The low conductivity of concrete is shown by the fact,
348 CEMENT AND CONCRETE
stated by Mr. Howard Constable in connection with the dis-
cussion of fire tests of concrete floor arches/ "that in some
thirty-five cases where the temperature ranged from 1,500 to
2,400 degrees, the time of exposure being from one to six hours,
the temperature of the upper flanges of six-inch to ten-inch
beams might be approximately placed at not much above 200
degrees." He also says "in one case, where the beam was pro-
tected by three inches of concrete, the fire was maintained for
five hours, and the temperature went as high as 2,300 degrees,
and there was no practical or permanent set produced in the
beams."
467. Behavior in Conflagrations. — As to the behavior of
concrete-steel arches in an actual fire, a board of experts was
appointed by the insurance companies to investigate the causes
and extent of damage to the fireproof buildings in the Pitts-
burg, Pa., fire of May 3, 1897. This board stated in their
report that they believed that in important structures of this
class "the fireproofing should be in itself strong and able to
resist severe shocks, and should if possible, be able to prevent
the expansion of the steel work "; and continued, "There seems
to be but one material that is now known that could be utilized
to accomplish these results, and that is first-class concrete.
The fire-resisting qualities of properly made concrete have been
amply proven to be equal, if not better than fire clay tile, as
shown by the tests carried on by the Building Department of
the City of New York."
468. In a report on the Baltimore fire, Captain Sewall,^
Corps of Engineers, U. S. A., says concrete "undergoes more or
less molecular change in fire; subject to some spalling. Molecu-
lar change very slow. Calcined material does not spall off
badly, except at exposed square corners. Efficiency on the
whole is high. Preferable to commercial hollow tiles for both
floor arches or slabs and column and girder coverings. In form
of reinforced concrete columns, beams, girders and floor slabs,
at least as desirable as steel work protected with the best com-
mercial hollow tiles. Stone conerete spalls worse than any
» Trans. A. S. C. E., Vol. xxxix, p. 149.
' Report to the Chief of Engineers, U. S. A., by Capt. John Stephen
Sewall, Ckjrps of Engineers. Published in Engineering News, March 24. 1904.
RESISTANCE TO FIRE 349
other kind, because the pieces of stone contain air and moisture
cavities, and the contents of these rupture the stone when
hot. Gravel is stone that has had most of these cavities eUmi-
nated by spHtting through them, during long ages of exposure
to the weather. It is therefore better for fire-resisting concrete
than stone. Broken bricks, broken slag, ashes and clinker all
make good fire-resisting concrete. Cinders containing much
partly burned coal are unsafe, because these particles actually
burn out and weaken the concrete. Locomotive cinders kill
the cement, besides being combustible. On the whole, cinder
concrete is safe only when subjected to the most rigid and
intelligent supervision; when made properly, of proper ma-
terials, however, it is doubtful whether even brickwork is much
superior to it in fire-resisting qualities, and nothing is superior
to it in lightness, other things being equal."
469. Aggregate for Fireproof Work. — Since air is a poor
conductor of heat, the more porous concretes are the better
protectors against fire. On this account, as well as because of
its lightness, cinder concrete is preferred for fireproofing. Care
should be taken that cinders to be used in fireproofing concrete
do not contain any appreciable amount of unburned coal; in
concrete to be used next to steel members the cinders should
also be practically free from iron rust. (See § 473.)
The strength of cinder concrete is much inferior to that
made with the ordinary aggregates, and there should be no
difficulty in making a porous concrete with the latter. In fact,
in many other classes of construction it has been seen that
great precautions must be taken to avoid porosity. By the
use of insufficient mortar to fill the voids in the stone, voids
may be left in the concrete, though at the expense of dimin-
ishing somewhat the strength of the mixture. In adopting such
an expedient one should not lose sight of the fact that in order
to preserve the imbedded steel from corrosion, it must be fully
covered with the mortar.
470. Broken bricks are excellent for fireproofing concrete.
The bricks themselves are fire resistant, porous and light, while
the adhesion of cement mortar to bricks is so great that unless
a very weak mortar is used, the strength of the concrete is
limited only by the strength of the brick employed.
Sandstones, especially those with siliceous cementing ma-
350 CEMENT AND CONCRETE
terial, are also well adapted for this purpose. Limestone, on
account of the low temperature at which it is broken up, is
not good, though as to just how far a Hmestone concrete would
be disintegrated by the heat of an ordinary building fire has
not, so far as the author knows, been fully investigated. It is
known, however, that limestone masonry is calcined to a cer-
tain depth in a conflagration.
Granite in large pieces is cracked by only a moderate degree
of heat, and spalls badly. Just how much danger there might
be of a similar action in concrete aggregates of this material is
not known, nor whether small pebbles or fine gravel would
have this property in the same degree, though it is believed
they would not, and this view has been confirmed by observa-
tions of the Baltimore ruins.
Before adopting a given aggregate for fireproof work, one
should satisfy himself by actual test as to the suitability of the-
materials available, but such tests should be conducted upon
concretes containing the proposed aggregates, rather than upon
fragments of the materials not incorporated with mortar.
Art. 60. The Preservation of Iron and Steel by Mortar
AND Concrete
471. The rusting of steel members in modern buildings and
other engineering structures is one of the most serious menaces
to their permanence. The introduction of concrete-steel con-
struction has given rise to some discussion, especially among
those unfamiliar with the properties of concrete, as to the
effect of the concrete upon the steel.
472. Action of Corrosion. — The rusting of iron takes place
only in the presence of moisture, air and carbon dioxide. In
perfectly dry air, or in perfectly pure water, iron does not rust.
Under the proper conditions, however, the iron, water and
carbonic acid combine to form ferrous carbonate, which at once
combines with oxygen from the air to form ferric oxide, the
carbonic acid being liberated to act on a fresh portion of the
metal. It is seen that only a very small amount of the carbon
dioxide is necessary. If, however, the carbon dioxide or other
acid fining the same role, is neutralized by the presence of an
alkaline substance, the foregoing reactions cannot take place.
As cement is strongly alkaline, it thus furnishes an almost per-
fect protection against rusting.
EFFECT ON CORROSION OF METAL 351
473. Tests of Effect of Concrete on Corrosion of Metal. —
To determine the cause of occasional rusting of steel surrounded
by cinder concrete, and consequently the proper methods of
applying cement mortar or concrete to steel, Prof. Chas. L.
Norton, engineer in charge of the Insurance Engineering Ex-
periment Station at Boston, made tests on several hundred bri-
quets in which steel was imbedded in mortars and concretes
of various compositions.^ The briquets were subjected to air,
steam and carbon dioxide, others to air and steam, to air and
carbon dioxide and to the ordinarily dry air of a room. At the
end of three weeks it was found that neat Portland cement had
furnished a perfect protection in all cases. The corrosion of
the steel in other specimens was always at a point where a void
existed in the concrete, or where a badly rusted cinder had lain.
In every case where the concrete or mortar had been mixed wet,
and the surface of the steel had been thus coated with a thin
layer of grout, no rust spots occurred.
In the first tests made by Professor Norton the specimens
were thoroughly cleaned before being imbedded in the concrete,
but later tests indicated that in specimens that had begun to
corrode before treatment, the rusting was arrested by the coat-
ing of cement mortar or concrete. After from one to three
months in tanks holding steam and carbon dioxide, specimens
which had' been in all stages of corrosion before being im-
bedded in the concrete had not suffered any sensible change
in weight or size except when the concrete had been poorly
applied.
474. The results of these experiments showed that the steel
need not necessarily be freed from rust before being imbedded
in the concrete; that the concrete to be applied next the steel
should be mixed wet, or that the steel should be first coated
with grout by dipping or brushing; and it appeared that the rust-
ing sometimes found in cinder concrete is due to the rust in the
cinders rather than to the sulphur, and that if proper precau-
tions are taken, cinder concrete is nearly as effective as stone
concrete in preventing corrosion. Prof. Norton says, "In the
matter of paints for steel there is a wide difference of opinion.
I cannot believe that any of the paints of which I have
* Report III of Insurance Engineering Exp. Station, Boston, Mass.
352 CEMENT AND CONCRETE
any knowledge can compare with a wash or painting with
cement."
475. Sulphur in Cinders. — The conclusions drawn by Booth,
Garrett and Blair from a series of tests made for the Roebling
Construction Co., were that cinders from anthracite pea coal
contained about two-tenths per cent, of sulphur which they
considered sufficient to cause corrosion of unprotected iron-
work, more or less rapidly, depending on the presence or absence
of moisture; but they further concluded that a "full" concrete
(one in which the voids in the cinders were entirely filled by
mortar of cement and sand) would fully protect the steel.
In a paper read before the Associated Expanded Metal Com-
panies, Prof. S. B. Newberry has this to say concerning cinder
concrete: ^ "The fear has sometimes been expressed that cinder
concrete would prove injurious to iron, on account of the sulphur
contained in the cinders. The amount of this sulphur is, how-
ever, extremely small. Not finding any definite figures on this
point, I determined the sulphur contained in an average sample
of cinders from Pittsburg coal. The coal in its raw state con-
tains rather a high percentage of sulphur, about fifteen per
cent. The cinders proved to contain only 0.6 per cent, sulphur.
This amount is quite insignificant, and even if all oxidized to
sulphuric acid, it would at once be taken up and neutralized
in concrete by the cement present, and could by no possibility
attack the iron."
476. Precautions. — While so far as the corrosion of steel
is concerned, the above experiments by Prof. Norton show that
the rusting is corrected by the concrete, yet it is quite possible
that the adhesion of cement to steel may be impaired by a coating
of rust. The cleaning of the steel may be accomplished by
first brushing with wire brushes to remove all scales, followed
by treatment with hot dilute sulphuric acid, and finally apply-
ing an alkaline wash such as hot milk of lime to neutralize all
traces of the acid. Oxalic acid may be used in place of the
sulphuric, and the application of the milk of lime dispensed with,
since the acid oxidizes. The crystals of oxalic acid as purchased
commercially should be mixed with about seven parts hot water
and the solution applied with a brush or sponge. When the
' Engineering News, Apr. 24, 1902.
PRESERVATION OF STEEL 353
adhesion of the mortar or concrete to the steel is of any impor-
tance, as it is in all concrete-steel construction where the stresses
are divided between the steel and concrete, any of the ordinary
oil paints will not only be quite unnecessary, but may be a very
serious detriment to the construction.
The experiments quoted indicate the importance of having
the steel covered with an unbroken coating of cement or cement
mortar. To insure this the steel must either be coated with a
layer, preferably of neat Portland, by dipping or brushing, or
the mortar placed next the steel must be wet enough to insure
intimate contact throughout. It may be added also, that the
addition of a small amount of thoroughly slaked lime to Port-
land cement mortar or concrete will not only render the mate-
rial more alkaline, but will make the mortar more plastic, and
thus insure a better coating of the steel. Such small additions
have no deleterious effect on the mortar.
477. Practical instances of the preservation of iron by con-
crete are not wanting. The writer has stored in water, briquets
with small iron plates imbedded in Portland cement mortar,
and at the end of six months the plates were found moist, but
entirely free from corrosion except where they projected beyond
the mortar. A concrete-steel water main built on the Monier
system at Grenoble, France, was taken out and examined after
fifteen years service in damp ground. The metal imbedded in
the mortar showed no signs of corrosion, and the mortar could
only be detached from it by hammering.
Mr. W. G. Triest ^ relates that in breaking up cast-iron, con-
crete-filled pillars, a wrench was found that had been buried
in the concrete for twenty-two years. The wrench had main-
tained its metallic surface in the concrete, while a part of it that
had been imbedded in coal ashes had corroded badly.
Similar instances showing the action of concrete on steel
and iron might be multiplied, but it is sufficient to state that
the preservation of iron or steel properly imbedded in Port-
land cement mortar or concrete is now seldom questioned, and
the use of cement paint, in place of the ordinary oil paints,
as a steel preservative, has been adopted in many places.
» Trans. A. S. C. E., April, 1894.
354 CEMENT AND CONCRETE
Art. 61. Porosity and Permeability; Efflorescence;
Pointing; Use in Sea Water
478. The porosity and permeability of mortars have been
thoroughly investigated by M. Paul Alexandre, who has pub-
lished his results in " Recherches Experimentales Sur Les Mortiers
Hydrauliques." * The results and conclusion in the following
notes on the subject are largely a resume of the systematic
investigation made by M. Alexandre.
The two qualities, porosity and permeability, should not be
confused, nor should it be thought that a porous mortar is
always very permeable, or that a permeable mortar must of
necessity be very porous. Porosity is measured by the amount
of water which will be absorbed by a specimen after drying,
while permeability is measured by the amount of water which
will pass through a specimen in a given time under certain de-
fined conditions of thickness, water pressure and area of face.
479. Porosity. — The porosity of mortars is due to, and in
fact is measured by, the volume of the voids contained. These
voids may be divided into three classes, according to the causes
to which 'they may be attributed, as follows: 1st, apparent
voids, due to the mortar not being properly compacted; 2d,
latent voids, due to the imprisonment of air in the mortar when
made; and 3d, voids resulting from the evaporation, during har-
dening, of a portion of the water used in gaging.
480. Apparent voids may occur as the result of using insuf-
ficient cement to fill the voids in the sand, or, in the case of
concretes, insufficient mortar to fill the voids in the aggregate.
They may also be due to improper manipulation as to tamping,
or improper mixing, giving an excess of matrix in one place and
a deficiency in another. It was found by experiment that
mortars made with coarse sand had the largest volume of ap-
parent voids.
It has been shown elsewhere that if dry sand be moistened
and agitated, the bulk of the sand is increased. This is caused
partially by the imprisonment of air bubbles in the mass, and
if a measure of sand so treated is filled with water, the bubbles
will rise to the surface on jarring the vessel. Latent voids in
mortar are due to a similar action, and hardened mortars con-
' Extrait des Annates des Fonts et Chaussies, September, 1890.
POROSITY AND PERMEABILITY 355
taining such voids refuse to absorb water to replace the air
bubbles, at least for a long time.
481. A portion of the water used in mixing mortar enters
into chemical combination with the cement, another portion is
absorbed by the sand grains, and a third portion goes to moisten
the sand. The quantity absorbed by the grains depends upon
the character of the sand, and the amount required to moisten
the sand depends upon the superficial area of the grains in a
given volume, being greatest for fine sands and least for coarse
ones. At least one fourth of the water ordinarily used in
mixing neat cement is given off later, if the hardened mor-
tar is allowed to remain in dry air. The water required to
moisten the sand, and at least a part of that absorbed by
the sand grains, also dries out, leaving voids of the third class
mentioned.
The apparent voids may be reduced to a very small per-
centage by care in the proportions and preparation of the
mortar. The latent voids may amount to six or seven per
cent, of the total volume. The evaporation of water may
leave from six to eighteen per cent, of voids in the mass.
482. The conclusions drawn from M. Alexandre's experi-
ments are briefly as follows: The porosity varies between wide
limits according to the fineness of the sand and the richness of
the mortar. It may be as low as thirteen per cent, and may
exceed thirty-one per cent.
With sand of the same degree of fineness, the porosity di-
minishes as the proportion of cement in the mortar increases.
With the same quantity of cement per volume of sand, the
porosity increases with the fineness of the sand. This is es-
pecially marked in rich mortars, where the increase in porosity
may reach 50 to 100 per cent., while in lean mortars the use
of a fine sand may not increase the percentage of voids more
than 20 per cent.
The least porous mortars are those rich in cement and made
with coarse sand. Mortars made with fine sand are relatively
very porous, even when made rich with cement.
Mortars gaged dry are more porous than those of ordinary
consistency, and mortars gaged wet are also likely to be more
porous, unless the manipulation is such as to allow the excess
water to rise to the surface of the mortar.
356 CEMENT AND CONCRETE
483. Permeability — The degree of permeability of mortara
is a more important property than the porosity, since not only
does it affect the suitability of the mortar for certain uses,
but the life of the structure may depend upon the difficulty
with which water may percolate the mass.
The permeability of mortar decreases as the proportion of
cement is augmented, and in the case of concretes the per-
meability diminishes as the percentage of mortar increases, at
least to the point where the latter is in excess of the voids in
the stone.
From experiments made at the Thayer School of Civil En-
gineering, Messrs. J. B. Mclntyre and A. L. True found that a
five-inch layer of concrete containing from 30 to 45 per cent,
of one-to-one Portland cement mortar, and some of the speci-
mens containing 40 to 45 per cent, of one-to-two mortar, were
impermeable with pressures of 20 to 80 pounds per square
inch, maintained for two hours.
484. Mortars made with fine sand are much less permeable
than those made with coarse sand. This difference is so marked
that a less permeable mortar is made with one barrel of cement
per cubic yard of fine sand, passing a sieve having, say, fifty
meshes per inch, than with two barrels of cement per cubic
yard of very coarse sand in which the grains are, say, one-
tenth inch in diameter. Mortars made with sands composed
of a mixture of grains of various sizes are neither very porous
nor easily permeated.
Mortars mixed very dry or very wet have greater permeabil-
ity than those of the ordinary consistency, and in the case of
concretes, it would probably be found that a deficiency of
water would result in a much more permeable mass. than the
use of what might be considered an excess.
All of the above conclusions indicate that a mortar may be
quite porous, and yet so long as the voids are very minute, the
percolation of water through it will be slow. This is especially
shown by the fact that mortars of coarse sand, not porous,
are more permeable than the porous mortars of fine sand,
485. When water is permitted to percolate continuously
through a mass of mortar, the interstices gradually become filled,
and the permeability decreases in marked degree. M, Alex-
andre found that a volume of water which passed a certain
WATER-PROOFING 357
mass of mortar in twenty minutes at the beginning of the ex
periment, required five hours to percolate the mass at the end
of a month. M. R. Feret has obtained similar results in making
extensive experiments ^ on the subject of permeabiUty, and
considers that fine particles of cement or lime are carried along
by the water, forming efflorescence at the surface and tending
to stop the flow.
486. The Preparation of Water-Proof Mortar and Concrete.
— To enumerate briefly the precautions necessary to attain
water-tightness in mortars and concretes, it may be said that
different brands of cement present different characteristics in
this regard. Fine grinding is a prime requisite, and sand
cement or silica cement, containing as it does very fine grains of
sand intimately mixed with cement particles of extreme fine-
ness, is admirably adapted to such uses.
The sand should, if possible, be composed of a mixture of
grains of various sizes, because such a mixture gives a mortar
not only little permeable, but one that is not porous, and that
has, besides, a good strength. The amount of cement in the
mortar should be in excess of the voids in the sand, not less,
in general, than three barrels of cement per cubic yard of sand.
In concrete the volume of mortar should exceed the volume
of voids in the aggregate, and to obtain this result without
too great expense, the aggregate should be so selected as to have
a minimum of voids. Gravel concrete properly proportioned
may be made water-tight somewhat more easily than broken-
stone concrete, but a mixture of gravel and broken stone will
give good results not only in this regard, but in the matter of
strength as well.
487. To make a compact mortar for use where the facilities
for tamping are ordinarily good, the consistency should be
neither very wet nor very dry. When the mortar is struck
with the back of a shovel, moisture should glisten on the surface,
but in a pile the mortar should appear but little moister than
fresh earth. This is the consistency which, with a moderate
amount of tamping, gives the least volume of mortar with
given quantities of dry materials. In places difficult of access,
* "La Capacity des Mortier Hydrauliques," Annales des Fonts et Chauss^es,
July, 1892.
358 CEMENT AND CONCRETE
or in the preparation of concrete, better results will be obtained
with a mortar somewhat wetter, than the above, since large
voids will be less likely to occur in the more plastic mass. In
fact, unless the supervision is very close, it is advisable to use
a rather wet mixture in preparing concrete where water-tight-
ness is desired.
488. Washes. — The application of certain washes to the
surfaces of walls intended to be water-proof, and the introduc-
tion of foreign materials into the mortar or concrete to make
it less permeable, have been practiced to some extent. Alter-
nate coatings of soap and alum solutions are applied with a
brush, not only to concrete, but to brick and stone masonry
surfaces. These penetrate the pores of the masonry, forming
insoluble compounds which prevent percolation. Washes of
grout, composed of cement, or of cement and slaked lime, are
used for a similar purpose.
"Sylvester's Process for Repelling Moisture from External
Walls" consists in applying first a solution of three quarters
of a pound of soap to one gallon of water, followed, after twenty-
four hours, by the application of a solution containing two
ounces of alum per gallon of water. Both solutions are applied
with a brush, the soap solution boiling hot, and the alum so-
lution at 60° to 70° Fahr. The applications are alternated,
with twenty-four hours intervening each time. Experiments at
the Croton Reservoir ^ indicated that four coats of each wash
were required to render brickwork impervious to a head of forty
feet of water and the cost of the four double applications was
about ten cents a square foot.
In Reservoir Number Two of the Pennsylvania Water Co.,
two washes of each solution were used on the walls at a cost
for materials and labor of twenty-three cents per hundred
square feet, and the results were said to be good,
A modified recipe for such a wash in which but one solution
is made is given as follows:^ A stock solution is prepared of
one pound lye, five pounds powdered alum, dissolved in two
quarts water. One pint of the stock is used to a pail of water
in which ten pounds Portland cement has been well mixed.
> Trans. A. S. C, E., Vol. i, p. 203.
* J. H. G. Wolf, Engineering News, June 30, 1904.
WATER-PROOFING 359
489. In a few cases the use of alum and soap solutions in
the body of the mortar has been tried with apparently success-
ful results. Mr. Edward Cunningham,' in making experiments
on water-proof concrete vessels, used powdered alum equal to
one per cent, of the combined weight of the sand and cement,
mixing this with the dry ingredients. To the water used in.
mixing, one per cent, of yellow soap was added. The results
were said to be very satisfactory. In the above proportions,
however, the amount of alum is made to depend upon the
amount of cement and sand used, while the soap added depends,
upon the amount of water, whereas the soap should bear a de-
finite ratio to the alum.
In experiments with mortar composed of one part cement
to two and one-half parts of bituminous ash, Prof. W. K. Hatt '
found that the alum and soap mixed with the mortar at the
time of gaging increased the strength and hardness of the ash
mortar about fifty per cent., and diminished the absorption by
the same percentage. One half of the water used for gaging
was a five per cent, solution of ground alum, the other half
being a seven per cent, solution of soap. The alum solution
was used first and the gaging completed with the soap solution.
Mr. W. C. Hawley * employed a stock solution of two pounds
caustic potash, five pounds powdered alum, and ten quarts
water, and used in the finishing coat three quarts of this solu-
tion in each batch of mortar containing two bags of cement.
The mortar was mixed with two volumes of sand to one of ce-
ment and covered forty-eight square feet to a depth of about
one-half inch. The extra cost for materials and preparing so-
lution was only about nine and a half cents per hundred square
feet. With less than two parts sand to one cement, it was
found the finishing mortar checked in setting. It was also
found that any organic matter in the sand was softened by the
potash, and an excess of potash caused checking, although an
excess of alum had no deleterious effect.
490. Use of Lime, etc. — The introduction of slaked lime in
mortars designed to be water-proof is suggested by the fact
' Trans. A. S. C. E., Vol. li, p. 128.
» Trans. A. S. C. E., Vol. li, p. 129.
• Journal New England Water-Works Association, 1904.
360 CEMENT AND CONCRETE
that the permeabiUty of mortar diminishes if water is allowed
to percolate it for some time, the theory being that fine par-
ticles of cement and lime are dislodged by the passage of the
water to form a deposit at or near the surface, and check the
flow. This suggestion, however, needs experimental confirma-
tion, since it seems quite possible that the introduction of a
substance containing such a large proportion of water as does
slaked lime, may increase the percentage of voids in the mor-
tar, if not the permeability.
The use of pulverized clay and pozzolanic materials for a
similar purpose has been suggested. It has already been shown
that moderate doses of clay have no deleterious effect on the
strength of mortars for ordinary exposures. The action of the
pozzolanic substances has been found by Dr. Michaelis and
M. Feret to be not mechanical alone, but chemical, and the
effect on the strength of the resulting mortar depends upon the
exposure to which it is subjected, such admixtures being dele-
terious for mortars hardened in air.
491. Efflorescence. — The white deposit sometimes formed
at the surface of brick and masonry walls is usually due to the
filtration of water through the mortar, dissolving out salts of
potash, soda, etc., and depositing these salts on the surface by
evaporation or by the formation of sodic carbonate. The ab-
sorption of water from the atmosphere may also account for
this deposit in some degree, especially near the sea. The same
term is applied to a more harmful deposit, sulphate of calcium,
which may be supplied by the filtrating water or may come
from the cement, either from the addition of gypsum or from
the fuel used in burning. The crystallization of this salt in the
pores of the masonry at the surface may cause disintegration.
On the other hand efflorescence may be quite harmless, as
when it is formed by washing out from the mortar an excess of
hydrate of lime. A portion of the latter may then be changed
to carbonate of lime near the surface of the wall and actually
stop up the pores or voids, and prevent further filtration.
492. The discoloration of brickwork and fine masonry by
efflorescence is sometimes serious. To ameliorate these condi-
tions, the use of water-proof mortars, and careful pointing of
the work, are precautions to be recommended. General Gill-
more, in "Limes, Hydraulic Cements and Mortars," suggests
EFFLORESCENCE 361
the use of about ten pounds of animal fat to one hundred pounds
of lime and three hundred pounds of cement; the object of the
fat being to saponify the alkaUne substance, the lime in form
of paste serving only as a vehicle for the fat. A more practical
method, however, would seem to be the application of soap
and alum washes on the surface, or the use of soap and alum
in the preparation of the mortar to be used near the face of the
wall, and especially for pointing. The remedy to be adopted,
however, will depend upon the cause of the efflorescence.
493. Pointing Mortar. — Pointing serves the double purpose
of making the joint practically water-tight at the edges, and giv-
ing a finish to the face of the wall. If the edge of the joint is
not well filled, moisture collects there either from the face or
from seepage through the wall. Subsequent freezing or the
crystallization of certain salts may spall the stones or loosen
them from their bed.
In laying cut-stone masonry, the joints should be raked out
for about two inches back from the face to be pointed.
Pointing mortar should be prepared from fine sand and the
best Portland cement. The proportion of sand should not
exceed two parts by weight to one cement, and in the highest
class work, equal parts of cement and sand are sometimes
used. No advantage is gained, however, by using a mortar
richer in cement than the one last mentioned. The use of fine
sand and rich mortars are specified not only because such mor-
tars are practically water-tight, but because they take a fine
finish.
494. The tools required for pointing are a bent iron to rake
out the joints (though this should be partially done while the
mortar is green), a moriar board and small trowel, a calking
iron and wooden mallet, a brush for moistening the joint, and
one or more beading tools. After raking out the joint it is
moistened by the brush, and the mortar, which is mixed quite
dry, is filled in with the trowel. When enough mortar is in
place to fill half the depth of the joint, it is tamped with the
calking iron and mallet much as a ship's seam is calked with
oakum. The joint is then filled to the face, and again tamped.
The bead is then formed by running the beading iron back
and forth over the joint. This beading iron is of steel with the
handle parallel to, but some two or three inches out from, the
362 CEMENT AND CONCRETE
line of the blade forming the bead. The blade is three to five
inches long and "hollow ground" or finished with a smooth
concave surface. Only such a length of joint is pointed at one
operation as may be quickly carried to completion. The wall
must be kept moist for some time after the pointing is done,
and it should be protected from the direct rays of the sun, as
fine cracks are very likely to appear in this rich, finely finished
mortar. If possible, pointing should be done in moderate
weather and must be entirely suspended in temperatures ap-
proaching the freezing point.
495. Cements in Sea Water. — The theory of the action of
sea water upon cements is not fully understood. It is known
that some cement structures exposed to the worst conditions
have given most satisfactory results, while others have failed
in greater or less degree. It may be said at once, however,
that many of the most eminent and conservative engineers
consider that the failures that have occurred in the use of Port-
land cement in sea water are due to improper specifications,
proportions and manipulation, rather than to any defect in
Portland cements as a class.
496. It is thought the following represents, in the main, the
most generally accepted theory of the chemical action. In the
setting of cements that are rich in lime, the whole of the lime
is not engaged in stable compounds, and when placed in the
sea the sulphate of magnesia of the sea water is able to com-
bine with the lime, forming calcic sulphate, the magnesia being
precipitated. The discovery of magnesia in decomposed mor-
tars led, at first, to the supposition that the cause of failure
was the presence of magnesia in the cement when used. If
the water level about the structure changes frequently, as is
usual, or if the wall is at times subjected to a greater head on
one side than on the other as in tide docks, the percolation of
water through the wall is stimulated, and the sulphate of lime
may then be washed out if the mortar is quite pervious, and
more will be formed from a fresh supply of sea water attacking
the lime of the cement, until the latter is destroyed. If, how-
ever, the sulphate of lime is not washed out, it may crystallize
and thus cause swelling of the mortar.
497. It would appear from the above that for successful
use in sea water the hydraulic index of the cement should be
ACTION OF SEA WATER 363
high; that is, that the lime should be comparatively low in or-
der that the lime compounds may be more stable. For this
reason it is not impossible that some of our natural cements,
which are so much more nearly uniform than the Roman ce-
ments of Europe that have been condemned for this reason,
may give fairly good results in sea water. The fact that the
mortars of natural cement are more permeable than those of
Portland, is, however, a serious defect.
Following a similar reasoning. Dr. Wm. Michaelis has ad-
vanced the theory that if trass, or other pozzolanas of proper
composition, be mixed with Portland cement subsequent to
the burning, the hydrate of lime which separates from the ce-
ment in hardening will at once combine with the pozzolanas,
forming a stable compound. This view, however, has been
vigorously opposed by the Society of German Portland Cement
Manufacturers, as well as by many engineers, especially of
France, and the discussion is not yet at an end.
M. Candlot ^ says that, from the experiments of various en-
gineers, "we have arrived at this conclusion, that the only
remedy to adopt against decomposition is to prevent the sea
water from penetrating the mortar. We are led thus to dis-
miss the chemical reactions of sea water on mortars and to
consider their action from a purely physical standpoint."
498. To resist the attacks of sea water the mortar should not
only be impervious, but also as little porous as possible. The
cement should be finely gfound and should not contain free
lime. The content of magnesia and of sulphuric anhydride
should be as low as possible, the latter not exceeding one and
five-tenths per cent. The proportion of lime should not be
too high, and above all, special pains should be taken with the
manufacture to insure proper comminution and mixing of the
raw materials, and uniform burning. The addition of sulphate
of lime to regulate the setting is believed to be injurious for
cements to be used in sea water; even two or three per cent,
is said to cause rapid disintegration, and in the specifications
for recent extensive works in dock construction, the addition
of gypsum or other foreign matter was entirely prohibited.
* "Le Ciment," September, 1896, quoted by F. H. Lewis, M. Am. Soc.
C. E. Trans. A. S. C. E., Vol. xxxvii, p. 523.
364 CEMENT AND CONCRETE
Although slag cements have given good results in the sea
for a short time, it is considered that they will not, in general,
resist the action of sea water for long periods.
499. Sand or aggregate containing argillaceous or soft cal-
careous matter should be avoided for works in the sea. Two
instances of failure of sea walls in which shells were used as the
aggregate are mentioned by Col. Wm. M. Black,^ and although
the failures are not definitely traced to the calcareous matter in
the concrete, the fact that experiments have shown that cal-
careous sands do not withstand the action of sea water, makes
it probable that this was an important cause of the failure.
Fine sands that give porous mortars, though not easily per-
meable, are to be strictly avoided. Coarse sands giving per-
meable, though not porous, mortars are better, but still leave
much to be desired as to immunity from decomposition. The
best sands are those containing various grades of sizes of par-
ticles from coarse to fine, as mortars made with such sands are
not only compact, but practically impermeable.
500. Since the mortar and concrete should be made as com-
pact as possible, the precautions mentioned under the head of
water-proof mortar and concrete should be taken in the prep-
aration of mortars and concretes for use in the sea. That is,
the proportion of cement should exceed the voids in the sand
and the mortar should exceed the voids in the aggregate.
M. Alexandre has found that the mortars mixed to the or-
dinary consistency are attacked least by sea water. When
specimens are merely immersed in the water, those mixed dry
suffer the most, but some tests indicate that if mortars are
submitted to the filtration of water soon after made, those
mixed wet are most easily decomposed. As to whether fresh
or salt water should be employed in mixing mortars to be used
in sea water, although Mr. Eliot C. Clarke, M. Paul Alexandre
and many others have investigated this subject, the conclusions
are not definite and it is probable that either may be used as
convenient.
» Trans. A. S. C. E., Vol. xxx, p. 601.
PART IV
USE OF MORTAR AND CONCRETE
CHAPTER XVIII
CONCRETE : DEPOSITION
501. Concrete may be molded into blocks which are allowed
to set and then are transported to the structure and laid as
blocks of stone. This is the block system of construction. The
adaptability of concrete to being built in place, however, is
one of its chief merits, and consequently the monolithic method
of construction is far more common Since it has been found
that expansion and contraction, due to changes in temperature,
affect concrete walls as they do any other walls of masonry,
it has become customary to mold the concrete in sections, usu-
ally alternate sections of equal size and shape being built first,
and the omitted sections built in later. This method of con-
structing a long wall is also called monolithic, since the blocks
are of large size and are built in place.
502. When concrete is deposited either in air or in water,
molds must be provided to keep the mass in the desired shape
until it has lost its plasticity and acquired sufficient strength
to stand alone. In foundations, the earth at the sides of the
excavation may supply the place of a mold, and sometimes
the mold forms a part of the permanent structure, as in the
case of masonry piers with concrete hearting, and in steel cylin-
der piers filled with concrete.
Art. 62. Timber Forms or Molds
503. The construction, placing and removal of forms fre-
quently represent a considerable percentage, from five to thirty
per cent., of the total cost of the concrete, and it is therefore
evident that an improper design may result in a considerable
waste of money, as well as in marring the appearance of the
365
366 CEMENT AND CONCRETE
work. The character of the form will of course depend on the
character of the work; in the construction of a large number
of small blocks of the same shape, where one mold may be used
over and over, the thickness of the pieces should not be stinted,
and the ease of knocking down the mold should be carefully
considered. When a form can be used but once, the size of
pieces should be no larger than necessary to give the requisite
stiffness, and the ease of first construction is a main considera-
tion. Forms should be left in place forty-eight hours to allow
the concrete to set, and in the case of arches and beams a
much longer time is necessary, so that the concrete may assume
considerable strength before it is called upon to support its
weight.
504. Sheathing. — Forms for massive walls of monolithic
construction usually have vertical posts, with iron ties across,
or braced by battered posts outside. The sheathing planks
are then placed horizontal. In a few cases horizontal wales
have been placed within the posts and vertical sheathing laid
against the wales.
The strength of the sheathing must be sufficient to stand
the pressure transmitted to it through the concrete when the
rammer is used close to the face of the mold. The concrete is
seldom built up fast enough to bring upon the sheathing a great
head of fluid pressure, but the ramming brings a heavy local
pressure upon it. If supported at intervals of four feet, two-
inch lumber dressed to one and three-quarters inches thick is
usually sufficient; for spans of more than 5 feet, 2 f inch lum-
ber is required to make a perfect face. Boards seven-eighths
inch thick are suitable only when supports are not more than
about 2 feet apart. In placing concrete in molds under water
there is more danger of bursting the mold by the weight of
semi-fluid concrete, and if the work is to be built up rapidly,
this must be guarded against by sufficient bracing.
505. For exposed faces, the duty to be performed by the
lagging includes leaving as smooth a finish as possible on the
concrete after the removal of the forms. If green lumber is
employed, the boards may shrink before use, leaving openings
between the sheathing that will show plainly on the fade of the
work. A slight tendency of this kind may be checked by
keeping the boards well wet with a hose until the concrete is
TIMBER FORMS 367
placed. On the other hand, thoroughly seasoned lumber will
swell when the concrete is placed; to obviate this difficulty the
lower edge of each sheathing plank may be beveled on the outer
edge; the thin edge on the inside will then crush when the
planks swell.
The use of tongue and grooved lagging has been tried, but
is not usuallj' satisfactory, as there is no opportunity to expand,
and the planks are particularly hard to place a second time.
To give a good face in work under water, however, tongue and
groove sheathing will assist in preventing washing of the cement.
Yellow pine lumber is found to be excellent for sheathing; on
account of the large amount of pitch contained, it absorbs
water slowly and holds its shape. For a similar reason, fir
timber would be suitable.
In order that the face of the mold shall be perfectly smooth,
it is necessary to size and dress the plank on at least one side
and two edges.
As it is almost impossible to avoid having some line of de-
marcation shown in the concrete at the joints of the sheathing
planks, care should be taken that the lagging is of uniform
width throughout, and laid horizontal so that consecutive sec-
tions show the joint continuous. The sheathing may be placed
for the entire form before concreting is commenced, or the
plank may be raised on the posts as the work advances. The
former method will usually give the neater appearance, but is
too expensive for high walls.
506. Lining. — The appearance of the finished concrete is
much improved, and the labor of preparing the forms probably
not increased, since less care may be taken in surfacing, by
lining the mold with thin sheet iron. Iron of number twenty
gauge (.035 inch thick, 1.42 pounds per square foot) has been
used for this purpose, but where the same lining is used several
times, a heavier iron is preferable. The joining of one sheet of
lining to another may present greater difficulties than the join-
ing of planks, but joints will occur less frequently.
In the construction of the Marquette Breakwater, Mr.
Clarence Coleman, Asst. Engineer, used sheet steel one eighth
of an inch thick for lining molds for building monolithic blocks.
Concerning the use of the steel, Mr. Coleman says:* "Very
Report Chief of Engineers, U. S. A., 1898, p. 2254.
368 CEMENT AND CONCRETE
smooth surfaces were produced on the slopes of the concrete
and the work of the molders was greatly facilitated on account
of the comparative ease with which the concrete was compacted
under the slope pieces of the molds. The steel effectually pre-
vented the aggressive friction of the sharp particles of broken
stone on the wooden surfaces of the molds, thus increasing the
life of the molds and decreasing the cost of molding the con-
crete."
507. Oiling the Forms. — Oiling or greasing the face of the
mold, in order that the latter may be removed without detach-
ing particles from the concrete face, is usually advisable. Soap,
crude oil, linseed oil, bacon fat, are some of the materials that
have been used for this purpose; the first mentioned probably
gives the best results, and if not applied too freely will have no
injurious effect upon either the finish or strength of the work.
Applying shellac to the molds improves the appearance of the
concrete surface. When the forms are lined with steel, the
adhesion of the concrete to the lining is more difficult to over-
come. In this case the ordinary oils are not entirely success-
ful, but fat salt pork has been found to give satisfactory
results.
508. Joints and Corners. — If desired, triangular strips may
be nailed to the inside of the forms in such a way as to block
off the face to represent stone masonry, and in this way the
marks of joints between planks or between strips of lining may
be avoided. Square corners should not be allowed on exterior
angles, as it is difficult to so tamp the concrete as to make the
corner perfect, and they are so likely to be chipped off. Tri-
angular strips or moldings should be tacked along the corners
of the mold as a fillet to cut off the corner by a plane making
equal angles with the adjacent faces. This plane may be from
one inch to two inches wide.
To form water drips on projecting ledges, such as door caps
and sills, abutment copings, etc., a small half-round should be
nailed to the upper surface of the mold a short distance back
from the projecting face. This leaves a ridge at the edge of
the under side of projection so that the water must drip from
the edge, and not follow back to the main wall face.
509. POSTS AND BRACES. — The sizes of posts and braces
must be such as to make a practically unyielding support to
TIMBER FORMS 369
the sheathing. With one and three-quarters inch lagging, posts
may be four feet apart; if five feet four inches apart (three to
each sixteen foot length), some yielding of the sheathing may
be expected if it is less than two and three quarter inches.
If sheathing is four inches thick, the distance between posts
may be six or seven feet.
Fir, yellow pine, and Norway pine are suitable for posts.
Three-inch by eight-inch is an ordinary size, and a post of
these dimensions should be supported, either by ties or braces,
at intervals of four to six feet. Where the posts are four inches
by ten inches, supports may be six to eight feet centers, while
with six-inch by twelve-inch posts, the distance between cen-
ters of supports may be eight to ten feet. Posts should be
sized and dressed on the side which is to receive the sheathing,
in order that the alignment may be perfect.
510. Methods of Bracing. — The general plan of the mold
may vary according to conditions, the following methods hav-
ing been employed on heavy work to support the vertical posts:
1st, With outside inclined braces, leaving the interior of the
mold unobstructed. 2d, Tie rods across the interior of the
mold connecting opposite posts at frequent intervals. 3d, Each
post trussed vertically and tied across at top and bottom only.
4th, Horizontal trussed wales outside of posts, spaced four to
five feet apart in the vertical and tied across at the ends.
511. Inclined Braces. — The sizes of inclined braces depend
on their lengths, the inclination to the vertical, and the amount
of shoring used. An approximate rule for the size of braces
under usual conditions and using ordinary dimension stufif,
not boards, is that the number of square inches area of cross-
section of brace should equal length of span in feet. If thin
planks are employed, they should be in pairs, one on either
side of the vertical post, and made to act together by cross-
pieces nailed to the two planks.
The aim should be to make the whole form practically un-
yielding under the action of the tampers, as it has been found
that this action is usually more severe than the mere pressure
of the concrete in a semi-liquid condition. The sizes of pieces
cannot, therefore, be accurately computed, but the above sizes
are derived from the general result of experience as to what
has proved satisfactory.
370 CEMENT AND CONCRETE
The advantage of the form of construction just described is
that the interior of the mold is left entirely unobstructed. On
high walls, however, the amount of timber required for braces
is excessive, and the braces may be almost as objectionable as
tie rods, since the former prevent the laying of tracks along
the side of the form.
512. Tie Rods. — When the vertical posts are supported by
tie rods across the mold and the wall is thin, it may be possible
in removing the mold to withdraw the bolts or rods if they
have been thoroughly greased or wrapped with stiff paper be-
fore the concrete is placed. If it is designed to leave the rods
in the concrete, they should be provided with sleave nuts near
the end, which, when unscrewed, will leave the end of the rod
within the concrete mass not less than two inches from the face.
The hole left by the nut should be carefully filled with mortar
after the mold is removed.
With vertical posts four feet apart, this method of support
is objectionable, as it leaves a network of ties within the forms
interfering seriously with the operation of a skip and with the
ramming. It is not necessary, however, to place all of the tie
rods to the top of the mold before beginning the concreting,
as it is sufficient to keep one or two rods in place above the
plane where tamping is being done.
A modification of this method is to use wires of large diam-
eter with an eye at the end just inside the finished face of
the concrete. A short bolt, with hook at one end and threaded
at the other, passes through the post, hooks into the eye of the
wire, and is tightened by a nut on the threaded end outside
the post. After removing the nut, the rod is unhooked and
the hole in the face filled with mortar, the wire remaining in
the concrete.
513. Trussed Posts. — The third method of support, where
the posts are trussed and provided with heavy tie rods at the
top, and held at the bottom either by tie rods or some other
means, seems to have fewer objections than the methods just
described. Less timber will usually be required to build this
form than for that where inclined braces are used, and the
obstruction to operations will usually be less than with either
of the other styles. This mold is also very readily taken down,
though the posts are heavier and more difficult to handle.
TIMBER FORMS 371
To secure the bottoms of the posts, they may be set in the
ground, or rest against sills braced to some other portion of
the structure, or to piles. A suitable support may also be
obtained by dumping a mass of concrete around the bottom
of each post and allowing it to set. Forms erected on rock
may have the posts rest against blocks bolted to the rock,
514. Trussed Wales. — The fourth method of supporting the
posts is particularly applicable where the work is divided into
blocks of moderate size in horizontal cross-section, say twenty
feet square. In longer lengths the horizontal trussed wales
become rather heavy for convenient handling. Within these
limits, however, this is an excellent form. In the construction
of Lock No. 2 between Minneapolis and St. Paul,* a form of
this kind was used for blocks about twelve by fifteen feet at the
bottom. The sheathing was one and three-quarters inches,
lined with No. 20 galvanized iron. Verticals were four by
twelve, spaced about two feet centers. The trussed wales were
twelve by twelve inch, trussed with one and one-quarter inch
rod, the king-post being of twelve by twelve inch about two
and one-half feet long, making depth of truss three and one-
half feet. The ends of opposite wales were connected by one
and one-quarter inch rod passing outside of the sheathing.
Each pair of the longitudinal wales was just above the corre-
sponding pair of transverse wales, so that they did not inter-
fere at the corners. The mold was twenty-nine feet in
height.
In describing this mold, Mr. Powell says: "One complete
form weighs twenty-eight tons; each piece about seven tons.
Each piece is moved separately by the cable-way in forty-five
to sixty minutes. The operation of removing one complete
form requires from three to four hours time. After being
moved, a small crew of men occupy nearly a day in plumbing
and bolting together the form." "The boxes containing 1.7
cubic yards of concrete are landed on top of the form by cable-
way and tipped from that position. Although the jar and
strain is severe, the forms have shown no ill effects therefrom,
remaining tight and secure."
* Major Frederic V. Abbot in charge. Mr. A. O. Powell, Asst Engr.,
RepoH Chief of Engineers, 1900, p. 2778.
372 CEMENT AND CONCRETE
Art. 63. Deposition of Concrete in Air.
515. Transporting to Place of Deposition, -r- In depositing
the concrete in place, care must be taken not to undo the work
of mixing. If the concrete is allowed to fall freely a distance
of several feet or to slide down an inclined plane, the stones
will be likely to separate from the mass, and the result will be
a layer of broken stone followed by a layer of mortar. If the
concrete is deposited in a pile, the stone will roll down the out-
side of the cone. This action is especially bad in concrete that
is mixed rather dry. The author has seen a pavement founda-
tion in which the limits of each wheelbarrow load of concrete
could be distinguished, the foundation presenting the appear-
ance of the cross-section of a honeycomb, made up of irregular
hexagons outlined by broken stone having a deficiency of
mortar. In all such cases, if the action cannot be avoided by
some other method of dumping, then care must be taken to
remix the concrete.
There is one method by which the concrete may be deposited
by gravity without separation of the materials. This consists
in allowing the material to slide down a tube, but the tube
must be kept continually full, the concrete being allowed to
run out at the bottom only as fast as it is filled in at the top.
This method is only applicable where the mixing is continuous,
as in the case of machine mixers.
516. Sometimes it will be found possible to mix the con-
crete so near to the place of deposition that it may be shoveled
directly into place. In mixing by hand this is practicable, as
the mixing platforms may usually be easily moved, and this
method of deposition is carried out even in street work where
the concrete is in thin layers and hence requires much moving
of platforms.
Where a machine mixer is used that is so mounted as to be
portable, the concrete may be delivered in place by a belt
conveyor. Such an arrangement for the building of walls and
for foundations of pavements, has already been described in
Chapter XIV.
The conditions are usually such, however, as to preclude the
possibility of mixing the concrete so close to the work that it
may be shoveled into place or handled economically on a con-
PLACING IN AIR 373
veyor of the style mentioned. The next cheapest method is
to use a derrick to handle skips or bottom-dump buckets, pro-
vided the work is sufficiently concentrated to have one posi-
tion of the derrick serve to place a large quantity of con-
crete. The skips should hold about a cubic yard, and if a batch
mixer is used, the skip should hold a batch, whatever that
may be.
517. If the concrete is mixed on the same level and within
less than two hundred feet of the work, wheelbarrows may be
used, but for greater distances, carts, or, what is usually cheaper,
cars running on a track, should be employed.
For large masses of concrete a cableway may be employed
to advantage, provided there is sufficient use for it to repay
the high original cost of plant. The selection to be made from
among these common methods is dependent on economy as in
handling other material, the only requirements being that the
concrete shall be conveyed to place quickly, and that the ma-
terials shall not be allowed to separate as a result of any of the
manipulation. In laying large quantities of concrete, the dif-
ference between success and failure from a financial standpoint
may easily rest in the proper transportation of the materials
to and from the mixer.
518. Ramming. — The concrete should be deposited in hori-
zontal layers about six inches thick, leveled with a shovel and
thoroughly rammed. The length of time ramming should be
continued and the vigor with which it should be done depend
largely on the degree of plasticity of the concrete. If the con-
crete is made of such a consistency that when struck a smart
blow with the back of a shovel a film of moisture will just show
on the surface, it shoula have vigorous ramming to insure a
compact mass. A flushing of water to the surface will then
indicate when to cease tamping.
With a little more water there is less danger of the larger
stones "bridging" and leaving large voids in the mass, and
less work will be required to flush water to the surface. With
such a consistency, cutting the mass with a spade before start-
ing, the ramming may assist in expelling air bubbles and pre-
venting voids. With still wetter mixtures ramming becomes
difficult, as the concrete will soon begin to quake, after which
the ramming should not be long continued as the mass is then
374 CEMENT AND CONCRETE
semi-fluid, and the stones may gradually work themselves to
the bottom of the layer, forcing the mortar to the top.
519. Hammers are frequently made of wood, but those of
iron are believed to be better. The weight of a rammer is
limited by the capacity for work of the man who wields it.
They are usually made to weigh from twenty to forty pounds.
If a man lifts and drops a forty-pound rammer with forty square-
inch face twenty times a minute, he is doing less good to the
concrete than if he dropped a twenty-pound rammer with twenty
square-inch face forty times a minute. If the face of the ram-
mer exceeds thirty-six square inches, the result is apt to be a
mere patting of the surface of the concrete, unless the rammer
is so heavy as to require two men to operate it. Iron rammers
with face, say, three by six inches, and weighing twenty to
thirty pounds, are believed to be the most efficient. Still thinner
rammers than this may be necessary in work involving such
detail as for filling in between iron beams, and are desirable
for tamping near the face of the mold.
520. Rubble Concrete. — In massive work the embedding of
stones of "one-man size," or larger, in the concrete is a practice
that has long been in vogue. The objection is sometimes made
that this interferes with the homogeneity of the wall and that
variations in expansion may result in injury to the work. It
is thought, however, that in large masses this danger is more
theoretical than real, and the author sees no objection to this
form of construction for many purposes if properly carried out,
and it is frequently permitted in important works. Thin walls,
the arch rings of bridges, shallow foundations, etc., should not
of course be built in this way, because the stresses to which such
structures are subjected should be met by a uniform resistance,
to avoid the effects of eccentric or irregular loading. In such
structures as dams, lock walls, breakwaters, retaining walls,
and in many cases bridge piers and abutments, the work may
be considerably cheapened without sacrificing the fitness of the
structure. The stones thus embedded should be perfectly
sound and should not lie nearer one to another than six inches,
nor should they lie nearer than this to the face of the wall.
The concrete should be mixed rather wet, and much care taken
that each stone is completely surrounded by a compact mass of
concrete. The stones should be settled into the concrete al-
PLACING IN AIR 375
ready laid far enough to assure their having a full bed. Stones
used in this manner are sometimes called "plums."
521. Another class of rubble concrete differing from the
above more in degree than in kind, is formed by placing large
stones in the work, and filling the joints between them with a
rather wet concrete in which spalls may be rammed if desired.
The difficulty of obtaining a compact wall by this method is
perhaps a little greater than when smaller stone are used, but
in either case if really water-tight work is desired, the inspec-
tion must be thorough.
The saving in cost by the use of rubble concrete depends
upon the local conditions, but under ordinary circumstances
when broken stone is employed, the cost of crushing the stone
and the cost of cement, for a volume of concrete equal to the
volume of the stone imbedded, are practically saved.
522. Joints in Concrete. — In the construction of large
masses of concrete in place, joints cannot be avoided; that is,
it is not possible to make the entire mass monolithic, as force
enough could not be employed to carry up the entire struc-
ture at once. Even if this were possible, it would not be de-
sirable, since the changes in length of the wall due to changes
in temperature would probably result in cracks which would
be irregular in outline and mar the appearance of the wall,
if they had no more serious effect.
When the concrete is subjected to vertical forces only, as
in foundations for buildings, horizontal joints are less objec-
tionable than vertical joints. But in the construction of con-
crete lock walls, dams, and breakwaters, vertical joints are de-
sirable to confine the cracks to predetermined planes. In the
building of such structures, therefore, the method has been
adopted of dividing the work into sections of such horizontal
dimensions as may be thought best, and completing each sec-
tion as a monolith. This will sometimes require the contin-
uous prosecution of work for twenty-four or forty-eight hours.
Whether this method, involving work at night, which is always
more expensive and usually less thorough, is justified by the
end sought, depends upon the character of the structure.
523. If this method is not adopted, and a horizontal plane
of weakness is a serious defect, special means should be pro-
vided for avoiding this plane of weakness. Such provision may
376 CEMENT AND CONCRETE
be made by iron dowels set in the concrete at the end of the
days work and projecting above the surface to be covered by
the concrete placed the next day; steps or hollows, or grooves
parallel to the length of the wall, may be left to be filled by
the next layer. Large stones weighing a hundred pounds or
more are frequently imbedded one half their depth in the
last layer of a days work to form a bond with the following
layer.
In any case special care should be taken to thoroughly wash
and clean the surface of hardened concrete before continuing
the work, using preferably wire brooms for this purpose and
removing any stones at the surface that appear to be loose.
A thin layer of rich cement mortar should then be laid upon it,
into which the first layer of fresh concrete is well rammed.
If the appearance of the finished face is of importance, special
care must also be exercised in joining at this point. Before
leaving a layer which is to be allowed to harden before contin-
uing the work, the line limiting the height of the concrete at
the face should be made perfectly horizontal, for a slight crack,
or at least a noticeable line, may be expected at this point, and
if not straight it will be the more unsightly.
524. If for any reason a layer of concrete cannot be carried
over the whole area of the wall or foundation, it should never
be allowed to taper off to a wedge, but a plank equal in width
to the thickness of the layer should be set on edge, firmly se-
cured, and the concrete tamped against it. In the construction
of arches, culverts and sewers, such stop planks may well be set
normal to the surface of the intrados instead of vertical. In
case more than one layer is left incomplete, they should be
stepped back, making an offset for each layer of at least one or
two feet. The concrete should never be built up on a smooth
batter if new concrete is to be joined to it later.
525. Keeping Concrete Moist. — All concrete should be kept
moist from the time it is in the wall until it has become well
hardened. Surfaces exposed to the air should therefore be
sprinkled frequently for at least several days after placing.
An excellent practice is to cover the surface with burlaps which
may be kept saturated, as this not only furnishes the necessary
moisture, but protects the work from the direct rays of the
sun. The interior of a large mass will probably take care of
SURFACE FINISH 377
itself in this regard, but the precaution has sometimes been
taken of leaving vertical holes or wells in the mass, which are
kept filled with water for some weeks and are then filled with
concrete.
526. FINISH. — Some of the precautions that must be taken
to secure a good finish to the face of concrete work have al-
ready been mentioned in considering the forms and the meth-
ods of deposition. These are usually supplemented, however,
by certain special means when the appearance is of much im-
portance.
We must say first, that the application of a plaster of ce-
ment mortar to a finished and set concrete face will almost
never be permanent. It is seldom that it will adhere with suf-
ficient strength to prevent scaling due to differences in expan-
sion of the materials of different composition and age. If
plaster must be used on the face of a wall, it should be applied
before the concrete has set, but it is safer to avoid plastering.
It is of course advisable to fill with rich mortar any voids that
may appear in the face of the work, but such places should be
few.
If the molds are removed while the concrete is still moist,
the face may be coated with a thin grout and then immediately
scraped off with the edge of a trowel. This results in filling the
small voids in the face of the work, but does not leave a coat of
plaster on the surface to scale off,
527. A good finish may be obtained when the molds are
smooth if the workmen will force the blade of a spade or shovel
between the fresh concrete and the mold, and pull the handle
away from the mold. This has the effect of forcing the large
stone back from the face and allowing the mortar to flow in. A
layer of mortar is thus left next the mold with no marked fine
of junction between mortar and concrete, as may be the case in
using a mortar facing, A similar effect may be produced by
throwing the concrete against the face of the mold with such
force that the larger pieces of aggregate rebound. In very
finely finished work this may mar the surface of the sheathing,
but ordinarily this method is effective.
528. When a special layer of mortar is used for facing, there
is more danger, perhaps, of making the layer too thick than too
thin. As to the richness of the mortar, two parts sand by
378 CEMENT AND CONCRETE
measure to one volume packed cement is usually sufficient,
though a more glossy finish may be made if desired, by using
equal parts of cement and sand. It is better to avoid too great
a variation between the richness of the mortar used for facing
and that used in the body of the concrete.
One of the best ways of applying such a layer is to prepare a
sheet of steel of width equal to the thickness of one layer of con-
crete, usually six to eight inches, with two handles on the upper
edge to facilitate moving it. At the ends of the sheet, on the
side next the mold, rivet short pieces of 1^ in. by l^ in. or 2 in.
by 2 in. angle iron. This sheet of iron with the projecting legs
of the angles against the face of the molds, forms, with the
latter, a space one and one-half or two inches thick, which
is to be entirely filled with the finishing mortar made rather
moist and tamped lightly with edge rammers. The concrete is
filled in behind the iron, after which the latter is withdrawn by
means of the handles, and the whole mass is thoroughly rammed.
The end sought is that the finishing mortar shall have some
approximately definite thickness, and that the stones of the
concrete shall be tamped into the finishing mortar, but not
through it, and thus destroy any sharp Hne of demarcation
between mortar and concrete, and ensure a perfect bonding of
the two. It is evident that this can only be accomplished by
placing the mortar and concrete at the same time.
529. One other cautionary remark concerning the use of fin-
ishing mortar. With the present state of our knowledge con-
cerning the rates of expansion of mortars and concretes of dif-
ferent composition, it is not considered wise to use too many
combinations in the same structure. To illustrate, a pavement
or surfacing of a large concrete structure was once built in layers
as follows: first, thick natural cement grout was placed on the
concrete foundation; second, natural cement concrete; third,
Portland cement concrete; fourth, a richer Portland cement
■concrete; fifth, Portland granoUthic; sixth, rich Portland mortar;
and seventh, floated with dry Portland cement and sand. We
cannot be absolutely sure that this is bad practice, but it would
seem that this structure might have served its purpose with
fewer varieties of material, and it is usually considered very
doubtful whether Portland cement mixtures will always ad-
here well to mixtures of natural cement, although the author
SURFACE FINISH 379
knows of instances where they have been used in juxtaposition
apparently with good results.
530. Granolithic is a facing or surfacing mortar composed
of crushed granite and cement. The granite is usually specified
to contain no particles larger than f inch to one inch, and about
one and one-half to two and one-half parts are used to one vol-
ume of cement. This is more frequently used for foot walks
and other places where resistance to wear is required, but may
also be used to surface walls, to line reservoirs, etc. It will be
mentioned again in connection with cement sidewalk construc-
tion.
531. Exposed concrete surfaces frequently present a patchy
appearance. This may be the result of lack of care in placing
the concrete next the mold, or it may be due to variations in
the purity of the sand or in the amount of water used in mixing.
On mortar-faced work this lack of uniformity is less noticeable.
The use of slag sand, or of a little fine pozzolanic material, may
be advantageous, and a small amount of lampblack in the facing
mortar also tends towards uniformity in appearance.
A very pleasing finish may be given by applying to the set
concrete a thin wash of cement and plaster of Paris, though the
permanence of such a wash may be open to question. The
sheathing should be removed as early as it is perfectly safe to
do so, and the concrete surface cleaned from any oil or grease
that may have come from the mold planks. The wash, which
should be very thin, may be applied with a whitewash brush.
A mixture of equal parts Portland cement and plaster of Paris
gives a very light gray finish, and one part plaster to three parts
cement gives a trifle darker shade.
532. A nibbed finish of excellent appearance may be given
by removing the sheathing before the concrete has set very
hard, say after twenty^four to forty-eight hours, and rubbing
the surface with white brick or with a wooden float. If there
are small voids in the surface, it may be covered with a thin
grout of equal parts of cement and sand and then rubbed
hard with a circular motion. The grout should not leave a
scale on the work, the object being only to fill surface imperfec-
tions.
If the mold boards are removed at just the proper time, a
good finish may be given by rubbing with a wooden float, with-
380 CEMENT AND CONCRETE
out the coating of thin grout. A somewhat similar effect is
produced by brushing the surface with brooms or stiff brushes.
533. " Pebble-dash." — What is called a pebble-dash finish
was used in the construction of a bridge in the National Park at
Washington, D. C* Eighteen inches of the concrete next the
face was made of one part cement, two parts sand, and five parts
of gravel and rounded stone from one and one-half to two inches
in their smallest diameter. After the removal of the forms the
cement and sand were brushed from around the face of the gravel
next the surface exposed to view. It was found by experiment
that the brushing should be done when the concrete was about
twenty-four hours old. At twelve hours the gravel was displaced
by the brushing, and after thirty-six hours the mortar had be-
come so hard as to be removed from the surface of the stones
with difficulty. The forms were therefore designed so that
sections of the lagging could be removed as desired. The cost
of the brushing was said to be about sixty cents per square yard.
A somewhat similar method is employed in giving to con-
crete the appearance of cut stone. The materials used in the
surfacing mortar are Portland cement and crushed rock, the
character of the rock depending upon the color and texture de-
sired in the finish. The molds having been removed after the
proper time has elapsed, the mortar covering the face of the
particles of crushed rock is removed by brushing or by washing
the surface with a weak acid solution, followed by clean water,
and finally by an alkaline solution to prevent any further action
of traces of the acid which might be left on the face. This last
method is said to be patented, "the patent covering the obtain-
ing of a natural stone finish for concrete by mechanical, chemi-
cal or other means." ^ It is hoped that such a blanket patent is
somewhat less formidable than it appears.
If the sheathing planks of the molds can be removed about
twenty-four hours after the concrete is placed, the same effect
may be produced without the use of acid. By using plenty of
water the cement and finer portions of crusher dust in the face
'Capt. Lansing H. Beach, (Dorps of Engrs., U. S. A., in charge. Work
described by Mr. W. I. Douglas, Engr. of Bridges, D. C, Engineering News,
Jan. 22, 1903.
^Engineering News, May 21, 1903.
SURFACE FINISH 381
may be washed out with a stiff corn broom, leaving the facets
of the crushed rock exposed.
534. Pointing and Bush-hammering. — If the molds have
been left in place until the concrete is set hard and it is found
that the face of the concrete is not what is desired, it may still
be improved although it may not be plastered. With this ob-
ject the face is sometimes tooled with the stone cutter's point to
give the appearance of rough pointed or rock face masonry.
Grooves may be cut to block off the work into rectangles of the
proper size, then a draft of one to two inches may be left along
all of these artificial joints, and within the draft hne the rough
pointing may be done.
A cheaper method, however, is to bush-hammer the entire
face, and this tends to mask any lack of uniformity in color or
smoothness. Bush-hammering may be done by ordinary labor-
ers at a small cost, as one man can go over from fifty to one
hundred square feet in ten hours, making the cost from If cents
to 3^^ cents per square foot, with labor $1.75 per day. Where it
is decided beforehand to bush-hammer the work, less pains need
be taken in dressing the lagging of the forms.
535. Colors for Concrete Finish. — The addition of coloring
matter to cement and concrete is not at present widely prac-
ticed, and consequently experience has not been sufficient to in-
dicate just what colors may be used without detriment to the
work. Lampblack has been most commonly employed, giving
different shades of gray according to the amount used. In any
large work where the use of coloring matter is desirable and
there is not time to institute thorough tests, the advice of a
cement chemist should be sought. The dry mineral colors,
mixed in proportions of two to ten per cent, of the cement,
give shades approaching the color used. Bright colors are diffi-
cult to obtain and would not be in keeping with a masonry
structure except in architecture.
When mixed with an American Portland cement mortar,
containing one part cement to two parts by weight of a yellow
river sand, the particles of which are largely quartz, the colors
indicated in the following table are obtained.
With no coloring matter added, the mortar was a light green-
ish slate when dry. Ultra marine green, in amounts up to 8
per cent, of the cement, had no apparent effect on the color of
382
CEMENT AND CONCRETE
this mortar. Variations in character of cement and sand will
affect the result obtained in using coloring matter. The colors
indicated below are for dry mortars ; when the mortar is wet
the shades are usually darker. None of the materials mentioned
in the table seems to affect the early hardening of the mortar,
though very much larger proportions might prove injurious.
With red lead, however, even one per cent, is detrimental, and
larger proportions are quite inadmissible.
COLORED MORTARS.
Colors Given to Portland Cement Mortars Containing Tw^o Parts
River Sand to One Cement.
So
Dry
Weight of Dry CoLOBma Mattkb to IOO^Pocuds of Cement
Material
OS
Used.
<B
i Pound.
1 Pound.
2 Pounds.
4 Pounds.
Dark Blue
Lamp Black
Light Slate .
Light Gray
Blue Gray .
Slate .
15
Prussian
Light Green
Light Blue
Bright Blue
Blue . .
Slate . .
Slate . . .
Blue Slate .
Slate
50
Ultra Marine
Light Blue
Bright Blue
Blue
Slate . . .
Blue -Slate
Slate .
20
Yellow
Ochre . .
Light Green .
Light Buff
3
Burnt
Light Pinkish
Dull Laven-
Umber
Slate . .
Pinkish Slate .
der Pink
Chocolate .
10
"Venetian
Slate, Pink
Bright Pinkish
Light Dull
Red . .
Tinge . .
Slate . . .
Pink . .
Dull Pink
2J
Chattanooga
Light Pinkish
Light Tena
Light Brick
Iron Ore .
Slate . .
Dull Pink . .
Cotta . .
Red . .
Light Brick
2
Red Iron Ore
Pinkish Slate
Dull Pink . .
Terra Cotta
Red . .
2i
536. In some cases it may be sufficient to color the surface
of the work by painting. Ordinary oil paints are sometimes
appUed after washing the surface of the wall with very dilute
sulphuric acid, one part acid to 100 parts water, but the per-
manence of such a finish seems very questionable.
The method of obtaining a gray finish by painting with a
thin grout of cement and plaster of Paris has already been de-
scribed (§ 531). Similar methods may be used with the dry
mineral colors, and, while their permanency cannot be vouched
for, it seems a more reasonable procedure than to paint a con-
PLACING UNDER WATER 383
Crete surface with oil paints. One pound red iron ore to ten
pounds cement mixed dry, and then made into a very thin grout
and applied to a well cleaned concrete surface with a white-
wash brush, gives a pleasing brick-red color; and a rich dark
red is given by one pound red iron ore to three pounds cement.
The earlier this is applied after the concrete has set, the more
likely is it to remain permanent.
Art. 64. Placing Concrete under Water
537. In building a concrete structure under water where the
site cannot be coffered, it must be expected that the expense
of the work will be increased, and the quality of concrete poorer.
The methods employed for subaqueous construction are: 1st,
the laying of freshly mixed concrete in roughly prepared forms;
2d, placing the fresh concrete in bags of burlap or canvas which
are deposited while the concrete is still soft; and 3d, molding
in air concrete blocks which are placed in the work when well
set.
lA the first method some cement will certainly be washed
out of the concrete, the extent of this loss depending upon the
condition of the water in which the work is done {i.e., its depth
and the amount of current and wave action) and the care with
which the concrete is lowered to place. Tamping cannot be
done with this method, and any movement of the concrete to
level it will cause further loss of cement.
In the second method the loss of cement will be much less,
but the adhesion between the different masses will be slight. In
the third method there is no loss of cement and the concrete
can be well rammed; but if small blocks are used, there may
be difficulty in so placing them under water as to make a solid
structure, while if large blocks are used, special hoisting ma-
chinery is required to handle them.
538. DEPOSITING IN Place.— The first method mentioned
above, depositing fresh concrete in place, is usually the cheap-
est and most expeditious method, though it is not likely to
^ve the best results. When concrete is lowered through water,
there is a tendency for the cement to separate from the sand
and stone. This tendency seems to be exhibited in a more
marked degree with some cements than with others. In con-
nection with the construction of the concrete foundations of
384 CEMENT AND CONCRETE
the Charlestown bridge, a tes.t was devised for determining the
relative values of the different lots of cement for depositing in
water.^ Concrete was laid, through a small chute, in a cement
barrel placed in a hogshead filled with salt water. It was found
that while some specimens would retain their form after twenty-
four hours when the barrel was removed, others showed but
little cohesion after twenty-four to forty-eight hours. In the
former, the cement and gravel remained well distributed through-
out the mass, but in the latter much of the cement had sepa-
rated from the gravel, and settled in the bottom of the barrel,
where it remained in an inert state, while the central portion of
the concrete, robbed of its cement, had many voids. As a
result of this test, some lots, of cement were not accepted for
use.
The finest portion of the cement is very liable to separate
from the remainder as the concrete passes through the water,
and if subjected to the action of waves or a current, much of
the cement will be washed away. In exposed situations it is
especially necessary to inclose the site of the work with sheet pil-
ing or cribs, or a wall constructed by the bag or block method.
When the water level outside the form is constantly changing,
the flow of water through' the joints in the sheathing is especi-
ally effective in washing out the cement, and in such conditions
the sheathing should be made as nearly water-tight as possible.
To this end tongue and groove lagging may be used, or the face
of the mold may be covered with tarred felt, or canvas, tacked
in place.
539. Laitance is the term applied to the whitish spongy
material that is washed out of concrete when it is deposited in
water. Before settling on the surface of the concrete, which
it does slowly, it gives to the water a milky appearance, hence
the name. In fresh water this semi-fluid mass is composed of
the finest flocculent matter in the cement, containing generally
hydrate of lime. It remains in a semi-fluid condition for a
long time and acquires very little hardness at the best. In sea
water the laitance is more abundant and is made up of silica,
lime and magnesia, with carbonic acid and alumina, its exact
* Report of Mr. William Jackson, Chief Engineer. Third Annual Report
Boston Transit Commission.
PLACING UNDER WATER 385
composition depending upon the character of the cement. This
interferes seriously with the bonding of the layers of concrete,
and when it has settled it should be cleaned from the surface
before another layer is placed.
540. The Tremie. — A method frequently employed to pre-
vent, as much as possible, the loss of cement, is to make use of
a large tube of wood or sheet iron, made in sections so that
its length is adjustable, and provided with a hopper at the
upper end. Such a tube is called a tremie. The hopper is
always above water, and the lower end of the tube, which may
also terminate in a hopper, rests upon the bottom of the founda-
tion.
The tremie is first filled with concrete, a box placed over the
lower end serving to prevent the escape of the concrete while
the tube is being lowered until the end rests upon the bottom.
The tube is then lifted from the bottom sufficiently to allow
the concrete to escape as fast as fresh concrete is added at the
top. The surface of the concrete in the tube should be kept
continuously above the v/ater surface. The tremie may be
held in position by a crane, or it may be so supported as to al-
low of two motions at right angles to each other. Such an
arrangement was used in building the piers for the Boucicault
Bridge, the tube traveling along a platform, which in turn
could move on a track at right angles to the first motion. In
using a tremie the thickness of a layer may be regulated at will.
In the construction of the Charlestown Bridge ^ a tube was
used fourteen inches in diameter at the bottom, and about
eleven inches in diameter at the neck, above which was a hopper
to receive the concrete. When the attempt was made to place
too thick a layer at one operation, it was found that the charge
was likely to be lost, and the best results were believed to be
obtained with layers two feet to two and one-half feet thick.
Some experiments were made with a plug designed to keep the
water from flowing up through the concrete when the tube
was being refilled after a loss of the charge. This plug was
made with a central core of wood and sides of canvas expanded
by steel ribs. It worked fairly well, but its use was not con-
tinued.
Third Annual Report, Boston Transit Commission.
386 CEMENT AND CONCRETE
541. This principle was employed by Mr. Daniel W. Mead
in placing concrete in a small shaft in ninety feet of water.*
An eight inch, wrought iron pipe was screwed together in sec-
tions, and provided with a hopper at the upper end and a wooden
plug at the lower end. After lowering the pipe into the shaft,
the pipe was filled with concrete and it was expected that its
weight would force out the plug at the bottom when the pipe
was raised. On the first attempt, however, the plug failed to
drop out, and on raising the pipe the cause was apparent. The
plug had evidently leaked, and as the first concrete was dropped
into the pipe it had separated, the broken stone being at the
bottom, the sand next, and the cement above had so plugged
the pipe as to support the weight of the concrete. The second
attempt, when a tighter wooden plug was used and a small
pipe placed inside the larger one to assist in loosening the plug
if necessary, was successful.
542. The Skip. — Since in submerged work the concrete
should be deposited in as large masses as possible, the use of a
large skip will probably give better results than the tremie.
A box form may be used with hinged lids at the top to permit
filling, and two hinged doors at the bottom which may be
opened from the surface by a tripping rope when the box has
reached the place for depositing the concrete.
A convenient form of skip is made in two halves, each half
having a cross-section either of a right angled triangle or a
quadrant of a circle. The two boxes are hinged at their upper
inside corners and the pieces through which the hinge rod
passes are prolonged upward, the lowering cables being at-
tached to their ends. Two opening cables are fastened to the
outer corners of the boxes. Two sheets of iron may be used
as covers to the boxes, being attached to the Kinge rod that
serves for the two halves of the skip.
It is seen that the skip will work on the principle of a pair
of ice tongs. While being filled with concrete the box is sup-
ported by the lowering cables, and the hinged lids are kept up
by some simple contrivance. When full, the lids are closed
and the skip lowered till it rests on the bottom; the skip being
then hoisted slowly by means of the opening cables, the con-
Trans. Assn. of Civil Engineers of Cornell University, 1898.
PLACING UNDER WATER 387
Crete is gently deposited in place. Such skips are supplied by
the makers of concrete machinery.
543. In depositing concrete by means of skips it is well to
have the latter of large size, holding not less than a cubic yard,
and preferably two cubic yards or more. The larger quantity
will compact itself better on account of the greater weight,
and the surface which is subjected to wash will have a lesser
area in proportion to the volume of' the mass. The skip should
be completely filled with concrete and tightly closed while it is
being lowered. It is important also that the skips be lowered
slowly, in order that the inclosed air may be replaced by water
without commotion.
544. The Bag. — Mr. Wm. Shield ^ devised a bag for de-
positing concrete under water which is said to work very satis-
factorily. The top of the bag is closed, and has a three-quarter
inch wrought iron bar fastened across the end with a loop to
receive the hook of the lowering line. The mouth of the bag
is slightly larger than the upper end, to facilitate the discharge
of the concrete. The bag is inverted to be filled, and the mouth
is then secured by a turn of a line provided with loops through
which a small tapering pin is passed. This pin is attached to
a tripping line, and when the bag has reached the place of
deposition, a pull of the tripping line releases the pin; when
the bag is gently lifted, the concrete is deposited in place with
such slight commotion that but little cement is said to be lost.
545. Other Methods of Depositing in Situ. — For deposition
under water the materials for concrete are sometimes mixed
dry, but this is not good practice. The mere soaking of water
into cement does not form a compact mortar; the moistened
materials need to be thoioughly mixed and, if possible, rubbed
together in order to obtain perfect adhesion. Then, too, if the
dry materials are lowered to place and water is suddenly al-
lowed access to the mass, much of the cement will be washed
away in the disturbance caused by the sudden inrush of water.
M. Paul Alexandre ^ found by experimenting on mortars of
"dry" (stiff), "wet" and "ordinary consistency," that mortars
• "Subaqueous Foundations," London Engineering, 1892. Abstract in
Engineering News, Vol. xxviii, p. 379,
* " Recherches Experimentales aur les Mortiers Hydrauliques," par M. Paul
Alexandre, pp. 93-96.
388 CEMENT AND CONCRETE
mixed "dry" suffered the greatest decrease in strength by im-
mersion in running water. Mortars mixed "wet" suffered the
least loss, though their resistance was less than those mixed to
the ordinary consistency, since when not subject to the current
of water, the wet mortars gave much lower results than those
of ordinary consistency.
546. In order to avoid the washing out of the cement, the
concrete is sometimes allowed to partially set before deposition.
Mr. Robert W. Kinipple has used this method and advocates
its adoption.^ In employing this method, the concrete, which
should be deposited when of the consistency of stiff clay, re-
quires careful watching that it does not set so hard as not to
reunite after being broken up. Under ordinary supervision,
this will probably not prove as successful as some of the other
devices, but it may be found valuable under certain circum-
stances. The writer made a few experiments with this method
on a small scale in swiftly running shallow water. Much of the
cement appeared to be washed out by the current, but the
results were somewhat better than were obtained when the
concrete was deposited fresh. (See § 456.) M. Paul Alexandre
made some short time experiments on this point, which indi-
cated that but little advantage was gained in allowing the
cement to partially set before deposition.
547. Depositing Concrete in Bags.— The second method
of depositing concrete under water, namely, by placing the freshly
mixed concrete in coarse sacks and immediately lowering them
to place, is very convenient under certain conditions. This
method is of especial value in leveling a foundation to receive
concrete blocks, or to form a base for concrete deposited in situ.
Small bags of concrete have been successfully used in filling the
spaces between pile heads which were to support an open caisson.
In such a case the bags should be lowered to a diver who places
and rams them. If the bags be properly leveled and the earth
firm, a part of the load is thus transmitted to the material be-
tween the pile heads, while if the earth be very unstable, the
bag construction compels the piles to act together, giving lateral
stiffness to the foundation and tending to prevent over turning.
1 "Concrete Work under Water," Proc. Inst. C. E., Vol. Ixxxvii. See
also "Notes on Concrete," by John Newman, pp. 116 and 117.
PLACING UNDER WATER 389
548. The bag method was successfully used in replacing
with concrete the timber superstructure of the breakwater at
Marquette, Mich,^ The main portion of the breakwater was
built of monolithic blocks on the rock-filled timber substruc-
ture. After removing a portion of the rubble fiUing, a bed was
made for the monolithic blocks by laying concrete in place two
feet thick, extending from one foot below to one foot above
low water datum. This method was afterward replaced by
the use of concrete in bags, which made it safe to remove a
lesser amount of the rock filling of the crib at the center, and
thus decreased the expense of the work. The bags were of
eight ounce burlap made 6 feet long and 6 feet 8 inches in cir-
cumference, and held about one ton of concrete. They were
filled while lying on a skip specially constructed, so that when
the skip was in place it could be tripped and the bag placed in
its exact position in the work.
549. In connection with this work a practical indication of
the character of the concrete deposited in this manner was
given by some small bags of concrete that were laid to protect,
during the winter storms, a portion of the crib filling. Mr.
Coleman says of this,^ "Only one layer of these sacks, laid
slightly overlapping from the lake side of the crib, was used.
The sacks were so lightly filled that when laid as described, the
average thickness of the concrete covering was not more than
six inches. The crib was storm swept many times without
displacing a single sack, and when they were removed in the
following spring to facilitate the work, they came away, when
pulled up with the floating derrick, a dozen or more at a time,
so firmly were they cemented together, and in many cases
large rubble stones were lifted up along with them, because of
the adhesion of the cement to their surfaces."
550. The Cost of the concrete in bags was as follows : —
Materials, cement, sand, stone, burlaps, etc $5,281
Mixing concrete and filling bags 912
Transportation 157
Depositing 408
Total cost per cubic yard $6,758
Or, cost in bags, exclusive of materials .... 1.477
Major Clinton B. Sears, Corps of Engineers, in charge; Mr. Clarence
Coleman, Asst. Engineer.
» RepoH Chief of Engineers, U. S. A., 1897, p. 2620.
390 CEMENT AND CONCRETE
The cost of the first plan, placing a two foot layer of con-
crete in situ, where different methods of handling were em-
ployed, was, for labor: —
Loading scow with materials $0,411
Mixing concrete 846
Depositing 524
Cost in situ, exclusive of materials $1,781
551. When concrete bags are used in forming a foundation,
the lower layers should usually cover a considerably greater
area than that required for the top. Especially is this true if
building upon insecure earth. This increased area at the bot-
tom may be obtained by building the sides on a batter, or by
the use of footing courses. If the latter are used, they should
be so designed that in any case the projection beyond the course
next above is not greater than the thickness of the layer.
Before filling the concrete into the bags it should be thor-
oughly mixed, as for deposition in the ordinary manner. The
practice of using dry concrete for this purpose is reprehensible
for the same reason as has been given in § 545. It has also been
found that if the concrete is mixed and filled into the bags in
a dry state, a layer of concrete on the outside may cake before
the water has had time to reach the interior portion. The
bags should be filled about three-fourths full, leaving the mass
free to adjust itself to inequalities in the rock, or to the irreg-
ular surface of the previously deposited layer. When strength
and compactness are desired, the bags should be placed by a
diver and gently rammed. In this way the mass may be well
bonded by "breaking joints."
552. Large Masses in Sacks. — Very large bags of concrete
are sometimes employed, as in the construction of a breakwater
at New Haven, England.^ "The top of the breakwater has a
width of thirty feet, is ten feet above high water, and is sur-
mounted by a covered way and parapet running along the outer
side, both sides battering one in eight. The breakwater is
unsheltered from the force of the Atlantic, is founded on the
rough, natural sea bottom, and the foundation course has a
* From London Engineering, quoted in Engineering News, Vol. xxvii,
p. 551.
PLACING UNDER WATER 391
width of fifty feet; the lower portion of the structure, from the
bottom up to a level of two feet above low water, consists of
one-hundred-ton sacks of concrete deposited while plastic.
The canvas with which the concrete was enveloped was of
jute, weighing about twenty-seven ounces per square yard.
The sacks were dropped into place by a specially designed
steam hopper barge. The 'sack-blocks' in the finished work
became flattened to a thickness of about two feet six inches.
With the exception of this sack work the breakwater is built
of plastic concrete laid in situ." Similar sack-blocks of one
hundred sixty tons have been employed in breakwater con-
struction.
It is evident that this method of depositing concrete in:
large sacks is peculiarly suited to forming a foundation on a
soft bottom, since, if the bags are made to project well beyond
the sides of the molded concrete to be deposited above, they
act in the double capacity of a mattress to prevent scour, and
a, foundation for the upper part of the structure.
553. Other uses for Bags of Concrete. — In the construc-
tion of the Merchants' Bridge at St. Louis, bags of concrete
were used to check the scour which occurred beneath the up-
stream cutting edge of one of the caissons while it was being
grounded. The bags were thrown into the river at such a dis-
tance above the pier that they settled to the bottom at the
point where the scour was taking place.
Burlap bags were used at St. Marys Falls Canal for laying
concrete under water next the face of the form to prevent
washing of the cement in building concrete superstructure for
canal walls. As the bags were placed by hand they were made
to hold only about two cubic feet of concrete.
554. Paper Sacks. — Paper sacks are sometimes employed
instead of jute bags. Dr. Martin Murphy * describes the meth-
ods employed in filling steel cylinders for the substructure of
the Avon Bridge as follows: "Bags made of rough brown paper
well stiffened with glucose, were employed and slipped into the
water over the required place of deposition. Each bag held
about one cubic foot of concrete; smaller ones were used be-
" Bridge Substructure and Foundations in Nova Scotia," by Martin
Murphy. Trans. A. S. C. E., Vol. xxix, p. 629.
392 CEMENT AND CONCRETE
tween dowels. The bags were quickly made up and dropped
one after another, so that the one following was deposited
before the cement escaped from the former one. The paper
was immediately destroyed by submersion, and the cement
remained; it could not escape. The bags cost one dollar thirty-
five cents per hundred, or thirty-five cents per cubic yard."
The success of this method will depend upon the character of
the sacks, for in some experiments on a small scale with sacks
of stiff manila paper the author found that the bags were not
destroyed, and that no adhesion took place between the separate
sacks.
555. THE Block system of concrete construction. —
The advantage of the block system of construction lies in the
fact that the individual blocks may be made with the greatest
care, and as they are allowed to harden thoroughly before being
put in place, the loss of cement incident to the other systems
is avoided. There is, however, the difficulty of forming a joint
between adjacent blocks. The joints are 'of great importance
when small blocks are employed, since the latter may not have
sufficient weight to escape being washed out of the work. Large
blocks may make a very solid structure by being simply super-
imposed, but special hoisting machinery will be required to
place such blocks.
Sometimes a large bed of mortar is laid in coarse sacking
and carefully lowered and spread on the block last laid, the
next block being placed upon it immediately. A very rich
mortar should be used for this purpose. Usually, however, it
is not attempted to place mortar in the horizontal joints in
concrete block work laid under water, but it is considered that
all vertical joints should be filled with rich Portland cement
mortar when the work is to be exposed to wave action. If
settlement is anticipated, and large blocks are used, no attempt
should be made to break joints in the direction of the longer
dimension of the work, but the blocks should bond in a direc-
tion transverse to the wall. Concrete blocks may be advan-
tageously employed to form the faces of a structure built under
water or exposed to wave action, the concrete hearting or
backing being built in situ.
556. For convenience in handling, a groove to receive a
chain or cable should be left down two sides and across the
PLACING UNDER WATER 393
bottom of the blocks to enable them to be placed close together
and to facilitate the withdrawal of the hoisting chain. These
grooves may afterward be filled with concrete; such recesses
are sometimes molded for the sole purpose of filling them with
fresh concrete when in place, and thus binding the work to-
gether. The molds for forming the blocks should be carefully
made in order that the finished blocks may have good bearings
one upon another. If the corners are rounded, they are less
hkely to be chipped off in handling or by having an undue
strain come upon the corner when in place.
If any recesses are desired in the blocks, the pieces placed
in the mold to form them should be trapezoidal in cross-section
with the longer parallel face against the side of the mold. If
such filling pieces are made rectangular, difficulty will be ex-
perienced in removing them when the concrete has set. The
molds should, of course, be so constructed as to be readily
taken apart to be used again. The opposite sides may be kept
from spreading by rods which pass through the mold, but such
rods are an inconvenience in packing the concrete into the
mold, and it is therefore better to truss the mold outside. If
such tie rods are used, they may be left imbedded in the con-
crete, or removed with the mold, as desired.
557. Cost of Molding Blocks. — An illustration of the use of
the block method is furnished in the United States breakwater
at Marquette.* The general plan of this breakwater has already
been briefly noted and two methods of laying a two foot layer
of subaqueous concrete, as a foundation for monolithic blocks
forming the superstructure proper, have been described. A
third method was to mold footing blocks, seven feet by five feet
in section and two feet high, which were afterward laid flush
with the lake side of the substructure cribs and filled in behind
with concrete laid in place. The footing blocks thus assured
a good quality of concrete beneath the toe of the monolithic
block on the lake side where it was most necessary to provide
a good foundation, and also served as a protection behind which
the remainder of the two foot layer could be placed with greater
facility.
Many of these blocks were built during the winter in a shed
* Report Chief of Engineers, 1897, p. 2624.
394 CEMENT AND CONCRETE
artificially heated, the materials being thawed out as required.
The molds were of six by six inch and four by four inch pine,
lined with two by eight inch plank dressed on one side. Strips
of trapezoidal cross-section, nailed inside the mold, provided for
two parallel grooves on the bottom and two sides of the block
to receive hoisting chains. A dovetail at the back of the block
was also formed by three wedge-shaped pieces placed against
the back face of the mold. The cost per cubic yard of making
forty blocks is as follows: —
1.42 bbls. Portland cement, at $2.75 $3.90
.45 cu. yd. sand, at $0.45 20
1.0 cu. yd. stone screenings passing f sieve, at $1.10, 1.10
Cost materials in concrete per cu. yd $5.20
Superintendence, labor and watchman ....... $2.21
Fuel 31
10 per cent, of cost of warehouse and molds .... .52
Total cost of making per cu. yd 3.04
Total cost per cu. yd. of blocks ready to place
in work $8.24
CHAPTER XIX
CONCRETE-STEEL
558. The ratio between the compressive and tensile strengths
of steel is nearly unity. The same thing is approximately true
of wood and some other materials of construction. In cement
and concrete, however, the conditions are quite different, the
strength in compression being from five to ten times the strength
in tension. Concrete cannot, therefore, be economically used to
resist tension, and in structures requiring transverse strength
concrete is at a great disadvantage.
559. The idea of supplementing the tensile strength of con-
crete by the use of iron in combination with it, seems to have
been suggested independently by a number of men. It is
known that combination beams were tested by Mr. R. G. Hat-
field as early as 1855. In 1875 Mr. W. E. Ward,^ M. Am. Soc.
Mech. Engrs., constructed a dwelling entirely of "b6ton," the
floors, roofs, etc., being reinforced with light iron beams and
rods. These early uses of the combination have some bearing
upon the ability of patentees to cover in their blanket patents
more than the peculiar form of the steel member which they
advocate in their particular system.
Art. 65. Monier System
560. A much more picturesque beginning of the concrete-
steel industry is furnished in the story, quite true, that about
1876, a French gardener, Jean Monier, used a wire netting as
the nucleus about which to construct his pots for flowers and
shrubs, and seeing that the practice might be extended, he
called to his aid engineers and capitalists who developed the
Monier system of construction.
This system consists of imbedding in the concrete two sets
of parallel rods at right angles to each other, the rods of the
two sets being tied together with wire at all intersections.
1 Proc. Am. Soc. Mech. Engrs., Vol. iv, p. 388.
395
396 CEMENT AND CONCRETE
The larger wires run in the direction of the greater tensile stresses
and are usually spaced two to four inches apart. The rods at
right angles to these main tension members are to assist in dis-
tributing the stress to the main members and may be of smaller
diameter.
The iron rods in this system are designed primarily to resist
the tension only, and the form of the bars is not such as will
stiffen the structure while the concrete is fresh. In an arch,
two systems of netting are used, one near the intrados and one
near the extrados.
561. The main advantages which this system has over some
of its competitors are the simple shapes required, that is, round
rods, which may always be obtained without difficulty, and
the fact that these may be so readily put together by ordinary
workmen under supervision. This system is especially adapted
to vertical walls, whether curved or straight, and found its
first extensive use in the construction of tanks and reservoirs.
It has been extended, however, to the construction of sewers,
floors, roofs, and arch bridges.
One of the practical disadvantages of the system is that the
nets are somewhat difficult to handle and keep in position, and
in thin sections it has not been found practical to imbed the
nets in concrete containing broken stone of the ordinary size.
The use of cement mortar, usually one part cement to three
sand, has been found necessary in order to get a perfect con-
nection between the wires and the body of the work. This,
of course, increases the cost. Another objection has been
urged against it, namely, that the transverse rods do not in
general have any duty to perform, and are simply a waste of
material so far as the final strength of the structure is con-
cerned. While this may be so in certain forms of construction,
it may be met by the statement that these cross-rods may be
made as small as desired if they are to act merely as spacers
for the main rods. In slabs, walls, etc., however, these cross-
rods have a purpose, and in some other systems members are
supplied to fulfill this necessary function.
562. Some very bold arches have been built on the Monier
system, including three bridges in Switzerland having 128 foot
span, 11 foot rise, and a thickness of but 6f inches at the crown
and 10 inches at the abutments.
PATENTED SYSTEMS 397
A Monier arch of 32.8 foot span, rise one-tenth of span,
width 13.2 feet, in which the mortar at the crown was six inches
thick and eight inches at the abutments, was tested in Austria
in 1890. It held a fifty-three ton locomotive on half the arch,
and finally failed at the abutments under a load of 1,700 pounds
per square foot over half the span.
563. Pipes are now made by this system at yards and trans-
ported to the place of use. It has also been used as a substi-
tute for iron in cylinders for bridge piers. A novel use of this
system consists in making a pipe covering for piles exposed to
marine borers. The pipe, which is long. enough to reach from
above the water surface to below the bed of the waterway, is
slipped over the head of the pile and settled a short distance
into the mud or silt of the bottom with the aid of a water jet.
A question, however, has been raised as to the action of con-
crete and iron in combination in sea water on account of the
possible setting up of galvanic action.
Art. 66. WiJNSCH, Melan, and Thacher Systems
564. Wiinsch System. — This system, which was invented
in 1884 by Robert Wiinsch of Hungary, consists of two iron
members of angle irons and plates imbedded in concrete, the
lower member being arched and conforming to the outline of
the soffit, while the upper one is horizontal and continuous.
The two members are riveted together at the crown, and at the
abutment are rigidly connected by a vertical member. The
several systems of rib bracing thus constructed are connected
laterally at the abutment by channel bars running transverse
to the arch and riveted to the bottom of each vertical in the
abutment. Assuming that the abutments are stable, it is evi-
dent that we have here not simply an arch, but also some ele-
ments of the cantilever. The spandrels being built up solid of
concrete, there is no definite arch ring, and the quantity of
material required, especially in long spans, is likely to be much
greater than in other systems. On the other hand, the great
depth at the springing permits the use of concrete only moder-
ately rich in cement.
565. A bridge of this type, built at Neuhausel, Hungary,
consists of six spans of about 56 feet each, rise 3.7 feet, thick-
ness at crown 9.8 inches, and at springing line 54.3 inches.
398 CEMENT AND CONCRETE
The total width of the arch was 19.7 feet and contained thir-
teen systems of arch ribs. Concrete in the abutments below
water was made mainly of Roman cement. Above water it
was composed of one part Portland to eight or ten parts sand
and gravel. Ten to twelve inches of the arch was built of
strong Portland concrete rammed in layers at right angles to
radial lines of the arch, special care being taken with that part
below the bottom arched member. An arch was usually com-
pleted in one day, and the centers remained in place thirty to
forty days, the greatest settlement on the removal of centers being
two-thirds of an inch. This bridge contained 1,346 cubic yards of
concrete and 88,180 pounds of iron, and cost, complete, $13,700.
566. Melan System. — This system, invented by an Austrian
engineer, Joseph Melan, consists of arched ribs between abut-
ments as in bridges, or between beams or girders as in floor
construction, the space between the ribs being filled with con-
crete. Steel I-beams curved to the proper form are usually
employed for the reinforcement, though angle iron flanges with
lattice connections have been used in some of the large bridges.
The steel members extend into the piers or abutments and are
there connected by angles or other shapes, and firmly imbedded
in the concrete.
567. This system as adapted to bridge construction has
probably met with greater favor among American engineers
than any other form. Perhaps this is because of the stiffness
of the form of iron beam used, and because by assuming a
rather high fiber stress for steel the reinforcement may be de-
signed to withstand the entire bending moment without exces-
sive dimensions for the steel members. There is thus a feeling
of security in its use that is not felt in the same degree with
other systems. The arch dimensions are determined by com-
puting the forces and required thickness of arch ring after
assuming certain safe working stresses for the steel and con-
crete; but if desired, the size of steel members may then be
increased slightly where necessary to such dimensions that
with unit stresses of, say, one-half the elastic limit, the entire
bending moment shall be taken by the steel. Some of the
largest bridges built after this system in the United States are
the five-span bridge at Topeka, Kan., and the three-span bridge
at Paterson, N. J.
PATENTED SYSTEMS 399
568. Thacher System. — A modification of the Mclan system
is that invented and patented by Mr. Edwin Thacher. Steel
bars are used in pairs and imbedded in the concrete near the
intrados and extrados of the arch and extending well into the
abutments. The bars of each pair may be connected by bolts
or stirrups, though Mr. Thacher's original idea seems to have
been to have no connection between two bars of a pair ex-
cept through the concrete. The bars are provided with pro-
jections which may be in the form of rivet heads, lugs, or
bolts, to increase the resistance of the bars to slipping in the
concrete.
569. Mr. Thacher has more recently designed a special form
of rolled bar having projections that serve the same purpose
as the rivet heads mentioned above. Several bridges have
been built on this system, one of the most notable of these being
the Goat Island bridge at Niagara Falls, one span of which is
110 feet in length,
570. In the construction of arch bridges many of the other
systems are simply modifications of the Melan. The shapes of
the steel members may have different forms, and the connec-
tions between the pairs of bars forming the arch ribs may vary
to suit the idea of the inventors. But though these systems
lose theit identity in long-span arches, their distinctive features
are more apparent in the construction of floors, roofs, columns,
etc.
Art. 67. Other Systems of Concrete-Steel
571. The Hennebique System. — The rods are here arranged
in pairs, one above the other, in a vertical plane. In girders,
the bar in the tension side is straight, while the other one of
the pair is horizontal for a short distance along the center of the
span, the ends being inclined upward near the ends of the
beam. The two bars are connected by bent straps or U-bars
so that the steel reinforcement may be compared to a queen
post truss within the concrete. This system has been used in
the construction of bridges, both arch and girder, floors, roofs,
stairways, etc., but it is in beams and girders that its distin-
guishing characteristics are best displayed.
572. A beautiful arch on this system is the bridge over the
river Vienne at Chatellerault, France, consisting of three spans,
400 CEMENT AND CONCRETE
the central one of which is 164 feet long, with rise of 15 feet,
8 inches. Four arch ribs 20 inches deep support the roadway,
25 feet wide, by posts forming a skeleton spandrel.
573. Kahn System. — In this system, which is somewhat
similar to the Hennebique, the distinguishing feature is the care
taken to provide against shear, or against that combination of
tension and shear which tends to cause failure in a beam by
cracks tiiat extend diagonally upward toward the center of
span from near the points of support. The steel plates forming
the tension members are sheared longitudinally at intervals,
and short ends are bent up at an angle of forty-five degrees
with the horizontal. These ends, which may be compared to
the tension diagonals of a truss, are thus a part of the main
steel member, and the stress is transferred directly to the
latter without dependence on the concrete.
The advantages are the great resistance offered by the bar
to being pulled out of the concrete and the thorough manner
in which all tension stresses may be provided against. The
main disadvantages would seem to be the necessity of detailed
shop work for each size of girder, the inconvenience of shipping
the steel in its complete form and the difficulty of thoroughly
tamping the concrete around the diagonals.
574. The Ransome System. — One of the earliest pfitents to
be issued in this country for a method of using concrete and
iron in combination was that issued to Mr. E. L. Ransome in
1884. The valuable and distinctive feature of this system is
the use of a square bar that has been twisted cold. This twist-
ing not only insures a good bond between the concrete and iron,
but actually somewhat increases the strength of the bar.
In building beams with twisted bars as tension members, the
latter are given a slight inclination from the center upward
toward the ends. For use in buildings, as in floors and columns,
and for covers to areaways, and similar uses, this system is
largely employed.
575. Roebling System. — As its name implies, wire forms
the main feature of this system, and in a general way it resem-
bles the Monier. Its application thus far is found principally
in floor construction, two distinct methods being used. In the
arched floor a wire netting, stiffened by round steel rods woven
through it is sprung between the lower flanges of the main
STRENGTH CONCRETE-STEEL 401
I-beams of the floor. This netting, further stiffened and held in
place by iron rods running parallel to the axis of the arch, forms
a permanent center for the placing of the concrete, which fills
all of the space to the level of the top of the I-beams. A level
eeiling below is obtained by a similar netting laid flat against
the under side of the I-beam and fastened thereto. This acts
as a wire lath to receive a coat of plaster. If the level ceiling
is not necessary, the plaster may be applied to the under side
of the arch netting, in which case the lower flange of the I-
beam should be encased in concrete to protect it from corrosion
and fire.
576. For lighter loads, flat bars are placed at suitable in-
tervals above and below the I-beams and clamped to the flanges.
To these bars the wire netting is attached, a thin layer of con-
crete laid on the upper wire incasing the bars, and plaster ap-
plied to the lower netting forming the ceiling. Cinder concrete
is usually employed with this system.
577. Expanded Metal. — The use of whai: is commonly known
as expanded metal lath has been extended to concrete-steel
construction. As in the Monier and Roebling systems, the
strength an'd stiffness of the structure are increased by the use
of steel rods in connection with the expanded metal, the chief
duty of the latter, where great strength is required, being that
of a distributing member. Expanded metal is made from
sheet steel by shearing short slits parallel to the grain, and
extending the sheet at right angles to the slits, resulting in a
network of diamond shaped openings. The metal used is of all
weights up to one-quarter inch thick with meshes six inches long.
578. The steel bars used in connection with expanded metal
by the St. Louis Expanded Metal Fireproofing Co. are square,
with frequent corrugations surrounding the bar. These corru-
gations serve only to prevent the slipping of the bars in the
concrete without adding to the strength.
The applications of this system include conduits, sewers,
and walls of buildings, as well as floors and roofs.
Art. 68. The Strength of Combinations of Concrete and
Steel
579. While we have in this country been somewhat slow in
acknowledging the worth of concrete-steel construction, there
402 CEMENT AND CONCRETE
is now a strong interest displayed in the subject; many experi-
ments are being made in our educational and commercial labo-
ratories and the theory of the action of concrete and steel in
combination is being rapidly developed. It is natural that in
the investigation of a form of construction permitting so many
variations in methods of preparation, that the opinions now
advanced, based on insufficient data, should be more or less
conflicting.
580. Experiments. — The experiments of M. A. Considere,
made in France between 1898 and 1901, which have been made
more available to us through the translation and collection of
his articles on the subject by Mr. Moisseiff,^ are exceedingly
valuable. The effect of the quality of the steel and the con-
crete, of repeated loads, of changes in volume in hardening,
and many other points are carefully analyzed by experiment
and theory.
One of the most important deductions drawn by M. Con-
sidere is that fibers of concrete within what may be called the
sphere of influence of a reinforcing rod of iron or steel, is capable
of enduring very much greater elongations without visible frac-
ture than similar concrete without reinforcement. The expla-
nation advanced for this is that the steel so distributes the
stress throughout the length of the concrete in tension that
the development of insipient fractures or excessive elongations
at the weaker sections of the concrete is prevented until each
section has taken its maximum load. The conclusion to which
this theory leads is that the resistance of the concrete through-
out the area of influence of the steel reinforcement, is main-
tained far beyond that degree of deformation which, in concrete
not reinforced, would cause its rupture.
581. Neglect of Tensile Strength. — Notwithstanding these
conclusions, it is believed that it is sufficient in most cases of
design to neglect the tensile strength of the concrete in concrete-
steel combinations. This course may be defended by the fol-
lowing considerations. The tensile strength of concrete is, at
best, not usually above two hundred to four hundred pounds
per square inch. If the stress on the extreme fibers of a beam
* "Reinforced Concrete," by Armand Considfere, McGraw Publishing Co.,.
New York.
STRENGTH CONCRETE-STEEL 403
is three hundred pounds, and we consider that this stress de-
creases uniformly toward the neutral axis, the mean stress is
but one hundred fifty pounds per square inch. Again, if we
disregard M, Consid^re's conclusions, we find that since the
modulus of elasticity of steel is, say, fifteen times that of con-
crete, the former is only stressed to forty-five hundred pounds
per square inch when the imbedding concrete has reached its
ultimate strength.
582. The resistance of concrete to tension may easily be
destroyed or impaired by accident, especially when fresh. The
properties of concrete vary so much with the materials, the
proportions, and the manipulation, and the investigation of
the behavior of concrete and steel under stress is as yet so in-
complete, as to make refinements in theoretical treatment not
only unwarranted but really undesirable for practical purposes,
since they lead to the appearance of greater accuracy than is
in reality attainable.
It is true that by the judicious selection of values for the
constant appearing in formulas for the strength of concrete-
steel beams, the results of such formulas sometimes show a re-
markable agreement with the results of that series of actual
tests for which the constants have been selected; but one has
only to recall his experience in other lines, hydraulics for in-
stance, to realize the importance of the almighty constant.
The opinion sometimes advanced, that the strength of a given
concrete-steel beam may be as accurately derived by formula
as can the strength of a steel beam, the writer does not believe
to be tenable, at least in the present state of our knowledge
concerning the behavior of concrete.
583. To neglect the tensile strength of the concrete will
result in a slight increase in the required area of steel reinforce-
ment, and, in so far as the tensile strength of the concrete
may be developed, will tend to make the compression side of
the beam weaker than the tension side. The only objection
to this is that the failure of the beam, though at a higher
load, may be more sudden. This possibility, however, seems
less serious than the error of depending on the tensile strength
of the concrete only to find it lacking at the critical mo-
ment.
Since the aim here is to develop a formula that may be used
404 CEMENT AND CONCRETE
with safety in the design of structures, and since to neglect
the tensile strength of the concrete is to add an unknown,
though probably small, factor of safety, the tensile strength
will not be considered in the following analysis.
Art. 69. Concrete-Steel Beams with Single
Reinforcement
584. Definitions. — In this discussion the word strain has
its technical meaning, the relative change in length of a piece
under stress. It is usually expressed as the ratio of the elonga-
tion (or shortening if in compression) to the original length of
the piece. But for our purpose it is the ratio of the increment
of change in length, occasioned by a given increment of stress,
to the length of the piece before the increment of stress was
applied. These two expressions for strain are usually consid-
ered equivalent, since, according to Hooke's law, the ratio be-
tween stresses and corresponding strains, for a given material,
is constant within the elastic limit. But in dealing with con-
crete it is found that, even before the stresses become excessive,
Hooke's law does not hold true. Bearing in mind, then, the
meaning of the word strain, we represent as usual the ratio of
stress to strain by E, the modulus of elasticity, or
„ _ stress
strain
Let E, = modulus of elasticity of steel.
Ec = modulus of elasticity of concrete in compression.
/, = tension in steel, lbs. per sq. in.
/ = compression in concrete, lbs. per sq. in.
a = thickness of steel considered as a flat plate, or the area of imbedded
steel bars per inch of width of beam z.
j/i = distance the extreme fiber of concrete in compression is from the
neutral axis.
2/2 = distance the center of the steel reinforcement in the tension side
of the beam is from the neutral axis,
t = depth of concrete below reinforcement.
d =2/1 + 2/2 and h = d + i.
Xi = unit compression of extreme fibers of concrete in compression.
Xa = unit elongation of steel in tension.
E f
Represent ^ by R, and ^ by r.
SINGLE REINFORCEMENT
405
585 . Formulas for Constant Modulus of Elasticity. — The
cross-section of the beam, the graphical representations of the
Strains and of the stresses are shown in the following diagrams:
Fig. 10.
XR0SS-8ECTI0N
Figure 12 shows the conditions when the stresses are so small
that the modulus of elasticity of the concrete may be considered
constant, and this case will be first considered.
In the strain diagram, A.^ represents the deformation of the
extreme fiber of concrete in the compression side of the beam,
and Xj the deformation of the steel. Since a section plane be-
fore bending is considered to be plane after bending, the steel
is considered not to slip in the concrete, and NN is the neutral
axis,
or
and
^1 Vi
but E. = f, and E
•
.A, = A and X, = A
K Vi f. eJ
U E, r
y^=iEy^=Ry^-
h
(Eq. 1.)
In the stress diagram the triangle NAB represents the
total compressive stress on the concrete for unit width of beam,
and is equivalent to a single force 'jUL applied at the center of
gravity of the triangle.
The total compressive stress for section of width z is
The total tension in the steel is T = zaf,.
406 CEMENT AND CONCRETE
As we disregard the tensile strength of the concrete, and as the
total normal compression and total normal tension on a section
must be equal, as they are the two forces of a couple, we have
P=T, or z'^U^zaU,
whence a = || = |. (Eq. 2.)
2
The point of application of the force P is ^ t/i above the neu-
O
tral axis, while the point of application of T is y^ below the
neutral axis; the arm of the couple is therefore (^ y^ + y\
and the moment of resistance is equal to either force into this
arm,
substituting the value of y^ given in (1) and reducing,
586. Formulas for Varying Modulus of Elasticity. — The fore-
going formulas are based on the supposition that the compres-
sive stress in the extreme fiber of the concrete has not passed
the point beyond which equal increments of stress no longer
produce equal increments of strain or deformation. They are
based, in other words, on the common theory of flexure, except
so far as we have departed from the application of this theory
in neglecting the tensile strength of the concrete. It is well
known that even for steel and wooden beams this common
theory does not, and is not meant to, apply outside the elastic
limit. In the case of concrete, however, it has been found that,
even for quite moderate stresses, the modulus of elasticity is
not constant (Art. 56), but that after a certain stress is reached
the modulus decreases with increasing stress. The effect of
this upon the internal forces may be illustrated by the curve
N B in Fig. 13. The extreme fiber is supposed to be subjected
to the stress fc] the fibers nearer the neutral axis have a smaller
stress per square inch, and the modulus of elasticity for this
smaller stress is greater; but in order that a section that is
SINGLE REINFORCEMENT 407
plane before flexure shall be plane after flexure, the strain must
be proportional to the distance from the neutral axis. It fol-
lows, then, that the stresses in the inner fibers do not decrease
according to the ordinates of the triangle, but are greater than
indicated by such ordinates. The exact form of the curve
B N is not known, but the examination of a number of de-
formation curves has indicated that it is parabolic, and for the
purpose of this discussion it may be considered a parabola
with axis A B without serious error, although it is known the
axis does not coincide with A B for stresses below the elastic
limit of the concrete.
587. While the formulas derived in § 585 may represent, then,
the conditions existing in a beam subjected to very moderate
stresses, it appears that beyond the limit of stress at which
the modulus of elasticity of concrete becomes variable, they
should be so modified as to take into account this variable
modulus.
Then if A B in Fig. 13 now represents /^ and M »S = /„ we have
as before,
2/2 = j-] f;?/i = ;^2/i- (Eq. 4.)
The total stress on the concrete above the neutral axis is
2
now represented by the area within the parabola, or ^ /c l/i > and
the total compression on section of width z is
P'
2
= 322/1/0,
and the total tension
r
= zaj,.
As these
are the two forces of
a couple
2 ,
3^2/Je
= zaj, ;
whence
-Vi
'^'3 r
(Eq. 5.)
The point of application of P' is on a line through the center
5
of gravity of the parabola, or ^ y^ from the neutral axis, while
o
the point of application of T' is at distance y^ below the neutral
408 CEMENT AND CONCRETE
5
axis; the arm of the couple is, therefore, ^yi + i/j, and the
o
moment of resistance
M„ = -zyjJ^yi +2/2)
5 2
= j2 ^^=2/1' + 3 zfcyiyi' (Eq. 6 a.)
Substitute value of t/2 given in (4)
M„= j^zfcyi^ + i^zfcyjj -^yi
In applying these formulas, it must be remembered that
(1), (2), and (3) are applicable where the stresses are below
the point at which the modulus of elasticity of the concrete
begins to diminish, while (4), (5), and (6) illustrate the con-
ditions for stresses above that limit.
588. Example. — Design a beam of 10 foot span to carry a
load due to 20 feet head of water.
Load per square foot = 20 X 62.5# = 1250#.
Total load per foot width of beam = 12,500 lbs. = Wj.
First, using Eqs. 1,2, and 3.
WL
M = ~= 187,500 inch-lbs. on beam 1 ft. wide, (2 = 12).
o
Assume
/.= 12,500, /, = 500, r=(' = 25;
E, = 28,000,000, E, = 2,000,000, R = ^ = 14.
From (3)
M, = 187,500 = 12 X 500 (| 4- 2^-^) Vx-
y^ = 25.5, yi = 5.05 inches.
From (2)
_ ^1 _
y. 5.05 ,r.^ • I.
P- — — - = .101 mch,
2 r 2 X 25 '
tu = .101 X 12 = 1.21 sq. in. of steel for beam 12 in. wide.
SINGLE REINFORCEMENT 409
From (1)
r 25
^8 — P ^1 = TT >< 5.05 = 9.02 inches.
If i = thickness of concrete below center of steel bars = 2 inches,
h = total depth beam = 5.05 + 9.02 + 2.00 = 16.07 inches.
Second, using Eqs. 4, 5, and 6.
Assume
/. = 50,000, /, = 2,000, r=(' = 25;
E, = 28,000,000, E, = 1,400,000, R = 'j = 20.
As the stresses per square inch given above are approxi-
mately the breaking strengths of the materials, we must supply
a factor of safety, say 4; i.e., design the beam to withstand four
times the required bending moment before the stresses assumed
above are attained.*
From (Eq. 6)
Mo = 4M = 4 X 187,500 = 12 x 200o(^ + | X |^)2/i';
, , 187,500 X 4 X 12 „^
whence i/,* = — -^ = 25,
^* 12 X 2000 X 15 '
or,. t/i =5.
From (Eq. 5)
2 5
a = 3 25 "^ 133 inch,
and az= 1.6 square inches of steel for 12-inch width of beam.
' The method of using the breaking strengths of the materials, and com-
puting the ultimate resistance equal to a certain number of times the desired
strength, is considered inferior to that of assuming safe working stresses and
computing directly the safe load. These safe working stresses should be
fixed with reference to the elastic limit of the materials, rather than with
reference to ultimate strength. The use here of the term factor of safety is
for the momentary purpose of emphasizing the fact that the conditions
assumed in deriving equation (6) are such as are supposed to exist under
comparatively high stresses; but the formulas may evidently be applied to
the safe working stresses the same as equations (1), (2) and (3), and in the
present example the same size beam will result by eliminating "factor of
safety" and using working stresses equal to one-fourth the values of the
stresses assumed.
410 CEMENT AND CONCRETE
From (Eq. 4)
r 25
!/a = ^2/i = 252/1 = 1.25 X 5" = 6.25 inches.
If i = 2 inches as before,
h = total depth beam = 5.00 + 6.25 + 2.00 = 13.25 inches.
It is seen that equations 4, 5 and 6 give, for the assumption
made, a lesser depth of beam with more reinforcement than
is given by equations 1, 2 and 3 with the corresponding as-
sumptions as to stresses and moduli.
589. An inspection of the equations shows that to increase
the amount of steel reinforcement in the tension side of the
beam tends to move the neutral axis nearer to the tension
side, and bring a greater area of cross-section of concrete into
compression. If we arbitrarily decrease the depth of the beam
which must withstand the same bending moment, it will in-
crease the required area of reinforcement, and if carried too
far will eventually raise fc beyond a safe value. On the other
hand, if we take the beam as designed in accordance with equa-
tions 1, 2 and 3 and subject it to a greater bending moment
than that for which it is designed, then so long as R remains
constant, r also remains constant, that is, the steel and con-
crete are equally overstressed; but since R increases with the
load, r will also increase, that is, the increment of stress in
steel will be relatively greater than that in concrete.
590. Excessive Reinforcement. — In the solution of the above
example if we introduce the requirement that the total depth
of the beam shall be but 12 inches, while the quality of the con-
crete is not improved, we may assume, as before, E, =
28,000,000 and E^ = 1,400,000. Let us introduce the same
factor of safety, 4, by using fe = ^^^ = 500 pounds instead
of designing the beam for four times the required bending
moment; as we have seen, this does not affect the result.
Since the depth of the beam is fixed, /, and r cannot be as-
sumed, but must be found, together with a.
We have
d = t/i -H 2/a = 12 — 2 = 10 inches, and 2/2 = 10 -• t/j.
From (6 a)
ilfo = fV X 12 X 500 ?/i« + § X 12 X 500 i/i (10 - Vi) = 187,500.
EXCESSIVE REINFORCEMENT 411
Solving, we have 2/i = 6 inches nearly,
and ^g =10— 6 = 4 inches.
From (4) Vl^llll .
Vi fcE.
Substituting values of 2/3,2/1, /c, Ec&nd E„ we have
/, = 6,667 lbs. per sq. in.
TT /-N 2/e 2 5000 ^ ^^ .
From(o) a = 3^- ^^ = - X ^^^ X 6 = .30 in.
and az = 3.6 sq. in. of metal to each foot width of beam. This
is more than double the amount of reinforcement required for
a 13.25 inch beam, while the steel is stressed only 6,667 lbs.
per square inch.
It may be asked why not use a smaller area of metal, say
2 sq. in., stressed to 12,000 lbs. per square inch, giving the same
total tension; but a moment's consideration shows that in order
that the metal should assume this higher stress, its elongation
must increase proportionally, involving a corresponding in-
crease of strain in the concrete in compression with an accom-
panying increase in stress beyond the assumed safe limit of
500 lbs. per sq. in.
591. To pursue this subject of excessive reinforcement a
little further, let us examine some tests of concrete-steel beams
made by Prof. Gaetano Lanza and reported in Trans. Am.
Soc. C. E. for June, 1903.
In these beams the width z = 8 inches, ^ = 12 and d == 10
inches nearly. The span was 11 feet. Proportions in concrete
by volume 1 part Portland cement, 3 parts sand, 4 parts broken
trap that would pass 1 inch ring, and 2 parts of the same rock
that would pass ^ inch ring. Both plain and twisted square
steel bars were used as reinforcement, the plain bars having a
tensile strength of about sixty thousand pounds per square
inch and the twisted steel about eighty thousand pounds per
square inch.
If we assume the ultimate strength of the concrete to be
2,000 pounds per square inch, the modulus of elasticity at this
high stress to be 1,400,000 and the modulus of the steel to be
28,000,000, we have,
P ^ 28,000,000 ^
1,400,000
412 CEMENT AND CONCRETE
and for twisted bars,
80,000 .-
r = — ■ = 40.
2,000
From Eq. (4) y^ = ^ y, = 2 y^,
.'. 3?/i = 10 inches, y^ = —inches.
o
FromEq.(5)a= -^=-x ^x — =— = .055, and az =.444.
That is, .444 sq. in. of twisted steel reinforcement is required
in the beam 8 inches wide in order that the stresses in concrete
and steel shall simultaneously reach the values of 2,000 and
80,000 lbs. per square inch, -respectively.
From (6) M = 8 X 2000 X (1 + | X 1«)150
= 311,100 inch-pounds.
One beam having .56 sq. in. reinforcement, or an area very
close to the theoretical amount called for above, broke under a
bending moment of 470,000 inch-lbs. Eight other beams hav-
ing a greater area of reinforcement gave moments of 355,000
to 443,000 inch-lbs., and the average of the nine bars was 403,000,
or 30 per cent, greater than the value derived by formula.
592. Included in the series of tests were three beams, in
each of which were placed two 1^ inch twisted rods. As we
have seen, the correct amount of steel to develop the full strength
of both steel and concrete is about .444 sq. in.; the three bars
mentioned had 3.12 sq. inches of steel, or a large excess of
reinforcement. To determine the theoretical moment of re-
sistance of these beams, assume as before:
E, = 28,000,000,
J^e= 1,400,000,
/, = 2,000.
From (4) y, = ^^ | y. = ^;^y^, (a)
a = i^^=.39.
STRENGTH OF BEAMS 413
2 2 000
From (5) a = .39 = 3 ^ y^, (6)
2/2 = 10 - t/i. (c)
Solving (o), (6) and (c), we obtain
/, = 22,000, i/i = 6.45 inches, and r/j = 3.55 inches;
whence r =^'= 11,
and from (6),
Mo = 8 X 2000 (^ + I X ^) (6-45)^ = 522,000 inch-pounds.
These three beams developed the following moments of re-
sistance: 553,550, 663,700 and 783,500, mean 667,000 inch-lbs.,
or 28 per cent, greater than that derived by formula. None of
them failed, however, by crushing of the concrete at the top
of the beam, but by longitudinal shearing "at or a little above"
the reinforcing rods.
593. It appears, then, that by increasing the area of steel
reinforcement over 600 per cent., or from .44 sq. in. to 3.12
sq. ins., the strength of the beams was increased about 68 per
cent, by theory, or 66 per cent, according to the few tests cited.
The cost of the beam, however, was increased about one hun-
dred per cent.
This method of increasing the moment of resistance of a
beam is not economical; it is better to improve the quality of
the concrete. It may, however, be necessary at times to use
excessive reinforcement on account of restrictions on the size
of beam, but one may easily carry this so far that he passes
outside the true theory of concrete-steel construction, and it
becomes a question of the steel being sufficient to carry the
entire load. In such cases double reinforcement may be adopted.
594. Tables of Strength. — In Table 160, equations (5)
and (6) have been reduced to simpler forms by the introduc-
tion of values of E, and /,. Selecting in the table the division
corresponding to the modulus of elasticity of the concrete
which is to be used, and the line opposite the assumed stress in
the concrete. Mo = quantity in column a times the square of the
depth of beam, d; and the area of steel in a beam of 12 inch
width, i.e. 12 a, equals quantity in column b times the depth
414
CEMENT AND CONCRETE
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STRENGTH OF BEAMS 415
of beam, d. Column c gives the area of cross-section of steel
expressed as the per cent, of the area of section above the center
of steel reinforcement.
595. For example, suppose we wish to know the strength of
a beam ten inches deep (d = h — i = 10 in.) and the amount
of steel required to develop a stress in the concrete of 400 lbs. per
square inch when the stress in steel is 10,000 lbs. per sq. in.,
and the modulus of elasticity of the concrete is assumed at
3,000,000. In column a under 3,000,000 modulus, and opposite
400 lbs. stress, we find 68.1; then the moment of resistance of a
beam one inch wide is 68.1 inch-lbs. X 10 X 10 = 6,810 inch-
lbs., and the resistance of a beam 12 inches wide is 6,810 foot-
lbs. The area of steel required in 12 inches width of beam is
.092 d or 0.92 sq. in. This beam is reinforced with ,77 of one
per cent, steel. Similar tables may be prepared for other values
of E, and /, if desired.
596. In Table i6i the equations have been completely
solved for certain typical values of E^ and fc, assuming the
values for E, and /, of thirty million and ten thousand respec-
tively, as in Table 160. Having computed the bending mo-
ment, and fixed upon the probable safe working stress and
modulus of elasticity of the concrete which it is proposed to
use, it is only necessary to take from the table the required
depth of beam and the amount of steel reinforcement required.
For example, a girder 10 feet long supported at the ends
carries two loads of 5,000 pounds, each load being 2.5 feet from
a support.
If the width of girder is 15 inches, working stress of concrete
300 lbs. per sq. in. and modulus of elasticity of concrete 1,500,000,
what is the required depth of girder and area of steel in tension
side?
The maximum bending moment (neglecting weight of beam)
is 12,500 ft.-lbs. throughout the central five feet. The required
12
moment of resistance ioj twelve inches in width is j^ of 12,500
= 10,000 ft.-lbs. Looking in the table for this bending moment
under 300 lbs. stress and 1,500,000 modulus, we find it is be-
tween d = 12 and d = 14, or at about d = 13 inches. If we
allow 2 inches below center of steel reinforcement, we have
total depth of beam, A = 13 -I- 2 = 15 inches. In the same
416
CEMENT AND CONCRETE
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STRENGTH OF BEAMS 417
lines we find area of steel for 12 inch width between 1.08 and
15
1.26, or, say, 1.17; then for 15 in. width the required area is^^
X 1.17 = 1.46 sq. in. The bars should not be more than 3 to
9
6 inches apart. We may use, then, 5 bars ^^ inch square or
^inch diameter, spaced three inches apart. In large beams it is
o
necessary to consider the bending moment occasioned by the
weight of the beam after miking a first approximation to the
size required.
597. The above tables are prepared on the assumption that
the stress in concrete shall be equal to the value selected when
the stress in the steel reinforcement reaches 10,000 lbs. per sq.
in. From the equations, other tables may be prepared if
desired, in which the working stress in steel shall be 12,500,
16,000 or any other assumed value. The tables are not suited
to the computation of beams in which excessive reinforcement
is used.
As to actual tests of the performance of concrete and steel in
combination, the possible variations in material are so diverse
and the cost of experiments so great that the results thus far
obtained appear somewhat fragmentary, but each investigator
has selected a small branch of the subject for experiment.
Among the more valuable tests in this line may be mentioned
the following : — •
Tests at Massachusetts Institute Technology, Prof. Gaetano
Lanza, Trans. Amer. Soc. C. E., vol. 50, p. 486.
Tests at Purdue University, Prof. W. K. Hatt, Jour. Western
Soc. Engrs., June, 1904.
Tests at Rose Polytechnic Institute, Prof. Malvard A. Howe,
Jour. Western Soc. Engrs., June, 1904.
Tests at University of Illinois, Prof. A. N. Talbot, Proc. Amer.
Soc. for Testing Materials, 1904.
Tests at University of Wisconsin, Prof. F. E. Turneaure, Proc.
Amer. Soc. for Testing Materials, 1904.
Art. 70. Concrete-Steel Beams with Double Reinforce-
ment
598. We have seen that when the depth of a beam is limited
by structural considerations we may increase the normal load
418
CEMENT AND CONCRETE
by excessive reinforcement, but that this method results in low
stresses in the steel and is not usually economical. We may
now consider the effect of placing reinforcing rods in the com-
pression side of the beam as well as in the tension side.
^-.-,
r
1
t
*
1
1
Area Steal, «
y.
i-
• ■ ■
~M.
A^eai-f-e*/, A'
ArmaSfvl
Al-a
Fig. 14.
CROSS-SECTION
Fig. 15. Fig. 16.
CROSS-SECTION STRAIN DIAGRAM.
(Single Reinforcement.) (Double Reinforcement.)
Let Fig. 14 represent the cross-section of a beam reinforced
on the tension side with sufficient steel, area a, to develop the
proper working stresses in the materials, and let the position
of the neutral axis be N N. If at distance x from the neutral
axis we add an area of steel A' in the compression side, the
position of the neutral axis would be changed for similar load-
ing; but if at the same time we place in the tension side an ad-
ditional area of steel A such that -p = —' the position of the
A 2/2
neutral axis will be unchanged. Let // = stress in steel in
compression; then since the steel must suffer the same deforma-
tion as the surrounding concrete ^ = — . Multiplying the last
two equations, we have, f>A= f\ A', that is, we have added
equal forces to the two sides of the beam, and have increased
the moment of resistance by f,A{x + y^) inch-pounds.
599. To illustrate the application of this principle we may
take the beam considered in § 591, in which ^ = 8, R = 20,
r = 40, az = .444, a
10
444 20
^ = .055, /, = 80,000, 7/2 = -^ inches,
Vi
in., and M = 311,100 inch-pounds.
When the area of reinforcement in the tension side of this
beam was increased to az = 3.12 sq. in. or a = .39, the theo-
retical bending moment was increased to 522,000 inch-pounds
(§ 592). What will be the result of a similar increase in steel
distributed between the two sides of the beam?
DOUBLE REINFORCEMENT 419
Let k =^ distance from top of beam to center of reinforce-
ment on compression side = 2 inches,
then X = t/i — 2" = -K — 2 = ^ inches,
o o
^ = -=^^^ = 0.4 or ^ = 0.4 A'.
A+A' = .39- .055 = .335
1.4 A' = .335 A' =.24 A'z = 1.92
A =.095 Az = .76
whence a = .055 az = .44
A + a = .150 Total steel, 3.12 sq. inches.
// = /!^ = . 4/. = 32,000.
2/2
Added moment of resistance equals
Az (x + 1/2) /. = .095 X 8 X ^ X 80,000 = 486.400 in.-lbs.
And total moment of resistance equals
311,100 -I- 486,400 = 797,500 inch-pounds.
None of the bars in the series mentioned in §591 had as large
an area of reinforcement as 1.92 sq. in. on the compression side.
It is noticed, first, that the double reinforcement gives bet-
ter results than such excessive reinforcement on the tension
side; second, that the stress in steel on the compression side is
less per square inch than that in tension; and third, that in
case a large addition of steel is made, this results in a greater
area of steel in compression than the total area of steel in ten-
sion. In practice the area of steel in compression is usually
made equal to, or less thp.n, the area in tension, but beams with
double reinforcement are seldom accurately designed.
Art. 71. Shear in Concrete-Steel Beams
600. There are several methods of failure of concrete-steel
beams other than those considered above, direct tension in the
steel or direct compression in the concrete due to the bending mo-
ment. These other methods of failure are popularly called failures
in shear, although some of them cannot properly be so classed.
601. We have seen that the shearing stress of concrete is
usually considered to be somewhat in excess of the tensile
420 CEMENT AND CONCRETE
strength (§458) and that the latter is one-fifth to one-tenth the
compressive strength. With a beam having only a normal
amount of reinforcement, then, there is little danger to be
feared from simple vertical shear, and as a matter of fact, tests
have not developed instances of such weakness. In compara-
tively short spans, however, failures have occurred near the
quarter points, in cracks starting at the under side of the beam
and extending upward in a direction inclined toward the center.
This method of failure has the appearance of being due to a
combination of shear and tension in the lower section of the
beam, since the cracks are approximately at right angles to the
theoretical "Unes of direct tension." Such failures, however,
are almost always accompanied by a slipping of the steel bar in
the concrete, and may frequently be prevented by taking
proper precautions against such slipping.
602. A more frequent cause of failure is a longitudinal shear
in the plane near the steel reinforcement and on that side of it
lying nearer the concave side of the beam.
It is evident that a failure caused by slipping of the bar in
the beam, although caused primarily by shearing forces, is
really a failure in adhesion, yet the two forms of weakness ar^
so closely connected that it is simpler to consider them together.
603. Comparison with Plate Girder. — In a steel plate girder
the lower flange is considered to carry the tension, the upper
flange the compression; the web connects the two flanges, caus-
ing them to act together as one beam, and we may think of
the web as preventing the ends of the compression flange sliding
beyond the ends of the tension flange. When the web is not
able to accomplish this without buckling, it is stiffened by
vertical angles.
In a concrete steel beam we have considered the entire
tension to be carried by the steel reinforcement, and the entire
compression to be carried by the concrete on the other side of
the neutral axis. The connecting web is also concrete. This
web is thick and not liable to buckle, but it may shear in a lon-
gitudinal plane as a wooden beam may do when short and deep.
All of the tension in the steel reinforcement must be trans-
mitted through the surrounding concrete. If there are no pro-
jections on the steel bar, the adhesion of the concrete to it
may, under certain circumstances, be not strong enough to
SHEAR IN BEAMS 421
safely carry this stress; and if the adhesion is sufficient, then
the shearing strength of the concrete may be too low to transmit
the stress to contiguous fibers or layers.
604. Illustration. — Let us consider a concrete-steel beam
twelve inches wide, twelve inches deep and of ten foot span,
supported at the ends; reinforcement, one square inch of metal
properly distributed in a plane two inches above the bottom
of the beam. Let us suppose this beam carries a uniform load
of 600 pounds per foot, giving a maximum bending moment of
90,000 inch-lbs., and a stress in steel of 10,000 pounds at the
center. The ends of the steel bars are of course without stress.
Since the bending moment at any section of such a beam is
proportional to the product of the segments into which the
section divides the span, the bending moment one foot from
the ends will be
^-^ X 90,000 = 32,400 inch-pounds,
t) X o
Let us consider the neutral axis in the same position at the
end of the beams as near the center. (This is not strictly true,
because of the lighter stress near the ends of the beam, but
the error made by such an assumption will be unimportant for
our present purpose.) Then the tension in the steel will have
the same proportion, or, tension in steel one foot from the end
= ^ff X 10,000 = 3,600 pounds.
The stress in steel, then, which is zero at the end, has in-
creased to 3,600 lbs. in one foot of length. To provide against
poor contact near the end, consider two-thirds of this length,
or eight inches, to be operative. If the reinforcement consists
of four one-half-inch square bars, the necessary adhesion per
square inch is ^ = 57 lbs. per sq. in.; but if only one bar
o X o
is used one inch square, the required adhesion is 114 lbs. per
sq. in. The latter would not be good practice, not only be-
cause of high adhesion required, but because the steel is not
properly distributed.
Where the stress in adhesion is greater than can be safely
relied upon for plain rods, it is necessary to use some kind of
deformed bar, or to anchor the bar securely at the end. This
may be done by passing the end of the tension bar around a
422 CEMENT AND CONCRETE
rod transverse to the beam near the end. Care should be taken
that the safe value of adhesion is not assumed too high.
605. Value of Shear. — The same total stress of 3,600 lbs.
must be transferred through the concrete immediately above
the bar. If the reinforcement is so distributed that the entire
width of the beam has practically the same stress, and we
consider, as before, that two-thirds of the length of the end
foot is operative, we have mean shear = ~ = 37.5 lbs.
^ 12 X 8
per sq. in. The value of stress in shear should not exceed one-
tenth the safe value in compression, and there is a general ten-
dency to use not more than one-twentieth.
If the same form of beam had a span of but five feet with
same bending moment, the value of the shearing stress by this
method becomes 75 lbs, per sq. in., and it will be necessary to
provide against this stress coming upon the concrete.
Another approximate method is the ordinary one for rect-
angular beams, viz. to consider the shear in horizontal plane
just above the steel reinforcement to be | times the total shear
at any section, divided by the area of vertical section of the
beam.
606. Provision is sometimes made for relieving the concrete
of all shearing stresses. In this case the beam is divided into
imaginary panels of length equal, say, to the depth of the
beam, and the diagram of maximum shear is drawn. The
shear in each imaginary panel is then provided for by a vertical
or inclined bar of the proper dimensions. Or, what is usually
better, the shear bars are all of one size and the proper num-
ber of them are distributed throughout each panel length; the
spacing of the shear bars thus becomes wider near the center
of the beam.
607. Resistance to Shear. — When provision against shear
is made by using small steel rods placed either vertical or in-
clined downward toward the center of the beam, as mentioned
above, these rods may well be made in the form of inverted
U-shaped stirrups, with their ends securely fastened to the
reinforcing metal in tension.
In many cases all the provision necessary is given by the use
of two longitudinal bars, parallel and close together near the cen-
ter of the span, but one of them leading to a plane near the top of
SHEAR IN BEAMS 423
the beam at the supports. This system is very conveniently
applied in concrete slabs supported by I-beams, one bar of the
pair being hooked over the upper flanges of the I-beam and
sagging toward the center. The Hennebique system (§571) is
a combination of the incHned bar and U-shaped stirrups.
608. A modification of the single inclined bar is the Cum-
mings system, wherein there are several pairs of bars of vary-
ing lengths; these are all horizontal and near the bottom along
the center of the beam; a short distance from the center the
shortest pair turns up at an angle of about forty-five degrees; a
littVe farther toward the end a second pair of bars is turned up,
and so on, leaving a single pair to go through straight to the
support.
Another, and more radical modification, is the Kahn system
(§573), in which the bar is square with wings of metal on oppo-
site corners which are sheared and bent up at angles of forty-
five degrees, so that the outline of the steel work in a beam
resembles the tension members of a Pratt truss.
CHAPTER XX
SPECIAL USES OF CONCRETE: BUILDINGS, WALKS,
FLOORS AND PAVEMENTS
Art. 72. Buildings
609. While the use of concrete and steel for the walls and
floors of buildings is about fifty years old, yet it is only in com-
paratively recent years that its value has become generally
known. It is now applied to all classes of structures, ware-
houses, factories, residences, station and office buildings, and
it is anticipated that in the next twenty years concrete-steel
will be as familiar in architecture as steel skeleton, stone, and
brick are now.
610. It happens that at present the concrete-steel building
industry is largely in the hands of companies who are exploiting
some particular form of steel rods or bars applied according to
some one of the many "systems" of reinforcement. \ This con-
dition has both good and bad features. A reputable concern of
this kind will have in their employ engineers who should sat-
isfy themselves that each design is a safe one, for the faihire
of a building will cast disrepute on their particular system. It
is this fact that leads the companies to keep the construction
entirely, and the design largely, in their own hands. Another
advantage is that these concerns are able to perfect methods of
construction by experience, and to lessen the expense of one
structure by making use of the concrete plant and the molds
that have been used on another.
611. In making plans for a building, the owner is usually
represented in the first instance by an architect whose business
it is to dictate the design. If concrete-steel is considered, the
architect may call an engineer in consultation and they may
together harmonize the features of utility and appearance with
economy and strength, but in letting the contract it is found
that the competition is limited to one or two companies using
the particular system which the engineer considers the best
adapted to the particular conditions in question.
424
BUILDINGS 425
On the other hand, the architect will hesitate to go to the con-
struction company for assistance, since he must first select the
system he shall use, a question upon which his ideas may be neither
clear nor well grounded, and he is then having the prospective
contractor assist in the design. Under these circumstances the
architect will usually consider concrete-steel construction as
something he wishes to avoid if possible. But this condition
will correct itself in time, for owners will demand a considera-
tion of this form of construction, engineers wall become fa-
miliar with its use and will be employed to design the engineer-
ing features, while reliable contractors in every city will obtain
permission to build in accordance with any "system" under
the supervision of a competent engineer.
612. Roof. — While a pitch roof is sometimes built of con-
crete-steel, this form of construction is particularly adapted to
so called flat roofs. The roof is constructed much the same as
a floor slab (Art. 65-67), except that expansion joints are some-
times provided, and the roof is covered with tar and gravel,
or some of the patent roofings ordinarily used. While the
roof loads are usually light, permitting a greater span of slab
between beams than for floor construction, it will seldom be
economical to introduce these longer spans because of the
changes necessary in the molds. In most buildings it is neces-
sary to provide against condensation, and for this purpose a
flat ceiling may be suspended at the level of the under side of
the beams giving an air space.
613. Floor System. — The floors may be constructed in con-
formity with the principles stated in Chapter XIX. The
strength of short span arches, such as are used for floors,
where the haunches are built up level with the top of crown
of arch, is a matter of experiment and cannot be accurately
determined theoretically. Empirical formulas may be derived
for a certain system based on a sufficient number of tests.
The principles underlying the strength of slabs may be con-
sidered the same as those applying to beams (Art. 69), although
if the length of slabs is not much greater than the span, they
are not strictly applicable, but will err on the safe side.
614. A decision must first be made as to the size of bays into
which the floor space is to be divided. This will of course de-
pend on the use of the building, the engineering features con-
426 CEMENT AND CONCRETE
forming to requirements of utility. If the bays are not square,
the girders should usually take the shorter span between columns.
This length is then divided into the number of slab spans that
will give maximum economy. The shorter these spans the less
the amount of material required in slabs and the greater the
number and cost of floor beams. Computations should be
made, therefore, for two or three arrangements to determine
this point. As this distribution for maximum economy will
vary with the loads to be provided for, it is well, if the floors
are not all to carry the same load, to take for this computation a
load intermediate between the heaviest and lightest, and use if
possible the same arrangement of spans throughout the building.
The strength of slabs for given bending moments may be
taken directly from Table 161, after deciding upon the working
stress to be allowed in the concrete and the probable modulus
of elasticity. The beams and girders, if single reinforcement
is used, are taken from the same table or computed by the
methods of Art. 69.
615. In some instances it may be found economical to use
concrete-steel slabs for floors supported by concrete protected
steel beams and girders. One advantage of this system is that
the forms for building the protecting concrete and for the
floor slabs may be hung from the steel girders and beams. For
this method of construction the enveloping concrete should
not be less than one and one-half inches thick over the edges of
flanges, and wire fabric or metal lath wrapped about lower
flanges of beams will insure the concrete remaining in place.
This is not properly concrete-steel construction, but simply
concrete protected steel, and except in case the concrete ex-
tends well above the steel, forming an independent compres-
sion flange, no added strength should be computed for the con-
crete covering.
616. Columns. — In the foundations of buildings of moder-
ate height the supporting columns may be built entirely of
concrete. Since, however, the pressure on the concrete, even
when it is constructed with the greatest care, should not ex-
ceed two hundred to three hundred pounds per square inch,
the required area of cross-section in the lower stories is usually
80 great as to preclude the use of columns built entirely of
concrete.
BUILDINGS 427
617. Concrete Filling and Covering. — A steel column of
any of the ordinary styles, built up of steel shapes may be
used, and protected from corrosion and fire by filling and cover-
ing with concrete. This not only serves as a protection against
rust, but materially increases the stiffness and permits the use
of a somewhat higher working stress in the steel. The concrete
filling should be mixed quite wet in order that it shall work
into all angles. The edges of the metal should not approach
nearer than one and one-half inches to the exterior of the con-
crete, and flat surfaces of metal should have a covering of at
least two and one-half inches. Where it is necessary to cover
large, flat surfaces, they should be first covered with expanded
metal or wire fabric, locked on by twisting around the edges
of the plate or channel.
618. Columns of Concrete Steel. — Concrete-steel col-
umns differ from the above in that the main dependence is
placed on the concrete rather than on the steel. For such
columns longitudinal reinforcement has generally been employed.
Steel bars extending from end to end of the column are dis-
tributed throughout the cross-section, and are tied together at
intervals of. four to twelve inches by smaller bars forming loops
to hold them in place. The splicing of the bars is effected by
placing a small tube over the upper end of the lower bar and
projecting above it, and then setting the lower end of the upper
bar within the tube resting on the lower bar. Where this is
done it is essential that the two ends be planed perfectly square,
and it is much better to avoid splices in a column between
lateral supports. In a building the reinforcing rods project up
through the floor above and are spliced into the bars of the
columns in the next story .
619. Strength of Columns. — When a column reinforced with
longitudinal bars is subjected to pressure, the concrete and
steel must shorten together. The relative stresses in the two
materials will then be proportional to their moduli of elasticity.
From this follows the formula,
P^fciC -hRS)
where P — total pressure on column,
/c = stress in concrete,
C and S = areas of concrete and steel respectively,
428 CEMENT AND CONCRETE
E
and R = ^,or ratio of the modulus of elasticity
of the steel to that of the concrete.
In a series of teats of twenty-one columns made by Prof.
Gaetano Lanza,* but three failed under a lower stress than that
computed by the above formula. The columns were eight to
ten inches square, six to seventeen feet long and reinforced
with either one or four bars, the latter being from f inch to 1^
inches square.
The lowest breaking load was fifty tons on an 8 by 8 inch
column with one bar one inch square, and the strongest column,
10 by 10 inches, with four | inch longitudinal bars, was not
crushed with a load of one hundred fifty tons, the limit of the
testing machine. The lowest result was twenty per cent, less
than that given by the formula, and the greatest excess strength
over the theoretical was fifty per cent.
620. While longitudinal reinforcement undoubtedly strength-
ens a long column against flexure, as well as adds to the resist-
ance to crushing, yet the added strength is gained at the ex-
pense of considerable additional cost. Suppose we have a ten
inch square column, twelve feet long, made of concrete with a
breaking load of 1,800 lbs. per square inch, or 180,000 lbs.
total breaking load. Suppose eight f inch square bars to be
built into this column as longitudinal reinforcement, and that
the modulus of elasticity of the steel is ten times that of the
concrete. Then the strength of the reinforced column would
be, by the formula above,
P = 1,800 (95.5 + (10 X 4.5)) = 252,900.
The longitudinal reinforcement has thus resulted in an increase
of strength of 40 per cent., while by the addition of 180
pounds of metal, the cost of the column has risen from about
$3.00 to say $8.50, an increase of about 180 per cent, without
counting the cost of lateral ties, and the additional trouble in
building a reinforced column.
621. Hooped Concrete. — In extended experiments on what
he has called "hooped concrete," M. Considered has shown that
» Trans. A. S. C. E., Vol. 1, p. 487.
' Comptes Rendus de VAcademie des Sciences, 1898-1902. Translation,
"Reinforced Concrete," by Armand Consid^re, translated by Leon S. Mois-
seiff, McGraw Publishing Co., New York.
BUILDINGS 429
reinforcemeni, is much more important and beneficial in a
transverse or circumferential direction than if longitudinal.
This may be accounted for by the fact that the natural method
of failure of concrete prisms, is by splitting along planes parallel
to the direction of pressure, and the ordinary method of failure
by shear along inclined surfaces is induced by the friction of
the plates transmitting the pressure to the prism. It was also
shown that while concrete reinforced by longitudinal bars with
the ordinary amount of lateral ties breaks suddenly, hooped
concrete fails gradually under a much heavier load.
622. M. ConsidSre concluded from his experiments that the
circumferential ties should not be farther apart than one-
seventh to one-tenth the diameter of the column, even when
longitudinals were used to assist in completing the network,
and that the results were more successful the nearer together
the hoops or ties were placed. He found that spirals were
better than individual single ties and that longitudinals were of
value chiefly in assisting to confine the concrete, transmitting
the bursting pressure at a given plane to the contiguous spirals
above and below.
623. M. Considere says ^ that the "compressive resistance of
a hooped member exceeds the sum of the following three ele-
ments : —
"1. Compressive resistance of the concrete without rein-
forcing.
"2. Compressive resistance of the longitudinal rods stressed
to their elastic limit.
"3. Compressive resistance which could have been produced
by imaginary longitudinals at the elastic limit of the hooping
metal, the volume of the imaginary longitudinals being taken
as 2.4 times that of the hooping."
To subject hooped concrete to a practical test, M. Considere
constructed, in 1903, a truss bridge of sixty-five foot span with
parabolic top chord of seven and one-half feet rise,^ the com-
pression members being of hooped concrete, and the tension
members of concrete-steel with longitudinal reinforcement, or
concrete protected steel. A central panel of the truss was con-
' "Reinforced Concrete," p. 159.
' Engineering News, May 5, 1904,
430 CEMENT AND CONCRETE
structed with a reduced section of top chord about eight inches
diameter reinforced by eight longitudinal bars .43 inch in
diameter and a helix 6^ inches in diameter of .43 inch metal
coiled to a pitch of about one inch. This reduced top chord
section showed signs of failure when the computed stress reached
about 5,000 pounds per square inch.
624. FORMS FOR BUILDINGS. —One of the most serious prob-
lems in the construction of concrete-steel buildings is the de-
signing of the forms. They must be as light as is consistent
with strength to facilitate handling. They should be of simple
construction so that they may be set up and removed without
too much supervision, and they should be so assembled with
bolts and screws that they may be used repeatedly. In erect-
ing a large building sufficient forms are usually provided to set
up one floor complete, including columns, beams, girders and
floor slabs. After placing the reinforcement, the concrete is
filled in as rapidly as possible, making the slabs, girders and
columns practically monolithic.
The forms for the girders usually rest upon the column
molds and are supported at intermediate points by posts rest-
ing on the completed floor below. While column molds are
sometimes filled from the top, better work is assured by having
one side of the mold built up as the concrete is filled in from
the side.
The mold to receive the concrete forming the floor slab is
either a part of, or is supported by, the pieces forming the
sides of the girders and beams. Provision is sometimes made
for leaving supports at intervals under the completed beams
and girders after removing the forms from the sides of the beams
and the bottom of floor slabs. This is done by making the
bottom piece of the girder mold separate, and attaching the
side pieces to it by screws which may be removed without dis-
turbing the bottom. The caps of the supporting posts are then
made long enough to permit the lower edges of the side pieces
to rest directly on them. This method was adopted in build-
ing the Central Felt and Paper Company's factory at Long
Island Citv.^
' Wight-Easton-Townsend Company, CJontractora, Engineering Record,
Jan. 16, 1904.
BUILDINGS 431
625. In the same building the walls were biiilt with molds
three feet high and sixteen feet long, placed in pairs on oppo-
site sides of the wall. When one section was completed, the
molds were "lifted until the lower edges were, two inches below
the top of the concrete. In the new position they were sup-
ported by horizontal bolts through their lower edges, across the
top of the concrete; the upper edges were tied together by
transverse wooden strips nailed to them about three feet apart,
and they were braced to the false work supporting the roof
and column molds." "The bolts passed through sleeves which
were left permanently embedded in the walls. At first, iron
pipes were used for this purpose, but afterwards it was dis-
covered that pasteboard tubes were equally efficient and much
easier to trim and point after the molds were removed."
626. An excellent system of molds was used in the con"
struction of the Kelley and Jones Company's factory at Greens-
burg, Pa.^ The floor molds were especially convenient, being
made collapsible by a hinge joint at the top along the longi-
tudinal center line. These floor molds were in reality cores
between adjacent floor beams; when in place the top surface
was horizontal, to form the under side of the floor slab, and
the vertical side pieces formed the sides of the floor beams.
When the concrete had set sufficiently, the lower edges of the
form were made to approach each other, thus coming away
from the concrete gradually. A special light wooden framework
or tower, with a working platform six feet below the floor, and
a rope sling to receive and lower the floor mold, permitted of
removing the molds rapidly and without injury. A special truck
was also used for moving the floor molds about the building.
627. A convenient adjunct for the construction of concrete
wall forms consists of a short section of I-beam having a width
between flanges equal to the thickness of the plank to be used.
These plank holders are laid in pairs, with web horizontal, one
on either side of the wall, and connected by a bolt passing
through them and through the wall.^ Two rows of planks on
edge are first placed around the building so as to inclose the pro-
' Mr. E. L. Ransome, Architect and Engineer, Engineering Record, Feb.
6 and 13, 1904.
' Patented by Thomas G. Farrell, Washington, N. J.
432 CEMENT AND CONCRETE
posed wall. At the upper side of each junction between two
planks in the same horizontal row is placed one of these plank
holders. Another horizontal row of planks may now be placed,
with the iron plank holders at the joints as before. As the
wall is built up, the lower planks and holders may be removed
and placed on top, and thus few forms are required. Tees and
L-forms are provided for partition walls and corners.
When an air space is desired in a wall a special terra cotta
tile or building block may be built into the wall, but this is
quite expensive, and an interior collapsible form may be made
of timber by the use of two planks held apart by a wooden
brace which may be knocked out. Special means of handling
the interior plank should be provided, and the building of a
high wall cannot be continuous with this method.
628. New York Building Regulations. — While city building
regulations are not always criteria of good practice, yet the
Regulations of the Bureau of Buildings of the Borough of
Manhattan concerning the use of concrete-steel construction are
exceptional. Emanating from a bureau that has been dis-
tinctly hostile to concrete-steel, they are naturally conservative,
but are, on the whole, excellent, and work conscientiously done
in accordance with them will not bring discredit on concrete
construction.
It is specified that the cement shall be only high grade
Portland standing certain tests, that the sand shall be clean
and sharp, aggregate, broken trap, or gravel of a size that will
pass a three-quarter inch ring, and that the proportions used
shall be one cement, two sand and four of stone or gravel, or
that the concrete shall have a crushing strength of two thou-
sand pounds per square inch in twenty-eight days. Only the
best quality of concrete is thus permitted.
629. The Regulations concerning the design are then stated
as follows: —
"Concrete-steel shall be so designed that the stresses in the
concrete and the steel shall not exceed the following limits: —
Extreme fiber stress on concrete in compression, 500 lbs. per sq. in.
Shearing stress in concrete 50 " "
Concrete in direct compression 350 " "
Tensile stress in steel 16,000 " "
Shearing stress in steel 10,000 " "
BUILDINGS 433
"The adhesion of concrete to steel shall be assumed to be
not greater than the shearing strength of the concrete.
"The ratio of the moduU of elasticity of concrete and* steel
shall be taken as one to twelve.
"The following assumption shall guide in the determination
of the bending-moments due to the external forces: Beams and
girders shall be considered as simply supported at the ends, no
allowance being made for the continuous construction over
supports. Floor plates when constructed continuous and when
provided with reinforcement at top of plate over the supports,
may be treated as continuous beams, the bending-moment for
WL
uniformly distributed loads being taken at not less than -—^ ;
WL
the bending-moment may be taken as -^r— - in the case of square
floor plates which are reinforced in both directions and sup-
ported on all sides. The floor plate to the extent of not more
than ten times the width of any beam or girder may be taken
as part of that beam or girder in computing its moment of
resistance.
"The moment of resistance of any concrete-steel construc-
tion under transverse loads shall be determined by formulas
based on the following assumptions : —
"(a) The bond between the concrete and steel is sufficient
to make the two materials act together as a homogeneous soUd.
"(6) The strain in any fiber is directly proportionate to the
distance of that fiber from the neutral axis.
"(c) The modulus of elasticity of the concrete remains con-
stant within the limits of the working stresses fixed in these
Regulations.
"From these assumptions it follows that the stress in any
fiber is directly proportionate to the distance of that fiber from
the neutral axis.
"The tensile strength of the concrete shall not be considered.
"When the shearing stresses developed in any part of a
construction exceed the safe working strength of concrete, as
fixed in these Regulations, a sufficient amount of steel shall be
introduced in such a position that the deficiency in the resist-
ance to shear is overcome.
"When the safe limit of adhesion between the concrete and
434 CEMENT AND CONCRETE
steel is exceeded, some provision must be made for transmitting
the strength of the steel to the concrete.
"Concrete-steel may be used for columns in which the ratio
of length to least side or diameter does not exceed twelve.
The reinforcing rods must be tied together at intervals of not
more than the least side or diameter of the column.
"The contractor must be prepared to make load tests on
any portion of a concrete-steel construction, within a reasonable
time after erection, as often as may be required by the Super-
intendent of Buildings. The tests must show that the con-
struction will sustain a load of three times that for which it is
designed, without any sign of failure."
Art. 73. Concrete Walks
630. One of the most important uses of concrete is in the
construction of street and park walks. It has not only driven
stone flagging almost out of use, but it is being employed to a
large extent in towns and villages where board walks have
formerly been used almost exclusively.
A concrete walk is made up of a sub-base or foundation, a
base, and a wearing surface.
631. Foundation. — As in other structures, one of the most
important essentials for success lies in the preparation of the
foundation, and the care that must be bestowed on it will
depend upon the character of the soil and the climate. In the
higher latitudes of the United States, frost may soon destroy a
walk the foundation of which is not well drained.
The excavation should be made to the sub-grade previously
determined upon, any objectionable material such as loam or
organic matter being removed, and the bottom of the excava-
tion smoothed and well rammed. Upon this is laid the sub-
base, its thickness varying from nothing to twelve inches. In
a sandy soil with good natural drainage and little danger from
frost, and where light traffic is expected, it may be unnecessary
to provide any special sub-base, since the soil itself furnishes a
good foundation for the concrete, but in clay soil in northern
climates, twelve inches of sub-base may be required. The best
material for this sub-base is broken stone varying in size from
one-half inch to two and one-half inches. Usually broken
stone is considered too expensive, and gravel, coarse sand.
CONCRETE WALKS 435
cinders, or broken brick is employed. A layer four inches thick is
usually sufficient for good materials, but six to twelve inches of
cinders are sometimes required. It should be well rammed to
a level surface, and when completed should be firm but porous.
The most important point is that this course shall have
good drainage, otherwise it may be a menace to the walk. If
it is more porous than the retaining soil, it will naturally drain
this soil, and if the water is not able to escape into the sewer
or elsewhere, it may be frozen and heave the walk. An ex-
cellent plan sometimes adopted is to lay at intervals of twenty
to twenty-five feet, a blind stone drain from the walk founda-
tion to the foundation of the curb. In exceptional cases it may
be necessary to lay a tile drain in the sub-base to lead the water
away from the walk.
632. Base. — The base is the body of the walk giving stiff-
ness to the structure. Its functions are to furnish a solid
foundation for the wearing surface and to give transverse
strength to the walk, transmitting the pressure uniformly to
the sub-base. The base is of concrete, which need not be very
rich for ordinary traffic. A proportion of one part packed
Portland cement to two and one-half volumes of dry sand
and six volumes broken stone is excellent, and proportions of
one, three and seven parts cement, sand and stone, respectively,
will usually be found sufficient, though the richer the concrete in
the base the better will the top dressing adhere to it.
The broken stone for this concrete should be of a size not
exceeding one and one-half inches in any dimension, some cities
requiring three-quarters inch or less. Crushed granite and trap
are excellent, though limestone or any other moderately hard
rock may be used that i& suited to making concrete for ordinary
purposes. If of a hard rock, the screenings may well be left
in the broken stone, and when this is done, the dose of sand
should be diminished. (See Art. 37.)
The thickness of the layer of concrete should not be less
than three inches. Four inches is much better and is recom-
mended for general use in sidewalks, while in exceptional cases
six inches is required. The top of the concrete base should
be finished to a plane parallel to the proposed surface of the
walk and at a distance below it equal to the proposed thickness
of the top dressing.
436 CEMENT AND CONCRETE
633. Wearing Surface. — The preparation and application
of the wearing surface require much care if satisfactory resuxM
are to be obtained. The most evident service of this layer m
to withstand wear, and it should therefore be made of rich
Portland cement mortar. With a sand consisting principally
of quartz particles, it is found that a mortar composed of equal
parts cement and sand gives about the best results in tests of
abrasion. If the mortar is used richer than this, it is likely to
check or crackle in setting, marring the appearance of the walk.
Mortar containing two parts cement to three parts sand gives
nearly as good results, and two parts sand or fine crushed
granite to one of Portland cement is usually satisfactory. The
sand for the mortar should be quartz if possible, or crushed
granite or trap. It should be screened through a quarter
inch mesh, and there should not be a large proportion of
very fine particles.
The thickness of the layer of top dressing is usually about
one inch, and this is probably the maximum thickness ever
required. One-half inch of top dressing is beheved to be suf-
ficient when the wear is not excessive, provided the base has
been carefully leveled.
634. The Construction of the Walk. — If the walk has not a
considerable longitudinal slope, it should be given a transverse
slope of about a quarter inch to the foot to provide for draining
the surface.
Stakes for grade and line having been given, a maitre cord
is stretched along the line stakes to mark the sides of the exca-
vation. After the material has been excavated to the proper
sub-grade and all soft material in the bottom removed, the
bottom of the trench is well rammed. If tile drain is necessary,
it is laid with open joints on this foundation. The material to
form the sub-base is now wheeled in and rammed to the proper
thickness, water being used freely if it facilitates the packing.
The top of the sub-base is brought to a level plane at the proper
distance below the grade stakes.
The molds for the walk are now to be laid. These are made
of two by four or two by six inch scantling, sized and dressed
on at least one side and one edge. Stakes are first securely
driven, about five or six feet apart, with their faces two inches
back from the side lines of the proposed walk, and their tops
CONCRETE WALKS 437
at grade. Against these stakes the scantHngs are placed on
edge with dressed side toward the walk, and smooth edge level
with the grade stakes. These molds are held in place by nail-
ing through the supporting stakes into the scantling, and if
these nails are not driven "home," they may easily be pulled
to release the mold when the work is completed. On the upper
edges of the mold are then marked off the sizes of blocks de-
sired, being careful that the marks defining a joint are exactly
opposite each other on the two scantlings.
635. The concrete materials having been previously deliv-
ered near the work, the concrete is mixed, either by hand or
machine, according to the methods already given, and rammed
in place after the sub-base has been well wet down to receive
the concrete. The concrete should be just short of quaking,
and in ramming care must be taken not to disturb the molds.
For tamping next the molds, the makers of cement working
tools offer a light rammer with square face at one end and
blunt, chisel shaped tamper at the other. The surface of the
base is brought to a plane parallel to the proposed finished sur-
face of the walk, and at a distance below it equal to the thick-
ness of the top dressing. A straight edge, long enough to span
the walk and notched out at the ends so that when placed on
the molds the straight edge will define the correct grade of the
base, is a convenience here.
636. The concrete is now cut into blocks exactly corre-
sponding to the proposed blocks in the top dressing. For this
purpose a straight edge is laid across the walk in line with
marks previously made on the molds to define the joints, and
with a spade or special tool the concrete base is cut entirely
through to the sub-base. This division is necessary to allow for
expansion and contraction, and prevent cracks in the top dressing
elsewhere than at the joints. This joint in the base should
then be filled with clean sand. If preferred, these joints in the
base may be made by placing thin steel strips across the molds
to be removed after the concrete for the next block is in place.
The end block made from a given batch of concrete should
be limited by a cross mold set exactly on line of a proposed
joint. When the base is continued, this cross mold is removed.
A part of a block should never be molded and then built on
after having stood long enough to begin to set. Any concrete
438 CEMENT AND CONCRETE
left over from finishing a block should either be mixed in with
the next batch, if this is to follow in a very short time, or it
should be wasted. A disregard of this rule will probably result
in a crack in the top dressing above the line of division between
adjacent batches.
637. When a block of base is finished, the top dressing or
wearing surface should be applied immediately. The lack of
adhesion between the base and wearing surface is one of the
most frequent causes of failure in cement walks. The mortar
should not merely be laid on in a thick layer and then struck
off to grade, but it should be worked and beaten into close con-
tact with the concrete at every point. The mortar should be
tamped with a light rammer and beaten with a wooden batten,
and to accomplish this properly the mortar must not be very
wet. The surface is then to be struck off with a straight edge
bearing on the top of the mold planks. Some hollows or rough
places will remain, and the straight edge should be run over a
second or perhaps a third time, a small amount of rather moist
mortar, made from thoroughly screened sand, having been first
appHed to such places.
When the surface film of water is being absorbed, the surface
is worked with a wooden float. The exact time when the work
should be floated will soon be known by experience. After the
floating is completed, the trowel may be used to give a smoother
surface, but this makes the walk so slippery that it is not usually
desirable.
638. If the top dressing is worked too long, the cement is
brought to the surface, robbing the next lower layer of its ce-
ment and resulting in scaling. The top dressing is now cut
entirely through on exact line above the joints in the base.
This may be done by a trowel working against a straight edge,
but special tools are made for cutting through the mortar and
rounding the edges of the joint at one operation. A quarter-
round tool is also run along the edges of the mold to give a neat
finish. When desired, an imprint roller run over the walk
gives it the appearance of having been bushhammered.
It is important that the top dressing be applied before the
concrete has begun to set, and it must not be applied to a por-
tion of a block and then some time allowed to elapse before
applying the remainder. The edge of the top dressing must
CONCRETE WALKS
439
be cut off squarely at the end of the block. If desired, the
wearing surface may be colored by the use of lamp black in the
mortar, giving a uniform gray color to the walk. (§ 535.)
639. When the walk is completed, it should be fenced off
so that animals may not walk over it while still fresh, and it
should be protected from a hot sun. The surface should be
kept moist, and this may be done after the first twenty-four
hours by spreading a layer of damp sand over the walk and
wetting the sand with a rose nozzle as often as may be needed.
The walk may be opened to light travel after about four days, but
it is better to remain covered with the damp sand for a week.
640. Cost of Concrete Walk. — The cost of concrete walks
varies from ten cents to twenty-five cents per square foot. A
fair price for a walk of average quality where there are no
special difficulties is twelve to eighteen cents per square foot.
As an instance of a walk built with special care, the one
constructed about the top of the bank of the Forbes Hill Reser-
voir may be mentioned.* The sub-base of this walk was of
stone and twelve inches thick, the layer of concrete was five
inches thick at the center of the walk and four inches at the
sides. The top was of granolithic finish one inch in thickness.
The walk was laid in separate blocks about six feet square.
The average gang employed on the concrete consisted of six
men and one team, while the finishing was done by two masons
and one tender. The amount laid per day was about forty
square yards. The cost per square yard was as follows: —
i cu. yd. stone in foundation or sub-base, at $.40 per cu. yd. . $0.1.3.3
Labor, placing stone at $1.50 per day
Total cost stone foundation per sq. yd. of walk
.158 bbi. cement, at $1.5.3 per bbl. . .
.065 cu. yd. sand, at $1.02 per cu. yd. .
.109 cu. yd. stone, at $1.57 per cu. yd. .
Labor, mixing and placing concrete . .
Total cost concrete base per sq. yd
.11 bbl. cement, at $1.53 per bbl. . , .
.022 cu. yd. sand, at $1.02 per cu. yd.
Lamp black
Labor, preparing and finishing surface .
Total cost top dressing or wearing surface
Total cost walk per sq. yd. { JJ^^^j;'
Materials $0.S1
1.10
,502
$0,242
.063
.170
.460
$0,168
.022
.008
.149
$0,635
$0,928
$0..347
$1,910
' C. M. Saville, M. Am. See. C. E., Engineering News, March 13, 1902.
440 CEMENT AND CONCRETE
641. The following is given as an estimate of cost of items
in a walk built with six inch cinder sub-base, four inch concrete
base and one inch top dressing .
Cost per sq. yd. of Walk
Materials Labok
Preparation of foundation, excavation and ramming . . . $0.20
Sub-base, 6 in. cinders J cu. yd., at $0.40 cu, yd $0.07
Placing and ramming cinders 0.04
^ cu. yd. concrete, at $3.00 per cu. yd. for materials alone , 0.33
J cu. yd. concrete, placing, at $1.80 per cu. yd 0.20
Top dressing -^^ cu. yd. mortar, at $9.00 per cu. yd. . . . 0.25
Placing top dressing and finishing walk 0.25
Superintendence and molds 0.10
Totals $0.65 $0.79
Total cost per sq. yd., $1.44, or 16 cents per sq. ft.
642. As an example of a low priced walk, the concrete walks
in San Francisco ^ are but three inches thick, two and one-half
inches of concrete composed of one part Portland cement, two
parts beach gravel, and six parts of crushed rock of size not
exceeding one inch; the top dressing being one-half inch thick
of equal parts Portland cement and beach gravel. With ce-
ment $2.50 per bbl., crushed rock and gravel from $1.40 to
$1.75 per cu. yd., and wages twenty cents an hour for laborers
and forty cents for finishers, this walk is constructed at from
nine to ten cents per square foot. It is stated that a gang of
three or four men will lay 150 to 175 square feet per day.
Art. 74. Floors of Basements, Stables and Factories
643. The principles governing the laying of walks apply also
in a general way to the construction of floors that rest directly
on the ground.
For residences, basement floors may be laid with three inch
base of concrete and one-half inch wearing surface. The thick-
ness of sub-base will depend upon the character of the soil.
Where natural conditions do not assure good drainage of the
foundation, this should always be provided for by either a blind
stone or tile drain laid around the outer edge of the building
and leading to the sewer or other outlet. The finished surface
of the floor should always have a slight slope toward the center
• Engineering News, March 4, 1897.
FLOORS 441
or one corner of the basement, and a trapped sewer connection
set at this lowest point in such a way that it is accessible for
repairs and cleaning,
644. Wet Basements. — Where much ground water is en-
countered, and especially where a basement is subjected to a
head of water from without, special precautions must be taken
in building the floor. The concrete must be made thick enough
so that its weight and the arch action set up, shall be able to
withstand the upward pressure of the water. In building such
a floor it is necessary to keep a sump hole, preferably in the
center, towards which the construction proceeds from the sides.
A pipe placed in the sump hole permits pumping until the con-
crete is laid about the pipe, when the latter may be filled with
rich cement mortar. In such cases the side walls of the base-
ment should be plastered with Portland cement mortar on the
outside and special care taken in joining the floor to the wall.
645. Size of Blocks. — As the changes in temperature in a
building are usually much less than in open air, the blocks of
concrete may be of much larger size, say ten feet square, and
many basement floors are laid without any joints, though
sooner or later they will probably crack if so laid. In factories
for certain purposes, however, the floors may be subjected to
greater changes in temperature than walks laid in the open
air. In such cases the blocks should not be more than three
or four feet on a side, and the joints may well be filled with
asphalt, especially if water- tightness is desired.
646. Stable floors may be made of six inch cobble or broken
stone sub-base, six inches of concrete made with mortar con-
taining three parts sand to one cement, and one inch of top
dressing containing three parts sand (mixed sizes) or crushed
granite to two parts cement.
Factories having heavy machinery with much vibration re-
quire strong floors. Such a floor may be made of six inches
of cobble stone sub-base covered by six inches of a lean concrete
made with one-to-four mortar, and above this, three to five
inches of rich concrete made with mortar containing two and
one-half parts sand to one cement, and one inch of top dressing,
equal parts cement and sand or cement and crushed granite.
647. Example and Cost. — In the construction of the new
printing building for the Government Printing Office at Wash-
442 CEMENT AND CONCRETE
ington, the basement floor is nine inches thick, made as fol-
lows : * —
1. Concrete sub-base, six inches thick of one part natural
cement, two parts sand and four and one-half parts broken
brick.
2. Concrete base, two and one-half inches thick of Portland
cement one part, sand two parts and fine broken gneiss four
parts.
3. Top dressing, one-half inch in thickness, of two parts
sand to one part Portland cement.
The cost of this floor was about $1.50 per square yard, or
about seventeen cents per square foot.
Art. 75. Concrete in Pavements and Driveways
648. Pavement Foundations. — The principal use of con-
crete in connection with city pavements has been as a founda-
tion, the wearing surface being of some other material, as brick,
asphalt, cedar blocks, etc.
Concrete for pavement foundations should not be less than
six inches in thickness, and a greater thickness will be required
where the ground is insecure. The excavation having been
made to the required sub-grade, and all loose soil removed and
the places refilled with broken stone, the earth is thoroughly
rolled to a smooth surface parallel to the surface of the proposed
pavement. Drainage for the foundation should be provided
where necessary by broken stone or tile drains beneath the
<;urb. Before beginning the placing of concrete, stakes may be
■driven in the foundation, with their tops at grade, at intervals
of five to ten feet over the entire pavement, to assist in securing
the proper grade of concrete surface.
649. The stone for the concrete should be broken so that no
piece is larger than two and one-half inches in its greatest di-
mension. If the stone is of good quality, it need not be screened
except to remove the finest dust, if this is present in consider-
able quantities. Sufficient mortar should be used to fill the
voids in the stone, this mortar being composed of about two
parts sand to one of natural cement, or better, two and one-
half or three parts sand to one of Portland cement. This con-
* Report of Capt. John S. Sewall, Report Chief of Engineers, 1896.
PAVEMENTS 443
Crete is thoroughly rammed in place, care being taken that
adjacent batches as laid in the street mingle with each other
so as to show no line of demarcation. In stopping work for
the night, the concrete should cut off sharply on a straight
line parallel to the direction of the proposed joints in the wear-
ing surface. Joints extending across the street should be left
at intervals of thirty to forty feet to allow for expansion and
contraction.
650. The concrete is finished to a surface parallel with the
proposed street surface, a templet being employed to secure
this. The concrete should be kept damp for a few days, and
no traffic allowed upon it until the wearing surface is laid. If
the wearing surface is of brick or wooden blocks, a layer of
sand about one inch thick is first spread over the concrete.
The advantages of a concrete foundation for street pave-
ments are its strength and durability and water-tightness.
651. Concrete Pavement. — Concrete has not been a popu-
lar material for a street surface except for short driveways and
in courts where both vehicles and pedestrians must be accom-
modated. One reason for this is that concrete is slippery, and
another, that owing probably to carelessness or ignorance, the
wearing qualities have not been good. The first objection may
be largely removed by cutting the surface into blocks, four by
eight inches, by deep grooves, or by the use of a deep imprint
roller on the wearing surface. As to wearing qualities, there
seems to be no good reason why a concrete cannot be made
tough enough to withstand heavy traffic. It will of course be
necessary to divide the work into blocks of twenty to twenty-
five square feet, with expansion joints of sand, asphalt, or
tarred paper between. A third objection is the glare of the
surface in summer. A partial remedy for this may be had by
placing some coloring matter, such as lamp black, in the top
dressing.
652. The sub-base may consist of a six inch layer of broken
stone, or twelve inches of cinders, well drained and thoroughly
compacted by rolling. For exceptionally heavy wear it may be
advisable to use a five inch layer of lean concrete for the sub-
base, after rolling the bottom of the excavation and providing
drainage.
Upon the sub-base should be laid a base, composed of four
444 CEMENT AND CONCRETE
inches of concrete made with first class stone, such as granite,
trap or hard hmestone crushed to pass a ring one and one-half
inches in diameter, and containing enough mortar, one part
Portland cement to two or three parts sand, to fill the voids in
the stone. The top dressing, a layer of granolithic one and one-
half or two inches thick, should then be immediately applied.
This mortar should be made with one or two parts granite, trap,
or other hard rock crushed to pass a five-eighths inch screen, to
one part Portland cement.
These two layers are placed in much the same manner as
that described for laying concrete sidewalks, but the joints in
base and top dressing should run at angles of forty-five degrees
with the curb to prevent ruts following the lines of the joints.
A roller making deep imprints is then run over the finished
surface to furnish a foothold for horses, or, for this purpose a
special roller may be used to mark the top dressing into blocks
approximately four by eight inches, with deep (one-half inch)
grooves.
When completed, the pavement should be kept moist, pref-
erably by a layer of damp sand, and no traffic should be al-
lowed upon it for at least a week or ten days.
653. Concrete pavement laid in Belief ontaine, Ohio, was
found to be in good condition after ten years' service;* the
only serious defect apparent being that, since the blocks were
marked off parallel to the curb, ruts have sometimes formed
along these joints. This pavement was made with four inches
base concrete, laid directly on sub-grade where foundation
is gravel, sand or porous soil; or if soil is impervious, the
base was laid on four inches of broken stone or cinders. The
top layer was two inches thick, equal parts cement and sand or
pea granite. Sub-drains of three inch tile were laid inside each
curb line, and the curb is formed as part of the outer blocks.
Both the base and top dressing were cut through in squares,
five feet on a side. The cost of the pavement is said to have
been $2.15 per square yard, and very few repairs have been
found necessary.
In Germany a cement macadam, made with six inch sub-
* Municipal Engineering, December, 1900, and Engineering News, Jan. 7,
.1904.
CURBS AND GUTTERS 445
base of broken stone or gravel, with a wearing surface of hard
macadam stone mixed with cement, has been successfully used.
Art. 76. Curbs and Gutters
654. The use of concrete for curbs and gutters is rapidly
increasing. Curbing is sometimes molded and afterward put in
place hke stone curbing, but the greatest advantages in the use
of concrete for this purpose are only attained by molding in
place the curb and gutter as one structure.
The Parkhurst combined curb and gutter is a patented form
that has proved very satisfactory. This form has a projection
of about one inch at the back and another along the bottom
just below the curb, this feature being patented.
A combined curb and gutter may consist of a curb four to
six inches wide at the top, and five to seven inches at the bot-
tom, and have a face of six to seven inches above the gutter.
The upper face corner of the curb and the angle between curb
and gutter should be rounded with a radius of one and one-
half to two inches. The gutter is sixteen to twenty inches
wide, and from six to nine inches thick, with top surface con-
forming to the grade of the street.
655. The sub-base should consist of a layer of broken stone
six inches thick, or six to twelve inches of cinders thoroughly
rammed. The preparation of the foundation should be similar
to that required for a pavement, care being taken that the
sub-base be thoroughly drained, tile being used if necessary.
Forms to receive the concrete are held in place by stakes, the
molds being carefully set to grade. The sub-base may now be
covered by a layer of four to six inches of Portland concrete of
only moderate richness, as one to three to six, and the concrete
to form the curb and gutter placed upon it before it has set,
or a six inch layer to form the gutter may be placed directly
on the sub-base.
656. Concrete to form the curb and gutter should be of good
quality, not more than two and one-half parts sand to one part
Portland cement being used for the mortar, and sufficient mor-
tar used to entirely fill the voids in the stone. The broken
stone for this concrete should be rather fine, with few, if any,
pieces larger than one inch in greatest dimension. The ex-
posed faces receive a top-dressing, or wearing surface, of one-
446 ■ CEMENT AND CONCRETE
half inch to one inch of granolithic containing not more than
one and one-half parts of trap or granite, pea size, to one part
Portland cement. This coating is applied as soon as possible
after the concrete is placed, as in sidewalk work. The surface
is troweled or floated, but a smooth, glossy finish is avoided.
The curb and gutter may well be laid in alternate blocks
about six feet long, but a somewhat neater appearance is se-
cured by making the work continuous, and cutting it entirely
through at intervals of six feet to provide for slight movement.
As the molds may be used repeatedly, they should be sub-
stantially made. Special forms are of course required at corners,
catch basins, etc. As in other concrete construction, the work
should be protected from injury and kept moist for at least a
week.
657. On business streets it is desirable to build the sidewalk
close to the curb, with only a joint between, the grade of the
walk conforming to the curb and sloping up toward the build-
ing line one-quarter inch to the foot. On residence streets the
walk should be separated from the curb by a park strip, the
walk being high enough to give drainage toward the curb.
Steel facing is sometimes used for curbs subjected to excep-
tional wear, as in front of shipping warehouses and freight
sheds. Where these are applied, they should cover the top
and the upper part of the face of the curb and must be well
anchored, by bolts or special webs, to a substantial mass of
concrete, otherwise they will work loose and defeat the object
for which they are used.
658. Cost of Concrete Curb and Gutter. — At Champaign,
111.,* a curb was built seven inches high and five inches thick,
the gutter, six inches thick, extending nineteen inches into the
roadway from the face of the curb. The foundation consisted
of six inches of gravel or cinders well rammed. The concrete
was composed of one part Portland cement to five parts fine
gravel, and the finishing coat, one inch thick, was of one part
Portland cement to one part clean, sharp, coarse sand. The
cost per foot was thirty-nine cents, including all excavation.
A similar curb at Urbana, 111., was 4^ inches thick at the
top, 5 inches at the base and 7^ inches high; the gutter being
^ W. H. Tarrant, Engineer, Proc. 111. Spc. Engr. and Surveyors, 1899.
STREET RAILWAY FOUNDATIONS 447
5 inches thick and extending 18 inches into the roadway. The
foundation was composed of eight inches of cinders or gravel.
The concrete was of one part Portland cement to five parts
clean gravel, and the finishing coat was one inch thick, com-
posed of one part Portland cement to two parts sharp sand.
The price per Unear foot, including the excavation, removal of
old curbing, and refilling, was forty-six cents.
At South Bend, cement curb alone, 6 inches wide at top,
7 inches at bottom and 16 inches depth, with the upper half
composed entirely of one to two Portland cement mortar, has
been constructed for eighteen cents per linear foot.
Art. 77. Street Railway Foundations
659. The heavy motor cars used on city and urban electric
railways subject the track to very severe service. As the head
of the rail must be practically flush with the pavement on city
streets, cross-ties, when used, are so far beneath the surface
that they decay rapidly and their renewal entails the tearing
up of the pavement. As there is not the same necessity for a
cross-tie on street tracks as on railroads, since the rails are held
to gage by the pavement, these objections to the cross-tie have
led to the adoption of a concrete girder under each rail. The
rails and ties (if ties are used) should not only rest upon the
concrete, but should be imbedded in it. Track in which the
rails rested upon concrete, but were not imbedded in it, has
been found to yield laterally and get out of alinement, while
on the other hand, if the ties rest upon earth or gravel and are
filled between with concrete, the tyack is likely to settle, break-
ing the bond of the concrete.
660. The method of placing concrete beams for street rail-
way tracks in MinneapoHs was as follows: * The rails were first
spiked to cross-ties at intervals of six to eight feet, and the rail
joints cast-welded. In laying the street pavement foundation
of natural cement concrete, a rough groove, fifteen inches wide
at the bottom and eighteen to twenty inches at the top, was
left under each rail. This groove was immediately filled be-
tween ties with concrete made of one part Portland cement.
' F. W. Cappelen, M. Am. Soc. C. E., Engineering News, Oct. 14, 1897;
Municipal Engineering, November, 1896.
448 CEMENT AND CONCRETE
two and one-half parts sand, and four and one-half parts broken
stone.
The rails were tied together every ten feet with wrought
iron tie bars, three-eighths inch by two inches, set on edge. These
tie bars were rounded at the ends, threaded and attached to
the web of the rail by two nuts, one on either side of the web.
The rails were then spiked to the concrete beam, the temporary
wooden ties removed, and the spaces left by them filled with
concrete, completing the beam. As the concrete beam was
eight inches thick and the rail five inches, the sub-grade was
thirteen inches below the top of the rail.
On the gage side of the rail were placed toothing blocks of
granite, 3^ by 9 inches by 4^ inches deep, held away from the
rail 1^ inches by temporary wooden strips. After removing
these strips, cement grout was poured into the groove to fill
2^ inches over the base of the rail, the remaining 2^ inches to
the top of the rail being filled by asphaltic cement which re-
mained soft enough to permit a flange groove to be made by the
first car over the track. The asphalt wearing surface was laid
against the rail on the outer side. Mr. Cappelen, in describing
this construction, says that a rail six inches high with six-inch
base should be used, with granite toothing blocks, six by nine
inches by five and one-half inches deep.
The cost per foot of rail for the concrete beam construction
only, was twenty-six to twenty-seven cents, and for the filler,
five cents per foot. The cost per mile of double track, exclusive
of rails and pavement, was about $8,670.00.
Somewhat similar methods have been employed in Toronto
and Montreal, Canada, IndianapoHs, Ind., and Scranton, Pa.,
Denver, Detroit and Cincinnati.
661. At Scranton, Pa.,^ the rails were laid directly on the
six-inch concrete base of the pavement. This thickness was
increased to twelve inches under the joints (which were rein-
forced by an inverted rail four feet long) and under steel cross-
ties spaced ten feet centers and formed of old girder rails in-
verted and riveted through the flanges at the intersection.
Flat steel tie bars, threaded at the ends, spaced ten feet centers,
were also used here as at Minneapohs.
* Description of the systems employed in several cities are given in En-
gineering News, Dec. 26, 1901.
STREET RAILWAY FOUNDATIONS 449
The concrete mixing plant was mounted on a car running
on the track; the materials were delivered to the machine by
hand measuring boxes, and the Drake mixer deposited the con-
crete directly into the trench. The total cost per foot of track
is given as $2.65, $1.17 of which was for grading, rolling, con-
creting and brick paving at $1.97 per square yard, and for extra
concrete at joints and ties at $0.72 per square yard.
662. At Toronto, Canada, the six-inch concrete base of the
pavement is increased to eight inches in thickness for twenty
inches width under each rail, and the base of the latter is im-
bedded one inch in the concrete. A 6^inch grooved girder
rail is used, with mortar rammed between the web and the
adjacent paving blocks.
663. At Cincinnati the bottom of the concrete stringer is
nine inches below the base of the nine-inch grooved girder rail,
and the concrete is built up from three to six inches on the web,
according to the thickness of the wearing surface of the pave-
ment. The space between the upper part of the web and the
adjacent paving is then filled with cement mortar, thus sup-
porting the head of the rail as well as protecting the web from
corrosion.
CHAPTER XXI
SPECIAL USES OF CONCRETE (CONTINUED). SEWERS, SUB-
WAYS, AND RESERVOIRS.
Art. 78. Seweks
664. There seems to be no very good reason why concrete i&
not more generally employed in the construction of all large
sewers. With sizes less than two or two and one-half feet in
diameter the difficulty of removing the centers prohibits the use
of concrete in the ordinary way, and although some appliances
have been devised for building these small sewers as monoliths
by a mold that advances as fast as the concrete is tamped in
place, they have not proved popular. The difficulty of obtain-
ing a perfect grade, and the undesirable feature of leaving the
green concrete unsupported, are probably reasons sufficient for
this lack of popularity.
For the larger size sewers concrete has several advantages
over brick. First may be mentioned the very smooth finish
that may be obtained on the invert, appreciably increasing the
velocity of flow over that usually obtained with brick inverts.
Cheaper labor may be employed in concrete work with less
danger of annoyances from strikes. The cost is from one-
third to one-half less than for brick.
665. METHODS OF Construction. — The City of Washing-
ton was one of the first to use concrete extensively in sewer
construction^. For sizes up to twenty-four inches internal diam-
eter the concrete is used only as a foundation and bedding
for the ordinary sewer pipe. For a twenty-four inch sewer
the pipe rests in a bed of concrete twenty-seven inches wide
at the bottom, flaring to forty inches wide at the level of the
center of the pipe, and then carried up with plumb sides for
six inches, and finally finished by planes tangent to the upper
curve of the pipe. At the joints there are bands of concrete
' Described by Capt. Lansing H. Beach, Corps of Engrs., U. S. A. Report
Operations District of Columbia, 1895.
450
SEWERS 451
extending over the top, so that at these places the pipe is en-
tirely inclosed. Similar forms are used for the smaller sizes
with corresponding decreased dimensions. For all sewers be-
tween ten inches and twenty-four inches the sub-grade is six
inches below the exterior of the pipe, and in all cases the band
about the joint is four inches thick at the top.
666. The method of laying these sewers is as follows: The
trenches are 2^ to 3 feet in width, with " headers" about 2 feet
wide, left at intervals of 10 to 16 feet, which are tunneled
through. The grade and line pegs are placed in the headers
at the ground surface, and a cord is stretched on the sewer Hne
over at least four stakes, at a convenient height above the
grade, and thus parallel to the bottom of the sewer.
When the trench is to the required grade, a six inch layer of
concrete, made with one barrel natural cement, two barrels
sand and four barrels gravel, is placed. This concrete is rammed
with iron rammers weighing sixteen pounds, and having eighteen
square inches ramming surface. The pipe is then laid upon
this bed and each section is tested for line and grade. For the
former, a plumb bob is used with its cord held against the
grade cord already mentioned, and for testing the grade a grad-
uated pole is used, with a projection at the bottom which sets
on the interior of the pipe, just within the open end.
Concrete is then lowered in buckets, deposited on top of
the pipe and allowed to fall down on the sides so as not to
disturb the alinement. When enough concrete to secure the
pipe has been thus placed, it is rammed and the concreting
continued until the required form is obtained, as already de-
scribed. The concrete in the bands carried over the joints is not
rammed but is beaten with wooden paddles and heavy trowels to
compact it and bring it to the desired form, four inches thick
and four inches wide at the top, and flaring to twelve inches
wide (in the direction of the sewer) at the top of the pipe.
667. Cost. — The quantities of concrete materials required
to lay one hundred linear feet of pipe sewers as described
above are given as follows : —
Size of sewer 8 inch 12 inch 18 inch 24 inch
Cement, bbls 6.76 10.58 14.77 19.14
Sand, cu. yd 2.07 3.23 4.52 5.85
Gravel, cu. yd 4.16 6.47 9.04 11170
452 CEMENT AND CONCRETE
With natural cement costing $0.79 per barrel in sacks, sand
$0.47 per cu. yd., gravel $0.75 per cu. yd., and laborers $1.50
to $1.75 per day, foremen, masons and inspectors $4.00 per
day, the average cost of laying pipe sewers in this manner was
approximately as follows, exclusive of the cost of the pipe:
8-inch, $1.11; 12-inch, $1.14; 15-inch, $1.46; 18-inch, $1.60;
21-inch, $1.67; 24-inch, $2.32 per foot.
668. Sewers at Chicago. — In the construction of some
17,000 feet of sewers for the Chicago Transfer and Clearing
Yards,* concrete was used for all sewers of thirty-six inches
diameter and over. The excavation was mostly in blue clay
and done by steam shovel to a depth of twenty feet, the re-
mainder being removed by hand shovels and swing derrick.
The material was such that in general the bottom of the trench
could be trimmed to the form of the exterior of the sewer.
The thickness of the ring of concrete was 8 inches for 36 and
42-inch sewers, 10 inches for 48-inch, and 12 inches for 84 and
90-inch sewers.
The concrete was composed of one part "Steel Pozzolana"
(slag) cement, three parts sand and five parts broken stone.
The cement was of course very finely ground and showed high
seven-day tests. The cost was $1.30 per barrel delivered.
The sand was the Chicago "torpedo" sand, coarse and of good
quality, and cost about ninety cents per cubic yard delivered.
The stone was a limestone from Summit, 111., crushed in two
sizes, namely, 1 to 2^ inches and ^ to 1^ inches. These two
sizes of stone were -mixed in proportions one part of the coarser
to two of the finer. The cost of stone was about $0.80 per
cubic yard delivered.
The concrete was mixed by a rotary mixer of the continuous
type provided with radial blades. The mixer was mounted on
a flat car, with engine and upright boiler. Three cars of stone,
the mixer car, two cars of sand and one of cement made up the
concrete train, which ran on a track laid close to the trench
and was kept near the work by a small locomotive. The mixer
was supplied by wheelbarrows running from the material cars
on plank runways attached to the cars. The concrete was also
transported in wheelbarrows from the mixer to the trench.
E. J. McCaustland, Trans. Assoc. C. E., Cornell University, 1902.
SEWERS 45;^
669. The bottom of the trench being cut to form, the con-
crete for the invert was laid directly on the sub-grade, tamped in
layers carried up until the invert occupied about one hundred
forty degrees of arc. The form of the inner face of the invert
was maintained by template, grade stakes being set 12^ feet
apart along the trench. The remainder of the sewer was laid
on centers resting on the invert. The ribs for this centering
were made in a complete circle, of three thicknesses of one by
twelve inch boards nailed together and cut to a true circle.
Ribs were placed four feet center to center, and covered with
lagging two inches thick and three inches wide, planed to radial
joints. The strips of lagging were held in place at each end of
a section by a t\ by 2 inch iron band passing over all of the
strips, and turned in at the ends, forming a hook in which rested
the lower lagging strip, the other strips being supported by this
one. The lower part of each rib rested on the invert, the upper
portion being cut to a diameter four inches less (that is, smaller
by twice the thickness of the lagging). While the trench was
near enough to the outside of the sewer ring not to measurably
increase the amount of concrete over and above the desired
thickness, the trench served as the outside form. Above this
point, planks were inserted and braced to the sides of the trench.
From the haunches to the crown the exterior was finished with
a template.
When completed, the exterior form planks were removed,
and a light covering of earth placed on the surface to protect
it from drying too rapidly. This was especially necessary in
this case on account of the kind of cement used. The centers
were removed usually after forty-eight hours, by swinging the
ribs about the vertical diameter and removing the lagging. As
soon as the centering was removed, the inner surface was plas-
ered with a mortar composed of three parts lake sand to one
part cement.
670. Cost. — The company furnished the materials used in
the sewer ring and manholes, and delivered it on the work,
while the contractor furnished all tools , and labor to dig the
trenches, complete sewer and manholes, and do the back filling.
The contract prices per foot are given by Mr. McCaustland, the
resident engineer, as follows: —
454
CEMENT AND CONCRETE
14 " 2,660
<(
3.00.
17
4,540
<i
3.57
22
1,000
<i
5.91
24
5,400
II
6.68
36-inch sewer in trench averaging 1 1 feet deep, 3,340 feet, at $2.30.
42
48 ■ "
84
90
From the data given we have computed the approximate
quantities of concrete per foot of sewer, and assuming the cost
of the materials for a cubic yard at $3.00, we obtain the follow-
ing approximate costs: —
Size
Sewer.
Depth
Trench.
Materials.
CoNBTROCnON
Contract
Price per
Foot.
estiilited
Total Cost
PER Foot.
Approximate
Cubic Yards
Concrete.
Approximate
Cost
Concrete.
36 in.
42"
48"
84"
90"
11 feet.
14 "
17 "
22 "
24 "
.286
.325
.47
.93
.99
$ .85
.97
1.41
2.79
2.97
$2.30
3.00
3.57
5.91
6.68
$3.15
3.97
4.98
8.70
9.65
671. Special Molds for Small Sewers. — In the construction
of a thirty inch sewer at Medford, Mass.,^ Mr. William Gavin
Taylor made use of a very convenient form. The lower 240
degrees of the sewer was of concrete, the upper 120 degrees
being of brick. To construct the concrete portion as a mono-
lith, the forms were constructed in lengths of ten feet, separat-
ing on a vertical line into two halves. The two halves were
connected by clamps, and held at the proper distance apart by
dog irons in the end ribs of each form. After smearing the
forms as usual, the concrete was deposited and rammed. When
it had partially set, the dog irons were removed and turn-buckles
used to slowly pull the two halves together. This method pre-
vented the green concrete being broken, although the concrete
extended up on the sides thirty degrees above the horizontal
diameter.
672. The centers used for the brick ^rch were also ingen-
iously arranged, and since they might have been used for a con-
crete arch they may be described here. These centers were
also in ten foot lengths. The ribs, of two inch plank, were
• Abstract from Annual Report of City Engineer, Engineering Record,
Not. 7, 1903.
SEWERS 455
spaced two feet centers, with lagging J inch thick by 1^ inch
wide, with one bevel edge to make a tight upper surface. The
rear end of each center was supported by wedges securely
fastened to the outer end of the preceding section, the forward
end being supported by a screw jack.
After turning the arch, these centers were removed by the
aid of a special truck the axles of which were bent at such an
angle as to make the cast iron wheels fit the concrete invert.
The axle of a roller was first fastened to the outer rib of the
center to be removed; the truck was then run back a foot or so
under the center and the screw jack supporting the forward
end of the center released. This allowed the forward end to
drop a short distance, the roller resting on the running board
of the truck. The latter was then pulled into the sewer far
enough to let the roller run off the end of the truck and lock
itself. The truck being then pulled out of the sewer toward
the finished end, drew the center away from the wedges sup-
porting the rear end, allowing the form to drop on the truck
and be wheeled out of the sewer. By this method the centers
were successfully removed without injuring the concrete.
673. Cost. — From data given, the cost of this sewer —
about sixteen hundred feet in length — is approximately as
follows, labor costing twenty-five cents an hour: —
1.25 cu. yds. excavation and back fill, at $.59 $0.74
.15 cu. yd. concrete, at $6.70 1.00
.037 cu. yd. brick masonry, at $12.05 44
Cost of linear foot, exclusive of manholes, estimated at . . $2.18
The total cost per linear foot is given as $2.39
674. New York Sewers. — In connection with the construc-
tion of the New York Rapid Transit Railway, some of the
sewers were built of concrete. This work was done with ex-
ceptional care, and on a large scale, and it was found that the
concrete sewers cost one-third less than similar sewers of brick.
The method of construction of one section may be described
as follows : ^ The forms for the invert of the straight lengths
of sewer were twelve feet in length, consisting of a strong frame-
work covered with closely matched lagging, planed smooth and
Engineering News, March 6, 1902.
456 CEMENT AND CONCRETE
greased with machine oil. After the trench was prepared, con-
crete was placed and rammed until the top of the concrete was
within about one-half inch of the flow line of the invert. To
accomplish this, a straight edge was used, bearing on the fin-
ished invert in the rear and a template secured to the trench
timbering just ahead of the section under construction.
The invert centers were then placed, resting on the finished
invert at the rear and on a solid foundation accurately set to
grade at the forward end. Mortar composed of equal parts
Portland cement and sand was then tamped between the invert
form and the bottom concrete already laid. When the flow
Une had been thus accurately formed, the center was braced
and vertical planking set to form the outside of the walls. The
concrete was then rammed in place.
Joists of two inch by four inch scanthng laid along the
center of the top of each side wall of the invert section, formed,
when removed, a mortise into which the fresh concrete of the
arch section was rammed to form a bond. Similar mortises
were also made in the forward end of each section as built.
After twenty-four hours or more the forms were removed, and
a thin cement wash was applied to the interior, sufficient only
to fill any slight imperfections in the surface.
The arch centers, similar in construction to the forms for
the invert, were put in place and plastered with one inch of
rich Portland mortar. Concrete was then placed sufficient to
make the arch eight inches thick, the outside of the walls being
formed by incHned boards braced to the trench, and the top of
the extrados was formed by hand.
675. Steel Forms. — Two novel types of centering have been
devised, in which the surface next the concrete is of steel. In
one of these ^ the forms are in sections about three feet long.
Two of the pieces of steel are of a width suitable to reach from
the bottom of the sewer to just above the spring line of the
arch, while a third piece forms the arch center. The strips are
bent at an acute angle at the sides, thus projecting into the
sewer along an element of the surface where the plates join ; the
two sides of adjacent plates, which flare away from each other,
are then connected by a continuous U-shaped clip of steel slipped
Engineering Record, Jan. 9, 1904.
SUBWAYS AND TUNNELS 457
on from the end of a three foot section, and the intervening
space in the clip filled with clay or melted paraffin. The form is
assembled outside the trench, and after the paraffin is in place,
the center may be handled. When the sewer is completed,
the paraffin is melted by a suitable heater, or the clay is washed
out, and the form may be collapsed and removed.
676. In the other form ^ the steel plates are in continuous
strips about six inches wide and are applied by setting up the
wooden form on an improvised axis, revolving the form and
wrapping the steel sheet about it as it is revolved. The wooden
form is in two parts, upper and lower, firmly connected while
in use, but the two parts may be made to approach each other
by driving out the wedges between them. After the winding,
the center, with its sheet steel jacket, is lowered into the trench.
When the concrete is completed, the form is collapsed and
removed, leaving the spiral of steel in place to support the con-
crete until the latter is well set. The steel is then removed by
simply pulHng on one end. As it comes away from the concrete
it is wound into a coil, and is then ready to be rewound on the
wooden form. Both of the above styles have been patented.
Art. 79. Concrete Subways and Tunnel Lining
677. The advantages of concrete in subway construction
and in tunnel lining are now well established. In subways
built in open cut, the side walls and invert are of concrete built
in place, while the roof is frequently made with I-beams with
concrete arches turned between them. The I-beams are sup-
ported directly on the side walls, which are usually made mono-
lithic with the invert.
678. Special precautions have to be taken to exclude water
from a subway, and for this purpose tarred felt and Portland
cement plaster are employed.
The specifications for the New York Rapid Transit Subway '
were carefully framed to secure a waterproof construction. On
the sub-grade was placed a layer of concrete, smooth and level
on top. This was covered by alternate layers of hot asphalt
and felt, from two to six layers of each being used as deemed
* Engineering News, Feb. 18, 1904.
* Abstracted in Engineering News, Feb. 13, 1903.
458 CEMENT AND CONCRETE
necessary for the conditions encountered. The remainder of
the concrete forming the floor was then laid upon the top layer
of asphalt. In dry, open soil the felt was not required, and in
dry rock excavations above water level both the asphalt and
felt were omitted. Similar provisions were made for water-
proofing the side walls and roof, resulting in a complete layer
of asphalt and felt imbedded in concrete about the entire tun-
nel, the waterproofing being protected both inside and out by
concrete.
679. In the construction of the Boston Subway * the por-
tion built in open cut was made as follows: The work was di-
vided into sections of convenient length, about twelve feet,
so that work on a section could be carried on continuously until
completed. Upon the prepared grade were laid three thick-
nesses of tarred felt with six-inch lap joints, well pitched be-
tween the layers, and the top of the upper layer thoroughly
covered with the pitch. When the latter had hardened, the
invert was laid over the entire width of the section.
At each side a back wall six inches thick was built up to a
convenient height and braced. The forms were then removed
and the face of this back wall was plastered with rich Portland
cement mortar. The main side walls were then built up be-
tween this layer of plaster and the forms defining the interior
face of the wall. This portion of the subway had an arch
roof, two feet thick at the crown, which was laid on wooden
centers. The exterior of the roof was plastered like the side
walls, and then covered with four inches of concrete to protect
the plaster from injury. The centers were removed after from
ten to thirty days; the span of the arch was about twenty-
three feet.
680. Tunnel Lining in Firm Earth. — In building tunnels in
earth that is sufficiently firm not to require extensive timber-
ing, concrete is well adapted for lining. An instance of this is
furnished by the extensive system of tunnels constructed for
telephone and telegraph service under the streets of Chicago.*
The trunk conduits for this system are about thirteen by four-
* Annual Report Boston Transit Commission, 1900; also described in
Engineering News, April 4, 1901.
* Mr. George W. Jackson, Engineer, Proc. W. Soc. Engrs., 1902; also in
Engineering News, Feb. 19, 1903.
SUBWAYS AND TUNNELS 459
teen feet inside, and the laterals about six by seven feet, all of
the five center horseshoe form.
The excavation was in hard clay which stood up well. Shafts
were located in basements of buildings rented for the purpose,
and in these basements were placed the compressed air plants,
material bins, concrete mixers, etc. The large air locks, some
of which would hold ten small construction cars, were placed
at the bottoms of the shafts. Work was done in three shifts,
working eight hours each. The two night shifts could excavate
about twenty-one feet of lateral tunnel in the sixteen hours,
and the day shift placed the lining.
681. The concrete was in general composed of five parts of
broken stone and screenings, or of mixed gravel and sand, to
one part Portland cement. For intersections but four parts
aggregate were used. This should make a very strong concrete.
The centers for the smaller conduits were made of three-inch
channels, each rib being in five parts bent to the proper form
and connected by flange plates bolted to the inside of the chan-
nels at the ends. These ribs were placed three feet apart, and
two-inch plank used for lagging.
The ribs for the trunk sewers were of similar construction,
but with heavier channels braced with angles. Steel lagging
was used, made of plates about twelve by thirty-six inches,
stiffened by 1^ inch angles on four edges. There were also
provided bulkheads or steel end plates of voussoir shape, twelve
inches along the intrados and twenty inches high, for the pur-
pose of retaining the end of each section of lining and permit
thorough tamping. These bulkhead sheets, or "end flights,"
were also stiffened along three edges, and could be attached to
the webs of the channel ribs by short bolts.
The concrete was mixed at the shaft head and conveyed to
the work in cars twenty inches wide and four feet long, running
on a fourteen-inch gage track. The floor of the tunnel was
first laid in the excavation, the steel ribs then put in place on
the floor, and the lagging placed at the bottom and built up
the sides just ahead of the concrete. When near the crown,
short pieces of lagging three feet in length covering but two
ribs were used, and the concrete rammed in from the end of
these short sections until they were complete, and then another
row of short pieces placed and the operations repeated.
460 CEMENT AND CONCRETE
The concrete floor of laterals was designed to be thirteen
inches, and the sides and arch ten inches thick, but in all cases
the entire space between the lagging and the sides of the ex-
cavation was filled with concrete.
682. In such work as this only the best materials should be
used, and, as early strength is desired, the use of Portland
cement is general in order that the centers may be removed
within a reasonable period. The ends of the sections into
which the work is divided should, if possible, be brought up
square, the bulkhead sheets described above being an ingenious
and effective method of providing for this. Where it is not
practicable to finish with a square end over the entire area of
section, then the work on the sides should be stepped back
from the bottom toward the crown, each step being bounded
by planes corresponding to coursing and heading joints in a
masonry arch.
683. Tunnel Lining in Soft Ground. — For tunnels in soft
ground requiring the use of a shield, some difficulties in using a
concrete lining are apparent. The principal one of these lies
in the fact that the fresh concrete is not capable of taking the
thrust of the jacks used in forcing the shield ahead. Attempts
have been made to overcome this difficulty by so constructing
the centers that the jacks may bear against them instead of
on the fresh concrete.
Another difficulty is that in materials requiring almost con-
tinuous support, the temporary timbering is in the way of the
centering for the concrete construction; and still another is the
difficulty of properly tamping the arch at the crown where the
tail of the shield confines the working space. Concrete blocks
were tried in the construction of sewers in Melbourne, but
without entire success. Such blocks were successfully em-
ployed in the underground road system of Paris, though at-
tempts to use fresh concrete in shield tunneling for this work
proved a failure.
684. East Boston Tunnel. — In the construction of the East
Boston Tunnel Extension of the Boston Subway, however, a
monolithic concrete lining has been successfully built, the
tunnel being excavated by shield.
This tunnel is about twenty by twenty-four feet for double
track electric line. The arch ring and the walls are thirty-
SUBWAYS AND TUNNELS 461
three inches in thickness, while the invert is twenty-four inches.
Two side drifts, eight feet square, were first driven a certain dis-
tance and timbered. The bottoms of these drifts were then
excavated, and the side foundations of concrete were placed in
lengths of sixteen to twenty feet. When the foundations had
set, the interior forms for the side walls were placed upon them,
supporting the caps, the exterior plumb posts removed, and
the concrete side walls, three feet thick, built up to within
sixteen inches of the springing line of the arch. This work was
kept about one hundred feet in advance of the shield.
The shield, provided with live rollers, rested upon these side
walls, the rollers running in a flanged plate placed on top 'of the
walls. The shield was forced ahead thirty inches at a time,
and sections of the arch thirty inches in length were turned
directly behind the shield.
685. The centers of the arch were of curved, ten inch steel
channels spaced thirty inches apart, and the lagging, four
inches thick, was placed from the bottom toward the key as
the concrete was built up. Each section of arch is keyed with
concrete pressed through two holes in the rear girder at the
top of the shield, special rammers being used to tamp the con-
crete into the space at the crown of the arch, the concrete being
directed into place by curved sheet-iron troughs.
In each section of arch sixteen cast iron bars, three and one-
quarter inches in diameter and thirty inches long, are built
into the concrete in position to receive the thrust of the shield
jacks. Wooden bulkheads on the jack plungers serve to con-
fine the fresh concrete, but the reaction is taken on the cast
iron bars which, being butted end to end in successive sections
of the arch, carry the stress back to concrete that is able to
sustain it. As the shield advanced, the space left over the
completed arch by the tailpiece of the shield was filled with
grout under pressure. The centers remained in place thirty
days. The invert was excavated and laid in ten-foot sections
about twenty-five feet in the rear of the shield. The concrete
was mixed at the bottom of the shaft and passed through the
air lock on cars. The concrete cars ran on a higher level than
the muck cars, in order not to interfere with the excavation.
686. Lining Tunnels in Rock. — If the rock through which
a tunnel is driven is seamy and insecure, concrete is in most
462 CEMENT AND CONCRETE
cases the cheapest and best lining. The cost of the lining is,
of course, less if it can be built in connection with the excava-
tion, but it is frequently difficult to foresee how a given rock
will stand exposure to the air and water, and it becomes an
exceedingly nice question to determine at the tinie of building
a tunnel whether lining is required. In many cases this ques-
tion is settled in the affirmative by other considerations than
the character of the rock, as the resistance to flow, in water-
works and sewers, or the ease of ventilation and the necessity
of a good appearance, as in street or steam railway tunnels.
687. New York Subway. — In the construction of portions
of the rapid transit subways of New York, a traveling center
which served also to support a working platform was carried
on six wheels running on a track laid on the footing courses of
the side walls. This center carried at the side, sections of lag-
ging curved to the required form of the side waHs. This lagging
was adjusted in place, and braced from the platform or center
by means of wedges. Directly behind this traveling center was
a similar platform carrying a derrick; and behind this, the
traveling center carrying the lagging for the roof. This third
platform was jacked up to place the roof lagging at the correct
elevation, and firmly supported by wedges.
The concrete was brought in skips on cars that ran on the
floor level and stopped beneath the derrick platform. The
derrick hoisted the skips through a hole in the platform and
placed them on cars on either the side wall or the roof platform,
so that the concrete was delivered either to the side wall forms
in advance, or the roof forms in the rear as required. The
concrete was rammed in a direction transverse to the tunnel
axis until the roof was completed, except for a space about
five feet wide at the crown. The arch was then keyed by
tamping the concrete in from the end of the form. The two
platforms carrying the forms were each forty feet long, and
the derrick platform was eighteen feet.
688. The excavated rock was crushed for the concrete on a
working platform erected over and around the shaft head.
Cars deUvered the excavated material at the shaft in steel skips,
which were hoisted to the working platform, set on push cars
and dumped into bins, from which stone was deUvered to the
crusher; these cars then passed under the crushed stone bins,
SUBWAYS AND TUNNELS 463
were loaded with broken stone, run back to the shaft head,
and the broken stone dumped into bins mounted over the
mixer. The skips were then lowered into the shafts by the
derricks, to be run to the headings and reloaded. The stone
And sand were fed to a measuring box by means of a hopper,
the measuring box discharging directly into a cubical mixer,
which was high enough above the tunnel floor to dump directly
into skips on the cars.
689. Cascade Tunnel. — In the construction of the Cascade
Tunnel of the Great Northern Railway a somewhat different
arrangement was used. ^ The working platform in the tunnel
was erected five hundred feet in length, and cars hauled by
cable up an incline to the platform. The side walls were built
in alternating sections, eight to ten feet in length, the support
of the arch timbering being thus gradually transferred from
the plumb posts to the concrete of the side walls. Arch sections
were built in twelve foot lengths, the centers being made of
four by sixteen inch plank without radials, so as to leave a
clear way for concrete cars on the working platform. The
latter were high enough to allow the material cars to run be-
neath them.
690. Concrete vs. Brick. — There are frequent instances in
engineering construction where brick masonry might well have
been replaced by concrete, -and the use of brick for tunnel lining
is still adhered to in many cases. This is partly because some-
what less elaborate centers can be used for brick arches, and
the centers may be struck somewhat earlier, and partly be-
cause of extreme conservatism on the part of the designer,
although without doubt there are cases where the use of brick
is entirely w^arranted.
An interesting instance of the greater adaptability of con-
crete under unforeseen conditions, however, is presented by the
Third Street concrete and brick lined tunnel at Los Angeles,
Cal.* This tunnel was excavated mostly through an argilla-
ceous sandstone. The side walls were of concrete up- to the
haunches, the upper part of the arch being of six courses of
brick. A streak of yellow clay was encountered, and it "was
' Mr. John F. Stevens, M. Am. Soc. C. E., Engineering News, Jan. 10,
1901.
' J. H. Quinton, M. Am. Soc. C. E., Engineering News, July 18, 1901.
464 CEMENT AND CONCRETE
soon demonstrated that the six ring brick arch, which occupies
the central portion of the roof, was not strong enough to hold
up the immense weight above it, and the temporary timbering
was crushed and broken in a most alarming way." The strength
of the arch was increased by using nine rows of brick instead
of six until the clay seam was passed. In such portions of the
six ring arch as had cracked, it was found that the inner ring
of brickwork had separated from the second ring, and in places
the second ring had separated from the third. The concrete
walls had shown no evidence of weakness.
To repair the brickwork, steel concrete beams or arches were
inserted in the brickwork at intervals of four feet, and extend-
ing from one concrete wall to the other. These beams were
twelve inches wide and eight to twelve inches deep, made of
rich concrete, and had imbedded in each beam two pieces of
three inch by three-quarter inch steel. The steel ribs were set
in recesses cut out of the brickwork, and rested at the ends upon
the concrete of the side walls. Substantial centers were used
for building the concrete beams, and when the latter had set,
the defective brickwork between adjacent beams was cut out
and replaced by rich concrete.
691. Aspen Tunnel. — Another illustration of the adaptabil-
ity of concrete when unexpected difficulties arise, is furnished
by the construction of the Aspen Tunnel on the Union Pacific
Railroad. ^ The original design provided for sets of timbers to
support the excavation, spaced about three feet, center to center^
but for nine hundred feet of the tunnel such pressures were
encountered that in places a solid wall of twelve by twelve inch
timber was forced in. For a portion of this section the lining was
built of a combination of concrete with steel ribs. The latter
were 12-inch, 55-pound I-beams spaced from twelve to twenty-
four inches, center to center, curved to conform to the interior
of the tunnel. The concrete was built up around and between
the beams, the inner flange being covered by from four to seven
inches, and the total thickness of the walls two to three feet.
692. The Perkasie Tunnel of the Philadelphia and Reading
Railroad was constructed through a firm rock, which, however,
was intersected by several strata of seamy rock. As trouble
* W. P. Hardesty, Engineering News, March 6, 1902.
SUBWAYS AND TUNNELS 465
was experienced from rock falling from these strata, it was
decided to line the tunnel at such places. This lining had a
minimum thickness of eighteen inches at the crown and twelve
inches at the sides. Traffic through the tunnel was not ob-
structed during the work of placing the lining. In laying
about five hundred cubic yards of concrete, the cost was about
ten dollars and eighty cents per cubic yard, exclusive of cost
of centering and dry filling.^
693. Water Works Tunnel. — The lining of portions of the
Beacon Street Tunnel of the Sudbury River Aqueduct was
undertaken some fourteen years after its excavation, and at a
time when it was necessary to use the tunnel intermittently to
supply water to the city of Boston. The methods employed
are described by Mr. Desmond FitzGerald in Transactions
American Soc. C. E. for March, 1894.
A substantial track of 2 feet 1^ inch gage was laid from a
manhole furnishing access to the sewer to the portion of the
tunnel to be lined. The rails, weighing thirty-six pounds to
the yard, were supported on small but substantial trestles,
built of three by four inch spruce joists, and placed eight feet
between centers. Every third trestle was braced from the
sides and roof of the tunnel to prevent the track being floated
when the tunnel was in use. The trestles also carried five rows
of planks for the workmen to walk on in pushing the cars.
The track was elevated by these trestles, so the work was not
seriously interfered with by a small amount of water in the
tunnel. The track cost about eighty-seven cents a foot.
Cars to run on these tracks to deliver materials and concrete
had frames five feet by one foot nine inches, with twenty inch
wheels, and cost about fifty-six dollars each.
694. Centers. — The centers were in three parts, two for
side walls and one for roof. The ribs were of three thicknesses
of two by ten spruce plank, without interior bracing for the
roof section. The side sections had each an inclined brace.
Wedges were iaserted between the tops of the side sections
and the bottoms of the roof ribs to hold the latter in place.
The lagging was two by four inch spruce, in eight foot lengths,
with beveled edges and planed both sides. The centers were
> P. D. Ford, M. Am. Soc. C. E., Trans. A. S. C. E., March, 1894.
466 CEMENT AND CONCRETE
spaced four feet apart, and seventy-five full centers were built;
these, with the lagging, contained 14,000 feet B. M, of lumber,
and cost $1,460.55, or $104.30 per thousand feet B. M.
695. Methods of Work. — Broken stone, sand and cement
were stored in shanties over and around the manhole leading
to the tunnel, and arrangements made by which the materials
could be deUvered through chutes down the manhole to the
cars. As it was found more convenient to work in winter,
special provision was made for storing large quantities of ma-
terial in the shanties. The sand was piled around an iron lined,
wooden bulkhead, in the center of which was a large stove.
The concrete was mixed within the tunnel as close to the
work as possible, and in places where the cross-section had
been sufficiently enlarged by falls of rock to permit easy work-
ing. The materials, delivered to the material cars down the
chutes already mentioned, were pushed to the mixing platforms
and combined in the proportions of 18.56 cubic feet of crushed
stone and 7.35 cubic feet of sand to one barrel of Portland
cement, being approximately 1 to 2 to 5^. The above quanti-
ties of materials made 20 to 21 cubic feet of concrete. When
mixed, the concrete was shoveled into cars, conveyed to the
work and then shoveled into place.
The tamping was done principally with oak rammer five
inches square, twelve inches long, with a short wooden handle
in one end. In tamping the key of the arch, long-handled iron
rammers were used. Much care was requisite here to prevent
the aggregate separating from the mortar and lodging next
the lagging, as it always has a tendency to do, thus resulting
in voids in the face of the work when the lagging is removed.
The concrete was built up on the sides in horizontal layers and
stepped back by inserting bulkheads, so that the adjacent
sections bonded together.
696. Cost. — The cost of this concrete lining, which was
built under great disadvantages, amounted to $16.15 per cubic
yard. This cost must be considered reasonable in view of the
fact that the materials had to be transported an average dis-
tance of more than one-half mile on small push cars, and the
work in the tunnel was suspended for three days of each week
to allow the tunnel to be used to maintain the water supply of
the city.
RESERVOIRS 467
Art. 80. Reservoirs: Linings and Roofs
697. Although the choice of the material with which to
construct a reservoir may in some cases be varied by local
conditions, it is found that under ordinary circumstances con-
crete offers the greatest advantages for a minimum cost. For
the side walls of small reservoirs, concrete furnishes the requi-
site strength and water- tightness with a moderate thickness;
earthen embankments and floors may be made practically im-
pervious with concrete and mortar, combined with asphalt
when considered necessary; while for the roofs, groined arches
or beams and slab construction, with supporting piers, all of
this material, make a neat, permanent, and altogether satis-
factory covering, at a smaller expense than would be required
for brick or stone masonry.
698. Details of Construction. — In the walls and floors,
water-tightness is a prime consideration, and this is best at-
tained by a layer of mortar on the inner surfaces or between
two layers of concrete.
As in floors, walks, etc., the necessity of providing for ex-
pansion and contraction will depend upon the extremes of
temperature to which the surface is to be subjected. In covered
reservoirs which are to be almost constantly filled with water,
or in very equable climates, the blocks may be large, say twenty
feet square, while under more severe conditions the blocks
may not contain more than twenty square feet. The joints
between the blocks may well be wide enough to be filled with
asphalt. This furnishes an elastic joint which is compressed
as the blocks expand, and swells when the blocks again con-
tract.
699. Reservoir Floors. — One of the principal difficulties ex-
perienced in the construction of floors is from settlement of the
foundation. The floor should, therefore, have strength enough
to bridge any small irregularities in the foundation that may
result from inequalities in settlement. For a similar reason, it
is not well to make the blocks too large, as smaller blocks with
compressible joints will more readily conform to an uneven
surface without permanent injury. In order that the reser-
voir shall not leak even if the foundation settles, the concrete
and mortar may be covered with one or more layers of asphalt.
468 CEMENT AND CONCRETE
in building the floor lining, alternate blocks are sometimes
placed first in molds and the intermediate blocks built in later.
In other cases the blocks are laid consecutively. The advan-
tage of the former method seems to lie principally in the ease
of construction, as access may be had to all sides of the
block.
700. In hard clay soil not liable to settlement, four inches
is sufficient thickness for the floor, the concrete to be covered
before it has set with a half-inch layer of rich Portland mortar,
troweled to a smooth surface. If the reservoir when empty
will be subjected to hydrostatic pressure from without, the
floor must be designed to resist this pressure. In this case, if
seepage from without into the reservoir is objectionable, a layer
of mortar may be placed over the first layer of concrete and
protected by the concrete laid upon it. This outside pressure
may be provided for in a covered reservoir by making the floor
of inverted arches between piers, the weight of the floor, piers,
roof, and earth filling over the roof, being made sufficient to
balance the upward pressure on the floor. If there is no ob-
jection to the water from without being led into the reservoir,
a porous layer of broken stone or gravel beneath the floor may
be connected with the interior of the reservoir through pipes
provided with check valves, and the outside pressure be thus
removed. Where it can be accomplished, it will usually be
better to lead this ground water through a pipe to a sewer or
a lower level rather than into the reservoir.
701. Walls. — The thickness of the wall is determined by
methods similar to those used in designing a retaining wall or
a dam according as the pressures are greater from the embank-
ment without or the water pressure within. In the case of a
covered reservoir, the thrust of the roof arches may convert
any vertical section of the wall into a beam, the earth pressure
from without being supported by the floor at the bottom and
the roof at the top. Or in case there is no back pressure from
earth filling, the thrust of the roof may be added to the inner
water pressure. In circular covered reservoirs the arch thrust
is usually taken by steel bands laid in the concrete and en-
circling the reservoir near the top of the wall. In narrow
reservoirs rectangular in plan, tie rods may be used, or the
wall may be buttressed to take the roof thrust. Concrete side
RESERVOIRS 469
walls are usually built vertical, or nearly so, on the inside, and
with a batter on the outside.
702. Linings. — Linings of sloping earthen embankments are
laid the same as the floors, and similar precautions are required.
There is greater danger of settlement of embankments than of
the floor foundation, and the blocks, therefore, may well be made
smaller. Some difficulty may be experienced with laying hori-
zontal asphalt joints on a sloping face, and some sliding of the
lining may be expected under ordinary conditions, the asphalt
joints being compressed. For this reason it would seem to be
better to use asphalt in the inclined joints only, and a mastic
in the horizontal joints. Another method which would probably
prove satisfactory is to lay first a tier of blocks next the floor,
and when these have set, apply a very thin coat of asphalt to
the upper edges of these blocks, following with another tier,
and so on.
703. Roofs. — Where it is necessary to cover a reservoir,
either to prevent the formation of ice, or the growth of algae,
or for other reasons, the groined arch is an excellent design for
the roof on account of the small amount of concrete required,
the clear head room given, and the ease of ventilation. The
extending use of reinforced concrete will also probably enter
this field to a greater extent in the future than it has here-
tofore.
The determination of the stresses in a groined arch roof is
complicated not only by the peculiar form of the arch itself,
but by the fact that the spandrels of the arches are filled with
concrete over the piers to the level of the extrados at the crown.
This evidently results in making of any given unit of the roof,
having a pier as its center, a cantilever, and the arch action is
interfered with. Unless, however, tension members of steel are
laid in the concrete near its upper surface, it is not wise to count
on the strength of the cantilever except to consider it a factor
of ignorance on the safe side. If one wishes to depart from
the ordinary and tried dimensions for groined arches in concrete,
such departure had better be based on some special experi-
ments and tests on full sized sections. Some of the dimensions
that have been used are given in the examples cited below.
704. Forms. — The preparation of forms or centers for
groined arches is one of the most difficult and expensive details
470 CEMENT AND CONCRETE
of the construction of such a roof. It will probably be best to
have each section of the form cover the space, square in plan,
between four piers. The ribs of the centering may well be
built up of planks, nailed together and sawed to proper form.
The lagging should be planed to size, and have radial joints to
make a smooth and even top surface. Care is necessary to make
a neat fit g-long the valley extending diagonally between piers,
and a small fillet may well be fitted into this valley to avoid
a sharp corner on the finished concrete, as well as to cover up
possible imperfections in the joints. The forms should, of
course, be designed to take the thrust of the adjacent com-
pleted arches, and if sufficient forms are not built to cover the
entire reservoir, and thus transmit the thrust to the walls, the
piers at the border of the forms must be thoroughly braced to
the opposite side walls or the piers will be toppled over and
the roof wrecked. This accident occurred to one reservoir
roof during construction, the pier braces having been removed
without the knowledge of the engineer.
705. In laying the concrete, joints between the work done
on consecutive days should cut the arches at right angles to
their axes, and bulkheads should be used to make such a joint
a vertical plane. The covering of each unit between four piers
is made monolithic, and care is necessary to prevent the stones
working to the bottom of the mass and thus becoming exposed
when the forms are removed. This may be prevented by plas-
tering the forms with mortar and placing the concrete upon it
before the mortar has begun to set.
706. A roof consisting of a network of concrete-steel beams
intersecting at right angles, supported by piers and covered by
concrete-steel slabs, makes a very simple design. The forms
are much easier to construct, and forms for only a limited area
need be erected at one time. An excellent article on "Covered
Reservoirs and Their Design," by Mr. Freeman C. Coffin, M.
Am. Soc. C. E., is contained in the July, 1899, number of the
Jour, of the Assn. of Engr. Soc. An article on the "Groined
Arch," by Mr. Leonard Metcalf, Assoc. M. Am. Soc. C. E., ap-
pears in Trans. A. S. C. E. for June, 1900; and Mr. Frank
L. Fuller presents an article on "Covered Reservoirs," in Jour.
Assn. Engr. Soc. for Sept., 1899.
707. Examples of Concrete Reservoirs. Wellesley. — The
RESERVOIRS 471
reservoir at Wellesley, Mass./ a part of the water supply sys-
tem, was designed by Mr. Freeman C. Coffin. It is eighty-two
feet in diameter, walls fifteen feet high, four feet thick at bottom
and two feet at top. The walls are of concrete and rubble
masonry. In the construction of the walls, concrete was used
containing three parts sand and five parts of stone to one
of cement, one cubic yard of concrete containing about 1.2
barrels of cement. The bottom of the walls, which were de-
signed to be built of concrete three feet four inches thick, were
actually built of rubble four feet thick, as a large quantity of
bowlders was at hand. The excavation was in hard clay con-
taining but little water, and the floor was made only four inches
thick, of concrete of the same quality as that used in the
walls.
The floor and side walls were plastered with two coats, the
first, one-half inch thick, of mortar containing two parts sand
to one of Portland cement, and a coat about one-eighth inch
thick, of neat Portland carefully rubbed and smoothed with
trowels. Such a plaster coat should be applied before the con-
crete has set. The two plaster coats cost twenty cents per
square yard.
708. The piers to support the groined arch roof were two
feet square, and built of brick. The span of the arches was
12 feet, rise 2.5 feet, and the concrete 0.5 foot thick at the
crown. A channel iron ring or band was set in the concrete
walls at the springing of the roof arches to take the thrust of
the latter. The centers were placed over one-fourth of the
area at a time, the piers being braced to take the thrust of the
arches until the roof was completed. The concrete in the roof
was composed of two and one-half parts sand and four and one-
half parts broken stone to one part Portland cement. The
centering cost twenty-two and one-half cents per square foot of
area covered. The spandrels were filled in level with top of
concrete at crown. On top of the concrete roof was placed six
inches of clean gravel for drainage and to prevent the earth
freezing to the concrete. This gravel was drained by four
inch vitrified pipe discharging at the toe of the slope wall.
' Engineering News, Sept. 30, 1897; Jour. Assn. Engr. Societies, July
1899; Trans. A. S. C. E., June, 1900.
472 CEMENT AND CONCRETE
One foot of earth filling and one foot of loam were placed upon
the gravel.
709. Astoria. — The reservoir for the Astoria City Water
Works ^ was designed and built by Mr. Arthur L. Adams, M.
Am. Soc. C. E. The reservoir has a capacity of six and one-
fourth million gallons, walls twenty feet high. The excavation
was in hard clay and sand mixed with clay, which in some places
resembled a soft sandstone. The embankment was in general
about five feet, the remainder of the depth being in excavation.
The floor consisted of six inches of concrete, f inch cement
mortar, one coat Uquid asphalt and one coat harder asphalt.
The slope lining was of six inches concrete, one coat asphalt,
one layer of brick dipped in asphalt and laid flat, and a final
finishing coat of asphalt. The concrete was composed of one
barrel Portland cement, one-tenth cubic yard sand, five-tenths
cubic yard gravel and nine-tenths cubic yard of crushed stone,
these quantities of the ingredients making one cubic yard of
concrete. Here we have an instance of the use of a mixture
of broken stone and gravel, a practice which has already been
commended as resulting in a small amount of voids.
The concrete of the floor was laid in blocks twenty feet on a
side, molds of two by six inch plank forming the outside edges
of a block, and serving as a guide to the straight edge used in
finishing, as in concrete walk construction. The finishing coat
was of two parts fine sand to one of Portland cement and was
applied, before the concrete base had begun to set, by two
finishers with smoothing trowels. When the next block was to
be laid, the plank were replaced by one-half inch weather
boarding. When the concrete had thoroughly set, these boards
were removed and the joints so formed were run full of asphalt,
when the first layer of this material was spread.
The concrete on the sides was also six inches thick and laid
in sheets ten feet wide, extending up and down the slopes,
expansion joints being provided on the inclined joints only.
The finishing coat of mortar was not used here, but all inequali-
ties in surface were smoothed by using a little mortar from the
next batch of concrete.
710. Each concrete gang was composed of twenty men and
1 Trans. A. S. C. E., December, 1896.
RESERVOIRS 473
one water boy. All concrete was mixed by hand on movable
platform in half -yard batches. On the entire work 1.84 cubic
yards of concrete per day were mixed and placed per man
employed, and on the floor alone this quantity was increased
to 2.35 cubic yards, an excellent showing for this class of work.
The cost of concrete per cubic yard, without profit, was as
follows: —
On Slopes:— Cement, at $2.45 per bbl $2.82
Other materials 1.94
Labor 1.07
Total per cubic yard for 600 yards $5.83
On Floor: —Cement, at $2.45 $2.64
Other materials 1.92
Labor 68
Total cost per cubic yard for 680 yards $5.24
The costs of the slope lining and floor complete, per square foot,
are given as follows : —
Slope: — 6 inches concrete $0.1187
.649 inch asphalt . , 0100
Brick in asphalt 0889
.851 inch asphalt 0131
Chinking crevices .0030
Ironing 0036
Total cost per square foot of slope $0.2373
Bottom: — 6 inches concrete $0.1031
Cement mortar finish .0113
.537 inch coat asphalt .0077
.573 uich coat asphalt 0082
Total cost of bottom per square foot $0.1303
711. Forbes Hill. — The Forbes Hill reservoir * forms a part
of the distribution system of the Metropolitan Water Works of
Boston and was built under the direction of Mr. Dexter Brack-
ett, M. Am. Soc. C. E. The reservoir is two hundred eighty by
one hundred feet, partly in embankment. The soil under the
embankment was first stripped to a depth of two and one-half
* Described by Mr. C. M. SaviUe, M. Am. Soc. C. E., Division Engineer,
before the N. E. Water Works Assn. Abstracted in Engineering News, March
13, 1902.
474 CEMENT AND CONCRETE
feet at the toe, increasing to five feet stripping at the inner edge
of the slope. The material was hard pan, and the embank-
ments were built in four inch layers, rolled with four thousand
pound rollers, so made as to leave a slightly corrugated surface.
The bank was extended one foot inside of the finished line to
assure a compact face, and afterward trimmed to grade.
712. The bottom of the reservoir was covered first with a
layer of concrete about four and one-half inches thick, com-
posed of one part natural cement, two parts sand, and five
parts stone. The sand was of good quality; the stone came from
the excavation and was washed before crushing. This layer of
natural cement concrete was covered by a layer of Portland
cement mortar one-half inch thick, made of two parts sand to
one cement, and finished with a richer mortar, one part sand to
four of cement.
This half-inch layer was laid in strips four feet wide and
finished like a cement sidewalk. Although this mortar coat
was kept well moistened, some cracks developed which were
filled with grout before applying the second layer of concrete.
If no joints were used in the lower layer or base concrete, and
joints in the coat of mortar were provided in one direction only,
as appears to have been the case, the cracking should have been
anticipated. At any rate, the value of the mortar coat be-
tween the two concrete layers was greatly impaired by this
tracking, and the experience points to the advisability of plac-
ing the upper layer of concrete on the mortar before the latter
ihas set, thus avoiding the expense of finishing the mortar layer.
The upper layer of concrete was composed of one part Port-
land cement, two and one-half parts sand and four parts broken
stone, and was laid in blocks ten feet square. These blocks
were laid alternately each way.
The slope was first lined with Portland concrete of 1 to 2^
to 6^, then one-half inch layer of mortar as for the bottom.
The upper layer of concrete on slope was same as the upper
layer of the bottom lining, but the blocks were eight by ten
feet and finished with one inch of granolithic, in which stone
dust and particles smaller than three-eighths inch were sub-
stituted for the one and one-half inch stone of the concrete.
713. Cost. — The cost of lower layer of concrete on bottom,
natural 1 to 2 to 5, was as follows : —
RESERVOIRS 475
1.25 bbl. natural cement, at $1.08 $1,350
.34 cu. yd. sand, at $1.02 347
.86 cu. yd. stone, at $1.57 1.350
Materials in concrete $3,047
Forms, lumber, at $20.00 per M ... $0,090
Forms, labor 0.100
Total forms .190
General expenses $0.08
Mixing and placing 1.17
1.250
Total cost per cu. yd $4,487
Cost of lower layer on slopes, Portland 1 to 2^ to 6^, was as
follows: —
1.08 bb!s. Portland cement, at $1.53 $1,652
,37 cu. yd. sand, at $1.02 377
.96 cu. yd. stone, at $1.57 1.507
Materials in concrete $3,536
Forms, lumber, at $20.00 per M $0,016
Forms, labor 0.121
Total forms .137
General expenses $0,177
Mixing and placing 1.213
1.390
Total cost per cubic yard $5,063
The cost of the upper layer on bottom and slopes, including
the finish on slopes, Portland 1 to 2^ to 4, was as follows: —
1.37 bbls. Portland cement, at $1.53 $2.09
.47 cu. yd. sand, at $1.02 48
.745 cu. yd. stone, at $1.57 1.17
Materials in concrete $3.74
Forms, lumber, at $20.00 per M $0.25
Forms, labor 0.26
Total forms .51 '
General expenses $0.15
Mixing and placing 1 .53
1.68
Total cost per cu. yd $5.93
^6 CEMENT AND CONCRETE
The cost of the half-inch plaster coat between the layers of
concrete was twenty cents per square yard.
714. Rock ford. — A reservoir for the city of Rockford, 111.,*
was built almost entirely of concrete after plans prepared by
the City Engineer, Mr. Chas. C. Stowell. The soil was a loose
gravel, and after excavation was completed, parallel lines of
drain tile were laid in trenches nine to ten feet centers and
leading to a fifteen inch vertical sewer pipe carried to the sur-
face of the street and capped. This sewer pipe served as a
sump for a pump should it be found necessary at any time to
repair the bottom. These trenches were filled with broken stone
and the whole area of the foundation covered with three inches
of clay. The concrete bottom was in two layers, eight inches
and seven inches thick, respectively, and composed of two
parts sand and five parts stone to one of Portland cement.
The walls were of similar concrete for the bottom twelve feet,
natural cement being used in the upper eight feet of the walls.
The thickness at the bottom was 4^ feet, walls being straight on
outside with one to ten batter on inside. The entire inner
surface of floor and walls was plastered with one-half inch of
Portland mortar, one to one. The cost of concrete in the work
averaged $6.50 for Portland and $4.00 for natural, and the
finishing coat cost seventy-five cents a square yard.
715. The roof was of concrete, expanded metal lath, and
steel rods, the finished thickness being but two inches. This
was supported by ribs of concrete, each twelve inches thick at
the crown and having a seven-inch channel on the under side.
The springing line of the ribs was eight feet below the top of
the walls, giving a good depth at the skew back. Ribs were
spaced about seven feet centers. The span of the roof was
about fifty-five feet, and rise about eleven feet. The cost of
roof was less than twenty-five cents a square foot.
716. Concord. — The groined arch roof of the Concord,
Mass.,^ sewage storage well, designed by Mr. Leonard Metcalf,
Assoc. M. Am. Soc. C. E., was fifty-seven feet diameter and
contained about one hundred cubic yards of masonry. The
cost of the roof per square foot of surface was as follows: —
* Described in Engineering News, Feb. 22, 1894.
RESERVOIRS 477
Centering $0,18
Concrete materials ... .15
Labor and supervision .05
Total $0.38
717. Albany. — The Albany filter plant roof/ designed by
Mr. Allen Hazen, Assoc. M. Am. Soc. C. E., was also of the
groined arch type, the arches having the same span and rise as
the Wellesley reservoir. The cost of the roof per square foot
of area was as follows: —
.029 cu. yd. concrete, at $6.30 $0,182
Piers 054
Earth filling and seeding .014
Manholes, entrances, etc .027
Total cost per sq. ft $0,277
For a list of reservoirs and filter beds, in the roofs of which
groined arches have been used, giving in tabular form the
general dimensions, the proportions used in the concrete, and
in several cases the cost of the roof per square foot of reservoir,
the reader is referred to Engineering News of December 24,
1903.
» Trans. A. S. C. E., June, 1900.
CHAPTER XXII
SPECIAL USES OF CONCRETE (Coniinued)
BRIDGES, DAMS, LOCKS, AND BREAKWATERS
Art. 81. Bridge Piers and Abutments and Retaining
Walls
718. The use of concrete in large bridge piers was at first
confined to the hearting or backing of stone masonry shells.
It was soon found, however, that in many cases the concrete
was able to withstand the effects of frost and ice better than
was the variety of stone available for building the masonry
shell, and many important bridges are now supported by piers
built entirely of concrete.
As an example of this use may be mentioned the bridge
across the Red River ^ in Louisiana, which has six concrete
piers of heights from forty-four to fifty-three feet. The pivot
pier is twenty-seven feet in diameter, with vertical sides. The
draw rest piers are seven feet wide under the coping, nineteen
feet between shoulders and twenty-six feet long over all. The
sides have a batter of one-half inch to the foot. The coping is
of limestone.
719. In the construction of the Arkansas River Bridge ^ of
the K. C. P. & G. R. R., ten piers and two abutments were
built of concrete. • The piers varied in height from twenty to
sixty-five feet, some of them containing over six hundred cubic
yards of concrete. The entire work was completed in eleven
months, although many difficulties were met. The concrete
was composed of one part Portland cement, two and one-half
parts coarse, sharp sand, and five parts of clean, broken stone.
The lagging for the forms was of two-inch yellow pine, sur-
faced one side and sized to one and three-quarters inches. On
* George H. Pegram, Consulting Engineer. Walter H. Gahagan, Engi-
neer for Contractors.
* Engineering News, Aug. 25, 1898.
478
BRIDGE PIERS 479
the straight part of the pier this lagging was laid horizontal and
supported by four by six vertical posts set four-feet centers,
posts on opposite sides of the pier being tied together by three-
quarter inch bolts passing through one and one-half inch gas
pipes spaced five feet vertically. The gas pipe was allowed to
remain in the finished pier, the bolts being withdrawn.
The lagging for the semicircular ends was of two by six with
bevel joints, placed vertical, and supported at five-foot inter-
vals by segmental ribs of double two by twelve planks. At
the ends of the ribs were bolted short pieces of eight by eight
inch angle irons with edge horizontal. These angle irons were,
in turn, bolted to four by six verticals at the corners or shoul-
ders of the pier.
720. The foundation piers of the Lonesome Valley Viaduct,'
thirty-six piers and two abutments, are entirely of concrete.
The piers are four feet square on top with batter of one inch
to the foot, and are from five to sixteen feet in height. The
total concrete laid was 926 cubic yards at a contract price of
about $7.00 per cubic yard. The piers were finished on top with
a steel plate, four feet square and one-half inch thick, taking
the place of coping stones. Where rock foundations were not
found, the lower portion of the pier was given an increased
batter to secure such a cross-sectional area at the bottom that
the unit pressure on the earth did not exceed one ton per square
foot. The cost of the concrete for this work has already been
given (§ 322).
721. Steel Cylinders. — Steel shells filled with concrete have
been used to good advantage, especially for bridge approaches.
Such shells are usually in pairs placed abreast, one under each
truss of the bridge or viaduct. The two cylinders of a pair
are usually connected by lateral bracing, and if desired in heavy
work, this bracing may be inclosed in a concrete wall and thus
protected from injury by running ice, etc. The thickness of
metal in the shells need not be great, three-eighths of an inch
\isually being sufficient, though this depends on the height, the
stresses, and the liability to injury. In soft ground requiring
piles, most of the piles are sawn off below the limit of scour, or
below the water line for land piers, but one or more may be
> Gustave R. Tuska, Trans. A. S. C. E., September, 1895.
480 CEMENT AND CONCRETE
allowed to project up into the cylinders and the concrete filled
in around the heads, thus anchoring the pier. In foundations
on rock if the cyhnders require an anchorage, this may be pro-
vided with bolts fox-wedged or cemented in the rock and pro-
jecting into the cyUnder. (For details of methods adopted in
this class of construction, see "Bridge Substructure and Foun-
dations in Nova Scotia," by Martin Murphy, Trans. A. S. C. E.,^
September, 1893.)
722. Repair of Stone Piers. — Where masonry piers are being
destroyed by the abrading or expansive action of ice, or by
other causes, concrete is successfully used to arrest such action,
the entire pier being incased in a layer, one to three feet
thick, of Portland cement concrete of good quality.
The piers of the Avon River bridge,^ originally built of ashlar
masonry, failed entirely to withstand the deteriorating in-
fluences of an extreme range in tide coupled with the severe
temperature of a Nova Scotia winter. Five of them were sub-
sequently incased in concrete, as follows: A form was made of
ten by ten inch spruce timber surrounding the ashlar masonry
of the piers and forming a mold to receive the concrete and
retain it in place until set. The thickness of the concrete casing
was two and one-half feet at the bottom and one and one-
third feet at the top, which was three feet above high water.
The concrete was composed of one barrel Portland cement,
one and one-half barrels clean sand, one barrel of clean gravel,
and in it was placed by hand four parts of common field stone
weighing from eight to twenty pounds each. This treatment
was entirely successful in preventing further disintegration.
723. An efficient cutwater for bridge piers is made by placing
old rails vertically on the upstream nose of the pier, anchoring
them to the masonry and filling between with concrete, leaving
only the Avearing surface of the rail head exposed.
724. Pneumatic caissons are usually filled with concrete, the
filling over the working chamber being carried up fast enough
to keep the work above water as the caisson is sunk. The
filling of the working chamber calls for special care in tamping
under and around the longitudinal and cross-timber braces. A
space of about three inches next the roof of the chamber is
• Trans. A. S. C. E., December, 1893.
RETAINING WALLS AND ABUTMENTS 481
^lled with a rich concrete, containing no stone larger than one
inch, mixed quite dry and soUdly tamped with special edge
rammers.
725. RETAINING WALLS AND ABUTMENTS. — Concrete is used
very largely for constructing retaining walls and bridge abut-
ments. The foundations of a retaining wall should be of ample
width, and if the wall is not founded on rock, some settlement
and outward movement may be expected if the common for-
mulas are used in computing the dimensions.
If this movement is not equal throughout the wall, cracking
is likely to take place, and to confine these cracks to prede-
termined vertical planes, it is well to construct the wall, if a
long one, with vertical joints at intervals of fifteen to thirty
feet. Such a joint is made by building one section and fol-
lowing with another, without special precautions to make a bond
between.
If there is an opportunity for water to accumulate, care
should be taken to drain the earth back of the wall, either by
drains leading around the ends, or by pipes passing through
the wall. The latter may result in discoloration of the face.
726. Coping. — The face of a retaining wall or abutment is
preferably given a batter, and a coping is provided to improve
the appearance. The coping should have a slight inclination
toward the back to prevent the discoloration of the face by
dripping. It should be divided by vertical joints into blocks,
not more than six to eight feet in length. The projection of
the coping will depend upon the dimensions of the wall. Wing
walls are preferably built with a sloping top or coping, but this
should be made monolithic with the wall by special molds
(§729).
727. Rules for Use of Concrete in Abutments. — In the use
of concrete for abutments and piers, the practice of the Illinois
Central Railroad, as set forth in their specifications, can hardly
be improved upon. The engineer of bridges and buildings on
this road, Mr, H. W. Parkhurst, M. Am. Soc. C. E., is one of
those engineers who early recognized the value of concrete in
bridge work, and as the result of his extensive experience along
this line, he is widely known as an able and conservative au-
thority.
These specifications are printed nearly in full in Engineering
482 CEMENT AND CONCRETE
News of July 18, 1901, from which the following extracts are
made: —
728. Natural and Portland Cement : Where used : —
Natural cement concrete "may be used where foundations
are entirely submerged below low-water mark, or where there i&
no risk of the same being exposed to the action of the weather
by cutting away the surrounding earth. It, however, shall be
used only where a firm and uniform foundation is found to
exist after excavations are completed. In all cases where
foundations are liable to be exposed to the action of the water,
or where the material in the bottom of excavations is soft or
of unequal firmness, Portland cement concrete must be em-
ployed for foundation work.
"The natural cement concrete shall usually be made in the
proportions (by measure) of one part of approved cement ta
two parts of sand and five parts of crushed stone, all of char-
acter as above specified. For Portland cement concrete foun-
dations, one part of approved cement, three parts of sand and
six parts of crushed stone may be used. Wherever in the
judgment of the engineer or inspector in charge of the work, a
stronger concrete is required than is above specified, the pro-
portions of sand and crushed stone employed may be reduced,
a natural cement concrete of 1, 2 and 4, and a Portland cement
concrete of 1, 2 and 5 being substituted for those above speci-
fied. .
"Portland Cement Concrete: — Concrete for the bodies of
piers and abutments, for all wing- walls for same, and for the
bench walls of arch culverts, shall generally be made in the pro-
portions (by measure) of one part of cement, two and one-half
parts of sand and six parts of crushed stone. Where special
strength may be required for any of this work, concrete in the
proportions of 1, 2 and 5 may be used; but all such cases shall
be submitted to the judgment of the engineer of bridges, before
any change from the usual specification is to be allowed.
"For arch rings of arch culverts and for parapet headwalls
and copings to same, Portland cement concrete, in proportions
of 1, 2 and 5, shall generally be used. Concrete of these pro-
portions shall also generally be used for parapet walls behind
bridge seats of piers or abutments, and for the finished copings
(if used) on wing-walls of concrete abutments, also for arch
USE OF CONCRETE IN ABUTMENTS 483
work in combination with I-beams or in combination with iron-
work for transverse loading.
"Bridge seats of piers and abutments and copings of con-
crete masonry which are to carry pedestals for girders or longer
spans of ironwork, shall generally be made of crushed granite
and Portland cement, in the proportion (by measure) of one
part of approved cement, two parts of fine granite screenings,
and three parts of coarser granite screenings, the larger of which
shall not exceed three-quarters inch in greatest dimension."
729. After specifying the method of building molds, which
is treated elsewhere (Art. 62), the specifications proceed: —
"The planking forming the fining of the molds shall in-
variably be fastened to the studding in perfectly horizontal
lines ; the ends of these planks shall be neatly butted against
each other, and the inner surface of the mold shall be as nearly
as possible perfectly smooth, without crevices or offsets be-
tween the sides or ends of adjacent planks. Where planks are
used a second time,, they shall be thoroughly cleaned, and, if
necessary, the sides and ends shall be freshly jointed so as to
make a perfectly smooth finish to the concrete.
"The molds for projecting copings, bridge seats, parapet
walls, and all finished work shall be constructed in a first-class
workmanlike manner, and shall be thoroughly braced and tied
together, dressed surfaces only being exposed to the contact of
concrete, and these surfaces shall be soaped or oiled if necessary,
60 as to make a smoothly finished piece of work. The top
surfaces of all bridge seats, parapets, etc., shall be made per-
fectly level, unless otherwise provided in the plans, and shall
be finished with long, straight edges, and all beveled surfaces
or washes shall be constructed in a true and uniform manner.
Special care shall be taken in the construction of the vertical
angles of the masonry, and where I-beams or other ironwork
are not used in the same, small wooden strips shall be set in the
corners of the mold, so as to cut off the corners at an angle of
45°, leaving a beveled face about one and one-half to two inches
wide, instead of a right-angled corner.
"Where wing- walls are called for, which have slopes corre-
sponding to the angle of repose of earth embankments, these
slopes shall be finished in straight lines and surfaces, the mold
for such wing-walls and slopes being constructed with its top
484 CEMENT AND CONCRETE
at the proper slope, so that the concrete work on the slope may
be finished in short sections, say from three to four feet in
length, and bonded into the concrete of the horizontal sections
before the same shall be set, each short section of sloped sur-
face being grooved with a cross-line separating it from adjacent
sections. It will not be permitted to finish the top surface of
such sloped wing-walls by plastering fresh concrete upon the
top of concrete which has already set, but the finished work
must be made each day as the horizontal layers are carried up,
to accomplish which the mold must be constructed complete at
the outset; or, if the wing- wall is very high, short sections of
the mold, including the form for the slopes, must be completed
as the horizontal planking is put in place."
730. This is followed by directions concerning foundation
work; the following is given relative to building steel into the
masonry : —
"Iron rails to be furnished by the railroad company shall be
laid and imbedded in such manner as may be specified in such
foundation concrete as in the opinion of the engineer of bridges
needs such strengthening, and no extra charge, except the
actual cost of handling the same, shall be made by the contrac-
tor for such work, but the volume of such iron shall be esti-
mated as concrete.
"Where I-beams are to be placed in the angles of conorete
piers as a protection against ice, drift, etc., these shall be set
up and securely held in position so that they will extend one
foot or more into the foundation concrete. The planking of
molds shall be fitted carefully to the projecting angles of these
I-beams, and small fillets of wood shall be fitted in between
the inner faces of the mold and the rounded edges of the I-beam
flanges, so that no sharp projecting angle of concrete w\\\ be
formed as the work is constructed.
"These fillets may be made in short pieces and fastened
neatly into the mold as the layers of concrete are carried up.
Such I-beams will generally be furnished of sufficient length to
extend at least six inches above the top of the battered masonry
into the concrete coping, and special pains shall be taken to
tamp the concrete thoroughly around the I-beams, and to
finish the coping above and around the ends of the same, so as
to make a compact and solid bearing against the ironwork.
CONCRETE PILES 485
"Where anchor bolts for bridge-seat castings are required,
they shall be set in place and held firmly as to position and
elevation, by templets, securely fastened to the mold and
framing. Such I-beams and anchor bolts shall be imbedded
in the concrete work without additional expense beyond the
price to be paid per yard for the several classes of concrete in
which such iron is placed, the volume of iron being estimated
as concrete.
"After the work is finished and thoroughly set, all molds
shall be removed by the contractor. They shall generally be
allowed to stand not less than forty-eight hours after the last
concrete work shall have been done. In cold weather, molds
shall be allow&d to stand a longer period before being removed,
depending upon the degree of cold. No molds shall be re-
moved in freezing weather, nor until after the concrete shall
have had at least forty-eight hours, with the thermometer at
or above 40° Fahr., in which to set."
731. After giving in detail the methods to be followed in
placing and ramming concrete and the use of facing mortar,
the following paragraph is especially applicable to the subject
in hand :
"Layers of concrete shall be kept truly horizontal, and if,
for any reason, it is necessary to stop work for an indefinite
period, it shall be the duty of the inspector and of the contractor
to see that the top surface of the concrete is properly finished,
so that nothing but a horizontal line shall show on the face of
the concrete, as the joint between portions of the work con-
structed before and after such period of delay. If for any reason
it is impossible to complete an entire layer, the end of the layer
shall be made square and true by the use of a temporary plank
partition. No irregular, wavy or sloping lines shall be per-
mitted to show on the face of the concrete work as the result
of constructing different portions of the work at different
periods, and none but horizontal or vertical lines shall be per-
mitted in such cases."
Art. 82. Concrete Piles
732. Piles may be made of concrete either with or without
steel reinforcement. In the former case they are built in place,
but where steel is used the piles are usually driven after they
486 CEMENT AND CONCRETE
have been prepared in suitable molds. Concrete is also em-
ployed to protect from decay, or from the ravages of the teredo,
wooden piles already in service.
Concrete piles are much more durable than wooden piles
and may be used without reference to the water line. A sav-
ing may thus be made under certain conditions, as the use of
concrete piles may obviate the necessity of excavating to the
water line and building up with masonry resting on a wooden
pile foundation. As the diameter of the pile is not limited,
a much greater load per pile may be provided for. There are
of course many places where piles of concrete are not as suit-
able as wooden piles; they are not as well adapted to with-
stand certain kinds of hard usage, such as violent shocks, and
they are much less flexible.
733. Building in Place. — In certain kinds of soil, such as
stiff clay, a wooden pile, or dummy, of the proper length may
be driven and withdrawn, the hole left being at once filled with
concrete. The application of this crude method is very lim-
ited, as it is seldom that the soil will stand until the hole is
filled with concrete.
For the building of piles without reinforcement, Mr. A. A.
Raymond ^ has patented a system by which a thin steel shell
or casing is driven to the desired depth and then filled with
concrete in place. A shell is first slipped over a steel pile core
made to fit it, and the shell and core are driven by a pile driver
in the ordinary manner. The core is then slightly shrunken
in diameter, by a simple device, and withdrawn, leaving the
shell in the ground. The core is hoisted in the pile driver
leaders, another shell is lowered into the one just driven and
then slipped up on the core, after which the driver is shifted
to the next location, and this shell is driven in the same manner
as the first. The filling of the shells with concrete is done as
soon as convenient. While the shape of the shells may be
varied to suit conditions, the ordinary size is about twenty
inches diameter at the top and six inches at the bottom, and
such a shell twenty feet long weighs about seventy pounds.
734. The same company has a system of sinking shells
in sand by the water jet. For this purpose the shells are in
* Raymond Concrete Pile Co., Chicago, 111.
CONCRETE PILES 487
conical telescopic sections about eight feet in length. A twa
and one-half inch pipe with three-quarter inch nozzle is attached
to the center of a cast iron point fixed to the inner section.
Water forced through the pipe causes the shell to settle, and
as the inner shell descends, its upper end engages with the lower
end of the second section, so that when fully lowered the sec-
tions form a continuous cone. The concrete is filled in simul-
taneously with the sinking, imbedding the two and one-half
inch pipe which remains permanently in the center of the con-
crete pile.
735. Concrete-Steel Piles : Molding. — Piles of concrete-steel
usually have three or more steel rods of about one square inch
cross-section imbedded longitudinally in the pile, and connected
by smaller rods or wires at intervals of six to ten inches.
Molds are so made that they may readily be detached and used
again. At least one side of the mold should also be in short
sections that may be put in place as needed, in order to facil-
itate placing the concrete. The molds should be set up verti-
cally with the longitudinal steel rods in position. Enough con-
crete is put in the molds to fill six to ten inches in length, when
a set of transverse tie rods or wires is placed, then another
layer of concrete, etc. The concrete, which is of Portland
cement, should be mixed rather wet, as thorough tamping is
difficult in the confined space. The piles should be provided
with a cast iron shoe at the bottom, or a steel plate covering
to protect the point. At the top, one of the main rods is bent
over to form a ring to facilitate handling the piles.
736. Driving. — When the concrete has hardened suffi-
ciently, say at the end of four to eight days, the mold should
be removed, and the pile allowed to remain in its original posi-
tion twenty to twenty-five days longer, sprinkling it occasionally.
When thoroughly set, they may be driven with an ordinary
pile driver, using a heavy hammer and short drop. A steam
hammer is preferred, however, and a special cap must be used
to prevent injury to the pile head. Such a special cap may
well be made of cast steel, fitting over the head of the pile
hke a helmet. The space between the lower end of the cap
and the side of the pile is calked with clay and rope yarn or
other suitable material. Through a hole provided in the top of
the helmet, the space between the pile and cap is then com-
488 CEMENT AND CONCRETE
pletely filled with dry sand. Such a cushion cap effectually
protects the pile head, distributing the pressure to the entire
head. Caps in the form of a steel ring filled with sawdust sur-
mounted by a wooden block, and also caps made of alternate
layers of lead, wood and iron plates have been successfully
used.
Art. 83. Arches
737. The use of concrete in the construction of arch bridges
is becoming so extended and diversified that it would require
a volume by itself to adequately cover the subject, 'and such
a treatment of it is well merited. All that can be attempted
here is to describe briefly one or two examples of well propor-
tioned arches, and to give a few hints on methods of design and
construction.
738. DESIGN. — Concrete arches may be built with or with-
out steel reinforcement, but for long spans concrete-steel is
usually employed. The design of a concrete arch without steel
is entirely similar to that of a stone masonry arch, except that
planes of weakness corresponding to joints between voussoirs
in a masonry arch, may be somewhat more arbitrarily arranged
in the former.
In fixed concrete-steel arches, the arch ring is continuous,
.and is capable of resisting a bending moment. The compu-
tations are therefore somewhat more complicated, and until the
:action of concrete and steel in combination has been more
(Carefully determined, it may be said, in the words of a promi-
;nent engineer, that "the development of the system of arches
'Of concrete must necessarily be largely based upon empirical
information coupled with sound judgment and work executed
with great care." ^ Fortunately, the saving effected by this con-
struction over a masonry arch is usually so great that it is
possible to use a large factor of ignorance, and it is to be hoped
that the use of concrete-steel for arches of long span will not be
given a serious check by the failure, perhaps under unforeseen
conditions, of some of the web-like structures that have been
built of it.
739. Where the span and rise of the arch are not fixed by
the local conditions, the comparative economy of different
» L. L. Buck, Trans. A. S. C. E., April, 1894.
ARCHES 489
arrangements and the appearance of the completed structure
must govern. Shortening the spans decreases the amount of
concrete required in the arches, but increases the pier work,
which is usually the most expensive part of the structure.
These points having been decided, the form to be given the
arch ring is next to be considered. While it is desirable that
the neutral axis of the arch ring should nearly correspond with
the Une of pressures for a full load, there is still considerable
choice allowed the designer as to the actual form to be given
the intrados without serious changes in the amount of material
required. As the semicircular arch can usually be adopted
for very short spans only, the choice must lie between the seg-
mental, the elliptical, and the polycentered arch approaching
more or less closely the ellipse, the parabola, or the transformed
catenary.
The segmental arch, the parabola and the catenary do not
give a pleasing effect at the junction of the arch ring and the
abutment, and the curve is sometimes departed from near the
springing to make the intrados tangent to the face of the abut-
ment. The final choice will thus usually lie between a true
ellipse and the basket-handled arch,
Mr. Edwin A. Thacher, M. Am. Soc. C. E., designer of the
Topeka bridge, considers that "arches with solid spandrel fill-
ing should be flat at the center and sharper at the ends, ap-
proaching an ellipse; while arches with open spandrel spaces
should be sharp at the center and flatter at the ends approach-
ing a parabola, or, which is better, sharp at the ends and center
and flat at the haunches." ^
The form of the intrados having been fixed, the depth of key-
stone for an arch without reinforcement is derived, tentatively,
from the rules of either Rankin or Trautwine, to be corrected
later if necessary. The form of the extrados is then so chosen
as to give the required depth of arch ring to confine the line of
pressure within the middle third.
740. Concrete-steel Arch. — The computation of a concrete-
steel arch is, as already stated, more involved. The graphical
analysis is much the simplest method of deriving the bending
moment, direct thrust and shear. The experience of Mr.
' Engineering News, Sept. 21, 1899.
490 CEMENT AND CONCRETE
Thacher has led him to endeavor to have the Hne of pressure lie
within the middle third of the arch ring, although this is not
absolutely necessary in reinforced concrete. The same author-
ity considers it good practice to design the steel work to be
capable of taking the entire bending moment with a unit stress
of about one-half the elastic limit of the steel.
The thrusts, bending moments and shears at successive sec-
tions of the arch ring having been determined, both for full
and half span loads, by the graphical methods explained in
Greene's "Arches" or Cain's "Elastic Arches," or by the analy-
sis given in Howe's "Treatise on Arches," the dimensions of the
arch ring and the steel reinforcement are to be derived by
the aid of such formulas as are given by Mr. Thacher^ involving
the allowable unit stresses in steel and concrete, and their
respective moduli of elasticity.
741. General Considerations. — In short spans, parallel
spandrel walls with earth filling between, may be used, but
for long spans the spandrels are usually op6n, that is, built
of vertical piers or walls running parallel to the axis of the
soffit, and arched over at the top to support the pavement or
ballast. This treatment has the following advantages: only
vertical forces are transmitted to the arch ring; decreased
loads on arch and abutments; increased waterway in case of
unusual floods; and better architectural effects.
The beauty of the structure is an important consideration,
inasmuch as the decision in favor of a concrete arch as against
a steel bridge is usually affected quite as much by considera-
tions of sesthetic effect as of cheapness and durability. In
this connection it may be said that in concrete-steel construc-
tion there may be little difference in the thickness of arch ring
required at the crown and near the springing, but the appear-
ance of the structure will usually be improved by accentuating
a little, if necessary, the increased thickness at the springing,
except in the case of the semicircular arch in which the eye is
accustomed to a nearly uniform thickness of the voussoirs.
The appearance is also frequently improved by molding the
concrete at the crown to represent a keystone, projecting a
little beyond the face of the rest of the arch ring.
* Engineering News, Sept. 21, 1899.
ARCHES 491
The beauty of a concrete arch may easily be marred by
faulty design, and some very ugly, as well as some very beau-
tiful, arches have been erected.
742. Stone Facing. — The practice which has been followed
to some extent of facing the spandrel walls with cut stone
masonry, is considered questionable. The cost of ashlar facing
is likely to be so great as to discourage the use of headers of
sufficient length to give a good bond with the concrete, and it
is next to impossible to make this equal to monolithic concrete
construction. Again, since concrete is frequently used to pro-
tect ashlar masonry that has started to disintegrate, it is rather
a reversal of what has been found good practice to face con-
crete with a thin layer of cut stone. No criticism is intended
of the method of building a pier of large dimension stone with
concrete hearting, as this is a diflferent matter. But a thin
parapet or spandrel wall faced with a mere shell of cut stone,
however beautiful it may be when built, is likely to take on a
somewhat dilapidated appearance after ten years' service, espe-
cially if it is called upon to pass through one or two floods of
unusual violence.
743. Quality of Concrete. — As already intimated, the cost
of a concrete arch, especially where reinforcement is used, is,
under ordinary circumstances, considerably less than a masonry
arch of equal appearance and strength. The only exceptions
to this rule are where the facilities for obtaining stone suitable
for masonry are exceptional, and where the work is far re-
moved from cement-producing regions and from the coast.
The ability to employ common labor for much of the construc-
tion work in a concrete arch is an advantage only partially
offset by the necessity of having somewhat more careful work
done upon the arch centers and more careful supervision of
construction.
The concrete of the arch ring should be of the best quality,
especially if steel reinforcement is not used. For this purpose,
the stone, broken to a size not exceeding two inches in any
dimension, should be mixed with a quantity of mortar a little
more than sufficient to till the voids, and composed of one part
Portland cement to two parts sand. Interiors of piers and
abutments may be made of a poorer mixture, such as one
Portland cement to three of sand and six of broken stone, or
492 CEMENT AND CONCRETE
even in some cases where abutments are massive, one to four
to eight concrete may be employed.
744. Centers. — Substantial centers must be provided for
concrete arches, and the lagging should be sized, dressed on the
upper side, and laid with radial joints parallel to the arch axis.
Two inch plank sized to one and three-quarters inches is usually
employed for lagging, and the supporting ribs should be from
three to four feet centers. For spans up to forty feet a braced
wooden rib with one center support and two end supports is
used, but for longer spans a trussed center with supports ten to
eighteen feet apart is employed. The centers should be made
rigid and the camber need be very slight, say from titVtt to
^^j} of the radius at the crown. Not less than twenty-eight
days should be allowed to elapse after building the arch before
striking the centers.
745. Construction. — A method that has been largely em-
ployed in building the arch ring is to divide the arch into lon-
gitudinal rings by planes at right angles to the arch axis. It
is believed to be better practice, however, to build the arch as
a series of voussoir courses beginning with the spring course,
but not necessarily proceeding in order from the springing to
the crown. The advantages of this method of building the
arch, in transverse courses parallel to the axis of the intrados,
are that the planes of weakness may be made at right angles
to the line of pressure; the unequal loading, and consequent
settlement of the centers, has less tendency to crack the sec-
tions or to separate one section from another. In cases of
failure of concrete arches under excessive floods, the tendency
of the arch to separate along a longitudinal joint forming a
plane of weakness has been clearly shown.
746. The tendency of the center to rise at the crown as the
arch ring is built up on the haunches is sometimes overcome by
temporarily loading the crown. In constructing the ring in
voussoir courses, the order of the work may be so arranged as
to distribute the loading on the centers in any manner desired.
Such an expedient was adopted in the construction of the
IlUnois Central R. R. arch across Big Muddy River, where the
arch ring was divided into nineteen voussoirs. The two spring-
ers were built first, then the fifth row of voussoirs towards the
crown on each side, followed by the ninth row, the third and
ARCHES 493
seventh. The intermediate blocks were then built in order
toward the crown, the second, fourth, sixth and eighth, and
finally the keystone. In this way the weight was well dis-
tributed on the centers, and the load on the two sides of the
crown was kept symmetrical. The monolithic blocks forming
the voussoirs that were built in molds had recesses on either
side, which were made by securing planks to the interior of
the mold. When the intermediate blocks were built, the con-
crete thus keyed into the blocks first made.
The division of the work into voussoir courses will usually
admit of such size molds or blocks that two, one on either side
of the center, may be completed in a day. If it becomes ne-
cessary to interrupt the laying of a block, however, a vertical
bulkhead should be constructed in the mold, with key or dowel
pins if desired, to assist in making a bond when the block is
completed.
747. Finish and Drainage. — To provide a smooth face, a
thin facing mortar of one part Portland to two parts sand is
desirable, laid at the time of building the concrete in accord-
ance with methods already described. A thicker layer of
granolithic may be used on the soffit and will somewhat more
effectually prevent the broken stone of the concrete settling on
the lagging, which is always likely to occur to the detriment
of the appearance of the finished work.
The division between adjacent voussoirs should be clearly
marked on the face, and additional joints may be indicated if
desired, by lines in a plane approximately perpendicular to the
line of pressure. Such lines are obtained by securing triangular
strips on the inner face of the molds. When spandrel walls are
used, these may be similarly marked on the face by horizontal
and vertical joints. On long spans the spandrels should have
expansion joints, and the coping and parapet, when of concrete,
should also have vertical joints to provide for changes in length
due to loading or thermal variations.
The arches over the spandrels should be provided with a
waterproof covering, either of Portland cement grout or an
asphalt mixture to prevent the percolation of water to the arch
ring. Pipe drains should be provided to carry the water to a
point over the piers where it may be discharged. Care should
be taken that such pipes have their outlets so located that the
492 CEMENT AND CONCRETE
even in some cases where abutments are massive, one to four
to eight concrete may be employed.
744. Centers. — Substantial centers must be provided for
concrete arches, and the lagging should be sized, dressed on the
upper side, and laid with radial joints parallel to the arch axis.
Two inch plank sized to one and three-quarters inches is usually
employed for lagging, and the supporting ribs should be from
three to four feet centers. For spans up to forty feet a braced
wooden rib with one center support and two end supports is
used, but for longer spans a trussed center with supports ten to
eighteen feet apart is employed. The centers should be made
rigid and the camber need be very slight, say from -rirV^ to
5^5 of the radius at the crown. Not less than twenty-eight
days should be allowed to elapse after building the arch before
striking the centers.
745. Construction. — A method that has been largely em-
ployed in building the arch ring is to divide the arch into lon-
gitudinal rings by planes at right angles to the arch axis. It
is believed to be better practice, however, to build the arch as
a series of voussoir courses beginning with the spring course,
but not necessarily proceeding in order from the springing to
the crown. The advantages of this method of building the
arch, in transverse courses parallel to the axis of the intrados,
are that the planes of weakness may be made at right angles
to the line of pressure; the unequal loading, and consequent
settlement of the centers, has less tendency to crack the sec-
tions or to separate one section from another. In cases of
failure of concrete arches under excessive floods, the tendency
of the arch to separate along a longitudinal joint forming a
plane of weakness has been clearly shown.
746. The tendency of the center to rise at the crown as the
arch ring is built up on the haunches is sometimes overcome by
temporarily loading the crown. In constructing the ring in
voussoir courses, the order of the work may be so arranged as
to distribute the loading on the centers in any manner desired.
Such an expedient was adopted in the construction of the
lUinois Central R. R. arch across Big Muddy River, where the
arch ring was divided into nineteen voussoirs. The two spring-
ers were built first, then the fifth row of voussoirs towards the
crown on each side, followed by the ninth row, the third and
ARCHES 493
seventh. The intermediate blocks were then built in order
toward the crown, the second, fourth, sixth and eighth, and
finally the keystone. In this way the weight was well dis-
tributed on the centers, and the load on the two sides of the
crown was kept symmetrical. The monolithic blocks forming
the voussoirs that were built in molds had recesses on either
side, which were made by securing planks to the interior of
the mold. When the intermediate blocks were built, the con-
crete thus keyed into the blocks first made.
The division of the work into voussoir courses will usually
admit of such size molds or blocks that two, one on either side
of the center, may be completed in a day. If it becomes ne-
cessary to interrupt the laying of a block, however, a vertical
bulkhead should be constructed in the mold, with key or dowel
pins if desired, to assist in making a bond when the block is
completed.
747. Finish and Drainage. — To provide a smpoth face, a
thin facing mortar of one part Portland to two parts sand is
desirable, laid at the time of building the concrete in accord-
ance with methods already described. A thicker layer of
granolithic may be used on the soffit and will somewhat more
effectually prevent the broken stone of the concrete settling on
the lagging, which is always likely to occur to the detriment
of the appearance of the finished work.
The division between adjacent voussoirs should be clearly
marked on the face, and additional joints may be indicated if
desired, by lines in a plane approximately perpendicular to the
line of pressure. Such lines are obtained by securing triangular
strips on the inner face of the molds. When spandrel walls are
used, these may be similarly marked on the face by horizontal
and vertical joints. On long spans the spandrels should have
expansion joints, and the coping and parapet, when of concrete,
should also have vertical joints to provide for changes in length
due to loading or thermal variations.
The arches over the spandrels should be provided with a
waterproof covering, either of Portland cement grout or an
asphalt mixture to prevent the percolation of water to the arch
ring. Pipe drains should be provided to carry the water to a
point over the piers where it may be discharged. Care should
be taken that such pipes have their outlets so located that the
496 CEMENT AND CONCRETE
in the clear, with 30 feet rise above springing Unes. The arch
ring proper is five feet thick at the crown, but as the spandrels,
which are built open over the haunches, have near the crown
only a false opening on the face, the actual thickness of concrete
at the crown is seven feet.
The piers and abutments already in place for the three
Pratt trusses formerly in use, were surrounded with new con-
crete masonry, making the piers 21 ft. 6 in. wide at the top.
As rock was found only at considerable depth, the piers rested
on piles. To relieve the load on foundations as much as possible,
as well as to avoid cracking, which would be likely to occur in
heavy longitudinal spandrel walls from temperature strains,
transverse spandrel arches were adopted. Since in case of de-
railment of trains these spandrel arches would be subjected to
shock, the concrete in this portion of the structure was rein-
forced by a self-supporting skeleton structure built of steel
rails. Longitudinal rails were laid horizontally, three feet
center to center, connected at frequent intervals by one inch
rods and held in place by vertical posts, which in turn rested
upon transverse horizontal rails laid in recesses left in the arch
rib.
752. Expansion joints were provided in the spandrel arches
at the ends, two at each pier and one at each abutment, to al-
low some movement due to changes in temperature. The ex-
pansion joints were made by placing in the joint several thick-
nesses of corrugated asbestos board protected by a ^-inch lead
plate folded into the joint, forming a trough at the top. The
lead plate lies flat on top of the concrete for five inches from
the joint, and about two inches at each end of the plate is bent
down at right angles and set into the concrete. An asphaltic
composition is then laid over the lead plate, entirely covering
it and filling the trough.
The centering was erected on pile bents spaced about 14
feet centers, the calculated pressure on each pile being about
eighteen to twenty tons. For the center span, five 60 foot
deck plate girders resting on pile piers were used over the deep-
est portion of the channel to provide for possible floods bring-
ing large amounts of drift.
753. The arch ring was laid in voussoir courses as described
in § 746. Face joints were made by securing triangular shaped
ARCHES 497
pieces to inner face of the molds in lines approximately at
right angles to the line of pressure. All exposed work was
faced with a layer of about 1^ inches of Portland cement mortar
placed and rammed with the concrete. The surfaces were not
given, in general, any further finish, no attempt being made to
remove or conceal the usual marks left by the mold boards.
Portland cement was used throughout, the quaUty of the
concrete being varied by the amount of cement used to given
quantities of the aggregates. In the centers of large masses
the poorer mixtures were employed, while the richer concretes
were used in those places subjected to the most trying conditions.
In making the concrete the principle followed seems to have
been to keep the mixer as near the work as practicable, moving
the mixer and carrying materials to it, rather than to transport
the mixed concrete from a certain fixed location of the mixing
plant. Much of the concrete was handled in barrows, but
derricks were also used in portions of the work. As traffic on
the old bridge had to be maintained during the erection of the
new structure, considerable extra handling of concrete was
necessary and additional work was involved in ramming the con-
crete in places difficult of access. The concrete was mixed rather
wet, so that but little tamping was required to make it quake.
754. Cost. — The total amount of concrete was over 12,000
cubic yards, which was placed at an average cost of $5.43 per
cubic yard. In cofferdams and centers 400,000 feet B. M. of
timber was used, and about 300,000 pounds of steel was em-
ployed in the skeleton structure of the spandrels. This steel
cost 1.2 cents per pound, the punching, fitting and erecting
costing but about 0.61 cent per pound. The total cost of the
bridge is estimated to have been $125,000.00, or about the
same as the estimated cost of a steel structure designed for
the same duty.
755. The Melan Arch Bridge at Topeka, Kan., is one of the
most important concrete-steel structures yet erected in the
United States. It consists of one span of 125 feet, two of
110 feet each, and two of 97.5 feet each. The foundations for
piers and abutments are piles in soft sand. The steel rein-
forcement is in the form of a latticed member. The bridge is
fully described in Engineering News of April 2, 1896, and En-
gineering Record, April 16, 1898.
498 , CEMENT AND CONCRETE
756. Concrete-Steel Viaduct. — A viaduct of ten concrete-
steel arches, of about 65 foot span, carries a double track elec-
tric line across West Canada Creek near Herkimer, N. Y.' The
piers rest on piles driven into hard blue clay, the surface of
which is 6 to 12 feet below the creek bed. The segmental
arches have a rise of 12 to 14 feet, with thickness of 21 inches
at the crown and 4^ feet at the springing; the radius of intrados
is about 46 feet, and of extrados about 57 feet. The stresses
were computed for full load and for live load on half span.
Prof. Cain's graphical method being employed. The maximum
stresses allowed were six hundred pounds per square inch com-
pression in concrete and ten thousand pounds per square inch
tension in steel. The stresses caused by a variation of fifty
degrees in temperature were allowed for. The tensile strength
of the concrete was disregarded. Thacher bars, 1^ inches dia-
meter, were used for the reinforcement, being placed eleven
inch centers near both intrados and extrados.
757. Expansion joints were provided in spandrel walls by
nailing to the sides of the forms for arch pilasters a narrow
strip of timber, thus forming a groove into which the spandrel
wall is tongued. These joints show some motion and allow
some water to leak through.
The concrete was mixed three parts sand and seven parts
gravel to one volume packed cement for foundations and piers,
and two and one-half parts sand and five of gravel to one ce-
ment for the arch rings and spandrel walls. All concrete was
mixed wet and by hand. The work was faced with mortar
composed of one part cement to two and one-half parts sand,
and after the removal of forms the face was brushed with thin
mortar wash and rubbed with sandstone blocks, giving a uni-
form color to the surface.
Art. 84. Dams
758. Concrete vs. Rubble. — Concrete has been employed to
some extent in most of the important masonry dams of recent
construction, and has formed the main portion of some of the
largest dams yet built.
The relative value of concrete and uncoursed rubble masonry
' Engineering News, Feb. 27, 1904.
DAMS 499
laid in Portland cement mortar is perhaps still an open ques-
tion, though it is believed that the former will eventually be
preferred by engineers who are familiar with both. Concrete
will require in general a larger proportion of cement than does
the masonry, so that in localities difficult of access, the ma-
sonry may for this reason be cheaper. Usually, however, con-
crete will be the cheaper, and less skilled labor will be required
in the building. With the same amount of inspection, concrete
of good materials properly proportioned will form at least as
impervious a wall as will rubble.
759. Quality of Concrete. — The up-stream face of the dam
should be made as nearly water-tight as possible, and therefore
a rich concrete employed in which the mortar is in excess of
the voids in the stone, and the mortar itself contains about
two parts sand to one cement. The body of the wall, however,
may be made of a poorer mixture, one to three to six usually
being sufficient. Bowlders may also be imbedded in the mass
to cheapen the concrete without any serious detriment. Such
bowlders should, of course, be sound and clean, and well wet
before being placed. They should be kept well back from the
face of the wall and should be separated one from another by
at least six inches, to allow of thoroughly tamping the concrete
between them.
760. Building in Sections. — In a wall of rubble the con-
traction and expansion are taken care of by minute cracks
between the stone and mortar which frequently are not notice-
able. In a concrete wall, unless provision is made for this,
these signs of movement may be concentrated in cracks at in-
tervals of thirty to sixty feet; these are always unsightly, and
may in exceptional cases be a serious defect. The remedy
evidently lies in so building the dam that if these cracks appear,
they shall be confined to predetermined planes where they will
not do any serious harm. Such contraction cracks will be
very much less likely to occur in a dam arched in plan than
in a straight dam, since in the former a slight movement of the
masonry up or down stream changes the length of the wall
and relieves the tension strains.
761. Joints. — The joints in a concrete dam should not be
unbroken planes for any great distance. That is, the concrete
should be so placed that the joints between work of different
500 CEMENT AND CONCRETE
days are not planes extending through the wall. The wall
may well be kept higher on the down-stream side and step down
toward the up-stream side. The vertical joints should also be
broken by right-angled oflf-sets, but the wisdom of using a dove-
tail joint in such work is very questionable. The joining of
one day's work to another necessarily forms a plane of weak-
ness, and therefore the work should be carefully planned to
the end that these planes shall be, in direction and location,
where they will not unnecessarily weaken the structure or render
it pervious to water.
762. Examples: St. Croix Dam. — A dam at St. Croix, Wis.,^
was built of sandstone masonry of uncoursed rubble in one-to-
three mortar, and faced with concrete of one Portland cement
to three parts sand to four parts broken stone of 1 to 3^ inch
size. The concrete was rammed in place between the stone-
work and the concrete forms. The selection of the uncoursed
rubble was probably made on account of the site being five
miles from the railway and the consequent difficulty of getting
cement. The dam was arched in plan, and in preparing the
foundation, several grooves or trenches were cut in the rock in
a longitudinal direction, to avoid, as usual, a through course at
the bottom, and these trenches were also filled with concrete.
Had the concrete for the facing contained five parts of broken
stone having maximum size of 2 or 2^ inches, it would have
been more nearly in conformity with the best practice.
763. Massena Dam. — In the construction of the dam at the
forebay of the Massena Water Power Company, Massena, N.Y.,^
it was sought to take up the tension stresses due to contrac-
tion by imbedding in a longitudinal direction in the concrete,
T-rails two feet apart horizontally and four feet apart ver-
tically,
764. Butte Dam. — The dam built in connection with the
Butte, Montana, water system is 120 feet high, 350 feet long,
10 feet wide at the top and 83 feet wide at the 120 foot point.
The bed rock was granite, which was first covered with four
inches of concrete made with small sized stone. In the body
of the dam, granite bowlders were thickly imbedded in the
* Engineering News, June 13, 1901.
* Engineering News, Feb. 21, 1901.
DAMS 501
concrete, care being taken that each bowlder was entirely en-
veloped in concrete and that there were no horizontal or nearly
horizontal courses either of concrete or bowlders.
765. San Mateo Dam. — The San Mateo Dam of California,
one of the highest dams in existence, is built entirely of concrete,
170 feet high. It is 126 feet thick at the base and is arched up-
stream with a radius of 637 feet. The dam was constructed in
blocks of 200 to 300 cubic yards each, of irregular heights, so as
to bond the courses together and have no through joints. Con-
crete, one, two to six, was delivered in small push cars on a
high trestle over the dam, and was dropped through iron pipes
16 inches in diameter to the place of deposition. In some
cases this drop was 120 feet, and it is stated that the concrete
appeared not to be injured by this method of handling.
766. Barossa Dam. — The Barossa Dam in South Aus-
tralia Ms of a bold arch design. The arch has a radius of 200
feet, and the chord is 370 feet subtending an angle of 135 degrees,
20 minutes, and the length of the arc 472 feet. The height of
the dam is 94 feet above the ground line, yet the greatest thick-
ness above the foundation is only 34 feet, with a top width of
only 4^ feet.
Special care was taken in selecting the materials and fixing
the proportions. The cement was aerated fourteen days before
use. Test cubes of concrete two feet on a side were prepared
with different proportions of materials and subjected to a
hydrostatic pressure of two hundred feet before deciding upon
the proportions to use in the concrete. As a result of these
tests, the aggregate was made up of one part screenings ^ to
^ inch, two parts "nuts" ^ to 1^ inch, and four and one-half
parts "metal" 1^ to 2 inch. This mixture contained about 35
per cent, voids. The mortar was made of one part Portland
cement to one and one-half parts sand, and was from seven and
one-half to fifteen per cent, in excess of voids in aggregate.
Plumbs were used in the dam to within fifteen feet of the top,
and above this level iron tram rails were placed in string courses.
The success accompanying the use of concrete in structures of
this magnitude is sufficient evidence of its value and adapta-
bility.
Mr. A. B. Moncrieff, Engineer in Chief, Engineering News, April 7, 1904.
602 CEMENT AND CONCRETE
Art. 85. Locks
767. The use of concrete in the construction of canal locks
is comparatively recent, but it has met with much favor, and
its use is extending. The requirements for a lock wall are that
it shall be reasonably water-tight, that its strength shall be
sufficient to withstand the thrust of the gates and support the
earth filling behind it (or in a river wall, the difference in water
pressure on the two sides), and that it shall withstand the
impact and abrading action of boats using the canal. In all
of these respects concrete is believed to be the equal of a good
class of stone masonry. At St. Marys Falls Canal, portions
of the lock walls which have been injured by boats and re-
paired with concrete have given entire satisfaction, although
in such cases the concrete had to be patched on, and some-
times in places difficult of access for work of this character.
768. Methods of Building. — The present accepted method
of concrete lock construction is to build the walls in alternate
sections, filling in the intermediate sections after the others
have set. It is sometimes thought necessary to make the
work on a section continuous from time of starting the con-
creting to its completion. That the exterior appearance of the
work may be somewhat better if such a course is followed, is
true, but it is very questionable whether the attainment of this
desirable result is worth the additional expense and the addi-
tional liability of having poor work done under the cover of
darkness when work at night is necessitated by such a rule.
With proper precautions, such as making steps in the top
surface of work left for the night, as already detailed elsewhere,
and being careful that the limit of work on exposed faces is
bounded by true horizontal and vertical lines, the plane of
weakness occasioned by a horizontal joint extending only par-
tially through the work cannot be a serious defect in a con-
crete wall.
769. The molds, so far as the walls alone are concerned, are
comparatively simple and have already been described under
the head of forms (Art. 62). Cable passages, gate recesses,
hollow quoins, culverts, etc., call for special carpentry work,
sometimes of quite intricate character. While the efficiency of
the machinery and the lock as a whole should not be sacrificed
LOCKS 503
to obtain easy construction, yet sharp corners should always
be avoided, and simpUcity of outline should be the constant
aim. Linings of hollow quoins (when steel quoins are consid-
ered necessary), gate anchorages, cable sheaves and other parts
built into the masonry, are in general placed with greater
difficulty in concrete forms than in stone masonry. Aside from
such special constructions, the walls may be built up much
more rapidly of concrete than of stonework.
As to the proportions to be used in concrete for locks there
is no rule of thumb. As a guide, the stresses in each part of
the structure should be determined as well as the knowledge of
the forces will permit, but the proportions will depend on the
question of water-tightness and freedom from deterioration quite
as much as upon required strength. It may be said, however,
that in a considerable portion of the cross-section of the walls,
weight is the main consideration and the concrete need not be
very rich. The concrete surrounding the culvert, however,
should be of good quality, as the stresses which may be devel-
oped here do not admit of close analysis.
770. The walls should be faced with mortar made of one
and one-half or two parts sand, or, better, two parts of granite
screenings one-half inch and smaller, to one part of the same
kind of cement used in the body of the concrete. This facing
need not be more than three inches thick, and if made of sand
and cement, it will probably be better if not more than one inch
thick, though this may depend on the materials and local con-
ditions. In any case this facing should be laid with the con-
crete by means of a removable steel plate similar to that de-
scribed in § 528. The top of the wall should be finished with
mortar or granolithic similar to a concrete walk or driveway.
While the walls should in general have a vertical face, a slight
batter is allowable at the top, starting at about upper pool level,
to protect the concrete from being chipped by the impact of
boats, and for a similar purpose the outer corner of the wall
should be rounded with six to twelve inch radius.
Special care must be taken in lining the culverts, particularly
in silt-bearing streams, and in such places as a change is made
in the direction of the flowing water. For high heads it may
be necessary to line the culverts with cast iron for a portion of
their length. Granite and hard burned bricks have also been
504 CEMENT AND CONCRETE
used for this purpose, but in locks of moderate lift, granolithic
lining will usually be found sufficiently resistant.
All necessary irons and bolts should be built into the masonry
as the work progresses, as they will be much more secure than
if set later in recesses left for them.
771. Cascades Lock. — The large lock in the canal at the
Cascades of the Columbia was one of the first in the United
States to be designed of concrete in this country. In this lock
the walls, wells, copings and portions of culverts were faced
with stone. The foundation rock was covered with eight inches
of rich concrete, one part Portland cement, two parts sand to
four parts gravel. Fourteen feet of the chamber walls and
ten feet of gate abutments or wide walls were of concrete, one
to three to six, while balance of masonry was of one to four to
eight concrete.
The molds were of four by six posts four feet apart, and
lagging of two-inch lumber, dressed to size for exposed faces.
The work was carried up in horizontal layers, not more than
two feet being placed in one day. The set concrete was picked
and washed when fresh concrete was to be laid upon it so as to
get as good a bond as possible. The inlet pipes to the turbines
to operate the machinery were built in the lock walls, and as it
was not desirable to place an iron pipe in this location, the pipe
was molded of concrete and afterwards laid in the wall. The
pipe was thirty-nine inches diameter, walls six inches thick and
contained, about 0.22 cubic yard of concrete per foot. It was
made in three foot lengths in vertical molds, and the cost of
about six hundred feet of it was at the rate of $3.56 per foot,
or $16.19 per cubic yard.
772. Hennepin Canal. — In the locks for the Illinois and
Mississippi Canal the walls are entirely of concrete, and were
built in alternate sections about thirty feet long. Work on a
given section once commenced was continued to completion
without intermission. The top was finished without any plas-
ter or wet coat, the excess concrete being simply cut off with
a straight edge and rubbed smooth and hard with a float.
Vertical wells one foot square were left in the walls at intervals,
and these were kept filled with water for about three weeks
after the completion of the section, and then filled with concrete.
To avoid weak places due to single batches made from cement
LOCKS 505
of poor quality which might have passed inspection, the ce-
ment was mixed in lots of five to ten barrels before being used
in the concrete.
The quoins of these locks were of cast iron. The founda-
tions and the spaces in rear of lock walls are cut off from upper
pool by cross-walls, and are underdrained to the lower pool to
prevent the action of water pressure due to the upper pool
level tending to force up the foundation. Ten inch and twelve
inch tile drains were used for this purpose.
The proportions used in general were one part Portland
cement, three to three and one-third parts gravel, and four
parts broken stone, the concrete containing about one and four-
tenths barrels of cement per yard. The average cost of con-
crete in quantities of two thousand to four thousand yards was
from $8.50 to $9.15 per cubic yard, distributed approximately
as follows : —
Materials $5.00 to $6.00
Molds 82 to 1.42
Mixing and placing 1.64 to 1.82
Miscellaneous 12 to .47
773. Herr Island. — In the Herr Island Locks, Alleghany
River, the failure of the cofferdam to exclude water from the
lock pit on account of porosity of the river bed, led to the adop-
tion of a concrete foundation, laid under water, of sufficient
weight to balance the hydrostatic pressure. After this founda-
tion was in place, the cofferdam was pumped out and the con-
crete side walls built in the dry.
The concrete was placed in one foot courses covering the
entire area of the wall, the forms being made of one course of
two by twelve inch plaiik set on edge and halved at the ends
to form two inch lap splices. Iron rods one-quarter inch diam-
eter were placed six feet eight inches apart to tie face and
back plank together. A two by twelve inch cross-plank was
placed on edge beside each tie rod, dividing the work into short
sections. After completing the concreting to the top of the
forms throughout, the cross-planks were removed and the space
filled with concrete, thus making a vertical joint. The forms
for the next course were then put in place in a similar manner.
The size of stone used as aggregate was first two inches in one
dimension, but this size was afterward reduced to one and
606 CEMENT AND CONCRETE
one-half inches, and finally to one inch, the smaller size stone
being preferred.
774. Mississippi River. — The lock in the Mississippi Rivei
between Minneapolis and St. Paul was founded on a soft sand-
stone rock having many water-bearing seams. The lock was
surrounded on three sides by a cut-off wall. A trench two
inches wide and ten feet deep was cut in the soft rock by jet-
ting a series of holes in close juxtaposition and then breaking
out the intervening wall with a drill and saw of special con-
struction. In this trench was first laid a double thickness of
three-quarter inch boards and the remaining space was grouted
full. Sections of this wall afterward uncovered, showed the
method to have been very effective. Similar methods of seal-
ing open seams in rock by the use of grout under pressures
have been used elsewhere.
The forms for the construction of this lock were of excellent
design^ and have been described under the head of "forms"
(§ 514). The walls were built in alternate blocks, twelve feet
long. At the ends of the blocks are left vertical spaces five by
seven inches, to be filled with mortar and other water-tight
composition. The forms are lined with sheet iron, and to
obtain a smooth face the concrete is thrown against the lining,
the stones rebound, leaving only mortar on the face. The
face is rammed with tampers of special form, wedge shaped,
and measuring | inch by 5 inches on the lower edge. This is
followed by a flat rammer. The finish is said to be excellent.
775. Sand-cement was used quite largely in the lock con-
struction. It was prepared at the site of the work, of equal
parts Portland cement and siliceous sand ground together in a
tube mill.
Proportions in the concrete were varied somewhat from time
to time, though in general it was mixed one part silica cement,
two and one-third parts sand and six and two-thirds parts of
crushed stone without screening. Tests showed that about ten
per cent, of this crusher product was fine enough to be consid-
ered sand, and account of this fact was taken in fixing the pro-
portions as above. The cost of the concrete, over 11,000 yards,
was as follows: —
Mr. A. O. Powell, Asst. Engr., RejtoH Chief of Engrs., 1900, p. 2778.
BREAKWATERS
Cement
$1.29
.38
.82
$2.76
$2.49
.52
Stone
Breaking stone for crusher . . .
Crushing stone
Total stone
Sand
Total materials
$5.77
Forms
1.21
Mixing and placing concrete . .
concrete .
1.44
Total cost per cubic yard
$8.42
507
Art. 86. Breakwaters
776. The use of concrete in the construction of breakwaters
in the United States was suggested as early as 1845. In recent
years it has been employed quite extensively, especially for
harbor improvements on the Great Lakes, where it has with-
stood the rigorous winters, the severe storms, the attrition of
ice, and the impact of boats, in a highly satisfactory manner.
Its use has been confined largely to the construction of a super-
structure on timber cribs, the concrete work being in the form
of blocks set with derricks, or of monolithic blocks molded in
place, or more frequently composed of a combination of these
two forms.
Since in breakwater construction weight is of prime impor-
tance, it is not necessary, in general, to use an exceptionally
strong concrete, as the increased expense had better be in-
curred in increasing the cross-section.
777. Buflfalo Breakwater. — In the construction of the ex-
tensive breakwaters at Buffalo,* concrete has been used in large
quantities and according to various plans. In 1887 the super-
structure of some 750 feet of timber-crib breakwater was re-
newed, mainly with natural cement concrete. 250 feet of this
superstructure was built with a facing of Portland cement
concrete, while 500 feet of it was faced with stone masonry.
The concrete started two feet below mean lake level. The
cross-section of the superstructure was about 350 square feet,
and the cost of concrete, exclusive of materials, was about $2.36
per cubic yard.
' Described by Mr. Emile Low, U. S. Asst. Engr. Trans. Am. Soc. C. E.,
December, 1903.
508 CEMENT AND CONCRETE
During the following year concrete footing blocks were used
on both the lake and harbor faces, since it was found that the
cement was washed out of the concrete laid in place below
water. The blocks contained about 3^ cubic yards and cost on
the average a little more than $30.00 each, or $37.35 each in-
cluding the setting, or at the rate of $11.29 per cubic yard.
The molds or forms, which were used repeatedly, cost about
$40.00 each.
778. Another style of concrete superstructure developed at
Buffalo is that recommended by Major F. W. Symons. It
consists of three longitudinal walls, connected at intervals by
cross-walls, filled between with rubble stone and provided with
heavy parapet and banquette decks. The longitudinal wall on
the lake side is founded on heavy concrete blocks 5 feet high,
8 feet thick at the base and 7.2 feet long ; the two minor walls
are formed by smaller blocks, 4 feet by 4.5 feet by 12 feet.
The total width at base is 36 feet. The space between lake face
blocks and center row is 14 feet, and between center row and
harbor face blocks is about 5 feet. The cross-wall blocks are
7 by 6 by 4 feet under the parapet, and 4 by 3 by 4 feet under
the banquette, all spaced 36 feet centers. All concrete blocks
have their bases set two feet below mean lake level and have
panels in their upper surfaces to provide a bond with the
concrete laid in place.
The lake wall above the concrete block is 8 to 4 feet thick,
with batter on face, and the decks are 3 to 4 feet thick, built of
concrete in place. The forms for the harbor face wall and cross-
walls were of | inch matched pine, with vertical posts two to
three feet centers tied through the wall with one-half inch tie
rods.
The concrete was composed of the following volumes: one
part Portland cement, one part screened gravel (about | inch),
two parts sand grit (nearly half of which was ^ inch to \ inch
gravel), and four parts unscreened broken limestone (about 11
per cent. dust). The cost of the concrete in blocks was $10.00
per cubic yard, and that in place cost $9.40 per cubic yard.
779. Cleveland Breakwater. — Several forms of concrete su-
perstructure have been employed in the work at the Cleve-
land breakwater. One section on a thirty-two foot crib has
three rows of concrete blocks, one each on lake and harbor
BREAKWATERS 509
sides and one in center of the crib, extending three feet below
mean lake level. The concrete in place is started at mean lake
level and is composed of a base five feet thick, with vertical
faces over the entire crib, and surmounted on the lake side by
a parapet five feet high and about twelve feet wide. The stone
filling of the cribs was covered with a cheap decking of wood
before laying the concrete in place.
780. Marquette Breakwater. — In the construction of the
superstructure of the breakwater at Marquette, Mich., the con-
ditions were peculiar in that it was desirable to provide a pas-
sageway within the superstructure through which the lighthouse
on the outer end might be reached in stormy weather. This
was accomplished by leaving near the harbor face a conduit,
6 feet 3 inches high and 2 feet 10 inches wide, the entire length
of the structure.
The old timber structure having been removed to about one
foot below mean lake level, a foundation course two feet thick
of Portland cement concrete was laid on a burlap carpet placed
over the stone filling of the crib. Upon this the monolithic
blocks were built in place, substantial molds being set up for
alternate blocks ten feet apart. After these had set, the molds
were removed and other molds set up to form the two faces of
the intervening blocks, the ends of the blocks already com-
pleted taking the place of end molds. The monolithic blocks
were of natural cement concrete in proportions of 489 pounds
of cement to one-half cubic yard of sand and one cubic yard of
broken stone. About twenty per cent, of these monoliths was
composed of rubble stone ranging in size from one-half to three
cubic feet, care being taken that no rubble should be placed
nearer than one foot to any outside surface. The standard
block was twenty-three feet wide on the base, which was one
foot above mean lake level. The lower five feet of the face had
a 45° slope. There was then a nearly level berm, 7.5 feet wide,
forming the banquette deck; from the back of this deck the
face sloped at an angle of 45° to the parapet deck, which was
6 ft. 4 inches wide. The harbor side of the block was vertical,
9.4 feet high. Since the structure proved very stable and free
from vibrations in heavy seas, the horizontal dimensions of the
block were reduced as the shore was approached.
781. The method of placing the Portland cement concrete
510 CEMENT AND CONCRETE
foundation was modified as described under the head of the
block and bag systems of concrete constructions (Art. 64).
The cost of the monolithic blocks of natural cement concrete
was as follows: —
490 lbs. cement, $1.04 per bbl $1,815
.5 cu. yd. sand, $0.50 per cu. yd .25
l.Ocu.yd. stone, $1.58 " " " 1.58
Materials in one cubic yard concrete $3,645
80 per cent, concrete in the finished block, .80 of
$3,645 $2.91
Loading materials .33
Mixing concrete .52
Depositing concrete .41
Handling rubble .09
Finishing blocks .09
Moving and setting forms .25
Timber waling, anchor bolts, etc .13
Total cost in place per cu. yd $4.73
Very interesting and detailed accounts of the construction
of this breakwater, which was carried out with special care as
to all details, were made by Mr. Clarence Coleman, Asst. Engr.,
and may be found in the reports of Major Clinton B. Sears,
Reports Chief of Engineers, U. S. A., 1896 and 1897.
CHAPTER XXIII
CONCRETE BUILDING BLOCKS, THEIR MANUFACTURE
AND USE
782. History. — Concrete building blocks are formed by
molding plastic mortar or concrete into shapes resembling blocks
of stone used in building construction. The blocks are usually
hollow, but certain special pieces, such as sills and lintels, are
frequently made solid, and in other cases the blocks for the body
of the wall are in themselves solid, but of such form as to make
a hollow wall when laid.
The manufacture of such blocks for use in the construction of
buildings has recently had such a remarkable development,
winning for itself a place as a new industry, that we are wont to
regard the method as a very recent invention. In fact, however,
it is the result of a natural evolution in the application of con-
crete, although the present generation may justly claim credit
for its development. The building of a concrete mass within a
timber form, and the use of concrete for the backing of a wall
laid in stone or brick, apparently suggested the idea of replac-
ing the wood, which has to be removed, or the expensive stone
facing, by a wall built up of concrete blocks which should form
a part of the completed structure. To omit the concrete backing
entirely and to make the blocks hollow for greater ease in set-
ting, were short steps to the modern hollow concrete block.
A patent for a hollow concrete block to be used as a form for
mass concrete was granted in England in 1850, and although the
inventor contemplated filling the block with plastic mortgir after
it was in place, yet it shows the application of the idea. In
1866, 1868, and 1874 patents were granted in the United States
to C. S. Hutchinson, T. J. Lowry, and T. B. Rhodes, respectively,
on forms of hollow block which strongly resemble the blocks
made under more recent patents and certainly involve the main
principle of such construction. Although some of the com-
panies furnishing concrete block molds make broad claims for
511
512 CEMENT AND CONCRETE
their patents, the fact that suits for infringement do not appear
to be vigorously pressed indicates a lack of faith in these claims.
Although it is very questionable whether the general principle
of making hollow concrete blocks is now covered by valid patents,
certain special features of blocks and molds undoubtedly
are so covered, and one^who contemplates going into the busi-
ness of manufacturing them should assure himself that the
machine or method he pays for has not a lawsuit attachment.
For a brief account of the main features covered by the patents
of some of the best known types of block, the reader is referred
to the paper by Mr. Wm, M. Torrance, published in " Engineer-
ing News " of Oct. 12, 1905, and " The Cement Age " of Novem-
ber, 1905.
Art. 87. General Methods of Manufacture
783. The apparatus used in making concrete blocks is called a
machine, although in its essentials it is merely a mold, and be-
comes a machine only because of the appliances provided to
facilitate the removal of the concrete, or rather in the removal of
the mold from the concrete block and resetting it to be filled
again.
There are three general methods of making concrete blocks,
depending upon the consistency of the mixture and consequent
method of compacting the mortar or concrete:
1st. Mortar or concrete only slightly moist, and compacted
by tamping.
2d. Mortar or concrete of medium consistency, and com-
pacted by pressure.
3d. Mortar or concrete mixed wet, and poured into molds.
It has been seen that in places where thorough tamping is
possible, a rather dry mortar or concrete will give the highest
strength in tension, but that in tests of adhesion and com-
pressioji a mixture containing more moisture gives higher results.
See §§ 278, 360, 425, 445, and 518. Mortar of the consistency
of moist earth contains sufficient water for the necessary chemi-
cal reactions if not permitted to dry out in the setting and the
early stages of hardening. The advantage of a greater amount
of water comes then from physical causes. Mortar that is fairly
dry can be well tamped and give good results, but place broken
stone in the same mixture, and the mass is likely to " bridge "
CONCRETE BLOCKS: MANUFACTURE
513
and cannot be so well compacted. More water lubricates the
mixture and insures close contact of mortar and stone at all
points. Strength is not, however, the only requisite in con-
crete blocks; impermeability, or the quality of being " water-
proof," is also essential for the best results. It has been stated
in Art. 61 that mortars mixed either very wet or very dry are
more permeable, less waterproof, than those of ordinary con-
sistency, but since in the case of concrete large voids are likely
to result from insufficient tamping, an excess of water is better
than a deficiency. A rather free use of water thus tends to
prevent the occurrence of large voids, but results in a larger
number of small voids through which water does not easily
permeate.
784. TAMPED BLOCKS. — This method was the first to
come into prominence in the manufacture of concrete blocks,
UPRIGHT MACmNE FOR TAMPED BLOCKS
and is ftow in general use. The ordinary machine used in this
method consists of a heavy base plate supported by a frame
bringing the plate to a convenient height. The plates to form the
ends and sides of the block are movable, usually on hinges, and
514 CEMENT AND CONCRETE
are drawn away from the blqck, after the molding is completed^-
by moving a lever or crank. The cores are likewise withdrawn
from the block after molding, either by raising or lowering the
cores, or by raising the completed block. The block is removed
from the machine on a pallet of iron or wood, and is set away to
" cure " or harden.
The block may be molded upright or with face down. If the
former, the pallet is set on the base plate and the cores are
either inserted tlirough holes in the pallet or lowered into
the mold from above. If the block is molded face down, the
cores are inserted horizontally, and the block is revolved 90
degrees to set it on the pallet. The special advantages claimed
for molding blocks face down are that a facing mixture may be
readily used, and, as the mortar is tamped in layers perpen-
dicular to the direction of percolation through the block, it is
more likely to be waterproof. A layer, one inch or more in
thickness, of colored mortar, or of richer mixture to secure water-
tightness, is first tamped against the face plate, and the block
then completed with the ordinary mortar. The disadvantage
of this method is that the mortar is tamped in layers lying par-
allel to the direction of stress in the wall, and is therefore less
adapted to resist this stress, and that thorough tamping around
the cores is more difficult. As to the variations in methods of
removing cores, it appears that for blocks molded upright, other
things being equal, it is mechanically better to withdraw the
cores rather than raise the block, and better to have the cores
enter from the bottom rather than to lower them into the mold
from above, since the space above the block should be kept clear.
Pallets may be of iron or wood. The latter are lighter and
much less expensive, and if properly made and cared for will do
good service, but if neglected will soon warp and become use-
less. Moreover, they can be made at any saw-mill, thus saving
cost of transportation.
In buying an outfit one should select first that machine which
will make the most serviceable block in the greatest variety of
salable shapes. The next most important point is that the
machinery shall be as simple as possible to accomplish the
necessary movements, and that the working parts be protected
from mortar that may be dropped in filling the mold. The
castings should be strong and well finished, especially where
CONCRETE BLOCKS: MANUFACTURE 515
the sides of the molds join, in order that the mold may be easily
assembled and the corners of the block properly formed.
785. Use of the Machine. — The inner faces of the mold plates,
the pallets, and all working parts, must be kept clean. A stiff
bristle brush such as the ordinary horse brush is excellent for
this purpose. If through neglect the mortar is allowed to harden
on the mold plates a wire brush will be found convenient for
cleaning, and if the mixture shows a tendency to stick to the
molds an occasional rubbing of the molds with fat salt pork may
be found advantageous.
The proportions and mixing of the mortar are treated else-
where. (See Chapter XII.) When thoroughly mixed the
mortar is shoveled into the mold, and tamping is commenced as
soon as a layer of about three inches is in place. Tamping
should be thorough, as in all concrete work where the mixture
is used dry enough to permit it; especial care must be taken with
the corners and cores, otherwise the angles of the block will not
be full and sharp, and crumbling will result. The face of the
rammer should be small and the tamping vigorous. In a large
factory a pneumatic tamper will be found advantageous. As
the mortar is added the ramming is continued until the mold is
entirely filled. It is then struck off with a straight edge and
the top quickly troweled smooth. The cores are now removed,
the sides of the mold disengaged, and the block removed to the
curing shed, or yard, on its pallet. When the block is molded
face down, the mold is first filled and tamped up to the level of
the lower side of the hollows, the cores are then inserted from
the sides, and the filling proceeds. When completed the cores
are removed, the mold opened, and the block turned through
ninety degrees on to the pallet.
The block is now carried, either by hand or cart, to" the curing
shed, where it is laid on scantlings to admit the air on all sides
equally. In case any accident happens to a block in course of
manufacture, the mortar should be returned to the mixing box
or machine and remixed immediately with a little added water.
It is unwise to give room in the curing shed to a block which there
is reason to suppose may be imperfect, and thus risk the loss
of material as well as labor.
786. CURING. — Those who are not familiar with the use and
characteristics of concrete may need to be told that moisture is
516 CEMENT AND CONCRETE
essential to the perfect hardening of fresh concrete, and even
those accustomed to its use should be reminded that more care
is necessary in the treatment of a hollow concrete block in the
early stages of hardening, that is, in " curing " it, than is required
with concrete in large masses. Concrete is almost always mixed
with more water than is required for the necessary chemical
reactions, and in a large mass it does not easily lose the water
except at the surface, yet to obtain a perfect face on mass
concrete it should not be allowed to dry out. But in a concrete
block the proportion of surface exposed to the atmosphere is
relatively so much greater, that precautions against drying out
must be correspondingly increased. Tt is not sufficient that a
block be sprinkled once or twice a day and be permitted to dry
out between sprinklings — for this may cause blotches in the
surface if not more serious defects in strength — but it should be
prevented from drying for at least ten days. To this end it is
advantageous to provide a curing shed, but, if this is impracticable,
at least a canvas protection from sun and wind should be used.
The blocks should be gently sprinkled with a rose nozzle as
soon as this can be done without washing the cement, usually
after about twenty-four hours, and thereafter kept uniformly
moist for at least ten days. -The longer they are free from the
action of sun and wind the better, and if shed room is restricted
they may be carefully removed to the yard after about three
days, and covered with canvas. Other materials are sometimes
used for covering, such as excelsior, hay, straw, etc., but there
is danger of staining the blocks, occasioning a loss greater than
the cost of canvas.
Blocks are seldom fit for use in a building until they are
three weeks old, and it is better to allow them to cure or season
longer if possible. Even with the present rapid hardening
rotary kiln cements they are constantly gaining in strength up to
six months. Though briquets made in a laboratory may some-
times indicate very little gain after three months, the conditions
are not the same.
Since concrete hardens most rapidly in a warm, moist atmos-
phere, the room in which the curing is done is sometimes filled
with steam. If the cement is sound and the block well made,
this should have no injurious effect, and would greatly hasten
the time when the block could be used.
CONCRETE BLOCKS: MANUFACTURE
517
For the manufacture of blocks in temperatures below freez-
ing, a heated building is essential for making and curing if perfect
blocks are scmght. Good work may be accomplished with mass
concrete in low temperatures, but with small, hollow blocks it is
not the same; there are too many points of attack, and variations
in temperature and rate of hardening introduce internal stresses
in the hollow structure, to say nothing of the difficulty of obtain-
ing a geod face under such conditions.
787. PRESSED BLOCKS. — Since the presence of cores would
interfere with the application of pressure, the method involving
such application is practically confined to blocks of the so-
called two-piece system. The most common block used in this
BLOCKS OF TWO-PIECE SYSTEM
method is in the form of a T, although L and U forms are also
made. On account of the heavy pressure used in the manu-
facture, it is possible to employ concrete more moist than is used
in tamped blocks, and it is usually considered that on this
518 CEMENT AND CONCRETE
account a larger proportion of broken stone or gravel may be
employed.
These blocks are molded in heavy metal molds. These are
filled with the mixture, a face plate is laid on the concrete,
and pressure is applied, by either hand or machine press. The
block is removed from the mold immediately and cured in the
same way as tamped blocks.
788. POURED BLOCKS. — The method employed in mak-
ing blocks of wet concrete is quite different from those described
above, inasmuch as neither tamping nor pressure is used to
compact the mass, and the block cannot be removed from the
mold until the concrete has set. This does away with much of
the so-called machinery used in other methods, but necessi-
tates, on the other hand, as many molds as there are blocks to
be made in one day.
The molds for this process are of steel or malleable iron with
cores of the same material. The mold is set up on a base plate
or plank with the cores in place, and filled with the mixed con-
crete. This is of such a consistency that it is only necessary to
cut the mass with a small spade or other implement to insure
thorough filling in the corners and about the cores. After
twenty-four hours the concrete is hard enough to permit the
removal of the molds, but the block is left upon the pallet or
base plate where made for several days.
The molds may be set up in the yard or curing shed, and the
mixed concrete brought to them in a cart, or the molds may be
set up in pairs on a cart specially designed for this purpose, and
taken to the mixing platform to be filled and afterwards con-
veyed to the yard. The advantage claimed for the latter method
is that in the trip to the yard the material is compacted in the
mold. On the other hand, however, if the material is very wet,
there will be a tendency to separate the aggregate from the
mortar.
These blocks are usually molded face up, and any special fac-
ing desired is placed on top of the block before setting begins.
In fact, such facings should be applied immediately after filling
the mold, just as a top dressing is applied in concrete sidewalk,
construction. Good effects may be obtained by finishing with a
float, or by sprinkling the top with screenings or pebbles. A
very smooth surface is obtained by finishing, with a trowel, a
CONCRETE BLOCKS: MANUFACTURE 519
thin layer of mortar containing two parts sand to one cement,
but there is always the danger that a troweled surface of rich
mortar will hair-crack.
789. COMPARISON OF METHODS. — To one who wishes to
engage in the making of cement blocks, the selection of the
method to be employed is of the greatest moment. Sufficient
experience has not been gained in the industry to indicate which
method will eventually come into most general use; the indica-
tions, however, are rather that all three systems will continue
to be employed, each under the conditions to which it is best
suited.
The tamped block has the undoubted advantage to the smalT
factory that no great amount of machinery is required, and at
present probably more different styles of block are made by this
method than by either of the others. The fact that coarse
aggregate is not successfully used in this system is one of its
disadvantages, for it has been shown elsewhere that a concrete
made with a proper proportion of good aggregate is as strong as
the mortar alone, and almost always much less expensive. The
attempt to cut down the quantity of cement in using this method
results in blocks that are porous and permeable, and lacking in
the early strength that is essential to the handling of blocks
without considerable loss from breakage. The endeavor to
make a less porous block without using a very rich mortar
throughout has led to the attempt to mold the blocks with a
face of richer mortar about an inch thick. This, however, in-
creases considerably the necessary labor in making the block, and
raises the question of adherence between the two qualities of
mortar, so that it is not very generally approved by practical
block-makers.
The pressed block is practically confined to the two-piece
system — that is, no single block reaches entirely through the
wall. This feature of the system — necessitated by the method
of making, since pressure would not be communicated through
a thick layer of concrete and give a compact mass — results in
some advantages. The chief of these advantages is that therie
are no webs to carry moisture through the wall, but that hori-
zontal and vertical air spaces are secured throughout. This ad-
vantage appears to be practically secured by some of the recent
forms of tamped blocks having so-called staggered air spaces^
520 CEMENT AND CONCRETE
Other advantages are that a certain proportion of coarse aggre-
gate may be used, and that the pressure is sufficient to compact a
somewhat wetter mixture than is required in the tamped block;
also that to make blocks for walls of various thicknesses it is
only necessary to make slight changes in the molds, and that the
blocks are of lighter weight and more easily handled.
The application to the cement block industry of the system
of pouring fairly wet concrete into molds in which it is allowed
to harden, is comparatively recent, although the use of this
method in ordinary concrete work is very familiar. While this
method is usually considered as one which requires concrete so
wet that it will mold itself and fill all corners without working,
there is no inherent reason why it cannot be employed with con-
crete that simply quakes after slight working. Such a propor-
tion of aggregate as will give the strongest concrete at a given
cost may also be used. The system is thus adapted to the use
of the mixture giving the best results in practice, and herein
lies its important advantage over other systems, giving a dense
block with well-defined angles and perfect surfaces. The so-
called cast-stone process is merely a modification of this method,
using molded sand in place of steel molds. It is possible to put
;any desired finish on a poured block if it is molded face up,
'This is at some additional expense, however, since it involves
:a separate operation. The disadvantage of the method is the
large number of molds required, the slower rate of hardening,
and the consequent greater time and space necessary to cure the
blocks. These objections cannot be denied, and may prevent
the use of the system under some circumstances.
Art. 88. Materials and Finish
790. CHARACTER OF MATERIALS FOR MORTAR AND CON-
CRETE. — It is unnecessary to repeat here the requisites
for proper materials for mortar and concrete. The cement
required for concrete blocks is first-class Portland, but no special
properties are necessary. The early hardening rotary-kiln
cements now on the market are well adapted to block making.
As it is not usually possible for the block manufacturer to make
elaborate series of tests, he should confine his choice to brands of
established reputation. The factory tests, checked occasionally
..by a reliable independent laboratory, will indicate uniformity.
CONCRETE BLOCKS: MANUFACTURE 521
Having selected a brand, it is well to continue its use as long as
it is satisfactory. It is almost useless to attempt to explain
away the effects of a bad run of blocks by saying the cement was
poor; the reputation gained by months of honest endeavor and
good results receives a serious set-back.
The first essential of a cement is soundness; strength for a
given cost comes next, and the great majority of tests of cement
are made to determine these two properties. Ease of working
and color are also important in cement block manufacture.
Having become acquainted with the manipulation necessary to
obtain the best results with one brand, some experimentation
will be necessary to become as familiar with a new brand. The
color of the cement is of more moment here than in other uses.
The color of the resulting product is influenced much more by
the sand and aggregate than by the cement, yet in working with
the same aggregate a change in the cement may affect the color
of the block.
The requisites for good sand are given elsewhere in this vol-
ume. Impurities in sand may be objectionable in concrete
block making, although the strength of the mixture may not be
affected thereby. Dirty sand used in mortar appearing on the
face of a block may give a " flat " appearance, lacking in charac-
ter and tone. On the other hand, some impurities give to the
product a most desirable color without any serious effect upon
the strength and durability. Where a choice of sands is pos-
sible, the block manufacturer, if not himself capable of judging
between them, should seek competent advice. The grading of
the fineness of the sand is another important question in its
relation to strength and texture. (See Chapter XI.)
Aggregate for concrete blocks must in general be quite fine.
Whether it be broken stone or gravel, it is seldom wise to use
particles too coarse to pass a one-inch square mesh, and usually
three-quarter inch pieces are better. The effect of size and
character of stone, and the desirability of decreasing the voids by
careful grading of size, have been fully covered elsewhere. (See
Chapter XIII.) The character of surface and color of the
aggregate are of great importance also in their effect on the
appearance of the product. If several kinds of aggregate are
available, the maker should experiment with them to determine
what variations he can make in the surface appearance without too
522 CEMENT AND CONCRETE
much expense. One who is destined to success will not be content
until he has learned the possibilities of the available materials.
791. Proportions of Materials. — The considerations which
must fix the proportions to be used in concrete block manu-
facture are impermeability, strength, — especially at early
periods, — and appearance. While strength is of great impor-
tance, it is not this property that will usually fix the amount of
cement necessary in a given quantity of sand or aggregate. If
made with sound cement it is not at all likely that a block which
stands transportation to the building will fail from lack of
strength when properly laid in an ordinary wall. This is evident
if we recall that the ultimate compressive strength of mortar con-
taining six parts sand to one Portland cement is about 1,000 lbs.
per square inch, and that a prism of mortar one inch square and
a foot high weighs only one pound. In order that a mortar or
concrete shall be impervious, however, the voids in the sand
must be filled with cement, and the voids in the broken stone or
gravel must be filled with the mortar; and as impermeability is
one of the most important qualities of a concrete block, the aggre-
gate should be so graded that the voids shall be as low as possible.
Since, as a general rule, concrete properly proportioned is not
only as strong, but nearly as impervious as the mortar alone, it
follows that concrete is much more economical than mortar for
use in making blocks. Thus, with a well-graded sand con-
taining both coarse and fine particles, a compact mortar may be
made with one part cement to three parts sand, while to the
same mortar we may add at least five or six parts of broken
stone, and the resulting concrete will be nearly as impervious as
the mortar alone. With ordinary sand it will be found neces-
sary to use one part cement to not more than three parts sand to
assure impermeability, but of well-graded gravel as much as five
parts to one cement may be employed. With artificial crushed
products, that is, broken stone, one cement to two and a half
or three parts sand by weight makes a good mortar. The quan-
tity of mortar to be used should somewhat exceed the voids in
the broken stone. If no broken stone is employed, the proportion
of cement required to secure imperviousness is so large as to
make the blocks expensive. This cost may be reduced by
using silica cement C§ 33). The use of hydrated, or slaked, lime
has also been recommended to assist in filling the voids; the
CONCRETE BLOCKS: MANUFACTURE 523
ORNAMENTAL BRACKET CAST IN SAND MOLD.
524 CEMENT AND CONCRETE
possibility of efflorescence from such use is sufficient to dictate
caution, however, until it is proved to be unobjectionable,
(Articles 34, 40, and 61 should be read in this connection.)
792. Special Fonns. — In the construction of a building many
special forms are required, such as sills, lintels, columns, steps,
etc. Block machines are now made to mold many of these
forms when of moderate length. Special molds of steel with
hinged sides are also made into which the concrete is tamped.
When the size of block required is beyond the capacity of the
machine in use, wooden molds may be readily made. Unless for
some form which is not to be duplicated, such wooden molds
should be so made that they may be used repeatedly. To
make a convenient form, fasten one plank on edge along one side
of the bottom piece or pallet, thus making an L; the remaining
side piece is not fastened, but is held in place by a strong iron
clamp of U form. Between the movable side piece and the
clamps place wedges to bring the mold to the proper width.
The end pieces are held by cleats talked to the side pieces and
pallets, which are made longer than the proposed block to allow
for this. For steps or sills requiring rounded corners, a strip of
molding is tacked along one corner of the mold. Lumber for
this purpose should be one and three-quarter inches thick,
dressed. To give a fine finish and to prevent the absorption of
water by the mold, sandpaper the interior and apply two or
three coats of shellac dissolved in alcohol.
Sand molds are also employed for casting concrete, much the
same as for cast iron, and beautiful effects have been obtained
by this method. This process,* which is patented by the Stevens
Cast Stone Company of Chicago, consists in preparing a sand
mold from a pattern, and pouring the mold with a wet mixture of
mortar or of concrete made with fine aggregate. While this
process is employed for making concrete blocks of the ordinary
hollow form, it is especially suited to molding lintels, columns,
treads, and all ornamental pieces. A bracket cast by this process
is shown in the cut, and the character exhibited in the finish is
especially noteworthy.
793. Facing. — The application of a special facing to concrete
blocks is for one of two purposes — to make the block more
• For detailed description, see article by Mr. Charles D. Watson in Cement
Age, May, 1906.
4
CONCRETE BLOCKS: MANUFACTURE 525
nearly waterproof, or give some special surface appearance. The
need of such a facing is most apparent in the tamped block
made of mortar alone. To make such a block waterproof
throughout requires a large percentage of cement, and by using
a waterproof facing and leaner mortar for the body of the block
it is sought to decrease the cost without sacrificing the imper-
vious quality. To insure this result the mortar for the facing
should not contain more than two or two and a half parts sand
to one cement, and should form a layer about a half inch in
thickness. If the surface can be troweled, a smooth face is
formed to repel the moisture.
When applied to improve the appearance of a block, the mortar
may be colored, or special sand or stone screenings may be
employed to give the desired finish. Since the quantity of such
facing mortar is small, the cost of special materials will be
correspondingly less important than would be the case if the
entire block were made homogeneous.
The method of applying such a facing differs with the method
of manufacture and the form of machine used. Some of the
machines for tamped mortar blocks mold the block face down in
order to place the facing mortar first. If molded in the ordinary
manner a separating plate must be placed just back of the face
plate to keep the two mortars apart until the mold is full. With
the pressed block the facing mortar is placed last and the press-
ure is applied directly upon it. The poured block is usually
molded face up and the facing mortar spread last. It may then
be troweled or screenings may be sprinkled upon it to give the
desired special finish. With the poured block the facing is
more frequently applied for the sake of appearance, since by
this method the body of the block may be made waterproof at
a reasonable cost. Whatever method of manufacture is em-
ployed, the face and body of the block should be made together,
or the facing applied immediately after the block is completed,
in order that the two may be thoroughly bonded together.
The difficulty in applying a facing mortar is greatest in that
method of manufacture in which such facing is most needed. It
is frequently a question whether the increased cost and trouble
of applying such a facing does not exceed the saving resulting
from the use of a leaner mixture in the body of the block. A
block made of an impervious mixture throughout is undoubtedly
526 CEMENT AND CONCRETE
better than one of which only the face is waterproof, and the
facing should only be adopted when it is found on trial to be
appreciably less expensive.
794. Waterproofing. — The precautions necessary to make
waterproof mortar and concrete and the application of surface
washes have already been discussed in Art. 61, and these remarks
are entirely applicable to concrete blocks. As already stated,
the cement paste should be in excess of the voids in the sand,
and the mortar in excess of the voids in the broken stone or
gravel. That sufficient water be used in mixing is also one of
the first requisites, as there is much greater danger of permea-
bility being due to a deficiency of water than to an excess,
especially in a comparatively small mass like a concrete block.
The washes mentioned in Art. 61 may be applied to blocks
as to other concrete surfaces, and they are sometimes used even
after the block is in the wall. In addition to the washes men-
tioned above, there are certain trade preparations used in a
similar way and to mix with the water used in gauging the mor-
tar. There is also a powder, the formula for which is a trade
secret, to mix with the cement for making waterproof concrete.
This has been on the market but a short time, but has given good
results.
Art. 89. Cost and Laying
795. COST OF BLOCKS. — Concrete blocks are usually made
to lay courses eight inches or nine inches high, and are for 8-
inch, 10-inch, and 12-inch walls. The blocks themselves may be
of any length, but 24 inches and 32 inches are the lengths most
commonly used. The lengths and heights above mentioned
include the thickness of one joint, that is, each block when laid
in the wall measures 24 or 32 inches long from center to center
of end joints, and eight inches or nine inches high from center to
center of longitudinal joints. These dimensions have been selected
for convenience in laying out the work, the lengths mentioned
being exactly divisible into halves, quarters, and eighths.
Blocks of the one-piece system are usually made with cores
occupying 20 to 40 per cent of the entire volume, that is, from
60 to 80 per cent of the entire volume of the block is solid.
With the two-piece system the spaces sometimes reach 50
per cent of the entire volume.
CONCRETE BLOCKS: COST
527
Table 162 gives the volume, in cubic feet, of solid mortar or
concrete in one block of each of the usual sizes when the voids
•or core spaces occupy 50 to 20 per cent of the total volume of
the block.
TABLE 162.
Volume of Mortar or Concrete in One Block, 'with Varying Propor-
tions of Core Space.
Size of block in inches.
Solid volume of block in cubic feet.
50% Solid.
60% Solid.
70% Solid.
80% Solid.
8 X 8 X 24
8 X 10 X 24
8 X 12 X 24
8 X 8 X 32
8 X 10 X 32
8 X 12 X 32
9 X 8 X 24
9 X 10 X 24
9 X 12 X 24
9 X 8 X 32
9 X 10 X 32
9 X 1 2 X 32
.444
.555
.667
.592
.740
.889
.500
.625
.750
.667
.833
1.000
.533
.666
.800
.711
.889
1.067
.600
.750
.900
.800
1.000
1.200
.622
.77f
.933
.830
1.03t
1.244
.700
.875
1.050
.933
1.167
1 .400
.71U
.889
1.067
.948
1 . 185
1.425
.800
1.000
1.200
1.067
1.333
1.600
796. The weight of concrete varies considerably with the
character of materials and method of making, the usual weight
with rock aggregate being 140 to 150 pounds per cubic foot.
At 150 pounds per cubic foot the weight of blocks 70 per cent
solid and of the sizes given in Table 162 is as follows: —
Weight of Blocks, 70 per cent Solid, in Pounds.
Height and I^nKth
of Block.
Thickness of Wall.
8 inch.
10 inch.
12 inch.
8 X 24
8 X 32
9 X 24
9 X 32
93
125
105
140
117
156
131
175
140
187
158
210
The cost of materials in a cubic yard of Portland cement
mortar of various compositions is given in Table 62, page 197.
From this table is deduced Table 163 giving the cost of materials
528
CEMENT AND CONCRETE
in one cubic foot of mortar containing 2, 3, 4, or 6 parts sand by
weight to one cement, the cost of cement varying from $1.20 to
$3.00 per barrel.
TABLE 163.
Cost of Cement and Sand in one Cubic Foot of Mortar. (Sand at
75 Cents per Cubic Yard.)
Cost, in Dollars,
of Portland
Cement per
Barrel .
Cost, in Cents, of Ingredients in Mortar.
Proportions in Mortar, Parts Sand to One Cement by Weight.
2.
3.
4.
6.
1.20
1.40
1.60
1.80
2.00
2.20
2.40
2.60
2.80
3.00
14.4
16.4
18.5
20.5
22.6
24.6
26.7
28.8
30.8
32.9
11.3
12.7
14.2
15.7
17.2
18.6
20.1
21.6
23.1
24.6
9.5
10.7
11.8
13.0
14.2
15.3
16.5
17.7
18.9
20.0
7.5
8.3
9.1
9.9
10.7
11.6
12.4
13.2
14.0
14.8
Taking from Table 162 the volume of solid mortar or concrete
in a given block, and from Table 163 the cost of the ingredients
in a cubic foot of mortar of the given proportions and at the
given price of cement, the product of these two gives the cost of
cement and sand in one block.
Example. — What will be the cost of the materials contained
in a hollow block 8 X 10 X 32, in which the cores occupy 30
per cent of the space, if the mortar is composed of 4 parts sand
by weight to one cement, the cement costing $2.00 a barrel and the
sand $1.00 a cubic yard?
From Table 162 we find the volume of solid mortar in such a
block is 1.038 cu. ft. From Table 163 the cost of the materials in
a cubic foot of mortar of proportions stated is 14.2 cents if sand
costs 75 cents a cubic yard, and at $1.00 per cubic yard for sand
the cost of mortar per cubic foot will be about nine-tenths of a
cent more, or 15.1 cents. Then 15.1 x 1.038 = 15.7 cents, the
cost of materials in one block.
797. For blocks made of concrete instead of mortar, it is more
convenient to use the cubic yard as the volume unit. Table 164,
derived directly from 162, gives the solid volume, in cubic yards,
CONCRETE BLOCKS: COST
529
of 100 blocks of various sizes, and containing 50, 40, 30, or 20
per cent core space.
TABLE 164.
Volume in Cubic Tarda, of Solid Mortar or Concrete in 100 Blocks.
Size of Blocks in Inches.
50% Solid.
60% Solid.
70% Solid.
80% Solid.
8 X 8 X 24
8 X 10 X 24
8 X 12 X 24
1.65
2.05
2.47
1.98
2.47
2.97
2.31
2.88
3.46
2.63
3.29
3.97
8 X 8 X 32
8 X 10 X 32
8 X12 X 32
2.19
2.74
3.30
2.64
3.30
3.97
3.08
3.85
4.60
3.52
4.38
5.27
9 X 8 X 24
9 X 10 X 24
9 X 12 X 24
1.85
2.32
2.78
2.22
2.78
3.34
2.60
3.24
3.89
2.97
3.71
4.45
9 X 8 X 32
9 X 10 X 32
9 X 12 X 32
2.47
3.09
3.71
2.97
3.71
4.45
3.46
4.33
5.19
3.97
4.93
5.93
The cost of concrete is discussed in detail in Art, 44. In
order, however, to give the approximate cost of materials per block
in the simplest way, Table 165 has been prepared covering the
usual proportions. With broken stone from which the screen-
ings have been removed, the left half of the table should be used.
With broken stone properly graded from coarse to fine, or with
gravel, the right half may be employed. This table is based on a
cost of 75 cents per cubic yard of sand and $1.00 per cubic yard
of broken stone. When higher prices prevail, add about one-
third the excess in cost of sand and the entire excess in cost of
stone or gravel for approximate results. If greater accuracy is
desired, see Art. 44.
We may now determine the cost of materials in a concrete
block as follows: —
Example. — Block 8 x 10 x 32, 30 per cent space. Pro-
portions, 1 cement to 3 parts sand by weight, and sufficient
mortar used to fill voids in gravel. Cost of cement $2.00 per bbl.,
sand $1.00 per cu. yd., and gravel $1.50 per cu. yd. What is
the cost of materials per block?
From Table 165 we find the cost of materials in such concrete
to be $2.63 per cu. yd. with sand at 75 cents and gravel $1.00
530
CEMENT AND CONCRETE
per cu, yd. For the prices in the example we must add 25/3 +
50 -= 58 cents, giving $2.63 + 58 = $3.21 per cu. yd. of rammed
concrete. From Table 164 we find the contents of 100 blocks of
the given size to be 3.85 cu. yds. Then 3.85 x $3.21 = $12.36
or 12.4 cents per block.
TABLE 165.
Cost of Materials in One Cubic Yard of Concrete,
cient to fill voids.)
(Mortar Saffi>
Cost
Broken Stone, Voids 50%.
Gravel, Voids 35%.
Cement
per
Barrel,
Mortar
Mortar
Mortar
Mortar
Mortar
Mortar
Mortar
Mortar
Dollars.
1-2 by
l-2i by
1-3 by
1-4 by
1-2 by
1-2J by
1-3 by
1-4 by
Weight.
Weight.
Weight.
Weight.
Weight.
Weight.
Weight.
Weight.
1.20
2.95
2.70
2.52
2.30
2.37
2.20
2.07
1.90
1.40
3.22
2.94
2.72
2.45
2.56
2.36
2.21
2.02
1.60
3.50
3.17
2.92
2.60
2.76
2.53
2.35
2.13
1.80
3.77
3.40
3.12
2.75
2.95
2.69
2.49
2.24
2.00
4.05
3.64
3.32
2.90
3.15
2.86
2.63
2.35
2.20
4.32
3.87
3.52
3.06
3.34
3.02
2.77
2.46
2.40
4.60
4.10
3.72
3.22
3.53
3.18
2.91
2.57
2.60
4.88
4.34
3.92
3.38
3.72
3.35
3.05
2.68
2.80
5.15
4.57
4.12
3.54
3.91
3.51
3.19
2.79
3.00
5.43
4.80
4.32
3.70
4.11
3.67
3.33
2.90
Cost of sand assumed 75 cents per cubic yard .
Cost of stone or gravel assumed fl.OO per cubic yard. •
798. The labor cost of making blocks depends upon so many
elements that average figures are little more than an indication
of the probable actual cost. The method of making — hand
tamped, pressed or poured — is of course a most important ele-
ment. The number of blocks turned out per man varies greatly
with the style of machine and the facility of operation. The
method of mixing the concrete, by hand or machine, and the
perfection of the arrangements for ease in manipulating and
handling the finished blocks, not to mention the efficiency of the
laborers, all have an important effect on the labor cost per
block.
The cost of mixing concrete in large quantities is seldom less
than 30 cents per cubic yard if allowance is made for plant. This
is for mixing alone, not including placing. The cost for hand
mixing is seldom less than 50 cents per cubic yard. In mixing
concrete in small quantities, as for cement block making, these
CONCRETE BLOCKS: COST 531
figures should be doubled. For a large output there is thus a
chance of saving about 40 cents a cubic yard, or from one to two
cents a block, by installing a small mixer to run by motor or
gasoline engine. The more important item of cost, however, is
forming the block and conveying to the curing shed. By suitable
cars and tracks and organization of force there is an opportunity
of making a considerable saving in this part of the work.
As a general average it may be stated that in making blocks by
the hand-tamped process 3 men can make, in one day, 60 blocks
weighing 200 pounds each, or 100 blocks weighing 100 pounds
each. With wages at $2.00 per day this represents a cost of
10 cents each for the large blocks and 6 cents each for the small
blocks. If the blocks have 30 per cent core space, or 70 per
cent solid, we would have the following approximate costs of
labor in making: —
8x8x24or9x8x24 6 cents each.
8 X 10 X 24 or 9 X 10 X 24 7 "
8 X 8 X 32 or 8 X 10 X 32 7 "
8 X 12 X 24 or 9 X 12 X 24 8 "
9 X 8 X 32 8 "
8 X 12 X 32 or 9 X 10 X 32 9 "
9 X 12 X 32 10 "
We have already found the cost of materials in an 8 X 10 X 32
inch block, assuming certain prices for cement, sand, and gravel,
to be 15.7 cents when made of mortar composed of 4 parts sand
to one cement by weight, and 12.4 cents when made of concrete
containing enough 1 to 3 mortar to fill the voids in the gravel.
The cost of labor to make such a block is shown to be about 7
cents, giving a total cost of 22.7 cents or 19.4 cents according
to the material used. In addition to the above is the cost of
delivery to the purchaser, a reasonable allowance for breakage
of from two to five per cent, and incidental expenses.
799. LAYING Concrete Blocks. — In order that the laying of
the blocks in the wall, once started, shall continue uninterrupted,
all necessary specials must be on hand promptly, and the chip-
ping of regular blocks to fit special places should be avoided if a
strong wall of good appearance is to result. To this end each
course of blocks must be carefully planned and a drawing made
showing the number and location of all specials.
The mortar for laying should be of Portland cement, but as
such mortar is brash unless very rich, it is well to add some well-
632 CEMENT AND CONCRETE
slaked lime paste. To one part Portland cement and three
parts sand add one half part of lime paste that has been thor-
oughly slaked and strained to remove lumps; or to a 1 to
4 mortar one part lime paste may be added. It is better not
to lay blocks in freezing weather, but if it becomes necessary to
do so, the blocks should be warmed and the lime should be
omitted from the mortar, which must be richer in cement, not
more than 2A parts sand being used to one part 'cement by
weight. In dry and warm weather the block should be
moistened just before laying. In spreading the mortar keep the
bed back from the face of the joint about one inch to leave room
for pointing. Be careful to have a full mortar bed, as the joint
is at best the weak point in the wall.
Cost of Laying. — The cost of mortar alone will vary from one
to three cents per block. One mason with two helpers to carry
and hoist blocks and mix mortar, will lay from 8 to 12 blocks per
hour, making the cost of labor for laying from 8 to 12 cents per
block.
800. COMPARISON OF COST OF CONCRETE BLOCK AND BRICK.—
We have now considered the elements of cost in detail, and
may compare the cost of concrete block and brick. A ten-inch
concrete block wall is usually considered as strong as a thirteen-
inch brick wall, and we will use one hundred 8 X 10 x 32 inch
blocks in the comparison, with prices of materials already
assumed.
Concrete in 100 blocks, 70 per cent solid Si 2. 40
Making and curing 7.00
Incidental expenses, 4 per cent .80
Breakage, 4 per cent .80
Profit, at 9 cents per block 9 . 00
Delivery to building 3 . 00
Mortar to lay 2.00
Labor to lay 10.00
Total cost, Wall of 100 blocks or 180 sq. ft. face . . . $45.00
Cost per lOb sq. ft $25.00
To lay 100 sq. ft. of brick wall requires 2,100 brick
2,100brickat $9.00 per thousand $18.90
Mortar to lay 2,100 brick 4 . 10
Labor to lay 2,100 brick 11.00
Cost of 100 square feet of brick wall $34.00
CONCRETE BLOCKS: REGULATIONS 533
The cost of a brick wall is thus about 35 per cent in excess
of the cost of a wall of concrete blocks of equal strength. If
pressed brick are used for the face at $20.00 per thousand, the
cost w^ill be increased by $10.00, allowing for additional cost of
laying.
A comparison of 8-inch walls of concrete block and brick will
be somewhat less favorable unless the extra strength of the
concrete blocks is considered. Using blocks 8 X 8 x 24 we
have : —
Concrete in 100 blocks, 70 per cent solid S7.42
Making and curing 6 . 00
Incidental exjjenses 4 per cent and breakage 4 per cent . . 1 . 08
Profit, at 4 cents per block 4 . 00
Delivery to building . 1 . 75
Mortar to lay 1 . 35
Labor to lay, at 8 cents per block 8 . 00
Ck)st of 100 blocks in place, or 133 sq. ft. of wall . . . $29.50
Cost per 100 sq. ft. of 8-inch wall $22.20
To lay 100 sq. ft. of 8-inch wall requires 1,400 brick
l,400brickat $9.00 per thousand $12.60
Mortar to lay 3.10
Labor to lay 1,400 brick 7.00
Cost of 100 sq. ft. 8-inch brick wall $22.70
The difference in cost of brick and concrete as shown by these
estimates is believed to be very conservative. In many cases
under favorable conditions it will be possible to build concrete
block walls at a lower cost, but the difference is sufficient to show
that under all ordinary conditions the concrete block wall can
successfully compete with brick.
Art. 90. Strength of Concrete Blocks, and Building
Regulations
801, STRENGTH. — The materials and proportions used in
the manufacture of concrete blocks vary so widely that it is
difficult to give any general statements concerning their strength.
With a knowledge of the proportions and ingredients, Chapters
XVI and XVII will give a good idea of the strength to be
expected. On page 304, tests of 12-inch cubes of mortar con-
taining 4 volumes sand to one cement showed a compressive
534 CEMENT AND CONCRETE
strength of 1 ,500 to 1 ,700 pounds per square inch at 20 months.
At 28 days the strength should be at least one-half of this, or,
say, 800 pounds per square inch. These specimens were made of
so-called " dry " mortar, the consistency of damp earth, well
tamped into molds. For a part of the specimens the storage was
similar to the curing of blocks. The specimens are therefore
comparable with concrete blocks of the same proportions. The
tests on pages 306 and 307 show that concrete made with mortar
containing 3 parts sand to one cement, the voids in stone being
filled, has a strength of 1,800 to 2,000 pounds per square inch.
A wall of concrete 100 feet high would give a load of 100 pounds
per square inch. If in a building four stories high, ten square
feet of space on each floor, loaded with 60 pounds per square foot,
were carried by each linear foot of wall four inches thick, the
resulting load on the concrete would be about 100 pounds per
square inch.
Walls of concrete blocks properly made and laid have little to
fear from direct crushing by a fairly applied load. Many blocks,
however, are made with more than four parts sand to one cement,
and the quality of the materials is frequently not good. Some
of the greatest sources of weakness, however, are poor design,
whereby the load from girders and beams is applied eccentri-
cally, and carelessness in laying resulting in lack of uniform
bearing on bed joints. The thickness of the shells of concrete
blocks might be made less so far as the strength of the block
itself is concerned, but with less than a two-inch shell the danger
of poor bed joints is too great. Improper laying may subject a
block to transverse stress, and on this account, as well as because
the cross-bending test is very easy to make, the transverse
strength is sometimes specified in building regulations.
802. BUILDING REGULATIONS. — The rapid development of
the concrete block industry has made it necessary for some of
the more progressive cities to frame building regulations govern-
ing the use of this material. Denver, Minneapolis, Chicago,
and Newark have adopted such regulations, but those of Phila-
delphia are very complete and are reproduced below.
CONCRETE BLOCKS: REGULATIONS 535
Rules and Regulations Covering the Manufacture and
Use of Hollow Concrete Building Blocks in the City
OF Philadelphia.
1. Hollow concrete building blocks may be used for building
six stories or less in height, where said use is approved by the
Bureau of Building Inspection, provided, however, that such
blocks shall be composed of at least one (1) part of standard
Portland cement and not to exceed five (5) parts of clean,
coarse, sharp sand or gravel, or a mixture of at least one part of
Portland cement to five (5) parts of crushed rock or other suit-
able aggregate. Provided further that this section shall not per-
mit the use of hollow blocks in party walls. Said party walls
must be built solid.
2. All material to be of such fineness as to pass a half-inch
ring and be free from dirt or foreign matter. The material com-
posing such blocks shall be properly mixed and manipulated,
and the hollow space in said blocks shall not exceed the per-
centage given in the following table for different height walls,
and in no case shall the walls or webs of the block be less in
thickness than one-fourth of the height. The figures given in the
table represent the percentage of such hollow space for different
height walls.
Stories. 1st. 2d. 3d. 4th. 5th. 6th.
1 and 2 33 33
3 and 4 25 33 33 33
5 and 6 20 25 25 33 33 33
3. The thickness for walls for any building where hollow con-
crete blocks are used shall not be less than is required by law
for brick walls.
4. Where the face only is of hollow concrete building block
and the backing is of brick, the facing of hollow concrete blocks
must be strongly bonded to the brick either with headers pro-
jecting four inches into the brickwork, every fourth course being
a heading course, or with approved ties, no brick backing to be
less than eight inches. Where the walls are made entirely of
hollow concrete blocks, but where said blocks have not the same
width as the wall, every fifth course shall extend through the
wall, forming a secure bond. All walls where blocks are used
shall be laid up in Portland cement mortar.
536 CEMENT AND CONCRETE
5. All hollow concrete building blocks, before being used in
the construction of any buildings in the city of Philadelphia,
shall have attained the age of at least three (3) weeks.
6. Wherever girders or joists rest upon walls so that there is a
concentrated load on the block of over two (2) tons, the blocks
supporting the girder or joists must be made solid. Where such
concentrated load shall exceed five (5) tons the blocks for two
(2) courses below, and for a distance extending at least eighteen
(18) inches each side of said girder, shall be made solid. Where
the load on the wall from the girder exceeds five (5) tons, the
blocks for three (3) courses underneath it shall be made solid with
similar material as in the blocks. Wherever walls are decreased
in thickness the top course of the thicker wall to be made solid.
7. Provided always that no wall or any part thereof composed
of hollow concrete blocks shall be loaded to an excess of eight (8)
tons per superficial foot of the area of such blocks, including the
weight of the wall, and no blocks shall be used that have an
average crushing strength less than 1,000 pounds per square
inch of area at the age of twenty-eight days, no deduction to be
made in figuring the area for the hollow spaces.
8. All piers and buttresses that support loads in excess of
five (5) tons shall be built of solid concrete blocks for such dis-
tance below as may be required by the Bureau of Building
Inspection. Concrete lintels and sills shall be reinforced by
iron or steel rods in a manner satisfactory to the Bureau of
Building Inspection, and any lintels spanning over four feet six
inches in the clear shall rest on solid concrete blocks.
9. Provided that no hollow concrete building blocks shall be
used in the construction of any building in the city of Philadel-
phia, unless the maker of said blocks has submitted his product
to the full test required by the Bureau of Building Inspection and
placed on file with said Bureau of Building Inspection a cer-
tificate from a reliable testing laboratory showing that samples
from the lot of blocks to be used have successfully passed the
requirements of the Bureau of Building Inspection, and filing a
full copy of the test with the bureau.
10. A brand or mark of identification must be impressed in or
otherwise permanently attached to each block for purpose of
identification.
11. No certificate of approval shall be considered in force for
CONCRETE BLOCKS: REGULATIONS 537
more than four months unless there be filed with the Bureau of
Building Inspection, in the city of Philadelphia, at least once
every four months following, a certification from some reliable
physical testing laboratory showing that the average of three (3)
specimens tested for compression and three (3) specimens tested
for transverse strength comply with the requirements of the
Bureau of Building Inspection of the city of Philadelphia, said
samples to be selected either by a building inspector or by the
laboratory from blocks actually going into construction work.
Samples must not be furnished by the contractors or builders.
12. The manufacturer and user of any such hollow concrete
blocks as are mentioned in this regulation, or either of them,
shall at any time have made such tests of the cements used in
making such blocks or such further tests of the completed
blocks, or of each of these, at their own expense, and under the
supervision of the Bureau of Building Inspection, as the chief
of said bureau shall require.
13. The cement used in making said blocks shall be Portland
cement, and must be capable of passing the minimum require-
ments as set forth in the " Standard Specifications for Cement "
by the American Society for Testing Materials.
14. Any and all blocks, samples of which, on being tested
under the direction of the Bureau of Building Inspection, fail
to stand at twenty-eight days the tests required by this regula-
tion, shall be marked condemned by the manufacturer or user
and shall be destroyed.
15. No concrete blocks shall be used in the construction of
any building within the city of Philadelphia until they shall
have been inspected and average samples of the lot tested,
approved and accepted by the chief of the Bureau of Building
Inspection.
Specifications governing method of testing hollow block:
1. These regulations shall apply to all new materials such as
are used in building construction, in the same manner and for
the same purposes, as stones, brick, concrete, are now authorized
by the building laws, when said new material to be substituted
departs from the general shape and dimensions of ordinary
building brick, and more particularly to that form of building
material known as hollow concrete block manufactured from
cement and a certain addition of sand, crushed stone or similar
material.
538 CEMENT AND CONCRETE
2. Before any such material is used in buildings an applica-
tion for its use and for a test of the same must be filed with the
chief of the Bureau of Building Inspection. A description of
the material and a brief outline of its manufacture and pro-
portions of the materials used must be embodied in the appli-
cation.
3. The material must be subjected to the following tests:
Transverse, compression, absorption, freezing and fire. Addi-
tional tests may be called for when, in the judgment of the
chief of the Bureau of Building Inspection, the same may be
necessary. All such tests must be made in some laboratory of
recognized standing, under the supervision of the engineer of
the Bureau of Building Inspection. The tests will be made at
the expense of the applicant.
4. The results of the tests, whether satisfactory or not, must
be placed on file in the Bureau of Building Inspection. They
shall be open to inspection upon application to the chief of the
bureau, but need not necessarily be published.
5. For the purposes of the tests at least twenty (20) samples
or test pieces must be provided. Such samples must represent
the ordinary commercial product. They may be selected from
stock by the chief of the Bureau of Building Inspection or his
representative, or may be made in his presence, at his discretion.
The samples must be of the regular size and shape used in con-
struction. In cases where the material is made and used in
special shapes and forms too large for testing in the ordinary
machines, smaller-sized specimens shall be used as may be
directed by the chief of the Bureau of Building Inspection, to
determine the physical characteristics specified in Section 3.
6. The samples may be tested as soon as desired by the
applicant, but in no case later than sixty days after manu-
facture.
7. The weight per cubic foot of the material must be deter-
mined.
8. Tests shall be made in series of at least five, except that in
the fire tests a series of two (four samples) are sufficient. Trans-
verse tests shall be made on full-sized samples. Half samples
may be used for the crushing, freezing, and fire tests. The
remaining samples are kept in reserve, in case unusual flaws
or exceptional or abnormal conditions make it necessary to
CONCRETE BLOCKS: REGULATIONS 539
discard certain of the tests. All samples must be marked for
identification and comparison.
9. The transverse tests shall be made as follows: The samples
shall be placed flatwise on two rounded knife-edge bearings set
parallel, seven inches apart. A load is then applied on top,
midway between the supports, and transmitted through a similar
rounded knife edge until the sample is ruptured. The modulus
of rupture shall then be determined by multiplying the total
breaking load in pounds by 21 (three times the distance between
supports in inches), and then dividing the result thus obtained by
twice the product of the width in inches by the square of the
depth in inches.
p _ 3W1
2bd2
No allowance should be made in figuring the modulus of rupture
for the hollow spaces.
10. The compression test shall be made as follows: Samples
must be cut from blocks so as to contain a full web section;
samples must be carefully measured, then bedded flatwise in
plaster of paris to secure a uniform bearing in the testing ma-
chine, and crushed. The total breaking load is then divided by
the area in compression in square inches. No deduction to be
made for hollow spaces; the area will be considered as the prod-
uct of the width by the length.
11. The absorption tests must be made as follows: The sample
is first thoroughly dried to a constant weight. The weight
must be carefully recorded. It is then placed in a pan or a tray
of water, face downward, immersing it to a depth of not more
than one-half inch. It is again carefully weighed at the follow-
ing periods: Thirty minutes, four hours and forty-eight hours,
respectively, from the time of immersion, being replaced in
the water in each case as soon as the weight is taken. Its
compressive strength while still wet is then determined at
the end of the forty-eight-hour period in the manner specified
in Section 10.
12. The freezing tests are made as follows: The sample is
immersed as described in Section 11, for at least four hours,
and then weighed. It is then placed in a freezing mixture or a
refrigerator, or otherwise subjected to a temperature of less than
15 degrees Fahrenheit for at least twelve hours. It is then
540 CEMENT AND CONCRETE
removed and placed in water, where it must remain for at least
one hour, the temperature of which is at least 150 degrees
Fahrenheit. This operation is repeated ten times, after which
the sample is again weighed while still wet from the last thawing.
Its crushing strength should then be determined as called for in
Section 10.
13. The fire test must be made as follows: Two samples are
placed in a cold furnace in which the temperature is gradually
raised to 1,700 degrees Fahrenheit. The test piece must be
subjected to this temperature for at least thirty minutes. One
of the samples is then plunged in cold water (about 50 to 60
degrees Fahrenheit) and the results noted. The second sample
is permitted to cool gradually in air and the results noted.
14. The following requirements must be met to secure an
acceptance of the materials: The modulus of rupture for con-
crete blocks at twenty-eight days old must average 150 and must
not fall below 100 in any case. The ultimate compressive
strength at twenty-eight days must average 1,000 pounds per
square inch, and must not fall below 700 pounds in any case.
The percentage of absorption (being the weight of water
absorbed divided by the weight of the dry sample) must not
average higher than 15 per cent and must not exceed 20 per cent
in any case. The reduction of compressive strength must not be
more than 33 1-3 per cent, except that when the lower figure is
still above 1,000 pounds per square inch the loss in strength may
be neglected. The freezing and thawing process must not cause
a loss in weight greater than 10 per cent nor a loss in strength of
more than 33 1-3 per cent, except that when the lower figure is
still above 1,000 pounds per square inch the loss in strength may
be neglected. The fire test must not cause the material to
disintegrate.
15. The approval of any material is given only under the
following conditions:
(a) A brand mark for identification must be impressed on or
otherwise attached to the material.
(b) A plant for the production of the material must be in full
operation when the official tests are made.
(c) The name of the firm or corporation and the responsible
officers must be placed on file with the chief of the Bureau of
Building Inspection, and changes in the same promptly reported.
CONCRETE BLOCKS: REGULATIONS 541
(d) The chief of the Bureau of Building Inspection may
require full tests to be repeated on samples selected from the
open market when, in his opinion, there is any doubt as to
whether the product is up to the standard of these regulations,
and the manufacturer must submit to the Bureau of Building
Inspection once in at least every four months a certificate of
tests showing that the average resistance of three specimens to
cross-breaking and crushing are not below the requirements
of these regulations. Such tests must be made by some labora-
tory of recognized standing on samples selected by a building
inspector or the laboratory, from material actually going into
construction, and not on ones furnished by the manufacturer.
(e) In case the results of tests made under these conditions
should show that the standard of these regulations is not main-
tained, the approval of this bureau to the manufacturer of said
blocks will at once be suspended or revoked.
APPENDIX I
PROGRESS REPORT OF COMMITTEE ON UNIFORM TESTS OF
CEMENT, AMERICAN SOCIETY OF CIVIL ENGINEERS
Presented at the Annual Meeting, January 21, 1903, and Amended at the
Annual Meeting, January 20, 1904.
Your Committee on Uniform Tests of Cement has devoted much
time, and given very careful consideration, to the subject. Frequent
meetings have been held, and a number of investigations carried on, some
of which cannot be finally reported at this time.
On several matters which have been considered, such as the sub-
stitution of a natural sand for the standard quartz, and the tests for the
normal consistency and constancy of volume, the Committee has not
reached final conclusions.
While not prepared to submit a final report, the Committee feels
that it should present a report of progress in order that the Society may
be informed of the results of its investigations and conclusions.
The work of the Committee has been confined entirely to the methods
for making tests, without attempting to specify v/hat tests should be
made.
In order to do full justice to the subject under consideration, it will
be necessary to compile and report the results of the experiments now
under way, and your Committee asks, therefore, that it be continued.
SAMPLING
1. Selection of Sample. — The selection of the sample for test-
ing is a detail that must be left to the discretion of the engineer; the
number and the quantity to be taken from each package will depend
largely on the importance of the work, the number of tests to be made, and
the facilities for making them.
2. The sample shall be a fair average of the contents of the package;
it is recommended that, where conditions permit, one barrel in every ten
be sampled.
3. All samples should be passed through a sieve having twenty
meshes per linear inch, in order to break up lumps and remove foreign
material; this is also a very effective method for mixing them together
in order to obtain an average. For determining the characteristics of
a shipment of cement, the individual samples may be mixed and the
average tested; where time will permit, however, it is recommended that
they be tested separately.
542
UNIFORM METHODS OF TESTING 543
4. Method of Saxnpling. — Cement in barrels should be sampled
through a hole made in the center of one of the staves, midway between
the heads, or in the head, by means of an auger or a sampling iron similar
to that used by sugar inspectors. If in bags, it should be taken from
surface to center.
CHEMICAL ANALYSIS
5. Significance. — Chemical analysis may render valuable service
in the detection of adulteration of cement with considerable amounts of
inert material, such as slag or ground limestone. It is of use, also, in
determining whether certain constituents, believed to be harmful when
in excess of a certain percentage, as magnesia and sulphuric anhydride,
are present in inadmissible proportions. While not recommending a
definite limit for these impurities, the Committee would suggest that the
most recent and reliable evidence appears to indicate that, for Portland
cement, magnesia to the amount of 5 per cent, and sulphuric anhydride
to the amount of 1.75 per cent, may safely be considered harmless.
6. The determination of the principal constituents of cement — •
silica, alumina, iron oxide, and lime — is not conclusive as an indication
of quality. Faulty character of cement results more frequently from
imperfect preparation of the raw material or defective burning than
from incorrect proportions of the constituents. Cement made from very
finely-ground material, and thoroughly burned, may contain much more
lime than the amount usually present and still be perfectly sound. On
the other hand, cements low in lime may, on account of careless prepara-
tion of the raw material, be of dangerous character. Further, the ash
of the fuel used in burning may so greatly modify the composition of the
product as largely to destroy the significance of the results of analysis.
7. Method. — As a method to be followed for the analysis of cement
that proposed by the Committee on Uniformity in the Analysis of
Materials for the Portland Cement Industry, of the New York Section of
the Society for Chemical Industry, and published in the Journal of the
Society for January 15, 1902, is recommended.
SPECIFIC GRAVITY
8. Significance. — The specific gravity of cement is lowered by un-
derburning, adulteration, and hydration, but the adulteration must be in
considerable quantity to affect the results appreciably.
9. Inasmuch as the differences in specific gravity are usually very
small, great care must be exercised in making the determination.
10. When properly made, this test affords a quick check for under-
burning or adulteration.
11. Apparatus and Method. — The determination of specific gravity
is most conveniently made with Le Chatelier's apparatus. This consists
of a flask (D), Fig. 1, of 120 cu. cm. (7.32 cu. ins.) capacity, the neck of
which is about 20 cm. (7.87 ins.) long; in the middle of this neck is a bulb
(C), above and below which are two marks (F) and (E); the volume
between these marks is 20 cu. cm. (1.22 cu. ins.). The neck has a dia<
544
CEMENT AND CONCRETE
meter of about 9 mm. (0.35 in.), and is graduated into tenths of cubic
centimeters above the mark (F).
12. Benzine (62 degrees Baum^ naphtha), or kerosene free from
water, should be used in making the determination.
13. The specific gravity can be determined in two ways;
(1) The flask is filled with either of these liquids to the lower mark
{E), and 64 gr. (2.25 oz.) of powder, previously dried at 100° Cent.
(212° Fahr.) and cooled to the temperature of the liquid, is gradually
introduced through the funnel (B) [the stem of which extends into the
flask to the top of the bulb (C)], until the upper mark (F) is reached.
The difference in weight between the cement remaining and the original
quantity (64 gr. ) is the weight which has displaced 20 cu. cm.
14. (2) The whole quantity of the powder is introduced, and the
level of the liquid rises to some division of the graduated neck. This
reading plus 20 cu. cm. is the volume displaced by 64 gr. of the powder.
15. The specific gravity is then obtained from the formula:
Specific Gravity
Weight of Cement
Displaced Volume
16. The flask, during the operation, is kept immersed in water in a
jar {A), in order to- avoid variations in the temperature of the liquid.
The results should agree within 0.01.
17. A convenient method for cleaning the apparatus is as follows.
The flask is inverted over a large vessel, preferably a glass jar, and shaken
vertically until the liquid starts to flow freely; it is then held still in a
vertical position until empty; the remaining traces of cement can be
UNIFORM METHODS OF TESTING 545
removed in a similar manner by pouring into the flask a small quantity of
clean liquid and repeating the operation.
18. More accurate determinations may be made with the picnometer.
FINENESS
19. Significance. — It is generally accepted that the coarser par-
ticles in cement are practically inert, and it is only the extremely fine
powder that possesses adhesive or cementing qualities. The more finely
cement is pulverized, all other conditions being the same, the more sand
it will carry and produce a mortar of a given strength.
20. The degree of final pulverization which the cement receives
at the place of manufacture is ascertained by measuring the residue
retained on certain sieves. Those known as the No. 100 and No. 200
sieves are recommended for this purpose.
'21. Apparatus. — The sieves should be circular, about 20 cm.
{7.87 ills.) in diameter, 6 cm. (2.36 ins.) high, and provided with a pan
5 cm. (1.97 ins.) deep, and a cover.
22. The wire cloth should be woven from brass wire having the
following diameters:
No. 100, 0.0045 in. ; No. 200, 0.0024 in.
23. This cloth should be mounted on the frames without distqrtion;
the mesh should be regular in spacing and be within the following Ifmits:
No. 100, 96 to 100 meshes to the linear inch.
No. 200, 188 to 200 " " "
24. Fifty grams (1.76 oz.) or 100 gr. (3.52 oz.) should be used for
the test, and dried at a temperature of 100° Cent. (212° Fahr. ) prior to
sieving.
25. Method. — The Committee, after careful investigation, has
reached the conclusion that mechanical sieving is not as practicable or
efficient as hand work, and, therefore, recommends the following method:
26. The thoroughly dried and coarsely screened sample is weighed
and placed on the No. 200 sieve, which, with pan and cover attached, is
held in one hand in a slightly inclined position, and moved forward and
backward, at the same time striking the side gently with the palm of the
other hand, at the rate of about 200 strokes per minute. The operation
is continued until not more than one-tenth of 1 per cent passes through
after one minute of continuous sieving. The residue is weighed, then
placed on the No. 100 sieve and tlie operation repeated. The work may
be expedited by placing in the sieve a small quantity of large shot. The
results should be reported to the nearest tenth of 1 per cent.
NORMAL CONSISTENCY
27. Significance. — The use of a proper percentage of water in
making the pastes^ from which pats, tests of setting, and briquettes
' The term " paste " is used in this report to designate a mixture of cement and water,
and the word " mortar " a mixture of cement, sand, and water.
546
CEMENT AND CONCRETE
are made, is exceedingly important, and affects vitally the results ob-
tained.
28. The determination consists in measuring the amount of water
required to reduce the cement to a given state of plasticity, or to what
is usually designated the normal consistency.
29. Various methods have been proposed for making this deter-
mination, none of which has been found entirely satisfactory. The
Committee recommends the following:
30. Method. Vicat Needle Apparatus. — This consists of a frame
{K), Fig. 2, bearing a movable rod (L), with the cap (A) at one end, and
Fig. 2.
at the other the cylinder (5), 1 cm. (0.39 in.) in diameter, the cap, rod,
and cylinder weighing 300 gr. (10.58 oz.). The rod, which can be held in
any desired position by a screw (F), carries an indicator, which moves
over a scale (graduated to centimeters) attached to the frame (K).
The paste is held by a conical, hard-rubber ring (/), 7 cm. (2.76 ins.) in
diameter at the base, 4 cm. (1.57 ins.) high, resting on a glass plate (J),
about 10 cm. (3.94 ins.) square.
31. In making the determination, the same quantity of cement
as will be subsequently used for each batch in making the briquettes (but
not less than 500 grams) is kneaded into a paste, as described in Para-
graph 58, and quickly formed into a ball with the hands, completing the
operation by tossing it six times from one hand to the other, maintained
6 ins. apart; the ball is then pressed into the rubber ring, through the
larger opening, smoothed off, and placed (on its large end) on a glass plate
and the smaller end smoothed off with a trowel; the paste, confined in the
ring, resting on the plate, is placed under the rod bearing the cylinder
which is brought in contact with the surface and quickly released.
UNIFORM METHODS OF TESTING
547
32. The paste is of normal consistency when the cylinder pene-
trates to a point in the mass 10 mm. (0.39 in.) below the top of the ring.
Great care must be taken to fill the ring exactly to the top.
33. The trial pastes are made with varying percentages of water
until the correct consistency is obtained.
34. The Committee has recommended, as normal, a paste, the con-
sistency of which is rather wet, because it believes that variations in
the amount of compression to which the briquette is subjected in moulding
are likely to be less with such a paste.
35. Having determined in this manner the proper percentage of
water required to produce a paste of normal consistency, the proper per-
centage required for the mortars is obtained from an empirical formula.
36. The Committee hopes to devise such a formula. The subject
proves to be a very difficult one, and, although the Committee has given
it much study, it is not yet prepared to make a definite recommendation.*
TIME OF SETTING
37. Significance. — The object of this test is to determine the time
which elapsed from the moment water is added until the paste ceases to
be fluid and plastic (called the "initial set "), and also the time required
for it to acquire a certain degree of hardness (called the " final " or
" hard set "). The former of these is the more important, since, with
the commencement of setting, the process of crystallization or harden-
ing is said to begin. As a disturbance of this process may produce a
loss of strength, it is desirable to complete the operation of mixing and
* The Committee of the American Society for Testing Materials on
Standard Specifications for Cement inserts the following table for temporary
use to be replaced by one to be devised by the Committee of the American
Society of Civil Engineers.
Percentage of Water for Standard Sand Mortars.
One Cement
One Cement
One Cement
Neat.
Three Standard
Neat.
Three Standard
Neat.
Tliree Standard
Ottawa Sand.
Ottawa Sand.
Ottawa Sand.
15
8.0
23.
9.3
31
10.7
16
8.2
24
9.5
32
10.8
17
8.3
25
9.7
33
11.0
18
8.5
26
9.8
34
11.2
19
8.7
27
10.0
35
11.5
20
8.8
28
10.2
36
11.5
21
9.0
29
10.3
37
11.7
22
9.2
30
10.5
38
11.8
1 tol
1 to 2
1 to 3
1 to4
lto6
Cement
50(
)
333
250
200
167
Sand .
50
066
750
800
833
548 CEMENT AND CONCRETE
moulding or incorporating the mortar into the work before the cement
begins to set.
38. It is usual to measure arbitrarily the beginning and end of
the setting by the penetration of weighted wires of given diameters.
39. Method. — For this purpose the Vicat Needle, which has already
been described in Paragraph 30, should be used.
40. In making the test, a paste of normal consistency is moulded
and placed under the rod (L), Fig. 2, as described in Paragraph 31; this
rod, bearing the cap (D) at one end and the needle (//), 1 mm. (0.039
in.) in diameter, at the other, weighing 300 gr. (10.58 oz.). The needle
is then carefully brought in contact with the surface ol the paste and
quickly released.
41. The setting is said to have commenced when the needle ceases
to pass a point 5 mm. (0.20 in.) above the upper surface of the glass
plate, and is said to have terminated the moment the needle does not
sink visibly into the mass.
42. The test pieces should be stored in moist air during the test;
this is accomplished by placing them on a rack over water contained in
a pan and covered with a damp cloth, the cloth to be kept away from
them by means of a wire screen; or they may be stored in a moist box
or closet.
43. Care should be taken to keep the needle clean, as the collec-
tion of cement on the sides of the needle retards the penetration, while
cement on the point reduces the area and tends to increase the pene-
tration.
44. The determination of the time of setting is only approximate,
being materially affected by the temperature of the mixing water, the
temperature and humidity of the air during the test, the percentage
of water used, and the amount of moulding the paste receives.
STANDARD SAND
45. The Committee recognizes the grave objections to the stand-
ard quartz now generally used, especially on account of its high per-
centage of voids, the difficulty of compacting in the moulds, and its lack
of uniformity; it has spent much time in investigating the various natural
sands which appeared to be available and suitable for use.
46. For the present, the Committee recommends the natural sand
from Ottawa, 111., screened to pass a sieve having 20 meshes per linear
inch and retained on a sieve having 30 meshes per linear inch; the wires
to have diameters of 0.0165 and 0.0112 in., respectively, i.e., half the
width of the opening in each case. Sand having passed the No. 20
sieve shall be considered standard when not more than one per cent
passes a No. 30 sieve after one minute continuous sifting of a 500-gram
sample.
47. The Sandusky Portland Cement Company, of Sandusky, Ohio,
has agreed to undertake the preparation of this sand, and to furnish it
at a price only sufficient to cover the actual cost of preparation.
UNIFORM METHODS OF TESTING
549
FORM OF BRIQUETTE
48. While the form of the briquette recommended by a former
Committee of the Society is not wholly satisfactory, this Committee
is not prepared to suggest any change, other than rounding off the corners
by curves of J-in. radius, Fig. 3.
Fia. 3.
Fia. 4.
MOULDS
49. The moulds should be made of brass, bronze, or some equally
non-corrodible material, having sufficient metal in the sides to prevent
spreading during moulding.
50. Gang moulds, which f)ermit moulding a number of briquettes
at one time, are preferred by many to single moulds; since the greater
quantity of mortar that can be mixed tends to produce greater uni-
formity in the results. The type shown in Fig. 4 is recommended.
51. The moulds should be wiped with an oily cloth before using.
MIXING
62. All proportions should be stated by weight; the quantity of
water to be used should be stated as a percentage of the dry material.
53. The metric system is recommended because of the convenient
relation of the gram and the cubic centimeter.
54. The temperature of the room and the mixing water should
be as near 21 degrees Cent. (70 degrees ' Fahr. ) as it is practicable to
maintain it.
55. The sand and cement should be thoroughly mixed dry. The
550 CEMENT AND CONCRETE
mixing should be done on some non-absorbing surface, preferably plate
glass. If the mixing must be done on an absorbing surface it should
be thoroughly dampened prior to use.
56. The quantity of material to be mixed at one time depends on
the number of test pieces to be made; about 1000 gr. (35.28 oz.) makes
a convenient quantity to mix, especially by hand methods.
57. The Committee, after investigation of the various mechanical
mixing machines, has decided not to recommend any machine that has
thus far been devised, for the following reasons:
(1 ) The tendency of most cement is to " ball up " in the machine,
thereby preventing the working of it into a homogeneous paste; (2)
there are no means of ascertaining when the mixing is complete with-
out stopping the machine, and (3) the difficulty of keeping the machine
clean.
58. Method. — The material is weighed and placed on the mixing
table, and a crater formed in the center, into which the proper percentage
of clean water is poured; the material on the outer edge is turned into
the crater by the aid of a trowel. As soon as the water has been absorbed,
which should not require more than one minute, the operation is completed
by vigorously kneading with the hands for an additional 1^ minutes, the
process being similar to that used in kneading dough. A sand-glass
affords a convenient guide for the time of kneading. During the opera-
tion of mixing the hands should be protected by gloves, preferably of
rubber.
MOULDING
59. Having worked the paste or mortar to the proper consistency,
it is at once placed in the moulds by hand.
60. The Committee has been unable to secure satisfactory results
with the present moulding machines; the operation of machine mould-
ing is very slow, and the present types permit of moulding but one
briquette at a time, and are not practicable with the pastes or mortars
herein recommended.
61. Method. — The moulds should be filled at once, the material
pressed in firmly with the fingers and smoothed off with a trowel with-
out ramming; the material should be heaped up on the upper surface of
the mould, and, in smoothing off, the trowel should be drawn over the
mould in sucTi a manner as to exert a moderate pressure on the excess
material. The mould should be turned over and the operation repeated.
62. A check upon the uniformity of the mixing and moulding is
afforded by weighing the briquettes just prior to immersion, or upon
removal from the moist closet. Briquettes which vary in weight more
than 3 per cent from the average should not be tested.
STORAGE OF THE TEST PIECES
63. During the first 24 hours after moulding the test pieces should
be kept in moist air to prevent them from drying out.
64. A moist closet or chamber is so easily devised that the use of
UNIFORM METHODS OF' TESTING
551
the damp cloth should be abandoned if possible. Covering the test pieces
with a damp cloth is objectionable, as commonly used, because the cloth
may dry out unequally, and, in consequence, the test pieces are not all
maintained under the same condition. Where a moist closet is not
available, a cloth may be used and kept uniformly wet by immersing the
ends in water. It should be kept from direct contact with the test pieces
by means of a wire screen or some similar arrangement.
65. A moist closet consists of a soapstone or slate box, or a metal-
lined wooden box — the metal lining being covered with felt and this felt
kept wet. The bottom of the box is so constructed as to hold water, and
the sides are provided with cleats for holding glass shelves on which to
place the briquettes. Care should be taken to keep the air in the closet
uniformly moist.
66. After 24 hours in moist air the test pieces for longer periods of
time should be immersed in water maintained as near 21° Cent. (70*
Fahr. ) as practicable ; they may be stored in tanks or pans, which should
be of non-corrodible material.
TENSILE STRENGTH
67. The tests may be made on any standard machine. A solid
metal clip, as shown in Fig. 5, is recommended. This clip is to be used
without cushioning at the points of contact with the
test specimen. The bearing at each point of con-
tact should be { in. wide, and the distance between
the center of contact on the same clip should be
IJ ins.
68. Test pieces should be broken as soon as they
are removed from the water. Care should be observed
in centering the briquettes in the testing machine,
as cross-strains, produced by improper centering, tend
to lower the breaking strength. The load should
not be applied too suddenly, as it may produce vibra-
tion, the shock from which often breaks the briquette
before the ultimate strength is reached. Care must
be taken that the clips and the sides of the briquette
be clean and free from grains of sand or dirt, which
would prevent a good bearing. The load should be
applied at the rate of 600 lbs. per minute. The aver- F«o- 5.
age of the briquettes of each sample tested should be taken as the test,
excluding any results which are manifestly faulty.
CONSTANCY OF VOLUME
69. Significance. — The object is to develop those qualities which
tend to destroy the strength and durability of a cement. As it is highly
essential to determine such qualities at once, tests of this character are
for the most part made in a very short time, and are known, therefore,
as accelerated tests. Failure is revealed by cracking, checking, swelling.
552 CEMENT AND CONCRETE
or disintegration, or all of these phenomena. A cement which remains
perfectly sound is said to be of constant volume.
70. Methods. — Tests for constancy of volume are divided into two
classes: (1) normal tests, or those made in either air or water maintained
at about 21° Cent. (70° Fahr. ), and (2) accelerated tests, or those made in
air, steam, or water at a temperature of 45° Cent. (115° Fahr. ) and upward.
The test pieces should be allowed to remain 24 hours in moist air before
immersion in water or steam, or preservation in air.
71. For these tests, pats, about 7 J cm. (2,95 ins.) in diameter,
1 J cm. (0.49 in.) thick at the center, and tapering to a thin edge, should
be made, upon a clean glass plate [about 10 cm. (3.94 ins.) square], from
cement paste of normal consistency.
72. Normal Test. — • A pat is immersed in water maintained as
near 21° Cent. (70° Fahr.) as possible for 28 days, and observed at inter-
vals. A similar pat is maintained in air at ordinary temperature and
observed at intervals.
73. Accelerated Test. — A pat is exposed in any convenient way in
an atmosphere of steam, above boiling water, in a loosely closed vessel,
for 3 hours.
74. To pass these tests satisfactorily, the pats should remain firm
and hard, and show no signs of cracking, distortion, or disintegration.
75. Should the pat leave the plate, distortion may be detected best
with a straight-edge applied to the surface which was in contact with the
plate.
76. In the present state of our knowledge it cannot be said that
cement should necessarily be condemned simply for failure to pass the
accelerated tests; nor can a cement be considered entirely satisfactory
simply because it has passed these tests.
Submitted on behalf of the Committee.
George S. Webster,
Chairman.
Richard L. Humphrey,
Secretary.
Committee
George S. Webster.
Richard L. Humphrey.
George F. Swain.
Alfred Noble.
Louis C. Sabin.
S. B. Newberry.
Clifford Richardson.
W. B. W. Howe.
F. H. Lewis.
APPENDIX II
REPORT OF COMMITTEE ON STANDARD SPECIFICATIONS FOR
CEMENT, AMERICAN SOCIETY FOR TESTING MATERIALS
Adopted by the Society, November 14th, 1904.
GENERAL OBSERVATIONS
1. These remarks have been prepared with a view of pointing out
the pertinent features of the various requirements and the precautions
to be observed in the interpretation of the results of the tests.
2. The Committee would suggest that the acceptance or rejection
under these specifications be based on tests made by an experienced
person having the proper means for making the tests.
SPECIFIC GRAVITY
3. Specific gravity is useful in detecting adulteration or underburning.
The results of tests of specific gravity are not necessarily conclusive as an
indication of the quality of a cement, but when in combination with the
results of other tests may afford valuable indications.
FINENESS
4. The sieves should be kept thoroughly dry.
TIME OF SETTING
5. Great care should be exercised to maintain the test pieces under
as uniform conditions as possible. A sudden change or wide range of
temperature in the room in which the tests are made, a very dry or humid
atmosphere, and other irregularities vitally affect the rate of setting.
TENSILE STRENGTH
6. Each consumer must fix the Uiinimum requirements for tensile
strength to suit his own conditions. They shall, however, be within the
limits stated
CONSTANCY OF VOLUME
7. The tests for constancy of volume are divided into two classes,
the first normal, the second accelerated. The latter should be regarded
as a precautionary test only, and not infallible. So many conditions enter
into the making and interpreting of it that it should be used with extreme
care.
8. In making the pats the greatest care should be exercised to
avoid initial strains due to moulding or to too rapid drying-out during the
.5.53
554 CEMENT AND CONCRETE
first twenty-four hours. The pats should be preserved under the most
uniform conditions possible, and rapid changes of temperature should be
avoided.
9. The failure to meet the requirements of the accelerated tests need
not be sufficient cause for rejection. The cement may, however, be held
for twenty-eight days, and a retest made at the end of that period. Fail-
ure to meet the requirements at this time should be considered sufficient
cause for rejection, although in the present state of our knowledge it
cannot be said that such failure necessarily indicates unsoundness, nor
can the cement be considered entirely satisfactory simply because it
passes the tests.
GENERAL CONDITIONS
1. All cement shall be inspected.
2. Cement may be inspected either at the place of manufacture or
on the work.
3. In order to allow ample time for inspecting"] and testing, the
cement should be stored in a suitable weather-tight building having
the floor properly blocked or raised from the ground.
4. The cement shall be stored in such a manner as to p)ermit easy
access for proper inspection and identification of each shipment.
5. Every facility shall be provided by the contractor and a p>eriod
of at least twelve days allowed for the inspection and necessary tests.
6. Cement shall be delivered in suitable packages with the brand
and name of manufacturer plainly marked thereon.
7. A bag of cement shall contain 94 pounds of cement net. Each
barrel of Portland cement shall contain 4 bags, and each barrel of natural
cement shall contain 3 bags of the above net weight.
8. Cement failing to meet the seven-day requirements may be held
awaiting the results of the twenty-eight day tests before rejection.
9. All tests shall be made in accordance with the methods proposed
by the Committee on Uniform Tests of Cement of the American Society
of Civil Engineers, presented to the Society January 21, 1903, and
amended January 20, 1904, with all subsequent amendments thereto.
10. The acceptance or rejection shall be based on the following
requirements :
NATURAL CEMENT
11. Definition. — This term shall be applied to the finely pulverized
product resulting from the calcination of an argillaceous limestone at a
temperature only sufficient to drive off the carbonic acid gas.
SPECIFIC GRAVITY
12. The specific gravity of the cement thoroughly dried at 100* C.
shall be not less than 2.8.
STANDARD SPECIFICATIONS 555
FINENESS
13. It shall leave by weight a residue ot not more than 10 per cent
on the No. 100, and 30 per cent on the No. 200 sieve.
TIME OF SETTING
14. It shall develop initial set in not less than ten minutes, and
hard set in not less than thirty minutes, nor more than three hours.
TENSILE STRENGTH
15. The minimum requirements for tensile strength for briquettes
one inch square in cross section shall be within the following limits, and
shall show no retrogression in strength within the periods specified : '
Age Neat Cement Strength
24 hours in moist air 50 — 100 lbs.
7 days (1 day in moist air, 6 days in water) . . . 100 — 200 "
28 days (1 day in moist air, 27 days in water) . . 200—300 "
One Part Cement, Three Parts ■'Standard Sand
7 days (1 day in moist air, 6 days in water) . . . 25 — 75 lbs.
28 days (1 day in moist air, 27 days in water) . . 75 — 150 "
CONSTANCY OF VOLUME
16. Pats of neat cement about three inches in diameter, one-half
inch thick at centre, tapering to a thin edge, shall be kept in moist air
for a period of twenty-four hours.
(o) A pat is then kept in air at normal temperature.
(6) Another is kept in water maintained as near 70° F. as practicable.
17. These pats are observed at intervals for at least 28 days, and,
to satisfactorily pass the tests, should remain firm and hard and show
no signs of distortion, checking, cracking, or disintegrating.
PORTLAND CEMENT
18. Definition. — This term is applied to the finely pulverized product
resulting from the calcination to incipient fusion of an intimate mixture
of properly proportioned argillaceous and calcareous materials, and to
which no addition greater than 3 per cent has been made subsequent to
calcination.
For example, the minimum requirement for the twenty-four hourneat cement test
■hould be some specified value within the limits of 50 and 100 pounds, and so on for each
period stated.
556 CEMENT AND CONCRETE
SPECIFIC GRAVITY
19. The specific gravity of the cement, thoroughly dried, at 100° C,
shall be not less than 3.10.
FINENESS
20. It shall leave by weight a residue of not more than 8 per cent
on the No. 100, and not more than 25 per cent on the No. 200 sieve.
TIME OF SETTING
21. It shall develop initial set in not less than thirty minutes, but
must develop hard set in not less than one hour, nor more than ten hours.
TENSILE STRENGTH
22. The minimum requirements for tensile strength for briquettes
one inch square in section shall be within the following limits, and shall
show no retrogression in strength within the periods specified: '
Age Neat Cement Strength
24 hours in moist air 150 — 200 lbs.
7 days (1 day in moist air, 6 days in water) . . 450 — 550 "
28 days (1 day in moist air, 27 days in water) . . 550 — 650 "
One Part Cement, Three Parts Sand
7 days (1 day in moist air, 6 days in water) . . 150 — 200 lbs.
28 days (1 day in moist air, 27 days in water) . . 200—300 "
CONSTANCY OF VOLUME
23. Pats of neat cement about three inches in diameter, one-half
inch thick at the centre, and tapering to a thin edge, shall be kept in
moist air for a period of twenty-four hours.
(a) A pat is then kept in air at normal temperature and observed at
intervals for at least 28 days.
(6) Another pat is kept in water maintained as near 70" F. as
practicable, and observed at intervals for at least 28 days.
(c) A third pat is exposed in any convenient way in an atmosphere
of steam, above boiling water, in a loosely closed vessel for five hours.
24. These pats, to satisfactorily pass the requirements, shall remain
firm and hard and show no signs of distortion, checking, cracking, or
disintegrating.
' For example, the minimum requirement for the twenty-four hour neat cement test
should be some specified value within the limits oi 150 and 200 pounds, and so on for each
perio<l stated.
STANDARD SPECIFICATIONS 557
SULPHURIC ACID AND MAGNESIA
25. The cement shall not contain more than 1 .75 per cent of anhydrous
sulphuric acid (SO,), nor more than 4 per cent of magnesia (MgO).
Submitted on behalf of the Committee.
George F. Swain, Chairman.
George S. Webster, V ice-Chairman.
Richard L. Humphrey, Secretary.
Committee
George F. Swain. John B. Lober.
George S. Webster. Andreas Lundteigen.
Richard L. Humphrey. Charles F. McKenna.
Booth, Garrett & Blair. W. W. Maclay.
C. W. Boynton. Charles A. Matcham.
Spencer Cosby. Spencer B. Newberry.
A. W. Dow. J. M. Porter.
L. Henry Dumary. Joseph T. Richards.
A. F. Gerstell. Clifford Richardson.
Edward M. Hagar. L. C. Sarin.
W. H. Harding. Harry J. Seaman.
Olaf Hoff. S. S. Voorhees.
Lathbury & Spackman. W. S. Eames.
Robert W. Lesley. H. G. Kelly.
F, H. Lewis.
APPENDIX III.
NEW YORK SECTION, SOCIETY FOR CHEMICAL INDUSTRY
Method Suggested for the Analysis of Limestones, Raw Mixtures, and Port'
land Cements by the Committee on Uniformity in Technical
Analysis with the Advice of W. F. Hillebrand.
SOLUTION
One-half gram of the finely-powdered substance is to be weighed
out and, if a limestone or unburned mixture, strongly ignited in a covered
platinum crucible over a strong blast for 15 minutes, or longer if the
blast is not powerful enough to effect complete conversion to a cement
in this time. It is then transferred to an evaporating dish, preferably
of platinum for the sake of celerity in evaporation, moistened with enough
water to prevent lumping, and 5 to* 10 c. c. of strong HCl added and
digested with the aid of gentle heat and agitation until solution is com-
plete. Solution may be aided by light pressure with the flattened end of
a glass rod.' The solution is then evaporated to dryness, as far as this may
be possible on the bath.
SILICA (SiOj)
The residue without further heating is treated at first with 5 to 10
c. c. of strong HCl, which is then diluted to half strength or less, or upon
the residue may be poured at once a larger volume of acid of half strength.
The dish is then covered and digestion allowed to go on for 10 minutes on
the bath, after which the solution is filtered and the separated silica
washed thoroughly with water. The filtrate is again evaporated to
dryness, the residue without further heating, taken up with acid and
water and the small amount of silica it contains separated on another
filter paper. The papers containing the residue are transferred wet to a
weighed platinum crucible, dried, ignited, first over a Bunsen burner until
the carbon of the filter is completely consumed, and finally over the blast
for 15 minutes and checked by a further blasting for 10 minutes or to
constant weight. The silica, if great accuracy is desired, is treated in the
crucible with about 10 c. c. of HFl and four drops of HjSO^ and evaporated
over a low flame to complete dryness. The small residue is finally blasted,
for a minute or two, cooled and weighed. The difference between this
weight and the weight previously obtained gives the amount of silica.'
' If anything remains undecomposed it should be separated, fused with a little
Na^COg dissolved and added to the original solution. Of course a small amount of sepa-
rated non-gelatinous silica is not to be mistaken for undecomposed matter.
* For ordinary control in the plant laboratory this correction may, perhaps, be neg»
lected; the double evaporation never.
558
METHOD OF ANALYSIS 559
ALUMINA AND IRON (A1,0, AND Fe,0,)
The filtrate, about 250 c. c, from the second evaporation for SiO„
is made alkaline with NH^OH after adding HCl, if need be, to insure a
total of 10 to 15 c. c. strong acid, and boiled to expel excess of NH„ or
until there is but a faint odor of it, and the precipitate iron and aluminum
hydrates, after settling, are washed once by decantation and slightly on
the filter. Setting aside the filtrate, the precipitate is dissolved in hot
dilute HCl, the solution passing into the beaker in which the precipitation
was made. The aluminum and iron are then reprecipitated by NH4OH,
boiled and the second precipitate collected and washed on the same filter
used in the first instance. The filter paper, with the precipitate, is then
placed in a weighed platinum crucible, the paper burned off and the
precipitate ignited and finally blasted 5 minutes, with care to prevent
reduction, cooled and weighed as Al^Oj + FejOj.*
IRON (FcjOj)
The combined iron and aluminum oxides are fused in a platinum
crucible at a very low temperature with about 3 to 4 grams of KHSO4,
or, better, NaHS04, the melt taken up with so much dilute HjSO^ that
there shall be no less than 5 grams absolute acid and enough water to
effect solution on heating. The solution is then evaporated and even-
tually heated till acid fumes come off copiously. After cooling and redis-
solving in water the small amount of silica is filtered out, weighed, and
corrected by HFl and H2S04.^ The filtrate is reduced by zinc, or prefer-
ably by hydrogen sulphide, boiling out the excess of the latter afterwards
while passing COj through the flask, and titrated with permanganate.*
The strength of the permanganate solution should not be greater than
.0040 gr. FejOj per c. c.
LIME (CaO)
To the combined filtrate from the AljOj + Fe^Os precipitate a few
drops of NH4OH are added, and the solution brought to boiling. To
the boiling solution 20 c. c. of a saturated solution of ammonium oxalate
are added, and the boiling continued until the precipitated CaC204 assumes
a well-defined granular form. It is then allowed to stand for 20 minutes,
or until the precipitate has settled, and then filtered and washed. The
precipitate and filter are placed wet in a platinum crucible, and the paper
burned off over a small flame of a Bunsen burner. It is then ignited,
redissolved in HCl, and the solution made up to 100 c. c. with water.
Ammonia is added in slight excess, and the liquid is boiled. If a small
» This precipitate contains TiO,, PiO.,, Mns04.
* This cf>rrection of .\IjO3FejO3 forsilica should not be made when the HFl correction
of the niain silica has been omitted, unless that silica was obtained by only one evaporatioD
and filtration. After two evaporations and filtrations 1 to 2 mg. of SiO are still to be found
with the Al,0, Fe,0,.
* In this way only is the influence of titanium to be avoided and a correct result ob-
tained for iron.
560 CEMENT AND CONCRETE
amount of AljO, separates this is filtered out, weighed, and the amount
added to that found in the first determination, when greater accuracy
is desired. The lime is then reprecipitated by ammonium oxalate,
allowed to stand until settled, filtered, and washed,' weighed as oxide by
ignition and blasting in a covered crucible to constant weight, or deter-
mined with dilute standard permanganate.'
MAGNESIA (MgO)
The combined filtrates from the calcium precipitates are acidified
with HCl and concentrated on the steam bath to about 150 c. c, 10 c. c.
of saturated solution of Na(NH4)HP04 are added, and the solution boiled
for several minutes. It is then removed from the flame and cooled by
placing the beaker in ice water. After cooling, NH^OH is added drop
by drop with constant stirring until the crystalline ammonium-magnesium
ortho-phosphate begins to form, and then in moderate excess, the stirring
being continued for several minutes. It is then set aside for several hours
in a cool atmosphere and filtered. The precipitate is redissolved in hot
dilute HCl, the solution made up to about 100 c. c, 1 c. c. of a saturated
solution of Na(NH4)HP04 added, and ammonia drop by drop, with con-
stant stirring until the precipitate is again formed as described and the
ammonia is in moderate excess. It is then allowed to stand for about 2
hours, when it is filtered on a paper or a Gooch crucible, ignited, cooled,
and weighed as MggPaO^.
ALKALIES (K,0 AND Na^O)
For the determination of the alkalies, the well-known method of
Prof. J. Lawrence Smith is to be followed, either with or without the
addition of CaCOg with NH^Cl.
ANHYDROUS SULPHURIC ACID (SOJ
One gram of the substance is dissolved in 15 c. c. of HCl, filtered
and residue washed thoroughly.'
The solution is made up to 250 c. c. in a beaker and boiled. To
the boiling solution 10 c. c. of a saturated solution of BaCla is added
slowly drop by drop from a pipette and the boiling continued until the
precipitate is well formed, or digestion on the steam bath may be sub-
stituted for the boiling. It is then set aside over night, or for a few
hours, filtered, ignited, and weighed as BaSO^.
TOTAL SULPHUR
One gram of the material is weighed out in a large platinum crucible
and fused with NajCOg and a little KNO^ being careful to avoid con-
tamination from sulphur in the gases from source of heat. This may be
* The volume of wash-water should not be too large; vide Hillebrand.
^ The accuracy of this in8th3d admits of criticism, but its convenience and rapidity
demand its insertion.
* Evaporation to dryness is unnecessary, unless gelatinous silica should have separated,
and should never be performed on a bath heated by gas; vide Hillebrand.
METHOD OF ANALYSIS 561
done by fitting the crucible in a hole in an asbestos board. The melt is
treated in the crucible with boiling water and the liquid poured into a
tall, narrow beaker and more hot water added until the mass is disinte-
grated. The solution is then filtered. The filtrate contained in a No. 4
beaker is to be acidulated with HCl and made up to 250 c. c. with distilled
water, boiled, the sulphur precipitated as BaSO^ and allowed to stand
over night or for a few hours.
LOSS ON IGNITION
Half a gram of cement is to be weighed out in a platinum crucible,
placed in a hole in an asbestos board so that about f of the crucible pro-
jects below, and blasted 15 minutes, preferably with an inclined flame.
The loss by weight, which is checked by a second blasting of 5 minutes, is
the loss on ignition.
May, 1903: Recent investigations have shown that large errors
in results are often due to the use of impure distilled water and reagents.
The analyst should, therefore, test his distilled water by evaporation and
his reagents by appropriate tests before proceeding with his work.
INDEX
Abrasion —
Resistance to, 343.
Tests of, 108.
Abutments, 481 .
Accelerated Tests (see Soundness), 91.
Acceptance of Cement, 167.
Accuracy Obtainable in Tests, 151.
Acid —
Sulphuric, in Cement, 48.
Use on Concrete Surface, 382.
Adhesion —
Cement to Brick, 287, 292.
Glass, 287.
Iron, 287.
Steel Rods, 298.
Stone, 286.
Terra Cotta, 287.
Effect of Character Surface, 290.
Plaster Paris, 291.
Regaging, 290.
Richness Mortar, 288.
Neat and Sand Mortars, 293,
Portland to Natural, 284.
Results of Tests, 284.
' Tests of Cement, 106.
Adulteration, 67.
Age and Aeration of Cement —
Effect on Time Setting, 82.
Specific Gravity, 56.
Strength, 249.
Aggregate —
Bowlder Stone, 336.
Brick, 200, 338, 349.
anders, 316, 323, 352.
aean, 202.
Cost, 209.
Crushing, 208.
Fireproof Concrete, 349.
Granite, 336.
Gravel as, 206, 312, 317, 323.
Material for, 200.
Aggregate —
Sand in, 216.
Sandstone, 308, 336.
Sea Water, 364.
Size and Shape of Fragments, 202.
Tests of, 312, 336.
Trap, 312, 323.
Voids in, 204.
Weight of, 203.
Air Hardened Mortars, 136, 246, 274.
Alum and Soap Washes, 358.
Alumina in Cement, 47.
Aliuninous Natural Cement, 39.
Amount of Mortar in Concrete, 214.
Effect on Compressive Strength,
307.
Effect on Transverse Strength, 332.
Analysis —
Methods, 49, 558.
Materials, 13, 14.
Natural Cement, 11.
Portland Cement, 8, 9.
Anchor Bolts, 298, 485.
Arch —
Big Muddy River, 496.
Highway, 494.
Mechanicsville, 494.
Melan, 398, 497.
Monier, 395.
Plain Concrete, 494, 496.
San Leandro, 494.
Thacher, 399.
Three Span, 494.
Topeka, Kan., 497.
Wvinsch, 397.
Arches —
Centers, 492. 496
Construction, 492.
Cost, 497.
Design, 488.
Drtunage, 493.
663
564
INDEX
Arches —
Finish, 493.
Viaduct, 498.
Bag for Depositing Concrete, 383, 387,
391.
Bag Method, 388.
Bags of Concrete to Form Face, 391.
to Prevent Scour, 391.
Baker, Classification of
Hydraulic Products, 3.
Ball Mills for Grinding, 16, 26.
Barrels, Cement —
Capacity, 186.
Records, 160.
Basement Floors, 440.
Base of Concrete Walk, 435.
Beams —
Concrete-Steel, 404.
for Street Railway Tracks, 447.
Steel, Protected, 426.
Strength, Experiments, 327, 417.
Fonnulas for, 405, 407.
Tables of, 414, 416.
Belt Conveyor for Concrete, 372.
Blast Furnace Slag —
Cement, 35, 36.
Sand, 173.
Block System, 365, 392.
Blocks, Concrete, in Breakwaters, 393,
507.
Blowing of Cement (see Soundness).
Board, Mixing, for Concrete, 218.
Bohme Hammer Apparatus, 128.
BoiUng Test, 91.
Bolts, Adhesion of Mortar to, 298.
Boston Elev. R.R. Tests Concrete, 306,
322.
Boston Subway, 458, 460.
Bowlder Stone as Aggregate, 336.
Box Mixer (see Cubical).
Braces for Forms, 368.
Breaking Briquets, 137.
Breaking Stone by Hand, 208.
Breakwater, 507.
Buffalo, 228, 507.
aeveland, 508.
Concrete in, 393, 507.
Marquette, 389, 393, 509.
Brick —
Adhesion of Cement to, 286.
as Concrete Aggregate, 200, 338, 349.
Brick —
Dust with Cement, 272.
Bridge —
Abutments, 461.
Piers, 478.
Forms for, 478.
Bridges (see Arches).
Briquets —
Area Breaking Section, 123.
Breaking, 137.
Form of, 122, 549.
Machine for Making, 128.
Methods of Making, 127.
Records, 161.
Storing, 131.
Broken Stone (see Aggregate).
vs. Gravel, 206.
Brushing Concrete Surface, 375, 380.
Buffalo Breakwater, 228, 507.
Buffalo, Concrete Mixing at, 228.
Buhr Millstones, 41.
Building Regulations —
New York, 432.
Philadelphia, 535.
Buildings of Concrete, 424. -
Burlap Bags for Placing Concrete, 383
391.
Burning —
Natural Cement, 39.
Portland Cement, 21.
Bushhammering Concrete, 381.
Caisson Filling, 480.
Calcium Chloride —
Effect on Setting, 84.
Test for Soundness, 95.
Calcium Sulphate —
Effect on Strength, 263.
Time Setting, 83.
Canal Locks —
Concrete for, 238, 371, 502.
Forms for, 371.
Capacity Cement Barrels, 186.
Carbonic Acid, 48.
Cars —
Concrete Plant on, 230.
for Transporting Concrete, 327.
Cascades Canal, Concrete for, 238.
Centers (see also Forms) —
for Arches, 492, 494.
for Tunnel Lining, 465.
Chamber Kilns, 22.
INDEX
665
Chemical Tests, 45.
Chicago Drainage Caual, Concrete on,
238.
Cinder Concrete —
Strength, 316.
Modulus Elasticity, 323
Cinders, Sulphur in, 352.
Classification Hydraulic Products, 1.
Clay —
for Cement Manufacture, 13.
in Concrete, 319.
in Mortar, 267.
Clip for Breaking Briquets, 138.
Cock, 142.
Form Suggested, 147.
Gimbal, 144.
Requirements for Perfect, 146.
Russell, 143.
Tests of, 145.
Clip Breaks, 140.
Cause, 140.
Prevention, 141.
Strength, 141.
Coarse Cement and Fine Sand Com-
pared, 71, 76.
Coarse Particles (see Fineness) —
Effect of, 66.
on Time Setting, 83.
Cock Clip, 142.
Cockbum Concrete Mixer, 225.
Coefficient Expansion, 346.
Cohesion and Adhesion Compared, 289,
293.
Cold, Effect on Cement, 274.
Color for Concrete Finish, 381.
of Cement, 50.
of Concrete Surface, 379, 381.
Columns, 426, 429.
Concrete-Steel, 427.
Steel, Filled and Covered, 427.
Strength of, 427.
Comparative Tests —
Natural Cements, 152.
Portland Cements, 152.
Compression Tests, 103, 302, 305.
Compressive Strength —
Concrete, 305.
Mortar, 302.
Compressive and Tensile Strength Com-
pared, 302, 327.
Compressive and Transverse Strength
Compared, 327.
Composition, Chemical, 5, 8, 11, 14, 37.
Effect on Specific Gravity, 56.
Concrete —
Amount of Mortar in, 214.
Building Blocks, 511.
Compressive Strength of, 305.
Con.struction, Rules for, 481.
Cost, 232.
Definition, 2(X), 214.
Deposition in Water, 340, 383.
Making, 214.
Mixers, 221, 226.
Mixing, Cost, 226.
Mixing by Hand, 217.
Mixing Plants, 226.
Proportions in, 214.
Thorough Mixing, 217.
Concrete-Steel, 395.
Conductivity of Concrete, 347.
Considere's Experiments, 402.
Consistency of Concrete, Effect on
Strength, 307, 310, 333.
Consistency Mortar, 190, 545.
Determination, 111.
Effect on Adhesion, 288.
Tensile Strength, 113,
246, 328.
Consistency Mortar —
Effect on Time Setting, 85.
Transverse and Compressive
Strength, 328.
Effect in Low Temperatures, 282.
Constancy of Volume (see Soundness).
Contraction Concrete in Setting, 345.
Coosa River Concrete Plant, 226.
Coping for Retaining Wall, 481.
Comers of Concrete Forms, 368.
Corrosion, Action of, 350.
Cost —
Aggregate, 209.
Concrete, 232.
Arch, 497.
Blocks, 526-532.
Curb and Gutter, 446.
Floor, 441.
Mixing, 226.
Tunnel Lining, 466.
Walk, 439, 440.
Mortar, 196, 528.
Sand, 185.
■Sand Washing, 184.
Cracks in Concrete, 375.
666
INDEX
Crushing Strength (see Compression)
Cubes, Concrete, Tests of, 306.
Cubical Concrete Mixer, 222, 226.
Curb and Gutter, 445.
Curing Concrete Blocks, 515.
Cut Stone Facing, 491.
Finish, 380.
Cylinder, Steel, Bridge Pier, 479.
Dams, 498.
Barossa, 501.
Butte, 500.
Concrete vs. Rubble, 498.
Massena, 500.
San Mateo, 501.
St. Croix, 500.
Definitions, 1.
Delivery of Cement, 158.
Density, Apparent, 51.
Deposition Concrete in Running Water,
340, 383.
Deterioration of Cement, 249.
Deval, Test for Soundness, 92, 95.
Diary, Use of, 167.
Dietsch Kiln, 22.
Drake Concrete Mixer, 225, 230.
Driers, 20.
Dromedary Concrete Mixer, 223.
Efflorescence, 360.
Estimates, Cost Concrete, 232.
Mortar, 196.
Excessive Reinforcement, 410.
Expanded Metal, 401.
Expansion —
Coefficient of, 346.
Concrete in Water, 345.
Joints, 496, 498.
Experiments —
Columns, 427.
Concrete-Steel, 402, 411, 417.
Considers '8, 402.
Hooped Concrete, 428.
Face of Concrete (see also Finish) —
Bushhammer, 381.
Colors for, 379.
Cut Stone, 380, 491.
Efflorescence, 360.
Lock Walls, 503.
Mortar, 377.
Pointed, or Tooled, 388.
Face Pressed in Compression, 306.
Facing Concrete Blocks, 524.
Faija, Mortar Mixer, 121.
Tests for Soundness, 92.
Failure of Concrete in Sea Water, 362.
Farrel's Wall Molds, 431.
Filtration through Concrete, 364, 366.
Fineness Cement —
Effect on Specific Gravity, 66, 73.
Strength, 68, 74.
Time Setting, 66, 74, 83.
Weight, 73.
Importance, 59.
Specifications, 65.
Tests, 59, 545.
Fineness of Sand, 111.
in Freezing Weather, 282.
Finish of Concrete Surface, 377.
Colors, 381.
Mortar, 377.
Pebble-dash, 380.
Plaster Paris, 379.
Rubbed, 379.
Shovel, 377.
Tooled, or Pointed, 381.
Fire, Resistance Concrete to, 346.
Fireproof Buildings, 346.
Fireproof Concrete, Aggregate for;
349.
Flexure, Concrete-Steel Beams, 404.
Tests Concrete, 328.
Mortar, 104, 327.
Floor, Systems of Concrete-Steel, 395,
425.
Floors —
Basement, 440.
Buildings, 425.
Reservoirs, 467.
Forms, Concrete, 365.
for Buildings, 430, 431.
Bridge Piers, 478.
Columns, 430.
Lock Walls, 502, 506.
Piles, 487.
Reservoir Roofs, 469.
Subways, 459, 462.
Tunnel Lining, 461, 463, 466.
Oiling, 368.
Time Left in Place, 366, 453, 485,
492.
Formulas for Concrete-Steel Beams,.
405, 407.
INDEX
667
Foundation
Concrete Walka, 434.
Pavements, 442.
Piles, 485.
Free Lime in Cement, 46, 90, 97.
Freezing Weather —
Use of Cement Mortar in, 274.
Use of Concrete in, 340.
Fuller-Leliigh Mill, 31.
Gage of Wire for Sieves, 60, 61.
Gaging Mortar —
by Hand, 119.
Effect of Thorough, 250.
with Hoe and Box, 120.
Gaging Concrete (see Mixing).
German Normal Sand, 110.
Gilmore Wires for Time Setting, 80.
Gimbal Clip, 144.
Glass, Adhesion of Cement to, 288.
Granite as Aggregate, 336.
Granolithic, Facing, 379.
Top Dressing, 436.
Granulometric Compo-sition —
Aggregate, 203.
Sand, 177.
Gravel as Aggregate, 200, 206, 312, 317,
323.
vs. Broken Stone, 206.
Gravity Concrete Mixer, 226.
Griffin Mill, 29.
Grinding Cement (see Fineness), 26.
Grout, to Seal Cracks, 506.
* on Surface Concrete, 377, 379.
Gutters and Curbs, 445.
Gypsum (see Plaster Paris).
Hammer, Bohme, 128.
Hardening Concrete Blocks, 515.
Heat, Effect on Concrete, 346.
Heating Materials in Cold Weather,
281, 466.
Hennebique System, 399, 423.
History, Hydraulic Products, 1.
Hoe and Box for Mortar Mixing, 120.
Hoffman Kiln, 22.
Hooped Concrete, 428.
Hot Materials in Cold Weather, 281.
Hot Tests (see Soundness)
House Walls, 431.
Huntington Mill, 31.
Hydraulic Index, 6.
Hydraulic Limes, 2.
Immersion of Briquets, 133.
Impervious Concrete, 364, 357.
"Improved" Cement, Strength of, 268.
Impurities in Sand, 182.
Ingredients —
in Cubic Yard Concrete, 232.
Mortar, 193.
Portland Cement, 5, 8, 9.
Interpretation Tensile Tests, 161.
Iron —
Adhesion Cement to, 288, 298.
Corrosion in Concrete, 350.
Iron Oxide, 47.
Jig for Mortar Mixing, 121.
Johnson Bar, 401.
Joints —
Expansion, 496, 498.
in Concrete, 375.
Blocks, 392.
Dam, 499.
Molds, 368.
Walks, 437, 438.
Kahn System, 400, 423.
Kent Mill, 31.
Kilns, Cement, 21.
Output, 21, 25.
Kominuter, 29.
Lagging for Forms, 366.
Tongue and Groove, 366.
Laitance, 384.
Lamp Black, in Concrete, 379, 381 .
Surface Finish, 382.
Laying Concrete Blocks, 531.
Fresh Concrete on Set Concrete,
375.
Le Chatelier, Apparatus for Specific
Gravity Test, 54.
Test for Soundness, 95.
Time Setting, 80.
Lime, Oassification, 3.
Hydraulic, 3.
Lime in Cement, 45, 269.
Lime Paste, Effect on Adhesion, 294.
Lime, Slaked, with Cement, 259, 369.
Limestone, Adhesion Cement to, 288,
291.
Limestone, Crushed, as Aggr^^te, 311,
336, 349.
Limestone Dust with Cement, 174, 201,
272, 339.
568
INDEX
Lining of Forms, 367.
Reservoirs, 469.
Loam in Sand, 182.
Lock —
Cascades, 504.
Hennepin Canal, 504.
Herr Island, 505.
Mississippi River, 506.
Locks, 502.
Culvert Lining, 503.
Facing, 503.
Methods Building, 502.
Molds, 502, 504.
Louisville and Portland Canal, Con-
crete on, 237.
Machine for Breaking Briquets, 137.
Concrete Mixing, 221.
Mortar Mixing, 121, 192.
Maclay, Test for Soundness, 92.
Magnesia in Cement, 46.
Magnesian Natural Cements, 37.
Manufacture Concrete Blocks, 512,
519, 530.
Natural Cement, 37.
Portland Cement, 12.
Marking Briquets, 131.
Materials —
for Concrete Blocks, 520.
Cubic Yard Concrete, 232.
Mortar, 193.
Natural . Cement Manufacture,
37, 38.
Portland Cement Manufacture,
12, 14.
Melan System, 398.
Arch, Topeka, 497.
Microscopical Tests, 50.
Mills —
Styles for Cement Grinding, 26-31.
Mixing Concrete —
by Hand, 218.
Cost, 220.
by Machine, 221.
Cost, 226.
Necessity of Thorough, 317, 333.
Mixing Mortar —
for Tests, 1.19, 549.
Use, 191.
Necessity of Thorough, 250.
Mixing Natural and Portland Cement,
257.
Modulus of Elasticity —
Concrete, 322.
Mortar, 320.
Modulus of Rupture in Flexure-^
Concrete Prisms, 328.
Mortar Prisms, 327.
Moist Closet for Briquets, 133.
Moistening Concrete, 376.
Moisture, Effect on Volume Sand, 18(K
Molder's Record, 161.
Molding —
Bbhme, Hammer, 128.
Hand, 129.
Jamieson Machine, 128,
Machine, 128.
Methods, 127, 549.
Molds —
Briquet, Cleaning, 127.
Forms of, 122.
Kinds of, 126.
Concrete (see Forms).
Blocks, 392.
Sewers, 453, 456.
Walks, 436.
Walls, 431.
Monier Arch, Test, 396.
Monier System, 395.
Mortar —
Amount in Concrete, 214.
Cost, 196.
Definition of, 169.
Facing, 377.
for Plastering Concrete, 377.
Ingredients for Cubic Yard, 1^,
Mixing, 119, 191.
Varying Richness, 241 .
Nattiral Cement —
Analysis, 10.
Definitions, 10.
Manufacture, 37.
Natural Cement Concrete, Strength of,
314.
Neat vs. Sand Tests, 109.
Needle Test for Time Setting, 80,
Numbering Briquets, 131.
Oiling Forms or Molds, 368.
Painting Concrete, 382.
Pallets, 514.
Pan Mixer —
for Cement, 20.
Concrete, 224.
INDEX
569
Paper Sacks for Concrete, 391.
Pat Test (see Soundness).
Pavement, Concrete, 443.
Pavement Foundation, 442.
Pebble-Dash Finish, 380.
Permeability of Mortars, 354, 357.
Piers, Bridge, 478.
Fonns for, 478.
Piles, Concrete, 485.
Protection by Concrete, 397.
Pipe, Sewer, in Concrete, 450.
Placing Concrete under Water, 340, 383.
Placing Consecutive Laj'ers Concrete,
375.
Plant, Portland Cement, 15.
Plants, Concrete, 226.
Plaster Paris —
Effect on .\dhesion, 291.
Strength, 263.
Soundness, 264, 265.
Time Setting, 83.
Plastering Concrete Surface, 377.
Platform, Mixing, 218.
Plums in Concrete, 375, 499, 509.
Point, Dressing Surface Concrete, 381.
Pointing Mortar, 361.
Porosity of Mortars, 354.
Portland and Natural Compared. 293,
296.
Portland Cement —
Composition, 5, 8.
Definition, 4.
Manufacture, 12.
Posts for Forms, 368, 370.
Pot Cracker for Grinding, 40.
Pouretl Concrete Blocks, 518.
Pozzolana Cement (see Slag Cement),
7, 36.
Pozzolana with Cement, 379.
Preservation of Iron and Steel, 350.
Pressed Concrete Blocks, 517.
Proportion.s in Concrete —
Theory of, 214.
Proportions in Concrete —
Effect on Strength, 309, 315, 331.
Modulus of Elasticity,
323.
Proportion.s in Mortar, 187.
Effect on Strength, 241.
Puzzolana (see Pozzolana).
Qualities, Desirable, in Cement, 42.
Rails Imbedded in Concrete, 484.
Rammers for Concrete, 374, 506.
Ramming Concrete, 373.
Effect on Strength, 311.
Ransome Bars, 298, 400.
Concrete Mi.xer, 223.
System, 400.
Rate of Applying Tensile Stress, 147.
Ratio Compressive to Tensile Strength,
303.
Raymond Pulverizer, 33.
Records of Testa, 160.
Regaging Mortar, 251.
Effect on Adhesion, 290.
Regrinding Cement (see Fineness).
Regulations, 432, 534.
Reinforced Concrete (see Concrete
Steel).
Reinforcement, Double, 417.
Excessive, 410.
Longitudinal, 427.
Single, 404.
Repair of Stone Piers, 480.
Reservoirs, 467.
Examples, 470.
Floor, 467.
Lining, 469.
Roof, 469.
Walls, 468.
Results of Tests, Treatment of, 149.
Retaining Walls, 481.
Retardation of Setting of Cement, 83.
Richness of Concrete, Effect on
Strength. 310, 331.
Rods, Adhesion of Mortar to, 298.
Tie, for Forms, 370.
Roebling System, 400.
Rolls, for Grinding, 30.
Roman Cement, Definition, 2.
Roof, Concrete, for Building, 425.
for Reservoir, 469.
Rosendale Cement (see Natural).
Rotary Kilns, 23, 25.
Rubbed Finish for Concrete, 379.
Rubble Concrete, 374.
Rubble t'«. Concrete, 498.
Rules for Concrete Construction, 481.
Russell Clip, 143.
Rust, Prevention of, 350.
Sacks of Concrete, 388, 391.
Salt, Effect on Mortars, 277.
570
INDEX
Salt, Effect on Time Setting, 84.
Use in Freezing Weather, 274, 340.
Sampling, Method, 159, 542.
Per cent, of barrels, 158.
Sand —
Character, 168, 171.
Cost, 185.
Damp —
Mortars Hardened in, 292.
Volume of, 180.
Detecting Impurities in, 182.
Fineness, 111, 173.
for Tests —
Comparison of, 110.
Fineness, 111.
German Normal, 110.
Natural, 110.
Ottawa, 548.
for u.se in Sea Water, 173.
Heating in Winter, 466.
Impurities in, 182.
in Aggregate, 216.
Quality, 184.
Shape and Hardness Grains, 169,
173, 176.
Slag, 173.
Varying Amounts of, 241.
Voids in, 176, 178.
vs. Neat Tests, 109.
Washing, 183.
Weight, 184.
Sand-Cement —
Manufacture, 34.
Use in Locks, 506.
Sandstone —
Adhesion of Cement to, 288.
as Aggregate, 308, 336.
Sawdust in Mortar, 373.
Screenings in Broken Stone, 201, 339.
Screw Concrete Mixer, 225.
Sea Wall, Concrete in, 230.
Sea Water —
Cements in, 362!
Concrete in, 362.
Storing Briquets in, 135.
Section, Breaking, of Briquets, 123.
Setting, Process of, 79.
Setting, Rate or Time of, 80, 547.
Approximate Method Determining,
81.
Effect of Aeration, 82.
Age, 82.
Setting —
Effect of Composition, 81.
Consistency, 85.
P'ineness, 83.
Gaging, 87.
Gj-psum, 83.
Medium, 88.
Plaster Paris, 83.
Salt and Sugar, 84, 86.
Temperature, 86, 87.
Gilmore Wires, 80.
in Air and Water, 88.
Mortar and Neat Cement, 86.
Requirements as to, 88.
Variations in, 81.
Vicat Needle, 80.
Sewers—^
Cost, 451, 453.
Forms, 453, 455.
Steel, 456.
Methods Construction, 450, 457.
Pipe, in Concrete, 450.
Shear —
in Concrete-Steel-Beams, 419.
Strength in, 342.
Tests of, 104.
Sheathing for Forms, 366.
Tongue and Groove, 366.
Shofer Kiln, 22.
Short Time Tests, Interpretation, 151.
Shrinkage in Setting, 345.
Sidewalk, Concrete, 434.
Base, 435.
Construction, 436.
Cost, 439.
Drainage, 434, 436.
Foundation, 435.
Wearing Surface, 436.
Sieves for Cement, 60, 65.
Value of Coarse, 77.
Sifting (see also Fineness).
Mechanical and Hand, 63.
Time of, 64.
Silica Cement —
Manufacture, 34.
Use in Locks, 506.
Skip for Placing Concrete, 386.
Slaked Lime with Cement, 259, 294,
Slag Cement —
Definition and Composition, 7, 10.
Manufacture, 36.
Use, 10.
INDEX
571.
Slag Sand, 173.
Smith Concrete Mixer, 224, 230.
Soap and Alum Solutions, 358.
Soundness, 90.
Tests for— A. S. C. E., 90, 661.
Boiling, 91.
Chloride Calcium, 95.
Deval, 93.
Discus.sion, 96.
Faija, 92.
German Normal, 91.
Hot, for Natural, 101.
Hot Water, 92.
Kihi, 91.
Le Chatelier. 95.
Records of. '65.
Warm Water, 92.
Spandrels, Arch, 490.
Special forms of Blocks, 524, 536.
Special Test Records, 167.
Specific Gra\'ity Cement, 53, 543,
553.
Effect Aeration, 56.
Coarse Particles, 66.
Specifications for Cement, 553.
Concrete Work, 481.
Specimens, Marking, 160.
Stedman Disintegrator, 33.
Steel Beams, Concrete Covered, 426.
Steel Facing for Curbs, 446.
Forms for Sewers, 456.
Lining for P^orms, 367.
Shell for Bridge Piers, 479.
Steel with Concrete, 401.
Steinbriich Mortar Mixer, 121.
Steps in Concrete Construction, 376.
Stone, Broken (see Aggregate) —
V8. Gravel, 206.
Character Surface of, 290.
Crushers, 208.
Crushing, 209.
Facing for Concrete, 491 .
Finish for Concrete, 381.
Stop Planks, 376.
Storage for Cement, 158.
Storing Briquets, 131, 550.
in Air, 136, 246, 260, 274.
in Sand, 137, 292.
in Water, 133.
Storing Concrete Cubes, Effect of
Medium, 307.
Street Railway Foundations, 447.
Strength (see Tensile, Transverse, etc.)
Compressive, of Concrete, 306.
Mortar, 302.
of Concrete Blocks, 533, 536, 539.
of Concrete-Steel, 414, 417.
Tensile, of Mortar, 241.
Transverse, of Concrete, 327.
Stringers for Street Rails, 447.
Subways, Concrete, 457.
Boston, 458, 460.
Chicago Telephone, 468.
New York, 457, 462.
Sugar, Effect on Time Setting, 85.
Sulphuric Acid, 48, 382.
Summary of Tests, Record, 161.
Surface Concrete (see Finish).
Surface Stone, Effect on Adhesion,
290.
Sylvester's Process, 358.
Tamping Concrete, 373.
Concrete Blocks, 513, 516.
Tempterature Cement and Water —
Effect on Tensile Strength, 117.
Time Setting, 86.
Temperature, Low —
Use of Concrete in, 340.
Mortar in, 274.
Ten-sile and Compressive Strength Com-
pared, 302, 327.
Tensile Strength —
Effect Sand, 241.
Neglect of, in Concrete-Steel, 402.
Tensile Tests Cohesion, 109.
Terra Cotta, Adhesion of Cement to, 288.
Dust with Cement, 274.
Test Monier Arch, 396.
Testing Machine, Tensile, 137.
Testing, Uniform Methods, 44, 542.
Teats (see also Tensile, Transverse,
etc.) —
Abrasion, 108, 343.
Adhesion, 106, 284.
Chemical, 45, 342, 558.
Cohesion, 109, 549.
Compression, 103, 302.
Concrete, 305, 328.
Concrete Blocks, 637, 638.
Fineness, 59.
Sand, 110, 169.
Shear, 104.
Soundness, 90.
572
INDEX
Tests-
Specific Gravity, 63.
Tensile, 104.
Time Setting, 79.
Transverse, 104.
Weight per Cubic Foot, 51.
Tetmajer, Boiling Test, 91.
Kiln Test, 91.
Thacher System, 399.
Theory of Concrete-Steel Beams, 401,
404, 417.
of Proportions in Concrete, 214.
Thermal Expansion Cement, 346.
Tile, Pulverized, Use of, 274.
Time Required to Sift, 63.
Time Setting (see Setting, Rate of).
Tooling Concrete Surface, 381.
Top Dressing, Concrete Walks, 436, 438.
Topeka Bridge, 497.
Transporting Concrete, 372.
Transverse Strength —
Comparison with Tensile, 327.
Concrete, 328.
Mortar, 327.
Tests of Cement, 104.
Tremie for Placing Concrete, 385.
Trussed Posts, 370.
Wales, 371.
Tube MiU, 28.
Tunnel Lining —
Brick vs. Concrete, 463.
Cost, 466.
Forms for, 461.
in Firm Earth, 458.
in Rock, 461.
in Soft Ground, 460.
Turmels —
Aspen, 464.
Cascades, 463.
East Boston, 460.
Perkasie, 464.
Sudbury River Aqueduct, 465.
Twisted Rods, —
Adhesion to, 298.
Ransome, 400.
Uniformity in Methods Testing, 44, 542.
Viaduct, Concrete-Steel, 498.
Vicat Needle for Consistency, 546.
Time of Setting, 80,
548.
Voids in Aggregate, 204, 215.
Voids in Sand, 176.
Effect Moisture, 180.
Shape Grains, 176.
Size Grains, 177.
Volume —
Changes in, During Setting, 345.
Concrete Blocks, 527, 529.
Proportions by, 187, 214.
Wales, Trussed, 371.
Walks of Concrete, 434.
Wall Molds, Buildings, 431.
Parrel's 431.
Warehouse for Cement, 158.
Washes for Concrete Walls, 358.
Washing Sand, 183.
Water in Mortar and Concrete (see
Consistency) .
Water, Deposition Concrete in, 340,
383.
Water of Immersion for Briquets, 133.
Water, Stale, for Immersing, 135.
Waterproof Construction in Subways,
457.
Waterproof Mortar and Concrete, 354,
357.
Waterproof Work in Reservoirs, 467.
Waterproofing Concrete Blocks, 526.
Wearing Surface of Walks, 436.
Wedge Rammers for Concrete, 506
Weight of Concrete, 313, 319.
Concrete Blocks, 527.
Weight per Cubic Foot Cement, 51 .
Wells in Concrete, 376, 504.
Wheelbarrows for Conveying Concrete,
373.
White Finish for Concrete, 379.
Williams Mill, 33.
Wire in Sieves, 61.
Wires for Testing Time of Setting, 80.
Wilnsch System, 397.
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