Full text of "Materials of engineering construction. Civil engineering 8"

See other formats

.migineering
Library

UNIVERSITY OF CALIFORNIA

DEPARTMENT OF CIVIL ENGINEERING

BERKELEY

December

Eighteenth

1922

Dear Professor Derleth:

I take pleasure in transmitting to you a
copy of the Extension Division Correspondence Course

.3RIALS OF ENGINEERING COHSTRUCTOT, the raultigraphing
of vrhich has Just teen oorapleted. I thought that you
might like to have a copy in the department files.

Sincerely yours,

professor C. Derleth Jr., Dean,
College of Civil Engineering,
C a m p u s.

1/IMU

UNIVERSITY QF CALIFORNIA
EXTENSION DIVISION.

Correspondence Course

MATERIALS QF ENGINEERING CONSTRUCTION
Civil Engineering 8.

] By

C. T.

Associate Professor

of
Civil Engineering.

A Course of Thirty Assignments,
In Two •tarts, 8a and 8b.

1922

:oqe.! •

.8 snii

II. .0

e;*£loc

.<fG lieu

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Correspondence Courses
Materials of Engineer ing -Const ruction

Civil Engr - 8. • Professor C. T. Wiskocil

PREFACE

The Course in MATERIALS OF ENGINEERING CONSTRUCTION will
consist of 30 assignments, or lessons, of mimeographed material which
will be sent out by the Extension Division of the University of
California. The course will be divided into two parts, designated
8A and 8B , each part consisting of fifteen assignments. University
credit in the amount of two units will be given on the completion
of both parts of this course. The textbook which is to be used
is Johnson's "Materials of Engineering Construction", published by

Wiley & Sons. It may be obtained from the Associated Students'

Union Bldg.
Store, .Student/-, Berkeley, California, for C6.20, postpaid.

Books on MaiLKlALS usually contain more information than
is necessary to give you a -.verking knowledge of the subjects treated.
These books are excellent sources of information and with proper
guidance they can be used as texts. JOHNSON'S MATERIALS OF
CONSTRUCTION, which has been used for the past two years at the
University of California, is such a oook. To use it effectively,
however, it was necessary to continually maintain the student's
interest. This was done by informal talks, in which the important
information was pointed out, and by frequent questions on the es-
sential facts discussed.

793908

Civil Engr.-8. Page 2.

Since university credit in the Extension course in
MATERIALS can be secured only by passing supervised examinations
similar to those taken by resident students, it has been decided to
use JOHNSON'S MATERIALS OF CONSTRUCTION as the text-book and par-
allel the resident-course still farther by supplying notes to take
the place of class-room lectures and discussions. The purpose of
the notes which will accompany each assignment is to assist you by
emphasizing, explaining, and supplementing the subject matter
assigned in the text. A -set of questions will also be sent out
with each assignment. You should test your knowledge of the subject
by answering these questions without reference to the notes or text-
book. At every opportunity, you should secure first-hand informa-
tion by observing all examples of occurrence, manufacture, or use
of the materials you are studying.

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Civil Engr. 8. Professor C» T- Wiskocil

INTRODUCT ION

The purpose of this course is to present information con-
cerning the mechanical and physical properties of the principal
materials of engineering. A knowledge of these properties is neces-
sary for the intelligent selection and use of materials for given
conditions or service requirements.

Since the adaptibility and limitations of materials de-
pend upon their mechanical and physical properties, it is important
to know about the modes of occurrence, methods of manufacture, or
preparation because variations in these factors affect the properties.
Other subjects properly discussed in this course are: testing of
materials and the fatigue and corrosion of metals.

Information on materials is obtained from various sources.
Most of the data on the properties are compiled from the published
results of investigations and researches while the principles in-
volved in the occurrence and manufacture are taken from treatises
on Botany, Ceramics, Chemistry, Geology, and Metallurgy •

Each material will be discussed in sufficient detail to
bring out the desired information. It would oe oeyond the scope of
the course to exhaustively treat each suoject or to take up all
engineering materials. The course will be given in accordance with
the following outline :

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Civil Engr 8A- Professor C. T. VJiskocil.

Assignment

1
2
3

5
6
7
8

11
12
13
14
15

Subject

Mechanics of kate rials
Machines and Appliances for Testing
Testing of Structural Materials
Uses and physical Properties of Wood
Deterioration and Preservation of Wood
Mechanical Properties of Wood
Building Stone

Structural Clay Products. Specifications
for Paving Bricks

Portland Cement

Results of Tests on Cement. (Natural
Cement)

Lime and plasters

Testing of Hydraulic Cement

Making of mortar and Concrete

Mixing, placing, and Curing of Concrete

Proportioning of Concrete

UNIVERSITY OF CAllFORNlA. EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Civil Engr -8B- Professor C. I. Wiskocil.

Assignment
16
17
18

19
20
21
22
23

24
25

26
27

28
29
30

Subject

Physical Properties of Mortar and Con-
crete

Permeability and Durability of Concrete.
(Portland Cement Products)

Metals and Their Ores. (Reduction of Iron
from Its Ores)

Manufacture of Wrought Iron and Steel
Manufacture of Steel Shapes
Formation and Structure of Alloys
Constitution of Iron and Steel

Properties of brought Iron. (Properties
of Steel)

Effects of Heat Treatment of Steel

Effects of Mechanical Work on Steel.
(Effects of Temperature on Mechanical
Properties of Metals)

Alloy Steels

Cast Iron and Malleable Cast Iron

Non-ferrous Metals and Alloys

Fatigue of Metals

The Corrosion of Metals

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Civil Engr 8A. Professor C. T. Wiskocil

Assignment 1
MECHANICS OF MATERIALS

Reading assignment ;- Johnson's Materials of Construction, Chapter I,

pages 1-48.

Preliminary :- Before studying the various materials it is advisable
to have a general knowledge of the effects of stress and deformation.
The subject of internal forces and deformations is ordinarily called
MECHANICS OF MATERIALS. Chapter I is a condensed treatment of this
subject which is a complete course of study in itself. The assign-
ment, therefore, will not be studied intensively. Only that infor-
mation which is necessary for a thorough understanding of the prop-
erties of the materials to be studied later -will be discussed. T'-r
The directions ''study" in these notes means that you should know the
contents of the immediate subject and be able to stace in your own
words what you have studied. Do this with each paragraph.

Study Article 1 in connection with the following notes:

Stress;- Stress is the force at a point or plane in a body or the
force between contiguous surfaces of two oodies. The forces or loads
producing the stresses, or the stresses themselves, may be represent-
ed by arrows and the bodies acted upon by small rectangles- Thus in
Figure 1 the weight is suspended from the support oy the rod as
shown. The situation could be illustrated as in Figure 2, the arrows

Civil Engr -8. Assignment 1. Page 2.

indicating the forces and the directions in which they act upon
the body. If the weight is 100 Ib. the total stress in the rod on
the Section A — A is 100 Ib. irrespective of the size of the rod
Plane sections are always taken.

Figure 2.

Figure 1

Unit Stress. Unit stress or intensity of stress is obtained by divid-
ing the total stress by the entire area of the section on which it

P
acts or over which it is distributed. Intensity of stress S - —

where P is the stress and A is the area. In mechanics it is

usually measured in pounds per square inch, which is abbreviated

Ib. per sq. in., Ib./ in., or $/£j"- S is the actual intensity of

stress only when the stress is uniform over the section. In the case
of a varying stress, S is the average intensity of stress.
Example - A body is subjected to a force of 1,000 Ib. Its dimensions
normal to the direction of the force are 1" by 2". What is the inten-
sity of stress?

Civil Engr 8. Assignment 1. .. Page 4.

divided by the length which is tan 0; this is also an abstract
number.

The following notes explain Article 2 which should be carefully stud-
ied.

Kinds of Stresses;- '.;.wo classes of stresses are usually considered;
(a) simple or uni-directional stresses and (b) combined or bi-dir-
ectional stresses. The simple stresses are tension, compression,
and shear which includes simple torsion. The combined stresses are
tension with tension or compression, compression with compression,
and shear (torsion) with tension or compression.

Tension

A body subjected to an axial pull is in tension. The
forces act in the same line and away from each other tending to pull
the body apart. The section on which the forces act is taken perpen-
dicular to the direction of the force, as A -- A in Figure 1,
which shows a rod in tension. Examples of bodies in tension are; tie
rods, guy wires, belts, and violin strings.

Compression

When axial forces act in the same line and toward each
other the body is in compression. The section is taken as in the
case of tension. Figure 4 represents a body in compression, Ex-
amples of bodies in compression are; posts supporting floors or other
loads, table legs and connecting rods in single-acting internal com-
bustion engines.

Civil Engr. 8. Assignment 1. Page 5.

Shear

When the forces act in parallel lines either toward or
away from each other, but sufficiently close so that there is no
bending, the body is in shear. The section is taken parallel to
the forces (note that this is different than in the case of tension
and compression). Shear is illustrated oest by the stress in a bolt
or rivet holding tv;o plates from sliding on each other as in fig-
ure 6.

The particles in a body under a twisting moment or torsion, as a
shaft transmitting power, have a tendency to slip on each other; the
stress produced is simple shear. Simple torsion rarely occurs, it is
usually combined with tension or compression.

Combined Stresses

Flexure is classed under combined stress. In simple flex-
ure or bending the fioers on the concave si^e of the body are short-
ened and are therefore ii compression whereas on the convex side/
they are lengthened anc are in tension. The stresses across the body
vary from tension to compression; at some point between these ex-
tremes the stress is zero - neither tension nor compression. Flex-
ure is usually produced by transverse loads which produce sihear in
addition to the stresses of simple bending. A loaded beam is an ex-
ample of flexure. A body may be subjected to flexure and axial stress,
This combination of simple stresses is illustrated in the rafters of

Civil Engr. 8. Assignment 1.

an A-frame roof. Shear (torsion) may be combined with compression
as in the case of a shaft of a vertical turbine. Shear may also be
combined -with flexure as in a line shaft with power taken oi'f by
belts between the hangers or bearings.

Loads:- The ability of materials to sustain loads depends upon the
manner in which they are applied. Loads u.ay be class if ied as static
and dynamic. Static loads include dead loads, whi'.ch are sometimes

called stationary or permanent loads, and gradually applied loads,
as in the case of a testing machine where the load varies from zero

to a maximum, during the period of the test. Dynamic or suddenly-
applied loads may be applied with or without shock or impact. They
may be applied occasionally or continuously. In the latter case
they would be called alternating or repeated loads, depending upon
whether the stress changed in character or was simply reapplied in
the same manner. In either case their effect -would be discussed
under the subject of FATIGUE.

Elastic and Plastic Bodier;:- Study Article 3. Materials may be
classified as brittle and ductile. Both classes are described in
this article. The term, ultimate strength, is alsc defined. Fre-
quently the maximum unit strtss carried by a material is siraply
called its strength; ultimate strength is a?.wa^ s uieant. It should
be understood that the kind of stress must be specified because a
material may have different tensile and compressrvc strengths.

Modulus of Elasticity :- Study Article 4, as it is vsry important.
Remember that the modulus of elasticity is always denoted by E

Civil Engr. 8. Assignment 1. Page 7.

and that although it is a ratio of unit stress to unit deformation

it is measured in Ib. per sq. in. because
P

E = A - Ib. per sq. in.

AT — = Ib. per sq. in. since

in. per in.
Li

the denominator is unity. E is the measure of the stiffness or
flexibility of a material. Fortunately the modulus of elasticity of
all kinds of steel is very nearly the same, namely 30,000,000 Ib.
per sq. in. E for concrete is aoout 1/15 that of steel, or
2,000,000 Ib. per sq. in. and for v;ood it is about 1,500,000 Ib. per
sq. in.

/
Poisson's Ratio:- This ratio (pronounced pwa sonz ) is about

- 1/4 for steel and about - 1/8 for concrete. The negative sign in-
dicates that it is opposite in character to the principal deforma-
tion. As explained in Article 5, it is the ratio of lateral to

longitudinal deformation. If a block of steel is compressed its

/ / 1

increase in width, measured perpendicular to the direction of the

applied force, will be about 1/4 of its decrease in length. These
relations hold only within the elastic limit of the material and the
changes are very small, requiring delicate instruments to measure
the amount of deformation. Poisson's Ratio is of importance in
theoretic discussions in MECHANICS OF MATERIALS, and of practical im-
portance in the manufacture of guns.

Volumetric Deformation:- Article 6 is not important. It is inter-
esting to note, however, that a body subjected to tension v;ill

Civil Engr. 8. Assignment 1. Page 8.

slightly increase in volume. For example, a piece of steel 4" by 4"
by 60" under a tension of 430,000 Ib. will increase aoaut 0.29 cubic
inches in volume or about three hundredths of one per cent.

Shearing Modulus of Elasticity :- Shearing modulus of elasticity is
explained in Article 7. It is sometimes called the modulus of
rigidity and is measured in Ib. per sq. in. For steel it is about
2/5 of E_.

General Properties of Laterials :- Study Article 8. The general
properties described in this article are important and "will be re-
ferred to during the discussion of the various materials.

Strength is obviously a property that materials must pos-
sess so as not to rupture or fail under stress. Frequently strength
is the principal consideration, as in chains, crowbars, stern-frames
of ships, and cranes. In other cases strength is of secondary im-
portance and some other property, such as stiffness, governs the
selection of the material. Wood because of its low degree of stiff-
ness will yield under impact and for that reason (besides its light
weight) it is used by seme manufacturers in the construction of
automobile frames. It also makes the best railroad ties for the same
reason. In other machines and structures stiffness is the prime
requisite.

Ductility and Malleability are closely allied. Toughness
and brittleness are antonyms. Toughness is the ability to withstand
impact stresses. It is dependent upon both strength end deformation.
Two bodies having the same strength, as ordinarily determined, can

Civil Bngr. 9. Assignment 1. Page S.

have different lengths providing their areas are the same. If
these t?;o bodies of the sane area are subjected to impact the longer
one -will withstand the greatest shock. With the same cross-section-
al area the toughness increases in direct proportion with the
length. For most mate-rials the energy of rupture, which is the
are?, under the stress-deformation curve, is an index of the toughness
(see the third papagraph, which begins about the middle of page 42,
of Article 37). The longer piece will undergo greater deformation
and will therefore have a greater area under the curve even though
the maximum strength is the same as the shorter piece. In Figure 3
page 8, the steel having a tensile strength of 75,000 Ib. per sq. in.
is tougher than the 105,000 Ib. per sq. in. steel. That is, it has
a greater resistance to rupture under impact. A-s shown in Figure 4,
on page 9, the 105,000 Ib. per sq. in. steel has a higher elastic
resistance to impact. Ix, will withstand permanent distortion under
greater impact stresses than the steel having a strength of 75 ,,000 Ib,
per sq. in. , because :.t hc.s n greater proportional or elastic limit
and consequently a greater - rea under thrt part of the stress-
deformation curve. Material v;ith a high elastic limit is used for
springs while meteri^l with less strength but more ductility is used
for machine parts subject to occasional heavy impact such as car
couplings are. Elasticity and plasticity were defined in Article 3.
Uniformity of properties is very desirable. Some mater-
ials such as steel can be produced with a high degree of uniformity,
whereas the properties - " of wood vary over vide limits.

Civil Bngr. 8. Assignment 1. Page 10.

Durability is probably one of the most inroortant proper-
ties and, for permanent construction, it must always be considered
because certain materials are very susceptible to decay or deterior-
ation. Destructive agencies such as corrosion, bacteria, fungi,
electrolysis, mechanical v;ear, chemical Action, ant? fire act on
materials used in engineering construction.

Materials under tensile stress;- Study Articles 11 to 16 very care-
fully. The stress-deformation diagram is important. Read Article
111 and see Figure 12 on page 476 and Figure 9 on page 620 for
typical examples of stress-deformation diagrams. Note that the^ulti-
mate strength is obtained by Dividing the maximum stress by the
original cross-sectional area.

Read the following in connection with your study of
Article 11.

Significance of elastic limit ;- The elastic limit of a ductile
material, when used in machines or machine parts which cannot be dis-
torted, is practically its ultimate strength in both tension and
compression. Very s.r,?ll permanent distortion will cause serious
damage to machines of precision. A brittle materiel has no well de-
fined elastic limit when that term is used to include the yield
point, and its ultimate strength is the most reliable criterion of
strength for static loads. Brittle materials are not used in direct
tension or where they would be subjected to shock or impact stresses.
Materials under compress ive stress:- Study Articles 17, 18,

that part of 19 which is given on page 14. Reed over the rest of the

Civil Engr. 8- Assignment 1.

article. Remember that short blocks of brittle materials under com-
pression fail in shear on a plane of rupture \vhich has an angle of
about 35 degrees with the direction of the conpressive force. Reac
Article 20. Study Article 21 up to Euler's Formula.
Materials under shearing stress;- The nature of shearing stresses
have been described. Read Article 23 up to equation 16 and study the
last paragraph in Article 24 on page 24.

Materials under cross-bending stress:- Study the first paragraph
of Article 25 and read the rest of the article. Read Article 26.
Study Article 27, omit ing the last paragraph.

Formula 20 on page 25 may be written S ~ Ml where
S is the modulus of rupture. This is an important quantity. It is
the nominal fiber stress at a definite point, that of greatest stress.
Remember that the stress varies across the section of a beam.. Modu-
lus of rupture is mer.sured in Ib. per sq. in. and may be tension otT
compression. M is the moment in inch pounds, c is the distance
from the neutral surface to the extreme fiber in inches, and I is
the moment of inertia of the section, sbout the neutral axis, in

inches to the fourth power. Therefore S = .. in" *]?• * in> =

Ib. per sq. in. Modulus of rupture is not the actual stress because
it is used v:ith the ultimate value of M whereas the formula was
developed on the assumption that the elastic limit rras not exceeded.
It is sufficient to remember that the actual stress is less than the
modulus of rupture. Modulus of rupture is easily computed and is
always given as the cross-breaking or transverse strength of materi-
al in question. Study Article 28, omiting the derivation of the

Civil Engr. 8. r Assignment 1. jo>^ _ i.fc.

intensity of shearing stress, and the last two paragraphs. Remem-
ber that wooden beans must be inventigatad for horizontal shear.
This is sometimes called longitudinal shear. Or.it Articles 29 to
32 inclusive.

Resilience:- Under this subject study only Article 33 and the third
paragraph of Article 37, omit ing the remainder of the chapter.

Civil Engr. 8. Assignment 1. pagr 1;'.

Reference Books on Mechanics of Materials.

Elementary texts-.

Kottoanp, J. P. STRENGTH OF MATERIALS, Wiley nnrt Sons,

Murdock, H. E. , STRENGTH OF MATERIALS, Wiley and Sons,

Smith, H. E. , STRENGTH OF MATERIALS, Wiley and Sons, 1914.

Slocum S. E.* RESIST/^CE OF MATERIALS, G-inn and Co., 1014.

More oonprehensive texts :

Boyd, J. E., STRENGTH OF MATERIALS, McGraw - Rill, l**f»
Fuller and Johnson, APPLIED MECHANICS Vol. II, Wiley and Sons

Merriman, MECHANICS OF MATER IALS, Wiley and Sons,

Merely, STRENGTH OF MATERIALS, Longmans, Green % Co,

London,

Civil Engr. 8. Questions to Assignment 1. page 14.

Answer all questions submitted to you as clearly as pos-
sible. Do not go into detail unless details are requested, "but do
not fail to answer all parts of each question completely. Arrange
your answers neatly. Use a typewriter if svailable.

1. Define intensity of stress, unit deformation, modulus of rupture
and modulus of elasticity. Note: Always give the units in which
the quantities are measured.

2. Define stiffness, toughness, and ductility.

3. Can stiffness be measured quantitatively? (If no other infor-
mation is given always answer a question of this type as completely
as possible, not simply by yes or no.)

4. The diagram on page 10, in the text, was obtained from an actual
test in which the load was applied continuously increasing from zero
to its maximum value as indicated. Was the so-called elastic limit
determined? (Do not read the description to answer this question,
you should know the answer if you have studied the assignment.)

Why is the point indicated the most probable value of the elastic 1 *
limit?

5. what is the unit stress in a rod having an area of 1/2 sq. in.
when subjected to a stress of 8,000 lb.? Ans. 16,000 Ib.

6. What is the allowable pull on a 1" diameter steel bolt if the

allowable intensity of stress is 16,000 lb. per sq. in.?

Ans. 12,600 lb.

7. The head of a 1" diameter bolt is 5/8" thick. When the bolt
is subjected to a pull of 15,000 lb. what is the unit shearing

Civil Engr. 8. Questions to Assignment 1.

stress tending to strip the head from the bolt? .'aAns. 7,600 Ib.

per sq. in.

8. Would the chattering of a machine tool (caused by bending of
the tool) be diminished by making it of stronger steel?

9. Which bolt - one left full site or one turned down to the di-
aneter at the base of the threads - will sustain the greatest
impact loading?

10. Name the kinds of stress developed in: (a) an inflated tire
casing, (b) the connecting rod of a double acting pump, (c) a
key in an axle shaft, (d) stud bolts holding on a man-hole in a
pressure tank.

11. Prepare a list of structures or machines in which the var-
ious properties listed below govern the selection of the material
to be used :

(a) Strength (d) Toughness

(b) Stiffness (e) Hardness.

12. Prepare a list of structures or machine? vhioh are liable to
occasional overloading.

13. Name several structures or machines that could be mads of
brittle materials.

14. What kind of stress exists at the neutrel surface of a load-
ed beam?

15. What kind of stress exists in the fibers on the leeward side of
a flag pole bent by the wind?

UNIVERSITY OF CALIFORNIA. EXTENSION DIVISION"

Correspondence Courses
Materials of Engineering Construction
Civil Bngr, S. professor C. T. Wi.skocil

Assignment 2.

MACHINES AND APPLIANCES FOR TEST ING

Reading assignment;* Johnson's Materials of Construction, Chapter
II, pages 49-96.

Preliminary:- In a comprehensive study of the important materials
of engineering construction, such as we are making, it is desirable
to have a knowledge of the machines and appliances used in determin-
ing the various properties such as strength, elasticity, and tough-
ness. If properly studied, this chapter will eive yo\i the necessary
information without an actual inspection of a testing laboratory.
There are testing machines in 'the San Francisco Bay region, Los
Angeles, Sacramento and Fresno - possibly in other California cities,
Make an effort to witness an actual test performance. If you should
visit a laboratory do not expect to see all the machines and appli-
ances described in this assignment. Probably no laboratory in the

i
country, not even the one in the Bureau of Standards at Washington,

b.C. , contains all of them.

TESTING MACHINES

The discussion of testing machines constitutes the first
part of the assignment. A. testing machine is defined in Article 42;
in general, it must provide means for (a) applying the load (b) mea-
suring the load and (c) holding the test specimen. A testing

Civil Bngr-8. Assignment £. Page 2.

machine is not necessarily a costly device like those illustrated
in the te;:t book; it may be a simple wooden lever arrangement with
the load, a bucicet of aand at the end of the long lever, such as is
used in the field testing of drain tiles. Testing machines vary
in capacity from the 10,OUC,OCC lb. machine shown on page 56 to
er.aH tension machines for testing faoric, or briquette-testing
machines like the ones shown on page 396. There are also various
types of machines which will now be discussed in detail. In general
all testing machines must be both accurate and sensitive.

Universal Testing Machines

Classes jsfjaniversal teeting machines:- Study Article 43. Univer-
sal testing machines may be divided into two classes, (a) vertical
and (b) horizontal. Both of these classes may be divided into two
groups based upon the method of applying the load; namely, screw-
gear and hydraulic. Hydraulic machines may be either plain or of
the Emery type. As a class universal machines &re in most general
use in the United States, probably because of their adaptibility.
They are mostly the vertical screw-gear type either of Olsen or
Riehle make, both of which will be described later. Weighing devices
used in testing machines are levers, gages, and manometers. The
Olsen and Riehle machines use the lever system.

The advantage of the horizontal machine, besides the one
riven on page 50 in Article 43, is the ease with which large speci-
mens can be put in place. The principal disadvantage, as indicated,
is the bending of the specimen due to its own weight, It also takes
up a large amount of floor space.

Civil Engr-8. Assignment 2. Page 3.

General conditions which should jbts obtained in universal machines;-

The principal requirements are accuracy and sensitiveness. Accuracy
is insured as indicated in paragraph 1, the second sentence in
paragraph 2 and the first sentence in paragraph 3 or Article 44.
paragraphs 1 and 6 of this article refer to sensitiveness. The
last sentence of paragraph 7 and paragraph 10, with those already
given, are the important ones of the article.

Olsen testing machines;- Study Article 45. The essential parts of
the Olsen machine are shown in Figure 1. These are usually four and
three-scret; machines. The screws referred to are the main ones
•which move the cross-head. In this machine the screws do not rotate
on their axes, but move the cross head to which they are attached
by the axial motion given to them by the rotation of the geared nuts
through which they pass. The geared nuts bear against the frame of
the machine. The weighing mechanism is shown diagramatically in
Figure 3. Note that when the scale beam is in balance the position
of the poise -weight indicates the amount of the load. It resembles
the usual Fairbanks platform scale. The purpose of the counter-
weight is to counteract the unbalanced weight of the various levers
in the system.

Civil Engr-6

Assignment 2

Page 4

—

Upper or Fixed Head
- --Position of Tensile Specimen

<r\ Main Screv/s (Do not twist)

---Position of Compression or Cross-
Bending Specimen

-•Weighing Table, rests on Levers
^-Weighing Levers

Machine Bed or Frame

-Threads on inside of gear hub for

Main Screws

-Main Drive Shaft

Figure 1,

Civil Erigr-8

Assignment 2

Page 5

-•--Position of Tensile Specimen

--Threads in Cross Head for Main Screws
--Cross Head

•-•Main Screws - Revolve to move Cross Head

...Position of Compression or Cross.

Bending Specimen

-- Weighing Table

Lever System

--•Machine Bed or Frame
:<~Main Drive Shaft

Figure 2

Counter
Weight

ffa

Frame

-Scale Beam

*v_ Frame

d — £

^Movable Poise Weight

mThrn
r>

-Frame

Figure 3

Civil Engr-8 Assignment 2, Page 6.

Riehle testing machines ;- Study Article 46, It describes the
liiehle (pronounced r8 lay) testing machine. This is the principal
competitor of the Olsen machine. Figure 2 shows the essential
pfirts of the Riehle machine. It is a two-screw machine. The cross-
head is threaded to receive the main screws which revolve and cause
it to move. The main screws revolve without axial motion. The
weighing mechanism is of the eatue design as the 'Olsen.
The Emery testing machine;- Study Article 47 and Figure 4 in the
text, The wide range in capacity and sensitiveness of this type of
machine is illustrated by the footnote on page 54. A high degree
of accuracy is not always necessary. The Emery machine is made to
order and is very expensive. Note that the load is applied to one
end of the specimen by the usual hydraulic press which can have
friction of any amount or variation without affecting the load which
is measured at the other end of the specimen by the pressure in a
completely closed chamber. There are two of these chambers or cap-
sules, one to take the full load on the specimen and another, of
smaller size, connected to it by hollow tuoing. The smaller capsule
actuates a lever system similar to Figure 3 (in the notes) which
measures the load on the capsule. The liquid in the capsules is
incompressible, therefore there is no friction. The diaphrans have
only very small exposed surfaces and can therefore be made of thin

material. In the Emery weighing levers the fulcra consist of thin

in
plates (in tension), whereas/ the Olsen and Riehle levers, the

fulcra are knife edges (in compression). The Emery lever system is
the more sensitive.

Civil Engr-8. Assignment 2. Page 7.

Tension Testing Machines

This type is not mentioned in the text book but there are ma-
chines which will test only in tension. In construction and operation
they are similar to the Olsen and Riehle universal testing machines.
A machine for testing briquettes in tension is shown on page 396. Ma-
terials frequently tested in tension are wire, various kinds of fabric,

leather and paper.

Compression Testing Machines

Study Articles 48 and 49, Read Article 50, remember that the
largest machine has a capacity of ten million pounds in compression
only. It is a hydraulic machine and the screws (shown in Figure 6 in
the text, page 56) are merely for changing the position of the cross-
head .

Transverse Testing Machines

Beams of wood, concrete, and steel are tested in this type of
machine. Study article 51 and Figure 9 together with the text referring
to it on the middle of page 59. Read Article 52. In the cross-bend-
ing test of cast iron which is made on the machine illustrated in Fig-
ure 9, page 59, the bending moment is a maximum under the load. The
span is usually 12 inches. The other type of transverse loading is
illustrated on page 202, Figure 2, It is known as the third point
loading, the beam being divided into three parts, usually equal.
Equal loads are applied at equal distances from the ends of the beam.
The bending moment between the loads is constant and the shear is zero.
This is a more desirable condition than that obtained by the center

Cold -Bend Testing Machines

Read Articles 54 and 55. The cold bend test is usually used
for various kinds of steel, both rolled and cast. The bend test is a
very important one for steel to be used for reinforced-concrete.

Civil Engr-8. Page 8.

Torsion Testing Mac nines

The torsion test is most satisfactory for testing the
shearing strength and elasticity of ductile materials. Torsion can-
not be put on a specimen in a machine of the universal type, it
takes a special form of machine such as shown in Figure 15 page 63.
Torsion test specimens are usually circular in section, either
hollow or solid. Read Article 57.

Impac t Testing Machines

TJber impact test is used to determine the amount of energy
(measured in foot-pounds or inch-pounds; necessary to stress a
specimen up to its elastic limit or to rupture it. The machine
shown in Figure 19, page 66 is used by the United States Forest
Service to test the toughnesfe of -wood. The usual impact test is
in flexure but impact compression and tension tests can be made in
the Turner machine. The pendulum t^;pe of impact testing machine
subjects the specimen to flexural stresses; it can be arranged
to test a specimen in tension. If ductile meter ials are tested in
impact-flexure the specimen is usually notched so as to localize
the stress and insure failure. Study Articles 58, 59, and 60 in
the text.

Endurance Testing Machines

Endurance or repeated stress testing machines in common
use are of two general types. The Upton-Lewis machine (not shov;n
in the text) and the Kommers machine (shown in Figure 26, page 72)
produce flexural stresses by simple bending of the specimen, where-

Civil Sngr-8. Assignment 2 Page 9.

as the White-Southtr machine produces flexural stresses by rotating

a loaded specimen (The machine is shown in Figure 25, page 71). In
both types of machines there is a reversal of stress ^from tension

to compression) as the specimen is bent or rotated. The Up ton- Lewi s
machine works best at stresses aoove the elastic limit. Read
Articles 64 and 6& and 1 ••-.study article 66-

Hardness Testing Machines

Hardness testers could not be classed as testing machines
if the definition previously given vere strictly interpreted. They
are comvaonly called testing machines and will, therefore, be dis-
cussed under this heading.

Filing, Cutting, and scratch tests have been proposed
to test hardness, but the indentation method has come into the most
general use. The Brinell machine and the Scleroscope represent,-,
machines using the indentation method- Read Article 61 and study
Articles 62 and $3.

AUXILIARY APPLIANCES BELOVED IN LOO) IMG SPECIMENS

In tension and compression tests it is essential to have
the load applied axially and uniformly over the cross-section of the
test specimen.

Devices For Tension Tests

Study Articles 68, 69, and read Article 70. If carefully
used the devices shown will give satisfactory results. None of
them give absolutely uniform distribution of stress.

Devices For Direct She?r Tests

Study Article 56 with Figures 13 and 14 which are given

Civil Engr-8. Assignment 2. Page 10.

under testing machines in the text. These devices give the approxi-
mate shearing strength of the material tested/ because it is im-
possible to make the test without producing some bending or com-
pressive stresses in the test specimen.

Loading Appliances for Compression Tests

Study Articles 71 to 74 inclusive. For ease in testing,
the spherical-bearing block should be placed on top of the specimen.
The radius of the bloc.*, r in Figure 32, page 76, should be equal
to r, the radius of the specimen tested.

Bedments

It is essential to have flat surfaces on the ends of
compression test specimens. If possible the use of bedments should
be avoided. If a flat surface cannot be secured plaster of Paris
is used. Porous surfaces should be shellaced before being capped
with plaster of Paris. A satisfactory surface can be secured by
pressing out the excess p3,aster on a smooth, plane surface of
glass or metal. The resulting bedment should not exceed 1/8" in
thickness, plaster of Paris bedments should be allowed to set
(about five hours) before testing the specimen. Study Articles 75
to 78 inclusive.

Deformeters

An instrument used to measure the change in length of
a specimen tested in tension is called an extensometer ; if used
in a compression test, it is called a compressoineter. Any device
for measuring the amount of bending of a beam is a def lectometer ,
whereas a troptometer is used to measure the amount of twist in
a torsion test.

Civil Li'.^r-S. ..3si0nrr.ent £. Page 11.

Extensoraeters :- Study the first paragraph aad those marked 1, 2
and 3 of Article 79, Article 80 and the last paragraph of Article
82 which describes the Berry Strain-Gage. Read Articlts 81, 83
and 84. Note that the Berry Strain-Gage could be used as a compress-
ometer. It requires very careful manipulation to get accurate re-
sults.

C orupre ssometer s ; - Study Articles 85 and 36. The instrument shown
in Figure <*6, page 87, is frequently made vjith a stiff rod instead
of wires to actuate the pointer on the dial. The rod is attached
to one ring and bears on the roller of a dial on the other ring.
TWO dials would be required if rocs v,ere used in the compressomfcter
shown. Read Articles SI and S2. These articles describe special
applications of compress outers and extensometers.
Deflectoneters:- Study Articles 87 and 90, read articles 88
and 89.

Troptcmeters :- Read Articles 93 and 94.
Miscellaneous devices:- Read Articles 95 and 97. Omit article 96.

Civil Er.gr -8. Questions to Assignment 2 Page 12.

Answer the following questions;

1. What is a testing machine?

2. What is a universal testing machine?

3. Describe the mechanism for applying the load tosihe 'test-
specimen in a testing machine of the screw-gear type.

4. Describe the weighing mechanise of a screw-gear testing machine.

5. Make a diagrarnatic sketch of the weighing system of a screw-
gear testing machine

6. What are the advantages t disadvantages, and limitations of

(a) screw-gear, (bj hydraulic, and (c) Emery types of testing
machines?

7. Describe the essential part of the Er.,ery testing machine.

8. Name the various types of impact testing machines.

9. What are the advantages and disadvantages of the vertical and
horizontal types of universal testing machines?

10. What are the essential requirements for (a) a universal test-
ing machine (b) an impact testing machine?

11. Name the types of hardness testing machines.

12. Describe a scleroscope.

13. Briefly describe the various types of endurance or repeated-
stress testing machines.

14. In what units are the test results of (a) Turner and (b) Rus-
sell machines measured?

15. What kind o5 a machine would you use to determine the Shearing

modulus of elasticity of a material?

Civil Engr-8. Questions to Assignment 2, page 13.

16. In what kind of tests are spherical oearihg blocks used?
Why are they used?

17. What is the purpose of a bedment?

18. Can the use of bedments be avoided?

19. Name the various types of def oraeters.

20. Describe a Berry Strain-Gage.

21. What are the advantages and disadvantages of the Berry Strain-
Gage?

22. What -re the essential requirements for extensometers?
25. Make a diagramatic sketch and describe a micrometer* screw

electric -contact extensoaeter.
24. What is a troptometer?

JfiUVBKSITY CF C*iLIFOKMI«, EXTENSION l> IV IS ION

Correspondence Courses
Materials cf Engineering Construction
Civil Er.gr -8. Professor C. T. Wiskocil

Assignment 3.

TESTING OF STRUCTURAL lidTER IALS

Reading assignment:- Johnson's Liiate rials of Construction, Chapter
III, pages 97 to 139.

preliminary :- The foundation for a comprehensive study of the
Materials of Engineering Construction will be completed with this
assignment. The information is closely related to the study of
ths materials themselves and will possibly be found more interest-
ing than the first two assignments.

Most of the properties of materials have been determined
by mechanical tests. Materials whose properties are not well known
rill be tested according to present standards or by methods to be
devised and perfected by research testing which is conducted for
the purpose of determining the proper size of test specimen, the
effect of methods of procedure on the test results, and similar
questions.

The results of mechanical tests are reliable criteria
for the acceptance or the rejection of structural materials.
Mechanical tests for quality and conformity to specifications,
chemical analyses, and microscopic examinations are used in com-
mercial testing. Examinations for surface defects, surface finish,
correctness of dimensions, and the supervision of manufacture to
insure adherence to predetermined methods are called inspection.

Civil Bngr-8. Assignment 3. Page 2.

General observations:- Study Article 98. The article emphasizes
the fact that test results are, in most instances, affected by the
methods by which they were obtained. For this reason it is neces-
sary to standardize methods of procedure in order that results se-
cured under such conditions may have relative value at least. The
selection of standard methods should be made with reference to
the practical use of the material. Materials anc? finished products
are tested under a wide variety of standards which frequently, in
certain tests, show exact agreement. Some of the standards in com-
mon use are: American Society for Testing Materials, Society of
Automotive Engineers, United States Bureau of Standards, United
States Navy Department, International Aircraft Standards, and those
of Lloyels of England.

Mechanical tests classified.-- Study Article 99. Static tests
yield most of the published test results. Dynamic and wearing tests
are very important but have not yet been thoroughly standardized.
Accelerated weathering tests have not proved satisfactory. Never-
theless such tests would supply very important information.
Structural tests are not so v;ell standardized as specimen tests;
frequently, however , acceptance depends entirely upon structural
tests. Full-size forms are not always tested to. failure; anchors,
for instance, are only subjected to proof-loads.

THE ACCURACY OF MACHINES AND APPARATUS

Methods of determining the accuracy and sensitiveness of testing
machines:- Study Article 100. Testing machines should be cali-
brated when installed and if the machine is in constant use the cali-

Civil Engr-8. Assignment 3. Pag© 3.

bration should be checked at regular intervals. The calibrated
tension bar or compression prism can be made of such size as to
load the machine to be calibrated up to its full capacity. This
produces large deformation and increases the relative accuracy of
the determination. Furthermore the apparatus is portable. This is
a desirable feature since few owners of testing machines have means
of calibrating them and must therefore call upon outside assistance.
The cost of such assistance would be greatly increased if standard
weights had to be shipped for each calibration.

The so-called standard bar has a known modulus of elastici-
ty (which was obtained in a machine of known accuracy or one whose
accuracy was determined by standard weights). Its cross-sectional
area and the gage length, length over which the deformation is
measured, are also known. The actual load producing any measured
deformation can be readily computed.

This computed load is then compared with the load observed
on the scale-beam of the machine. The difference between the loads,
divided by the actual or true load is the percentage error in the
machine. Its sign, indicating whether the machine reads high or
low, should always be given. In a well-designed machine the per-
centage error is constant over its entire range. The extensometer
must be permanently attached to the standard bar.
The calibration of apparatus for measuring deformations;- Read
Article 101. It is not necessary that measuring apparatus be cor-
rect. The errors, however, must be known and they should pre-

Civil Engr-8. Assignment 3. Page 4.

ferably be constant or should change at a constant rate. For any
important test or investigation all apparatus, including machines
and instruments, should be calibrated. If in error, the required
corrections must be applied to the observed measurements.

SELECTION AND PREPARATION OF SPECIMENS

Selection of specimens;- Study Article 102. The proper selec-
tion of samples is of great importance. Careless or improper
sampling is one of the most serious sources of trouble in commercial
testing.

The preparation of the specimen:- Study Article 103. It has been
known for a long time that the size, s;hape and method of preparation
of the test specimen affect the test results. The effect of these
controlable variables is studied in research testing which is be-
ing carried on in government, industrial, and educational labora-
tories.

XENSION TESTS

Tension tests are universally used to specify the proper-
ties of ductile materials. They are so generally used because they
give the elastic limit strength, ductility, and toughness besides
the tensile strength and modulus of elasticity. When the strength
of a material is spoken of it is generally understood to mean the
maximum tensile strength. The -best practice is, however, to
specify the particular strength meant. Brittle matter ia Is, namely
cast iron and cementing materials, are tested in tension.

Only the ultimate tensile strength of these materials

Civil Engr-8- Assignment 3. Page 5.

is obtained. Cements are tested in tension, because the machine
for such tests is much cheaper than a compression machine and the
specimens are more easily prepared and tested. Tension tests are
gradually giving wa^ to the compression test, because cement and
mortar, which are brittle materials, are generally used in com-
pression.

Study Articles 104, 105, the first and last paragraphs
and the tsxt under Figure 2 on page 106 in Article 106,

Read ^j-ticle 107. The essential points to remember are:
The averagb diameter or dimensions are determined and the gage
length then laid off (usually 2" or 8";^ The gage length is not
divided into equal spaces as indicated in the text. The speed of
testing should be such that the scale-beam can be kept in balance
so chat the phenomena of yield point and maximum can be accurately
determined. The properties of soft steel do not seem to be effected
by speeds up to six inches per minute.

Study Article 108, 109, 110 and 111. See the typical
stress-deformation curves on pages 210, 256, 476 and 601. The
drop of the scale-beam indicates the yield point in the commercial
tension test of medium carbon steel or any material having a de-
cided yield point. The load is applied continuously and the scale-
beam is kept balanced. In order to keep the beam in balance the
poise -weight must be advanced at a steady uniform rate, depending
upon the speed at which the cross-head of the machine is moving.
At the yield point the rate of increase in load is suddenly changed

Civil Fngr-8. assignment 3. Page 6.

and in sane cases actually becomes negative (see Figure 2 page 811,
diagrams for G.37f0 and 0.53$ oar boa steels). Before the rate of
motion of the poise-weight can be changed it has advanced too far
and causes the beam to fall, sometimes the load actually decreases
as in Figure 2 just referred to, so that the beam is out of balance.
This phenomenon is known as the drop JD£ beam.

COMPRESSION TESTS

The compression test is used chiefly for the brittle
materials. Study Article 112. Read Article 113, study Figure 7
on page 114 in this article. Whereas the compression test specimens
in the past have been cubes, the tendency is to increase the length
of the specimen. Most concrete specimens are 6" in diameter and
12" long.. Mortar specimens are 2" in diameter and 4" long while
met^l specimens %re aoout 1" in diameter and 4U long. Omit Article
114.

Tne important facts in Article 115 are: that when the
elastic limit and modulus of elasticity are determined the defor-
mation should be measured on at least two sides and the yokes of
the compressometer should be placed not less than half of the
diameter from the nearest bearing surface. A spherical bearing
plate should be used.

Study Articles 116 and 117.

TRANSVERSE TESTS

Study Articles 118 to 122 inclusive, omit only Table 1,
page 122. The calculated stresses of tension and compression -
modulus of rupture - are nominal values and are higher than the

Civil Engr-8. Assignment 3. Page 7.

actual stresses. Cast iron is the only material in which the size
of the test piece affects the modulus of rupture. In other materi-
als it is independent of the size of the specimen, provided, of
course, that the material is the same, but depends upon the shape
of the cross-section.

IMPACT TESTS

Study Articles 123 to 127 inclusive. No impact test has
"been accepted as a universal standard because the results are
affected by both the design of the machine and the shape and size
of the test specimen. A drop-test for railway rails has been
standardized and adopted, see Figure 20, page 67. Lloyds Register
of Shipping specifies a definite drop-test for ship anchors. The
notched-bar test of the Charpy and similar pendulum machines is
quite widely used in Europe but has not been adopted here.

HARDNESS TESTS

Study Articles 128 to 135 inclusive; Omit Taole 2 on
page 129 and the formulas in Article 134. The Brinnell machine
and the Scleroscope both test the relative hardness or the uni-
formity in hardness of a given material. The Scleroscope is well
adapted to testing the hardness of gear teeth. When a manufactured
piece has given satisfactory service, its hardness may be determin-
ed; and other. pieces bought later may be required to show the same
degree of hardness. Hardness depends upon other properties and
for any given material the hardness indirectly measures the tensile
strength.

Civil Er.gr-8. Assignment 3. Page 8.

Study Articles 136 to 139 inclusive. Remember that the
direct shear test will determine only the breaking strength in
shear.

TORSION TESTS

Study Articles 140 to 142 inclusive. Remember that the
torsional modulus of rupture, the ultimate shearing stress in tor-
sion computed from formula 16 on page 22, is not the actual shear-
ing strength of the material. The formula is similar to the one
for extreme fiber stress in bending, the modulus of rupture. Ten-
sion is a secondary stress developed in the torsion test; for
brittle materials it is less than the shearing strength and brittle
materials subjected to torsion will, therefore, fail in tension.
The torsion test will, however, determine the modulus of rigidity
of brittle materials.

BEND TEST OF METALS

Study Articles 143 to 148 inclusive. The bend test is
generally used to estimate the ductility of metals, the metal may
be cold or heated. The test can be used to determine whether a
given metal is ductile enough to be put through certain manu-
facturing processes.

DRIFTING TEST OF METALS

The drift test like the bend test gives an indication of
the ductility of metals. It is used on steel plates to be fastened
together by rivets because rivet holes in field joints are brought
into alignment by the use of a drift pin. This operation should

Civil F-ngr-3. Assignment 3. Page 9.

not cause the metal to crack or tear. In the best grade of wori£
rivet holes should be reamed, because drifting weakens the joint.
Study Article 149.

RESUME OF CHAPTER III

Study Article 150; it is a condensed statement of the
properties revealed by the testa described in the assignment and
the uses made of the tests.

Civil Engr-8 Questions to Assignment 3. Page 10.

Answer the following questions;*

1. What should be the guiding. principle in the preparation of
new testing methods and the design of testing machines?

2. Make a list of structural forms, machines or machine parts
which are tested as a v/hole or full-size.

3. Name the different ways of calibrating testing machines.

4. Describe the standard bar method of calibrating a testing
machine.

5. In the method described in question 4 make a sample calcula-
tion to show how the error and the percentage error in a
testing machine is calculated. Assume all necessary data.

6. What are the objects to be kept in view when selecting samples
for test specimens?

7. What are the general requirements for the preparation of test
specimens?

8. What is the significance of the tension test?

9. What is a commercial tension test?

10. Describe the tensile fracture of medium carbon steel.

11. How is the yield point in a tension test determined?

12. What causes the drop of beam in the tension test of medium
carbon steel?

13. How is the elongation in a tension specimen distributed with
reference to the point of fracture?

14. Prepare a stress-deformation diagram. Put in a curve for
mild steel and show the elastic limit, the apparent elastic
limit, the proportional limit and the yield point.

15. Make a list of materials usually tested in tension.

16. What information can be secured from a compression test?

17. Make a list of materials usually tested in compression.

18. How are the deformations in the transverse test measured?

19. What materials are tested in bending?

Civil Er.gr-8. Questions to Assignment 3. Page 11.

20. What is the object of the impact test?

21. Compare the Brinnell and Scleroscope methods for measuring
hardness.

22. How does direct shearing stress differ from the shearing
stress computed in the torsion test?

23. What information can be obtained in the torsion test?

24. How do brittle materials fail in torsion?

25. What property of materials is determined in the bend test?

26. Name materials which are tested in bending.

UNIVERSITY OF CALIFORNIA. EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
C'.vil Engr-8. Professor C. T. Wiskocil

Assignment 4.

USES AND PHYSICAL PROPERTIES OF WOOD

Reading Assignment:- Johnson's Materials of Construction, Chapter
IV, pages 140 - 178.

Introduction;- Wood is one of the primary materials of construction
and, due to the ease with which it can be worked and its comparative
light weight, it has always been used as a structural material.
Wood has sufficient strength and hardness for general purpose s^but ..
is inflammable and subject to decay. Its general use is therefore,
confined to inexpensive or temporary construction. It is used for
railroad ties chiefly because of its resilience.

Wood is an organic material. Its physical and mechanical
properties are dependent upon its structure, which in turn is de-
pendent upon life processes, age, and other physiological causes.
Because of its complex cellular structure specimens of wood cut from
the same stick and appearing to be identical often show marked
variations in strength.

Importance of Wood:- Read Article 151. The latest estimates in-
dicate that there is a total of 2,800 billion board feet of standing
timber in the United States. (Timber is usually measured in board
feet. The unit is one foot square and one inch thick or 144 cubic
inches). This estimate includes only trees of sawlog size and aot
wood that could be used for such purposes as fuel and pulp.

Civil Engr-8. Assignment 4. page 2.

It has been frequently stated that the -supply of timber in
the United States will be exhausted within the next thirty or
forty years because the rate of annual depletion by insects, fires,
and lumbering (wood cut for all purposes) is aoout 100 billion
board feet. Remember that these are scientific estimates and the
extent to which known factors will control the result cannot be
exactly determined and the possibility of unknown factors must be
provided for. The virgin forests of Douglas fir and southern
yellow pine alone, will continue to supply satisfactory structural
timber for several generations. The increasing practice of forestry
will insure an increased annual growth and minimize the occurrence
of fires. Three California redwood companies have announced plans
for permanent forest management whereby they will work their prop-
erties so as to yield regular crops of timber and thus insure a
permanent supply of raw material for their plants. Large tracts
of non-agricultural land which are well suited for the production
of timber could be utilized if necessary. Furthermore the more
general use of preservatives and the more economical use of wood
both tend to conserve the supply. The exhaustion of our forests is,
therefore, problematic.

Production:- About one half the available supply of timber in the
United states is in the Pacific Coast forests (Washington, Oregon,
California, Idaho, and Montana). It consists principally of
Douglas fir, western hemlock, sugar pine, western yellow pine,
redwood, and cedar.

Civil Engr-8. Assignment 4. page 3.

The annual production of timber is about forty billion
board feet. Washington and Louisiana produce the most; together they
supply about one fifth of the total production.

About one fifth of the wood cut annually is used in engineer-
ing construction. The following table gives the approximate dis-
tribution:

Structural timber and lumber 13 %

Ties 4

Mine timbers 2

Car construction 1
Poles .2

Ship construction .2

About 40 % is used for firewood and \Z% for pianing-miil products
such as doors and window-sashes. Wood is also made into pulp,
shingles, laths, furniture, posts and containers (barrels, boxes,
and crates).

Wood, Timber, and Lumber:- Wood is the hard fibrous substance of
trees and shrubs. It is composed of lignocellulose , which is a
starch- like substance, permeated by materials known as lignin,
resin, coloring-matter, water and small proportion of inorganic
matter (evident as ash).

Timber is wood suitable for construction whether in the
tree or cut and seasoned. When applied to cut wood the term is
used to designate pieces of comparatively large breadth and width.

Lumber is timber that is sawed or split into boards, planks,
or other forms of comparatively small dimensions. This term is
used chiefly in the United States.

Civil Fngr-8 Assignment 4.

GENERAL. CHARACTERISTICS OF WOOD

Structure and appearance : -Read Article 152. A knowledge of the
structure of wood is important because of its relation to the mechani-
cal properties. In general the structure is cellular, consisting of
minute, hollow, elongated tubes grown together and closed at the
ends. In some woods the tubes are open to permit the movement of
sap. Because of its structure and composition wood can "be cut
easily and nails and other fastenings can be readily driven into it.
The empty cells are dead air spaces and retard the conduction of
heat and sound. Because of its porous nature it will take up pre-
servatives. Paint and ether surface finishes will readily adhere
to its surface and thus prolong its life.

Classes of trees:- Read Article 153. The botanical classification
of trees whose wocd is used in construction in the United States is
as follows :

I Gymno sperms

I A Coniferae

II Angiosperms

IIA Dicotyledons

The seeds of the gymnospermB are not enclosed in fruit. The gymno-
sperms are divided into three groups. TWO of them grow principally
in the tropics; tne other one, the coniferae, is the only one that
yields merchantable lumber. The pines, firs and cedars are some
of the trees included in this group. The seeds are borne on a
series of overlapping scales, arranged on cones. The leaves are
narrow, stiff or needle-like. The trees are sometimes designated

Civil Engr-8. Assignment 4. page 5.

as needle-leaf, softwood, evergreen, coniferous, and cone-bearing.

The seeds of the angiosperms are always enclosed. There are
two groups of angiosperms. They differ principally in the structure
of their stems or trunks. The first group, the monocotyledons,
have one seed leaf or cotyledon (therefore the name mono-cotyledon;.
These trees, which include the palm and the bamboo, grow principally
iu the tropics. The second group, the dicotyledons, have two seed-
leaves. This group includes the oaks, maples, and hickories, which
are sometimes called broad-leaf, hardwood, or deciduous trees.

The conifers yield the largest proportion of woods used for
structural purposes.

Classification of Woods;- Frequently woods instead of trees are
classified. In the botanical classification of trees given in a
previous paragraph the two important groups were the conifers and
the dicotyledons. They grow in the same manner and their woods,
therefore, are in one group sometimes called out side -growers,
banded woods, or exogens. The elements of the woods in this group
develop in the cambium layer which is just inside the bark of the
tree. Each growing season new wood is added to the previous growth.
In cross-section, these seasonal additions appear as concentric
circular layers or rings. The names conifers and dicotyledons are
applied to the divisions of this group. The designation soft-wood
for the conifers is not logical because some of the woods of this
division are actually very hard as in the case of some of the pines,
while the term hardwood is incorrectly applied to the dicotyledons

Civil Engr-8. Assignment 4. page 6.

basswood and chestnut whose wood is soft. The terms needle-leaf
and broad-leaf are more exact but the designation conifers and
dicotyledons is preferable.

The other group of woods includes the unimportant mono-
cotyledons in which the wood elements are in separate bundles scat-
tered throughout the tree. The cross-section of these woods has
a dotted appearance. The trees grow largely by expansion of the
cells already formed and do not continually increase in diameter
but attain their maximum diameter early in their growth. The name
endogen is sometimes given to this group; other names are inside-
grower and non-banded woods. The use of the terms endogen and exo-
gen should be avoided because engineers and botanists seldom em-
ploy them in the same way.

Botanical Names:- The use of botanical nomenclature obviates the
confusion v,'hich occurs when trees are designated by common or local
names. Thus the names of the species Pinus palustris are longleaf,
yellow, hard, Georgia, and southern pine, in addition to some 25
others.

Botanical names are made up of terms which denote genus and
species. Sequoia is the generic name for all species of redwoods.
Sempervirens and washingtoniana are names of particular species of
redwoods; the latter is the Big Tree or Mammoth Redwood.

Botanists have sometimes given different names to the same
species* The abbreviated name of the person responsible for a given
designation is therefore added to the complete name. An example
is Sequoia sempervirens Endl.

Civil Engr-3. Assignment 4. page 7.

A genus is a group of related species while a species is the
smallest group of individuals to which distinctive characteristics
can "be assigned.

Structure of wood in general:- Read Article 154. The accompanying
diagram shows the cross-section of a tree. The pith stores up plant
food for the young stem and it seems to be of only temporary service.
A layer of spring wood and one of summer wood constitute a so-called
annual ring. Early and late growth would be better designations for
the parts of the annual rings. Early growth is usually formed in
the spring when the tree requires most water. The water-conducting
wood -elements predominate and produce porous or less compact wood.
The late growth is formed in the summer and early fall; it is
heavier and denser than the early growth. Distinct periods of rapid
and slow growth may be caused by wet and dry seasons which sometimes
occur oftener than once a year. The number of so-called annual

rings does not always give the exact age of the tree. This has been

at
found to be the case in certain trees which were c:ut/a known age.

Pith
Cambium^ _J Heart \\ ood

3ar.< ^ ,, , ^ „-

Wood

_ Spring Wood (light)
-SuiEraer Wood $ark

Cross Section of Tree

Civil Engr-8 Assignment 4. page 8-

HBARTWOOD;- While the ceil structure of heart-wood is the same as
that of sapwood, the protoplasm is absent and inert minerals and
pigments appear. The thicker cell-walls of heartwood are probably
caused by the accumulation of deposited materials. The change from
sapwood to heartv/ood does not take place ring by ring or a little
each year but may skip many years and eight or more rings may change
to heartwood in one year. The change is not uniform around the tree,
it may occur in one side before the other so that one ring may be
part heartwood while, the other part remains sapwood. (Reference -
U.S. Bureau of Plant industry Bulletin No. 14 p. 15.; In most trees,
however, the line of division between the heartwood and the sapwood
and that between the sapwood and the bark, are concentric around the

pith. ,

S^PWOOD :- Sapwood lies between the bark and the heartwood. It de-
rives its name from the fact that it carries up-ward sap currents.
(The descending currents pass through the inner bark)
BARK:- The barK affords protection to the tree and is an agent in
its development.

CAMBIUM LAYER:- The cambium layer consists of a thin layer of small
cells between the bark and the sapwood. These cells develop into the
wood cells of the sapwood and form the annual rings. The outer
cambium cells develop into new bark.

GRAIN OF WOOD:- Study Article 155. Wood is said to be straight
grained when the direction of the wood elements is parallel with the
pith- If the elements are arranged in a spiral course around the

Civil Engr-8. Assignment 4. Page 9.

pith, the wood is spiral grained. The grain of a small stick is
influenced by the way it is cut from the log. If the lines on the
surface (formed by cutting the annual layers of v;ood cells) run
diagonally across the piece, the bending and compress ire strength
will be reduced. Iriclination of more than 1 in 20 to the edge of
the stick should not be allowed in high grade material. Spiral
grain can be detected by season checks or by splitting the stick.
STRUCTUHAL ELEMENTS OF WOOD:- Study Article 197. The four princi-
pal wood elements are tracheids, wood fibers, vessels, and parenchyma,
The cell walls of these elements are composed of Xylem (xl/ - lem)
or wood tissue.

Tracheids are small thin-walled tubular cells which, in
coniferous wood, are about 0.2 inches long and polygonal in cross-
section with a diameter of aoout 0.002 inches, The cells with
their longitudinal axis parallel with the pith of the tree, are
arranged in radial rov;s. The thick walls of the cells formed to-
ward the end of the season's growth reduce the size of the opening
in the cells but add to the strength of the element. Tracheids
have bordered pits in their side v;alls. These pits are small por-
tions of the wall where the original cellulose membrane of the
cambia 1 cell has not been thickened by the addition of lignin
(inert minerals). These pits allow the passage of water between

adjacent cells.

Wood fibers are small thick-walled tubular cells with taper-
ed ends rarely over 0.1 inch in length. They usually have small

Civil F.ngr-3. Assignment 4. page 10.

simple pits. They are not found in coniferous -woods, but are -che
principal source of hardness and toughness of broad leaved woods.

Vessels are long tubular elements with mfcny border pits.
Vessels often extend the entire length of the tree. The;, vary in
diameter from 0.003 to 0.03 inches. They are formed by the union
of original cambial cells in which the end walls become partially
or wholly absorbed so that they present an unobstructed passage for
water from the roots to the branches of the tree.

Parenchyma are made of thin-walled cells joined end to end.
The end and side walls are of equal thickness and have many simple
rounded pits. Parenchyma resemble wood fibers in shape. Their
chief function is the storage and distrioution of food materials.

Pays, often called medullary rays, are radial bands of cells
which cross the tree at right angles to the pith. In some species
the rays are composed of parenchyma, in others, the cells are tracheids
The principal function of the rays is the lateral distribution of
plant food.

Coniferous woods are composed principally of tracheids with
rays at right angles to these cells. Resin ducts occur in the resin-
bearing trees usually between the early and the late wood. These
ducts have no walls of their own but are only intercellular channels
with an average diameter of 0.01 inches for the larger ducts. Coni-
ferous woods are quite uniform in cross -section and because of the
absence of large vessels are called non-porous. The thick-walled
cells in the late wood give that portion of each annual ring a
darker color than the early wood. Study Article 198.

Civil Engr-8. Assignment 4. page 11.

Broad leaved woods have a more complex structure. They con-
sist chiefly of wood fibers with prominent medullary or pith rays
of parenchyma. Broad leaved woods are ring-porous or diffuse-
porous depending upon the distribution of vessels or pores. In
the ring-porous woods the pores are grouped in the early wood and
make a pronounced annual ring, whereas in the diffuse-porous woods,
the vessels have a uniform dispersion and the annual rings are not
so distinct. Stuoy Article 199, note the statement regarding tyloses
£See Figure 2 on page 143). Omit Article 200.

DEFECTS IN TIMBER:- Study Article 156. The most common defects in
timber are knots, checks, and shakes. Knc*s are classified as sound,
loose, or decayed. They affect the compressive and transverse
strength of wood, also its workability and shrinkage. Checks are
caused by stresses set up in seasoning. Large structural timbers
are difficult to season without checking. The outer portions dry
and shrink while the inner part is still tooist, thus bausing the
wood to split.

A shake is a separation between two annual rings.

Both checks and shakes decrease the resistance to longitudinal
shear besides affecting the durability by admitting air and moisture*
poles with checks the entire length are also weak in torsion - the
cross-arms twist the pole when the wires break.

Density and weight;- Study Article 158. The term specific weight
means the weight of a specific or definite volume, which in this
book is taken as the cubic foot. The specific weight of different

Civil Engr-3. Assignment 4. .Vage 12.

woods varies with the moisture Content. With a given percentage
of moisture, however, the specific weights for each species are not
the same hut they vary due to the structure of the •wood. The amount
of wood substance, then, determines the specific weight. Wood sub-
stance itself with a specific gravity of 1.55 would not float on
w&ter. A cubic foot of water weighs 62.5 pounds, a cubic foot of
wood substance (not possible in natures) would weigh 1.55 times
62.5 or approximately 97 pounds. (A cubic foot of anthracite coal
weighs about 97 pounds, j The following table indicates the effect
of moisture on the specific weight of the species of wood listed.
Air -dry wood contains from 12 to 15 % moisture while a wood with
Q% moisture is said to be kiln dry. Note that the average specific
weight for a given lot of wood may vary by ± 5 % from the values
in the table and individual pieces may show as auch as - 20 %

variation. Air' Kiln-

Green Dry Dry

Blue gum (Eucalyptus globulus; 70 54 52

White oak (Quercus alba) 61 47 46
Douglas fir (Pseudotsuga

taxifolia; 40 33 32
?fe stern yellov, pine (Pinus

ponoerosa, 53 29 28

Sugar pine (pinus lambertiana) 50 27 26

Sitka spruce (Ficea sitchensis) 33 26 25

Redwood (Sequoia sempervirens) 38 24 23

Western red cedar (Thuja plicata) 24 22 21

Moisture in wood ;- Study Article 159. Water exists in only two
conditions in wood, - (1) as free water in the pores and (2) as
absorbed water in the cell walls. (1) and (2) as given in the
text are practically identical. The moisture content of green wood
as given in Table I, facing page 196, is computed on the basis of

Civil Eiigr-8. Assignment 4. page 13.

cried to a constant weight at luO degrees Centigrade.
The crying of tinker:- Study Article 160. The principal reasons
for ,se-uscn.tn£ v.ood are given in the first part if Arti:;l<? 160. Most
wood is se? p.oneo in the open air, Under these conditions the rata
of drying varies v/ith the temperature and humidity of the air, size
and! species of wocd and method of piling. Sawed lumoer is piled
so as to permit the free circulation of air. In piling wood for
air -seasoning care must be taken to have good foundations for the
stacks, rrhich wust be Kept free from debris and the yards should be
well drained. Air seasoning usually takes considerable time a§
ixidicated in Figure 6 on page 151. Defects produced by improper
drying, have sorbet imes caused losses of 25^ of the seasoned -wood.

Hi In drying is re-sorted to "when ^cod must be seasoned quickly.
A recent development of a kiln-drying process which makes use of
superheated stea-ri has been announced by the U.S. Forest products
Laboratory. C-rean coniferous lumber (such as Douglas Fir and
Southern Yellow P:'ne) one inch thick can be dried to 10 % moisture
content in 14 hours by this method. It is not recommenced for
lumber over 2 irshes thick,

In the rap'.o .seasoning of \<cou care must be taken to prevent
the evaporation o.C water fVcm the surface at a faster rate than
ic is brought from the interior of the -?ood. The surface evaporation
can be controlled in a ^vell designed kiln by regulating the humidity,
temperature and amount of air passiag. through the kiln. Evaporation
in a kiln depends upon the relative humidity of the air. Air -with
a relative humidity of 100 ^.cannot dry 7/ood because it already

Civil Lngi'-S. Assignment 4. Page 14.

contains ail the water it can carry, but if the relative humidity
is .'educed to say 60 % it can taice up a certain amount of moisture.
A large amount of air is required in the successful operation of
a kiln. Typical kiln conditions in drying 2 inch thick fir are as
fellows; The wood is given a preliminary steaming for several
hours, the temperature is aoout 130 degrees Fahrenheit, the relative
humidity of the air is 100 % and the moisture in the 7/ood about
60 %. The object of this preliminary treatment is to soften the
surface in case it iias been casehardened and also to facilitate the
transmission of water from the interior of the wood. The temperature
then fir ops to 110 a no the relative humidity of the air decreases to
30 %. The temperature is then gradually increased and the relative
humidity of the air decreased. rue to these changes the moisture
in the v;ood is decreased gradually to about 30 % at the end of the
first week. At the end of twenty days, with the temperature
gradually increasing to 150 degrees Fahrenheit and the relative
humidity of the air decreasing to 20% the wood nas been reduced to
a moisture content of 10^. An^ caseharcening that has been produced
is then removed by a final steaming of a few hours duration, during
•which the temperature is loG and the relative humidity of the air
is 100^. This treatment increases the moisture content of the wood
to \b%, v;hich is again reduced to 10$, by a few hours drying under
the conditions ~ust preceding the final steaming.

The moisture in ivood will tend to come to equilibrium with
that of the air in which it is stored. Kiln-dry vrood (about Q%_
moisture) will reabsorb water if stored under open-air sheds so that

Civil Engr-8. Assignment 4. Page 15

its moisture content will be about 15?o- The time required for such
readjustment depends upon the size and shape of the pieces. Air-dry
wood if stored in a wood -working shop will tend to come to a moisture
content of about 6 %. This shows that wood is a hygroscopic sub-
stance. Since changes in the moisture content produce changes in
the dimensions of cut lumber it is essential that the moisture con-
tent of the rvood at the time it is used in cabinet work and other
exact construction be the same as it would be under conditions of
later use. High-grade furniture is varnished or given other surface
treatment on all exposed surfaces (back and underneath) so as to re-
duce the tendency of the thoroughly-seasoned wood to absorb water,
which would cause it to swell, or to give off moisture and produce
shrinkage. paraffin has been found to be the most effective sub-
stance used to treat air-dry wood so as to prevent shrinkage and
spelling when the wood is subjected to atmospheres of variable
humidities.

The table at the Dottom of page 152 is not important.
Shrinkage and its effects:- Study Article 161. The removal of
free water reduces the weight of wood but it does not affect the other
properties. When all the i'ree water is removed the fiber-saturation
point is reached. Further decrease in water content causes wood to
shrink. 3ee Figure 12 on page 156. The fiber -saturation point
usually ranges from 25 to "50% of the dry weight of the wood. The
common defects produced by improper seasoning are checking, case-
hardening, honeycombing, and warping. Each of these defects is ex-
plained in this article.

Civil ringr-8. Assi^ruient 4. page 16.

Amount of shrinkage;- ST-udy Article 162. Wood in an air -dry con-
dition has reached about one-half of its possible shrinkage. Length-
wise shrinkage is negligible because the thickness of the end walls
of the wood elements is very small vhen compared to the length of
these elements. Shrinkage in a direction tangential to the annual
rings is about twice as great as in a radial direction. Consider-
able force is developed when confined wood s'/ells due to the ab-
sorption of water. This is strikingly shown in an illustration in
Engineering news, 70, 615, September 25, 1S13. Slabs of oak veneer-
ed with maple were stacked in a basement to "within 1 inch of the
lower side of a 12 by 24 inch reinforced concrete beam which formed
part of the first floor framing. The wood was saturated during a
flood which caused it to swell. The force developed, raised the
beam 3 inches at the point of contact making its replacement neces-
sary. The shrinKage from green to over-dry condition for different
species of wood is given in Table I, which faces page 196.
principal native woods:- Study Articles 167, 168, 173, 174, 185,
and 189. They give data on Western Yellow Pine, Sugar Pine,
Douglas Fir, Western Hemlock, Redwood, and Western Cedar respectively.
These are the principal species of wood grown on the pacific Coast.
Article 164 descrioes Southern Yellow pine which is an important
species of wood; in its properties and uses it resembles our
Douglas Fir.

Read the other articles, not listed aoove, up to Article 197.

Civil Eugr-8. Questions to Assignment 5. page 17

1. Name the principal woods grown in the pacific Cost forests.

2. Distinguish between wood , timber, and lumber.

3. Sketch the cross-section of a tree and show the bark, heart-
wood, cambium, pith, summer wood, sapvvood , and spring wood.

4. What are the common defects in structural timber?

5. What is the approximate weight of air-dry wood? (Be sure to

give unit of measure)

6. What are the reasons for seasoning wood?

7. How is Tf:ood seasoned?

8. What is the fiber-saturation point? What is its significance?

UNIVERSITY OF C.JL, IF OR1-J JA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Civil En^r-a. Professor C. T. Wiskocil

Assignment 5=

DETERIORATION AMD PRESERVATION OF WOOD

Reading Assignment:- Johnson's ksterials of Construction, Chapter V,
pages 179 to 194 inclusive.

The Durability of Wood :- The durability of wood depends upon the
conditions under which it is used. The life of Sycamore lumber,
when placed under conditions which subject it to decay, is from three
to five years. Weiss, in his book, Preservation of Structural Timbers,
gives an illustration of an Egyptian coffin of Sycamore dating from
the XII dynasty (2000 - 1788 B.C.; which is still in perfect condi-
tion. When wood is Kept dry its resistance to decay is indefinite.

Black locust and osage orange are probably the most durable
woods. Their life is estimated as being over 15 years, even under
adverse conditions. They are used principally for planing mill
products, vehicle and vehicle parts, and ship and boat construction.
The life of redv/ood ~nd cypress is from 12 to 15 years under similar
conditions. These woods are used principally for planing luill
products and general cill work. The amount of cypress used is about
si:: times that of redwood. Redv;ood is known to have lasted for
much longer periods. Stakes 2 by 3 inches in section driven by the
U.S. Coast and Geodetic Survey along the California coast in 1874
were found in a fair state of preservation in 1921, 47 years after
having been driven into the ground. Large redwood sills under a

Civil ^ngr-8. Assignment 5. Page 2.

bridge pier near Eealdsburg, California, were recently (December
1921) found to be in a perfect state of preservation, 35 years after
being placed in a position which was aucve low water level.
Douglas fir and southern yellow pine, the principal structural woods,
have an estimated life of S to 11 years when placed under conditions
subjecting them to decay.

In general, sapwood is less resistant to decay than heartwood,
and, "when used without preservative treatment in situations favoraole
to decay, sapwocd is likely to have much shorter life than heart-wood.
But when properly treated sapwood and heartwood are practically
equal in resistance to decay.

Some woods are more duraole than others. The reason for this
difference is not Known. Density does not seer, to oe a criterion
of durability. Durability, however, can be judged by the presence
of sapwood, the moisture content, the presence of sap stain,
structural defects, and the amount of resin, pronounced variations
in color, especially when wood is spotted or streaked, indicate in-
cipient decay. Resin keeps out moisture and air and thus acts as
•^^

a preservative. Fence posts having a high pitch content last longer
than those having less pitch. Such defects as checks.. and knot
holes offer places for the lodgement of the spores of fungi and form
starting places for decay.

The color of cypress was thought to be a criterion of its
resistance to decay. But investigations by the U.S. Forest products
Laboratory have proved that the color of the wood makes little

Civil Engr-8. Assignment 6. Page 3.

difference. If durability is desired it is important to select
heartwood of cypress regardless of its color.

The moisture content of wood to be used in building construc-
tion, particularly in poorly ventilated places, is of importance
because poor ventilation is favorable to the attack of the so-called
"dry rot". (See discussion on page 181). Mill construction with
poorly seasoned wood has been known to have become infected within
a year or two after completion, whereas well -seasoned wood has re-
sisted decay under similar conditions for more than ten years. The
term "dry rot" is frequently applied to any decay in comparatively
dry wood. Dry rot, however, is the result of the attack of the
house fungus, merulius lachryraans, which is frequently found growing
in dry wood without any apparent supply of moisture. The U.S.
Forest Products Laboratory has proved that this fungus will not
grow in thoroughly dry wood out it will germinate in moist wood and
make its way for long distances into dry wood, drawing the necessary
water from the moist wood through a system of minute porous strands.
Wood in the advanced stage of dry tot is shrunken, yellow to brown
in color, and so brittle that it can easily be crushed into powder.
The dry rot fungus is active throughout this country attacking coni-
ferous woods more commonly than the dicotyledons.

The following are the principal causes for the rapid deteriora-
tion of wood in buildings:

1. The use of green lumoer.

2. Allowing lumber to get wet during construction.

3. Allowing lumber to absorb moisture after the
building is completed, because of leaks or lack..
of ventilation.

4. The use of lumber containing too much sapwood.

Civil Engr-3. Assignment 5. page 4.

The avoidance of these conditions ^ill, as a rule, prevent decay.

In certain cases, however, decay can only be prevented by preservative
treatment.

The chief causes for deterioration are decay, marine borers,
insects, mechanical abrasion, and fire. Birds and alxali soils cause
deterioration but it is estimated that decay is the most important.
C opposition of Wood:- Read Article 202. In the previous assign-
ment the composition of wood was given as lignocellulose , which is
a starch-like substance, permeated by lignin, resin, coloring-
matter, water, and a small proportion of inorganic matter.
Causes of Decay :- Study Article 203. The attack of bacteria and
fungi cause the decay of wood. Only a small percentage of these
parasites, v/hich are low forms of plant life, have the ability to
decay wood. Most wood-rotting fungi thrive at temperatures around
80 degrees Fahrenheit; small rises aoove this optimum temperature
are often fatal. It is good practice to heat newly completed wood
buildings i:i order to kill surface growths of fungi, practically
all fungi survive the coldest winters. Spores of fungi are known
to have remained alive for 8 years when in a dry condition.
Insects:- Study Article 204. Insects damage wood in any form by
cutting out ourrows or galleries. Borers like termites and powder-
post borers, enter the stick of v:ood through a small hole and then
excavate winding burrovs, whose extent cannot be estimated by sur-
fact indications. White ants or termites, black ants, carpenter
bees, and powder-post borers are the principal wood boring insects.
It has been reported (1922) that in some localities near Los Angeles,
California, as many as 50$ of the cedar poles set by the Southern

Civil fcngr-8. Assignment 5. Page 5.

California Edison Company prior to 1910 have been attacked by
termites. The infected area extends from San Diego to Santa Barbara
and east to Red land d. The insects enter the poles at the ground
line and frequently attack the pins on the cross-arms without coming
to the surface of the pole. Creosote oil has been found to be an
effective preservative.

Marine Borers :- Study Article 205. Destruction by marine borers
during IS 19 and 1920 in San Francisco Bay and the adjoining San
Pablo Bay and Suisun Bay has been estimated by a committee of the
American Wood Preservers1 Association who reported in "San Francisco
B^y Marine piling Survey", to be in excesc of 15 million dollars.
There are three species of moliuscan borers: Teredo navalis,
Teredo diegensis, . . . , • and Xylotraya setacea, besides

tliree species of crustacean oorers: Linmoria, Sphaeroma and Chelura,
active in this region, tohere the attacK of these oorers is severe,
untreated piles are destroyed in 6 to 8 months. In otner places
they may last 2 to 4 years. Properly creosoted piles of Douglas Fir
have a life of aoout 25 years- Destruction of creosoted piles
has been the result of untreated -wood being exposed to attacK by

damage to the surface in handling or placing the piles. Various

not

kinds of protection to -wood piles have/ been very effective. Pre-
servative treatment with creosote has been most satisfactory. The
attacks of marine oorers is not new. They were known to the ancient
Romans. The following note was taken from Voyages and Travels,
Vol. II, C.R- Beazley, in regard to the ships sent out to discover

Civil tngr-8. Assignment 5. Page 6.

the Northwest Passage during the reign of Henry VI:

"They cover a piece of the keels of the shippe with their
sheets of leade, for they had heard that in certaine
partes of the ocean a kindo of wormes is bredde , which
many times pearceth and eateth through the strongest oake
that is."

Other Deteriorating Influences;- Read Article 206. Mechanical
abrasion and fire are important destroyers of wood, whereas alkali
soils, and birds are only minor causes of deterioration.
The Need of Preservation \- Read Article 207. The idea of wood
preservation is not new. Pliny writes thrt in his time, wood was
protected from attacks by worms by treating it with garlic boiled in
vinegar. The early Greeks and Romans used the oils from Cedars
and Junipers for their antiseptic value. These oils were rubbed
over the surface of the wood to f be, preserved. The Britons made
various attempts to protect their wooden warships from decay. Wood
preservation is now practiced all over the world. The necessity of
preservation is given in the text (Article 2o7j. There are two
methods of protecting wood from destruction by living organisms.
The first is to control the conditions necessary for life and thus
inhibit their growth. This means the control of the temperature and
the moisture content, which is not practical in the commercial use
of wood. The second method is to inject a material which will kill
or poison the organisms themselves or the enzymes through which
they accomplish their destruction. This latter method is now the

Civil Engr-8. Assignment 5. Page 7.

standard practice.

The Relation of Structure to the Penetration of Preservatives :-
Study Article 208. This article shows the effect of the various
structures upon the diffusion of preservatives and indicates why all
woods cannot be given the same treatment if uniform results are to
be expected. Douglas Fir, as noted, cannot be easily impregnated.
It is now being mechanically perforated so that a uniform, pre-
determined, penetration of preservative can be secured.
The Treatment of Timber before Preservation:- Study Article 209.
Wood is thoroughly seasoned before being given preservative treat-
ment. The preliminary treatment is described in this article.
Superficial Treatments:- Read Articles 210 to 213 inclusive.
Superficial processes 'simply give the wood a thin surface coating of
preservative. Timber so treated is apt to have the protecting coat-
ing broken either by abrasion or checking which exposes untreated
wood and subjects the entire piece to decay.

Superficial processes are inexpensive and are used only when
small quantities of wood are treated. Dipping is more effective
than brush treatment. Recent tests by the U.S. Forest Products
Laboratory have proved that charred posts were less durable than
untreated ones. The charred surface is usually not a solid cover-
ing. It is checked through in many places. If seasoned posts are
charred the charring does not reach to the oottom of the season
checks which are always present. If green posts are charred season
checks open up through the charred exterior. In either case the

Civil Engr-8. Assignment 5. Page 8.

*
uncharred interior is exposed to infection and will decay as rapidly

as untreated wood. Charring deep enough to resist decay would un-
doubtedly weaken a post of ordinary size.

Non-pressure Processes of Impregnation;- Study Articles 214 to 216
inclusive. Non-pressure methods are carried on in open tanks. They
insure a better penetration than is ootained by the superficial
processes. Open-tank and Kyanizing are the tv;o non-pressure im-
pregnation processes now in use. They differ from pressure processes
in that the latter use pressures aoove atmospheric to force the pre-
servative into the wood. Farmers and mine and telephone companies
are the principal users of open-tadk methods of preserving wood.
Mercuric chloride was first used as a wood preservative in 1705. The
process of preservation in which this salt is used was patented in
England by John H. Kyan in 1832. It was introduced into the United
States about 1840 and is said to be the oldest method of treating
wood now practiced in this country. The details of the process are
given in Article 216.

Pressura Processes of Impregnation:- Study Articles 217 to 223 in-
clusive. Pressure processes use pressures aoove atmospheric to force
preservative into the wood. The fie the 11 process (Article 219) is
named after John fietheli who took out patents in England in 1838.
It is commonly called the full-cell process. Green or seasoned
wood can be treated by this method. It is considered the standard
process of treating wood with creosote. The process has been modi-
fied because of its excessive use in~ preservation.

Civil Engr-8. Assignment 5. Page 9.

The boiling process (Article 220) was patented in the United

States by W.G. Curtis and J.D. Isaacs in 1895. With the exception

m
of the preliminary treatment which the wood is given, it resembles

the Bethell process.

The Lowry process (Article 222) is sometimes called the empty-
cell process. It was patented in the United States by C.B- Lowry
in 1906.

The Rueping process (Article 220) is also called an empty-
cell process. It was patented in 1902.

The Card process (Article 223) was patented in 1906 by J.B.
Card.

The Burnett process (article 219) was patented in England
in 1838 by William Burnett. It is the standard zinc chloride
process.

Study these pressure methods and be able to outline the
process and give the kind of preservative used in each.
Preservatives :- Study Article 224, which describes the preservatives
commonly used for treating wood. The principal requirement for a
good preservative is that it be able to kill the organisms which
attack wood or destroy the agents (enzymes) through which these
organisms work. In addition the preservative must be soluble in the
body fluids of the organisms. Since organisms which attack wood
have water as their chief body fluid, it is necessary that a material
to be toxic must be soluble in water to a certain extent. In this
respect oil solutions and inorganic salts must De similar. Wood im-
pregnated with zinc chloride has all the toxic zinc in solution

Civil Engr-8. Assignment 5. page 10.

and the concentration of this zinc becomes weaker and weaker by
any leach;.ng to which the wood may be subjected. Creosote oil, which
may include hydrocarbons (such as benzene, toluene and naphthalene)
or tar acids (such as the cresols and naphthols) or tar bases (such
as quinoline and isoquinoline) or a comoination of all three, is
(according to Baternan) divided into two groups. The first one con-
tains those oils that are sufficiently soluble in water to render
their water solutions capable of -killing the wood -destroy ing
organisms and are celled toxic oils. 'Ihe second group, which are
called non-toxic oils, are not sufficiently soluble to produce a toxic
water solution. Toxic oils are completely soluble in non-toxic oils
and are partially soluble in water. Ihe toxic oils, therefore, di-
vide themselves between the water and the non-toxic oils in such a
manner that their concentration in water and the non-toxic oils is
in proportion to their solubility in the respective media. The non-
toxic oils act as a reservoir for the toxic oils. Assume a toxic
oil as being 50 times as soluole in a non-toxic oil as it is in
water. Take a 10$ solution of the toxic oil in the non-toxic oil.
When such a solution comes in contact with an equal volume of water
the concentration of the water will be 0.2$» If the toxic limit of
the water solution is 0.05$. then the water solution is four times
as toxic as is necessary to kill. Suppose that this water is with-
drawn and an equal amount added, which in turn takes up its propor-
tion of toxic oil. This change of water could take place seventy
times before the toxicity of the water would be below Killing
point. This is Bateman's theory.

Civil Engr-8. Assignment 5. Page 11.

In actual practice the rapidity of this change depends upon
the conditions under which the wood is used. If alternately wet and
dry, such as piling between high and low tides, a high rate of deple-
tion of preservative could be expected. A much slower rate of solu-
tion would take place in dry places, such as those of telephone
poles.

The difference between oil and inorganic salt preservatives
according to this theory is in the method of retaining the reserve
supply of toxic materials. Zinc chloride has no reserve supply,
all of the material is soluble in the usual amount of moisture
present in air-dry wood.

Bateman has proved his theory by experiments with tar acids.

Study this theory carefully and compare it "with statements
in Article 224 in the text.

Article 225 is relatively unimportant - omit it.

Civil Engr-8. Questions to Assignment 5. Page 12.

1. What are the principal causes for the deterioration of woods?

2. What causes wood to decay?

3. What is dry-rot? How can it be prevented?

4. Differentiate between the attach on wood piles of the limnoria

and the" teredo.

5. What methods are used to preserve wood?

6. Outline the full-cell process. What are its disadvantages?

7. Name the preservatives commonly used for impregnating wood as

protection against attack of living, organisms.

8. Explain why creosote is more effective than zinc chloride in

preserving wocd ?;hen it is subjected to alternate wetting
and drying.

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Civil Engr-8. Professor C-T- Wiskocil

Assignment 6.
The Mechanical Properties of Vfood

Introduction:- Read Article 226. The effective use of wood requires
a thorough knowledge of the factors which affect its mechanical
properties. Some of these factors have already been studied but in
•this assignment their relative importance will oe emphasized.

When comparing the general quality and the strength of "wood,
the term "strength" must be carefully defined. In the strict sense,
strength means the ability to resist a definite stress or load, as
compressive strength* Generally the term strength may have a number
of meanings, depending, upon how the wood is used. In the case of
beams, transverse or bending strength is implied, in columns com-
pressive strength is meant, whereas for implement handles both
hardness and toughness are included in the term strength*

Table I, in the text, gives comparative values of the mechani-
cal properties of woods. A more comprehensive compilation of test
results is given in "MECHANICAL PROPERTIES OF WOODS GROVnN IN THE
UNITED STATES" by Newlin and Wilson, Forest Service Bulletin 556,
United States Department of /Agriculture, from which the following
table is abstracted :

11 Ln-,r-8.

jrage

^ ;

. CO

3* i

c :

H-

i-/.

ft-

c~t-

<-*-

f+-

t-^

»7J

>— i

(— '

ff>

' 9:

H-

>• en

2! (B

s~* M-

-— v H<

•^1

*>d

P ^

*rJ CD

*T? f

H-

^— ,,

s—^

H* H*1

H- H- '

O '

, — ..

, — »

3 h-1

3 H-

hrt

*rJ

C Q

C O

--— «.

-•"»•

CD i

cr •-•

cf H-

0) 5

C" S;

c*~ "rj

C^ *^j

r»-

B 1

CD i-J i

CD 3

P CO

C' cn

_. 0

t-- 0 :

1 C

vj £

*r3 "T?

IV^ ^

X CT»

x ™

>-j

^ £

cy c

c*- cn

<-+• en

O H-

H- C

H-

B CO

P CO

I-"

3 3

Hh Qj

t-*> CL>

f-f-

v_ X-

£l> 1^ _J

SB *->

d. CD

CX CT)

0 0

3 ff>

rj JO

H-* C^"

t— ' C*"

S» 3

- g

>-<

t-" CO

H- *^

•v_ •• i

0 C

o c

l/ro

.- i

^ ' 0q

r ""*"

-.. T

— o s

O5
CO

£ '

(— '

T! 0

CD 3

-i.

•

r~o •-j (-*• i

rtl

•

kfc

CD CD

3 3

^_-

H- *C H-

t— •
ro

ro
0

ro t
0

ro
ro

3 ^5 3

!•*

»— • CD P co »*J

V— • (D

o
o

O
O

O
o

H- i— J r1- f- h1-
B P "! a

H- CO CD CD

a 3

•\ Q-

H-

c*- (•*• co *^

p. CO

co 3

h" C/.

CO
OJ

cn
ro

CO
CD

r*- » C
C C -0-

3 c+

CTt

C/:

o
o

CD '
O

H-

co O

cn
O

-3

0
0

o
o

CT>
C

O
0

0
0

•^^ 0^5 ^^

g T ~-

fi> 03 Q
* M-

fl> ^

tt
H--

0^ <D

c*co

<-*•

3^ co

' H-

H-

O> i

-J

^--OT L.

1—0

cn
O

en
C

»— ' CD *1
H- V— P C*

g P H- o

o 3

CT.

• cn 3

i-O

' *

I--

1— •

-g

OT ^ H-

H- C/2

*r>

cn
o

CD
C

~j
O

CD
CD
O

H- c+- en

3 r»-
CX' <D

H-

3 O 03

3" 3

ct OT
P c+

I—1

t— '

,_,

*-- O H-

H- CO

„

>•

CT >-t. D

3 rt-

ro
en
O

cx>
o

co
O

ro
C

h- '

^^^

en ,_,

H-
fl) ^

>•

t*^ &? j<^

3 3

O
O
0

o
8 !

O
O

c
c

z co O

c* Q-

a- CD

< CO

0)
3

*"t3" f *™^' o^"

S'*?

\->

*-•

H-"

•-"j H S •
& Q Q cn
H- ct o o o

fl1^ O
( 0

f-' C M H-,

c o f »-•

cr ^J

*75 CO f+ C7' CX>

(-•• CD

CD O * *^

t-« W

w O

H- CD

r-*73

^ H-

* |

Civil Engr-S. Assignment 6. page 5.

Table I is an excellent reference. If recent data are need-
ed Forest Service Bulletin 556 will be found to be more complete.
It is a good idea to take some common species of wood such as
Douglas Fir and remember the data, given in the abstracted table in
these notes, for the wood in the green condition. Most of the tests
from which such values are obtained were made at the Forest products
Laboratory at Madison, Wisconsin (see page 195 in text).

The test pieces v;ere all straight -grained and free from de-
fects, such as knots, shakes and checks, and in the same condition
of seasoning. The values given were based on about 130,000 tests
on 126 species of wood. Data are given for green and air dry con-
ditions because the properties of all species are not changed in
the same proportion bj. drying and all the properties are not equally
affected, .air-dry woods should have the same moisture content in
order to be strictly comparaole, but in the case of wood in the
green condition, even though quite different for the different
species, the moisture content is adov.a. the fiber saturation point
and above this point changes in moisture do not affect the strength.
Tests on individual pieces may be expected to vary from "t j to
"i 14^ from the values given in these tables.

Compressive Strength:- btudy Article 227. The compressive strength
parallel to the grain is important in estimating the strength of
columns and struts. It is determined by tests on 2 by 2 by 8 inch
specimens. A compressometer with a 6 inch gage length is used so
that the elastic limit and the modulus of elasticity can be determin-
ed. A typical curve is shovjn in Figure 6 on page 210. The maximum

Civil Engr-8. Assignment 6. Page 4.

strength is more easily determined than elastic limit strength and
is also less variable. Working stresses must be well below the
elastic limit. For columns in dry interior construction having a
length less than 10 times the least dimension, a working stress of
about 1/3 of the c empress ive strength of green wood is used.

Wood is also tested in compression perpendicular to the
grain. The specimen is 2 by 2 by 6 inches with the load applied
through a steel plate 2 inches wide. The area under load is, there-
fore, 4 sq inches. A def lectometer of the type shown in Figure 48
on page 89 is used to get a stress-deformation curve similar to the
one shown in Figure 6 on page 210. Only the stress at the elastic
limit is determined because this is the maximum stress that can be
applied without injury. Greater loads crush the specimen without a
definite point of failure. Furthermore, the deformation measure-
ments are easily obtained so that the elastic-limit determination is
a simple one. Strength perpendicular to the grain is developed in
bearing areas of beams, railroad ties, and in any construction where
the load is similarly applied. A working stress of approximately
2/3 the elastic limit of green wood may be safely used in dry in-
terior construction. Omit Tables 2 and 3; They are useful only
when specific information is needed.

Tensile strength of wood:- Read Article 228. The tensile strength
of wood parallel to the grain is rarely determined. The Forest
Service tests the tensile strength perpendicular to the grain. The
form of specimen and the manner of loading are shown in Figure 1
on page 201. The data from this test are of value in establishing

Civil Engr-8- Assignment 6. Page 5.

the resistance of wood to the splitting action of bolts and other
fastenings.

The shearing strength of wood:- Read Article 220. Shearing stress
parallel to the grain is developed in most structural uses of wood.
It is of importance in beams (see Figure 2 on page 202), where it
is called horizontal or longitudinal shear. It is also of importance
in the design of wooden joints (see Figure 3 on page 203). Shearing
stress across the grain is rarely listed. The specimen and the
method of making the shearing test parallel to the grain are shown in
Figure 14 on page 63. Longitudinal shear is greatest at the neutral
surface of the beam and is affected by checks and shakes which re-
duce the effective area resisting shearing stresses. These defec^s
must be expected in structural timber; therefore safe working
stresses for longitudinal shear in beams are about 1/8 of the values
obtained from tests on clear, straight grained pieces. For joints
and small details where checks and shakes can be avoided the work-
ing stress may be increased to 1/4 the strength of green wood. Omit
Tables 4 and 5.

Transverse strength of wood .-- Study Article 230. This property
of wood is determined by the static bending test. The specimen is
2 by 2 by 30 inches, tested on a 23-inch span. The load is applied
at the center. A def lectometer is used so that a load-deflection
curve similar to that in Figure 6 on page 210 can be drawn. Large
timbers are loaded at the third-points as shown in Figure 2 on page
202. The static bending test is easily made and yields important
data. Working stresses in bending must be below the elastic limit

Civil Engr-8. - ssignment 5.

for if wood is stressed to its elastic limit in static bending it
will ultimately fail. Determinations of elastic limit are not so
reliable as those of the maximum fiber stress, ^'hich is known as
the modulus of rupture. Working, stresses should, therefore, be based
on the latter. Remember that the modulus of rupture is not the
actual fiber stress, because it is based upon a theory which is
valid only when the elastic limit is not exceeded.

A green timber relatively free from defects will have a modu-
lus of rupture of about 3/4 as large as small deter pieces cut from
it.

Safe working stresses for structural timber in interior con-
struction should be about 1/5 the modulus of rupture for green wood.
For exposed construction the working stresses should be lower.
Strength in longitudinal shear must also be considered when design-
ing wooden beams. Omit Taole 6.

The time element in loading wood:- Read Article 231. The strength
of wood is affected by the rate at which the test load is applied.
The speed of testing should, therefore, be considered (See the
Forest Service program as given in this article). The most import-
ant fact in this article is that the resistance of wood under per-
manent loads is less than 7; hen it is under temporary loads. It
takes about 50^ of the ultimate load as applied in a testing machine
to cause failure if permanently applied. This is another reason
why working stresses are so low when compared with ultimate strength
as determined by tests made in a testing machine.

Civil Engr-8. Assignment 6. Page 7.

Stiffness and other mechanical properties:- Study Articles 232, 253,

234 and 235. Stiffness, which is measured Dy the modulus of elas-

ticity, has an average value of aoout 1,200,000 Ib. per sq. in. In
the case of a beam the modulus of elasticity is a measure of its
resistance to deflection. The importance of this property is in-
dicated in Article 232. Green wood is not so stiff as air seasoned
wood. Stiffness is usually determined in the static bending test.

Toughness is sometimes defined as the ability of wood to
withstand impact loads. Impact loads are sustained by spokes of
an automobile wheel, ax or implement handles and athletic goods
such as baseball bats. A measure of toughness is ootained by the
impact bending test and the energy of rupture in the static bending
test. Impact bending is made on a 2 by 2 by 30 inch specimen
tested on a 28 inch span. The machine used is shown in Figure 19
on page 66. A 50 Ib. hammer is usually used. The height of drop
to produce failure indicates the toughness of the wood as stated
in Article 233. Wood in the green condition is tougher than after
it is seasoned. A suddenly applied load has tvrice the effective
force as -when gradually applied. The fiber stress at the elastic
limit in impact is approximately douole the fiber stress at the
elastic limit in static bending. Stated in another way: a small
beam, if the load is suddenly applied, will deflect twice as much
as under the same load gradually applied - provided the loads are
under the elastic limit.

The height of drop is an aroitrary value but it gives an
excellent comparison of the toughness of the different woods tested.

Civil Engr-8. Assignment 6. page 8.

While cleavability is an important property in some uses of
wood, it is not usually tested. A special test for it is described
in Article 234.

The hardness of wood is frequently determined. The method is
to measure the load required to embed a 0.444 inch ball to 1/2 its
diameter in the wood. The test is applied to end, tangential, and
radial surfaces. Radial and tangential hardness are quite similar
and are called sice hardness as distinguished from end hardness,
•which is usually much greater. Hardness is an important quality in
wood used for paving blocks, floors, railroad ties, and furniture.
Read Article 235 in the text.

•

Conditions affecting Lechanical Properties of timber:- Read care-
fully Articles 236 to 245 inclusive. Differences in the strength
of wood are usually due to differences in defects, moisture content,
or density. Defects, while discussed at this time, would be more
properly taken up under the subject of grading. The most important
conditions, then, which affect the mechanical properties of wood are
moisture and density.

Density or specific gravity was defined under the subject of
physical properties of wood. Apparent specific gravity (the ratio
of the weight of a given volume of wood to the weight of an equal
volume of water) is an indefinite quantity unless the circumstances
under which it is determined are specif ied, because the weight in a
given volume changes with the shrinkage and swelling caused by
changes in the moisture content. Specific gravity is based on the

Civil Bngr-8. .assignment 6. page fc,

volume of wood when green, and when air-dry or ov'eft-dry. Specific

gravity based on green volume is not affected by the shrinkage of

wood and is therefore more reliable than air or oven dry specific

gravity.

Note: Correction is made for the amount of moisture in the wood.

Specific gravity, aside from actual strength test data, is
the most reliable criterion on the strength of clear wood. The
Forest Products Laboratory examined seven species of woods, both
conifers and dicotyledons and found only a 4 1/2 % variation in the
specific gravity of the wood substance. The specific gravity of a
piece of wood is, therefore, a measure of the amount of wood sub-
stance it contains. The greater the density the more wood it con-
tains and therefore the greater its strength. This relation is
shown in Figure 3 on page 213.

Since the weight per cubic foot depends upon the moisture in
a green wood, it is quite variable. The conditions under which it
is obtained should, therefore, be specified.

The effect of rate of growth, measured by the number of rings
per in^jis shown in figure 10 on page 215. Rate of growth is ex-
tremely variable. The curves show no definite relation between rate
of growth and strength. Wood which has tfrown slowly is usually
below average strength. In coniferous wood of very rapid growth the
strength is also likely to be below average. In the dicotyledons,
however, the wood of rapid growth is usually above average strength.

The amount of summerwood in any species is indicative of

Civil Engr-8. Assignment 6. Page 10.

the density. The amount of summerwood is measured along a repre-
sentative radial line and expressed in percentage of the entire
area. When the difference in color between spring and summer
(early and late) wood is not clear and distinct, accurate measure-
ments cannot be made and the results are of no practical value.

of
The relation of the percentage/ summerwood to certain mechanical

properties are given in Figure 12 on page 216.

Differences in strength of wood as caused by differences in
location, of growth, and of differences in position in the tree
have usually been overestimated.

The influence of defects such as knots, checks, and shakes
is described in Article 240. Stucly this article carefully.
Heartwood and Sapwood:- The difference between the strength of

heartwood and sapwood is not discussed in the text. The following

recent
statement is taken from a/ report by the Forest Products Laboratory:

"in over 300,000 tests which have been made at the Forest products
Laboratory, Madison, Wisconsin, on the various species of wood
grown in the United States, no effect upon the mechanical properties
of wood due to its change from sapwood into heartv:ood has ever oeen
noticed. Any difference in the strength of heartwood and sapwood
can usually be explained by the growth and density of the wood".
Comparative value of wood cut from live and dead trees:- This sub-
ject is not discussed in the text but some specifications preclude
the use of lumber cut from dead trees. This subject has been
studied at the Forest Products Laboratory and they report that there

Civil Engr-6. assignment 5- page 11.

is no known method by which lumber cut from dead' trees can "be
distinguished from that cut from live trees- Furthermore all avail-
air 13 information indicates that wood cut from insect or fire killed
trees is just as good for any structural purpose as that cut from
live trees of similar quality, providing the wood has not been sub-
sequently injured by decay or further insect attack. Heartwood in
a living tree is entirely dead and in the sapwood only a few cells
are alive. Most of the wood cut from trees is. dead, regardless of
whether the tree itself is lining or not. Specifications, instead
of providing that wood must we cut from live trees, should state
that mate-rial showing evidence of decay or insect attack exceeding
a definite limit will not be accepted.

Articles £42 to 245 are relatively unimportant - just read
them over- In the case of preservatives, Article 243, it would be
more exact to say that the effect of preservative treatment on the
strength of wood is independant of the type of preservative because
it is the method or process and not the kind of preservative used
that affects the strength of wood. Creosote, which is the most
common preservative, does not appear to effect the strength of wood,
A preservative process that weakens one species of wood may -not
affect the strength of another species. The results are also
affected by the form and size of timber treated as well as its con-
dition.

Article 241 - The Effect of Moisture on the Mechanical
Properties. The relation between moisture content and strength is

Civil Engr-8. Assignment 6. Page 12.

clearly shown in Figure 15 on page 220. ibis is. for small, clear
pieces. For large timbers, the increase in strength produced by

a decrease in moisture is often entirely offset by checks and

Similar defects which develop during the seasoning process. Under
most conditions it is advisaole not to expect additional strength
due to seasoning. Seasoning of beams increases the liability to
failure by horizontal shear. The curves shorcn are typical. The
importance of the fiber- saturation point is evident from this
illustration. It occurs at about 25$ moisture. Table I opposite
page 196 was obtained from small green sticks which were clear,
straight grained, and free from defects. In general, air dry
wood is about 50$ stronger and kiln dry wood is about 100$ strong-
er than wood in the green condition. Re soaked -wood is not so
strong as green wood.

The modulus of rupture in static bending and the compressive
strength parallel to the grain are changed about 4$ by a change of
1$ in moisture content (when it ie aoout 12$). For example, com-
pare the modulus of rupture of Douglas Fir and Western Yellow Pine
as given in the table in these notes. Douglas Fir at 9.4$ moisture
has a modulus of rupture of 10,300 Ib. per sq. in. The Western
Yellow Pine has a moisture content of 10.8$ with a modulus of rup-
ture of 9,300 Ib. per sq. in. To change the latter to 9.4$
moisture will increase the strength

(10.3 - 9.4) x 4 - 5.6$

.056 x 9,800 = 550 Ib. per sq. in.

550 + 9,800 = 10,350 Ib. per sq. in.

Civil Engr-8. Assignment 6. page 13.

The modulus of rupture of Western Yellow pine at- 9.4$ moisture is*
therefore, about 10,350 Ib. persq. in. For large differences in
moisture content this 4$ difference iB strenth v;ill not be accurate.
Strength of Nails in Wood :~ Read Articles 246 to 248 inclusive.
The holding force of nails, expressed in terms of adhesive strength,
in Ib. per sq. in. of imbedded surface varies with the density of
the wood and the form of the ".nail.

The most recent tests, reported in Bulletin No. 1, "Tests
on the Holding Power of Railroad Spikes11, Dy Beyer and Krefeld,
Department of Civil Engineering, Columbia University, show that the
driving of spikes into holes, bored into the tie to receive them,
reduces the crushing and bunching of the wood fibers. The pre-
bored hole increases the resistance to withdrawal of the spike.
In soft woods the elastic limit of the fastening is reached at very
small withdrawals - Q.004 to 0.006 inches - and in oak the elastic
limit is somewhat higher. A rail fastening, to approach permanance,
must &t no time be stressed beyond its elastic limit holding power.

The shearing strength of nails, in nailed joints, varies with
the density of the wood and the size and depth of penetration of
the nail.

Working Stresses :- Study Article 249. Safe working stress for a
material is the unit stress which, under conditions of use, will
not cause structural damage, \ior£ing stresses must be considerably
below the ultimate strength of the material for several reasons,
(a) Where stressed to the point of failure materials undergo

Cvil Engr-8. Assignment 6. Page 14.

mrked distortion and have less stiffness. These changes would
cuse unsatisfactory service in the case of a machine or structure.
( ) The exact loading to which a structure will be suojected can-
rt be determined. Actual conditions may vary considerably from
csign assumptions, (c) Structures are liable to overload and some

,^in of safety nust be provided for such contingencies, (d) The
:act strength of the materials used is never available, furthermore
•he strength may be affected Dy deterioration or accidental damage.

Where human life is endangered by failure of a structure,
Drking stresses should be low. Under other conditions "where the
esults of temporary collapse are not important, the use of higher
tresses are justified.

Working stresses are frequently determined by dividing the
Itimate strength of the material, as determined by actual test,
y a factor of safety. This factor varies from 2.5 to as much as
0 for different materials and different conditions of use. If a
structure is designed with a factor of safety of 4, it does not
aean that it will fail at four times the working or design load,
forking stresses should be based on and be well below the elastic
limit of the material.

All large timbers, since they have season checks, knots and
other defects should not be considered to be stronger than green
timber. "Working stresses should be based on tests of green wood.
In the design of wooden structures it should be remembered
that the actual dimensions of commercial lumber are usually less

Civil Engr-8.

Assignment 6,

Page 15.

than the nominal dimensions. Sawed lumber is not considered as
"short" in dimensions unless an actual dimension is 1/4 inch or more
less than nominal. For dressed lumber (as lumDer which has been
planed is known) ,an allowance of 1/4 inch for each dressed face is
made. A 12 by 12 inch stick, if dressed on four sides, would,
therefore, actually measure about 11 1/2 by 11 1/2 inches.

Working stresses for structural timbers which pass the grad-
ing rules proposed by the Forest Products Laboratory are affected by
the moisture content. The following table was taken from recent
Forest Service publications:
Working Stresses permissible for Structural Timbers, Ib. per sq. in.

Species

Bending

Compression

Stress in extreme
fiber

Horizon*
al Shear

// to t

'...
1
Wet . Out**

loca-* side

tion! l°ca
i tion

rrain

In-
side
- loca-
tion

J. t<

Wet
loca*

tion

3 grain

Out-J In-
side jside

loca-j loca-
tion it ion

Wet

loca-
tion

Outside :. Inside
loca- loca-
tion tion

1 _ 4

loca-
tions

Douglas Fir
(No. 1 Struck
tural)

1100

1400

L - «,

1600

1
100

i
i

900 1100

1200

225

250 350

i
i __.

Douglas Fir
(No. 2 Struc-
tural)

900
900

1100

1300 90

-
800 900

1000

200 225 300

Western Hem-
lock

1100

1300

i
i

800 900

750 I 900

900
1000

200
125

225 300

Redwood

,
800

1000

1200 ! 70

! l

'
160 ;250

Wet or damp location - docks, piling, and sills

Outside location -not in contact with soil, bridges, and

open sheds
Inside location - under shelter in a dry location,

factories and wa-rehouses.

Civil Engr-8 Assignment 6. page 16.

Gracing rules:- Read Article 250. Structural timbers are
graded or classified, by inspection, into groups or grades so that
each stick in a jiven group T.;;ill have the same value for a certain
purpose. Grading rules are generally prepared by timber producers
such as saw mill associations and lumber manufacturers' associations
while timber specifications, which are written for the purpose of
having timber that fulfills the requirements suitable for a definite
purpose, are prepared bj the timoer user.

iiany grading rules are based on the number and the character
of defects; they have been satisfactory in classifying saw mill
products for wood v or king industries out they have not been effective
in classifying timber in accordance v;ith strength. The Forest Ser-
vice, the American Society for Testing Materials, and the Southern
Pine Association have adopted rules which provide for the quality
of the wood as v;ell as limit the position, size, and condition of
defects.

Since the quality of wood is indicated by the character of the
annual rings as seen on the cross section, and the location and
size of defects, it is possible to use these factors in grading wood
as to strength. Durability is judged largely from the proportion
of sapvrood which is less resistant to decay than heartwood. Dura-
bility is also affected by the degree of seasoning as indicated by
the moisture content.

Study Figure 21 on page 232 and the text paragraph describ-
ing it .

Civil En^r-8. ^signment 6. page 17,

Laminated Wood ;- Wood, as has been thoroughly explained, is a
non-homogeneous material. It has widely different properties in
the various directions relative to the grain. Were wood homogeneous,
with the sane strength properties in all directions that it has
parallel to the grain, it would be unexcelled for all structural
uses where, strength with small weight is desired. Laminated wood
approaches this desired condition in that it produces equality of
tensile strength in two directions - parallel and perpendicular to
the board. Ply.vood is the name usually given to this type of con-
struction.

plywood Is made by gluing together plies of wood, usually an
odd number, so laid that the grain of alternate layers is approxi-
mately at right angles. Three-ply and five -ply construction is
most common. The -niddle layer or core with equal layers on both
sides gives a construction that is symmetrical causing an equaliza-
tion of shrinkage stresses so that the wood should not warp. Warp-
ing does occur, howev<?f. , The causes are first, the use of plain-
sawed and quarter-sawed lumber in the sa^e construction and second,
the combination of materials of different moisture content. Both
of these factors can be easily avoided, feoist are -resistant coatings
are resorted to in order to maintain uniform moisture conditions
in the ~;ood. Plywood is used in the manufacture of automobiles,
in street and railway cars, and in airplanes, where light construc-
tion is required.

Veneer is another type of laminated wood construction. Thin

Civil Engr-8. Assignment 6. Page 18.

sheets of hard wood known as veneer are glued to cheap lumber to
give it a hard wood surface. Veneer is cut by three different
methods. The oldest method is sawing, but the saw kerf ^vhich can-
not be made much less than 1/20 of an inch wastes considerable wood.
The second method is known as slicing. Veneer made by this method
is essentially a thick shaving cut by a large plane. The third
method is called the rotary-cut. A thin continuous sheet of veneer
is cut off the surface of a log which is rotated in a huge lathe.

Sawed and sliced veneer are relatively expensive and are
used primarily for ornamental and finish purposes, host, of the
veneer produced at the present time is rotary cut. Veneer is used
in the manufacture of plywood.

Average sawed veneer sheets are from 12 to 16 feet long,
usually not less than 1/28 of an inch thick and their v;idth is
limited by the diameter of the log.

Sliced veneer is about 10 feet long and seldom less than
1/16 cf an inch thick (but some species are cut 1/100 inch or less
in thickness) and the diameter of the log in width.

Rotary -cut veneer is about six feet long, on an average,
with a maximum length of 16 feet, some species may be cut from
1/100 inch to almost 1/2 inch in thickness and to any width in
which the material can be handled.

Mill-Building Construction :- One of the uses of heavy timber is
in the construction of large buildings. The marked success of early
heavy timber structures of the ;:iill-construction type, which

Civil Engr-8. Assignment 6. Jfage IS.

originated in the New England States } led to the popular use of
this form of construction. The term mill-construction as commonly
used is the name given to that type of building construction in
which the interior framing and floors are of timber, arranged in
heavy solid masses with smooth flat surfaces, so as to expose the
least number of corners, and to avoid concealed spaces which may
not be reached readily in case of fire. AS usually designed the
walls are of brick or concrete, the floors are of heavy plank laid
flat upon large girders which are spaced from 8 to 11 .feet on
centers. These girders are supported by wood posts or columns
spaced from 16 to 25 feet apart.

Civil Lngr-6. Questions co Assignment, 6. r^ge 2C.

1. Would a higher unit stress be ailowaole in a £iece of spruce
for a strut in an airplane frame or a strut in a large timber
bridge? ~Vftiy?

2. What are the most important tests of wood?

3. What is the importance of stiffness in wood? Hov: is it measured?

4. What is the effect of permanent dead load on the resistance
of wood?

5. Explain why the use of plain-sawed and quarter-sawed ^ood in
the construction of a piece of plywood will cause warping under
changes in moisture content.

6. Differentiate oetv-een grading rules and timber specifications.

7. What precautions are taken in the selection of test specimens?

8. Discuss the effect of moisture on the mechanical properties
of *A'

9. Give the approximate ultimate strengths of Douglas Fir, in
the air-dry condition, as determined by the usual tests mads
by the Forest Products Laboratory.

10. State the allov;aole working stresses for Douglas Fir when used
in dry locations.

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION
Correspondence Courses .

Materials of Engineering Construction

Civil Engr.-8 Assignment 7 Prof. C. T. Wiskocil

BUILDING STOlfflS

Uses and Production: Read Article 251. As stated in this
article stone has been used asa building material since the earliest
known times- It was used principally in the construction of walls,
foundations, arches, and dams. Many old stone monuments are still
in a fair state of preservation. Stone and wood are the only im-
portant. s^ructural materials used in their natural state. The use
of stone for structural purposes is decreasing because of the de-
velopment of reinforced concrete for these purposes. Half a cen-
tury ago building stone composed nearly the entire output of the
quarries* Some of it was made into lime but the use of concrete
for foundations, bridges, culverts, curbing, and other structures
has reduced the demand for building stone and lime. Important
buildings in which appearance is a large factor, are still usually
built of stone. About 70 million tons of stone are quarried an-
nually in the United States. The approximate value of this output
is 90 million dollars. These figures were taken from the United
States Geological Survey reports from which the following table,
showing the percentage of the entire output used for different
purposes, vas compiled:

Engr.-8. Materials of Engineering Construction. Assignment 7, page 2.

Structural purposes

Building stone II. Oft

Paving blocks 3.0

Curbing 1.0

Flagging 0.5

Rubble 1.0

Riprap 2.0

Crushed stone 38.0

Monumental stone 15 «5

Furnace flu* 20.0
Other uses 8.0

The last item includes stone used for such purposes as fur-
nace linings, for which refractory stone - dolomite, quart zite,
and mica, schist - is required, and pulverized stone, used by sugar
factories, paper mills, glass works, alkali and other industrial
•works.

Crushed stone is used for railroad ballast, roads, and con-
crete aggregate.

In Article 251, the part of the first paragraph v/hich deals strength

of building stone, is important. It will be noted that
rath the conditions which govern the select ion/^is not included in

these conditions. The corapressive strength of stone is nearly suf-
ficient to support safely, the weight of the superimposed masonry
and other loads that come upon it. If a stone had a compressive
strength of 6,000 Ibs. per sq. in. and it weighed 170 Ibs. per
cubic foot, it would have to be built into a tower about 5,000 ft.
high (6000^ 144) before the iciest block would be brought to the
point of failure. The Washington Monument in Washington, D.C. is
only 550 ft high and the Woolworth Building in New York City, with
its 51 stories, is only 792 ft. high. These, to be sure, are not
ordinary structures; but it should be remembered that there are

Engr«.-8. Materials of Engineering Construction. Assign. 7, page 5.

few stones that have an ultimate compressive strength less than
6,000 Ibs. per cq. in- Granites average 20,000 Ibs. per sq« in.,
while recently a :Tephelite Basalt quarried near Austin, Texas was
found to have an ultimate oompressive strength of 53,900 Ibs- per
s^» in. This is an extreme case*

Dead load, ho\vever, is not the only factor that must be con-
sidered in the design of masonry structures* TJlnd and other live
loads r;.ay cause a large increase in the loading on certain parts
of the foundation • The load in a masonry vra.ll is probably never
uniformly distributed over the individual members of the different
courses because of uneven bedding, and the stresses due to loads
may be augmented by expansion and contraction of the stone, ex-
pansion of water in the pores while freezing, and vibration in
structures such as bridge piers- Furthermore, the strength of
masonry is influenced by the kind of mortar used. The highest
class of masonry, known as a shlar , laid in Portland cement mortar,
is not loaded in excess of 500 Ibs. per sq. in. This is well with-
in the compressive strength of stone used in building construction
and the foregoing statements show the reason why strength is not
considered in the selection of stone for this purpose.

Transportation charges effect the cost of stone because of its
weight* A block of granite 2 by 2 by 3 ft. weighs a ton-
Fashion also is frequently an important consideration in the
employment of stone in building. Considerable demand for Califor-
nia travertine was created in the San Francisco Bay region by the

Iingr-8. Materials of Engineering Construction. Assign. 7, page 4.

use of artificial travertine in the construction of buildings at
the Panama-Pacif ic International Exposition at San Francisco. The use
of a particular decorative stone in the construction of homes for
prominent people will influence others in the selection of a similar
building stone.

Appearance and cost aside from durability are the considera-
tions given t/eight by the architect. There is considerable dif-
ference in the appearance of the dark colored, somber igneous rocks
such as diorite and gabbro, and the light, pleasing colors of most
limestones and granites.

Durability is the most important consideration and in the case
of an untried stone its determination is quite uncertain. The
durability of stones in use, however, can be raadily judged by
careful inspection. Stone to be used in steps, floors and other
pavements, since it is to be subjected to abrasion, should be one
that shows greatest endurance under such conditions. Frequently
stone is required to withstand the abrading action of water-borne
sand, as in bridge piers, and air-blown sand, as in structures in
certain arid regions, and must be tested for endurance under those
special conditions-

The ivlineral Constituents of Rocks: Read Article 252; it is
of interest in connection with the subject of stone but it is not
of such importance that the details should be remembered.

Classes of Rocks; Study Article 253. Be able to classify
rocks according to geographical origin. Other classifications are

Engr-8. Materials of Engineering Construction. Assign. 7, page 5.

used] on the basis of texture and structure, miner alogical composi-
tion, chemical composition, and geological age*

Important Building Stone a: Study Article 254 to 260 inclusive.
Suitable stones for structural purposes are widely distributed; the
principal classes include granite, limestone, sandstone, marble,
and slats. The follovring table gives the approximate production
of the different classes of stone during 1919. It was prepared
from the U.S.G.S. report, "STONE IN 1919" by Loughlin and Coons.

PRODUCTION IN THOUSANDS OF TONS
Grai

Building stone

Monumental stone

Paving stone

Curbing

Rubble

Riprap

Crushed stone

Other uses

TOTALS,

It is interesting to note that the proportion of cut stone used for
structural purposes is only a snail (about 11$) part of the total
production. The principal use for limestone is as a flux in the
manufacture of pig iron. See Article 580 page 537 in the text.

Granite ; \Vhile granite is one of the principal building stones
its greatest single use is for crushed stone* Vermont leads in the

Granite

Basalt (Trap)

Lime stone

Sandstone

Marble

304

394

150

305

— _

...

364

«••»

— •»•

328

IH»

379

231

833

214

—

2,700

7,053

21,760

1,180

—

26,400

790

153

4,220

7,409

49,722

2,538

333

Engr-8. Materials of Engineering Construction. Assign. 7, page 6.

production with Massachusetts, Maine, and New Hampshire closely
following* Minnesota and Wisconsin rank with the New England
States in the production of granite while California leads the
We stern States.

Granite is quarried in about ten counties in California. The
principal quarry, which is controlled by the Raymond Granite Com-
pany is at Krowles, Madera County. About a quarter of a million
cubic feet of stone have already been removed from this quarry.

The stons is a very fine-grained light granite. Many important

in California
structure s^have been built vrith Raymond granite. Among them are:

the Municipal Auditorium, the Post Office, the Sub-Treasury Build-
ing, the Bank of California, and the Fairmont Hotel in San Francisco;
California Hall, the Doe Library, Wheeler Hall, Hearst Mining
Building, Boalt Hail, Sather Gate, and the Sather Tower of the Uni-
versity of California at Berkeley; the Time Building, and Citizens
National Bank Building in Los Angeles.

Granite is an ideal building stone. It is durable yet not
too hard. It is interesting to note that in the recent addition
to the Anglo and London Paris National Bank in San Francisco, solid
granite columns were used. They were 4^ ft. in diameter and 22ft.
long and weighed about 20 tons. It took about three months to
shape each column.

Lime stone ; TiTnile limestone is one of the principal building
stones most of the production is used for other purposes. As al-
ready mentioned it is used for a flux in the production of pig

Engr-8. Materials of Engineering Construction. Assign. 7, page 7.

iron and for various industrial uses- It is also used in the manu-
facture of portland cement (Article 339, page 310), and in the
manufacture of lime (Article 379). More limestone is pulverized
and used to improve soil than is used for structural purposes-
Limestone is also used as a filler for asphalt, paint, rubber,
soap, and other materials. It i s quarried in about 20 counties
in California. At present the principal use for this product is
for macadam roads and concrete aggregate. Indiana leads in the
production of limestone for building purposes. The best known
and most 7/idely used American limestone is the Bedford limestone
which is quarried at Bedford, Indiana, and Bowling Green, Kentucky.

Marble ; is a crystalline limestone. It is quarried in about
six counties in California.

Travertine is a compact fine-grained limestone deposited on
the surface by the water of springs or streams holding lime in
solution. The Roman palaces of the period of Augustus were made
of travertine quarried at Tivoli near Rome. A quarry at Fairfield,
California, supplies an excellent grade of travertine. The bench
.at the foot of the Sather Tower on the campus of the University of
California at Berkeley is made of travertine from the Fairfield
quarry .

Sandstone : Sandstone is composed of sand grains cemented
together to form a solid rock. The strength and durability de-
pends upon the cementing material. Sandstone is quarried in about
seven counties in California. A large number of the buildings at
Stanford University are built of sandstone. The St. Francis Hotel

Bngr-8. Materials of Engineering Construction. Assign. 7, page 8.

and the Flood Building in San Francisco are made of Colusa sand-
stone. A large part of the sandstone quarried is known as quartz ite
(g.anister) and is used for making silica brick, for furnace lining
(see Article 592 on page 548 of the text).

Trap: Trap is a designation (not used by the geologist) which
includes fine-grained basic rocks such as basalt, diabase, and gab-
bro. These rocks usually occur in columnar structure and present
a stepped appearance. The Swedish word "trappe" means stairs;
therefore, trap has reference to the occurence of the rock in the
quarry. Trap is tough and strong (stronger than granite) but it
does not weather well. It is hard to quarry and is used princi-
pally for paving blocks and crushed stone.

Slate ; The most valuable characteristic of slate is its ten-
dency to split into thin sheets, leaving smooth plane surfaces-
Slate does not absorb water, posses considerable toughness and
strength, and is moreover a good insulator for electric current*
Its structural use is confined to roofing.

Durability of stone : Read Articles 261 to 266 inclusive.
Frost is probably the most destructive agent for stone when it is
exposed to the weather. Many varieties of stone show signs of dis-
intergration after a few years of such exposure. The estimated
life of stone under exposure varies frcm!2 years for soft sandstone
to several centuries for hard granites. Study Article 261 in the
text on the weathering of stone. Atmospheric conditions affect the
durability of stone. The Egyptian Obelisk commonly known as

Engr-8. Materials of Engineering Construction. Assign. 7, page 9.

Cleopatra's Needle, was built about 1500 B.C. ' For over 3000 years
it stood unharmed in the mild Egyptian atmosphere. "When it was
brought to New York in 1879, immediate steps had to be taken to
save it from the ravages of our American climate by giving it a
surface coating. See the third paragraph of Article 262 in the
text. Limestone and sandstone are not in general very durable and
many exanples of their rapid disintegration might be cited. There
are, however, very durable varieties of both these stones*

Preservative coatings are effective in preventing the absorp-
tion cf *.-ater :.nd protecting the surface of the stone but they do
not last long and r,ust be frequently renewed.

Durability tests for stone : The most reliable test is the
examination of exposed quarry ledges or cut stone that has been ex-
posed to the weather. The action of destructive agents may be
closely imitated in the laboratory but data on the actual dura-
bility are not thus obtained and the interpretation of laboratory
results is therefore, quite difficult. The f reeling and thawing
test, and the acid test are the principal laboratory tests for
durability. The absorption test is of value in determining the
probable effect of weathering. The more water a stone absorbs,
other things being equal, the more softening and harm will be done
by atmospheric acids.

The heat occasioned by fires in large buildings often exceeds
150C decrees Fahrenheit . ilo stofre will withstand this* Limestone
is decomposed at about 1200 degrees Fahrenheit and granite spalls

Engr-8. Materials of Engineering Construction. Assign. 7, page 10.

and cracks at these high temperatures. Quenching intensifies the
effects of fire. Clay products, brick and terra cotta, are superior
to stone in their resistance to the effects of fire.

The Physical properties of_ stone : Read Articles 267 to 270
inclusive- The coefficient of thermal expansion is not constant
as in the case of metals. It increases with an increase in tem-
perature. An average value is .000004 inches per inch per degree
Fahrenheit. Stone once heated does not return to its original di-
mensions when cooled. This permanent expansion is mentioned in
Article 267; it is important. Stone slabs, particularly those of
marble, frequently warp when exposed to the weather. Since marble
is formed by a process of slow deposition, and it is estimated that
the formation of one inch took about a thousand years, it is reason-
able to suppose that the stone is not uniform in structure perpen-
dicular to its bedding plane. Different layers may have different
thermal properties which would cause variable permanent sets under
heating and cooling, sufficient at least to produce warping. The
surface of a stone monument exposed to the direct rays of the sun
may easily exceed 120 degrees Fahrenheit. Marble slabs and shafts
in cemetaries are frequently warped. Recent tests show that con-
crete road slabs warp, but not permanently, due to differences in
temperature of the upper and lower surfaces. During the day the
slab is concave downward and at night when the air is cooler than
the ground it is concave upward so the the edges are actually lifted
off the subgrade.

Bngr-3. Materials of Engineering Construction. Assign. 7, page 11.

To remember the approximate specific weight of stone, take
the weight of granite, about 170 Ibs. per cu. ft. Trap rocks weigh
more and the other building stones weigh a little less.

Mechanical properties of stone : Study Articles 271 to 273 in-
clusive. The strength of stone is rarely developed except in lin-
tels and top- slabs for culverts where the stone is used as a beam.
The compression test is frequently the only test made but the
transverse test, which gives the modulus of rupture and the modulus
of elasticity, is also made. In your study of a new material make
a table with average values to compare it with some material you
have already examined*

Average Ultimate Strength, lb. per sq. in.

Compression Modulus of Modulus of

Rupture,

Elasticity

Granite

20,000

1,500

8,000,000

Limestone

9,000

1,200

8,000,000

Douglas Fir
(air dry)

Parallel Perpendicular

10,000

1,500,000

to the grain.

7,000 900

The above values are from tests on small test specimens. Re-
member that although average sandstone is stronger than average
limestone, a good limestone is stronger than a poor sandstone.
Tests of stone are always made on overn dry specimens. Soaking
decreases the strength of stone, a fact which has been noticed in
tests of marble*

Engr-o. Materials of Engineering Construction. Assign. 7, page 12.

Stone, like other brittle materials such as cast iron and con-
crete, does not obey Booke's lav:. The stress-deformation curves,
instead of being straight, to the proportional limit, are concave
upward - see Figures 2, 3, <.-, and 5 on pages 256 and 257 in the
text.

Stone is used in the construction of various types of roads,
from the block or cobblestone pavements, to the bituminous macadam,
cement concrete, and the water bound macadam pavements. The
characteristics of the stone used depend upon the type of pavement
and the character of the traffic. In the case of stone for road
pavements as well as in the case of building stone, the crushing
strength is of secondary importance, while toughness, hardness and
resistance to wear are of the most importance. Tests to determine
each of these properties have been standardized by the United Stated
Bureau of Public Roads and the American Society for Testing
Materials. They also publish requirements to guide in the selection
of available material.

The specifications for crushed stone for concrete aggregate
are rather general. They usually state that any durable crushed
fiftone or any clean, hard gravel not subject to ready disintegration
may be used.

Stone quarrying : Blocks of stone are removed from the quarry-
ledge by blasting or hand tools. Early Egyptians cut grooves in
the rockledge with crude bronze piclcs. Dry wooden vedges were

Engr-3. Materials of Engineering Construction. Assign. 7, page 13.

pounded into the grooves and soaked with water. The expansive
force produced by the swelling of the wood forced out the block of
stone. Hand methods at the present time require the use of a
steel drill to make a series of holes in the rock into which steel
wedges are driven to force the rock apart. Power operated drills
and channelers with the use of explosives are replacing hand meth-
ods* Power-driven saws, planers and lathes are used to shape the
blocks of rough stone.

Stone ma sonry : There are three classes of stone masonry -
riprap, rubble and cut- stone. Riprap is uncut stones piled up to
form masonry. It is used for low walls and to protect stream banks
from erosion. Rubble is riprap with stones held together with
mortar* Cut or squared stones laid-up with mortar produce the
highest class of masonry. The term ashlar is applied to masonry
of the last class, when the joints are not more than -j=f inch thick.
This requirement can be met only by having plane surfaces on in-
dividual stones. This construction insures uniform distribution
of loads, so that the highest loads are allowed on ashlar masonry.

The strength of stone masonry depends largely on the strength
of the mortar used and the thickness of the joints between adjacent
stone s.

Riprap is not meant to carry loads. Rubble in lime mortar
with individual stones placed at random, is designed for 60 Ibs.
per sq. in«, while the allowable load on ashlar masonry made of
granite in port land cement mortar is 600 Ibs- per sq. in.

Engr-6. Materials of Engineering Construction. Assign. 7, page 14.

QUESTIONS:

1. If granite weighs 170 Ibs. per cu. ft. what is its apparent
specific gravity?

VJhich beam Yri.ll support the greatest load; one of granite or
G. T/ooden bean (Douglas Fir) of the same dimensions, span and condi-
tion of loading?

3» Which of the beans mentioned in question 2 will deflect the
most under a given load? Why?

•*• What are the requirements for a good building stone?

5. What are the principal building stones?

6. HOY: is the durability of stone determined?

7. What is ashlar masonry? ^ Jw ^^

8. What is the allowable load on ashlar masonry?

9. Draw a typical stress-deformation curve for stone.

10. How do you account for the v/arping of marble slabs v/hich have
been exposed to the weather?

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION
Corre spondence Cour se s

Materials of Engineering Construction
Civil Engr-3 Assignment 8 Prof. C. T. Wiskocil

STRUCTURAL GUY PRODUCTS

Introduction: Clay products are widely used in engineering
construction. The material itself is not used in its natural state,
as stone and wood are used, but is first manufactured into various
products. This is a simple process because moist clay, which is-
very plastic, can be molded into the desired form and then easily
converted into a stone-like mass by firing or burning. Burnt-clay
is, then, the actual material used in engineering construction.
It is one of the most durable materials as is proved by the good
state of preservation of specimens found in ancient ruins. It
has been used since earliest times. Clay pipe found on the Island
of Crete dates back, according to one record, to 5,000 B.C. Other
records show that clay products were used in 2247 B-C. and in the
book of Genesis we read that the Israelites made bricks from mud
of the river Nile.

Brick, the principal clay product, has been used for many types
of structures. Parts of the Great Wall of China, 211 B.C., were
made of brick. J. A. L. Uaddell reports in "FOLLOWING THE GREAT
WALL OF CHINA11 (Engineering News-Record, 88, 642, April 20, 1922),
that the bricked wall is still in a fair state of preservation.
London was rebuilt with brick after the fire of 1666 A.D. The first
brick house in America, built in 1634 in Medford, Massachusetts, by

Engr~8» Materials of Engineering Construction. Assign. 8, page 2.

Gov. Craddock of the Massachusetts Bay Colony, was made with bricks
brought from Europe. Independence Hall, Philadelphia, and the famous
old State House of Boston were built with brick. The first brick
pavement in the United States was laid in 1871 in Charlestown, West
Virginia. At Great Falls, Montana, the Boston and Montana Copper
Company erected what is probably the tallest brick chimney in the
world. It is 506 feet high and 50 feet across the top.

Read Article 274* Remember the classification of structural
clay products as given in this paragraph. Clay suitable for the
manufacture of ordinary building brick occurs in large deposits in

many leoa*r3ren-»» Special grades of clay are required for the
making of paving brick, fire bricks, terra cotta, and chemical
stoneware •

The following table gives the approximate distribution of the
clay products made in the United States:

product Percentage of

Total Production

Common brick 20

Fire brick 18

Sewer pipe 8

Hollow tile 6

Drain tile 5

Paving brick 5

Face brick 4

Tile (not drain) 3

Arch. Terra Cotta 3

Other products 5

Pottery 23

Ravr materials used in the manufacture of_ clay products: Study
Articles 275 and 276; they describe the various classes of clays in
common use and give the composition of clays, notice that clay,

Engr-6. Materials of Engineering Construction. Assign. 8, page 3»

shale j and slate differ only in degree of consolidation and that
the principal elenents are silica, alumina and iron oxide.

Pure clay is hydrated aluminum silicate (kaolin) and is pure
•white. It is produced by the -weathering of pure feldspar, a group
of mineral substances consisting of silicates of alumina, potash,
soda and lime* Potash feldspar is known as orthoclase.

Common clays are formed by the weathering of igneous rocks
and clayey limestones. They contain iron oxide, lime and magnesia.

Che^iical action is not necessary in the di sintergration of
rocks; weathering cashes out some of the silica, as in the case of
the weathering of feldspars.

Soda, potash, lime, magnesia, and ferrous oxide combine with
silica and form fusible compounds which act as fluxes. If they
are absent the burnt clay is porous. If they are present in suf-
ficient quantities, the granules of clay are fused and a vitrified
product is formed.

Article 275 divides clays according to the geological manner
of formation into residual, sedimentary and glacial clays. All
classes are used for brick making but the sedimentary clays are
most frequently found satisfactory. Sedimentary clays may be
marine clays., lacustrine, flood-plain, or estuarine clays. The
marine clays yield the most satisfactory material for the manufacture
of brick. In tais class are the white-burning clays - ball clays
and kaolins - also fire clays and impure clays and shales.

Engr-8. Materials of Engineering Construction. Assign. 8, page 4.

The I'ollo.ving table gives a typical distribution of clays sold
annually in the United States. The figures are in tons. The clays
sold are estimated to be only a small proportion of the total
amount mined. The table is interesting, nevertheless, since it
gives the commercial names of the various clays and shows the uses
to v:hich clay is put other than for structural purposes.

Kxolin
Paper clay
Slip clay
Ball clay
Fire clay
Stoneware clay
Brick clay
Miscellaneous

Clay available for the manufacture of clay products is one of
the most widely distributed minerals. Hence there are clay-working
plants in every State in the United States. The manufacturers who
use low-grade clays usually mine their own raw material but the
percentage of manufacturers mining their own clay decreases as the
use of a higher-grade clay is employed. Nearly every manufacturer
who makes the highest-grade ware buys the clay he uses.

Kaolin, the purest form of clay, is produced principally in
the Southern States. It is used mostly in the manufacture of
china, white ware, such as semiporcelain, and semivitreous porce-
lain ware. Some is used also for fire brick and in the manufacture
of paper.

Paper clay, as the name indicates, is used principally in the
paper mills for a filler and coating for paper. A largo part of
this clay sold is used for the purposes listed under kaolin, and

Engr-8. Materials of Engineering Construction. Assign. 8, page 5.

also in the production of pottery and tile. About six percent of
the paper clay sold is used by the cement mills in the manufacture
of white cement. This clay is also used in the manufacture of oil
cloth and phonograph records and paint filler and pigment. Georgia,
North Carolina, and Illinois are the principal producers of paper
clay.

Slip clay is an easily fusible material. Its chief use is in
the manufacture of artificial abrasives, such as emery wheels, and
for glazing. Slips are applied to architectural terra cotta and
pottery to give the product an impervious surface. Ohio and
Michigan are the principal producers of slip clay.

The principal use for ball clay, which is a plastic white-
burning clay, is for white-ware, such as high-grade pottery and
tile, porcelain electrical supplies and sanitary ware. Most of the
supply comes from Tennessee and Kentucky.

Fire clay finds its greatest use in the manufacture of re-
factory products. It is used for fire brick, converter and cupola
linings (in the steel industry), and in the manufacture of terra
cotta. These are hov/ever, only the principal uses; there are
many others. This type of clay is probably used for more dif-
ferent purposes than any other. It is mined in 32 states, Penn-
sylvania and Missouri producing the greatest amounts. See the
note on fire-clay in Article 275 in the text.

Stoneware clay is refactory or semirefractory and is used
chiefly in the manufacture of stoneware and chemical stoneware.

Engr-8. Materials of 'Engineering Construction. Assign. 8, page 6.

Lover -grade clays are used in the manufacture of building and
paving brick, drain tile, sewer pipe, and fireproof ing. Almost all
of the manufacturers of these products mine their own clay.

Read Article 277 carefully. It gives the physical properties
of raw clay and the relation of these -properties to those of the
burnt -product. Plasticity is an important physical property. The
necessity for a certain degree of plasticity is evident to anyone
•who has ever attempted to work wetted clay* Most of us are not
familiar with clay working methods; yet even those who are have
often wondered therein the hardship for the Israelites lay when
they were forced by Pharoah's taskmasters, according to the Bible
story, to make bricks without straw. Some have thought that the
straw was added to the clay as a binder just as hair is added to
plaster; but because of the weakness of the straw fiber this is
not an adequate explanation- No more satisfactory explanation was
offered until Dr. E« C-. Ache son, the discoverer of carborundum,
found in his experiments that the plasticity of clay was increased
by additions of dilute solutions of tannic acid. Moreover the
strength of the dried clay was greatly increased. Although straw
does not contain tannic acid it was found that the water-extract
of straw was just as effective as were solutions of tannic in in-
creasing the plasticity and strength of clay.

Excessive shrinkage of clay is undesirable, but a small amount,
about Q%, aids in making a more compact material.

Engr-8. Materials of Engineering Construction. Assign. 8, page 7.

Manufr.ctv.re of clay products: The method 'of manufacture is
approximately the same for all classes of clay products. Study the
steps in the process as given in detail in Articles £78 to 286
inc lv, sive •

Any clay which possesses a sufficient plasticity for molding
and which will burn to the proper hardness is used in the manufacture
of bricks- Usually impure clays are employed and they require special
treatment as described in Article 278.

The molding processes are described in Article 279. A small
proportion of common brick is still made by hand methods* There
are two methods of hand molding, slop-molding and sand-molding.
In the former, water is used to prevent the clay from adhering to
to the mold and in the latter method the same result is accomplished
by the use of sand. Eond made brick is the lowest grade of brick.
Machine-made brick is made by three methods, soft-mud, stiff -mud,
and dry-press. The process used depends upon the characteristics
of the clay employed and the class and quality of brick desired.

Artificial methods of drying clay products, as described in
Article 280 are coming into general use in the manufacture of brick.
Higher gro.de products are seldom dried any other way.

The two classes of kilns, the intermittent and continuous, are
described in Article 281. The intermittent kiln consists of tr/o
types, the up -draught and down-dr aught kilns* The doT;n- draught
principle is used in the continuous kiln. The old scove kiln,
which is essentially an up-draught kiln, is still common in small

Engr-8. Materials of Engineering Construction. Assign. 8, page 8.

yards where the hand process of molding brick is used. The down-
draught kiln is more efficient than the up-draught; and it burns
very evenly terra cotta and pottery, as well as brick. The con-
tinuous type of kiln is more economical than any other but it is
more expensive to install.

The heating of clay, \vhich is necessary to give it its maximum
strength and hardness, is known as firing or burning. The process
is described in detail in Article 282. The firing of a scove kiln
usually takes about &. week*

Read Article 233; It will be referred to when terra cotta
and sewer pipe are discussed.

The degree of burning of light-colored ware* in a normally
operated kiln, can be quite accurately estimated by the color of
the product if the characteristics of the clay ate known. Flashing,
however, (see Article 285) makes it difficult to judge the degree
of burning by means of the final color of the waVe.

Annealing is of highest importance in the manufacture of all
clay products. After the ware has been properly burned the tem-
perature of the kiln is reduced at a slow, uniform rate until that
of the surrounding astmo sphere is reached; the ware is then removed.

When the ware is removed from the kiln it is sorted according
to quality, which is determined by the degree of burning, and the
freedom from such imperfections as excessive warping, cracks, and
deep kiln-marks. There is a special market for inferior products.

Engr-8. Materials of Engineering Construction. Assign. 8, page 9.

Tests of structural clay products: Study 'Articles 287 to 296
inclusive and read Appendix A, pages 807 to 814 inclusive. Be able
to list the two classes of tests, those made en the job and those
made in the laboratory.

Examination of appearance in the strict sense is not a test,
it is visual inspection. Intelligent physical inspection, with
the hammer and hardness tests, are often sufficient to determine
the acceptability of structural clay products. In order to de-
termine mechanical properties and the effect of changes in materials
or methods of manufacture it is necessary to have more elaborate
tests made. The transverse test, described in Article 300, is the
most important test made on building brick. It is also used for
paving brick. The compression tests are made on brick of all kinds
anc5. on various other clay products such as hollow building tile and
clay pipe. The methods for making the pipe tests are shown in
Article 293. In addition to these tests, pipe is also tested for
its resistance to internal pressure* Single lengths, and often
several lengths put together; are subjected to hydrostatic pressure.
The rattler test described in detail in Appendix A is still the
standard abrasion test for paving bricks. Tests of this character
are intended to imitate the conditions under vhich the product is
to be used. In spite of the fact that the rattler test does not
fulfil these requirements it has been in use for some time. The
test described in Article 295 has never been standardized and ac-
cepted by the American Society for Testing Materials. In all

Engr-8. Materials of Engineering Construction. Assign. 8, page 10.

testing, as described in the case of the alternate freeing and thaw,
ing test in Article 293, the conditions of actual testing should
be standardized so that the results of different laboratories and
tests made at different times will be comparable* Differences in
the shape and size of the test specimen, rate and manner of apply-
ing the load and method of general procedure all affect the results
of the test.

Building Brick; Read the text, Articles 297 to 303 inclusive,
on the subject of building brick.

The manufacture of clay products has already been described,
and specific information on brick has been given. Article 297
emphasizes some statements previously riade. Bricks after being
molded are dried for a period varying from several hours to several
days depending upon the method of molding and drying. After dry-
ing they are burned in a kiln for about a week, the temperature of
the bricks being very gradually raised. The cooling process takes
place gradually over a period of several days.

Brick may be classified, as stated in Article 298, according
to method of molding, degree of burning, form and use. In general
all bricks have the same proportions: the width of two bricks
plus a mortar joint will equal the length. When used in the facing
of masonry, bricks must have true surfaces and sharp edges. Face
bricks c.re pressed or repressed before firing in order to insure
these necessary qualities. Glazed brick are made by coating one
side of the unburned common brick with a slip cloy of the desired
color over which a second cor.t of transparent glaze is applied.

Engr-6. Materials of Engineering Construction. Assign 8, page 11.

These coatings fuse into the brick in the burning process. Enameled
brick are made of a higher -grade clay. In the burning it fuses and
unites with the body of the brick* The enamel, which usually
contains an oxide of tin is applied to the unburned *or to the
finished brick. Glazed and enameled bricks are used for build-
ing courts and interior finish. Tapestry brick, the peculiar sur-
face cf which is formed by cutting off a thin slice by a wire, is
also used as a face brick.

Study the requirements of good building brick listed in
Article 299. This is an important article. The first paragraph
in this article mentions efflorescence. It is a surface dis-
coloration, usually white, but occasionally green or yellow,
formed by the leaching out of soluble salts from the interior
of the brick, and the depositing of these on the surface by the
evaporation of the v.rator. Besides being unsightly this process is
liable to disintegrate the brick. Efflorescence can be prevented
by using water and clay free from the soluble salts of magnesium,
sodium, and potassium. If this cannot be done, an effective method
of prevention is the preliminary treatment of the raw materials
with barium salts to convert the soluble salts, which usually exist
as sulphates, into the insoluble barium sulphate. Careful, rapid
drying of the molded brick to prevent the salts fron coming near
to the surface and hard burning to volatilize the alkalies and to
mnke r. dense brick both help to prevent efflorescence. After the
brick are in place efflorescence can be prevented only by keeping

Engr-S. Materials of Engineering Construction. Assign, 8, page 12

the brick dry. Defective drain-spouts often saturate the surround-
ing brick; the source of water should be removed, as efflorescence
is likely to result. Brick can be kept dry by surface coatings
of waterproofing material such as paraffin.

Tests of brick are given in Article 300, • Look over the tables
given on pages 282 and 283; note the variation for the same class
of bricks. Determine average values to compare with similar data
already obtained for the materials you have studied* Take good
building brick; assign an average compressive strength of 4,000
Ibs. per sq. in., an average modulus of rupture of 1000 Ibs, per
sq. in, and an average modulus of elasticity of 6 million Ibs, per
sq, in. The strength of brick masonry, just as in the case of
stone masonry, is much less than the strength of its component
parts. The compress ive and tensile strength of individual brifeks
is of relative value in the comparison of different kinds of
brick* The fractured surface of the brick in the transverse test
affords an opportunity to observe the texture and uniformity of
structure. The stress-deformation curves are similar to those of
cast iron and concrete - also briille materials - and usually are
not as straight as indicated in Figure 6 on page 284, The modulus
of elasticity, therefore, is not uniform but decreases with in-
creasing loads.

Brick Masonry : At the time brick was made by hand (the first
power-operated machinery being used about 1840), stone made the
highest-grade masonry. At present, however, with a large variety

Engr-8. Materials of Engineering Construction* Assign. 8, page 13,

of high-grade bricks available, brick masonry compares irell vrith
the best gro.de of stone masonry. Well made masonry of good brick
is as nearly permanent as any structural material. Brick masonry
is more resistant to fire, more easily built, and usually cheaper
than ston3 masonry.

Mortar is an important factor in the construction of masonry.
Its principal function is to form a bedment ar.d to hold the bricks
together. The influence of the joint upon the color of the brick-
v/ork can be understood rrhen consideration is given to the fact that
the :nortar joint constitutes from 1/10 to 1/5 of the surface of the
finished •wall. The mortar also adds effectiveness to the appear-
ance of the bond, vrhich is the torn used for the brickwork patterns
or relative position of the faces and heads of the bricks as laid.
! lor tar is made of lime and sand, cement and sand, or a combination
of lime, cenent, and sand.

1. The kind of nortar has an important effect upon the
strength of brick masonry. 2. Lime mortar is not as strong as
cement mortar. 3. The strength of masonry is proportional to the
transverse strength of the bricks used in its construction, llortar
joints should be as thin as possible and of uniform thickness.
Regularity in the shape of the bricks is essential. 4. Since the
initial failure of brick masonry is caused by a transverse failure
of individual bricks the ultimate strength of this type of con-
struction can be increased by laying the bricks on edge instead
of flat or by using bricks of more than ordinary thickness.

Engr-6. Materials of Engineering Construction. Assign. 8, page 14.

£and Lime Brick; Study Articles 304 to 307 inclusive. A sand
lir.e brick is not a burnt clay product but it is used for the same
purposes and has the sane size and shape as a clay brick. The
sand-lime brick consists of about 90$ sand and 10$ line. About
&5fo of the sand is retained on a 100-mesh sieve and constitutes
the aggregates, ivhich are bound together by a calcium-silicate.
This binding material is formed by a chemical combination of the
lime and part of the sand Tvhich passes the 100-mesh sieve.

The bricks have fairly high strength when they are removed
from the hardening cylinder and it increases for some months after
they have been made. Their ultimate strength is about three-fourths
that of good building brick.

Paving Brick: Study Articles 308 to 310 inclusive. Paving
bricks differ from building bricks in several -ways. The selection
of suitable clay is more limited, shale being usually employed.
The burning tempera.ture is higher because it is necessary to bring
the clay to the point of actual vitrification so as to secure the
proper hardness in the finished brick. The prevailing size of
paving bricks is 3 by 4 by 8-1/2 inches. For maximum toughness
the annealing period should be about 10 days as stated in Article
285. Only the properly vitrified bricks make satisfactory paving
material; the overturned bricks are used for foundations and for
sewer construction vrhile the underburned bricks make and excel-
lent building brickc Average values for compressive strength are
10,000 Ibs. per sq. in.; for transverse strength use 2,000 Ibs.

Engr-8. Materials of Engineering Construction. Assign. 8, page 15.

per sq, in. and 6,000,000 Ibs. per so. in. for the modulus of elas-
ticity. Remember that the maximum permissible loss in the rattler
test is 28$, and that the bricks must be dry when tested. The
abrasion loss of wet bricks or bricks saturated Tilth bituminous
materials is greatly reduced.

Refacwory Brick: Study Articles 311 to 315 inclusive, Re-
factory bricks are capable of withstanding the effects of high tem-
p3ratures. There ere three classes of refr.ctory bricks: acid,
basic, and neutral. All are burned at a high temperature. The
principal use of these bricks is in the steel industry where the
type of brick selected depends upon the process of steel manufacture,
whether acid, basic or neutral.

Ho 11 ow Building Blocks: Study Article 316. These blocks,
which are often referred to as hollow tile, develop their greatest
strength when laid on end. The material resembles ordinary hax*d
burned brick. The average compressive strength of well burned tiles
is 7, COO Ib. per sq. in. with a modulus of elasticity of about
4,000,000 Ib. per sq. in. The strength of light-burned tiles is
about 30?£ lower.

Head Article 317 on the strength of hollow tile columns; it
is not very important.

Read Articles 318, 33.9 and 320 on roofing tile, c.nd floor and
wall tils. Roofing tile is usually made of terra cotta and burned
at a high temperature to insure hardness and low absorption. Tile
makes a very durable but rather heavy roofing mr.terir.l.

Engr-8. Materials of Engineering Construction. Assign* 8, page 16.

Terra Cotta.: Read Articles 321 and 322. Terra cotta lumber
is not extensively used. Architectural terra cotta, however, is
one of the standard building materials. Permanent buildings faced
vrith terra cotta are made in the United States, Australia, Japan,
and South America and the material is 'not thought of as a substitute
or an imitation of stone. Terra cotta requires considerable strength
and accuracy in the finished -.rare, therefore, clays of appropriate
composition are limited and nust be carefully selected. Clays form-
ing the body of the vrr.re are nixed for "both chemical and mechanical
reasons. Plaster of Pr.ris molds are taken fror. plaster of Paris
models * These molds have to be specially made to provide for the
shrinkage that normally occurs in drying and burning. A mold with-
stands the -;;er.r of from 20 to 50 pressings according to size* In
the pressing shop the molds are faced v;rbh from 1 to 2 inches of

6 £

and partitions about 1 inch in thickness* leavwsk§ spaces or

cells of about six inches^ The partitions are built up to rein-
force and strengthen the unit. The piece is then turned out on
the drying boards "There it is retouched, After drying, the piece
passes before the sprayers vrtiere the surface glaze, /finish, slip,
•or color is applied "by an atomizer vrith compressed air. In burn-
ing, the ware is piled in muffle kilns on fire-brick posts and . *
slabs so that each piece is free from r.ny extra weight. The burning
temperature is about 2,200 degrees Fahrenheit.

Almost any color tone can be had in terra cotta, from, the
pure rrhito through the crean coid buff shades into the greys. The
texture ranges from the natural clay and the smooth or honed

Engr-8. Materials of Engineering Construction. Assign. 8, page 17.

finish through different degrees of tooling, dragging, and stippling
to any degree of desired roughness. The surface is made impervious
with a slip, varying through matt or dull to lustrous and brilliant
glazes. The use of color or polychrome in terra cotta is being ap-
plied to both interior and exterior decoration.

There are many examples of the use of terra cotta in building
construction in California. The Fireman's Fund Insurance Building
in San Francisco and the Yolo County Courthouse in Woodland are
particularly good ones. Others are the Golden Gate Valley Branch
of the San Francisco Public Library, the Hobart Building and the
trim on the Southern Pacific Building in San Francisco; the Bank
of Italy in Fresno; the Northern California Bank of Savings in
Harysville; the First National Bank in Santa !!aria; and the
Farmers and Merchants National Bank in Stockton. Then there are
notable examples in buildings in the large cities in the United
States; such as the Woolworth Building, the Hudson Terminal
Buildings, the Produce Exchange and the r'orld Building in New York
City. Terra cotta is well adapted to interior facings, as is shown
in the United States Post Office at Pasadena, California.

Study Articles 323, 324 and 325 on sever pipe, drain tile,
and conduit. Sewer pipe is usually made with socket ends, referred
to is bell ends in the text, and the joints are made tight by the
use of cement mortar. Sewer pipes, while often spoken of as vit-
rified pipes, are not actually vitrified. The salt-glaze .general-
ly used gives them the appearance of a vitrified product. Common
salt (sodiurt chloride) is thrown on the kiln fires. It volatilizes

Materials of Engineering Construction. Assign. 8, page 18

and the sodium vapors react with the clay and form a fusible
sodium-aluminum-si lie ato which covers the surface with a glaze.
This glase is very thin and is not as effective as vitrification
in reducing "Sweating" of pipes under hydrostatic pressure tests.
Salt glazed pipe is much cheaper than a vitrified pipe would be.
There is considerable loss in the manufacture of this product be-
cause cf warping and distortion in the drying and .firing processes.

Drain tile is a cheaper product. It is fired at a lower
temperature and is not very dense. No r.ttenpt is made to nake the
material porous because the water enters the pipe through the
joints and not through the walls of the pipe.

— >:< -

QUESTIONS:

1. Classify clays according to geological formation.

2. TJfhat can be considered a good brick?

3. Could a brick be satisfactory for one purpose and unsuited
for another?

4. What bricks are made in your locality? which are preferred
and why?

5. How does sewer pipe differ from drain tile?

6«i How are sand-lime bricks made?

7. '.That is efflorescence? Can it bo prevented?

8. HOT; is architectural terra cotta madey

9. Give the average compressive strength, transverse strength,
and modulus of elasticity of building bricks r.nd paving bricks.

10. How does the strength of brick masonry compare with that of
the individual brick used in its construction?

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Civil Engr-S.A. Assignment 9. Professor C. T. Y/iskocil

PORTLAND CEMFNT

Introduction:- The cementing materials used in engineering
construction are classified in Article 326- Portland cement is not
only the most important of these materials but it ranks as one of
the principal structural materials.

Fortlr.nd cement is a grey powder (some white Portland cement
is made) which when mixed with water to form a paste has the property
of hardening into a stone-like mass whether in air or under water.
Its property of hardening under water together with the fact that
it develops considerable compressive strength gives Portland cement
a -vide variety of uses it would not otherwise have. It is rarely
used neat, that is, as a mixture of cement and water. Neat cement
is too expensive and besides it is subject to excessive shrinkage.
Cement is usually mixed with an inert material. If this inert
material is sand, the resulting mixture is called mortar; if larger
broken stone or gravel is used with the sand, the mixture is known
as concrete. In both cases the cement paste is the binding material.
Mortar is used in the fabrication of stone, brick and terra cotta
masonry; where used for surfacing interior and exterior walls,
it is called plaster or stucco. AS concrete it is poured into molds
to form monolithic structures such as foundations, walls, dams and
all types of pavements. When steel is placed in concrete to take

Civil Engr-8. Assignment 9. page 2.

tensile stresses tne product is known as reinforced concrete.
Proper reinforcement makes it possible to use concrete for practical'
ly every type of engineering, structure, such as complete ouildirigs,
from the foundation tnrough the columns,, beams, floor slabs, and
walls, to the roof; and as "bridges, reservoirs, arches, chimneys,
and evsn ocean-going ships. Read .article 326 in the text.
Definition:- '.Yhile port land cement is only an artificial mixture

of calcareous (which means lime bearing), and argillaceous (which
means clayey) materials, ourned to a clinker at a temperature of
incipient fusion and afterward ground to a fine powder. It is well
to know the definition given in Article 327 because many times a
verbatim repetition is required.

Incipient fusion is the stage at v;nich fusion is just about
to occur. It is sometimes spoken of as initial fusion.
Characteristics of portland cement;- Study Article 323. The
weight of portland cement is usually taKen as 9<t lb. per cu. ft.
A sack contains a cubic foot and there are four sacks in a barrel.
The chemical elements:- Study .urticle 329. Remember only average
figures; lime §2%, silica 22%t alumina 7%t with the remainder con-
sisting of iron oxide, magnesia, sulphur trioxide, and water,
proportioning of raw materials :- Read Article 330. The proportion-
ing of the raw materials in making portland cement is not a simple
matter. As stated in Article 336 the temperature to which the raw
materials &re raised is only sufficient to start fusion and con-
sequently complete solutions of all the elements are not obtained.

Civil Engr-3. Assignment 9. Page 3.

After calcination the product is not a mixture of clayey and cal-
careous materials, but is what is often spoken of as a solid solu-
tion of the various components consisting principally of silicates
and aluminates of lime. While the conclusions of Nev/berry and
Le Chatelier have been shown to be not entirely correct, the
methods of proportioning based on their conclusions have produced
excellent cement.

Effect of minor constituents:- Read Articles 331 to 335 inclusive.
White portland cements contain very little iron oxide. The color
of the ordinary port lands is due principally to this oxide of
iron. The amounts of carbonic oxide are indicated by the loss on
ignition. The specified limits for the loss on ignition of sul-
phur anhydride and magnesium oxide are given on page 372 in the
text.

The consitution of portland cement :- Read Article 336. Portland
cement consists of a mechanical mixture of chemical compounds which
have constant physical and chemical properties. These compounds
are tricalcium silicate ( 3 CaOSiC^), tricalcium aluininate
(SCaO'AlgGs), tricalcium ferrite (3CaO.Fe203) and calcium ortho-
silicate in the beta form (2 CaO.SiOg) given in the decreasing
order of their cementing qualities. In addition to these compounds
there is usually about Z% of gypsum. Magnesia in the form of the
oxide (JigO) is in a state of solid solution in the other components,
usually in such snail quantities that it does not have much effect.
Traces of other elements - potassium and sodium and particles of

Civil Engr-8. Assignment 9. page 4.

quartz from the flint pebjle<s in the ball mills, metallic iron
from the machinery and even particles of semi-fused ash, when coal
is used as the fuel in calcining the cement,-- are sometimes found
in normal port land cements.

The compounds of alumina, lime, and silica have been shown
to constitute the bulk of normal port land cement in studies of the
ternary ane binary systems of the three principal components by
technicians f ohoainta, physical-chemists, and chemists) of various
university laboratories, the Bureau of Standards, and the Geo-
physical Laboratory. A chemical analysis of a cement does not
give the actual composition because the results are in terms of
the oxides and the principal elements do not exist in the form of
oxides. It is possible, however, to recast an analysis according
to known laws of chemical combination and obtain the percentage
composition of the cement in terms of the actual compounds that
exist instead of the oxides.

Setting and hardening of portland cement;- Study Article 337. The
setting and hardening of cement pastes are defined in the first
paragraph of this article. Vvhen mixed with water the components
previously mentioned are hydrated, with the production of amorphous
hydrated silicates and a?_uminates of lime, and considerable cal-
cium hydrate in both crystalline and amorphous forms. The different
components do not hydrate with equal ease. It is quite generally
agreed that the tricalcium aluminate is the first to hydrate and
that this compound affects the initial set. The tricalcium sili-
cate, which has been found to have the greatest cementing value

Civil Engr-8. Assignment S. Page 5.

and to be the best hydraulic component by actual experiment , is
next to hydrate. It is this reaction that causes cement to
harden. Calcium orthosiiicate is the most inactive of the cement
components.

Iviichaelis' colloidal theory of the hardening, and setting of
Portland cement is given in this article. Study this carefully
and be able to give it in your own words. It is essentially as
follows: The hardness, strength, and duraoility of cement depend
upon the fact that the products of hydration are formed in the
non-crystalline colloidal state. Under the microscope, freshly
hydrated compounds are non-crystalline and do not crystallize for
from 10 to 20 days.

Hydration must begin at the surfaces - grains of cement be-
come coated with colloidal gel -which causes them to stick together.
The gel is impervious and the centers of the grains are not im-
mediately hydrated. They become hydrated only as water can diffuse
through the colloid coating. At this stage the cement is not
hard.

The hardening depends upon the drying of the thin coating of
colloid which envelopes the grains. It is not necessary that the
absorbed water in the colloid coating evaporate (some does when the
cement sets in air). The free water may be taken up by the un-
hydrated centers of the grains and converted into combined water.
Here it cannot manifest itself as -water. (Crystals containing more

than half their weight in water, in the form * of crystallization,

Civil En-r-3. Assignment 9. Page 6.

do not appear tc be wet). It is riot difficult to understand that
cer.ent gel can dry out in this manner even under water. Water can-
not readily pass from grain to grain because of the impervious
coating of collcid. The grain centers use up free water faster than
it can ce supplied from the outside and the gel Decodes dry and hard.
It is an irreversible colloid and therefore remains hard.
Historical notes;- Read Article 338 on the growth and importance
of the Portland csment industry.

Some knowledge of cements, similar to portland, which set
under water, was possesed by the Romans. It is said that the base
of the Temple of Castor and Pollux in the Roman Forum was a solid
mass of puzzolana concrete.

The first impetus was given to hydraulic cements by John
Smeatcn who rebuilt the lighthouse on Eddystone Rock in 1756. See
Article 587 on page 365 in the text.

About fifty years later the French chemist Vicat produced a

product similar to that used by Smeaton. Vicat 's semeni •-;?&$ produce^
by burning a finely pulverized chalk and clay after he had mixed

them to form a paste.

The first patent was granted in 182<± to Aspdin, a Yorkshire
bricklayer, who heated pulverized chalk with clayey river mud.
Because of a fancied resemblance (actually there was very little)
between his product and a well known limestone quarried near

•

Portland (which is on the South East coast of England) and known
as Portland stone, he named it Portland cement. The name has been
universally adopted. Aspdin is usually given credit for the in-
vention of portland cement.

Civil £ngr-8. Assignment 9. Page 7.

In 1874 the first port land cement was made in the United
States. In I92U, 100,302,000 barrels were produced at an average
cost of $2.01 per barrel.

Ra-7 materials;- Read Article 339. Some of the rav; materials
used by California plants are as follows: The Standard Portland
Cement Company at Napa Junction, Napa County uses a pure limestone
end a clayey limestone; the California Portland Cement Company
at Gait on, San Bernardino County, uses clay and a pure limestone;
the C owe 11 Portland Cement Company at C owe 11, at the foot of Mount
Diablo near Concord, Contra Costa County, uses travertine and
shaiy clay; the plant of the Santa Cruz Portland Cement Company,
at Davenport, just north of Santa Cruz, uses shale and a pure
limestone; the Riverside Portland Cement Company operates a
plant at Riverside using a mixture of clay and limestone.
Manufacture :- Study Articles 340 to 349 inclusive, they describe
the manufacture of port land cement by both wet and dry methods.
Most cement manufactured in the United States is made by the so-
called dry process. Only one California plant, that at San Juan
(just south of Gilroy), making the Old Mission brand, uses the wet
method of manufacture. Crude oil is the fuel used in the Cali-
fornia cement mills.

The average temperature of burning is about 2,800° Fahren-
heit. In most plants the clinker is cooled in air but if it is
cooled as stated in Article 345, by being sprayed with water, note
that the water does not injure it. Clinker has no cementing
properties; it must first be finely ground.

Civil Lngr-8.

Assignment 9.

page 8.

The amount of gypsum which can be added after the cement
has been buried is Z%, It is added to retard the set of the cement.

Be aoie to -visualize the process of manuiacture as indicated
in the following diagram:

en
o

•c
s ^

p o

r»- 0>
0>
"« O

H. Mj

H-1 »

tn P

H-

SB
M

"=W

co Hr
o o

P -o

I-" 0
CD *J
to <:*•

H-

0
3
H-
3
<fi

H- >1

d. (B

H« *T!

O
CO h-1
c*- H.
0 3

OJ
3-

Civil Engr-8. Assignment 9, Page 10-

Conditions Affecting the Properties of Cement:- Read Articles 350
to 354 inclusive. The properties mentioned in these articles will
be described in detail in Chapter XII begining on page 371 in the
text.

Soundness is the most important property of cement. Un-
sound cement cracks and disintegrates after it has set. It is
thought that the principal element causing unsoundness is free lime.
Thorough seasoning, fine grinding of the raw materials and the
clinker, and the use of the nininum amount of gypsum tend to pre-
vent unsoundness.

Fineness of grinding is the principal factor affecting the
tensile strength of cement :nortf>r. The tensile strength of sand
mortars is improved, "but that of neat cement mortar is decreased by
fine grinding.

The time of set is decreased by fine grinding of the cement.
Finely ground cements sometimes develop a flash set which makes
them unfit for use in engineering structures. The degree of season-
ing, the temperature of the air and the mixing water all affect the
time of set.

The fineness of cement is influenced by the hardness of the
klinKer and the efficiency of the grinding machinery used. There is
no relation bet-ween the strength of concrete and the fineness of
cement if different cements are considered.

Long seasoning is the chief cause of a low specific gravity
of cement.

Civil Engr-8. Questions to Assignment 9. page 11.

1. Define ^Ttland cement.

2. Explain the derivation of the term port land in the name
Portland cement.

3. Outline the process of manufacture of portland cement.

4. What are the nair.es of the principal constituents of portland
cement?

5. State the colloidal theory of setting and hardening of cement
as advanced "by Michaelis.

6. What is the temperature at which cement is calcined?

7. What is meant by incipient fusion?

8. How does fine grinding effect the strength of neat cement
mortar?

9. What is the principal cause of unsoundness in cement?

10. Define unsoundness.

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction

Assignment 10.
Civil Engr-e.A^. Professor C.T- Wiskocil

PORTLAND CELERY (continued) and NATURAL CEi&NT
Tensile and compressive strength of cement;- Read Articles 355
and 356. As has already been mentioned, neat cement is rarely used
in engineering construction. Recently it has been used to make
joints in laying be 11-and -spigot cast iron pipe. The cement is
mixed with juwt enough water to hydrate it so that when ready for
use it is not a paste but is merely moist. In this condition it
can be rammed into the joint where it hardens -without shrinkage
cracks. These joints have been very successful.

Most of the tests on neat cement were made during the develop-
ment and standardization of this important structural material.
Those reported in Bulletin 333 of the United States Geological
Survey (mentioned in Article 356) were made in the period from
1905 to 1907. They were published in 1908. Sinr:e that time it
has been found that the strength of neat cement is no criterion of
the strength of mortar or concrete made from it. Furthermore,
tensile strength tests of a given cement h?.ve been found to be de-
cidedly influenced by the methods of mixing and molding and other
variables that may be grouped into what is called the personal
equation. Standard specifications once included the test of neat
cement, but it should be noted that at the present time only a
1 to 3 standard sand mortar is tested (see page 372 of the text).

. •

;.-; .

Civil Engr-S. Assignment H>. page 2.

The data given in Figure 13 on page 331 do not checic tnose
given in Figure 16 on pa^e 335. Remember that in addition to the
personal equation, conditions of storage t temperature of mixing
water, form of briquette, and amount of mixing water used all effect
the strength of the cement: moreover, different brands have in-
dividual qualities. The principal difference between the sets of
data mentioned is that those in Figure 16 do not show the decided
decrease in strength at the age of one year. Since the tensile
strength of neat cement is not inportant it is sufficient to remem-
ber that the strength increases with age to a maximum of about
1,000 Ib. per sq. in*

The cornpressive strength of neat cement also varies with
age, the size and shape of the test-specimen, and the amount of mix-
ing water used. The consistency of the freshly made cement paste
varies considerably with the amount of water used; yet, in spite of
the fact that this factor has a great influence on the ultimate
strength of the hardened mortar, it v/as seldom recorded in early
experiments, such as these used in preparing Figure 14 in the text.
The data in Figure 14 shew that the c oppressive strength of neat
cement one year old varies from about 11,OCO to 13,000 Ib. per sq.
in. Some tests reported by A.C. Alvarez in THE C OPPRESSIVE STRENGTHS
OF PORTLAND CEfcENT hCHTARS OF VARIOUS PROPORTIONS, University of
California puoiications in. Engineering (1915), give the compressive
strength of neat cement mortar cubes, 4& days old, as 10,000 Ib.
per. sq. in. The cement paste was of normal consistency, ZZ% water

Civil -Engr-8. Assignment 10- Page 3.

being used. Increasing the amount of mixing water v;ould decrease
the ultimate strength. The relation would prooably be similar
to that shown in Figure 1 on page 816 in the text. The effect of
the variaale amount of mixing water and another variaole, the mold-
ing pressure, is clearly shown in an article, PRESSING OUT MIXING
WATER ADDS TO CEAiErIT IIORTAR STRENGTH bj, C.I. Wiskocil, Engineer ing -
News Record, 83, 13C (July 17, 1919). The following facts are
taken from that article: "Neat cement mortar made with 25% water
had a compressive strength of 6,800 ID. per sq. in. at 7 days. In-
creasing the amount of water to 37$ reduced the 7-day strength to

2,500 Ib. per sq. in. The paste used in making the latter speci-

WAS
mens ^we** molded under a pressure of about 30,000 Ib. per sq. in.,

TKe4€ f resort

allowing the expressed water to escape, Dr oduo ec spec imens whoae
d #

7-day strength w«a^l7,000 Ib. per sq. in."

Since the strength of neat cement is not. important, take
10,000 Ib. per sq. in. as the average eonipressive strength. It is
easily remembered with the 1,000 lo. per sq. in. for the average
t.SRsile strength.

"Expansion and contraction dae to changes in moisture content :-
Read Article 357. The important fact is that dry mortar as well as
concrete (see Article 522 on page 480 in the textj will expand
when it becomes vTet and contract again upon drying. Frequent ly
changes in moisture content are as important as temperature
changes in producing variations in linear and volumetric dimensions
of mortar and concrete.

Civil Engr-8. Assignment 10. Page 4.

Effect of remixing on the strength of cement ;- Read Article 358.
The practice of using cement that has set is seldom allowed in
engineering construction. Remixing is the use of set cement while
retempering, is the addition of water to set cement; but since
neither practice is in general use the subject is not important.
Remixed mortar is frequently used in laying floor and v/all tile
because of the impression among the artisans that this procedure
increases the cementing qualities of the mortar. The data in
Figure 21 show that the compressive strength of neat cement mortar
is not materially affected by remixing even several hours after it
has been prepared.

The central mixing plant, which necessitates some long
hauls of wet concrete, is frequently used in road construction,
particularly on large contracts. Recent tests by the Bureau of
Public Roads show that the compresaive strength of concrete will
not ''be affected so long as it remains workable. Test specimens
mace from wet concrete which had been hauled in trucks for periods
up to three hours showed no appreciable decrease in compressive
strength. The concrete, howerer, became too dry for hand finishing
45 minutes after it had been prepared. These remarks are inserted
at this point uecause the subject is not discussed under CONCRETE
in the text.

Effects of high and low temperature on ceiaent;- Read Articles
359 and 360. The setting and hardening of cement paste is retard-
ed and may oe entirely stopped by decrease in temperature. These
effects are not appreciaole until the temperature falls below

Civil Engr-8. Assignment 1C.

40 degrees Fahrenheit, Alternate freezing and thawing of cement
before it sets is particularly harmful.

High temperatures produce marked reductions in the strength
of cement mortar. Remember that cement begins to fuse at approxi-
mately 2,800 degrees Fahrenheit.

Temperature of cement during, period of set;<- The effect of
alkali on the durability of cement concrete is being intensively
studied at the present time. As yet no conclusions are available.
There are numerous examples of failure of cement subjected to the
influence of alkali but the history of the preparation of the con-
crete, v;hich is thought to have considerable effect on its dura-
bility, is not always available.

Sugar and animal and vegetable oils disintegrate cement mortar
and concrete.

Effect of storage on cement :- This subject is not satisfactorily
discussed in the text (see page 373) but it is one that can -.be
taken up at this point. The question is important because a
shortage of fresh cement on a joo will frequently necessitate the
use of cement that has been stored from six months to a year or
produce an enforced delay until a new shipment can be secured.
The storage of cement is of interest to the manufacturer and dealer
as well as the user oecause it is becoming the practice tc deliver
concrete materials on the job prior to the opening of the construc-
tion season. The principal study of this question has been made
at the Structural Materials Research Laboratory, Lewis Institute,

Civil Engr-3. Assignment 10. page 6.

Chicago, and reported in Bulletin 6, EFrECX OF STORAGE OF CE&ENT, by
D-A. Abrams.

The cement was stored in cloth and paper sacks under three
different conditions; namely, indoors v;ith uniform temperature and
low humidity, indoors at lower temperature and higher humidity
(average basement conditions), and under average shed conditions,
which afford protection from direct contact with rain and snow but
allow free circulation of outside air with variable temperature
and humidity.

The principal conclusions are the following: There is no
marked difference in the quality of the cement stored in paper and
cloth sacks for periods up to 1 1/2 years of storage. The exact
condition of storage is not of ^reat importance so long as the
cement is protected from direct contact with moisture.

•

The deterioration of stored cement is probably due to the
absorption of moisture fron the air, which causes a partial hydra-
tion of the cement. The principal effect on the mortar and concrete
making qualities are the decrease of early strength and the pro-
longing of the time of setting.

The effect of storage is clearly shown in the accompanying
diagram.

Civil Engr-8.

Page 7

0 4 8 12 16 20 24

Age of test specimens, in months

The Effect of Storage of Cement on the compressive strength of 1-5
concrete tested at different ages.

The compressive strength of concrete and mortar showed a
decrease in strength with storage of cement for all samples, for
all conditions and periods of storage and at all test ages. The
decrease was greatest for the samples stored in the shed and nearly
as great under basement storage.

The age of the concrete has a large influence on the re-
sults obtained. Taking the poorest condition of storage, that
under the shed, the specimens tested at the age of 7 days, made
from cements and all periods of storage, was 64$ of the strength
of the specimens made with cement when received from the vrarehouse;
at 28 days, 71%; at 6 months, 73%: at 1 year, S2% and at 2 years
85%. Similar results were obtained from specimens under

Civil Engr-8. Assignment 10. page 8.

other conditions of storage. These data tend to show that the
strength of concrete, say 3 or 4 years after it has been poured,
is not affected "by the length of time (age) the cement was stored
prior to use.

The use of reclaimed cement, that is cement that is obtained

cement
from used/sacks of pneumatic methods or shaking, is questionable

practice and should not be permitted on any engineering structure.
Effect of fineness of cement;- Fineness is a distinct property
of cement and should be discussed at this time. It is briefly
noted on page 322 in the text. The most important tests were made
by D.A. Abrams and reported by him in EFFECT OF FINENESS OF CEMENT
in the Proceedings of the American Society for Testing katerials,
Vol XIX, part II, 1919. The following are his principal con-
clusions :

There is no necessary relation between the strength of
concrete and the fineness of the cement, if different cements are
considered.

In general, the strength of concrete increases with the
fineness of a given lot of cement.

Fine grinding oi cement is more effective in increasing the
strength of lean mixtures than rich ones.

The principal result of finer grinding of cement is to
hasten the earl;/ hardening (strength; of the concrete.

Fine grinding of cement reduces its time of set.

Ordinary concrete mixtures shov an increase in strength of
about l.&% for \% reduction in the residue of the cement on the No.

Civil Engr-8. Assignment 10. page 9.

2CO sieve. (Kemember that the fineness is measured by the residue
on a No. 2uO sieve . )

It has been found by other investigators that the principal
cause for rejection of finel^ ground cement is the development of
a flash set after delivery; the mill tests shoeing the cement to
be normal at the tiire cf shipment.

Natural cement:- Keac Articles 365 to 369 inclusive on natural
cement. When clay-bearing limestone is heated to about 200C de-
grees Fahrenheit, it g.ivea off carbon dioxide and forms a clinker,
•which when finely ground is knov;n as natural cement. The clinker
will not ^.ir slr.ke but when mixec vith water the resulting paste
•will harden in air or under vjater just as portland cement does.

Natural cement is not as uniform as portland cement ar\d it has less

15
strength. In spite cf its cheapness H *« very littleAused. It

has been used for mortar for masonr^ and ior concrete where
strength we. 6 not a r,rir:e requisite.

Miscellaneous cements:- Read Articles 370 to 373 inclusive. White
portland cement is crobajiy the jiost important of the varieties
mentioned. It is impossible to get the proper shades cf color in
stucco made with colored aggregate when using the ordinary grey
portland cement; white portland cement is used almost exclusively
for this purpose. In the construction of light colored masonry
it is necessary to have a mortar that will not stain the stone.
\Vhite portland is much more satisfactory than a natural cement
(which is also stainless) for this purpose.

Civil Engr.-8. Assignment 10. Page 10.

Pazzolana cement:- iazzolana is the name used in Europe to desig-
nate the cements made from volcanic material. These were first
used as a cementing meter ial at pczzuoli, Italy, Puzzolan (pro-
nounced pot-S'.vo-lan) cements v;ere widely used in the days of
the Roman Empire. A fe-.v of the structures made at that time are
still in a fair state of preservation. This class of cements in-
clude all hydraulic cementing materials ^/hich are made by the
incorporation of natural or artificial puzzolans v;ith hydrated
lime without subsequent calcination. The only natural puzzolan
materials of importance are puzzuolana, trass, and tuff or tufa.
Blast furnace sla^, ie an artificial puzzolan materiel. PC not con-
fuse the so-called slag ceuent with the true portland cement made
•with blast furnace slag. The tufa cement used in the construction
of the Los Angeles aqueduct was neither a true pert land nor c true
puzzolan cement. It was a blended ce:ient as described in Article
572.

These blended, improved, or puzzol&n cements are never
brought into competition ^ith portland cement where ^reat strength
is required.

Alumina cements^:- Alumina cements are not discussed in the text
probably because they have nexer been made on a commercial scale
in this country. In France, where they were produced first, they
are only now coming into .general use.

Alumina cements differ from portlend cements in che.racil
composition and the rate of hardening. Both mortars and concretes

Civil Engr-3. Assiemmeut 10. Page 11.

develop greater strength within 48 hours (and in most instances
within 24 hours) than corresponding mixtures made with portland
cement develop in 28 days. Furthermore, alumina cements have
great resistance to the action of sea water and alkali -"bear ing
•waters.

Investigations on these cements were begun about 1902 by
H.S. Spackman and E. W. Laze 11 in the United States. In France,
J. Bied began his studies on this material in 1908* Recently
P. H- Bates of the United States Bureau of Standards has reported
on his study of alumina cements. In 1912 the firm of J. and A.
Pavin Lafarge marketed alumina cement under the name of CE&ENT
FONDU. It was manufactured for military use, only during the war,
but in 1919 its commercial use was resumed.

The approximate composition of alumina cement is 50$ lime,
4C$ alumina and IQf* silica and impurities. It is sometimes referred
to as a mono-calcic aluminate. It is low in lime and silica, and
high in alumina as compared with normal portland cement. In
France it is made in small blast furnaces which are charged with
coke, limestone and bauxite. The fused slag or clinker is cooled
and ground. If the bauxite is pure the cement is white in color
but the commercial cements are dancer than Portlands because of the
impurities in the raw materials. Since actual fusion is not
necessary this cement could be made with the same machinery used
in the manufacture of portland cement. The cost of manufacture of
the cements would be about the same but the actual cost of alumina
cement is dependent upon the cost of bauxite which at present would

Civil Engr-8. Assignment 10. page 12.

bring it over that of ordinary port land cement.

Alumina cements are slow setting and are gaged like the
ordinary port land cement, heports on the French cements give, for
a 1:1:3 gravel concrete, compressive strengths of

7,500 Ib. per sq. in. at 3 days
8,500 lo. per sq. in. at 28 days
9,000 Ib. per sq. in. at 3 months

Other reports sta^e that a 1 to 3 sand mortar developed 75% of its
own 28-day strength in 24 hours. During the war heavy guns were
moved on alumina-cement -concrete foundations 24 hours after they
had been poured.

Civil Engr-8. Questions to Assignment 10. page 13.

1. How does a change in moisture content of hardened cement mortar
effect its volume?

2. Give the approximate tensile and compressive strengths of
neat cement mortar.

3. Name the various factors that affect the strength of cement
mortars.

4. Does the long haul of wet concrete, made necessary by the use
of central mixing plants, affect the strength of the hardened
concrete?

5. What is the principal precaution to be taken when storing
cement ?

6. Would you allo?/ the use of cement that had been stored on the
job - say for 18 months?

7. Under what conditions would you allow the use of so-called
reclaimed cement?

8. How does the fineness of the cement affect the time of set and
what is the importance of time of set?

9. What is the relation between the strength of concrete and the
fineness of the cement used?

10. Differentiate between slag cement and portland cement made from
blast furnace slag.

11. Will natural cement set under water?

UNIVERSITY OF CAL IF CRN IA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction

Assignment 11.

Civil Engr-8. A. Professor C-T. Wiskocil

LIMB

Introduction:- Line, as used in the preparation of mortar, was
one of the building materials used by the early Greeks and Romans.
Probably the earliest known use of line-mortar was in the con-
struction of the Egyptian pyramids. During the recent war the manu-
facture of lime was declared to be an essential industry, not be-
oause of its use in building construction - although large quanti-
ties were used in the construction of buildings by the United States
Housing Corporation - but on account of its importance as a chemical
reagent in the manufacture of guncotton, leather and other essential
products .

Definition and classification:- Lime is the product obtained by
heating limestone so as to drive off the carbon dioxide. It is,
therefore, a calcium oxide. Study Article 379; it contains a more
detailed definition and a partial classification of lime. There
are two general grades of lime; selected and run-of-kiln, both of
which are described in the article noted. Lime is frequently sold
as lump lime, in -which the size of the individual pieces is left
as they come. from the \kiln, '.and pov.'dered lime, which is oroken up
so that it will all pass a 1/4 inch screen. The classification
adopted by the American Society for Testing Materials is referred

Civil Engr-3- Assignment 11. Page 2.

to in Article 379; it is as follows: high calcium lime, not less
than 90^ calciur oxide; calcium lime, not less than 85 or more
than 9C/o calcium oxide; magnesian lime, not less than 10 nor more
than 25$, magnesium oxide; and high magnesian lime, not less than
25$ magnesium oxide. If these limes contain less than 5f0 of
silica, alumina, and iron oxide, which are known as impurities,
they are called rich or fat limes. Limes containing more than 5$
of these impurities (noted adovej are known as poor or lean limes.
Sometimes lime is classified according to the purpose for which it
is best fitted, as agricultural, building, finishing, or chemical
lime.
Manufacture ;~ Study Article 380 and read Article 381. While lime-

- -
stone has been described before, rege&p some of the important facts

about it ::.since it is the raw material from which lime is made.
Since limestone is of sedimentary origin it is never found pure. It
is essentially calcium carbonate with impurities of magnesia, iron,
alumina, and silica. Very pure cyrstallized limestone ie called
calcite. when the amount of magnesia increases it is called
magnesian limestone until the ratio of calcium to magnesium caroon-
ate becomes 100 to 84; it is then called dolomite. When magnesia
remains low but impurities increase, the rock may tie an argillaceous
limestone, natural cement rocic, or calcareous shale.

There are three principal types of kilns for burning lime;
the pot kiln, the patent kiln and the rotary kiln. The mixed-feed
type described in the text is the pot kiln. The separate-feed type

Civil Eiigr-8. Assignment 11. Page 3-

is the patent kiln, and is the best type.

As indicated in Article 37S the reaction produced in the
heating cf limestone is essentially

CaCG, -r heat — «* QaO -t- CO,,
w 2

The carbon dioxide is driven off as a gas which leaves the lime as
a mixture of oxides. The amount of heat required depends upon the
chemical composition of the stone. Under ordinary conditions cal-
cium carbonate breaks ur at 898 °C (1648° F- ) When the temperature
reaches about 219G°F, the calcium oxide and the impurities in the
stone combine to form compounds that produce partial vitrification
and retard the slaking of the lime. The required amount of heat
may be supplied quickly at a high temperature or over a longer
period at a lower temperature. Since the activity of the impuri-
ties becomes noticeaule belovv 21GO°F- , better quality is secured
at lower temperatures of ourning. Wood-burned lime, oecause of
the lower temperature of burning, usually commands a higher price
than coal-burned lime. The introduction of steam into the kiln
during the burning process tends to increase the quality of the
lime by decreasing the temperature of decomposition from 1648°F
to aoout 1450°F.

Slaking or hydration of lime;- Study Article 382. Quicklime is
prepared for use in building construction by slaking *hich is the
addition of water to form a paste. Slaking is a process of hydra-
tion, in which the calcium oxide combines with -water to form the
hydroxide.

•

Civil Fugr-8. Assignment 11.

CaO T h20 — 9- Ca (QHJg

Slaking is usually done in a shallow watertight box. The water is
poured over the lime. Hiah calcium lime must de stirred continu-
ously to prevent the heat generated from ourning the lime. The
•water absorbs the excess heat. Too much water lowers the tempera-
ture and retards the slaking, impairing the plasticity of the
product. The addition of too much v;ater is known as drowning. A
high-caiciuir. lime is subject to burning, while the slaking of a
high-magnesian lime must be watched to prevent drowning. A skilled
operator is required to slake quicklime properly. Both underburned
and over burned lime will slake more slowly than that which is prop-
erly burned. The rate of hydration (slakingj indicates the burning
temperature. Slaked lime, which is a thick paste, is sometimes
called lime-putty. It will keep indefinitely if it prevented from
drying out. It is stored in casKs or in the boxes in which it is
made. It w5.11 not harden under water.

Setting and hardening:- The setting is caused by the evapora-
tion of excess water from the lime paste. Hardening is a chemical
action involving the replacement of the water in the hydroxide by
car con dioxide, with the result that the lime paste reverts to the
calcium carbonate. Hardening is accelerated by increasing the
amount of carbon dioxide in the air and by the use of moist air.
The first condition is produced by the use of salamanders and the
second by the frequent wetting of mortar. These methods are used
in hardening interior plastering

Civil Engr-8. Assignment 11. Page 5.

Properties of lime:- Study Article 385. In general, lime is a
white substance which v.rill slake when water is' added to it. Dur-
ing the slaking process the "w^ter enters into chemical combination
r?ith the lime with a resulting, generation of heat and increase in
•volume. When exposed to air, slaked lime will set and harden.
The carbon dioxide from the air combines with the lime and forms
the carbonate. Setting is always accompanied by a decrease in
volume.

Lime when exposed to air will air-slake as described in
Article 382. This term air-slaked lime is rather confusing, be-
cause the substance is practically identical with finely ground
limestone and therefore has no value as lime for structural pur-
poses.

The strength of lime mortar depends principally upon the
method by which it is prepared and the kind of sand used. Mortar
made with dolomitic lime is generally stronger than that made with
high-calcium lime. This may be due to the fact that the greater
shrinkage in high-calcium lime mortars may tend to weaken the oond...
Moreover, magnesian mortars are made up with less water so that
they contain more actual binding material; and again, since high-
calcium limes will carry more sand they are frequently overloaded;
that is, the proportion of lime paste to sand is relatively large
and hence the resulting mortar is weak.

Lime mortar is never used where strength is required. The
choice between limes should be made not on the basis of strength
but rather on relative cost and previous experience.

Civ;.I Fingr-8.

Lor tar joints ir. iTK-,soury are seldom over 1/2 inch thick. The
actual resistance to c oppressive loads is therefore greater than
indicated in the tables such as the one given on page 364.
Commercial forms:- Lime is put on the market in two forms, lump
and ground. Lump lime is shipped in DulK and in wooden barrels of
180 or 280 Ib. net capacity. Ground lime is screened through a
60 mesh sieve and shipped in air-tight casks.
Hydrated lime :- Study Article 333- Ordinary quicklime is
treated at the mills, with only enough water to slake it completely.
Hydrated lime is a fine powder consisting of calcium hydrate and
magnesium oxide. Lechanical hydrators are used and the product is
under strict control. The tensile and compressive strengths of
hydrated lime mortars are higher than those of the corresponding
quicklime mortars, Hydrated lime mortars, besides having greater
strength, set more quickly and shrink less than ordinary quicklime
mortars, but the latter excel in plasticity, sand-carrying capacity,
and yield.

The consumer must pay freight on a considerable amount of
water when he bays hydrated lime, out in its use the danger of burn-
ing or drowning and the time and laoor required in the slaking of
quicklime are eliminated.

The principal use of hydrated lime as a structural material
is in portlarid cement mortars and concretes.
Testing of limes:- Read Article 384.

Uses of lime:- Read Article §86* Besides the uses mentioned in
this article lime is used for the manufacture of sand-lime brick,

Civil Bnfer-8. ^ssigruusnt 11. .Fags 7.

and of glass, paints and pf.per. It is also used as c. fertiliser
and in the tanning of leather-

Hydraulic liiue and grappier cement:- Read Articles 387 and 388.

liyoraulic line was used for structural purposes before the superior
natural and port land cements were introduced. Its use at the
present ti;Tie is limited.

The raw material is a siliceous or argillaceous limestone.
The ideal stone is one that has sufficient free lime remaining after
calcination to disintegrate the clinker by its disruptive action
•when slaked. During calcination the silica combines with the lime
to form lime silicate which gives the product its hydraulic proper-
ties. The slaking of hydraulic lime, as in the case of hydrated
line, is done by the producer. The lumps that are not disintegrated
during the slaking process do not contain a sufficient amount of
lime or they are under-burned. These lumps have been called grappiers
When they contain sufficient lime silicate they are finely ground
and marketed as grappier cement. Lafarge cement, noted in Article
388, is a grappier cement.

The properties of hydraulic lime are very low in value, when
compared to those of port land cement.

GYPSUM

Introduction:- Read Article 389- Wall plasters and plaster of
Paris, as noted in this article, are made of gypsum. It is also
used in the manufacture of precast structural products and struc-
tural members cast in place. Gypsum is added to portland cement
to retard its set, a ad raw gypsum, which is known as land-plaster,

Civil En§i--8. Assignment 11. Page 8.

is used as a fertilizer.

Occurrence:- Read Article 320. Gypsum is a common mineral; its

iiios-c distinguishing characteristic is its extreme softness. The

pure material consists of approximately 32.6$ lime, 46.5^ SO* a^d

20.9$ water. It is a neutral substance; that is, it is neither

acio nor as. sic.

Calcined gypsum;- Read Article 392. Calcined gypsum is known

by many name 3, some of which are derived from the purpose for which

it is used, as dental plaster, molding plaster, casting plaster

and potter's plaster. These materials are all calcined gypsum and

differ only in the tirae of set, which has been regulated. The most

common name for calcined gypsum is plaster of Paris.

Calcined gypsum is produced by heating finely ground raw
gypsum. The product is made in kettles which hold from 2 to 20
tons. During the heating process the gypsum is continuously
stirred oy a power -driven paddle. The water held in chemical com-
bination is driven off as steam which fluffs up the whole mass and
makes it appear to boil. It settles down to its normal volume
when the boiling action ceases; this usually te.Kes about an hour
for a kettle full of material. The exact time depends upon the
charge and the temperature. The product is calcined gypsum but
to the operator it is known as first-settle stucco. It is partially
dehydrated gyps am, with chemical formula usually written CaS04* 1/2
HgO Calcined gypsum, when mixed with water, sets and hardens

rapidly to form a material identical with the original gypsum

Civil Er.£i'-8. Astsi^iiirsnt 11. Page 9.

. The setting of n.c?rae.l calcined gypsura occurs in from 5
to 10 minutes. When used for dental purposes the time of set is
accelerated but when used as a wall plaster the time of set is
retarded. Some wall plasters are regulated so as to set in about
20 minutes while in others the set is retarded to aoout six hours.

Set gypsum, when the normal calcined gypsuia is used, has an
approximate eompressive strength of 1,500 Ib. per sq. in. and a
tensile strength of 400 Is. per sq. in. bince moisture in the
specimen decreases its strength, the maximum value can be develop-
ed . only when the material is dry. The amount of mixing water has
a dec iced effect on the strength of set gypsum. For maximum
strength the least possible amount of mixing water should be used.
Gypsum wall plaster:- Read Article 393- It has been estimated
that three-quarters of the gypsum mined is made into wall plaster.,
Calcined gypsum is the simplest wall plaster. It is not used pure
but is added to lime paste.

Calcined gypsum is not plastic and therefore is difficult
to spread with a trowel. It has become the practice to add aoout
fifteen percent of clay or rvydrated lime to it at the mill. A
retarder is added to the material so that it will set in from one
to six hours. This product is known as hard -wall plaster on the
eastern market, but in the west, the same material is called
cement plaster.

The principal disadvantage of calcined gypsum when used pure
is its lack of plasticity. By proper methods of manufacture, which

Civil Er.gr -8. Assignment 11. page 10.

are explained in an article, PLASTIC GYPSUJa &ADE POSSIBLE BY A
NEW METHOD, by w.E. Emley, Engineering News-Refcord 86, 1U23, June
3.6, 19P1, it can be mace as plastic as lime. Fine grinding of
ctlcined gypsum liberates the water of crystallization just as heat-
ing does. If the escape of the water is prevented, so that the
finely ground gypsum contains the water of crystallization, it
produces not only a more plastic and slower setting material but
also a stronger one. If the water of crystallization is allowed
to escape during the grinding process the product will be the
soluble anhydrite which rapidly reabsorbs water from the air and
reverts to the calcined gypsum. There is no advantage in fine
grinding under such conditions. The new plastic -gypsum is very
stable; it has been exposed to air for four months without
apparent detriment to its plasticity.

Second -settle calcined gypsum:- If calcined gypsum is properly
heated it will appear to boil and subside just as the raw gypsum
did when it was heated. During the second uoiling all the water
held in chemical combination is driven off so that CaSO^ remains;
this is anhydrous calcium sulphate. To distinguish between this
product and the natural anhydrite which has the same formula but
very different physical properties, the former is called soluble
anhydrite. The mineral anhydrite is quite inactive. It is
weeks before it combines with water to form set gypsum. The sol-
uble anhydrite sets more rapidly than the calcined gypsum and
makes a harder and stronger set gypsum. The soluble anhydrite is
not stable - it readily absorbs water from the air to form the

Civil Engr-8. Assignment 11. Page 11.

calcined gypsum; but because of its greater strength it is used
at the mill to make precast products. The material cannot be
shipped or stored.

Hard finish plasters:- Read Article 394. Calcined gypsum is chang-
ed to the soluble anhydrite at aoout 500 degrees Fahrenheit. The
latter material is converted into the natural or mineral anhydrite
by prolonged heating or higher temperatures. In spite of its slow
set, the natural anhydrite is used in Europe as a floor surface.

Keene's cement is described in the text on page 369. It
sets more slowly than calcined gypsum and makes a harder surface.
Gypsum building products:- Read Article 395. One variety of
gypsum tile, which is generally used for partitions, is made at the
mill with calcined gypsum to which aoout b% of wood fiber has been
added. This variety is made cellular like the clay partition blocks
shown on page 2S3. The usual dimensions are 12 by 30 inches with
thicknesses varying from 2 to 8 inches.

Roofing tile must be stronger than partition tile. They are,
therefore, made of second-settle calcined gypsum and are frequently
reinforced with steel rods and v; ire -mesh. Standard roof coverings
are used to protect gypsum tile from the weather. Kiln-dried
gypsum products, like roofing tile, gain their full strength within
a few hours.

Gypsum plaster board is made in laminations - a thin layer
of calcined gypsum between layers of paper. It is used as sheet-
lath as a base for plaster. The gypsum usually contains a wood-
fiber to decrease its brittleness. Gypsum wall board is

Civil En^r-8, Assignment 11. Page 12.

similar to the plaster "board. In the case of the latter, however,
plaster is apoiieo to the surface wnile the wall "board has a
sraoc-h surface and is not plastered, tut forms the finished wall.
Saeetrock is the trace name for a gypsum -flail- board now bsing
widely advertised.

otractural members such as roofs can be poured into place
just as in cemenc-corcrete construction. On page 4 of the ad-
vertising, section of the March 23, 1922 issue of the Engineering
News-Record, is an illustration in which the roof of the National
Tube Company's pirnc, at Lorain, Ohio, is being poured with gypsum.
Structural gy?sun gains strength rapidly; the forms are taken off
the day after the gypsum has been poured. The compressive strength
is affected by several variable factors, the principal ones being
the amount of mixing water used and the amount of aggregate -
send or wood-fiber. Prolonged moisture reduces the strength of
structural gypsum. An average value of the compressive strength
is 1,500 lb. per sq. in. It weighs about 80 lb. per cu. ft. and
has a modulus of elasticity of about 1,000,000 Ic. per sq. in.
Magnesia cement;- This material is not discussed in the text.
It is made by mixing magnesium oxide v;ith a solution of magnesium
chloride. Various aggregates such as, sand, sawdust and asbestos,
are added to the cement. It is sometimes called Sorel cement,
after its inventor, Stanislaus Sorei, and also megnesium oxychlor-
ide cement. It is used principally as an interior \vall finish and
as flooring. In the East it is nov; being used as an exterior wall
surface.

Civil Engr-8. Assignment 11. Page 13.

The magnesium oxide is prepared by calcining and grinding
inagr.es it e (^~00,). There are large deposits of magnesite on the
Pacific Coast. The more important deposits which are being worked
are in Greece, ItP.ly, and Austria.

The methods of manufacture and the properties of magnesia
cenents are being studied by the U.S. Bureau of Mines and the Dow
Chemical Company, who operate a well equipped magnesium-oxychlor-
ide research laboratory.

The following notes were taken from reports by the Dow
Chemical Company.

The stancarc stucco mix is 1 part calcined magnesite to 2
parts Silex (powdered silica) to 5 parts graded silica sand mixed
with 22 degree Eaunie magnesium chloride. The strength of this
material varies (from various test results) from 200 to 1000 Ib.
per sq. in. at 30 days. When placed on the wall its average ten-
sile strength is about 500 Ib. per sq. in. Its compressive
strength is about 5 1/2 times its tensile strength. Its modulus
of elasticity is approximately 3,000,000 Ib. per sq. in.

Standard flooring mix is 5 parts calcined magnesite, 3 parts
Silex, 1 part ground talc, 1 part fiber (wood or asoestosj and one
part color pigment, all mixed with 22? Baume magnesium chloride.
For heavy duty the following mixture is used: 12 1/2% calcined
magnesite., 35^ Silex, 62 1/2^, pure silica sand. This is also mix-
ed with 22 degree Baume magnesium chloride, kagnesite makes a
sanitary, resilient floor which has a good appearance and excellent

Civil Engr-3. ^ssigni^snt 11. Page 14.

•wee.riiig qualities. It is fre<= fron, the splintering action of wood
floors and ir not suoject to dusting or sanding. By actual test
it v.as found to oe more durable than linoleum.

Most of the early literature on the suoject states that
cxychlcride cements are disintegrated by continuous wetting or
i;amer;=ion in water. &t the present time lit is oelieved that the
degree of burning affects the water resisting properties. Since
oxychloride cements are usec for exterior stucco it is evident
that -vhe.n properly designed and applied they are water resistant.
Commercial magnesium cements can be secured which make a stucco
that is practically water resistant.

Ci'.'il Engr-S. Assignment 11. page 15.

QUESTIONS

1. What is slaked lime?

2. Vifiiat precautions must be ta&en in slaking lime?

3. Can lime mortar be used uncler water?

4. What is doloinitic lime?

5> HOV? is .lydrated lime made?

6. Outline the manufacture of calcined g,ypsum«

7. What are the general uses of gypsum as a structural material?
What factors affect the strength of gypsum?

9. How does plastic -gypsum d lifer from ordinary calcined gypsum?

10, irVhat is magneaiua-oxychlorid* cement? Whet is it used for?

UNIVERSITY OF CALIFORNIA EXILNSION DIVISION

Correspondence Courses
Materials of Engineering Construction

Assignment 12.
Civil Engr-gA Professor C-T- Wiskocil

TESTING OF HYDRAULIC CEL-£NTS

Necessity for testing cenent:- Read carefully that part of Article
396 which is given on page 371, and then Article 443. The third para-
graph on page 371 is v-sry important - study it. The physical tests
are the most important and are made for the purpose of comparing
the given cement with a standard -which has been adopted after long
experience. The results of laooratorj tests do not represent the
properties of the material under v/ or king conditions but they are of
relative value when compared -.vrth test results of cements that have
been found satisfactory in practice.

Standard ^specifications ior portland cement:- Read the remainder
of Article 396. Study the perts narked II and V, because they are
important. Be acle to name the various tests and give the standard
requirements. These specifications are used throughout the United
States. The United States Government specifications are substanti-
ally the same.

STANDARD TESTS

Samp 1 ing : - Read Articles 397 to 401 inclusive. The important
thing to be remembered in selecting a sample of cement is that it
should be fairly representative. This is -well emphasized in the
text, together vith the importance of proper storage and mixing.

Civil Engr-8. Assignment 12.. Page 2.

in the quartering process described in Article 401, it is the usual

re\®Or

practice to^dibie&aid opposite quarters of the pile and combine the
remaining quarters which are again mixed and divided into quarters.
The process is repeated until the amount remaining gives the size
of the sample desired.

Chemical analysis:- Read Articles 402 and 407. Since the chemi-
cal tests are relatively unimportant, omit Article 403 to 406
inclusive.

Specific Gravity:-. Read Articles 408 and 448. This test is not
very significant. For that reason, as indicated in the specifi-
cations on pags 372, it is made only when specifically called for.
Adulterants such as, Slag, limestone, and natural cement could be
present in quite appreciable amounts before the specific gravity
would be noticably affected. The specific gravity test does,
however, indicate the degree of seasoning. Cement clinker and
ground cement both absorb water and carbon dioxide from the air,
causing the specific gravity to decrease. The loss due to season-
ing is regained upon ignition of the sample.

Low specific gravity may be the result of adulteration.
It is also indicative of the degree of seasoning. Since seasoning
is desirable in portlar.d cements a value below 3.10 for the spe-
cific gravity should not be cause for rejection without some ,*• f
definite reason based on the history of the cement in question.
Fineness:- Read Articles 409 to 412 inclusive, and Article 447.
The paragraphs nar::ed 34, 35, and 36, in Article 409, are the most

Civil Engr-8 Assignment 12. Page 3

important. The standard method^ of hand sieving is given preference
over mechanical methods^ Since the eand carrying capacity and
comprcssive strength of mortar and concrete are increased by fine
grinding it is desirable for the manufacturer to obtain the
maximum degree of fineness compatible with reasonaole manufactur-
ing costs. Fine grinding decreases the time of set.

Fine cements itfill leave a residue of about 2f0 on a No. 200
sieve while those of average fineness leave from 10 to 15^.

Article 412 is relatively unimportant. The air analyser
developed by the united States Bureau of Standards, mentioned on
page 381, has proved to &e ver^ {satisfactory in separating into
smaller sizes cement which passes the No. 200 sieve.
Liixing oi cement paste and normal consistency:- Read Articles413
to 418 inclusive The making of cement paste and mortar is of
importance in the laboratory in which test specimens are prepared.
Tbe cement paste is useo in the determination of soundness and
the time of set. Cement mortar is made into briquettes for the
tension test. In order to ootain results comparable to those
jiven in the text the cement paste and mortar snould be made in
strict accordance with the directions in the text. In a general
course in iiA-IER LaLS these directions are relatively unimportant.

The plasticity or consistency, as it is called in the text,
affects the strength and also the time of set. It is necessary,
therefore, to have cements tested ur.cer tie same conditions ae
those under which the stancarc tests were made* This is ac-
complished by having the cement paste of a given plasticity as

Civil Engr-8. Assignment 12. Page 4.

determined in a specified manner with the Vicat apparatus illus-
trated on page 383. This determination is of importance only in
the laboratory. A cement paste is of normal consistency when the
rod of the Vicat apparatus, which weighs 300 g. and is 1 cm. in
diameter, sinks 10 ens. into the paste in 1/2 minute after being
released. This method is very satisfactory - but only for neat
mixtures. The amount of water to be used for sand mixtures, in
the standard tension tests is given in the table on the top of page
384. Articles 417 and 418 are not important.

Soundness:- Read Articles 419 to 424 inclusive and Article 444.
Soundness is the most essential property of cement. The ability of
a cement to develop a high degree of strength is of no value if it
is not able to withstand the disintegrating effects of the atmosphere
•when it is finally placed in the structure, tyhile the conditions
in this test are more severe than those to which the cement will be
subjected when it is put in use, the results are, nevertheless,
quite satisfactory in indicating the durability of a given cement.
The illustrations on page 386 show par^s that have failed to pass
the soundness test. Articles 421, 422, and 423 are not important.
Time of setting;- Read Articles 425 to 427 inclusve and
Article 446. The rapidity with which a cement sets is a criterion
of its adaptibility under given conditions of use. In some types
of construction it might be desirable to have a cement which would
set quickly. In other circumstances, where it is impossible to
place the concrete without delay, it is necessary to have a slower

Civil Engr-8. Assignment 12. Page 6.

setting cement. The influence of the temperature and the amount
of mixing water used ere explained on pages 327 and 328 in the
text. The tables are given in a previous assignment but it is
desirable to review the general affect of these variables at this
time. Paragraphs marked 48 and 50 in Article 425 are the most
important.

Tension test:- Read Articles 428 to 439 inclusive, and Article
445. The standard tension test is made on briquettes of sand
mortar. The proportions of the mortar are, one part cement to
three parts standard sand, mixed with the amount of water deter-
mined by the normal consistency test, according to the table on
page 384. A special sand, described in the paragraph marked 52
on page 391, is used.

Study Articles 429 and 431. The latter article explains
that the stress across a briquette under test is not uniform.
This non-uniformity of stress in a test specimen is an undesir-
able feature in a tension test. Since the modulus of elasticity
of mortar varies with age, the temsion tests at various ages do :.
not give a true indication of the variation .in. the average
tensile strength of the material. This is not important in the
standard tests here described but it is important in research
problems. In such work the compression test on cylindrical
specimens is more generally used.

Articles 432, 433 and 434 ere not important. •
Storage of test specimens :- Test specimens are stored in
a moist closet, as described in Article 441, for 24 hours. Alter

Civil Engr-8. Assignment 12. Page 7.

that they are removed from the molds and immersed in water. As
stated in Article 440, it is important that the temperature of the
air in the moist closet and the temperature of the water, in which
test specimens are stored, should be as nearly 70 degrees Fahren-
heit as possible.

Miscellaneous methods of testing cements :~ Read Articles 449 to
453 inclusive. All of these tests are unimportant. In most re-
search problems it is frequently necessary to devise new methods
of testing, and special apparatus.

Civil Engr-8. Assignment 12.

QUESTIONS

1. Name the standard physical tests for portland cement.

2. Give the standard requirements for the tests given in (1).

3. What is the relative importance of the tests given in (1)?

4. What constitutes grounds for rejection of a biven cement?

5. Explain the quartering process as applied to the sampling
of cement.

6. HOW is unsoundness of cement usually manifested?

7. What is meant by the tsrm"normal consistency of cement'*?

8. Why is it necessary to determine the normal consistency?

9. What are the two methods used to determine the t,ime of
setting?

10. What are the reasons for the tension test of cement?

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Coi respondence Courses
Materials of Engineer ing Construction

Assignment 13.

Civil 3ngr-8A. Professor C-T- Wiskocil

C ONC9ETE AgGKES ATE S

Int rod action:- Study Article 454; it is important. There is a
growing tendency among engineers to specify the consistency and
strength requirements for concrete on various portions of a job,
and to give the contractor an opportunity to furnish concrete of
required strength according, to his own methods.

DEFINITIONS

Study Articles 4£5 to 464 inclusive. All the terras used
in the discussion of mortar and concrete are defined and it is
necessary trat they "be thoroughly understood.

Mortar :- As defined in Article 455, mortar is essentially a mix-
ture of fine aggregate, which is usually sand, cement and water.
Concrete:- Concrete is defined in Article 456. It consists of a
large bulk of inert materials in a finely divided state, bound to-
gether "by a comparatively small amount of cement. The amount of
water used in mix.ing the ingredients is of great importance. Con-
crete is frequently named according to the kind of aggregate used,
as crushed-stone concrete, gravel concrete, cinder concrete and
rubble or cyclopsan concrete.

Cement:- Cement has been previously defined. In this text only
Portland cement concrete is discussed. Bituminous concrete is
used principally for the surfacing of roads and highways.

Civil Engr-8. Assignment 13. Fage 2.

Aggregate:- As stated in Article 453 aggregates are divided by
the 1/4 inch screen. TLhose that pass, are classed as fine
aggregates and those that are retained are called coarse aggre-
gates. Sand is tLe principal fine aggregate, while crushed stone
and gravel are the predominating coarse aggregates.
Silt:- See Article 459. Silt is usually considered as the fine
material which passes a No. 200 sieve. In rich mixtures silt is
an undesirable ingredient and is classed as an impurity. A cer-
tain amount of silt, however, will benefit or improve the strength
of lean mixtures.

Specific Weight :- This term is defined in Article 460. It is
the weight in pounds of a definite volume, usually specified as
one cubic foot. Since there are no standardized methods for its
determination it is necessary to state the conditions under '-vhich
it is determined. The moisture content as shown in Figure 5 on
page 418 is an important factor in the case of fine aggregates.
For coarse aggregates the shape and size of the measuring oox
affects the specific -wei^iTt. The method of filling the measure or
of compacting the aggregates into it are important for both fine
and coarse aggregates.

Voids:- Voids as described in Article 461 are the spaces between
the particles of aggregate. The vcid space is alv.-ays expressed
as a percentage. The two methods of determining the void space
in an aggregate are described in this article. There is a direct
relation between the specific weight and the percentage voids.

Civil Fn^-r-3 Assignment 13. page 3.

method of determining the percentage voids the first term in the
numerator gives the weight of a cuoic foot of solid material, the
second term gives the actual weight of a cuoic foot of the aggre-
gate; the difference is, therefore, the amount of void space,
which, wnen divided by the first term, gives the percentage void
spaces.

Mechanical analysis-.- The first paragraph in Article 462 and
the second paragraph on page 411, which describes the method of
making a mechanical analysis, are the most important. All scien1-
tific methods of Delecting and proportioning aggregates are based
on mechanical or sieve analyses. The amounts passing or retained
on each sieve in the series are expressed in percentage and usually
put in the form of a diagram similar to that on page 417.
Yield;- The customary method of determing yield is described in
Article 463. The minimum yield obtained by varying the proportions
of given aggregates, but keeping the proportion of cement to total
aggregate cor.ste.nt, is used as a means of proportioning concrete
aggregates. This method will be discussed in the next assignment.
See page 429. Yield is frequently determined in investigations on
concrete. It is taker, as the ratio of the volume of concrete t2
produced by a given volume of mixed aggregates. The volume of the
concrete is measured when the specimens are removed from the molds.
For 1 to 6 concrete the yield is usually about unity (1.0) but
for rich mixtures, one part cement to two parts sand, it may in-
crease to 1.3. For lean mixtures, such as 1 to 9, it may be con-
sidered as being unity. Additions of hydrated lime cause an in-

Civil Enbr-8. Assignment 13. • page 4.

crease in the yield of the us^al concrete mixtures.
Density: As defined in Article 464, density is the ratio of
total solid material in the concrete to its volume. The volume of
the concrete is determined after it has hardened. It is one minus
the void space -when the latter is expressed as a ratio of voids to
total volume. The density of 1 to 5 mortars is about .71, while
for 1 to 5 concrete having aggregates up to 1 1/2 inch it may in-
crease to aoout .S3 Density is affected by the richness of the
mix anc the amount of water used in the mixing -

CH^RACriRISTICS AND PROPERTIES OF FINE AGGREGATE
Importance of good aggregate is emphasized in Article 465. The
last sentence in that article is important. What it says is this:
the best criterion for the suitability of a given aggregate for
concrete is actually to maKe some concrete with the aggregate and
test it. This means thai the value of a fine aggregate cannot be
determined by a mortar test.

Sampling aggregate:- Read Article 466. Considerable judgment is
required in securing a representative sample from a sand or gravel
deposit. Care is necessary in sampling material that is piled.
This is intimated in the last paragraph in the article.
Requirements for fine aggregate:- Study Article 467. The last
sentence in the article is particularly important. Note that the
sharpness of sand grains is not essential. At one time all specifi-
cations stated that the sand grains should be sharp. When it is
necessary to use an untried sand, which appears to have a satis-
factory grading and hard grains, its suitability can be quickly

Civil Engr-8. Assignment 3.3 Page 5.

estimated by the color test described at the bottom of page 4J.5.
The presence of organic matter which might prevent the setting of
the cement can be readily detected by this method. On important
r.'ork an untried sand should not be used.

Composition of particles;- Read Article 468, and study the last
paragraph, '.vhich gives a list of some of the objectionable minerals
in fine aggregates -

Impurities :- Ltudy Article 469. A sufficient number of tests
have been made tc substantiate the statements made in the first
paragraph regarding clay. From the discussion thus far it is
evident that strength tests on the finished concrete would prove
the suitability of given aggregates without tests for impurities.
Gradation of the sizes of the particles:- Study Article 470 and
the curves in the diagram on page ^17. Stone- screenings are gen-
erally not as desirable as sand for fine aggregate for concrete,
because they decrease the plasticity of the concrete, and if the
plasticity of the mixture is brought to the desired point with
water the strength of the concrete "will be decreased.
Voids and specific weight;- Study the first two paragraphs of
Article 471, and read the remainder of the article. Remember the
general tendency oi the curves in diagram 5. The voids in a satur-
ated sand my be equal tc or lo^er than those in the dry sand.
The moisture content must be known when the voids are determined.
The actual amount of fine sand, containing two to ten percent
moisture, in a cuoic foot of the material is much less than it

Civil Engr-8. Assignment 13. Page 6.

would be if the sand were dry or saturated.

Remember these average values for sand: Specific gravity,
2.65; voids, SOjfe; weight in Ib. per cu. ft., 11Q.

Mortar tests :- Study the second paragraph in Article 472 and read
the remainder of the article. In comparing mortars of given pro-
portions it is necessary to mix them so that they have the same
consistency. The consistency of sand mortars is not so easily de-
termined as that of neat cement paste. The Vicat apparatus is not
satisfactory and other methods must be resorted to; one of them is
outlined on page 420. Compressive tests on cylindrical specimens
are cmost. satisfactory. The molds for these specimens are 2 inches
in diameter and 4 inches long.

CHARACTERISTICS AND PROPERTIES OF COARSE AGGREGATE
Requirements for coarse aggregate :- Head Article 473. Roughly
cubical or rounded stones are preferable to those of other shapes.
The use of the different stones as concrete aggregate has been given
in a previous assignment.

Characteristics and properties of broken stone :- Read Article 474.
For unreinforced concrete the usual size of coarse aggregate varies
from 1/4 to 1 1/2 inches. The maximum size of particle is smaller
for reinforced concrete, usually being limited to that which will
pass through a 1 inch ring. If the amount of reinforcement is
large and closely spaced, as was the case in the concrete ships,
the maximum size of aggregate is_tstill smaller.

Table 2 on page 423 is interesting in that it shows the effect

Civil Engr-8. Assignment 13. page 7.

of jarring and vibration caused oy hauling, on the specific weight
of crushed stone. This increase may be expected in the case of any
course aggregate as was intimated under the discussion on specific
weight.

The diagram on the upper part of page 423 will be referred
to when proportioning is discussed in the following assignment.
Characteristics and properties of gravels ;- Read Article 475.
Gravel, when properly graded and otherwise satisfactory in regard
to absence of impurities and hardness of material, makes an ideal
coarse aggregate for concrete.

Broken stoae and gravel compared:- Study Article 476, Either class
of aggregate may "be perfectly satisfactory and neither can be said
to be entirely superior to the other.

Miscellaneous aggregates :- Read Article 477. During the develop-
ment of the concrete ship various light-weight aggregates, such as
crushed brick, slag, volcanic scoria and puarnice, were used. The
aggregate finally adopted was a specially burnt clay or shale which
was full of nonconnecting cells so that it made a strong aggregate
of light weight. It was crushed to two sizes, the coarse ranged
from 1/2 to 3/16 inches, and the fine passed a screen with 3/16
inch round openings. The concrete was rich, being made in the pro-
portions of 1 part cement to 2 parts total aggregate. In addition
a special fine -ground cement, 9Q% passing the No. 200 sieve, was
used. The concrete weighed about 118 Ib. per cu. ft instead of the
usual 150 Ib. per cu. ft. of ordinary concrete. Its strength was
from 3,500 to 5,000 Ib. per sq. in. in 28 days. It was necessary

Civil Eagr-8. Assignment 13. Page 8.

to make the concrete rich in cement because, in order to pour it
in thin sections with heavy reinforcement it had to be very wet. A
sl^mp of 9 inches was specified.

The artificial aggregate was essentially a bloated brick.
It ras '.nade of basic clay or shale which when subjected to a tem-
perature of aoout 2,000 degrees becomes plastic and sears over on
the surface. The coating which is formed retains the gases gener-
ated by the decomposition of the contained chemicals. This expand-
ing gas blows the cla^ full of cells and bloats it to several times
its original volume.

Civil Engr-8. Assignment 13. Page 9.

QUESTIONS

1. What is concrete?

2. Dsfine density as applied to concrete.

?. How is the void space in concrete aggregates determined?

4. What is the relation between the voids and the density of

concrete V

5. What is the value of the mortar test in determining the suit-
ability of a given se.nd as a fine aggregate for concrete?

6. What is the use of the so-calied color test?

7. How 7;ould the proportions of a mortar be affected if a damp
sand, say one having aoout 6% moisture, and the cement were
proportioned by volume?

8. What are the principal requirements for a coarse aggregate for
concrete?

9» Compare the merits of gravel and broken stone aggregates.

10. Name some aggregates other than stone and gravel that are used
in the making of concrete.

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Civil Engr-8-A- Professor C-T. Wiskoci 1

Assignment 14.
PROPORTIONING OF CONCRETE

The principles of proportioning:- Study Article 478. The
statements made in this article are a summary of the discussion of
strength and permeability of concrete which will be taken up in
assignments 16 and 17.

Proportioning concrete is a subject which involves the
question of relative costs as affected .by the selection and com-
bination of aggregates.' When different materials which have differ-
ent characteristics are available, the proportioning involves the
selection of those which are best suited for the purpose. After the
aggregates of proper size and grading have been selected it is
necessary to decide upon the proportions, or the ratio of cement to
total aggregates, so that concrete of proper strength may be made.
The consistency, as affected by the quantity of mixing water used,
must also be considered. Frequently the concrete must T*be very
plastic so that it can be poured into the molds. If high strength
is an additional requirement the concrete must contain more cement
than would be required to produce the same strength if drier con-
crete could be used. Proportioning of concrete must take into
account all of these factors.

The first methods of proportioning concrete were based on
the theory that the maximum strength and impervious ness were secured

:M...:, & •;.,' JLilSt

-. <-i ••

Civil Engr-3. Assignment 14. page 2.

Tchei, the concrete v;as of ma::imum density. According to these
methods there *.vere : arbitrary proportions, proportions based on
roics, proportions based on minimum yield, and proportions based
on mechanical analysis. The more recent methods, one based on
surface areas of materials and the other based on fineness modulus
ana -water ratio, do not use the maximum density criterion. These
ruethods tvill now be explained in detail.

The measurement of proportions : Read Article 47S. The
tendency at the present time is toward greater accuracy in the
measurement of concrete aggregates. The vheel barrow is the measur-
ing device in general use but automatic measuring scales are on
the market. Tnese devices can be economically used only on large
jobs. In the laboratory the materials are proportioned by weight,
unless otherwise specified.

Arbitrarily selected proportions ;- Study Article 480. Con-
crete proportions are usually stated by volume. A 1:2:4 mixture,
one part cement to two parts fine aggregate to four parts of coarse
aggregate, is standard. In this method it is assumed that there
are generally about 50^ voids in the coarse aggregates. The amount
of fine aggregate (sand) specified is, therefore, one half the
volume of the coarse aggregate even though the cement and water
used v;ill bring the resultant mortar to more than 50^ of the vol-
ume cf the coarse aggregate. The ratio of volume of cement to
volume of fine aggregate is determined by the engineer on the basis
of py§t experience and the strength the concrete must have. Arbi-
trarily selected proportions seldom exceed 1:4:8, which is a lean

Civil Engr-8. Assignment 14. Page 3.

mixture used only in large masses for unimportant ;vork» Arbitrary
proportions are less than 1:1-1/2:3, which is a rich mixture used
•where strength is a prime requirement. As indicated in the text
the proportion of fine aggregate is sometimes varied according to
the proportion of void space in the coarse material. In general,
arbitrary proportions are made without regard for the size and
grc-.ding of the aggrebates; the method is, therefore, not scientific
and yields satisfactory results only in the hands of those exper-
ienced in its use. In. most instances the cement is not economically
used. Yet this method is probably more widely employed than any
other at the present time.

Proportions based on voids:- Study Article 481- While this
method is not in general use it is believed, by those who use it,
to be quite scientific. The text points out the inaccuracies in
the method and some of the errors in the assumptions upon which the
method is based.

Proportions based on minimum yie Id:- btudy Article 482.
The method described in this article is sometimes called "Propor-
tions based on Maximum Density" and "Proportions by Trial Mixtures".
It is a very satisfactory method and gives immediate results if
only one fine and one coarse aggregate are available. It is not
well adapted for the selection of aggregates when there are several
of each type available. When the method is applicable it deals
with the materials mixed under field conditions and yields good
results.

•• •' ' :.

.vssignraent 14. page 4.

Proportioning by mechanical analysis : - Study fs t ic le 433 .
Tne methods of proportioning, concrete aggregates previously des-
cribed might be classed as cut -and -try methods. The use of me-
chanical cr sieve analysis of aggregates gives the engineer an
opportunity to make intelligent use of the materials a^ his disposal
anc brings proportioning out of the rule -of -thumb class into the
scientific field.

Mechanical analysis was probably first used to proportion
coacrete aggregates by Fuller and Thompson in 1907. Their method
of proportioning is described in the text in Article 483. This
method will, in general, give a dense, impermeable concrete. It
permits the determination of the best proportions of coarse and

fine aggregates; it also enaoles the engineer to tell -what sizes

of material;.- should be added or tvhat sizes
/should be screened out to improve trie grading of given aggregates.

By this process he is aole to o&tain an ideally graded aggregate
which, in large work, may also be found to be economical, inasmuch
as the cost of screening and handling the aggregates may be less
than the cost of the additional cement that would be required to
produce concrete of equal strength and imperviousness from ungraded
materials. The cement ratio is usually assumed, being taken as the
ratio of cement to total aggregate a& 1:7. The ratio of cement to
sand and coarse aggregate may come out as 1: 2.3:4.7, depending
upon the combination that most nearly approaches the ideal curve.
The proportions may be expressed by weight or volume.

... ,. t. '.}•*«:•..

Civil Lngr-3. Assignment 14. Page 5.

Fineness modulus method for proportioning concret.^:- Read
^pp<=ndix 3, pages 815 to 824 inclusive. This information is given
in mere detail by Duff A. Abrams in Bulletin 1 of the Structural
I'aterials Research Laboratory, Lev;is Institute, Chicago DESIGN OF
CONCRETE ...JXiURES. Abrade ' method of proportioning is based upon
the principle that v;ith given concrete materials the quantity of
mixing water used determines the strength of the concrete so long
as the concrete is plastic and the aggregate is not too coarse for
the quantity of cement used. The relation between strength and water
ratio is shc-vn in Figure 1 on page 816. Water ratio is the usual
designation for the ratio of volume of water to volume of cement as
defined on page 316. Figure 1 is very important, it is unfortunate
that the same symbols should have been used to designate two differ-
ent mixes. If it is remembered, however, that the concrete must be
plastic, the difficulty will be overcome. Notice, for instance, that
x is used to designate a 1 :2 mix as well as a 1 ;9 mix. The symool,
however ; could not designate the latter mix in the upper part of tfoe
curve. In this part, it indicates strengths of approximately 6,000
I'D. per sq. in, and since the cor re spending water ratio is 0.50,
very dry mix would result if the proportions were 1:9. These x's
must, therefore, represent the 1:2 mix. The 1:9 evidently is repre-
sented by those marks under 1,000 Ib. per sq. in. and the 1:2 by
those above that strength

The amount of mixing, water used must be carefully considered.
This factor has not been taken into account in those methods of pro-
portioning so far discussed in the assignment, Figure 1 indicates

•;•:: ,'V.

Civil Engr-8. Assignment 14- page 6.

the effect of excess -water. A slight excess of water may reduce
the strength as much as 40%. Abrams ' tests show that the strong-
est concrete is that which requires the least amount of -water in
terms of cement (water ratio; to produce concrete of the required
consistency, i/vith a given aggregate and increasing amounts of
cement - that is. increasing the richness of the mix- the -water re-
quired to produce a plastic consistency will give a decreased
Tiater ratio. This is in accordance with previous tests which show
that for the same aggregate the richer mixtures are the strongest.

While the effect of water on the strength of concrete had
been known in a general way Abrams was the first to express the re-
lation in the definite terms of water ratio and make tests covering
a wide range of aggregates and mixtures. He found that aggregates
of considerable difference in grading may give the same strength
but that there is a definite relation between the grading of the
aggregate and the quantity of water required to produce a plastic
concrete. The size and grading of the aggregate and the proportion
of cement all affect the amount of water necessary to produce a

workable concrete. The fineness modulus, ^vhich is defined on page

is
815 - see also table 1 on page 8 17, /a measure of the grading of a

material. A coarse aggregate may have a fineness modulus over 7.00
while a fine sand may be as low as 1.25 The amount of water is
required to :vet an aggregate of a given fineness modulus is always
the same irrespective of its grading. Study the relation betwe.-en
fineness modulus and strength as given in Figures 2 and 3 on pages

Civil Engr-3. Assignment 14.

817 and 818 respectively.

Read cart3 fully the outline of method of designing concrete
mixes beginni;Dg on page 821. Add the following to the paragraph
marked 1. Experience or trial is the only guide in determining
the relative consistency of concrete necessary in the work. A
relatix^e consistency of 1.00 is dry and requires taaiping. Con-
crete having a relative consistency of 1.10 is about the driest
that can be used for concrete road construction. For most rein-
forced concrete construction the relative consistency should be
about 1.20;' and it' should never be aoove 1.25

It is not expected that you be able. to design .a concrete
mixture by Abrams ' method, but you should be able to tell in a gen-
eral way how it is done. Remember the following criterion: Use
the smallest quantity of mixing water that will produce a concrete
of the required plasticity.

Proportioning by surface areas :- This method of proportion-
ing is not described in the text. It was proposed by L.N. Edwards,
who applied his theory to the proportioning of mortars. R.B- Young
later used the surface area method to proportion concrete aggregates
The underlying principle assumes that the strength and other prop-
erties of mortars and concretes are dependent upon the amount of
ceirent used in relation to the total surface area of the aggregates.
The use of the method is simplified by tables prepared by Edwards
and Young from which the surface area of an aggregate can be de-
termined i&hen its sieve analysis is known. They have also made

'.f

Civil Engr-8. Assignment L*. Page 8.

diagrams which give the relation of strength to ratio of cement
to surface area. These latter diagrams have been prepared from
actual test data. When several aggregates are available, the best
combination, -which is also the most economical, is the one which
has the least surface area for a given volume. The effect of water
on the strength has been taken into account in this method of pro-
portioning. When the method is used in the field, as it has been,
very successfully, by R.B. Young, the water content and cement con-
tent are changed in the same proportion until the desired consist-
ency is obtained- This procedure does not effect the strength of
the ;nix. It is not always necessary to change the water ratio
determined in the laboratory.

Comparison of methods of proportioning concrete:- The
methods of arbitrarily selected proportions, proportioning by voids,
and proportioning by minimum yield do not require a laboratory
study of the aggregates, but they may be wasteful of cement. When
high strength, imperviousness and resistance to abrasion are required,
the proportioning must be done with more care and the methods based
upon sieve analyses yield economical and satisfactory concretes.
Abrams ' Fineness Modulus method and the Surface Area Method are proo-
ably most satisfactory, in such cases, since they were determined
by t-ests in which a wide variety of aggregates was used. For in-
stance, Fuller and Thompson's method, which led to the conclusion
that concrete of maximum density was the strongest, was based on
tests of a very limited number of aggregates. Abrams' tests, in

Civil Engr-8 i.ssignr.ient 14. Page 9.

the determination ana study of the fineness modulus Method, baseo
on a much ^;ider selection of concrete aggregates proved on the
contrary that concrete of maximum density was not always the
strongest.

Proportions commonly used in different constructions.— Read
Article 454. Do net attempt to memorize the tabulation given in
this article. The l;2:-i concrete is a common standard. -Sometimes
a strength specification of 2,000 lo. per sq. in. at 28 tteys, is
made .

Jesting the quality of -concrete :~ Strength tests are most
valuabl-e in determining the quality and uniformity oi concrete. 1'he
usual specimen is a 6 by 12 inch cylinder, tested at 28 days. I1 he
specimens should be poured with concrete ta^en from the mixer or
just before it is placed in the structure. Rea<3 Article 435.

Quantities of materials required for one cubic yard of
concrete:- Read article 486. Omit laoles 4 and 5. Remember
Fuller1s rule as given on page 434.

Interpretation of the meaning, of proportions:- Study Article
487; it is important, ihe statements given in this article will be
evident to the student v;no has stadieo the assignments up to this
point. If two cuoic feet of sand are mixed with four cubic feet of
rock it is obvious that the combination will not fill a six cubic
foot measure. When the proportions of fine and coarse aggregates
are stated, the specifications should read "each of the con-
stituent materials shall be measured separately".

Civil Engr-8. Assignment 14. Page 10.

QUESTIONS

1. What is meant by proportioning as applied to concrete aggre-
gates?

2. How are the relative amounts of fine and coarse aggregates
determined in the method called aroitrary selection?

3- What determines the ratio of cement to total aggregates in the
method of arbitrary selection?

4. What are the errors in the assumptions used in proportioning
concrete aggregates by voids?

5. Discuss the adapt ibility and limitations of the proportioning
of concrete aggregates by trial mixtures.

6- Describe Fuller and Thompson's method of proportioning con-
crete.

7. What are the advantages of methods using mechanical analyses
over earlier methods in which such analyses were not used?

6. Define water ratio as used in Abrams ' method of proportioning.

9. What is meant by the term fineness modulus?

10. How does the amount of mixing water used affect the strength
of concrete?

11. What is the surface area method of proportioning concrete?

12. Which of the methods discussed is the most widely applicable
and why?

13. Approximately how much cement, sand, and stone will be requir-
ed to make 20 cubic feet of concrete if the proportions are
1:2:4?

OF CALIFOHN la LXj^Nb'ION DIVISION
Correspondence Courses

iv.aterials of Engineering Construction
Civil Engr.-3 Assignment 15 Prof. C. T.

klXING, JrUC ING AND CURING OF CONC&ETE.

Principles of proper mixing.- Study Article 488. The
materials should be uniformly distributed throughout the mass so
that the mixture is hor.o?ene->us and uniform in color. The same
amount of v,ater should be added to each batch in order to maintain
the desired consistency.

In hand nixing the water is usually measured in buckets
v:hile machine mixers are provided v/ith -water -measuring devices.

Kand mix ing. - Read article 489. The following
specifications were taken from the latest reports of the A«S«T«L. :
"i.hen hand mixing is authorized oy the engineer it shall be done on
a water-tight platform. The sand shall be spread on the platform
and the cement spread evenly over the sand. The material shall then
be shoveled into a cone shaped pile by casting centrally on the
pile. This pile shall then be divided by casting into two or more
cone shaped piles and the operation of dividing and reuniting

continued until the batch is uniform in color. Only sufficient
water to produce the desired consistency shall then be added by

sprinkling as the batch is turned. The coarse aggregate previously
moistened shall then be mixed v/ith the mortar in the manner
specified for mixing sand and cement." This method is productive of
better results than can be secured by the methods commonly used.

£ngr.-8 Materials of Engineering Construction. Assn. 15, pgge 2

Machine mixing.- Study Article 490. The A. S.T.k. specifica-
tions read, "Li:: ing, unless otherwise authorized -by the engineer,

shall be done in a batch mixer of approved type " The Continuous

mixer, while it can be operated rapidly and cheaply, rarely gives
a uniform product. Since it cannot be relied upon, the batch mixer
is preferable.

The tirje of mixing is specified as follows: "The mixing of
each batch shall continue not less than 1 minute after all the materials
are in the mixer, during which time the mixer shall rotate at a
peripheral speed ef about 200 feet per minute....." Although the
data given in the text, shown in Figures 9 and 10, would indicate that
a longer period of mixing vould be desirable, and the A. S«£«k« formerly
recommended 1 1/2 minutes as the mixing tL.,e, recent tests seem to
•warrant the minute mix.

fixing produces a change in the consistency of concrete, the
water content remaining constant. The change is particularly
marked between 30 seconds and 1 minute, but the additional change
after 1 minute is slight.

It is possible to obtain the same degree of plasticity (consistency)
oy mixing for 1 minute as -would be obtained oy mixing for 1/2 minute
with 25f0 more water. Contractors sometimes resort to the shorter
mixing periods in order to save time, and add more water in order to
bring the concrete to the desired consistency. The A. S.T.M«
specifications, however, do not permit the retempering of mortar or
concrete, that is the remixing with or without additional cement,
aggregate, or water.

Engr.-8, materials of Engineering Construction. Assn. 15, page 3
Hand vs. machine mixing*- Head Article 491. Good mixing

can be secured by hand as well as machine mixing;' the former
however, requires heavy labor and is usually not thoroughly done.
For all except the smallest jobs, machine mixing will be less
expensive than hand mixing.

The tests referred to in this article would indicate that
hand mixing is inferior to machine mixing. With reference to hand
mixing as it is usually done , this is probably true. The last
sentence in the article, which states that the hand mixed concrete
referred to in the test required more water to bring it to the con-
sistency of that mixed by the machine, shows that the mixing by
hand had been slighted. If the hand mixing had been thoroughly
done there would have been no marked difference between the concrete
produced by the two methods.

Handling of concrete.- Read Article 4S2. The fundamental

principle in the handling of concrete is that there must be/ oppor-
tunity afforded for a segregation oetween the mortar and the
course aggregate.

Besides the methods descrioed in the text, concrete is
transported in large motor-trucks from a central mixing plant
in road construction. Sometimes the hauls are very long. In order
to determine the effect of such transportation the Bureau of Public
Roads has recently made a series of tests in which the concrete was
hauled for diffenent periods, up to 3 hours. They found that after
45 minutes of hauling the concrete became too stiff for hand finishing,
but that the strength was not reduced as long as the concrete remained
workable.

s *f iMgiueer ing Construction. ..ss. . '.E,
Concrete should not be deposited under water if it is
practical to exclude the water by means of cofferdams. There is
always uncertainty in depositing concrete under water even if the
methods described in the text are used* If it is impractical to
use other methods concrete should be placed under water only under
experienced supervision. This is particularly true in the case of
sea water. The usual methods in which the trernie, drop-bottom
bucket s, and bags are used, are described in the text.

Placement of concrete.- Read Article 493. Concrete should
be placed in the forms in its final position so as to make re-
handling unnecessary. It should be placed in uniform horizontal
layers and not allowed to flow down a slope so as to permit a
segregation of fine and coarce materials. During and immediately
after depositing, the concrete should be thoroughly compacted by
spading or rodding. Some compacting is necessary to make the
concrete flow into the corners of the molds and around the rein-
forcement since it is usually mixed with as little water as possible.
The days of wet, soupy concrete which did not require rodding are
over. Relatively dry concrete can be used in the construction of
concrete pavements since power -driven tampers and metal rollers can
be used to compact it. Concrete used in reinforced construction

must be more plastic so that it can be properly placed.
d^*v be.

Cement mortar *« deposited by an apparatus known as a cement
^

gun. This device is described on page 444 of the text. The cement
gun is being widely used. It produces a dense strong mortar.

Engr.-S Materials of Engineering Construction, .-.ssn. 15, page 5.

Joining old and new work.- Read Article 494. If work is
not continuous, joints cannot be avoided. In making joints every
precaution should be taken to make the bond as strong as possible.
The methods of bonding are described in this article. Laitance
is mentioned. It is a whitish scum which comes to the surface of
wet concrete. Laitance is formed when concrete is deposited under
water or vrhen water comes to the surface of the concrete xvhich has
been mixed with an excess of water. It is composed of finest
particles of cement and the dirt in the aggregates. While the
composition of laitance is practically the same as that of cement it
does not have the same properties. It does not harden or acquire
much strength and consequently if it is not removed it prevents tfoe
bonding of successive layers of concrete.

Forms. *» Read Article 495. Forms should be sufficiently
tight to prevent the leakage of mortar and they should be so
braced andtied together as to maintain their position and shape.

Before concrete is deposited in the forms all debris should
be removed from the place to be occupied by the concrete. The
forms should be cleaned fcnd thoroughly wetted or oiled to prevent
absorption of water from the concrete. Steel has been used for
some time for forms for concrete pipe, tunnels, sewers, curbs, retain-
ing walls and dams, and it is gradually replacing wood for formwork
ir. standardized building construction.

Read the information regarding the pressure of wet concrete
againit'.the forma .as given on page 447. More recent experiments
give lovrer values. The most reliable are given in POURING AND

Engr.-8 Materials 6f Engineering Construction. Assn.15, page 6.
PRESSURE TESTS OF CONCRETE by Slater and Goldbeck, U.S. Bureau of
Standards, Technologic Paper No. 175. Their principal conclusions
are: (a) The maximum pressure against the forms during pouring of
concrete izras fouAd to be equivalent to that of a liquid weighing
about 124 Ib. per cu. ft. (b) The maximum pressure was found to be
that due to the head of concrete existing at the end of about 40
minutes. After that time the pressure gradually decreased in spite
of increasing the head of concrete. These data are of value in
the design of forms.

The time for removing forms is determined by the strength of
the concrete. As indicated in this article the strength of the
concrete can be found only by actual tests. The removal of the
forms from concrete structures that have not developed sufficient
strength has resulted in many failures. On the othsr hand, much
money value is sacrificed if the forms are left on too long. Weather,
position of the form, quality of the cement, and the load are the
principal factors which influence the time of removal of the forms.
Warm, dry weather hastens the setting and hardening of concrete,
while cold, damp weather retards hardening, Forms for horizontal
members, such as beams, should remain in place longer than forms
for vertical members, such as columns and walls. The forms may
obviously be removed sooner from concrete made with quick-hardening
cement than from normal concrete. When the load carried by a

member i<5 nearly all live load/ such as machinery, equipment, and
people, the forms may be removed sooner than when the total load
on the member is largely dead load. For this reason roof forms and

Engr.-8 Materials of Engineering Construction . ^ssn. 15, page 7.
top -story columns arc left on longer than those for other floors.
The following table is abstracted from Hool and John son ' s CONCRETE
ENGINEER'S HANDBOOK:

Removal of forms

Above 60° p.

50-60° F.

40-50° F.

Column Sides
Beam Bottoms

Within 3 days
Within 14 days

5 days
18 days

10 days or more
24 days or more

Expansion joints*- Read Article 496. Concrete shrinks
when it sets in air and expands when it sets in water. After it
has set, changes in moisture content cause volume changes. Concrete
expands when it is wet and contracts when it dries out. Expansion
and contraction are also caused by heating and cooling respectively.
The forces which produce volume changes may counteract one another
so that there will be no effect on the concrete. They may also
act together or separately and cause volume changes which become
evident as expansion and contraction. The change in length in
100 ft. of concrete is about O.Sinches per 100 degrees Fahrenheit.
In contraction, this produces cracks in walls, walks and pavements.
In expansion, it buckles curbs and walks unless expansion joints
are provided. Long stretches of wall may be built without expansion
joints provided that enough steel is put in to hold the concrete
together- The steel does not stop the movement but it distributes
the total change in length and produces a large number of very fine
cracks \?hich do no damage. The A.S.T.M. specifications provide
that "structures exceeding 200 ft. in length andof width less than

2ngr.-S ..later Lils of Engineering Construction. Assn 15, page &•
about one-half the length, shall be divided by means of expansion

joints, located near the middle, but not more than 200 ft* apart >
to minimize the destructive effects of temperature changes and
shrinkage.*..." When such expansion joints are used they should
be arranged to separate completely the parts of the building and
should extend from the bottom 60 the top of the structure. An
expansion joint should separate all parts such as beams, columns
and slabs from the main part of the structure. When expansion joints
are placed in retaining walls they should be spaced about 30 ft.
apart.

Curing.- Read Article 497. The process of keeping concrete
damp is called curing. Concrete is cured by immersion, sprinkling
and the use of steam. Hydration of the cement goes on after the
concrete has hardened, so that it is necessary to prevent it from
drying out too rapidly. Allowing the forms to remain in place helps
to retain the moisture. Newly laid concrete pavements are protected
from the direct rays of the sun by means of canvas and after the
concrete has set, it is covered with moist earth or flooded vdth
water .

Concrete products such as described in Chapter XV are cured
by the three methods mentioned above, immersion, sprinkling and the
use of steam. The American Concrete Institute specifies protection
from the sun and strong currents of air for at least 7 days;
continuous sprinkling andmaintenance of a temperature of not less
than 50 degrees Fahrenheit and storing in the yards for about £1
days before shipment. For steam curing, their specifications

Engr.»3 ^at-arials of Engineering Construction. Assn. 15, page 9t
read, "The products shall be removed from the molds when the

conditions permit and shall be placed in a steam curing chamber
containing an atmosphere of steam saturated with water for a
period of at least 48 hours. The curing chamber shall be kept at
a temperature between 100 and 130 degrees Fahrenheit- The product
shall be removed and stored for at least 8 days."

Protection against freezing. - Read Article 498. Concrete
should not be mixed or deposited at a freezing temperature unless
precautions are taken to overcome the effects of low temperature.
Uork nay be carried out during freezing weather by heating the
materials and the structure or by the addition of some substance to
lower the freezing-point of water. Wherever the temperature drops
to 35 to 40 degrees Fahrenheit the materials should be heated.
After concrete has been placed it should be protected against the
cold for 48 hours to 5 days, dependingupon the temperature. ?Jhen
important structures must be constructed during periods of low
temperature they are completely enclosed with tarpaulin or heavy
canvas even though they may be large buildings. The interiors are
then heated, as explained in the text.

QUESTIONS

1. 7/hat constitutes proper mixing?

2. Describe the method of hand mixing recomnended by the A- S-T.M

3. ^/hat are the principal factors that should be considered in
the purchase of a concrete mixer?

Engr.-8 Materials of Engineering Construction- Assn. 15, page 10

QUESTIONS, con.

4. How long should concrete be mixed when a batch mixer is used?

5« What is the fundamental principle in the transportation and
deposition of concrete?

6. What methods are used to deposit concrete under water?

7. What precautions should betaken in bonding to old concrete work?

5. ?i/hat approximate lateral pressure is exerted against the forms
by fresh concrete?

9. What causes concrete to shrink? What is the effect of shrinkage
and hovr is it overcome?

10. What precautions must be taken -when concreting at or belovr
freezing temperatures?

11* What is meant by curing concrete?

12. Why is a batch mixer considered better than a continuous mixer?

IS. In "what way may the quality of concrete be impaired by methods
of placing in ordinary construction?

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION
Correspondence Courses

Materials of Engineering Construction

Civil Engr.-8 Assignment 16. Professor C.T.Wiskocil

PHYSICAL PROPERTIES OF MORTAR AND CONCRETE.

Introduction.- Read Article 499. While the effect of the
important factors which influence the physical properties of mortar
and concrete are discussed in this assignment it should be remembered
that in any investigation all factors are not known, and that it
is consequently not possible to control them all properly, and that
the re suits, therefore, should be taken as being indicative only.
In many of the data given in the tejtfc, no attempt is made to state
the conditions under which the tests were made. This information
is frequently omitted even from the original publications fron
which the data were compiled.

Strength of mortar s» - Read Articles 500 to 506 inclusive.
The principal use for mortar is in the construction of masonry. Mien
strength is required in stone, brick or terra cotta structures,
Portland cement mortar is used. Cement mortars in various proportions
are also used for stucco. Stucco may be defined as a material used
in a plastic state to form a hard coating for the exterior walls
or other surfaces of any building or structure. Mortar is relatively
unimportant when compared to concrete «

The effect of proportion of cenent on the strength of mortars
is discussed in Article $00 and shown in Figure 1 on page 452.
Compare the strength of neat cement given in Figure 14 on page 332

Engr.-8 Materials of Engineering Construction Assn. 16. page 2.

•
with the compressive strength given for neat cement on page 452.

Compare also the figure on page 354 with that on page 452. The
strength of neat cement as well as mixtures of cement and fine
aggregate varies with the brand of cement used - cements cb not
all have the same cementing value. Other factors which affect the
strength of cement and cement mixtures are: the amount of water

used in mixing, the conditions of storage and testing and the

453
gradation of the sand (as shown in the figures on pages 452/and 454.)

Because of the relative unimportance of mortar as a structural
material make no attempt to remember the data in Article 500 to 502
inclusive.

Probably the most comprehensive tests of ceuent mortars are
reported in Technologic Paper No. 58 of the U. S.Bureau of Standards.
From this publication the following information is taken u(a) The
quality of a sand cannot be judged from its gradation alone. (b) For
most fine aggregates the highest strengths are obtained with those
having a gradation of particles approaching a straight line, but
often materials having a gradation varying widely from a straight
line will give high strength in mortars* (c)No fine aggregate
should be rejected because of its silt content (determined by
washing or assuming the material passing the No. 200 sieve as silt)
as it may be advantageous even in relatively large quantities or
detrimental in small quantities, depending upon its form, character
and distributicn.(d)The only satisfactory method of determining the

Engr.-8 Materials of Engineering Construction. As.sn. 16, page 3.

value of a fine aggregate in mortar mixtures is to test it in
the mixture, in the proportion to be used, exposed to the same
conditions as in the proposed structure." These above remarks
are of importance in the consideration of mortar.

The strength in compression and in cross bending can be
estimated with sufficient accuracy from the average strength
of neat mortar, 10,000 lb. per sq. in. (compression) and 1,000 lb.
per sq. in. (cross bending), and from the general shape of the curves
on page 452, which give the relation between strength and proportion
of cement to aggregate. A 1:6 mortar has an approximate compressive
strength of 1,000 lb« per sQ. in. and an average transverse strength
of 300 lb- per s£. in.

The effect of the amount of mixing water on the compressive
strength of mortars is similar to that shown on page 816 in
the case of concrete. This relation for neat and 1:5 mortars is
shown in Figure 10 on page 33, Bulletin No. 8, of Structural Materials
Research Laboratory, Lewis Institute, Chicago.

Mica decreases the compressive strength of mortar. Recent
experiments made by Professor Abroms at Lewis Institute bear out
this statement but his tests indicate that the decrease is not as
marked as that found by Wills. See Article 504.

Tests reported in Bulletin No. 8 of the Structural Materials
Research Laboratory, previously referred to, indicate that the use
of hydrated lime decreases the strength of cement mortar. About

Engr. 8, Materials of Engineering Construction. Assn. 16, page 4.

8,000 tests on briquettes and 2 by 4 inch cylinders were made during
this investigation* The tests mentioned in Article 505, since they
are few in number, cannot be given as much consideration.

Merely read Article 506 on adhesion of mortars; it is relatively
unimportant.

Strength of concrete.- Read Articles 507 to 517 inclusive.
The strength of concrete is affected by various factors, the most
important of which are; age, proportions of cement to aggregate,
kind of aggregate, amount of mixing water, and curing conditions.
In view of these variables, good average figures to remember are:
2,000 Ib. per sq. in. in compression, 200 lb» per sq. in« in tension
and 1,000 Ib* per sq* in. in shear at 28 days. At the age of one
year concrete is about 2 1/2 times stronger than at 28 days, the
usual testing period. Concrete is a brittle material, and as the
average values given indicate, is strongest in compression. Its
tensile strength is lov; and is neglected in the design of reinforced
concrete structures. The shearing strength of concrete is about 1/2
its compressive strength.

The compressive strength increases vrith the richness of the
mix. The tables on pages 459, 460 and 461 shew this fact - but not
in a form that can be easily remembered. The following diagram
gives average values for soft limestone concrete stored in a damp
location* The proportions are the total of fine and coarse aggregates
measured separately. The diagram also indicates the normal increase

Engr-8. Materials pf Engineering Construction. Assn. 16, page 5»

in strength with age. The dotted curve vas plotted from data for
gravel, hard limestone or hard sandstone concrete 28 days old, taken
from the report of the Joint Committee on Concrete and Reinforced
Concrete. The values are based on tests of 8 by 16 inch cylindrical
specimens stored under laboratory conditions*

5000

4000

3000

2000

1000

10 11 12

Proportion of Aggregate to one part of Cement

Figure 1

Engr.-8 Materials of Engineering Construction* A.ssn.16, page 6.

Under ordinary conditions concrete will not gain much strength
after one year but if concrete does not dry out its compressive
strength increases indefinitely. See EFFECT OF AGE ON THE STRENGTH
OF CONCRETE by D. Abrams, A. S. T.M. Proceedings, 1918, page 317.
The age- strength relation for mortar and concrete is expressed by
the equation
og a + k where 3 is the compressive strength, a_ is the age and n and £

are constants whose value depends upon the cement and other test
conditions. This equation has been derived from tests in American
and European laboratories on specimens up to nine years in age.

Since there are so many factors which affect the density-
strength relation (see Article 509), density is not a reliable
criterion of strength.

The effect of size of coarse aggregate, v/hich is discussed in
article 510, is well illustrated in Figure 3 on page 818.

The effect of proportion of mixing water on the strength of
concrete is explained in Article 511. The water ratio - strength
relation - is shown in a clear-cut, definite manner in Figure 1 on
page 816. The following conclusion is made by Abrams: Vi/ith given
concrete materials and conditions of test the quantity of mixing
water used determines the strength of the concrete, so long as the
mix is of a workable plasticity.

The information in Article 512 is relatively unimportant.
Remember that the tensile strength of concrete is about 1/10 of its
compressive strength.

Engr.-8 Materials of Engineering Construction. Assn. 16, page 7.

Because of its low tensile strength concrete without steel
reinforcement is rarely used where it would be subjected to trans-
verse loads. The discussion on transverse strength in Article 513,
therefore, is of little importance.

Read carefully the first paragraph of Article 514. The
remainder of the article is not important. Remember that the
shearing strength (punching shear) of concrete is about 1/2 of its
compressive strength*

The effect of type of aggregate is well illustrated in the
Joint Committe Report (previously referred to) from which the
following data were taken:

Granite, trap rock 2,200

Gravel, hard sandstone, hard limestone 2,000

Soft limestone, soft sandstone 1,500

Cinders , 600

fe & ^1* S<7, I*.

The values given are for compressive strength^at 28days for 1:6
concrete, the fine and coarse aggregates being measured separately.

The conditions under which concrete is cured have a great
influence upon its strength. The following statements were taken
from EFFECT OF CURING CONDITION ON THE v/EtoR AND STRENGTH <DF CONCRETE,
by D.A.Abrams, Bulletin No. 2, Structural Materials Research
Laboratory, Lev/is Institute, Chicago. "All consistencies of concrete
show great increases in strength under favorable curing conditions
as compared with specimen's which were allowed to dry out at once.

The dryer mixes show a more rapid improvement due to storage in a
damp place during the first few days than the 7/etter ones. Even

Engr.-8 Materials of Engineering Con srbr action. Assn. 16, page 8.

three days in damp sand results in increase in strength of dryer

concretes of about 35% as compared with that of the specimen^ stored
in open air for the entire period. Concrete stored in damp sand
and tested danp is about 3 times as strong as similar concrete
which had been exposed to room atmosphere for the same period-
Protecting concrete from drying out for only 10 days gives an
increase in strength of about 75% for the dryer mixes."

Elastic properties of concrete.** Read carefully Article
518. In it the true elastic stress-deformation and gross
deformation curves are described- The gross deformation is usually
plotted against stress, as indicated in Figures 12 and 13, on pages
476 and 477 respectively. These curves SHOT; a decided curvature,
concave downward, as stress-def or nation curves for other brittle
materials do; see Figure 11 on page 710. The elastic stress-deform-
ation relation is of importance in the determination of stresses in
structural members under load. Under long time loads, concrete
undergoes a greater deformation than it does for the same load ap-
plied for a short period, as in the usual testing machine. The
gross deformation of a given fiber cannot be used to compute the
actual stress; the elastic deformation must be used.

It should be noted at this time, that there are investigators
who believe that the stress deformation curve for concrete up to and
even over -.-or king stresses is a straight line. They show data to
support their views and state that in their judgment the curvature
in most stress-deformation curves is due to inaccurate apparatus

Engr«-8 Materials of Engineering Construction, Assn. 16, page 9,

and technique on the part of the investigator. Note that the stress-
deformation curves given in Figure 12 on page 476 are practically
straight lines up to 1,000 lb. per sq. in., which is well above
working stresses for concrete. Stress-deformation diagrams for tests
reported by C.T.Wiskocil in the Report on California Highways -
California Automobile Clubs, 1921, part IV, page 18, for concrete
whose average compressive strength at 28 days was 2,430 Ib. per sq.
in., were straight lines up to an average stress of 1,080 Ib. per
sq. in. For 2,000 lb. concrete the wor Icing stresses vary from 450
to 650 Ib. per sq. in. depending upon the kind of stress, that is
whether it is direot compression or extreme fiber stress in bending.

Read Article 519. The difference between the initial and
secant moduli is explained and illustrated. Since these terms
are in use, their meaning should be known by the student.

Read Article 520. The modulus of elasticity of concrete
varies from about 1,000,000 to 4,000,000 Ib. per sq. in. For
2,000 Ib. concrete the average value is about 2,000,000 Ib. per
sq. in., being 1/15 that of steel. This value is used in most
design calculations.

Poisson's ratio, given in Article 521, is of value in
theoretical discussions and in the determination of stresses in
certain types of structures, such as arch-dams. For practical
purposes the ratio may be taken as 1/10.

A change in moisture content, as well as variation in direct
load and change in temperature, has an important effect on the

Sngr.-8 Materials of Engineering Construction. Assn» 16, page 10.

deformations produced in concrete. Read carefully the first paragraph
in Article 522. Since concrete and steel have practically the same
coefficient of expansion they change length at the same rate, and
variations in temperature do not cause any stress unless the member
is restrained. Changes in moisture content, on the other hand,
effect only the concrete, which expands when it absorbs water and
contracts when it dries. After concrete sets it ordinarily shrinks
a considerable amount. This shrinkage during hardening may be as
much as 0.05% in an ordinary structure. Contraction in concrete
when it is restrained by an external force, as by other members
in a structure or by steel reinforcement, causes stress in the
concrete. In reinforced concrete the shrinkage produces stress
in the steel, when the reinforcement is less than 1.5% , which may
reach ordinary working stresses (16,000 Ib. per sq. in») If the
amount of steel reinforcement is greater than 1.5^ the stress
produced by the drying out of the concrete may reach the ultimate
tensile strength of the concrete* The greater the amount of steel,
the greater will be the tensile stress produced in the concrete for
a given reduction in moisture content. Under atmospheric conditions
where concrete is alternately wet and dry the alternation in

stress may crack the concrete even if the stress is below the
ultimate tensile strength of the concrete as determined in the usual

static test. Excessive expansion and contraction can be reduced by
waterproofing the concrete*

Engr.-8 Materials of Engineering Construction* Assn. 16, page 11.

QUESTIONS

1. IVhat is the principal use for cement mortars?

2, Give the average compressive strength of neat and 1:6 cement
mortar when about 1/2 year old.

5* what is the approximate strength of 1:6 concrete (the fine and
coarse aggregates being measured separately) in compression,
tension, and shear at 28 days?

4« What would be the approximate compressive strength of the
concrete specified in question 3 at the age of one year'

5. How does the rate of increase in strength vary for different
ages? \Vhat influences the increase in strength besides age?

6. Approximately what difference in compire ssive strength would
you expect between (a) concrete exposed to air and (b) ~
the same concrete kept in a damp condition?

7. Draw a curve to show the ititial and secant moduli of elasticity
for concrete in compression.

3* l<7hat is the average modulus of elasticity for 2000 Ib. concrete?
9. What is the approximate ivorking stress used for 2000 Ib* concrete?

10. In an ordinary structure what percentage change in length can
be expected in concrete during hardening?

11. If the amount of steel in an unloaded reinforced concrete
member is greater than 1.5$, v/hat stress may be produced in
the concrete if it becomes thoroughly dry?

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION
Cor re spondence Cour se s

Materials of Engineering Construction

Civil Engr.-8B Assignment 17. Professor C. T.Wiskocil
PERMEABILITY AND ABSORPTION OF CONCRETE

Read Articles 523 to 552 inclusive* Impermeable concrete
is required in the construction of basements, tunnels, and subvrays,
and of tanks for the storage of liquids, \7aterproof is the term
more commonly used to designate concrete which prevents the passage
of water through it. Leaks not only defeat the purpose for which
impermeable concrete is intended but permit the entrance of sea
water, alkalies, and frost, all of which affect the durability of
concrete. If concrete is properly proportioned, mixed, placed and
cured, it 'is possible to secure a finished product that will be
impermeable under water pressure up to and exceeding that produced
by a 100 foot head. If the structure is liable to crack, water-
tight expansion joints must be provided or the use of waterproof
membranes, as described in Article 538, must be resorted to.

Read Article 523, v/hich explains the difference between
absorption and permeability. Mote that the statement is made that
there is no relation between these properties. Both are important.
Absorption is easily determined but permeability can be determined
only by the use of an elaborate arrangement to test the specimen,
and even this does not always work satisfactorily.

Read Article 524. The principal types of permeability specimens
are illustrated on page 483. The main cause of trouble in tests of
this kind is leaks particularly at high pressures, uhile several

Fngr.-8 Materials of Engineering Construction Assn. 17, page 2.

types of specimens are illustrated there is no accepted standard
and moreover tais test is not frequently made.

With increasing proportions of cement, other variables
remaining constant, the imperineabilit/"- of concrete increases- See
Article 525.

Figure 16 on page 486 and figure 9 on page 464 show that the
density of concrete affects its permeability more than it does the
strength. & porous concrete might have considerable strength and
yet be very permeable to water.

The use of insufficient mixing water makes the placing of
concrete difficult and usually results in a pouous product. An
excessive amount of water produces a large amount of water-voids
and decreases the density. The most impervious concrete is made
from a plastic, workable mix. See Article 527.

The one-minute mix, recommended by the Joint Committee previously
referred to, is undoubtedly sufficient to insure homogeneity of mix
and will therefore produce impermeable concrete, providing that the
aggregates are well graded and the correct amount of cement and
mixing water are used. With these latter conditions properly
provided, insufficient mixing will cause permeability; but it is
obvious that two or more minutes of mixing will not be able to
overcome deficiencies in mix, grading of aggregates, or amount of
water used, and will not under these conditions produce an
impermeable concrete. Read Article 528.

Engr.-8 Materials of Engineering Construction. Assno 17, page 3«

Permeability as vrell as strength of concrete are greatly
affected by improper curing. Inherent impermeability is destroyed
by allowing concrete to dry out at early ages. Concrete must be
kept damp in order to cure properly. See article 489.

I!inor factors vhich influence the permeability of concrete
are given in Article 550. They are relatively unimportant.

The degree of absorption holds a prominent place in all
specifications for quality of concrete products. Not-withstanding
its importance it has not been thoroughly investigated* Read
Article 531.

The A.3« T.M. Standards for testing cement-concrete seTrer
pipe for absorption state that the test spscimen, a piece of broken
pipe, shall be heated for not less than 3 hours at a temperature of
not less than 110 degrees Centigrade (230° Fahrenheit). The specimen

is than cooled, weighed and placed in water which is brought to
the boiling point and boiled for five hours. After the water has
cooled to room temperature the specimen is removed and the superficial
moisture i-'iped off. The specimen is then veighod and the per-
centage absorption calculated on the basis of the dry weight.

As indicated in the first paragraph of Article 531, the
excessive drying of the specimen undoubtedly increases the absorption.

In a recent report issued by the Structure.! Materials Research
Laboratory, Lewis Institute, Chicago, the absorption of concrete
i-ras studied, 'while it was not determined in accordance with the
A. S.T.1,1, specifications, various factor s which influence absorption

Engr.-8 Materials of Engineering Construction. Assn. 17, page 4.

were studied and the results should be of value* The following
are the principal conclusions:

1. The absorption of concrete was reduced by using coarser
aggregate s, so long as the concrete was plastic. The absorption of
concrete made vrith aggregate graded 0 -38 (fineness modulus of 1*8)
7/as about 5/£, v/hile for OD ncrete vrith aggregate graded 0-1 1/2 inch

(fineness modulus 6.0) the absorption was reduced to <%•

2. The absorption of concrete -;:as reduced by increasing the
quantity of cement.

3. Ths absorption was increased as more mixing water was used.

4. The storage of concrete in a moist place immediately after
molding decreased the absorption. The longer the concrete was kept
moist the lower the absorption.

5. In general, in concrete of high strength there was lo^
absorption.

'WATERPROOFING

Read Articles 522 to £38 inclusive. In many cases concrete
is poorly proportioned, mixed, placed and cured, and in such instances
it is necessary to close up the pores in order to make the concrete
impermeable. In nost instances it would be cheaper to make good
concrete than to resort to the use of waterproof ing materials.

The principal method of filling the pores is by the addition
of inert and active fillers. They are listed in Article 532. Some
are added to the mixing water while others are dry powders and are
added to the cement.

Engr.i-8 Materials of Engineering Construction. Assn. 17, page 5«

The statements made in Article 533 on the effect of hydrate
lir-e should be seriously questioned. According to EFFECT OF
BYLRATED LUvE AND OTHER POWDERED ADMIXTURES IS CONCRETE by Duff
Abrams, Bulletin 8 of the Structural Materials Research Laboratory,
Lev-is Institute, Chicago (Dec. 1S20): (a) Ifydrated lime as an
adniixture reduces the compressive strength of concrete of all mixes
and consistencies, (b) The reduction of concrete strength is nearly
proportional to the quantity of hydrated lime used, (c) Rich
concrete mixtures show a greater loss in strength due to hydrated
lime than lean ones.

If shrinkage cracks occur or construction joints are not veil
made the integral fillers will not keep out the water. Surface
treatments are resorted to. In general they are not very successful.
Sylrester's trash of soap and alum is described in Article 537.
Other treatments are hot paraffin, bituminous materials and rich
mortar.

The most positive method of waterproofing, but the most expensive,
is the use of layers of v/aterproof membranes laid on the surface
of the concrete subjected to water pressure. Tarred felt, burlap
and canvas are some of the membranes used. They are cenented to
the concrete with various bituminous materials. See Article 538.
EFFECTS OF TEMPERATURE ON CONCIiETE

The effect of low temperature on fresh concrete is explained
in Articles 539 to 542 inclusive- It is a well krxnvn fact that
heat hastens the setting and hardening of concrete and that cold

Engr.-8 Materials of Engineering Construction. Assn. 17, page 6.

delays it. Low temperature produces an appreciable effect below 50
degrees Fahrenheit and becomes more effective in retarding the
phenomena of setting and hardening as it decreases, until the freezing
point of -water is reached. Below this temperature, fresh concrete
will freeze.

?i/hen water is added to portland cement a chemical reaction occurs
which evolves heat of sufficient quantity to raise the temperature
of fresh concrete. Under favorable conditions the rise in temperature
is greatest in the period from 6 to 12 hours after mixing.

If concrete is to be subjected to low temperatures it is
important that it acquire all possible strength at an early age.

It is the general opinion that freezing temperature will not
injure concrete that has had an opportunity to harden at least 48
hours under favorable conditions. Alternate freezing and thawing
at an early age may cause injury.

Concrete should be protected from the elements for at least
12 hours after being poured during which time the heat from the
chemical action accelerates hardening and retards the later cooling.

Light structures with thin sections need more protection
than concrete poured in large masses. Furthermore, since the
circulation of air hr,s a marked effect on the cooling of heated bodies;
fresh concrete should be protected frora wind.

The diffusivity of fresh concrete of the usual mixes i£
•0063 in e.g. s. units. This constant expreesses the rate of flow
of temperature. It is a function of the density, specific heat and

'TV/

Engr.-8 Materials of Engineering Construction. Assn. 17, page 7*

thermal conductivity. The emissivity of fresh concrete is the
rate of lo^s of heat by radiation, convection, and evaporation
of surface -v/ater. In c.g.s. units its average value is «046.
These values have been determined by Tokujiro Yoshida. -.vho has
also prepared various cooling diagrams, thus affording data which
perinit calculations of the time required for concrete to reach
freezing or any other given temperature under knovm conditions of
initial temperature, mass and atmospheric temperature of the concrete,
and the amount of protection given it after it is poured*

Heating of materials, which is an excellent method of ensuring
early hardening and delaying the fall in temperature, should,
not be carried above 100 to 120 degrees Fahrenheit.

If the temperature of the concrete over a given period is
kno'vn, the comparative strength may be estimated from Figure 15 in
INFLUENCE OF TEMPERATURE ON TEE STRENGTH OF CONCRETE by A.B.
lucDaniel, Bulletin 81, of the Engineering Experiment Station,
University of Illinois. This is an aid in deciding on the safe time
to remove forms when the temperature is low.

The three methods of concreting in cold v:sather are: heating
the materials, placing protective coverings over the poured concrete,
and the use of chemicals to lo^er the freezing point. Calcium
chloride, see Article 542, is being used to accelerate the setting
of concrete at low temperature, even on large and important work.
Part of the 410,000 cu. yds. of concrete on Ontario's Niagra
Pov/er Development, according to an article by Blanchard and Young^

Engr.-8 Materials of Engineering Construction. Assn. 17, page 8.

in the Engineering News-Record of April 6, 1922, page 554, was
poured in *. eesing weather. Two and one half percent of calcium
chloride was used end due to the acceleration it caused in the
hardening, the forms were stripped in 12 hours. It is interesting
to note that all this concrete was scientifically proportioned
to meet a definite strength requirement at 28 days.

Actual practice and laboratory experiments have demonstrated
the value of calcium chloride in highway construction to such an
extent that the Highway Department of the state of Illinois, during
the past year (1921) has allowed its use for accelerating the setting
of concrete in cold weather construction. They also have spread
it over the usual concrete pavement to accelerate the setting under
normal conditions. It was applied 3 to 16 hours after the concrete
had been poured. About 3 lb» were used per square yard of surface.
Experiments have proved that the hardening effect occurs during the
first 24 hours the salt is on the concrete.

Calcium oxychloride, known as Cal, is readily soluble in
voter, in which it decomposes into calcium hydroxide and calcium
chloride. It is a dry white powder and is not hygroscopic, like
commercial calcium chloride. Portland cement mortars treated with
Cal and stored in air, attained at 2 days a strength greater than
that of untreated mortars at 28 days. Three-year tests by the
Bureau of Standards on concrete gaged with a solution of calcium
chloride are sufficient grounds for believing that the addition of
Cal vrill not injuriously affect the ultimate strength and durability

Engr.-S Materials of Engineering Construction. Assn. 17, page 9.

of portland cement concrete.

The effect of high temperatures on concrete.- Read Article
54:5. VJhile concrete is a good fire resistant material, ranking
•with burnt clay products such as brie!' and terra cotta, it 77111
actually fuse and be destroyed v,rhen exposed to high temperature So
The temperature at which average concrete t/ill fuse is about 2,200
degrees Fahrenheit. It probably varies slightly with the brand of
cement .and the type of aggregates used. Fused concrete has been
found in ruins of hot fires such as those of the Edison plant, the
chemical plant of the Barrett Manufacturing Co., in 1920, and the
Seamless Rubber Company's plant in 1921, in which highly inflammable
liquids caused the high temperatures. Such temperatures are
generally not encountered but they are possible even in ordinary
structures. In the fire in the office building of the Chicago ,
Burlington and Quincy Railroad Co. in Chicago, March 1922,
temperatures in excess of 2,000 degrees Fahrenheit were reached.
These temperatures were undoubtedly confined to relatively small
areas. It is interesting to note that -while the contents of the
building within these areas were completely destroyed, the concrete
adequately protected the steel frame of the building. There rvas a
certain amount of spalling.

About 2 1/2 inches, of concrete is generally considered sufficient
thickness of fireproof ing for steel work. Reinforced concrete
columns should have 2 inches, vhile floor slabs are adequately
protected vrith 1 inch of concrete.

Engrc-8 Hater i:. Is of Engineering Construction. Assn»17,page 10.

It has "been observed that concrete made with silicious aggregates
is not as resistant to fire as concrete made with limestone, trap
rock, and "burnt clay aggregates* The distinct advantage in the use
of concrete to fireproof steel is that its expansion and contraction
-re nearly the same as those of steel (see Article 544), and the
spelling action (under heating and cooling) is therefore, reduced
to a minimum.

Other thermal properties given in Article 545 are relatively
unimportant. Recent tests by Carman and Nelson give .0037 as the
average thermal conductivity for average concrete; see Table 26
on page 503 in the text.

DURABILITY OF CONCRETE

Read Articles 546 to 550 inclusive. The reliability of
existing information on the disintegration of concrete by alkali is
questionable. This statement does not apply to that given in
publications listed at the end of Article 547 in the text, since
these contain v/ithout question the most important contributions
on the subject at the present time. Other investigations have been
made but, taken as a trhole, the results of these investigations and
tests are not conclusive.

The most import-ant examples of failure of concrete which have
been reported are in Canada. The articles announcing these failures
describe only the extent of disintegration and attribute the cause
to alkali because of its presence in the surrounding soil. In no
instance do they give the history of the concrete, %?hich may have

Engr.-8 Materials of Engineering Construct ion . Assn. 17, page 11.

been a lean mixture, or made of poorly graded aggregates, or sand
with orgaric matter in it; or which again, may have been poorly
mixed or made with an excess amount of water. Any of these conditions
would yield a concrete of low durabii^ ty or resistance to weather-
ing. The Winnipeg aqueduct is probably the most important structure
which shov;s disintegration but there are many other concrete
structures which are satisfactorily withstanding forces similar
to these which seem to be disintegrating this structure. The
subject is important and is at present being thoroughly investigated
by the Portland Cement Association v/ith other engineering societie s
and interested engineers.

Structures of concrete and reinforced concrete have shown partial
disintegration under the action of sea water, frost, • rnd stray
electric currents, as well 0.3 alkali. They have usually been made
of porous concrete or ure of such shape that they crack under the
action of the loads which come upon them, so that the water entering
the concrete can exert its disintegrating influence. Well made
concrete thut has been properly cured has not been affected by these
disintegrating agencies. The materials and methods to be used in
order to secure good concrete have been discussed in previous
assignments.

Portland cement products.- Read Articles 551 to 561 inclusive.
Concrete blocks were probably the first product in the pre-cast con-
crete industry. As a whole they were poorly made and fashioned after
an imitation of rock-faced stone. The inferior quality of the

Engr.-8 Materials of Engineering Construction- Assn 17, page 12.

product, \7hich was a poor imitation of cut stone, caused the early
failure of the industry. At the present time, however, architectural
concrete stone is successfully competing vrith natural stone for the
facing and trimming of buildings. Important examples of such
construction are found on the campus of the University of California
at Berkeley, in the case of Hilgard EaXl and Gilman Hall. The
color combinations in Hilgard Hall are particularly pleasing. The
color designs were executed in what is knoivn as scraffito. Pre-cast
trim and scraffito offer a permanent material that is relatively
inexpensive (when compared -.vith natural stone) and *;nLll undoubtedly

VV& OJai ifc cva'tniefciftv «& JW*4/ UvUftu JW U Ctvtfc (U^iM*1*'1

be used in the construction of other buildings on the campus.* Most
pre-cast trim is made by the dry cast method in \?hich specially
prepared molds are used. The product is immediately removed from
the molds, pointed-up 7;here defective in surface finish, and set
aside to cure. Considerable care must be taken in curing these
products- Concrete stone is also m^.de by pressure and wet oast
methods. The American Concrete Institute has given the name concrete
architectural stone to this product.

Concrete pipe is another important pre-cast product. The
cost of manufacture depends largely upon the method of manufacture.
Under present methods of manufacture a very satisfactory product is
being made. The principal difficulty in the use of pre-cast concrete
pipe for pressure purposes is the joint.

Engr.-8 1,'laterials of Engineering Construction- Assn. 17, page 13.

QUESTIONS.

!• Define impermeability. I/hat is its relation to absorption as
applied to concrete?

2. What are the two methods used to determine permeability of concrete?

3. \7hat are the principal causes for permeable concrete?

4. V.'hat are the principal causes for high absorption in concrete?

5. V/hat is the most effective method of xraterproofing concrete?

6. Y/hat factors affect the length of time it takes fresh concrete
to cool in freezing vreather?

7. ?*'hat is the mininum tin© that fresh concrete should be kept
at a temperature favorable to hardening?

8. What is the temperature at which concrete Trill fuse?

9. Are temperatures necessary to fuse concrete ever reached
when buildings are destroyed by fire?

10. What are some of the causes of the disintegration of concrete?

11. Discuss the effect of sea water on the durability of concrete.

12. "What are the principal portland cement products?

13. HoTr are pre-cast concrete products cured?

r • ••

•

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Civil Engr-SB. Professor C.T. Wiskocil

Assignment 18.
METALS AND THEIR ORES

Read Articles 562 to 568 inclusive. This chapter is an

introduction to the study of metals which is now to be taken up.
That part of Article 564 which describes certain metals may be
omitted at this time because it must be reviewed later in the course

when these metals are discussed in detail.

Since this chapter is introductory it is relatively unim-
portant. The essential parts will be discussed later.

Article- 563 lists the important base metals used in
engineering construction. They are iron, copper , .lead } and zinc.
Aluminum is an importpnt metal of secondary rank. Iron and
aluminum, in the list given belov/, are small in percentage, but
are found in abundant quantities.

Average composition of earth's crust

Oxygen

47.05

Phosphorus

0.11

Silicon

28.26

Sulphur

.11

Aluiainum

7.98

Florine

.10

Iron

4.47

Barium

.097

Calcium

3.45

Manganese

.077

Magnesium

2.34

Chlorine

.06

Potassium

2.50

Chromium

.033

Sodium

2.54

Strontium

.033

Titanium

0.45

Zirconium

.025

Hydrogen

0.16

Nickel

.023

Carbon

0.13

Vanadium

.018

Civil Engr-8B. Assignment 18. page 2.

Read carefully the first paragraph of Article 564.

An ore may be said to be a mineral or a mixture of minerals
from which one or more elements may be extracted with profit. As
indicated in Article 565 it is seldom that a deposit consisting of
but a single mineral is encountered.

Read carefully *l;s article on the principles of extraction
of metals, Article 568» This brief outline of principles will be
useful when the methods are studied in detail.

REDUCTION OF IRON FROM ITS ORES

Iron Ores and Ore Deposits:- The reading assignment covers
Articles 569 to 573 inclusive.

Read Article 569 on the economic importance of iron and
steel and review the paragraph on iron in article 564, previously
referred to. Iron is sometimes referred to as the master metal.
No other one metal has contributed so much to our welfare and com-
fort. There is scarcely an artiale we use that is not produced
from iron or by means of it. There is no exact substitute for it,
The automobile and the railroad could not have been developed
without it.

The native sources of iron ores that are being exploited
at the present time are listed in Article 570. As the United
States becomes more densely populated the deposits in the western
states, such as those now known to exist in Colorado, Utah, New
Mexico, Idaho and Montana, will be developed.

The Lake Superior district is the most important ore region

Civil Engr-8B. Assignment 18. Page 3.

in the Qnited States. It is made up of isolated bodies of ore
surrounding Lake Superior. These ore Dodies or ranges are scat-
tered over Michigan, Wisconsin, Minnesota and Ontario '^in Canada;.
The Marquette range is in Michigan, along the shore of Lake Superior
It was discovered in 1844 and operation was begun in 1854. The
ere is principally red hematite, and small amounts of magnetite
and limonite. The Menominee range, also in iiichigan, was opened in
1872. It is composed mainly of hematite. The Gogebic range is
partly in Michigan and partly in Tn/isconsin. It was opened in 1884.
The ores are mostly dklv^rated hematites which are red in color and
rather soft. The Vermillion range, which lies in Minnesota, ras
opened the same year as the Gogebic range. The ores are hard
hematites of red and blue color. These ranges constitute the old-
est group. The latest ranges opened, the Missabe in 1892 and
Cuyana in 1911, are the most important. The greater part of the
ore used in the production of pig iron today comes from the
Missabe range. It lies in Minnesota, and yields soft hydrated hema-
tites and limonites. The deposits are comparatively shallow, xhe
Guyana range also lies in Minnesota. i\^ny of the ores in this range
contain manganese and are mined for their manganese content only.
Some have as much as 45?£ of manganese. Both underground and open-
pi* mining is carried en in the Superior District. Most of the
mining on the Missabe range is done with steam shovels.

The Birmingham district is second in importance of the Lake
Superior district. It is in Alabama. The ore is a variety of red

Civil Engr-3 B . Assignment 18. page 4.

hematite and occurs with shale, sandstone and some limestone.
Most of the mines now being operated are worked by underground
me^hods On account of the proximity of ore, limestone, and coal
suitaole for making coke, this district has an advantage over other
districts in the country. The ore usually contains about .8%
phosphorus. Tne duplex or triplex process is employed and a slag
•with a high phosphorus content is obtained when the pig iron is
purified- This slag is used as a fertilizer.

Grouped according to chemical composition the chief iron
bearing minerals are the iron oxides, iron carbonates, iron sili-
cates and iron sulphides. Only the oxides are a factor in the
manufacture of steel in the United States.

In Article 571 the iron ores are considered in order of
their iron content.

Magnetite is ferro-ferric oxide. It is found in Arkansas
and Nev: Jersey, as well as in the states named in Article 571.
Its magnetic property is made use of in the location of ore oodies
below the surface of the ground and in mechanically purifying the
the ores, by magnetic concentration.

Hematite is anhydrous ferric oxide, FeO-?- It furnishes

the base of the world's most important ores. Hematite ores are
widely distributed and vary in iron content; the principal ones are
red hematite, specular hematite, oolitic hematite and fossil ore.

Limonite is a hydrous ferric oxide. The group of ores
from turgite to lirnonite varies in iron content from 66 to 52f0.
The formula for limonite and its iron content is given in the text.

Civil Engr-8 B . Assignment 18. page 5.

These minerals are widely distributed throughout the United States.
In Virginia tney make up the greater part of the availaole ores.

Siderite , a ferrous carbonate, is the principal ore in the
car Donate group. It is sometimes called kidney ore, spathic iron
ore, or blackoand. It is not a commercial ore in the United States
bnt is important in England. The ores of the above divisions are
usually calcined before they are charged into the blast furnace.

The manufacture of pig iron:- Reading assignment, Articles
574 to 584 inclusive.

While the purple of this part of the assignment is to dee
scribe the manufacture of pig iron, a fev; remarks on the history
of iron T>;ould be of interest %t this point. The date of the first
use of iron is not known. Archaeological research has determined
that it has been in use through a period of only about 4,000 years.
Since iron corrodes and therefore leaves no trace, it is difficult
to find evidence of its early use. Doubtful evidence exists to
show its use in the construction of the pyramids about 4000 B.C. ,
but its use by the Assyrians about 1500 B.C. and later by the Greeks
is more certain. The Romans became quite proficient in the use of
metallurgy, as is shov»n uy their •weapons. The Britons had some
knowledge of iron before the Roman occupation of England under
iC-aesar- At that time iron v;as probably produced by heating ore and
charcoal in a flat bottomed forge until a small body of pasty metal
was obtained -which could be hammered and worked into wrought iron.
A process similar to this 7/as used in Europe until about 1350. At

Civil Engr-8 B. Assignment 18. Page 6.

this time there was first used a crude blast furnace in which
was produced an iron that could be cast. The blast furnace
method was improved in England in 1619 by the use of coke instead
of charcoal as the fuel. Aoout 200 years later the hot blast -was
introduced. The first American iron -works was operated in Vir-
ginia in 1619 and the first blast furnace was built about 100
years later. The most important advances in blast furnace con-
struction and operation began to be made about 1880.

The reduction of iron ore to pig iron is brought about by
alternate layers of ore, fuel, and flux in proper proportions
through a specially designed opening into the top of a blast fur-
nace (a tall vertical stac.i: , lined with fire brick) , while hot
air is blown into the bottom of the furnace. The nitrogen and
the products of combustion pass upward through the furnace and es-
cape at the top. At periodic intervals impurities , in the form
of slag, are drawn off near the bottom and molten metal is re-
moved through a tap-hole in the hearth. In early furnaces the
metal was cast in sand molds which were arranged in rows and re-
sembled a litter of pigs; hence the metal was called pig iron.

The operation of a blast furnace is continuous, one
charge following another without a creak. Since iron ore is gen-
erally an oxide it must be deoxidized or reduced in order to
obtain metallic iron. Carbon is the reducing agent and, in the
form of coke, it is used as fuel. During the reducing process the
iron absorbs carbon so that pig iron has a high carbon content.

Civil Engr-8 B- Assignment 18. Page 7.

Coke is the principal fuel used in the manufacture of pig
iron. Anthracite coal anc: charcoal are used to a limited extent.
Coke is the residue of the destructive distillation of bituminous
coal. For blast furnace use it must be porous, so as to be
readily burned, and strong so as to withstand the load of the ore
and other materials above it without crushing. The by-product or
retort process for making coke is rapidly replacing the bee -hive
process. In the latter process air is admitted into the coking
chamber and the products of distillation are burned and thus wasted,
In the by-product process the coking chamber is air tight and heat
is supplied to the outside to coke the coal. The products of
distillation are recovered. These products are hydrocarbon gases,
tar and ammonia. The method of manufacture has little effect on
the quality of the coke.

Smelting is a metallurgical operation in which metal, in a
state of fusion, is separated from impurities with which it is

combined. It involves two processes, one, the reduction of the
metal, and the other, the separation of the metal from the mix-
ture. These operations are facilitated by the use of a flux. The
primary function of the flux is to render the materials more
readily fusible and the secondary function is to supply a substance
with which the elements originally combined with the metal may
combine. The flux should be free from impurities such as sulphur
and phosphorus. The materials to be fluxed determine the character
of the flux. If they are basic, an acid flux must be used. In
most ores, however, the impurities are acid so that the predomina-

Civil Engr-3 B. Assignment 18 Page 8.

ting flux is basic, basic fluxes are limestone and dolomite. In
the smelting zone of the blast furnace the flux combines with the
gangue to form slag. Slags furnish the means by v;hich impurities
are separated from the metal and removed from the furnace. In
the blast furnace the slag, on account of its fusibility and dis-
solving power ,( forms the only positive method of removing sulphur.
Slag has a lew density and floats upon the metal. It protects the
metal from the hot gases and prevents overheating and at the same
time conserves the heat in the metal. Since it has the power of
dissolving oxides it keeps the metal clean and also facilitates
the separation of impurities from the molten metal.

The modern blast furnace and its accessories are illustrated
in Figure 1 on page 534. Be able to sketch the cross section of
a blast furnace. Be sure to shov; the double Dell-hopper at the
top.

The beet practice today in blast furnace construction is
represented by furnaces from 90 to 100 ft. high (see the informa-
tion at the bottom of page 533 in the text). In these furnaces,
the hearth or crucible is about 10 ft high. The bosh zone is from
10 to 12 ft. high, and the stacK 70 ft. or more.

Be able to describe the operation of the hot stoves. The

air is heated to about 1000 degrees Fahrenheit in the stoves and

» 0
forced into the furnace through tuyeres (pronounced twe~ yar ) at

abcut 15 Ib. per sq. in. pressure. The temperature in the blast
furnace varies from a maximum of about 3500 degrees F» at a point
just above the tuyeres to about 500 degrees F. at the stack line,

Civil Enpr-8 B. Assignment 18. Page 9.

at tne top of the furnace. The efficiency of the furnace is greatly
increased by the use of preheated air.

The greatest single improvement in blast furnace operation
since Neilson's hot blast is James Gay ley's dry blast process. It
has been estimated that in the summer months a furnace which uses
40,000 cu. ft. of air per minute will take in with this amount of
air about 225 gal. of water per hour. It is obvious that this
water will reduce the efficiency of the furnace. In Gay ley's
process, the moisture is removed from the air by drawing it over a
system of pipes coded with brine which in turn is cooled with
liquified ammonia. The moisture is condensed and frozen on the
pipes., leaving the air practically dry. This is a refrigeration
process. The dry air is forced through the hot stoves and then in-
to the furnace. In spite of the advantage of the dry blast it is
still most common practice to use undried air. It is probable,
however, that the dry blast will soon become as universally used
as Neilson's hot blast.

The amount of materials used by a modern blast furnace in
24 hours is very impressive. These are given in the last paragraph
of Article 578 on page 535. It is evident that even a single unit
plant means a large production which necessitates large working
capital.

Civil Engr- 8 B

assignment 18..

page 10.

BIASH

i MATERIAL

9000 #s

^
\

^ CHAINED
\

Limestone 1200jjte~

Coke 2000 #s

Iron Ore 4000 #s

Tunnel Head

mat 5i

Gases
12,360 #s

HITERIA.L
S PRODUCED

Slag^ 1600 $s

Pig iron 2240 #s

"ial charged and produced in making <

of pi'g iron.

This represents American olast furnace practice in the
northern district.

If pib iron is to be used in the production of steel it is
transferred to the converters or steel furnaces in the molten con-
dition if they are near by. When the blast furnace is not part of
the steel plant it is necessary to cast the metal into pigs and
transport it in that condition. The old method was to use sand
molds, from the arrangement of which, as has-oeen stated, pig iron

Civil Engr-8 B. Assignment 18. page 11.

got its name. The present method is to use casting machines. These
are an endless chain of buckets lined with fire clay which receive
the molten metal as it comes from the blast furnace and dump the
solidified pigs into cars. The length of the bucket line is such
that the iron has time to solidify before the bucket is dumped.

Blast furnace slag is run off into slag cars and dumped on
the waste pile or granulated with a stream of water and used later
in the manufacture of port land cement, A. stream of vrater is more
effective than dumping the slag into a body of water. Some slag is
used for ballast for railway tracks and some in the manufacture of
mineral 7/ool; most of it, however, is wasted.

Fig iron itself is not. a structural material. When remelted
and cast into molds it is called cast iron. Cast iron forms the
basic material for the manufacture of steel.

Civil Engr-8 B. Assignment 18. Page .112..

QUESTIONS

1. Where are the principal iron ore deposits in the United States?

2. What are the principal iron ores? Give the miner a logical name

and the approximate iron content in tabular form.

3. Outline the process of manufacture of pig iron*

4. What is pig iron? Why is it called pig iron?

5. What is a flux? Why is a flux used in the manufacture of pig
iron?

€. Of what use is slag in the process of smelting?

7. Sketch the cross section of a blast furnace, give the approxi-
mate dimensions and name the essential parts.

8. What are the two recent improvements in blast furnace operation
which have greatly increased its efficiency?

9. How much raw material is charged into a blast furnace to pro-
duce a ton of pig iron?

10. What are the principal changes involved in the production of
pig iron from the iron ore?

11. What are the requirements for blast furnace coke?

UNIVERSITY OF CALIFORNIA. EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Cixil Engr-8 B. professor C.T. Wiskocil

Assignment 19.
TrE MANUFACTURE OF YiROUGHT IRON

Introduction:- Read Articles 585 and 586. In the blast
furnace operation the metal absorbs large amounts of carbon which,
together with other impurities, render it too brittle and coarse
for structural use. .all the methods used to refine pig iron are
essentially processes for the removal of the carbon by means of
oxidation. As sty own in Article 586, carbon is the only impurity
that is removed in the form of a gas. Other impurities are taken
up by the slag and separated from the metal in that way.

Before large-scale production of steel was possible, wrought
iron was the most important metallic structural material. it was
rolled into various shapes, •which were used in the construction of
buildings, ships, bridges and structures of all kinds. It had
sufficient strength besides it* toughness and ductility. Further-
more it was easily forged. These properties made it more adaptable
than cast iron. it was used for tools and implements that did not
require a tempered edge. The development of the Bessemer and open-
hearth processes for making steel occurred in the latter part of
the nineteenth century; since that time steel has replaced wrought
iron as the principal structural material. Wrought iron is still
extensively used for general blacksmith work, and for water and

-*'- •' '**-"••• «•

Civil Engr-8 B. Assignment 19. page 2.

gas pipes, because of the belief that it resists corrosion better
than steel, it is also used for rods and bolts which are to be
subjected to impact or shock because of the belief that this
material, with its fibrous structure, is more resistant to shock
than steel. Wrought iron has failed to compete successfully with
soft steel chiefly on account of the high cost of labor. The
process of manufacture is most laborious and yet requires consider-
able skill. The skill gained by experience in the process is
superior to a theoretrical knowledge of it. These conditions make
it difficult to obtain men since the intelligence required could
obtain higher rewards in other pursuits.

The International Association for Testing Materials defines
wrought iron as "malleable iron which is aggregated from pasty
particles without subsequent fusion, and containing so little car-
bon that it does not harden usefully when cooled suddenly."
Bradley Stoughtor.'s definition is, "Wrought iron is almost the same
as the very low-carbon steel except that it is never produced by
melting and casting in a mold but is always forged to the desired
size and form. It usually contains less than 0.12^ of carbon. Its
chief distinction from the low-carbon steels is that it is made by
a process which finishes it in a pasty, instead of a liquid form
and leaves about 1 to 2 7£ of slag mechanically disseminated through
it,"

The puddling process.-- Read Article 588. In the manufac-
ture of wrought iron, a special grade of pig iron known as forge pig
is used. It is high in silicon. The silicon is desirable since

Civil Engr-8 B. Assignment 19. Page 3.

it aids in the formation of sufficient slag to cover the bath and
prevent excessive oxidation of the iron. Phosphorous and sulphur
must be kept low since they are not completely removed with the
slag.

Basic iron oxides are used to fettle the hearth. Iron ore
is frequently used to line or fettle the furnace. The position of
the fettling material is shown in Figure 1 on page 544. During
the boiling stage the carbon unites with the oxygen supplied mostly
by the fettling material and later by the air passing over the
bath. The slag mu'st be strongly basic at this stage so that it
will retain the phosphorous and sulphur.

Slag is never completely removed in the squeezing process*
It is always present in wrought iron in the form of fibers which
extend in the direction of rolling. This is the distinguishing
characteristic of wrought iron. It can be detected by etching a
polished surface with acid. Under the microscope the structure is

clearly revealed, as shown in Figure 1 on page 598. The nick-bend

T^eMAtVy
test is also used to d^te^t wrought iron. The piece of metal is

cut partly through and then bent. The fibrous structure will be
shown by this test.

The classes of wrought iron are given in Article 589.
Charcoal irons are the purest grades of wrought irons. They are
used in the manufacture of electrical apparatus and boiler tubes,
as well as for those purposes listed in Article 589. Wrought iron
costs more than low-carbon steel. It is, therefore, sometimes
adulterated with steel scrap. The scrap and the wrought iron are

.
V P-:-;: . ••• ...-, . I* hV>. . i:

Civil Engr-8 B. Assignment 19. Page 4.

piled together and brought to a welding temperature and rolled
into merchant bars. The product Is sold as wrought iron. This
material should not be confused with the charcoal or knobbled iron
described in the text. Read Article 589.

THE MANUFACTURE OF STEEL

Introduction:- Read Article 590. It is not possible to give
a concise definition of steel. Probably the most satisfactory one
is that given by R.M. Howe. "Steel is that form of iron which is
malleable at least in some one range of temperature, and in addi-
tion is either (a) cast into an initially malleable mass; or (b) is
capable of hardening greatly by sudden cooling; or (c) is both so
cast and so capable of hardening.11 Cast iron and pig iron are
not malleable but chrome and manganese steels are malleaole only
through a short range of high temperatures; at ordinary temperatures
they are not malleable. The condition in (a) distinguishes steel
from malleable oast iron, which is made malleable by special treat-
ment after it is cast. Wrought iron is not cast and it cannot be
hardened by sudden cooling. Cementation steel (see page 656) is
not cast, but it will harden upon sudden cooling; there are also
many carbon steels which are cast but will not harden. These facts
will show why it is difficult to define steel.

Iron oxide and air are available for the purification of pig
iron. The oxide of iron is the principal substance used in the manu-
facture of wrought iron. Iron ore and air ar« the oxidizing sub*
stances used in the manufacture of steel but they require different

• .

•

s »

••« .

Civil Engr-8 3. Assignment 19. Page &•

kinds of apparatus. The two chief methods of -purification are the
pneumatic and the open hearth. In both methods the purification
may be accomplished by oxidation alone, in which c§se they are
called acid processes. If oxidation is carried on in the presence
of strong bases the process is known as the basic process. In the
acid process, only carbon, silicon, and manganese are removed from
the iron. In the basic process, in addition to these elements, the
phosphorus is also removed. The pig iron produced in this country
is best adapted to treatment by the basic open hearth and the acid
Bessemer process. These are the leading methods used in the manu-
facture of steel.

The Bessemer process of making steel;- Read Articles 591
to 595 inclusive. This process consists essentially in blowing air
under a pressure of 20 Ib. per sq. in. through a bath of molten
iron contained in a specially constructed vessel known as a convert-
er. The silicon and manganese combine with oxygen and form a slag
while the carbon forms Co and COg and passes out of the bath. The
heat required to maintain the temperature of the bath is obtained
from the chemical action which occurs when the elements are oxidized
Steel made in this way contains oxides which render it unfit for
use. A recarburizer must, therefore, be added after the metal is
blown to give it the necessary strength and toughness. The process
is explained in detail in Article 593; study this article carefully.

The mixer described in Article 593 and illustrated in Figure
3, on page 548, is very important in the Bessemer process. Besides
acting as a storage place for hot metal as indicated in the text

• -i •;*•;' • ••::•' -'t ' • -3 ' 'I1'" •', I '• • '•

1 • " ' " ' - ...>.!..

I ..-•/'. -. • ;. '. ., •
3j -.-; J •: :• :.' . .

Civil En5r-8 B. Assignment 19. page 6.

: conserves the heat in the molten metal and makes the charge
taken to the converters more uniform. Mixers average in size from
200 to 1200 tons capacity.

Pig iron suitable for the manufacture of steel by the
pneumetic process (acioj should contain 3 to 4$ carbon, 1 to 1.5$
silicon, less than Q.lf0 phosphorus, and small amounts of sulphur
and manganese.

Basic Bessemer is successful only with pig iron which -is
high in phosphorus and low in silicon. There are practically no
ores mined in the United States that are high enough in phosphorus
for the basic Bessemer process. Pig iron with too much phosphorus
for the acid Bessemer is made into steel by the basic open hearth
process.

The Siemens process of making steel:- Read Articles 596.
to 598 inclusive. The process is described in detail and is very
important.

There are several distinct modifications of the basic open
hearth process. There is the pig-and-ore process, the pig-and-
scrap process and the ail-scrap process. The pig-and-scrap process
is now in most general use. When pig iron is expensive, as it is
out here on the Pacific Coast on account of high transportation
charges, the all-scrap process is most economical. The mills in
the bay region, such as the Pacific Coast Steel Company at South
San Francisco, the Judson Steel Company at Emeryville, and the
Columbia oteel Company at Pittsourg, all use the all-scrap process.

Civil Engr-8 B. Assignment 19. Page 7.

The basic open hearth method is employed and a high grade of steel
is produced. The nearest blast furnace is at Pueblo, Colorado.

Remember that the recarburization of basic steel cannot be
accomplished in the furnace because the carbon, silicon and manganese
in the recarburizer would reduce the phosphorus in the slag and re-
store it to the metal. For this reason the recarburizer is added
to the metal in the ladle. Since the recarburizer cannot convenient-
ly be molten, it must be ferro-rnanganese instead of the spiegeleisen
which is used in the acid open hearth process.

Study Article 599. In it is a summary of the two most im-
portant processes for making steel.

Read Articles 600 and 601. A method by which the acid
Bessemer and the basic open hearth processes are combined is de-
scribed in the latter article. This process is known as the duplex
process. It is used extensively in the south where the ore has a
high phosphorus content.

Read Articles 602 to 604 inclusive on the minor methods of
making, steel.

The manufacture of blister steel or cementation steel is
described in Article 602. This steel is very expensive but is of
high quality. The cementation process has never been used to any
great extent in the United States. The cementation process re-
sembles the case hardening process used to give wrought iron and
soft steel a hard surface of high-carbon steel. See Article 710
in the text.

-• •

•• -•'

Civil Engr-8 B. Assignment 19. Page 8

The manufacture of crucible steel is described in Article
603. This method of making steel is widely used when a high grade
product is wanted. Obviously crucible steel cannot be made in
large quantities. This steel is superior to open hearth and
pneumatic steel because it is made in closed vessels out of con-
tact with the air. Crucible steel is less expensive than blister

steel.

Electric steel:" Study Article 604. The Stassano furnace

is of the radiation arc type. From an electrical standpoint this
furnace has the important advantage of uniform power consumption.
Only small sized Stassano furnaces have been built and are not
in wide use.

The induction type of furnace was adapted to the manufacture
of steel by Kjellin. It is impossiDle to obtain high temperatures
in this type of furnace, hence it is not adapted for desulphuriz-
ing operations in which sulphur is removed as sulphide. The
Heroult furnace of the arc resistance type heads the list of
electric furnaces in use for the manufacture of steel.

The following information was taken from a paper by Keeney
and Lyon, of the United States Bureau of Mines: "For many years

all high grade steels were manufactured by the crucible process but
since the advent of the electric furnace there has been a gradual

adoption of that furnace for refining steel. For the complete
refining of the higher grades of steel, the use of the electric
furnace is now thoroughly established. Any products that cen be

Civil Engr-8B - Assignment 19. page 9.

made by the crucible process can be made by the electric process,
and in most cases with cheaper raw materials and at a low cost.
In the electric furnace complex alloy steels can be made with pre-
cision. The hig;h temperatures attainable facilitate the reactions,
and alloys need not be used so largely for the purpose of removing
gas. Very low carbon steel can be kept fluid at the high tempera-
tures. Steel free from impurities and of great value for electri-
cal apparatus can be made. With the electric furnace large cast-
ings can be made from one furnace, whereas in the crucible process
steel from several crucibles must be used. For small castings,
which require a very high grade metal free from slags and oxides,
electrically refined steel is especially adapted. The electric
furnace gives a metal of low or high carbon content as desired,
hot enough to pour into thin molds, and steel free from slags and
gases.

"Recent experiments show that electric processes have the
following advantages over acid Bessemer and basic open hearth
methods, A more complete removal of oxygen; the absence of
oxides caused by the addition of silicon, manganese, etc.; the
production of ingots of 8 tons and smaller that are practically
free from segregation; the reduction of the sulphur content to
.005^ if desired; and the reduction of the phosphorus to .005$c,
but with the complete removal of the oxygen."

Considering the various methods of making steel, the process
in which the electric furnace is used in connection with the basic

•

.'"

Civil Engr- 8 B Assignment 19. Page 10.

open hearth will yield the greatest amount of 'steel \vith highest
efficiency "and quality of product.

The assigned subject is thoroughly covered in the text,
Chapter XVIII, and it should be carefully studied since it is very
important. The following questions cover only a few of the im-
portant point's. You should be able to answer similar questions x*

on the other points in the chapter.

Civil Lngr-8 B- Assignment 19, page 11,

QUESTIONS

1. What is the importance of wrought iron as a structural
material?

2. Define wrought iron.

3. Describe "briefly the process by which "wrought iron is made.

4. What is the source of the oxygtn required to purify pig iron

in the p-ucl cling process?

5. Why is it necessary to have a basic slag?

6- What tests are used to distinguish wrought iron from soft or
or lov -carbon steel?

7, Why is wrought iron sometimes adulterated with steel scrap?

8. Whe.t are the leading methods of making steel in the United
States?

3. Describe briefly the pneumatic process.

10. What is a recarburizer and why is it used?

11. Why is the basic Bessemer process not used in the United States?
12 Sketch the cross section of a converter.

13. What are the principal chemical changes that take place during
tiie open hearth process of making steel?

• 14« Why are different furnace linings used for the acid and basic
processes?

15. When is the recarb"»-izer added in the basic process and "why?

16. Compare the pneumatic and the open hearth processes for making
steel by tabulating the advantages and disadvantages.

• 17. Why is crucible steel more expensive than open hearth or

Bessemer steel?

• 18. Why is it that a higher grade of steel can be obtained by the

crucible process than by the Bessemer method?

19. What are the advantages of the electric furnace in the manu-
facture of steel?

20. Why does the electric furnace produce a higher grade of steel

na^> Via»*«+ Vi r>v /•»/» e e « 9

UNIVERSITY OF CALIFORNIA. EXTENSION DIVISION
Correspondence Courses •

Materials of Engineering Construction
Civil Engr-8 B» Professor C-T. Wiskocil

Assignment 20.
THE MANUFACTURE OF IRON AND STEEL SHAPES

Study Article 605 to 616 inclusive.

Methods of shaping steel:- Read Article 605. The next
step in the manufacture of steel, after the refinement of the cast
iron, is to make it into the various shapes and forms required by
the uses to which it is to be put. The shaping is a process
either of casting or of mechanical working. Since steel is usually
in a molten state after being refined, it would appear that cast-
ing vjould be the nost economical method of shaping it. But metal
cast from the molten state has an inherent lack of strength and
ductility when compared with similar metal which has been mechanic-
ally worked into shape. Some shapes are so intricate in form that
they must be cast and in others no great strength is required so
that casting is a regular method employed for shaping many steel
products. The chief causes of weakness in steel castings are
blow holes, segregation, and crystallization. These defects can
be minimized by proper methods of manufacture and the use of
alloys is resorted to so that steel castings can be made of rela-
tively high strength and quality of metal.

The mechanical v/orking of steel can be carried out by three
different methods; namely, hammering, pressing, and rolling. Ham-
mering and pressing are frequently classed together as forging.

Civil Engr-8 B. Assignment 20. Page 2.

Steel is probably more widely used in rolled shapes than in any

other form. Steel plate for tanks and boiler shells; structural
shapes, such as I-beam* , channels and angles; bolts, nuts, rivets,
nails, rails, wire, chain; and tubing and pipes are some of the
products made from rolled steel.

Steel ingots:- Read Article 606. Steel ingots for roll-
ing or forging usually weigh from 3 to 10 tons. The average life
of an ingot mold is about 100 heats.

During cooling, ingots naturally develop certain defects.
The principal defects are mentioned in this article. They are
pipes, blow holes, segregation, and crystallization. Other de-
fects, such as. checks, scabs, and slag inclusions, are incidental.

Pipes are caused during the solidification of the metal,
as described in the text. The size of the pipe in Figure 2 on
page 560 is rather larger than usual. Pipes are caused where the
surface of the metal becomes oxidized so that it will not weld
up in rolling; when thi.p occurs : v.-'; the pipe appears as a defect
even in the smallest section into which this part of the ingot may
be rolled. Pipes are liable to cause accidents in rolling. The
only way of dealing with the pipe is to crop the ingot and dis-
card the part which includes the pipe. This method causes con-
siderable waste and various schemes have, therefore, been devised
to overcome the pipe without having to crop the ingot. The most
promising is the hot-top mold. The idea is, to .putt it briefly,
to keep the top of the mold molten and thus prevent the formation
of the pipe. In the ordinary mole the top is the first to solidify.

Civil Engr-8 B. Assignment 20. page 3.

To .Tjaice the top the last to freeze the upper part of the ingot is
Ljade larger, anc the upper part of the mold is made thinner. A
different method, whicb has been used to a limited extent, is that
in which the ingot is compressed while the interior is molten.
This also tends to prevent the formation of the pipe.

Blow holes are another serious defect. The illustration
(Figure 2, on page 560) is again slightly inaccurate. The surface
cavities are very small, while the deep seated blow holes are
frequently large. The latter may be over an inch in diameter.
While the holes just beneath the sicin of the ingot may be micro-
scopic in size they are, nevertheless, the most troublesome. They
are nore lia&le to develop oxidiaed surfaces and thus to produce
seams in the finished products. The deep seated holes are not
subject to oxidation and since they tend to reduce the size of the
pipe they are not harmful. The method of compressing the ingot,
previously referred to, prevents the formation of large blow holes
as well as pipes, but it is expensive. It is not "widely used, be-
cause the cropping of the ingot is after all more economical.
The metal discarded in cropping is used in the refining process as
steel scrap. Steel that has been properly made and deoxidized at
the time of recarburization will not have troublesome blow holes.
Molten steel which is not properly deoxidized, and from which gas
is bubbling, is known as wild steel. Aluminum is very effective
in quieting or killing wild steel and it does not affect the
properties of the steel. The killing is done in the ladle. Steel
should be quiet before it is poured.

Civil Engr-3 B. Assignment 20. page 4.

Electric steel, on account of its being refined without
contact with air currents is particularly free from blov; holes.
Segregation is the localization of the impurities in the ingot.
The ingredients in the molten ^netal have different freezing
points. The substance with the lowest freezing point will be
located near the top and center of the ingot, about at the bottom
cf the pipe. Segregation cannot be overcome but it can be mini-
mized by rapid cooling.

Coarse crystalline structure or ingotism is inherent in
netal that is cooled s lovely from a high temperature. The size of
the crystals depends upon the rate of cooling. Large crystals
make the ingots likely to tear in rolling. The rolling process
refines the grains and prevents the effects of coarse crystals
showing up in the finished product, if it has been properly worked

A. mold having a rough surface causes resistance to the
natural contraction of the cooling metal and produces checks or
small cracks in the ingot skin. If the ii:old is improperly poured
so that the metal is splashed against the sides of the cold mold
•where it sticks anc oxidizes, the ingot •will have scabs on its
surface after it is stripped. These defects produce a seamy pro-
duct. In plates they will form surface defects.

Slag inclusions may be formed by dirt in the ladle or mold,
or slag may be formed by the oxidation of the metal in the ladle.
Small slag inclusions do not have time to rise to the surface of
the metal. In the finished product, slag inclusions are the
source of surface blisters

Civil Engr-3 B. Assignment 20. Page 5.

Pipes, blow holes, and segregations cannot be entirely
prevented. Their bad effects can be minimized, howex^er, by the
use of aluminum to quiet the metal and by rapid cooling. Since
slow cooling is necessary to minimize piping, careful study and
exercise of judgment are necessary to secure the best quality in
any lot of steel.

Heat treatment of ingots ;- Study Article 607. Ingots are
placed in the soaking pits in a vertical position. This is
necessary because the ingot should be stripped as soon as possible
so as to conserve the most heat and also so as to require a mini-
mum of extra he&ting in the soaking pit. Since the interiors in
the ingots when they are stripped are still soft the ingot must
remain in the upright position in which it was cast. Otherwise
the extent of the pipe may be increased and its position altered.
The upright position also exposes the greatest surface of the in-
got so that it will more quickly come to a uniform temperature.

General method of rolling;- Read Article 608. Rolling,
as a method of shaping steel, is now most extensively used.
Kenry Cort is credited with having rolled the first steel in 1783.
Other metals were evidently rolled before that time. Rolling is
a very rapid method of shaping steel.

In the breakdown of the heavy ingots large mills are used.
These reduce the ingots to lighter sections, in such simple shapes
as round, square, and rectangular. When the ingot is reduced to
a square section six inches .In r grr on a side, or to rectangular
sections in which the widths are less than twice the thickness,

Civil Engr-8 B. Assignment 20. Page 6.

these sections are called blooms. If the section of the metal is
square, and between 1 1/4 and 6 inches on a side it is called a
billet. If in width the section far exceeds the thickness it is
called a slab. Blooms, billets and slabs are cut into convenient
lengths. Mills for the shaping of steel are named after the prod-
uct they make; as olooming mill and slabbing mill. In England
a mill making blooms is known as a cogging mill.

Rolling mills; Read Article 609. The various types of
mills are described in this article. The rolls are illustrated in
Figure 3 on page 561. They are made of cast iron, steel, or
alloy mixtures. Rolls must be tough to withstand the shock pro-
duced as the piece enters them: they must have high transverse
strength to work under the high pressures developed in rolling;
they must be hard so as to have good wearing qualities; and they
must be sound so that they will not develop surface defects, and
thus cause the rejection of the finished products. Cast iron
rolls are known as sand rolls and chilled rolls; alloy steel rolls
are given the trade names of steel rolls and adamite rolls.
Chilled rolls are expensive but they must be used where a high
grade finish is required. A higher tonnage is obtained from these
rolls than from any other kind. Chilled rolls for plate mills
have been made as heavy as 40 tons. These require a mold about
23 feet in length. Besides being subject to violent impact and
heavy pressure, rolls are unevenly stressed, and unevenly heated,
and even over heated and then suddenly cooled. These are very
severe conditions and they can be stood only by well made rolls.

Civil Engr-8 B. Assignment 20. page 7.

Steel rolls, while they hava the required strength, do not hold
their finish uncer the high temperatures of rolling. They are
seidOiQ used for finishing rolls, but they are well adapted to the
work of the blooming mills and heavy roughing stands. The adamite
rolls have not ^et been very Widely used.

plates ;- Read Article 610. Plates are rolled in an
ordinary mill and sheared, as indicated in this article, or they
are roilec in a universal mill. Plates are known as sheared or
universal mill plates, according to the method by which they were
rolled. Sheared plates are not suitaole for girder construction;
universal mill plates with rolled edges are desirable for this
purpose. Universal mill plates can be rolled to exact and uniform
widths so that shearing, costs are reduced, and furthermore, machin-
ing is frequently unnecessary. Moreover, universal mills turn out
great tonnage so that universal mill plates are lower in cost
than sheared plates.

Sheets:- Read Article 611 on the manufacture of thin
steel sheets.

Pipes:- Read Article 612. The manufacture of seamless,
but -welded, and lap-welded tubing is explained in this article.

Wire:- Read Article 613; it explains the manufacture of
wire. Wire dies are made of steel plate and chilled iron. The
latter are most extensively used in this country. They are ex-
tremely hard.

Forging and pressing :- Read Article 614. Shaping by
hammer forging is a slow process. However it is a simple one and

Civil Engr-8 B- Assignment 20. page 8.

was the first method used to shape metals. The first power
hammer was built in England but the first steam hammer was a
French invention. It was first operated in 1842. It was a single
acting hamraer in which the head or top was raised by steam. The
invention of the double acting steam hammer, which employed steam
power on the downward stroke, was a decided improvement. The
first one was built in Pennsylvania, in 1888.

The suddenness of the hammer blow tends to localize the
effect and hence only the exterior of the metal is refined. If
each blow of the hammer reduces the metal to a considerable de-
gree, or if the metal is thin, this method will produce material
that is superior to rolled steel. Small objects made of high-
grade steel, such as stock for cutlery and tools, are usually
hammered into shape . The making of drop forgings is explained in
the text.

Forging presses are an English invention of about 1860.
They were introduced into the United States in 1887. The sizes &
and working pressures are g,iven in Article 614. The action and
effect of pressing is different from that of hammering. Pressing
is so slow that a kneading action takes place and the effect,
therefore, penetrates deep into the steel instead of refining only
the surface as does hammering. Both methods improve the quality
of steel.

Steel castings:- Read Article 615. During recent years
there has teen much development in the quality of steel castings

Civil Engr-8 B. Assignment 20. Page 9.

and also in the types of objects cast. Large castings which are
subjected to heavy stresses are now made of cast steel. Loco-
motive frames, stern frames for ships, anchors, buckets, and bucket
tumblers for gold dredgers are some of the articles made of carbon
ard alloy steels in the form of castings. The Columbia steel
Company at pittsburg, California, is the largest steel casting
plant on this part of the pacific Coast. Most of their steel is
made in basic open hearth furnaces of steel scrap. They also
operate a small acid open hearth furnace.

The production of good steel castings requires considerable
foundry experience. Many complex foundry problems are involved.
In order to produce sound castings it is necessary to have large
sink heads so placed in the mold that the hot steel is available
to fill any part of the casting where there is a tendency on
account of too rapid cooling, to produce a cavity. Due to the
excessive shrinkage of steel castings there are severe internal
stresses set up in the cooled product. These stresses can "be
relieved and the structure of the casting refined by proper anneal-
ing. Steel castings must be carefully designed so that there are
no sharp angles in the outline. The molds for large castings
must be well reinforced to withstand the heavy loads of molten
metal.

Omit Article 616 on page 5(qf. The statistics given in
this article are not important.

Civil Engr-8 B. Assignment 20. Page 10.

QUESTIONS

1. What methods are used in shaping steel?

2. How do the various processes employed in shaping steel
affect its quality?

3. What is an ingot, a blooa, a "billet?

4. What is a pipe? How is it caused? Can its occurrence be
prevented? How does it affect the metal in a rolled section?

5. What is segregation and how is it minimized?

6. How are blow holes formed? Can their formation be prevented?

7. What is a universal mill?

8. What are the rolls of a steel mill made of?

9. How is steel tubing made?

10. How are the cooling stresses in steel castings relieved?

11. Why is it necessary to soften wire during the drawing process?
How is this softening accomplished?

UNIVERSITY OF CALIFORNIA. EXTENSION DIVISION

Correspondence courses '

loiter ials of Engineering Construction

Civil Engr-8 B < professor C-T- Wiskocil

Assignment 21,

FORMATION AND STRUCTURE OF ALLOYS
Alloys in general-.- Read Articles 617 to 6266 inclusive*

Reasons for alloying metals are given in Article 617. By
the alloying process, desirable properties may "be improved and un-
desirable properties may be lessened „ An alloy may be tougher,
harder or more ductile than any of the constituent metals. The
cost of production may be decreased by introducing cheaper metal
into the alloy and by producing an alloy that is more easily
worked (cast and machined) than the metals from which it is
made..

A mixture is defined in Article 618. In a mixture the
tiro or more ingredients do not bear a fixed proportion to one

another, and however thoroughly corn-mingled maintain a separate
existance^ The constituents of a mixture can alv/ays be detect-
ed by microscopic examination.

As indicated in Article 619, elements combine in definite
fixed proportions to form compounds. The formation of chemical
compounds is not of much importance in the consideration of iron
and steel.

Solid solutions are described in Article 620. The most
familiar examples of solutions are in the form of liquids. How-
ever it should be remembered that every mixture of gases is a

solution

Civil Engr-8 B. Assignment 21. Page 2.

and that even metals may form solutions which, when they solidify,
are known as solid solutions. The solidification of a liquid
solution does not necessarily produce a solid solution. If the
constituents separate rr>on solidifying the solid is a mixture.
In a mixture the individual ingredients may be seen although in
some cases of thoroughccccBrciiingling the use of a microscope is nec-
essary . But if the constituents remain completely merged so that
they retain in the solid state the essential characteristics of a
solution, the solid is called a solid solution. The solid solu-
tion must possess such uniformity of structure that the constitu-
ents cannot be detected by physical means such as microscopic
examination, and furthermore the combination of the component parts
in any proportion must be possible. In these regards it differs
from a compound- Glass is a solid solution; an alloy of gold and
silver is another. In the latter case the elements combine into
the same kind of crystal no matter -v?hat their relative amounts
may be .

Study Article €?? carefully. As explained in this article
most alloys of steel are formed by fusion. Low carbon steels are
given a hard exterior surface by the method of diffusion in which
the diffusing material may be solid, liquid or gas. The term
miscible used in this article means capa"bldl*-y of being mixed;
raixable

Read Article 622 on allotropy- Allotropy may be defined as
the ability of an element to exist in two or more conditions,

Civil Engr-8 B- Assignment 21. Page 3.

which are distinguished by differences in properties. Carbon,
for instance, may exist as diamond, charcoal, lampblack, and black-
lead. Iron has several allotropic forms. See Article 658 on
page 590.

Study Article 623 on the crystalline structure of metals.

Metals are inherently crystalline, and it is, therefore, in-

»
correct to speak of the crystallization of iron and steel as a

result of fatigue. See Article 822, on page 771.

The strength and toughness of metals are influenced by
the shape and size of the crystals as well as by the chemical com-
position of the metal. Steel of high strength has very small
crystals and they can be detected only under a powerful microscope.
The microphotographs on pages 596 and 597 will illustrate this
point. The effect of heat treatment on the shape and arrangement
of crystals is shown in the illustrations on pages 628, 629 and
630. Until recently the examination of the fresh fracture of iron
and steel was the only method of classifying the product. Even
at the present time, melters in charge of open .hearth furnaces
cast, break and examine the fresh fracture of small bars of metal,
in order to watch the elimination of the impurities from the bath,
and at the end of the heat to determine the carbon content, which
they predict to within a few points. If the carbon content of a
piece of steel is known, skilled inspectors can determine approxi-
mately by its fracture the heat treatment it has received, and its
probable strength and toughness.

Civil Engr-8 3. Assignment 21. page 4.

As explained in Article 623, when steel passes from the

liquid to the solid state, the molecules of the various constitu-

i
ent£ arrange themselves to form small bodies having regular

geometrical outlines. This phenomenon is called crystallization.
Individual crystals may be octahedral or cubical bodies, and under
ideal conditions of high fluidity, absence of foreign particles,
slow cooling, and undisturbed liquid, will form perfect geometric
shapes. However, under conditions of manufacture, steel solidifies
into imperfect crystals v;ith irregular form, which are sometimes
called grains.

Read Article 62<t on the effects of solubility relations
in alloys. Since no examples are given it may b^' rather difficult
to comprehend the information given. If this article is reviewed
after the study of Art Vies 627 to 636 inclusive, in which defin-
ite cases are taken up the more general statements will be under-
stood.

Study Article 625. Microscopic examination and examination
of heating and cooling curves afford the most important means of
investigating the properties of pure metals and their alloys. The
method of obtaining cooling curves is explained. It should be
remembered that the temperature of the material must be observed
and recorded at uniform intervals of time during a uniform heating
or cooling. This method will produce diagrams liice those shown
in Figure 2, on page 573.

If a body undergoes an abrupt change in physical properties

Civil Engr-8 B- Assignment 21. page 5.

(as -when it melts or vapor izes), a quantity of heat is aosorbed
or given off without changing the temperature of the body. The
heat absorbed during the change in state of a body is called
latent heat. Latent heats will have a marked affect on the cool-
ing curves. If all the heat given off by a body is furnished at
the expense of the temperature of the body, that is, if it dis-
appears as sensible heat, the cooling curve will be smooth and
continuous as (a), in Figure 2, on page 573. Horizontal portions
or arrests in the cooling curve indicate that the temperature is
maintained by the evolution of a certain amount of latent heat.
See (b) in Figure 2. The curve belo\v the freezing point or
arrest in the cooling is similar to that in Diagram (a). The
cooling curve for water should be familiar, since it falls -within
ordinary experience. When water is subjected to a low temperature
it will lose heat steadily until the freezing point is reached
at zero degrees Centigrade. At this point the -water will continue
to lose or radiate heat, but its temperature will remain at zero
until all the water is changed into ice. During this second
period radiated heat is given off at the expense of the so-called
latent heat of fusion of ice. Further radiation is at the expense
of sensible heat and the temperature of the ice falls until it
becomes that of the surrounding medium. The cooling curve of
liquid antimony or any pure metal near its solidification point
is very similar to the cooling curve of water. The curve is
similar to that in diagram (b) in Figure 2.

Civil Engr-8 B-

Assignment 21.

Page 6

Study Article 625 on cooling curves. Temperature - time
diagrams such as are shown in Figure 2 are not well adapted to
show small evolutions o* heat in an alloy such as steel. An
inverse rate curve, however, will magnify the changes in direction
of the cooling curve and permit a more accurate determination of
critical temperatures. The data for an inverse-rate curve are
obtained by reading and recording the time required for the body
to cool through equal intervals of temperature. The following is
an inverse-rate cooling curve for 0.4$ carbon steel ;

1
t+

CD
6-1

Time Intervals
Figure 1.

The equilibrium diagram for alloys of carbon and iron is
obtained from inverse-rate cooling curves for a complete series of
alloys. The critical points are more readily determined from
these diagrams tha& from the ordinary cooling curve. An ordinary
cooling curve for 0.4% carbon steel is as follows:

Civil Engr-8 B.

Assignment 21,

Page 7

Time
Figure 2

The critical points are scarcely perceptiole, and if the curve
were dra?/n from experimental points, the breaks or arrests in the
curve would be determined only with difficulty. The superiority
of the inverse -rate curve is evident.

An equilibrium diagram is shown on page 591. It is of
great importance in the study of iron and steel. Other names
for this diagram are given in Article 626:p about the middle of
page 574. Equilibrium diagram is as good a name as any of those
listed.

Study Articles 627 to 630. The freezing of binary alloys
which solidify by selective freezing is fully explained in these
articles. The constituents in this type of alloy separate in
freezing. Lead and tin form such an alloy. An equilibrium
diagram for water and salt is like that shown on page 575. That
part of the iron-carbon equilibrium diagram (shown on page 591)
to the right of the 2% carbon line is analagous to that of the
binary alloys in which the state of solution is not maintained in

Civil Engr-8 B. Assignment 21. Page 8.

the solid state, namely to those -which solidify by selective
freezing. Primary austenite which will be described later, in-
stead of iron, separates from the melt to the left of the
eutectic point.

The temperature at which an alloy of this type begins to
solidify depends upon the relative percentages of the constitu-
ents. If this is, say, the point X, in the diagram in Figure 3,
freezing v/ill begin at temperature j. Remember that only the
melt or mother liquor is enriched in constituent B , since crystals
of W separate out of the solution. The composition of the alloy
always remains as represented by the percentages at the point X.
Note that the cooling curve for an alloy of the composition X is
represented in Figure 2, diagram (d), on page 573.

The term eutectic is used for the first time in this
article. It is taken from a combination of the two Greek words
which mean "well" and "melting". The meaning of the term eutectic
is taken as easily-melted , or literally, low-melting. A mother
liquor which always has the same composition for given constituents,
and a-ioonstant freezing point, and which remains liquid longest,
or in other -words which has the lowest melting point, is called
the eutectic of the given constituents. The fact that a eutectic
has a constant melting point and hence a constant composition
led early investigators to believe that it was a chemical com-
pound,. Later it was shown that its constituents were not in any
simple molecular ratio. Furthermore microscopic examinations of

•• ' •' ' :..

. Civil Engr-8 B. Assignment 21. Page 9.

eutectics (see the illustrations on page 597), showed that they
are not homogeneous substances, but a mechanical mixture of
minute cyrstal grains of the const ituents.

Study Articles 631, 632, and 633 on the binary alloys in
which the constituents in solution in the liquid remain in solu-
tion in the solid state; in other words those in v?hich they form
a solid solution. The diagram in Figure 8 on page 579 illustrates
the binary character of the gold-silver alloys, which are of this
type. The regions II and IV to the left of the 2$£ carbon content
as indicated by the point S in the iron-carbon equilibrium diagram
in Figure 1, on page 591, is a region of non-elective freezing and
shows a situation analagous to the freezing of the alloys discussed
in this article.

Study Articles 634, 635, and 636. These articles, together
with similar ones previously studied, form the basis for a study of
the iron-carbon equilibrium diagram which is of importance. The
area of this diagram to the left of the 2% carbon content line
shows selective freezing from a solid solution with the formation
of a eutectic. To differentiate this latter eutectic from the
one at point E in the diagram on page 591, which is a true eutectic.,
since it is formed from a mother liquor or solution, it is given
the nane sutectoid , a term which is interpreted as meaning "some-
thing of the nature of a eutectic".

Be able to draw characteristic equilibrium diagrams and ex-
plain the process by which freezing takes place.

Civil Fngr-8 B. Assignment 21. Page 10.

The discussion of alloys of more than two components need
not be studied. It would "be of use in the discussion of alloy
steels "but in this text they are not treated in much detail.

The information in this assignment is rather different
from that in any so far studied. The student should put forth an
effort to master the fundamental principles discussed in the text.
No thorough discussion of iron and steel can be made without use
of the equilibrium diagram and before it can be used with facility
the fundamentals given in Chapter XX in the text must be understood.

Civil Engr-8 B . Assignment 21. page 11.

QUESTIONS

1. How does a mixture differ from a solution? From a compound?

2. What is a solid solution?

3. What is a eutectic?

4. What is a eutectoid?

5. Define allotropy. What is its relation to the study of

iron and steel?

6. Draw a cooling curve for water near its freezing point.

7. What is an inverse -rate curve? What is it used for?

8. Explain the reason for the horizontal parts or arrests in

a normal cooling curve-

9. Would you expect to find perfectly shaped crystals in

commercial steel? Why?

10. Draw an equilibrium diagram for a "binary alloy and explain

hovr it freezes if the state of solution is not maintained
in the solid state.

11. Why are metals alloyed?

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Civil Engr-3 B. Professor C.T. Wiskooil

Assignment 22.
THE CONSTITUTION OF IRON AND STEEL

The necessity for alloying pure iron is briefly stated in
Article 639. The reasons for alloying metals in general were
given at the "beginning of the previous assignment on the "Forma-
tion and Structure of Alloys". In this discussion, pure steel
will be considered as an alloy of iron and carbon. In ordinary
steels there are, besides these elements, sulphur, manganese,
phosphorus, oxygen, and silicon, together with traces of copper,
aluminum, and nitrogen. Carbon and other elements added purposely
are essential ingredients; the others are impurities. The marked
effect that additions of carbon to pure iron have on the result-
ant alloy are due to the changes caused in the structure. This is
very evident from microscopic studies of these alloys. See the
illustrations on page 596 > Because of the effect carbon has on
the physical and mechanical properties of steel, its presence is
necessary in very small amounts only. Even in the hardest tool
steels it does not exceed 1.5$ by weight. Carbon is usually
measured in hundredths of one per cent, each unit (or 1/100 of one
percent) of which is spoken of as a point. A steel having a
carbon content of 0.25$ would be designated as 25-point carbon
steel.

Civil Engr-8 B-

Assignment 22.

Page 2,

Steel was defined in Assignment 19 under the subject
Manufacture of Steel. You should be able to give definitions in
Articles 640 to 655 at the time the materials in question are dis-
cussed and should make no attempt to remember definitions of
materials that are not discussed* Furthermore, you should not
memorize definitions in the words of the text, but should define
materials and processes in your own words. Read over Articles
640 to 655 inclusive and see hovr your own definitions agree with
those in the text.

Read Article 656 but omit the table. The equilibrium
diagram for alloys of iron and carbon will now be taken up in de-
tail. The remainder of the chapter should be carefully studied.

The critical temperatures for pure iron are given in
Article 658. Critical temperatures were referrecd to in the previ-
ous assignment, number 19, under the discussion of cooling curves.
If eutectoid steel is considered it will be found to have only one
critical point. The heating and cooling curve would be approximate'
ly as f ollov/s :

^ecalescence

Point

r— Removed from furnace

Recalescence Point

Cooling

Time

Civil Bngr-8 B- Assignment 22, Page 3.

As explained in the text the critical points 'are higher on heating
than on cooling. The recalescence point for eutectoid steel
(0. $% car"bon) is about 690 degrees Centigrade, Since the structur-
al changes -which occur do not take place suddenly the critical
temperature or critical point is more properly designated by the
term critical range, "When eutectoid steel passes through its
critical range during the process of cooling the temperature of
the steel will actually rise if the conditions are favorable. An
attempt has been made to show this condition in the diagram just
given. In the case of pure iron the change in rate of cooling is
not very marked. There is no actual rise in temperature , or
recalescence, at the critical temperature which occurs about 900°
Centigrade The leaver critical range at 760°C. is less marked
than the first. Below 760° the steel cools normally to atmospheric
temperatures. In a lor; carbon steel, say one having 0.1$ carbon,
there are three thefVftl retardations.. The most pronounced is at
850° c, the second about 760° and the third near 700°c The last
tvro are quite indistinct. As carbon is added to the alloy the two
upper critical temperatures, found in the 10-point carbon steel,
will approach each other and at carbon contents of .35 to .4C$ will
merge into one, so that these steels have only two critical tempera-
tures, one at about 740° and the other at about 700°. Further

additions of carbon seera to cause the t7/o remaining critical tem-
peratures to merge into one at about C.6^ carbon and over- Theoreti-
cally the merging should not occur until the eutectoid composition
is reached at O.S?£ carbon, The actual determination of two critical

Civil Engr-3 B. Assignment 22, Page 4.

temperatures, -when they are close together, is very difficult, and
this fact accounts for the apparent merging with the lesser per-
centage of carbon .

The critical ranges are illustrated in the equilibrium
diagram. The diagram on page 591 refers to the critical ranges
on cooling. All critical ranges are denoted "by the letter A.
TO indicate the period of heating the A is followed by a small
c, which stands for the French word "chauffage" which means
heatingo Ar denotes a critical temperature on cooling, the r
being the abbreviation for the word "refroidissement" , meaning
cooling. The designation Ac and Ar are further modified by
the numerals 1, 2 and 3 to signify the critical ranges in the
order they are encountered; thus, Acj means the first critical ra
range encountered upon heating the steel.

In carbon steels there is a difference of about 30 degrees
between the critical temperature on heating and the critical
temperature on cooling.. Theoretically these temperatures should

be the same. It lias been proved that one important factor caus-

teiaperature
ing this/lag is the ordinary phenomenon of hysteresis* The process

of slow heating and cooling bring these critical temperatures
closer together. Two other minor causes for the difference are
the impurities contained in the steel The maximum temperature
to which the steel is heated is another factor which causes a
temperature lag between the critical points. For ordinary com-
mercial steels and usual practice these latter causes are of no
consequence.

Civil Engr-8 B. Assignment 22. Page 5.

Cementite and ferrite, two important constituents of steel,
are lefined in Article 659. Ferrite is soft, weak, and ductile.
Its tensile strength is estimated to "be about 40,000 lb, per sq.
in. It is strongly magnetic and has a high electric conductivity*
It has no hardening poorer * Ferrite appears "best in microphoto-
graphs of low carbon steel, containing from 10 to 30-point of
carbon; in these raicrophotographs it has a white color., See
(b), (c), and (d) in Figure 3 on page 596.

When steels are cooled from a high temperature all the
carbon is combined with iron in a chemical compound ^nich in
microphotographs is alyrays referred to as cementrte. Steel made
by the cementation process contains considerable cementite
(Fe-zC) Little is known of its actual properties except that
it is the hardest constituent of steel. It will scratch glass
but not quartz . It is very brittle. Cementite is thought to
have a high shearing strength but to be weak in tension. It
occurs free in hypereutectoid steels; see (g) and (h) in Figure
3 on page 596.

Pearlite is defined in the first paragraph on page 592.
The eutectoid of steel is called pearlite because of its resenfa
b lance to mother of pearl* It is a mechanical mixture of minute
crystals of cementite and ferrite. always in definite proportions
as given in the text. It contains approximately 0,9$ carbono
Pearlite commonly occurs in slowly cooled steels in the lamellar
phase which is shown in (b) of Figure 4 on page 597, in which

Civil Engr-8 B. Assignment 22. Page 6.

it is composed of alternate layers of ferrite and cementite. Note
the high magnification necessary to bring out the required detail
in the illustration referred to. Besides existing in globular
form," ras shown in (a) of the same figure, pearlite has been found
to exist in three other, but less important, forms. The size of
the grains has a marked effect on the strength of pearlite. Under
normal conditions its maximum tensile strength is estimated to be
over 100,000 Ib. per sq» in. It is about 2.5 times harder than
ferrite, but it is not hard enough to make tools which require a
cutting edge.

Austenite (named after Sir Roberts -Austen) is a substance
determined microscopically as a constituent of steel under certain
conditions and regarded as a solid solution of carbon or iron
carbide in iron. See paragraph IV on page 591 in the text.

Be able to draw the iron-carbon equilibrium diagram given
on page 591. Include in this diagram as much information as
possible. In the construction it is necessary to remember the
location of certain important points, such as A, G, 0, P, S,
and E. When these points are located the main lines in the diagram
can be sketched in. The eutectic contains about 4.3$ carbon.
This is point E in the diagram. For hyper-eutectic alloys
graphite separates from the melt along ED until the point E is
reached, when the eutectic solidifies* It might be expected that
iron would separate from the melt along the line jffi. This, how-
ever, is not the case, but a mixture of iron and carbon contain-
ing approximately 2% carbon and knovm as primary austenite sepav-

Civil Engr-8 Bo Assignment 22. Page 7.

rates from the melt to the right of the point S in the diagram.
In this portion of region II the iron-carbon alloys exhibit the
phenomenon of selective freezing, as do the lead-tin alloys- See
Figure 3 on page 575. To the left of point S, or in alloys
having less than 2$ carbon, the freezing is non-selective, simi-
lar to that of the alloy whose equilibrium diagram is shovm on
page 579* This kind of freezing is characteristic of the gold-
silver alloys. Consider an iron-carbon alloy having about
1.5% carbon at a temperature of 1500° C° It is a solution of
carbon in iron, which if allowed to cool will begin to crystallize
trhen the temperature reaches the line AE or about 1400° C- Solidi-
fication will continue until the temperature reaches a point on
the line AS, or about 1220° C, at which point the solution is ex-
hausted and the entire mass becomes solid. Each crystal that
separates from the me It will contain 1.5$ carbon; therefore, the
entire mass is a solid solution of carbon and iron. It is also
known as primary austenite.

During the cooling of primary austenite ih the region IV,
below the line AS, it undergoes changes similar to tlt&ps&t which
occur the cooling of a liquid solution. Along the line PS, for
alloys having more than .9$ carbon and known as hyper-autectoid
steels, cement ite is precipitated . For alloys having less than
•9$ carbon, that is hypo-eutectoid steels, pure iron or f err ite
is thrown out along the line GOP until the eutectoid composition
is reached. At this point both f err ite and cement ite are precipi-

Civil Engr-f8 B- Assignment 22. page 8.

tated at the same time and the eutectoid pear lite is formed. The
change from austenite to pearlite is not instantaneous; "but, as
irill be explained under the discussion of heat treatment and
tempering, the austenite may pass through a series of stages in
•which it is known as martensite, troostite, and sorbite; finally
it becomes pearlite. If a steel which contains 0. 9j£ carbon is
cooled slowly from a point above its critical temperature, so that
it will have an opportunity to pass through all transition
stages, it will consist entirely of pearlite and be known as a
eutectoid steel.

Steel having above 0.3$ carbon is supposed to have the
ability to harden but edge tools are usually made from low carbon
steels, in which the carbon ranging froa 50 to 125 point. While
2.Q;^is the theoretic division line between steel and cast iron,
coiimercial tool steels rarely exceed 150 point carbon (1.5$
carbon). Commercial cast irons usually range between 2.2 and
4«0j£ carbon-

Most of the information discussed in connection with the
iron-carbon equilibrium diagram is given in- the following sketch:

Civil Engineering-SB

Assignment 22

Page 9

ro
-a
O

ro
O
o

en
O

CO O

c* I

CD C

H» C+-

. H«

CD
O
<+
O

CO
0

t-« ro

en -3

O OJ

o o

Temperature

•-b •
O CO

H' "1

"I O

O H-

3 P

CO H-

Dividing '.

»
ro

W
3

ine between steel and cast
«j iron

j»

P
3
Q-

CD
O

h»-
O

.EMtflCtiC.

CD
3
H"
c+
CD

3
0,

<t>
3

CD
3

ct-
CD
O

CD
O 3
M H-
e+ c*-
CD CD
3

O
CD

H-

P
3
CX

CD
O

H-
O

CD
CD

CD
CO

<D
V

/**

f3>

>—• CD

CD CD

3 3
<r*

CO H-

O e*-

K-< <t

<r*- H-

H- 3
O

C
H-
CX

O O
3 3

<° §
w/J

CD
O
c+-

H-
CD

Civil Engr-8 Bo Assignment 22. Page 10«

QUESTIONS

le What is meant "by the critical temperature of steel?

2. Define the term "recalescence point" as applied to steel.

3. Why are the critical temperatures higher when steel is
"being heated than when it is "being cooled?

4. What is ferrite? What are some of its properties?

5. What is cementite? Write its formulae

6. What is austenite?

7. What is pear lite? In what forms does it usually exist?
8» What is hyper-eutectoid steel?

9c What is the usual range in carbon content for steels used in
the manufacture of edge tools?

10- Draw a carbon- iron equilibrium diagram. Uark all important
points ancl areas. It is important that the temperatures
and carbon contents be indicated on the diagram.

UNIVERSITY OF C AL IF ORFIA EXTENSION DIVISION

Correspondence Courses •
Materials of Engineering Construction

Assignment 23.
Civil Fngr-8 B. Professor C-T- Wiskocil

PROPERTIES OF WROUGHT IRON

Structure ;- Read Article 664- The structure of wrought
iron is clearly shown in Figure 1 on page 598. The greater part

of wrought iron is pure ferrite; in fact, this material approaches

:ahy/
nearer to pure iron than /.other coonercial form of iron. In

both the transverse and longitudinal sections the characteristic
slag inclusions can "be seen. In the longitudinal section, the
slag follows the direction of rolling in dark lines of varying
thickness; and in the transverse section it appears as irregular
dark areas. An examination of the structure of wrought iron, which
can "be made in several ways, is the only positive method of dis-
tinguishing this icaterial from low carbon steel. In the •wrought
iron a snail amount of carbon is always present and this combines
with the ferrite to form cenentite. The cernentite is present in
such small quantities that none remains in the free state; it is,
however, present in the form of pear lite. .The pearlite is not
conspicuous but is distributed in small isolated areas between the
grains of ferrite » Normal wrought iron contains about 2.5% slag,
96 . 5$ iron, and the remaining l*v$ silicon, phosphorus, sulphur,
carbon and manganese.

"When wrought iron is tested in tension, the fracture reveals
a fibrous structure. As explained in this article the fracture of

Civil Engr-8 B. Assignment 23. Page 2.

•wrought iron which is impure or adulterated (with steel scrap) may
have a crystalline appearance. This type of fracture may occur,
too, when the load is suddenly applied so that the fibers do not
have time to drav: out as under conditions of the normal tensile
test.

Defects ;- Read Article 665° Since the impurities usually
combine with the slag they are not as important as in the case of
steelc Sulphur and phosphorus are the principal impurities*

Tens i le strength : - Read Articles 666 and 667. As would
"be expected, the tensile strength of wrought iron depends upon the
relation between the direction of the fibers (which in turn depends
upon the direction of rolling) and the direction of the applied
stress. Even when the tensile stress is parallel with the fibers
the strength of wrought iron is quite variable . An average value
may be taken as 50 .,000 Ib. per sq. in. ultimate, with a proportional
limit of about 30,000 Ib. per sq. in. The strength when stressed
norral to the direction of rolling, as may occur in plates, may
be taken as 3/4 of the values given for the strength parallel
with the fibers.

The ductility is also quite variable. The average may
be taken as 35 %, measured in terms of the elongation in a 2-inch
gage length.

The stress-deformation curves resemble those for mild steel.

Tensile strength across the grain;- Read Article 667.
As already stated this may be taken as 75 % of the strength
parallel with the grain* The text gives more detailed information

Civil Engr-8 B Assignment 23. page 3o

on 'wrought iron than is warranted "by its importance .

Corxpressive strength:- Read Article 668° The ultimate
strength of ductile materials like wrought iron is taken as the
proportional limit strength; 30,000 Ib* per sq* ine

Shearing strength:- Read Article 669 * If wrought iron
re re one of the important structural materials it would be necessary
to remember the details of information such as are given in this
article. Since it is not, it is sufficient to note that the
shearing strength is about the same as the tensile strength.,
30,000 Ib. per sqn in., and that it varies in a manner similar
to that exhibited by the tensile strength.

Modulus of elasticity:- Read Article 670. Take the
average modulus of elasticity as 27,000,000 Ib. per sq. in*

Effects of overstrain; - Read Article 671. Overstrain
is produced by cold working, such as rolling, hammering and
pressing at a temperature below 690° C- In general the effect of
overstrain is to raise the ultimate strength and decrease the
ductility.

Toughness of wrought iron;- Read Article 672. Toughness
is determined by the impact test. The toughness of wrought iron
and mild steel are about the same; no quantitative value is
assigned*

Wrought iron chains— Read Article S73. The strength of
wrought iron chains may be taken as 1.6 that of the material
from which the links are made*

Civil Engr-8 Be Assignment 23? page 4.

The welding of wrought iron- Read Article 674. One of
the most important properties of wrought iron is the ease with
i7hich.it can "be welded. Low carbon steel, when the impurities are
lor;, can "be welded quite as easily as wrought iron, but other
steels are not so readily welded. The welding temperature is
close to the melting point, at which point or range in temperature
the iron is very plastic. But at this high temperature two con-
ditions arise which affect the weld. One affects the operation of
v/elding while the other affects the strength of the weld» In the
first case, the oxygen in the air combines readily with the iron
at ITS Id ing temperatures and the coating of iron oxide which forms
on the surface prevents a perfect union of the parts of the weld.
In the second case, welding temperatures also cause a coarse
crystalline structure which decreases the strength of the metal and
increases its brittleness.

The oxide or slag which forms on the metal is forced out of
the weld when the surfaces are made convex, as indicated in Figure
8 on page 607. The parts come into contact at the center and as
the joint is hammered or forged, the slag is squeezed out. This
action is facilitated by the use of a flux such as borax which
makes the slag more liquicu Sand is used as a flux in welding steel,

Coarse crystallization can be prevented by working the'
metal until it has cooled through its critical range in temperature .
The metal just at the weld is usually thoroughly worked by hammer-
ing so that the welds as a rule do not break at the joint but some

Civil Engr-8 B. Assignment 23= page 5 .

distance "back. As welding is usually done the pieces are only
slightly scarfed and the joint only is hammered. If a bar welded
in this manner is "bent, it will usually break just outside the
weld. Blacksmiths often assert that the weld is stronger than the
bar. The weakness in the bar, however, has been developed by the
method of welding. If the ends of the bar to be welded are first
heated to a moderate welding temperature and stove up (hammered
on the ends to make the section thicker) and if a well beveled
scarf is made, instead of the short, blunt one usually put on, the
chances for a better weld are much improved. The ends are then
reheated to welding temperature, the flux applied and the weld made
in the usual manner. If the ends have been properly stove up, the
bars will have to be hammered where the grain size has been in-
creased by the high temperature, so that when the joint is worked
dorm to size it will have been hamnered well back from the center of
the weld, on account of the long scarf, and no weak spots will
be left. The bar trill then have a uniform structure and should be
equally strong throughout its length. Electric heating is more
efficient than forge heating and power fudging produces a better
weld than hand methods.

Methods of distinguishing wrought iron from soft steel ;-
Read Article 675. Methods for distinguishing wrought iron from
steel have been discussed in Assignment No* 19. It is proper to
emphasize at this time that the only positive method of identifying
wrought iron is by an examination of its structure. This can be

. • '- *•

Civil Engr-3 B. Assignment 23. page 6-

made "by methods suggested in this article or "by the regular micro-
scopic methods..

PROPERTIES OF STEEL

The principal factors which influence the properties of
steel:- Read Article 676* The quality and mechanical prop-
erties of steel are affected "by (a) the method of manufacture,
(b) the composition, (c) mechanical TTorlc, and (d) the heat
treatment,, It must "be remembered that while these factors are
discussed separately, all of them may have an effect on the
quality and properties of a given piece of steel.

Effect of carbon:- Read Articles 677 to 685 inclusive*
This element is employed as the controlling constituent in reguia
lating the properties of common steels (so called straight
carbon steels). The effect it has on the mechanical properties
is discussed in detail in the text. Its most important influence
is on the strength, hardness and ductility of the metal. Heat
treatment, which Trill be discussed separately, has a marked effect
on carbon steels. Beginning with pure iron which is soft and
ductile, additions of carbon to normally cooled steel increase
the hardness and strength and decrease the ductility, until
eutectoid composition (0.9 % carbon) is reached. For each 10
points (1/10 of one par cent) of carbon added,, the yield point
is raised about 3,990 Ib. per sq. in* , the maximum tensile
strength is increased about 9,360 lb. per sq. in., and the per-

Civil Engr-8 B . Assignment 25» Page 1,

centage elongation is reduced about 4.3 f** Above this point
further additions of carbon result in increasing hardness and
strength but more rapidly decrease the brittleness« The use of
high carbon steel is restricted to products in which great hard-
ness is the principal requirement and toughness and ductility are
not so necessary. Commercial steels rarely exceed 1.20 % carbon.
Straight carbon steels most generally' usfful in the hardened

state have carbon contents ranging from .9 to 1.2 %\ they are
sufficiently hard for most uses and yet are not brittle to an
objectional degree.

The general shapes of stress-deformation curves as influence
ed by the carbon content are given on pages 611 and 612. Note
that the slope of the curve, which determines the modulus of

elasticity, is not affected by changes in the carbon content.

the statements in
The results shown agree v/itly Article 681, The average value

for the modulus of elasticity may be taken as 30,000,000 Ib. per
sq. in. for all steels and for both tension and compression.
Average figures should be remembered. Take ordinary
structural steel (rolled inild carbon, steel) which has an average
carbon content of approximately 0.2 $. Its proportional limit
is 30,000 Ib. per sq< in. and its ultimate tensile strength is
60,000 Ib. per sq. in. The compressive strength may be taken as
the proportional limit, which is the same in tension and in
compression, 30,000 Ib. per sq- in. Its ductility as measured by
the elongation is about 35 j£.

Civil Engr-8 B. Assignment 23. Page 8.

Read Article 683 carefully. It explains why it is imposs-
ible to determine a yield point in high carbon steels. The drop-
of -the -"beam is veil adapted to the determination of this point in
the case of Ioi7 carbon steels. This is also clearly shovm in
the diagrams on pages 611 and 612 previously referred to. In the
strict interpretation of the term, high carbon steels do not have
a yield point. The proportional limit can "be obtained only with
an extensometer,

THE EFFECT OF IMPURITIES

Read Articles 686 to 693 inclusive. A great deal has been
•written, with considerable difference of opinion, on the effect
of various elements on the properties of steel. I&nganese -while
it is listed in the text as an impurity, is unquestionably
beneficial. Oxygen, 7/hich is not mentioned in the text in this
particular article, is decidedly harmful. The effects of sulphur
and phosphorus are considered to be harmful but opinion seems to
be changing in this respect. Recently a committee organized
jointly by the A. S.T.L!« and the U«S. Bureau of Standards, and
composed of representative engineers and investigators has been
studying the effect of sulphur and phosphorus on the properties
of rivet steel.

Influence of oxygen:- Oxygen causes both red shortness
(or hot -shortness) and cold shortness in steel. The terms red-short
or hot-short are used to designate a condition of brittleness
in the hot metal. Cold-shortness is the term used to designate

Civil Engr-8 3 Assignment 23v Page 9,

brittleness at ordinary temperatures. These terns are used
principally in connection with the process rolling* As little
as .03 % of oxygen produces brittleness under impacts Large
amounts of oxygen are not necessary to produce harmful effects^
Overblown Bessener steel without deoxidization contains only
.15$ oxygen, yet this renders the netal unf it f or use.,

Influence of manganese :~ Read Article 690= Manganese
is a powerful deoxidizing agent* That which is left in the
steel after deoxidizing it causes it to roll and forge better and
also slightly increaseesthe tensile strength and hardness.. As
was brought out in the discussion under Sulphur, in Article 689,
manganese conbines with sulphur to form manganese sulphide..
For manganese to exert its nest beneficial effect it should be
present in amounts greater than 1.7 times the amount of sul-
phur ; (the proportion indicated in the text) About five times
more manganese than the amount of sulphur present should be used.

Influence of sulphur ;- Read Article 689, In the form
of ferrous sulphide this element will cause red-shortness but it
can be neutralized by manganese so that it is comparatively harm-
less. The opinion has been expressed that sulphur up to 0, 1 %
does not effect the strength and ductility of steel, The results
to be published by the A-S't°H< joint committee, previously re-
ferred to, will be valuable since no other thorough investigation
has been made on this subject. Specifications commonly limit the
sulphur content to 0.05 %,

Civil Engr-8 B. Assignment 23. Page 10,

Influence of phosphorus :- Read Article 688. The con-
sensus of opinion is that phosphorus causes cold -shortness, Some
evidence has "been given to prove that up to 0. 1 $ it does not
produce harmful brittleness. This question is also "being investi-
gated by the A«. S-T.M- Joint Committee., It is quite generally
agreed that additions of phosphorus increase the tensile strength
and hardness and decrease the ductility, with an effect similar
to that caused by the addition of carbon. ^°r structural steels
most specifications limit phosphorus, as they do sulphur, to about
0,05

Civil Engr-8 B- Assignment 23. page 11

QtJEST IONS

1. Describe the normal structure of wrought iron.

2. List the ultimate strength and proportional limit of wrought

iron in tension and compression; also its modulus of
elastic ity<.

3. How may wrought iron be distinguished from low carbon steel?

4. Why is the ordinary weld weaker than the original bar?
SP What is the proper method of making a weld?

6. What are the factors that influence the mechanical properties

of steel?

7. Ho?/ does carbon affect the tensile strength and hardness of

steel?

8. What effect does carbon have on the modulus of elasticity of

steel?

9. Explain why the drop-of -the -beam method cannot be used to

determine the yield point in the case of high carbon steels,

10. What are the impurities in steel?

11. How does manganese effect the properties of steel?

12. What is meant by hot- or red -shortness? Can it be pre-

vented ?

13. Give the approximate strength of ordinary structural steel

in tension and compression. What is its proportional
limit? What is its modulus of elasticity? Give oiailar
values gor v/r ought iron.

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction
Civil Engr 8 B. Assignment 24. Professor C»T. Wiskccil

Effects of heating above the critical range:- Read Article

694. As will "be noted in this article, there is a change in type
and size of crystals when steel is heated above its critical temper-
ature. When it is heated through the critical range, its pre-
viously existing structure is obliterated, or tends to become ob-
literated; and just above this range in temperature, the steel
possesses the -.'smallest crystalline structure which it is capable
of assuming. The rate at which the structure is obliterated de-
pends upon the temperature reached and the time the steel is
kept at that temperature. Simultaneously with the obliteration
of the old structure a new one begins to grow; the size of
crystals increases, as a result both of the increase of tempera-
ture above the critical range and the duration of the high tem-
perature; but more rapidly as a result of the increase.

The range in critical temperatures for straight carbon
steels is given in the equilibrium diagram on page 591. The
range in critical temperatures for various alloy steels is always
supplied by the manufacturer. It should be noted that only
eutectoid steels obtain their maximum refinement of grain size
upon being heated through the Ac^ temperature. As seen on

Civil Engr-8 B. Assignment 24. Page 2,

the equilibrium diagram, the critical range becomes a single
temperature for eutectoid steels. In all cases complete refine-
ment is obtained only when the constituents pass into a state of
solid solution, assuming the form of austenite. Because of the
lag or hysteresis effect the temperature should slightly exceed
the upper critical temperature on the equilibrium diagram.

Effects of cooling from above the critical range:- Read
Article 695. The size of the crystals in the austenite will
largely determine the size of the final grain structure since the
grain size does not change (decrease) with a decrease in tem-
perature., For this reason the steel should be heated to as
little above the critical range in temperature as considerations
of time will allow. The rate of cooling through the critical
range also affects the final structure. This change will be
discussed under the subject of tempering.

Effect of grain size*- Read Article 696. With other con-
ditions the same, the ductility, toughness and resistance to
fatigue are increased with a decrease in grain size. In general,
coarse grain size is indicative of inferior steel. Refinement
of grain is effected by working steel as it cools to the Ar^
temperature.

Annealing:- Read Article 697- Annealing of steel is
practiced in order to accomplish three principal purposes, (a)
to remove coarseness of grain and thereby secure a more desirable

combination of toughness, strength, and ductility; (b) to re-
lieve internal stresses set up in the cooling of castings and

Civil Engr- 8B. Assignment 24. page 3.

the working of the steel in processes of dra\Ting, forging, and
rolling; and (c) to soften the steel to facilitate machining
operations and meet certain physical requirements.

Annealing is generally applied to steel castings in order
to refine their inherent coarse structure and thus to correct the-
lack of ductility and to increase the strength. Hot forged
products are annealed to refine the relatively coarse structure
\vhich is caused "by the high finishing temperature. Cold worked
steel, such as cold drawn wire, must be annealed in order to
increase or restore its ductility. The overstrain of wrought
iron and steel (see Article 671 for wrought iron and 717 for
steel) increases the yield point and ultimate strength "but de-
creases the ductility. Iron and steel chains are frequently sub-
jected to overstrain when links kink or heavy loads are suddenly
applied. Chains in constant use should be annealed at regular
intervals to relieve the internal strains. This practice is
carried out in large plants where chains are used.

Annealing consists of three operations (1) heating the
steel to some predetermined temperature, (2) keeping the steel
at this temperature for a given length of time, and (3) cooling
the steel according to some predetermined method to atmospheric
temperature.

In order to soften steel for machining and to relieve in-
ternal strains it is not always necessary to heat the steel to the
critical range. In the drawing of wire, in which the so called

Civil Engr- 8 B

Assignment 24,

Page 4,

"process" or "works" annealing is used and in the white anneal-
ing of cold rolled steel sheets the metal is not heated to the
critical temperature. This treatment relieves the strain con-
dition of the ferrite and restores the ductility. It does not,
however, develop the maximum softness produced in true annealing.

For true annealing the steel must be heated past its
critical range. Diagram 10 on page 627 gives the annealing
temperatures recommended by various authorities. Draw the lines
to represent the upper critical range in this diagram. The Ar,
line extends from 0-900 to 3.5% carbon - 750° C., the Ar_ ,,

O—fc

line extends from the latter point to 0.9 % carbon - 690° C. It
will be seen that the recommended temperatures are well above
the critical range.

The time required for annealing depends upon the size of
the piece and may range from several hours to several days. The
furnace should not be brought above annealing temperatures in
order to accelerate the heating of the interior of large pieces.
This treatment increases the grain size of the exterior, producing
the harmful results previously mentioned.

There are three principal methods of cooling; furnace, in-
sulated, and air cooling. Furnace cooling can be made the slowest
and it will, therefore, give the best results in softness and
ductility. In the process of insulated cooling when steel is taken
from the furnace, it may be covered with an insulating material,
such as sand, lime, or ashes. In air cooling, the steel is re-
moved from the furnace and allowed to cool in air.

-, .

Civil Engr-8 3r Assignment 24. Page 5.

Effects of annealing on the mechanical properties of steel:-

Read Article 698. In general annealing reduces the strength and
hardness of steel, "but increases its ductility and toughness.* The
actual quantitative changes are relatively unimportant.

Overheating and "burning:- Read Article 699. Sometimes
rivets are overheated or burnt o Such treatment can be easily de-
tected by microscopic examination. The quality of burned steel
is destroyed and it cannot be restored by heat treatment. It
can be made into steel again only by being again melted and re-
fined.

Theories of hardening steel:- Read Article 700 » The
retention theories are probably the most generally accepted even
though, they do not satisfactorily explain all of the observed
facts. According to these theories hardened steel is in a
state of unstable equilibrium and, therefore, is tending to
assume a more stable form. That is, the iron has a constant
tendency to return to the alpha form, and the carbon to revert to
segregated cementite.

Essentials in hardening:- Read Article 701= Hardening
results from heating the steel above its critical temperature and
suddenly cooling it. Heating is done in various ways. For
simple pieces, the ordinary blacksmiths forge is satisfactory ,
Electric or gas fired furnaces and baths are used when nuch
hardening is to be done. Baths of molten lead or chlorides of
calcium or potassium are commonly used for certain types of

Civil Engn-8 B. Assignment H4t. Pag$ 6.

work. But in all cases the steel is cooled by being plunged in-
to a suitable liquid. This part of the process is called quench-
ing.

The heating for hardening is the same as that for true
annealing. Steel will not harden unless heated above its criti-
cal temperature. It should be thoroughly and uniformly heated
at a slow rate to the lowest temperature that will give the de-
sired results. This temperature should not be exceeded.

Methods of hardening. Read Article 702. Since the rate
of cooling controls the hardening process, and since the cooling
medium is the means of withdrawing heat from the steel, its
selection is of importance. The various hardening media, in
order of their hardening pov/er, are listed in the text. The com-
mercial use of these materials is also given. After water the
chief quenching media are oils, all of which are slower than
water. Combination methods of hardening, and their use and
value, are discussed -in the text.

Much skill is required on the part of the operator in
quenching steel to prevent warping and cracking. Some of the
difficulties are discussed on page 636 and methods for overcom-
ing them are also given.

Steels containing less than 0. 3 % carbon cannot be
appreciably hardened by ordinary methods of heating and quenching
because of the separation of ferrite from the solution during
the process. This separation occurs even with the most rapid
methods of cooling.

Civil Engr-8 B» Assignment 24. Page 7«

Effect of carbon on hardening : Read Article 703. The
majority of the evidence on the effect of carbon does not agree
with Figure 21 on page 636. Eutectoid steels posses the maximum
hardening power. The difference in hardness between quenched
and unquenched steels of this composition is greater than that of
steels T7ith other carbon contents. Steels with more carbon,
hyper-eutectoid steels, may show greater hardness both before and
after hardening because of the free cementite they contain or
because the martensite has a higher carbon content. Hyper-eutecr
toid steels gain less in the hardening process than do eutectoid
steels.

For the hardening process hyper-eutectoid steels are heat-
ed just above the Ac- r> -, temperature. This, as can be seen in

O ~ & * J»

the equilibrium diagram, is the critical temperature for eutectoid
steel. To convert both the pearlite and the free cementite in
hyper-eutectoid steels into austenite it T/ould be necessary to

heat them to a point above the A temperature. This would

cause a coarsening in the grain size, an undesirable condition
which is avoided by heating only to the Ac temperature .

O~fe*"l

Steel quenched from the lower temperature is harder because it
contains some free cementite, which is harder than martensite.
IThen quenched at the higher temperature (Acm) it contains all

Microscopic structure of hardened steels:- Study Article
704. If high carbon steel is rapidly cooled, say in brine, a

Civil Engr-S B° Assignment 24. page 8*

considerable portion is left in the form of austenite. Austenite
is rarely an ingredient of low carbon steels at normal tem-
peratures except in the cases of some alloys- If the steel is
cooled at a slower rate, the characteristic structure of marten-
site will be developed. See Figure 22 on page 637» Martensite
is very hard and brittle. It is suitable for sharp-edged tools,
"but, on account of its brittleness, not for machine parts sub-
jected to impact o With slower cooling the structure known as
troostite is developed. This structure gives a steel that is
slightly weaker but more ductile than martensite. Steel com-
posed of troostite or a mixture of troostite and martensite is
used for cutting tools and machine parts . With still slower
cooling the steel assumes the structure known as sorbite. This
is an intermediate structure between that of hardened and that
of annealed steels. This structure produces steel of high
strength with fair ductility; in other words a tough steel.

Steel of Ao or bite structure is considered to be ideal for use in

stress-carrying parts of machines . Annealing produces a struc-
ture made up of pear lite and ferrite for hypo-eutectoid steel,
and of pearlite and cenientite for hyper -eutectoid steels.

Tempering:- Read Article 705 to 709 inclusive. In the
diagram in Figure 25, it should be noted that as the weight F
decreases the end of the spring rises to the indicated positions;
this action is analagous to the passing of the steel through the
various transitional stages in the decomposition of austenite,

Civil Engr-8 B. Assignment 24. page 9.

as a result of the release of fractional restraint.

Fully hardened steel is too brittle for use. It is tem-
pered or draTm to regulate the hardness and brittleness, to tough-
en it, or to release the hardening strains- The process consists
in reheating the steel to some temperature be lor; the critical
range, after it has been hardened. The tempering of edge tools is
explained on page 643. The end of the piece to be tempered is
heated just above the critical range and only the tip of this end
is quenched; then the desired amount of heat, as judged by the
change in color of the cleaned tip, is allowed to flow into the
tip from the uncooled shaft. When the secondary heating has
proceeded to the desired point the influ;: of heat is stopped by
quenching the whole of the heated portion. Care should be taken
to avoid a sharp line between the hardened and the unhardened
portions of the steel. The tool should be kept in motion to pre-
vent the development of this line during the quenching process.
High carbon steels must not be kept at high temperatures any
longer than necessary because the carbon is precipitated out under
great heat in the form of graphite and thus the carbon content is
reduced • This occurs only in the case of the presence of large
amounts of carbon. Silicon also aids the precipitation of
graphite.

Drawing is usually done in furnaces or baths maintained
at the proper temperature0 This temperature is determined by
pyrometers; judging temperature by color of the steel is too
uncertain for accurate work.

Civil Engr-8 3. Assignment 24. Page 10.

Maintaining steel at the drawing temperature for a con-
siderable length of time will result in additional temperingc

The details given in Article 711 on the influence of
hardening and tempering on the mechanical properties of steel can-
not be remembered o Read this article and summarize in general
terms the effect of this treatment on steel. Remember that
tempering decreases the hardness and brittleness, and also the
tensile strength and elastic limit. The ductility, as ex-
pressed by the percentage elongation and reduction in area, is
increased by tempering.

Toughening consists in heating the steel to its critical
range, quenching it and then drawing it back at a relatively
high temperature so that little if any of the hardness due to
the quenching remains. This practice is usually limited to steel
with carbon contents ranging from .4 to .6 f0, that is, to
medium carbon steels. Toughening produces greater strength and
ductility than annealing.. In annealing; strength is sacrificed
for ductility and softness- The quenching retains the fine
grain size of austenite so as to insure the maximum strength of
which the steel is capable. The drawing process relieves the
quenching strains without increasing the grain size. Toughened
steel is largely composed of sorbite, which gives the highest
combination of strength and ductility.

Case hardening:- Read Article 710. Case hardening is
essentially a special application of the cementation process.

Civil Engr-8 3.

Assignment 24.

Page 11.

T/Then case hardened, the products are partially cartmrized so
that the exterior case penetrates only a short distance "below the
surface and leaves the interior unchanged. It is employed to
give a hard, v/ear -resist ing surface to a tough core. Low carbon
steels are used in this process.

Civil Engr-83. Assignment 24. page 12.

QUESTIONS.

1. Explain why eutectoid steels only reach complete refinement

in structure just above the Ac-^ temperature.

2. Describe changes in structure which occur on heating hypo-

eutectoid steels through their critical range in
temperature.

3. Why is steel annealed?

4. What is meant by "works" or "process" annealing?

5. What are the three steps in the process of true annealing?

6. What are the properties of burnt steel?

7. Will proper heat treatment restore the quality of steel that

has been overheated or burnt?

8. HOT; is steel hardened?

9. Why cannot lov; carbon steels (such as structural steel) be

hardened by ordinary methods? Why is it necessary to
specify the method of hardening of steel according to its
use?

10. How does an increase in carbon affect the hardening power of

steels?

11 . How does the quenching nedium affect the hardness of quenched

steel? What are the principal quenching media?

12. What are the names given to the transition stages occurring

in the process of the hardening of steel.

13. What is meant by the tempering or drawing of steel?

14. What is the structure of toughened steel? What are the

advantages of toughening over annealing?

15= Why are lor; carbon steels used for case hardening?

UNIVERSITY OF CALIFORNIA. EXTENSION DIVISION

Correspondence Courses'
Materials of Engineering Construction
Civil Engr-S B. Professor C-T. Wiskocil

Assignment 255
EFFECTS OF MECHANICAL WORK OH STEEL

Effect of hot -work on the structure:- Read Article 712,
If steel is worked at its critical range by any of the methods
previously discussed the grain structure -will "be refined. After
the critical range has "been passed additional work will not cause
any change in size of the grains , The refinement of grain
structure in a steel casting due to forging is shown in Figures 11
and 13 on page 628. By the time the steel has "been worked, its
temperature should be near the lower critical value so that the
grain structure will not be changed by heat that may remain in the
piece „ No changes will occur below the critical range.

Effects of hot work on the properties:- Read Article 713.
Since hot work during the cooling of steel through the critical
range in temperature refines the grain size it is to be expected
that the physical properties of the steel will be improved* Cer-
tain examples are given in the text. Large shafts must be forged
with heavy blows so that the effect of the mechanical work will
penetrate the material, or they should be made hollow so that better
metal will be assured.

Effects of cold working:- Read Articles 714 to 717 in-
clusive. Steel is ordinarily rolled at a red heat, and through this
process the strength and ductility are increased, because of the

Civil Engr-8 3. Assignment 25-' Page 2

refinement in grain size, as previously noted. If steel is "brought
to its final size at temperatures "below its critical range, it is
called cold-rolled steel. Working the steel at this temperature
increases its tensile strength and elastic limit but decreases
its ductility c The grains are distorted and do not reduce in
size as they do at temperatures within the critical range. The
distortion of the grains or crystals produces internal stresses
that raise the strength and elastic limit c Cold drawing of rods
and wires has the sane effect as cold rolling of steel. Cold rolled
steel is used for shafting "because the process leaves a smooth
surface and true dimensions so that machining is not necessary. If
machining is done, such as cutting keyways or holes, it is liable
to distort or warp the shaft due to the redistribution of the
stresses caused by the cole! working. Most steel wire is cold
drawn and cold dravm shafting may be obtained up to 3" in diameter.

The effect of cold working can be removed by annealing.
From previous discussions on the changes in grain structure caused
by annealing the refinement of structure and release of internal
stresses in cold worked steel can be readily under stood » This
change is well illustrated in Figure 39 on page 659.

Grain growth in steel— Read Article 718. Cold working
may cause the growth or enlargement of crystals in the case of
certain pure metals but not in the casge'of commercial iron and
steel. Overheating, that is heating over the critical temperature,
will cause increase or coarseness in the structure of steelo

Civil Engr-8 B* .Issigiment 25. Page 3*

Stead's "brittleness is a condition caused by heating from 650°

to 750°C for long periods of time,, It occurs in lov: carbon

steel and causes large crystallization with a decrease in ductili-

ty. It is not often encountered "because the necessary conditions

rarely occur in practice. Where it does occur, cthe original grain

structure can be regained by proper annealing.

Influence of form on properties of steel:- Read Articles
719 to 723 inclusive . The form of the piece affects both the dis-
tribution of stress and the elongation under tension. These con-
siderations are of most importance in design and investigation.
It is natural to expect that where steel is confined, it -will have
greater strength and elastic properties, as discussed in Article
723. These matters, however, are relatively unimportant in a
course in Materials.

Wire rope :- Read Articles 724 and 725ii The properties of
steel wire are given in Article 724i Methods of manufacture have
been previously discussed, plow-steel is one of the strongest
materials used in the construction of wire rope. The name originat-
ed in England where it was applied to a strong grade of crucible
steel wire which VTB.S used in the construction of strong ropes
employed to pull gangs of plows. At present it is used to designate
a high grade of open hearth steel; and in wire rope made of plow-
steel, the tensile strength of the wire is about 250,000 Ib. per
sq. in. The proportional limit of plow steel is about 70f0 of its
ultimate strength while its ductility is very lor;; the average

Civil Engr-8 B. Assignment 25. Page 4.

percentage elongation is 5$. While ploy/ steel is an unsatis-
factory name it has been associated with the trade for such a
long time that it has come to have a fairly definite meaning »

Lang-lay rope is defined in Article 725, The difference
between this type of rope and ordinary rope should be remembered.
In regular lay rope, the wires of the strands are twisted in one
direction and the strands laid into the rope in the opposite
direction. Most of the rope used in America is regular lay rope;
and rope of this type has become standard for most work. In Lang-
lay rope both the vires in the strands and the strands are in the
same direction. It is more easily untwisted than regular lay rope
and it is also more difficult to splice. It is well adapted to
external wear and grip action. Its use is rather limited compared
to that of regular lay rope.

Most rope is made right lay, which means that it is twisted
to the right, like the threads of a right hand screw of long
pitch. The majority of oil-well drilling ropes are made left lay.
The construction is specified by giving the number of strands in
the rope and the number of vires in each strand. A 6 by 19 rope
is one having 6 strands of 19 wires each. The strands are laid
around a hemp or manila center to form the complete rope. The
hemp or fiber center holds the lubricant and affords a bedding for
the strands The life of a rope depends on a number of factors :
the character of the metal used, the construction of the rope, the
diameter of drums, sheaves, and pulleys over which it operates;

Civil Engr-8 B «. Assignment 255 Page 5-

and to a great extent how it is lubricated. When intended for
heavy wear the henp center should be saturated with a suitable
lubricant. The lubricant reduces friction between the component
parts of the rope and prevents corrosion.

The diameter of a rope is usually baleen a a the diameter of
'\4s CJrosr-Sc-dktj*. «*

a circle just enclosing t&firxape ... In a 1 1/2 inch rope the

smallest cross -sectional dimension may be as little as 1 3/8 inches

'this latter measurement is Domo times taken as the diameter.

There are various classes of wire rope. Tiller rope is
the most flexible. It is used motly for boat tillers. Guy rope
is used for guying steel stacks, derrick masts, and gin poles/
and for similar purposes where there is static load without im-::
pact. It is sometimes used also in hauling where the ropes are
not bent over sheaves. The wires are usually galvanized. Hoisting
rope of crucilb$ steel is eommonly used for mine hoists,
elevators, conveyors and derricks. Hoisting rope *>£u plow steel
is used in heavy work, as for instance in locomotive and wreck-
ing' cranes, Extra-flexible rope of plow steel is used on
steam-shovel gear and in cases where it is wound around small
diameter drums .

The ratio of strength of rope to average strength of wires
is usually called the efficiency of the rope. This value ol'is
usually about 85^. The strength of the rope depends upon the
material and method of its construction upon its diameter.

Civil Engr-8 B. Assignment 25S Page 6*

THE STRENGTH AMD ELASTIC PROPERTIES OF iJETALS
AT ElEVATED TE1.SEKATUHES

Read Articles SOS to 82.0 inclusive. The uses of metals

under conditions of high temperature are listed in Article 809.

«
In spite of the importance of the subject there has "been little

systematic research undertaken. In a general "way, the diagram in
Figure 6 on page 763 gives the results of investigations so far
completed. Steel reaches a maximum tensile strength a"bout 600°
Fahrenheit, and for temperatures over that value the strength
decreases quite uniformly to about 1600° F- at which temperature
it looses practically all its strength. It is possible that dif-
ferent steels will exhibit different points of maximum strength but
in general the figures given represent average conditions. The
ductility decreases until about 600° F. is reached and for

higher temperatures it continually increases. The proportional

gradual
limit and modulus of elasticity show a/decrease with the increase

over atmospheric temperature. Cast, iron and wrought iron are
similar to steel in their reaction to elevated temperatures.
Brass and aluminum show a uniform decrease in tensile strength as
the temperature is increased.

When steel is used at elevated temperatures as the fire-
box of a boiler or the stays in an open hearth shed furnace it
is under stress: investigations , therefore, should be made with

long -continued or permanent loads. Up tc this time no such

• •• • ' V

studies have been undertaken.

Civil Engr-3 B. Assignment 25. Page 7.

Welding of steel:- This subject is not discussed in the
te::t. The welding of wrought iron urns referred to in Article 674
on page 606. Steel welding, which is known as welding at plastic
heats, is successfully practiced with soft steel , but hard steel
(high carbon) can be welded by this method only by an experienced .
operator. Cast iron cannot be welded by plastic welding,, Plastic
welding is done in a forge fire or by electricity. The parts to
be joined are brought to a temperature a little below fusion and
pressed or hammered together. When electricity is used the
method is called resistance or spot welding. Pieces that do
not have to transmit heavy stresses are fastened together by
this method. Pieces which are later to be more thoroughly joined
are often tacked together by spot welding. Spot welding is often
well adapted to certain kinds of manufacturing operations, such as
the making of wire fabric for concrete reinforcement, and of wire
reinforcement coils for concrete pipe, chain manufacture, and

Ke^tis

welding valve stems to valve seats. The temperature can be
closely controlled in this process.

There are three principal methods of fusion or autogenous
welding. The first is oxyacetylene welding in which the metal is
actually fused by high temperatures resulting from the burning of
the gas, usually acetylene, in a stream of pure oxygen. The two
gases are fed through a blow pipe torch and ignited at the tip.
The high temperature, approximately 5000 degrees Fahrenheit, fuses

MteXXt*

a narrow strip of metal at the joint and vmfri^o the parts. A
narrow steel, or iron rod is melted in the joint to supply additional

Civil Engr-8 B « Assignment 25* page 8°

me tal0 Most metals can be "welded "by this process.

In this operation, the oxyaoetylene torch is used as a
cutting toolo For this purpose the oxygen is supplied in excess
and the temperature is increased so that the steel is burned.
It is used in cutting off lugs, gates and risers from steel cast-
ings where the cold -saw was previously used. The torch has
brought about large savings in this operation., It is also used
to cut up scrap and wreckage of various kinds, Osyacetylene
veld ing is applicable to thin plates of metal. It produces a
coarse structure since it is essentially a casting., A connon
weakness in this method is that the metal at the joint is not
thoroughly welded at the middlelof the thickness of the plates.
Joints of this kind can be made so that the average efficiency
is about 8C^ but as usually made under ordinary conditions by the
average workman the efficiency approaches nearer to 5($. Torch
welding is widely used in repair work in which cast as well as
rolled metals are to be repaired, and is the method in most
general use.

A second method of fusion welding is the thermit methods »
The necessary temperature is secured by igniting a mixture <nf
iron oxide and aluminum. The materials are ignited in a crucible
and where they reach a temperature of approximately 4500 degrees
?. , the hot metal is poured into the joint to be repaired. It
forms a casting and is therefore adapted to the repair of heavy
sections such as locomotive and heavy engine or machines frames.
Repairs by this method can be readily made in the field.

Civil Engr-8 3 . Assignment 25. page 9»

A fusion weld can also be made "by the use of an electric
arc. The arc is drawn between the metal and an electrode of
steel or iron which is held in the hand of the operator. The
metal to fill the joint is supplied partly by the metal to be
repaired and partly by the electrode, both of -which are fused by
the temperature of the arc,. This method! cannot be used in the
field unless electric current is available.. It is an excellent
shop method. If alternating current is supplied a mot or -gene rat or
set or rotary converter is necessary tp produce direct current.
As reported in Bulletin 179 United States Bureau of Standards on
EIECTRIC-ARC WELDING OF STEEL, the mechanical properties, as
measured by the tension test and by microscopic examination, v'-
show that arc-fused metal is an inferior grade. The ductility-
is particularly low. With careful manipulation and annealing,
however, very satisfactory welding can be done by this method.

Civil Engr-8 B

Assignment 25

page 10,

QUESTIONS

lr In what -way does hot-work affect the structure and properties
of steel?

2* What is meant "by cold-working? How does it affect the
properties of the steel?

3. Is it possible to restore the original ductility to cold- drawn
steel wire?

4.. What is plow steel? What is its approximate tensile strength,
proportional limit, percentage elongation and modulus of
elasticity?

5o What is a Lang lay rope?

60 What is a left lay rope and what is its principal use?

7c What factors determine the life of wire rope?

80 Define efficiency as applied to wire rope. What is the average
e f f i'ciencyT""

9« Would the strength of steel "be affected if it were used at a
temperature of 500 degrees F. ?

10. Wha.t:. are the two principal types of welding?

11. What welding process would you advise for the repair of a

broken locomotive frame? For a cracked automobile fender?
For filling blow holes in a defective steal casting? For
repairing a wr ought iron tie rod? For replacing a broken
tooth in a cast iron gear?

UNIVERSITY OF CALIFORNIA. EXTENSION DIVISION

Correspondence Courses
Materials of Engineering Construction

Civil Engr-8 B. Professor CM. Wiskocil

Assignment 26
ALLOY STEELS

Introduction:- Read Article 728* This may be said to be
the age of alloy steel. It lias been demonstrated that the develop-
ment and manufacture of airplanes, automobiles, tractors, artillery,
armour plate and cutting tools would have been impossible without
alloy steels. Langley's original airplane, which antedated the
successful machines of the Wright brothers, could not be success-
fully operated because of the heavy and inadequate power plant.
It was recently equipped with a modern motor and it flew perfectly.
Early automobiles, commonly known as horseless-carriages at the
time they were first introduced, were cumbersome, expensive
devices compared with the automobile of today. The development of
automotive machinery is thus due to alloy steel. During the past
fifteen years and especially during the War many problems have been
encountered that could not be successfully met with ordinary
carbon steels. The builders of the lowest priced automobile in
the world today, which contains the highest percentage of relative-
ly expensive alloy steels, acknowledge that it is the use of these
alloy steels which has made their product possible.

High grade steels, other than structural grade and machine
steel, reach the user in a condition in which the properties are

Civil En^r-3 B- Assignment 26. . Page 2.

still to "be developed. In the case of carbon steels the applica-
tion and renoval of heat to bring out or develop the properties
inherent in the steel were thoroughly discussed. Alloy steels also
require heat treatment to produce the physical properties which
they are capable of developing.

Many different alloy steels have been developed but relative-
ly few have gained commercial importance . Probably the first
commercial alloy steel -was the s3 If -hardening tungsten tool steel
developed by I!ushet in 1863 c About fifteen years later a chrome
steel was put into use for the manufacture of projectiles. Then
in 1382 the well-knov;n manganese steel was discovered by Hadfield.
The development of nickel and the other commercial alloy steels
followed the discovery of manganese steel.

The definition of alloy steel as given by Hibbard is similar
to that ^iven in the te:rb, "Alloy steel is steel that contains
one or more elements other than carbon in sufficient proportion to
modify or improve substantially and positively some of its useful
properties".

Ternary Alloys

A simple forn of alloy steel is that which is sometimes
called (as in the text) ternary steel. It is one which contains
one alloying element besides carbon and iron. The term ternary is
used because of the fact that the steel is made up of three
principal constituents, while the designation simple alloy is

Civil Engr-8 B« Assignment 26. Page 3.

logical, because in steel of this type, only oue alloying
element is added to carbon steel. The tungsten and manganese
steels previously mentioned are simple alloy steels,,

As has been noted in the discussion on manufacture of
steel, in all steels various elements are added for curative pur-
poses during the making process. Uanganese in quantities less
than 1 1/2 ^ was added to prevent red -shortness , aluminum is

added to quiet the molten steel before pouring, and other elements
such as silicon, titanium and vanadium are added in small quantities
for similar reasons. The introduction of these alloying elements
does not bring steel into the strict alloy steel class., It re-
sults merely in what is called alloy-treated steel.

Alloy steels are usually heat treated because heat treat-
ment adds to the superior qualities which have been gained by the
use of alloys . Certain structural steels ivhen made into large
units such as rails and members for bridges are used without heat
treatment. Their superior properties are due solely to the pres-
ence of the alloying element - usually nickel. Where practical,
structural steel products are heat treated. Structural steel
is used for stationary and moving parts of vehicles, machines,
ships, and armor plate, as well as for bridges and buildings.
Alloy steels for cutting tools and electrical purposes are placed
in separate classes and furthermore they are usually treated with
different alloying elements.

Sometimes alloy steels are heat treated before they are
machined. This process is very difficult if the elastic limit is

Civil Engr-8 3. Assignment 26. page 4.

in excess of 100,000 Ib. per sq. in. It is claimed that chrome-
vanadium steel can be commercially machined even up to such
strength as represented "by 150,000 Ib. per sq. in. elastic limit,
Chrome -molybdenum steel is even more easily machined than Chrome-
vanadium. Ho commercial alloy steels exceed 100,000 Ib. per sq.
in. in elastic limit strength in the normal state.

Alloy steels are made by pneumatic, open hearth, crucible,
and electric processes. The largest tonnages are made by open
hearth and electric methods. They are usually alloys of nickel,
chromium and vanadium.

Nickel Steel;- Read Article 792. Nickel steel was used
for the first time about 1888. It aggregates a large tonnage at
the present time but the field is being reduced by the cheaper and
in some trays better chrome -nickel steels. ££a!lost of the straight
nickel steels are made by open hearth methods. Additions of leas
than 2$ nickel are not v;orth the extra cost. Useful nickel
steels range from about 2 to 46$ nickel. This is a voider range
than has been found for any other alloying element. Untreated
nickel steel has higher elastic limit and ultimate strength than
similar carbon steel without nickel, but practically the same
ductility. Heat treatment increases the strength of nickel steel,
both elastic limit and ultimate, but it also decreases the
ductility.

Nickel may be added to the steel at any time just so that
it has opportunity to becorae thoroughly diffused throughout the
melt before it is poured. It is usually added to the bath just

Civil Engr- 8 B. Assignment 26. page 5»

before it is tapped. It is not added for curative purposes; it is
preeminently a strength giving element. Unfortunately nickel steel
is subject to cortain defects such as seams and surface marks,
which limit its user

Ordinary niche 1 steel contains from 3 to 4 % nickel. T3hen
the percentage of nickel is not specified in an order steel contain-
ing about 3.25 % is furnished since this percentage produces the
best properties for most structural purposes. This type of nickel
steel is well adapted to service conditions that are too severe for
ordinary carbon steel, such as in certain kinds of bridges, gun
forgings, engine and automobile parts, and large dynamos.

In the range used in ordinary nickel steel (2 to 4$) each

€A\

addition of \% nickel increases the tnfrsile strength about 6,000

lb<, per sq. in, over carbon steel, -without affecting the ductility-
This increase occurs through the additions of nickel, without
heat treatment. The use of nickel saves some weight, which is a
factor in the construction of long span bridges such as the Quebec
bridge in which untreated nickel steel was used. Steel having about
So 5f0 nickel is good case hardening stock.

With the addition of from 5 to 8 % nickel the metal becomes
very hard and is difficult to work in both the hot and cold con-
ditions. Its principal use is for the manufacture of thin armor
plates which are used for protecting field artillery from rifle

fir*.

Steels containing about 10 fa nickel cannot be hardened by

quenching .

Civil Engr-8 B. Assignment 26. Page 6.

In 1914 a steel containing 12% nickel and .55$ carbon was
discovered which had a yield point of about 134,000 and an
ultimate tensile strength of 195,000 Ib. per sq. in. This alloy
of nickel is thought to be the strongest in the entire series of
nickel steels. It is very hardc It cannot be machined or
drilled. Its elongation is about 12 $. Its commercial use is
very limited; it is only made into shafting to replace shafts
made of other steels that could not withstand the particular
service conditions-

Steels containing about 22$ nickel have high rust resist-
ing qualities. Steels having from 24 to 32$ nickal are used for
electric resistance , in such articles as electric iron, toasters,
and other household heaters.

Invar steel, which contains 36$ nickel, is mentioned in the
te;rt. Not more than a few hundred pounds a year are used; yet
in certain industries it is important. Its principal uses are
listed in the text. Some invar tapes have been made with coeffici-
ents of thermal expansion as low as ,0000008 per degree centigrade,
This means a change of 0.05 inches per mile for one degree centi-
grade change in temperature- Some invar steels have been found
to have negative coefficients; that is they actually contract when
heated «.

Platenite is also mentioned in the text. It contains 46$
nickel and .15$ carbon. It was at one time more used than it is
w., principally for wires which lead into electric lamp bulbs.

Civil Engr-8 B. Assignment 26. Page 7.

It was a substitute for platinum. Other alloys are now replacing
platenite for the purpose mentioned.

There are other alloys of nickel "but they are of scientific
interest only.

Ilanganese steel;- Read Article 730. Commercial man-
ganese steel contains from 11 to 14$ manganese and from 1.0 to
1.3 f0 carbon. Host of the manganese steel produced is made into
castings. The field for manganese steel is not very large and
there are relatively few concerns making it. About six companies
in United States supply practically all that is made.

i&nganese steel is made by the pneumatic, open hearth, and
electric processes. In the process of manufacture, ferromanganese

is added to the decarburized metal. This supplies all of the
manganese and practically all of the carbon, in the finished metal.
Ilanganese steel cannot be successfully made from manganese steel
scrap. On the whole it is more difficult to make and cast than
carbon steel. At the present time it cannot be commercially
machined. It is used for jaws of rock cmafchers, for rails,
frogs and crossings for railroad work, and also for burglar-proof
safes. These safes are made of a laminated construction having
alternate layers of hard and soft steel thus making it difficult
for a drill to penetrate . Manganese steel, as well as all other
kinds, however, can be readily cut with an oxyacetylene flame.
Ilanganese steel has a low yield point. Under many field condi-
tions it peens-out or flows under repeated blows. This makes

Civil Engr-8 B. Assignment 26= Page 8.

it unsatisfactory for uses for -which its high abrasive resistance
would otherwise make it preeminently successful. Manganese
steel for buckets in gold dredgers is "being replaced by other
alloys with higher elastic limits. The breaking of a bucket line
causes expensive delays and a reliable product is required. It
is more difficult to obtain uniform material and finished castings
in manganese stael than in other types of alloy steels. The
principal demand for hot-rolled manganese steel is for use as
railroad rails..

Chrome steels;- Read Article 731. Steels alloyed -with
chromium have great strength and hardness. Chrome steels are

cast, rolled and forged just as carbon steels are. They are
rarely used in the untreated condition. Chrome steels have been

used for stamp shoes in pulverizing gold and silver ores, and for
safes. Some chrome-steel is also made into files and balls and
rollers for bearings. Simple chrome steel was one of the first
alloy steels: commercially used.

Chromium, hot/ever, is usually alloyed with other elements
to form quarternary alloys.

Quartenary Alloys

Tungsten steel:- Read Article 732. Simple tungsten steel
is noV becoming obsolete. It was important at one time and
formed an important stage in the development of high-speed tool
steels. Ilushet's air-hardening steel, while it contained 6f0
tungsten and 2 % manganese - the latter added to give it the

Civil Bngr-8 B. Assignment 26. Page 9.

self hardening property - iras usually classed as a simple
tungsten steel.

Vanad ium Ste e 1 ; - Read Article 733. Vanadium adds great
strength to steel and makes it free from flairs and seams . It is
used in high spaed steels. It is not used much as a simple alloy
"but usually is combined with chromium. Chrom- vanadium steels are
used principally for locomotive forgings, automobile springs and
axles and gun forgings.

Silicon steeds :- Read Article 734. Silicon is an ingredi-
ent of practically all steels. It is added to tool and structural
steels to promote soundness, and is added just before the metal
is teemed, and should preferably be in a molten stats . The
principal use for silicon steel is in the manufacture of leaf
springs for automobiles.

Chrome-nickel steel: Ores found near llayari, Cuba, yield
a natural chrome-nickel steel, llayari steel, as this product is
called, has been found to have excellent qualities for certain pur-
poses; but it is generally inferior to synthetic chrome-nickel
steels. This type of alloy steel is vridely used in the manufacture
of automobile parts and for arraor plate and armor piercing pro-
jectiles. Chrome-nickel shafts and gears have excellent -wearing
qualities.

Chrome -vanadium steel:- Read Article 736. Chrome -vanadium
steels are made in the open hearth furnace and the alloying elements
are ;. jadded just before casting. Chrome -vanadium steels slightly

Civil Engr-8 B . Assignment 26* Page 10.

surpass chrome -nickel steels in physical properties. Most of the
output goes into the manufacture of automobiles. Vanadium is a
strong deoxidizer while nickel is not. Vanadium steels are,
therefore,, more free from surface imperfections such as seams than
are steels which contain nickel.

I!o lybd e nuis steel:- Molybdenum is. added in the form of
ferro-molybdenum or calcium molybdate. The final molybdenum
content of the present commercial molybdenum steels is less than
\%* Since the YJar molybdenum steels have become commercially

important. They v/ill probably soon replace chrome -nickel and
chrome -vanadium steels v/hich are now so generally used in auto-
mobile construction. During 1921 the Studebaker Corporation
used over 2,000 tons of molybdenum steels. The high grade Willis
Sainte -Glair automobile is made largely of molybdenum steel.
Chrome-molybdenum steel is more easily machined than the nickel
and vanadium alloys of chromium.

During the ¥ar molybdenum vras used as a substitute for
tungsten in the manufacture of tool steel (high-speed). Its largest
use was for light armor plate, and vital parts of airplane motors
and automotive vehicles*

For its high strength chrome -molybdenum steels have great
ductility. Automobile parts such as axles and shafts, made of
molybdenum steel can be distorted and twisted without rupture.
Heat treated chrome -molybdenum steel has the following approximate
strengths; 140,000 Ib. per sq» in. elastic limit, 150,000 Ib.

Civil Engr-8 B. Assignment 26. Page 11.

per sq. in. ultimate tensile strength, 18$ elongation and 60$
reduction in arear

High-speed steels;- The presence of tungsten or molybdenum
in steel affects its critical temperature. With proper heat treat-
ment steels containing these alloys retain their hardness and
consequently a cutting edge at a red heat. One form of heat treat-
ment is the heating of the steel to incipient fusion, and quench-
ing in oil. Tungsten, molybdenum, cobalt and vanadium are
those alloys used in the manufacture of high-speed steels, which
are usually made by the crucible or electric process.

Stellite, a competitor of high-speed steels, is not a steel,
being composed of approximately 60$ cobalt, 11$ chromium, 23$
molybdenum, the remainder being manganese, iron, carbon, etc.

Civil Engr-8 Be Assignment 26. page 12.

QUEST IOWS

What is an alloy steel?

2. What was the first commercial alloy steel and what was it
used for?

SB What is a ternary alloy steel? Name several.

4. ¥hat processes are used in the manufacture of alloy steels?

5. What is invar steel? Give its composition and principal

uses,

6. What is the percentage of nickel in simple nickel steel used

for ordinary structural purposes? Why is this steel better
than carbon steel?

7r What is the range in manganese in commercial manganese steels?
What are the outstanding properties of this steel? What
are some of its uses?

8. What is Eayari steel?

9. What are the principal alloy steels used in the automobile

industry?

10. What is the advantage of vanadium over nickel in quarternary

alloys using chromium?

lie What are the particular advantages of chrome -molybdenum
steels? What are the uses for this steel?

12 o What is meant by a high-speed steel?

13. Explain why high speed steels retain their hardness at high

temperatures.

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION
Corr e spondence Cour se s

Materials of Engineering Construction

Assignment 27

Civil Engr-8B Professor C. T. Wiskocil

CAST IRON

Importance of cast iron: Read Article 738, which gives the
principal uses for cast iron. In building construction it is not
as -widely used as steel; its greatest field of use is in machine
construction. As indicated in this article, however, other metals
must also be frequently used in machine construction because cast
iron does not adequately supply the necessary qualities. These
competing materials are malleable cast iron, cast steel, and cast
brasses, bronzes, and other alloys.

Cast iron has a comparatively coarse crystalline structure,
as sho\vn in Figure 4 on page 697* It is readily cast into useful
shapes and is easily machined, but is lacks toughness and ductility.
It has considerable hardness but cannot be deformed by forging
without being broken. Its constitution is very complex, and it is
subject to much variation resulting from relatively minor changes
in the detai 1 s of manuf actur ing .

Manufacture of cast iron: Study Articles 739 to 743 inclusive.
When pig iron is remelted and cast into final form it is called
cast iron. See the definitions previously given on page 586. A
limited amount of ironAcast directly from the molten state as it
comes from the blast furnace. Ingot molds are made in this way.

Ci.vil Engr-8B« Materials of Engineering Construction. Assignment 27, page \

Most cast iron is made, hoover, by a mixture of scrap iron with
pi'g ?ron. The reasons for r erne It ing pig iron and mixing different
grades of iron and scrap are given in Article 739. Most cast iron
is made in this manner; either the cupola or air furnace is used.

The materials used in the manufacture of cast iron are de-
scribed breifly in Article 740. The major portion of the charge
in the furnace usually consists of foundry pig iron* The amounts
of the constituents usually specified are listed on page 540,
Article 582. Most foundry pig is bought on the basis of its analy-
sis. Bessemer pig, ferro-silicon, and other materials mentioned
in the text are used to bring the final composition of the cast
iron to desired limits. Some classes of castings are made without
scrap while others contain as much as 40$ scrap. The term "scrap"
includes, besides worn and discarded iron castings, defective
castings, gates, sprune s, risers, and other pieces of iron re-
claimed in cleaning up castings.

The flux is used to form a slag and carry off the impurities
and non-metallic residue. Since the amount of impurities is small
the amount of flux required is also small, being ordinarily about
1$ of the weight of the iron charge. Calcium carbonate usually in
the form of limestone is used as a flux but marble, dolomite, and
oyster shells are sometimes added to the charge.

The fuel is used to melt the iron. Coke is most commonly em-
ployed but mixtures of coke and anthracite coal are sometimes used
in cupolas. Gas and bituminous coal are used in the air furnaces.

Civil Engr-SB* Materials of Engineering Construction. Assignment 27, page

The fuel requirements are determined by the type of castings
to "be made, thin castings requiring a more fluid and therefore a
hotter metal than that necessary for large thick castings.

A typical cupola furnace is shown in Figure 1 on page 689.
It is essentially a small blast furnace. Only a light blast is
used, and no attempt is made to attain reducing conditions required
in the regular blast furnace. The only function of the cupola is
to melt the charge. The proportion of fuel to iron is usually
about 20^,

The usual type of air furnace is illustrated in Figure 2 on
page 690. The heat from the fuel passes over the bath and is re-
flected by the roof of the furnace. For this reason it is some-
times called a reverberat>ory furnace. An air furnace resembles
the puddling furnace used in the manufacture of -wrought iron. The
copula is used for melting iron for gray iron castings T?hile the
air furnace is used in the production of vhite cast iron for mal-
leable cast iron and for cast irons of special compositions.

The open-hearth furnace is used to a limited extent in the
manufacture of cast iron. It is more economical in the consumption
of fuel than the air furnace - but to be used to advantage it must
be operated continuously. This requires a large floor space for
molding and a l^rge output of cast iron-
Study Article 743 on the comparison of the cupola and the air
furnace. The air furnace uses about ttrice as much fuel as the

il Engr-8B. Materials of Engineering Construction* Assignment 27 , page 4.

cupola "but it produces purer metal and in larger quantities. Both
types of furnace are widely used.

Molding o£ cast iron: Read Articles 744 to 749 inclusive.
Only in the case of the chilled castings is the quality of the
metal affected by the mold. Under normal conditions of cooling the
quality of the metal depends upon its composition.

The molding of cast iron is of importance to the engineer and
machine designer. The pattern must be so designed j?hat it can be
removed from the sand and leave the mold intact and the shape of
the casting must be so designed that dangerous shrinkage stresses
are not set up when the casting cools« The three methods - green-
sand, dry- sand, and loam molding - are all explained in the text.

Patterns are divided into two classes. In the first class,
which includes most of the castings, the patterns are solid. In
the other class the hollow part is formed by a core which is in-
serted in the mold after the pattern is removed. The materials
from which patterns and cores are made are described in the text

The use of chills is described in Article 748. They are used
to produce a hard wearing surface on such castings as rolls and
car wheels. Chilled-iron car wheels are cast with a chill against
the tread and the inside of the flange, the remainder being in sand.
The composition of the metal is such that under the imposed condi-
tions the metal against the chill will show white iron to a depth
of about 7/8 of an inch, the remainder of the wheel being graphitized
or gray. So as to relieve the severe cooling stresses the wheels

Civil Engr-8B. Materials of Engr. Construction-* Assignment 27, page 5.

are stripped from the mold while still red hot and placed in a
soaking pit where they are allowed to cool slowly. A maximum tem-
perature of about 725 degrees Centigrade has been found to be sat-
isfactory for this annealing process. If the temperature is higher
an under sirable formation of graphite occurs within the xvhite tread.
The effect of chills on the structure of cast iron is shown in
Figure '6 on page 6S5.

The cleaning of castings is described in Article 749. The
three methods are rattling, pickling, and sand blasting. Rattling
is satisfactory only in the case of the simplest castings. Pick-
ling is in more general use; and sand blasting is most convenient
for large castings. Often the sand blast is followed by pickling.
In all these methods, the final cleaning operation is the smoothing
of irregularities such as are left where gates and fins have been
broken off. This is done with a cold chisel, with a pneumatic
chipping tool, or an emery wheel.

Composition and constitution of_ cast iron; Read Article s
750 to 758 inclusive. Cast iron is a complex alloy composed of
six important elements - iron, carbon, silicon, phosphorus, sulphur,
and manganese; other unimportant elements are often present. The
most important element is carbon because of its pronounced effect
on the strength of cast iron. It occurs free as graphite and in
the combined form as cementite (FegC) which is sometimes called
iron carbide or combined carbon. The importance of the other

Civil Engr-8B. Materials of Engr. Construction* Assignment 27, page 6

elements is due to their influence upon the carbon. There are
three distinct classes of cast iron, depending upon the state in
which the carbon occurs. In gray cast iron the carbon occurs chiefly
as free carbon in graphite flakes. In white cast iron it is prin-
cupally in the combined form, while 'in mottled cast iron there is
a mixture of particles of gray and white iron. A product of the
air furnace or cupola containing from 20 to 50$ steel scrap is
known by the misleading trade name of semi-steel (see definition
on page 588). The metal is actually a fine grained cast iron. It
is much stronger than ordinary cast iron but it is not steel. It
is used v;here a strong, close grained metal is required, as in
hydraulic cylinders; and in parts requiring strength and shock re-
sisting ability, as in shear and punch frames.

The composition and the rate of cooling, through the range of
solidification and immediately below that temperature determine
whether a given mass of molten cast iron will be gray, white or
mottled. The more rapid the cooling the less the graphitization
(white cast iron, for instance, made by chilling the molten irori)-

Carbon in cast iron is discussed in detail in Article 751.
The range in carbon content for commercial cast irons was given on
the equilibrium diagram for iron ^nd carbon. The strength and
other properties of the casting are dependent upon the form in which
the carbon occurs. Figure 6 (after Howe} on page 699, shows the
effect of graphite and combined carbon. The important features in

Civil-Engr-8E« Materials of Engr» Consturction.. Assignment 27, page 7.

this diagram are: the names of the cast irons in the upper part
of the diagram; the tenacity, ductility, and hardness of the whole
with ordinates and abscissaes in the central portion; and all of
the lower part of the diagram. In this latter portion, note that
mottled cast iron is not alluded to except to state that it is
harder o Irons of this type have no special adaptation and their
production is not intentional.

Graphitization, that is the decomposition of the combined car-
bon to form graphite, is facilitated by increased carbon or silicon
content and by slow cooling. Graphitization is retarded by sulphur,
excess manganese, and rapid cooling* This is a brief summary of
Article 751. The effect of the various elements will be discussed
separately in detail.

Silicon in cast iron is discussed in Article 752. It ranks
below iron and carbon in its importance as a constituent. The
amount of silicon in cast iron can be controlled. It acts prin-
cipally as -"•- precipitant of graphite, causing a maximum precipita-
tion when about a quantity of 5%. Below 3^ it will aid in the
production of gray iron, but over 3% causes iron silicide, which
results in a hard brittle metal. Small amounts decrease shrinkage
and minimize blowholes-

The effects of sulphur are discussed in Article 752. As in
the case of silicon the amount of sulphur in the cast iron can be
controlled during the manufacturing process. Sulphur has a decided

Civil Engr. SB. Materials of Engr. Construction. Assignment 27, page 8.

effect upon the properties of cast iron. It prevents graphitiza-
tion and produces hard, "brittle iron. Specifications limit the
sulphur content to 0.1$ and some even to as little as 0.50^. Sul-
phur causes red- shortness and blow-holes. It is an undesirable
element. The effect of sulphur can be neutralized by silicon and
manganese, About 15 parts of silicon or tv/o parts of manganese
are required to neutralize one part of sulphur*

In the best grades of- gray iron the phosphorus content is
limited to O.SJb. High phosphorus causes cold- shortness. But when
fluidity is important, as in the pouring of thin castings which
must have a good impression of the mold, and where toughness is
not required, about 1.0^ phosphorus is used. The amount of phos-
phorus cannot be controlled, 5t is determined by the amounts present
in the materials from which the cast iron is made.

When manganese is present in small amounts it combines with
the sulphur to form manganese sulphide and tends to decrease the
hardness and brittleness of the iron; but in greater quantities it
causes increased hardness.

The other elements that may be present in cast iron are of
importance to the iron manufacturer but not to the student of a
general course in Materials. Article 758 with Table 1 can be onitted
since the approximate allowable proportions of the various elements
have already been discussed and the student therefore has a general
idea of the composition of good cast iron.

E:igr-8B- Materials of Engr. Construction. Assignment 27, page 8.

Read Article 757 on defects and remember what the principal
defects are and how they are caused.

PROEBRT J1RS_ 0£ OAST IRON

Shrinkage: Read Article 759. The pattern maker must make
allowance for shrinkage and the designer and the iron founder must
consider this phenomenon "because of the induced stresses and con-
sequent danger of checking. It is usually assumed that shrinkage
is about 1/8 of an inch per foot. It is quite variable, the
chief factors vrhich influence it being the presence of silicon, the
rate of cooling, and size of the cross- sect ion of the casting.

Hardness: Read Article 760. Hardness is the term generally
used to designate that quality which has to do with the resistance
of a metal to cutting or machining, or to xvearing or abrasion. As
shown in Figure 5 on page 699, the hardness increases directly
vrith the amount of combined carbon. This may be due to the hardness
of the cement ite itself and to the decrease in graphite which acts
as a lubricant to the cutting tool. Hardness is measured by the
drill test and the ball-indentation test. Both are empirical.
Review Article 129 on page 127.

Tensile strength: Article 761 is relatively unimportant.
Tensile strength is important but in a direct test it is difficult
to determine. For average gray iron the ultimate tensile strength
is about 20,000 Ib. per sq. in. Omit the tables on pages 707 and
708. Remember the typical stre ss-def ormation curves on page 709.

01;?.l Fr.'.g."«8}3. Materials of Engro Construction.. Assignment 27, page 9.

They show that ca»~t iron has no proportional limit. It is important
to not ^ that cast iron is weakest in torsion. In torsion or com-
er nad stress the piece vill fail in tension and its strength will
be limited "by the tensile -stcpngth of the metal.

Compressive strength: Read Article 763 o The average compres-
sive strength of ordinary gray cast iron at the proportional limit,
or yield, point, as it should more properly be called, is about
30,000 Ib. per sq. in. The ultimate strength is about 70,000 Ib.
per sq* in. Figure 11 on page 710 represents a typical stress-
deformation curve.

Transverse strength : Read Article 764. The arbitration bar
is described in this article. It is the most important test speci-
men of cast iron. Under standard conditions an arbitration bar of
average gray cast iron \vill give a modulus of rupture of about
45,000 Ib. per sq. in. This test gives a valuable criterion of the
quality of the metal. It is necessary that the conditions for the
test be standardized, because the size of specimen and its method
of preparation affect its strength. The removal of the skin by
machining decreases the strength, while tumbling hardens the skin
and increases the strength.

The A.S.T.M. minimum requirements for the modulus of rupture
in the test of the regulation arbitration bar are 39,000., 45,000
and 50,000 Ib. per sq. in-, respectively, for light, medium, and
heavy castings. The minimum deflection is 1/10 of an inch.

inl Engr«3B. Materials of Engr » Construction. Assignment 27, page 10

Modulus of elasticity: Read Article 765. The modulus of

G&o
elasticity of cast iron is quite variable; 15,000)Klb. per sq. in.

nay be taken as the average*

Articles 766 to 771 inclubive are relatively unimportant.
Remember that the shearing strength of cast iron is greater than
its tensile strength. When subjected to torsion cast iron fails
in tension which in this case is a secondary stress.

Ductility : The ductility of cast iron is very slight.

MALLEAEIE CAST IROH

Introduction: Read Articles 772 and 773 on the nature and
importance of malleable cast iron. Malleable cast iron is white
cast iron, which, after it has been cast into final form, is ren-
dered malleable by an annealing process. Malleable cast iron can
"be cast into complicated forms, and after casting, its toughness,
ductility, and strength can be materially increased. It is used
principally for implements, machinery, and rolling stock. For these
purposes it is surpassed only be steel castings and forgings* It
is also ussd in the manufacture of articles whose form is too com-
plicated for economical forging.

1,-anuf acture : Read Articles 774 to 776 inclusive. Malleable
cast iron is made from foundry pig iron, scrap from the casting
floor, steel scrap, and to a limited extent annealed malleable iron
scrap. The cupola, air furnace, and openhearth furnace methods
are those chiefly used in melting the charge. The metal must be

il Engr~-8B. Materials of En^r. Construction. Assignment 27, page II

poured ^hile very hot and as rapidly as possible. The annealing
process consists in heating the castings to a red heat (about 1300
degrees Fahrenheit) for several days. This treatment changes the
ccubiued carbon in the Yfhibe oast iron into graphite. The carbon
does not precipitate in flakes as in the case of gray cast iron
but in a finely divided form called temper carbon. In this amor-
phous form, hovrever, carbon is readily oxidized, and in order to
prevent oxidation the castings may be packed in any inert material
like sand, or clay. Stronger castings are made -when a decarboniz-
ing material such as iron oxide is used.

Constitution: Read Article 777. The composition of malleable
cast iron is not of great importance; it is important, however, to
remember that good malleable cast iron consists principally of fer-
rite and temper carbon* None of the carbon remains in the combined
form. If sand or clay is used as packing material the heat and
slow cooling are sufficient to change the combined carbon into tem-
per carbon, and the fractured section of an annealed casting is
black. Hovrever, if iron oxide is used to pack the castings, it will
oxidize the carbon, forming CO, so that the outer surface will be
practically pure iron. When such a casting is broken the fracture
has a white exterior with a black center. The white skin of carbon-
less iron is rarely over -J- of an inch thick. This type of casting
is called "black-heart." The outer layer may be case-hardened,
hardened, or tempered.

Civil Engr-8B. Maxerials of Engr. Construction. Assignment 27, page 12

Mechanical properties: Read Article 779, omit Table 7. The
proportional limit of malleable cast iron is about 20jOOO Ib. per
sq«. in. In compression, since it is a ductile material, this
yr.iue is practically its ujtimate strength for long slender speci-
mens. In tension its ultimate strength is about 45,000 Ib. per sq.
in. Its average modulus of elasticity is about 20,000,000 Ib. per
sq. in. In tho transverse test of a l«inch square specimen its
modulus cf rupture is about 70,OCO Ib. per sq. in. on a 12 -inch
span. Under these conditions its deflection is about -|- inch. The
ductility of malleable cast iron as measured by its elongation is
about 7f0.

QUESTIONS:

1. What are the principal uses for cast iron in engineering
construction?

2. Define cast iron.

3. Why are castings not made directly from the molten iron as
it comes from the blast furnace?

4. Compare the foundry cupola and the blastfurnace.

5. Is the cupola or the air-furnace cheaper to operate and why?

6. Compare the two principal methods of producing cast iron.

7. What are the various types of molds used in the production
of iron castings?

8. What is chilled iron? What is it used for?

9. How does annealing from a high temperature (say over 750
degrees Fahrenheit) affect chilled cast iron?

Civil Engr-8B. Materials of Engr. Construction. Assignment 27, page 13

10. What is semi- steel? What is it used for?

11. How does the rate of cooling affect the graphitisation of
cast iron?

12. Discuss the effect of silicon and carbon on the properties
of cast iron.

15. What is white cast iron? How can gray cast iron be produced?

14 • What is the maximum sulphur content allowed in cast iron by

most specifications? Could raw materials having more than
the allowable amount of sulphur be used?

15. Name the principal defects in iron castings.

16. What is malleable cast iron? Hov; is it made?

17- Why must a packing material be used in the annealing process?

18. List the strength, elasticity, and ductility of malleable and
gray cast iron*

• •

UNIVERSITY OF CALIFORNIA EXTENSION DIVISION
Correspondence Courses

s of Engineering Construction

Assignment 28

Civil I^igr-SB Professor C.T.ftiskocil

NQN-FERROOS METALS

Introduction." Iron, copper, aluminum, zinc, lead, tin, and
nickel are the metals of greatest industrial importance. Iron is the
most important metal used in engineering construction and for this
reason it is usually classed by itself. The other metals are
usually grouped together and called, as in the heading of this
chapter in the text, non- ferrous metals. Many secondary metals
such as cotalt, molybdenum, tungsten, and vanadium have no industrial
importance except as alloying elements.

Copper. - Read Articles 780, 781, 782 and the paragraph on
copper on page 522. Copper ores exist in a great variety of forms,
usually as sulphides or oxides. The principal deposits of copper
in the United States are in the I^.ke Superior region and in the
Rocky ilountains. In the Lake Superior region it exists as native
copper ^.hile in the mines of Arizona, Utah, and Montana it is
found as copper sulphide and copper-iron sulphide. Copper sulphide
is known as chalcocite or copper glance, CusS« Most of the world's
supply comes from the copper pyrites or chalcopyrite, CuFeS,, • Cupr ite
and malachite, both given in the text, are decomposed sulphides.

If the copper ore does not contain sulphur the extraction of
the metal is simple. Lake copper, for instance vhich is free from

Civil Sngr-8B assignment 28. page 2.

sulphur^ is mechanically concentrated and then melted, usually in
a reverberatory furnace, and the slag skimmed off. The resulting
metal is refined by electrolytic or fire methods. If copper is
obtained from sulphide orss the process is more difficult. It
usually involves four stages; roasting, smelting, converting, and
refining. The object of the roasting is to drive off most of the
sulphur in the form of dioxide gas and leave th3 metal in the form
of oxides* All of the sulphur is not driven off because it is
desirable to retain some to facilitate smarting which is the next
step. The purpose of the smelting is to concentrate the ore by
removing the gangue in the fom of slag. The metallic concentrate
is known as matte vhich is essentially metallic sulphides of
copper, iron, and any other metals originally present in the ore.
Smelting is done in a blast furnace or in a reverberatory furnace,
the latter furnishing a richer matte. The matte is purified in a
Bessemer converter. The air blown through the molten metal
eliminates the sulphur and forms -That is knovrn as blister copper.
Blister copper is refined by fire and electrolytic methods. The
electrolytic method is used to produce the finer grades of copper,
.jaodes of blister copper are placed in a strongly acid copper
sulphate solution. Cuthod.es of very pure copper are used and
pure copper from the anodes is deposited on them -rhen an electric
current is passed through the circuit. Impurities are insoluble
in the electrolyte, and fall to the bottom in the slices. T.hen
these include trie precious metals they can bo recovered from the
re siduc.

Civil £ngr.~8E Assignment 23. page 3.

The two principal classes of copper are electrolytic copper,
v/hich is obtained by the method just described; and Lake copper,
v;hich is obtained from ores mined in the Lake Superior region.

Copper is a malleable, ductile metal having high electric
conductivity and great resistance to atmospheric corrosion. Copper
does not cast veil, most copper products being therefore dravm or
rolled. Ilechanical working, such as drawing has a greater effect
on the physical properties of copper than it does on steel. Hot
rolled copper has an ultimate tensile strength of 30,000 Ib. per
sq. in., and an elastic limit of 7,000 Ib. per sq. in., -vvith an
elongation of 5C^. Cast copper has approximately the same strength
but its elongation is much less, being about 7/b. Cold drawn
copper in the form of wire, has an ultinate tensile strength of
50,000 Ib. per sq. in., an elastic limit of 30.000 Ib. per sq. in*
with an elongation of about 2^. Its modulus of elasticity is
about 15,000,000 Ib, per sq. in.

The uses of copper are well stated in Article 782.

Zinc.- Eead Articles 783,734, 765 and the Daragraph on
zinc on page 523.

Zinc sulphide, which is known as zinc blendq (ZnS)> is the
principal source of zinc. The deposits of zinc carbonate, called
zinc spar or calamine (ZnCO^), are being rapidly exhausted. 2.inc
silicate (Zn^SiOS- rL-,0) is of lesser importance. The chief deposits

(•• rr C»

in the United States are in Wisconsin., .lisscuri and NOT Jersey.

Civil Engr.-8B Assignment 28. page 4.

Zinc ores are roasted to convert them into the oxides, -rhich
are then mixed with carbon and heated. The carbon combines with
the oxygen of the oxide and pure zinc is volatilized. The zinc
vapor is condensed and poured into ingots. In this form it is
known to the trade as spelter. Spelter is rcmelted and rolled
into sheet sine.

Since zinc is rarely usod as a stress-carrying member of

• - - i
a machine or structure its tensile strength is not important.

The fact that it casts well and has a high resistance to atmospheric
corrosion makes it adaptable for a protective coating for iron and
steel. ,<hen so coated the materials are known as galvanized iron.
Zinc is put on in several -//ays. The metal may be dipped in molten
spelter or the zinc may be deposited electrolytically, or the coat-
ing may be formed by the condensation of volatilized zinc dust,
as the result of a process known as stierardizing. Zinc is used
as the negative element in nearly all primary batteries. Zinc
dust and pigments, such as zinc oxide and lithopono, arc commercial
forms of zinc.

Aluminum* - Read ^ticies 786,787,788, and the paragraph on

aluminum on page

In 5) ite of its abundance, aluminum is never found in the free
state, and it is only since 1886 that it has been produced on a
commercial scale. Bauxite is -a hydrated oxide (^IpOg.SHgO). It
is the principal source of aluminum. Aluminum oxide is called

Civil Engr-8B Assignment 28 page 5

fJ^EH1! ^-12°3> which is a" essential ingredient of clays. The
bauxite is converted into alumina which is dissolved in molten
cryolite (AlPj.SHaF) from ^vhich mixture the metallic aluminum
is separated by electrolysis.

Aluminum is very light but has considerable strength; it
is malleable, non-corrosive, and ductile, and it has high electric
conductivity. It is made into various shapes by rolling, pressing,
drawing, and casting. Because of its low electric resistance
and lightness it is v/ell adapted for use on long-span transmission
lines. It is also used for bus-bars and rode in power houses.
aside from the uses stated in Article 738 it is used to quiet molten
metal before casting, for thermit, which is used in welding (pre*-
viously referred to), and in the form of powdered aluminum, as
a paint pigment and in explosives.

Cast aluminum has a tensile strength of about 13,000 Ib.
per sq« in. rith an elastic limit of 9,000 Ib. per sq. in. and
elongation of 20%. When drawn its tensile strength increases
to 30,000 Ib. per sq. in. and its elastic limit to about 20,000
Ib. per sc. in. while its ductility is decreased.

Lead.- Read Article 789 and the paragraph on lead on page
522. Galena (?bS) is the only important ore of lead. The United
States le?^s in the production of lead. The essential steps in the
extraction of lead from its ores are roasting and smelting. There
are other secondary operations, ^jaong these is the desilverizing

Civil Bngr-8B Assignment 28

page 6

the lea 4, if there are sufficient amounts cf silver present. The
properties of lead which are of most importance are its malleability,
plasticity, and resistance to atmospheric ccrrogim. Its chief
uses ars listed in the text but an important use is omitted, namely,
its use in the manufacture of storage battery plates.

Tin.- Read article 790. The ores of tin, their occurence,
and the method used in extraction of the metal are clearly described
in the text. The uses of them are also given. Its high degree
of malleability and its resistance to atmospheric corrosion mc.ke
it of commercial importance. Tin plate is thin sheet steel (a soft
lo*v-carbon steel is used) covered r/ith a coating of pure tin.

Nickel.- Read /article 791. Nickel is highly resistant to
atmospheric corrosion. It has a silvery appearance and is used to
plate iron, steel and other metals. Pure nickel \voulc be an
excellent structural material, since its properties ?re similar to
those of medium carbon steel, Taut it is too expensive. Alloying
nickel with copper to form v/hat is known as monel metal makes the
product somerrhat cheaper, iionel metal contains about 67f0 nickel,
28% copper and b% other metals, among which are iron, silicon,
manganese, and carbon. Its values for tensile and compressive
strength, and its uses are listed in the te:rt. Its strength compares
well with that of steel, and this fact coupled with its great re-
sistance to corrosion and the action of sea vater, make it a very
desirable naterir.l.

Civil Engr.-8B. Assignment 28. . page 7o

NON-FERROUS ALLOYS

Introduction.- Lietais are alloyed to change their properties.
Undesirable properties can "be decreased and desiraole properties
G'-.n be increased through the use of alleys. Alloys may be harder,
tougher, more ductile, and may have better casting qualities, or
greater tensile strength than any of the constituent elements,
Furthermore the cost of production can Le lessened.

Brasses. - Read Article 722 and 793. An alloy of copper and
zinc is knov/n as brass-, la special brasses a third metal is
added* Brass and bronze, an a] loy of copper and tin, which vill
be discussed later, form the commonest yet the .-lost important
of the non-ferrous alloys. They can be cast into the desired
shapes or rolled into sheets c.nd rods. Brass can be draivn into
-.vire, while bronze is usually cast into shape. In general, brass
hrs less strength than bronze. Brasses and bronzes are not so
strong c.s iron and steel, but they are less subject to corrosion,
and are used ivhere long exposure to moisture is necessary, as in
pumps, and for hydraulic fittings. Br<.'.ss is also used as a bearing
metal for steel shafts. Brass is relatively expensive, being aboat
seven tirr.es more costly than steel.

The proportions of copper and zinc, in the manufacture of
brass, may be varied ever vide limits. I he figure on page 741
is quite complex. It is sufficient to remember that ~hat is
knov;n as standard brass (about 2 parts copper to 1 part zinc)

Civil Engr.-8B. Assignment 28. . page 8.

is most commonly used of all tne brasses. Jn the cast form its
ultimate tensile strength is about 50,000 Ib. per sq. in. and the
elongation is about 30%, with a modulus of elasticity of about
13,000,000 Ib. per 54. in. Standard brass is more resistant to
corrosion than brasses which contain less copper. Munz metal,
60$ copper to 40% zinc, is not used as much as formerly.

Manganese bronze is the nost important of the special
brasses. The manganese is added to the brass in the form of
ferro-nanganese as a deoxidizer. The effect is to strengthen
and harden the alloy. Usually there are only traces of manganese
left in the finished product since most of it is fluxed off. Its
strength and toughness are equal to those of steel; besides, it is
readily cast and is highly resistant to corrosion by sea wtter,
alkali vater, and r/eak acids.

Bronze.- Read ^irticles 794 and 795. ^J.loys of copper and
tin have oeen known since prehistoric times. Commercial bronzes
usually contain more than 80^o copper. LJachinery bronze generally
contains about 85$£ copper. It is used as a bearing inet^l, for
cut gears, bushings, stuffing boxes, and plumbing fixtures. Gun
netal and bell metal are uhe more important of the simple bronzes.
Machinery bronzas, in the cast form, has a tensile strength of
about 30,000 Ib. per so. in. with an elongation of 10/i and a
modulus of elasticity of 15,000,000 Ib. per sq. in.

Civil Engr.-8B ^ssigrnnent 28- pc.ge 0".

The special bronzes, copper -tin- zinc alloys, are the most
valuable and in most general use. Machinery bronze referred to
sbotf-e is usually made with some zinc. The addition of phosphorus
to any bronze produces a mcrked increase in its strength and
ductility, '.-Then of proper composition, phosphorus -bronze can be

dr-^wn cold, forged, rolled, and cast. It is used where high
strength '.nd resistance to corrosion are controlling factors,
phosphorus, as in the case of manganese, is a strong deoxidizing
agent. Only small amounts of residual phosphorus remain in the
finished metal.

The three -metal alloys (copper-zinc-tin) can be m^de so
that they have high strength and considerable ductility. The
final properties of the alloy depend upon the mechanical treatment,
such as rolling and drawing, as ^ell as upon composition and
foundry practice, which Y/ould include temperature of pouring.
Cold v/orking, driving, or rolling generally raises the elastic
limit uid ultimate strength of these alloys.

Season crack:.ng of brass and bronze.- Read Articles 796,
797, and 798. Sound metal in the form of sheets, rods, and tubes
vili often develop crocks under service or even while in storage.
Crocking of this kind is also produced by corrosion and sudden
changes in temperature. It is called season crocking anc sometimes
corrosion cracking.

Season cracking may be prevented by annealing ana springing.

Civil Engr. -SB- ^ssigniaent 28. . page io.

Springing is described in the text. Annealing must be carefully
done so us not to weaken the metal, especially if it is to be
used for springs. The concentration of stresses .at the base of
scratches and corrosion pits can be prevented by polishing the
metal. These localized stresses are a source of season crack-ing.
The chief cause of season cracking is the internal stresses set up
in the metal by cold "working.

The presence of internal stresses, besides subjecting the
metal to possible season cracking, causes distortion, if part of
the stresses are relieved by the removal of some of the metal, by
boring, or by the cutting of keyivays. This condition exists also
in the c^ss of cole1 rolled steel shafting.

Alloys of aluminum.- Read Articles 799 to 803 inclusive.
The Uoes of thsse alloys are given in ^tide 799. The principal
alloys are aluminum bronze, aluminum-zinc alloys, and duralumin.

^iuminum bronze contains about 90^ copper and 10^' aluminum.
Since it contains no tin it is really not a bronze. Aluminum bronze
is an alloy of high strength and ~ood ductility.

Duralumin contains about 9b% aluminum with copper, magnesium
and manganese as indicated in the text. On account of the large
percentage of aluminum, it is very light in weight, about 175 Ib.
per ctu ft. , as compared with 480 Ib. per cu. ft. for rolled
steel. It is used for drawing and rolling. Similar alloys are
sold under various trade names but their properties are similar to

Civil &npr.-8B ^jssignment 23.

tliose of duralumin. These alloys have made the large dirigibles
(air ships of the Zeppelin type) possible. In their constr action
the strength of stesi with the lightness of aluminum is necessary.

Bearing metals.- Read ^jrtidsfi 804 to 808 inclusive.
Satisfactory bearing metals must have sufficient compressive
strength to withstand the bearing pressure, and they must develop
little friction \/hen the surfaces coine into actual contact, as
*vhen a shaft stops rotating. j.± Yrell oiled bearing in notion vill
hr.ve little friction irrespective of the kind of metal used because
of the oil film on the moving surfaces but when motion stops the
oil film is broken and the metal surfaces come into contact and
anti-friction metal is then necessary. Host shafting and sliding
p^rts of machines are made of steel; bearings cannot be ma.de of
steel because steel surfaces ruboing together v;ould cut and tear
each other* Cast iron, bronze, brass, Babbit metal and other anti-
friction matals are used. Lead is too soft for a bearing metal.
;Ls indicated in Table 4 on page 757, alloys of lead and antimony
(used to hirden the lead) are the softest bearing metals.

Good bearing metals have a crystalline structure composed
of tvjo types of crystal, soft and hard. The hard crystals carry
the load r-nc resist wear. The soft crystals yield and allow the
harder crystals to adjust themselves to any irregularities in the
moving surface, and also wear out belcr.v the actual surface of the
bearing, thus forming a surface which readily holds the lubricant.

The soft bearing metals, of which Babbitt metal is the bast
c^wnift ^y^ o *+. rM reetlv in clr.ce and usually require no machining

Civil Engr.-8B Assignment 28. page 12'

QUESTIONS

1. Name the metals of greatest industrial importance. HOT; :.re
they generally classified?

2. V.hTt are the principal copper bearing ores?

3o HOY; is metallic copper obtained from the sulphide ores?

That are the appro:: irac.te tensile strength and elastic limit
of hot rolled and cold drawn copper?

5. Vvhat is galvanized iron? HOW is it made?

6. Why is aluminum particularly adapted for use in long-span
transmission lines?

7o What are the principal uses for lead e.nd tin?

8. What is monel metal? uhat are its chief characteristics?

9. What is brass?

10. What is bronze?

11. Row does manganese affect the properties of brass?

12. Why is brass that has been i/orked cold more liable to season
cracking than orass that has been worked while hot?

13. What precautions can be taken to prevent season cracking?

14. What are the requirements for a good bearing metal?

15. Name the different bearing metals.

16* What ?.re the advantages of bronze over BabDitt metal as a
bearing metal?

17. Why would bronze be preferrable to cast iron for a bearing
for a steel shaft?

UNIVERSITY OF CALIFORNIA EXIEfc'Sia* DIVISION
Correspondence Courses

Materials of Engineering Construction
Civil Engr-8B Assignment 29 Prof. C. T. Wiskocil

FATIGUE OF METALS

Introduction: Read Article 821. Fatigue results from the
inability of a metal to carry repeated loading rrhich does not
stress it in excess of its elastic limit. The fatigue strength
or endurance limit, as it is often called, seems to be a definite
unit stress, as isrell defined a property as the ultimate tensile
strength.

Vihen metal parts of machines or structures are subjected to
static or impact stresses they either withstand the load or they
fail, that is, they are actually ruptured or else rendered un-
usable by distortion or deformation. The maximum loading under
these conditions can be quite accurately estimated by the results
of relatively simple tests; but under conditions of repeated stress
such as occur vhen a piece of metal carries a load perhaps a mil-
lion times and then suddenly ruptures, the maximum safe load is
not so easily determined. The load, up to the time of actual
fracture, apparently does no\ damage. This is the characteristic
feature of the fatigue of metals.

In the design of metal bridges and buildings the loads are
kept v/ithin the elastic limit and localized stresses do not cause
static failure. It has been estimated that the stresses in mem-
bers of an ordinary railway bridge are repeated less than tiro

Oivil Eng:*-8B Assignment 29 Page 2

million times during a period of fifty years. In these structures
the unit stresses are not large and they are repeated a relatively
small number of times. Fatigue, therefore, is not important and
the criterion of static strength governs the design.

In the case of machine parts, however, fatigue is a major
factor. The crankshaft of an airplane motor is subjected to about
twenty million reversals of stress in less than 200 hours of fly-
ing. The stresses are relatively high since the motor is constant-
ly operated at nearly maximum power. The stresses in the shaft
of a steam turbine, if operated continuously for ten years, would
"be reversed about sixteen billion times. Fatigue, therefore, must
te considered in the design of machine and automobile parts such
as crankshafts, piston rods, connecting rods, crankpins, springs
and axles.

If a loud is put upon a piece of steel and then removed, the
metal is said to have been subjected to a cycle of stress. Since
steel isAhomogenous, the minute constituent particles move on one
another during a cycle of stress. For a single cycle, if the
maximum stress is within the elastic limit, the heat generated by
the microscopic movement is not appreciable but if the stress
cycle is repeated the rise in temperature of the metal is noticeable
The friction, 7/hich presumably causes this heat, finally weakens
some minute element to such an extent that it actually ruptures.
This failure of some minute element undoubtedly forms a concentrated

Civil Engr-8B Assignment 29 Page 3

area of high stress and from this nucleus the fracture spreads to
adjacent crystals and the progressive increase in the size of the
original cleavage plane or crack causes the failure of the entire
member. High localized stress is also formed at the base of sur-
face scratches or at the root of a screw-thread or at a minute
blow-hole or similar internal defect. These are typical conditions
which lead to failure from fatigue. It should be noted too, that
failure of machine parts is often the result of a combination of
fatigue and damage by occasional overstrain.

The relative movement of the elements of minute steel crystals,
v.'hen under stress, was first observed by Evring and Rosenhain in
1899 r The movement became evident as dark parallel lines across
the faces of individual crystal grains as they were viewed under
the microscope when illuminated by oblique lighting. The accomp-
anying diagramatic cross- sectional sketch shows how the light would
cast sh.".dovs T'hich vould appear as parallel lines, called slip-
lines, v.-hen viewed from the direction indicated. Four years later
Eving and Humphrey (as will be described under the subject of slip-
lines) observed that the slip-lines developed in steel by subjecting
Direction of observationL, ^Direction of light

*MX *j

Polished surface ^-J*~JF

Crystal boundaries not shown

Civil Engr-8B Assignment 2-9 Page 4

it to repeated cycles of stress, would develop into microscopic
cracks which in turn vrould spread and cause ultimate failure of
the entire member.

Crystallization of steel: Study Article 822. \flien steel is
subjected to a sufficient number of reversals of stress, even
though the stress is -within the elastic limit, the induced fatigue
makes it liable to sudden rupture. With this type of failure there
is no preliminary deformation (read third paragraph on page 779)
and the fracture is crystalline as in the case of cast iron or any
brittle metal. The appearance of the break and the characteristic
suddenness with -which failure occurs gave rise to the theory of
the cold crystallization of steel - and it is still popularly be-
lieved that fatigued steel becomes crystallized. This misconcep-
tion is fostered by the fact that sudden failures display the
crystalline structure of a metal, which in the case of gradual
failure as in a static test, is disguised by the elongation and
necking of the piece due to its ductility. Therefore, when fatigue
failure occurs in a ductile metal, such as steel, it is argued that
since it brote suddenly with a crystalline fracture the material be-
came crystallized, and hence was made brittle, by the induced
fatigue .

Sudden failure is attributed to brittleness but it is possible
to produce a crystalline fracture in a piece of mild steel of known
ductility by cutting or sawing a rod .part way through and then
completely breaking it by a single blow with a hammer. The

Civil Engr-8E Assignment 29 Page 5

resultant fracture will be granular because the grains haye had
no time to elongate and disguise the crystalline structure- The
fracture resembles that c.f brittle metals which fail suddenly and
•without apparent warning.

The popular conception of fatigue being caused by vibration
and repeated stress under conditions of continuous service is cor-
rect, although the deterioration is not produced as easily as is
beleived; but the phenomenon implied by the term crystallization
does not exist. The crystallization of steel occurs when it^
solidifies from the liquid state, therefore, the metal in the solid
state is inherently cyrstalline. The crystalline structure of
steel has been repeatedly referred to; see illustrations such as
those on pages 628, 632 and 637 in the text. Change in crystal
size or recry stallization can nevertheless be produced by thermal
treatment. (The increase in grain size by overheating without
proper annealing has been discussed under the subject of Steel).
The misconception arises in the meaning of the term crystallization
because the laymen who still adhere to the theory of cold crystal-
lization believe that the fatigue of steel, which occurs under in-
fluence of shocks and vibration, produces gradual enlargement of
the crystals and corresponding brittleness.

Two reports on failures attributed to cold crystallization
because of the large crystals appearing in the fracture were later
discredited when it was found that the ruptured members had at one
time been heated - undoubtedly overheated. These reports appeared

Civil Engr-8B Assignment 29 Page 6

in the Engineering Record of December 13, 1913 as an editorial
note, and in the Report made on Division Street Bridge Failure in
Spokane, Engineering Record, Vol.73, page 29 (January 1, 1916),
and also an editorial on the saae subject in the following issue
(January 8, 1916). It will be recalled from previous discussions
on this subject that fresh fractures of overheated steel show
large brilliant facets which are a criterion of the actual struc-
ture. The overheating causes an increase in the size of the
crystals and a decrease in the strength and ductility of the metal.
The large facets in a fatigue failure are formed -while the deterio-
ration is in progress by a continuous cleavage plane extending
through two or more adjacent crystals which tends to exaggerate
the apparent size of the crystals on the surface of the break.
But according to Deseh a microscopic examination of the metal be-
hind a fatigue fracture shows no change in its structure or in-
crease in size of the individual crystals.

While crystal size can be increased by thermal treatment
there is no evidence that crystal growth of steel can be produced
by strain at atmospheric temperatures. This statement is true
for nearly all metals. Lead is an exception, however, inasmuch as
overstrain by plastic deformation results in a decided crystalline
grovrbh in this metal even at atmospheric temperature s«

The popular idea of cold crystallization of steel still exists,
&***. in spite of the fact that the true cause of fatigue, which
will be discussed later, was discovered in 1903. The statement

:•- -.. •- ••_ •= -.-'.. . ••'..• •-'-. '•

Civil Engr-83 Assignment 29 ' Page 7

is often heard that the axles of Ford automobiles crystallize in
service due to continued vibration. This is not to be wondered
at since as late as 1915 many engineers still believed in cold
crystallization. In THE LIFE OF IRON AND STEEL STRUCTURES by
Frank?/. Skinner (consulting engineer, Nev York) Paper No. 107 of
the International Engineering Congress, IS 15, San Francisco,
California, Volucne on Materials of Engineering Construction, page
442, we find the following statement on the subject of crystalli-
zation: "That iron and steel are often found after severe service
with a damaged crystalline structure, is undoubted, but it is many
times a moot question i/hether this condition vras developed in ser-
vice, or during the original manufacture of the metal»u In the
discussion of the same paper, however, Edgar Marburg cautioned
against the perpetuation of the erroneous cold crystallization
theory.

Slip -lines: Study Article 823; it is very important. Marked
progress in the study of the fatigue of metals ?ras made by the
English scientists, Swing and Humphrey. Their investigations are
remarkable for the accuracy of observation and the ingenious
check on their theories- In 1903 the paper "The Fracture of Metals
under Repeated Alternation of Stress" explained their experiments
and proved that the primary cause of fatigue failure in a ductile
metal (steel) was the result of localized deformation which was
evident under microscopic observation as a sliding of the crystal
elements on each other and the final rupture of individual crystals.

Civil Sngr-CB Assignment 29 page 8

Their test pieces which could be subjected to any desired bending
moment, ^ere short rods supported in a revolving mandrel. The
region of greatest stress was polished and etched beforehand, for
the purpose of observation under the microscope before and after
a definite number of revolutions, which produced reversals of
stress in the rods. These observations 'were repeated at frequent
intervals. The formation of and development of slip-bands or
slip -lines, are clearly described in the text.

The slip-bands, which were first observed by Ewing and
Rosenhain on the polished surface of overstrained metal, mark the
boundaries or cleavage planes between the elements of the indi~
vidual crystal as its resistance is weakened by repeated reversal
of stress, and it draws out, the elements slipping on each other
like a pack of cards. The formation of slip-bands does not involve
any change in the crystal arrangement or any increase in crystal
size. In normal metal the actual failure or break passes through
the crystal.

From these phenomena and the observations of Beilby which
lead to the discovery of the nature of the surface produced on
metals by polishing, we get a satisfactory explanation of the action
oi1 metals under stress. The mechanical movement in polishing
causes the extreme outer layer of metal to flow thus forming a skin
possibly hundreds of molecules in thickness. Similar but much
thinner films of amorphous metal are formed on the surface of intra-
crystalline cleavage planes which become so strongly cemented by

Civil Engr-8B Assignment 29 Page 9

the hardening of the film, after a period of temporary mobility,
that planes where no slip has occurred are weaker in comparison.
In this manner the weak portions have their strength increased
and a greater stress is necessary to effect slip or deformation
than was first required. This process results in the increase in
elastic strength of the material when the metal has been over-
strained. It has been shown that there is slight movement along
the inter crystal line surfaces but it appears that the actual do-
ne sion between adjacent crystals is much stronger than that be-
tween different layers of the same crystal. This explains the
high elastic limit given to drawn wire by the overstraining of the
metal as it is drawn through the die.

In the action of metal under reversals of stress the slip
between different layers of a crystal is continuously reversed in
direction and at such frequent intervals that the mobile amorphous
film eventually solidifies without cementing the adjacent layers-
A microscopic crack develops which weakens that particular crystal,
and additional stress is thereby -transferred to adjacent crystals,
which undergo slip and gradual deterioration in the same way.
Final rupture occurs at a unit stress below the primitive elastic

limit*

Experiments on fatigue: Read Article 824. The first study
of fatigue and its effect on iron and steel was undoubtedly made
by Fairbairn who published his results in 1864. His experiments
are referred to in the text. In 1870 Wohler presented his data,

•••

Civil Engr-8B Assignment 29 ' Page 10

which were talisn during an investigation extending over a period
of 12 years. Wohler!s conclusions are substantially in accord
with the latest experimental information. Spangenberg substantiated
Wohier's conclusions in 1874, while the famous Baushinger published
the results of his work twelve years later. The first information
on the true action or mechanism involved in fatigue failure was
not knovna until 1903 when Ewing and Humphrey reported their study
of metals under repeated stress. Fatigue tests of metals have also
been made at the Watertovm Arsenal. Important conclusions were
reached in an investigation of the fatigue of metals conducted by
The Engineering Experiment Station, University of Illinois, in co-
operation with The National Research Council, The Engineering
Foundation, and The General Electric Company. The results are re-
ported in Bulletin No. 124 of the University of Illinois Engineering
Experiment Station, by H. F. Moore and J« B« Kbmmers (Dated October
1921).

The most important conclusion in the Illinois tests was the
confirmation of the existence of a limiting stress (see paragraph
4, Figures 1 and 2, and the discussion relating thereto on page
773) ivhich they named the endurance limit, belovr vhich fracture
will not occur, no matter hov often the stress is repeated. Their
conclusion is, "For the metals tested under reversed stress there
was observed a well-defined critical stress at which the relation
between unit stress and the number of reversals necessary to cause
failure changed markedly. Below this critical stress the metals

Civil Bngr-8B Assignment 29 ' Page 11

withstood 100,000,000 reversals of stress, and, so far as can be
predicted from test results, vrould have withstood and indefinite
number of such reversals. The name endurance limit has been given
to this critical stress." Other conclusions will be referred to
later •

The rotating beam type of machine, see Figure 25 on page 71,
is most commonly used in repeatsd stress investigations.

Effect o£ heat treatment: Read Article 825. The results of
the Illinois investigation are summarized as follov/s: "The test
re sluts indicate the effectiveness of proper heat treatment in
raising the endurance limit of the ferrous metals tested. It should
be noted that an increase in static elastic strength due to heat

treatment is not a reliable index of increase of endurance limit

rever se
under Astr ess.

Effect of speed: In the Illinois tests the speed was varied
from 200 to a maximum of 5,000 r.p.m. and the endurance limit at
extreme speeds was not different from that obtained for the same
steels when tested at 1,500 r.p.m. The information given in
Article 826 is, therefore, inaccurate.

Effect of surface condition and change o£ section: The in-
formation given in Article 327 was confirmed by the Illinois in-
vestigation. "Abrupt changes of outline of specimens subjected to
repeated stress greatly lowered their resistance. Cracks, nicks,
and grooves caused in machine parts by wear, by accidents.! blovs,
by accidental heavy overload, or by improper heat treatment may

Civil Engr-8B Assignment 29 • Page 12

cause such abrupt change of outline. Shoulders with short radius
fillets are a marked source of weakness."

"poor surface finish on specimens subjected to reversed stress
was found to te a source of TO a lone ss. This weakness may be explained
by the formation of cracks due to localized stress at the bottom

of scratches or tool marks."

with different heat treatments.
composition: Alloy steel s/\such as nickel and chrome -

nickel steels, were used in the Illinois investigation. The re-
sults showed that the higher the ultimate strength the higher the
endurance limit* That is, if a heat treated carbon steel had a
higher ultimate strength than a chrome-nickel steel the carbon steel
v/ould also have the higher endurance limit.

Relation to elastic limit and ultimate : Read Article 829*
The conclusion on this subject from the Illinois investigation is
as follows: "in th^econnaissance tests made in the field of
ferrous metals no simple relation was found between the endurance
limit and the elastic limit, however determined. The ultimate
tensile strength seemed to be a better index of the endurance limit
under reversed stress than was the elastic limit. The Brinell
hardness test seemed to furnish a still better index of the en-
durance limit a" The mechanism of fatigue as viewed under the mi-
croscope is a phenomenon of actual rupture - the crystal elements
slide on each other and finally tear apart.- Some microscopic
element, an individual crystal, reaches its ultimate strength and
starts the crack which produces failure of the entire piece.

Civil Engr-SB Assignment 29 Page 13

Under fatigue ^here is no flow of the material such as occurs at
the elastic limit, and it seems reasonable that the endurance
limit is more closely correlated to ultimate strength than to
elastic limit.

Te st s beyond the y ie Id point: Read Article 830. Up to the
present time no mechanical device has been found in which the
specimen can be stressed beyond the elastic limit at a relatively
small number of reversals of stress, say less than one million, and
the endurance limit thereby predicted. In stress-number of rever-
sal curves like those on page 775 in the text, the endurance limit
is clearly indicated by a decided break in the curve. For all re-
versals of stress over 10 million the curves in the Illinois tests
were horizontal lines. The most reliable method of determining
the strength to resist repeated loading is to determine the endur-
ance limit by testing a series of specimens, subjecting them to re-
versals of stresses of various magnitudes, and constructing dia-
grams based on stress and number of reversals. The ultimate
tensile strength and the Brine 11 hardness tests are less reliable
indices of fatigue strength.

"Accelerated or short-time tests of metals under repeated
stress, using high stresses and consequent small numbers of repeti-
tions to cause failure, are not reliable as indices of the ability
of metal to with stand millions of repetitions of low stress. '
This is one of the important conclusions of the Illinois tests.

Civil-Engr-8B Assignment 29- Page 14

Rapid determinations of fatigue strength: Read Article 831.
The rise-in-temperature method suggested by Stromeyer (see page
778 in text) gives promise of becoming a satisfactory commercial
method of determining the endurance limit of steel. Temperature
measur events were made in connection with the Illinois tests with
the following conclusions: "The endurance limit for the ferrous
metals tested could be predicted v^ith a good degree of accuracy by
the measurement of rise of temperature under reversed stress ap-
plied for a fev: minutes." The endurance limit is indicated by the
sharp break in the curve drawn between unit stress, and by rise in
temperature after 1,000 reversals of stress.

Bauschinger ls theory of fatigue failure as explained in
Article 832 has never been applied to recent test results. But
while it does not imply a change in crystalline structure such as
was outlined in the erroneous cold-crystallization theory, it does
imply change in the inherent nature of the material. The localized
stress theory proposed by Moore and Kommers, therefore, seems more
probable. "The effect of external non-homogeneity due to scratches,
tool marks, square shoulders and notches is well known. Internal
non -homogeneity niay be due to blow-holes, pipes, inclusion of slag,
irregularity of crystalline structure on account of the presence
of two or more constituents of varying strength, variation in
orientation of crystals, or the presence of initial stresses caused
by mechanical 7/orking or heat treatment. Owing to the minute area

Civil Engr-8B Assignment 29 Page 15

over which it exists, this localized stress produces no appreciable
effect under a single load, but under load repeated many times
there is started from this area a microscopic crack, at the root
of which there exists high localized stress -which under repetition
of stress spreads until it finally causes failure. Fatigue
failures are not necessarily due to accidental flaws or irregu-
larities. Such failures may, in practice, often be due to such
causes, but the definiteness of the endurance limits points to the
conclusion that the endurance limit is a property of the material
just as much as the ultimate strength- If failure is due to flaws,
these flaws are an inherent part of the structure of the steel."

Articles 832 and 835 inclusive give no information on the
phenomenon of fatigue and since the diagrams and formulae were
worked out on the basis of incomplete data these articles may be
omitted.

Endurance limit in terms of ultimate tensile strength: The

following is taken from the Illinois report: "in none of the

under
ferrous metals tested did the endurance limit completely reversed

stress fall below 36$ of the ultimate tensile strength; for only
one aaetal did it fall below 40^, while for several metals it was
more than 50f0. However, these metals were to a high degree free
from inclusions or .other internal defects; the specimens had no
abrupt changes of outline, and had a good surface finish."

Endurance limit under repeated stress: A reversed stress is
one that varies alternately from tension to compression. A repeated

• -.V,

; :

Civil Engr-88 Assignment 29 Page 16

stress is one which varies from zero to a maximum either in ten-
sion or compression. Recent experiments made at the University of
Illinois indicate that the endurance limit under repeated stress
is approximately 1.5 times that under reversed stress.

QUESTIONS:

1. Define fatigue*

2. What is the theory of cold crystallization of steel?

3. Is a crystalline fracture necessarily the result of brittleness?

4. What causes the crystalline appearance of a fatigue fracture?

5. Explain the mechanism of fatigue failure.

6. What is meant by the term endurance limit? How can the en-
durance limit be determined?

7. How does heat treatment effect the endurance limit of steel?

8. What is the effect of surface condition and change of sec-
tion on the endurance limit of steel?

9. VJhat is tne best criterion of fatigue strength or so-called
endurance limit?

10. Can endurance limit be predicted by tests in which the
specimen is stressed beyond the yield point of the material?

11. Discuss the value of the rise in temperature of steel under
repeated stress as an index of fatigue strength.

12. What is the relation between the endurance limit under re-
peated stress and reversed stress?

-.,"•- ' v .•- .

* - « - . ^.

UNIVERSITY 0? CALIFORNIA. EXTEKaiON DIVISION
Correspondence Courses

.Materials of Engineering Construction
Civil Engr.-8B Assignment 30 Prof, C.T.Yttskocil

THE CORROSION OF METALS

The importance of corrosion* - Study Article 83V.
The rapid coating of the light-colored glistening surface of
machined iron and steel by a dull layer of oxide is a familiar
phenomenon. Prolonged exposure to air and moisture increases the
conversion of the netal into a loosely coherent compound known

as rust r;hich has a dark reddish-brown color. The formation of

unif ore. coat ing of ,

a/rust, is not as injurious as the corrosive action known as pitting.

The corrosion of iron and steel usually occurs in the latter form,
in ivhich small deep holes are eaten into the metal. The importance
of protecting exposed ferrous metals against corrosion has long
been recognized, but unfortunately the experimental studies made
have lead to contradictory results and hence there is little
agreement between investigators as to the true mechanics of the
phenomenon of corrosion.

Corrosion implies the conversion of metallic elements into
compounds which are usually insoluble in water. The corrosion
of iron and steel is generally known- by the term rusting. Rust,
which is a hydrated red-oxide of iron, (Fe2<^*H20) occupies
about ten times the volume of the original steel. The x in the
formula indicates that there is a variable amount of combined
water in rust.

Oi\-ll Engr.-SB -Assignment 30.

page

All metals, with the possible exception of gold, are subject
to corrosion. In the case of steel, corrosion, when once started,
continues until the metal is destroyed; but the thin film of
o^ids that forms on the exposed surface of aluminum brings
atmospheric corrosive action to a standstill. Ferrous metals are
protected by being plated with nickel, although nickel itself
corrodes. It is relatively stable, however, because as in the
case of aluminum, a surface film of oxide forms and protects
the underlying natal. Copper is also one of the stable metals.
Upon exposure to the atmosphere the surface of the metal is rapidly
converted into the green basic carbonate which retards the cor-
rosive action.

In spite of the fact that those metals which resist corrosion,
such as nickel, aluminum and copper, become coated with a filn
which prevents the actual contact between the corroding nedium
(a combination of air and moisture) and the metal, little ex-
perimental work has been done on the formation of protecting
films.

If a protecting film is the solution of the rust problem
it is evident that it must be a self-healing film. It will be
remembered that in the case of the preservative treatment of
wood the most effective method was to maintain a perfect toxic
coating. If this surface was broken so as. to expose the untreated
vood the whole piece was then subject to the attack of fungi

Civil Engr.«8B Assignment 30, page 3>

which could gain entrance at the break in the protective coating.
Parkerized iron resists corrosion "because of a film of oil and
phosphate but the film must be unbroken to protect the underlying
matal. It is common practice to paint or varnish metals to pro-
tect them from atmospheric corrosion. More durable protective
films are those of zinc, as on galvanized iron, and nickel, on
nicks 1 -plated iron and steel. At the present time (1922) all

authorities seem to agree that corrosion of iron will occur only

Irst
in the presence of both water and oxygen. See /statement to this

effect given on page 791 - the sentence in the first paragraph
of article 846. Iron will not rust in dry air. Furthermore,
when submerged in v/ater from which all the dissolved oxygen
has been excluded, iron will n6t rust. The water must be placed
in a sealed tube which contains no air. If the surface of the
water is exposed to air it will absorb cocygen and the immersed
iron will begin to rust*

Variation in durability of iron.- Read Article 838. The
remarkable state of preservation of the Pillar of Delhi is re-
ferted to in this article. Examples of buried cast iron water
mains, in which the water is in motion, which have withstood
corrosion for long periods are more numerous than examples of
exposed iron such as the Pillar of Delhi. It is quite evident,
hov/ever, that unprotefcted exposed iron will, in occasional instances
only, resist the destructive action of atmospheric corrosion.
Any examples are noteworthy.

ttivtl r_jiig:r.-8B Assignment 30 Page 4.

It should be noted that the destruction of the shin
.ic^aera, also referred to in this article was not due to atmo-
spheric corrosion. It is obvious that iron Trill be destroyed by
electrolytic action. This is referred to in Article 843 under
the heading of local couples. Electrolytic action is sometimes
referred to as galvanic action. While action of this kind is
confaon, many engineers do not take into consederation its pre-
vention in their designs, so that replacements are necessary. A
striking example occured at the Panama Canal in the corrosion of
certain parts of the lock machinery, as noted in Article 843.
Electrolytic action was set up between bronze and ..steel and
also betv/een babbitt metal and cast-steel. The bronze had to be
replaced and the Babbitt metal iras removed and Greenheart, a
durable tropical wood, was substituted. This tupe of corrosion
-:hich here occured, can be prevented by preventing electrolytic
action. Dissimilar metals, in the presence of water, will always
be corroded when a closed circuit can be established." TThen the
netals cannot be effectively insulated a poor conductor must be
used. Bronze bearings in submerged turbines would soon corrode.
These bearings are usually made, therefore, of wood such as
lignum vitae. Ele ctrolytic action was responsible for the de-
struction of the $500,000 yacht Sea Call. As noted in Iron Age,
February 1, 1917, the plates of the hull frere made of Monel.
iietal and Mere fastened directly to the steel frame of the ship.

Civil Engr.-SB Assignment 30 Page 5,

The contact of these dissimilar metals set up destructive eloc-
t^olytic action.

Validity of the acid test.- Read Article 839. AS yet the
acid test has not been developed so that it can be used as a
measure of resistance to atmospheric corrosion.

Relative corrosion of ferrous metals.- Read Article 840.
Manufacturers of wrought iron and steel widely advertise the rust
resisting qualities of their products. Steel marketed under the
trade name of ingot iron is advertised as being particularly
durable. Few comparative tests have been made by disinterested
parties, so that the relative durability of these metals is not
accurately knorm. Une relative rust-resistive qualities of
•ur ought iron and steel are therefore much disputed.

Read Articles 841 to 845 inclusive. Pitting and local
couples have already been referred to. It has been knoivn for a
long time that dissolved air stimulates corrosion* The uncertainty
as to the true action of atmospheric corrosion is demonstrated
by the varied practice of the steel manufacturers. Some attempt
to secure the maximum purity r/hile others, add copper, a foreign
metal, in the attempt to obtain increased durability. The com-
mittee on Corrosion of Iron and Steel of the American Society
for Besting Materials have recently reported that, "copper -bear ing
metal ; shows marked superiority in rust-resisting properties as
compared to non-copper-bearing metal of substantially the same

Civil 3ngr.-8B Assignment 30. page 6.

general composition." It should be noted that copper, in copper-
bearing steels, is no protection when the steels are immersed in
liquids.

:iill-scale, the black oxide of iron (Fe^O/), forms a good
protective coating, but unfortunately it is brittle and is easily
broken. If an unbroken layer could be maintained, no further treat-
ment would be necessary. Since this is impractical the best prac-
tice is to remove the mill-scale before applying any of the common
metal or paint coatings.

The Electrolytic Theory of Rusting.- Read Article 846.
The follor/ing statement is taken from Cushman and Gardner, see
references listed at the bottom of page 787. " Iron has a certain
solution tension.; even -when the iron is chemically pure and the
solvent pure -water, the solution tension is modified by impurities
or additional substances contained in the metal and in the solvent.
The effect of the slightest segregation in the metal vill throw
the surface out of equilibrium, and the solution tension will be
greater at some points than at others. The points or nodes of
maximum solution pressure v/ill be electro-positive to those of
minimum pressure, and a current will flow, provided the surface
points are in contact, through a conducting film. If the film is
water, cr in any way moist, the higher its conductivity the faster
the iron will pass into solution in the electro-positive areas,
and the faster the corrosion proceeds. Positive hydrogen ions

Civil Engr.-3B Assignment 30. Page 7.

migrate to the negative areas, negative hydroxyls to the positives.

"If the concentration of the hydrogen ions is sufficiently
high, the hydrogen ions will exchange their electrostatic charges
w:th the iron atoms sweeping into solution, and gaseous hydrogen
is seen escaping from the system. This takes place \vhenever iron
is dissolved in an acid. If, however, as is usual in ordinary
rusting, the acidity is not high enough to produce this result,
the hydrogen ions r/ill polarize to a great extent around the
positive nodes vdthout accomplishing a complete exchange. This
polarization effect resists and slows dcr.m action. Nevertheless,
some exchange takes place and iron slowly pushes through."

According to this theory iron goes into solution as a
result of electro-chemical action similar to that which occurs
in a simple form of primary cell.

Carbonic acid theory.- According to this theory, which is
also mentioned in Article 846, iron will not rust without the
action of carbonic or some other acid. This explanation of the
corrosion of iron is plausible but the theory has been discredited
by investigators who have made iron rust in water containing
oxygen without a trace of carbon dioxide. In fact they have made
iron corrode in slightly alkaline solutions in which the effect
of any acid v/ould have been neutralized.

Due to the controversial status of the subject of corrosion
the remainder of this chapter in the text is not important. It
should be read, however, and the following points noted:

Civil Sn^r.-SB Assignment 30. Page 8.

The electrolytic action between strained and unstrained
metal as explained in Articles 852 and 853 is sometir.es of im-
portance.. Article 855 on the protection of iron and steel against
corrosion is, in a "way, repetition, since many of the nethods
mentioned have already "been referred to. Surface coatings of painx
protect steel quite well against atmospheric corrosion. Two thin
coats are better than one thick one. The results observed from
prolonged exposure under v/ater shor.v that painted steel is not
protected against corrosion.

^.t one time, alkalies "were supposed to inhibit corrosion
but it has been shov/n that weakly alkaline solutions of many
salts induce corrosion. It has been found very difficult to
protect iron and steel laid in alkali soils from the destructive
effects of pitting.

The difference between atmospheric corrosion and the often
preventable galvanic action between unlike metals, and corrosion
caused by stray currents should be recognized.

Civil Engr.-83 Assignment 30. Pa^e 9.

QUESTIONS

1. What is rust?

2. Yifhat is meant by corrosion?

3. Why is pitting more destructive than a uniform coating cf
rust?

4. Explain the reason for the relative stability of aluminum,
nickel and copper when subjected to atmospheric corrosion,

5. What is the chief requisite for protecting films?

6. Why do unlike netals such as steel and bronze corrode when
placed in contact under water?

7. Why are submerged turbine bearings made of wood?

8. Discuss the value cf copper in copper -be a ring steels as a
means to increase the durability of steel against corrosion.

9. Give a clear statement of the electrolytic theory of corrosion.

10. Explain the acid theory of corrosion.

11. Why is the acid theory an unsatisfactory explanation of the
corrosion of iron and steel?

12. What methods are used to protect steel from corrosion?

Civil Engr.-SB

Assignment 30.

Page 10.
(Special)

Summary of important physical properties of materials given in
the order in which they r:ere studied. Approximate values given.

Material

Compressive

Strength,
lb. per sq, in,

Ilodulus of
Rupture
lb. per sq. in

Modulus of
Elasticity,
lb« per sq. in.

Granite 20,000

1,500

8,000,000

Douglas Fir (air dry)

(parallel to grain) 7,000

10,000

1,500,000

(perpendicular to grain) 900

Building brick 4,000

1,000

6,000,000

Paving brick 10,000

2,000

6,000,000

Hollow tile (on end) 7,000

—

4,000,000

Portland cement (neat) (6 mo. )10,000

1,OCO

Portland cement mortar 1.6 1,000

300

(6 no.)

Gyp sun 1,500

400

1,000,000

Magnesite stucco 2,700

Tension 500 ;

Ftear 3,000,000

Concrete (1 to 6 at 28 days) 2,000

200 — 1

,000 2,000,000

Tensile strength
lb. per sq. in.

Elastic
Unit

Ult iuate

Fr ought iron 30,000 50,000

Steel (6. 2$;carbon ) 30,000 60,000

Plo-u steel iire 170,000 250,000

Cast iron (gray)* 20,000

Halleabie cast iron 20,000 45,000

Copper(hot rolled) 7,000 30,000

*4uninun (draT/n) 20,000 30,000

Iionel netal (Rolled) 50,000 85,000

Brass (Cast) 50,000

Bronze (Cast) 30,000

Compressive
strength lb,
per sq, in*

30,000
30,000

70,000
20,000

percentage codulus
elongation of

Elastic-
ity, lb.
per sq.in.

27,000,000

30,000,000

—

15,000,000

20,000,000

— -

20,000,000

13,000,000

15,000,000

*;iodulus of rupture 45,000 lb. per- sq. in.

YE 03745

Library

UNIVERSITY OF CALIFORNIA LIBRARY

UNIVERSITY OF CALIFORNIA LIBRARY
BERKELEY

Return to desk from which borrowed.

This book is DUE on the last date stamped below.
FNG1NEERING LiBRAnt

/•- 1950

i 1950

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "Materials of engineering construction. Civil engineering 8"

See other formats