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Full text of "The construction of roads and pavements"

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Jrreliiiger 

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THE CONSTRUCTION 

OF 

ROADS AND PAVEMENTS 




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THE CONSTRUCTION 

OF 

ROADS AND PAVEMENTS 



BY 
T. R. AGG, C. E. 

PROFESSOR OF HIGHWAY ENGINEERING 
IOWA STATE COLLEGE 



SECOND EDITION 

REVISED AND ENLARGED 

THIRD IMPRESSION 



McGRAW-HILL BOOK COMPANY, INC. 
NEW YORK: 370 SEVENTH AVENUE 

LONDON : 6 & 8 BOUVERIE ST., E. C. 4 
1920 



COPYRIGHT, 1916, 1920, BY THE 
McGRAw-HiLL BOOK COMPANY, INC. 



THE MAPLE PRESS YORK FA. 



PREFACE TO SECOND EDITION 

Since the publication of the first edition of "The Construction 
of Roads and Pavements/' considerable progress has been made 
in the field of highway engineering, especially with regard to the 
construction of rural highways. 

In the second edition, the errors and omissions of the first 
edition have been corrected so far as they have been noted and 
new material has been added where it was apparent that practice 
had really changed. However, the unsettled conditions that 
have recently prevailed in the highway field have made it very 
difficult to determine what was real progress and what was merely 
compromise construction due to abnormal conditions. 

The more important new material is that on assessments for 
pavements; the chapter on Drainage and the Control of Erosion; 
the chapter on Maintenance; the section on proportioning ag- 
gregates for concrete roads; and the completely rewritten chapter 
on Testing Highway Materials. 

The author is greatly indebted to those teachers who offered 
suggestions relative to revisions that would make the book more 
useful in the class room and to those highway engineers who 
furnished material for a revision of the parts of the book that 
deal with current practice. 

T. R. AGG. 

AMES, IOWA, 
May 20, 1920. 



PREFACE TO FIRST EDITION 

"The Construction of Roads and Pavements" was written to 
meet the need for a concise presentation of approved practice 
in the construction of roads and pavements and of the principles 
involved. 

The book is intended primarily for use as a text in a two or three- 
hour course in roads and pavements, but numerous tables and 
typical designs and specifications have been included that should 
add to its value as a reference book for highway engineers. 

The ultimate object of all highway engineering is the construc- 
tion of durable and well-designed roadway surfaces. The attain- 
ment of this object involves selecting and testing the materials, 
assembling those that are suitable, and incorporating them in the 
roadway surface. A knowledge of the construction of roads and 
pavements is therefore the basis of highway engineering. 

Much of the material used in the text has been prepared from 
notes that have been accumulating for several years. During 
that time the author has attended numerous conventions of high- 
way engineers and has often discussed the various problems of 
roadway construction with engineers with whom he has been 
associated. Doubtless many of the ideas expressed in the text 
have thus unconsciously been absorbed. A considerable amount 
of material has been obtained from current periodical literature 
and acknowledgment has been given for material abstracted 
from the writings of other engineers. 

The author is especially indebted to Mr. T. H. MacDonald, 
Chief Engineer of the Iowa Highway Commission, for his assist- 
ance and encouragement; to Mr. J. W. Eichinger, Editor of the 
Iowa Service Bulletin, for valuable suggestions and especially for 
furnishing photographs for cuts; to the Illinois Highway De- 
partment for much valuable data, and to a score or more other 
highway engineers who have furnished plans, specifications, 
photographs or data on construction. 

Special acknowledgment is made of the very valuable assist- 
ance of Mr. C. S. Nichols, assistant to Dean of Engineering, Iowa 
State College, who has assisted in the preparation and arrange- 
ment of the manuscript. 

T. R. AGG. 

August, 1916. 

vi 



CONTENTS 

PAGE 
PREFACE v 

CHAPTER I 

THE DEVELOPMENT OF HIGHWAY SYSTEMS 1 

Use of Highways Administration of Highway Systems Highway 
Systems Highway Finance City Streets Administration of 
Paving Assessments for Paving Selection of Pavements High- 
way Engineering. 

CHAPTER II 

SURVEYS FOR ROADS AND PAVEMENTS 22 

Reconnaissance Surveys Surveys for Earth Road Construction 
Complete Surveys Direction for Making Surveys Surveys for 
Paving Special Surveys Plans for Roads Plans for Paving. 

CHAPTER III 

DRAINAGE AND CONTROL OF EROSION 39 

Drainage in Humid Areas Side Ditches Drainage of Embank- 
ments Ground Water Drainage in Arid and Semi-arid Regions 
Run-off Erosion Control of Erosion Examples of Drainage 
Practice. 

CHAPTER IV 

THE DESIGN OF RURAL HIGHWAYS 60 

Classification of Soils Clay Loam Surface Drainage Under- 
drainage Catch Basins Culverts Cross-sections Grades for 
Earth Roads Balancing Quantities. 

CHAPTER V 

THE CONSTRUCTION AND MAINTENANCE OF EARTH ROADS 76 

Grade Reduction Side Slopes Overhaul Shrinkage Comput- 
ing Quantities Methods of Grading Methods of Maintenance 
Machinery Used. 

CHAPTER VI 

SAND CLAY ROADS 93 

Types of Soils Sand Clay Construction on Gumbo Clay and 
Loam Construction on Sand Examples of Good Practice. 

vii 



viii CONTENTS 

CHAPTER VII 

PAGE 

GRAVEL ROADS 103 

Ideal Materials Wearing Qualities Bonding Properties Selec- 
tion of Gravel Preparation of Road Cross-sections Placing 
Gravel Characteristics Examples of Good Practice. 

CHAPTER VIII 

WATER-BOUND MACADAM ROADS AND PAVEMENTS 117 

Materials Quality of Rock Size of Stone Telford Construc- 
tion of the Surface Thickness of Macadam Roadbed and Shoul- 
ders Placing Stone Cross-sections Blind Drains Rolling 
Applying Screenings Puddling Maintenance Tools and Ma- 
' chinery Used Examples of Good Practice. 

CHAPTER IX 

CONCRETE ROADS AND PAVEMENTS 141 

Stresses in Concrete Road Surfaces Materials Proportioning 
Preparation of Subgrade Placing Concrete Cross-sections 
Integral Curbs Expansion Joints Reinforced Concrete Pave- 
ments Monolithic Concrete Concrete with Bituminous Top 
Machinery Used Examples of Good Practice. 

CHAPTER X 

VITRIFIED BRICK ROADS AND PAVEMENTS 176 

Kinds of Brick Physical Characteristics of Brick Cross-sec- 
tions Construction of Surface Proportioning Base Integral 
Curbs Macadam Base Bedding Courses fillers Expansion 
Joints Brick Rural Highways Monolithic Brick Character- 
istics Tools and Appliances Used Examples of Good Practice. 

CHAPTER XI 

WOOD BLOCK PAVEMENTS 204 

Size and Kind of Wood Blocks Preservative Treatments Preser- 
vatives Manufacture of Blocks Construction of Pavements 
Cross-sections Expansion Joints Fillers Examples of Good 
Practice. 

CHAPTER XII 

STONE BLOCK PAVEMENTS 223 

Kinds of Stone Used Size of Blocks Foundation Bedding 
Course Laying Blocks Tamping Fillers Recut Blocks Cross- 
ing Stones Characteristics Examples of Good Practice. 

CHAPTER XIII 

BITUMINOUS ROAD AND PAVEMENT MATERIALS 239 

Asphalt Bitumen Natural Asphalts Petroleum Asphalts 
Tars Fluxes Classes of Commercial Materials. 



CONTENTS ix 

CHAPTER XIV 

PAGE 

DUST LAYERS AND BITUMINOUS CARPETS . . . .......... 260 

Dust Suppression on Earth Roads Dast Suppression on Gravel 
and Macadam Bituminous Carpets Examples of Good Practice. 

CHAPTER XV 

PENETRATION AND MIXED MACADAM ROADS AND PAVEMENTS .... 276 
Penetration Macadam Size and Kind of Stone Cross-sections 
Foundation Rolling Applying Bituminous Binder Machinery 
and Appliances Used Example of Good Practice Mixed Maca- 
dam Kind of Stone Foundation Construction of Surface 
Appliances Used Examples of Good Practice. 

CHAPTER XVI 

SHEET-ASPHALT AND ASPHALTIC CONCRETE SURFACES 302 

Earth Foundations Base Course Cross-sections Binder Course 
Surface Mixture Construction of Surface Characteristics 
Asphalt Blocks Topeka Asphaltic Concrete Bitulithic War- 
renite Tools and Appliances Examples of Good Practice. 

CHAPTER XVII 

SELECTION OF TYPE OF SURFACE FOR RURAL HIGHWAYS 337 

Traffic Census Forms Traffic Limits Increase in Traffic 
Maintenance Local Materials Foundations Aesthetic Consid- 
erations. 

CHAPTER XVIII 

SELECTION OF TYPE OF PAVEMENT SURFACE 350 

Durability Slipperiness Appearance Dust Sanitariness 
Cleaning Noise Tractive Resistance Maintenance Location 
Cost Economical Life Residual Value. 

CHAPTER XIX 

THE DESIGN OF PAVEMENTS , . . . . . . 360 

Grades Widths Crown Unsymmetrical Streets Car Tracks 
Intersections Design Curbs Manholes and Catch Basis 
Combined Curb and Gutter Car Track Paving Pavement 
Foundations Examples of Good Practice. 

CHAPTER XX 

MAINTENANCE . 400 

Rural Highways Patrol Maintenance Equipment of Patrol- 
men Patrolling Earth Roads Patrolling Surface Roads 
Gang Maintenance Maintenance of Streets Pavement Repairs 
Street Sprinkling Sweeping Cleaning Snow Removal Exam- 
ples of Good Practice. 



x CONTENTS 

CHAPTER XXI 

PAGE 

ROAD MATERIALS TESTING 416 

Abrasion Toughness Weight per Cubic Foot Specific Grav- 
ity Mechanical Analysis Clay and Silt Colorometric Test 
Percentage of Shale Slump Test Fixed Carbon Ductility 
Consistency Distillation Specific Viscosity Flash and Burning 
Point Volatilization Solubility Joint Fillers Emulsions. 

GLOSSARY 442 

INDEX 449 



CONSTRUCTION OF 
ROADS AND PAVEMENTS 

CHAPTER I 
THE DEVELOPMENT OF HIGHWAY SYSTEMS 

There are, in the nature of things, more restrictions on the 
social activities of those who live in the rural districts, than on 
those who live in the towns, due to the distances the residents 
must travel if any considerable number are to meet together. 
The nature of rural activities and the sequence of farming 
operations restrict social opportunities to a degree while the crop 
season is in full swing. During the part of the year when farm- 
ing operations permit some leisure, weather and the condition of 
the highways determines the ease and comfort with which social 
gatherings may be attended. In the towns and smaller villages, 
social life is more or less dependent upon the participation of 
those who live in the surrounding farming community and any- 
thing that prevents the country people from joining with the 
village in social affairs is a deterrent to healthy community 
intercourse. 

A certain amount of social intercourse is a necessity to all men 
and in the rural communities it is particularly salutary to the 
health and happiness of the people that reasonable opportunities 
be presented for social meetings. There is plenty of evidence 
in the records of sanitariums and asylums to show that isolation 
and the resulting loneliness have had a tendency to disturb the 
mental balance and undermine the health of those who have 
lived in the partial isolation of the farm. 

With the advent of the rural telephone and free mail delivery, 
the automobile and parcels post, conditions of living are much 
improved in the rural communities, but nothing takes the place 
of social gatherings and the opportunity for them depends largely 
upon the condition of the highways. If the highways are well 
kept and comfortable to travel at all seasons of the year, that 

1 



2 CONSTRUCTION OF ROADS AND PAVEMENTS 

will do much to encourage frequent social gatherings and the 
whole life of the community will respond to the interchange of 
ideas and experiences that will thus be had. 

There are those who have secured a competence on the farm 
and who would prefer to continue living there were it not for the 
lack of social opportunities, but this lack is often one of the 
principal things that induces them to move to town. They are 
usually the class of citizens who are most progressive and whose 
example is invaluable to their neighbors on account of the 
advanced methods of farming they follow and their enlightened 
attitude toward all rural problems. Good highways which will 
give them free intercourse with their neighbors and with the 
towns, will do much to induce this class of citizens to stay on 
the farm to the advantage of the commonwealth and to their 
own profit. 

Highway improvement also has an important bearing on the 
educational opportunities of the children who live in the country. 
They should have as good opportunities for an education as is 
offered to children in the towns and, indeed, the solution of the 
problem of furnishing an adequate supply of food stuffs to the 
nation depends upon the proper education of the children in the 
rural communities. Educators think that in order to give ade- 
quate training in the country districts, group schools are a 
necessity and the success of group schools depends upon ade- 
quate facilities for the children to get back and forth, that is, 
upon there being good, serviceable roads throughout the district 
tributary to the schools. 

Many institutes, farmers' clubs, and college extension activities 
have developed in recent years, which have a broad educational 
value, and all depend for success upon the possibility of people 
assembling at some convenient place for instruction and dis- 
cussion. They will do this only when roads are reasonably 
good. 

While the various social and educational aspects of the rural 
highway problem are of great importance, they are less so than 
is the transportation phase. Highways should be considered 
as important links in the transportation system of a nation and 
as such it is vital that they be maintained in usable condition 
throughout the year. In some communities serviceable roads 
may be nothing more than well-drained, well-dragged earth 
roads; others may furnish traffic requiring gravel or macadam, 



DEVELOPMENT OF HIGHWAY SYSTEMS 3 

or roads of the highest degree of durability such as is furnished 
only by brick or concrete. No matter which may be required, 
the roads are a part of the equipment for the transaction of 
business and any reasonable expenditure of money in road con- 
struction is justifiable as a matter of enlightened public policy. 

Instances have frequently been noted where the system of 
farming and the whole rural business life has been transformed 
after the highways had been improved and, in general, both the 
rural population and the urban population of the market center 
of the district have been greatly benefitted by the changed 
conditions. The financial benefits derived have been many 
times the cost of the improvement of the highways. 

It is particularly true that the territory tributary to the 
larger cities (which should be a source of supply for the more 
perishable food stuffs) is quite often cut off from its most logical 
market by the poor conditions of the highways over which the 
supplies must move. Such a condition causes a direct financial 
loss to both producer and consumer which in a few years will 
aggregate a sum far in excess of the cost of any reasonable system 
of highway improvement that would be necessary to serve 
such a community. 

From the social, educational and transportation standpoints, 
then, it is apparent that money expended for highway im- 
provements is a good investment. Such an expenditure, how- 
ever, should be made only after a careful analysis of the many 
factors that will have a bearing on the adequacy of the re- 
sulting road system. Haphazard expenditures, on the other 
hand, can never produce results of commensurate value. 

The public highways of a commonwealth comprise a great 
system of routes for transportation and should be constructed 
and administered as such. In sparsely settled districts they are 
primarily routes which serve the rural communities for the 
necessary intercourse between farm and market center and are 
infrequently used. In such places insufficient funds are available 
for the construction of other than the cheapest earth roads and 
those who use the highways for business or pleasure must of 
necessity accommodate themselves to the varying conditions of 
the highways. The important consideration in such a com- 
munity is not the possibility of building roads designed for low 
tractive resistance and long life but is rather the possibility of 
getting the most systematic and economical expenditure of the 



4 CONSTRUCTION OF ROADS AND PAVEMENTS 

meager funds alloted to highway purposes. The problem is one 
of administration rather than one of design and construction. 
But when only small sums are available it becomes the more 
important to study carefully all of the economies possible and 
to make extraordinary use of the materials and equipment at 
hand. Such a study may result in sand-clay or gravel roads being 
built as has been the case in many sections of the United States, 
or it may result in the development of a new device or method 
of construction being adopted. Such conditions resulted in the 
invention of the split-log drag and the road planer, which have 
proven so useful in earth-road maintenance. 

The more thickly settled the district the more important this 
transportation system becomes. In those sections of the 
country which are so densely populated that there is a succession 
of towns and cities the public highways are a vital part of the 
transportation system. 

The public highways, in such instances, are utilized for both 
business and pleasure by great numbers of citizens and assume 
an importance that rapidly increases each year. 

Obviously in populous districts large sums of money may be 
had for highway improvement and, moreover, the types of roads 
that would suffice for sparsely settled country are totally 
inadequate. The problem then becomes one of construction as 
well as one of administration and the greater the cost of roads 
the greater the care that should be given to the selection of 
type and to the character of the construction. 

In general, public highways serve first of all the territory, be 
it large or small, which is tributary to some market center 
Many roads may converge to such a city and on the outlying 
roads of the system the traffic may be light. Nearer the city 
the traffic increases until some of the roads are carrying a traffic 
fully as heavy as many city streets. 

Besides the local traffic there is a considerable amount of 
neighborhood traffic which uses the highways between adjoining 
towns both for business and pleasure and this class of traffic is 
constantly increasing in amount and importance. In many places 
the commercial motor truck is being used for transporting goods 
a distance of 30 miles, and this class of traffic will doubtless in- 
crease rapidly when the highways are improved sufficiently to 
make it possible. Motor cars, for pleasure or business trips, 
have greatly extended the territory of business establishments 



DEVELOPMENT OF HIGHWAY SYSTEMS 5 

and have thereby greatly increased the amount of neighborhood 
traffic on the public highways. 

Public highways are also receiving an appreciable amount of 
through motor-car traffic, particularly those roads that consti- 
tute direct routes between the larger cities. This class of 
traffic knows no limitations as to distance traveled, passing 
entirely across a state or several states or even entirely across the 
continent. It also will greatly increase in volume as the condition 
of the highways is improved. 

Since the traffic on the public highways is so diversified in 
character and consists of so many small units under separate 
ownership, the tremendous handicap and loss due to poor roads 
does not make itself felt at once. It is apparent, nevertheless, 
that the amount of energy required to move a load over a public 
highway is of vast importance. If only a few vehicles use the 
road each day the cost for power may be unimportant economic- 
ally, although it may be a serious matter to those who use the 
road. If, however, the number of vehicles that pass over the 
road is large then the amount of energy expended is an important 
consideration. 

In general, hard surfaced roads are of lower tractive resistance 
than earth roads but the aggregate energy saving on a hard sur- 
faced road over an earth road will be small or large depending 
upon the amount of traffic that uses the road. 

Numerous attempts have been made to estimate the decrease 
in the energy expended and consequent reduction in the cost of 
hauling that results from road improvement. Such estimates 
have little value due to the great diversity of conditions under 
which hauling is done. If a certain quantity of material is to 
be transported daily over a certain road the cost can readily 
be computed, but for intermittent hauling, often with part loads, 
and at times that can be chosen to suit the condition of the 
roads, the cost can not readily be determined. 

The fact that it costs much less to haul a load on good roads 
than on bad roads is the one fact that is well established. Just 
how much less it costs is not known and really is not of first 
importance. Highway improvement is very often brought about 
by a desire for greater comfort and convenience rather than 
from a desire to save on the cost of hauling, although the fact 
that a saving in hauling costs results, is undoubtedly a factor 
in bringing about all road improvement. 



6 CONSTRUCTION OF ROADS AND PAVEMENTS 

ADMINISTRATION OF RURAL HIGHWAYS 

The administration of highways like the use of highways, has 
undergone continual change during recent years. 

For a long time the control of the highways had been entrusted 
entirely to elective officials of the township or county. Such 
officials gave only a part of their time to the administration of 
the road system. Standards of construction were exceedingly 
diverse among the various units and the efficiency of the main- 
tenance methods adopted was generally low. So long as the 
roads were purely local in character there was little cause for 
complaint, because the officials were elected by the community 
and probably reflected the attitude of the public toward highway 
work. 

With the development of neighborhood and through traffic, 
the conditions of the highways became of more than local interest, 
resulting in many cases, in the concentration of authority in 
the county rather than in the township. 

Finally the state was given some authority in the administra- 
tion of highway affairs and a somewhat chaotic condition arose, 
with many questions of the jurisidiction of each unit more or 
less undefined. This has to a considerable extent been corrected 
by recent legislation, but still exists in some states. 

The enactment of legislation providing for a limited participa- 
tion in highway construction by the federal government through 
federal aid granted to the states, carried with it the provision that 
before a state could participate in federal aid it must have an 
authoritative State Highway Department. This provision of the 
federal law was the occasion for creating a number of state highway 
departments and of reviving the authority of others that had 
drifted into a state of lethargy. Every state in the United States 
now has a state highway department that is active and progressive. 

With all of the progress that has come about durng the past few 
years, highway laws are still pretty much a patchwork of conflicting 
provisions, with highway officials having poorly defined and over- 
lapping authority and responsibility. Every session of a state 
legislature adds to the mass of highway laws but in spite of this 
condition progress is being made in highway administration. In 
the United States there is good reason to believe that the con- 
struction of a National system of highways will continue at a rapid 
pace. 



DEVELOPMENT OF HIGHWAY SYSTEMS 7 

In order to insure the improvement of rural highways in the 
order of their importance and to facilitate administration, they 
are often divided into several groups or systems in each of which 
is included the highways that are considered to be of about equal 
importance. These groups are not clearly established in all states 
but are gradually being defined. 

National Highway System. The national highways are those 
that are routes for long distance highway travel. They are con- 
tinuous across several states or even entirely across the continent. 
Such highways should follow routes that are fairly direct, but may 
detour somewhat to include important cities and places of historic 
interest or scenic beauty. In addition they should be selected 
with a view to possible military value. A few national highways 
already exist in the United States, such as the Lincoln Highway 
from New York to San Francisco, the Jefferson Highway from New 
Orleans to Winnipeg, and the Dixie Highway from Chicago to 
Jacksonville. 

The cost of improvements on national highways is at present 
paid from a fund made up of the proceeds of county or township 
road taxes and allotments of state and federal aid funds. In 
states where the national highways are a part of the State Road 
System, and this is the case in most of the states, the cost of im- 
provements would be paid jointly by the state and federal 
governments. There is a concerted movement looking to the 
financing of national highways from federal funds, which plan 
may eventually materialize. 

State Roads. A proper system of state roads will connect all 
cities and towns having a population of 1500 or more. It will pro- 
vide for the important routes of travel across the state and within 
the state and will connect all county seat towns and afford access 
to and facilities for agricultural areas, manufacturing centers and 
scenic and recreational districts. The percentage of the total 
road mileage of the state required in the state system will be from 
five to ten. The national highways may also be included in 
the state system for administrative purposes. 

The improvement of state roads is financed in the following 
ways: 

1. Entirely with state funds obtained from one or more of the following: 

a. Bond issues. 

b. General taxation. 

c. Assessments on lands. 

d. Automobile licenses. 



8 CONSTRUCTION OF ROADS AND PAVEMENTS 

2. Jointly by state and county. 

3". Jointly by state and Federal Government. 

4. By county, township and state. 

I. Township of Town Roads. This group comprises the purely 
local roads and is ordinarily under the jurisdiction of the town- 
ship highway officials. In mileage it comprises about 80 per 
cent, of the total of the country, but probably does not carry to 
exceed 25 or 30 per cent, of the traffic of the country. Four 
methods of financing the improvement of all or a part of the 
township road system are in effect in the United States, the 
practice varying widely in the several states. 

1. Entirely by the township. 

2. Jointly by the township and the county. 

3. Jointly by the township and the state. 

4. Jointly by the state, county and township. 

II. County Roads. County roads are those highways in the 
county that are administered by the county officials. Not 
every state has such a system. Where it is in effect, the system 
generally comprises about 15 per cent, of the mileage of the 
county, but these roads carry 60 per cent, or more of the traffic 
of the county. Such roads are sleeted so as to include the main 
market roads and when taken over by the county, the township 
is thereby relieved of the necessity of caring for them. 

The improvement of the county road system is financed in 
four ways. 

1. Entirely by the county. 

2. Jointly by the county and state. 

3. By the county, township and state together. 

4. The national government may be an additional party in 
any of the above groups. 

III. State Roads. State roads are those main highways that 
are improved largely or entirely at the expense of the state. In 
general they comprise about 5 per cent, of the mileage of the 
state and carry a relatively large amount of traffic, only a small 
percentage of which is of local origin. 

State roads are often still further classified by the selection of 
those roads that comprise links in the great through routes for 
traffic, such as Lincoln Highway, Jefferson Highway, Dixie 
Highway and similar roads, interstate in character. The portions 
of these highways in a state are often administered separately 



DEVELOPMENT OF HIGHWAY SYSTEMS 9 

from the balance of the state system, as is warranted by the im- 
portance they assume. 

The state roads are improved from funds variously provided, 
from state property taxes, vehicle licenses, bond issues and federal 
funds, or from a fund made up from several of these sources. 

ADMINISTRATIVE AUTHORITIES 

I. Township. The township roads are under the jurisdiction 
of an elective board, generally consisting of three men. In some 
states the elective officials delegate the supervision of township 
road work to a statutory township superintendent who is em- 
ployed by them. The elective officials receive a per diem and 
the superintendent is paid a monthly stipend. 

II. County. The county highway affairs are generally ad- 
ministered by a county board which is elected by the voters of 
the county and which is designated by various titles in the 
several states. Some states provide that the county court shall 
designate special commissions for expensive road-improvement 
projects. 

The elective boards have many county affairs to look after 
and in some states the management of road work is delegated 
to a statutory county engineer or county superintendent who is 
employed by them. The county board members receive a per 
diem for their services. The county engineer or superintendent 
is paid a per diem or is employed by the year, and in some states 
must be an engineer and in others is not a technical man. The 
size and nature of the county organization depends upon the 
amount and character of the road improvement being carried 
out. 

III. State. State highway affairs are administered by a state 
department which consists of one or more commissioners and an 
organization of highway engineers. The commission is elected 
in one or two states, but is generally appointed by the governor. 
The number of men comprising the commission varies from one 
to five, and the service is gratuitous in some states and in others 
each commissioner is paid a statutory salary. The engineering 
force in the state department is employed by the commission 
either directly or through the medium of a civil service body. 
Fig. 1 shows the organization of a state department that is 
carrying out an extensive construction and maintenance program. 



10 CONSTRUCTION OF ROADS AND PAVEMENTS 

IV. The administrative authority of the Federal Government 
in highway matters is at present vested in the Secretary of Agri- 
culture and the executive authority is vested in the Director of the 

Department of Public Works and Buildings 




Fig. 1. Organization of Illinois State Highway Department. 

Bureau of Public Roads. All matters relating to Federal partici- 
pation in highway construction are handled by the Bureau of 
Public Roads, and, in addition, the Bureau carries on a large 
amount of investigative and educational work of a general char- 



DEVELOPMENT OF HIGHWAY SYSTEMS 11 

acter. The employees of the Federal Bureau are secured through 
the United States Civil Service. 

The funds for the support of the Bureau are obtained from 
congressional appropriations and from a percentage of federal aid 
appropriations allowed for engineering expenses in connection with 
federal aid projects. 

FINANCE 

Direct Taxes. The cost of highway construction and main- 
tenance is paid in part from funds derived from taxes levied on all 
taxable property in the township or county. Funds so ob- 
tained are generally expended indiscriminately in the political 
division in which they are obtained, for the ordinary upkeep and 
extension of the highway system. In some instances funds 
obtained by general taxes are expended in hard surfacing or 
other expensive improvements on a few sections of road or for 
paying the community's part of the cost of improvements on 
state-aid or county-aid roads. 

Special Taxes. In many states it is possible for either the 
county or the town to levy a special tax for certain classes of 
permanent highway improvement. Almost invariably it is 
necessary to have such levies approved by a vote of the property 
owners of the political unit affected. Special taxes must in 
general be expended for certain definite and stated purposes and 
not for the general upkeep of roads. These taxes are often 
levied to provide for the local allotment of the cost of tstate-aid 
roads. 

State Aid. When a part of the cost of road improvement is 
paid from state funds the money so expended is known as state- 
aid money. State aid, where it is in effect, is extended for the 
improvement of main traveled roads such as those comprising 
state roads and the more important county roads. The pro- 
portion of the cost that is paid from state funds varies from one- 
third to about three-fourths of the total cost of the construction. 
The remainder of the cost is paid either by the county or the 
township or by the two jointly. Some state roads are built 
entirely at the expense of the state but these are not generally 
referred to as state-aid roads. 

State Rewards. The state-reward system differs from the 
state-aid system in that the roads are built by the county or 
township and, if when completed, they come up to a certain 



12 CONSTRUCTION OF ROADS AND PAVEMENTS 

standard, the state pays a certain reward to the county or town- 
ship. The amount so paid is generally fixed for each class of 
construction and varies from a few hundred dollars a mile to 
about $1,000 a mile. The state-reward system is merely a form 
of state aid, but the entire responsibility for the construction is 
placed on the political unit initiating the improvement. 

National Aid. The propriety of participation by the federal 
government in highway improvement has been recognized by 
the enactment of legislation providing for the allotment of federal 
funds to the states, these funds to be used in part payment of 
the cost of road construction in that state. The general character 
of the improvement and the standards of construction are fixed by 
the federal government and the work is supervised by it, but the 
letting of contracts and the engineering work is cared for by the 
State Highway Departments. The director of the Federal Bureau 
of Public Roads is the executive head of the bureau, and in the 
bureau are the various divisions for carrying on investigation, for 
testing of materials, for the publication of timely information 
relative to highway matters and for the supervision of all highways 
constructed with federal aid, the last named activity entailing 
an enormous amount of work. 

Automobile Licenses. In many states owners of automobiles 
are required to pay a state license and the money so obtained is 
added to the road funds. In some states it is added to the 
state-aid or state-reward funds and in other states it is dis- 
tributed to the various counties or towns to be added to their 
road funds. 

In recent years the tendency is toward a greater contribution 
to road maintenance on the part of owners of motor vehicles 
through the medium of license fees. An equitable license should 
be based on these factors; the weight of the car, the speed of the 
car and the cost. The two first named bear a rather direct rela- 
tion to the destructive effect on the road surface, and the last 
named may be assumed to indicate the ability of the owner to 
pay. In some states the automobile license is based entirely on 
vehicle cost, in others on horse power, while in still others it is a 
flat rate for all cars. Where the vehicle is taxed as property in 
addition to the license fee, probably a flat rate is most nearly 
equitable for the license but it would seem to be preferable to 
provide a graduated license fee in lieu of all other taxes and use the 
revenue entirely for highway purposes. 



DEVELOPMENT OF HIGHWAY SYSTEMS 13 

Bonds. States, counties and townships each have issued bonds 
for highway construction but there are only a few states in which 
the township may do so. The county is permitted to issue such 
bonds in many states and a great many millions of dollars worth 
of such bonds are outstanding. Several states have also issued 
bonds for highway improvement. The permissible life of such 
bonds and the rate of interest is not at all uniform in the several 
states, but the practice has quite generally been to provide for 
relatively long term bonds. There is a growing belief that 
the bond method of financing road improvement is both logical 
and equitable, if the life of the bond is well within the useful life 
of the road. 

Special Assessments for Rural Highways. The special- 
assessment method of financing has long been employed in the 
cities, but has had limited application in connection with rural 
highways. Where it has been attempted, the principle has 
been to assess a small percentage of the cost against the adjacent 
lands for a depth varying from J4 m il e to 5 or 6 miles. 

Various mechanical methods of determining the benefits are 
employed, and like all such devices are likely to result in inequitable 
assessments if rigorously applied. No system of spreading the 
assessment can eliminate the need for engineering judgment in 
finally equalizing the assessment. 

One method employed for spreading assessments is to assume 
that the benefit decreases on the lands assessed as the ordinates of 
a parabola, which is drawn in the following manner: A base line 
is drawn to represent to scale the width of the zone to be assessed. 
Upon this base line an ordinate representing one hundred units 
is erected at one end and a parabola is passed through the point 
thus fixed and the other extremity of the base line. The rate of 
assessment for any parcel of land in the area to be assessed is 
determined by the difference of the ordinates at the two boundary 
lines of the tract. If the tract is irregular in shape, the difference 
between the ordinates at the point nearest the improvement 
and the one at the point most remote may be taken. These 
rates are obtained from the curve. 

The length of the tract parallel to the improvement is then 
determined and each rate multiplied by the length gives the 
assessment factor. The sum of the assessment factors divided 
into the amount to be assessed gives the amount of assessment 
per unit of assessment factor. 



14 CONSTRUCTION OF ROADS AND PAVEMENTS 

The same general plan is employed in another method where the 
area to be assessed is divided into two or more zones parallel to the 
improvement and an arbitrary percentage of the total assessment 
is allotted to each. If there were two zones the percentages might 
be 60 and 40 or 70 and 30 respectively. If four zones the per- 
centages might be 10, 15, 25 and 50, or 12, 18, 30 and 40. After 
the rates have been adopted the percentage allotted to each zone 
is spread according to the area of the tracts in the zone. 

After the assessment has been spread, it must be reviewed and 
any injustice rectified. This will be necessary because some tracts 
of land may be of such low value that they cannot stand the full 
assessment. 

CITY STREETS 

Pavements are as necessary for a city of any commercial im- 
portance as are railroads and it is taken as a matter of course 
that all except the least important residence streets in outlying 
districts will be paved. Transportation demands, convenience, 
cleanliness, and appearance are all potent factors in creating a 
desire for improved streets and pavements are laid as a matter 
of public necessity. 

Cities and towns everywhere pave their streets as a matter of 
convenience and cleanliness just as they paint the houses or 
build sidewalks. Many streets are paved where the traffic is so 
small in volume that transportation needs alone would not justify 
it, but the other considerations are such that the residents are 
willing to pay for the improvement. 

ADMINISTRATION OF STREET PAVING 

Street paving is administered in a number of different ways in 
American cities, but in general is under the jurisdiction of an 
elective body, which delegates its authority to a subordinate 
department. 

Where the affairs of a city are administered by a city council 
or board of aldermen, the paving is supervised by one or the other 
of the following organizations. 

1. A committee of aldermen which is known as the Committee 
on Streets and Alleys, the Board of Local Improvements or by 
some similar designation. Final action on contracts is generally 
required of the entire board. 

2. A special Board of Public Works which is either appointed 



DEVELOPMENT OF HIGHWAY SYSTEMS 15 

by the mayor or is elected. Such boards generally have final 
authority in paving matters. 

When the city is organized with the commission form of govern- 
ment, one of the commissioners usually has charge of public 
improvements, including paving and final action on contracts 
is by the commission. 

Cities that are organized under the city-manager plan usually 
have a department for handling the street work which is sub- 
ordinate to the city manager. The contracts are subject to 
approval of the city manager and the advisory board. 

Street repairs and street cleaning are commonly administered 
by the same organization that is responsible for the construction 
of new pavements but the street cleaning is generally handled 
through a special bureau. 

FINANCE 

Special Assessments. In most cities the cost of new pave- 
ments is borne largely by the owners of abutting property, which 
is assessed directly. In many cities the assessment may extend 
back halfway to the next street, but not farther than a specified 
distance. Various portions of the cost of new pavements and 
of repaving are borne by the city at large. 

Payment for paving is by means of paving certificates or 
paving bonds which are issued as soon as the pavement is ac- 
cepted. These evidences of indebtedness are payable in annual 
installments for a period of years and thus the property owner 
is given from 5 to 10 years for paying for the paving. 

The variation in practice is indicated by the following excerpt: 

New Paving 1 

In 62 per cent, of these cities the property pays all. 
In 6 per cent, the property pays 50 per cent. 

In 10 per cent, the property pays more than 50 per cent, and less than 60 
per cent., except in one city, where the property pays 30 per cent. 
In 22 per cent, the city pays all. 
Repaving 

In 42 per cent, of these cities the property pays all. 
In 10 per cent, the property pays 50 per cent. 
In 8 per cent, the property between 50 and 100 per cent. 
In 40 per cent, the city pays all. 

1 Report of Municipal Committee of Cleveland Chamber of Commerce. 



16 CONSTRUCTION OF ROADS AND PAVEMENTS 

Approximately 25 per cent, of the cities pay the major part 
of the original paving, while 40 per cent, of the cities do the major 
part of repaying. 

SPECIAL ASSESSMENTS FOR PAVEMENTS 

The cost of constructing pavements on city streets is almost 
invariably paid in whole or in part from a fund raised by a special 
assessment on the property abutting or adjacent to the street that 
is paved. In this connection, property that has some frontage on 
the paved street is known as abutting property and property 
having no frontage on the paved street, but lying in the block along 
which the pavement is laid is known as adjacent property. Usually 
the law specifies the limit of area adjacent to the paved street 
within which it is permissible to levy special assessments for pav- 
ing. Many systems of making special assessments have been 
devised, all of which seek by some mechanical means to spread 
the assessment equitably to all parcels of land involved, which 
necessarily includes the assumption that all parcels can bear 
assessment. This may not be true in many instances and after 
the assessment has been spread by some appropriate system, 
the whole plat is studied in the light of the character and value 
of the several properties and adjustments are arbitrarily made 
where it seems equitable. 

Amount to be Assessed. If it be assumed that the total cost of 
the improvement including intersections is to be assessed, the total 
cost for each continuous section of identical construction will be 
computed. If the laws permit assessing the cost of grading, man- 
holes and storm water inlets including connection to storm sewers 
and alley returns, the cost of these items will be added to the cost 
of the paving, although the actual cost of these incidental items 
may vary in the several blocks. It is not usual to assess the cost 
of grading, but it is sometimes done. When the total cost of the 
construction has been determined the cost of legal and engineering 
expenses, cost of printing official notices and similar incidental 
expenses will be added. The grand total thus obtained will be 
assessed to such property as the law provides may be assessed for 
the improvement. 

If the cost of intersections or any other part of the cost may be 
paid from funds other than the proceeds of the assessments, such 
amounts are deducted before spreading the assessment. 

The assessment is spread in various ways depending partly upon 



DEVELOPMENT OF HIGHWAY SYSTEMS 17 

the laws relating thereto and partly upon the opinion of the as- 
sessing officer as to what constitutes an equitable assessment. 
In every case the purpose is to spread the costs in accordance with 
the benefits and with equity to the various properties involved. 

Front Foot Rule for Assessments. In many cities, only the 
abutting property is assessed and the cost is spread in proportion 
to the length of frontage of each lot or parcel of land on the paved 
street. This rule is of course simple of application, but does not 
take into account the depth of the several lots, which would be 
desirable if the lots were not practically uniform in depth. 

Area Method of Assessment. Another simple method of 
assessing paving benefits is to spread the assessment according to 
the area of each lot or parcel of land. This takes account of the 
differences in size of the lots but does not compensate for differ- 
ences in frontage on the improved street and this would be desirable 
if the lots were not of about the same width throughout the area 



Zone and Area Method. In this method the area to be assessed 
is divided into equal zones, each zone extending the length of the 
pavement for which the assessment is being prepared. A rate of 
assessment is then determined for each zone. In the example 



TABLE A 
ILLUSTRATING THE ZONE AND AREA METHOD OF ASSESSMENT 





Parcel 




Rate 


Area 
Sq. Ft. 


Rate x Area 


Unit of 

Assess- 


Total 

Assess- 


Section 


Lot 


Block 








ment 


ment 


h 
i 


12 
11 


10 
10 


30 
30 


3250 
1250 


97,500 
37,500 


.00181 


155.25 
50.45 


j 


9 


10 


30 


3000 


90,000 




143.40 


y 






70 


1800 


126,000 




200.28 


k 


8 


10 


30 


4800 


144,000 




228.72 


1 


4 


10 


30 


2000 


60,000 




96.00 


















W 

v 


5 
6 


10 
10 


70 
70 


6000 
1800 


420,000 
126,000 





612.30 
184 00 


u 


4 


10 


70 


3250 


227,500 




333 16 


t 


3 


10 


70 


3250 


227,500 




333 16 


8 


2 


10 


70 


3250 


227,500 




333.16 


V 


1 


10 


70 


3250 


227,500 




333.16 


q 


1 


10 


30 


3250 


97,500 




144 . 67 


P 


2 


10 


30 


3250 


97,500 




144.67 


o 


3 


10 


30 


3250 


97,500 




144.67 


n 


4 


10 


30 


3250 


97,500 




144.67 


X 


6 


10 


30 


3000 


90,000 




133.80 


m 


7 


10 


30 


4800 


144,000 




212.10 



18 CONSTRUCTION OF ROADS AND PAVEMENTS 

given herewith, the assessed area is divided into two zones and the 
one nearer the street is assessed 70 per cent, of the cost per front 
foot and the one more remote 30 per cent. There might be any 
desired number of zones and the rates might be adjusted in any 
manner that appears to be equitable. The area of the portion of 
each lot lying in each zone is determined and the assessment is 
made up as given in Table A. 



100 
90 

80 
70 

360 


h 

| 50 

d 

J- 
1- 

20 
10 
c 
































x 


^ 


^*" 


































X 




































/ 






































/ 




































/ 


/ 




































/ 






































/ 


/ 




































/ 


f 




































/ 


/ 






































/ 






































/ 






































/ 








































/ 






































/ 








































/ 






































/ 








































/ 






































/ 








































/ 








































/ 









































20 



40 



60 80 100 120 140 160 ISO 
Depth of Lot in Feet 



FIG. 2. Benefit factor curve. 

Zone and Benefit Method of Assessment. This method is very 
similar to the zone and area method except that the benefit accru- 
ing to each lot is based upon a curve which is platted to show the 
variation in benefit from the paved street to the most remote line 
in the assessment area. To plat such a curve it is assumed that 
the benefits fall off as the distance from the paved street increases. 
If the benefits were assumed to fall off directly as the distance, 
then the curve would be a straight line. If the benefits are as- 
sumed to fall off 70 per cent, in the first half of the area, then the 
curve would be as shown in Fig. 2. To plat this curve a base 
line was laid off to scale 182J/ ft. long, that being the maximum 
depth of the assessment area for the plat shown in Fig. 3. At half 
the depth (in this case 91 J4 ft.) the assessment was to be 70 per 



DEVELOPMENT OF HIGHWAY SYSTEMS 



19 



cent. At 182J/ ft. the assessment was shown as 100 per cent. At 
zero depth of course the assessment is zero. A smooth curve was 
drawn through the three points thus located. Similar curves may 




FIG. 3. Assessment plat, benefit factor method. 

be drawn for any other ratio of assessment between the various 
depth of lots. In determining the benefit factor, the per cent, 
intercepted on the curve between the distances to the front and 
rear extremities of the lot is taken from the curve and multiplied 




FIG. 4. Plat for zone and area method of assessment. 

by the width of the lot parallel to the paved street. The sum of 
the benefit factors divided into the total amount to be assessed 
gives the cost per unit of benefit factor. An assessment made up 
in this way is shown in Table B. 



20 CONSTRUCTION OF ROADS AND PAVEMENTS 



TABLE B. 
ILLUSTRATING THE BENEFIT FACTOR METHOD OF ASSESSMENT 



Lot 


Block 


Rate 


Length 


Benefit 
Factor 
RxL 


Assessment 


3 


11 


50 


280 


1400 


151.33 


4 


11 


22 


227 


4994 


535.31 


5 


11 


15.7 


179.5 


2818.15 


305.72 


2 


11 


87.7 


35 


3069 


332.24 


1 


11 


87.7 


20 


1754 


190.80 


5 


11 


50 


120 


6000 


649.36 


6 


10 


22 


120 


2640 


278.48 


7 


10 


15.7 


120 


1884 


205.08 


4 


10 


87.7 


50 


4385 


472.94 


3 


10 


87.7 


50 


4385 


472 . 94 


2 


10 


87.7 


50 


4385 


472 . 94 


1 


10 


87.7 


50 


4385 


472.94 


14 


10 


87.7 


50 


4385 


465.11 


13 


10 


87.7 


50 


4385 


465.11 


12 


10 


87.7 


50 


4385 


465.11 


11 


10 


72.0 


50 


3600 


162.94 


4 


10 


15.7 


50 


785 


84 


10 


10 


50 


120 


6000 


639.34 


9 


10 


22 


120 


2640 


274.78 


8 


10 


15.7 


120 


1884 


192.76 


8 


11 


87.7 


20 


1774 


180.82 


7 


11 


87.7 


35 


3104.5 


325.38 


6 


11 


59.5 


77.5 


4611.25 


488.66 



SELECTION OF PAVEMENTS 

The type of pavement for a street is selected in many ways as 
will be noted in the following outline. Generally the city 
authorities have the final word in the matter, although this is 
not always true. 

Methods of Ordering Pavements. 1 In 50 per cent, of the 
cities heard from, any city street may be ordered paved by the 
common council, by a majority vote varying from one-half to 
five-sixths, it usually being two-thirds. In 30 per cent, of the 
cities, no new paving can be ordered except by a petition of from 
one-half to two-thirds of the abutting property owners. In 
10 per cent, of the cities, the common council is permitted by 
ordinance to order a stipulated amount of new pavement each 
year. 

How Type of Pavement is Selected. In only 15 per cent, of 
the cities do the abutting property owners have the final de- 
cision in selection of type of pavement. In a few cases, the 
common council or even a single alderman has the deciding power. 

1 Report of Committee of Chamber of Commerce of Syracuse, N. Y. 



DEVELOPMENT OF HIGHWAY SYSTEMS 21 

In about 80 per cent, of the cities, however, the type of pavement 
is selected by a paving commission, highway or engineering de- 
partment, after due consideration of the wishes of the abutting 
property owners. 

HIGHWAY ENGINEERING 

It will be apparent from the foregoing that in the construction 
of roads and pavements many problems peculiar to that field of 
engineering will arise. Preliminary investigations, the selection 
of type of construction, the design of roads and pavements, the 
preparation of specifications, and the supervision of construc- 
tion and maintenance all require a knowledge of the principles 
that have been evolved by experience and experiment. The 
field of the highway engineer is thus apparent, and with the 
rapid expansion of systems of surfaced roads, and the greater 
attention that is being given to systematic maintenance both 
for street pavements and rural highways, the need for trained 
men is obvious. 



CHAPTER II 

SURVEYS AND PLANS FOR ROADS AND PAVEMENTS 

ROAD SURVEYS 

The completeness and detail with which a road survey should 
be made depends upon the character of the improvement con- 
templated and whether the work is to be done by contract or by 
force account. Surveys by various engineers differ in many 
respects even though made for the same class of construction, 
and it is not possible to standardize them because of that fact. 
So far as the actual work of making the surveys is concerned, no 
principles are involved that are not involved in making surveys 
for other engineering projects. As with other surveys, the 
information obtained and the method of tabulation are adapted 
to the needs of the work in hand. 

For the purposes of discussion it is convenient to divide all 
surveys into four general classes: (a) reconnaissance surveys; 
(6) surveys for earth-roads to be graded by force account; 
(c) surveys for hard-surfaced rural highways; and (d) surveys 
for paving. These represent four broad classes of surveys which 
inevitably overlap to some extent. 

Reconnaissance Surveys. These surveys are of two kinds, 
the first of which is identical in purpose with the reconnaissance 
survey made in railroad work. Its purpose is to find the best 
location or route for a new highway or relocation of an old one. 
This type of survey needs no explanation. 

The second type of reconnaissance survey is one that has been 
adapted primarily to highway work and has for its purpose the 
selection from among several roads, of the most feasible for im- 
provement. It involves the examination of the road to secure 
data for the preparation of a map showing the various physical 
characteristics such as bridges, culverts, embankments, cuts, 
hills, the apparent width of right-of-way, the character of the 
soil and any other fact that would have a bearing on the selection 
of a route. 

22 



SURVEYS AND PLANS FOR ROADS 23 

Apparently such a survey differs widely from the ordinary 
reconnaissance and yet it serves substantially the same purpose, 
namely, the selection of a tentative route. The survey is made 
by walking or driving over the road. Distances are obtained 
by the pedometer or odometer and checked by intersecting roads 
and survey monuments when these are encountered. The notes 
are kept in the ordinary field book upon which the route has 
already been platted from existing maps so that it remains only 
to fill in the detailed information. 

Surveys for Earth-road Construction. For earth-road grad- 
ing, especially blade grader or elevating grader work to be done 
by force account, it is not always necessary to make complete 
detailed surveys. Grading done by force account is not usually 
finished very closely to grade, nor will it be necessary to balance 
earthwork on the plans because adjustments can be made in 
the field as the work progresses. The object of this kind of a 
survey is to give an approximate grade for the outfits to work to 
so that drainage will be assured and reasonable gradients re- 
sult. The transit survey usually consists in running a center 
line and locating fence lines, bridges, culverts, and other physical 
characteristics relative to this line and to the adopted station- 
ing. Houses, entrances to farms, trees, pole lines, bridges and 
similar physical characteristics are indicated as well as the type 
of soil encountered. 

The level survey consists in running a center-line profile, and 
possibly a profile in each ditch If a section is encountered where 
it appears that a considerable change in grade will be desirable, 
cross-sections are taken at 100-ft. stations and at intermediate 
breaks in grade if such occur. 

This kind of a survey is suitable for force-account grading and 
is permissible where funds are not to be had for a more complete 
detailed survey. It is used especially on earth-road grading or 
low-grade surfacing where the local conditions are such that the 
requirements are not exacting. 

Complete Detailed Surveys. The complete detailed survey 
is made on state and county roads that are to be brought to an 
exact grade or are to be surfaced with a high-class roadway. 
It is a requisite for the preparation of suitable plans for contract 
road work of any class. The survey includes the accurate loca- 
tion of all the physical and topographical features that may 
affect the design. The center line of the road is found by means 



24 CONSTRUCTION OF ROADS AND PAVEMENTS 

of the permanent monuments or the records filed when the 
road was established. The topography is taken with this line 
or one parallel to it as a reference line. Bridges, culverts, fences, 
traveled way, ditches, lines of tile, pole lines, trees, entrances and 
all similar features of the highway are noted. Cross-sections 
are taken every 100 ft., and more frequently if the topography 
demands it, together with the elevations of beds of intersecting 
streams, elevation of culvert tops, bridge floors, tile outlets, 
etc. In other words, the survey is complete and detailed in 
every respect. 

This sort of survey is to be recommended wherever extensive 
improvement is undertaken and is a necessity for contract work 
which is let on a unit price basis. The scope of such a survey 
is indicated by the following set of instructions : 

DIRECTIONS FOR MAKING ROAD SURVEYS 1 

Keeping the Notes. In keeping the notes of the transit survey 
the arrangement shown on Plate A should be followed. Here the 
sketch appears on the right hand page plotted from the bottom 
of the page up. The station numbers with additional notes appear 
on the left hand page. It is not necessary 'that any fixed length 
of road be covered on a double page; sufficient space should be 
allowed that the notes will not be crowded. 

The form for keeping the level notes is shown on Plate B. 
These also are carried up from the bottom of the page, which leaves 
no doubt as to which side of the road the notes refer to. Always 
leave a line between the stations so that when the notes are 
reduced there will be ample room to write in the elevations. 

The notes shall show (preferably in the first alignment book) 
a sketch map of the entire project, drawn approximately to scale 
with the line or lines as surveyed plainly marked. All relocations 
or alternate lines shall be indicated by a system of lettering. If 
the chief of party so desires, he may use a print of the project 
diagram instead of drawing a sketch map. If this is done the 
print should be pasted in the first alignment book. 

Indexing Notes. The notes in each book shall be completely 
indexed. In the case of alternate lines or relocations the same 
system of lettering used on the sketch map shall be followed in 
the index. 

1 Field Manual, Iowa State Highway Commission. 



SURVEYS AND PLANS FOR ROADS 25 

Staking the Line. The following method should be followed in 
staking the line: 

I. Set all hubs on the center line in their true position. 

II. Set adjacent hubs at such stations that each can readily 
be seen from the other. This will usually be on the top of hills 
or ridges. 

III. In no case should hubs be more than one-half mile apart 
even though it may be possible to see further than that distance. 

IV. For all hubs use 2 by 2 by 18 in. hard wood stakes. 

V. Drive all hubs down until the top is three inches below the 
ground surface. 

VI. All hubs shall be referenced to four points so located that 
a line drawn between the diagonally opposite reference points 
will intersect at the hub. Give the distance from each reference 
point to the hub. 

NOTE. In order to avoid crowding the transit notes, it will be 
found convenient to set aside several pages of the note book on 
which pages detailed reference data for all hubs is recorded. 

VII. The reference points shall in all cases be located far enough 
away from the center line to be well outside of the limits of the 
cuts or fills. If possible, at least two of the reference points shall 
be located on trees, buildings or other permanent objects. The 
other two reference points shall be located so that an instrument 
can be set up over them. 

VIII. Where no other suitable reference points are available, 
stakes should be used. These stakes shall be of the same size 
and quality as the hubs. All reference stakes shall be driven flush 
with the ground surface, and the location shall be indicated by 
suitable guard stakes. 

IX. On tangents or on curves set a center line stake on each side 
of each water course where a bridge or culvert is required. These 
stakes should be back 30 or 40 ft. from the stream bank so as 
not to be disturbed by the excavation. Such line stakes shall be 
driven until their tops are 3 in. below the ground surface, 
and shall be referenced to convenient points, such as corners of 
old bridges, trees, telegraph poles, etc. If no such convenient 
reference points exist, then stakes shall be used for reference points. 

On curves these center line stakes can be located at convenient 
stations which will be located in the ordinary process of running 
out the curve. It is not necessary to set special points at the curve 
for these stakes. 



26 CONSTRUCTION OF ROADS AND PAVEMENTS 

NOTE. In setting line stakes at bridges or culverts, use small 
stakes, that is, stakes about 1J/2 by % by 12 to 15 in. Do not use 
the 2 by 2 by 18 in. hub stakes, as the small stakes will serve the 
purpose and are less expensive. 

X. The ordinary station points between hubs need not be 
staked in a permanent way. Where the line is in the traveled 
portion of the road, it will often be found convenient to use spikes 
with a small piece of cloth attached for marking stations. In 
such cases small stakes bearing the station number should be 
set at the side of the road opposite the station point. On re- 
locations and on portions of the road where the center line is off 
of the traveled way, the stations may be marked by small stakes 
at the station points. 

Alignment and Right of Way. I. Location of Center Line. 
One of the most difficult features of the field survey is the deter- 
mination of right of way limits and the proper location of the center 
line. In flat or gently rolling country where the roads follow land 
lines and where relocations are not necessary, the problem is very 
much simplified. In hilly country and on angling roads, the most 
mature judgment on the part of the chief of party is required. 
In many such cases the location of the road as shown by the records 
does not in any way conform to the road as now traveled. The 
following general instructions should be followed as closely as 
possible, but many cases not covered by these instructions will be 
encountered. 

(a) Get copies of all records in the courthouse relative to the 
location, establishment, and right of way of the road included in 
the project. 

(6) Run center line before running bench levels. 

(c) If the established location follows the present road, and the 
location and alignment are desirable, follow the established loca- 
tion. 

(d) If the established location does not follow the present road, 
the choice as to which to follow will depend on a comparison of 
the two lines as to 

1. Topography. 

2. Alignment. 

3. Improvements on or along the present road. 

Unless there is a decided advantage in favor of the established 
location, the survey should in general follow the present road. 
It should be noted that whichever alignment it is determined 



SURVEYS AND PLANS FOR ROADS 27 

that the survey should in general follow, relocations may be made 
to take advantage of the topographical features, to better the 
alignment, or to make the line conform to existing permanent 
improvement on or along the road. 

(e) In cases where the alignment follows land lines, or where a 
land monument is erected on or near the alignment chosen, 
a diligent effort should be made to find these monuments, and the 
line should be tied to all such monuments that can be found. If 
a monument cannot be found, no elaborate land surveys should 
be made to locate it. 

(f) Many existing bridges and culverts will not conform to the 
center line of the road on which they are located. In the case 
of important permanent structures the line may be varied so as 
to conform, but this is not always advisable. The chief of party 
must use his judgment in this matter, taking into consideration 
the amount of variation of line necessary, the size and importance 
of the structure, and all other facts in the case. In many in- 
stances it would be poor practice to make such variation in the 
alignment. 

(g) Where the records show the right of way lines, the notes shall 
show the position of these right of way lines with reference to the 
center line. 

//. Relocations. The matter of relocations has been partly 
covered in the above instructions. Where the topography is 
flat or gently rolling the profiles readily lend themselves to satis- 
factory grades at a moderate cost, and relocations to any extent 
are seldom necessary. But in the rougher country relocations 
will frequently be necessary and the field man must constantly 
watch for opportunities to better the alignment, avoid steep hills, 
or improve stream crossings by relocations The necessity for 
or advisability of relocating must always be balanced against the 
cost, and in general it is true that a proposed change of any mag- 
nitude is advisable only when it can be shown that such change will 
be economical or will produce a decidedly better road. It is there- 
fore important that the cost or relocations be thoroughly investi- 
gated. In this connection the field man must remember to take 
into consideration the various improvements along the existing 
road, such as farm buildings, orchards, permanent bridges and 
culverts, heavy cuts and fills, etc. 

The following instructions should be followed : 

(a) In all cases where it appears that an excessive amount of 



28 CONSTRUCTION OF ROADS AND PAVEMENTS 

earthwork will be required to reduce the present road to 6 per cent, 
grades, the possibility of relocations to reduce grades to 6 per cent, 
or less shall be fully investigated. 

(6) In cases where there is a succession of grades which may be 
reduced to 5 or 6 per cent., but which cannot be reduced below 
that figure without considerable work, the question of relocation 
should be fully investigated. 

(c) In case of doubt as to the feasibility of any relocation, a 
survey should always be made. 

(d) In all cases where relocations are surveyed a survey shall be 
made on the old road also. 

(e) In the case of minor relocations the margins of the old road- 
way should always be shown by a sketch indicating the old road- 
way by dotted lines, and by data in the cross section notes. In 
such cases the survey of the old road may consist only of ex- 
tending the cross sections over the same. 

(/) The notes shall show which location is to be used or shall 
state that the determination of which route to follow cannot 
be made until the notes are worked up in the office. The chief 
of party shall enter this notation in the field notes after consulta- 
tion with the district engineer. 

///. Intersection Angles. Intersection angles, however small, 
shall be measured and recorded All intersection angles shall be 
measured by the repetition method. 

IV. Horizontal Curves. At all points of intersection where the 
intersection angle is greater than 10 degrees, horizontal curves 
shall be run in, and the stationing shall be carried continuously 
around such curves. In running in curves the data given in the 
Harger & Bonney Highway Engineer's Handbook shall be followed. 

Drainage /. Bridges and Culverts. The chief of party is re- 
quired to secure the following data for each bridge and culvert: 

a. Size (length and roadway). 

b. Type. 

c. Number of spans. 

d. Drainage area (up to about 1300 acres). 

e. Elevation of high water. 

f. Elevation of present grade over culverts. 

g. Elevation of present grade at both ends of bridges. 
h. Elevation of flow lines of culverts. 

i. Elevation of stream bed under bridges. 

j. Profile of stream bed 100 ft. each way from each culvert. 

k. Elevation and location of headwalls on culverts. 

1. Profile of stream bed 500 ft. each way from each bridge. 



SURVEYS AND PLANS FOR ROADS 29 

In taking the notes to show the slope of the stream bed each way 
from the bridges and culverts, three cases will be encountered: 

(a) Where the general direction of the stream is at right angles 
to the road. 

(6) Where the general direction of the stream is not at right 
angles with the road. 

(c) Where there is a combination of (a) and (6). 

In the first case, a cross section taken at the center line of the 
stream and extending out the necessary distance each way will 
give the desired data. The notes should show that this cross 
section is taken to show stream bed elevation and is not to be used 
for computing quantities. 

In the second case, the cross sections on either side of the bridge 
or culvert should be extended out far enough to show an elevation 
on the stream bed the necessary distance both above and below 
the road. These cross sections will be taken at right angles to the 
road in all cases. The elevations on the stream bank and stream 
bed should be indicated in the notes by suitable letters. It should 
be noted here that on a skew culvert the elevation of headwall and 
flow line at both ends cannot be shown at the same cross section. 
Two cross sections will be required. 

In the third case the elevations on stream bed will be secured 
by a combination of the methods used in the other two cases. 
It should always be remembered that elevations on stream bed 
should always be taken the same way as any cross section, i.e., in 
a practically straight line and at right angles to the road. 

When a stream or ditch is not at right angles with the road, the 
cross section notes shall show accurately the location of such 
stream so long as it remains within 100 ft. the center line of the 
road. 

The district engineer, the county engineer, and an engineer 
from the bridge department will complete the bridge and culvert 
survey, determine the size and type of structure required, and 
make recommendations relative to the elevation at which the new 
grade should be located. 

Miscellaneous Data. I. Pluses. As the transit party proceeds 
they should take plus measurements to the following : 

a. Corner stones. 

b. Section and quarter section lines. 

c. Division fences. 

d. Buildings, giving exact distance from center line if within or immediately 
adjacent to the right of way lines. 



30 CONSTRUCTION OF ROADS AND PAVEMENTS 

e. Rows of trees kind, usefulness, and distance from center line. 

f . Existing tile lines, size and outlet. 

g. Field and yard driveways, 
h. Sidewalks. 

i. All culverts and bridges. Pluses to center line of culverts is sufficient, 
but for bridges give plus to both ends. 

j. Telephone and transmission lines, distance from center line, 
k. Guard rails and rataining walls. 
1." Gravel pits. 

V. Railroad Crossings. On federal and state aid projects all 
railroad grade crossings will be eliminated if possible. If it is not 
possible to eliminate a grade crossing, such crossing will be im- 
proved in the best manner possible. The district engineer will 
outline to the chief of party the surveys that shall be made at each 
crossing. In case of existing railroad subways or overhead cross- 
ings the notes shall show: 

(a) Type of structure. 

(b) Horizontal clearance of subways. 

(c) Vertical clearance and roadway of overheads. 

(d) Intersection angle between center line of highway and 
railway. 

(e) Elevation of low steel, or clearance elevation of subway. 
(/) Elevation of top and base of rail. 

VI. Railroad Bridges and Culverts, and Location. When a 
railroad comes within 500 ft. of the highway the following data 
on such railroad shall be secured : 

(a) Location of center line of railroad with respect to the center 
line of the highway. 

(6) Elevation of base of rail at intervals not exceeding 500 ft. 

(c) Location, size and type of all bridges and culverts on the 
railroad, the waterway, and the elevation of flow lines of water- 
way structures. 

Bench Marks. /. Selection of Datum. Sea level datum is to 
be used wherever the same can be obtained. If this is not avail- 
able, the county datum should be used. If no county datum has 
been adopted, it will be necessary to assume an arbitrary datum, 
but care should be taken to assume the elevation of the original 
bench mark at such height that all elevations will be plus. 

//. Establishing Bench Marks. Bench marks should be 
established at least every 1500 ft. and at closer intervals in rough 
country, particularly at high and low points. A bench mark 
should be established at each bridge and culvert that will probably 



SURVEYS AND PLANS FOR ROADS 31 

be rebuilt. They should not be established on objects which are 
likely to be disturbed previous to or during construction, but rather 
on such points as bridge seats, wingwalls, headwalls of culverts, 
stone or concrete steps, etc. If such points are not available, 
use pieces of gas pipe or bar iron about 4 ft. in length, driven 
nearly flush. Such bench marks should be so placed as to be 
visible in both directions along the road, in all cases they should be 
carefully and accurately described so that they may be readily 
found for future use. 

All bench marks shall be numbered consecutively beginning at 
One. 

///. Running and Checking Bench Mark Levels. Bench levels 
on any portion of the road shall be checked prior to running the 
cross section levels on that portion. In running check levels 
each bench mark must be taken as a turning point in order to get 
a true check. The maximum allowable variation in the difference 
of elevation between any two bench marks is 0.05 V distance in 
miles. 

Should the variation in the difference of elevation between two 
adjacent benches exceed this amount, the check levels shall be re- 
run between these benches until two differences of elevation 
between these benches check within the above limits. The chief 
of party shall then make up a bench mark adjustment sheet on 
which the benches are listed. In the first column show the 
bench mark numbers. In the second column show the station 
of the bench mark. In the third column show the book and page 
numbers where description of the bench will be found. In the 
fourth column show the elevation of each bench and the difference 
in elevation between each two adjacent benches as obtained by the 
first bench levels. In the succeeding columns show the corre- 
sponding elevations and differences of elevations as obtained by 
succeeding check levels. In the column next to the last show the 
adjusted difference in elevation between each two benches, and 
in the last column show the corrected or adjusted elevation for each 
bench. This corrected elevation shall be used in running cross 
section levels. 

Cross Sections. 7. Cross Sections on the Main Road. Cross 
sections are to be taken at every 100 ft. station, and at plus stations 
where breaks occur in the center line profile. Sections are also 
to be taken at points where the cross section breaks even though 
the center line profile may continue on a uniform grade. This 



32 CONSTRUCTION OF ROADS AND PAVEMENTS 

refers particularly to existing 0.0 points where changing from 
cut to fill. Sections are always to be extended at least 33 ft. on 
each side of the center line, and in rough country where there is 
no reason to suppose that the proposed improvement will extend 
beyond the right of way limits, the sections must be extended ac- 
cordingly. In the case of level cross sections a 66 ft. right of way 
will permit a center cut of 7 ft. and a center fill of 14 ft. using the 
standard county road cross sections with \Y^\ 1 side slopes. 

Knowing this and taking into consideration the existing grades 
on the road, the field chief can roughly determine if it will be 
necessary to extend the cross sections beyond the 33 ft. limit. 
Additional sections should always be taken at both ends of bridges 
and at the ends of the wingwalls. Center line elevations should 
be taken at the end and at all intermediate supports. Similar 
sections should be taken at culverts. In the case of permanent 
culverts the distance back to back and elevations of headwalls 
must always be taken. Without this information it is impossible 
to determine the height of grade that the culvert will carry. 
Each cross section shall show the distance to the fence line on each 
side of the road. 

Any abbreviations appearing in the cross section notes shall be 
explained by suitable notations or a key on the page where such 
abbreviations first occur. This key will be construed to apply 
to any further use of the same abbreviations on that project 
survey. 

//. Levels on Branch Roads. The center line profile of branch 
roads should always be taken and continued a sufficient distance 
to enable the designers to establish the grade lines to fit both 
roads. In level or gently rolling country, the profiles for branch 
roads shall be continued a minimum distance of 300 ft. from the 
intersection point. Where there is a hill on the side road near 
the main road, the profile of the side road shall be continued far 
enough to enable the designer to establish a grade on the side road 
to fit the grade on the main road, and to balance the cut and fill 
on said side road. 

Whenever it seems possible that the proposed improvement will 
necessitate the grading of branch roads for a short distance in 
order to make proper connections with the main roads, the branch 
roads must be cross sectioned far enough to permit the computa- 
tion of the necessary earthwork. 



SURVEYS AND PLANS FOR ROADS 33 

III. Levels on Driveways. When passing farm or field en- 
trances, side shots are to be taken out in the driveway about 
100 ft. from the center line, or at some other distance as will show 
how the existing grade of the driveway will be affected by the pro- 
posed improvements. 

ROAD PLANS 

As might be expected, the plans prepared for road improvement 
vary in completeness and form among the various engineers and 
state departments. In general makeup they are much the same, 
consisting of a plan and a profile always, and frequently being 
accompanied by the cross-section for each station. 

Profile. A center-line profile is usually shown. It is some- 
times the profile of the finished roadway, sometimes that of the 
foundation for the hard surfacing and sometimes a "grade" 
profile or profile passing through the balance line of the cross- 
section. Probably the most common practice is to show the 
profile of the finished surface. 

The scale to which the profile is drawn also varies greatly. 
A scale of 8 ft. per inch vertically and 100 ft. per inch hori- 
zontally, or of 200 ft. to the inch horizontally is often used. 

A horizontal scale of 40 ft. to the inch and a vertical scale 
of either 8 ft. to the inch or 4 ft. to the inch is also widely used 
and is probably the most satisfactory. Profiles drawn to this 
scale are voluminous and inconvenient to handle in the field, but 
are desirable from the standpoint of design. 

The profile of the existing road surface and the established 
grade line are always shown and sometimes the profile of the 
ditches. The profile should also show all bridges and culverts, 
lines of tile and catch-basins. The location of bench marks and 
their elevation is given and the elevation of the established grade 
line is marked at every break in the grade line and sometimes at 
every station. The name of the road, the date of the plan and 
the scale are essential parts of the plan. 

Plan View. The plan view is usually on the same sheet as the 
profile and the horizontal scale is the same as the horizontal scale 
of the profile. The plan view is sometimes broken at turns or 
deflections and the center line maintained as a straight line so as 
to keep the plan on the sheet. On this view is shown the exist- 
ing features such as fences, culverts, bridges, houses, driveways, 
intersecting roads, and such other information as may assist in 

3 



34 CONSTRUCTION OF ROADS AND PAVEMENTS 




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SURVEYS AND PLANS FOR ROADS 



35 



the design. The lines of the hard surface and the location of any 
bridges or culverts to be built are also shown. 




Cross-sections. The cross-sections are platted in computing 
the quantities of earth work and are of use in construction in 



36 CONSTRUCTION OF ROADS AND PAVEMENTS 

showing where surplus material is found and where it is to be 
moved to. Usually the area of each cross-section and the 
quantity of material between sections is indicated. The sec- 
tions are platted to a scale of 10 ft. per inch, 8 ft. per inch, or 
4 ft. per inch. The larger the scale the more accurately the 
cross-section areas can be obtained, but the sections become ex- 
ceedingly voluminous if platted to a scale of 4 ft. to the inch. 
Figs. 5, 6, and 7 show typical road plans. 

SURVEYS FOR PAVING 

The surveys made as a preliminary to paving must be made 
with greater accuracy and detail than is required of surveys for 
road work. Whereas in road work the accuracy required is 
seldom greater than 0.1 ft., except on bench marks and grade 
stakes, in surveys for paving the measurements must usually 
be made to 0.01 ft., and the elevations except on cross-sections 
are taken with equal accuracy. At intersections and where 
the paving and curbing are fitted onto previously constructed 
improvements such as sidewalks and sewer openings and where 
buildings have been constructed without due regard to a future 
pavement, it is desirable to have exact information as to these 
existing structures. As with the road survey the topography is 
located with reference to the transit line which is run in as long 
tangents as circumstances will permit. Property lines are ac- 
curately located from official maps and recorded surveys. In 
surveys for pavements the block is usually the unit, although 
50- or 100-ft. stations are frequently established and cross- 
sectioned for determining the quantities of earth work. The 
transit and level surveys are made as described above, except 
that all the work must be done with much greater accuracy. 
Usually the survey must include those streets that intersect or 
are an extension of the ones to be improved. This is to insure 
that further paving operations will be correlated with those for 
which the survey is being made. 

PLANS FOR PAVING 

Plat. A plat on a scale of 100 ft. to the inch is prepared for the 
portion of the city or town in which the streets are being paved. 
This may be omitted when only one or two streets are being 
improved, but if any considerable system of streets is to be paved 
the plat is very convenient. On this plat the proposed pavements 



SURVEYS AND PLANS FOR ROADS 37 

are shown to scale and the radii at curb corners indicated; catch 
basins, curb inlets, storm sewer lines, valley gutters, crossing plates, 
and similar special features of the basin are shown where required. 

Profiles and Plan. Profiles are prepared showing the ground 
at the center line of the proposed pavement. At each station the 
elevation of the existing curb (if any) and of the sidewalk, or 
ground where the sidewalk should be, are shown by a short dash 
properly marked as north or south, east or west as the case may be. 
Profiles should always be platted from north to south or from west 
to east, beginning at the left hand end of the sheet. A convenient 
scale to use is 10 ft. to the inch for the vertical scale and 100 ft. 
to the inch for the horizontal scale. Some engineers prefer either 
8 ft. to the inch or 4 ft. to the inch for the vertical scale and 40 ft. 
to the inch for the horizontal scale. It is appropriate to employ 
various vertical scales, and in general the more nearly flat the 
topography, the larger the vertical scale should be. There is no 
particular advantage in scales larger than 100 ft. to the inch for 
the horizontal scale except where very difficult or peculiar condi- 
tions require that considerable detail be shown on the plan view. 

The profile should show the established grade for the curb of the 
pavement, and if the curbs on opposite sides of the street are not 
at the same elevation, then both should be shown unless the 
difference in grade is so slight that the two lines would be very 
close together on the drawing. In such cases the profile of one 
curb may be shown and the grades for the other indicated. The 
grade for the top of the curb is shown at the intersection with the 
curb line of intersecting streets and at every break in grade between. 
Where vertical curves are employed, three elevations should be 
shown ; the points of tangency and the middle point. 

The profile of the gutter should be shown if it is not parallel to 
that of the top of curb. The profile should also show new man- 
holes or catch basins and new storm sewer lines. 

The plan view is drawn on the same sheet as the profile and 
below it. It will be to the same scale that is adopted for the 
horizontal scale for the profile. The proposed pavement will be 
shown with all catch basins, curb inlets, manholes and tile lines 
or storm sewer lines. Special details such as gutter plates at 
crosswalks, valley gutters, warped-up crosswalks and alley re- 
turns will be accurately indicated. The elevations at inter- 
sections of curb lines and at each break in grade will also be shown. 



38 CONSTRUCTION OF ROADS AND PAVEMENTS 

Cross-sections. A sheet showing the details of the cross- 
section for the pavement will be included but usually the cross- 
sections at each station are not included. These will be platted up 
for use in computing the quantity of earth work but are not 
required for laying out the work. If several widths of pavement 
are included, a single typical cross-section may be shown with a 
note indicating how the total crown will vary with the width of the 
pavement. 

General Infromation. Generally several sheets of special 
details will be required in order to show the design of catch basins, 
curb inlets, manholes, crossing treatment at intersections and 
similar minor details. 



CHAPTER III 
DRAINAGE AND CONTROL OF EROSION 

I. DRAINAGE IN HUMID CLIMATES 

General Problem. In areas where the annual precipitation 
exceeds 25 or 30 in., two distinct drainage problems will be en- 
countered in connection with road construction. The first in- 
volves the disposal of storm water and water resulting from melting 
snow and ice, in such a manner as to prevent the soil under the 
roadway from being made unstable through partial saturation 
with water. This requires a drainage system designed to effect 
the prompt removal of storm water from the proximity of the road. 
The second is the prevention of the percolation of underground 
water into the soil under the roadway. Such water originates in 
precipitation but may flow some distance through the soil before 
reaching the highway. The former is for convenience referred to 
as surface drainage, and the latter as under drainage. 

Side Ditches. The cross-section usually adopted for a public 
highway lends itself naturally to the construction of drainage 
channels at the side of the traveled portion of the road, and these 
are commonly referred to as side ditches. In many cases a simple 
design of side ditch is adequate but quite frequently conditions are 
encountered where special provision should be made for disposing 
of storm water. 

Run-off. The amount of water to be carried away is the run- 
off from the area contributing to the ditch. Primarily this water 
comes from the portion of the road between the ditches and the 
surface of this area is likely to be hard baked or covered by an 
imprevious wearing surface. It may be assumed that for storms 
of a very short duration not more than 75 per cent, of the water 
that falls on the road will run off to the ditches, but that for storms 
exceeding 15 minutes duration, all the water will run to the ditch. 

Some water will run to the road ditches from the area between 
the ditches and the right-of-way line and from adjacent lands 
that slope toward the road. The rate of run-off from this area 
will depend upon the slope, the character of the soil and the nature 

39 



40 CONSTRUCTION OF ROADS AND PAVEMENTS 

of the growth thereon. Cultivated lands will absorb practically 
all of the water from storms that last an hour or more except when 
the storms recur so frequently that a condition of saturation is 
maintained in the soil. Rocky soils will absorb very little water 
after the first few minutes. Flat lands will absorb more water 
than those that are sloping. All of these things may properly be 
taken into account in estimating the amount of water that will 
reach the side ditches. For general purposes it may be assumed 
that for storms of more than 40 minutes duration all of the water 
falling on the drainage area will run to the side ditch. Knowing 
the total area, the rainfall characteristics of the region and the 
slope that may be obtained, the area of cross-section of ditch may 
be computed by determining the velocity by means of the familiar 
Chezy formula, using Kutters formula for determining C. For 
the usual highway condition N in Kutters formula may be assumed 
as 0.022. 

While it is not necessary to go to this refinement in the design 
of side ditches for many conditions, there are many examples of 
failure of surface drainage due to the inadequate capacity of the 
side ditches. A careful analaysis should be made where the side 
ditches must carry the water for long distances, or where a con- 
siderable area adjacent to the highway drains to the road ditches. 
In this latter case, especially in hilly country, a surprisingly large 
volume of water may reach the highway. 

Shape of Ditch. The side ditch may be V-shaped or may have 
a trapezoidal cross-section as may be preferred. Both types of 
ditch are used extensively and there does not seem to be any 
particular advantage to either. It is somewhat easier to con- 
struct V-shaped ditch with the road grader, but the flat bottom 
ditch is easier to construct with slip or wheel scrapers. 

Supplementary Ditches. It is often desirable to intercept, by 
means of supplementary ditch roughly parallel to the road, 
water flowing from adjacent land toward the road ditch. The 
supplementary ditch is especially advantageous when the amount 
of drainage area to be provided against is large or the slope toward 
the road such as to make it difficult to control erosion. The 
slopes of cuts can be protected in this way by means of a supple- 
mentary ditch about 10 ft. back of the upper edge of the side slope. 

Drainage of Embankments. The removal of storm water from 
a road surface located on an embankment, is given little considera- 
tion where the embankment is not high or long. But on long high 



DRAINAGE AND CONTROL OF EROSION 41 

embankments the maintenance of the side slopes becomes a 
troublesome problem if storm water is allowed to flow over the 
edges at will. The alternative is to construct a ridge along the 
edge of the roadway to confine the water and then to carry it 
down the slope in paved gutters placed at intervals of about 
150 ft. 

Tile to Supplement Side Ditches. If side ditches with flat 
grades must carry storm water for long distances, it is to be ex- 
pected that the ditches will carry a large volume of water for a 
considerable period of time. Sufficient water may percolate under 
the roadway during this period to lower its stability. To expedite 
the removal of the ditch water, tile drains are laid below the side 
ditches to supplement the ditch. To be effective such tile must 
be of ample capacity and have a suitable outlet so that full ad- 
vantage may be taken of the capacity. Frequent catch basins 
or inlets should be provided to carry the water from the ditch to 
the tile. These may be of masonry, concrete or of tile, but must 
be provided with a bee-hive grating on top so that they will not 
readily clog with weeds or other trash carried by the water. 
The so-called blind catch basin, which is merely a section of about 
3 ft. of the trench back filled with broken stone, tile bats or gravel, 
will also serve the purpose. 

The principal advantage of supplementary tile is realized when 
snow or detritus has blocked the ditches to some extent. When 
the snow begins to melt, often accompanied by rain, the ditch 
will not be fully serviceable, but the water will find its way to the 
tile through the frequent catch basins. Generally the storm water 
will have passed through the tile before much ground water from 
the same storm reaches the tile, so that the tile will also serve to 
lower the ground water level. In continued wet weather the 
efficiency of the tile in lowering ground water will be reduced by 
using it to carry storm water. 

Ground Water. The storm water that goes into the soil flows 
slowly laterally and downward, its course depending upon a 
great many conditions of soil and topography. The distance from 
the surface of the ground to the ground water varies greatly, being 
much less in the lower levels than in high ground. Under ground 
water may be the cause of unstability in the soil under a road and 
very often is the cause of failures of roadway surfaces. The level 
of underground water may be held to such a depth that it will 



42 CONSTRUCTION OF ROADS AND PAVEMENTS 

not jeopardize the stability of the soil supporting a road surface if 
properly designed tile drains are employed. 

It will be convenient to consider three distinct conditions that 
are encountered in providing tile drains for highways. The first 
has already been mentioned in connection with surface drainage 
and is the case where the tile drain serves to supplement surface 
drainage in addition to lowering the ground water level. For tile 
drains of this character the safe rule is to provide sufficient capacity 
for both purposes on the assumption that water is being delivered 
to the tile from both sources simultaneously. 

The second is the case where the tile is employed to lower the 
ground water level of roads with low rates of grades, that is, roads 
in generally level country. Here the generally accepted principles 
of land drainage may be employed except that it is desirable to 
place two lines of tile along the road at a depth sufficient to lower 
the ground water level to at least 4 ft. below the road surface. 
On the basis usually adopted for land drainage one line of tile 
would be adequate to drain the right-of-way of a road four rods 
wide, but experience has shown that this is not generally true and 
that two lines of tile are needed. It seems to be established that 
the carrying capacity should be one and one-half times that con- 
sidered sufficient for land drainage in order to expedite the re- 
moval of water. The minimum depth for the tile is 6 ft. below 
the elevation of the center line of the road. 

The third condition is encountered in hilly country more 
frequently than elsewhere but is likely to exist under any topo- 
graphical condition. It is manifested by seepages of water in 
the most unexpected places and by partial saturation of the road 
surface in locations remote from accumulations of surface water. 
These are evidences of underground water which, in following 
along on top of dense strata or in veins or porous layers in the 
soil, finally reaches the surface of the ground, or near enough to 
the surface to effect the stability. This condition results from 
the erratic behavior of underground water in hilly country and 
sometimes even in prairie country. Where the layers of each 
type of soil are nearly horizontal and of considerable thickness, it 
is comparatively easy to predict the behavior of underground 
water. When the soil consists of thin layers or pockets of materials 
of greatly different porosity lying at various angles with the hori- 
zontal, and more or less faulted, it is impossible to predict the 
trend of underground water. This condition exists not only 



DRAINAGE AND CONTROL OF EROSION 43 

where ledge rock, shale or dense clay underlies the surface soil, 
but also where the more porous clays, gravelly soils or sandy loam 
underlie the surface. 

The drainage requirements for roads where such conditions exist 
will be exceedingly variable and can only be determined by 
careful surveys of the road prior to beginning construction work 
and during the progress of the construction. In regions where 
the soil freezes to a depth of several feet, the most reliable informa- 
tion will be obtained by an examination of the road just after the 
frost comes out of the ground in the spring, and during the month 
or six weeks subsequent thereto. In regions where the ground does 
not freeze the examination is most advantageously made during 
the season of maximum precipitation and immediately subse- 
quent thereto. The purpose of the examination is to locate those 
sections of road that are affected by underground water. When 
these are found, the exact nature of the flow of underground 
water can be determined by test holes, and the drains designed 
in accordance with the exact conditions encountered. 

The topographical conditions that are most likely to require 
examination are side hill cuts, moderately deep cuts, hills and 
sections of road that lie somewhat lower than the land alongside. 
Hills or elevations some distance away may be the source of water 
that finds its way to the supporting soil of a road. 

The drainage method for all of these conditions is to lay tile so 
as to intercept the flow of water at a depth of 5 or 6 ft. below the 
surface of the road and the exact design will vary with conditions. 
It is a wise precaution to always lay tile drains along the foot of 
the slope in cuts and to back fill the trench with broken stone or 
coarse gravel to facilitate the entrance of water into the tile. The 
size of tile to use is purely a matter of judgment as there is no 
means for computing it. 

II. DRAINAGE IN ARID AND SEMI-ARID REGIONS 

General Problem. In arid and semi-arid regions the problem 
of drainage is primarily one of controlling surface water. It is 
exceeding rare to find a need for under drainage in such climates, 
except that springs or seepy places may occasionally exist in 
mountainous districts. 

Run-off In semi-arid and arid regions the little rain that falls 
may come during a very short rainy season and while the total 
annual precipitation may be less than 15 inches, the rate of pre- 



44 CONSTRUCTION OF ROADS AND PAVEMENTS 

cipitation may be high. Usually the run-off from such areas is 
relatively high and flood conditions may prevail for short periods 
of time. The ditches required to properly accommodate the 
flood flow may be of as great capacity as those usually constructed 
in humid regions, but they may be dry for many months in the 
year. The run-off should be estimated on a basis of the recorded 
maximum rate of precipitation and the ditches designed on that 
basis. 

Erosion. An important part of the problem of drainage in 
semi-arid regions has to do with the control of erosion, which 
subject will be discussed in the next section. 

m. CONTROL OF EROSION 

General Problem. Wherever precipitation is considerable or 
where it comes at a very high rate, erosion is sure to occur, and no 
small part of the problem of design of drainage facilities has to do 
with minimizing the tendency of flowing water to carry away the 
soil. 

Two systems of controlling erosion are available and all works 
intended to control erosion employ one or the other of these me- 
thods, and often the two are employed in combination. The 
first system is one in which drainage channels are lined with 
concrete, rubble, planking or some similar material that will 
carry water with very slight erosion. The second employs the 
principle that the quantity of soil carried by flowing water varies 
inversely as the velocity of the water and that, consequently, 
quiescent water will deposit any solid matter it may have carried. 
In applying this principle, drainage channels are so designed that 
a low velocity results and erosion is thereby reduced to a negligible 
factor. 

Controlling Erosion of Ditches. Where open ditches are 
designed for a velocity exceeding 2 ft. per second, erosion will be a 
problem that is not to be neglected. The simplest method of 
controlling erosion is to provide a succession of weirs across the 
ditch, thereby insuring a succession of pools of quiescent water 
at times of minimum flow. In a comparatively short time, soil 
will be deposited above each weir to the level of the top thereof, 
and erosion of the side ditch will be effectually checked. Just 
below each weir a small amount of erosion will occur but if the 
weirs are sufficiently close together such erosion as occurs will not 



DRAINAGE AND CONTROL OF EROSION 45 

be troublesome. The difference in the elevations of the top of 
successive weirs should not exceed 3 ft. 

The weir may be constructed of plank or of masonry and the top 
should be about 6 in. lower at the middle than at the ends so that 
the water will not flow around the ends, but will flow over the 
middle part of the weir. The weir should extend 2 ft. into the 
back slope of the ditch and the end toward the roadway should 
extend to the edge of the travelled way. 

When the grade of the ditch is in excess of 5 per cent, the cost of 
the weirs will be such that it will usually be economical to provide 
a paved gutter the entire length of the hill. Such gutters are con- 
structed of cobblestones carefully set in place and grouted with 
cement mortar, or are constructed of Portland cement concrete. 
Various designs are used and the carrying capacity will of necessity 
vary with the amount of water to be carried. This method of 
controlling erosion is advisable only when the road area between 
gutters is paved with some material that resists erosion, otherwise 
erosion of the road between the gutters is likely to become so 
serious as to materially increase the work of maintaining the 
surface. 

It is often desirable to combine the pavement for the area 
between gutters with the gutter so that in reality the entire road 
surface is a drainage channel and at times' of heavy storms will 
have great capacity. At times of slight flow the gutters will 
carry the water. 

At some point near the bottom of the hill the water must be 
taken from the gutters to earth channels, which are usually at a 
somewhat lower level. Whatever method of controlling erosion 
may have been used for the ditch, the transition channel must be 
carefully designed. One method commonly employed is to carry 
the water through the transition channel in a concrete gutter 
carefully alinged so that the water will readily follow it. Another 
method is to take the water from the ditch directly into a masonry 
catch basin and from there carry it in a tile to a proper outlet. 
This method is not advantageous if large quantities of water must 
be handled, because of the size of catch basin and tile required. 

Controlling Erosion of Side Slopes. The erosion of the side 
slopes of cuts and fills becomes a serious problem if any con- 
siderable amount of water flows down them. There is no way 
to prevent the water that actually falls on the slopes from running 
down the slopes, but the water that falls on the land adjacent to 



46 CONSTRUCTION OF ROADS AND PAVEMENTS 

a cut is diverted by means of a ditch above the upper edge of the 
slope of the cut and is carried to a suitable outlet. If this is not 
possible it is concentrated at one or two points and then brought 
down the slope of the cut in a plank flume. 

The water that falls on the roadway of a fill section of road 
will cause troublesome erosion if allowed to flow down the slopes 
at will, and to prevent this it is diverted by means of a ridge of 
earth at the top of the slope and carried to paved channels or 
flumes that lead down the slope to the lower level. 

Erosion can be greatly retarded on slopes of cuts and fills if a 
rank growth of grass can be secured. This is difficult to secure 
because of lack of moisture during some seasons of the year. Few 
grasses will prove hardy enough to live on the slopes, but Western 
Wheat grass and Hungarian Brome grass will survive in most of 
the humid areas, but of course no growth can be maintained in the 
arid and semi-arid regions. 

Control of Stream Erosion. To a limited extent the drainage 
structures on a highway can be utilized to minimize stream 
erosion adjacent to the road. In some instances the drainage 
area for a culvert consists of a few acres, and a tile may be used 
instead of a culvert. The tile may be extended by land owners to 
drain the area above the culvert thereby limiting erosion. 

In other instances the culvert may be set high enough to cause 
considerable sedimentation above it thereby retarding stream 
erosion. The drop-inlet type of culvert is particularly effective 
for such a purpose. 

EXAMPLES OF GOOD PRACTICE 

ILLINOIS 1 

Improperly designed or located roads on steep grades often result 
in expensive upkeep. 

It is admitted that the most important problem connected 
with the design of a modern highway is that of properly providing 
for all drainage. At least good drainage insures that the upkeep 
cost will be reduced to a minimum. 

Yet in view of this well established principle of construction it 
is not uncommon to find many pavements in use where drainage 
has not been properly provided for. This is especially true on 
steep grades and on soils that wash badly. 

1 B. H. Piepmeier in Engineering Contracting, Sept. 8, 1915. 



DRAINAGE AND CONTROL OF EROSION 47 

Earth in some localities erodes more readily than in others, 
so necessarily needs more attention. The tendency in construc- 
tion is to reduce the first cost of the road and in doing so often 
neglect important features of the pavement that make for more 
permanent and safer highways. 

The writer has had an occasion to examine a very large number 
of pavements constructed on long, steep grades and on soils that 
erode very easily and it is evident that some form of cross-section 
that will confine the water on the pavement or within a paved 
gutter is usually necessary on long grades that exceed about 5 
per cent., and particularly on soils that are inclined to wash badly. 

A number of concrete and brick pavements with macadam, 
gravel and earth shoulders constructed on grades varying from 4 
to 10 per cent, have been inspected and in nearly every case the 
side ditches soon become unnecessarily deep and the macadam, 
or earth shoulders gullied out until the road becomes unsafe. 

Occasionally a road is constructed on a tight soil which does not 
wash badly even on the steep grades. There are also times when 
circumstances permit the earth roads and ditches to sod rapidly 
and in such cases the formation of sod prevents excessive erosion 
for several years. However, in a majority of cases the entire 
road is loosened up during construction and before it becomes 
thoroughly compacted and set rains will cause trouble. 

It is evident that a steep crown on a cross-section carries the 
surface water to the side ditches more rapidly and gives much 
better results on steep grades than the ordinary flat crown. The 
steep crown sheds the surface water quickly and more uniformly, 
which prevents a great many side gullies. But with the rapidly 
moving traffic it is not always safe to construct a crown that will 
permit this without endangering traffic during wet, slippery 
weather. It is evident therefore, that some other form of section 
is necessary in many cases to provide for the surface water, and 
afford safety to traffic. 

From the results of a very careful study of the various cross- 
sections in use on steep grades, the writer has concluded that 
some form of section where there is an integral curb or concrete 
gutter, in connection with the pavement, is the safest and most 
economical cross-section for a majority of roads on steep grades. 

Where the pavement is constructed with a curb as shown in 
Fig. 8 a, it should in no case be less than about 18 ft. between curbs, 
and as much more as traffic may require. In this form the pave- 



48 CONSTRUCTION OF ROADS AND PAVEMENTS 

ment proper acts as a gutter for carrying the water down the hill. 
The slight crown in the pavement forces the small volumes of 
water next to the curb and leaves the center of the pavement 
free of water. Excessive rain may of course fill the pavement 
to the top of the curb but such rains are of short duration and there 
is no inconvenience in the results. 




FIG. 8. Showing methods of controlling ditch erosion. 

Where the integral curb slopes back at an angle of about 45 
it presents a better appearance than where the face of the curb 
is vertical and is recognized as safer for traffic. Should a team 
become frightened on such a pavement and turn around very 
quickly the sloping curb permits the wheel to climb over the curb 
without upsetting the vehicle or breaking the wheel. The vertical 
curb often prevents the wheel from climbing and the result is 
a break down. 



DRAINAGE AND CONTROL OF EROSION 49 

From the top of the curb back to the embankment the earth 
slope should be about 4 to 1 for a distance of at least 4 ft. where 
possible. The cut presents a good appearance and insures satis- 
factory sight distance at slight curves and will also act as a table 
to catch any earth slides that may come down from the side slopes 
of the cuts. 

Where the above sections are used there is no possible chance for 
the gutters to become clogged with resultant serious washouts. 
This is an important consideration on the average county highway 
as there is not the same opportunity to clean the gutters and catch 
basins, on the country roads that there is on city streets. To re- 
duce the cost of upkeep to a minimum therefore, it is necessary to 
design a pavement section so to be "Fool proof." In a majority 
of cases the small repairs that are necessary on the average country 
road often require a greater expense in getting someone on the job 
to do the work than the cost of doing the work itself. 

A number of pavements have been examined where a large tile 
was embedded 2 or 3 ft. below the side ditches and catch basins 
constructed at intervals to carry the surface water into the tile. 
This method of providing for surface and underground water is in 
first cost somewhat cheaper than other methods but there is always 
some unexpected heavy rain that is sure to clog the tile inlet with 
earth or debris of some kind and the result is that the tile and a 
good portion of the earth shoulder is washed out. Such drainage 
construction should be avoided as it is sure to mean expensive 
upkeep for the road. 

Where the water is confined between two curbs on the pavement 
there is no possible chance for excess wash, and the water upon 
reaching the bottom of the hill may be carried off to the side ditch 
as shown in Fig. 8 6. The side ditch at the bottom of the grade 
should have a natural slope for carrying the water so there will be 
no excessive washing result from turning the water in the side 
ditches. When conducting the water from the side gutters, at the 
bottom of the hill, to the side ditch the flume should deflect from 
the pavement at an angle of not to exceed about 30. If a greater 
angle is used the water will refuse to make the turn on account of 
its velocity and some form of additional protection as shown in 
Fig. 8 c is necessary to prevent the water from washing out the earth 
shoulder just beyond the end of the gutter. 



50 CONSTRUCTION OF ROADS AND PAVEMENTS 
EXAMPLE OF GOOD PRACTICE 

ROAD DRAINAGE AND FOUNDATIONS* 

BY GEO. HOGARTH 
CHIEF ENGINEER, ONTARIO DEPARTMENT OF HIGHWAYS 

In building any roadway, whether for light or heavy traffic, two 
of the most important points to be considered are drainage and 
foundations. 

The stability of the entire road surface depends upon the founda- 
tion and the strength and life of the foundation depends largely 
upon the facilities provided for drainage. While proper attention 
may be given to the drainage of the surface of the road by giving 
the roadway sufficient crown to shed the water, the great import- 
tance of subsurface drainage may be entirely overlooked. There 
are, therefore, surface and subsurface methods of drainage and 
the very great importance of each must be realized and used to the 
fullest extent if we desire a permanent foundation. 

A sound and enduring foundation cannot be secured on subsoil 
saturated with water, but a good foundation can be secured by the 
simple means of keeping the subsoil dry. If water is not excluded 
from the foundation it will sooner or later destroy the road sur- 
facing, since no road ever built could escape destruction should 
the foundation become yielding and soft. 

Importance of Proper Drainage. The ordinary clays and earths 
form a naturally strong foundation when dry, but where the 
ground is wet and springy and a good road cannot be constructed 
without proper subdrainage since when wet the earth loses its 
sustaining power and the surface formation goes to pieces. Where 
the subsoil is gravelly, underdrains will usually not be required, 
but where it is sandy, give close attention to the damp or wet spots 
and provide ample subdrainage. 

It may be said that the whole problem of improvement and main- 
tenance of ordinary country roads is one of drainage. Upon earth 
roads drainage is especially important because the material of the 
road surface is very susceptible to the action of water and so is 
more readily destroyed than are the surfaces of the better class of 
roads. An undrained earth road offers a splendid opportunity 
to the frost, and a spring thaw may result in such a road being 
impassable for days or weeks. A road on a wet undrained bottom 

J Paper presented at the Canadian Good Roads Congress, May, 1919. 



DRAINAGE AND CONTROL OF EROSION 51 

will always be troublesome and expensive to maintain, and it will 
be economical in the long run to go to considerable expense in 
making the drainage of the subsoil as perfect as possible. 

There are three systems of drainage, namely: Underdrainage, 
side ditches and surface drainage. 

Underdrainage will lower the water level in the soil and keep it 
at a safe distance from the foundations. This aids the action of 
the sun and wind, which tend to dry the surface of the road, but if 
the foundation, due to lack of Underdrainage, is soft and spongy, 
the road will soon become a mass of mud. 

Underdrainage dries the ground quickly during the spring when 
otherwise a saturated condition of the soil would exist. 

Underdrainage intercepts the subsurface flow of water beneath 
the crust of the road. 

Some Points on Underdrainage. In many cases it will be 
noticed that though the ground is dry when it freezes in the fall, it 
is very wet and soggy in the spring when the frost comes out. The 
reason for this condition is that after the ground freezes, water 
rises slowly in the soil and if it is not drawn off by Underdrainage 
it saturates the subsoil and rises further as the frost goes out. 
Underdrainage not only removes the water but reduces and will in 
many cases prevent the destructive heavy effects of frost. 

The heaving and cracking of pavements may be entirely at- 
tributed to the freezing of water in the subgrade under the pave- 
ment. Underdrainage will greatly lessen the damage done in this 
way by the frost, but to prevent entirely such destructive action 
may be very difficult. It may be said that when underdraining 
a section of road known to have a wet subgrade it is well to provide 
a liberal number of drains. Too many cannot be laid. Particular 
attention to the Underdrainage should be given at points on the 
road from 50 to 200 ft. or more down grade from the top of a hill 
or slope and particularly so if the roadway is in an excavation. 
Water will usually filter out to the surface at such points and the 
entire skill of the roadbuilder will have to be exercised in locating 
subdrainage to prevent heaving and cracking. In all such cases 
do not curtail the Underdrainage, but rather put in every foot of 
tile that can be placed. 

Wherever the Underdrainage is provided be careful to provide 
proper grade and good outlet for the tile since poor results will 
come from the tile that are indifferently laid and improperly 
vented. 



52 CONSTRUCTION OF ROADS AND PAVEMENTS 

Tile drains furnish the usual means for subdrainage, but in some 
cases a blind drain may be used to good advantage. The construc- 
tion of a blind drain is accomplished by opening a trench several 
feet deep along or across the road and afterwards filling the trench 
with stone. The depth, distance apart and location of such 
trenches will depend entirely upon the conditions encountered 
and the result desired. Careful attention to the subdrainage of 
the road is of great importance and the money spent for such work 
is always a splendid investment. 

Surface Drainage. Side ditches for all country roads are 
essential. Their object is to receive the water from the surface of 
the traveled roadway and the grade of the ditch should be such 
that the water is carried rapidly to a good outlet. Such ditches 
also intercept and carry away water that would otherwise flow 
from the side hills upon the road. Side ditches need not be very 
deep; a depth of 2% or 3 3/2 ft. below the crown of the roadways 
will usually be found sufficient and the sides should be given a 
slope flat enough to prevent caving. In order to be effective, 
ditches should have as great a grade as possible, they should be 
well cleaned out and have free outlet in some creek or stream. 

Surface drainage of the travelled portion of the road affects 
mainly the maintenance of the road and is accomplished by giving 
the road or pavement surface a crown which tends to shed the 
water to the side ditches. The slope of the crown should be 
sufficient to carry the water freely and quickly to the side ditch. 
The proper crown to use will .vary with the nature of the roadway; 
when a good surface is maintained, a moderate rise will be found 
sufficient. For earth, clay or gravel roads a usual crown is 1 in. 
per foot, while for bituminous or concrete pavements ^ or J4 
in. per foot is ample. 

WHY BITUMINOUS MACADAM IS SUCCESSFUL IN RHODE 

ISLAND 

BY IRVING W. PATTERSON 
CHIEF ENGINEER, STATE BOARD OF PUBLIC ROADS, RHODE ISLAND 

IN 

ENGINEERING NEWS-RECORD, DEC. 11, 1919 

The first instance of the use of bituminous macadam built by 
the penetration method upon the state highway system of Rhode 
Island was in 1913. During the period between 1906 and 1912 
inclusive a rather extensive use of bitumens was made, but during 



DRAINAGE AND CONTROL OF EROSION 53 

this earlier period the use of bitumens was confined almost without 
exception to the cold-mixing method. The aggregate employed 
for the cold-mixing work was crusher-run stone from J^in. to lJ/ 
in. in size. This type of construction according to present defini- 
tion should be termed bituminous concrete, although the character 
of the aggregate would seem to warrant its designation as bitu- 
minous macadam by the cold-mixing method. The roads built 
by the cold-mixing method were described in many publications a 
number of years ago by Arthur H. Blanchard, and for this reason 
and also because of the fact that this type of construction no 
longer is employed in Rhode Island, the writer will confine his 
remarks to penetration work. 

In 1913 the conditions surrounding the state road situation in 
Rhode Island were rather discouraging because of the fact that 
funds for reconstruction and maintenance had been so meagre 
that little had been accomplished toward rebuilding or resurfacing 
the wornout waterbound macadam roads built in the period of 
1896 to that time. The funds available in 1913 also were so 
limited that it was deemed out of the question to lay pavements 
of the so-called durable type. The engineering force, which 
had recently undergone considerable change in personnel, was 
called upon therefore to select types of construction which were 
relatively inexpensive. An examination into the results secured 
in Rhode Island in previous years by the use of the cold-mixing 
method disclosed the fact that the results were erratic. Some of 
the roads built by this method were in almost perfect condition 
and had required little maintenance, while other roads built under 
the same specification had given very poor service. It appeared 
that very slight variations in the quality of crushed stone employed 
in this type of construction were responsible for widely varying 
results secured. 

This examination brought to light the surprising paradox that 
the best quality of stone according to usual standards gave the 
poorest results. The fact that a soft stone broke up under the 
roller sufficiently to bring about a more perfect grading of sizes 
than was involved in screening very likely accounted for this 
peculiarity. Although good results were secured by the use of 
soft stone in our cold-mixing work, we have found that only a 
hard, tough stone gives good results in our penetration work. 
A continuation of the use of the cold-mixing method was not 
deemed advisable. An investigation into the penetration method 



54 CONSTRUCTION OF ROADS AND PAVEMENTS 

led us to believe that very good results could be secured by that 
method in certain localities. It appeared that bituminous maca- 
dam had failed in many sections by reason of foundation defects, 
by reason of raveling of the wearing surface. An attempt was 
made therefore to adopt a practice in regard to the design of 
foundations and drainage facilities, in regard to selection of 
materials and in regard to construction details, which would 
remedy to some extent these defects. The specification first 
employed for the work done in 1913 has been modified somewhat 
in minor detail but no radical changes have deemed necessary. 
The results secured upon our penetration roads have exceeded 
our expectations somewhat. Resealing of none of penetration 
roads has as yet been necessary and the repairs have been com- 
paratively inexpensive. 

Our construction has not been confined to bituminous macadam. 
For several years past we have selected frequently other types of 
construction such as bituminous concrete both upon a macadam 
base and upon a concrete base and cement concrete. We still 
believe, however, that there is a field in Rhode Island for bitu- 
minous macadam upon our main trunk lines. 

In our early investigation into bituminous macadam by the 
penetration method it appeared to us that waving or corrugation 
of the wearing surface of penetration roads was due to five causes, 
viz. ; the use of asphalt of too high penetration, the use of excessive 
amounts of binder, the use of crushed stone of too small sizes in 
the wearing course, the use of soft stone in the wearing surface and 
inferior construction methods. Waving of the surface of penetra- 
tion roads is one of the most serious defects of this type of con- 
struction as frequently built and is, if it develops, very nearly 
irrevocable. Attributing the cause of waving to the conditions 
mentioned previously, we adopted the use of an asphalt of com- 
paratively low penetration, we employed a hard crushed stone 
screened to large sizes for the wearing surface and we exercised 
care in the construction. 

The depth of crushed stone composing the wearing surface is 
made as nearly uniform as is possible. In surfacing of old maca- 
ams especially it frequently happens that the depth of crushed 
stone constituting the wearing surface varies considerably because 
of the very common practice of laying the crushed stone in one 
course only over an irregular base. In all of our penetration work 
we make a practice of laying the crushed stone in two courses so 



DRAINAGE AND CONTROL OF EROSION 55 

that the top course or wearing course may be made very uniform 
in depth. 

The sizes of crushed stone employed in both the base course and 
in the wearing course are the same, being of sizes passing a 2}/ in. 
screen and retained upon a IJ^ in. screen. The depth of the wear- 
ing surface is made 2^ in. thick after compression. 

The bottom course of crushed stone always is filled with sand or 
with crusher-run screenings. The depth of the base course does 
not vary greatly over various types of foundations and subsoils. 
We very seldom increase the depth of the base course of crushed 
stone in order to strengthen the pavement where subsoil condi- 
tions appear to make a stronger construction desirable. It has 
been our experience that crushed stone therefore always is em- 
ployed where the subsoil conditions are unfavorable. 

As a rule the base course is made 3J/ in. thick after compression 
so that the total depth of the pavement is 6 in. Over heavy rock 
foundations, however, we make a practice of laying the base course 
of crushed stone 2}^ in. thick. We are not in favor of laying the 
crushed stone in one course even over heavy rock foundations. In 
order to secure a smooth uniform surface it is very essential to have 
the crushed stone constituting the wearing surface free from 
irregularities which would be objectionable in the finished surface 
previous to the application of the bitumen. We have discovered 
no method of repairing irregularlities due to faulty spreading of the 
crushed stone constituting the wearing surface after the bitumen 
has been applied. 

ROLLED TO GET MAXIMUM MECHANICAL BOND 

Previous to the application of the bitumen the crushed stone 
constituting the wearing surface is thoroughly rolled. We make 
a practice of rolling until there is no sinking or creeping ahead of 
the roller and until a loaded cart or truck leaves no appreciable 
mark. It frequently is claimed that over-rolling of the stone 
constituting the wearing course is a condition prejudicial to the 
securing of good results. The theory which we work upon is 
to secure the maximum mechanical bond which is possible and 
to augment this bond with the bitumen. One of the reasons 
frequently given for not rolling the wearing course of stone heavily 
is that the individual pieces of stone fracture to such an extent 
that proper penetration of the bitumen is not secured. The writer 
is of the opinion that no crushed stone should be used for the 



56 CONSTRUCTION OF ROADS AND PAVEMENTS 

wearing course in penetration work which is soft enough to break up 
seriously under rolling as heavy as is described. 

Our best results have been secured with trap rock (basalt). 
Our observation leads us to believe that the ability to secure trap 
rock for the wearing surface of the ability to secure a stone ap- 
proximately as good should be a condition precedent to the selec- 
tion of bituminous macadam. Although a hard granite, a good 
quality of quartzite, a hard indurated sand stone and a number of 
other types of rock usually considered rather inferior may give 
very satisfactory service for a few years, our experience indicates 
that the use of anything but the best quality of crushed stone for 
the wearing surface involves high maintenance costs unless very 
light traffic is to be provided for. It is a fact, however, that the 
initial "surfacing-up" process is much more rapid where a rather 
soft stone is employed. We have noted that as a rule a penetra- 
tion road built of fairly soft stone presents a tighter surface for 
approximately two years after its construction than does a road 
built of trap rock. In the selection of stone to be employed for 
the wearing surface it is also essential to avoid rock which is 
characterized by adhesion of fine rock powder to the large sizes 
of crushed stone. Some of the quartzites have this peculiarity 
in marked degree. 

The greater part of our bituminous macadam work lias been con- 
structed of asphalt of penetration between 90 to 100. There 
has been a general tendency within the last few years toward the 
use of harder asphalt for penetration work, but when our first 
penetration work was done in 1913 the use of an asphalt of such 
low penetration was unusual. We have secured excellent results 
from the use of an asphalt of penetration of approximately 55. 
We never have employed an asphalt of penetration higher than 
130. At present our specifications invariably call for an asphalt 
of penetration between 90 and 100. 

The first or binding application of asphalt is made at the rate of 
1/4 gal. per square yard of surface, volume measured at air 
temperature. We have employed both the hand pouring method 
and machine distribution. Our results indicate that hand pour- 
ing is fully as efficient as machine distribution, but we do not feel 
justified in stating that results secured by the hand-pouring method 
are superior to the results secured by machine distribution. 

Immediately after the application of binder the keystone or the 
crushed stone employed to fill the surface voids in the wearing 



DRAINAGE AND CONTROL OF EROSION 57 

course is spread. As the key stone is spread, so does the finished 
surface appear. We attempt only to fill the surface voids but 
we are careful to see tnat practically all of the surface voicis are 
filled. Workmen may become so proficient at spreading the key 
stone that little sweeping is necessary, but ordinarily sweeping of 
the key stone into the voids is required. We employ for the key 
"stone crushed stone of sizes passing a 1 in. screen and retained upon 
a % m - screen. We urge the necessity for having this stone free 
from stone dust. After the key stone has been spread satis- 
factorily the surface is well rolled. It usually is necessary to 
touch up spots which show a deficency of key stone during the 
rolling operation. 

POSITIONS GOVERNING SEAL-COAT APPLICATION 

Conditions affecting accumulation of dust upon the surface of 
the road influence the length of time intervening between the 
spreading of the binder application of asphalt and of the spreading 
of the second application of asphalt, or the seal-coat. In general 
we do not favor applying the seal-coat upon the same day that the 
first application is spread. If, however, there is a car track in the 
highway or if traffic is carried upon a portion of the highway, there 
is a possibility that dust will be blown upon the surface to such an 
extent that the application of the seal-coat should be made as 
soon as possible. Care of course always is taken to avoid applying 
asphalt upon wet stone. 

We apply the seal-coat at the rate of between % gal. and 1 gal. 
per square yard of surface. The fact that the key stone is fairly 
large in size permits the use of a heavier seal-coat than would be 
possible if a smaller stone were employed. The use of key stone 
of comparatively large sizes does not permit the seal-coat to lay 
upon the surface in blanket form. Puddling of the seal-coat is 
very rare in our work in spite of the fact that the amount employed 
for it is more liberal than is customary. 

Immediately after the application of the seal-coat a cover of 
crushed stone of sizes passing a ^ in. screen and retained upon a 
% in. screen is applied. The cover is applied in amount only 
sufficient to cover the surface. Care is essential to avoid bunches 
in the material employed as a cover, because while the road is 
plastic irregularities in the finished surface may result from these 
bunches during final rolling. We consider it a disadvantage to 
have the cover applied in amount materially greater than will 



58 CONSTRUCTION OF ROADS AND PAVEMENTS 

bond to the seal-coat. For work finished late in the season we 
consider a large excess of covering material very detrimental in 
view of the fact that the "surfacing-up" process is retarded and 
the pavement is called upon to go through the winter covered by 
a layer of mud produced by the grinding up under traffic of the 
covering material. A penetration road which does not have an 
opportunity to complete its initial "surfacing-up" process before 
winter sets in is, in the opinion of the writer, greatly handicapped. 
Anything which retards the surfacing process should be avoided 
and anything which will hasten it is desirable. 

ROLLING COMPLETED SURFACE 

Rolling of the pavement after it is completed is a matter which 
appears to be slighted frequently. The rolling of a penetration 
road is a vastly different proposition from the rolling of sheet 
asphalt or of bituminous concrete having a well graded mineral 
aggregate. The extent of rolling means little, however, unless 
care is used to roll at the right time. It is desirable to have the 
temperature high enough so that the road is somewhat plastic in 
order to secure the best results in final or back rolling. We en- 
deavor to have the rolling of the finished pavement carried out for 
a period of two weeks. The time of rolling of course is dependent 
upon the season of the year during which the work is done. Rolling 
of the finished pavement should be avoided when it is raining or 
when the pavement is wet from previous rains. In the fall rolling 
of the finished surface is not efficacious when done in the early 
morning or late afternoon. When the weather becomes cold it 
is essential to do the back rolling at the time of day that the 
temperature is the highest. The "surfacing-up" process is greatly 
hastened by heavy rolling after the pavement is completed. We 
deem it also desirable to roll the finished pavement after traffic is 
allowed upon the road. The combination of vehicular traffic and 
rolling seems to be more effective than mere rolling without traffic. 
It is of course possible to roll too much at one time. During very 
warm weather especially the effect of rolling must be observed 
carefully in order that too much rolling may be avoided. During 
the summer months the final rolling frequently is more effective 
when done in the early morning or late afternoon. Although the 
writer was of the opinion that extensive rolling after the completion 
of the pavement is policy, he did not appreciate the value of this 
feature until he had an opportunity to observe the effect of very 



DRAINAGE AND CONTROL OF EROSION 59 

heavy rolling upon a section of newly finished road referred to was 
occasioned by extension of a contract upon the end farther from 
the source of supply of stone. The crushed stone was hauled 
over the newly completed section, much against the desires of 
those in charge of the work, immediately after the road was open 
to traffic. The section of road involved in the extension of the 
contract never presented such a perfect surface as did the section 
over which the hauling by means of the steam roller was carried 
out. The section done last, however, was finished about mid- 
summer so that the difference in the surfaces of the two sections 
could not be attributed to the fact that the section done later 
was finished late in the season. The difference in the surfaces 
of the two sections is not microscopic in any sense of the word, 
but is evident even to the casual observer. We feel that the matter 
of rolling penetration roads has not received generally the atten- 
tion that it deserves. 



CHAPTER IV 

THE DESIGN OF RURAL HIGHWAYS 
CLASSIFICATION OF SOILS 

General Characteristics of Soils. In earth-road construction, 
the material used is the soil which is found on the public highway 
to be improved, and this material varies greatly throughout the 
country, and, indeed, often varies considerably on a single mile 
of public highway. 

From the road builder's standpoint there are certain character- 
istics which are common to many soils, although these soils 
differ very widely from the agriculturist's standpoint, and certain 
broad principles of highway construction can be laid down that 
can be applied with some modifications to all soils in these 
groups. 

Most of the studies of types of soils have been made from the 
agriculturist's standpoint, and the classifications so made are 
of little interest to the road builder. The names given to the 
various kinds of soils by the scientist often differ from the 
colloquial name, and the local name given to the soil in one 
community may differ from the local name given to the same 
soil in some other community. It is, therefore, of little value 
to the road builder to study types of soils from the standpoint 
of their scientific classification. Nevertheless, since soil is the 
material which will be used in road construction by the road 
builder, some understanding must be had of the characteristics 
and behavior of these materials. 

For this purpose, soils may be divided into two groups, 
which are referred to as clays and loams, since these terms are 
more commonly used by the layman than the more scientific 
designation. 

It should be borne in mind that the line of demarcation between 
these two groups is not clearly drawn. They shade into each 
other, and many types will be encountered which could not 
readily be placed in either. The designation, however, is suffi- 

60 



THE DESIGN OF RURAL HIGHWAYS 61 

ciently definite for the general purpose of discussion of earth 
roads. 

Clay. The name clay is herein given to those soils which 
possess dense, tough and relatively impervious structure. These 
soils are black, yellowish, or reddish in color; are exceedingly 
sticky when wet, absorb water slowly, and retain it tenaciously. 

A road surface constructed on such a soil when once firmly 
compacted turns water readily, softens from the surface down- 
ward somewhat slowly, but when permeated, becomes very 
sticky, balling up on the heels of vehicles in large masses; dries 
out slowly; is very tough when partially dry, and, during the 
summer months, bakes into a hard crust which is exceedingy 
difficult to handle with any ordinary earth-working machinery. 

These soils in general cannot be dragged when wet, rarely 
becoming sufficiently plastic to work with a drag. On the 
contrary, the dragging must be done after the soil is in a crumbly 
condition. If an attempt is made to grade a road of this type 
of soil in the summer months, it is found that the material can 
be moved only with considerable difficulty, and if it is loosened 
with a plow, breaks up into large pieces which are so hard that 
it is almost impossible to pulverize them and smooth the surface 
down to a passable condition. 

These characteristics exist to a large extent in all soils of this 
general type, and present a distinct problem in earth-road con- 
struction. The degree to which the characteristics are found may 
vary in individual cases. 

Theses soils also have a distinct characteristic as regards 
drainage. On account of the density and close texture of the 
soil, water permeates them but slowly, and underground drainage 
is much less effective than on porous types of soil. In general, 
tile drains along roads of this type of soil remove the water from 
the soil very slowly, and it is a serious question as to whether the 
tile is worth while so far as its effect in removing the ground 
water is concerned. These types of soil are also quite likely to 
lie in strata between which underground water will percolate. 
These strata often come near the surface on a public highway, 
and the water which is flowing between the layers will, in these 
places, work out to the surface causing bad mudholes commonly 
called "seepy" places. When such conditions are encountered 
underground drainage is essential, but the tile must be laid so 
as to intercept the flow of water between the strata and carry it 



62 CONSTRUCTION OF ROADS AND PAVEMENTS 

to the outlet, and thus prevent its coming to the surface of 
the road. 

Loam. The term loam is used herein to designate that group 
of soils which is of a porous and somewhat granular nature. 

The loams may be yellow, reddish, brown or gray in color; in 
fact, many of them resemble the clays in general appearance, but 
all have a distinctly porous structure. Such soils absorb water 
readily, become more or less unstable when water-soaked, dry 
out rapidly, and the mud which forms on the highway is apt to 
be plastic and not very sticky. 

A road surface of this type of soil will soften very rapidly 
after heavy rains, but in drying out the mud will be plastic and 
can be readily dragged when wet. On account of the porous 
nature of the soil it responds readily to underground drainage, 
the water percolating rapidly to the tile, and on account of the 
unstable condition of the soil when wet, underground drainage is 
of great assistance in maintaining a satisfactory roadway. 

The so-called "seepy" places are also frequently encountered 
on this type of soil, due to underground water which works out 
to the surface of the road, and, as in the cases of similar places 
on the clay soil, underground drainage is necessary to remove 
the water to prevent its softening the road surrface. 

While these soils become hard when thoroughly dry, as is 
usually the case during the summer months, yet they are not as 
difficult to work at that time as are the clays. If a road of this 
type of soil is graded during the late summer months, some 
difficulty will be encountered in moving the material, yet it will 
be much easier to pulverize and get a smoothly finished surface 
than would be the case with clay soils. 

CULVERTS 

Purpose of Culverts. The culvert is an important part of 
the drainage for a highway system, being employed to carry the 
water from small streams across the highway or to carry the 
ditch water from one side of the road to an outlet on the op- 
posite side. No uniformity exists in the various states in regard 
to the the distinction between "culvert" and "bridge." This 
discussion is limited to structures of 6-ft. span or less. 

Culverts should so far as possible be constructed at such a 
height that they will not make it necessary to raise the profile 
of the road in order to carry the roadway over the culvert. In 



THE DESIGN OF RURAL HIGHWAYS 



TABLE I. 1 TALBOT'S FORMULA FOR WATERWAYS 



Area of Waterway in Square Feet. = C y/( Drainage Area in Acres) 3 
C being variable according to circumstances thus: 

"For steep and rocky ground C varies from % to 1. For rolling agricultural country 
subject to floods at times of melting snow, and with length of valley three or four times its, 
width, C is about \$, and if stream is longer in proportion to the area, decrease C. In 
districts not affected by accumulated snow, and where the length of valley is several times 
its width, \i or ^6 or even less may be used. C should be increased for steep side slopes, 
especially if the upper part of the valley has a much greater fall than the channel of the 
culvert." 

The following table gives \'\ roots of cubes, or the value of area of waterway for C = 1* 



Acres 


Sq. mi. 


VJ~ 


Acres 


Sq. mi. 


VZi 


Acres 


Sq. 
mi. 


VTs 


Acres 


Sq. 

mi. 


VJi 


1 


0.002 


1.0 


56 


0.09 


20 


525 


0.82 


110 


5,500 


9 


639 


2 


0.003 


1.7 


58 


0.09 


21 


550 


0.86 


114 


6,000 


9 


682 


3 


0.005 


2.3 


60 


0.09 


22 


575 


0.90 


117 


6,500 


10 


724 


4 


0.006 


2.8 


65 


0.10 


23 


600 


0.94 


121 


7,000 


11 


765 


5 


0.008 


3.3 


70 


0.11 


24 


625 


0.98 


125 


7,500 


12 


806 


6 


0.009 


3.8 


75 


0.12 


26 


650 


1.02 


129 


8,000 


13 


846 


7 


0.011 


4.3 


80 


0.13 


27 


675 


.05 


132 


8,500 


13 


885 


8 


0.013 


4.8 


85 


0.13 


28 


700 


.09 


136 


9,000 


14 


924 


9 


0.014 


5.2 


90 


0.14 


29 


750 


.17 


143 


9,500 


15 


962 


10 


0.016 


5.6 


95 


0.15 


30 


800 


.25 


150 


10,000 


16 


1,000 


11 


0.017 


6.0 


100 


0.16 


32 


850 


.33 


157 


10,500 


16 


1,037 


12 


0.019 


6.4 


105 


0.16 


33 


900 


.41 


164 


11,000 


17 


1,074 


13 


0.020 


6.8 


110 


0.17 


34 


950 


.48 


171 


12,000 


19 


1,147 


14 


0.022 


7.2 


120 


0.19 


36 


1,000 


.56 


178 


13,000 


20 


1,217 


15 


0.023 


7.6 


130 


0.20 


38 


1,050 


.64 


184 


14,000 


22 


1,287 


16 


0.025 


8.0 


140 


0.22 


41 


1,100 


1.72 


191 


15,000 


23 


1,355 


17 


0.027 


8.4 


150 


0.23 


43 


1,150 


1.80 


197 


16,000 


25 


1,422 


18 


0.028 


8.7 


160 


0.25 


45 


1,200 


1.88 


204 


17,000 


27 


1,489 


19 


0.030 


9.1 


170 


0.27 


47 


1,250 


1.95 


210 


18,000 


28 


1,554 


20 


0.031 


9.5 


180 


0.28 


49 


1,300 


2.03 


216 


19,000 


30 


1,618 


21 


0.033 


9.8 


190 


0.29 


51 


1,350 


2.1 


223 


20,000 


31 


1,682 


22 


0.034 


10.2 


200 


0.31 


53 


1,400 


2.2 


229 


22,000 


34 


1,806 


23 


0.036 


10.5 


210 


0.33 


55 


1,500 


2.3 


241 


24,000 


38 


1,928 


24 


0.037 


10.8 


220 


0.34 


57 


1,600 


2.5 


253 


26,000 


41 


2,048 


25 


0.039 


11.2 


230 


0.36 


59 


1,700 


2.7 


265 


28,000 


44 


2,165 


26 


0.041 


11.5 


240 


0.38 


61 


1,800 


2.8 


276 


30,000 


47 


2,280 


27 


0.042 


11.8 


250 


0.39 


63 


1,900 


3.0 


288 


35,000 


55 


2,559 


28 


0.044 


12.2 


260 


0.41 


65 


2,000 


3.1 


299 


40,000 


62 


2,828 


29 


0.045 


12.5 


270 


0.42 


67 


2,100 


3.3 


310 


45,000 


70 


3,090 


30 


0.047 


12.8 


280 


0.44 


68 


2,200 


3.4 


321 


50,000 


78 


3,344 


32 


0.05 


13.5 


290 


0.45 


70 


2,300 


3.6 


332 


55,000 


86 


3,591 


34 


0.05 


14.1 


300 


0.47 


72 


2,400 


3.8 


343 


60,000 


94 


3,834 


36 


0.06 


14.7 


320 


0.50 


76 


2,600 


4.1 


364 


65,000 


102 


4,071 


38 


0.06 


15.3 


340 


0.53 


79 


2,800 


4.4 


385 


70,000 


109 


4,304 


40 


0.06 


15.9 


360 


0.56 


83 


3,000 


4.7 


405 


80,000 


125 


4,757 


42 


0.07 


16.5 


380 


0.59 


86 


3,200 


5.0 


425 


90,000 


141 


5,196 


44 


0.07 


17.1 


400 


0.63 


89 


3,400 


5.3 


445 


100,000 


156 


5,623 


46 


0.07 


17.7 


420 


0.66 


93 


3,600 


5.6 


465 


120,000 


188 


6,447 


48 


0.08 


18.2 


440 


0.69 


96 


3,800 


5.9 


484 


140,000 


219 


7,238 


50 


0.08 


18.8 


460 


0.72 


99 


4,000 


6.2 


503 


160.000 


250 


8,000 


52 


0.08 


19.4 


480 


0.75 


103 


4,500 


7.0 


549 


180,000 


281 


8,739 


54 


0.08 


19.9 


500 


0.78 


106 


5,000 


7.8 


595 


200,000 


312 


9,457 



1 Office and field practice of Iowa Highway Commission. 



64 CONSTRUCTION OF ROADS AND PAVEMENTS 

some instances in very flat sections of road this is not possible 
and it becomes necessary to raise the road grade at the culvert. 
At such places the slope should be carried a sufficient distance 
each side of the culvert to insure an easy-riding crossing. Abrupt 
raises at culverts are uncomfortable for traffic and often are 
dangerous. 

The culvert should be fitted to the traveled way so as to be 
practically unnoticeable until the traveler is close to it. It 
should also fit the stream so that the water will flow through with 
the least disturbance of its natural course consistent with reason- 
able economy. 

The bottom of the culvert should not be placed too low, be- 
cause of the tendency for the stream above the culvert to erode 
to the level of the culvert floor. If the stream has eroded a deep 
channel, the culvert proper may be placed at the level of the 
existing stream bed so that the lower end will discharge without 
causing undue erosion, but the upper end may be provided with 
a drop inlet, the top of which is several feet above the old stream 
bed. The stream bed above the culvert will gradually fill up 
to the top of the drop inlet, and thus valuable land will be 
reclaimed. 

The size of culvert is best determined by estimating the drain- 
age area contributory to it, and then applying one of the well- 
known formulas to determine the area of waterway. One of 
these formulas is shown in Table 1. 

TYPES OF CULVERTS 

Reinforced Concrete. Reinforced concrete is a desirable 
material for culverts because the form of the culvert can be 
readily adapted to the site. The materials are obtainable in 
almost every locality, and can readily be transported to the 
site because they can be carried in small units. The resultant 
structure is proof against injury from the elements, and the 
strength of the culvert can be adapted to the location. Figs. 
9 and 10 show a few typical plans for concrete culverts. 

Pipe Culverts. Culverts are made of clay pipe, cast-iron pipe, 
concrete pipe, and, to a limited extent, from steel pipe riveted 
into appropriate lengths. The load on a pipe in a ditch is made 
up of two factors; (1) the earth fill, and (2) the portion of the 
weight of traffic units that is carried to the culvert. 



THE DESIGN OF RURAL HIGHWAYS 



65 



Grade -\ 




Elevation 

Note Horizontal bars in wing and 
bar re I to be continuous splicing 
" no case to occur at junction, 
wmc] and barrel J n " **' 
through each 




| Drainage Area/ 
\ Area Waterway 




Plan 




Longitudinal Section 
. C^nterJLine -of Proposed Road'"}. 







.._ 





i 

i 










i 

4 










I 




' 






1 
1 


i::::::::. 














Half Plan 




I 



//U- 



.3 

^L 



E.nd View 

PIG. 9. Plans for concrete box culverts. 



66 CONSTRUCTION OF ROADS AND PAVEMENTS 

Table No. 2 may be employed for estimating the load on pipe 
culverts or box culverts when the culvert is laid or constructed 



Jbp ofBas/n to be 
'Ga/vanizeat 
Grafing 



^"i 7 r"^"i?^ /A 



"3arsd>/2fs 
i" Bent Bars Around 
' Corners a>/2"$'s 
F/oor-Sameasfloorj 
in Bar re/ 



<* ^ 3$&_ p| an 
Reinforcing jn Apron 
Transverse -/ "Bars a>/2"<t's 
Longitudinal-^ 




Elevation 



3- Bars Bent 



S*'*\ Nofe 




'Bars a)/2 fa-Trans 
'"Bars-Long. 
Longitudinal Section 



Around Eeach Ofhe.r 

Barrel Reinforcing 7- 

tofRoad/s&O'from Slqb-fBarsai8*<wTrans 

Back of North Parapet Wall t "Bars Oi8h Bent Around 

p Fillatt is 4'-ll*Above Slab Corners as Shown _ , 

'Catch Basin on North End, 3-fBarsLong 



of 




inisLnaTODe/-/ Above walls-* 

South End Fall Equals M'inWtf I2"<t<t Ve, 
7" Angle of Flaring Wings is 45 9 j> Barst 

Top of Catch Basin io be, Floor-i '"Bars ft 12 "<rt Trans. Section 

Covered nith Cl.Pipe Grating 3-'Bars Long Trough 

Bars in Wings and Barrel fo Barrel 
6e Continuous:Splicmgof 
Bars in no Case to Occur 
, near Junction of n/ngg, Barrel 



FIG. 10. Plans for drop inlet culverts. 



in a trench of a depth greater than the height of the culvert so 
that the berm of undisturbed soil extends a few inches above the 
top of the culvert. It should be noted that the breadth of the 



THE DESIGN OF RURAL HIGHWAYS 



67 



TABLE 2. 1 APPROXIMATE ORDINARY MAXIMUM LOADS ON DRAIN TILE 

AND SEWER PIPE IN DITCHES PROM COMMON DITCH FILLING 

MATERIALS. IN POUNDS PER LINEAR FT. 



H = 
Height of 


B = Breadth of ditch, at top of pipe 


fill above 




top of 
pipe 


IFt. 


2 Ft. 


3 Ft. 


4 Ft. 


5 Ft. 


IFt. 


2 Ft. 


3 Ft. 


4 Ft. 


5 Ft. 


Partly compacted damp top soil. 


Saturated top soil. 


90 Ib. per cubic foot 


110 Ib. per cubic foot 


2 ft. 


130 


310 


490 


670 


830 


170 


380 


600 


820 


1,020 


4 ft. 


200 


530 


880 


1,230 


1,580 


260 


670 


1,090 


1,510 


1,950 


6 ft. 


230 


690 


1,190 


1,700 


2,230 


310 


870 


1,500 


2,140 


2,780 


8 ft. 


250 


800 


1,430 


2,120 


2,790 


340 


1,030 


1,830 


2,660 


3,510 


10 ft. 


260 


880 


1,640 


2,450 


3,290 


350 


1,150 


2,100 


3,120 


4,150 


Dry sand. 


Saturated sand. 


100 Ib. per cubic foot 


120 Ib. per cubic foot 


2 ft. 


150 


340 


550 


740 


930 


180 


410 


650 


890 


1,110 


4 ft. 


220 


590 


970 


1,360 


1,750 


270 


710 


1,170 


1,640 


2,100 


6 ft. 


260 


760 


1,320 


1,890 


2,480 


310 


910 


1,590 


2,270 


2,970 


8 ft. 


280 


890 


1,590 


2,350 


3,100 


340 


,070 


1,910 


2,820 


3,720 


10 ft. 


290 


980 


1,820 


2,720 


3,650 


350 


,180 


2,180 


3,260 


4,380 


12 ft. 


300 


1,040 


2,000 


3,050 


4,150 


360 


,250 


2,400 


3,650 


4,980 


14 ft. 


300 


1,090 


2,140 


3,320 


4,580 


360 


,310 


2,570 


3,990 


5,490 


16 ft. 


300 


1,130 


2,260 


3,550 


4,950 


360 


,350 


2,710 


4,260 


5,940 


18 ft. 


300 


1,150 


2,350 


3,740 


5,280 


360 


,380 


2,820 


4,490 


6,330 


20 ft. 


300 


1,170 


2,420 


3,920 


5,550 


360 


,400 


2,910 


4,700 


6,660 


22 ft. 


300 


1,180 


2,480 


4,060 


5,800 


360 


,420 


2,980 


4,880 


6,960 


24 ft. 


300 


1,190 


2,540 


4,180 


6,030 


360 


,430 


3,050 


5,010 


7,230 


26 ft. 


300 


1,200 


2,570 


4,290 


6,210 


360 


1,440 


3,090 


5,150 


7,460 


28 ft. 


300 


1,200 


2,600 


4,370 


6,390 


360 


1,440 


3,120 


5,240 


7,670 


30 ft. 


300 


1,200 


2,630 


4,450 


6,530 


360 


1,440 


3,150 


5,340 


7,830 


Infinity 


300 


1,210 


2,730 


4,850 


7,580 


360 


1,450 


3,270 


5,820 


9,090 


Partly compacted damp yellow clay. 
100 Ib. per cubic foot 


Saturated yellow clay. 
130 Ib. per cubic foot 


2 ft. 


160 


350 


550 


750 


930 


210 


470 


730 


1,000 


1,240 


4 ft. 


250 


620 


1,010 


1,400 


1,800 


340 


840 


1,330 


1,870 


2,370 


6 ft. 


300 


830 


1,400 


1,990 


2,580 


430 


1,140 


1,900 


2,630 


3,410 


8 ft. 


330 


990 


1,720 


2,500 


3,250 


490 


1,380 


2,360 


3,360 


4,400 


10 ft. 


350 


,110 


2,000 


2,920 


3,880 


520 


1,570 


2,760 


3,980 


5,270 


12 ft. 


360 


,200 


2,220 


3,320 


4,450 


540 


1,730 


3,100 


4,560 


6,050 


14 ft. 


370 


,280 


2,410 


3,650 


4,950 


560 


1,850 


3,410 


5,050 


6,760 


16 ft. 


370 


,330 


2,570 


3,950 


5,400 


570 


1,940 


3,660 


5,510 


7,440 


18 ft. 


380 


,380 


2,710 


4,210 


5,810 


570 


2,020 


3,880 


5,930 


8,060 


20 ft. 


380 


,410 


2,830 


4,450 


6,180 


580 


2,090 


4,070 


6,280 


8,610 


22 ft. 


380 


,430 


2,920 


4,640 


6,500 


580 


2,140 


4,240 


6,610 


9,130 


24 ft. 


380 


,450 


3,000 


4,820 


6,800 


580 


2,180 


4,380 


6,910 


9,590 


26 ft. 


380 


1,470 


3,060 


4,980 


7,080 


580 


2,210 


4,500 


7,160 


10,010 


28 ft. 


380 


1,480 


3,120 


5,100 


7,310 


580 


2,240 


4,610 


7,380 


10,430 


30 ft. 


380 


1,490 


3,170 


5,230 


7,530 


580 


2,260 


4,700 


7,590 


10,780 


Infinity 


380 


1,520 


3,410 


6,060 


9,480 


580 


2,340 


5,270 


9,360 


14,620 



Page 46, Bulletin No. 31, Engineering Experiment Station, Ames, Iowa, 



68 CONSTRUCTION OF ROADS AND PAVEMENTS 

ditch and not the diameter or span of the culvert is to be used in 
taking the load from the table. 

When a culvert is constructed in the open and then covered by 
a fill deposited in the usual manner as would be the case when a 
trestle is replaced by a fill, or when a truss bridge is replaced by 
a box culvert and fill, the load on the culvert is considerably 
greater than given in Table 2. No authentic data are as yet 
available to show exactly what the dead load on the culvert will 
be in these cases, but for fills up to 20 ft. in height, the following 
is a fair approximation. First determine the load on the culvert 
assuming B in Table 2 to be the outside diameter or the total 
breadth of the culvert, then multiply this quantity by 1^. This 
will give values slightly too high for shallow fills and slightly too 
low for deep fills, based on what now seems to be the probable 
actual load in such cases. 

The proportion of the weight of traffic units that is carried to 
culverts through fills of varying depths depends upon many 
factors, such as the character of the filling material, the condition 
of the fill as regards water content, the extent to which it is 
compacted and the manner of the application of the load. This 
subject has been and still is a matter of investigation, and no 
conclusive data are available. Designs based on the following 
assumptions have proven adequate, but eventually a more 
rational distribution will be deduced. 

The percentage of the live load carried to the culvert may be 
assumed to vary from 100 per cent, for fills of 1 ft. to zero for fills 
of 10 ft. This refers to the portion of the weight on one wheel 
or the roll of a power roller. Estimate the dead load (weight of 
fill) from Table 2 and add to the dead load in pounds per foot of 
length of culvert the proper percentage of actual live load per 
foot of length and assume this to be uniformly distributed over 
the 1 foot length of culvert. This applies to culverts built in 
trenches. For culverts over which fills are built, estimate the 
dead load as provided in the preceeding paragraphs and then 
add the proper percentage of live load. 

This emphasizes the necessity for care in the use of sectional 
pipe, especially under shallow fills. The pipe should be carefully 
bedded and concrete should be employed for bedding except 
on the most stable soil. The joints should be close and should 
be filled with cement mortar. The back filling should be well 
tamped, especially at the sides of the pipe. 



THE DESIGN OF RURAL HIGHWAYS 



69 



Pipe culverts are preferably provided with adequate head 
walls, to retain the fill and to prevent under-cutting or other 
harmful erosion. The head walls should extend at least 2 ft. 
below the barrel of the culvert, and the top should be 1 ft. to 
18 in. above the top of the barrel. The wings to the head wall 
are designed to fit the slope of the fill, assuming a slope of 2 on 1. 




Pipe 
Size 


A 


B 


C 


D 


Ouemfs. Each End 
/-2^-SConcrete 


/5tol8 


2-i 


1-3 


3^6 


6'j" 


.93CuYds 


ZO'to?? 


? : 6 


<4-l 


j^; 


6-y 


U3 - - 


24" 


Mo 


4-6 


4'0 


7-3" 


1.44 


JO' 


3-4 


s'-o 


4 '6 


7-11 


174 - 


36' 


3'- 


s-s 


'-0 


8 : 7' 


^07 - - 



P,pe 
Size 


A 


B 


c 


D 


t 


QuantS /-2j-f Concrete 


/nlef 


Outlet 


/S'fo/8 


?'/' 


/' 


J" 


2-1' 


stf 


.fOGutob 


/.ISCuYc/* 


?0to2?' 


Ik 


// 


^ 


?-? 


n:'' 


/./S - - 


/.S/ - - 


?4" 


2/0 


3 


4 


1-3 


6-10 


1.47 - - 


IS6 - " 


30' 


3-4 


3 


2 


?-4 


8'4 


ISf' - 


241 - - 


36" 


3'-/O 


r 


(' 


2-5 


v3 


24S- * 


300 ' 



End Views of Typical Headwalls 
H- As Shown on Plan 
Length of 'Wall- 2 x Difference Between Elevation of Slope 
over End of Pipe and Elevation of Bottom of Pipe 
No Wall to be L ess than & Ft Lona 



-j-J T Top of Wall to be Para tie/ to F/n/shetf 
Grade and Cen ter / me, and not Lest 
than O.SFt Above Finished Grade 
Ends of Pipe to Suit Surrounding Conditions 




-I"/- 

>j/?|f-- & ",n * (*-- 

<_JMU ,i_tz5_ 

I qjijjl. 

^1 




End View 



FIG. 11. Plans for pipe culverts. 

Figure 11 shows some designs of pipe culverts and head walls, 
and Fig. 12 shows some views of completed culverts. 

Paved Fords. In many locations, particularly in prairie country, 
the streams are shallow and broad and have an insignificant 
flow except in flood seasons, when they may carry a large volume 
of water flowing in a comparatively thin sheet of considerable 
width. The cost of bridges or culverts of sufficient capacity for 
the flood flow is entirely out of proportion to the utility of such 



70 CONSTRUCTION OF ROADS AND PAVEMENTS 




FIG. 12. Views of completed culverts. 



THE DESIGN OF RURAL HIGHWAYS 71 

structures. An economical solution of this problem consists in 
constructing a paved ford across the flood water channel of the 
stream, with a few concrete posts to serve as markers for the edge 
of the pavement if it is long or obscured. If there is constant flow 
a culvert under the ford can be constructed to care for the ordinary 
flow. If the stream is a dry run, except for a few weeks a year, 
no culvert is needed. 

CROSS-SECTIONS 

For convenience in discussion, the cross-section of the road 
may be considered as made up of three parts: the traveled way; 
the ditch ; and the back slope and berm. 

Traveled Way. The traveled way, as its name indicates, is 
that portion of the roadway that is used by traffic. It should 
have a shape that will insure its being well drained, that is, it 
should be well rounded up or "crowned." 

The comfort and safety of those who travel must also be 
considered in designing the cross-section. 

If the cross-slope of the traveled way is excessive, it will be 
uncomfortable to travel, and, when wet and consequently slip- 
pery, it will be dangerous as well. The exact amount of cross- 
slope that may be used is a matter that has been determined by 
experience, and it is believed that an average of 1 in. per foot of 
width is about the maximum that is permissible. For con- 
venience in construction, the shape of the traveled way may be 
an arc of a circle or a parabola. It has frequently been said 
that the cross-slope should be greater on hills than in level 
country, the argument being that if the cross-slope is not made 
greater, storm water will have a tendency to follow the wheel 
tracks down the hill rather than run crosswise to the side ditches. 
While there is reason to this argument, still, from the standpoint 
of comfort and safety, it is undesirable to have any greater 
cross-slope on hillsides than in level country. The tendency to 
slide is greater on hillsides than in level country, and the results 
of skidding or sliding to the ditch are much more aggravating. 
For that reason, it is believed to be undesirable to use a much 
greater cross-slope on hillsides than is used in level country. 

If there is any probability that the earth road may at some 
future time be surfaced with some hard material, then the shape 
of the traveled way should be such as to render it easily con- 
vertible for the hard-road cross-section. If it is so designed that 



72 CONSTRUCTION OF ROADS AND PAVEMENTS 

when the hard surface is built, the only necessary earth work 
will be that which is done in flattening the cross-slope to an 
amount which is desirable for the hard surface, the most eco- 
nomical design has been adopted. 

The width of the traveled way is also a matter which deserves 
consideration. If the traffic consists of a few vehicles daily, 
then a comparatively narrow roadway is all that is necessary, 
but, if the road is subjected to mixed traffic some of which moves 
at relatively high speed, which is the common condition en- 



Oross Section For Earth Road 

For Roads on a Grade of 8j or lees 
-24-0-" 




5 Min. Depth . 
Longitudinal Tile Drain . 

Cross Section For Earth Road 

Por Roads on a Grade of 2 g le;s than 4 J 



Concrete Gutter 
M ,Widt: 




'X "Granolithic I 

5 & "Concrete - 

Rubble Gutter 

4'Minimum 




Cross Section For Earth Road 
For Roads on a Grade of i^or More 





TEoidal Gutter longitudinal Tile.Drain 



FIG. 13. Cross sections for earth roads. 



countered on most main traveled highways, then the section 
should be wide enough to accommodate readily this mixed 
traffic, and it is believed that 24 ft. is a minimum width, although 
on some secondary roads a width of 20 ft. might be used. Un- 
doubtedly other cases are encountered where the traffic is 
sufficient in amount to necessitate a width greater than 24 ft. 

Ditches. The portion of the road outside of the traveled way 
is utilized for ditches and the berms along fences. The ditch 
should be of ample capacity, and, if it is assumed that all sur- 
face water is carried in these ditches, the size or capacity neces- 



THE DESIGN OF RURAL HIGHWAYS 73 

sarily will vary with the slope. This should never be less than 
1/10 per cent, if the water is to flow away before it injures the 
road. As the slope of the ditch increases, its depth may be 
decreased. It is not convenient in road work to change the 
size of the ditch constantly, and, consequently, two or three 
sections are usually adopted which will fit a variety of conditions. 
Fig. 13 shows sections that may be used on various grades. 

It is important that the slope from the shoulder to the ditch 
should be flat enough to permit a vehicle to run to the bottom of 
the ditch in case of accident without danger of over-turning, and 
this is possible on a slope of 2J/ on 1. The slope of the back of 
the ditch may be whatever the natural soil will stand, but should 
be uniform. It will usually be about 1^ on 1. The ditch may 
have the V section, or may have the trapezoidal section. The 
former is the easier to build, but the latter has greater capacity. 

The Berm. The portion of the road between the ditch and 
the fence or property line will vary in width, being least where 
cuts have been made. The only necessary requirement is that 
it be sufficient to obviate the possibility of endangering the 
stability of the fences. As a rule this space is an unkept weed 
or brush patch on the road, but eventually it will be made use 
of in some manner. Probably on a great many roads it will be 
planted to useful trees and shrubs or be given over to ornamental 
plants and trees. 

GRADES FOR EARTH ROADS 

In discussing the principles of selecting grades for earth roads 
the fact that the road may be surfaced at some future time must 
be taken into account. It cannot be foretold what class of hard 
surface will be used in many cases, but usually it is possible to 
determine about the character of the surface from the classes of 
material available. For convenience in .discussing the various 
grades, such terms as maximum grade, average grade, and ruling 
grade are often used. These terms have no exact or generally 
accepted meaning, and merely serve to facilitate discussing the 
various conditions encountered. 

Maximum Grade. The maximum permissible grade is that 
which can be allowed without making it necessary to reduce the 
ordinary size of load hauled over the road. It is well known that 
a team can increase its pulling power for short periods of time 



74 CONSTRUCTION OF ROADS, AND PAVEMENTS 

to two or three times that which it would be expected to exert 
continuously. 

Theoretically, the increased pull required on grades is 20 Ib. 
per ton for each per cent, increase in grade, and this has been 
proven by experiment to be true in practice. If, then, a team 
is loaded with the amount it can haul readily on level road, 
having a surface offering a resistance of 100 Ib. per ton, and it 
is assumed that the team can for a short time double its pull, it 
would be possible to haul the load up a 5 per cent, grade. For 
earth roads, in good condition, the tractive resistance will be 
about 106 Ib. per ton, and if the hauling is done entirely on 
earth roads, the maximum grade could be about 6 per cent, with- 
out necessitating a reduction in the size of the load. If the hill 
is surfaced as with a material offering a tractive resistance of 60 
Ib. per ton, the capacity of the team would be increased so that 
the maximum grade could be 8 per cent. As a matter of fact, 
grades of 8 per cent, and 10 per cent, are not infrequently en- 
countered on earth roads, and do not necessitate reducing the 
size of loads hauled. 

If the entire road is to be surfaced at some later time with 
material offering a tractive resistance of 60 Ib. per ton, and it 
is assumed as before that the team can double its pulling power 
for short periods of time, then the ideal maximum grade would 
be 3 per cent. 

As a matter of practice, many highway engineers take 6 per 
cent, as the maximum grade to be obtained, permitting steeper 
grades only when topographical conditions necessitate. 

Ruling or Average Grades. In determining grades on long 
sections of road in rolling country, there will be many hills 
below the maximum adopted which may easily be reduced. Ob- 
viously it is uneconomical to spend money to reduce a grade on 
one hill from 3 per cent, to 2J/ per cent, when near it is another 
hill that cannot economically be reduced below 3 per cent. It is 
customary to select some ruling grade for all hills below the maxi- 
mum grade, except, of course, those already below the ruling 
grade selected. There is no rule by which this average grade 
can be determined, but when the maximum is 6 per cent, the 
ruling grade is usually selected at about the grade where erosion 
becomes a factor in the maintenance of the ditches. 

Minimum Grades. An earth road or any kind of surfaced 
road may have a level profile, the ditches being sloped for drain- 



THE DESIGN OF RURAL HIGHWAYS 75 

age. The cross-slope insures drainage for the surface of the 
road. 

Undulating Roads. When roads are in rolling country, many 
slight grades are encountered, and, as a general rule, no economy 
results from removing or reducing them. Experiments have 
shown that the travel downhill compensates for the travel uphill, 
so long as the grade is below that at which the vehicle would 
coast. On earth roads, then, if no grade of over 5 per cent, 
exists, the travel downhill will compensate for the travel uphill, 
and the average tractive effort for a round trip will be no greater 
than on a level road. 

Safety Considerations. Steep grades, sharp curves and knolls 
that obstruct the view ahead should be avoided in the interest 
of safety. There should always be a clear view ahead for at 
least 250 ft. and if a curve exists on a hill, the grade should be 
flattened around the curve if possible so as to permit a quick 
stop in case of emergency. 

Balancing Quantities. The amount of material removed in 
excavation should all be used in the fills, that is, the grade line 
should "balance." It is well known that most soils removed in 
excavation will occupy less room in embankment after settle- 
ment. The amount of this shrinkage depends upon the kind 
and condition of soil, the method of placing, and the depth of the 
fill. For fills under 2 ft. in depth, 20 per cent, is about an average 
allowance for shrinkage. For fills over 2 ft. in depth the allow- 
ance may be reduced to 15 per cent. Instances have been 
encountered where the shrinkage amounted to as much as 30 per 
cent, in fills less than 6 ft. deep. 

Fills constructed of rock do not settle and instead of there being 
a shrinkage in the volume of the excavated rock there is an increase 
in volume when the material is placed in the fill. This is due to 
the fact that loosely piled fragments of rock will contain from 30 
to 50 per cent, of air voids. These may be partly or entirely filled 
with earth as the fill is constructed, but the actual volume of the 
stone in the fill will be about 1J^ times that of the ledge from 
which the rock was blasted. 



CHAPTER V 

THE CONSTRUCTION AND MAINTENANCE OF 
EARTH ROADS 

GRADE REDUCTION 

. When in accordance with the principles of design already 
discussed it becomes desirable to reduce the grade on a section 
of road, certain preliminary work should first be completed. 
If there are weeds, brush or trees on the portion of the road to be 
graded, these should be cut away or grubbed out and the 
resulting debris burned. It is especially undesirable to leave 
organic matter under a fill because it will decay and cause unequal 
settlement. It may also cause under-cutting from water that 
works under the fill where it is porous from the decay of organic 
matter. 

If fills are made on side hills where the cross-slope is steeper 
than 4 on 1, provision should be made to insure a bond between 
the new fill and the old ground. If the existing soil is porous 
and the slope does not exceed 3 on 1, this can be accomplished 
by plowing a series of furrows about a foot apart parallel to the 
center line of the fill. For dense soils or slopes greater than 3 
on 1, the area to be covered by the fill should be graded to a 
series of horizontal benches about 4 ft. wide. After this prep- 
aration is completed the fill may be placed in a series of horizontal 
layers not over 2 ft. thick. 

When the fill is constructed on a road that has a cross-slope 
flatter than 4 on 1, the new material may be placed without 
special preparation of the site except to remove the vegetable 
matter. For fills of this class it is undoubtedly advantageous 
to place the fill material in layers not exceeding 2 ft. in thick- 
ness. The teams and scrapers will compact the material as they 
travel over it, and the fill that is built up will not settle exces- 
sively. Some engineers require that each layer shall be rolled 
before the succeeding layer is placed, but it is doubtful if there is 
enough benefit obtained from the rolling to compensate for the 
cost. If fills less than about 2 or 3 ft. in height are to be con- 

76 



CONSTRUCTION OF EARTH ROADS 77 

structed and a hard surface of some kind is to be built 
immediately, it is probably advisable to place the fill in layers of 
6 or 8 in. and roll each thoroughly. This does not apply to earth- 
road building, however. 

In general, it may be said that satisfactory practice for earth 
roads is to permit the fill to be placed without restrictions as to the 
thickness of the layers, and without rolling. Suitable provision 
must be made in any case for possible shrinkage. 

Side Slope in Cuts. The side of cuts should be trimmed to 
a slope suitable to the soil. Some soils will stand on a much 
steeper slope than others, and the side slope of the cut should 
be as nearly as possible that at which the soil will stand without 
sliding. For loam, 1% on 1 will generally prove satisfactory. 




FIG. 14. The elevating grader drawn by mules. 

For most of the clays the slope may be 1 on 1, and for some 
peculiar soils, such as loess, the sides of cuts will stand better if 
vertical than if they are on a slope. For the sake of appear- 
ances, the side slopes are neatly hand-trimmed to the slope that 
has been determined upon. 

Side Slopes for Fills. Since the fill material is of necessity 
loose when placed, the side slopes will shape themselves to the 
angle of repose of the material in the condition in which it is 
deposited. This slope will invariably flatten out as the fill 
settles, and as the material becomes saturated with water. 
It is good practice to employ a side slope of 2 on 1 for fills, but 
here again some variation is permissible if the soil exhibits special 



78 CONSTRUCTION OF ROADS AND PAVEMENTS 

or peculiar characteristics. The side slopes should be neatly 
shaped so as to present a good appearance, and the filling should 
be carried out against head walls and abutments to the final 
slope desired. 

Protection of Slopes. A considerable amount of maintenance 
work on side slopes is obviated if they are seeded with some sort 
of hardy grass having strong roots. There is some type of 




FIG. 15. Blade grader outfits for earth road construction. 

grass suitable for this purpose that can be grown successfully in 
each locality, and the species best adapted to the locality can be 
ascertained. For the Middle West, Hungarian Brome grass is 
best for slopes facing the north, east or west, but western wheat 
grass is better for slopes facing the south. 

Overhaul. The price for grading is commonly based on a 
specified length of haul, and if any part of the material is hauled a 
greater distance, the excess haul is known as " overhaul" and is 



CONSTRUCTION OF EARTH ROADS 79 

paid for at a higher rate than that for earth which is moved only 
the specified distance or less. The proper length of the "free 
haul/' as it is called, i.e., the length of haul for the contract 
price, has been the subject of considerable discussion, most of 
which has reached no definite conclusion. Undoubtedly overhaul 
provisions are desirable when a part of the fill material or extra 
excavated material must be moved appreciably further than 
the remainder and large portion of the material. When such a 
condition exists, the average haul for the larger portion of the 
excavation can be used as a basis for payment, with an overhaul 
provision to take care of the balance. 




FIG. 16. The leveler employed for earth road construction. 

If, on the other hand, the excavated material will all move 
substantially the same distance, no matter what that distance 
is, no overhaul provision is necessary. 

It is, therefore, undesirable to fix any free-haul limit for 
general application. If material moves less than 500 ft., there 
would usually be no overhaul provision, and, on the contrary, 
the free-haul distance may be as great as 2,000 ft. 

Shrinkage. Most earth will, when deposited, finally compact 
into a smaller space than it occupied before being excavated, and 
fills will generally settle slowly for some months after they are 
placed. The amount of shrinkage will depend upon the moisture 
content of the earth during and immediately after it is moved, 
the manner in which it is moved, the depth of the fill, and the 
character of the soil. Shallow fills compact more than deep ones, 
wet soil more than dry, and porous soil compacts more than 
dense soil. If the material is handled in small units, it will shrink 



80 CONSTRUCTION OF ROADS AND PAVEMENTS 

less after the fill is completed than if it were handled in large 
units. That is, slip-scraper work will shrink less than work 
handled by a 2-yd. dump car. 






FIG. 17. Properly constructed and maintained earth roads. 



No reliable general rule for shrinkage can be laid down that 
will fit all conditions, and the shrinkage for moderate or heavy 



CONSTRUCTION OF EARTH ROADS 81 

fills is best estimated after an examination of the material to be 
moved. The shrinkage will seldom be less than 10 per cent, 
(although there may be none at all in rare cases) and not often 
more than 30 per cent. For approximate estimates of shrinkage 
15 per cent, may be used for fills over 2 ft. deep, and 20 per cent, 
for fills less than 2 ft. deep. 

Computing Quantities. Payment for grading is ordinarily 
based on measurement in excavation, the quantities being 
computed by the average end area method. This applies to 
borrow excavation as well as to excavation of roadway. In 
exceptional cases payment is made on a basis of quantities in 
embankments. This is a desirable method where the material 
for filling must be obtained from scattered borrow pits, or from 
borrow pits that are very irregular and, therefore, difficult to 
measure. In determining overhaul, the following method is 
satisfactory, and is believed to be equitable: Determine the 
distance between the center of mass of the material to be 
excavated and the center of mass of the fill. Subtract from this 
the free-haul distance. Multiply the distance in feet thus ob- 
tained by the total quantity of excavation in cubic yards, and 
the result is the cubic yards-feet of overhaul. This can readily 
be reduced to the proper unit for payment. A typical case 
would be where payment for overhaul is to be at the rate of J^ ct. 
per cubic yard for each 100 ft. of overhaul. The cubic yards- 
feet of overhaul would be divided by 100 and multiplied by 
$0.005 to obtain the overhaul allowance. 

Methods of Grading. Many kinds of equipment are used 
for grade-reduction work in highway construction just as is true 
of any other kind of grading. Each has its particular field of 
usefulness. 

Steam -shovel Excavation. Where heavy grading is being 
done so that an outfit can be used continuously for a long time 
without frequent costly moves, the steam shovel is economical. 
A standard railroad outfit would be employed for very heavy 
work, and the materials would be handled in dump cars on the 
industrial railway. For lighter work the traction type of shovel 
would be more satisfactory, and the earth would be hauled 
in horse-drawn dump wagons. 

Elevating Grader and Dump Wagons. If the cuts are rela- 
tively shallow, the elevating grader would be utilized for loading 
the dump wagons. 



82 CONSTRUCTION OF ROADS AND PAVEMENTS 



Wheel or Fresno Scrapers. If the excavation is light and 
outfits must move frequently, the wheel or Fresno scraper may 
be used. If the topography is unsuited for the elevating grader, 
the wheel or Fresno scrapers would also be most economical. 

Costs. The cost of moving earth for a free' haul not exceeding 
500 ft. will vary from 17 cts. to 25 cts. per cubic yard in prairie 
country, and from 20 cts. to 50 cts. per cubic yard in rough 
country with heavy soils, depending, as would be expected, on 
a variety of conditions. 




FIG. 18. The steam shovel employed for highway construction. 



RESHAPING AND LIGHT GRADE REDUCTION 

Elevating Grader Work. If a road is designed in accordance 
with the principles already set forth, particularly as regards cross- 
section, the elevating grader can be used to good advantage in 
the construction. 

In general, the work to be done consists in rounding up the 
traveled portions of the road with material obtained from the 
side ditches. The best results will be obtained with this outfit 
in flat country or slightly rolling country where sections a mile 



CONSTRUCTION OF EARTH ROADS 83 

or more in length can be constructed at one time, thus obviating 
frequent turning of the outfit. 

Before the grading is started, the portion of the right-of-way 
upon which work is to be done should be cleared of grass, weeds, 
and brush. This may be accomplished by cutting off the growth 
and raking it into piles and burning. When only a small amount 
of growth exists, it is sometimes cut off with the blade grader 
and pushed off the portion of the road upon which work is to be 
done. 

Classes of Road Work for Elevating Grader. There are the 
three following classes of roads encountered where the elevating 
grader has proven satisfactory: 

1. Roads practically level where the new grade line is parallel 
to the profile on the old road, there being only a few knolls to 
be removed. 

2. Roads on which there are a succession of knolls and conse- 
quently a succession of cuts and fills, most of which do not 
exceed about 2 ft. in depth. 

3. Roads where extensive grade-reduction work must be done. 

Grader Outfits. The outfit necessary for roads of class 1 con- 
sists of the elevating grader drawn by six or eight teams or by a 
tractor, a blade grader, a few slips or wheelers, a heavy disc 
harrow, a heavy straight-tooth harrow, and a split-log or plank 
drag. If a roller is also available a better road can be con- 
structed than is possible without it. For roads of class 2, a 
number of dump wagons are also necessary. 

Construction Methods. In starting the construction, the 
first cut is taken at the shoulder line, and the material thus re- 
moved is deposited near the shoulder line of the opposite side 
of the road, but in the roadway. 

Stakes are set for the first cut so that the driver can follow them 
conveniently. If the outfit is horse-drawn, the stakes are set 
so that the tongue of the elevating grader will follow them. If 
the grader is drawn by a tractor, the stakes are set so that the 
front wheel on the steering side will follow them. The exact 
distance of these stakes from the line of the cut will vary some- 
what with the type of elevating grader used and must be 
determined before the stakes are set. 

The first cut is a light one and usually one horse of the lead 
team follows this first furrow and thereby guides the grader 
in making the succeeding cut. If the grader is drawn by a 



84 CONSTRUCTION OF ROADS AND PAVEMENTS 

tractor, a side hitch is used so that the tractor will travel on 
the "land" side. 

On roads of class 1, the successive rounds of the elevating grader 
are made without reference to the slight knolls that occur ; and the 
material deposited on the roadway on top of the knolls is hauled 
away by slips or wheelers while the elevating grader is com- 
pleting its round. A suitable adjustment of the working forces 
can be made so that the slips or wheelers can keep up with the 
grader. 

On roads of class 2, teams with dump wagons follow the ele- 
vating grader, loading where cuts are to be made and dumping 
the materials in the fills, the elevating grader continuing its 
rounds and depositing directly on the road in the low places. 
Here again a suitable adjustment of working forces must be made 
so that the elevating grader will not have to wait for the wagons. 
It is more economical to construct a mile or more of road at a 
time than it is to turn the elevating grader constantly, as would 
be necessary if each cut were completed by itself. 

As the elevating grader makes successive rounds it gets farther 
away from the center of the road, and, consequently, when it 
is at the deepest part of the ditch where the heaviest cutting is 
being done, the earth is deposited in the middle of the road, 
where the greatest filling is necessary to give the crown. 

The material deposited on the roadway will consist of many 
large lumps as well as of sods and fine material. To work this 
material down to a surface that can be traveled, the clods and 
sods must be broken up with a disk harrow until small enough 
to form a satisfactory surface. Often the sods and weeds are 
collected by harrowing with a stiff-tooth harrow and thrown out 
with pitchforks. 

To bring the surface to its final shape a few rounds must be 
made with a blade grader. Then, after the first rain, the surface 
is smoothed with a road drag, and, when partially dry, rolled. 
Constant dragging is necessary during the first year to keep the 
road in shape, while it is becoming compacted by traffic. 

Cost Data. The cost of constructing earth roads by this 
method varies from about $100 per mile for class 1 roads, to 
$250 per mile for class 2. As an average of the work done by a 
well-organized outfit, $150 per mile may be taken. 

The cost of the elevating grader outfit is from $4,000 to 
$5,000, depending upon its size and the number of accessories 



CONSTRUCTION OF EARTH ROADS 85 

used. To secure economical construction requires experienced 
supervision and proper working conditions, but when these are 
had, the use of the elevating grader is one of the most econom- 
ical methods of earth-road construction. In general, it is not 
suitable for any unit smaller than a county, because of the cost 
of the outfit and the mileage of work that must be done yearly 
to make it pay. 

Blade -grader Work. When the blade grader is used for 
shaping the cross-section, it is necessary to complete all grade- 
reduction work before beginning the shaping. The grade- 
reduction work is commonly performed with the wheel scraper, 
Fresno scraper, or with the elevating grader as described in the 
preceding section. The latter is not common, however, because, 
if the elevating grader is available at all, it is generally employed 
to the exclusion of the blade grader. 

Having brought the road to the adopted profile, the blade 
grader is used to shape the cross-section. The first cut is made 
near the shoulder line and succeeding cuts farther out in the 
ditch, and the material thus excavated is dragged to the middle 
portion of the road and used to round up the roadway. Two 
graders, hitched together, are sometimes drawn by one tractor, 
thus increasing the speed with which the work can be completed. 

The road is finally smoothed with the drag and is maintained 
by frequent dragging until thoroughly compacted, and later by 
less frequent dragging. 

The cost of work done with the blade grader does not differ 
greatly from the cost of similar work done with the elevating 
grader, but the blade grader is not adapted to as many conditions 
as the elevating grader is. 

The blade-grader outfits, consisting of a tractor and a heavy 
grader, cost from $3,000 to $3,500. 

METHODS OF MAINTENANCE 

The maintenance of the earth road must be carried on through- 
out the year, because, in the very nature of the case, it is a class of 
road that will deteriorate steadily and rapidly otherwise. 

The principal part of the maintenance work will be most 
readily accomplished by means of the split-log or some similar 
form of drag. Fig. 19 shows some satisfactory types of drag. 
In addition, some blade-grader work will be needed and there 



86 CONSTRUCTION OF ROADS AND PAVEMENTS 

will be some miscellaneous work such as cleaning out culverts, 
cutting weeds, and general shaping of ditches and the slopes of 
cuts and fills. 

Use of the Drag. 1 The successful operation of a drag involves 
two principles, which, when thoroughly understood and in- 
telligently applied, make road working with this implement very 
simple. The first concerns the length and position of the hitch, 
while the second deals with the position of the driver on the 
drag. Each influences the other to a large extent, and suc- 
cessful manipulation of the drag is dependent upon an under- 
standing of both of them. 

For ordinary purposes the clevis should be fastened far enough 
toward the blade end of the chain to force the unloaded drag to 
follow the team at an angle of 45. This will cause the earth to 
move along the face of the drag smoothly and will give com- 
paratively light draft to the team, provided the driver rides in 
the line of draft. Sometimes, however, conditions are met which 
require special treatment, and in a rolling country such conditions 
are not infrequent. Often a flat place several rods in length, or 
a seepy spot, needs special attention. 

The distance from the drag at which the team is hitched 
affects the depth of the cutting. Shortening the chain tends to 
lift the front slab from the ground; a longer hitch causes the 
blade to cut more deeply. The length of hitch may be regulated 
by lengthening and shortening the chain at the end which runs 
through the hole in the blade end of the drag. 

If small weeds are to be cut or a furrow of earth is to be moved, 
the doubletree should be attached rather close to the ditch end 
of the drag. The drag will now move nearly ditch end foremost, 
and the driver should stand with one foot on the extreme forward 
end of the front slab. This will swing the drag back to the 
proper angle and will cause the blade to plow. This hitch re- 
quires slow and careful driving in order to prevent the drag from 
tipping forward. If the blade should plow too deeply, as it 
may do in a wet spot, the driver should shift his weight toward 
the back slab. 

If straw and weeds clog the blade, they can usually be removed 
if the driver shifts his weight to a point as far as possible from 
the ditch or blade end. Similarly, if he steps quickly away 

1 Abstract from Bulletin No. 597, U. S. Department of Agriculture. 



CONSTRUCTION OF EARTH ROADS 87 

from the ditch end, the load of earth may be dropped into a low 
place or mudhole. 

Usually two horses are enough to pull a drag over an ordinary 
earth road. When four horses are used, they should be hitched 
to the drag by means of a four-horse evener. The team should 
be driven with one horse on either side of the right-hand wheel 
track or rut, the full length of the portion to be dragged, and the 
return made over the other half of the roadway. 

The object of such treatment is to move the earth toward the 
center of the roadway and to raise it gradually above the surface 
level. While this is being accomplished, all mudholes and ruts 
will be filled into which traffic will pack the fresh earth. 

When to Use a Drag. The drag does the best work when the 
soil is moist, but not sticky. The earth then moves freely along 
the faces of the slabs. If the roadway is very badly rutted and 
full of holes, it would be well to use the drag once, when the 
ground is slushy. This treatment is particularly applicable 
before a cold spell in winter when it is possible to have a roadway 
freeze smooth. 

A smooth road surface is secured by this method. Clay, 
when mixed with water and thoroughly worked, becomes re- 
markably tough and impervious to water. If compacted in this 
condition it becomes extremely hard. 

Another valuable result of dragging is the reduction of dust, for 
the particles of clay cohere so tenaciously that there is but little 
wear when the surface is smooth. Dust on an earth road is 
due to the breaking up under traffic of the frayed and upturned 
edges or ruts and hoof prints. If the surface is smoothed after 
each rain and the road dries hard and even, no edges are exposed 
to crushing and the only dust which forms is that due to actual 
wear of the road surface. 

There are so many influences at work and conditions are so 
varied in different localities that it is quite impossible to lay 
down a general rule for the number of treatments needed to keep 
a road in good condition. A tough clay or a stiff sandy clay 
will resist the action of wheels and hoofs for a longer period than 
a loam, other things being equal. Certain sections of a road- 
way will require more attention than others because of steep 
grades, exposure to hillside wash, etc. The best guide in meet- 
ing these conditions is the knowledge and experience gained while 
dragging the roadway. 



88 CONSTRUCTION OF ROADS AND PAVEMENTS 

There is one condition, however, in which special treatment 
should be given to a road. Clay hills under persistent dragging 
frequently become too high in the center. To correct this, it is 
best to drag the earth toward the center of the road twice and 
away from it once. 

Use of a Drag on Rocky or Gravelly Roads. In soils full of 
loose stones, or even small boulders, the drag has done good 
service. The loose stones are drawn into a windrow down the 
center of the road while the earth is deposited around the boulders 
in such a way that the surface is leveled. The loose stones in 
the center of the road should, of course, be removed. Where 
there is a large proportion of small stones or gravel, the drag 
will keep down the inequalities in the surface. 

General Maintenance Work. Even when the drag is used 
properly the road will gradually become too flat and the ditches 
will fill up with material carried off the roadway by storm 
water. When this condition reaches the stage where it becomes 
a menace to the drainage, the blade grader is used to draw in the 
material from the ditch and restore the crown to the road. 

The earth and weeds that accumulate at the ends of culverts 
must be removed periodically, and the weeds and grass along 
the fences must be cut once or twice a year. 

Drainage channels and tile will require occasional attention 
to keep them in good working condition. 

Cost of Earth -road Maintenance. Little data bearing on the 
cost of earth-road maintenance has been published, but from 
that which is available, it is believed that the cost of adequate 
earth-road maintenance is from $30 to $50 per mile per year. 

MACHINERY USED FOR EARTH-ROAD WORK 

Picks, Mattocks. These tools are used for grubbing, dressing 
up earth work, and for similar familiar purposes. They are 
used so commonly and are so well known that no comment is 
necessary. 

Shovels, Spades. For moving loose earth or slightly tramped 
material, the ordinary No. 2 shovel is commonly used. It is 
not an economical tool for digging hard earth, and either the 
ordinary flat spade or the solid back tile spade should be used 
for that purpose. 

For handling broken stone, sand, gravel, and similar mate- 



CONSTRUCTION OF EARTH ROADS 89 

rials, the No. 1 ore shovel is used. It is slightly larger than 
the No. 2 shovel, and turns up a little more at the sides and does 
not spill loose material as readily as does the ordinary No. 2 
shovel. Sometimes a small scoop shovel is used for handling 
sand and gravel, and it is satisfactory if the material is loosely 
piled and is on a good surface for shoveling. 

Plows. The plow used in highway construction is subjected 
to very severe service and must be strongly made. It should 
have a long iron-shod beam with a shoe and the width should 
not exceed 10 in. It should be strong enough to stand up when 
drawn by a tractor. 

Rooter Plows. If old gravel roads or roads containing stony 
material or hard-baked earth are to be loosened, the rooter plow 
is the most suitable. It is heavy and often has a cast beam. It 
has a point, sharpened on both ends, for breaking the soil, and can 
be reversed or the working length adjusted. 

Harrows. For breaking up the sods and large lumps of soil 
after a road has been graded, a disc harrow heavily loaded is 
most commonly used, but a stiff-tooth iron harrow may be satis- 
factory if the soil is not too throughly dried out. 

If the harrow is to be used for crushed stone or gravel, then a 
stiff-tooth harrow, having a weight of 10 to 15 Ib. per tooth, is 
best. It should be strongly built and not so large as to require 
more than one team. A harrow about 4 ft. square with a corner 
hitch is well adapted for this work. 

Slip Scrapers. Slip scrapers are suitable for moving rough 
materials, especially earth, if the haul does not exceed about 
100 ft. They are well suited to small work since they require 
no loader other than the driver, and no dumper. The slip scraper 
may be used in connection with an inclined chute for loading 
crushed stone or gravel from a storage pile into wagons. 

Fresno Scrapers. The Fresno scraper is used widely in the 
Pacific Coast States, and, to a less degree, elsewhere for the 
same purposes as the slip scraper. It is more efficient than the 
slip scraper, and is suitable for hauls up to about 500 ft. 

Wheel Scrapers. The wheel scraper is used for general earth- 
moving work where the haul is 200 ft. or more, but is not efficient 
if the haul exceeds about 1,000 ft. It is made in several sizes 
ranging in capacity from about 5 cu. ft. to 16 cu. ft. The larger 
size is preferable on heavy work, as a "snap" team must be em- 
ployed in loading in any case. A loader and a dumper must 



90 CONSTRUCTION OF ROADS AND PAVEMENTS 

always be employed and usually the material to be moved must 
be loosened with a plow before it can be loaded. The common 
practice is to plow two furrows on one side of the cut, then wheel 
them out while two furrows are being plowed at another 
place in the cut. It generally requires one wheeler to each 100 
ft. of haul to keep a crew in continued operation. 

Road Graders. The road grader is the most commonly used 
and best-known machine used for general highway construction 
and needs no description. The later models have many devices 
for convenience in adjusting the cutting blade for various kinds 
of work, and most of them can be steered by the operator so that 
they are not entirely dependent upon the accuracy with which the 
tractor hauling them is steered. It should be noted that these 
machines move earth by sliding it along the surface of the 
road, and it is, therefore, better adapted for light or medium work 
than for construction requiring large amounts of material to be 
moved. 

Elevating Graders. The elevating grader is so arranged that 
a plow loosens the soil and deposits it upon a moving apron which 
in turn deposits it in a wagon or upon the road surface as de- 
sired. The elevating grader is used widely in grade reduction 
work for loading the dump wagons. It is also used in earth road 
construction for crowning up the middle part of the road and for 
general earth-road construction, depending upon size and kind. 

Levelers. In recent years there has been developed a new 
type of machine designed to perform the work of a light grader 
and road drag at one operation. In brief, the leveler consists of 
a truck to which is suspended a pair of long blades which form 
a V lying on the road with open end to the front. The width 
covered at one trip is often as much as 30 ft. and the action of 
the machine is to draw a little material from the sides of the 
road to the middle, smoothing out all depressions as it does so. 
The machine is well adapted for the purpose, but, up to this time, 
it has not been built with blades that can be adjusted to the 
curved cross-section usually specified for earth roads. It also 
has a tendency to leave a ridge of loose material in the middle 
of the road. 

Maney Grader. The Maney grader consists of a gear similar 
to a dump-wagon gear upon which is mounted a scraper very 
much like that used on wheelers, and having a capacity of about 



CONSTRUCTION OF EARTH ROADS 



91 



1 cu. yd. It is used for the same kinds of work as the wheel 
scraper. 

Dump Wagons. A great many types of dump-bottom wagons 
are manufactured, and these are used for handling all sorts of 
road materials. They are very satisfactory for hauling earth 
on grade-reduction work if the haul exceeds about 1,000 ft., and 
are also used in connection with the elevating grader on earth- 
road construction. They may be had in capacities from 1 cu. 
yd. to 5 cu. yd. as desired, but the lJ/- or 2-yd. sizes are best 
adapted for highway construction. 

This type of wagon is commonly used for hauling broken stone, 
sand, gravel, and other similar surfacing materials. 




Split Logor'King'Drag 

FIG. 19. Types of road drag. 



c ) L^D^ or Smoother 



Road Drags. The first drags used were the split-log type de- 
veloped and made a factor in road maintenance by Mr. D. Ward 
King. This type of drag is variously constructed, but, except 
in details, is always much the same. It consists of the two 
halves of a log about 10 in. in diameter, held about 2 ft. apart 
by suitable cross-pieces and is provided with a chain for the hitch. 
The length is from 6 to 9 ft. 

The plank drag is similar in form to the split-log drag except 
that 3 by 12-in. plank are used instead of the halves of logs. It 
is recommended that the front log or plank be shod with a metal 



92 CONSTRUCTION OF ROADS AND PAVEMENTS 

strip for at least half its length, the metal strip extending from 
the end of the log that is run foremost. 

The lapped-plank drag consists of three or four 2-in. planks 
12 in. wide nailed together with the edges overlapping. This 
kind of drag acts more as a smoother than as a drag, but is very 
satisfactory for clay soils. 




o'o- 



2x6 

2"x8"x2' 
-- 50'- - - 

Shod with Iron 
tf x 2" 



FIG. 20. The Minnesota road planer. 

Many steel drags are now offered, and they are built in the 
same general way as the plank drag, except that all parts are of 
metal. Most of them are constructed so that the blades can be 
tilted to any desired angle. 

A new type of drag known as the Minnesota road planer has 
been devised by Mr. Geo. W. Cooley, State Engineer of Min- 
nesota, which has features that give promise of great usefulness 
for the planer. It is shown in Fig. 20. 



CHAPTER VI 
SAND-CLAY ROADS 

The name sand-clay is given to a type of road surface that con- 
sists of natural or artificial mixtures of sand and clay, loam or 
gypsum, or of all of these materials. Such surfaces are con- 
structed on clay, loam or gumbo soils and on deep sand. The 
character of the sand and of the soils encountered varies so 
greatly that it is impossible to lay down specific rules and pro- 
portions for the construction that will have universal application. 
Surprising results are often obtained with most unpromising 
materials and under unscientific methods of construction, yet in 
general the best results are obtained when a few well-established 
principles are observed. The methods of construction and the 
combinations of materials that have been most successful and 
the principles involved may profitably be studied. 

The essential requirements for success are that the materials 
be reasonably suitable in character, and that they be thoroughly 
mixed. The aim is to secure on the surface of the road a layer 
or crust which is made up of sand into which has been introduced 
a binder of clay, loam, or gypsum and clay. The amount of this 
binder needed is approximately that which will fill the voids in 
the sand, and as a rule the more nearly that amount is used, the 
better the results will be. Lumps of clay or other binder are to 
be avoided and thorough and persistent mixing is, therefore, 
imperative. If natural mixtures of sand and clay are used, these 
will rarely be uniform, and after they are spread on the road 
they must be mixed to secure a homogeneous layer. 

TYPES OF SOILS 

Gumbo. This soil is the familiar black or yellow waxy soil 
found in widely scattered localities throughout the United 
States. It is exceedingly fine-grained, dense, sticky and when 
wet rolls up on the wheels of vehicles until they become solid 
balls of mud. It is broadly classed as a clayey soil. 

Slaking Clay. This type of clay is found mixed with a varying 
percentage of sand, is somewhat coarse-grained and becomes soft 



94 CONSTRUCTION OF ROADS AND PAVEMENTS 

and mushy when wet. It is a yellow to reddish color and of 
varying degrees of stickiness. Since it is not uniformly sticky 
and is unstable when wet, it is not the best material to use on 
a deep sand soil, but where it is the only material available, it is 
used with more or less satisfactory results. 

Semi-plastic Clay. This material is of a gray, yellow, or 
reddish color, of fine texture, tough, dense, and in physical char- 
acteristics resembles gumbo. Since it is sticky and fairly stable 
when wet, it is a good binder for a sand road, but on account of 
its physical characteristics it is more difficult to handle than the 
slaking clay. 

Sand -clay Soils. In some localities there is found a soil which 
consists of a natural mixture of sand and one of the types of clay, 
proportioned about right for road surfacing. If deficient either 
in sand or clay, the mixture can be adjusted during the con- 
struction by the addition of the material that is lacking. The 
soil is rarely uniform in composition, and usually must be mixed 
on the road to secure a homogeneous surface layer. 

Loam. Loam is a brown or black, porous, coarse-grained soil 
containing varying percentages of sand. It is not a good 
material for road surfacing on account of its poor bonding proper- 
ties and its lack of stability, but it is sometimes the only material 
available in a region of sand roads. Its use is advisable only 
under such conditions. 

Sand. The sand soils vary greatly in fineness and clay or loam 
content. When deep and free from clay or other bonding 
material they become loose when dry and in this condition on 
a highway they make a surface of very high tractive resistance. 
If on a low-lying road so that they are constantly water-saturated, 
they remain fairly stable, but in such instances are not of interest 
in this discussion. 

Gypsum. In a few localities, notably western Kansas, there 
are deposits of a mixture of gypsum and clay, together with more 
or less sand and gravel. The gypsum serves to augment the 
bonding effect of the clay, and these mixtures when incorporated 
with a sandy road make an excellent sand-clay, or as commonly 
designated, gypsum road. 

SAND-CLAY CONSTRUCTION ON GUMBO, CLAY OR LOAM 

When the natural soil is gumbo, clay or loam, the general 
method of construction is identical but varies in detail. The 



SAND-CLAY ROADS 



95 



object sought is to secure stability by the addition of sand or a 
sand-clay mixture. 

I. By Addition of Natural Sand-clay Mixtures. The road to 
be improved is graded so that proper side ditches are obtained. 
The middle portion is made about flat, as shown by Fig. 22. 
Upon this section the natural sand-clay mixture is spread in a 
layer about 10 in. thick at the middle and 6 in. at the edge, the 
width being from 10 to 16 ft. The sand-clay mixture is smoothed 




fero^ 

After Spreading Sand and Clay Mixture ^fa^^. 

20-0"- 





Finished Road 



Sand Clay Construction on Clay, Gumbo or Loam 
FIG. 21. 



E^^^S^;S^i^X 

HI^MTl^fe^ 



ym 



Sand-Clay Road Before Consolidation 

O/l'-/)' _ 

\jU U 



! |V Earth Shou tc/er - - . J *-y^ j 

' 




. Subgrade- 

Sand-Clay Road After Consolidation 
Spnd'Clay Constrtrction on Deep Sand 
FIG. 22. Cross-sections for sand clay roads. 



with a grader and as soon as thoroughly soaked by rains is 
harrowed to break up the lumps and mix the materials until a 
layer of uniform texture is obtained. The road is then reshaped 
with a blade grader and is ready for traffic. If the natural sand- 
clay mixture is deficient either in clay or sand, the material that 
is lacking is added before the mixing is done. 

II. By Addition of Sand. The roadway is shaped as described 
before and the surface to be covered with sand is plowed to loosen 



96 CONSTRUCTION OF ROADS AND PAVEMENTS 

it. The sand is spread on the surface to a depth of about 6 in. 
While still dry the road is plowed again to mix the soil and the 
sand. After the plowing the mixing is completed with a disc 
harrow and this can best be done when the road is wet. After 
a thorough mixture is obtained, the surface is shaped with a 
grader and is compacted by traffic. 

The same results are obtained by spreading the sand or fine 
gravel on the road in a layer 3 or 4 in. thick and allowing traffic 
to use it. When the road is soft after rains, the sand will be 
mixed with the soil and if it appears that additional sand is 
needed, it is added. This method is less effective than the one 
first described, but in time a serviceable road will result if it is 
given proper attention and is kept free of ruts. 

SAND-CLAY CONSTRUCTION ON SAND 

I. By Addition of Natural Sand-clay Mixtures. The sandy 
road is shaped to a slightly crowned section with shallow ditches 
and with a nearly flat section in the middle portion upon which 
the clay mixture is to be placed. The sand-clay mixture is then 
spread on the sand in a layer about 10 in. thick at the middle 
and 6 in. thick at the edges, and when wet is thoroughly mixed 
with a harrow and smoothed with a grader. If the sand-clay 
mixture is deficient in sand, the defect is remedied by throwing 
on sand from the roadside. The mixing is done merely to secure 
uniformity of the surface and not to mix the surface material 
with the sand. 

II. By Addition of Clay. The amount of clay that should be 
added is theoretically the amount necessary to fill the voids in 
the sand in a layer the desired thickness. The voids can be 
determined by the water-displacement method which will indicate 
roughly the amount of clay to use. A somewhat larger pro- 
portion of clay of the slaking type is needed than of semi-plastic 
clay. The use of too much clay should be carefully avoided. 
Enough clay is spread on the surface of the sand road to fill the 
voids in a layer about 10 in. thick. This is then mixed with the 
sand by plowing and discing until a thorough mixture is obtained 
and the mixing must be done while the road is wet. This is 
the vital part of the construction and is a tedious and disagreeable 
job but the success of the construction depends upon the thor- 
oughness with which it is done. The surface is then smoothed 
with the blade grader and is compacted by traffic. 



SAND-CLAY ROADS 97 

Where no clay can be found to mix with the sand and no natural 
sand-clay mixtures are available, loam is used instead. The con- 
struction is carried out as just described. The results to be 
expected are not as good as if proper materials were available but 
a crust is formed that will be serviceable except in long-con- 
tinued dry weather. It is apt to break through to the sand if 
not made of ample thickness. 

Gypsum Roads. This type is almost always constructed on 
sandy soils and the method of construction is the same as de- 
scribed for the placing of natural sand-clay mixtures. 

In all sand-clay and gypsum construction, thorough mixing 
and careful proportioning are essential if first class roads are to 




FIG. 23. A well-built sand-clay road about five years old. 

result. As the road is opened to traffic it is not a finished product 
but will require smoothing with the grader or drag at intervals 
for a year or more. Quite often it will be apparent as time goes 
on that more sand or clay, as the case may be, is needed, and 
such should then be added a little at a time until the road be- 
comes smooth and firm. 

Not infrequently the ingredients for a sand-clay road are 
thrown together in a haphazard manner, the mixing being left 
to be done by traffic and the road receives little care, and in 
spite of the neglect becomes a fairly good road. The time 
and expense necessary for the best results are, however, fully 
justified by the better service the road will give. 

Characteristics. The sand-clay road is resilient, dustless, and 
will be smooth if properly built. It becomes only slightly muddy 



98 CONSTRUCTION OF ROADS AND PAVEMENTS 

on the surface, is serviceable for moderate traffic, and requires 
little care after it finally becomes solid. It may be damaged by 
traffic during long-continued dry weather. The cost ranges from 
$350 to $1,200 per mile for roads 14 ft. wide, depending as would 
be expected on the availability of materials and the cost of labor. 

EXAMPLES OF GOOD PRACTICE 

KANSAS 1 

SELECTING THE BINDING MATEKIAL 

In the construction of a sand-clay road it is a difficult problem 
to select a proper clay for the binding material; laboratory tests 
will assist in determining what to expect from different clays, 
but it is much better to check the laboratory test by building 
only a few miles of road at a time until the practical test demon- 
strates the worth of the clay. The properties of clay which are 
of the greatest importance in road construction are plasticity 
and the property of slaking when they first become wet after 
having been uncovered. The most plastic of these materials 
are technically called "ball clays. " A lump of such clay im- 
mersed in water will usually preserve its form a long time. 

Nonslaking clays, although they are very sticky when wet, 
generally mix readily with water. There are other clays, how- 
ever, which will immediately fall to pieces when immersed, as a 
lump of quicklime will do. This is due to the rapid absorption 
of water in the porous structure of the clay. These are known 
as slaking clays and are more easily mixed with other materials 
than the more plastic ball clays, and this is, of course, to their 
advantage for road building; but, on the other hand, they 
often have inferior binding powers. 

There is still another physical characteristic of clay of great 
importance in the construction of roads. Many clays shrink 
when dry. This shrinkage is the measure of their expansion, 
and expansion renders the sand-clay -mixture unstable. When 
water removed by evaporation is restored to the sand-clay 
mixture, its entrance is accompanied by a simultaneous ex- 
pansion which separates the grains of sand. This property is 
inherent in the clay and cannot be overcome, but by using less 
clay its destructive action can be modified in a measure. The 
best kind of clay for this construction is one which slakes easily 

1 W. S. Gearhart, Highway Engineer, Kansas Agricultural College, in 
Bulletin No. 6. 



SAND-CLAY ROADS 99 

enough to enable the lumps to be readily broken up and which 
at the same time, without being too plastic, has sufficient bind- 
ing power to cement the grains of sand and form a smooth 
impervious road surface. 

The available materials should also be tested in order to secure 
a clay having the least possible shrinkage. The best method is 
to examine the roads in which this material is found. The best 
wearing surface of the sand-clay road is obtained when the 
voids in the sand are entirely filled with a good binding clay. 
Any excess of clay above the amount required to fill the voids 
in the sand is a detriment. 

METHOD OF CONSTRUCTING SAND-CLAY ROADS ON A SANDY 

SUBSOIL 

In constructing a sand-clay road on a sandy subsoil, adequate 
permanent drainage should be provided and the road well 
crowned. Shoulders should be thrown up to confine the clay as 
it is deposited. The work should begin at the end of the road 
nearest the supply of clay and the clay deposited in layers from 
6 to 12 in. deep and from 10 to 18 ft. wide, depending upon the 
volume and kind of traffic to be carried. The large lumps 
should be broken up while dry and the whole surface smoothed 
up and 2 to 4 in. of sand placed on top. The sand and the clay 
should then be thoroughly mixed and puddled with water by 
plowing and harrowing with a disc harrow. If the water is not 
available it is well to wait until after a prolonged rain to do 
the mixing and puddling. Dry mixing has generally been 
unsuccessful. 

If sufficient funds are not available to do the mixing and 
puddling by machinery it may be left for the traffic to do it. 
If this method is followed a muddy road will result for some time, 
however, and it will require probably 2 years to get the road in 
good condition. When the clay balls, add more sand, and if the 
surface loosens during the dry weather add more clay, or better, 
use a clay with good binding power. 



100 CONSTRUCTION OF ROADS AND PAVEMENTS 
AN INVESTIGATION OF SAND-CLAY ROAD SURFACES* 

CONCLUSIONS 

A study of nearly a thousand analyses, in the laboratory, and 
in comparison of the results attained with such materials in actual 
road construction, have led the writer to formulate the following 
tentative, working rules for examining sand-clay mixtures and as a 
basis for making up proper combinations for artificial mixtures: 

1. The total relative sand content, disregarding the size of 
the sand grains, is not criterion of the value of the material. 

2. The sand smaller than No. 60 is of little value in the mixture, 
that smaller than No. 100, except in very small quantities, is 
detrimental. 

3. The greater the proportion of coarse to fine sand the harder 
and more durable wiE be the road surface. 

4. For the best possible results with sand-clay mixtures the sand 
smaller than No. 10 and larger than No. 60 should not be less than 
45 per cent, nor more than 60 per cent., by dry weight, of the entire 
sample. In addition, the sand smaller than No. 10 and larger than 
No. 60 should be composed of about equal parts of Nos. 20, 40, 
and 60. The total sand content should in no case exceed 70 per 
cent, by weight of the total sample. 

5. Test cylinders of the sand-clay mixture, 1 in. in diameter and 
3 in. long, should, when thoroughly dried in air bath at 100 C. 
take at least 2 min., when immersed in water at 21 C., to crumble 
down to the natural slope of the material, and preferably should 
take 6 min. If the cylinder fails in this test it should be regarded 
with suspicion. If the sand analysis is poor and the cylinder test 
is also poor the material is not worth using. 

6. Test cylinders, made from the clay removed from the sample, 
1 in. in diameter and 3 in. long, should take at least 2 min. to 
crumble down to the natural slope of the material when immersed 
in water at 21 C. If it fails in this test, but passes the test of the 
preceding paragraph, it may be used, but it indicates a poor 
quality of binder. 

The material comprising the top soil of cultivated land, when 
composed of the proper combination of sand and clay, has probably 
been more thoroughly weathered and therefore is less likely to 
wash and disintegrate when placed on the road. Cultivation has 

* Abstract of a paper by Mr. John C. Koch, Pro. Am. Soc. Civil Engrs., 
Vol. XL, page 269. 



SAND-CLAY ROADS 101 

also produced a more thorough and complete mixture of the two 
materials. 

METHOD OF CONSTRUCTION 

Mr. Koch recommends the following method of construction: 

The sub-grade of the roadway is brought to a level or slightly 
convex cross-section. The sand-clay is then placed in a continuous 
layer, from 10 to 12 in. thick, the material being spread as fast as 
delivered and not dumped in piles here and there. This layer 
is spread for a width of 20 ft. for a nominal 30 ft. roadway. After 
a sufficient quantity has been placed in this manner, an ordinary 
road machine is drawn along the ditch line cutting about 4 in. 
deep at the outside, and the blade is set so as to cast the material 
from the ditch against the edge of the sand-clay layer. In this 
way a shoulder is built up against the sand-clay to hold it in place. 
This also shapes the ditch. After both sides have been thus 
shaped the road machine, in successive passages, rounds up the 
cross-section of the sand-clay so as to give proper crown to the road- 
way and a smooth line from the crown to the ditches. As soon 
as the road is shaped, traffic and the construction teams begin to 
compact it, and it rapidly becomes consolidated without the use 
of a road roller. As the consolidation progresses ruts are formed, 
and they should be filled and a proper cross-section maintained 
by the occasional use of the road machine for a period of about 
2 months. Unless this is done the road surface will become rutted 
and rough, and eventually compacted with a concave crown which 
will prevent proper drainage. After the material has been con- 
solidated into a hard mass the difficulty of securing a good-cross- 
section is largely increased. 

The cross-section which seems to have given the most generally 
satisfactory results is a parabolic form with a crown of % in. per 
ft., that is, for a roadway surfaced for a width of 20 ft. the crown 
would be 5 in., and the height of the center of the road above the 
ditch (for a road having a width of 30 ft. between ditches) would 
be 7.5 in. With steeper crowns than this it has been found that 
the surface cuts into a series of parallel ridges running from the 
wheel tracks to the ditches and making it very disagreeable for 
travel. If less crown is given the provision for wear is too small, 
and the drainage may not prove satisfactory after a comparatively 
short time. 

For several months rains are apt to soften the top crust and cut 



102 CONSTRUCTION OF ROADS AND PAVEMENTS 

up the smooth surface, but if patience is exercised and the road 
machine is used to maintain the cross-section properly it will be 
found that the puddling action of the traffic when the road softens 
is a great aid to final consolidation. 

Construction with Artificial Mixtures. From analyses made of 
materials proposed for use on account of accessibility and from a 
study of their sand analyses, the proper ration in which two or 
more materials should be mixed can be determined so as to secure 
the best possible results with the available materials. Three cases 
arise in which artificial mixtures are to be used : 

1. Sand foundation, where clay is to be hauled and proper mix- 
ture made by disk plowing and puddling. 

2. Clay foundation, where sand is to be hauled and mixture made 
as above. 

3. Soil foundation, where both sand and clay are to be hauled 
and mixture made. 

In any of these three cases the proper mixture of the materials 
and the puddling action of traffic are necessary to secure a good 
consolidation. It takes considerable labor to secure a satisfactory 
mixture, but, except for this, there is no essential difference in the 
fundamental principles applying to construction with either arti- 
ficial or natural sand-clay mixtures. The use of the road machine 
to maintain the cross-section and the height of the crown should 
be the same for each type of construction. For the softer varieties 
of sand-clay the split-log and other forms of light drags may be used 
effectively in maintenance. 



CHAPTER VII 
GRAVEL ROADS 

Ideal Materials. The ideal gravel for road construction should 
be hard and durable, should possess good bonding properties 
and should be reasonably well graded. Any pit gravel, washed 
gravel, or river gravel may, however, be used in the construction 
of gravel roads if the proper methods are followed. The roads 
will not all be equally durable although all will be serviceable. 
For high-class construction gravel approximating closely the 
ideal is necessary. 

Wearing Qualities. The hardness and toughness of the stones 
in the gravel may be determined in the Deval machine in the 
manner in which similar properties of broken stone are de- 
termined. The results are neither as uiform nor as significant 
as for broken stone, but serve as a reasonably accurate measure 
of the value of the material. Quite often individual stones among 
the lot tested are of some partially disintegrated material and 
lose a disproportionate amount during the test. A gravel con- 
taining a few stones of this kind would probably wear better in 
the road than the test would indicate. Again a selected sample 
would often show better in the test than the material from which 
it was taken would under traffic in a road. 

A careful examination of the gravel in the pit will usually 
indicate, in a general way, whether or not it is durable enough for 
road purposes. If a large proportion of soft or partially disinte- 
grated stones are encountered, the gravel should not be used 
unless it is very cheap and contains a fair proportion of a good 
sand and is to be used for what might be termed high-grade sand- 
clay construction. Fig. 24 shows the face of a typical gravel 
deposit. 

Bonding Properties. The bonding element in gravel is usually 
clay or loam but may be of mineral composition such as ironoxide. 
The bonding qualities of some gravels are due partly to the 
angular shape of the particles and only partly to the clay. The 
amount of clay in the gravel should not exceed about 20 per 

103 



104 CONSTRUCTION OF ROADS AND PAVEMENTS 

cent, but a considerable range in clay content is found in gravels 
of good bonding properties. The kind of clay and the nature 
of the gravel with which it is mixed varies so much in the different 
deposits, that in many cases only service tests will reveal the 
behavior of the material under traffic. 




FIG. 24. Face of a bank gravel deposit. 

Grading. The gravels should be fairly well graded from a size 
that will pass a 2-in. screen down to the fine clay and the better 
it is graded the more stable the road will be. Not more than 80 
per cent, nor less than 60 per cent, should pass a lj^-in. screen. 

Selection of Gravel. Knowing the desirable characteristics of 
an ideal gravel to be used for road purposes, the one nearest the 
ideal may be chosen from among those available, or two gravels 
may be mixed on the work and thus a material produced which 
will be superior to either used alone. It often happens that gravel 



GRAVEL ROADS 105 

roads must be built from local material which is far from ideal 
and such gravel can be made into a serviceable road by careful 
manipulation. 

The pit gravels fall into four groups: those that approximate 
fairly closely the ideal gravel; those that are too_coarse; those that 
are too fine; and~those that are deficient in bonding material. 

If the gravel is too coarse, the larger pieces may be screened 
out and thrown aside or crushed and mixed with the material 
that has passed the screen. It may be desirable in some cases 
to add sand to increase the amount of fine material and facilitate 
compacting the gravel in the road. 

When gravel is encountered which is too fine, usually no coarse 
material is available to mix with it. Such a gravel can be used 
if sufficient clay is present or is added to bond the gravel and 
the road thus constructed will be much like the sand-clay road in 
character. It will be dusty in dry weather and somewhat sticky 
on the surface in wet weather, but will usually be a fairly 
satisfactory road for moderate traffic. 

The gravels which are deficient in bonding material are usually 
found in stream beds or have been deposited by stream action 
on bars, but some bank gravels are also of this class. The de- 
ficiency in bonding material can be supplied by mixing clay with 
the gravel after it has been gpread on the road. If this is care- 
fully done, excellent roads result because gravels of this class 
are usually very durable. Limestone screenings are an excellent 
binder for gravels of this character, particularly if a little clay 
is also added. 

Preparation- of Road for Gravel Surface. Before a gravel 
surface is placed the road is brought to a suitable grade and cross- 
section and ample surface and subsurface drainage provided as 
described in Chapter III. It is unwise if heavy grading has been 
done to place the gravel surface for a year after the earthwork 
was done. This will give time for the road to become so thor- 
oughly compacted by traffic as to form a stable foundation for the 
gravel. If the gravel must be placed immediately after the earth- 
work is completed, then everything possible should be done to 
compact the foundation thoroughly. A roller will be of great 
help if it is available, particularly if the road can be rolled a few 
days after having been soaked by rains. In this case it is best to 
place only the lower course of the gravel the first season. This 
lower course will probably become rutted and uneven as the 



106 CONSTRUCTION OF ROADS AND PAVEMENTS 

foundation settles, but it will become firm and stable after a 
time, even though uneven. 

The surface layer can then be placed and a much more durable 
road secured than if both layers had been placed at the same time. 
Even on good foundation there is reason to believe that for best 
results one-half of the gravel should be placed each season. This, 
however, is impractical under many systems of administration, 
and both layers are usually completed under one contract. When 
such is the case, the lower layer is spread for a part of the dis- 
tance and rolled, and followed immediately by the placing of the 
upper layer. 

Since the gravel will compact slowly after it is spread, it is im- 
portant to provide earth shoulders at the sides to hold it in place 
in the meantime. These shoulders may be formed by bringing 
in material from the ditches or back slopes with a grader, or they 
may be formed by plowing a few shallow furrows in the middle 
of the road and scraping the material thus loosened to the sides 
to form the shoulders. If the cross-section of the earth road 
upon which the gravel is to be placed is somewhat flat, the former 
method will be used, but if the cross-section of the earth road is 
well rounded up, then the latter will be followed. The shoulders 
should be straight and true so that the finished road will have a 
workmanlike appearance. 

Width and Thickness of Gravel. The prevailing width of 
single-track roads is 10 ft. and of double-track roads 15 or 16 ft. 
On all well-drained soils a layer of well-packed gravel 8 in. thick 
is adequate and if the roadway is double-track width the thick- 
ness of the layer at the edge may be reduced to 4 or 5 in. The 
gravel should be placed in two approximately equal layers, per- 
haps allowing a little more thickness to the lower layer than to 
the top. It is difficult to say just how much the gravel will 
shrink while being compacted, but for average conditions a layer 
11 in. thick measured after being spread on the road will make a 
finished road 8 in. thick. 

Crown. On account of the tendency of the gravel road to 
become uneven and to flatten under traffic it is desirable to con- 
struct it with cross-slope of 1 in. per foot. The cross-slope is 
usually an arc of a circle and the crown of 1 in. per foot would 
therefore be an average, the actual cross-slope being small near 
the middle of the road, increasing in rate toward the edge. 
Since the gravel surface will be somewhat porous for a time r 



GRAVEL ROADS 



107 



some storm water will penetrate to the foundation which should 
therefore be crowned enough to cause the water which reaches 




2t'-O in Cuts 
23 L O"in Fills 
Maine -Single Track Road 




S/o/oe 3tol- 
Minnesota-SingleTrack 

k- --20 -O"- H 

f< I6'-0 -x J 



Minnesota- Double Track 



- -IZ'-O- ->j- iz'-o f - ->U ~6'-0*- 




Iowa-Double Track Gravel Road 



Longi+udihi 
Til 9 Drain--' 



b-r-f-OX-..** ....... rfO'- ...... -). ------- ll'-0" ......... >K !(7-'- 

-- - 




.. , . Iowa- SingleTrack Gravel Road 

UseAll Dimensions +o Correspond 
with Standard Earth Road Sections 
for Covnty orlbwnship Road System 



5'Minimum-"^-.-'3 

.4"*- 
Longitudinal 

Tile Drain 



FIG. 25. Cross-sections for gravel roads. 

it to work to the edge of the gravel. It will then gradually 
soak away in the earth shoulder. If held on the subgrade, it 
might soften it sufficiently to cause the surface to become 



108 CONSTRUCTION OF ROADS AND PAVEMENTS 

uneven. Fig. 25 shows some typical cross-sections for gravel 
roads. 

Placing the Gravel. The gravel is dumped on the road in a 
quantity that will spread to the thickness desired for one course 
and is then spread with shovels or rakes. In many instances 
the blade grader is ussd to spread the gravel and has proven 
to be a cheap and efficient machine for the purpose. It is 
nearly always necessary to do a little hand-spreading to finally 
bring the road to a true and even surface, but the amount of 
hand work is much reduced if the grader is used first. After 
the lower layer has been placed it is thoroughly harrowed to 
mix the materials into a homogeneous mass. It is then opened 
to traffic for as long a period as possible, or is thoroughly rolled 
before placing the top course. Many gravels are of such a nature 
that they do not compact readily under rolling and become 
firm and dense only after traffic has been on the road for a 
considerable time. As mentioned before, the best results 
will be obtained if the lower course is used for a year before the 
upper course is placed. During the time that the lower course 
is under traffic it should be patrolled regularly and if ruts and 
depressions appear they should be filled with gravel. 

The top layer of gravel should be placed in the same manner 
as the lower course but if the lower course has been made single- 
track width, and additional width of finished road is desired to 
permit of vehicles passing on the gravel, the top layer may be 
made wider than the lower. Since the travel on the outer 
portion will be infrequent, a layer 4 or 5 in. thick at the edge 
will prove adequate. The gravel along the edges will eventually 
become more or less mixed with the soil of the side road, forming 
virtually a sand-clay road along the edge of the gravel. 

Considerable care should be used in spreading the gravel so 
that the surface will be smooth and have a suitable cross-slope. 

As was mentioned in connection with the placing of the lower 
course, rolling assists in compacting the surface with many 
gravels and with others does little good. In general as service- 
able a gravel road can be constructed without a roller as with 
one, except that traffic will be discommoded during the process. 
After the road is opened to traffic it must be patrolled regularly 
for at least 6 months and the ruts and depressions that appear 
must be filled with gravel. 

If very clean gravel such as is obtained by dredging or pump- 



GRAVEL ROADS 109 

ing from river bars is used, it is necessary to add clay to bond 
the road surface. After the gravel has been spread on the road, 
it is covered with about 2 in. of clay or -loam from along side 
the road. Most of this clay will shake down among the pebbles 
as the traffic uses the surface and the road will get out of shape 
easily. But frequent dragging will restore the shape as fast as 
it is destroyed by traffic and the road will gradually become 
solid. A little additional clay may be necessary from time to time 
during the first 6 months at least on portions of the road. If 
the surface can be reshaped after about a month of traffic and 
then covered with about 1 in. of good bonding limestone screen- 




FIG. 26. A well-built gravel road. 

ings, the next rain will cement the surface together into an 
exceedingly durable road. 

A split-log or plank drag is very useful for maintaining the 
surface during this period, and if the dragging is done carefully 
after the rains, a smooth, even, durable surface will result, and 
a comparatively small amount of maintenance work will keep 
it in good condition. 

Characteristics of Gravel Roads. Gravel roads have a surface 
that is comfortable to travel, that affords good traction for 
motor vehicles and that can be easily maintained under normal 
conditions. It resists the destructive effect of motor traffic 
better than a broken-stone road, but is apt to be dusty in dry 



110 CONSTRUCTION OF ROADS AND PAVEMENTS 

weather. Usually it is advisable to provide an earth side road 
for use in dry weather. 

The cost of the road varies from $1,500 per mile to $2,500 per 
mile for a double-track surface. 

Maintenance. The tendency of traffic to keep in one track 
eventually causes two broad ruts to appear in the surface and 
when this rut becomes of sufficient depth to cause inconvenience 
it should be filled with good gravel. Very little good is done if 
the rut is filled with fine material because traffic will quickly dis- 
place it. Nor is it advisable to fill the rut when the road is 
dry because the material added will not bond with the old 
surface. But if the new material is added after a rainy period 
of some duration, the old surface will be soft enough that the 
new material will bond with it. The new material should 
be added in excess of that necessary to fill the rut so that when 
it has been thoroughly compacted, there will be no depression. 
The traffic will avoid the strip of new gravel at first so that it 
will come into general use only gradually. 

With intelligent maintenance the gravel road will last in- 
definitely and be satisfactory for moderate traffic of a mixed 
character, that is up to J200 vehicles per day of which not more 
than two-thirds are motor-driven. 

GRAVEL-COATED EARTH ROADS 

In a few sections of the United States there is found a black silty 
clay soil that bears up well under heavy loads but is very sticky 
in wet weather. If the surface is coated with just enough gravel 
to prevent the soil becoming sticky, a satisfactory road is ob- 
tained. The following is a brief description of the method of 
surfacing such roads as followed in Polk County, Minnesota. 

A well-drained and well-crowned dirt road is necessary for a 
foundation. The road should be well packed and should have 
been traveled for several years, and should be at least 20 ft. 
wide on top, and should have a crown from 6 in. to 1 ft. 

The gravel is hauled and placed along the center of the road 
at the rate of about 1 cu. yd. to every 10 ft. or length of wagon 
box. This amounts to about 530 cu. yd. per mile. 

The gravel is then spread with a blade machine, with shovels, 
or left to spread itself and be beaten in by traffic. It becomes a 
smooth hard, well-beaten road in 2 or 3 months. This coat is 



GRAVEL ROADS 



111 



left on the road from 3 to 6 years or till clay begins to show in the 
surface and the road becomes rough, then a second coat is put on 
in the same manner as the first coat. 

In the above method, earth shoulders are not necessary. They 
only increase the cost of construction and prevent the top of the 
road from draining off properly. 

Most of the gravel is hauled in the winter after the ground 
freezes since teams can be got in abundance at that time of the 
year and at a lower price than at any other season. In the winter 
the price per cubic yard per mile for hauling will range from 12J^ 
to 20 cts. Gravel generally costs from 10 to 15 cts. per cubic 
yard in the pit. 




FIG. 27. Harrow suitable for gravel road construction. 
EXAMPLES OF GOOD PRACTICE 1 

GRAVEL 

Gravel shall be furnished by the contractor from banks ap- 
proved by the engineer and shall be of a quality satisfactory to 
the engineer. In general, it shall consist of hard, sound, durable 
stones of various sizes, ranging from pea stone to a maximum size 
of 3^4 m - The quality of the binding material shall be de- 
termined by the engineer. The amount of binder contained 
in the gravel shall be not less than 15 per cent, nor more than 25 
per cent, and in case the fine material which occurs in the bank 
is deficient or is not suitable as a binder the contractor will 
furnish suitable material and spread a layer of such material on 
each course, mixing and rolling the same, as directed by the 
engineer until it is thoroughly bonded. Gravel shall be spread 
in either two or three courses. The roller shall weigh at least 

1 Abstracted from Maine specifications for 1914. 



112 CONSTRUCTION OF ROADS AND PAVEMENTS 

10 tons. Any depressions shall be filled and compacted, at the 
time they appear, with the same material which is being used. 

TWO-COURSE ROAD 

Whenever the smaller sizes of stone predominate, the bottom 
course shall have a thickness of 4 in. after rolling. This course 
shall be bonded with fine material before the second course is 
applied. The second, or top course shall be similar to the bottom 
course and shall have the same thickness. It shall be bonded 
with fine material until a firm, hard, smooth surface is produced. 
The rolling of each course shall be done while the gravel is wet, 
using a sprinkler if so ordered by the engineer. 

THREE-COURSE ROAD 

Whenever the larger sizes of stone predominate, the bottom 
course shall have a thickness of 3 in. after rolling. The second 
course shall be of the same kind of material and of the same 
thickness. The top course shall have a thickness of 2 in. after 
rolling, and contain stones not larger than 1J^ in. in size. Each 
course shall be thoroughly bonded with fine material by mixing, 
rolling and sprinkling until a firm, hard, smooth, surface is 
produced. 

SPREADING 

Spreading wagons may be used when approved by the engineer. 
When dump carts are used, the gravel shall be dumped upon plat- 
forms or upon the ground on the sides and then spread uniformly 
over the surface to be built. It may be also spread with shovels 
from the carts. The contractor shall deposit where directed by 
the engineer, along or near the edge of the road in piles neatly 
formed and approximately 500 ft. apart, 5 cu. yd. of gravel for 
use in maintenance of the road. Gravel surface when finished 
shall conform to the lines and grades given by the engineer 
in accordance with plans and specifications. No allowance will 
be made for material which may be driven into the subgrade by 
rolling. 

Payment for gravel road will be made per cubic yard com- 
pacted into place in accordance with the thickness specified on 
plans. 



GRAVEL ROADS 113 

Gravel for maintenance shall be paid for at the price bid per 
cubic yard, but measured in the wagon at point of delivery on 
the road. 

Gravel Bed and Shoulders. After the road has been graded, 
the gravel bed shall be formed in the central part of the road grade 
as follows: Shoulders of firm earth or other suitable material 
shall be placed on each side of the gravel bed not less than 9 
ft. apart or such greater distance as may be required to retain 
the width of gravel specified. The shoulders shall extend to the 
side ditches or gutters at the same grade and curvature as required 
for the finished road. Where the road grade is high, the shoulders 
may be formed by moving earth from the center of the present 
road grade to the sides, or, if the grade is low, by crowning the 
present road grade by scraping earth from the sides toward the 
center, or if sufficient suitable material cannot be had along the 
roadway, it shall be brought from other places along the line of 
work. 

Rolling Subgrade. After the shoulders and gravel bed have 
been formed as above described the whole roadway shall be rolled 
until no more compacting is possible. The hollows developed 
by this rolling shall be filled with suitable material under the 
direction of the officers in charge and the roadway again rolled 
and left in solid and firm condition everywhere parallel to the 
finished roadway, the metal bed being 8 in. below the finished 
grade and having the same crown. In deep mealy sand, where 
rolling is impracticable when subgrade is shaped, marsh hay, 
wet straw, or fine brush shall be laid on subgrade to prevent the 
first course of gravel from mixing with the sand. 

First Course of Gravel. After the road has been graded and 
rolled in the manner above described, a layer of gravel shall be 
spread on the prepared bed to such uniform thickness as to be not 
less than 5 in. deep after compacting, 6 in. deep, loose measure. 
The gravel for this course shall consist of good, clean bank gravel, 
not less than 60 per cent, by weight, a larger per cent, if possible, 
of which shall be pebbles that will be retained on a screen of 
J-in. mesh and pass through a screen of 2J^-in. mesh. If clay 
gravel is used, it should contain only clay enough to coat the 
pebbles, no free lumps. In no case should the clay exceed 10 
per cent, of the mass, for clay makes mud and adds no wearing 
qualities. The gravel course shall then be harrowed with a spike- 
tooth harrow and rolled until no further compacting is possible. 



114 CONSTRUCTION OF ROADS AND PAVEMENTS 

The rolling must be done only when the road has been well wetted 
by sprinkling or after rains. Any hollows that may develop in 
the gravel during the process of rolling shall be filled with the 
same kind of gravel and the rolling continued until the surface is 
uniformly smooth and hard and everywhere parallel to, and 3 
in. below the surface of the finished road. The crown can be 
preserved during construction by the occasional use of the grader 
or other suitable floating tools. Ruts formed by hauling over the 
gravel shall be kept filled by using the harrow twice or more 
every day preferably just before quitting time both noon and 
night. 

Second Course of Gravel. The gravel for the second course 
shall consist of good, clean bank gravel, 60 per cent, by weight, 
a larger per cent, if possible, or which shall be pebbles that will 
be retained on a screen of 3^~ m - mesh and will pass through a 
screen of 1^-in. mesh. Other requirements for gravel in this 
course are the same as specified for gravel in the first course. 
This gravel shall be spread on the road to such uniform 
thickness as to be not less than 3 in. deep after compacting, 
4 in. loose measure, after which it shall be harrowed and rolled 
in the same manner as prescribed for the first course. Any de- 
pressions that may be formed during the rolling shall be filled 
with the kind of gravel prescribed for the second course and the 
road re-rolled until the surface is uniformly smooth and hard 
and everywhere conforms to the proposed grade and cross-section 
of the road. 

Manner of Rolling. Rolling shall be done only when the gravel 
has been thoroughly wetted by sprinkling or recent rains, and 
shall at all times begin at the sides, rolling lengthwise of the 
road, but gradually working toward the center. In the final 
rolling the whole surface of the roadway, including the shoulders, 
shall be rolled from ditch to ditch and the whole road grade left 
in such perfect condition that water will flow without obstruc- 
tion to the side ditches. Rolling may be done with a power 
roller, a heavy horse roller or a traction engine followed by a 
weighted field roller, if one of suitable strength to bear weighting 
to 3 or more tons can be obtained. 

With any kind of a roller the spike-tooth harrow, preferably 
of the lever type, should be used as long as the teeth will penetrate 
the surface. 



GRAVEL ROADS 115 

NEW HAMPSHIRE 1 

The economic value of gravel roads is such that they should 
constitute four-fifths of all the roads of a state. By "gravel" 
I do not necessarily mean a combination of sand and water- 
washed stone, but any combination of material which contains 
not less than 60 per cent, of metal in shape and size so that it 
need not be crushed, whether the binder be true sand, clay or 
marl. 

If the binder is of the latter, it must contain a larger percentage 
of metal than if composed of either sand or clay. To me, gravel 
means an aggregate containing either a stone which from its 
own disintegration will form a binder or one to which must be 
added some material which is adhesive in wet weather and in 
drying forms a binding shell. 

CONSTRUCTION 

In most gravel pits there is stone too large to use in the sur- 
facing but which serves well as a foundation either on sand or in 
wet clay holes. Telford is not absolutely essential under gravel, 
if it is used, the stones should be laid with some regularity. 
Stones as large as 3 in. may be used in the bottom course. The 
crown of the subgrade should be 1 in. to the foot. 

Surfacing may be accomplished by building the shoulders of 
other material and rolling the gravel 8 in. deep over the metalled 
surface of the road. I prefer to leave the rough grading with a 
crown of 3 in. to 10J^ ft. (most of the roads we build are 21 ft. 
wide) and to give the gravel 10J/ in. in the center and 3 in. on 
the outside edge of the road. This reduces the average thickness 
of the metal but gives a gravel shoulder which is invaluable in 
the maintenance. It also gives a 10-in. depth for the 5-ft. strip 
in the center upon which the major portion of the travel comes. 

The gravel should be laid in two courses. By the first method 
this affords proper compactness; in the second it is not so im- 
perative, provided the gravel is self-binding and the load is 
dumped far enough ahead so that it must be completely forked 
and shoveled over. Where laid in one course it is very easy to 
spread the gravel so that the larger stones are all in the bottom 

1 From a paper delivered at the Third American Road Congress by S. 
Percy Hooker, State Superintendent of Highways. 



116 CONSTRUCTION OF ROADS AND PAVEMENTS 

of the road, keeping ahead of the work in this way and leaving 
the surface composed of the finer material. 

If a binder consisting of clay or marl is to be used, two courses 
besides the binder should be laid. It is advisable to work the 
clay course thoroughly through the top surface with a harrow. 

Frequently enough rain falls to allow the building of the road 
without the use of a sprinkler. This summer has been extremely 
dry, however, and for a considerable time after completion the 
roads upon which no water has been used have failed to "come 
together." I find, however, that a good soaking rain will com- 
pact a soft road readily, and where sprinkling is expensive it is 
wiser to build without it. 

COST 

The cost of gravel roads will vary to a greater degree than that 
of either bituminous or water-bound macadam. The pit price 
of the gravel may be only 5 cts. per cubic yard; its cost is fixed 
by the average haul. With the material very near, the cost of 
gravel construction may not exceed $1,600 a mile, while with a 
2-mile haul it may reach $3,500. Assuming grading and drain- 
age expenses to be $1,200 per mile, the total cost per mile varies 
from $2,800 to $4,800. The average of all the gravel roads built 
in New Hampshire has approximated $3,900. It must be 
remembered that many of these roads are in remote sections, 
where the cost of the more expensive road would be far higher 
than the average in states where the railroad facilities are 
better. 



CHAPTER VIII 
WATER-BOUND MACADAM ROADS AND PAVEMENTS 

Road surfaces constructed of broken stone cemented into a 
solid mass by means of stone dust and water are known as 
water-bound macadam. The surface thus constructed depends 
for its stability upon the somewhat weak but effective cementing 
property that is possessed by the dust from many kinds of rock. 
The water-bound macadam surface made with good stone will 
be sufficiently stable to carry loads of considerable weight, but 
the integrity of the surface depends upon the excellence of the 
cementing properties of the stone dust used. 

When the surface layer is cemented together by means of a 
bituminous material which has been poured into the openings 
between the stones the surface is known as penetration 
bituminous macadam. 

Materials. Limestone, granite, and the various kinds of 
rocks designated as trap are the principal water-bound macadam 
materials, limestone and trap being employed much more 
extensively than ,the other kinds. 

Slag, shells, burnt shale, low-grade iron ore, and sandstone are 
occasionally utilized, but cannot be considered of wide im- 
portance as macadam materials. 

Quality of Rock. A macadam road is subjected to the con- 
stant abrasion of steel-tired vehicles, which tends to grind off 
particles from the surface stones. In order to resist this action 
the stone must possess the quality of hardness. 

The surface is also subjected to constant pounding from 
horses hoofs and from the jar of steel-tired vehicles. The 
tendency of these forces is to chip off fragments from the rocks 
or to break the rocks into smaller pieces. The quality of the 
rock that enables it to resist destruction in this manner is known 
as toughness. 

The individual pieces of stone in the surface of the road are 
constantly being moved slightly in the mass, due to distortion 
of the surface under heavy loads. This causes the pieces of 
stone to rub and grind against each other, and to resist this 

117 



118 CONSTRUCTION OF ROADS AND PAVEMENTS 

effect the stone must have good wearing properties. The abrasion 
test which determines the wearing property is also to a degree 
a measure to the ability of the stone to resist the grinding 
action of traffic and shock, so that the test is really a combined 
hardness and toughness test. 

The individual pieces that make up the surface of the road are 
held in place partly by the mechanical interlocking induced by 
the rolling and partly by the cementing action of the stone 
dust or screenings that fills the interstices between the larger 
stones. It is, therefore, exceedingly important that the stone 
have good cementing properties. 




FIG. 28. A poorly construction macadam which is raveling. 

Since the surface stones are held in place by the cementing 
action of the screenings and since these screenings will blow 
away, will be whipped off the surface and out of the spaces be- 
tween the stones by automobiles and will be washed away by 
storms, it is necessary for this bonding material to be replaced 
from some source. If the stone wears fast enough, the dust 
thus made will serve to replace that which is removed and 
therefore the surface will remain in better condition under 
mixed traffic if the stone wears fast enough to furnish the right 
amount of dust. Just what grade is best for any particular road 
will depend upon the traffic. 

Size of Stone in Surface Layer. The maximum size of stone 
is that size which is just strong enough to carry the loads on the 



WATER-BOUND MACADAM ROADS 119 

road without crushing. A tough stone need not, therefore, be 
as large as one low in this property. The size is further limited, 
however, when in order to secure a stone large enough to with- 
stand traffic, a size is reached where the stone will tip in the 
surface as a wheel rolls over it. While some engineers permit 
the use of a stone passing a 3-in. ring, it is probable that a size 
passing a 2^-in. ring is about the largest that can be recom- 
mended. If the stone is high in the property of toughness the 
size need not be so great. As a general principle it may be said 
that if the French coefficient of wear exceeds 12, the size for the 
surface layer may be from 1J^ in. down to Y in., and the size 
from J in. down may be utilized as screenings for bonding the 
surface, but for motor roads it is better to use 2-in. or 2^-in. 
for the upper course. If the stone has a coefficient of wear less 
than 12, the size may be from 2^ in. down to about % in. and 
the screenings may be from J^ in. down. Probably the lower 
limit of size for this stone could be either 1 in. or % in. without 
materially affecting the construction, but the screenings should 
not be run coarser than J^ in. The trend of current practice 
is toward the use of 2j^-in. stone in the wearing course. 

Size of Stone for Lower Course. It is not so important to 
have the stone for the lower course of any particular size so long 
as it is convenient to place and roll. Good serviceable roads 
have been built with the lower course made from screenings J- 
in. down, but this cannot be recommended as good practice. 
Any size obtainable up to that which passes a 3-in. ring will 
serve. The lower course is generally made of a stone larger in 
size than that which composes the upper course because of 
the economy in cost of crushing. Not infrequently, however, 
where the upper course is made of stone ranging from 2^ in. 
down to about % in., the same size is also used for the lower 
course. 

Size of Stone for Telford Foundation. The requirements as 
to the permissible size of stone for Telford foundation are not 
very rigid. A size that can be readily handled by one man is 
suitable. One dimension ought to be within 1 in. of the specified 
thickness of the foundation which may be 6 or 8 in., the width 
as set is from 5 in. to 1 ft. and- the length from 8 to 15 in. The 
essential requirement is that the pieces can be readily handled, 
and that they conveniently lay up to the required thickness of 
course. If too large, the stone will not lock together so as to 



120 CONSTRUCTION OF ROADS AND PAVEMENTS 

be stable under rolling. The larger pieces are " chinked" with 
spalls so as to hold them firmly in place. 




Courtesy O.and A.Koppel Co. 

FIG. 29. Transferring crushed stone to industrial railway. 

Crusher Run Stone. Stone is sometimes taken directly from 
the crusher and placed on a road. Since the screenings are 



WATER-BOUND MACADAM ROADS 121 

mixed with the stone, it may be compacted by rolling or by 
traffic and will bond into a fairly stable surface. Such a method 
of construction is suitable only for light-traffic roads, and the 
surface is not likely to wear evenly. 

CONSTRUCTION OF THE SURFACE 

It will readily be seen that a macadam surface cannot dis- 
tribute the load it carries over a very great area of surface. 
It is commonly assumed that the load is carried to the foun- 
dation on 45 lines from the area of application of the wheel or 
other load. Whether or not this is true, it has been shown by 
unlimited examples of successful construction that any ordi- 
nary soil, when well drained, will carry all normal loads if the 
macadam is made 8 in. thick. 

Exceptions must be made to those soils that are of seepy or 
peaty nature, and are impossible of adequate drainage. Here 
the Telford type of foundation would be used. 

The roadbed is, therefore, prepared by constructing the 
necessary side ditches and placing suitable under-drainage as in 
building a good earth road. The results will be more certain 
if such work could be done some months prior to the placing of 
the macadam, a fact that was discussed in connection with 
gravel roads. 

Thickness of Macadam. For roads constructed on an earth 
foundation of ordinary clay or loam the thickness after rolling 
is 8 to 10 in., but the 8-in. thickness is more common. If the 
foundation is of gravel, deep sand or other equally stable ma- 
terial, the thickness may be reduced to 6 in. It is doubtful if a 
macadam surface will do at all if a thickness greater than 10 in. 
is necessary for stability. The thickness given is in each case 
that which is obtained after thorough rolling which is about 
80 per cent, of the thickness of the loose material. 

A roller will not compress properly more than about 6 in. of 
loose stone ; therefore it is common practice to place the material 
in two approximately equal layers, rolling the lower course thor- 
oughly before the upper is spread. 

When the Telford type of lower course is employed, its thick- 
ness is usually about 6 in., but may be as great as 8 in. The 
Telford base is carefully placed by hand and all chinks between 
the stones filled with spalls, gravel, or crushed stone and then 
rolled with a 15-ton roller. 



122 CONSTRUCTION OF ROADS AND PAVEMENTS 






FIG. 30. Macadam surfaces under construction. 



WATER-BOUND MACADAM ROADS 123 

The upper layer for a Telford macadam is about 3 in. thick 
after it has been rolled. 

Quantity of Stone Required. A macadam surface after rolling 
requires 27 cu. yd. of stone per 100 ft. of road 9 ft. wide, to which 
must be added 3 cu. yd. of screening if the upper course only is 
bonded, and 5 cu. yd. if both courses are bonded. Pavements 
of other widths and thicknesses may be computed on a basis of 
a shrinkage of 20 per cent, in the layer of stone during rolling. 
The quantity of screenings required to bond a layer of stone is 
about 20 per cent, of the volume of the layer. These quantities 
hold true for most materials within the limits required for esti- 
mates, but will inevitably vary slightly with the size of stone, 
fineness of screenings and actual density of layer after rolling. 




FIG. 31. A portable stone crushing plant. 

Roadbed and Shoulders. It is imperative that the broken 
stone be placed between substantial berms or shoulders of earth 
so that when rolled it will be compacted, not merely spread out. 
The earth shoulders may be formed by removing the earth from 
the middle of the road for the required width and grading it out 
to the sides, thus forming a trench for the stone, and this method 
is followed when the road to be surfaced is already well shaped 
up and has the requisite cross-slope. 

If the road to be improved lacks the cross-slope or crown neces- 
sary for good drainage the shoulders are formed by drawing 
material from the sides of the road and the ditches. The 
shoulders thus obtained will be loose and will require thorough 
rolling prior to placing the stone to insure that they will not spread 
out when the stone is rolled. 



124 CONSTRUCTION OF ROADS AND PAVEMENTS 

It not infrequently happens that both methods of forming 
shoulders will be necessary on adjacent sections of a road, on 





FIG. 32. Hauling stone with the contractor's railroad. 

account of the lack of uniformity of the existing earth-road 
section. 

The surface upon which the stone is placed is referred to as the 



WATER-BOUND MACADAM ROADS 125 

subgrade, and usually is made with a convex cross-section. This 
is desirable for any kind of hard surface that is even slightly 
porous so that there is a possibility that some water may soak 
through to the subgrade. When the subgrade is crowned such 
water will work to the edge and soak away into the shoulder or 
be conducted away through broken-stone drains. 

If, as is generally the case, the amount of crown given to the 
hard surface exceeds the difference in thickness at the middle and 
at the edge, this also necessitates a crown in the subgrade. 

The subgrade must be shaped with care so that no uneven 
places exist because they will either reduce or increase the thick- 
ness of the macadam depending upon whether they are above or 
below grade. 

Since the stability of the surface depends to a large measure 
upon the solidity of the subgrade, it is rolled thoroughly. If soft 
and yielding places are encountered, they are dug out and good 
material substituted, or, if ground water is encountered, the 
necessary under-drainage is put in to remove the water and permit 
the proper compacting of the earth. 

Placing the Stone. If the Telford base is employed, it is 
placed and rolled as previously described, the stones being care- 
fully set by hand and the spalls and smaller pieces being wedged 
into the openings between the irregular larger pieces. The whole 
is then covered with a thin layer of gravel or broken stone and 
is rolled thoroughly. 

When the lower course is of broken stone and is spread by 
hand, the loads of stone are dumped in such a manner as to be 
convenient for spreading and the stone then spread by means 
of ballast rakes. 

The thickness is gaged in one method by means of cubes of 
wood of a size equal to the thickness of the course of stone. These 
are placed before the load is dumped, and the material is raked 
down until even with the tops of the blocks. They are then 
taken out and placed in position for the next load. This method 
is impractical if the material cannot be spread as rapidly as it 
is hauled. 

In another method the thickness is gaged by means of iron pins 
set with the top at the proper height to gage the thickness, but 
otherwise the method is identical with the one in which the blocks 
are employed. 

When stone is hauled in wagons that are constructed so as 



126 CONSTRUCTION OF ROADS AND PAVEMENTS 




-280- 
-18' 0^- 



{ Bituminous Wearing Surface 



6 of 1 to 8 U Crushed Stow 

L-Fort Worth, Texas 



m^^--t2" 



1*6 








Metal ( f Slope IJj to 1 in Heavy Soil 

Vlfitb of Metal 16 & '6 glcpe 4 to lln light Soils 

J3-Mlchigan State Reward Road 




8 Telford 4V Stone 

-Philadelphia Suburban ( Telford Base ) 




Frcucb Drain Z)-Orgecn Standard Section 





B-Illinois Standard Sections 

FIG. 33. Cross-sections for macadam roads. 



Cut Section 



WATER-BOUND MACADAM ROADS 127 

to spread the material partially when dumped, the driver at- 
tempts to move at such a rate as to spread the stone about the 
proper thickness but the layer must be finally trued up by means 
of rakes. The larger dump cars that are drawn by tractors are 
usually equipped in this way and spread the material quite 
satisfactorily. 

Another method that is not infrequently employed utilizes 
the blade grader for spreading the stone. The loads of stone are 
dumped at such a distance apart that when spread they will cover 
the road to the proper thickness. After a number of loads have 
been dumped they are spread by means of the grader. Usually 
a little hand work with the rakes is necessary to take out uneven 
places. 

When the loads of stone are dumped the finer material of which 




FIG. 34. A macadam road in need of surfacing. 

there is always a certain amount mixed with the coarse, will be 
deposited in the center of the pile while the coarse will roll to the 
edges. After the stone is spread the finer material will be in the 
middle portion of each space covered by one load of stone. This 
has a tendency to cause unevenness during rolling and is obviated 
by thorough harrowing, which mixes the finer material with 
the coarse or causes it to work to the bottom of the layer. 

No matter what system of spreading is employed, it will be 
found advisable to go over the stone with a blade grader just 
before rolling, to finally smooth the surface. Only a very small 
amount of stone will be carried along by the grader and this 
will fill the low places that exist and the blade will drag down the 
high places. 



128 CONSTRUCTION OF ROADS AND PAVEMENTS 

When stone is being spread in a layer less than about 4 in. 
thick the spreading must be done by rakes to insure the proper 
degree of accuracy, and this is particularly true of the upper layer 
of a road that is to be finished as penetration bituminous mac- 
adam. In spreading these thin layers, a templet is used as a 
guide to the thickness, the ends of the templet being supported 
on side forms set to the proper grade. 

Blind Drains. During the construction period any rains that 
come will soak through the unfinished road and the water will 
collect along the shoulders. To protect against damage at this 
time, blind drains which are merely trenches sufficiently deep to 
permit the water to run freely from the subgrade are dug and 
are partially filled with coarse broken stone which is covered 
with earth to the level of the shoulder. The stone is generally 
put in them when the lower course is placed. These drains are 
spaced about 50 ft. apart on each side of the road but may be 
closer together in the low places in the road and be omitted near 
the hilltops. On long hills it is desirable to dig every third pair 
of the lateral drains to a depth of about 10 in. below the subgrade 
and extend them to meet at the middle of the road. The drains 
are sloped slightly downhill on grades and are at right angles to 
the center line elsewhere. 

Rolling. For limestones a roller weighing about 400 Ib. per 
inch of width of roll is used and for trap and similar stones one 
weighing about 600 Ib. per inch of width is employed. On the 
lower course the rolling begins at the edge of the stone and the 
roller moves parallel to the edge of the stone and at a speed of 
about 100 ft. per minute. The machine moves backward and 
forward, edging in toward the middle at each trip and when the 
'middle is reached the roller is taken to the opposite side of the 
road and the process repeated. The roller then returns to the 
side first rolled and this is repeated until the stone is thoroughly 
compacted. A roller will properly compact and bond about 
50 sq. yd. of road surface per hour. 

When the stone is thoroughly rolled, each piece will be wedged 
tightly between its fellows, and will thus be restrained against 
any lateral displacement. At this stage of the rolling it will be 
noted that the stones have begun to break under the roller. 
If the rolling is continued after this stage is reached, the stone 
will wear and begin to loosen in the surface. 

Rolling on the upper course of the macadam road is carried 



WATER-BOUND MACADAM ROADS 



129 



out as for the lower course except that the rolling begins out on 
the shoulder about 4 ft. To do this successfully the shoulders 




FIG. 35. Some types of macadam and tandem rollers. 

must be trimmed to such a height that they will roll down level 
with the stone. 



130 CONSTRUCTION OF ROADS AND PAVEMENTS 

During the rolling some uneven places will appear and these 
are brought up by the addition of a small quantity of stone of 
the same size as is used in the course. A skilful roller operator 
will frequently sight along the surface of the macadam to detect 
uneven places and will so conduct the rolling as to produce a 
smooth, uniform, tightly keyed surface. Much depends upon 
the skill and experience of the roller operator and thorough 
rolling is a vital part of the construction of macadam roads. 

Applying Screenings. After the rolling on the upper course is 
completed, no vehicles are permitted to drive over it until the 
screenings have been applied. These are dumped in piles at the 
side of the macadam and are thrown onto the surface with a 
sweeping motion of the shovel so that they will not be deposited 
in piles. The quantity used is that which will just cover the 
stones. Frequently they are brushed into the surface with 
fiber brooms. Some engineers then sprinkle the surface lightly 
and others roll the screenings dry. As the rolling proceeds, 
bare places will appear and screenings are added until the layer is 
filled and a small quantity remains on the surface. 

Puddling. When the required quantity of screenings has. been 
spread, the surface is sprinkled and rolled, the roller following 
immediately behind the sprinkler so that the spray of water falls 
on or just ahead of the roller. As successive trips are made, the 
dust on the road and the water form a mortar under the roller 
which is worked into every crevice in the surface. This opera- 
tion of puddling is exceedingly important if a durable surface is 
to be constructed. 

When puddling is completed the road is closed to all traffic 
until the screenings set up, which may be for 2 days or a week 
depending upon the weather. If it is very hot and dry, it is well 
to sprinkle daily for 2 or 3 days. 

After the screenings have set the surface may be rolled again 
after each rain and the more rolling it gets at such times the 
better. 

Finishing Side Roads. The shoulders should be neatly 
trimmed to the proper cross-slope, the back slopes to the ditches 
and the side slopes on cuts and fills be hand trimmed, and the 
ditches be properly shaped and cleaned of all loose earth. 

Wearing Properties of Stone Roads. A broken-stone road 
suffers deterioration from four distinct traffic effects. The 
first of these is an actual grinding away of the rock by abrasive 



WATER-BOUND MACADAM ROADS 131 

action of steel tires. This is quite likely to be confined to a width 
of about 1 ft. at each wheel track unless the road carries enough 
traffic to keep the vehicles using the entire width of surface. As 
a rule the traffic will keep in the middle unless forced to one 
side. Even well-built roads will have some variation in texture 
and will not wear uniformly and unevenness will result. 

The second of these traffic effects is the removal of the screen- 
ings from the surface by automobiles. The wind caused by the 
motion of the car carries the finer particles away and the shearing 
action of the tires brushes the larger pieces away. When the 
surface has been denuded of binding material the wheels begin 
to loosen the larger stones. 

The third effect results from single-horse traffic primarily 
but is also caused to some extent by two-horse traffic. The 
pounding of the hoofs on the surface causes the displacement of 
the stones and to a limited extent breaks up the softer pieces. 
Single-horse traffic moves so that the horse usually travels in 
the middle of the macadam where the surface receives little 
wheel travel to make dust and keep the surface rolled down. 
Two-horse teams usually travel with each horse about in the 
wheel track and they do not, therefore, damage the surface as 
do single-horse vehicles, but have somewhat the same effect. 

The fourth effect is due to the elements, such as rains that 
wash off the screenings and temperature changes that by alter- 
nately freezing and thawing the road disintegrate the stones and 
disturb the foundation. This latter is a minor cause of deteriora- 
tion on well-drained and well-built roads where good materials 
have been used. 

Maintenance. The surface may suffer almost entirely from 
one of the above causes or it may be subjected to all of them 
simultaneously. The method of maintenance will depend upon 
just how the surface wears. 

If the motor traffic predominates, loss of binder will result, 
and in order to maintain the surface under such conditions it 
will be necessary to renew the binder as fast as it is swept off. 
Screenings or bonding gravel may be used for this purpose, and 
where possible should be put on while the road is wet. 

If the surface wears rapidly, new material must be added 
from time to time to maintain the thickness. Chuck holes and 
ruts will appear and these must be filled to maintain the smooth 
surface. 



132 CONSTRUCTION OF ROADS AND PAVEMENTS 

When new stone is added, the old surface must be loosened to 
insure that the new surface will unite with the old. Where the 
area to be patched is small the loosening is done by hand with 
picks but when extensive resurfacing is necessary, the scarafier 
or spikes in the roller wheel can be most economically employed. 
The surface is loosened to a depth of about 4 in., the new material 
is added and rolled or tamped to place. Screenings are then 
spread, and the patches or new surface bonded, just as in the 
construction of a new road. 

It is important to keep a broken-stone road in a smooth con- 
dition because if a chuck hole starts or a rut appears, it will 
rapidly increase in size and the comfort and convenience of 
traffic will be interfered with. 

No matter how faithfully a water-bound macadam road is 
maintained, it will be inadequate to meet the demands of exces- 
sive motor traffic unless treated with a bituminous binder to 
keep the surface intact. 

TOOLS AND MACHINERY USED FOR GRAVEL AND MACADAM 

CONSTRUCTION 

Earth-working Tools. The earthwork incident to hard sur- 
facing is performed with the tools and machinery that have al- 
ready been described in the chapter on earth-road construction. 
In addition, many other types of machinery are needed. 

Stone Forks. For unloading coarse crushed stone from cars or 
loading it from storage piles the stone fork is preferable to shovels. 
The forks are of various sizes, but one about 14 in. wide with 
tynes 1 in. apart is very suitable. 

Stone Rakes. A rake of some sort is needed for spreading 
crushed stone in macadam construction. The type known as 
the ballast rake has tynes about 6 in. long and five or six in num- 
ber. It is best to fasten two rakes together "back to back" 
so as to make a "two-man rake." Two men who become 
accustomed to this form of rake can handle a large amount of 
stone with ease. 

Wagons for Traction Hauling. If road-building materials 
are to be hauled 2 miles or more and the road over which the 
hauling is to be done is in good condition, heavy wagons drawn 
by a steam or gasoline tractor are economical. Neither the 
tractor nor the wagons should be too heavy or they will do serious 
injury to the road over which they move. The capacity of the 



WATER-BOUND MACADAM ROADS 133 

wagons should not exceed 5 cu. yd. and the tractor should not 
exceed 10 tons in weight. The wagons have adjustable dump 
bottoms so that material can either be dumped in a pile or spread 
in a layer on the roadbed. The wagons are arranged with cross- 
reaches or some such device that will insure their following each 
other in a single track around turns. In the operation of such 
outfits weather conditions may reduce the average capacity much 
below the maximum capacity, especially in territory where the 
roads over which hauling is done are not improved. On long 
hauls the capacity of such an outfit is comparatively small be- 
cause it must travel at a slow pace and hence cannot make many 
trips per day. 

Narrow-gage Dump Cars for Hauling. When the haul for 
materials exceeds 2 miles and the amount of material to be hauled 
is 10,000 cu. yd. or more, a narrow-gage industrial railway is 
economical, unless the grades exceed 6 per cent. These outfits 
are made with sectional portable track which can be placed 
quickly and cheaply and can readily be shipped. The cars have 
a capacity of 1J^ or 2 cu. yd. and are arranged to dump sidewise. 
About six of these can be drawn by a team or from 20 to 30 by a 
dinky locomotive. The initial cost of the equipment precludes 
its use except on large work. 

Motor Trucks. The motor truck for hauling road materials 
is of recent development and possesses advantages, particularly 
where the hauling is over improved roads or for delivery over 
paved streets. 

Motor trucks are made with capacities up to 5 cu. yd., and 
motor trucks of the trailer type are of even greater capacity. 
These trucks are self-dumping, travel rapidly and when used in 
connection with some quick loading device will handle large 
quantities of materials. In recent years they have proven to 
be especially advantageous for handling the hot mixtures for 
street pavements such as asphalt and bituminous concrete. They 
are somewhat uncertain if the hauling is over unimproved roads. 

Loading Devices for Materials. If road materials are being 
used in small quantities some economy in team hauling can be 
effected by the loading chute. These chutes are built to be 
attached to the side of the car and the material is shoveled into 
them from the car. When an empty wagon arrives, the con- 
tents of the chute is dumped into it by merely tripping the door. 
Thus there is no team time lost while the wagon is being loaded. 



134 CONSTRUCTION OF ROADS AND PAVEMENTS 

If large quantities of road materials are being handled and it 
is possible to secure railroad cars with dump bottoms, the loading 
can more economically be done with a bucket elevator. The 
hopper is constructed under the track and the boot of the elevator 
placed so that when the car is dumped the contents are fed into 
the elevator. An outfit of this kind can be installed that will 
readily load a cubic yard of stone per minute. In order to obvi- 
ate the delay while the railroad cars are being shifted, a hopper 
is sometimes built into which the elevator deposits the material. 
From the hopper the material is let into the wagons through 
chutes. The cost of loading materials from cars to wagons with 
this equipment is not much less than for shoveling it by hand, 
but the loading is much expedited and the necessity for a large 
force of laborers done away with. 

The locomotive crane with clam-shell bucket is also well 
adapted for loading materials on large work. 

Horse-drawn Rollers. Rollers with a single divided roll and 
weighing from 4 to 8 tons are employed for compacting the foun- 
dation for pavements and for rolling earth roads. This type of 
roller is drawn by horses or by a tractor. A roller of this type is 
not very effective on macadam or gravel roads. 

Self-propelled Rollers. Steam- and gasoline-driven rollers are 
quite general in macadam-road construction and in various kinds 
of pavement construction. Two types known respectively as 
macadam rollers and tandem rollers are built. The macadam 
or three-wheeled roller is designed for compacting embankments, 
for rolling the foundation for roads and pavements and for the 
construction of the various kinds of macadam roads. The 
weight may be from 8 to 20 tons, but for all-around work the 
10-ton size is most suitable. The width of the roller varies with 
the weight but the relative amount of weight on the front and 
rear rolls should be about the same for all sizes and since the rear 
roll is larger in diameter than the front, the weight on the rear roll 
should be about 0.6 of the total weight. The combined width 
of the two rear rolls should equal the width of the front roll and 
the path of the rear roll should overlap the path of the front roll 
about 4 in. 

The tandem roller has two divided rolls so arranged that they 
cover the same path when the machine is in operation. The 
steering roll is smaller in diameter than the driving roll, but the 
weight is so distributed that both give about the same compres- 



WATER-BOUND MACADAM ROADS 135 

sion to the surface. The tandem roller is built in sizes weighing 
from 4 to 16 tons, the lighter ones being used for the first rolling 
on sheet asphalt and bituminous concrete surfaces and for rolling 
brick pavements before the filler is poured. The heavier sizes 
are used for rolling embankments and for the final rolling on 
sheet asphalt and bituminous concrete surfaces. 

Scarafiers. The scarafier is designed for loosening the surface 
of gravel or macadam roads when repairs are to be made. It 
consists of two or more hard-steel teeth set in a heavy frame so 
arranged that the depth to which the teeth penetrate the surface 
of the road can be adjusted. The scarafier is usually drawn by 
a tractor or roller and some types are built so that they can be 
steered independent of the tractor. 

Portable Stone -crushing Plants. For portable crushing out- 
fits the jaw type of crusher is most commonly employed although 
the gyratory crusher is also made in small sizes. The crushing 
plant consists of the crusher which will have a capacity of about 
10 cu. yd. per hour, and the screening equipment and storage 
bins. The cylindrical revolving screen is used and is equipped 
with sections of screen to suit the work in hand. Storage bins 
are provided with sufficient capacity to take the output between 
loads so that the plant can run regardless of the regularity of 
hauling. For portable outfits the ordinary well-driller's rig is 
used for drilling the ledge for blasting the stone out. 

Stationary Crushing Plants. For the larger installations the 
gyratory type of crusher is employed and the other machinery 
and method of operation is much the same as for the smaller 
plants except as regards size. The drilling is done by means of 
steam or air drills. 

All stone crushers are built in such a way that the size of the 
product can be changed and the size of the screens can be changed 
by removing the perforated metal and replacing with another 
size. 

EXAMPLES OF GOOD PRACTICE 

WISCONSIN 1 
SURFACING QUANTITIES REQUIRED 

The following table gives the number of cubic yards of material 
per mile to make a given loose depth for various widths of roads: 
1 From Bulletin No. 4, Wisconsin Highway Commission. 



136 CONSTRUCTION OF ROADS AND PAVEMENTS 
TABLE 10. QUANTITY OP MATERIAL REQUIRED FOR MACADAM ROADS 



Depth of loose material in inches 


Width of surfacing 


9 ft. 


14 ft. 


15 ft. 


16 ft. 


18 ft. 


Cu. yd. 


Cu. yd. 


Cu. yd. 


Cu. yd. 


Cu. yd. 


1^ in. (screenings). 


180 
440 
587 
734 

880 
5,280 


280 
684 
913 
1,141 
1,369 
8,213 


300 
733 

979 
1,222 
1,466 

8,800 


325 

782 
1,043 
1,304 
1,565 
9,387 


367 
880 
1,174 
1,468 
1,760 
10,560 


3 in 


4 in 


5 in 


6 in 


Square yards of surface per mile . 



The following table gives the number of linear feet of 9-ft. 
road a load of a given size should cover for various loose depths. 
Foremen must compel spreaders to use this table. 

TABLE 11. SHOWING LINEAR FEET OP 9-FT. ROAD FOR VARIOUS SIZES OF 

LOAD 



Weight of load 


Size of load 


Loose depth in inches 


Granite, 
pounds 


Limestone, 
pounds 


3 in. 


4 in. 


5 in. 


6 in. 


2,800 


2,500 


1 cu. yd. 


12ft. 


9.0 ft. 


7.2ft. 


6.0ft. 


3,500 


3,125 


IK cu. yd. 


15ft. 


11.25ft. 


9.0ft. 


7.5ft. 


4,200 


3,750 


1^ cu. yd. 


18ft. 


13.5 ft. 


10.8ft. 


9.0ft. 


4,900 


4,375 


1% cu. yd. 


21 ft. 


15.75ft. 


12.6ft. 


10.5ft. 


5,600 


5,000 


2 cu. yd. 


24ft. 


18.0 ft. 


14.4ft. 


12 . ft. 


6,300 


5,625 


2M cu. yd. 


27ft. 


20.25ft. 


16.2ft. 


13.5ft. 


7,000 


6,250 


2^ cu. yd. 


30ft. 


22.5 ft. 


18.0ft. 


15 . ft. 


7,700 


6,875 


2% cu. yd. 


33ft. 


24.75ft. 


19.8ft. 


16 . 5 ft. 


8,400 


7,500 


3 cu. yd. 


36ft. 


27.0 ft. 


21.6ft. 


18.0ft. 



WEIGHTS OF MATERIAL 

When buying by weight, to find the amount required, estimate 
that limestone weighs 2,500 Ib. per cubic yard of 27 cu. ft.; 
granite, disintegrated granite and quartzite 2,800 Ib. ; unscreened 
gravel or sand 3,000 Ib., and crushed gravel 2,650 Ib. Finer- 
crushed sizes will weigh more than coarse sizes. The above 
averages the three sizes commonly used if they are dry. Screen- 
ings, sand and gravel are often shipped wet and will weigh far 
in excess of the above. 



WATER-BOUND MACADAM ROADS 137 

SPREADING 

The simplest and most satisfactory way to spread stone 
accurately to a definite depth is to know how many cubic yards 
are in a load, and figure from the foregoing table how many feet 
of road it should cover to the depth required, and to spread it 
over that many feet and no more or no less. It is much the most 
convenient to have all loads hauled the same size, in which case 
the spreader can measure accurately just how to dump each 
load. To find the capacity in cubic yards of a wagon, multiply 
the inside length by the width and then by the height (all in 
feet) and divide by 27. 

It takes a good man to make a good spreader. Much of the 
looks of the road depends upon his work and much of the money 
available can be wasted by a careless workman who puts on too 
much material. Check the loose depth of the stone often and 
see that he is spreading each load to the proper distances so that 
stone is neither too thick nor too thin. 

FIRST COURSE 

(No. 1 stone usually 2 in. to 3^4 in. in size, usually spread to a 
loose depth of 5 in., never more than 6 in. and seldom less than 
4 in.) 

The first course of rock or gravel can now be dumped on the 
subgrade and spread to the required thickness with rakes and 
shovels, after which it is to be rolled until it is packed firm and 
hard and there is no movement under foot as you walk on it. 
On very sandy soils, to keep the sand from working up through 
the stone, place a fair covering of clay, marsh hay, straw, or 
weeds (good in the order named) before placing any stone. 
Shoulder trenches should be filled with the No. 1 stone so as to 
make blind drains. Cover the stone in the trench with sods, 
grass side down, or with hay or straw to keep dirt from clogging 
the water course. Care should be used in rolling the first course 
to keep the roller in the trench and not to overlap the stone and 
crush the shoulders. Roll from outer edge toward center. Clay 
or screenings are seldom necessary on the first course. Place 
about 200 ft. of first course stone before starting to lay No. 2. 
No. 1 bin does not usually hold this much, but No. 2 stone can 
be put in the bottom course until the first course is laid 200 ft. 



138 CONSTRUCTION OF ROADS AND PAVEMENTS 

ahead, provided the two sizes are kept in separate strips, laying 
say the first 125 ft. of No. 1 and then starting with No. 2. Some 
prefer to pile the No. 2 until the No. 1 is far enough ahead 
and use it when the end of the work is reached. 

HARROWING 

Although not much used in Wisconsin, many highway engineers 
claim that a good stout spike-toothed harrow is a necessity in 
properly compacting stone and gravel, and that a large part of 
the rolling of the two first courses can be saved by thorough 
harrowing after spreading. The Commission will have this 
method thoroughly tried out on several jobs this summer, and 
hopes that some of the County Highway Commissioners will 
also experiment with such harrows. 

SECOND COURSE 

(No. 2 stone, usually J^ in. to 2 in. in size; usually spread to a 
loose depth of 4 in., never more than 5 in., seldom less than 3 in.) 

The second course of stone is now hauled on top of the first 
and spread evenly to the depth called for. This course is rolled 
commencing on each outer edge with the rear wheel half on the 
stone and half on the shoulders and rolling toward the center. 
The roller should be run over this course a number of times until 
the stone or gravel is brought to shape and fairly well compacted 
before screenings or dust is applied. All low places that have 
shown up should be filled with No. 2 stone and high spots raked 
down so that the surface presents a smooth even appearance. 

THIRD COURSE OR SCREENINGS 

(No. 3 stone, usually from dust to J in. in size. Not necessary 
in pit-run gravel or shale roads.) 

Screenings may be hauled at any time after subgrade has 
been finished. Dump in piles with inner edge about 2 ft. from 
edge of trench or subgrade. Never dump screenings on the 
second course. If 1 cu. yd. of 27 cu. ft. is dumped in one place, 
the centers of piles should be about 30 ft. apart for 9-ft. road or 
about 18 ft. apart for a 15-ft. road. A cubic yard of screenings 
under ordinary conditions will cover about 275 sq. ft. of surface. 



WATER-BOUND MACADAM ROADS 139 

A cubic yard of screenings bought by weight is not a cubic yard 
by measure, especially if wet. 

Use a square-point dirt shovel to apply screenings. Put them 
on very thinly with a quick sweeping motion, working from one 
end of the road toward the other. Keep roller running con- 
stantly while putting on the screenings. Repeat this process 
until all voids between stones are filled. Roll until stone stops 
moving and the surface is hard, and all second-course stone 
slightly covered with screenings. It is necessary to bind quartz- 
ite or granite with some good cementing material, such as 
clayey pea gravel or disintegrated granite. If neither of these 
are available, it is best to use a limestone top course or bind the 
granite with a bitumen. Clays and limestone screenings have 
not proven to be satisfactory binding materials for this class of 
stone. If clay is used, apply it dry a little at a time, and after 
the voids are well filled and the road is rolled, cover the surface 
with screenings, preferably with the dust screened out. Don't 
use too many screenings just enough to nicely cover the road 
at all stages is just right. Too many screenings simply allow 
the road to rut more easily. 

FLUSHING 

With the stone covered with screenings the road is ready for 
water. On clay soils trim down shoulders with road machine 
before applying water to prevent too much'mud at sides. Don't 
try to finish over 400 ft. of road at one time. It will dry out 
before you get it soaked. It is customary to finish up each night 
or' every other night the road ready for finishing. If screenings 
stick to tires, scrape them off or keep tires well wet, or both. 
Sprinkle road until screenings are thoroughly soaked and tires 
run clean. When road is wet enough, follow sprinkler with 
roller. If screenings pick up on roller wheels, stop rolling and 
apply more water. Keep roller as close to sprinkler as possible. 
If bare spots or holes appear, put on enough dust to cover them. 
Sprinkle and roll until water is continually carried along in front 
of the roller wheels at every point of the road being flushed. 
Road is then finished. Pit-run gravel roads are flushed in about 
the same way, but must be very wet when rolled or quite dry. 
A rainy day is the best time to finish a road. 

If the road fails to compact and is spongy under the roller, 



140 CONSTRUCTION OF ROADS AND PAVEMENTS 

the subgrade is too wet. Take the roller off and wait until the 
road dries out, or if conditions are very bad, dig out the stone 
and mud underneath, refill with good dry material and surface 
again. Use tile drain where necessary. Never have more than 
600 ft. of unfinished road on your hands. Keep the work com- 
pact and finish as you go. 



CHAPTER IX 
CONCRETE ROADS AND PAVEMENTS 

The use of concrete for the wearing surface of the road or pave- 
ment is a recent development in the utilization of this material. 
Concrete has for many years been used as a base for various types 
of pavements, and as such its function was to distribute the load 
carried by the pavement surface over sufficient area of the earth 
subgrade to insure stability. In this use the material is subjected 
principally to compressive stresses. It is also subjected to tem- 
perature stresses but these are generally of no moment since the 
cracks that result are not numerous enough to affect the stability 
of the surface. 

When concrete is used as a wearing surface it must perform all 
of the functions required of the concrete foundation and must 
in addition resist the abrasive action of traffic. Concrete of 
the composition employed for the pavement base is not well 
adapted to resist abrasion. 

Stresses in Concrete Roads and Pavements. The stresses to 
which a concrete road or pavement is subjected are as follows,: 
tension, and compression, due to the distortion of the pavements 
under loads or to an irregular settlement of the subgrade; ten- 
sion due to temperature changes and changes in moisture con- 
tent and abrasion due to the wear and shock of traffic. Of these 
the last two are undoubtedly the most important. 

MATERIALS 

Sand. In proportioning the concrete for a pavement, account 
must be taken of the character of each of the ingredients, cement, 
sand, and coarse aggregate. A good grade of Portland cement 
is assured by requiring that it pass the standard tests for Port- 
land cement adopted by the American Society for Testing Ma- 
terials. The sand should also be of good quality. It must be 
clean and must consist of sound particles of quartz or other 
siliceous materials and must be reasonably well graded from J^ 
in. down. It seems to be established that the sand should not 

141 



142 CONSTRUCTION OF ROADS AND PAVEMENTS 

contain to exceed 20 per cent, passing a 50-mesh screen and not 
more than 5 per cent, that will pass a 100-mesh screen. It 
ought not to contain to exceed 3 per cent, (dry measure) of clay 
or loam. In order to test the quality of the sand it is made into 
briquettes of 1 to 3 mortar and these briquettes tested in com- 
parison with 1 to 3 briquettes made of the same cement and 
standard Ottawa sand. A suitable sand will make a briquette 
of at least as great strength as that of the briquettes made of 
standard Ottawa sand. Unfortunately, there is as yet no gener- 
ally accepted test for the quality of sand as regards its ability 
to withstand abrasion. If such a test were extant it would be 
particularly applicable to sand for concrete for road surfaces. 

Coarse Aggregate. The coarse aggregate should have suffi- 
cient strength to withstand abrasion at least as well as the mortar 
which surrounds it and while no value for the coefficient of wear 
can be given that will apply to all conditions, it may be taken 
as a safe general rule that no coarse aggregate should be used 
having a coefficient of wear of less than 7 as determined by the 
Deval test described in Chapter XXI. If the coarse aggregate is 
somewhat harder than the cement mortar, that is of no particular 
moment, because when the mortar has worn down even with the 
stones in the surface it will be protected by them. 

It is not only important that the coarse aggregate be made up 
of a material having a proper coefficient of wear but that it should 
also be of uniform quality so that the surface will wear evenly. 
Especial precaution should be taken to insure that the coarse 
aggregate does not contain occasional soft particles. Frequently 
broken stone or stone screened from bank gravel will contain a 
percentage of soft pieces. These are quite likely to be found 
near the surface after the road is finished. If so, they will dis- 
tegrate under traffic and climatic action leaving pits in the surface 
which will rapidly enlarge under the abrasion of steel-tired 
vehicles. 

Size of Coarse Aggregate . There is no theoretical considera- 
tion entering into the selection of the size of the particles of the 
coarse aggregate other than that the smaller they are the more 
uniform and smooth the surface will be. Experience has shown 
rather conclusively that the best results can be obtained if the 
coarse aggregate used does not exceed a size that will pass a 2j/- 
in. screen, and frequently the size is limited to that which will pass 
a 2-in. screen. 



CONCRETE ROADS AND PAVEMENTS 143 

Materials for Two-course Pavements. When it is impossible 
at reasonable cost to secure coarse aggregate of the durability 
required for the wearing surface, the pavement may be con- 
structed in two courses. The lower course is mixed substantially 
as a pavement base would be but the upper course is constructed 
of durable aggregates and placed within a few minutes after the 
lower course has been completed. The composition of the wear- 
ing course may be cement, sand and granite, or trap-rock chips; 
or may be cement and a good grade of coarse sand. 

PROPORTIONING CONCRETE 

Concrete for a One-course Pavement. The first step in deter- 
mining the proportions to employ for a concrete pavement is to 
decide upon the desired strength for the concrete. In a general 
way, the higher the compressive strength of the concrete the great- 
er the wearing properties, but this assumes aggregates of the 
general character of those described in the preceding paragraphs*. 
There is at present no generally accepted standard compressive 
strength for concrete for road surfaces. The character of concrete 
most widely used probably ranges in strength from two thousand 
to three thousand pounds per square inch in compression at the 
end of twenty-eight days. It would seem that twenty-five hun- 
dred pounds per square inch is about the minimum for general 
purposes and that far the heavier traffic, road surfaces should be 
made with concrete having a compressive strength at the end of 
twenty-eight days of itoreejbhmisa^^ 

Having decided upon the strength of concrete desired, the next 
step is to design a mixture of the available aggregates that will 
give the desired strength. This is accomplished by determining 
the fineness modulus of the aggregates and thus establishing the 
mixture required. For convenience in field proportioning this may 
be expressed in terms of the volume of fine and coarse aggregate 
required for each bag of cement in the mixture. 

In this connection, it is well to use every precaution to prevent 
the use of too much water in the mixture. Experiments have 
shown that the quantity of water employed in the mixture has a 
very marked effect on the strength of the resulting concrete. In 
order to secure workable concrete it is necessary to use slightly more 

* Bulletins of Structural Materials Research Laboratory, Lewis Institute, 
Chicago. 



144 CONSTRUCTION OF ROADS AND PAVEMENTS 



ABRAMS' TABLE OF PROPORTIONS AND QUANTITIES FOR ONE CUBIC YARD OF 

CONCRETE 

Based upon laboratory investigations, using approved materials, compres- 
sive strength, 28 days, with workabla plasticity, 6 by 12-inch cylinders, 3,000 
pounds per square inch. 



SIZES 


FINE AGGREGATES, SCREEN PER INCH 


COARSE 
AGGREGATE 
Inches 


Cement 
in Barrels 
AT^regates 
In Cubic Yards 


0-28 


0-14 


0-8 


0-4 


Q-% in. 


3 







1 


Cement 






1 

1 


"c 

1 


.2 


1 



| 


.3 


6 


I 


E 




6 


No. 4 


Proportions 


i 


1.3 


2.4 


1 


1.6 


2.4 


1 


1.3 


2.3 


1 


2.0 


2.3 


1 


2.7 


1.5 


Screen 


Quantities 


1.96 


.37 


.69 


1.85 


.44 


.66 


1.82 


.48 


.62 


1.75 


.52 


.59 


1.79 


.72 


.40 


No. 4 


Proportions 


1 


1.3 


2.7 


1 


1.6 


2.6 


1 


1.8 


2.6 


1 


20 


2.5 


1 


2.6 


1.8 


Screen 
tol 


Quantities 


1.90 


.36 


.76 


1.77 


.42 


.68 


1.72 


.46 


.66 


1.67 


.50 


.62 


1.72 


.66 


.46 


No. 4 


Proportions 


1 


1.2 


3.1 


1 


1.6 


32 


1 


1.7 


3.1 


1 


2 


3 


1 


2.4 


2.4 


Screen 


Quantities 


1.82 


.32 


.84 


1.68 


.40 


.79 


1.63 


.41 


.75 


1.61 


.47 


.72 


1.62 


.57 


.57 


No. 4 


Proportions 


1 


1.2 


3.5 


1 


1.5 


3.5 


1 


1.6 


3.7 


1 


13 


3.6 


1 


2.2 


3.1 


Screen 
to 2 


Quantities 


1.75 


.31 


.90 


1.63 


.36 


.85 


1.55 


.36 


.85 


1.52 


.43 


.81 


1.53 


.50 


.70 


No. 4 


Proportions 


1 


1.1 


3.8 


1 


1.4 


3.9 


1 


1.6 


4.0 


1 


1.8 


4.0 


1 


2.1 


3.5 


Screen 


Quantities 


1.72 


.28 


.97 


1.58 


.33 


.91 


1.51 


.35 


.89 


1.49 


.40 


.88 


1.50 


.46 


.78 


No. 4 


Proportions 


1 


1.1 


3.9 


1 


1.4 


4.1 


1 


1.5 


4.1 


1 


1.7 


4.1 


1 


2.0 


3.7 


Screen 
to 3 


Quantities 


1.69 


.28 


.97 


1.58 


.33 


.97 


1.49 


.33 


.90 


1.49 


.37 


.90 


1.49 


.44 


.81 


H 


Proportions 


1 


1.3 


2.3 


1 


1.7 


2.3 


1 


1.9 


2.3 


1 


22 


22 


1 


2.8 


1.4 


to 


Quantities 


1.96 


.37 


.67 


1.85 


.46 


.63 


1.82 


.51 


.62 


1.75 


.57 


.57 


1.79 


.75 


.37 


H 


Proportions 


1 


1.3 


2.6 


1 


1.7 


2.6 


1 


1.9 


2.5 


1 


2.2 


2.4 


1 


2.7 


1.7 


to 

1 


Quantities 


1.90 


.36 


.74 


1.77 


/A 


.68 


1.72 


.48 


.64 


1.67 


.54 


.59 


1.72 


.68 


.43 


H 


Proportions 


1 


1.3 


3.0 


1 


1.7 


3.0 


1 


1.9 


3.0 


1 


2.1 


23 


1 


2.6 


2.2 


to 


Quantities 


1.82 


.35 


.80 


1.68 


.43 


.75 


1.63 


.46 


.73 


1.61 


.50 


.68 


1.62 


.63 


.53 


H 


Proportions 


1 


1.3 


3.3 


1 


1.7 


3.4 


1 


1.8 


3.5 


1 


2.0 


3.4 


1 


2.4 


2.9 


to 
2 


Quantities 


1.75 


.34 


.86 


1.63 


.41 


.83 


1.55 


.42 


.80 


1.52 


.45 


.77 


1.53 


.62 


.66 


H 


Proportions 


1 


1.3 


3.7 


1 


1.6 


3.7 


1 


1.7 


3.9 


1 


2.0 


3.8 


1 


2.3 


3.3 


to 


Quantities 


1.72 


.33 


.95 


1.58 


.37 


.87 


1.51 


.37 


.87 


1.49 


.44 


.84 


1.50 


.51 


.74 


tf 


Proportions 


1 


1.2 


3.8 


1 


1.6 


3.9 


1 


1.7 


4.0 


1 


1.9 


40 


1 


2.2 


3.5 


to 
3 


Quantities 


1.68 


.30 


.95 


1.58 


.37 


.91 


1.49 


.37 


.88 


1.49 


.42 


.88 


1.49 


.48 


.77 



CUNCHUTE KUAUa AND PAVEMENTS 



145 



ABRAMS' TABLE OF PROPORTIONS AND QUANTITIES FOR ONE CUBIC YARD OF 
CONCRETE Continued 



SIZES 


FINE AGGREGATES, SCREEN OPENINGS PER INCH 


COARSE 
AGGREGATES 
Inches 


Cement 
in Barrels 
Aggregates 
in Cubic Yards 


0-28 


0-14 


0-8 


0-4 


Q-y 8 in. 





J3 

E 


1 

i 


1 




a 

E 


1 


1 



c 

E 


i 


~s 



a 

E 


I 


I 


| 

E 


O 


H 


Proportions 


1 


1.5 


2.3 


1 


1.9 


Z2 


1 


2.1 


22 


1 


2.3 


2.1 


1 


2.8 


1.3 


to 


































K 


Quantities 


1.96 


.44 


.67 


1.85 


.52 


.61 


1.82 


.56 


.59 


1.75 


.59 


.54 


1.79 


.75 


.34 


H 


Proportions 


1 


1.5 


2.5 


1 


1.9 


2.5 


1 


2.1 


2.4 


1 


2.3 


2.4 


1 


2.8 


1.6 


to 


































1 


Quantities 


1.90 


.42 


.70 


1.77 


50 


.66 


1.72 


.53 


.61 


1.67 


.57 


.59 


1.72 


.72 


.41 


M 


Proportions 


1 


1.4 


2.8 


1 


1.3 


2.9 


1 


2.1 


23 


1 


22 


2.3 


1 


2.7 


2.1 


to 


































IH 


Quantities 


1.82 


.37 


.75 


1.68 


.47 


.73 


1.63 


.51 


.69 


1.61 


.52 


.66 


1.62 


.65 


.51 


H 


Proportions 


1 


1.4 


3.3 


1 


1.9 


3.3 


1 


2.0 


3.4 


1 


2.2 


3.3 


1 


2.7 


2.7 


to 


































2 


Quantities 


1.75 


.36 


.86 


1.63 


.46 


.79 


1.55 


.46 


.78 


1.52 


.50 


.74 


1.53 


.62 


.62 


H 


Proportions 


1 


1.4 


3.6 


1 


1.8 


3.6 


1 


13 


3.7 


| 


21 


3.7 


1 


2.6 


3.1 


to 


































2H 


Quantities 


1.72 


.35 


.91 


1.58 


.43 


.85 


1.51 


.42 


.83 


1.49 


.46 


.81 


1.50 


.57 


.69 


H 


Proportions 


1 


1.3 


3.7 


1 


1.8 


3.8 


1 


1.3 


3.9 


1 


2.1 


4.0 


1 


2.4 


3.3 


to 


































3 


Quantities 


1.68 


.33 


.92 


1.58 


.42 


.89 


1.49 


.40 


.86 


1.49 


.46 


.88 


1.49 


.53 


.63 


K 


Proportions 


1 


1.7 


2.4 


1 


2.1 


2.4 


1 


2.4 


2.1 


1 


2.6 


22 


1 


3.1 


13 


to 


































1 


Quantities 


1.90 


.48 


.68 


1.77 


.55 


.63 


1.72 


.61 


.53 


1.67 


.64 


.55 


1.72 


.79 


.39 


K 


Proportions 


1 


1.7 


2.7 


1 


20 


2.3 


1 


2.3 


2.7 


1 


23 


2.7 


1 


3.0 


2.0 


to 


































m 


Quantities 


1.82 


.46 


.73 


1.79 


.50 


.70 


1.63 


.55 


.65 


1.61 


.59 


.64 


1.62 


.73 


.48 


X 


Proportions 


1 


1.7 


3.1 


1 


2.0 


3.1 


1 


2.3 


3.1 


1 


2.5 


3.0 


1 


3.0 


2.4 


to 


































2 


Quantities 


1.75 


.44 


.80 


1.63 


.48 


.75 


1.55 


.53 


.72 


1.52 


.56 


.67 


1.53 


.68 


.55 


K 


Proportions 


1 


1.7 


3.3 


1 


2.0 


3.5 


1 


2.3 


3.4 


1 


2.4 


3.4 


1 


2.9 


2.8 


to 


































2>i 


Quantities 


1.72 


.43 


.84 


1.63 


.47 


.83 


1.51 


.52 


.76 


1.49 


.53 


.75 


1.50 


.64 


.62 


H 


Proportions 


1 


1.7 


3.5 


1 


2.0 


3.7 


1 


2.3 


3.7 


, 


2.4 


3.6 


1 


2.8 


3.1 


to 


































3 


Quantities 


1.68 


.43 


.88 


1.58 


.47 


.87 


1.49 


.51 


.81 


1.49 


.53 


.79 


1.49 


.62 


.68 


1 


Proportions 


1 


1.7 


2.8 


1 


2.0 


2.9 


1 


2.3 


2.7 


! 


2.6 


2.6 


1 . 


3.1 


Z.O 


to 


































1H 


Quantities 


1.82 


.46 


.75 


1.68 


.50 


.73 


1.63 


.55 


.65 


1.61 


.62 


.62 


1.62 


.75 


.48 


1 


Proportions 


1 


1.5 


32 


! 


1.9 


3.5 


1 


22 


3.3 


! 


2.4 


3.3 


1 


3.0 


2.6 


to 


































2 


Quantities 


1.75 


.39 


.83 


1.63 


.46 


.85 


1.58 


.51 


.76 


1.52 


.54 


.74 


1.53 


.68 


.59 


1 


Proportions 


1 


1.4 


3.4 


, 


1.3 


3.3 


1 


2.0 


3.7 


1 


2.3 


3.7 


1 


2.7 


3.1 


to 


































2H 


Quantities 


1.72 


.35 


.86 


1.58 


.45 


.89 


1.51 


.44 


.83 


1.49 


.51 


.81 


1.50 


.59 


.69 


1 


Proportions 


1 


1.3 


3.6 


1 


1.8 


4.0 


j 


2.0 


3.9 


1 


2.2 


3.9 


1 


2.7 


3.3 


to 


































3 


Quantities 


1.67 


.33 


.90 


1.58 


.42 


.94 


1.49 


.44 


.86 


1.49 


.48 


.86 


1.49 


.59 


.73 



10 



146 CONSTRUCTION OF ROADS AND PAVEMENTS 



Direction of Flow Across Hoad 




(a) WISCONSIN CROSS SECTION FOR OVERFLOW ROADS 



40* 




Tile Drain Ln Box Trough 

STATE OF WASHINGTON STANDARD 



i 8" 



-76 



240 



tic Oil Wearing Surface 

'^AWrf'-W^&tf^idWftR 






4 Concrete Foundation 
CALIFORNIA STATE HIGHWAY FROM HEALDSBURG TO SANTA ROSA 



Slope Variable 




Macadam Shoulder 
(d] PHILADELPHIA SUBURBAN ROAD 



>l 




Longitudinal Drains x Blind Lateral Drains 

(6) ILLINOIS SECTION FOR LEVEL COUNTRY 




(/) STATE OF WISCONSIN (MILWAUKEE COUNTY) 

FIG. 36. Cross-sections for concrete roads. 



CONCRETE ROADS AND PAVEMENTS 147 

water than that which would give maximum strength, but the 
excess should be held as low as practicable. With mechanical 
devices for tamping and smoothing the concrete, the water may 
be held to a safe amount and still produce concrete that can be 
placed and properly finished. It is believed that a slump* of one 
inch will indicate the proper consistency. 

The foregoing table shows the proportions of various materials 
required to produce concrete having a compressive strength at the 
end of 28 days of 3000 Ibs. per square inch. 

Cross-section for the Concrete Road. The concrete road is 
commonly constructed with a small amount of crown, the usual 
practice being to make the crown at least equal to one one- 
hundredth of the width but not greater than one seventy-fifth 
of the width. These ratios of crown to width are not always 
adhered to but represent the best practice. 

Various attempts have been made to evolve a rational design for 
the concrete surface for a road or a pavement, but in all of these 
some assumptions relative to the supporting power of the soil 
must be made which are not yet fully substantiated by experi- 
mentation. For that reason, the generally accepted practice will 
be discussed rather than to go into theoretical considerations that 
are not yet fully accepted. 

Experience seems to prove that the concrete surface is less 
likely to crack if placed on a flat subgrade and accordingly for 
widths up to 20 ft. the subgrade is made flat and the crown is 
secured by making the thickness of the concrete greater at the 
middle than at the edge. For heavy traffic the thickness at the 
middle is usually 8 in. and at the edge about 7 in. For lighter 
traffic the thickness at the middle is made 7 in. and that at the 
edge about 5 in. A number of cross-sections are shown in Figs. 
36, 37 and 38. 

Cross-section for Concrete Pavements. The rules for crown 
given above are applied to pavements as well as to roads. On 
account of the width of a pavement it is impossible to have 
enough difference in thickness between the middle and edge to 
secure the proper crown. Consequently the concrete pavement 
is designed of uniform thickness, which is seldom less than 6 in. 
and rarely more than 8 in. This, of course, requires the use of a 
crowned subgrade. Typical cross-sections for concrete pavements 
are shown in Fig. 40. 

* See Chapter XXI for description of the slump test. 



148 CONSTRUCTION OF ROADS AND PAVEMENTS 




SINGLE TRACK CONCRETE ROAD 
LEVEL GROUND WITH 4'MACADAM SHOULDERS 




X Bars 2'O.C. 

SINGLE TRACK CONCRETE ROAD 
ON GRADES OF 5% OR OVER IN CUTS 



(6) 



Q Under Drains 
where necessary 



-Not less than 16- 
PreferablylS' 



DOUBLE TRACKCONCRETE ROAD 
EARTH SHOULDERS 




J^'Bars 2'O.C. 



DOUBLE TRACK CONCRETE ROAD IN CUTS 

w 

FIG. 37. Outline cross-sections for special conditions. 




^vW^^ ; -^M0^^4^1^ \^^^:;::^ 



Slope 2 to 1 

' N T~"^"* V "C V ^Ixy/i^^^xv^v/ ^v/v^ 
fpeStol' 5 Minimum. Wlat Sub-grade 

h 2'to4' ^*-Z'0^-^r< \i Wuptoio'fl- 

S.ECTIQN ON FILL 

Slope l>i'tol" 



~1 




-Ji W up to 100 



SECTION IN CUT AJ4D ON LEVEL GLR.OUND 

FIG. 38. Cross-sections recommended by American Concrete Institute. 



CONCRETE ROADS AND PAVEMENTS 149 

By casting concrete curbs, 1 gutters and pavements as monoliths 
the cost of highway and suburban road construction has been 
considerably reduced. Typical cross-sections of the various 
designs are shown in Fig. 39. Integral curbs add but a small 
amount in yardage of concrete, and the cost, depending on the 
type, should not be more than one-fifth to one-tenth of the cost 
of separate curbs. Distributed over the total area of the pave- 
ment there is added but a few cents per square yard to the 
pavement cost. 

With reinforcing in the slab it is usual to place the concrete 
in two layers, adding the curb with the second coat. On flat 
grades the curb height varies between inlets from 2 to 8 in. On 
streets having sufficient longitudinal slope to insure good drainage 
the curb height is made 6 in. and even as low as 3 in. 

Where the pavement is laid in one course, some form of curved 
gutter is used. The strike board is then cut away at the end to 
give the proper shape. 

Integral curbs are most conveniently constructed after the 
pavement proper has been finished. Just as soon as the final oper- 
ation of finishing has been completed, and before the concrete 
has set, the curb forms are set in place and the concrete placed, 
tamped and finished. If this work is done promptly the curb 
concrete will bond to the pavement sufficiently to insure against 
displacement. 

EARTH FOUNDATION 

Preparation of Subgrade. It is believed that in many instances 
the cracks in concrete road and pavement surfaces are due to 
unequal settlement of the foundation, and, therefore, it is de- 
sirable to take every precaution in preparing the subgrade, to 
insure but slight and uniform settlement. The effect of long- 
continued traffic on an earth road is to form a crust of hard-packed 
earth over the portion of the road most used. On a country 
road the width of such a crust is about 10 or 12 ft., and on a street 
15 to 20 ft. This crust or dense layer of soil often extends to the 
depth of 2 ft. In shaping the subgrade only the upper portion 
of this is disturbed. At each edge of the hard portion, the earth 
roadway is less dense because it has had less traffic. The edge 
of the concrete road or pavement, therefore rests on slightly 

1 See Engineering Record, Jan. 23, 1915. 



150 CONSTRUCTION OF ROADS AND PAVEMENTS 

less dense soil than that at the middle and settlement at the edge 
will be more marked than at the middle. This will be likely to 
result in longitudinal cracks near the center line of the pave- 
ment. No amount of rolling will bring the outer portion of this 
subgrade to the density of the middle portion if that middle portion 
has received the puddling action of traffic for years. There- 
fore, in the preparation of the subgrade the problem is to bring 
the middle portion to somewhere near the density of the outer. 
This can be done by plowing the entire width of the subgrade, 
bringing it all to a uniform condition, shaping it and then rolling 
until solid. Such treatment will insure nearly uniform density 
across the subgrade. 

Similarly, when the profile of the road passes from cut to fill, 
there will be in the vicinity of the transition a section of con- 
crete which is on top of the old undisturbed roadway for a part of 
its length and on new made cut or fill for the remainder. Here 
again unequal density exists in the foundation and unequal settle- 
ment and transverse cracking is inevitable. The difficulty can be 
overcome by loosening the entire subgrade, shaping it and then 
rolling it to bring it uniform density. 

As with many other types of hard surfaces the best results will 
be obtained when the grade-reduction work is completed and the 
earth surface traveled for a time prior to placing the concrete sur- 
face. This will insure that there will be little settlement of the 
fills after the concrete surface has been constructed and excessive 
cracking will, therefore, be avoided. 

Rolling. Rolling that is so carried out as to make the soil more 
dense than when in its natural state is believed to be undesirable. 
Light rolling that will compact newly placed earth is permissible, 
but very satisfactory results have been obtained where the earth- 
work was not rolled. It is impossible to compensate by rolling 
for inadequate drainage of the road bed for removing both surface 
water and underground water. 

It is apparent that thorough subsurface and surface drainage 
are prerequisites of successful concrete road construction. While 
drainage is important with any type of surface, it is probably 
more so with concrete than with any other. 

PLACING THE CONCRETE 

Mixing and Placing. A well-designed batch mixer is specified 
for concrete for road or pavement construction, and the type of 
self-propelled machine with a material hoist for loading and either 



CONCRETE ROADS AND PAVEMENTS 151 

a boom-and-bucket, or a chute for delivering the concrete is 
commonly employed. Of these, there are many kinds about 
equally satisfactory, and the advantage in their use lies in the 
fact that concrete is deposited directly from the mixer and the 
aggregates, therefore, have no opportunity to separate as some- 
times happens when concrete is conveyed for a distance in carts 
or barrows. The sand and stone for the concrete are deposited 
on the subgrade, after it has been rolled, in quantities just suffi- 
cient to make the requisite thickness of pavement. The mate- 



Concr l 

with i Ib Carbon 
Black Per Sack 
Cement _ ^ 
Tile Drain 3-0 




! ------ ..... ZS-O'Width 

Kimberly WIS. 
FIG. 39. Cross-sections for integral curbs on concrete pavements. 



"- ------ l8 : 0~Width 

Wirtnetka ILL. 



rials are put in at one end of the mixer and discharged at the 
other, the mixer moving along the subgrade as fast as the material 
is used up. 

The sand and stone for a batch of concrete are carefully meas- 
ured in special barrows or in bottomless measuring boxes placed 
in the ordinary barrow. 

A recent development is to load the aggregates into a small 
tram running on 18-in. gage track. The box on the tram is di- 
vided into two compartments of the right size for sand and stone 
respectively. The tram is run up to the loading hopper and 
dumped. The track is in sections which are taken up as fast as 
necessary and shifted farther back along the stock pile. 



152 CONSTRUCTION OF ROADS AND PAVEMENTS 



Some outfits of recent design have a mixer of sufficient capacity 
to mix 40 cu. ft. of material at a batch. The aggregates are hauled 
in 1^-yd. industrial railway cars, each car being loaded with the 
proper amount of sand and stone for one batch of concrete. The 
cars are drawn to the mixer and dumped directly into the hopper. 

Less than 10 Feet 



r *- to jL Width of Pa 



^^^^V^-*^*^ 

Jfe'* ; * : '^ : y^^^^ 

^^^^^^^^^^^ 




Flat Sob-grade 
- 10 Feet and over 



j~ Width of Pavement ^__ ^ 

^.^ HSa^^ 




Beinforcing Crown Sub-grade 

Not less than 6" 

Mansion Joint QN CO UR.SE PAVE.MENT 




TWO COURSE PAVEMENT 

FIG. 40. Cross-sections for concrete pavements. 

Central Mixing Plants. Recent experiments have indicated 
the possibility of hauling the mixed concrete for distances of up- 
wards of five miles, where the road over which the hauling is done 
will permit truck operation. As a result central mixing plants are 
set up at the unloading station for materials and the mixed latches 
are hauled in trucks or industrial cars to the site of the construction. 
Rather meagre tests indicate that the concrete is stronger at the 
end of the haul than at the beginning. It seems quite probable 



CONCRETE ROADS AND PAVEMENTS 153 

that this method of placing concrete for roads will be widely 
adopted. 

If the width of the pavement does not exceed about 30 ft., the 
entire width is placed at one operation and is struck off by means 
of a template which spans the entire width of the roadway. On a 
street carrying a car track the section between the track and the 
curb can be placed at one operation and the form at the track will 
serve as a guide for the template, while the curb which has been 
previously constructed will serve as a guide at the gutter. If the 
pavement is wider than about 30 ft., as would be the case with 
pavements on streets having no car tracks, transverse forms are 
usually set and the concrete struck off by means of a straight 
edge resting on the transverse forms. Longitudinal form boards 
at the middle of the pavement are avoided since they inevitably 
form a line of weakness which results in longitudinal cracks. The 
transverse forms are usually placed so as to form expansion joints. 
Strike boards spanning streets as wide as 40 ft. have been used 
successfully but extreme care is required in their construction if 
sagging is to be avoided. 

In country-road construction side forms are placed at each edge 
of the pavement and the strike board is drawn along the tops of 
the side forms. Several types of strike board are shown in Fig. 44. 

Mechanical tampers of various kinds are used for finishing 
the surface. These consist of a frame carried on rollers running 
on the side forms. The frame carries a gasoline engine which 
operates the tamper and the finishing mechanism. These machines 
produce a dense concrete and a very uniform texture and contour 
of surface. 

A vibrator is also used to finish concrete surfaces. The machine 
consists of a mechanical vibrator operated with a gasoline engine. 
After the concrete has been struck off to the proper cross section 
wooden duck boards are placed on the surface and the vibrator is 
run over the boards until the concrete has been thoroughly com- 
pacted. Sometimes the concrete is mixed with coarse aggregate 
that is not considered sufficiently durable for the wearing surface 
and then a thin layer of some high grade coarse aggregate is spread 
dry on the surface. The boards are placed on top of this and the 
vibrator drives the dry material into the concrete, affording a 
durable surface. The concrete thus produced is dense and strong 
and if the vibrating operation is followed by belt finishing, a 
smooth surface is produced. 



154 CONSTRUCTION OF ROADS AND PAVEMENTS 

Extreme care is exercised in placing the concrete to insure a 
uniform texture of surface. The concrete must not be mixed 
too wet, or separation of the aggregates will occur when the 
concrete is deposited. After the surface has been struck off to 
the desired shape it is finished with a wood float, the laborers 
working from a bridge which spans the roadway. Excessive 
floating is undesirable because of the possibility of wearing hollow 
places in the surface, and the finishing is preferably delayed until 
the cement begins to set up, which is generally about an hour 
after the concrete has been mixed. Some engineers prefer to finish 
the surface as soon as possible after the concrete has been 
placed. 




FIG. 41. Mixing and placing concrete on a rural highway. 



Curing the Concrete. Since the surface of the concrete road 
will be subjected to abrasion it is desirable for the concrete to 
be as tough as possible. Concrete that dries out is much in- 
ferior to concrete that is kept moist and sets properly, and the 
curing, therefore, consists in protecting the surface from drying 
and in furnishing plenty of water for the setting. As soon as 
the cement takes the initial set, the surface is covered with can- 
vas which is sprinkled constantly. Then as soon as the concrete 
has set sufficiently, it is covered with about 2 in. of clay or loam. 
Because of its tendency to dry out rapidly, sand is not a good 



CONCRETE ROADS AND PAVEMENTS 155 

covering unless it is put on to a depth of 3 or 4 in. The cover- 
ing is kept wet for 2 or 3 days and then kept moist for about 10 
days. The first 10 hr. after the concrete surface has been finished 
is the critical period for it and the durability of the road is largely 
determined by the care taken during this brief period. 

Expansion Joints. The value of expansion joints in concrete 
pavements is as yet unestablished, and the trend is toward their 
elimination. Custom and current practice is to make expansion 
joints at intervals of 25, 35 or 50 ft. if they are used at all. Some 
engineers prefer one spacing, others another. If it is assumed 
that the tensile strength of concrete is 50 Ib. per square inch, then 




FIG. 42. A water supply station for concrete road construction. 

theoretically the spacing of the joints should be about 50 ft. 
nevertheless many roads have been constructed with this spa- 
cing and the concrete slabs have cracked between joints. There 
are, however, apparently about as many transverse cracks on 
pavements having joints spaced 35 ft. apart. The American 
Concrete Institute recommends that where joints are used they 
be spaced at intervals of from 50 to 75 ft. and that the expansion 
material consist of a layer of felt % in. thick. 

Protection plates have been used extensively at the expansion 
joints. These plates are so placed that the edge is flush with the 
surface of the concrete. They are made of soft steel and the two 
plates that constitute a joint are separated by a layer of treated 
felt the thickness of which may be as little as J/g in. and is sel- 
dom more than % m - Experience seems to indicate that the 



156 CONSTRUCTION OF ROADS AND PAVEMENTS 

metal plate is unnecessary and even a detriment. It does not 
wear down as fast as does the concrete, the result being a high 
place at the joint and a low place at each side. 

Whatever type of expansion joint is employed, the concrete 
at the joint ought to be neither higher nor lower than the slab 
back from the joint. Considerable difficulty has been experi- 
enced in finishing the concrete to the same elevation on both 
sides of the joint, but recently a split-wood float has been de- 
vised that insures a good finish at the joint. This float spans 
the joint and thus brings the concrete on each side of the same 
elevation. 




FIG. 43. Well-built concrete road. 



Reinforced-concrete Pavements. It is often recommended 
that when pavements exceed 20 ft. in width, reinforcement of 
some kind be used for the purpose of preventing sizeable cracks 
and to distribute the stresses due to temperature and moisture. 
The advisability of such reinforcing is still a matter which is 
based on opinion rather than on definite experimentation and no 
conclusive results have as yet been forthcoming. If the concrete 
road or pavement is laid on soil subject to heaving from frost ac- 
tion or of variable drainage characteristics like the average clay, 
it is the usual practice to employ reinforcing of some kind. 

Two general types of reinforcing are available; mesh or fabric 
and rods. The mesh or fabric type of reinforcing is made in a 
variety of forms and weights, and both from wire or rods woven 
together and of the expanded metal type. Where bar reinforcement 
is used, any of the ordinary types of deformed bars may be used. 



CONCRETE ROADS AND PAVEMENTS 157 

The function of the reinforcing is to hold the parts of the slab 
together if cracks occur and to prevent the cracks widening and 
to prevent the adjacent parts of the slab from becoming displaced 
vertically. It is not intended to materially strengthen the slab as a 
beam. Mesh reinforcing is generally placed about two inches 
below the surface of the pavement with the main tension members 
cross-wise of the pavement. Bars are usually placed so as to 
divide the surface into squares about 16 ft. on a side, and like the 
mesh, the bars are placed about two inches below the surface. 

Characteristic of the Concrete Road. The well-constructed 
concrete road has a granular, uniform, easy-riding surface which 
affords excellent traction for motor vehicles and fair foothold 
for horses. It is relatively free from dust, but is somewhat trying 
to the eyes in bright sunshine due to its white color. When built 
well, it resists abrasion well, except at unprotected cracks or joints, 
but when a break occurs deterioration is rapid. The cost varies 
from $1.25 per square yard of surface to $1.65 for a thickness of 
8 in. at the crown line and 6 in. at the edge. As to the durability or 
ultimate life, experience does not yet permit a definite statement to 
be made but every indication is that it is a durable type of pave- 
ment if properly built and properly maintained. 

Maintenance. The defects that appear in the concrete pave- 
ment under traffic are (a) longitudinal and transverse cracks, 
(6) pits in the surface where pebbles or stones have disintegrated 
and been picked out, (c) abrasion or breaking down at the ex- 
pansion joints, and (d) gradual wearing of the surface. The 
method of maintenance is the same for all of these defects. A 
bituminous material, usually a soft grade of tar, but occasionally 
a similar grade of asphalt, is poured into the cracks and into the 
pits in the surface and into the expansion joints and is then cov- 
ered with coarse sand or chips of hard stone. This method of 
maintenance if properly carried out will probably serve- indefi- 
nitely and the only deterioration will be the natural wearing 
away of the surface under traffic. Many attempts have been 
made to minimize this effect by covering the entire surface with 
a layer of some kind of bituminous material. These attempts 
have been made with varying success, but appear to give promise 
that a material will eventually be manufactured that will ad- 
here to the surface and will thus form a cushion protecting the 
concrete from abrasion. As a matter of fact, such a surface 



158 CONSTRUCTION OF ROADS AND PAVEMENTS 

is being used extensively on the California State highways and 
is proving successful. The climatic conditions are perhaps ad- 
vantageous to this material in California, but it seems that a 
similar treatment will be worked out for roads in other localities. 
The best results so far seem to have been obtained with a light 
grade of tar and with a light grade of asphaltic oil. Such a 
surface apparently will be satisfactory for 2 or 3 years when it will 
need to be replaced. This, however, does not constitute an expen- 
sive maintenance charge, and if, as believed, it prolongs indefi- 
nitely the life of the pavement, it will be justified. 

Concrete Road with Bituminous Top. The State of California 
has constructed many miles of concrete roads with a thin wear- 
ing surface of asphalt and stone chips. The concrete road proper 
is 4 in. thick and the mixture is l-2}/-5. This method of con- 
struction has attracted wide attention and the following is a brief 
description of the methods employed and the material used. 

"In this method of construction, 1 the base is the same as if the 
1^2- to 2-in. asphaltic concrete covering were to be applied, 
but instead a thin coating of asphaltic oil of special quality is 
put on to the concrete by spraying machines at the rate of about 
J/2 gal. to the square yard. Clean stone screening or coarses and 
are then added in sufficient quantity to absorb the oil. The 
process requires much care in the selection of the materials used 
and in their manipulation but the result is a bituminized coating 
about ^g m - thick. The cost of such surface work ranges from 
5 to 10 cts. per square yard of pavement, depending on the cost 
of materials and local conditions. This means that more than 
90 per cent, of the cost of the work on the road goes into grading, 
culvert work and the concrete base, all of which may be con- 
sidered as practically permanent, and the remainder into the 
thin wearing surface. 

"Such a wearing surface should last from 2 to 4 years before 
it requires renewal, which renewal should cost considerably less 
than the original application. The thin surface is best adapted 
to rubber-tired vehicles, but it wears well under a considerable 
volume of mixed traffic consisting of both rubber- and iron-tired 
vehicles. The thin road surface can be recommended for a road 
carrying as many as from 500 to 600 vehicles a day, provided a 
considerable portion of the vehicles are rubber-tired." 

1 A. B. Fletcher, State Engineer of California, in "California Highways." 



CONCRETE ROADS AND PAVEMENTS 159 

The following is the specification for the asphaltic oil used on 
the California work. 

Specification for Road Oil. (a) The oil shall be a natural oil 
with an asphaltic base, treated to remove water or sediment, or 
the residuum of such an oil from which the volatile material 
has been removed by distillation, and shall be satisfactory to the 
engineer. It must not have been injured by overheating, and it 
must not be obtained by adding solid asphalt to lighter oils or 
distillates. 

(6) In determining the quantity of oil delivered, the correction 
for expansion by heat shall be as follows: From the measured 
volume of oil received at any temperature above sixty (60) de- 
grees F. an amount equivalent to four-tenths (0.4) of one (1) 
per cent, for every ten (10) degrees above sixty (60) degrees F. 
shall be subtracted as the correction for expansion by heat. For 
the purpose of measuring oil, a temperature of sixty (60) degrees 
F. shall be deemed a normal temperature. 

(c) Deduction will be made for water and sedient in exact 
proportion to the percentage of water and sediment found therein, 
and the oil shall not contain over two (2) per cent, of such water 
and sediment. 

(d) After being freed from water and sediment, the oil shall 
contain not less than ninety (90) per cent, of asphalt, having at a 
temperature of seventy-seven (77) degrees F. a penetration of 
eighty (80) degrees District of Columbia standard. The per- 
centage of asphalt shall be determined by heating twenty-five 
(25) grams of said oil or residuum in an evaporating oven at a 
temperature of four hundred (400) degrees F. until it has reached 
the proper consistency, when the weight of the residuum shall be 
determined and the percent, calculated. 

(e) The oil shall show an adhesive strength of not less than 
three hundred (300) seconds when tested at a temperature of 
seventy-seven (77) degrees F. by the Osborne adhesive test 
apparatus at the laboratory of the California Highway Commis- 
sion. The oil shall show a specific viscosity of not more than 
one hundred (100) when tested with the Engler viscosimeter at a 
temperature of two hundred and twelve (212) degrees F. 

(/) Residuum shall not contain in excess of two-tenths (0.2) 
of one (1) per cent, of organic matter insoluble in carbon tetra- 
chloride at ordinary temperature, after the removal of the per- 
centage of water and sediment. 



160 CONSTRUCTION OF ROADS AND PAVEMENTS 



MACHINERY USED FOR CONCRETE ROAD WORK 

Mixers. Any batch mixer of good design may be used for 
concrete road and pavement construction, but the self-propelled 
type with some sort of boom or chute for distributing the con- 
crete has come into wide use. It is best to spread and finish the 
concrete immediately behind the machine, which makes this type 




FIG. 44. Vibrating and Tamping Finishers. 

of mixer particularly desirable. The two-sack batch size is quite 
widely used. The later models have the batch meter for indica- 
ting when the batch has been mixed long enough, automatic 
water tanks, and loading skips. 

The delivery may be by means of a bucket traveling on a 
swinging boom, by means of a rotating cylindrical chute, or by 
means of a straight chute. Probably there is no great difference 
between the first two methods of depositing the concrete so far 



CONCRETE ROADS AND PAVEMENTS 161 

as flexibility is concerned, but the third has a somewhat limited 
radius of delivery due to the fact that a relatively short spout 
must be used to secure enough slope. 

The mixer travels along the road under its own power, being 
equipped with a special clutch which can be thrown in with a 
lever whenever it is desired to move the machine. 

Rollers. The three-wheeled roller weighing about 8 tons or 
the tandem type of roller of about the same weight is used for 
compacting the foundation. 

The single roller drawn by teams is also used, but it is not to 
be recommended. 

Finishing Bridge. The essential of the finishing bridge is that 
it be reasonably light so as to be easily moved and that it be 
strong enough to support two men. It must be supported low 
enough to permit the men to reach the surface readily with the 
floats. 

Strike Board. The strike board or template used to strike 
off the surface is a 2-in. plank about a foot wide at the ends and 
having one edge cut to fit the crown of the road. The striking 
edge is faced with a metal strip. At the ends metal handles are 
provided for convenience in operation and if the length exceeds 
about 10 ft. a rod is attached at the middle so that a laborer can 
assist in pulling the board along. 

In some instances a strike board is made double, and that is 
with two lj^-in. planks about 6 or 8 in. apart. This form of 
template does not have any advantages over the single-plank 
to compensate for the greater weight. 

For streets wider than 16 ft., the strike board must be care- 
fully trussed to prevent its springing while in use. Not infre- 
quently the longer templates are arranged with rollers at the 
ends which follow the top of the side form thus carrying the 
weight of the template and facilitating its operation. 

Finishing Floats. The concrete road or pavement is almost 
universally finished with a wooden float. It may be the ordinary 
float about 6 in. wide and 12 to 14 in. long with the handle affixed 
to the top, or it may be the larger float which is about 12 in. 
by 16 in. and has a handle about 4 ft. long. 

Several attempts have been made to construct mechanical 
floats and doubtless these will eventually be successful. The 

general plan is to arrange a series of small wooden floats on a 
11 



162 CONSTRUCTION OF ROADS AND PAVEMENTS 

chain or cable and to cause them to be dragged across the 
surface. 

For finishing at the expansion joint the split float is used, the 
two parts of the board being separated by a slot about 2 in. wide. 
The slot spans the joint filler and insures that both sides will be 
finished to the same elevation. 

Joint Setting Devices. If metal protection plates are used at 
the expansion joints, special devices are sometimes employed for 
setting them. The device consists of a bar of tee section bent 
to conform to the cross-section of the road surface. The pair of 
protection plates with the felt filler between is clamped to the 
setting bar, the ends of which rest on the side forms. After the 
joint is in place and the concrete has been spread and has partially 
set, the teebar is removed and the surface next the joint 
smoothed to remove the marks of the clamps. 




FIG. 45. Split float for finishing along expansion joints. 

Water Supply Equipment. Where concrete roads are con- 
structed in the country a special water-supply system must be 
installed. This outfit consists of a plunger pump having a 
capacity of about 100 gal. per minute and the necessary engine 
for driving it. Usually a gasoline engine is used for the purpose. 
The supply pipe, which is never smaller than 1J m - an d is 
usually lj^ or 2 in. is laid along the road. The mixer is con- 
nected by means of a hose of sufficient length to permit the 
machine to move along the road for some distance before 
changing the hose to a new connection on the pipe. Hose 
connections are also provided for convenience in sprinkling the 
finished concrete. 

Oil Distributors. For bituminous-coated concrete road the 
pressure distributor described in connection with bituminous 
carpets is used. 



CONCRETE ROADS AND PAVEMENTS 



163 



TABLE 12. COST OP CONCRETE ROADS 
Milwaukee County, Wisconsin 

Average cost per square yard for an average thickness of 7 in. 

Cost of sand and stone $0 . 27 

Unloading aggregates to hauling vehicles . 05 

Hauling materials average of 2% miles 0.27 

Mixing and placing 0.20 

Metal protection plates for expansion joints 0.03 

Furnishing water . 02 

Cement 0.45 

Allowance for contractor's profit and for liability insurance 
in addition to the above. 

TABLE 13. ILLINOIS STATE AID CONCRETE ROADS, 1914 
(Actual Contract Prices) 







. < 


"osts per mi 


e 




Cost of 


J XT 


Width 








Length, 


concrete 












feet 


per square 






Grading 


Concrete 


Macadam 




yard 


I. 


10 ft. concrete; 














4 ft. mac 


1,965 


8,400 


1,780 


7,200 


1.43 


II. 


10 ft. concrete 


1,430 


6,300 




6,009 


1.07 


III. 


10 ft. concrete; 














4 ft. mac 


1,330 


7,840 


2,380 


9,000 


1.34 


IV. 


18 ft. concrete 


6,040 


11,600 




24,000 


1.10 



EXAMPLES OF GOOD PRACTICE 

CONNECTICUT STATE HIGHWAY DEPARTMENT 1 

Among the features to which special importance is attached are 
the following: Thorough rolling of the subgrade; adequate pro- 
vision for drainage ; a specified minimum time for the mixing of 
each batch of concrete; careful grading of the concrete aggre- 
gates; thorough washing of sand; curing of the finished road; 
accurate measurement of concrete materials in boxes instead of 
rough wheelbarrow measurement; use of steel reinforcement; 
and the placing of tar-paper expansion joints at 30-ft. intervals. 

The Milford turnpike is a single-course reinforced-concrete 
road, 18 ft. wide, with 5-ft. macadam shoulders. It is 8 in. 
thick at the center and 6 in. at the side and is reinforced with the 
American Steel & Wire Co.'s No. 29 wire mesh. The new pave- 

1 Engineering Record, Apr. 17, 1915. 



164 CONSTRUCTION OF ROADS AND PAVEMENTS 

ment rests upon an old macadam foundation which had begun 
to show signs of wear. 

PROVISION FOR DRAINAGE 

Before the construction season opened a thorough examination 
of the old macadam road was made to detect poorly drained 
sections. After a heavy rain, when the frost was leaving the 
ground, these bad spots were located with stakes, and when work 
began they were replaced by a 15-in. subbase of washed gravel, 
varying in size from Y to 1% in. This gravel subbase was 




FIG. 46. Concrete road and concrete guard rail. 

drained into the side ditches at suitable intervals. In Con- 
necticut the experience has been that a gravel foundation of this 
type is more satisfactory, under concrete, than a Telford base, 
for it is less subject to the influence of frost. The 15-in. gravel 
base can be put in at the same price as an 8-in. Telford foundation. 
In preparing the new subbase, which is flat, a definite policy 
of cutting down the old macadam crown was adopted. If the 
full thicknes.s of the old 7-in. surface at the center line of the road 
had been used to support the new pavement, the fill necessary to 
bring the grade horizontal at the shoulders would have been ex- 
cessive, and even if rolled thoroughly might have settled and 
caused cracking in the finished concrete. On the other hand, 



CONCRETE ROADS AND PAVEMENTS 



165 



if too deep a cut was made at the crown the full supporting value 
of the old road surface would not have been realized. On the 
Milford turnpike the depth of cut at the crown was fixed at 3H 
in., giving a fill of 2 in. at the side, using the material which has 
been removed from the center of the roadway. 

Where it was necessary to put in the gravel subbase particular 
attention was given to making the foundation compact, and the 
material was watered and rolled to a solid bearing with a 15-ton 
steam roller. On side-hill work a drain, 2 ft. wide and 40-in. 
deep, filled with crushed stone, was constructed on the uphill 
side to intercept the water before reaching the roadbed, and 6-in. 
tile pipe with open joints was used for carrying the water. 



CONCRETE AGGREGATES 

The coarse aggregate for the concrete was a local trap rock with 
high abrasive qualities. Coarse sand was used and the washing 



FIG. 47. Cracks in a concrete road filled with tar to prevent excessive wear. 

of the fine aggregate was made compulsory. For the sand it 
was specified that not more than 15 per cent, should pass a 50- 
mesh sieve and that the tensile strength should be equal to that 
of briquettes made with standard Ottawa sand. The contractor 
was required to deliver the stone on the work in three sizes 



166 CONSTRUCTION OF ROADS AND PAVEMENTS 



%, % and \y in. No mixing of these sizes was permitted before 
delivery. When the stone reached the work tests were made to 
determine the proportions for the densest mixture and the one 
which could be worked to best advantage, special attention being 
paid to these points. The value of washing the sand was proved 
conclusively by an experience on a nearby contract, where 
this requirement was not made, and where the work was of an 
inferior quality as a result. All of the cement was required to 
pass the test of the American Society for Testing Materials. 

PLACING CONCRETE 

The mixture used was 1 part Portland cement, 2 parts sand 
and 4 parts crushed trap rock. These materials were mixed 
and delivered to place by a bucket and boom. A rigid rule was 
enforced requiring the contractor to turn each batch in the mixer 
at least 1J^ min. The good quality of concrete produced is 
attributed in part to this feature of the construction routine. 
The progress in concreting was 300 ft. of 18-ft. roadway per day 
of 9 hr., amounting to about 120 cu. yd. of concrete. 

BOOM MIXER USED 

It was noted that the boom bucket which received the mixed 
concrete was not water-tight and that after the plant had been 
in place for awhile the drippings of cement and sand grout formed 
a small mound under the loading point. If this mound of 
material had been allowed to remain in place, it would have 
produced a soft spot in the finished pavement, for since it con- 
tained no coarse aggregate it would have had slight resistance 
to the abrasion of passing traffic. These mounds of grout, 
therefore, were always removed wherever the position of the 
mixer was changed and were replaced with concrete containing 
the standard proportions of coarse stone. This is one of the 
small details of the work which are believed to have been 
responsible for good results. 

The wire-mesh reinforcement was delivered in rolls of 60-in. 
width and was laid transversely. At places where bad spots had 
existed in the old subbase, the reinforcement was placed near 
the bottom of the concrete slab to take up any stress due to set- 
tlement. Elsewhere the steel was placed 2 in. below the top 
surface, to counteract any heaving due to frost action. 



CONCRETE ROADS AND PAVEMENTS 



167 



EXPANSION JOINT 

The pavement was laid in 30-ft. sections with an expansion 
joint of three thicknesses of tar paper between sections, when 
the weather was cool, and two thicknesses during the warmest 
period. For the placing of these joints a 1^-in. pine board was 
set up across the roadway and the tar paper tied to it with string, 
allowing about % in. of the paper to project above the finished 





FIG. 48. Bituminous surface on a concrete road. 

surface of the roadway. A split float, straddling the expansion 
joint, was used to bring the surface of the concrete to the same 
elevation at each side, thus avoiding any bumps in the finished 
work which the wheels of passing vehicles would chip off. When 
the concrete had reached its final set, the projecting tar paper 



168 CONSTRUCTION OF ROADS AND PAVEMENTS 

was cut off a quarter of an inch above the surface of the road with 
a shovel, and when traffic was allowed on the road the projecting 
edges of the paper were broomed over, forming a protection for 
the edges of the concrete. Joints of this type have given about 
a year's service and then are treated with a mixture of tar and 
sand, a maintenance operation costing about $15 per mile. As a 
result of the experience the engineers believe that the tar-paper 
joint is better than steel, for with a steel joint it is difficult to 
bring the top surface of the concrete to the same curve as the 
steel plate. The steel joint also adds about 4 cts. per square 
yard to the cost of the pavement. 

Parallel to the center line of the roadway at either side are 
placed 6 by 6-in. wooden stringers held in position by 1-in. iron 
pins. These stringers serve as the side forms for the concrete 
work. 

The pavement is floated from a plank bridge, and is scored 
transversely with rattan brooms to prevent slipperiness. The 
screeds used are 2j^-in. plank with iron shoes, resting upon the 
6 by 6-in. wooden stringers. 

A FEW CONSTRUCTION DETAILS 

In forming the joints it is important not to work the concrete 
so that cement mortar alone is present at the end of the section. 
If this happens the joint will be weak and will chip off quickly 
under traffic. It is essential to have a certain quantity of stone 
at the end of each section to resist abrasion. 

Another detail of construction which experience has shown is 
well worth following is the accurate measurement of concrete 
aggregates prior to their delivery to the mixer. The ordinary 
wheelbarrows were not allowed for this purpose but instead, the 
wheelbarrows were fitted up with calibrated boxes. With these 
devices available for accurate measurements, there was no 
guesswork in the proportioning of the concrete. 

The final operation in the construction of the concrete road 
consisted in covering it with 2 in. of earth, which was kept moist 
for a period of 8 days. Water was pumped from the river to a 
standpipe at the middle of the job through a 2-in. pipe line laid 
by the contractor. No section of the road was opened to traffic 
until 2 weeks after the concrete had been placed. 



CONCRETE ROADS AND PAVEMENTS 169 

CONCLUSIONS OF THE SECOND NATIONAL CONFERENCE ON 
CONCRETE ROAD BUILDING, FEBRUARY, 1916 

SPECIFICATIONS 

Since no specifications were considered by the Conference, the 
Standard Specifications for Pavements and Roadways of the American 
Concrete Institute are recommended. 

DRAINAGE 

The drainage of the roadbed is of vital importance. If the subgrade 
is not well drained there is danger of unequal settlement or frost action, 
which will cause cracks. The method of drainage to be used will de- 
pend on local conditions. For streets, as well as roads, tile drains may 
be used which should be laid on each side of the roadway, or on one side 
only, with cross-drains leading thereto at a suitable depth, depending 
on the width of the pavement. Drainage trenches, if placed under 
the subgrade, should be completed before final rolling. 

GRADING 

When roadways are constructed over fills, extreme care should be 
observed to insure the use of proper materials in layers of such thick- 
ness that they may be thoroughly compacted so that when the fill is 
completed there will be a minimum of settlement. In general, fills shall 
be made in thin layers, the depth depending on the character of material 
to be used in making the fill. The fill should be allowed to stand for 
as long a time as possible, giving it an opportunity to settle thoroughly 
before the pavement is placed thereon. Deep fills should be allowed to 
settle through one winter wherever such procedure is possible. Pud- 
dling will be found advantageous in compacting deep fills. Wetting and 
rolling shall be performed when making a fill in order to secure thorough 
compactness. Fills should never be made with frozen materials nor 
with lumps greater than 6 in. in their greatest dimension. 

SUBGRADE 

The fundamental requirement of the subgrade is that it should be of 
uniform density so that it will not settle unevenly and cause cracks in 
the surface of the pavement. No part of the work is more worthy of 
intelligent care and painstaking labor than the preparation of the 
subgrade. The slight additional cost necessary to insure good results 
is abundantly justifiable. When the pavement is constructed on virgin 
soil, care should be taken to remove all soft spots so as to insure a 



170 CONSTRUCTION OF ROADS AND PAVEMENTS 

uniform density; and if constructed on an old roadbed, even greater 
care must be taken to secure uniform density, as the subgrade is likely 
to be more compact in the center than at the sides. An old roadbed 
should be scarified, reshaped and rolled. The subgrade adjacent to 
curbs should be hand-tamped. 



MATERIALS 

Portland Cement. Portland cement shall meet the requirements of 
the standard specifications for Portland cement of the American Society 
for Testing Materials and tests should be made in accordance with the 
methods of tests outlined by the American Society of Civil Engineers. 

Aggregates. The selection of proper aggregates for concrete road con- 
struction is of utmost importance. Clean, hard, well-graded materials 
are absolutely essential to success. For this reason samples of the 
materials proposed for use should be submitted to the engineer 
for approval before orders are placed. These samples should be 
carefully inspected; and if possible, laboratory tests made to determine 
their suitability. If laboratory tests on shipments cannot be made, 
field tests can be used to furnish a general indication of quality. 

The different aggregates should be kept clean and separate. 

Aggregates to be used in the wearing course of two-course pavements 
bhould never be placed on the subgrade but on planks or some other 
means provided to keep them free from dirt. When aggregates are 
placed directly on the subgrade care should be used by the shovelers 
to avoid getting clay or earth shoveled from the subgrade into the mix. 
Aggregates should not only be clean when they are delivered on the 
job, but clean when placed in the mixer. 

Water. Water supply is a most important factor and is frequently 
overlooked by the engineer and contractor. A large supply of water is 
necessary for (a) sprinkling the subgrade; (6) mixing the concrete; and 
(c) keeping the concrete moist during early stages of hardening. For 
this latter purpose 25 or 30 gal. per square yard of pavement will be 
required during the summer months. Insufficient sprinkling is 
detrimental to the wearing qualities of the pavement. 

Reinforcement. The use of reinforcement in concrete pavements is 
increasing. 

A coating of light rust will not be detrimental to satisfactory results 
but care should be exercised that no excessive rust, paint or other coat- 
ings are present to interfere with proper bond. Care should also be 
exercised to see that the reinforcement is so stored, prior to use, that it 
is not covered with mud or clay when placed in the pavement. Re- 
inforcement left on a job when contract is not completed at the end of 
the season should be collected and stored so that it is protected from the 



CONCRETE ROADS AND PAVEMENTS 171 

elements. Occasional tensile and bending tests should be made to see 
that the requirements of the specifications are fulfilled. 

Joint Filler. Joint filler should preferably be of a single thickness. 
Transverse joint filler should be cut to the crown of the pavement 
by the manufacturer when metal plates are used. A type of joint filler 
which will iron out readily under traffic is preferable for use in unpro- 
tected joints. A joint filler which will not bend easily when concrete 
is deposited against it is to be preferred. 

Joint-protection Plates. Metal joint-protection plates should be 
properly bundled and wired by the manufacturer so that they will 
arrive on the work in good condition, free from warp. Protection plates 
up to 20 ft. shall be shipped in single lengths. The exact length should 
be provided so that the contractor will not find it necessary to cut plates. 
In cutting plates for length, spacing between eccentrics on the installa- 
tion bar should be considered to avoid interference with anchorage lugs 
on plates. Particular care should be used by the manufacturer in 
crowning the installing bar, to avoid the necessity of duplication of work 
by the contractor. 

FORMS 

Metal forms of sufficient strength to withstand the necessary hard 
usage are preferred. When wooden forms are used they should be of 
at least 2-in. stock and capped with a 2-in. angle iron, so constructed 
that adjacent sections can be lapped. Forms should have a width not 
less than the thickness of the pavement at the sides. Particular care 
should be exercised to see that the top edge of forms are clean so as to 
avoid unevenness in the finished pavement. If forms are warped or 
stakes not properly placed, a poor alignment of the edge of the concrete 
slab will result. 

PAVEMENT SECTION 

Thickness. The thickness of a concrete road or pavement is con- 
trolled by many factors, each of which should be given consideration. 
In view of the increasing use of the heavy motor truck and bus, it seems 
unwise to build pavements with a thickness of less than 6 in. at any 
point. In general, pavements shall be thicker at the center than at 
the sides. Alleys with an inverted crown and narrow one-slope roads 
should have uniform thickness. Wherever the thickness can be in- 
creased without excessive cost, to secure a flat or nearly flat subgrade, 
such increase is advisable. 

Width. The desirable width for single-track road is 10 ft. The 
desirable width of double-track roads is 18 ft. The total width of the 
roadway should not be less than 20 ft. for single-track roads and not 
less than 26 ft. for double-track roads. 



172 CONSTRUCTION OF ROADS AND PAVEMENTS 

Crown. The crown of roads and pavements should be not less than 
one one-hundredth nor more than one-fiftieth of the total width. 
Except in unusual cases, one one-hundredth will be sufficient for 
country roads and one-fiftieth will be considered satisfactory for alley 
pavements. For city streets an average crown of one seventy-fifth will 
generally be found sufficient and should not be reduced, except on 
grades. 

JOINTS 

Transverse Joints. Joints should be placed across the pavement 
perpendicular to the center line about 50 ft. apart. 

There seems to be a tendency to widen the distance between joints. 

Joints should extend entirely through the pavement as well as through 
the curb if integral curbs are used. Joints should be constructed 
perpendicular to the surface of the pavement to avoid the possibility 
of one slab rising above the other. 

Longitudinal Joints. Longitudinal joint filler should be staked or 
otherwise securely held against the curb. Joint material should also 
be placed around manholes, catch-basins, etc. 

Protected Joints. The tendency of present practice is toward the 
omission of metal protection plates for joints. It is possible that the 
value of metal protection plates is dependable somewhat on the char- 
acter of aggregate used, and it is considered that they are more essential 
in street pavements than in country highways. 

Plates. Plates for protected joints should be wired together with the 
joint filler in place and securely held in the installing bars. When 
short sections of joint filler are used they should likewise be wired 
together. Supports for the joint should be used when the pavement is 
of such width that the installing bar deflects. On wide streets every 
joint should be checked as to crown with sighting T's. When neces- 
sary to have joint plates in two sections, the contractor should arrange 
with the manufacturer, to have holes drilled in the abutting ends of the 
plates so that the plates may be securely wired or strapped together. 
As the joint plates usually do not fit tight to the installing bar, a 34 -in. 
shim is placed under each end of the installing bar, to insure that the 
plates are not covered by the concrete. 

MIXING AND PLACING CONCRETE 

Measuring. The method of measuring materials for the concrete, 
including water, should be one' which will insure accurate proportions 
of each of the ingredients at all times. It is recommended that a sack 
of Portland cement, containing 94 Ib. net, be considered the equivalent 
to 1 cu. ft. 



CONCRETE ROADS AND PAVEMENTS 173 

Proportioning. The proportions should not exceed 5 parts of fine 
and coarse aggregate measured separately to 1 part of Portland cement, 
and the fine aggregate should not exceed 40 per cent, of the mixture of 
fine and coarse aggregates. 

Aggregates. Bank-run material should not be used. Proportioning 
based on sieve analysis or by relative density tests is not practicable for 
concrete roads, except where laboratory direction is available; but where 
proper facilities are available the above proportions should be varied as 
the tests warrant. 

Mixing. The ingredients should be mixed in a batch mixer. The 
mixing should be continued for at least 1 min., after all the materials 
are in the mixer and before any of the concrete is discharged. The 
speed of the mixer should not exceed 16 revolutions per minute; however, 
the time and not the number of revolutions should be the gage of proper 
mixing. 

Consistency. The practice is to mix concrete entirely too wet. The 
consistency should be such as not to require tamping, but not so wet 
as to cause the separation of the mortar from the aggregate in handling 
and placing. The strength and wearing qualities of the concrete are 
vitally lessened by an excess of water in mixing. 

Placing. If the subgrade has been disturbed by teaming or other 
causes, it should be brought to its former surface, and thoroughly satu- 
rated with water. The concrete should be deposited rapidly to the 
required depth and width. The section should be completed to a trans- 
verse joint, without the use of intermediate forms or bulkheads, or a 
transverse joint may be placed at the point of stopping the work. In 
case the mixer breaks down the concrete should be mixed by hand to 
complete the section. Where reinforcement is used it should be em- 
bedded in the concrete before the concrete has begun to set; the concrete 
above the reinforcement should be placed within 20 min. after the placing 
of the concrete below. 

In two-course pavements the top should be placed within 20 min. 
after the placing of the bottom. 

Finishing. The surface of the concrete should be struck off by means 
of a template moved with a combined longitudinal and transverse 
motion. The excess material accumulated in front of the template 
should be uniformly distributed over the surface of the pavement ex- 
cept near the transverse joint, where the excess material should be 
removed. 

The concrete adjoining the transverse joint should be dense and any 
depressions in the surface should be filled with concrete of the same 
composition as the body of the work. After being brought to the 
established grade with a template, the concrete should be finished, 
from a suitable bridge, with a wood float to true surface. A metal float 
should not be used. 



174 CONSTRUCTION OF ROADS AND PAVEMENTS 

Brooming of the surface is not necessary and grooves are objectionable 
even on grades. 

RETEMPERING 

Retempering of mortar or concrete which has partially hardened, 
that is, mixing with additional materials or water, is strongly condemned 
and should not be permitted. 

'PROTECTION AND CURING 

Even the best concrete may be seriously damaged by too rapid drying 
out, early exposure to low temperature, or by being opened to traffic 
at too early a period. Hot sun and drying winds are most liable to dry 
out the concrete too rapidly, thus causing shrinkage cracks or causing 
a surface which will not wear well under traffic. The use of a canvas 
covering will be found effective in overcoming this condition. 

Sprinkling should also be employed as soon as the concrete is hard 
enough to prevent the surface being pitted. An earth covering or 
protection by ponding should be employed after the first day. Under 
most favorable conditions such protection should be given the pave- 
ment for at least 2 weeks. Water should be added during this period 
to keep the concrete wet. 

In cool weather it is often advisable to omit the earth covering, thus 
allowing the concrete to harden more rapidly. Sprinkling should not 
be omitted during the day in case the surface shows a tendency to dry 
out. When there is danger of frost, sprinkling should be omitted and 
a covering of canvas or straw and canvas used. 

Placing concrete in roads and pavements in temperatures at or near 
freezing is not advisable, and if in special cases, such work is unavoid- 
able, the water and aggregate should be heated and precautions taken 
to protect the concrete from freezing for at least 10 days. Chemicals 
to lower the freezing temperature of the mixture should not be used. 

Concrete should not be deposited on a frozen subgrade. 

OPENING TO TRAFFIC 

Under most favorable conditions a concrete pavement should not 
be opened to traffic in less than 2 weeks and when conditions permit this 
interval should be at least 4 weeks. 

ONE-COURSE PAVEMENT 

Where the materials most readily available are such as to give good 
construction in one-course pavement, this convention recommends 
that the one-course be used. 



CONCRETE ROADS AND PAVEMENTS 175 

INTEGRAL CURB 

The integral curb for concrete street pavements is recommended in 
preference to straight curb or combined curb and gutter. Such con- 
struction eliminates the longitudinal joint along curb, maintains a 
permanent grade and alignment. Precaution should be taken to insure 
that the curb is thoroughly bonded to the pavement proper. The 
integral curb can be used on wide as well as narrow streets. 



CHAPTER X 
VITRIFIED BRICK ROADS AND PAVEMENTS 

The brick pavement is one of the older and more widely used 
types of pavement developed in the United States. The first 
brick pavements were built with soft brick and under unsuitable 
methods of construction and hence were neither smooth nor 
durable, but both the process of manufacturing the brick and 
the methods of constructing the pavements have been steadily 
improved until the brick pavement has become one of the most 
widely used of all the types. At present, nearly one-half of the 
paved streets in the United States are of brick. 

While it is assumed that the reader has already become familiar 
with the process of manufacture of paving brick, attention will 
be called to a few physical characteristics of brick that are of 
special significance in the paving industry. 

KINDS OF BRICK 

Repressed Vitrified Brick. The repressed brick is first mould- 
ed slightly thicker than the finished brick is to be, and without 
spacing lugs. It is then repressed in a mould that puts raised 
letters or lugs on one face of the brick. The letters or lugs serve 
to separate uniformly the brick in the pavement so that the filler 
will flow freely into the joint between courses. If the lettering 
is too elaborate, it retards the flow of filler somewhat, and a 
simple design or merely raised lugs are preferred to the more 
pretentious lettering. 

It is generally recognized that repressing has a tendency to 
weaken the structure of the brick, especially with some kinds of 
clay. Since practically all paving brick are manufactured by 
the stiff-mud process, incipient laminations are inevitable, and 
these may be made more pronounced by the repressing process. 
In this process the corners of the dies in which the brick are 
pressed have a small fillet which produces a slightly rounded 
edge on the brick, a fact that will be noted again. A type of re- 
pressed brick is shown in Fig. 49, e. 

176 



VITRIFIED BRICK ROADS AND PAVEMENTS 177 

Non-repressed Brick. In order to eliminate any possible 
objectionable effect of repressing and to cheapen the process of 
manufacture several types of brick are now made by processes 
which avoid repressing. The lugs for spacing the brick in the 
pavement are secured by various means, and the differences in 
the processes are chiefly differences in the method of securing the 
lugs. 

Wire-cut Lugs. In the Dunn process the column of clay is 
cut the long way of the brick, i.e., the brick are "side cut," and 
the cutting wire is guided so that it cuts lugs on the brick as 
shown by Fig. 49, c. The vertical faces of the brick are, therefore, 




01 b 



FIG. 49. Types of vitrified paving brick, (a) Vertical fibre, (b and d) 
Non-repressed, (e) Repressed, (c) Non-repressed wire cut lug. 

the cut faces, and being rough, afford a good surface for the 
filler to adhere to. It will also be noted that the edges of the 
brick which form the upper edge of the transverse joint between 
the rows are square instead of rounded as in the case of the re- 
pressed brick. 

Vertical Fiber Brick. The term "vertical fiber .brick" is a 
trade designation for paving brick that are manufactured in 
such a way that the laminations, if any exist, will be perpendicular 
to the surface when the brick is laid in the pavement. This 
type of brick is wire cut, but instead of the wire-cut face being 
vertical in the pavement, it is the top or wearing face of the 
brick. To secure lugs, ridges or beads are moulded on one edge 
of the brick. These beads are vertical when the brick is laid, 
and extend entirely across the brick. This type of brick also 
has a square edge at the joint between rows in the pavement 
(see Fig. 4<5, a), 
12 



178 CONSTRUCTION OF ROADS AND PAVEMENTS 

Another type of non-repressed brick is shown in Fig. 49, 6. 
This brick is moulded with two beads outstanding on one face 
which are subsequently flattened for the middle half of the length 
of the brick. This leaves four short sections of the bead out- 
standing to serve as lugs and these are in a horizontal position 
when the brick has been laid. This type of brick also has rounded 
edges along the joint between rows. 

Still another type of non-repressed brick is shown in Fig. 49d 
The spacing lugs consist of four raised knobs about }/% in. in 
diameter. These are moulded on the brick as the clay comes 
through the dies by a special device attached to the die. 

PHYSICAL CHARACTERISTICS OF BRICK 

Wearing Qualities. The wearing properties of brick are de- 
termined by the rattler test described in Chapter V. The limits 
placed on the loss during the rattler test will vary with the class 
of service demanded. The uniformity of the brick will be shown 
by the loss of individual brick, and it is, therefore, advisable in 
many instances to specify both the average loss of the batch of 
ten bricks and the maximum permissible loss for individual brick. 
The following table will indicate in a general way the limits that 
should be put on these two amounts: 

LIMITS FOR RATTLER Loss OF PAVING BRICK 

Average Max. loss 
loss for any brick 

For brick for heavy traffic 20 24 

For brick for medium traffic 22 26 

For brick for light traffic 25 28 

The quality of brick that should be used in any case is a matter 
that must be determined for each piece of pavement after a 
careful analysis of the traffic conditions as explained in 
Chapter IX. 

Effect of Absorption. The absorption test indicates the den- 
sity and in a measure the degree of vitrification of the brick. 
These facts are also shown by the rattler test, and the absorp- 
tion test is rarely specified for paving brick. When both the 
average and maximum loss during the rattler test are specified, 
it is superflous to also include the absorption test. 

Cross-breaking Test. The cross-breaking test is rarely speci- 
fied for paving brick except when brick other than standard 



VITRIFIED BRICK ROADS AND PAVEMENTS 179 

blocks are used. As a matter of experience, brick rarely fail 
by cross-breaking or crushing. 

Size of Brick. The size of brick commonly used for paving is 
called the paving block. The length lies between 8 and 9 in.; 



Brick Road 




Cross Section l Joint 
Vitrified Brick Citj Pavement 
( Standard Construction ) t< 

Cement Grout Tiller 1 to 1 j,,\" 4 Brick .1 H Sand Cushion 



4 Concrete Foundation 

e'of Concrete, Broken 
Itoce or Clndsrs tround Curb 




Parenwm. with Mortar Bedaicg Coarse 

M Below RailCI* Mortal l"lhick 
I Joint 



Exp.Jt. 




Section AA of T oU ni fr. K 

Detail of Rail along Template for Cushion,, _ 
Amfaalt Joint, Joint 




Section in Cut 



Section in Fill 



Monolithic Brick 

FIG. 50. Cross-sections for brick roads and pavements. 



the width between 3 and 3J^ in.; and the depth between 3% and 
4% in. The block size may be taken as the standard brick for 
use in all ordinary cases. For light traffic or special conditions 
of light service, a brick may be used that will give a somewhat 



180 CONSTRUCTION OF ROADS AND PAVEMENTS 

thinner surface. These special brick are usually about the same 
width and length as the paving block, but the depth is some- 
times as little as 2J^ in., and 3 in. and 3^ in. are coming into 
use for the thinner pavements intended for medium traffic. 

Regularity of Shape. The paving block must be sufficiently 
regular in shape to lie evenly in the pavement and form a smooth 
surface. For that reason, the brick must be reasonably straight 
and have one good face. Warped, twisted, or spalled brick can- 
not be used. 

Kiln marks are found on many good brick, but if these are not 
too deep and the brick has one good face, it may be used. 

Checks that are serious enough to indicate careless burning, 
too rapid cooling, or poor material, are a cause for rejection of 
the brick. 

Laminations, as has already been explained, are an indication 
of poor quality, and if serious are, therefore, a cause for rejection 
of the brick. 

Summary of Requirements for Paving Blocks. 1 "The brick 
for the roadway must be number one pavers, the size to be not less 
than 3 by 4 by 8 in., nor more than 3^4 by 4 by 9 in. In width 
and thickness they must not vary in size to exceed J/g m - They 
must be thoroughly annealed, tough, durable, and evenly burned. 
When broken, they must show a dense, stone-like body, fairly 
uniform in color and free from lumps of uncrushed clay, lime or 
air pockets, and show but slight laminations. Kiln marks or 
surface cracks must not exceed %> in. in depth. The brick must 
be straight, and no bricks distorted so as to lie unevenly in the 
pavement may be used." If the edges are rounded the radius 
must not exceed Y% in. 

CONSTRUCTION OF BRICK PAVEMENTS 

The brick pavement is almost universally designed with a 
Portland cement concrete base. Under some conditions the 
macadam base or the base of No. 2 vitrified brick may be used, 
but the instances where either of these methods is economical 
are very much in the minority. For the concrete base good 
materials should be used, and ample thickness be provided, 
but the requirements for the concrete materials are not as rigid 
as for those used in the concrete road or pavement. It should 

1 Specification of Illinois Highway Department, 1915. 



VITRIFIED BRICK ROADS AND PAVEMENTS 181 

be noted that the base is used only to transmit the load to the 
earth subgrade and in so doing distribute it over sufficient 
area to insure stability. 

Earth Subgrade. The earth foundation upon which the con- 
crete foundation rests is known as the subgrade or roadbed. 
It is apparent that it must be carefully prepared and well drained. 
After the pavement is completed, surface water will be cared 
for in pipe drains and will have no opportunity to percolate to 
the subgrade or roadbed. But usually the pavement lies low 
in the street and below the level of the parkings, and lawns along- 
side. Some underground water will, therefore, be likely to work 
under the foundation, but the amount usually is insignificant. 
With porous soils and unfavorable topographical conditions the 
subgrade may become water-saturated and unstable. When it 
appears that such may be the case, underground drainage must 
be provided. Frequently storm-water sewers, or sanitary sewers 
along the street will afford sufficient drainage, but in other in- 
stances tile drains must be laid. These usually are laid just back 
of the curb line and at a depth of 4 to 6 ft. In all doubtful cases 
the tile is advisable. For country brick roads the drainage must 
be taken care of as faithfully as if the road were to have no hard 
surface, and the principles involved have been discussed in 
Chapter III. 

The subgrade is brought to the proper elevation and cross- 
section by excavating or filling as the case may be. If fills less 
than 2 ft. are constructed, they are built up in layers of not to 
exceed 6 in. in thickness, and each layer is rolled before the next 
is placed. For satisfactory results the soil must be moist when 
it is rolled. Where cuts are made it is advisable to plow within 
2 or 3 in. of the subgrade grade and then roll to compress the sub- 
grade to the proper elevation. The exact amount that the sub- 
grade can be compressed varies with the type of soil and its con- 
dition, but it can readily be determined for each particular in- 
stance. A roller weighing 8 to 10 tons should be used for com- 
pacting the subgrade. 

When finished, the surface of the subgrade should be true and 
smooth and so compact that the roller makes no perceptible 
track upon it. Unevenness in the subgrade means inequalities 
in the thickness of the concrete base, and since the base is often 
but 4 in. thick, any high places in the subgrade will reduce the 
thickness of the base to a point that makes failure imminent. 



182 CONSTRUCTION OF ROADS AND PAVEMENTS 

Concrete Base. The foundation or concrete base, as it is 
commonly called, should be made of good sound stone, whether 
limestone or some harder variety is used. The size of the stone 
may be from 3 in. down, but in practice, material larger than 
2 in. is rarely used. The sand may be any clean, siliceous or 
equally durable material and should be well graded from M m - 
down. The Portland cement used should be a standard brand 
passing the tests usually specified for this material. 

The aggregates specified above will not always be readily ob- 
tainable and represent the materials that would make concrete 
of any desired strength with the minimum amount of cement. 
Aggregates with other ranges of sizes may be employed if used in 
the proper porportions. It has been customary to employ fixed 
proportion for the concrete for the base, which is illogical because 
such procedure does not give concrete of the same strength with all 
classes of aggregates. It is convenient to employ fixed proportions 
in specifications for concrete and if the fixed proportions are based 
on known properties of aggregates that are available, good concrete 
will result. For aggregates of the kind described in the first para- 
graph of this section, concrete for the base for brick and other 
clock pavements would be mixed in the proportions of 1 part 
cement, 3 parts fine aggregate and 5 parts coarse aggregate, or 1 
part cement, 2J/2 parts fine aggregate and 5 parts coarse aggregate. 
For the base course of monolithic brick pavement it is desirable 
to secure high crushing strength and the concrete is generally 
mixed in the proportions of 1 part cement, 2 parts fine aggregate 
and 3}/ or 4 parts coarse aggregate. 

It seems to be fairly well established that it is better to use 
concrete of moderate strength for the base and use at least 5 in. 
of thickness than to use very strong concrete and a thin base. 
Up to a certain point the addition of weight to the base is an ad- 
vantage in assisting to resist impact because the greater the weight, 
the greater the resistance to displacement from impact. 

Aggregates consisting of natural or artificial mixtures of fine and 
coarse aggregate may be employed for the concrete for the pave- 
ment base if aggregated contains at least 45 per cent, by volume of 
fine aggregate. Considerable care must be exercised in propor- 
tioning the cement with such materials and this subject has been 
investigated by several laboratories during the past few years. Of 
the theories that have been advanced for determining the basis of 
proportioning, the one preferred by the author bases the cement 



VITRIFIED BRICK ROADS AND PAVEMENTS 183 

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Per Cent Sand in Aggregate 

FIG. 51. Illustrating method of proportioning mixer aggregates. 



184 CONSTRUCTION OF ROADS AND PAVEMENTS 

content of the concrete upon the proportion of the total aggregate 
that will pass the J/ m - screen and the weight of the sand per cu. ft. 
When that has been determined, the amount of cement to use is 
read from the proper diagram in Fig. 51. 

Class 1 concrete will have a strength of 3000 Ibs. per sq. in. 
at the end of 28 days. 

Class 2 concrete will have a strength of 2200 Ibs. per sq. in. 
at the end of 28 days. 

Class 3 concrete will have a strength of 1500 Ibs. per sq. in. 
at the end of 28 days. 

The thickness of the base for the brick pavement will depend 
upon the class of traffic and the nature of the soil. For heavy 
traffic and average soil conditions, the base should be 5 in. thick; 
for moderate traffic and ordinary soils, the thickness of the base 
is reduced to 4 or 4}^ in. Probably it is unwise to use the 4-in. 
base except where very good soil is found and where good work- 
manship is assured so that the thickness will everywhere be 
very close to that specified. With poor foundation conditions, 
the thickness of the base is made as great as 6 in. Much emphasis 
is placed on the necessity for good foundations by all author- 
ities on brick paving, and it is much better to use too great a 
thickness than to use too little. 

Thin-section Concrete Base. For country road construction 
the cost of the pavement becomes a serious consideration, and 
the thickness of the base is reduced as much as is consistent with 
stability. It appears certain that country roads will be con- 
structed with the base 3 in. or less in thickness. If that is at- 
tempted, two facts must be borne in mind. The earth founda- 
tion must be shaped with exactness so that the concrete will be 
uniform in thickness. The concrete must be of extra good quality 
such as is afforded by a 1-2-4 mixture. Probably on good soil, 
carefully rolled, with good concrete and good workmanship, the 
thin foundation will prove adequate for country-road traffic, but 
it is a doubtful expedient for general conditions. 

Whatever may be the thickness or mixture used for the base, it 
should be finished carefully so that no porous places remain, and 
there are no protruding stones. The excellence of European 
block pavements has been frequently noted, and is believed to 
be due in a large measure to the thickness of the concrete founda- 
tion and to the care with which it is placed and finished. 



VITRIFIED BRICK ROADS AND PAVEMENTS 185 

Base with Integral Curbs. For rural highways the roadway 
is constructed with curbs designed merely to hold the brick in 
place and protect the edge of the pavement. The curb is built 
flush with the surface of the brick instead of extending above it 
as it does on a street pavement. This curb is constructed in- 
tegral with the base, and either of the same mixture or of a richer 
mixture, the latter being preferable. For best results, the curb 
should be a 1-2-4 mixture. Usually it is 6 in. wide. This type 
of base is shown in Fig. 50. 




FIG. 52. Methods of laying vitrified brick along car tracks. 

Macadam Base. Where concrete materials are expensive 
(sand and cement), and stone with good cementing properties is 
available, the base for the brick pavement is made of 6 or 8 in. of 
water-bound macadam. On good soil, this type of foundation will 
prove adequate if it is well constructed, but can never be as satis- 
factory as the concrete base. Such a base is constructed just as 
water-bound macadam surface would be (see Chapter VIII). 

Two-course Pavements. The base for the brick pavement is 
sometimes made of a layer of No. 2 vitrified brick laid flat. The 
subgrade is prepared as for the other kinds of base, and the layer 
of sand 2 in. thick is spread on it. On this a layer of No. 2 
brick is laid flat and rolled with a 4-ton roller. This type of base 



186 CONSTRUCTION OF ROADS AND PAVEMENTS 

is economical only when the No. 2 brick can be purchased at a 
low price, and when concrete materials are relatively expensive. 

Sand Cushion. The sand cushion affords a means of bedding 
the brick so that the upper surfaces will conform to the pave- 
ment surface, and serves as a means of taking out any unevenness 
in the foundation. 

Obviously the bricks will not all be exactly of the same depth 
and some will have slight imperfections, such as kiln marks or 
slightly warped faces. These defective faces are placed down when 
the brick is laid. In laying the brick there will be some uneven- 
ness due to inevitable differences in skill of workmen. When the 
brick surface is rolled the lower face is bedded into the sand un- 
til the upper face comes even with the other brick in the surface 
and thus a smooth pavement is secured. For this purpose the 
sand cushion need not be to exceed 1 in. thick. But some lack 
of uniformity in the base is inevitable, and the sand cushion must 
equalize it. Therefore, while the minimum thickness of the 
sand cushion is about 1 in., 1^ or 2 in. is more commonly em- 
ployed. The wider the pavement, the more difficult it is to 
keep the surface uniform, and the more likely it is to require 
considerable thickness of the sand cushion. The sand cushion 
is a weakness in any case, and should be kept as thin as con- 
sistent with proper bedding of the brick. 

The sand should be reasonably course and fairly clean, but the 
requirements are not as rigid as for sand for concrete purposes. 

Sand-mortar Cushion. If car tracks exist on a street, the 
constant vibration has a tendency to loosen the brick near the 
rails, and to afford openings that will let water down to the sand 
cushion which will work toward the curbs, carrying the sand 
with it. The track will be forced down by the weight of the 
cars and will spring back up after the cars pass, pumping the 
water in and out, and this also tends to force water through the 
sand cushion and to displace it. The vibration from traffic tends 
to shift the sand cushion when it is dry, resulting in hollow places 
under the brick surface. 1 To overcome these tendencies 
a mortar composed of 1 part cement and 3, 4 or 5 parts of sand 
is now being used. The sand and cement are mixed dry and 
spread for the cushion and the brick are laid and rolled. The 
pavement is then sprinkled lightly and the water penetrates 
the cushion in sufficient quantities to cause the cement to set. 

1 Mr. Mont Schuyler in Engineering Record, July 3, 1915. 



VITRIFIED BRICK ROADS AND PAVEMENTS 187 

A cushion of this sort is generally recommended for streets on 
which there are car lines or where for any other reason there is 
a possibility of the pavement being broken so as to permit the 
entrance of water into the cushion. It is rapidly replacing the 
ordinary sand cushion. 

Placing the Sand Cushion. The sand is spread on the base in 
a layer about J/ in. thicker than the cushion is to be. Strips 
of wood of the thickness of the finished sand cushion are placed 
first on the base near the curb and at the crown, and on top of 
these a second set of strips % in. thick is placed. The sand is 
struck off by dragging a screed along these strips, thus spreading 
the sand to the thickness of two strips combined. The screed 
is cut to the proper cross-section and the cutting edge is shod 
with a metal plate. If the pavement does not exceed 25 ft. in 
width, the screed may be constructed to span the entire width of 
the pavement, but for wider pavements it is better to span half 
the width. 

After the sand has been struck off, it is rolled with a hand 
roller about 30 in. long and weighing about 15 Ib. per in. of 
length. When the cushion has been thoroughly rolled, the J^-in. 
strips are removed and the screed is drawn along the remaining 
strips and thus the well-packed sand is trimmed to exact thick- 
ness. The sand is most readily handled if it is in a moist con- 
dition, this being better than to have the sand either very wet 
or very dry. 1 

Where the sand-mortar cushion is used, it is placed in exactly 
the same way, except, as before noted, it is handled dry. 

Laying the Brick. The brick are laid in straight rows 
at right angles to the center line except at intersections 
where they are either laid parallel to the diagonals of the 
intersection, or by the herringbone pattern. The end joints in 
each row are placed opposite the middle of the bricks in the ad- 
joining rows and part bricks are used only in starting rows and 
making closures. The bricks are placed with the best face up 
and the lugs all in the same direction. After five or six rows 
have been placed, they are closed up by driving with a maul. 
This is done to make the cross-joints as close as the lugs will 
permit. 

1 See No. 1 Specifications, National Paving Brick Manufacturer's Associa- 
tion. 



188 CONSTRUCTION OF ROADS AND PAVEMENTS 

After the brick have been laid, the chips and spalls are swept 
off the surface which is then inspected and all defective brick are 
replaced with good brick. 

Rolling the Brick. The brick are then rolled with a tandem 
roller weighing between 4 and 6 tons. The object of the rolling 
is to bring all the brick to a true surface, individual bricks being 
adjusted by being pressed into the sand cushion under them. 
If any are too low they are detected and raised by removing 
them and adding a little to the sand cushion. The rolling is 
started at the curb, the roller moving parallel to the curb and 
gradually working to the crown. The roller is then taken to the 
opposite side of the street and the operation repeated. After 
the first rolling, the suface is again inspected, and all broken or 
spalled brick removed and replaced. The brick are again rolled, 
this time diagonally across the pavement, first in one di- 
rection and then in the other. Sometimes a final rolling 
parallel to the curbs is required. The brick cannot be rolled, 
if the sand cushion is wet, without forcing the sand up between 
the brick to an extent that will interfere with the penetration 
of the filler. 

If the dry mortar cushion has been used, the surface is sprinkled 
after the rolling to furnish water for the cushion, providing the 
bituminous filler is used, but if the cement grout filler is to be 
used the sprinkling is done just before the grout is poured. 

Fillers for Brick Pavements. Sand, bituminous cement and 
Portland cement grout are each used for filling the joints be- 
tween the brick. A suitable filler serves to bind the brick to- 
gether so they will not be disturned by traffic, supports the upper 
edge of the brick so as to reduce the abrasion and closes up the 
surface so water and street liquids cannot penetrate to the sand 
cushion. 

The Sand Filler. Sand filler is permissible only when the 
traffic is light. It does not bind the brick together and furnishes 
only partial support against displacement. It does not support 
the upper edge of the brick against abrasion and only partially 
closes the joints against street liquids. When the rolling has 
been completed, the surface of the pavement is covered with 
sand which is swept into the joints. A surplus is left on the 
surface which either works into the joints or is washed off by 
rains. 



VITRIFIED BRICK ROADS AND PAVEMENTS 189 

The Grout Filler. 1 The cement grout filler unites the surface 
into a monolithic layer, and, if properly applied, will be flush 
with the tops of the brick and thereby protect the edges against 
abrasion. If the grout is of poor quality it will be chipped out 
of the joints by iron-shod horses and leave the edges exposed. 
The object of the filler is to make the pavement monolithic and 
so unite the brick units that the wear on them will be no more 
than that of friction and grinding. 




Courtesy of Mr. Will P. Blair. 



FIG. 53. Applying grout filler to brick pavement. 



The filler should be composed of 1 part each of clean, sharp, 
fine sand and Portland cement. The sand should be dry. The 
mixture, not exceeding one sack of the cement, together with a 
like amount of sand, is placed in a box and mixed dry, until the 
mass assumes an even and unbroken shade. Water is then added, 
forming a liquid mixture of the consistency of thin cream. 

The sides and edges of the brick should be thoroughly wet by 
sprinkling before the filler is applied. 

From the time the water is applied until the last drop is re- 
moved and floated into the joints of the brick pavement, the 

1 From No. 1 Specifications, National Paving Brick Manufacturers' 
Association. 



190 CONSTRUCTION OF ROADS AND PAVEMENTS 

mixture must be kept in* constant motion. Long-continued 
mixing is essential. 

The mixture is best removed from the box to the street surface 
with a scoop shovel, the mixture in the box being continuously 
stirred as it is emptied. 

The box recommended for this purpose is 4 ft. 8 in. long, 30 
in. wide and 14 in. deep, resting on legs of different lengths so that 
one corner will be lower than the other. The mixture will readily 
flow to the lower corner of the box, which is not to be more than 
6 in. above the pavement. 

Two such boxes are to be provided in case the street is 20 ft. 
or less in width; if it exceeds 20 ft. in width, three should be 
used. 

The mixture the moment it touches the brick should be thorough- 
ly swept into the joints. 





FIG. 54. Cross-sections of joints between paving brick. 



The work of filling should be carried forward in line until an 
advance of 15 to 20 yd. has been made, when the same force 
and appliance are turned back and cover the same space in like 
manner, except that the mixture shall be slightly thicker for the 
second coat. 

To avoid the possibility of thickening at any point, the sur- 
face ahead of the sweepers and al;ead of the mixture should be 
gently sprinkled, using a sprinkling can the head of which is per- 
forated with small holes. 

Any attempt to thin the mixture on the pavement by the 
application of water will result in the separation of sand and 
cement and "bad spots" will appear in the pavement where this 
practice has been permitted. 

After the joints are thus filled flush with the top of the brick 
and sufficient time for hardening has elapsed; so that the coating 
of sand will not absorb any moisture from the cement mixture, 
Yi in. of sand is spread over the whole surface, and in case the 
work is subjected to a hot summer sun, the sand should be sprinkled 



VITRIFIED BRICK ROADS AND PAVEMENTS 191 

lightly for 2 or 3 days. The street should be kept closed for 
10 days in warm weather, and a longer time if the weather 
is cool. 




FIG. 55. Comparison of pitch and cement grout fillers. 

(6) Grout filler. 



(a) Pitch filler. 



Pouring Bituminous Filler. When a bituminous filler is used 
instead of a cement grout filler, the pavement is completed in 
the same manner as when the grout filler is used, up to the point 
where the filler is applied. Bituminous fillers must be poured 



192 CONSTRUCTION OF ROADS AND PAVEMENTS 

into the joints at a temperature sufficient to insure adhesion to 
the brick. This varies with different classes of materials, but 
usually is about 400F. for asphalt fillers and about 250F. for 
pitch fillers. The device which is used for pouring the filler con- 
sists of a cone-shaped vessel having at the point a cast-iron tip 
with an opening about % m - m diameter. The pouring can is 
drawn along the crack between the rows of brick, the point rest- 
ing in the crack. The opening in the point is controlled by means 
of a valve with a handle conveniently arranged so that the flow 
of the bituminous material can be adjusted. As the vessel is 
drawn along, the bituminous material is allowed to flow out 
into the joint in sufficient quantity to fill it. A helper repleni- 
shes the supply in the pouring can from time to time so that 
the pouring goes on continually. Recently there have been de- 
veloped pouring cans with multiple spouts which pour several 
joints at one time. These are mounted on wheels and are drawn 
across the pavement with each of the points in the joint between 
two rows of brick. A steering device attached to the point serves 
to retain it in the joint. A slight excess of bituminous material 
is usually put in the joint, but this wears down flush with the 
brick in a short time. 

In connection with the use of the filler, attention is called to 
a fact already mentioned, viz., that some kinds of brick have 
a rounded edge while others have a square edge. With the round- 
ed edge the filler must extend back from the joint to a thin 
edge, while with the square-edge brick the filler does not extend 
beyond the width of the joint. This is illustrated by Fig. 54. 
The thin edge is quite likely to wear away quickly and is to be 
avoided. 

Expansion Joints. The object of using the expansion joint is 
to take up the change in dimension of the pavement following 
temperature changes. It is, therefore, important on street pave- 
ments to provide for ample expansion along both curbs where 
the joints should not be less than J^ in. wide, for streets over 14 
ft. wide, and not less than 1 in. for streets between 25 and 40 ft. 
wide. 

Opinion differs as to the advisability of transverse joints. It 
seems to be well established that they are unnecessary and that 
the expansion will merely produce compression in the brick 
surface. This, of course, is impossible crosswise of the pave- 
ment, because the curbs do not afford sufficient support. Recent 



VITRIFIED BRICK ROADS AND PAVEMENTS 193 

practice is to omit the transverse joint. When used, it is common 
to use a H~ m - joint about every 50 ft. 

There are several prepared joint fillers such as the Carey elas- 
tite filler and the Genasco asphalt filler which consist of sheets of 
a bituminous material of the requisite width and thickness to 
fill the joints. This filler is set in place before the brick are 
laid. 




Courtesy Mr. R. L. Bell. 

FIG. 56. Special template for monolithic brick road construction. 

Filling Expansion Joints. The expansion joints along the 
curbs and those transverse to the pavement are formed by slight- 
ly wedge-shaped strips of wood which are placed in position 
before the brick are laid. Shortly after the cement grout is poured, 
these wooden strips are pulled out of the expansion joints and 
the space filled with bituminous material of the same character 
that would be used for filling the joints between the brick. In 
some cities a mastic composed of equal parts of bituminous ma- 
terial (usually asphalt) and sand is used for expansion joints. 
The bituminous material and the sand are heated separately and 
then mixed on a heated metal platform and while in a plastic 
condition tamped into the joints. 

Whatever type of filler is used for expansion joints, precau- 
tions are taken to insure that it shall extend entirely through 
the pavement and particularly that it shall be flush with the top 
of the pavement. When the prepared expansion joint fillers are 
used they are, of course, placed in position prior to the laying of 
the brick, and require no further attention. 

13 



194 CONSTRUCTION OF ROADS AND PAVEMENTS 

COUNTRY BRICK ROADS 

Design. In the construction of brick roads for country traffic 
all of the general principles must be observed that have been 
discussed in connection with brick pavements. The width is 
usually 9 ft. for single-track roads and 18 ft. for double-track. 
The units that make up the traffic on the average country road 
are neither so numerous nor so heavy as those encountered in 
the city, and the base is sometimes made of less thickness than 
for city pavements. Frequently it is made about 4 in. thick. 
It is comparatively easy on these narrow pavements to strike 
the concrete base with a templet to the exact cross-section de- 
sired, and it therefore becomes unnecessary to use a sand cushion 
more than 1 in. thick. 

Since the country road is narrow, traffic will continually pass 
from the brick surface to the earth road alongside; therefore, the 
curbs used to retain the brick pavement at the edge are made 
level with the brick surface instead of extending above as with 
city pavements. The curbs are usually monolithic with the base. 

The transverse expansion joint is commonly omitted from 
country roads. The transverse cracks which form as the pave- 
ment contracts will be of little significance under the class of 
traffic encountered. The longitudinal expansion joint is placed 
along one curb and prevents the pavement from arching under 
temperature changes and prevents the brick surface from breaking 
the curbs from the base. 

The use of the cement grout filler is recommended and the con- 
struction of the pavement is carried out as carefully as the first- 
class city pavements and with materials of the same quality. 

Monolithic Brick Pavements. 1 The monolithic type of brick 
pavement is constructed by laying the brick wearing surface 
directly on a freshly placed concrete base and rolling the brick 
to bed them in the concrete before it takes a set. 

The general design and the requirements for materials are the 
same as for any other high-class brick pavement. When con- 
structed on a country road no marginal curb is used. 

It is recommended that the concrete base be 4 in. thick for 
moderate traffic conditions, but there seems to be no reason why 
it need be more than 3 in. thick for country roads of light or 

1 Data furnished by Mr. R. L. Bell, District Engineer, Illinois Highway 
Commission. 

See also Engineering Record, July 10 and July 17, 1915. 



VITRIFIED BRICK ROADS AND PAVEMENTS 195 

moderate traffic. For city pavements 5 in. is sufficient for the 
severest conditions for which the brick surface is" suitable. 

The subgrade is carefully prepared and thoroughly rolled and 
during the construction the wagons hauling aggregates are kept 
on the side of the road as much as possible if on a country road. 
The roller is kept at work on the subgrade smoothing out the 
wheel tracks that are made by the wagons when they turn in on 
the subgrade to deliver concrete materials. 

The concrete is mixed to a plastic consistency and struck off 
to the proper cross-section by means of a special templet which 
is a feature of the construction equipment that has already been 
developed for this particular type of pavement. It is shown in 
Fig. 56. 

The templet consists of one I-beam crossbar and one channel 
crossbar spaced about 2 ft. apart and supported on the steel side 
forms by means of rollers. The templet is drawn along the side 
forms by the mixer. The forward member of the templet cuts 
the concrete base %s in. below the finished grade and dry mortar 
of 1 part cement and 5 parts sand is spread over the concrete 
ahead of the rear bar of the templet. This dry mortar is spread 
over the base by the rear part of the templet and the brick are 
laid directly thereon. 

The setters place the brick carefully with the best side up and 
the lugs all in the same direction, and while the laying cannot pro- 
ceed quite as rapidly as on the sand cushion, probably under 
favorable conditions a laborer can lay three-fourths as many per 
day as he would on a sand cushion. 

The carriers who deliver the brick to the setters walk over 
the brick already laid and apparently do not disturb them, al- 
though as a precaution a 1-in. plank is laid over the brick where 
the carriers first step onto the newly laid surface. The bats are 
cut and set as fast as the courses are completed so that the sur- 
face is kept finished up close to the setters. 

As fast as the laying is completed, the surface is rolled with a 
hand roller about 30 in. in diameter and 30 in. long and having a 
weight of about 600 Ib. The rolling irons out the little irregulari- 
ties of the surface and beds the brick slightly in the dry mortar 
on the concrete base. 

The surface is grouted in the manner described in this chapter 
for the brick surface on a sand or mortar cushion. 

It will be noted that the feature of this construction is that the 



196 CONSTRUCTION OF ROADS AND PAVEMENTS 

brick are laid directly on the concrete base before the concrete 
hardens. A thin mortar layer is used merely to smooth the sur- 
face of the base. 

This type of construction has the following advantages over 
the type in which the sand cushion is employed : 

1. It is at least 10 cts. per square yard cheaper. 

2. It eliminates the trouble experienced in rolling if a rain 
comes on before the rolling is done. 

3. It insures a firm support for each brick. 

4. It eliminates the danger of sand squeezing up into the joint 
and preventing the proper penetration of the grout filler. 

5. It eliminates the necessity for the marginal curb on country 
roads. 

APPLIANCES USED 

Grading Appliances. The grading is done with the tools and 
appliances which have already been discussed in connection with 
earth roads. The particular combination suitable for each in- 
dividual piece of work varies somewhat; but the elevating grader 
and dump wagons are often used for the rough grading and the 
blade grader and hand tools for finishing. 

Rollers. The macadam roller weighing 8 to 10 tons is used 
for the subgrade and the tandem roller weighing 4 to 6 tons for 
the brick surface. The single roll drawn by horses is sometimes 
employed, but is not quite as satisfactory as the power-driven 
roller. 

Mortar Box for Grout. The special type of grout box recom- 
mended by the National Paving Brick Manufacturing Associa- 
tion is used for this purpose almost exclusively. 

Carriers for Brick. Brick are carried from the piles to the 
setters by means of clamps holding about six brick and operating 
on the familiar principle of the ice tong. These are also used for 
handling the brick at the cars. Rolling carriers are also used to 
convey the brick from the piles to the setters. These consist 
of a series of rollers set in an inclined frame and the brick move 
by gravity down the incline. 

Concrete Mixers. The mixers used are of the same general 
types that are used for concrete road work. In addition the 
stationary type is often used, being set up at the end of the block 
and the concrete being conveyed in carts to the work, but the 
limit of haul is about 350 ft. if segregation of the aggregates in 
the concrete is to be avoided. 



VITRIFIED BRICK ROADS AND PAVEMENTS 197 

CHARACTERISTICS OF BRICK PAVEMENT 

The brick pavement affords a rigid surface having good trac- 
tion for motor vehicles and fairly good footing for horses. It has 
a pleasing appearance if well laid and is sanitary and very dura- 
ble. It is rather noisy under horse-drawn traffic, especially 
if grout-filled. It is reasonably easily opened for repairing service 
pipes and repairs are readily made. It must be kept scrupu- 
lously clean to avoid dust as the particles will not cling to the 
surface. 

Cost of Brick Pavements. The cost varies somewhat in dif- 
ferent communities, and yet the range is not great. On city 
streets brick pavements cost from $1.75 to $2.25 per square yard 
of surface, exclusive of the heavy grading and exclusive of the 
cost of curbs. On country roads the cost where the haul does 
not exceed about 2 miles is usually estimated at $1,000 per mile 
per foot of width of pavement. 

EXAMPLES OF GOOD PRACTICE 

DETAILS OF CONSTRUCTION WHICH MAKE BRICK PAVEMENTS 

GOOD OR BAD ! 

The importance of details as factors of good-roads construc- 
tion is emphasized by the brick highways in Erie and Niagara 
Counties, New York, which were inspected during the recent 
annual convention of the National Paving Brick Manufacturers' 
Association, at Buffalo. Good construction, bad construction 
and intermediate grades were exemplified. Different kinds of 
brick, and different makes of the same kind of brick have been 
used, but while the brick highways range in quality from bad 
to perfect the differences among them are not wholly attributable 
to variations in the quality of brick. Both good and bad roads 
are built of the same kind and make of brick, and sometimes 
the same contractor built both kinds or roads with one kind of 
brick. 

A noticeable distinction between types of brick was found in 
the fact that even on roads of inferior construction the sections 
laid with square-edge brick were uniformly better grouted 
than were sections of the same roads laid with round-edge brick, 
although instances of faulty grouting occur with both types of 
brick. 

1 Will P. Blair, Engineering Record, Nov. 7, 1914. 



198 CONSTRUCTION OF ROADS AND PAVEMENTS 

DAMAGE AT EXPANSION JOINTS 

The contractor has not been at fault in all cases, although 
his sins of omission and commission are many. The worst roads 
are those having cross-expansion joints. Pavements otherwise 
in good condition show courses of broken and sunken joints at 
regular intervals of 50 ft. on account of transverse expansion 
joints. In some instances courses of brick on each side of the 
cross-expansion joint are broken. But cross-expansion joints 
were specified, and the contractor was obliged to put them in. 

The best pavements, and the only perfect pavements, were 
those having longitudinal expansion joints only, although not all 
pavements having longitudinal joints were found in good con- 
dition. It can, however, be affirmed, without fear of successful 
contradiction, that neither in Erie County nor in Niagara Coun- 
ty was there seen a cross-expansion joint pavement in perfect 
condition after 2 years of service. On some highways, notably 
road No. 2 running out of Hamburg, cross-expansion joints and 
longitudinal expansion joints occur in different sections of the 
same road; but in every instance cross-expansion joints show at a 
great disadvantage. 

GROUTING AND ROLLING 

The visitors received ample proof that a perfect brick highway 
can be laid and that it will remain unimpaired under traffic con- 
ditions for years. The reverse of the picture was exhibited as 
well. Slipshod methods of construction have been responsible 
for poor pavements. Faulty foundations and poorly prepared 
sand cushions are accountable for some defect, but by far the 
most prolific cause of poor pavements excepting cross-expan- 
sion joints is poor grouting. Poor material and materials 
mixed in wrong proportions contribute to poor surfacing, but as 
a rule either ignorance or carelessness in applying the grout is 
the source of failure. Too much care cannot be exercised at 
this stage of construction, but observation teaches that some 
contractors attach little importance to the details of grouting. 

A tour over construction work discovers another cause of 
poor pavement in the laying of long stretches of brick ahead 
of rolling and grouting. This method is destructive in case of 
rain, as brick on a wet sand cushion cannot be rolled without 
forcing the sand up between the joints. This disrupts the smooth 



VITRIFIED BRICK ROADS AND PAVEMENTS 199 

compacted bed upon which the brick rest and the sand between 
the bricks prevents the bonding material from penetrating to 
the bottom of the courses and forming a strong bond. Brick rolled 
on a wet sand cushion will rock, nor can a smooth, even pave- 
ment be made with a wet sand cushion under it. Contractors 
are not ignorant of these facts but they take chances and some- 
times, unless closely watched by the engineer in charge, they 
grout over a pavement laid on a wet sand cushion and cover up 
their folly temporarily. It saves taking up the brick and relaying 
them. It is easy to uncover such fraudulent work by pulling 
out a brick here and there and noting how far the sand has been 
forced up by rolling of the brick. 

All work should be rolled before leaving it at night. The roller 
should follow the pavers closely and the grouters should keep 
as close to the roller as practicable, closing up the work each 
night. Yet sometimes engineers permit contractors to lay a quar- 
ter of a mile or more of brick ahead of the grouters. 

Two evils arise from this course first, the danger of rain on 
the sand cushion; second, the mixing and the dumping of too 
much filler at one time in order to rush the work. Unless closely 
supervised grouters will mix batches too big, and they will put 
enough grout on the pavement to grout 15 ft. instead of the maxi- 
mum permissible limit of 5 ft. The inevitable result of mixing 
batches that are too big is, separation of sand from cement and 
consequent weakening of the bonding material. Bridging of 
joints is another peril from dumping grout on the pavement. 

PROPORTIONING GROUT 

Another observed tendency of grouters is to mix the final coat 
of grout too thin or too thick. If too thick, the grout bridges 
the joint; if too thin it settles in the joints instead of setting 
flush with the pavement. The general tendency is to mix the 
first grout too thick and the final course too thin. The final 
grout should be somewhat thicker than previous courses, but it 
should not be too thick nor should too much of it be put on at 
one time; it is imperatively necessary not only that the batch be 
kept thoroughly mixed but it must be thoroughly squeegeed 
into the joints. In one instance workmen were observed thin- 
ning grout by pouring water on it on the pavement, thereby 
separating the constituent elements of the grout and destroying 
its efficiency. This fault was corrected, but there is reason for 



200 CONSTRUCTION OF ROADS AND PAVEMENTS 

believing that that method of thinning grout is somewhat general. 
The right way, therefore the only way allowable, is to thin in the 
grout box and keep constantly stirring. 

Contractors and engineers, unless thoroughly experienced in 
highway work and conscientious in their work, are prone to 
neglect or slight what appears to be minor details, nor in their 
methods do they always discriminate between the two kinds of 
brick commonly used for paving. 

METHOD OF FINISHING GROUTING 

The method of finishing the grouting of a brick pavement 
differs with the type of brick used. The final course of grout 
on a round-edge brick pavement should be squeegeed until the 
surface of the pavement is as nearly as practicable free from 
grout; otherwise, when the excess grout breaks under the pound- 
ing of traffic and comes off, it will pull portions of the grout from 
the round-edge joints. No such danger from a heavy surface 
coating of grout menaces a pavement laid with square-edge 
brick. The square edges of the brick protect the joint and the 
excess of grout comes off the pavement without impairing the 
grout at the joint. The difference between round-edge brick 
and square-edge brick in respect to the final grouting is this: 
Whereas in the case of the former all surplus grout ought to be 
squeegeed off the pavement, in the case of the latter the surplus 
may be taken off or left on without deleterious effect. The objec- 
tion to leaving a thick covering of grout over the pavement is 
that it is unnecessary and, therefore, wasteful. 

The tour of the brick roads of Erie County disclosed the fact 
that in some instances the failure of contractors properly to pro- 
tect the freshly grouted pavement with a blanket of moistened 
sand had resulted in too rapid setting of the filler. The result 
was "crazing" and pin-cracking of the grout. The same con- 
dition was found on the Kennilworth Avenue pavement recently 
laid by the city of Buffalo. 

LAYING THE BRICK 

Bricks laid with lugs the wrong way brought together two 
smooth sides of adjoining brick, thereby preventing the penetra- 
tion of filler and preparing the way for defective spots in the 
completed pavement. Such faults are the result of inexcusable 



VITRIFIED BRICK ROADS AND PAVEMENTS 201 

carelessness, but competent engineers and inspectors detected 
them in time to forestall serious consequences. 

Another indication of neglect to follow specifications was ob- 
served in the placing of the uneven or broken edges of bats next 
to the curb. This is not, perhaps, a serious structural defect, 
yet it is both aesthetically and practically wrong. It detracts 
from the symmetrical appearance of the pavement at the sides by 
giving it a rough, uneven edge, and it deprives the pavement of 
the extra bonding strength afforded by union of the filler with 
the rough surface of the bat. Some persons may regard these 
strictures as hypercritical, but no detail of construction is negli- 
gible. A good pavement represents the homogeneous aggregate 
of all constructive details properly wrought out. 



FOUNDATION DRAINAGE 

The necessity for proper drainage of foundations was strongly 
impressed upon the observers of brick highways in Erie and 
Niagara Counties. There are miles upon miles of pavements 
without cracks, sunken spots, broken bonds or other noticeable 
defective features, yet several highways show cracks and sunken 
spots unquestionably due, in the first instance, to ineffectual 
drainage. While it is probably true that longitudinal cracks 
sometimes result from causes other than defective drainage, a 
well-constructed foundation, properly drained, is a sure prevent- 
ive of sunken spots in a pavement, nor are cracks likely to occur 
unless moisture is taken into the foundation either by direct con- 
tact or by capillary attraction. 

The tour of inspection around Buffalo found apparent evi- 
dence of negligence in the matter of drainage, but conclusive 
proof was adduced that a well-drained and well-constructed 
grouted brick pavement is impervious to surface water. Por- 
tions of the brick boulevard running from Buffalo to Niagara Falls 
were submerged by the flood a couple of years ago, for a period 
of 2 or 3 weeks, yet they were absolutely unharmed and were 
marked neither by cracks nor depressions, nor by broken bonds. 
Damage to brick pavements resulting from moisture originates 
beneath the foundation. That the problem of drainage can be 
solved even under adverse natural conditions is a fact which was 
demonstrated on the tour. 



202 CONSTRUCTION OF ROADS AND PAVEMENTS 

CULL BRICK 

For almost its entire length of 23 miles the boulevard between 
Buffalo and Niagara Falls runs through a level country, and 
the same is true of the highway between Lewiston and Youngs- 
town. Yet in the former only a few bad spots exist, and in the 
latter none at all. The worst spots on the boulevard are attri- 
buted to the use of cull brick. This brick, it is alleged, was con- 
demned in Niagara County, but by some means the culls found 
their way across the line into Erie County and were placed in 
the pavement at two points. It might be an idle waste of time 
to speculate on the sequence of events which eventuated in the 
translation of brick from a cull pile in one county to a snug place 
in a state boulevard in the county adjoining, but it is only fair 
to say that the manufacturer who furnished the brick says he 
received cull prices for the cull brick and was not cognizant of 
the high testing which awaited them. M Without attaching to 
the incident any remote significance, the incident does empha- 
size the need for close supervision of construction work by en- 
gineers in charge, and it puts an acute accent on the necessity 
for honest, capable and diligent inspection. Eternal vigilance 
is the price of a good pavement. 

INSPECTION 

Poor judgment of the qualities of brick is a weakness not infre- 
quently found in inspectors. Among culls thrown into the dis- 
card by inspectors on construction work were found what prac- 
tical men declare to be the very best brick in the shipment. Con- 
versely, some of the brick that were passed were of inferior quality. 
Without making any specific application to individuals, or 
to any particular job, it is safe to affirm that inspection 
of brick on the roadway is to some extent a matter of individual 
preference, and in many cases inspectors are not qualified 
by experience or by native ability to judge correctly of the quality 
of brick by its appearance. The result is an almost total absence 
of uniformity in standards of judgment and an insistent demand 
for a better system, or at least for expert inspection. 

There does seem to be among inspectors a common prejudice 
against brick of a dark shade, although it is quite possible that 
such brick may be exceptionally durable. The shade is not always 
an indication of everburning. The inspection of brick is often 



VITRIFIED BRICK ROADS AND PAVEMENTS 203 

delegated to persons selected without regard to their fitness for 
the duty; and brickmakers may be mulcted from 2 to 3 cts. per 
brick on large consignments by the ignorance of inspectors appoint- 
ed for political reasons or for other reasons equally obnoxious. 
Nor is the abrasion test always fair to the brickmakers. 

These reflections and comments are based upon observations 
made on old and new work in a recent tour of 200 miles over 
highways in Erie County and Niagara County, New York. 



CHAPTER XI 
WOOD-BLOCK PAVEMENTS 

Wood-block pavements have been used in Europe for many 
years, and for at least 40 years in the United States. The earlier 
types were made from blocks sawed from round logs and laid 
as closely as their shape would permit. They were not treated 
with any kind of preservative and consequently the life was 
short and the pavement was rough, due to the shape of the blocks 
and the method of laying. The later developments produced a 
pavement made up of blocks cut to a rectangular shape so as 
to lie closely and evenly in the payement. The wood was 
impregnated with a preservative and was more durable than any 
of the earlier pavements. In the last few years this type of 
pavement has come into very wide use, both in Europe and 
America. 

SIZES AND KINDS OF BLOCKS 

Kinds of Timber Used. In the United States, southern long- 
leaf pine, short-leaf pine, red gum, tamarack, Douglass fir and 
Norway pine have all been used for the blocks. Probably three- 
fourths of the blocks laid, however, are made from southern 
long-leaf yellow pine. In this connection, the term long-leaf 
pine is used to designate quality rather than species and short- 
leaf pine of sufficiently dense structure would be acceptable as 
well as the long-leaf pine. Abroad, short-leaf pine, white pine, 
redwood and fir are used principally, although Australian hard- 
wood is used to some extent. 

Of the timber available in the United States it is generally 
conceded that the southern long-leaf yellow pine is the most 
durable. It is, however, a hard wood and consequently the 
pavement in which it is used is likely to be more slippery than 
one constructed of some of the softer woods. Where traffic 
conditions are not severe and in parts of the country where the 
yellow pine is not available, other timber, such as tamarack and 
fir, are used successfully. 

The essential characteristics of the timber are uniformity of 
texture and ability to resist wear, adaptability to the preservative 

204 



WOOD-BLOCK PAVEMENTS 205 

treatment, and freedom from defects that will impair the life or 
wearing properties of the block pavement. Uniformity of 
texture is secured by specifying the minimum number of annual 
rings per radial inch in the block. Other defects are eliminated 
by inspection of the timber before it is cut into blocks and by 
inspection of the blocks during and after the laying. 

Size of Blocks. The depth of the block is varied to suit the 
traffic conditions, but in most of the pavements laid they have 
been either 3, 33^ or 4 in. deep, the last-named being used on 
the heavier-traffic streets. The width of the block is not im- 
portant so long as it is not greater than about 4 in., and blocks 
made by various manufacturers vary from 2J^ to 4 in. in width. 
The length of the block is equal to the width of the plank from 
which it is cut, and consequently varies in any lot. It should 
never be less than 5 in. nor greater than about 10 to 12 in. If 
the block is too short it will not sufficiently distribute the load 
that may come upon it, and if it is too long it will split under 
heavy loads, or not lie evenly in the pavement. All blocks 
used on any one contract should be of the same depth, except 
that sufficient variation must be permitted to allow for the 
uncertainties of manufacture. Usually specifications permit 
variations in depth of Jfe in. Likewise for convenience in 
laying, all blocks used in any one contract should be of the same 
width, except such variations as are incident to manufacture 
and this is limited to J in. 

Quality of the Blocks. The blocks must be free from defects 
such as large or loose knots, wind shakes, heart rot and pitch 
pockets. It is always desirable that the block be composed 
largely of heart wood and specifications usually require that 
a certain percentage (varying from 65 to 80 per cent.) of the 
block shall be heart wood. To preclude the use of coarse-grained, 
second-growth wood or short-leaf pine of poor quality, the number 
of annual growth rings per radial inch should be at least six and 
at no place on the face of the wood should the number of such 
rings be less than four. 

PRESERVATIVE TREATMENT 

Character of Preservatives. Wood blocks when used as a 
pavement surface are laid with the grain vertical. The block 
in this position will wear for a long time if the wood does not 
decay. The cause of decay is fungus growth in the wood, and 



206 CONSTRUCTION OF ROADS AND PAVEMENTS 

to prevent decay the blocks are impregnated with an antiseptic 
which will prevent fungus growth. The material most com- 
monly used for this purpose is coal-tar creosote. 

The wood used for block pavements possesses another char- 
acteristic that is of some significance in connection with the 
preservation treatment. Untreated wood will absorb con- 
siderable quantities of moisture and in so doing will increase in 
size very materially. Treated blocks will absorb some water 
but by proper treatment the quantity can be reduced to an 

Bituminous coal 



I 

Gas Tar Coke 



Oils lighter Pitch 

than water 

Oils heavier 

than water 
(creosote) 

I 

Distillation limits and general nature of the aromatic compounds 



Light oils rich 
in phenols 


Naphthalenes 


Constituents of anthracene nature 


Liquid at room 
temperature 


Solid at room 
temperature 


Liquid at room 
temperature 


Solid at room 
temperature 



To 205C. 255C. 295C. 360C. 

FIG. 57. Source and composition of creosote oil. 

amount so small as to obviate trouble from swelling. Excessive 
absorption of water has caused considerable trouble due to the 
difficulty of taking care of the expansion, especially on wide 
streets. Recent practice is to impregnate the blocks in a 
manner and with a material intended both to preserve and 
waterproof the wood. This is accomplished by using a mixture 
of creosote and tar. 

Creosote Oil. The preservative employed for wood blocks is 
creosote oil, a coal-tar distillate, or a mixture of creosote oil and 
tar. Pure creosote is a distillate of coal tar and its properties 
are represented by the following diagram: 1 

Pure creosote, therefore, consists of varying percentages of 
the four groups of compounds indicated in the above diagram. 

1 Weiss, "The Preservation of Structural Timber," p. 80. 



WOOD-BLOCK PAVEMENTS 207 

Of these compounds the first group (phenols) is highly antiseptic 
and it is desirable that there be sufficient of these compounds 
mixed with the creosote to insure preservation. The second 
group (naphthalenes) is also antiseptic, but is also volatile at air 
temperature and will gradually leave the block by evaporation 
during the first years of the life of the pavement. The third and 
fourth groups (anthracenes) are not as highly antiseptic as the 
phenols, but are much less volatile and are insoluble in water, 
while the phenols are soluble in water. It is generally believed 
that the creosote oil used for paving blocks should contain a 
considerable proportion of the anthracenes. The specific gravity 
of a pure creosote oil obtained by the distillation of tar will be 
from 1.03 to 1.08 at 25C. Generally speaking the higher the 
specific gravity the greater the proportion of the anthracenes 
in the creosote oil. 

Mixtures of Tar and Creosote. The commercial creosote oil 
employed for the preservation of wood-paving blocks frequently 
has a specific gravity greater than 1.08 and sometimes as great 
as 1.14. Such an oil is a mixture of pure creosote and tar. It 
is contended that an oil of this character contains sufficient pure 
creosote to preserve the blocks and that the admixture of tar 
serves to increase the waterproofing properties of the oil. It 
is not known that such an oil is a suitable preservative since it 
has not been in use for a sufficient time to demonstrate this 
point. It is known, however, that the presence of tar in the oil 
tends to increase the difficulties due to the blocks bleeding and 
that the presence of appreciable quantities of free carbon (soot) 
in the creosote oil is particularly objectionable. 

Creosote Oil Specifications. Two types of creosote oil are 
being used for the preservation of wood-paving block, the one a 
light practically pure creosote oil and the other a heavy creosote 
oil and tar mixture. The latter has been much more widely 
used than the former, but it is probable that the lighter oil will 
come into more extensive use in the future. 

SPECIFICATION FOR LIGHT CREOSOTE OIL 1 

"Specific gravity at 38C., 1.03 to 1.08. 

When distilled in the standard manner 2 the creosote shall give 
distillate within the following limits, calculated in percentage of dry 
oil: 

1 No. 1 oil as specified by the American Railway Engineering Association. 

2 See description of method, p. 405. 



208 CONSTRUCTION OF ROADS AND PAVEMENTS 

To 200C. no distillate. 

To 210*0. not more than 5 per cent. 

To 235C. not more than 25 per cent. 

The residue at 355C. if it exceeds 5 per cent, shall be soft. The 
oil shall be a pure distillate of coke-oven tar or coal-gas tar without the 
admixture of any other material. It shall be completely liquid at 
38C., shall contain no suspended matter and shall contain not to exceed 
3 per cent, of water. 

SPECIFICATION FOR HEAVY CREOSOTE OIL 1 

The preservative shall be wholly derived from coal-gas tar or coke- 
oven tar, and shall comply with the following requirements: 

The specific gravity shall not be less than 1.06 nor more than 1.12 
at 38C. 

Not more than 3 per cent, shall be insoluble by continuous hot 
extraction with benzol and chloroform. 

On distillation which shall be made exactly as afterwards described, 
the distillate, based on water-free oil, shall be within the following 
limits: 

Up to 210C., not more than 5 per cent. 

Up to 235C., not more than 30 per cent. 

Up to 315C., not less than 35 per cent., nor more than 70 per cent. 

Up to 355C., not less than 65 per cent. 

The specific gravity of the distillate between 235C., and 315C., 
shall be not less than 1.02 at 38C., compared with water at 15.5C. 
The specific gravity of the distillate between 315C. and 355C., shall 
be not less than 1.08 at 38C., compared with water 15.5C. 

The specific viscosity at 82C., when taken in an Engler viscosimeter 
shall not exceed 1.3. The term specific viscosity shall mean the 
number of seconds found for the sample tested divided by the number 
of seconds for water at 20C., as given in the official certificate for 
the viscosimeter used. 

The oil shall not contain more than 3 per cent, of water. Oil samples 
taken by the inspector from the treating tank during the progress of 
the work shall at no time show an accumulation of more than 2 per 
cent, of foreign matter, such as sawdust and dirt, and due allowance 
shall be made for all foreign matter, either water or material insoluble 
in benzol and chloroform, by injecting an additional quantity of oil 
into the block. 

SPECIAL SPECIFICATION FOR HEAVY CREOSOTE OIL 

"The oil shall be a distillate obtained wholly from coal tar. 

It is required by this specification that the oil used shall be wholly 

1 Proposed by committee American Society of Municipal Improvement, 
1916. 



WOOD-BLOCK PAVEMENTS 



209 



a distillate oil obtained only by distillation from coal tar. No other 
material, of any kind, shall be mixed with it. 

The oil shall contain not more than one (1) per cent, of matter 
insoluble in hot benzol and chloroform. 

Its specific gravity at twenty-five (25) degrees C. shall be not less 
than 1.08 and not more than 1.12. 

The oil shall be subject to the standard distillation test and the 
amount of distillate shall not exceed the following limits in percentage 
of dry oil: 

Up to 150C., 2 per cent. 

Up to 210C., 10 per cent. 

Up to 235C., 20 per cent. 

Up to 315C., 40 per cent. 

There has been much discussion as to the relative merits of 
the light and heavy oils for the treatment of wood block, and 
exact data on the subject are lacking. The following facts are 
apparently well established: 

TABLE 15. COMPARISON OF LIGHT AND HEAVY OILS FOB WOOD BLOCK 

PRESERVATION 



Heavy 



Light 



(a) Cheaper than the light oil. 
(6) A little better for waterproofing 
than the light oil. 

(c) Will probably preserve the 
blocks until they wear out. 

(d) Contributes to bleeding. 

(e) Does not volatilize readily. 

(/) Contains little material soluble 
in water. 



(a) More expensive than heavy oil. 
(6) Has better preservative proper- 
ties than the heavy oil. 

(c) Bleeds less than the heavy oil. 

(d) Not quite as good a waterproofing 
material as the heavy oil. 

(e) Volatilizes more readily than the 
heavy oil. 

(/) Contains more water soluble por- 
tions than the heavy oil. 



Some attempts have been made to employ products of water- 
gas tar and of petroleum for wood preservation, but the use of 
these materials is, as yet, in the experimental stage, and is not 
common practice. 

Quantity of Preservative. Experiments have demonstrated 
that for proper preservation of the blocks it is probably un- 
necessary to use to exceed 10 Ib. of creosote oil per cubic foot 
of timber, but that for securing the necessary degree of water- 
proofing at least 16 Ib. per cubic foot must be used, and it seems 
to be established that little benefit is obtained from the use of 

14 



210 CONSTRUCTION OF ROADS AND PAVEMENTS 

more than 16 Ib. per cubic foot of timber. Practice in the United 
States is to treat with quantities varying from 12 to 20 Ib. of 
creosote oil per cubic foot of timber, while in many cases a much 
less quantity is used for the blocks laid in European cities. 

Sometimes when blocks are to be used for streets on which the 
traffic is very heavy, they are treated by merely dipping in hot 
tar. The amount of preservative thus absorbed is sufficient to 
preserve the blocks for the length of time that they can be 
expected to wear under the traffic conditions. 

Bleeding. Complaints are often made that creosoted block 
pavements become sticky in warm weather, the tar exuding from 
the blocks and sticking to the shoes of pedestrians, soiling clothes 
and being carried into stores and residences, and becoming a 
general nuisance. The causes of bleeding are several: 1 

1. The use of a tar and creosote mixture containing too much 
tar. Such an oil does not penetrate the blocks as thoroughly 
as do the lighter oils and the carbon in the tar has a tendency to 
lodge in the outer fibers of the block. When the oil in the block 
warms up and increases in volume the exudation brings with it 
the carbon. The heavy and sticky mixture of tar and carbon 
adheres to everything coming into contact with it. For these 
reasons specifications frequently limit the amount of free carbon 
in the oil to 1 per cent. In the past as much as 4 per cent, has 
been permitted. 

2. The use of too much oil. If the treatment is in excess of 
16 Ib. per cubic foot, it is inevitable that some bleeding will 
occur and treatments of 20 Ib. per cubic foot or more are sure to 
bleed excessively. 

3. Improper seasoning and treatment of the blocks. Arti- 
ficial seasoning and the preliminary and final vacuum are thought 
to be advisable as reducing the amount of bleeding. The im- 
pregnation should be complete not merely in the outer part of 
the block. 

4. Insufficient provision for expansion of block in the pave- 
ment. If the block cannot increase in size when it swells, the 
effect will be to squeeze out the creosote. 

5. The use of a filler soluble in creosote oil. Such a filler 
will soften up in time and exude at the joints. If too much 
filler is used, the trouble is aggravated. 

The preventive for bleeding then is to use not to exceed a 16-lb. 

1 Weiss, "The Preservation of Structural Timber," p. 201. 



WOOD-BLOCK PAVEMENTS 211 

treatment, to use pure creosote or creosote in which there is but 
little carbon-free tar, either to treat green timber or to steam 
season the timber, and to use a filler not soluble in creosote and 
to provide ample expansion joints. 

The cure for bleeding is to keep the pavement surface covered 
with torpedo sand until the bleeding stops. 

MANUFACTURE OF THE BLOCKS 

Cutting of Blocks. The planks from which the blocks are to 
be manufactured are sawed with a thickness equal to the width 
desired in the finished block, which is from 2^ to 4 in. The 
planks are run through the planer to size them so that all blocks 
will be of the same width. A plank that is unusually dense, is 
wet, or is filled with pitch will come through a little thicker than 
one that is dry or soft, so that some slight variations in thickness 
of plank and consequently width of block is unavoidable in the 
process of manufacturing. The planks are inspected and any 
sections that contain inferior wood are cut out and rejected. 
The good portions of the planks are cut into lengths varying 
with the number of saws in the cutting machine used. The 
cutting machine generally consists of a gang of saws that will cut 
a number of blocks at one time. From the cutter the blocks are 
delivered into iron racks in which they are piled loosely. The 
racks when filled are run into the treating cylinders which are 
usually about 8 ft. in diameter but of various lengths. Most of 
the treating cylinders will contain ten or more racks of blocks. 

Seasoning and Treating. When the blocks have been put 
into the cylinder it is closed tightly and the blocks are steamed 
to soften the pitch and resinous material. The steaming process 
to be of the greatest benefit must continue for at least 5 hr., 
although frequently a shorter period of steaming is specified. 
After the steaming process, the cylinder is subjected to a vacuum 
which is intended to draw out from the blocks the moisture and 
some of the pitch and resinous material. All water that may 
have come out into the cylinder is pumped off and after the 
vacuum has continued until the blocks are dry the creosote oil 
is introduced into the cylinder and pressure applied until the 
proper quantity of oil has been forced into the blocks. The 
pressure permitted is generally limited to 200 Ib. per square inch 
and often a less pressure is effective. The pressure must continue 



212 CONSTRUCTION OF ROADS AND PAVEMENTS 

for about 3 hr. to insure thorough impregnation. When the 
proper impregnation has been secured the excess oil is pumped 
away and the blocks are allowed to drain for about 30 min. before 
being removed from the cylinder. It is also recommended 
that a final vacuum be drawn and held for about 30 min. to dry 
the blocks, but this practice is not general. 

Inspection of Blocks. The timber is inspected before it is cut 
into blocks and most of the defective material thus eliminated. 
The blocks can be weighed before they are placed in the creo- 
soting cylinder and can be weighed again after coming out and 
thus the quantity of creosote injected can be computed. A slight 
error exists due to the fact that some moisture is extracted from 
the blocks during creosoting, but probably this is a small amount. 
A more reliable way of determining the amount of creosote in- 
jected is to observe the gage readings on the tanks before and 
after the creosoting treatment. Knowing the temperature of the 
creosote during treatment and in the tanks, the quantity injected 
can be computed. After the blocks are laid in the pavement they 
are again inspected and those that are checked or that contain 
large knots or other defects are removed and turned over or are 
replaced by good blocks. 

CONSTRUCTION OF THE PAVEMENT 

Foundation for the Wood-block Pavement. The principles 
to be observed in the construction of the concrete base for a 
wood-block pavement do not differ from those discussed in con- 
nection with the brick pavement, and need not be repeated. It 
may perhaps be said in passing that the thickness of concrete 
base should never be less than 5 in. and on the heavier-traffic 
streets should be 6 to 8 in. in thickness. It should be very care- 
fully finished so as to have a smooth surface true to cross-section. 
This is of great importance with this type of pavement. 

Bedding Courses. Several methods of bedding the blocks are 
employed of which the most common in the United States is to 
place a sand cushion on top of the concrete foundation, similar 
in character to that which is used for the brick pavement and 
constructed in the same manner. Experience with the sand 
cushion has not been entirely satisfactory because it has been 
prone to wash from under the blocks or to shift when dry, allow- 
ing the pavement to become uneven. This is particularly 



WOOD-BLOCK PAVEMENTS 



213 



noticeable on streets carrying car lines, the jar of the cars being 
sufficient to loosen the blocks along the track and afford an open- 
ing for water. This has led to the adoption of the mortar cushion 
which has been described in connection with the brick pavement, 
and it is much superior to the sand cushion for wood-block pave- 
ments. In other instances a thick coating of tar is spread on 
the concrete foundation and covered lightly with sand and the 
blocks are laid on the mastic thus produced. When the blocks 
are laid in this manner the concrete foundation must be finished 
with the surface as true to shape as that of the finished pavement 



1 Exp.Joint 



4 Block Surface 




and Cushion 



v 6 of 1-2^-5 Concrete 



1 Exp.J 



1 of 1 to 4 Mortar 
4"Block Surfa 




6 of 1-2 J3-5 Concrete 




Paint Coat of Heavy Tar 



oncrete 
riEh Smooth Trowel Finish 



FIG. 58. Cross-section for wood-block pavement. 

and with a troweled mortar surface. This method is used ex- 
tensively abroad and is coming into use in the United States, and 
undoubtedly is one of the very best methods for laying this type of 
pavement. A slight modification of the above method is found 
where one face of the block is dipped in tar just before it is placed 
on top of the concrete foundation which has previously been 
coated with a thin layer of sand. In other instances the concrete 
foundation is coated with tar and the blocks laid directly thereon. 
The blocks are laid in regular rows either at right angles to the 
curb or an angle of 65 therewith, the latter probably being the 



214 CONSTRUCTION OF ROADS AND PAVEMENTS 

more common method. In the latter method it is assumed that 
no transverse expansion joints will be required, the blocks carry- 
ing the expansion to the curb in both directions. This has, how- 
ever, not proven satisfactory, on streets more than 50 ft. wide, 
but is satisfactory for the narrower streets. Since the blocks 
usually have no lugs for spacing them in the pavement., it is 
possible to lay them too close together and thereby increase the 
difficulties caused by expansion. The blocks should be laid 
loosely, especially if they are dry when laid. Some engineers 
advocate thoroughly wetting the piles of blocks some hours be- 
fore it is desired to use them. Other engineers use a thin wooden 
strip between rows to space the blocks, the strips being removed 
after the blocks are laid. 

Expansion Joints. If the blocks are laid diagonally, expansion 
joints are placed along the curbs, the width being 1 in. to 1% in. 
It is customary to lay two or three rows next the curb with 
long dimension of the block parallel to the curb and to provide 
the expansion joint between the row next the curb and the curb- 
stones. If the combined curb and gutter is employed no longi- 
tudinal rows are laid but the expansion joint is provided next the 
edge of the gutter slab. If the blocks are laid in rows perpen- 
dicular to the curbs, transverse joints J^ in, wide are provided 
every 50 ft. These expansion joints are rilled either with bitu- 
minous cement or the bituminous mastic described in the chapter 
on Brick Pavements. 

After the blocks have been laid they are rolled with a tandem 
roller weighing about 4 tons and in exactly the same manner that 
a brick pavement would be rolled. As in the case of brick pave- 
ment, the blocks are inspected before and after rolling, and all 
split or otherwise defective ones are removed and replaced with 
good blocks. 

Filler for Wood-block Pavements. The filler may be sand, 
cement grout, asphalt or tar, but probably a bituminous filler 
is more often used than any other. The tar filler must be used 
sparingly on account of the tendency for it to soften with the 
creosote from the blocks and to bleed badly. Where the sand 
filler is used it is assumed that the sand becomes mixed with a 
considerable amount of tar and -creosote from the blocks so as 
to form a mastic in the joints. Probably this happens to a 
considerable extent and if the blocks are placed on a heavy-traffic 
street such a filler will be satisfactory because traffic will quickly 



WOOD-BLOCK PAVEMENTS 215 

close the joints between the blocks by cushioning down the fibers 
of the wood. The asphaltic filler must be very hot when poured 
so as to penetrate the joints and care must be taken not to use 
an excess. Bituminous fillers are usually applied to the surface 
very hot and spread with a fiber broom or squeegee so as to fill 
the joints. The surface will also be coated and must therefore 
be covered with torpedo sand or stone chips. This coating does 
not adhere to the blocks well and eventually will scale off. 

The grout filler is applied just as it would be for a brick pave- 
ment and as has already been described. 

Characteristics. The wood-block pavement is adapted to any 
sort of traffic and is exceedingly durable even under the heaviest 
traffic. It is smooth, resilient and quiet but its one undesirable 
characteristic is its slipperiness. It is not suitable for grades in 
excess of about 4 per cent, and if subjected to heavy horse-drawn 
traffic should not be used where the grade exceeds 2 per cent. 
The slipperiness can be overcome to a large extent if the pave- 
ment is sanded at the proper time. Some difficulty is en- 
countered from expansion due to the wood swelling when wet, 
but this is eliminated by the use of suitable expansion joints. 

Maintenance. The maintenance consists almost exclusively 
in sanding the blocks to prevent slipperiness, or to absorb the 
creosote and filler that may exude under certain conditions, 
especially when the pavement is new. There will be some 
displacement of the blocks along car tracks and these must, of 
course, be repaired. 

Cost. The wood-block pavement varies in cost from $2.50 
per square yard to $4 per square yard. Under ordinary or aver- 
age conditions the cost is about $3 per square yard. 

EXAMPLES OF GOOD PRACTICE 

WOOD-BLOCK PAVEMENT WITHOUT CUSHION LAYER OF SAND X 

Following European practice in the omission of a sand cushion, 
Chicago has recently completed an experimental wood-block 
pavement in front of the post office on the Dearborn Street side. 
The fact that no sand cushion was used between the blocks and 
the 8-in. concrete slab made it necessary to give the latter a 
sidewalk finish. On that portion between Jackson Boulevard 

1 Engineering Record, Jan. 9, 1915. 



216 CONSTRUCTION OF ROADS AND PAVEMENTS 

and Quincy Street hot asphalt was spread over the concrete im- 
mediately before the blocks were laid. For the remainder of the 
pavement, north to Adams street, the blocks were placed on the 
bare concrete and covered with a coat of hot pitch and sand. 
Blocks of yellow pine were purchased under the standard speci- 
fications of the Chicago Board of Local Improvements, which 
prescribe the use of 12 Ib. of creosote oil. 

The main reason for the experiment, as given by the city 
officials, is to find some method which will avoid the shifting 
of the sand cushion under vibration due to street cars and team 
traffic. Experience with blocks laid on bare concrete in Europe, 
as ascertained last summer by L. E. McGann, Commissioner of 
Public Works, indicated that the method had merit. 

TRAFFIC CENSUS 

The post-office block was considered an excellent place for an 
accelerated test of the method as the heavy traffic is augmented 
by numerous teams which stand along the curb while second class 
mail is being unloaded. A traffic census as taken by the Citizen's 
Street Cleaning Bureau between 8 A.M. and 5 P.M. is as follows: 
Feb. 28, 1907, 2,557 vehicles; Mar. 6, 1911, 3,005 vehicles; Aug. 
25, 1912, 3,103 vehicles; Aug. 12, 1913, 2,711 vehicles; Mar. 
12, 1914, 2,910 vehicles. 

In 1914 the traffic consisted, on a daily average, of 2,050 
horse-drawn vehicles, 53 mounted horses, 568 motor cars, 232 
motor trucks and 7 motorcycles. During the same period 478 
street cars passed the observer. On blocks north and south of 
the post office the total number of vehicles on Dearborn Street 
was 2,546 and 2,263, both less than in front of the post office. 
While the pavement in question did not receive its proper pro- 
portion of the passing traffic, the actual wear due to the stand- 
ing teams undoubtedly compensated to no small extent. 

WARPED CONCRETE SURFACES 

One of the most difficult parts of the new work was to obtain 
the proper warped surfaces due to the rise and fall of the gutter 
elevation between inlets to the level grade at the rail and to the 
corresponding elevations on the parabolic curves halfway be- 
tween the rail and curb. Only the west side of the street, 16.6 



WOOD-BLOCK PAVEMENTS 217 

ft, wide from curb to rail, was paved. On top of the main body 
of the concrete, 1 by 6-in. dressed boards were secured at the 
rail and curb and bent over stakes set at the center. These 
boards were laid flat, 12 ft. apart, and a screed was used to 
strike off the lj^-in. coat of 1 to 3 mortar. Finishing was done 
from a bridge with a wood float aboflt 1^ ft. long. 

RECENT PRACTICE IN LAYING WOOD BLOCKS 1 

The wood principally used has been long-leaf (yellow) Southern 
pine, which from experience has been found to give excellent 
results. Most specifications now, however, admit Norway pine 
and tamarac and white birch as a result of experimental pave- 
ments laid in Minneapolis, which showed the suitability of these 
woods. No doubt other species of wood make satisfactory 
pavements, but on account of the incomplete knowledge of 
their value city engineers, as a rule, prefer a wood that has 
proved satisfactory. 

The blocks are from 3 to 4 in. wide and vary in depth from 
3 to 4J^ in., with a length of from 5 to 10 in. As for all timber 
specifications, the blocks should be sound, free from large or 
loose knots, shakes, wormholes and other similar defects. As 
to the proportion of sap and heartwood, the present specifications 
are not very rigid, as experience has shown that treated blocks 
having both sapwood and heartwood do not vary in their wearing 
qualities. 

The preservative used is a creosote oil having a specific gravity 
of from 1.08 to 1.14, containing a percentage of tar, free from 
carbon. Coal-tar oils are used in preference to water-gas creo- 
sote, as sufficient experiments have not yet been carried out 
with the water-gas creosote to determine its relative value. 

The writer has been corresponding with a number of city 
engineers with a view of obtaining opinion as to the most satis- 
factory amount of treatment required per cubic foot of block, 
according to the experience of each city, and in replies from 
twenty cities in the United States has ascertained that six of 
these cities use 16 lb., two of them 18 lb., and twelve of them 
20 lb., spending to some extent on local conditions. 

Laying the Pavement. The base for wood-block pavements 
should be of concrete, from 5 to 6 in. deep, having the crown 

1 Andrew F. Macallum, City Engineer, Hamilton, Ontario. Read at 
Canadian and International Good Roads Convention, Toronto. 



218 CONSTRUCTION OF ROADS AND PAVEMENTS 

parallel to the finished crown on the blocks. An uneven or 
irregular base is detrimental to any pavement, as it is liable to 
cause a depression in the surface to hold water, which the re- 
peated impacts of wagon wheels is certain to increase, giving an 
uneven surface. Upon this concrete base is placed either a 
sand or mortar cushion. This cushion is usually 1 in. deep, 
and has its surface struck by templates to a surface parallel to 
the contour of the finished pavement. Where sand is used, 
the sand is such that it will all pass through a J^-in. screen, be- 
sides being clean. If a mortar cushion be used, some engineers 
use a proportion of 1 of cement to 3 of clean sand, to which 
sufficient water is added to insure the proper setting of the cement. 
Other engineers obtain good results by mixing and placing the 
cement and sand dry. This custom is simply a means of securing 
a uniform surface for the blocks to rest upon and distribute the 
load. Alongside or between street car tracks, however, or on 
grades, sand cushions are apt to become uneven or flow, caused 
by the vibration of the rails, or by water getting in alongside 
the rails, so that under these circumstances a concrete cushion 
should be used. Away from the car tracks the question of 
whether a sand or mortar cushion should be used is a matter of 
opinion. Sand gives a better cushioning effect and the blocks 
do not have to be rolled so soon after laying as when a mortar 
cushion is used. 

English and French practice does away with this cushion 
altogether, but the concrete base is finished off as smooth as a 
concrete sidewalk and to the exact contour of the surface of the 
pavement. This extra care and workmanship obtain results 
that are excellent, inasmuch as the finished surface of the blocks 
has no depression, and consequently the wheels cause no impacts. 

In most cities it is not possible to lay the blocks shortly after 
coming out of the treating plant, and the hot sun and wind during 
shipment and before laying is apt to check the blocks and cause 
oil to exude. The blocks should be piled closely when delivered 
on the street and sprinkled before laying. 

Generally, the blocks are laid at right angles with the curbs, 
with an expansion joint at each curb of from % to 1J^ in., ac- 
cording to the width of the pavement. Alongside the curbs 
three rows of block are laid parallel to the curbs, with the ex- 
pansion joint next to the curb. Placing a longitudinal row of 
blocks, with an expansion joint on each side is sometimes done, 



WOOD-BLOCK PAVEMENTS 219 

but is not good practice, as the single row of blocks between the 
joints will almost certainly rise up about the level of the adjoin- 
ing pavement as the joints close up. Cross expansion joints 
have been used also by the writer when the treated block used 
had been piled on a street for several months, but for fresh 
blocks, properly treated, they are not necessary on streets of 
heavy traffic. On streets of light traffic, however, there should 
be cross expansion joints, placed from 30 to 50 ft. apart and 
having a width of about % i n - It is hardly necessary to say that 
the blocks should be laid with the grain vertical and having the 
joints in adjacent rows broken by a lap of about 2 in. The blocks 
should be laid neither too loose nor too tight, so that a block can 
be raised without disturbing the surrounding blocks, or % in. 
apart. After the pavement is laid it should be rolled thoroughly 
with a roller varying from 3 to 5 tons until a perfect surface has 
been secured, with no depressions and the blocks firmly in place. 
There should be no difficulty in this, as the usual specifications for 
blocks allow of a variation of but Jf 6 m - m depth, so that if the 
foundation and cushion have been properly laid there is usually 
very little trouble about depth of the blocks. 

Alongside street railway tracks and about manholes special 
care should be taken in laying the blocks. It is usual in such 
cases to thicken the cushion so that the blocks shall be about 
3/4 in. above the wearing surface of the rail or cover, and in a 
very short time the traffic will rub these blocks down to the level 
of the rail. Alongside rails, to prevent water flowing down and 
under the blocks, two methods are used: One is to place a 
specially cut creosoted plank under the rail to give a vertical 
surface against which the blocks are paved; and the second 
and usual method is to plaster the web with a rich mixture of 
sand and cement to the width of the rail-head, and the blocks 
are then laid against this. As with other pavements it has 
been found that the girder lip-rail is more satisfactory than the 
ordinary tee-rail, unfortunately in use in most towns, for the 
permanence of the block on the inside or gage side of the rail. 
Incidentally, it may be said that no pavement will be satisfactory 
alongside a street railway track if the rails lack sufficient weight, 
stiffness and foundation to prevent movement, especially at 
the joints. 

There is diversity of opinion among engineers as to the best 
ioint filler to be used. The American Society of Municipal 



220 CONSTRUCTION OF ROADS AND PAVEMENTS 

Improvements recommends a suitable bituminous filler when the 
blocks are laid upon a sand cushion and a sand filler when laid 
on a mortar cushion. It is claimed for the bituminous filler, 
which fills the joints between the blocks two-thirds their depth 
(the remaining depth filled with sand), that it makes an abso- 
lutely waterproof pavement, and that it eliminates all expansion 
difficulties, as each block is surrounded with an individual ex- 
pansion joint. Unless the filler is a suitable asphaltic cement, 
with a high melting point and low penetration, there is apt to 
be a sticky surplus left on the surface. This filler will cost about 
15 cts. a square yard more than a sand filler. 

A cement grout filler has been used, but unless the traffic 
can be kept off the pavement for at least 10 days it is little 
superior to a sand filler. 

The sand filler is generally used on streets of heavy traffic, 
the sand being coarse and sharp-grained, and preferably heated 
before placing. The writer has used with excellent results a 
bituminous filler between and 1 ft. outside of street railway tracks 
and a sand filler for streets. From results obtained he does not 
consider the extra expense in using bituminous filler justified for 
such streets unless the traffic be very light. On bridge floors it 
is better practice to use a bituminous filler with the blocks. 
After the pavement is rolled, sand to the depth of about J^ in. 
is spread over the surface and the street is thrown open to 
traffic. 

This method of construction is satisfactory up to a 3 per cent, 
grade, beyond which the blocks are laid in a different manner. 
The crown should be as light as possible, being just sufficient to 
shed the water freely, which applies also to the pavements be- 
tween street railway tracks. 

When the grade of the street exceeds 3 per cent., a creosoted 
lath is inserted between each cross-row of blocks to leave a space 
of about % in. The lath fills this space practically for two- 
thirds of the depth of the block and a bituminous filler is used. 
This method of laying the blocks forms a good foothold for 
horses, and is satisfactory up to and including a 6 per cent, 
grade. 

One of the criticisms made of treated wood-block pavements is 
that it is slippery, but in the writer's experience he has found that 
there is very little difference between these blocks and sheet- 
asphalt pavements. When covered with a light frost or snow, 



WOOD-BLOCK PAVEMENTS 221 

or when the weather is foggy and damp, the pavement may 
become objectionably slippery. 

In traffic observations made at Philadelphia, New York and 
other cities, the evidence shown by the engineer at these places 
indicated that where treated wooden block and granite blocks 
were on parallel streets, 70 per cent, of the teaming went on the 
wooden blocks. 

On Stuart Street, in the city of Hamilton, the writer laid treated 
wooden blocks between the street car rails and granite block 
between the outside rails and curbs, the pavement being on a 5 
per cent, grade. Although most of the traffic was of a heavy 
teaming nature, it was found that fully 80 per cent, of the traffic, 
except on wet days, was on the wooden block. 

The first cost of wood-block pavement is undoubtedly higher 
than that of most of the other paving materials, averaging in 
the city of Hamilton from $2.85 to $3 per square yard, exclusive 
of grading. When its cheapness of maintenance, ease of clean- 
ing, low tractive resistance and durability are taken into con- 
sideration, this pavement, with its relatively high first cost, will 
compare favorably and prove ultimately cheaper than one lower 
in first cost. 

CEMENT-SAND BED BEST FOR WOOD-BLOCK PAVING 1 

Portland cement should be mixed with the sand used as a 
bedding course in the laying of creosoted wood-block paving for 
the following reasons: 

1. Along streets with car lines, the rise and fall of the rail 
and the jar of passing cars will cause the shifting of a plain sand 
cushion. Where water gets in around the rail this rise and fall 
seems to have a pumping action, forcing the water and sand 
considerable distances. 

2. When service cuts are made a dry, loose sand cushion may 
run for some distance, especially on a grade, due to the blows of 
cutting the foundation. This displacement of the cushion may 
be slight, and pass unnoticed when the cut is repaved. Any 
settlement of a portion of blocks causes unnecessary wear. 

3. When any bulging of the blocks or other accident occurs 
which makes necessary the relaying of a portion of the blocks, 

1 Clark R. Mandigo, Assistant City Engineer, Kansas City, in Engineering 
Record, May 22, 1915. 



222 CONSTRUCTION OF ROADS AND PAVEMENTS 

the work is more easily and accurately done where the bed for 
the blocks retains its original position and is smooth and hard. 

4. A cement-sand bed is good insurance against the displace- 
ment of the surface due to water getting underneath the blocks 
on a grade and shifting a loose sand course. This would apply 
to springs and leaky service pipes or mains as well as storm 
water. 

5. Wood blocks are usually laid with as true and even grade 
and crown as it is possible to get. If the surface is kept true 
there is practically no wear on the blocks. 

The term "cushion" where cement is used, is, of course, a mis- 
nomer. It should be called leveling course or laying bed. The 
blocks themselves are a cushion. Probably the best way to lay 
wood blocks is in asphaltic cement mopped on an absolutely 
smooth floated concrete foundation. Such a base, however, is 
very difficult to obtain in the present state of municipal contract- 
ing and a cement-sand bedding course accomplishes very nearly 
the same results except for the waterproofing of the under side 
of the blocks. 

BEDDING THE BLOCKS 

The cement and sand should be mixed dry in the proportions 
of about 1 to 4, spread on the foundation, templated and the 
blocks set and rolled in the same manner as where a plain sand 
cushion is used. This allows the blocks to be properly bedded 
before the cement has set and avoids any difficulty in placing 
them on a wet mortar. After the blocks are rolled, the water 
necessary for the cement can be added by sprinkling the surface 
of the pavement, or enough moisture would probably be ab- 
sorbed from the concrete foundation to set the cement. The 
bedding course should be only thick enough to level up the un- 
evenness in the base, and with ordinary care in laying the con- 
crete foundation, J^ in. should be sufficient. The increase in 
cost of such a cement-sand course over plain sand is so slight, 
while the advantages gained are so important to the wearing 
surface, that continuing the use of plain sand as a bed for wood- 
block paving appears to be poor economy. 



CHAPTER XII 
STONE-BLOCK PAVEMENTS 

The stone-block pavement is one of the oldest types of pave- 
ment and one that has been very widely used in Europe and 
America, especially for streets of heavy traffic. For dock and 
warehouse districts, and for streets subjected to very heavy 
loads, it is the only type of surface having the requisite dur- 
ability. The earlier pavements of this type often became rough 
and noisy, but better methods of construction have been gradually 
developed until those constructed in recent years are high-class 
surfaces of great durability. 

Kinds of Stone Used for Paving Blocks. By far the larger 
proportion of the pavements of this type have been constructed 
with granite blocks. For this purpose several varieties of granite 
of varying degrees of hardness are employed. Trap blocks have 
been employed to some extent, but in recent years the granite 
block has largely superseded the trap block. 

Sandstone block have been used to a considerable extent, 
where suitable material is available and where traffic conditions 
require that the pavement shall be as free from slipperiness as 
possible, and at the same time be one adapted to heavy loads. 
Quartzite blocks have been used to a limited extent. 

Requirements for Paving Blocks. A stone block that is to be 
used for a pavement will be subjected to impact and abrasion 
just as any kind of pavement block is, but since stone blocks are 
laid on streets carrying the heaviest kind of traffic, the abrasion 
is particularly severe. The stone must be dense and hard and 
fairly tough. It also is desirable that it wear without a polish 
and therefore with a slightly granular surface so that excessive 
slipperiness may be avoided. Any stone will likely wear down 
to a smooth surface but some kinds of stone are more apt to 
become slippery than others. 

Size of Blocks. The length of the block cannot be too great 
or it will not fit closely to the curved section of the pavement or 

223 



224 CONSTRUCTION OF ROADS AND PAVEMENTS 

it will tip under the action of the traffic. The block must not 
be too short or it will have insufficient bearing to support the 
loads. Specifications are by no means uniform in the length 
requirements but if the blocks are not less than 6 in. long nor 
greater than 12 in. long they will be well within the usual re- 
quirements. Blocks of various lengths are used on the same 
street, being mixed indiscriminately and laid as they happen to 
come so long as joints are broken properly. 

The width of the block is to be such as will insure good foot- 
hold. If the block is too wide the cross-joints that give a foot- 
hold lor horses will be too far apart and the horses will slip badly. 
If the blocks are too narrow there will be excessive wear on ac- 
count of the large number of cross-joints, and, moreover, the 
blocks are likely to be unstable in the pavement if they do not 
have enough width to give good bearing. Generally speaking, 
the blocks are seldom made less than 3J^ in. wide or more than 
6 in. wide, but all blocks used on any job should be of the same 
width. This is to insure uniformity of the courses and even 
width of cross-joints. 

Thickness and Depth of Block. Early pavements were laid 
with blocks 6 or 8 in. deep because it was desired to secure stabil- 
ity to the surface. Obviously the blocks could not wear out by 
grinding down until the pavement was too thin to support traffic. 
Long before that was possible the pavement would be too uneven 
for service. More recent practice is to put a good foundation 
under the blocks and to reduce the thickness of the wearing 
surface to 5 in. or, in exceptional cases, 6 or 7 in. American 
practice is like European practice in that deep blocks have been 
used quite generally in the past. 

Special Kinds of Blocks. In addition to the blocks already 
described, which may be considered the standard type of stone 
paving block, some special blocks have been tried out in Europe 
in recent years and may be introduced into the United States. 

Grooved Blocks. For pavements on steep grades, blocks 
having a groove along the middle are used for the purpose of 
giving better foothold for horses. The groove is usually about 
% in. wide and % in. deep. The blocks are generally 6 in. wide 
so that there is a transverse groove every 6 in., alternating with 
the cross-joints which are also 6 in. apart. 

Stone Cubes. Cubes 4 or 6 in. in size are used to some extent. 
Commonly they are laid with the edges diagonally across the 



STONE-BLOCK PAVEMENTS 225 

street, but occasionally they are laid in transverse rows with 
transverse joints. The cubes used in some German pavements 
are about 2J^ in. in size, and for the Durax pavement about 
3J^-in. cubes are used. 

Uniformity of Paving Blocks. Since stone paving blocks are 
handmade, the degree of uniformity secured depends upon the 
price that the municipality is willing to pay for them. The 
stones used have well-defined planes of cleavage so that skilled 
workmen can produce blocks of any desired degree of uniformity 
if they are paid sufficiently for it. In specifying the permissible 
variation it should be borne in mind that nothing is gained by 
severe requirements in this direction. For strictly high-class 
pavements it is desirable to require that the variation from the 
specified width shall not exceed Y in., and in depth not to exceed 
Y or % in. The faces of the block should be free from bulges 
or depressions exceeding about J^ in. It is also customary to 
require that not more than one block per square yard shall show 
a drill hole on the side, and that no drill holes shall show at the 
ends. The sides of the block must be smooth enough to insure 
room for the filler, and the upper face should be as nearly a 
plane as practicable to make it. The edges to the upper face 
should be practically straight lines, and the faces should be per- 
pendicular to each other at the top. It is permissible, however, 
for the block to be slightly smaller on the bottom than on the 
top, i.e., a truncated pyramid, but the difference in width at the 
bottom and top should not be greater than 1 in. 

For second-rate paving a greater variation in the various 
dimensions is permissible, but otherwise the blocks are of the 
same general shape and size as for first-class pavements. 

Requirement for Blocks. To sum up, the stone block should 
be made from a fairly tough stone having a crushing strength of 
at least 16,000 Ib. per square inch. If made of granite the stone 
should be of fairly uniform composition, the constituent minerals 
being well distributed and free from an excess of mica. No 
block that shows signs of disintegration or that is cracked, 
chipped or irregular in shape, may be used. The dimensions 
must comply with those specified within Y in., and the faces 
must be substantially plane and free from bunches or depres- 
sions. The following table shows the variations in the several 
dimensions permitted by American cities: 

15 



226 CONSTRUCTION OF ROADS AND PAVEMENTS 



TABLE 16. ALLOWABLE VARIATION IN DIMENSIONS OF STONE PAVING 

BLOCKS 





Length 


Width 


Depth 


Width of joint 


Minimum 


6 in. 


3^ in. 


4 in. 


YA in. 


Maximum 


10 in. 


6 in. 


8 in. 


Y 2 in. 


Average specification. . 




4 in. 


5 in. 


H in. 



Foundations for Stone-block Pavements. Like many other 
kinds of paving surface, the stone block has in the past been 
laid on various sorts of foundation such as concrete, macadam, 
Telford, old cobblestones and sand or gravel. Modern practice 
has settled down to the almost universal use of Portland cement 
concrete for a base. Sometimes old gravel or macadam founda- 
tions are utilized, and a few cities still permit the construction 
of a base of those materials. It is obvious that a pavement of 
this class requires a very stable foundation if it is to remain free 




FIG. 59. Cross-section for granite-block pavement. 

from depressions and unevenness due to the settlement of indi- 
vidual blocks. It is also apparent that if the traffic requires as 
durable a surface as a granite block, it will be heavy enough to 
require a very substantial foundation to support the surface. 
The concrete foundation is constructed of the materials and in 
the manner that has already been discussed. The thickness is 
rarely less than 6 in. and is often made 8 in. 

Sand Cushion. Since there is likely to be a variation of K m - 
in the depth of adjacent blocks in a course, the sand cushion 
must be thick enough to permit adjusting the blocks so as to have 
a uniform surface. Generally the layer of sand is spread and 
shaped to a thickness of 2 or 3 in. As in other types of pavement 
that have been placed on a sand layer, some dissatisfaction is 
felt with the use of the sand layer because of its tendency to 
shift under the blocks. The sand used need be only a fairly 



STONE-BLOCK PAVEMENTS 227 

clean sand composed of good .hard particles and graded from 
about Y in. down. 

Mortar Cushion. Instead of the layer of sand for bedding the 
blocks, the lean mortar bed is coming into use, and has much to 
recommend it. The mortar is mixed dry in the proportions of 1 
part cement to 3 parts or 4 parts of sand, and spread to the proper 
thickness. After the blocks have been placed, the surface is 
sprinkled to give water to hydrate the cement in the mortar bed. 

Whether the sand layer or a mortar layer is used, it should be 
spread, rolled and struck off to the proper thickness in the manner 
described for the brick pavement. 

Laying the Blocks. The block layer uses a hammer with a 
curved metal blade at one end. With the blade he scoops out 
a depression in the bedding course and places the block so that 
the top conforms to the finished surface and taps the block gently 
to place. If the blocks are quite uniform in depth he may be 
able to bed them by means of the hammer without scooping out 
the sand. Special care is taken to have the joints as close and 
uniform as possible. 

The courses are generally laid perpendicular to the curbs, 
except at street intersections where they are laid parallel to the 
four diagonals of the intersection. In a few instances stone- 
block pavements have been laid with the courses diagonally 
across the street, but where so laid they do not wear as well nor 
furnish as good footing as when laid perpendicular to the curbs, 
and the method has not been used extensively. 

Tamping. After the blocks have been placed they are rammed 
to place with a heavy tamper, a part of the work that must be 
carefully and thoroughly done. If low places develop under the 
ramming, the block so affected should be removed, sand added to 
the bed and the blocks replaced and again tamped. The blocks 
are inspected before the ramming begins, and all defective blocks 
removed and replaced with good ones. After the ramming, any 
blocks that have spalled or split are replaced. The surface when 
thoroughly tamped is ready for the filler. 

Some idea of the importance of proper ramming may be ob- 
tained from the fact that it requires one man ramming for every 
three setters, and it would be better if there were one rammer for 
every two setters. The object of ramming is not merely to 
produce a uniform cross-slope, but to thoroughly bed each block 
so that it will not settle -under traffic. If in bedding the block 



228 CONSTRUCTION OF ROADS AND PAVEMENTS 

it is driven below grade, it is raised, the requisite amount added 
to the bedding course and the block replaced and again rammed. 
Some engineers believe it to be desirable to sweep enough gravel 
of pea size into the joints to fill them about 2 in. before ramming. 
This serves to hold the blocks more securely in place until the 
filler has been applied. 

Sand Filler. Where stone blocks have been laid on a sand or 
gravel foundation, it has usually been customary to fill the joints 
with sand or pea gravel and sand mixed. The filler material is 
spread dry on the pavement and swept into the joints, an excess 
being left to be worked into the joints under traffic. For pave- 
ments that are to be made waterproof, the pitch fillers and cement 
grout are used. 




FIG. 60. Crossing stones in stone-block pavement. 

Pitch Fillers. When a pitch filler is used, the grade commonly 
specified for brick-block pavements is employed. Sometimes the 
joint is partly filled with pea gravel before the filler is poured and 
sometimes no gravel is used. The pitch is applied at a tempera- 
ture that will insure complete penetration and the joint is filled 
flush with the surface and then sanded. English practice is to 
use for a pitch filler a mixture of tar pitch and creosote oil in the 
proportions of about 1 part of the creosote oil to 10 parts of 
pitch. In many instances English practice is to fill the joints 
partially with pea gravel before the pitch is poured. 

Asphaltic Fillers. Asphaltic fillers have been used on stone- 
block pavements to only a limited extent on account of the diffi- 
culty in securing adhesion to the blocks. When adopted it is 
applied just as the pitch filler would be. 



STONE-BLOCK PAVEMENTS 229 

Cement-grout Filler. This type of filler is being adopted more 
and more for the stone-block pavement. As for other types of 
fillers, the joint is frequently partly filled with pea gravel before 
the grout is poured. The grout filler is mixed and applied in 
exactly the same manner as the grout filler for the brick-block 
pavement. 

Recut Granite Blocks. Many of the earlier block pavements 
were laid with blocks 6 and 8 in. deep. These have worn until 
the pavement is exceedingly rough and uneven. A few cities 
have tried taking up these blocks and cutting off the rounded 







FIG. 61. Old style open-joint block pavement. 

part of the head and relaying them, as they are still of sufficient 
depth to give long service. 

Generally the old blocks are taken up and re-dressed and piled 
along the sidewalk until the new base course and cushion have 
been laid, and are then placed exactly as new blocks would be. 

Crossing Stones. In order to contribute to the comfort of 
pedestrians, crossing stones are often provided in stone-block 
pavements. These consist of two or more rows of slabs at the 
crossings. The slabs are usually 18 in. wide and from 4 to 6 ft. 
long, and are placed with two or three rows of ordinary paving 
blocks between them. The slabs are about 5 in. thick and are 



230 CONSTRUCTION OF ROADS AND PAVEMENTS 

laid on the sand bed with the top conforming to the surface of 
the pavement. Granite is generally used if the paving is granite, 
although trap is sometimes substituted. On streets paved with 
the sandstone blocks, the crossing stones are also of sandstone. 
Characteristics of the Stone -block Pavement. The granite- 
block pavement possesses characteristics adapted to the severest 
traffic conditions, and is generally laid only where it is necessary 
to provide something that will withstand the hardest kind of 
wear. It will have long life under such conditions if it has been 
properly laid. It has a tendency to become slippery, especially 
if the harder granites have been used, and the tops of the indi- 




Courtesy Mr. Zenas Carter. 

FIG. 62. Granite-block pavement with close joints. Age 15 years. 

vidual stone will wear off rounding unless a good filler is provided. 
Grout-filled block pavements are more slippery than the pitch- 
filled. In any case a granite-block pavement is apt to be noisy 
and somewhat rough. It is not an easy pavement to keep clean, 
nor is its appearance as pleasing as that of many types, but, 
as before noted, it is built where a very durable pavement is 
essential. 

The trap-block pavement has all of the characteristics of the 
granite-block pavement except that it is more slippery after 
traffic has worn the blocks to a polish. 

The sandstone-block pavement is not adapted to such severe 
traffic conditions as those to which the granite and trap blocks 
may be subjected, without undue wear. The sandstone-block 
pavement is less noisy than the other stone-block pavements, 
and much less slippery. It has most of the other characteristics 
of the granite-block pavement. 



STONE-BLOCK PAVEMENTS 231 

EXAMPLES OF GOOD PRACTICE 

NEW YORK CITY I 

The highway officials of New York City consider that for streets 
with any considerable amount of city traffic, the most satisfac- 
tory pavements are granite block, wood block and sheet asphalt. 
A considerable part of the latest report of the Bureau of High- 
ways is given to the discussion of stone block, and from this we 
abstract the following: 

Granite block, even under the best conditions, is noisier under 
steel tires and horse-drawn vehicles than others. It is not so 
easy to clean. With tar-filled joints a cut can be restored prac- 
tically as good as the original pavement. Its slightly roughened 
surface gives a good foothold for horses' hoofs, and its durability 
is superior to all other types. 

The popular idea of granite pavement in this country is based 
on the old block pavements laid with wide joints, where the head 
speedily became rounded, producing a cobblestone effect. As 
laid under the present specifications, with flat heads and close 
joints, it presents a nearly smooth surface and one which cannot 
wear rounded and uneven. Very hard granite is liable to wear 
as smooth and slippery as any other type. 

It is now universally admitted that granite block for pavement 
should be accurately cut to standard dimensions and laid with 
close joints. There are, however, two distinct points of view in 
regard to the physical composition of the blocks used. That 
taken by Mayor Gaynor's committee on pavements is to the ef- 
fect that all deterioration in stone pavement is due to wear con- 
sequent on lack of sufficient crushing strength and hardness, and 
that only the hardest granites can stand the wear of traffic under 
present conditions. 

The other point of view is exemplified in the following state- 
ment of Mr. McClure, city engineer of Worcester, Mass., which 
is of interest, as that city has made extensive use of granite 
for paving purposes and its streets are admittedly in excellent 
condition : 

"I attribute much of our success in the use of granite blocks 
to the fact that we have always used the New Hampshire granite, 
the greater part of the blocks coming from the Marlboro quarries, 

1 Engineering Record, Jan. 3, 1914. 



232 CONSTRUCTION OF ROADS AND PAVEMENTS 

which is soft enough to wear without polish and hence with a 
slight degree of slipperiness." 

Rounded blocks are not an evidence of lack of hardness, but 
rather the contrary. Many of the older pavements where the 
blocks are in the poorest condition, with rounded tops and ex- 
tremely polished surfaces, are known to have been laid with 
hard material, the constant friction of horses' hoofs and steel 
tires on the edges of the blocks, combined with the wide sand 
joints, producing the above results. Under similar conditions a 
soft block would wear on the top as well as on the edges, as can 
be observed in the Medina sandstone pavements of Rochester 
and Buffalo. 




FIG. 63. Granite-block toothing course along car track. 

The Fourth Avenue pavement was practically the first laid 
under the improved specifications. With the exception of cer- 
tain portions where faulty work was done or where operations of 
the Department of Water Supply, Gas and Electricity and the 
gas company have injured it, and excepting, also, the railroad 
area including between limits 2 ft. outside of the tracks where 
the pavement has not yet been relaid, and where, due to the poor 
condition of the rails it has settled in many places, the surface 
is good, and the blocks show little evidence of wearing round 
after two seasons of service. Work is shortly to be started in 
the railroad area, which is to be entirely repaved with new blocks 
after the rails have been changed. 



STONE-BLOCK PAVEMENTS 233 

The following table contains the names and locations of the 
principal granite quarries available at present for New York 
paving blocks, and indicates approximately the present capacity 
of each : 

TABLE 17. NAMES AND LOCATIONS OF GRANITE QUARRIES AVAILABLE FOR 

NEW YORK 

Capacity 

Quarry in blocks 

per year 

Salisbury, N. C.,Harris Granite Quarries Co 3,000,000 

Rockport, Mass., Rockport Granite Co 6,000,000 

Westerly, R. I., Booth Bros 500,000 

Alexandria Bay, N. Y, J. Leopold 500,000 

Long Cove, Me., Booth Bros 2,500,000 

Roberts' Harbor, Vinal Haven, Me., Booth Bros. 1,000,000 

East Boston, Vinal Haven, Me., J. Leopold 1,500,000 

New England Granite Co., H. H. Mass and Vt. 6,000,000 
Mt. Waldo and Mosquito Mountain, Me., John 

Pierce ' 2,500,000 

Mt. Airy N. C 500,000 

The quarries are arranged approximately according to the 
hardness of their output. Salisbury, Rockport, Westerly and 
Alexandria Bay are extremely hard. The Rockport stone has a 
coarse grain, rendering it very difficult to obtain a finely dressed 
block. 

The Borough of Manhattan alone is at present requiring an- 
nually between 200,000 and 300,000 sq. yd. of granite block, or 
from 6,000,000 to 9,000,000 blocks. 

RE-DRESSED GRANITE BLOCKS IN NEW YORK CITY 1 

For repaving purposes existing granite blocks, originally laid 
on a sand foundation, have an economic value. In 1908 the 
suggestion was made to the authorities of the Borough of The 
Bronx, New York City, as to the advisability of making use of 
the old granite blocks by splitting and re-dressing them. Strange 
to say, the person to make this suggestion was a paving con- 
tractor, largely interested in granite quarries. The scheme met 
with approval and a contract was awarded for repaving Webster 
Avenue from 165th Street to 171st Street, with the result that an 
excellent pavement was obtained at very low cost. There has 
been practically no maintenance cost since the contract was com- 

1 R. H. Gillespie in Proceedings American Road Builders Association, 1913. 



234 CONSTRUCTION OF ROADS AND PAVEMENTS 

pleted, and the pavement at the present time is in very satis- 
factory condition. 

The blocks laid on sand, under the old specifications, are in 
most cases fully up to the length specified ; in fact, a considerable 
proportion run from 12 to 14 in. in length and are rarely less than 
7 in. in depth. The splitting and dressing consists in breaking 
in two, blocks 11 in. or more in length, using the broken face as 
the head and dressing the ends and sides for J^-in. joints. The 
finished blocks are from 6^ to 8 in. long, 3^ to 4% in. wide, and 
5% to 6J^ in. deep. Blocks shorter than 11 in. are reheaded 
where necessary, dressed to lay the required joints, and as a rule 
are used along the street railway tracks. The splitting and dress- 
ing are done on the street by cutters who receive about 1J^ cts. 
for each re-dressed block. Each produces from 450 to 600 blocks 
per 8-hr, day, depending partly on his skill and speed and partly 
on the character of the granite and condition of the blocks. As 
the blocks are dressed they are piled along the sidewalk until 
the concrete is in readiness for the pavement. 

The blocks are laid in the usual manner, in rows, at right angles 
to the curb line on a 6-in., 1-3-6 concrete foundation with a \}/- 
in. sand cushion. Up to Nov. 15, 1913, 207,150 sq. yd. (or 7.96 
miles) of this type of pavement has been laid in the Borough of 
The Bronx, all of it with vertical joints filled with Portland 
cement grout, at an average cost of $1.21 per square yard, ex- 
clusive of concrete base, as compared with an average cost of 
$3.20 per square yard for new improved granite block exclusive 
of foundation. 

During the past 4 years all the improved and re-dressed gran- 
ite pavements in The Bronx have been laid with joints filled with 
Portland cement grout, while in Manhattan and the other bor- 
oughs they have been filled for the most part with paving cement 
or paving cement and gravel. Under like conditions a well- 
grouted granite pavement will give better results than one where 
paving cement and gravel are used. The grouted pavement is 
more easily cleaned, is apt to shed water more readily, is slightly 
smoother, and there is less tendency for the blocks to "turtle- 
back." There is one temporary but serious objection, while it 
lasts, to the grouted pavements interference and inconvenience 
to business interests along the line of the street due to the time 
that the street must be kept from traffic while awaiting the setting 
of the grout. This time should be, under the most favorable 



STONE-BLOCK PAVEMENTS 235 

conditions, not less than one week. Still it is quite practicable 
to pave one-half of a street at a time, and thus to some extent 
minimize this objection. 

For streets which are called upon to accommodate a large 
amount of heavy commercial traffic, the pavement of the granite- 
block type (whether new or re-dressed, grouted or tarred) under 
the present specifications will prove economical and generally 
satisfactory. 

RECUT GRANITE-BLOCK PAVEMENTS IN BALTIMORE* 

A large area of granite-block pavement, laid in accordance 
with the old specifications on streets for whose traffic modern 
paving science would presumably provide totally different sur- 
faces, is Baltimore's heritage from a period when stone surfaces 
were thought ideal for all purposes. How to replace these pave- 
ments with more suitable ones without going to a considerable 
expense was the problem facing the Municipal Paving Commission 
when it was created in 1911. About that time, however, the 
economic value of the old block for repaving purposes was being 
investigated by the highway engineers of the Borough of The 
Bronx, New York City, who seem to have been the first exten- 
sively to re-dress the blocks and make a new surface of them. 
This practice was adopted by the Baltimore Commission, but 
only during the last 2 years have extensive areas been laid. The 
expense of removing, dressing and relaying the block has been 
less than two-thirds the prevailing price for new granite block 
surface. 

The old stones were of the usual heavy type, many as large as 
14 in. in length, 6 in. in width and 8 in. in depth. The broken 
blocks are from 4J^ in. to 6 in. deep, and those which are less 
than 3 in. in either surface dimension are not used. 

As much of the old block was laid on streets bearing a light 
traffic only, little trouble is experienced because of the operations 
of the working gangs. From the old pavements the blocks, 
which are sand-filled, are removed with crowbars and placed con- 
venient to the cutters, who work in the street, producing about 
225 of the small blocks per 8-hr. day. The price for re-dressing 
is about 2^4 cts. per block, although as the work has been let in 
many contracts this price varied somewhat. The renovated 

1 Engineering Record, Nov. 14, 1914. 



236 CONSTRUCTION OF ROADS AND PAVEMENTS 

blocks are carried to the heavy-traffic streets on which they are 
to be used. They are then laid in transverse courses on a 6-in., 
1-3/^-7 concrete foundation with a 2-in. sand cushion. The 
joints are grouted with a 1 to 1 mortar, a thin coat of which is 
finally applied to the surface. Traffic is kept off the completed 
pavement for 14 days. 

During 1913 there were laid of this new paving about 5,000 
sq. yd., and in 1914, to Nov. 1, 3,900 sq. yd. Approximate 
costs per square yard of finished pavement for this surface are as 
follows: Breaking up old pavements, $0.09; recutting, $1.00; 
hauling, laying and grouting, $0.71; total unit cost, $1.80. As 
the old blocks have practically no value unless used in this way, 
the cost of laying the recut prisms, exclusive of foundation, may 
be compared with that for improved granite block, exclusive of 
foundation. As an average figure for the latter in Baltimore is 
$2.80, recutting means a saving of 36 per cent. 

There still exist in the city about 750,000 sq. yd. of the old 
granite-block pavement, and it is planned to make similar use 
of this as opportunity offers. The work is being done under the 
direction of the assistant engineers of the Municipal Paving 
Commission, of which R. Keith Compton is chairman. 

IMPROVED GRANITE-BLOCK PAVEMENTS 1 

To secure a smooth, even surface so perfect, in fact, that no 
crosswalks or bridgestones are used or needed it is necessary 
that the citizen require and the engineer specify a carefully made 
granite block having no projections on the surface exceeding 
%-in. from an even plane, and that the blocks be laid in the 
street on a properly drained subfoundation, a substantial con- 
crete foundation, and with close, even joints, and that these 
joints be filled with a bituminous filler of asphalt or pitch, or 
grouted with a cement grout consisting of 1 part cement and 
1 part sand. 

Bituminous vs. Cement Fillers. The use of the two different 
types of fillers is largely a question of the likelihood of future 
openings being made in the pavement. If frequent openings 
are apt to be necessary, the bituminous filler is more convenient, 
and where traffic conditions demand quick repair it is preferable. 
Where openings are not apt to be frequent or where traffic con- 

1 Mr. Zenas Carter in "The American City Pamphlets," No. 143. 



STONE-BLOCK PAVEMENTS 237 

ditions would allow blocking off for a reasonable period for the 
cement grout to set properly, the cement grout filler should be 
used and will give better results usually than the bituminous 
filler. 

Size of Blocks and Joints. The next feature of importance is 
to specify and secure blocks which permit laying with even, close 
joints; joints for bituminous-filler pavements not to exceed % 
in. and for cement-grout filler pavements not to exceed % in. 
When blocks are laid with wider joints than % in. for bituminous- 
filler work, the blocks will begin to "turtle" or round on all the 
edges within a few years, on account of the steel shoes of horses 
tending to chip and break off small pieces every time the calk 
slips into the joint. With the close, even joint, properly filled, 
the horses can secure good footholds when handling heavy loads, 
and the edges are so close together that both blocks on the sides 
of the joint are forced to take the strain and blow, and neither 
block is broken or chipped. 

A slightly wider joint may be used for cement-grout filler work, 
as the filler must penetrate well down to the bottom of the block 
and thoroughly bond the blocks into a monolith form. 

Granite blocks vary in size in different locations, and no spe- 
cific size can be given preference; but it is important to see that 
all blocks in any single course across the street or area being paved 
are of the same width; as the use of a 4^-in. block in the course 
with a 3%-in. block will leave a chance for the narrow block to 
become loosened, and this gives a chance for the next and the 
next blocks to move. As a result, an opening in the joint de- 
velops and water seeps through to the concrete and shifts the cush- 
ion below or upheaves the blocks in the area through freezing in 
the winter. Of course, with the grout filler the danger is not so 
great, but it exists. 

Granite blocks should not vary more than % m - m depth in 
any case. Much of the old-time unevenness of surface came 
about through carelessness on this point. 

Variations in length are not important, with the exception that 
blocks over 12 in. in length should not be used, and the variation 
in lengths should be sufficient to always allow for breaking the 
joints at least 3 in. so that ruts cannot develop from two end 
joints being continuous. 

Laying the Blocks. When laying blocks, great care must be 
used to see that the sand cushion or mortar cushion over the bed 



238 CONSTRUCTION OF ROADS AND PAVEMENTS 

of the concrete is not deeper than necessary. A cushion of % in. 
to 1 in. is ample, and the frequent practice of using a cushion of 
1^4 in. to 2 in. should be abandoned. Before the specifications 
for improved granite blocks developed there was some excuse 
for this practice, as the blocks frequently varied 1 in. or more in 
depth; but engineers now know that this extra depth of block and 
sand cushion were the cause of much unevenness of -surface. 

After the blocks are laid in proper courses, they must be thor- 
oughly rammed. All low blocks should be lifted and rebedded 
and retamped until the entire surface of the pavement is both 
even and firm. It is best to specify one rammersman to two 
pavers to insure that every block is rammed to a firm bed. The 
main trouble from poor ramming is that the poorly bedded blocks 
will go down under traffic and the surface of the pavement will 
soon be very uneven; while, on the other hand properly laid 
granite block pavements have given service for periods of 20 
years and more without a single block showing appreciable wear, 
or any unevenness of surface developing. 



CHAPTER XIII 
BITUMINOUS ROAD AND PAVEMENT MATERIALS 

Asphalt. The term " asphalt" was until very recent years 
applied to certain deposits or exudations of black or brownish 
mineral matter that were found in many places on the earth's 
surface. These materials were in some instances intimately 
mixed with finely divided rock and in others were simply masses 
of a solid or a very viscous liquid in crevices in the earth. All 
of the deposits had the common property of melting on the appli- 
cation of heat, and of possessing sufficient stickiness when hot 
to render them valuable as cementing agents. Only within a 
comparatively few years has the term been applied to various 
similar materials resulting from manufacturing processes. The 
asphalts were all more or less soluble in chloroform, benzole and 
carbon disulphide, and the soluble portion was called bitumen. 
For commercial reasons the many miscellaneous compounds that 
resemble those originally designated as asphalts have been ex- 
ploited as asphalts and the term is, therefore, no longer of sig- 
nificance technically, but is a commercial designation for a large 
group of generally dissimilar materials having a few similar 
characteristics. The word asphalt as now used has no more 
exact meaning than does the word paint. The same is true of 
the word bitumen which has been used to include not only the 
soluble portions of commercial asphalts, but also the portion of 
tar that is soluble in carbon disulphide. 

The road builder, therefore, encounters a chaotic and irrational 
system of nomenclature and definition when he takes up the 
study of the many kinds of binders that are known commercially 
as bituminous materials. When cleared of the encumbrances of 
a haphazard nomenclature and an illogical classification, the 
study of these materials becomes one of absorbing interest and 
one of great profit for the highway engineer. 

The geological origin of bitumen is, like that of many other 
common minerals, a matter of speculation and scientific contro- 
versy. Of the many theories that have been advanced, two stand 

239 



240 CONSTRUCTION OF ROADS AND PAVEMENTS 

out as being most probable, but neither has been proven or dis- 
proven. The one is that bitumen is the result of chemical action 
which has taken place without heat, the various hydrocarbons 
making up the bitumen having been formed by the interaction 
of the several elements present in a manner unknown and unex- 
plained. This is generally known as the inorganic theory. The 
other is that bitumen is the result of decomposition of either 
terrestrial or of marine animal or vegetable organic matter. 

Either theory accounts for the complexity and variety of the 
bituminous materials that are now common articles of commerce 
and standard road-building materials. 

Asphalt Defined. Asphalts are now defined as follows: As- 
phalts are solid or semi-solid native bitumens, solid or semi-solid 
bitumens obtained by refining petroleum, or solid or semi-solid 
bitumens which are combinations of the bitumens mentioned 
with petroleums or derivatives thereof, which melt upon the 
application of heat and which consist of a complex mixture of 
hydrocarbons and their derivatives of complex structure, largely 
cyclic and bridge compounds. 

Asphalts as here defined have a common property in that they 
are soluble to a greater or lesser degree in cold carbon disulphide 
or similar solvents, and experience indicates that the portion 
thus soluble is the binding or cementing agent in the compound. 

Bitumen. Bitumen is defined as a " mixture of native or pyro- 
genous hydrocarbons and their nonmetallic derivatives which 
may be gases, liquids, viscous liquids or solids, and which are 
soluble in carbon disulphide.'* 

The first class of bitumens mentioned (gases) is of no interest 
to the road builder, but each of the others is used in some part 
of the art of road making. 

Bitumen is a black or brownish-black substance, and that ob- 
tained from the various classes of road materials has very much 
the same general appearance. Some bitumens have distinct 
odors, especially when hot, and that of tar is easily recognized, 
while others have very little if any odor. 

In physical characteristics the various bitumens differ greatly. 
Some are highly ductile, and others possess that characteristic 
to a very limited degree; some are brittle, others tough, some 
sticky, some greasy, some stable, some unstable. 

In chemical characteristics there is also a great variation in the 
several classes of bitumens. They consist of mixtures of hydro- 



BITUMINOUS ROAD MATERIALS 241 

carbons, mostly cyclic and bridge compounds, of great complex- 
ity. From the road builder's standpoint little or no attention 
is given to the chemical composition, except as the physical 
characteristics are affected thereby, and such relations are diffi- 
cult to establish. 

Since the value of the bituminous materials for highway pur- 
poses depends upon the character of the bitumen in them, most 
tests have for their object the determination of the character 
of the bitumen. 

It is necessary to utilize bituminous materials that occur in 
nature or are made from materials thus obtained, and the char- 
acter of a paving cement or binder can be controlled only to a 
somewhat limited extent. It is possible to mix two or more 
materials and thus produce a product differing from any of them 
in physical properties, but such a procedure does not necessarily 
produce a superior road material. Many commercial road and 
pavement materials, however, are produced in this way, it being 
possible to correct some one fault of a basic material by the mix- 
ture of some other product. As an example, mention might be 
made of the practice of mixing a highly ductile and brittle mate- 
rial with a "short" material to produce a road binder having 
reasonable ductility without being brittle. 

It is not always possible to predict what durability will result 
from the mixture of two bitumens, and all such combinations 
should be worked out carefully in an experimental way before 
being undertaken on a commercial scale. Undoubtedly the 
manufacture of bituminous road materials in this way will be 
gradually perfected until compounds of specified properties and 
assured durability can be readily produced. At present, hap- 
hazard mixtures are looked upon with more or less suspicion 
because of numerous failures of pavements where such materials 
have been used. The compounding has had for its object the 
production of a material that will meet a certain specification, 
rather than the production of a good binder. This is more a 
fault of specification than of manufacture. 

A peculiarity of bitumens is that there seems to be no definite 
and constant relation between their chemical and physical prop- 
erties as determined by test, and the value of the bitumen as a 
paving material, that is applicable to all classes of bitumens. 
It is not always possible to examine and analyze an untried bitu- 
minous material and predict with certainty the behavior of the. 

16 



242 CONSTRUCTION OF ROADS AND PAVEMENTS 

material when subjected to traffic. The more experienced ana- 
lysts are, of course, able to do so to a considerable extent, but 
even they occasionally err, and no basic and established laws 
have been promulgated. 

It is apparent from what has been said that a bituminous 
cement cannot be manufactured to a standard formula as can 
Portland cement, but the engineer must use the materials that 
are produced commercially from the various classes of raw mate- 
rial, or mixtures of them. 

Experience is the best guide in determining the value of any 
binder of this class, and until it has been successfully used for 
paving purposes it must be looked upon as an experimental 
product. On the other hand, many kinds of bituminous paving 
materials have been in continuous service for years so that their 
behavior has been well established. 

Sources of Bituminous Materials. From the standpoint of 
the highway engineer, all bituminous materials may be placed 
in three classes as follows: (a) natural asphalts, (6) petroleum 
asphalts, and (c) tars. This classification is an arbitrary one, 
but it is commonly employed. 

NATURAL ASPHALTS 

Natural asphalt is a bituminous material that is obtained from 
deposits existing in nature in which the material is of such char- 
acter that it needs only to be freed of foreign matter to be suit- 
able for use. This is the class of material originally known ex- 
clusively as asphalt. 

Trinidad Asphalt. The largest and best known of the natural 
deposits is that on the Island of Trinidad in the British West 
Indies, which is known as the Pitch Lake. This deposit is in 
the nature of a lake of about 125 acres extent and having a depth 
of more than 135 ft. in places. The material obtained from this 
deposit contains pieces of wood, gas, water, and a considerable 
quantity of fine sand and clay. The refined material is of uni- 
form quality and contains 56.5 per cent, of pure bitumen, the 
remainder being sand, clay and organic matter insoluble in car- 
bon disulphide. Other deposits of similar material are scattered 
over the islands, but they are of much less importance commer- 
cially. Trinidad asphalt has been long and widely used as a 
binder for sheet asphalt and asphaltic concrete pavements. It 
is unlike any other asphalt known. 



BITUMINOUS ROAD MATERIALS 243 

Trinidad Petroleum. A heavy asphaltic petroleum oil is ob- 
tained from wells on Trinidad Island, and this oil field has been 
extensively developed. This material contains a relatively 
small amount of the lighter oily constituents common to pe- 
troleum, and the body of the oil is of a truly asphaltic nature 
and exceedingly sticky and stable. This material is soluble in 
carbon disulphide to the extent of 99.9 per cent. It is refined 
and marketed as a dust layer and as a binder for the construc- 
tion of bituminous carpets. 

Bermudez Asphalt. Another well-known deposit of natural 
asphalt is on the north coast of Venezuela and is known as the 
Bermudez deposit. It is a comparatively shallow deposit, being 
in most places about 7 ft. thick, but has an area of about 900 
acres. The material has exuded from the earth and spread over 
a swampy area which is often covered with water. It contains 
decayed vegetable matter, sticks and a little clay and water. 
The water-free material is somewhat variable in composition 
.and contains from 93 to 97 per cent, pure bitumen with an aver- 
age of 95 per cent. The remainder is clay and organic matter 
insoluble in carbon disulphide. Bermudez asphalt is widely 
used as a binder for sheet asphalt, asphaltic concrete and mac- 
adam surfaces. 

Cuban Asphalt. Several deposits of natural asphalt exist in 
Cuba, most of which are of rather recent development. In 
general, the Cuban asphalt that has been utilized for paving 
purposes resembles slightly the Trinidad Lake asphalt, but is 
more variable in its characteristics. It contains from 65 to 75 
per cent, of bitumen, the remainder being sand and clay and 
organic matter insoluble in carbon disulphide. Cuban asphalt 
is used to some extent for sheet and asphaltic concrete pavements, 
and for macadam surfaces. 

Mexican Asphalt. Deposits of natural asphalt also exist along 
the Gulf Coast of Mexico, and for a short distance inland in the 
Tuxpam district. These deposits are variable in composition, 
but are being developed rapidly and will likely be used extensively 
in the future. The various deposits contain from 60 to 99 per 
cent, pure bitumen. The Mexican asphalts have been used prin- 
cipally for sheet and asphaltic concrete surfaces. 

Miscellaneous other deposits of natural asphalt are found 
throughout the world, and the material has been an article of 
commerce from the earliest times. Asphalt is found in the vicin- 



244 CONSTRUCTION OF ROADS AND PAVEMENTS 

ity of the Dead Sea, and its properties and value have been known 
locally from the earliest Bible times. The Dead Sea deposits 
have not been developed on a large scale. Other deposits in 
Asia and Europe have been known and utilized for centuries, 
and many European cities have been paved with asphalt ob- 
tained from these sources. 

Deposits of minor importance are known in South America, 
and in Texas and California. 

Gilsonite. Deposits of a bitumen known as gilsonite, which 
is not an asphalt, are found in parts of Colorado and Utah. It 
is of importance because it is practically pure bitumen, and has 
been extensively used in the paving industry, being fluxed with 
an asphaltic residue and forming an exceedingly tough and rub- 
bery cement. 

Natural Rock Asphalt. In many parts of the world there are 
extensive deposits of limestone or sandstone rock which by some 
process of nature have become impregnated with asphalt, usually 
in the form of a soft maltha. The best known deposits in the. 
United States are in Kentucky, Oklahoma, Texas and Southern 
California, while those in Germany, France, Sicily and Russia 
are best known abroad. This class of material has had a limited 
use for sheet-asphalt surfaces in the United States, but has been 
extensively used in Europe. As might be expected, the rock 
asphalts vary greatly in character and few of them can be used 
for paving purposes without the addition of either sand or bitu- 
men or both. The rock asphalts are also extensively used for 
mastic floors in factories and laboratories. 

Refining Natural Asphalts. It is doubtless apparent from the 
foregoing that the various materials discussed differ greatly in 
consistency and other physical characteristics, and that all must 
be prepared in some manner to render them suitable for paving 
purposes. In some of the deposits the materials vary from hard 
pitches to soft asphalts or malthas that flow slowly at ordinary 
temperature; in other deposits the consistency is fairly uniform. 

A brief description of the method of refining the Trinidad Lake 
asphalt will indicate in a general way the usual preparation 
necessary before natural asphalts can be used for paving purposes. 

The Trinidad Pitch Lake is some miles inland and about 140 
ft. above sea level. The asphalt is broken out of the surface in 
irregular pieces by means of picks, and is loaded onto small cars. 
These are hauled out from the region of the lake and the remov- 



BITUMINOUS ROAD MATERIALS 245 

able bodies of the cars attached to a cableway and transported 
to the dock where the material is loaded into vessels. When 
the cargo reaches the refinery (Maurer, N. J.) the asphalt is 
picked loose in the hold of the vessel and removed to the melting 
tanks. It is then heated by means of steam coils to a tempera- 
ture exceeding 212F., after which it is agitated by means of 
jets of steam from pipes in the bottom of the tank. As the heat- 
ing progresses the entrained water and gas are given off and the 
sticks and other vegetable matter are removed. The material 
is then drawn off into barrels to be shipped to the place of use. 
There it is fluxed with a suitable petroleum oil to reduce its 
consistency to that desired for the paving cement. 

PETROLEUM ASPHALTS 

Petroleum, as is well known, is composed of complex and vari- 
able mixtures of hydrocarbon compounds, and, in the process of 
refining, the various burning and lubricating oils are distilled off, 
leaving a residue which is a black, viscous substance. The resi- 
due may consist of hydrocarbons of the paraffine series or may 
contain none of them, in which case it is called asphaltic, or it 
may be composed of both classes of material. Hence petroleums 
are referred to as asphaltic, semi-asphaltic or paraffine, depend- 
ing upon the character of the basic compounds. The residue 
from the asphaltic and semi-asphaltic petroleums are converted 
into paving materials by various processes which will now be 
described briefly. 

Residual Asphalts. The residue from refining some kinds of 
petroleum is suitable for road construction without further treat- 
ment, and is marketed substantially as obtained in the process 
of refining the petroleum. This is particularly true of California 
and Mexican oils. In other instances the residues are either 
too hard or too soft and must be brought to a suitable consistency 
by variation in the refining process or by the addition of asphalts 
or fluxes from other sources. When an asphaltic material left 
from the refining process is suitable for use without further treat- 
ment, it is known as a residual asphalt. Residual asphalts are 
employed for dust laying, for carpeting, and for macadam con- 
struction, and when properly fluxed, for sheet pavements. 

Gilsonite Products. Some petroleum residues are unsuitable 
for paving purposes because of the poor quality of the bitumen 



246 CONSTRUCTION OF ROADS AND PAVEMENTS 

they contain, or because of their being of improper consistency. 
Gilsonite can be mixed with such of these residues as are of an 
asphaltic nature and thus produce a paving material of suitable 
character. The mixture may or may not be " blown" as de- 
scribed below. It is used for all classes of road construction 
where the mixing processes are employed, and for penetration 
macadam. 

Blown Oils. Petroleum residues are sometimes subjected to 
the process known as blowing, which improves them for use in 
paving work. The process consists in first heating the residue 
to a temperature of about 200F. Air is then blown into the 
material from perforated pipes in the bottom of the tank, the 
heating being meanwhile continued. Under this treatment the 
temperature gradually rises to about 400F. at which it is held 
until the material is brought to the desired consistency and 
quality. The process is usually continued for from 5 to 20 hr. 
With some grades of residue it is also necessary to add gilsonite 
or some other material rich in bitumen to produce a paving mate- 
rial of good quality. Products manufactured in this way are 
known as blown oils. The blowing has the effect of producing 
a waxy asphalt of low ductility but of reasonable stability. The 
blown oils are used for sheet asphalt and asphaltic concrete, and 
for mixed and penetration macadam construction. 

TARS 

Tar is classified commercially as a bituminous material, al- 
though the bitumen it contains is entirely unlike that contained 
in asphaltic materials. 

Coal tar is a byproduct of the destructive distillation of coal. 
If the tar is produced during the manufacture of illuminating gas 
from coal, it is commonly called gas-house tar. If it is produced 
as a byproduct in the manufacture of coke, it is known as coke- 
oven tar. The gas-house tar is produced at a higher temperature 
than the coke-oven tar, and usually contains more free carbon 
(soot) than the coke-oven tar, due to the differences in processes 
of which the tars are a byproduct. Tars are almost pure bitu- 
men, aside from the free carbon. They have the same general 
appearance as asphalts but have the characteristic and familiar 
tar odor which differs from the odor of any of the asphaltic 
materials. Tars are refined to prepare them for paving purposes, 



BITUMINOUS ROAD MATERIALS 247 

the process consisting in distilling off the water and lighter or 
more volatile oils, leaving a residue of the desired consistency. 
Coal tar is used for penetration and mixed macadam, and for 
carpeting. 

Cut-back Pitches. Tars are used widely in the arts in obtain- 
ing the basic materials for dyes, medicines, etc., and incident to 
manufacturing these products, residues are often obtained that 
are too hard for paving purposes. These are softened or " fluxed" 
by means of lighter distillates obtained as a byproduct from other 
manufacturing processes and the resulting mixture is known as 
a cut-back pitch or simply as a " cut back." These tars are manu- 
factured with various consistencies suitable for the different 
classes of macadam road work. 

Water-gas Tar. Water-gas tar is produced as a byproduct of 
the manufacture of illuminating gas from oil and water. It is 
the result of destructive distillation or " cracking" of a petroleum 
oil. It has the same general appearance as coal tar and has much 
the same odor, but is generally thought to be less useful for road 
purposes. It also differs in that it carries a much lower amount 
of free carbon than do the other classes of tars. It is refined and 
marketed for all classes of macadam construction. 

Mixtures. Many road binders and paving cements are mix- 
tures of two or more of the classes or types of bituminous mate- 
rials that have been mentioned. As an illustration, the practice 
of mixing California residues with Texas residues might be men- 
tioned. Water-gas tars and asphaltic materials are also mixed 
in manufacturing some brands of road materials. These prod- 
ucts often appear to have desirable physical properties, but 
their behavior under traffic has not yet been fully established. 

Fluxes. A flux is a soft bitumen or bituminous oil that is 
mixed with a harder bitumen to soften it. The ordinary as- 
phalt cement is usually a mixture of a hard bitumen and a flux. 
The practice of softening a hard pitch with tar distillates has 
already been mentioned as a fluxing process and the distillate 
thus used is a flux. 

Fluxes for asphaltic materials are obtained from petroleum 
and are of three classes, paraffine, semi-asphaltic and asphaltic, 
the classification depending upon the predominating basic com- 
pounds of which the flux is composed as has been mentioned in 
connection with petroleum asphalts. The paraffine fluxes are 
obtained to a limited extent from the petroleums of the Pennsyl- 



248 CONSTRUCTION OF ROADS AND PAVEMENTS 

vania and Ohio oil fields and to a large extent from those of 
Kentucky, Kansas, Oklahoma and Texas. It is the most com- 
monly used of all the fluxes and when of the proper specific 
gravity and carefully manufactured so as to give uniformity is 
a satisfactory material for the purpose for which it is used. 

Semi-asphaltic flux is obtained principally from Kentucky and 
Texas and only in limited quantities. As the name indicates, the 
basic compounds are partly asphaltic and partly paraffine. This 
is one of the best grades of flux obtainable. 

Asphaltic flux is obtained principally from the California 
petroleums. It is a dense, heavy flux and a larger proportion of 
it must be used with a hard bitumen than of other types. When 
carefully prepared so that it will remain soft in the pavement, it 
can be used successfully. 

The properties of fluxes obtained from the various sources will 
vary greatly, but certain characteristics are essential to all of 
them. 

1. The flux should be prepared at high temperature, yet with- 
out injury to the material from overheating. It is essential that 
the paving cement in which the flux is used remain unchanged 
for years, and, unless the flux has been prepared at a temperature 
near 450F., it is likely to volatilize in service and leave a brittle 
pavement surface. 

Since the sheet asphalt and asphaltic concrete pavement sur- 
faces are usually mixed at temperatures ranging from 250 to 
350F., it is necessary to use a flux that will not catch fire, i.e., 
" flash" at these temperatures, which is an additional reason why 
the flux should be manufactured at high temperature. 

2. The flux should be fluid enough to have the property of 
mixing with hard bitumens in such a manner that it will reduce 
the harder materials to a proper consistency without the neces- 
sity of using an excess of about 30 Ib. of flux to 100 Ib. of the 
harder bitumen. This characterisitic is only partly dependent 
upon the fluidity of the flux, being influenced also by the char- 
acter of the hydrocarbons of which it is composed. 

3. The flux should consist of stable compounds so that it will 
not change after it has been incorporated in the pavement. This 
property should not be confused with volatility. A volatile flux 
will evaporate and cause the pavement to become brittle. Other 
fluxes are composed of unstable compounds that change in the 
pavement with the passage of time. The result may be a bitu- 



BITUMINOUS ROAD MATERIALS 249 

minous cement that is of good binding properties when the pave- 
ment is laid, but which loses its binding properties with time, and 
the pavement may fail as a result. 

Asphalt Cement. Asphalt cement is defined as a fluxed or 
unfluxed asphaltic material, especially prepared as to quality and 
consistency so as to be suitable for direct use in the manufacture 
of asphaltic pavements, and having a penetration 1 between 5 
and 250. Generally it has a penetration between 40 and 70. 

The asphaltic cement, as its name indicates, is an asphaltic 
material that is used to bind together the particles of sand or 
other mineral matter of which the pavement is composed. It is 
analogous in purpose to the Portland cement used in concrete. 

The unfluxed asphalt cements are usually petroleum products, 
manufactured to the proper consistency for use without further 
treatment. They are received at the paving plant ready for use. 

A fluxed asphalt cement is usually made at the paving plant. 
The hard asphalt and the flux are received separately and com- 
bined at the plant prior to mixing with the mineral aggregate. 

CLASSES OF COMMERCIAL BITUMINOUS MATERIALS 

(For explanation of the various tests, see Chapter XX) 

Dust Layers for Earth Roads. The materials prepared for 
this purpose are petroleum products of a semi-asphaltic or par- 
affine nature. They must be exceedingly fluid to mix with the 
soil and are usually applied cold. The following analysis indi- 
cates the general characteristics of materials obtained for this 
purpose. Many others have been used that differ more or less 
from this analysis, but this is one that has been used successfully : 

Specific gravity at 25C . 93 

Fixed carbon 6 . 00 per cent. 

Loss in 5 hr. at 163C 25 . 00 per cent. 

(Residue from above slightly greasy). 

Specific viscosity (Engler) 50 c.c. at 50C... 46.00 

Solubility in carbon disulphide 100.00 per cent. 

Bitumen insoluble in 86 naphtha 8 . 50 per cent. 

Dust Layers for Gravel or Macadam. The materials used for 
this purpose are slightly more viscous than those used on earth 
roads. They are commonly heated before being applied, but 
some kinds are applied cold. They may be petroleum products 

1 For definition of penetration, see Glossary. 



250 CONSTRUCTION OF ROADS AND PAVEMENTS 

or soft natural malthas, but the former are more widely used, 
while the latter are probably preferable. Light refined water- 
gas and coal-tar products are also extensively used for this pur- 
pose. If an oil is used, it should have a truly asphaltic base, and 
should have the property of hardening somewhat after applica- 
tion, that is, it should " set up" within a reasonable time. The 
following analyses and specifications will serve to indicate the 
nature of the tars and oils used for dust laying on macadam and 
gravel roads: 

1. Petroleum Oil (Specification). 

Specific gravity at 25C. not less than 0.93. 

Solubility in carbon disulphide, not less than 99.5 per cent, and not over 
0.3 per cent, of organic insoluble matter. 

Bitumen insoluble in 86Be". naphtha not less than 3 per cent, nor more 
than 15 per cent. 

Specific viscosity (Engler) 50 c.c. at 50C. between 40 and 80. 
Fixed carbon, not less than 3.5 per cent. 

Loss on heating at 163C. for 5 hr., not more than 20 per cent. (Resi- 
due must not be greasy.) 

2. Asphaltic Oil (Soft maltha, analysis). 

Specific gravity at 25C 0. 961 

Consistency by float test at 50C 10. 00 sec. 

Loss on heating 5 hr. at 163C 26 . 10 per cent. 

(Residue sticky and asphaltic). 
Consistency of residue by float test at 50C. 2 min. 25 sec. 

Solubility in carbon disulphide 99. 95 per cent. 

Organic matter insoluble in carbon disulphide . 05 per cent. 

Bitumen insoluble in 86Be. naphtha 8 . 20 per cent. 

Fixed carbon 3 . 70 per cent. 

3. Light Refined Tar (Analysis). 

Specific gravity at 25C 1.16 

Consistency by float test at 50C 25 sec. 

Free carbon 4 . 40 per cent. 

Distillation. 

Distillate to 110C 0.00 per cent. 

Distillate from 110 to 170C. 0. 00 per cent. 

Distillate from 170 to 270C 34.00 per cent. 

Pitch 66 . 00 per cent. 

Bituminous Carpets. Bituminous materials and stone chips 
or screened gravel are applied to macadam road surfaces so as 
to build up a layer of appreciable thickness. Such a coating is 
called a "bituminous carpet" or the process is referred to as 
bituminous surfacing. The asphaltic products and the tars are 
used for this purpose, and the following are analyses of materials 



BITUMINOUS ROAD MATERIALS 251 

that have been successfully employed. Similar materials are 
employed for carpeting concrete road surfaces, but not with the 
same degree of success. 

1. Asphaltic Materials (Analysis). 

Specific gravity at 25C 0.989 

Flash point . 110C. 

Burning point 130C. 

Consistency by the float test at 50C 20 sec. 

Loss on heating for 5 hr., at 163C 15.9 per cent. 

(Residue very sticky, asphaltic). 
Consistency of residue by float test at 50C., 2 min. 30 sec. 

Bitumen soluble in carbon disulphide 99.9 per cent. 

Organic insoluble matter 0.0 per cent. 

Bitumen insoluble in 86 naphtha 10. 1 per cent. 

Fixed carbon 5.9 per cent. 

2. Refined Coal Tar (Analysis). 

Specific gravity at 25C 1 .22 

Consistency by float test at 50C 38 sec. 

Free carbon 18 . 00 per cent. 

Distillation. 

Distillate to 110C 0.0 per cent. 

Distillate between 100 and 170C 1 . per cent. 

Distillate between 170 and 270C 28.0 per cent. 

Pitch residue 71.0 per cent. 

Penetration Macadam. This type of surface differs from the 
bituminous carpet in that the bituminous material is applied at 
the time the stone is placed, and in a manner to insure that the 
binder will penetrate an inch or more into the surface. Natural 
and petroleum asphalts and refined tars are used successfully. 
The following specifications cover the three classes of material 
usually employed for this purpose: 

1. Refined Tar (Specification). 

Specific Gravity. The specific gravity at 25C. shall not be more than 
1.26. 

Free Carbon. The free carbon shall not exceed 20 per cent, by weight. 
Consistency. The consistency as determined by the Howard and Morse 
float apparatus at a temperature of 50C. shall not be less than 1^ min. 
nor more than 2^ min. 

Distillation. Fractional distillation shall give results within the follow- 
ing limits, all measurements being by volume: 
Up to 110C. the distillate shall not exceed 2 per cent. 
Up to 170C. there shall be not to exceed 5 per cent, distillate of which 
not more than one-fourth shall be naphthalene. 
The total distillate up to 315C. shall be at least 18 per cent. 



252 CONSTRUCTION OF ROADS AND PAVEMENTS 

2. Natural Asphalts and Gilsonite Products (Specification). The material 

shall be free from water. 

Specific Gravity. The specific gravity at 25C. shall not be less than 

unity. 

Total Bitumen. The bituminous material shall be soluble in chemically 

pure carbon disulphide at air temperature to the extent of at least 99.5 

per cent, for residual asphalts and gilsonite products, 95 per cent, for 

Bermudez products, 80 per cent, for Cuban products, and. 65 per cent. 

for Trinidad products. 

Naphtha Insoluble Bitumen. Of the total bitumen not less than 15 per 

cent, nor more than 28 per cent, by weight shall be insoluble in 86Be\ 

paraffine naphtha at air temperature. On evaporation of the naphtha 

solution the residue obtained shall be sticky and not merely oily. 

Fixed Carbon. The fixed carbon shall be not less than 8.0 per cent, nor 

more than 14.0 per cent. 

Penetration. The penetration as determined with the Dow penetration 

machine, using a No. 2 needle, 100 grams weight, 5 sec. time, and a 

temperature of 25C., shall not be less than 14 mm. nor more than 16 

mm. 

Loss on Evaporation. When 20 grams (in a tin dish 2^ in. in diameter 

and M in. deep, with vertical sides) are maintained at a temperature of 

163C. for 5 hr., the loss shall not exceed six (6.0) per cent, by weight. 

The surface of the residue at air temperature shall be smooth and show 

no sign of blistering or cracking, and when tested the penetration in 5 

sec. at 25C. with a No. 2 needle, and 100 grams weight, should be at 

least five (5.0) millimeters. 

Ductility Test. The ductility at 25C. shall not exceed eighty-five (85) 

centimeters. 

Flash Test. The flash point in an open cup shall not be less than 163C. 

Paraffine Scale. The asphaltic binder shall not contain more than two 

(2.0) per cent, by weight of paraffine scale. 

3. Petroleum Products (Specification). 

The bituminous material shall be free from water. 
Specific Gravity. The specific gravity at 25C. shall not be less than 
0.965 nor more than unity. 

Total Bitumen. The bituminous material shall be soluble in chemically 
pure carbon disulphide to the extent of at least 99)^ per cent, by weight 
at air temperature. 

Naphtha Insoluble Bitumen. Of the total bitumen not less than 20 nor 
more than 26 per cent, by weight shall be insoluble in 86Be. paraffine 
naphtha at air temperature. On evaporation of the naphtha solution, 
the residue should be sticky and not merely oily 

Loss on Evaporation. When 20 grams (in a tin dish 2% in. in diameter 
and 4 in. deep, with vertical sides) are maintained at a temperature of 
163C. for 5 hr., the loss shall not exceed 2 per cent, by weight. The 
surface of the residue at air temperature shall be smooth and shall pre- 
sent no greasy spots nor any sign of blistering or cracking. The pene- 
tration in the residue shall not be decreased more than 40 per cent, from 
the original consistency. 



BITUMINOUS ROAD MATERIALS 253 

Fixed Carbon. The fixed carbon shall not be less than 7 nor more than 

13 per cent. 

Penetration. The penetration, using a No. 2 needle, 100 grams weight, 

5 sec. time, and a temperature of 25C. shall not be less than 7 nor more 

than 12 mm. 

Carbenes. The bituminous binder shall not contain more than % per 

cent, by weight of bitumen insoluble in chemical pure carbon tetra- 

chloride at air temperature. 

Flash Test. The flash test in open cup shall not be less than 200C. 

Melting Point. The melting point shall not be less than 60C. 

Ductility. The ductility at 25C. shall not be less than 25 cm., according 

to the District of Columbia standard. 

Macadam Constructed by the Mixing Methods. This type of 
construction lies between the penetration macadam and the as- 
phaltic concrete, and the bituminous materials used are of the 
same general character as those used in penetration macadam. 
The following analyses will illustrate the kind of material that 
has been successfully used for this purpose. 

Asphaltic Binder. 

Specific gravity at 25C 1 . 06 

Consistency by penetration at 25C., 100 grams, 5 

sec., No. 2 needle 72 

Loss in heating 5 hr., at 163C 4 . 26 per cent. 

Penetration of residue as above, relative to original . . 36 . 00 per cent. 

Solubility in carbon disulphide 95 . 6 per cent. 

Insoluble organic matter 1.2 per cent. 

Bitumen insoluble in 86 naphtha 26 . 6 per cent. 

Fixed carbon 11.1 per cent. 

Tar Binder. 

Specific gravity at 25C 1 . 24 

Consistency by the float test 65C 55 sec. 

Free carbon 22 . per cent. 

Distillation. 

To 110C . 4 per cent. 

110 to 170C 4.4 per cent. 

170 to 270C 22.0 per cent. 

Asphaltic Concrete. The requirements of the bituminous 
material for this class of construction are more rigid than for the 
other types of bituminous pavement. Practice is confined al- 
most entirely to the use of asphaltic materials and frequently 
the asphalt cement is manufactured at the paving plant as has 
been mentioned before. It is not possible to draw satisfactory 
exact specifications that will cover all classes of good asphalt 



254 CONSTRUCTION OF ROADS AND PAVEMENTS 

cements, but general specifications are sometimes drawn under 
which any suitable material may be used. Such general speci- 
fications are in reality a combination of class specifications. The 
following is an example, and it should be noted that the use of a 
manufactured asphalt cement, or one prepared at the paving 
plant, is permitted. 

REFINED ASPHALT 1 

The refined asphalt to be used for paving mixtures shall be 
derived in the following manner: 

1. By heating, if requiring refining, crude, native, solid asphalt 
to a temperature of not over four hundred and fifty (450) degrees 
F. until all water and light oils have been driven off. Crude, 
native, solid asphalt shall be construed to mean any native 
mineral bitumen, either pure or mixed with foreign matter having 
a consistency harder than one hundred (100) degrees penetration. 
At least ninety-eight and one-half (98^) per cent, of the con- 
tained bitumen in the refined asphalt which is soluble in cold 
carbon disulphide shall be soluble in cold carbon tetrachloride. 

2. By the careful distillation of petroleum with steam agita- 
tion, at a temperature not exceeding seven hundred (700) degrees 
F., until the resulting residue has a consistency not harder than 
thirty (30) degrees penetration. 

(a) The solid residue so obtained shall be soluble in carbon 
tetrachloride to the extent of ninety-eight and one-half (98J^) 
per cent. 

(6) If the solubility in carbon tetrachloride of the solid residue 
is less than ninety-nine (99) per cent., the bitumen shall yield 
upon ignition not more than fifteen (15) per cent, of fixed carbon; 
if the solubility is ninety-nine (99) per cent, or more, the bitumen 
shall yield upon ignition not more than eighteen (18) per cent, 
of fixed carbon. 

(c) When twenty (20) grams of the material are heated for 
five (5) hours at a temperature of three hundred and twenty-five 
(325) degrees F. in a tin box two and one-quarter (2J) inches in 
diameter, after the manner officially prescribed, it shall lose not 
over five (5) per cent, by weight nor shall the penetration after 
such heating be less than one-half the original penetration. 

(d) When the refined asphalt is brought to a penetration of 

1 Recommendation of the Association for Standardizing Paving Specifi- 
cations. 



BITUMINOUS ROAD MATERIALS 255 

fifty (50) by the use of the flux with which it is to be combined in 
making the asphaltic cement, or by heating at a temperature 
below five hundred (500) degrees F., it shall have a ductility of 
not less than thirty (30) centimeters. 

(e) All shipments of material shall be marked with a lot num- 
ber and penetration, and then ten (10) samples taken at random 
from each lot shall not vary more than fifteen (15) per cent, from 
the average penetration. 

3. By combining crude, native, solid asphalt with asphaltic or 
semi-asphaltic flux of the character hereinafter designated, pro- 
vided that the proportion of the flux to the contained bitumen of 
the crude asphalt does not exceed forty (40) per cent, by weight 
or result in a refined asphalt having a penetration greater than 
forty (40) degrees. 

In the use of combinations of refined asphalts for asphaltic 
cement, only asphaltic or semi-asphaltic fluxes shall be used, 
except in those cases where the solid natural asphalt is of such 
character that when mixed with paraffine flux without the addi- 
tion of any other material it will produce an asphaltic cement 
complying with the requirements set forth under that head. In 
such cases any of the fluxes elsewhere specified may be used. 

FLUX 

The flux material may be a paraffine, asphaltic or a semi- 
asphaltic residuum which shall be tested with and found suitable 
to the asphalt to be used and must have a penetration greater 
than three hundred (300) degrees with a No. 2 needle at seventy- 
seven (77) degrees F. under fifty (50) grams weight applied for 
one (1) second. All residuums shall be soluble in cold carbon 
tetrachloride to the extent of ninety-nine (99) per cent. 

(a) The paraffine residuum shall have a specific gravity of 
ninety-two hundredths (0.92) to ninety-four hundredths (0.94) 
at seventy-seven (77) degrees F. It shall not flash below three 
hundred and fifty (350) degrees F. when tested in a New York 
State closed oil tester, and shall not volatilize more than five (5) 
per cent, of material when twenty (20) grams are heated five (5) 
hours at three hundred and twenty-five (325) degrees F. in a tin 
box two and one-quarter (2%) inches in diameter as officially 
described. 

(6) The semi-asphaltic residuum shall have the same general 



256 CONSTRUCTION OF ROADS AND PAVEMENTS 

characteristics as paraffine residuum, except that it shall have a 
specific gravity of ninety-four hundredths (0.94) to ninety-eight 
hundredths (0.98) at seventy-seven (77) degrees F. It shall 
have a viscosity coefficient at two hundred and twelve (212) 
degrees F. of less than sixteen (16) Engler viscosimeter. 

(c) The asphaltic residuum shall have the same general char- 
acteristics as paraffine residuum except that the specific gravity 
shall be not less than ninety-eight hundredths (0.98) nor more 
than one and four hundredths (1.04) at seventy-seven (77) 
degrees F. The asphaltic residuum after evaporation at five 
hundred (500) degrees F. to a solid of fifty (50) to sixty (60) 
penetration shall have a ductility of not less. than thirty (30) 
centimeters. 

ASPHALTIC CEMENT 

The asphaltic cement shall be prepared from the refined asphalt 
or asphalts and flux, where flux must be used, above designated, 
provided that mixtures of the refined asphalts, if used, shall be 
equal parts of each, and that the total proportion of refined 
asphalt or asphalts comprising the asphaltic cement shall be not 
less than fifty (50) per cent, by weight. 

When the weight of flux in the asphaltic cement prepared from 
solid native asphalts exceeds twenty-five (25) per cent, thereof, 
asphaltic or semi-asphaltic flux shall be used. 

The refined asphalt and flux used in preparing the cement 
shall be melted together in a kettle at temperatures ranging from 
two hundred and fifty (250) degrees to not over three hundred 
and seventy-five (375) degrees F., and be thoroughly agitated 
when hot by air, steam or mechanical appliances, until the result- 
ing cement has become thoroughly mixed into a homogeneous 
mass. The agitation must be continued during the entire period 
of preparing the mixtures. The cement shall always be of uni- 
form consistency and if any portion should settle in the kettles 
between intervals of using the same, it must be thoroughly agi- 
tated before being drawn for use. 

(a) The asphaltic cement shall have a penetration of from 
thirty (30) to eighty-five (85) degrees, which shall be varied 
within these limits to adapt it to the particular asphalt used in 
the paving mixtures and to the traffic and other conditions of 
the street. 

(b) When fifty (50) grams of the asphaltic cement of the con- 



BITUMINOUS ROAD MATERIALS 257 

sistency used in the paving mixture shall be heated for five (5) 
hours at a temperature of three hundred and twenty-five (325) 
degrees F.,in a tin box two and one-quarter (2J4) inches in diame- 
ter, there must not be volatilized more than five (5) per cent, 
of the bitumen nor shall the penetration at seventy-seven (77) 
degrees F. after such heating be less than one-half of the original 
penetration. 

(c) A briquette of the asphaltic cement of the consistency used 
in the paving mixture shall have a ductility of not less than ten 
(10) centimeters. 

Asphalt Cement for Sheet-asphalt Pavements. The specifica- 
tions given above will also cover the requirements of this class 
of work but the consistency will vary in different localities de- 
pending upon climatic conditions and the class of traffic on the 
pavements. Generally the A. C. for sheet pavements is 10 
harder than for asphaltic concrete in the same locality. 

FILLERS FOR BRICK AND BLOCK PAVEMENTS 

The essential characteristics of a bituminous filler for expansion 
joints and for filling the joints between the courses of a block 
pavement are: 

1. The filler must adhere to the brick or block readily so as to 
completely fill the joint. 

2. The filler must remain sufficiently ductile at the lowest 
temperature to which it is subjected 'to accommodate itself to 
any movement of the pavement. It must also be sufficiently 
stable at the highest temperature to which it is subjected to 
remain intact in the joint rather than to flow slowly to the lower 
part of the pavement. 

3. The filler must possess sufficient toughness at low tempera- 
ture to resist the abrasive action of traffic. 

4. The filler should be proof against the destructive action of 
water and street liquids. 

The following is a general specification covering a suitable 
material of any class: 

The filler must have a melting point varying not more than 
5 from 135F. and must not be brittle at zero F.; it shall remain 
ductile, shall be absolutely proof against water and street liquids, 
shall firmly adhere to the brick and stone, be pliable rather than 
rigid, thus providing for expansion and contraction and traffic 
conditions. 

17 



258 CONSTRUCTION OF ROADS AND PAVEMENTS 



The following specification provides for a suitable grade of 
asphalt filler: 

1. The asphalt filler shall have a specific gravity of not less 
than 0.98 nor more than 1.04. 

2. It shall be soluble in chemically pure carbon disulphide to 
at least 99.5 per cent. 

3. It shall contain not less than 25 nor more than 40 per cent. 
of bitumen insoluble in 86Be. paraffine naphtha. 

4. The penetration shall conform to the following limits for 
the conditions stated: 

At 25C., No. 2 needle, 100 grams, 5 sec. 2.5 to 5.0 mm. 
At 4C., No. 2 needle, 200 grams, 1 min. not less than 2.0 

mm. 
At 46C., No. 2 needle, 50 grams, 5 sec. not more than 

10.0 mm. 

5. The melting point as determined by the cube method shall 
not be less than 80C. nor more than 120C. 

6. It shall be free from water and shall not foam when heated 
to 350F. 

The following specification covers a suitable grade of tar filler : 
1. The filler must be obtained wholly from coal tar without 
the admixture of any other material. 

TABLE 18. SOME PROPERTIES OP VARIOUS BITUMINOUS MATERIALS 



Material 


Specific 
gravity 


Solubili- 
ty in CS2, 
per cent. 


Fixed 
carbon, 
per 
cent. 


Asphaltenes 
in the bitumen, 
per cent. 


Carbenea 
in the 
bitumen 
per cent. 


Trinidad asphalt 


1.4 


56.0 


10-11 


37 


1.3-1.6 


Trinidad asphalt cement . 
Cuban asphalt . . 


1.25-1.30 
1 . 30-1 . 35 


65.0 

65-75 


10-12 
15-25 


20-30 
30-50 


1.0-1.5 
1.5 


Grahamites 


1 12-1.17 


99.5 + 


30-50 


only slightly 


20-45 


Maracaibo asphalt 


1 . 06-1 . 08 


90-98 


15-20 


soluble 
45-55 


1.2-1.7 


Bermudez asphalt .- . . . . 


1 . 05-1 . 08 


93-95 


10-15 


15-25 


1.5 


Gilsonite 


1 04-1 08 


99.5 


12-14 


30-50 


+ 0.5 


California residuals 


1.00-1.03 


99.5 + 


12-15 


20-30 


+ 0.5 


Mid-Continent residuals . 
Paraffine fluxes 


0.97-1.00 
90-0 95 


99.0+ 

99 5 + 


10-15 


15-25 


0.5 
1.0-0.5 


Semi-asphaltic fluxes 


94-0 98 


99 5 + 






1.0-0.5 


Asphaltic fluxes 


96-1 04 


99 5 + 






1.0-0.5 


Blown oils 


0.97-1.00 


99.5 + 


10-15 


20-30 


0.5 


Mexican 


1.02-1.05 


99.5 + 


12-20 


25-35 


+ 0.5 















BITUMINOUS ROAD MATERIALS 259 

2. Specific gravity at 25C., 1.17 to 1.30. 

3. Free carbon, 22 per cent, to 37 per cent. 

4. Distillation of 100 grams to 600C. shall give not to exceed 
8 per cent, of distillate. 

5. Melting point, 130F. to 140F. 

6. Penetration at 100F., 5 sec. under weight of 50 grams not 
less than 30. 

Specifications for creosote oils for paving blocks are discussed 
in the chapter on Wood-block Paving. 



CHAPTER XIV 

DUST LAYERS AND BITUMINOUS CARPETS 
I. DUST SUPPRESSION ON EARTH ROADS AND STREETS 

The earliest attempts to use asphaltic oils and petroleum resi- 
dues for laying the dust and preserving the surface of earth roads 
and streets were made in California. On account of the nature 
of the soil' and the excellent quality of the oils available, the 
California experiments gave promising results and attracted wide 
attention. Similar attempts in other portions of the United 
States and with oils of a different kind and under other soil and 
climatic conditions have not been so successful. This is particu- 
larly true of those attempts that have been made to secure per- 
manent results with mixtures of heavy asphaltic oils and earth. 
In most cases the results have been of little value and have 
almost universally failed if the roads carried heavy traffic. 

Where oils of a more fluid nature have been used to suppress 
the dust on earth roads the results have been more satisfactory 
and there has been a gradual increase in the use of such oils for 
dust prevention. 

Preparation. If a road or street is to be oiled for the first 
time, preparations should be started some weeks before the oil 
is actually applied. 

The effect of the oiling is to render the earth partially impervi- 
ous to moisture and if the surface of the road be uneven when 
oiled or becomes uneven afterward, the depressions will become 
basins for holding water. Traffic will gradually work the soil and 
the water thus retained into mud, deepening the depressions to 
the serious detriment of the street. If the street be smooth and 
well crowned the water will run to the gutters so quickly that 
only in long-continued wet weather will the street be softened 
to any great extent and therefore traffic will not make any con- 
siderable amount of mud on the surface. 

260 



DUST LAYERS AND BITUMINOUS CARPETS 261 

The principal object in oiling a street is to prevent dust; there- 
fore, there should be no dust on the street when the oil is applied. 
If dust has formed, it had better be removed, which costs some- 
thing. It is therefore cheaper to treat the surface before the 
dust has formed, if possible. 

For the best results the street oiling should be planned ahead 
and the preparation of the street be carried out in the early sum- 
mer so that the oiling can be done before a layer of dust forms on 
the street. 

Grading. Good results with oil cannot be expected on a flat 
and poorly drained street. Early in the summer the street should 
be carefully rounded with an even slope from the middle to the 
gutter. The gutter or ditch should be deep enough to readily 
carry the water and to permit a slope of about an inch to the foot 
from the middle of the street to the gutter. Generally the bot- 
tom of the gutter should be about 18 in. below the middle of the 
street where the width of the street is not over 35 ft. between 
gutters. This is about right on a residence street. On a busi- 
ness street having a width of 50 ft., the bottom of the gutter 
should be at least 2 ft. below the middle of the street. 

After the street has been shaped with a grader, it will undergo 
a period of settling during which some depressions and uneven 
places will appear. These should be filled with earth and the 
entire roadway be kept dragged until it finally becomes hard and 
smooth and free from depressions. 

It is very important to secure a firm, smooth surface for the 
oil, and the small expense incurred will be more than made up by 
the increased effectiveness of the oil treatment. 

When the street has been brought to this stage it is ready for 
oiling. If the oiling is delayed until a layer of dust has formed on 
the street it is best to scrape off most of it before oiling. 

The decision to oil a street may sometimes be reached after 
the summer is well along and the streets have become hard and 
dry. In that event, it is not advisable to do any extensive earth- 
work because in continued dry weather newly placed earth will 
not compact readily and if oiled before well packed the results 
are unsatisfactory. Such a condition is not ideal and only medio- 
cre results can be expected. 

Kinds of Oils to Use. The various kinds of oils employed for 
this purpose have already been discussed at length in Chapter 
XIII. 



262 CONSTRUCTION OF ROADS AND PAVEMENTS 

Applying Oil. After the street has been prepared as described, 
the oil is applied at the rate of not less than J^ gal. nor more than 
J/ gal. per square yard of surface. If the street has never been 
oiled before, or if more than a season has elapsed since a previous 
oiling, it will be necessary to use about % gal. per square yard, 
but if the street has been oiled regularly each season, about J 
gal. per square yard is sufficient after the first year. For a street 
in a small-town business district, it is necessary to oil every year, 
using about J^ gal. per square yard of surface for each oiling. 
In many towns it is desirable to oil the business streets twice a 
year. 

After the oil has been spread it is allowed to stand without 




FIG. 64. An oiled earth road. 

being covered for about a day, to permit it to soak into the sur- 
face. It is then covered with just enough sand to keep the oil 
from picking up. Emphasis is placed on the importance of 
employing sand for this purpose rather than dust from the old 
road surface. The amount of sand needed is small and at any 
reasonable price the benefits derived from the sand justify its 
use wherever it can be secured. 

After the road has been put into service it may be apparent 
that more sand is needed in spots to prevent vehicles from pick- 
ing up the oil, and such places should be covered lightly, the 
operation being repeated two or three times if necessary. 



DUST LAYERS AND BITUMINOUS CARPETS 263 

When a street is oiled the second time, the method to be fol- 
lowed is exactly the same as is followed the first time, except 
that the quantity of oil may be reduced to about J^ gal. per square 
yard of surface. It is advisable to repeat the oiling the second 
year in any case, and it may be then omitted the third year and 
resumed the fourth year. Better results would be obtained if 
the treatment were repeated every year. 

Results to be Expected. Surface oiling forms a surface cov- 
ered with a layer of granular or finely powdered soil which is oil- 
saturated and consequently does not blow about readily. The 
suppression of dust is the principal benefit to be expected. Be- 
neath the thin layer of loose, oil-soaked soil the firmer portion 
of the street is saturated with oil for a depth that varies from 1 
in. to perhaps 6 in. 

Water penetrates this layer rather slowly. If the street has 
plenty of cross-slope so that water does not stand on the surface, 
only a small amount of mud will form under light or moderate 
traffic. A street that is oiled systematically for a series of years 
gradually acquires an oil-soaked crust which becomes more and 
more impervious as the oiling is repeated. An oiled street never 
gets to the place where it will not be muddy in those seasons of 
heavy rainfall nor will the surface be stable in ordinary wet 
weather if the road carries a heavy traffic. 

Unloading the Oil from. Tank Cars. The oils used for dust 
suppression can be purchased so much more cheaply in tank-car 
lots than in barrels that it is always advisable to purchase in 
such lots. If a siding on an embankment 8 or 10 ft. high is 
available, the car can be placed thereon and the oil allowed to 
run into the sprinkler wagon through a pipe connected to the 
tap in the bottom of the tank car. 

When such a siding is not available the oil must be pumped 
from car to wagon. For this purpose the ordinary tank pump 
used with traction engine tanks is as good as anything. It 
should be placed on top of the tank car with all connections made 
of pipe, as hose does not last long in oil. If a small steam or gas 
engine driven pump be available, it will, of course, be faster than 
a hand pump. 

Cost of Surface Oiling. The total cost of oiling earth roads or 
streets will vary between the following limits, assuming a treat- 
ment of y% gal. per square yard of surface, and the cost of oil to 
be 4 cts. per gallon. 



264 CONSTRUCTION OF ROADS AND PAVEMENTS 
TABLE 19. COST PER SQUARE YARD FOR OILING 



Item 


Min. 


Max. 


Aver. 


Cleaning surface 


0.0025 


0.0050 


. 00375 


Hauling and distributing oil and sanding 
Cost of oil 


0.0075 
0200 


0.0125 
0400 


0.0100 
0300 


Cost of sand 


0.0025 


. 0075 


0050 












0.0325 


0.0650 


0.04875 



II. DUST SUPPRESSION ON GRAVEL AND MACADAM 

The use of oils for dust suppression must not be confused 
with the construction of the bituminous wearing surface or 
carpet which will be described later. For dust laying, the object 
sought is to mitigate the disagreeable characteristics of the 
ordinary gravel or macadam road without attempting to use a 
type of oil or method of construction that will preserve the 
surface to any considerable degree. 

Dust results from the wearing or loosening of particles of the 
road surface and from the grinding up of soil carried onto the 
surface from adjacent earth roads or streets. To this may be 
added droppings from horses, material that leaks from vehicles 
during the time it is being transported over the road, and a 
small amount of miscellaneous refuse of unclassified origin. The 
process of dust suppression does not contemplate the prevention 
of dust from these sources, but merely a treatment that will 
prevent it from blowing about. This is accomplished by period- 
ical sprinkling with an oil that possesses sufficient binding 
power to hold the particles together and prevent them from 
being carried away by the wind. The bituminous materials 
suitable for this purpose have already been discussed in Chapter 
XIII. 

As with earth surfaces, the gravel or macadam surface should 
be practically free from dust when the oil is applied, and should 
be smooth and true to cross-section. If repairs are necessary 
these should be made some weeks prior to oiling if possible so 
as to give the new material time to compact in place before 
being oiled. 

The oil must be applied with more care than on earth roads 
because less will be absorbed and an excess will be disagreeable. 



DUST LAYERS AND BITUMINOUS CARPETS 265 

One of the multiple-nozzle pressure distributors described in 
Chapter XV is best adapted for the work, and the oil or tar 
may be applied hot or cold, depending upon the grade used. 

A first application usually consists of J gal. per square yard 
of surface, and subsequent applications of J^ to J^ gal. per 
square yard. If, however, too long a time elapses between 
treatments, it would, of course, increase the quantity of oil needed. 
Two applications the first season and one each succeeding season 
usually suffice, but this also depends upon the character and 
amount of traffic and the nature of the surface. 

It has been shown that repeated oiling will gradually render 




PIG. 65. Cleaning a surface for carpet coating. 

the surface impervious to water and cement the particles to- 
gether to a limited degree, especially if a good grade of oil or 
tar is applied. On the other hand, there is some danger of in- 
troducing into the surface an oil that will act as a lubricant 
instead of as a binder, and in that event the road will become 
loose and rapidly develop pot holes and ruts under traffic. 
Considerable difficulty has been experienced throughout the 
United States from that source and too much emphasis cannot 
be put on the importance of using a good asphaltic base oil or a 
suitable grade of tar. 

While it is desirable to cover the oil with a light dressing of 



266 CONSTRUCTION OF ROADS AND PAVEMENTS 

coarse sand or screenings, it is possible to overdo the matter 
and thus offset to some extent the benefit of the oil. One cubic 
yard of the sand or screenings should cover at least 200 sq. yd. 
of surface. 

Light oils and tars are also used for the suppression of dust on 
broken stone roads and the general principles that have been 
discussed in connection with gravel roads apply to macadam 
roads as well. Since the macadam surface is hard to clean, it 
is advisable when possible to apply the oil before the surface 
becomes dusty. When a new road is put in service, traffic 
will gradually brush off most of the excess of screenings and 
there will follow an interval when the surface is almost bare. 
Later the stone may begin to wear and produce more dust or the 




FIG. 66. Applying the oil for a carpet coat. 

larger stones may loosen and work out on the surface. In either 
case the surface has gone beyond the proper stage for oiling. 
The oil or tar used on macadam surfaces is of the same char- 
acter as is used on a gravel road and the method of application 
and quantity varies in the same way. The use of greasy oil is 
even more detrimental to macadam than to gravel. 

The oils and tars used for dust suppression on gravel and 
macadam surfaces range in price from 4 to 7 cts. per gallon and 
the cost of application varies from % to 2 cts. per gallon. The 
actual cost of oil treatments has generally been from 3 to 5 cts. 
per square yard of surface for each application. 

Oil on Hard Pavements. Light oils have been used to a 
limited extent on brick and concrete pavements for the sup- 



DUST LAYERS AND BITUMINOUS CARPETS 267 

pression of dust, but definite conclusions as to the desirability 
of the practice have not been reached. It seems probable that 
where systematic flushing cannot be carried out, the oil may 
serve to palliate the dust nuisance. Emulsions of oil and 
water have also been employed to a limited extent with only 
small success. 

Other Palliatives. Many proprietary compounds have been 
advanced from time to time as dust preventatives. The most 
widely used have either been hygroscopic salts or semi-sticky 
byproducts soluble in water. These compounds are usually of 
only temporary effect and have not come into wide use. 

Water is, of course, the most common form of palliative and 
needs no discussion in this connection. Water sprinkling must 
be kept up with great regularity in hot weather to be of benefit, 
and is the most expensive method of dust suppression, and at 
the same time one of the least effective. 

BITUMINOUS CARPETS 

Purpose. A bituminous carpet serves several distinct pur- 
poses: (a) it prevents the formation of dust by attrition of the 




FIG, 67. Spreading the oil with a brush. 

road surface; (6) it has a tendency to catch and hold dust carried 
onto the surface from external sources; (c) it forms a somewhat 
elastic cushion, thereby increasing the comfort of those who use 
the pavement; (d) it renders less noisy hard surfaces; (e) it takes 
the wear, thus preserving the material upon which it is placed; 
(0 it prevents the removal of the binder from a gravel or macadam 
surface by automobiles. 



268 CONSTRUCTION OF ROADS AND PAVEMENTS 

Requirements of Bituminous Material. It is apparent that a 
thin layer of plastic material placed on top of a hard surface will 
be subjected to constant kneading from the rolling wheels and 
the hoofs of animals, which will work into it such inert material 
as may be deposited on the surface. The kneading will also 
have a tendency to shear the bituminous layer from the rigid 
material under it and the constant addition of inert matter will 
gradually reduce the ability of the bituminous material to ac- 
commodate itself to the constant slight motion. Necessarily 
then, the bitumens used for "carpets" must be ductile and ad- 
hesive and must be of a stable and durable nature. The mate- 
rials employed for this purpose are described in Chapter XIII. 




FIG. 68. Showing the effect of using an excess of oil. 

The bituminous surface is used on gravel, broken stone, and 
to a limited extent on concrete roads and pavements. It was 
first adopted for use on macadam to prevent destruction by 
automobiles, but has been recognized for its value in the other 
particulars mentioned and is now one of the standard main- 
tenance methods for gravel and macadam roads. 

The bituminous carpet is employed under two widely different 
conditions: (1) to a newly completed gravel or broken-stone 
macadam; (2) to a badly worn gravel or broken-stone macadam, 
or one that has been under traffic for some time. The purpose 
of the surfacing is the same in both cases, but the method of 
preparation is somewhat different. 



DUST LAYERS AND BITUMINOUS CARPETS 269 

Applying the Bituminous Carpet to a New Road. Both the 
gravel and the macadam type of surface depend for their stability 
upon the binding properties of the finer material in the surface. 
This may be stone dust or silt and clay. It is not desired to 
replace this binding material with the bituminous binder but 
rather to insure its retention in the surface. Accordingly roads 
that are to be surfaced with a bituminous material are finished 
as water-bound surfaces. 

It is customary to finish these surfaces with some excess of 
binder, that is, with some fine material on the surface for reasons 
already explained (Chapter VIII). The bituminous material 




FIG. 69. Covering the oil with chips. 

cannot be applied successfully to a dusty surface. Therefore, 
a newly constructed road is opened for traffic for a time to 
permit it to "season" or compact and to bring to attention any 
weak places that may have been overlooked during the construc- 
tion. This may require only a few weeks if the traffic is heavy, 
or it may require several months. During this period the fine 
material will be gradually brushed and blown from the surface 
by traffic and eventually it will approach the proper condition 
for bituminous surfacing. The surface to be covered should have 
a close-knit texture, but be free of dust and loose chips or pebbles. 
The binder between the stones should be intact, but the surface 
itself should be clean and free of the screenings or other bonding 



270 CONSTRUCTION OF ROADS AND PAVEMENTS 

material. There should be no ruts or depressions in the surface, 
or, if any have developed, they should be repaired. It is not 
usual to find the surface clean across its entire width, and the 
outer portion will usually require sweeping which may be done 
with a power machine or by hand. 

When the surface is properly prepared the bituminous material 
is spread with the pressure distributor which is the only machine 
that can be successfully used for the work. 

The quantity of bituminous material applied ranges from J 
gal. to % gal. per square yard of surface, with J^ gal. as about 
the average treatment. If for any reason an excess of the bitu- 
minous material is used in spots, these places should be broomed 




FIG. 70. Oiled gravel road. 

to thin them out. With care and a good machine such instances 
will be rare. The best results are obtained when the material 
is spread out. 

After the road has been covered, a thin layer of torpedo gravel 
or of stone chips is spread over the bituminous material. The 
success of the treatment depends very greatly on the class of 
material that is used to cover the bituminous coating. It must 
be apparent that the thin layer of plastic surface will be subjected 
to severe treatment and if soft screenings or chips are used they 
will grind up quickly and lose their value. Granite or trap or 
equally hard stone chips must be used. If a clean coarse torpedo 
sand is available it will be satisfactory, provided it is not too 
fine. A size passing a J^j-in. screen and containing little material 



DUST LAYERS AND BITUMINOUS CARPETS 271 

that will pass a %-in. screen is about right. Chips may be graded 
from Y in. or 1 in. down, but should contain no dust. 

The chips or sand is applied sparingly, being spread on from 
piles alongside the road. Just enough should be used to prevent 
the bituminous material from picking up on the wheels of vehicles. 
It is difficult to judge beforehand just how much will be required 
and it is good practice to put on a light coating and open the 
road for traffic and then to add more as the need becomes ap- 
parent. The surface should be rolled thoroughly to set the chips 
in the surface. 

Since the bituminous carpet does not penetrate the surface 
appreciably, it depends for its stability upon adhering to the 
stones of the road. A greasy material or one lacking ductility 
is certain to give disappointment. 

The surface produced will be black after a few weeks of use, 
will be 34 to M in. thick and will be ductile and show the imprint 
of wheels or hoofs readily. Its life is variable but usually is 
about two seasons. The cost ranges from 3 to 6 cts. per square 
yard of surface exclusive of the cost of minor repairs to the 
surface. 

Bituminous Carpets on Worn-gravel and Macadam Roads. 
Many broken-stone and gravel roads were built before the advent 
of heavy motor traffic and these have sufficed until recent years. 
With the ever-changing routes of travel such roads are constantly 
becoming a part of a motor route and bituminous surfacing 
becomes necessary to eliminate the dust nuisance and to preserve 
the surface. 

The first step in the preparation of such a road is to restore it 
to a true cross-section and an even surface. This is done by re- 
pairing the ruts and depressions in the manner explained in 
Chapter VIII. After this has been done it is well to permit 
traffic on the road for a time to try out the repairs and further 
consolidate the patches, it being well known that a road is 
effectively consolidated by the vehicles using it even though 
the roller has been used for the repair work. 

The next step is to clean the surface of the accumulation of 
stone dust, clay and other detritus. This is a troublesome task, 
especially on the older roads. The clay is usually caked on the 
surface and has been forced down into the interstices between the 
stones. If soft stone has been used for the road there will be 
an excess of dust to deal with. Sometimes the larger pieces of 



272 CONSTRUCTION OF ROADS AND PAVEMENTS 

stone have been badly fractured by the constant pounding of 
wheels and although the stone retains its form due to being con- 
fined in the road, it has become chalky. When this condition 
is encountered, proper cleaning becomes difficult if not impossible. 
The road is first swept with a power broom, and mud or other 
material that has become caked on the surface is loosened with 
picks or shovels between trips with the broom. Material lodged 
in slight depressions is swept off with hand brooms. If the road 
were very dusty it may be necessary to flush it with water to 
remove the fine film not easily swept off. Every precaution 
must be taken to insure that the road metal is entirely free from 
dust because the bituminous surface will not adhere if any dust 
is left. If it is found impossible to secure a clean surface, the 




FIG. 71. Oiled macadam road. 

attempt to place the bituminous carpet should be abandoned 
because it cannot be successfully accomplished. 

When the surface is properly cleaned, the bituminous material 
is spread and covered in the manner already described for new 
macadam or gravel roads. 

The cost of the surfacing is the same as for new roads but the 
cost of repairing and cleaning will vary widely as will be readily 
understood. 

Bituminous carpets on gravel roads have never been very 
satisfactory and it is questionable practice to employ other than 
very fluid oils or tars for the purpose. It seems impossible to 
carry out the construction in any manner that will insure the 
resulting surface against peeling off. 



DUST LAYERS AND BITUMINOUS CARPETS 273 

Bituminous Carpets on Concrete Roads. The bituminous 
carpet is applied to concrete roads and pavements for the reasons 
that have been mentioned in connection with gravel and macadam 
roads, except that there is no tendency for a concrete road to 
ravel under motor traffic. In addition to those reasons two 
others are of moment. Concrete roads have a tendency to 
crack in an erratic manner and if the crack is unprotected the 
concrete breaks down alorig it and the deterioration that follows 
is difficult to repair. It is common practice to fill the crack and 
cover the surface along both sides of it with a bituminous 
material. Covering the entire surface obviates the necessity for 
constant watchfulness in repairing cracks. 

On account of the hardness of the concrete pavement it suffers 
somewhat from abrasion of steel-tired vehicles and eventually a 
slight tendency for the smaller pieces of the aggregate to break 
out is observed. A bituminous coating effectually prevents 
any considerable deterioration from this cause. 

The concrete surface is cleaned by sweeping and washing so 
that every vestige of dust has been removed and the bituminous 
material is applied and covered with chips just as described for 
gravel and macadam surfaces. 

The resulting surface is similar in every respect to the bitu- 
minous carpets already described. 

No little difficulty is encountered in securing a material 
suitable for this work and the tendency for the carpet to peel 
off the concrete has never been entirely overcome. Bituminous 
materials suitable for this purpose are described in Chapters IX 
and XIII. It has been established, however, that with a suit- 
able bituminous material and good workmanship such a carpet 
can be applied successfully. It will last for 2 or 3 years on 
fairly heavily traveled streets or roads. The cost of applica- 
tion, including the cleaning, ranges from 4 to 6 cts. per square 
yard of surface. The application should never be made until 
the concrete has been under traffic long enough to wear off the 
mortar film from the surface if any exists. 

OHIO EXPERIENCE IN THE USE OF ROAD OILS 1 

Poor results in the use of oil treatments frequently come 
from the fact that the surface had not been previously cleaned in 

1 From Bulletin No. 27, Ohio State Highway Department. 



274 CONSTRUCTION OF ROADS AND PAVEMENTS 

a proper manner. If possible, the surface should be swept with 
horse sweepers, and afterward with hand brooms, so as to remove 
the dust from between the stones to a depth of from Y to % in. 
The heavier the grade of oil used, the more important it is to 
have a clean surface on which to apply it. The surface should 
be dry and the warmer the air temperature the better. 

There has been considerable discussion during the past year 
concerning sprinkling of the stone with water before applying 
the bitumens, it being claimed by some that better results may 
be obtained by first lightly sprinkling the stone with water 
before applying the bitumen; this information is likely to be mis- 
leading for it is believed that it is not the presence of water that 
might cause the better results, but the effect the water has in 
cleaning the dust which gives a better adhesion of the oil. 

Hence, we would conclude that if sprinkling with water before 
applying the oil is done, it should be only on hot, dry days, and 
then sufficient time be given after the sprinkling for the water 
to practically all evaporate before the oil is applied. Therefore 
we are still warranted in saying that bitumens should be applied 
only to dry, warm surfaces. During June, July and August is 
the best time of the year to apply such materials to the road. 
(Note that this applies to Ohio.) 

The amount of oil that should be applied to the road at any 
one time will depend upon the condition of the road surface, the 
quality of the oil used, and the nature of the traffic. In general, 
it may be said that a couple of light applications during the year 
will give better results than a single heavy application of the same 
amount of oil. For the lighter oils on a comparatively smooth 
surface, an application of not to exceed % gal- per square yard 
may be all that should be applied at one time while on a rough, 
pitted surface (with the binder swept from the top surface of 
the road to a depth of from ^ to % in.) as much as % gal. per 
square yard of the heavier oils might give more satisfactory 
results. 

The aim should be to put on just sufficient oil (and screenings) 
to form a thin mat over the surface of the road. This mat 
should not be of any appreciable depth over the surface of the 
larger stones, but sufficient to well seal up the voids between 
them. This will hold the binder in the stones and make the road 
surface water-tight. 

A medium heavy cold oil will cost from 4J^ to 6 cts. per gallon 



DUST LAYERS AND BITUMINOUS CARPETS 275 

delivered in tank cars. The cost of applying the cold oil varies 
from J^ to 1 ct. per gallon. 

CARPET COATS ON CONCRETE IN CALIFORNIA 1 

A shortage of funds lead the California commission to seek a 
type of road cheaper in first cost, notwithstanding a conse- 
quential higher maintenance expenditure during the early years 
of its existence and the type called " concrete base with bituminous 
top" was adopted rather generally. 

In this method of construction, the base is the same as if the 
1%- to 2-in. covering were to be applied, but instead a thin 
coating of asphatlic oil of special quality is put on to the concrete 
by spraying machines at the rate of about J^ gal. to trie square 
yard. Clean stone screening or coarse sand are then added in 
sufficient quantity to absorb the oil. The process requires much 
care in the selection of the materials used and in their manipula- 
tion, but the result is a bituminized coating about % in. thick. 
The cost of such surface work ranges from 5 to 10 cts. per square 
yard, or $600 to $1,200 per mile, roughly, for a 20-ft. pavement, 
depending on the cost of materials and local conditions. This 
means that more than 90 per cent, of the cost of the work on the 
road goes into grading, culvert work and the concrete base, all 
of which may be considered as practically permanent, and the 
remainder into the thin wearing surface. 

Such a wearing surface should last from 2 to 4 years before it 
requires renewal, which renewal should cost considerably less 
than the original application. This thin surface is best adapted 
to rubber-tired vehicles, but it wears well under a considerable 
volume of mixed traffic consisting of both rubber- and iron- 
tired vehicles. I would have no hesitancy in recommending 
the thin road surface for a road covering as many as from 500 
to 600 vehicles a day, provided a considerable portion of the 
vehicles are rubber-tired. 

1 A. B. Fletcher, State Engineer of Cal. in "California Highways". 



CHAPTER XV 

PENETRATION AND MIXED MACADAM ROADS AND 

PAVEMENTS 

PENETRATION MACADAM 

Bituminous macadam may be constructed by the penetration 
method with any of the kinds of stone that are used for the 
ordinary macadam. The methods of construction vary slightly 
in detail depending upon the character and size of the stone used, 
but the distinguishing characteristic is that the binder is poured 
onto the surface of the layer of stone and is expected to penetrate 
sufficiently to hold the surface together. 

Sizes and Kinds of Stone. Certain general principles govern- 
ing the size of stone to use have been discussed in connection 
with water-bound macadam roads and these apply to penetration 
macadam as well, and the sizes commonly employed are sum- 
marized as follows: 

A. Hard stone ranging in size from about 1J^ in. down to 
J^ in. Chips from the same kind of stone and ranging 
from J^ in. down but with the dust removed. 

B. Medium stone ranging in size from about 2J^ in. down to 
1 in. Chips from the above, screened through a %-in. 
screen and with the J^-in. and finer removed. 

C. Crusher-run stone of either hard or medium grade but 
containing no material passing J^-in. screen. 

D. Stone of either of the above grades but screened to a fairly 
uniform size such as 2)^ in. to 1)-^ in., or 1^ in. to 1 in. 

E. When chips of suitable hardness cannot be obtained, pebbles 
screened from hard gravel may be substituted. The size 
ranges from J^ in. down to J^ in. 

It will be apparent that when rolled, class A stone will give 
a surface having smaller openings for the bituminous material 
to penetrate than will class B stone and that class C stone will 
produce a surface with smaller voids than either class A or B. 
It will also be seen that class D stone will produce a more porous 
surface than either class A or B or C. 

276 



PENETRA TION AND MIXED MACADAM ROADS 277 



It is therefore desirable to apply the bituminous binder to 
class C stone before any rolling is done and without spreading 
any chips prior to the application of the binder. Class A stone 
is rolled but no chips are spread before the binder is poured. 
Class B or D stone is rolled and the voids partially filled with 
chips before any binder is poured. Where class E material is 
used it is substituted for chips and is handled in the same manner 
as chips. 

Bituminous Binders. Both tar and asphaltic binders are used 
for the penetration macadam and the general characteristics 
have been discussed in Chapter XIII. 

Foundation. The stability of the bituminous macadam con- 
structed by the penetration method depends largely upon the 



2 Gal. Bit. Binder per Sq. Yd., 





ZOa/Bt+BinderperSq Yd 



***'(* ^ 

'?% Sfone Bonded with Screenings 

Single Track Road 



&VWS>**. 




if*' 

*P "I l^T/KC^/iX- Vg ~ ; / // - 

'2j> Sfone Bonded with Screen ings 
Residence Street Pavement 
FIG. 72. Cross-sections for penetration macadam. 

kind of foundation provided and it is usually placed on top of 
either a Telford foundation or a broken-stone foundation which 
is bonded with screenings exactly as the surface of the water- 
bound macadam would be. Especial emphasis is placed upon 
the necessity of having the foundation true to shape. Its thick- 
ness will vary somewhat with the character of the earth subgrade. 
On good soils a foundation course 6 in. thick at the middle and 
4 in. at the edge is not uncommon. Sometimes the base course 
is made a uniform thickness of 5 or 6 in. Fig. 72 shows typical 
cross-sections of penetration macadam roads and pavements. 



278 CONSTRUCTION OF ROADS AND PAVEMENTS 

The upper course of the surface is usually made of uniform 
thickness and seldom is less than 2 in. or more than 3 in. thick, 
depending primarily upon the size of stone used. If the 1^-in. 
size is used, the upper course would ordinarily be about 2 in. 
thick. If 2j^-in. stone were used the layer would ordinarily be 
about 3 in. thick. 

Wearing Course. After the foundation course has been com- 
pleted, the stone for the upper course is spread to the required 
thickness. Whether or not it shall be rolled before the bitu- 
minous material is poured into it depends upon the size of the 
stone and the texture of the surface. If the surface appears to 
be fairly well filled with fine material as would be the case with 
class C stone, it would be so dense when rolled that the bitu- 
minous binder could not penetrate into it. Therefore with such 
stone it is best to spread the bituminous binder before the 
surface is rolled. 

Rolling. It is desirable to have as great mechanical stability 
in the upper course as can be obtained and therefore it is better 
practice to use a coarser stone and roll the layer before the 
bituminous material is spread. If the stone has been rolled until 
the surface is closely knit together there will be little danger of 
the finished road becoming rutted or uneven and the bituminous 
binder will hold the chips in place and thus maintain a close-knit 
texture in the surface. 

Examination of the surface after it has been rolled will show 
it to be' made up of angular pieces of stone closely packed 
together between which are voids of varying size, depending 
upon the size of the stone and the thoroughness of the rolling. 
If the voids are large they must be partially filled with chips to 
prevent the bituminous binder from penetrating too deeply 
into the layer. Usually with stone of classes B and D the 
application of chips at this stage of the construction is advisable, 
but with class A stone the texture will be close enough without 
the chips. 

When chips are used they are spread thinly over the surface 
from piles alongside and are brushed into the openings in the 
surface, any excess being brushed off at the edges. Care and 
persistence are necessary to secure an even texture in the surface 
and it can only be obtained if the chips are carefully spread and 
properly brushed into the surface. 

The chips used must be of tough stone, otherwise they will 



PENETRATION AND MIXED MACADAM ROADS 279 

grind up rapidly under traffic because of their small size. If no 
hard, tough chips are available, clean screened gravel of the 
proper size may be substituted. 

Applying Bituminous Binder. The bituminous material is 
spread at a temperature that will insure its being fluid which 
may be anywhere from 250F. to 450F. depending upon the 
kind of material used. It may be spread by means of hand 
pouring cans, but this method is likely to result in a somewhat 
uneven distribution of the material. 

The gravity type of distributing wagon is often used but it is 
also open to objection because of the variation in flow as the tank 
empties. The pressure distributing wagon is best from all stand- 
points and is coming to be the standard apparatus for this class 
of construction. 

The quantity of bituminous material used for the first ap- 
plication varies from 1 gal. to 1J^ gal. per square yard of surface. 
It is desirable to secure a penetration of about 1 in. and to 
coat all of the stones that show at the surface. Here again care 
must be exercised to secure uniformity. 

After the first spreading of the binder, the surface is covered 
with chips which are brushed into the remaining voids in the 
surface and rolled lightly. The second application of binder 
then follows, the amount used being about % gal. per square 
yard of surface. It is covered with chips and rolled. In some 
instances a third application of about J/ gal. of binder is used 
which is covered with coarse sand or chips and rolled. 

Characteristics. 1 The results of the experience so far gained 
with this type of construction seem to show: 

First. The necessity of providing as stable a foundation 
course as possible, and that probably the best method would 
be to lay the first course of the road as water-bound macadam, 
applying the bituminous top about 3 in. thick the following 
season when the foundation course has become thoroughly 
compacted. 

Second. The necessity for using durable stone in the bitumi- 
nous top. Where limestone alone is available, the chips used for 
filling the voids and dressing the surface of the bituminous 
layers as they are applied should be trap, granite, or washed 
gravel and torpedo sand. Where the rock of which the road is 
made is tough and hard, rock chips could be used. 

1 See Fourth Report of Illinois Highway Commission. 



280 CONSTRUCTION OF ROADS AND PAVEMENTS 

Third. It is necessary that the bituminous binder be spread 
so as to present as uniform a surface as possible. This may 
not necessarily mean the uniform distribution of the binder 
since the texture of the surface itself may not be quite uniform. 
Therefore, the more finely divided the form in which the binder 
can be applied, the better the control of its distribution. The 
form of the application whereby the material is spread by a jet 
of steam has given excellent results (see Fig. 73). 

Fourth. Too much binder should not be used as it will result 
in a less stable wearing course than if only sufficient binder is 
used to coat the stone and chips. 

Fifth. It is essential that the surface of the road have very 
close texture and usually this cannot be secured in less than 
three applications except by using an excessive amount of binder. 
The most economical and durable results can be secured when the 
binder is put on in three applications. 

Sixth. The bitumens which do not possess some ductility at 
freezing temperatures are usually not satisfactory. 

Seventh. It is important that bitumens be applied at high 
temperatures, and if possible, during hot weather, as some 
unsatisfactory results obtained can be attributed to the cold 
weather prevailing at the time of construction. 

Eighth. The roads constructed with tar binder under ordinary 
traffic conditions seem to require a paint coat at the end of the 
second, or at the furthest, during the third season. By this time 
the tar near the surface of the road seems to have lost most of 
its adhesive qualities. Those constructed with asphaltic binders 
seem to require the same treatment during the fourth year. 

Ninth. The size of stone in the bituminous layer should 
range from 2j/ in. to % in. where limestone is used. When trap 
rock or other equally hard material is available, stone should 
not exceed 1J^ in. in size; the chips for filling the stones not to 
exceed 1 in. in size and the grit for the top dressing should not 
exceed J^ in. in size, and all of the material should be free from 
dust. 

Tenth. Experience indicates that this form of construction 
is adapted to moderate traffic roads, that is, where there is no 
large amount of extra-heavy hauling. Where the traffic is com- 
posed of automobiles and farm loads of not to exceed 2 tons, this 
form of construction will prove satisfactory, although not as 
durable as some more expensive roads. Where traffic consists 



PENETRATION AND MIXED MACADAM ROADS 281 

of heavier loads such as wholesale trucks, coal trucks and loads 
reaching to 5 and 6 tons, it is believed this form of construction 
is not at all suitable. 

It presents a pleasing appearance and is well adapted to 
horse-drawn traffic as well as automobile traffic, but requires 
close attention to maintenance, and there is some evidence that 
during warm weather when the bitumen is least stable there is a 
tendency for the surface to creep and undulations develop. 

The cost of this form of construction over that of first-class 
water-bound macadam is approximately 20 cts. per square 
yard, but there has not been had sufficient experience to deter- 
mine definitely the maintenance cost and its final economy. 
The construction requires the utmost care in every detail, and 
this fact has not always been appreciated, with the result that 
much poor work has been done. 

Where attention is given to the construction, and suitable 
materials are used, there is no difficulty in duplicating results. 

Bituminous macadam is of doubtful value on those sections of 
road so situated that considerable quantities of mud will be 
tracked on them from adjoining earth roads. 

MACHINERY AND APPLIANCES USED FOR BITUMINOUS 
MACADAM CONSTRUCTION 

Pouring Cans. Bituminous materials are sometimes spread 
on road surfaces by means of hand pouring cans which are much 
like a garden watering pot except that the spout is larger and 
the nozzle is a slot instead of a perforated disc. In some types 
of cans the slot is horizontal and in others vertical, the latter 
being preferable. It is also an advantage if the width of the 
slot is adjustable so as to help control the rate of flow of material. 

Gravity Distributing Wagons. Wagons of this kind are used 
for spreading bituminous materials on road surfaces either for 
penetration construction, carpeting or dust laying. As the 
name indicates, the bituminous material flows from the tank by 
gravity and is consequently somewhat variable in amount de- 
pending upon the height of material in the tank. The dis- 
tributing devices or nozzles are of many types but in the essential 
consist of a pipe supported about 1 ft. above the road surface 
and having circular openings or slots for the material to flow 
through. The pipe is suspended from the rear of the tank and 



282 CONSTRUCTION OF ROADS AND PAVEMENTS 

is slightly longer than the tread of the wagon. A control valve 
is attached to the delivery pipe in most wagons of this kind and 
many of them are equipped with fire boxes so that the contents 
of the wagon may be heated. 




FIG. 73. Distributing outfit utilizing steam spray. 

Pressure Distributing Wagons with Multiple Spray. In order 
to give better control of the quantity of material being dis- 
tributed and to force it into the minute openings in the road 
surface, pressure distributors have come into extensive use. 
In general design they are similar to the gravity distributor except 



PENETRA TION AND MIXED MACADAM ROADS 283 

that air or steam pressure is applied to tank so as to force the 
material out of the nozzles at a high velocity. The distributing 
devices usually consist of a series of small nozzles screwed into 
a pipe which is suspended across the rear of the wagon about 
6 in. from the road surface. In some machines of this type the 
pressure is obtained by pumping the hot material out of the 
tank and forcing it through the nozzles. The horse-drawn 
distributors usually have a tank capacity of about 500 gal. 

In recent years many elaborate motor-driven distributors 
have been constructed and these have a wide range of capacities. 
For surfacing country roads the motor-truck type is very much 
to be preferred to the horse-drawn because of the saving in time 
effected in getting the material from the railroad siding to the 
road. The sprays are of many designs and the pressure is some- 
times obtained by pumping the binder and sometimes by pumping 
air into the tank. 

These motor distributors are well adapted to the purpose for 
which they are used. The quantity of the bituminous material 
that is used can be controlled within very narrow limits. 

SINGLE-NOZZLE DISTRIBUTOR EMPLOYING A STEAM SPRAY 

This type of distributor is shown in Fig. 73. The bituminous 
material is heated in the tank wagon or in an auxiliary kettle 
and drawn into the tank wagon by pumping the air out of the 
tank. 

The hot binder is then applied to the road surface through a 
nozzle at the end of a length of flexible metal hose. The operator 
spreads the binder according to the needs of the surface. 

At the orifice in the nozzle a jet of steam is introduced into the 
binder forcing it out in a finely divided spray and the quantity 
is varied by a valve in the supply pipe. This method is very 
satisfactory for macadam construction. 

EXAMPLES OF GOOD PRACTICE 

MAINE 1 

Crushed Stone. The crushed stone used in this work shall 
be newly broken, or uniform quality throughout and free from 
tailings, slaty and flat fragments, soft or disintegrated stone, 
dirt or other objectionable matter. 

1 Specifications, Maine Highway Department, 1915. 



284 CONSTRUCTION OF ROADS AND PAVEMENTS 

The following designations and sizes shall obtain: 

Dust. That portion of the product of the crusher which will 
pass through a screen having one-quarter (J^) inch circular 
openings. 

Chips. That portion of the product of the crusher which will 
be retained on a screen having one-quarter (J) inch circular 
openings and will pass through a screen having one (1) inch 
circular openings. 

No. 2 Stone. That portion of the product of the crusher which 
will be retained on a screen having one (1) inch circular openings 
and will pass through a screen having circular openings not less 
than two (2) inches nor greater than two and one-quarter 
inches in diameter. 




FIG. 74. A penetration macadam road. 

No. 1 Stone. That portion of the product of the crusher which 
will be retained on a screen having circular openings not less 
than two (2) inches nor greater than two and one-quarter (2J) 
inches in diameter, and will pass through a screen having circular 
openings not less than three (3) inches nor greater than three 
and one-half (3J) inches in diameter. The stone shall be granite 
or trap. 

Bottom Course. The bottom course shall consist of a single 
layer of No. 1 stone, 3J^ in. in thickness when compacted, and 
shall be spread so that after being thoroughly compacted with 
a road roller of the macadam type, its surface will be parallel 
to and uniformly below the finished road surface by an amount 
equal to the thickness of the wearing course. Stone screenings 
or sharp sand shall be spread over this course. In no case, how- 



PENETRATION AND MIXED MACADAM ROADS 285 

ever, shall such an amount of screening or sand be used as to fill 
the bottom to within less than J in. of its surface. 

In the event that any course of stone shall have become rutted 
or loosened by travel before the application of the next succeeding 
course, the contractor shall bring the said course of stone to its 
proper cross-section with such materials and in such manner as 
the engineer shall direct. 

Second Course. The second course shall consist of a layer of 
No. 2 stone evenly spread over the bottom course to a depth of 
3 in., loose measurement. This course shall be dry-rolled until 
the fragments of stone are well keyed together and the surface 
conforms to the cross-section shown in the plans. In order to 
allow penetration of the hot bituminous binder applied in the 
manner hereinafter specified, the surface of this course shall be 
open and porous. 

Bituminous Binder. Sufficient and approved facilities for 
delivering and heating the binder shall be provided. It shall be 
maintained within a temperature range of 250F. to 300F. for 
tar products and 300F. to 350F. for fluxed native and oil- 
asphalt products. 

First Application of Bituminous Binder. The hot bituminous 
binder shall be uniformly distributed over the second course at 
the rate of lj^ gal. to the square yard, either by pouring pots or 
applied under pressure from a tank wagon equipped with hose 
and nozzle of a type approved by the engineer. Immediately 
after this application, clean stone chips shall be spread over the 
surface in sufficient quantities to just completely fill the surface 
voids, after which the course shall be thoroughly rolled. When 
rolling is completed, any surplus chips shall be swept from the 
surface. The bituminous binder shall be applied only during 
dry weather, and the stone of the second course must be dry and 
clean at the time of application. 

Seal Coat. A seal coat of hot bituminous material shall be 
uniformly distributed as above described, at the rate of one- 
half (J^) to three-quarters (%) of a gallon to the square yard. 
It shall be immediately covered with a layer of clean stone chips, 
in an amount sufficient to take up all excess bituminous material, 
and shall then be thoroughly rolled. 

Weather. No bituminous material shall be applied at any 
time when the air temperature is below 60F. or when the air tem- 
perature within the preceding 24 hr. has been 35F. or lower. 



286 CONSTRUCTION OF ROADS AND PAVEMENTS 

ILLINOIS 1 

As is well known, the stability or strength of a macadam-road 
surface to resist the action of traffic depends entirely on the 
mechanical locking together of the pieces of stone making up the 
road surface, and until this is accomplished the road surface has 
no cohesion. The more perfect this keying or locking together 
of the pieces of the stone, the more rigidity; therefore, the object 
of any binder, whether of stone dust or of a bituminous character, 
is to hold the pieces of stone firmly in position after they have 
become well keyed and locked together. In many pieces of road 
that have been constructed, and in some forms of construction 
that have been proposed, this essential principle of the macadam 
construction seems to have been ignored. It would appear that 
if bituminous macadam is to be successful it is necessary in its 
construction to follow what has been learned by long experience, 
and that is to have the macadam itself firmly locked and keyed 
together and the stability of the road thereby assured before any 
binder has been applied. 

The next step, therefore, after the base course has been pre- 
pared, as has already been described, is to spread the stone for 
the wearing layer. The stone for this layer, if limestone, should 
be composed of pieces 2J^ in. in size and graded from this 
downward. If a 3-in. layer is to be made when consolidated, 
which is as thick as this layer need be, the stone should be spread 
to a thickness of 3J^ in. and thoroughly raked or harrowed so 
as to bring the larger pieces to the surface in order that the 
surface may be composed in the first instance of as nearly 
uniform sized material and to give as great compactness as 
possible after it is rolled. As soon as spread uniformly and 
harrowed, the surface is to be rolled until it is thoroughly tight- 
ened. It may be found that there will be places where the stones 
do not lock together firmly; on such places a small amount of 
stone should be spread, just sufficient to fill the interstices, 
and then rolled. The effect of this rolling is to force the pieces 
of stone into the interstices, thus keying the whole surface until 
tight. It is important that great care be taken in rolling this 
upper layer that it be thoroughly tightened. When this has 
been accomplished, there will still remain interstices of appre- 
ciable size which should be filled with stone chips. These chips 

1 From the Fourth Report of Illinois Highway Commission. 



PENETRA TION AND MIXED MACADAM ROADS 287 

should be preferably of some harder material than limestone, 
and it is often possible to secure screened gravel that will prove 
excellent for this purpose. The size of the chips should vary 
from Y to % in., and they should be spread over the surface of 
the upper course in just sufficient quantity to fill the interstices. 

A good method to insure this being done is first to shovel the 
chips on by hand, throwing each shovelful so as to cover as 
much area as possible; then follow with hand brooms, sweeping 
ahead the surplus pieces and allowing all the interstices to become 
thoroughly filled. When this is done, the road is ready for the 
bituminous binder, as no rolling should be attempted after the 
chips have been spread and before the binder is applied. If 
the chips are rolled before the binder is applied, the effect would 
be merely to allow them to set in between the stones which have 
already been well compacted and tend to loosen the surface 
rather than tighten it. It is important that after the surface has 
been thoroughly keyed and the chips spread, no rolling be done 
until after the bituminous binder has been applied. 

The amount of the binder to be applied should be as little as is 
necessary to secure a thorough coating for all the exposed surfaces 
of the stone. This usually requires from % gal. to 1 gal. per 
square yard. When this amount has been applied, the surface 
should again be dressed with the stone chips or screened gravel 
so as to make practically one layer of the chips evenly distributed 
over the entire surface of the road. This gravel had better 
be applied as soon as possible after the binder has been spread, 
if practicable following immediately behind the spreader. It 
may be spread somewhat in excess and swept ahead with a 
broom. It is important that the gravel be clean and have as 
little dust adhering to it as possible. 

After the gravel has been spread the second time more binder 
is applied which should be sufficient thoroughly to cover all of 
the gravel. This usually requires J to % gal. per square yard. 
Coarse sand, if available, should then be spread upon the road, 
or finely screened gravel may be used. After the surface has 
been covered with the fine gravel graded from ^ in. to % in., 
a seal coat of binder, using % gal. per square yard, is applied. 
The surface is then covered with the fine gravel and rolled. 
The roller should be provided with pipes with small orifices an 
inch or two apart so as to keep the wheels of the roller wet while 
rolling. If this is done, there will be no difficulty whatever with 



288 CONSTRUCTION OF ROADS AND PAVEMENTS 

the binder sticking to the roller wheels. The rolling should con- 
tinue until the surface is seen to be well set and compacted. It 
will then perhaps be found that there are some spots needing 
further treatment to bring them to a uniform appearance with 
the remainder of the road, in which case, if there be any dust, it 
should be swept away, fine gravel and binder applied and the 
whole rolled to give a uniform surface It is probable that quite 
as good or better results can be obtained, after the road has been 
sanded and rolled, to throw it open and let the traffic develop any 
places in the road that need further attention. 

This form of construction, it will be seen, gives a road which 
has the strength and rigidity of the ordinary macadam, with a 
water-tight covering of bituminous compound holding the 
surface of the road intact against the action of the motor traffic 
or dislodgment by the mud that adheres to the wagon wheels. 
So long as the waterproof covering can be maintained, the 
road should be in perfect condition. The gravel in the surface 
furnishes the resistance to abrasion. This is greatly helped by 
the binder, if of proper quality, which will tend to keep the 
particles covered or imbedded as fast as they may become 
loosened or broken by the traffic. When in the course of time 
the surface has become sufficiently worn to expose the stone 
making up the wearing course, it can be renewed by thoroughly 
cleaning the road, putting on a light application of the binder 
and renewing the fine gravel. 

MASSACHUSETTS 1 

Size of Stone Important. The size of stone in the top course 
is regarded as a matter of vital importance in the construction 
of a road by the penetration method. The Massachusetts 
Highway Commission employs stone ranging from 1J^ to 2J^ 
in. in size. The large stone, it has been found, binds together 
more firmly than smaller stone and consequently is subject 
to less wear from the grinding of one fragment against another 
in the body of the pavement due to the passage of vehicles over 
the road surface. Small-sized stone tends to loosen quickly 
under this grinding action, and if the bituminous binder loses its 
life and is not speedily renewed, the road quickly goes to pieces. 
With stone of large size no such result may be expected. It 

1 Abstracted from Engineering Record, May 15, 1915. 



PENETRATION AND MIXED MACADAM ROADS 289 

is true that with the larger stone the voids are greater and 
consequently a larger amount of bitumen must be used to fill 
them, the excess being generally about % gal. per inch depth of 
top course for the large-stone type of construction. Thus a 
small stone pavement with tar as a binder and a 2-in. top course 
would cost about 6 cts. less a square yard than the large-stone 
type of pavement. In spite of this slight increase in cost the 
large stone is believed to be amply justified. 

With small stone it is practically impossible to secure any 
great depth of penetration with a single application of bitumen. 
It becomes necessary, therefore, if small sized stone is used, to 
build the top course in several layers and apply the binder to 
each obviously a more costly procedure than the distribution 
of the binder in a single operation, as is feasible when large stone 
is used. 

As to the quality of the stone in the top course, this depends 
to a large extent upon the character of the traffic to be handled. 
For very heavy teaming the Massachusetts Commission believes 
that the best results can be secured with trap rock and a high- 
grade asphalt. With a tar binder, instead of asphalt, a softer 
grade of rock is permissible, for the tars deteriorate more quickly 
than do the asphalts. Asphalts are preferred because of their 
greater cementing value and their higher resistance to disin- 
tegration by moisture. 

Preparation of Subgrade. The first step in the construction 
of a road by the penetration method, according to the Massa- 
chusetts standards, is the provision of adequate drainage. In 
loamy or clayey soils it is common to put in a subbase of gravel 
1 ft. thick or a Telford base from 1 ft. to 18 in. thick. The 
Telford base may even be underlaid by a layer of gravel not 
exceeding 8 in. and the interstices at the tops of the stone filled 
in with smaller-sized materials. In springy ground stone drains 
with open-jointed sewer pipe are insisted upon. These are 
located at the sides of the road when the grade is level and on 
the uphill sides if along a hill. It is important that this subbase 
be thoroughly compacted and it is therefore rolled with a 10-ton 
steam roller until no settlement is discernible. 

Upon this base course is spread a layer of broken stone from 
J^ to 3 in. in size which is compacted to a depth of 4 in. after 
rolling. This forms the bottom course for the penetration roads. 
There should not be too much fine stone in this layer. After 

19 



290 CONSTRUCTION OF ROADS AND PAVEMENTS 

it has been thoroughly rolled the pieces in the bottom course 
are partly bound by filling the interstices with smaller-sized 
stone, sand, screenings, or stone dust. For this bottom course 
the size of the stone is not of particular importance. It should, 
however, not be bound too thoroughly and may or may not be 
sprinkled, depending upon the nature of the material. It must 
be rolled until thoroughly compacted. This is most important, 
for if the base is not rigid depressions will develop in the wearing 
surface. The bottom course is placed generally in several spread- 
ings and varies somewhat, due to the nature of the foundations 
and the character of traffic. If placed on an old macadam road- 
way 2 in. of new stone may be sufficient; for a new roadway 
to carry heavy traffic it may be necessary to use 5 in. of stone in 
the bottom course. 

Top Course. The methods outlined for the base apply to all 
types of bituminous macadam construction. It is next in order 
to describe the top or wearing course for heavy traffic conditions. 

Upon the base prepared, according to the method outlined, 
the best results have been secured by spreading trap rock varying 
in size from 1% to 2^ in. to a depth of 2 in. after rolling. This 
2-in. thickness for the wearing course is sufficient for ordinary 
traffic, but for exceedingly heavy traffic the top course might be 
made 3 in. and placed in two layers. The stone is carefully 
spread from dumping boards, thoroughly rolled and all depres- 
sions filled. No sprinkling is allowed on the top course. 

When it shows no movement under the steam roller the top 
course is ready to receive the bituminous binder. While good 
results have been secured by hand-pouring, the best work has 
been done with pressure distributors using air for pressure. 

Preference as to Binders. The preference for binders on 
penetration work is as follows: First, lake asphalt; second, oil 
asphalt; third, tar. Tars, it is stated, have stood up under traffic 
which the oil asphalts could not bear, but the disadvantage of 
the tar is that it does not retain its life as long as the oil asphalt. 

If a natural asphalt is used it must be heated at least to a tem- 
perature of 300F. usually about 350 and applied under a 
pressure of 60 Ib. per square inch. The rule of the Massachusetts 
Highway Commission is to use about 1 gal. of binder to each 
inch of thickness of the top course. The greatest care is neces- 
sary to apply the binder uniformly. With the 2-in. top course 
used on most of the roads the application of binder has amounted 



PENETRATION AND MIXED MACADAM ROADS 291 



to about 1% gal. per square yard of road surface. When the 
binder has been applied the surface of the roadway is imme- 
diately covered with a light layer of pea stone, just thick enough 
to prevent the roller from picking up the surface. The pea stone 
is broomed and used to fill the voids and is then thoroughly rolled. 
For this operation the best results are secured with a heavy roller 
from 15 to 18 tons. After rolling, the surplus stone is swept off 
and a second application of binder made to form a seal coat. 
The seal coat is applied at the rate of about J gal. per square 
yard. The road surface is again covered with pea stone and 
thoroughly rolled. This completed the operation of building 
a pavement by the penetration method. 

MIXED BITUMINOUS MACADAM 

Mixed bituminous macadam is a road surface consisting of 
crusher-run stone or of gravel cemented together by means of a 
bituminous binder. The materials are hot-mixed and the 
mineral aggregate is selected and graded in such a way as to 
secure reasonable density in the surface. In appearance the 
finished mixed macadam resembles the penetration macadam 
very closely. 

Stone for Mixed Macadam. Crusher-run stone with the dust 
removed or mixtures of stone and sand are employed for the mixed 
macadam. The principles that are observed in selecting the 
proper size of stone for the penetration macadam are also applied 
to the selection of stone for the mixed macadam. If medium 
or soft stone is to be used a larger size is required than if a hard 
and tough stone is available. Quite generally the crusher-run 
stone with the dust removed is employed. It is apparent that 
the voids in the aggregate will be a considerable per cent, and 
the essential difference between the hot-mixed macadam and the 
asphaltic concrete is in the care with which the aggregate is 
graded for the latter type of surface. 

It will be recalled that in the discussion of penetration 
macadam, attention was called to the use of crusher-run stone 
and the difficulties of securing penetration of the bituminous 
material. The mixed macadam was developed to overcome that 
difficulty and yet secure the advantages of the better grading 
obtained by the use of crusher-run stone instead of screened 
stone. 



292 CONSTRUCTION OF ROADS AND PAVEMENTS 

Foundation. The mixed macadam is placed on top of an old 
water-bound macadam or gravel road or upon a newly constructed 
base of water-bound macadam or gravel. The necessity for 
a rigid foundation course has been frequently referred to in con- 
nection with the other types of construction and is equally im- 
portant for the mixed macadam. If an old macadam or gravel 
road is used for a foundation it must be brought to a true surface 
parallel to that prescribed for the finished road and enough below 
it to permit placing a uniform surface layer of the requisite thick- 
A foundation course of lean concrete is sometimes used 




FIG. 75. Portable melting tank for bituminous materials. 

but this type of base is not common. When used the mixture is 
usually 1-3-6 or leaner. 

When a new macadam base is constructed for this surface it is 
built exactly in the same manner as the base for the penetration 
macadam. 

The bituminous cement and the stone or gravel are heated 
separately and then mixed either by hand or in a hot mixer of the 
type resembling the concrete mixer. The amount of binder used 
is from 15 to 20 gal. per cubic yard of stone. 

The hand-mixing method has little to recommend it except 
that but small expense is entailed for equipment which is a 
factor to consider on small work. 

The portable type of hot mixer which is drawn along the road 



PENETRATION AND MIXED MACADAM ROADS 293 

as work progresses is frequently employed and is satisfactory 
although somewhat limited in capacity. Fig. 76 shows such an 
outfit in operation. 

The permanent or semi-permanent plant located near the stone 
supply is also frequently employed and is the most economical 
in operation. The distance that the mixture can be hauled must 
be considered and this will usually necessitate the use of the 
portable plant for rural highway surfacing. 

The mixture is prepared at a temperature of about 200F. 
and must be spread at a temperature of not less than 150F. 
These temperatures vary somewhat with the kind of bituminous 
binder used as would be expected. 




FIG. 76. Portable mixer for macadam construction. 

The mixture is conveyed to the road in dump-bottom wagons 
or in motor trucks and is dumped on metal shoveling platforms 
from which it is shoveled into place in the road, and raked to the 
thickness necessary to provide for compression during rolling. 

The rolling is done with a tandem roller weighing about 6 tons, 
and is continued until the surface is thoroughly compacted. 
The roller moves parallel to the edge of the road as in rolling 
water-bound macadam, and the operation proceeds in much the 
same way. 

After the surface has been properly compacted it is covered 
with a thin coating of the bituminous material applied as a 
seal coat. The quantity required for the seal coat varies from 
M to % gal. per square yard of surface and the material is spread 
over the surface with a fiber broom or with a squeegee. 



294 CONSTRUCTION OF ROADS AND PAVEMENTS 

The surface is finally covered with a light dressing of stone 
chips % in. in size and free of dust, or of pea-size gravel and is 
rolled just enough to bed the dressing in the seal coat. 

The mixed macadam surface varies in cost between 60 cts. 
and $1 per square yard, exclusive of the base course. 

Its characteristics are in general similar to those of penetra- 
tion macadam except that it is more uniform in texture and 
consequently more durable. It is not widely used, but has 
passed the experimental stage and its construction is well 
standardized. 

SPECIAL APPLIANCES USED 

Sand and Stone Heaters. These usually consist of a furnace 
around which a metal hopper is built. The material to be 




FIG. 77. Portable heater for stone and improvised sand heaters. 

heated is thrown into the top of the hopper and when heated is 
shoveled out at the bottom. Sometimes the heater consists 
merely of metal pipe about 2 ft. in diameter which is laid on the 
ground and covered with the sand or stone. A fire is built 
inside the pipe and as the material becomes hot enough for use 
it is shoveled away and a new supply placed around the pipes. 

Melting Tanks. Melting tanks are made in a great variety of 
shapes and capacities but all are designed on the same general 



PENETRA TION AND MIXED MACADAM ROADS 295 

principle. The outfit consists of a comparatively large furnace 
over which is mounted a tank for the material. The furnace 
will burn either coal or wood. The capacity varies from a 50-gal. 
kettle to a 500-gal. tank. In the larger sizes a barrel rack is 
sometimes mounted above the kettle and enclosed in a sheet- 
iron case. The kettle is partly filled with the cold material and 
the rack is filled with barrels open end down. The heat from 
the kettle gradually softens the material in the barrels so that 
it will flow down into the kettle to replace the hot material as 
it is drawn off. The tanks are mounted on wheels so as to be 
easily portable. 

Mixers. The portable type of hot mixer is used. In design 
it is very similar to the concrete mixer except that the drum is 
jacketed leaving a space between the mixer drum and the jacket 
through which the hot gases from the furnace are forced by means 
of a fan. The materials are heated before they are placed in 
the mixer and it is only necessary to have the drum hot enough 
to maintain the temperature. 

EXAMPLES OF GOOD PRACTICE 

MASSACHUSETTS 1 

The bituminous mixture shall be laid in one course and shall 
be after rolling two (2) inches in thickness. 

The width shall be thirty (30) feet. 

The broken stone shall be trap rock and shall vary in size from 
one-quarter (J4) mcn to one and one-quarter (\Y) inches in their 
longest dimensions. All broken stone used shall be absolutely 
clean and free from adventitious matter. 

When the broken stone has been heated to not less than 150F. 
or more if the engineer so requires, it shall be mixed with the as- 
phalt, by machines, which shall be approved by the engineer, 
and as the engineer may direct, until all particles of stone are 
covered with asphalt. 

Sixteen (16) gallons of asphalt measured at temperature of the 
air shall be mixed with each cubic yard of stone. 

Before mixing with the stone, the asphalt shall be carefully 
heated to not less than 350F. and at that temperature shall be 
mixed with the stone. No asphalt shall be used after it has 

1 From specifications kindly furnished by Massachusetts Highway 
Commission. 



296 CONSTRUCTION OF ROADS AND PAVEMENTS 

been injured by overheating or burning. The contractor shall 
heat the asphalt in suitable kettles satisfactory to the engineer. 

After being properly prepared as hereinbefore stated, the 
mixture shall be teamed to the road and spread before it has 
cooled to a temperature below 100F. 

The mixture shall be dumped on steel dumping platforms or 
shoveled directly from the cart into place. As the spreading is 
done rakes shall be used to obtain a uniform distribution of 
stones and an even surface before rolling. 

The mixture, after being satisfactorily spread and raked, shall 
be at once rolled with a tandem roller, weighing not less than 
seven (7) tons, care being taken not to push the mixture out of 
place by the roller, but to roll so as to lay it down, compressed 
to a perfect cross-section, and true to line and grade. During 
very hot weather the rolling shall be postponed until cool enough 
to roll without pushing out of place and shape. 

If any unevenness or depressions appear during or after rolling 
the bituminous mixture, suitable material (mixed), satisfactory 
to the engineer shall be added, and rolled in a manner to remove 
all such unevenness or depressions. 

Immediately after the bituminous mixture is rolled to a firm 
surface and free from irregularities, a seal coat of Bermudez 
asphalt shall be so applied as to completely cover the surface, 
using one-third (J-) of a gallon of asphalt per square yard of 
surface. It shall be carefully spread with "squeegees" or 
brooms. 

Immediately after it has been spread it shall be covered with 
clean trap-rock pea stone and rolled until the pea stone is bonded 
with the asphalt of the seal coat. 

No teaming or travel of any kind shall be allowed to pass over 
the new surface until 24 hr. have elapsed after the final rolling 
or until the surface has become sufficiently hardened to prevent 
injury by picking up or tracking. 

No bituminous work shall be done during rainy weather nor 
when weather conditions as to temperature or otherwise are, in 
the opinion of the engineer, unfavorable to obtaining satisfactory 
results. 

In order to provide for passing traffic during the progress of 
the work it will be necessary to construct only one-half of the 
width of the roadway at one time. The lower course of that 
portion of the roadway which shall first be laid shall be extended 



PENETRATION AND MIXED MACADAM ROADS 297 

two (2) feet beyond the center of the road or two (2) feet beyond 
the inside edge of the bituminous mixture so as to provide a firm 
base for the bituminous mixture, also to Satisfactorily bond into 
the remaining portion of the bottom course when laid. 

The bituminous mixture and sealing coat of that portion first 
laid shall lap over the line of the joint at the center of the road- 
way, so that when the second half is laid the first half can and 
shall be cut back to a uniform longitudinal line and perfect 
vertical section so as to obtain a perfect joint and cross-section. 

From the time of commencement of laying the bituminous 
mixture during and until the time the final covering of pea stone 
is spread on the seal coat, the adjoining surface on any or all sides 
of the portion under construction shall be kept watered as directed 
by the engineer to prevent dust alighting on the bituminous 
surface. 

GRAVEL AGGREGATE 

Broken stone consisting of local stone or gravel stone shall be 
spread and rolled on the road bed, prepared as hereinbefore 
described, as follows: 

The width of the broken stone and bituminous surfacing shall 
be eighteen (18) feet. 

The lower course shall consist of stones varying in size from 
one-half (^) inch in the smallest dimensions to three (3) inches 
in the largest dimensions and shall be four (4) inches in depth 
at the center and sides after rolling. 

It shall be understood that the crusher will be set up at the 
gravel pit and that all gravel run through the crusher shall be 
used, the finer material being used in the oil mixture, and if there 
is not sufficient stone in the gravel for the lower course, the other 
stone shall be obtained from the fields and crushed. 

If there should be too much stone after allowing the one-half 
(J^) inch stone for the lower course, the size of the smaller stone 
to be used in the lower course shall be increased, according to the 
directions of the engineer, and the half (J^) inch or larger stone 
not exceeding one and one-half (1J^) inches used in the bitu- 
minous mixture. 

The lower course shall be shaped to a true section conforming 
to the proposed cross-section of the highway and thoroughly 
rolled. 

Any depressions or irregularities which may occur shall be 



298 CONSTRUCTION OF ROADS AND PAVEMENTS 

filled with smaller stones as directed by the engineer, and again 
rolled until the surface is true and unyielding. The interstices 
in this course shall then be filled with clean, sharp sand, or stone 
screenings, and after being thoroughly rolled dry the sand or 
screenings shall be just below the top of the broken stone, as 
directed by the engineer, and no sand or screenings shall be left 
on top of the stones. 

Upon the lower course shall be spread the bituminous mixture, 
which will form the wearing surface and shall consist of sand and 
gravel stone mixed with asphaltic oil; the sizes of sand and gravel 
stone, proportions of sand, gravel stone and oil, and the method 
of mixing and spreading to be as hereinafter described. 

The bituminous surfacing shall be laid in one course and shall 
be two (2) inches in thickness after rolling. Sand of a quality 
satisfactory to the engineer shall consist of particles that will 
pass through a screen with meshes one-quarter (J4) of an inch 
square, and be free from clay, loam and adventitious matter. 

The gravel stones shall vary in size from one-quarter (J^) inch 
to one and one-half (lj^) inches, and no stones larger than one 
and one-half (lj) inches in their largest diameters shall be used. 
Screenings from the crusher may be used in the bituminous 
mixture. 

Of the sand and gravel aggregate not more than 75 per cent, 
and not less than 15 per cent, shall consist of gravel stones of 
the size hereinbefore specified. 

The proportions of sand shall vary according to the proportions 
of stone used. 

When the sand and gravel stones have been heated to not less 
than 180F., or more if so directed by the engineer, it shall be 
mixed with the oil by machines, which shall be approved by the 
engineer, and as the engineer may direct, until all particles of 
sand and gravel are covered with oil. 

Before mixing, the stone and sand shall be heated separately 
and carefully measured to obtain the correct proportions of each. 

Not less than fifteen (15) gallons, nor more than twenty (20) 
gallons, of the oil, as the engineer may direct, shall be mixed with 
each cubic yard of sand and gravel. 

Before mixing with the sand and gravel, the oil shall be care- 
fully heated to not less than 200F. and at that or such higher 
temperature as the engineer may direct shall be mixed with 
the sand and gravel. 



PENETRATION AND MIXED MACADAM ROADS 299 

No oil shall be used after it has been injured by overheating or 
burning. 

The contractor shall heat the oil in suitable kettles or by steam 
coils or in such manner as may be satisfactory to the engineer. 

After being properly prepared as hereinbefore specified, the 
mixture shall be teamed to the road and spread before it has 
cooled to a temperature below 100F. 

The mixture shall be dumped on steel dumping platforms, or 
shoveled directly from the cart into place. 

As the spreading is done, rakes shall be used to obtain a uniform 
distribution of the sand and gravel stone and to smooth the top 
surface before rolling. 

The mixture, after being satisfactorily spread and raked, shall 
be at once rolled with a tandem roller weighing not less than seven 
(7) tons, care being taken not to push the mixture out of place, 
with the roller, but to roll so as to lay it down, compressed to 
the proper cross-section, and true to line and grade. 

When necessary, in the opinion of the engineer, the rolling 
shall be postponed until cool enough to roll without pushing out 
of place and shape. 

If at any time before the acceptance of the work any soft or 
imperfect places or spots shall develop in the surface, all such 
places shall be removed and replaced with new material and then 
rolled until the edges at which the new work connects with the 
old becomes invisible. All such removal and replacement of 
unsatisfactory surfacing shall be done at the expense of the 
contractor. 

RHODE ISLAND 

Since 1906 the Rhode Island State Board of Public Roads has 
constructed a large amount of bituminous macadam by the cold- 
mixing method. Some features of the process are described as 
follows : 

For the standard 14-ft. road, crushed stone which passed a 
3-in. screen and was retained on a lj^-in. screen was first spread 
over the well-rolled subgrade to a depth of 4 in. after compres- 
sion. This course was not filled with sand or stone screenings 
but was well rolled. Crude tar was very lightly sprinkled over 
this first course. Crushed stone of the same sizes was then mixed 
with crude tar in the proportion of 15 gal. of tar per cubic yard 
of stone. Mixine was carried out on a portable wooden mixing 



300 CONSTRUCTION OF ROADS AND PAVEMENTS 

platform near the point where the mixture was being spread. 
The mixture of stone and tar was spread over the first course of 
crushed stone to a depth of 2 in. after compression, and was well 
rolled, after which a covering of stone screenings was applied. 
The results secured on this first experimental section of bitu- 
minous macadam were remarkably successful, largely due to the 
stable, gravelly subsoil. 

Seal Coat. Subsequent experiments have proved the advisa- 
bility of seal-coating. We attribute the marked success of the 
early work in spite of the absence of a seal coat largely to the 
character of the travel. The horse-drawn traffic is very light, 
and we believe that the blows of horses' shoes on the exposed 
surfaces of the soft stones would be destructive were it greater. 

Precautions Needed. It has been proved in our work that 
the utmost care in using the cold-mixing method is necessary. 
The crushed stone must be perfectly dry at the time of mixing 
and all stones must be perfectly covered with bitumen in order 
that good results may be secured. The matter of carrying out 
the rolling is also important in its effect on the results obtained. 
It is, of course, necessary to secure by rolling as compact a mass 
as possible, but we have found that considerable care must be 
exercised in regulating the time and amount of rolling. If the 
weather is cool at the time of construction, we frequently post- 
pone the heavy rolling until midday, when the maximum warmth 
is experienced, although the initial rolling is done as soon after 
the mixture is laid as possible. 

Character and Size of Stone. The character and size of the 
crushed stone employed are also of importance. We h.ave secured 
the best results, as far as stone is concerned, with our native rock, 
which is rather variable in character. As a rule, our native rock 
is softer than trap rock and breaks with a much more irregular 
fracture. There is more or less breaking by rolling, and this 
appears to be beneficial rather than otherwise in that a denser 
pavement is secured. We feel that if trap rock were employed 
smaller sizes would be necessary than with a softer stone, unless 
there is a certainty of securing a perfect crusher-run from lj*j 
in. to % in. or less. 

WEATHER CONDITIONS 

Weather conditions influence the results considerably. Roads 
built late in the fall, just before freezing sets in, are not likely to 



PENETRATION AND MIXED MACADAM ROADS 301 

be as satisfactory as those built in midsummer, even though the 
temperature at the time of construction is not low. It seems to 
be a decided advantage to roads built by this method of con- 
struction to have a comparatively long period of warm weather 
immediately after construction in order that the surface may 
become freed from the top covering of stone screenings and well 
smoothed out before snow and ice appear. In Rhode Island we 
consider the season most favorable to this type of construction 
to be between the middle of May and the middle of October. 

On the whole the cold-mixing method of constructing bitu- 
minous macadam as practised in Rhode Island appears to be an 
economical pavement for motor-vehicle traffic. It does not 
appear to the writer as suitable for heavy horse-drawn traffic 
or for a heavy mixed traffic. The travel on several of the trunk 
lines in Rhode Island consists of motor vehicles to the extent of 
more than 90 per cent., and it is on these roads that we expect 
in the future to confine our bituminous macadam roads built 
by the cold-mixing method. Through large villages where the 
percentage of horse-drawn traffic is large we expect to take up a 
stronger method of construction. 



CHAPTER XVI 

SHEET-ASPHALT AND ASPHALTIC CONCRETE 
SURFACES 

I. SHEET-ASPHALT PAVEMENTS 

The sheet-asphalt pavement consists of three layers, the Port- 
land cement concrete or other base, the binder course, and the 
wearing course. It receives its name from the fact that the 
wearing course consists of a layer or sheet of a mastic composed 
of fine mineral aggregate and asphalt cement. 

Earth Foundation. All of the principles relating to drainage 
that have been discussed heretofore apply with equal force to 
the foundation for the sheet-asphalt pavement. The nature 
and thickness of the base will depend upon the character of the 
earth foundation and the care with which it is compacted, as 
in other types of pavement. 

Base Course. The sheet-asphalt surface is elastic and serves 
only as a wearing course. It cannot have stability unless ade- 
quately supported by a rigid base. Various kinds of base 
courses have been used, such as macadam, tar macadam, natural 
cement concrete, Portland-cement concrete, and old brick and 
block pavements. Portland-cement concrete is specified almost 
exclusively for new construction. Sometimes sheet asphalt is 
employed for resurfacing badly worn brick or block pavements, 
and on rare occasions is placed on top of old macadam. When 
properly carried out, resurfacing can be successfully accomplished 
in this way, but asphaltic concrete is more commonly employed 
in such instances. 

The thickness of base depends upon the character of the soil 
constituting the foundation, and the class of traffic to which the 
pavement will be subjected. For business streets where the 
individual loads are heavy the base is 6 in. thick when over a 
good subsoil, and a greater thickness if the soil is anything other 
than strictly first class. 

For residence street paving the base need not be so thick and 
for average conditions 5 in. will be adequate. On exceptionally 

302 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 303 



good soil and for light traffic the base may be as thin as 4 in., 
but the use of so thin a base is rarely justifiable. 

The materials used for the base should be carefully selected and 
properly proportioned as they would be for the construction of 
the base for any other pavement. The mixture for the con- 

-195- - -t>\6^- 

y Street Rocl< Aspha ii; ; j" a 3 6"c.toc . Concrete.. f'./8c.foc, f-^^pp^ 
\V7F77777m//MMMMJ/$///w *.;*$&* 

^:^1^^V^ ' 



Rock Asphalt Pavement and Concrete Base, San Antonio.Texas 



Asphalt Block Pavement. N ewburgn,N.Y 




Bituminous Concrete Pavement 
Washmgton.D.C 

5 v4'Bn<* 




s neet Asphalt-Brick Gutter 

Seattle.Wash 
-4'-IO--^l L 6\<- ....... - ---------- ..... I8'-0'- ..... -- ....... *| 1-6'* 4'-IO-- 

> ' ' 



Sheet Asphalt Pavement 
Base e. Curb. Seattle.Wash, 



fVfejX^y^^^ 

^^ ' '"'Old 8 "Macadam ' ^SJU/ 

^'Shoulder Width Var/ab/e.Average/W Hew Shoulder' 

Suburban Roads.City of Chicago 
i-6 "Cone Header Curb 2 'Bituminous Surface ^Slope jffo4" Dfl . r f 



i# "Macadam-' 
Old Tel ford 



4 1 Concrete' 



Suburban Roads. City of Philadelphia 
FIG. 78. Cross-sections for sheet pavements and roads. 

crete may be either 1-2^-5 or 1-3-6, depending upon the nature 
of the materials and the kind of subsoil. 

There is some tendency to finish the base with a rough or porous 
surface, or to shape it carelessly, which results in considerable 
variation in texture. Stability and durability in the asphalt 
surface require that the surface of the base shall have a uniform 
texture, free from porous patches and also free of patches of mor- 



304 CONSTRUCTION OF ROADS AND PAVEMENTS 

tar. It should not receive a troweled finish. If the sheet-asphalt 
surface varies in thickness it will compress more during rolling in 
some places than in others and the difference in density will result 
in the pavement developing undulations under traffic. Hence 
the necessity for a base that is carefully constructed to the 
required cross-section. 

Binder Course. Formerly the sheet-asphalt wearing surface 
was placed directly on the base, but it was found to creep and 
become uneven, and the intermediate or binder course was 
accordingly introduced. The binder course consists of a layer 
of asphaltic concrete placed directly on top of the concrete base. 
The thickness of the binder course depends upon the class of 
traffic and the total thickness of wearing surface that it neces- 
sitates. For heavy-traffic streets the binder course is usually 
1J^ in. thick, while for residences or other light-traffic streets 1 
in. is sufficient. For streets carrying traffic made up of very 
heavy individual loads, it is recommended that the binder be 
2 in. thick. 1 

The binder mixture is of two types, known respectively as open 
binder and close binder, the difference being in the grading of the 
mineral aggregates. 

Open Binder. The open binder is composed of stone ranging 
in size from J^ or J^ in. to 1 in., to which is added from 5 to 8 
per cent, of asphalt cement. Other size limits for the stone 
are sometimes specified, but in this type of binder no attempt is 
made to secure a dense mixture, nor are the voids filled with the 
asphalt cement as is apparent from the proportions given. 
The asphalt cement must be sufficient in quantity to coat all 
the stones so that when rolled the binder will be well cemented 
together. The surface of the binder course after it is rolled 
will be porous and open; hence the designation that is given it. 
The surface interstices of the binder course will be filled with the 
surface mixture by the rolling. 

Close Binder. Close binder differs from open binder in that 
the mineral aggregate is graded so as to secure a fairly dense 
mixture in which the voids are filled. This is accomplished by 
mixing broken stone and sand in such proportions that the sand 
will fill the voids in the stone. The stone ranges in size from 1 in. 
down and crusher-run is frequently employed. The sand should 
be well graded, but the requirements are not so rigid as those for 

1 Mr. D. T. Pierce, in No. 133 of "The American City Pamphlets." 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 305 

sheet-asphalt surface mixtures. The following specification is 
typical of those used for the close binder: 1 

"The binder stone shall be graded from 1 in. down ward,, to 
which sand shall be added so that the mixture shall contain be- 
tween 25 and 35 per cent, of material passing a 10-mesh sieve." 

The amount of asphalt cement required for the close binder is 
somewhat greater than that required for the open binder. 

The close binder is recommended for streets carrying moderate 
or heavy traffic and the open binder is permissible only on very 
light-traffic residence streets. 

Character of Materials for Binder Course. The stone for the 
binder course must transmit the load from the wearing surface 
to the concrete base, but since the medium is somewhat plastic 
the requirements for the stone are not exceedingly rigid. Any 
good, hard, tough limestone, or trap rock or granite may be used. 
The stone should be clean and should run with reasonable 
uniformity as to grading. The sand for the close binder should 
be of the quality and cleanness required for high-class concrete. 

Old Surface Mixtures for Binder. Old sheet-asphalt surfaces 
that have been removed in resurfacing streets are utilized for 
the preparation of close binder. The old surface mixture is 
melted in kettles heated by steam and then mixed with the 
proper amount of stone. Additional asphalt cement is added 
to renew the life of that which is in the old surface mixture. 
Suitable precautions must be taken to insure that the old mix- 
ture is thoroughly broken up and distributed through the mass 
of stone and that the right amount of new asphalt cement is 
added. The asphalt cement in the ordinary binder course is of 
the same quality as that used for the surface mixture except 
that it can advantageously be about 15 points softer. 

Asphalt Paint Coat for Binder. In a few instances the binder 
course as described above is omitted entirely and instead a paint 
coat of asphalt cement is applied to the concrete base. In 
order to insure adhesion, the asphalt cement is heated and 
then removed to a safe distance from the fire and fluxed with 
commercial naphtha. This softens the cement sufficiently to 
insure adhesion to the concrete base. The naphtha quickly 
evaporates, leaving a layer of asphalt cement on the concrete. 
This method has not had sufficient tests under diverse con- 

1 City of Chicago Specifications for 1916, 



306 CONSTRUCTION OF ROADS AND PAVEMENTS 

ditions to warrant general adoption, but has been used very 
successfully by some of the cities in California. 1 

Surface Mixture. The surface mixture for the sheet-asphalt 
pavement consists of sand, filler and asphalt cement. 

Sand. It has long been recognized that the stability of the 
sheet-asphalt surface depends to a large extent upon the care with 
which the mineral aggregate is graded. Experience with cement 
mortars has shown the importance of using a sand that is properly 
graded, to insure density and strength, and the sand grading 
is no less important in the sheet-asphalt surface mixture. In- 
asmuch as the mineral aggregate comprises about 90 per cent, 
of the volume of the surface, it is reasonable to expect that it 
needs to be carefully selected and properly graded. The sand 
should be clean and free of slate, shale or other friable material. 
It is generally thought that sharp sand is better than sand made 
up of rounded particles, but this cannot be stated as a general 
fact because successes and failures have been recorded with 
both classes of sands. 

Filler. The filler is the portion of the mineral aggregate 
passing the 200-mesh screen and may consist of finely ground 
rock dust or of Portland cement. The filler plays an important 
part in the mixture, since it serves to fill the small voids and 
to give density to the surface. A good filler should not only be 
fine enough to pass the 200-mesh sieve, but also contain a good 
percentage of particles that will pass a 400- and also a 600- 
mesh sieve. Since sieves are not made commercially with more 
than 200 meshes per inch, the amount of the finer particles is 
estimated by a modification of the method of elutriation which 
is employed in soil analysis. The method is described in Chapter 
V. Portland cement is a desirable filler since it is finely ground 
and is made up of very durable particles. It is more expensive 
than limestone dust, and for that reason the stone dust is often 
used. Limestone dust ground to the proper degree of fineness is 
widely used for filler, and while it is probably not as good as 
Portland cement, it is satisfactory. Silica dust is also employed 
for filler and seems to be as good as Portland cement. In the 
preparation of stone dust for the filler, the stone is first heated 
so as to thoroughly dry it and then crushed and finally ground 
in a ball mill using flint pebbles for the abrasive. Some grind- 

1 Mr. A. E. Loder in "California Highways," Jan. 1, 1915. 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 307 



ing mills use steel rollers for grinding but the resulting product is 
usually not as finely ground as that produced in the ball mill. 

Established Gradings. The following gradings are recom- 
mended 1 for sheet-asphalt surface mixtures. These have been 
well established in practice and in general it can be said that the 
nearer the surface mixture approaches these in composition the 
more certain the pavement will be to have the desired stability. 
It will be noted that the various sizes are separated into three 
groups, and while it is desirable to have the specified amount of 
each size, it is not always possible to secure sands so graded. 
If each group is present in the right amount, that is sufficient. 

TABLE 20. STANDARD SHEET-ASPHALT GRADINGS 



Per cent, by weight 
Heavy traffic Light traffic 



Bitumen 

200-mesh, filler. . . 
100-mesh . . . . 

80-mesh 

50-mesh 

40-mesh 

30-mesh 

20-mesh 

10-mesh.. 



10.5 

13.0 

13.0 

13.0 

24.0 

10.5 

8.0 

5.0 

3.0 



39.0 



34.5 



16.0 



10.0 

10.0 

9.0 

9.0 

26.0 

12.0 

10.0 

8.0 

6.0 



18.0 



38.0 



24.0 



The finer portion of the mixture is the most important and the 
grading may more safely depart from the above as regards the 
material above the 40-mesh size than as regards the material 
finer than the 40-mesh. The amount of filler that can be used 
in a mixture depends upon the amount of fine sand present. 

TABLE 21. COMPARATIVE SUPERFICIAL AREAS OF FINE AGGREGATES 



Material 


Number of 
particles 
per pound 


Surface area 
of particles 
per pound 
(square feet) 


Ordinary sand . 


129,000 000 


44378 


Sand of which 30 per cent, passes the 80- 
and 100-mesh, and 7 per cent, passes the 
200-mesh . . 


232 075 000 


60503 


Filler or dust 


192,715,475,500 


527,820 



The amount of bituminous cement required is dependent upon 
the grading of the mineral aggregate and especially upon the 
1 "The Modern Asphalt Pavement," by Clifford Richardson. 



308 CONSTRUCTION OF ROADS AND PAVEMENTS 

proportion of the finer material in the mixture. The bituminous 
cement must coat all of the particles and the amount required 
will, therefore, vary with the surface area to be covered. The 
foregoing table shows the enormous increase in superficial area 
per unit weight with a decrease in the size of the particles. 1 



CONSTRUCTION OF THE PAVEMENT 

The concrete base is finished and ample time is allowed for 
the concrete to set before the binder course is placed. If the 
binder is hauled too soon, injury to the base will result unless 




FIG. 79. Spreading sheet asphalt mixture. 

a plank driveway is provided for the wagons hauling the binder. 
The base should be clean and dry when the binder is spread. 

The binder course is mixed in the twin-pug type of mixer which 
is also used for mixing asphaltic concrete. The stone must not 
be too hot or some of the asphalt cement will run off while the 
mixture is being hauled; it must not be too cold or it cannot be 
spread and rolled satisfactorily. For most materials 275 to 
325F. is about the permissible range of temperature, but this 
is subject to some variation for the different asphalt cements. 

The binder is dumped on the concrete in advance of the point 
of spreading and is shoveled into place and raked to a thickness 
that will, when rolled, give the prescribed thickness of binder 
course. Experienced rakers need no guide in this operation and 

1 Mr. D. T. Pierce in No. 133 of "The American City Pamphlets." 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 309 

usually none is employed except possibly a line on the curb at 
the top of the layer. As soon as spread, the binder is rolled, 
first with a 3-ton tandem roller and later by one weighing 8 to 
10 tons. The rolling must proceed rapidly so that compression 
is secured before the asphalt cement cools too much. The rolling 
is carried out both crosswise and longitudinally and is a vital 
part of the construction, especially as regards the evenness of 
the finished surface. Only a skilled operator can be expected 
to secure satisfactory results. 

The wearing course must be placed soon after the binder course 
has been rolled. It is especially desirable that close binder be 
covered with the wearing course the same day it has been laid, 




FIG. 80. Rolling sheet asphalt surface. 

and it is safer to follow the same rule for all classes of sheet-asphalt 
construction. 

The mixture for the surface is prepared by weighing the sand, 
filler and asphalt cement into a twin-pug mixer and thoroughly 
combining the ingredients by mixing. The temperature should 
be somewhat higher than for the binder material. With many 
kinds of asphalt cements a temperature of 350F. may be reached 
without inj ury to the materials. Other asphalts must be handled 
at a somewhat lower temperature. 

The amount of asphalt cement required for the surface mixture 
depends upon the character of the asphalt cement to a small 
degree and upon the character and grading of the sand and the 
amount of filler, as has been noted. Specifications generally 



310 CONSTRUCTION OF ROADS AND PAVEMENTS 

give the limits for the amount of bitumen, but within these limits 
the amount can be varied to suit conditions. The asphalt 
cement must be used in sufficient quantity to coat all of the 
particles. The finer particles have a very much greater surface 
per pound than do the coarser, as is shown by Table 21. It is, 
therefore, apparent that the amount of asphalt cement neces- 
sary in any mixture will depend upon the grading of the mineral 
aggregate and especially upon the amount of fine sand and filler 
contained therein. The appearance of the mixture is the best 
guide for proportioning the asphalt cement and to an experienced 
plant man the characteristics of a suitable mixture are well 
understood. As a check on quality of the mixture, the pat test 
devised by Mr. Clifford Richardson has been widely used. He 
describes it as follows: 1 

The Pat Test. " A small wooden paddle with a blade 3 or 4 in. wide, 
5 or 6 in. long, and ^ in. thick, tapered to an edge at one end and with 




FIG. 81. Sheet asphalt surface destroyed by concentrated traffic. 

a convenient handle at the other, is used to take as much of the hot. 
mixture from the wagon as it will hold, being careful to avoid any of the 
last droppings from the mixer which may not be entirely representative 
of the average mixture. Samples of mixture should never be taken 
from the mixer itself, but only from the wagon after mixing is completed. 
"In the meantime a piece of brown Manila paper with a fairly 

1 "The Modern Asphalt Pavement," by Clifford Richardson. 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 311 

smooth surface, 10 to 12 in. wide, and torn off at the same length from 
a roll of this paper, which can be had at any paper warehouse, is creased 
down the middle and opened out on some very firm and smooth surface 
of wood, not stone -or metal, which would conduct heat too rapidly. 
The hot mixture is dropped into the paper sideways from the paddle and 
half of the paper doubled over on it. The mixture is then pressed down 
flat with a block of wood of convenient size until the surface is flat. 
It is then struck five or six sharp blows with the block until the pat is 
about % in. thick. 

"The paper will be found to be stained to a different degree depending 
upon whether there is a deficiency, a proper amount or an excess present. 

"In this way the amount of asphalt cement to use in making a mixture 
can be readily regulated, and the pat papers obtained will be evidence 
of the character of the mixture turned out. Where a laboratory ex-- 
amination is to be undertaken, a sample of surface mixture which is 
made from the material compressed between the paper can be used for 
this purpose, trimming it down into the proper form and sending it,| 
accompanied by the paper, for the purpose." 

The surface mixture is hauled to the work in covered wagons, 
and is dumped on metal or wooden platforms or on the binder 
course at a distance from the point of laying that will necessitate 
the entire load being shoveled into place. When shoveled into 
place, the mixture is thoroughly broken up with the rakes and 
is spread to the proper thickness for rolling. The rolling begins 
as soon as possible after the spreading, the light tandem roller 
being used first and being followed by the 8- or 10-ton tandem 
roller. Here again the character and uniformity of the surface 1 
will depend to a considerable extent upon the skill of the roller 
operator. A uniformly smooth surface will result if the rolling 
is properly done and unevenness is inevitable otherwise. Fig. 79 
shows the method of spreading the surface mixture and Fig. 80 
the rolling. 

The surface is sometimes dressed lightly with cement or stone 
dust prior to the final rolling, although the necessity of this is 
a mooted point. 

Asphalt Plants. The plant required for making the mixtures 
used in sheet-asphalt and asphaltic concrete pavements is 
described at the end of the chapter. The filler is not heated 
before being added to the mixture. The twin-pug mixer is 
adapted to making both the surface mixture and the binder 
course, but shorter and fewer paddles are used for mixing the 
binder. 



312 CONSTRUCTION OF ROADS AND PAVEMENTS 

Proportioning Asphalt Cement. The proportion of asphalt 
cement is determined by weight. Since it is desired to use enough 
bitumen to coat all the particles, it is apparent that a more 
rational method would be to proportion the asphalt cement by 
volume. As a matter of convenience and accuracy, however, 
weighing is resorted to. The weight of asphalt cement per unit 
volume varies considerably, and if the proportioning is by weight, 
account must be taken of the variation in the specific gravities 
of the asphalt cements that might be used. Attention is also 
called to the fact that the percentage of bitumen is always speci- 
fied not the percentage of asphaltic cement. This is necessary 




FIG. 82. Results of use of poor asphalt and improperly graded sand. 

because of the differences in the proportion of bitumen in the 
various asphalt cements. In determining the amount of asphalt 
cement to use it is, therefore, necessary to take account of the 
specific gravity and bitumen content of the cement. 

To illustrate the significance of these facts in proportioning 
the asphalt cement in a paving mixture, consider a sheet-asphalt 
surface mixture in which the percentage of bitumen by weight is 
8.9. Assume that Trinadad Lake asphalt cement were used in 
which the percentage of bitumen is 65 and the specific gravity 
1.28. The percentage by weight of the asphalt cement neces- 
sary to give 8.9 per cent, of bitumen is 8.9/0.65 = 13.5 per cent. 

If the mineral aggregate has a specific gravity of 2.65, the 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 313 

actual percentage of asphalt cement by volume is equal to 
2.65/1.28 X 13.5 = 27.0 per cent. 




FIG. 83. Showing defective sheet asphalt surfaces. In (a) the asphalt 
cement is too soft and in (6) it is too hard. (Views about one-half natural 
size.) 

If, however, an asphalt cement produced from petroleum were 
used, the percentage of bitumen in the asphalt cement would 



314 CONSTRUCTION OF ROADS AND PAVEMENTS 

be about 99.5, and the specific gravity about 1.03. The per- 
centage of the asphalt cement required by weight would be 
substantially the same as the percentage of bitumen. The 
percentage by volume in the example cited would be 2.65/1.03 X 
8.9 = 22 per cent. 

Since the bitumens extracted from the various asphalt cements 
vary somewhat in specific gravity, a proportion based on weight 
is not exactly a constant proportion by volume. This is the 
reason for the variation in the allowable percentage of bitumen 
provided for in specifications. 

Some Features of Design. If a street has sufficient longi- 
tudinal slope to insure that no water will stand along the curb, 
the straight concrete or stone-block curb may be used, but if 
the slope of the gutter is less than 0.5 per cent, it is better to 
design the street with the combined concrete curb and gutter, 
or with a straight curb and block gutter. 

It is undesirable to use sheet asphalt on a street where vehicles 
continually stand along the curb unless that portion of the 
street is paved with blocks of some kind. Wood-block and 
grouted vitrified-brick surfaces are used for that part of the 
roadway. 

The maximum grade for which the sheet-asphalt surface is 
permissible depends upon the kind of vehicles that use the surface. 
If the horse-drawn loads are fairly heavy, the grade probably 
should not exceed 4 per cent., but for automobile traffic and 
light-team traffic the grade may be steeper. Instances of sheet- 
asphalt surfaces on grades up to 8 per cent, have been noted and 
no especial difficulty is reported. 

Where street car tracks occupy the middle portion of the street, 
there is a decided tendency for traffic to concentrate on the strip 
of pavement between the track and the curb, especially if the 
track paving is rough or noisy. This can be overcome to some 
extent by paving the car track area with sheet asphalt or wood 
blocks. Where traffic concentrates on the sheet asphalt, creep- 
ing and unevenness quickly develops and the pavement wear? 
out very rapidly (see Fig. 81). 

Characteristics of the Sheet-asphalt Surface. The sheet- 
asphalt surface is compared with other pavements in another 
chapter. It is desired here to call attention to certain char- 
acteristics that are inherent. Sheet asphalt requires a certain 
amount of traffic to keep the asphalt " alive." It is noticeable 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 315 

that on light-traffic streets the part of the pavement next the 
curb becomes granular and sometimes cracks badly, while the 
middle portion is kept in good condition by the action of traffic. 
Sheet asphalt also deteriorates rapidly under concentrated steel- 
tired traffic such as may be expected on a narrow street with a 
busy double-track car line. 

ASPHALT-BLOCK PAVEMENTS 

The asphalt-block pavement surface is constructed of blocks 
of a mixture similar to that used for sheet asphalt, compressed 
by very heavy pressure. Since the blocks are made in a specially 
equipped factory, all of the details of manufacture are subject to 
close control and the proportions of the various ingredients and 
the quality of the materials can be determined accurately. 
The product is, therefore, likely to be uniform. The blocks are 
formed under much greater pressure than can be secured in roll- 
ing a sheet-asphalt surface and consequently they have greater 
density than does the average sheet surface. 

Composition of the Blocks. Asphalt blocks are composed of 
graded crushed stone or sand, filler and asphalt cement. A 
typical specification provides as follows: 1 

"On sifting (the mineral aggregate) not more than 3 per cent, shall 
be retained on a 3-mesh per inch sieve, at least 40 per cent, shall be 
retained on a 20-mesh per inch sieve, and at least 12 per cent, must 
pass a 100-mesh per inch sieve. If the stone does not contain the de- 
sired amount of fine material, mineral dust shall be added to make up 
the deficiency and in any case at least 5 per cent, of such mineral dust 
shall be added. 

"The mineral dust shall be any fine, absorbent, inorganic dust, not 
acted upon by water, the whole of which shall pass a 30-mesh sieve, 
and at least 85 per cent, pass a 100-mesh sieve." 

The mixture for blocks contains from 6 to 9 per cent, of 
bitumen. 

Size of Blocks. The blocks are made either 3, 4 or 5 in. thick 
and are 12 in. long and 5 in. wide. A variation of Y in. from 
the specified size is permitted. The blocks are formed under a 
pressure ranging from 240,000 Ib. to 360,000 Ib. per block. 

Subgrade. The earth subgrade is prepared in the same 
manner as for the other types of pavement and has been pre- 
viously described. 

1 Washington, D. C., specification, 1915. 



316 CONSTRUCTION OF ROADS AND PAVEMENTS 

Foundation. The asphalt block pavement is laid on a base of 
either gravel, macadam or concrete, each type being constructed 
in the manner already described. 

Bedding Course. The bedding course is generally a layer of 
sand 1 or 2 in. thick, which is placed in the same manner as for 
the other types of block pavement. 

Laying the Blocks. The blocks are laid on the sand cushion 
in regular courses at right angles to the center line of the street, 
with the joints broken by a lap of at least 4 in. Each block is 
driven against the course already laid by means of a heavy maul 
so as to give close transverse joints, and the end joints are tight- 
ened by means of a lever from the end of the course. The surface 
is covered with fine sand (passing a 20-mesh sieve). A plank 
or an iron plate is then placed over several courses and the 
blocks are rammed to place by tamping through the medium of 
the plank or metal plate. 

Characteristics. The asphalt-block pavement has much the 
same appearance as the sheet-asphalt pavement, but is less 
slippery and somewhat more durable. Its cost is on the average 
about 50 cts. a square yard greater than that of sheet asphalt in 
the same locality, the average price being about $2.50 per square 
yard. 

H. ASPHALTIC-CONCRETE PAVEMENTS 

Asphaltic concrete is the name given to a paving mixture con- 
sisting of graded stone, sand and rock dust or other fine material, 
which is cemented together by a bituminous material. It 
receives its name from its analogy to Portland-cement concrete, 
although the cementing action of the bituminous material differs 
from that of Portland cement in that the cementing action 
of bitumen is a purely mechanical effect due to the stickiness of 
the binder. 

Bituminous concrete, like sheet asphalt, is used for the wearing 
surface of pavements, the thickness being 2 to 3 in. 

The mineral aggregate is made up of three parts; stone, sand 
and dust or filler. 

Stone. The stone must be tough enough to resist the crushing 
effect of the loads that will use the pavement. While the individ- 
ual pieces of stone are at first surrounded and protected by the 
finer part of the mixture, eventually many of them will be exposed 
at the surface of the pavement. If the stone is soft or of variable 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 317 

hardness, these exposed stones will crush and the fragments will 
be removed by traffic, leaving a pitted surface. No stone softer 
than good granite, quartzite or trap should be used. 

If the stone is of such a nature that it absorbs any appreciable 
percentage of water, disintegration will occur during periods of 
freezing and thawing, which is of importance with pavements 
constructed in northern climates. At first the stones will be 
well protected by the seal coat but eventually this will wear down 
and expose the stones to traffic. 

Sand. The sand is subjected to the same crushing and 
abrasive action as the stone. Clean quartz sand is best but in 
any case the sand particles must be of some hard and durable 
material. Particles of clay, shale, coal or other friable material 
are objectionable if present in any appreciable quantity. A sand 
suitable for the sheet asphalt surface is suitable for asphaltic 
concrete. 

The dust or filler may be a finely ground rock powder or 
Portland cement and is identical with the filler employed in the 
sheet-asphalt surface. 

The stability of the asphaltic-concrete surface depends 
primarily upon the grading of the mineral aggregates, and 
experience has shown conclusively the limits of the various sizes 
for satisfactory results. 

The Sand Grading. The grading for sheet-asphalt surfaces 
has already been discussed at some length and the same sand 
grading should be employed for asphaltic concrete. If stone 
containing fine particles is used, these fine particles will take 
the place of an equal amount of sand of the same size. 

Types of Asphaltic Concrete. Two distinct classes of bitu- 
minous concrete are constructed and these are differentiated 
by the grading. They are known respectively as the Bitulithic 
and Topeka types of asphaltic concrete. 

Bitulithic. The Bitulithic type is a patented surface mix- 
ture controlled by the Warren Bros. Co., and the two essential 
features of the patent are: (1) the grading of sand and stone is 
such as to reduce the voids in the mineral aggregate below 21 
per cent.; (2) the amount of stone passing the J^-in. screen and 
retained on the J^-in. screen is greater than 10 per cent., and 
stone up to a size equal to half the thickness of the pavement is 
generally recommended. 

A feature of importance is that the stone may exceed % in. 



318 CONSTRUCTION OF ROADS AND PAVEMENTS 



in size and usually it is as large as 1 in., or half the thickness of 
the wearing course. The exact grading of the stone and sand 
for the Bitulithic surface is determined for each piece of work 
after an examination of the available materials has been made. 
Theoretically the stone, sand and dust are proportioned in such 
a way as to reduce the voids in the resulting mixture to about 
10 per cent., and to give what is considered a satisfactory grad- 
ing for good stability. The per cent, of the various sizes of stone 
and sand grains will vary with the character of the material and 
depends upon the shape of the pieces of stone and grains of sand. 
Table 22 gives the sieve analysis of the mineral aggregates from 
two Bitulithic pavements and indicates in a general way the 
proportions of the various sizes required to produce a low per- 
centage of voids. The table includes a typical specification for 
Bitulithic grading. 

TABLE 22. SIEVE ANALYSIS OF MINERAL AGGREGATE FROM BITULITHIC 

PAVEMENT 





Typical 


Gradings 


employed 




per cent. 


Sample No. 1, 
per cent. 


Sample No. 2, 
per cent. 


Bitumen.. 


7-QU 


7 6 


7.02 


Passing 200-mesh sieve. 


4-7 


5 3 


4 90 


Passing 100-mesh sieve 




5.0 


4.27 


Passing 80-mesh sieve 




3.5 


2.96 


Passing 50-mesh sieve. 




7 9 


8.44 


Passing 40-mesh sieve 




3.4 


1.36 


Passing 30-mesh sieve 




2.6 


2.56 


Passing 20-mesh sieve. 




2 4 


2.28 


Passing 10-mesh sieve 


24-32 


5.5 


4.04 


Passing -j^-in. screen 


8-12 


9.8 


5.19 


Passing %-in. screen 


12-20 


20.9 


13.72 


Passing 1-in screen 


26-35 






Refrained on )^-in. screen and pass- 
ing 1/^-in screen 


36-50 


33.7 


50.28 











Topeka Asphaltic Concrete. The Topeka asphaltic concrete 
is a type that has some of the characteristics of the Bitulithic, 
but the mineral aggregate is mostly sand and J^-in. stone and 
contains in excess of 21 per cent, of voids and is graded so that 
it does not infringe the Bitulithic patent. The following is the 
formula for the Topeka type of asphaltic concrete established 
in the decree in the Topeka case: 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 319 



TABLE 23. SHOWING TOPEKA GRADING 

Bitumen 7 to 11 per cent. 

Mineral aggregate passing 200-mesh 5 to 11 per cent. 

Mineral aggregate passing 40-mesh 18 to 30 per cent. 

Mineral aggregate passing 10-mesh 25 to 55 per cent. 

Mineral aggregate passing 4-mesh ~ 8 to 22 per cent. 

Mineral aggregate passing 2-mesh Not over 10. 

(Sieves to be used in the order named.) 

It will be noted that a wide variation in the grading is possible 
under the above specification, especially in the finer portions of 
the mixture and it has, therefore, been found advisable to provide 
a closer grading for the sand in this class of pavement. In effect 
the Topeka type of surface is sheet asphalt plus a limited amount 
of stone not greater than % in. in size. The following are 
analyses of Topeka asphaltic-concrete mixtures and illustrate 
the care that ordinarily is taken in grading the sand. 

TABLE 24. SHOWING GRADING OF MINERAL AGGREGATES FOR ASPHALTIC- 
CONCRETE PAVEMENTS 





No. I 


No. II 


No. Ill 


No. IV* 


Bitumen 


8.9 


8.9 


8.1 


8.4 


Passing 200-mesh 
Passing 80-mesh 
Passing 40-mesh 


11.9 
14.5 
18.6 


12.3 
10.8 
24.2 


8.9 
10.7 
25 3 


3.4* 
2.5* 
26 


Passing 10-mesh 


18 9 


16 3 


15 7 


22 


Passing 4-mesh 
Passing 2-mesh 


19.1 
8.1 


21.5 
5.4 


13.0 
18.3 


20.0 
17.7 













* Unsatisfactory grading, deficient where marked. 

Other Types of Asphaltic Concrete. Many proprietary pave- 
ments of this type have been promoted but all are based on one 
or the other of the two types already mentioned. 

Warrenite. Warrenite is similar to Bitulithic but it is not 
as carefully graded and is intended more especially for rural 
highways. It is covered by the Bitulithic patents. 

Mineral rubber, Sarcolithic, Amiesite, and F libertine are pro- 
prietary pavements mostly intended to promote the use of certain 
kinds of materials. They involve no new basic principles and 
a discussion of them is of no importance herein. 

Foundation for the Asphaltic-concrete Surface. The as- 
phaltic-concrete pavements are laid on a Portland-cement 



320 CONSTRUCTION OF ROADS AND PAVEMENTS 

concrete foundation and on macadam or gravel foundations. 
If the Portland-cement concrete is adopted it is of the same 
composition and thickness as for the sheet-asphalt pavement. 
It is thought that the Topeka type of asphaltic concrete is liable 
to creep on a concrete foundation if the concrete is given a 
smooth finish. It is, therefore, customary to finish the surface 
of the foundation by tamping and to avoid striking or troweling 
in any manner. Some engineers require that the surface be 
finished with a knobbed tamper so as to leave pits in the surface. 
These are satisfactory except that they are difficult to clean when 
the base is swept preparatory to laying the wearing surface. 

Sometimes the surface of the base is roughened by scattering 
coarse (lj^ or 2 in.) stones over the green concrete and tamping 




FIG. 84. Laying bitulithic pavement. 

them until half bedded in the base. This produces a good bond 
but decreases the effective thickness of the wearing course. 

In other instances the base is roughened by sweeping the 
mortar from around the stone just before the cement takes final 
set. If this work is carefully done, the 'corners of the stone 
will be exposed and will form a good anchorage for the wearing 
surface. Everything considered, this is probably the most 
satisfactory method of roughening the base. 

At best there is a possibility of the wearing surface creeping 
and becoming uneven, particularly if the asphaltic concrete itself 
is not of the proper composition. This difficulty is encountered 
less frequently with the Bitulithic type of surface than with the 
other types, and less frequently with a macadam base than with 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 321 

the concrete base. It is probably safe to say, however, that on 
any city street except one in a residence district with light traffic, 
the asphaltic concrete should be placed on a concrete foundation. 

Macadam Base. If the macadam base is used, an old and 
worn macadam may be utilized by resurfacing it to restore its 
shape and thickness, which should never be less than 6 in. and 
must be in most instances 8 in. The same thing is true of an 
old gravel surface that is to be used for the foundation, but unless 
it is of ample thickness and thoroughly compacted the surface 
will get out of shape due to the failure of the foundation. 

The foundation may be a newly constructed macadam or gravel 
of good quality, but the greatest care is necessary in this case to 
insure an unyielding foundation. It is well known that new 
macadam gradually increases in density for some time after it 
is opened for traffic and if the asphaltic concrete is placed before 
traffic uses the macadam, some unevenness is almost sure to 
develop. 

Thickness of Surface. The thickness of the surface after 
rolling is rarely less than 2 in. even on light-traffic streets or roads 
and that thickness is used almost universally on all classes of 
streets and roads. It seems to be impractical to use a less thick- 
ness without its being displaced by traffic and a greater thickness 
is apparently unnecessary except for very heavy-traffic streets. 

A few pavements have been constructed where the thickness 
of the surface has been made 3 in., but these are on very heavy- 
traffic streets. 

The surface layer is ordinarily placed directly on the founda- 
tion without any intermediate or binder course such as is used 
in the sheet-asphalt pavement. Undoubtedly the Topeka 
type of asphaltic concrete would be more stable if placed on a 
binder course. 

Mixing and Placing. The mixing is accomplished in a plant 
identical with that used for sheet asphalt. The mineral aggre- 
gate and the bitumen are heated separately and combined by 
weighing accurately the proportion of each size of stone, sand, 
filler and bitumen, and then mixing in the twin-pug or some 
similar mixer For the Topeka type of asphaltic concrete the 
mineral aggregate is separated into two sizes in the storage bins, 
while for the Bitulithic seven sizes are recommended. The 
proper quantity of each size is weighed into the mixer, the dust 
and asphalt cement added and the whole thoroughly mixed. 



322 CONSTRUCTION OF ROADS AND PAVEMENTS 

The mixing is accomplished at temperatures ranging from 
250F. to 350F., the variation being necessary on account of 
difference in the asphalt cement. 

Laying the Surface. The paving mixture is hauled in covered 
dump wagons from the plant to the place where it is to be laid 
and at the place of delivery the mixture is dumped on the foun- 
dation somewhat ahead of where it is to be spread* It is then 
shoveled to place and spread by means of rakes, care being taken 
to loosen the entire mass in so doing. It is then rolled with a 
light roller both longitudinally and crosswise of the street. 
On narrow pavements or country roads the transverse rolling is 




FIG. 85. Heater for tampers and smoothing irons. 

impractical and all rolling is done longitudinally and diagonally. 
After the light rolling a heavy roller is substituted and the roll- 
ing continued in a longitudinal direction until ultimate com- 
pression is reached. Careful and thorough rolling is a very es- 
sential part of the construction because it effects not only the 
durability but the evenness of the pavement. The tandem 
type of roller is commonly used for the Topeka type of asphaltic 
concrete, the lighter one having a weight of about 3 tons, while 
the heavier should have a weight of at least 8 tons. The 
macadam type of roller weighing about 10 tons is recommended 
for the Bitulithic type of asphaltic concrete. 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 323 

Dressing the Surface. Several methods of finishing the surface 
are employed. 

After the first rolling a light dressing of Portland cement 
may be spread on the surface, and subsequent rolling will in- 
corporate the cement with the surface. 

A seal coat of the asphalt cement may be spread with the 
squeegee or with brooms and this covered with pea gravel and 
rolled just enough to set the gravel into the seal coat. The 
surface is sometimes covered with pea gravel or stone chips and 




FIG. 86. Showing essential parts of an asphalt plant. A. Cold sand 
elevator. B. Sand heater. C. Fan. D. Power plant. E. Melting tank. 
F. Screen. G. Hot sand storage. H. Weighing hopper. 7. Twin pug 
mixer. 



the seal coat omitted. Probably the seal coat with stone chips, 
or pea gravel, forms the best surface. 

Suburban Roads. Asphaltic concrete is widely used for 
suburban and state roads, being in most instances placed on a 
foundation of macadam or gravel. These roads are com- 
paratively narrow, being seldom over 20 ft. wide and often 
being of less width. Vehicles are sure to cross and recross the 
edge of the wearing surface and if no marginal curb is employed 
the edge of the wearing surface will gradually break down and 



324 CONSTRUCTION OF ROADS AND PAVEMENTS 

start the disintegration of the surface. The marginal curb 
of concrete or a substantial shoulder of macadam is necessary 
for such roads but otherwise they are constructed in the 
same manner as city streets of like material. Instead of Bitu- 
lithic, the Warrenite is more commonly specified for suburban 
roads. 

Characteristics. The asphaltic concrete is resilient, dustless, 
quiet and easily cleaned. It is only slightly slippery, being less 
so than the sheet asphalt. Its durability depends upon many 
factors, but in general is about the same as sheet asphalt. 

The cost varies between $1.75 and $2.50 per square yard, 
exclusive of grading. 

Maintenance. Assuming that the pavement has been well 
built, the first need will be a renewal of the seal coat and dressing. 
If a heavy asphaltic oil is used for this purpose it will renew the 
surface and restore the elasticity of the asphalt cement near the 
surface and thus give the pavement a new lease of life. 

Patching will finally become necessary because of the forma- 
tion of pot-holes. 



TOOLS AND APPLIANCES USED FOR SHEET -ASPHALT AND 
ASPHALTIC-CONCRETE CONSTRUCTION 

Mixing Plants. Mixing plants are of many types and designs 
and vary in size from those that can be loaded on a single flat 
car and Have a capacity of 1,000 sq. yd. a day to those that are 
permanently located in the larger cities and have a capacity up 
to 10,000 sq. yd. a day. Regardless of the size of plant, the 
essential parts are the same, the difference being only in details 
and size. 

Sand and Stone Heaters. The same heaters are used both 
for sand and stone and they consist of metal cylinders mounted 
so they will revolve over the furnaces. The cylinders are 
mounted at a slight inclination and structural angles are riveted 
to the inside of the shell with one leg projecting. As the cylinder 
revolves the material is carried up on these projecting angles 
until it finally drops. But since the cylinder is inclined the 
material will fall ahead of where it started and thus gradually 
move through the cylinder while being heated. A fan is pro- 
vided to force heated air through the cylinder, and to remove 
any dust that may be in the sand. 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 325 

Screens. The material is introduced into the heater in about 
the proportions experience and tests show is desired but after 
being heated the material is elevated to a revolving screen where 
it. is separated into two or more sizes and deposited in the 
storage bins. The number of bins and the sizes into which the 
material is separated depends upon the character of the pavement 
and the degree of refinement desired in the mixture. For sheet- 
asphalt wearing surfaces two sizes are commonly used as follows : 
(a) passing a 10-mesh screen and (6) retained on a 10-mesh screen 
and passing an 8-mesh screen. For asphaltic concrete of the 
Topeka type two sizes are commonly used, namely, stone 
passing a J^-in. screen and retained on a 10-mesh screen, and 
sand passing the 10-mesh screen. 

For asphaltic concrete of the Bitulithic type a larger number 
of sizes is desirable for satisfactory grading and the following are 
recommended: The minimum screen opening to be Jio m - an d 
the maximum not greater than 13^ in. The difference in the width 
of openings of the portion of the screen having openings less than 
% in. in size shall not exceed Y in., and in the sections having 
openings larger than J/ in. the difference in size between suc- 
cessive sections shall not exceed J^ in. The following sizes of 
.opening prove satisfactory: Jfo~ m -? Ji~ m -> M~ m -> /4- m -> l-in-> 
1^-in. 

Storage Bins. 1 The hot sand and stone will retain heat for 
some hours and to prevent delays and to facilitate the work 
storage bins are provided for the hot aggregates. These storage 
bins are below the screen, the several compartments of the bins 
corresponding to the several sizes of the screen. The problem 
that presents itself in connection with the storage of aggregates 
is how to prevent segregation of sizes either when the material 
is deposited in the bins or when it is drawn off from them. If 
the materials fall directly into the bin from the screens, the fine 
material will fall on one side and the coarse on the other. A 
hopper should be provided into which they will fall and flow to a 
central spout and thence to the bin. The bin should be conical, 
at least have a conical bottom, and should be kept fairly well 
filled up during the working period so that the weight will keep 
the entire mass down to the gate. If the bin gets low the sand 
is likely to draw down in the middle of the bin, and the coarse 

l See also "The Modern Asphalt Pavement" by Clifford Richardson. 



326 CONSTRUCTION OF ROADS AND PAVEMENTS 

particles will inevitably run down into the hollow thus formed and 
be drawn out first. Most troubles of this sort are avoided if the 
bin is worked at least half full. 

Asphalt Cement Melting Tank. The melting tanks are heated 
by wood, coal, or with steam coils. The tank is rectangular- 
shaped with a cylindrical bottom, the capacity varying from 
2 to 50 tons. Regardless of the method of heating used perfo- 
rated steam or air pipes are placed in the tank so that a jet of 
steam or air may be blown through the asphalt cement to stir 
it. In the larger plants steam heating and agitation are used, 
but in many of the smaller plants the coal or wood furnace is 
used for heating and air for stirring. 

Mixers. For sheet asphalt and asphaltic concrete the twin- 
pug type of mixer is used, the only difference between the 
machines for the two kinds of mixture being that the one used for 
asphaltic concrete has fewer and shorter paddles than are used 
for the surface mixture. The mixer is often steam-jacketed so 
that it can be kept hot during the mixing. It is placed on a 
platform which is high enough to allow the wagons to drive under- 
neath. The batch is dropped into the wagon through a door in 
the bottom of the mixer. 

Proportioning. The basis of the proportioning is the "box" 
or 9 cu. ft. which is the amount commonly mixed at one batch. 
The mixture is set for the proper weight of each kind of material 
for this quantity, and all proportions are determined by actual 
weighing. The Bitulithic plants are equipped with a multi- 
beam scale for convenience in weighing the several portions that 
make up the mixture. 

Rakes. A special type of stout rake with straight tynes is 
used for spreading the mixtures on the street. 

Smoothing Irons, Tampers. These are of special design with 
metal handles so that they can be used hot. 

Rollers. The 2- to 4-ton tandem roller is used for the initial 
compression and the 8- or 10-ton tandem roller for the final 
rolling, except that the three-wheeled or macadam type is 
generally recommended for the Bitulithic pavement. 

Asphalt Wagons. The wagons used for hauling the surface 
mixture may be the ordinary 2-yd. dump bottom wagon or any 
similar wagon that is quick dumping and has a tight closing 
bottom. The motor truck with or without trailer is also widely 
used for the purpose. 



SHEET-ASPHALT AND ASPHALT 1C CONCRETE 327 
EXAMPLES OF GOOD PRACTICE 

CHICAGO 1 
Sheet-asphalt Pavement 

Sand. The sand shall be hard-grained and moderately sharp. 
It shall be free from loam or any other foreign material, and shall 
be so graded as to produce, in the finished surface mixture, the 
mesh requirements elsewhere herein specified. It shall contain 
not to exceed six (6) per cent, of sand that will pass a 200-mesh 
sieve. 

Binder Stone. The stone or gravel to be used for asphaltic 
concrete binder shall be hard and durable, free from all foreign 
substances, and of varying sizes from one (1) inch downward. 

Asphaltic-concrete Binder. The asphaltic-concrete binder 
shall be prepared as follows: 

The binder stone and sand shall be heated to from two hundred 
(200) degrees to three hundred and twenty-five (325) degrees 
F., measured off separately at the mixer and then mixed with 
asphaltic cement, in such proportions that the resulting aggregate 
will contain, by weight, material passing a 10-mesh screen 
between twenty-five (25) arid thirty-five (35) per cent, and 
bitumen in quantity from five (5) to eight (8) per cent, of the 
entire mixture. The proportion of asphaltic cement shall at 
all times be determined by actual weighing with scales attached 
to the asphaltic-cement bucket. The concrete thus prepared 
shall be a compact mass containing a minimum of voids. With 
the permission of the Board of Local Improvements in lieu of 
the above, where available, old asphaltic surface paving mixtures 
may be used in combination with the binder stone, such mixtures 
having been previously crushed or disintegrated and augmented 
with fresh asphaltic cement, so that when combined the resulting 
concrete shall form an equally compact mass and correspond as to 
aggregate passing a 10-mesh screen, and its contained percentages 
of bitumen with the requirements for the mixture previously 
specified. 

NOTE. Inasmuch as the percentage of bitumen in the as- 
phaltic-concrete binder will depend upon the grading of the ag- 
gregate, the proportions of the materials used in the above 
may be varied by the Board of Local Improvements, but only 
within the limits designated. 

1 From Specifications in use in 1916. 



328 CONSTRUCTION OF ROADS AND PAVEMENTS. 

The asphaltic-concrete binder shall be brought to the work in 
wagons, covered with canvas or other suitable material, and 
upon leaving the plant shall have a temperature of two hundred 
(200) degrees to three hundred and twenty-five (325) degrees F. 
It shall then be placed upon the street and raked to a uniform 
surface to such depth that, after being rolled and thoroughly 
compacted, it shall have a thickness of one and one-half (lj) 
inches. The surface after compression shall show at no place 
an excess of asphaltic cement, and any spots covering an area 
of one (1) square foot or more showing an excess of asphaltic 
cement shall be cut out and replaced with other material. 
Smaller spots may be dried by the use of stone dust and 
smoothers. Any asphaltic-concrete binder broken up during the 
process of laying must be removed and replaced with new 
material. 

Wearing Surface. The surface mixture shall consist of 

asphaltic cement (the desired filler) and sand, so 

proportioned that the mixture will contain average proportions 
by weight of the whole mixture as follows: 

Bitumen 1 1 . to 13 . 5 per cent. 

(Filler) passing a 200-mesh sieve 10 . to 15 . per cent. 

Sand passing an 80-mesh sieve 18 . to 36 . per cent. 

Sand passing a 40-mesh sieve 20 . to 50 . per cent. 

Sand passing a 10-mesh sieve 8 . to 25 . per cent. 

Sand passing a 4-mesh sieve to 10 . per cent. 

Sieves to be used in the order named. 

The item designated as " (filler) passing a 200- 
mesh sieve" within the limits named herein includes in addition 

to the (filler) fine sand passing a 200-mesh sieve 

not exceeding four and one-half (4J) per cent, of the total 
mixture, and such 200-mesh mineral dust naturally self-contained 
in the refined asphalt. 

The item designated as "Sand passing an 80-mesh sieve" 
within the limit named herein includes, in addition to sand pass- 
ing an 80-mesh material contained in the (filler) 

and such 80-mesh material naturally self-contained in the re- 
fined asphalt. 

The sand and the asphaltic cement shall be heated separately 
to about three hundred (300) degrees F. The maximum tem- 
perature of the sand at the mixer shall not be in excess of three 
hundred and seventy-five (375) degrees F. and the maximum 



PHEET-ASPHALT AND ASPHALTIC CONCRETE 329 

temperature of the asphaltic cement shall not exceed three 
hundred and thirty-five (335) degrees F. at the discharge pipe. 

The (filler) shall be mixed with the hot sand in 

the required proportions, and then these shall be mixed for at 
least 1 min. with the asphaltic cement at the required temperature 
and in the proper proportions in a suitable apparatus so as to 
effect a thoroughly homogeneous mixture. 

The proportion of asphaltic cement shall at all times be 
determined by actual weighing with scales attached to the as- 
phaltic cement bucket. 

The (filler) and sand must also be weighed unless 

a method of gaging approved by the Board of Local Improve- 
ments is used. 

If the Board of Local Improvements directs, the proportions 
of the materials in the surface mixture shall be changed within 
the above limits for any part or parts of this improvement. 

The contractor shall furnish every facility for the verification 
of all scales or measures. 

The surface mixture shall be hauled to the work in wagons 
provided with a canvas or other suitable cover. It shall leave 
the plant at a temperature between two hundred and fifty (250) 
and three hundred and thirty-five (335) degrees F., as suitable 
for the asphalt used. Upon arrival at the street it shall be 
dumped at such distance from the work that all of the mixture 
must be turned and distributed to the place where it is to be 
raked. It shall be spread while hot upon the asphaltic-concrete 
binder, which must be dry and free from foreign matter. The 
last load of the day shall be spread at least 1 hr. prior to the 
official time of sunset. The lowest permissible temperature of the 
surface mixture when spread, shall vary from two hundred and 
thirty (230) to two hundred and eighty (280) degrees F., accord- 
ing to the asphaltic cement used. After receiving its ultimate 
compression by rolling, it shall have a thickness of two (2) 
inches. The initial compression must be effected by means 
of a small roller, after which a small amount of hydraulic cement 
shall be swept over the surface. Final compression shall be 
effected by a roller of not less than two hundred (200) pounds 
per inch tread. The rate per hour of rolling with the heavier 
roller shall not exceed two hundred (200) square yards of 
surface. 



330 CONSTRUCTION OF ROADS AND PAVEMENTS 

ASPHALTIC CONCRETE FOR SURFACING 1 

Asphaltic concrete used for topping old macadam streets and 
roads in the outskirts of Chicago is made under city supervision 
in a railroad portable plant. It is of the Warren type, cost 
$15,000 and can turn out material to pave 2,500 sq. yd. of 2-in. 
top in a 9-hr. day. Topping old macadam roads can be done 
at 60 cts. per square yard. The estimated life, without repairs, 
is 5 years, and with reasonable repairs 20 years. Country 
roads have cost about 20 cts. per yard per year to maintain, and 
the condition is not satisfactory at that. 

Costs per square yard are: 89,123 sq. yd. of sheet asphalt, 
95 cts.; 30,440 sq. yd. on brick $1.06; 30,900 sq. yd. on granite, 
55 cts., and 376,960 sq. yd. on macadam, 20 cts. 

Methods of preparing old macadam roads for a 2-in. asphalt 
topping in Chicago differ somewhat in different localities. Where 
the existing surface is in good condition and has suitable line, 
grade and contour, the surface is swept thoroughly to remove all 
the loose particles and expose the rough stone. If any depres- 
sions exist they are filled with binder and tamped. In this way 
the existing road is made parallel to and 2 in. below the finished 
surface. Along the edges of the road care is taken to provide a 
good shoulder to hold the pavement in place. Where the soil 
is soft, stone is added and the shoulder thoroughly rolled. 

Where the old macadam is flat or depressed at the center 
the sides are picked up and the material moved to the center. 
Care is taken not to lower the sides so that less than 4 in. of stone 
exist in a firm condition. If additional material is required the 
street is scarified to a depth of 3 in. and material added, making 
the center at least 10 in. in depth and the sides 6 in. About 
2% in. is found sufficient for drainage from the crown to the 
edge. 

PERCENTAGE OF MIX 

The percentage of mix for the topping will average 6.5 bitumen; 
37.2 torpedo sand; 52.3 stone; and 4 filler. The aggregate is 
Portland cement, torpedo sand and crushed granite, ranging 
from Y to 1 in. in diameter and costing $2.25 per cubic yard. 
A mile of road is surfaced each week at a cost of 70 cts. per square 

1 Walter L. Leiniger, Superintendent of Streets, City of Chicago, in 
Engineering Record, Aug. 15, and Oct. 3, 1914. 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 331 

yard. At the plant the force consists of a foreman, chief drum 
man, kettle man, mixer man, 2 timekeepers and material men, 
25 laborers, 18 teams, 1 assistant chemist and 2 watchmen. The 
field force comprises 1 asphalt foreman, 2 rakers, 2 smoothers, 
2 tampers, 15 helpers, 2 watchmen and 2 roller engineers. These 
men produce and lay 2,500 sq. yd. of 2-in. top per day. 

BITUMINOUS CONCRETE PAVEMENT CONSTRUCTION 
IN WASHINGTON, D. C.i 

In composition this pavement is practically a sheet-asphalt 
pavement, the binder and top courses of which have been con- 
solidated into a single course by combining a sheet-asphalt 
surface mixture with a binder course composed of run-of-crusher 
stone, in such proportions that the surface mixture fills the voids 
in the stone. 

The proportions of coarse and fine aggregate for this concrete 
were fixed after a number of sieve tests of local sand and trap 
rock at about 2 parts by volume of stone to 1 of sand, to which 
is added about 5 per cent, of dust to supply the deficiency in 
fine material of the stone aggregate. 

The specifications for bituminous concrete surfacing provide 
for laying both on a concrete base, similar to that used for sheet 
asphalt, and on a broken-stone or gravel base. The ingredients 
consist of crushed trap rock devoid of dust and varying in size 
from 1 in. to screenings, sand, mineral dust and asphaltic cement. 
A hard-grained moderately sharp sand is used. Upon sifting at 
least 25 per cent, must be caught on a 20-mesh sieve and 5 per 
cent, pass an 80-mesh sieve. A deficiency in fine sand may be 
corrected with mineral dust, which consists of any fine Portland 
cement or limestone dust at least 86 per cent, of which passes a 
100-mesh screen and the whole of which passes a 30-mesh. A 
refined fluxed asphalt is used, free from water and having a 
penetration of from 40 to 70 when tested in a Dow machine at 
77F. with No. 2 needle, 100 grams for 5 sec. The penetration 
and percentage of cement used is varied to fit conditions of traffic 
and variation in material but in no case is more than 7 to 9 per 
cent, of bitumen soluble in carbon disulphide used. 

The paving mixture is prepared in an asphalt paving plant. 
The sand and stone after being heated in separate dryers to about 

1 Capt. Mark Brooke in Engineering and Contracting, Apr. 7, 1915. 



332 CONSTRUCTION OF ROADS AND PAVEMENTS 

300F. are conveyed to the box used for mixing binder stone 
where the hot asphaltic cement and cold limestone dust, are 
added and the whole thoroughly mixed. The method of laying 
is described in the specifications as follows: 

The mixture will be hauled while hot to the site of the work and 
shall be covered until deposited on the street. The temperature 
at the time of dumping shall not be less than 220. The hot 
mixture shall be evenly spread with hot tools upon the base to 
such a thickness as will make a layer 2 in. thick after rolling. 
It shall then be rolled with a steam roller weighing not less than 
1 ton per foot of tread of roller, until no further compression 
occurs. After the rolling of the asphaltic-concrete wearing sur- 
face has been completed there shall be spread over such surface 
a thin coating of asphaltic cement as used in surfacing not to 
exceed on an average J^ g&L to the square yard, of such con- 
sistency as shall be approved, which shall be thoroughly brushed 
into the wearing surface so as to fill all voids and smooth out any 
minor unevenness of the said surface. There shall then be spread 
over and rolled into this flush coat a thin layer of trap screenings 
so far as practical, devoid of dust, in size from 38 in. down, to 
secure a gritty, non-slippery surface. 

This material, particularly if there is a slight excess of cement, 
tends to separate during the haul to the street, the fine material 
and cement working to the bottom of the wagon. 

In cold weather it is essential that the material arrive on the 
street amply hot, as the slightest chill stiffens it and makes it 
very difficult to spread and roll. For these reasons, aside from 
other considerations, motor trucks have been found to be better 
than carts or wagons for the hot haul. 

Some difficulty has been experienced in applying the flush coat 
in sufficient quantity to seal the surface without causing the 
formation of a mat which would cover up the stone aggregate 
and produce a slippery surface. 

The specification originally provided for the application of a 
thin coat of hot asphaltic cement. On several streets the hot 
cement used in the paving mixture was tried. It was poured 
from pots, broomed and squeegeed and a small hand spreader was 
used, but notwithstanding the care taken to get it on thin it 
was found impossible to prevent the formation of a mat which 
became very slippery in spite of the application of the stone 
chips. On one street this surface was so objectionable that it has 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 333 



been necessary to sand it each summer. The effect of the coarse 
sand and the partial wearing off of the mat and consequent 
exposure of the stone are gradually curing this slipperiness. 

After this experience the hot application was abandoned for 
an asphaltic emulsion which is applied cold, broomed in and then 
covered with chips. After the evaporation of the water and 
emulsifiant (ammonia) a light coating of asphalt is left. This 
method gives the rough mosaic surface which is desired but it is 
questionable if there is sufficient body of cement to bind the fine 
material and effectually seal the surface. 

It is believed it would be practicable to get a satisfactory flush 
coat by applying a lighter cement with a power distributor such 
as is used in macadam surface and penetration work and the 
engineer department intends to try this method. 

An apparent defect in this specification is the lack of any 
requirement as to grading of the stone. It is evident that the 
composition of the mixture might vary within wide limits. How- 
ever, from Table 25 showing the average of the tests of the mix- 
tures actually laid in five working seasons, it will be seen that the 
aggregate runs fairly uniformly. 

TABLE 25. AVERAGE GRADING, BITUMINOUS CONCRETE MIXTURES 
WASHINGTON, D. C., 1910-14 



Retained on square mesh 


1910 


1911 


1912 


1913 


1914 


1-in. mesh 


1.0 


0.0 


0.3 


0.0 


0.0 


%-in. mesh. . .... 


13.0 


20.2 


12.8 


5.0 


0.0 


2-mesh. 


30 


18 


18.7 


13.7 


17.6 


4-mesh 


19.2 


21.2 


26.3 


19.2 


25.2 


8-mesh 


2 6 


9.6 


9.5 


17.0 


14.5 


10-mesh 


3 


1 


1.3 


3.8 


2.8 


20-mesh 


1.3 


3.0 


4.9 


10.2 


8.0 


40-mesh. 


10 7 


6 6 


8.0 


13.0 


12.3 


60-mesh 


10.7 


7.0 


7.0 


6.1 


5.8 


80-mesh. 


6.2 


3.6 


3.5 


3.2 


3.2 


100-mesh 


1 6 


1 7 


1 2 


1.0 


0.8 


Passing 100-mesh 


3.2 


7.8 


6.3 


8.0 


8.8 


Spec. gr. stone. . . 


2.85 




2.93 


2.97 


2.86 


Spec. gr. sand 
Per cent, of voids in aggregate. . . 
Per cent. bit. sol. in CSa (not in- 
cluding flush coat) 


2.69 
26.4 

7 1 


6 8 


2.70 
21.98 

6 9 


2.70 
20.76 

7.35 


2.63 
21.39 

6.80 


Average penetration of asphaltic 
cement . . 


60.0 


60.0 


60.0 


60.0 


60.0 















334 CONSTRUCTION OF ROADS AND PAVEMENTS 

The sand is tested before use for compliance with the specifica- 
tion for that material, but no attempt is made at selection, or 
separation or grading of any sort of the run-of-crusher stone. 
The material below the 8-mesh is fairly uniform due no doubt to 
the sand entering into this part of the mixture. The increase 
in material passing 100-mesh from 1910 to 1911 is due to a change 
in specifications increasing the amount of mineral dust. In the 
1910 mixture only about 1 per cent, of dust was added, whereas 
not less than 5 per cent, has been used since. 

The stone used up to this year was a trap from a quarry near 
the Potomac about 30 miles above Washington. The 1914 stone 
is a differnet stone from a quarry on the Susquehanna near 
Havre de Grace, Maryland. 

The average price of this pavement laid to a thickness of 2 in. 
after compression, including a 6-in. gravel concrete base and 
grading for same, has been $1.79, which includes a 5-year guar- 
antee. The average cost of macadam base has been $0.345 
making cost of bituminous concrete pavement on macadam 
base $1.31. 

The average price of standard sheet asphalt with base during 
the same period was $1.84 and exclusive of base $1.06, with same 
guarantee. 

Bituminous concrete surfacing has been laid on both concrete 
and macadam base, the latter usually consisting of an old 
macadam roadway shaped to a proper cross-section. The use 
of a well-bonded macadam roadway as a base has not in practice 
effected as great a saving as might have been expected as the 
work of scarifying, building up on the quarters and rolling 
necessary to bring the macadam to a cross-section 2 in. below 
and exactly parallel to the finished surface has always proved 
much greater than was anticipated. Moreover, this shaping 
of the old roadway very largely destroys its bond, one of the 
valuable assets of the old pavement. For these reasons the use 
of macadam base has been discontinued save in exceptional 
cases. 

It is too soon to determine the ultimate economy of this 
pavement or its relative value as compared with sheet asphalt 
with which it is in competition in Washington. Its first cost is 
slightly less than that of sheet asphalt; it apparently requires less 
traffic to keep it in good condition, and will carry heavier traffic 
than sheet asphalt. It has been notably free from the defect 



SHEET-ASPHALT AND ASPHALTIC CONCRETE 335 

of creeping or rolling which has become more significant since 
the advent of fast-moving motor traffic, and it has an ideal surface 
for horse traffic. 

On the other hand it is not so dense as a sheet-asphalt top 
mixture and may not prove as durable. 

As far as can be judged from the limited experience of our five 
seasons' work, this pavement will prove satisfactory and its 
use will be continued on an increasing scale. 



COST OF ASPHALT REPAIRS IN DAYTON 1 

During a test of a new portable asphalt repair plant at Dayton, 
Ohio, from Dec. 1 to 8, inclusive, the costs ranged from 36 to 
51 cts. per square yard. Old materials were used in a Smith 
mixer. The following table of costs was obtained by Mr. C. O. 
Dustin, staff engineer, of the Bureau of Municipal Research, 
Dr. L. D. Upson, Director: 

TABLE 26. OPERATION STATISTICS AND UNIT COSTS WITH OLD ASPHALT 



Date 


Hours 
plant 
run 


Number 
batches 
mixed 


Minutes 
required 
per batch 


Cubic feet 
mixed 


Square yard 
laid 


Total 
cost 


Cost per 
square 
yard 


1 


5 


14 


21.0 


210 


84.0 


$32.60 


$0.39 


2 


9 


32 


17.0 


480 


194.0 


70.35 


0.36 


3 


9 


39 


14.0 


624 


197.5 


84.10 


0.43 


4 


9 


40 


13.5 


640 


203.0 


88.10 


0.43 


5 


6 


29 


14.0 


464 


115.5 


57.30 


0.51 


6 


9 


34 


15.0 


544 


173.0 


69.40 


0.40 


8 


9 


21 


22.0 


384 


123.0 


59.35 


0.48 


Total 


56 


212 




3,346 


1 086 


461 20 




Average . 






16 


557 






042 



















These costs, calculated to a 2-in. equivalent, would be about 
one-half of the above figures, as most patches were 4 in. thick. 

Mr. Dustin reports that it was impossible to obtain a definite 
proportion of aggregate and bitumen when remelting old material, 
but analysis of early runs indicated 17 per cent, bitumen. As 
the city specifies 10 to 13 per cent, bitumen, the amount of new 
asphaltic cement was reduced somewhat. He is of the opinion 
that the costs of laying asphalt using old material can be greatly 

1 Engineering Record, Jan. 24, 1914. 



336 CONSTRUCTION OF ROADS AND PAVEMENTS 

reduced in the summer season with a more efficiently organized 
crew. 

The unit costs per square yard of paving actually covered 
were: Coal, 2.5 cts.; asphalt (standard paving), 3.4 cts.; crushed 
stone (used 3 days only), 0.7 cts.; marble dust, 0.2 cts.; total for 
materials 6.8 cts.; plant and truck, 10.8 cts.; laying 20.3 cts.; 
undistributed, 4.8 cts.; total labor 35.7 cts.; grand total, 42.5 cts. 



CHAPTER XVII 

SELECTION OF TYPE OF SURFACE FOR RURAL 
HIGHWAYS 

The choice of the type of surface for the improvement of a 
public highway requires an analysis of many factors that have 
a bearing on the ability of the type of construction selected to 
meet the needs of the community in which it is to be built. Some 
of these factors are not susceptible of exact tabulation, and 
their bearing on the problem is a matter in which the only guide 
is the engineer's judgment and experience. Others have an 
effect that has been definitely established by experience and 
observation, so that their relation to the design is well under- 
stood and is generally recognized. The following are the more 
important factors, and those encountered in the ordinary com- 
munity, but others peculiar to individual roads sometimes 
modify the design in an important manner. 

THE TRAFFIC CENSUS 

The facts in regard to traffic are sometimes sufficiently well 
understood from general observation to eliminate the necessity 
for taking the traffic census. Such general data cannot be 
depended upon, and where costly permanent improvement of 
important highways is to be undertaken, the traffic census is a 
preliminary that should never be omitted. Its value is too often 
underrated and, in general, is little understood by American 
engineers, but it has had long and widespread use in England 
and in Continental Europe. 

Not only is the traffic census invaluable as an aid to the 
selection of the type of surface and the design, but if continued 
after a road is improved it gives valuable information as to rate 
of wear and maintenance costs per ton of traffic. Without 
these, scientific and economical administration is impossible. 

Present Traffic. The gross amount of traffic is one of the 

first things to be determined. This is primarily of importance 

as affecting the width of the road, but also has a bearing on the 

kind of surface to be provided, although other factors are also 

22 337 



338 CONSTRUCTION OF ROADS AND PAVEMENTS 

of significance in that respect. It is undesirable for a vehicle 
to turn off a hard surface too frequently in passing other vehicles. 
Probably with earth side roads this should not occur oftener 
than about five times per mile, and if the amount of traffic is 
such that the average number of passings per mile exceeds five, 
the road should be provided with some reasonably stable type 
of side road for the vehicle to turn out on. If the average number 
of passings exceeds about ten per mile for each vehicle using the 
road, then the side road will receive so much traffic that it must 
be about as well constructed as the main trackway, or, in other 
words, the main trackway should be wide enough to permit two 
vehicles to pass and still remain on it. The amount of passing 
can only be determined after the number and character of the 
vehicles using the road has been ascertained together with the dis- 
tribution of the traffic during the day. 

Kinds of Traffic. The kinds of vehicles and the weight of the 
individual loads have a direct bearing on the type and thickness 
of the surface that will be required. If the traffic consists of 
miscellaneous hauling of farm products and of light vehicles and 
automobiles for pleasure driving such as may be encountered in 
a rural community, that is a condition which presents a definite 
problem in highway design. In other instances the traffic may 
include in addition to this miscellaneous traffic, many heavj r 
horse-drawn trucks with loads ranging up to 6 tons and motor 
trucks with loads of 8 to 10 tons. The problem thus presented 
is also definite but requires a different design from the one first 
described. These illustrations are two out of a large number 
of sets of conditions that are encountered, and emphasize the 
importance of learning by investigation just what are the 
requirements before deciding upon the design of the surface. 

Peculiarities of Traffic. On many roads there are peculiarities 
of traffic that affect the choice of type very materially. The 
traffic is much heavier at certain times of the day or at certain 
seasons of the year than at other times in some communities. 
Not infrequently the travel on rural highways is nearly all 
toward town in the morning and away from town in the after- 
noon, and, although a great many vehicles might use the road 
each day, a single-track surface would suffice because of this 
peculiarity. Roads used for pleasure driving will have heavy 
traffic in the summer, especially at week ends, which will not show 
up in a traffic census taken in the winter or spring. This must be 



SELECTION OF TYPE OF SURFACE 339 

taken into account and the census must be planned so as to bring 
out any peculiarities that may exist. 

The Traffic Census. All of these facts in regard to present 
traffic must be determined as the first step in the choice of the 
type of road surface to build. Some of them are at once apparent 
to an experienced engineer who makes a careful inspection of the 
road, and some can only be determined by taking a traffic census. 

The traffic census to have the greatest accuracy should be 
taken by an experienced observer, but very good results can often 
be obtained by employing a resident convenient to the road if 
a suitable form is furnished for his use, even though he is inex- 
perienced. The form can be so clear and so easily filled in that 
few errors are probable. Since the traffic is apt to vary at dif- 
ferent hours of the day, on different days of the week and during 
different seasons of the year, the traffic census ought to be taken 
for a year if a complete record is desired. Records need not be 
made daily during this period, but may be taken for a few days 
at a time at intervals throughout the year. It is conceded that 
for important roads the traffic census should always be taken for 
a considerable period prior to deciding on the design for the road. 
On roads of lesser importance the information that would be 
given by the traffic census may be obtained as nearly as possible by 
expert inspection, but considerable care and judgment are neces- 
sary for such inspection work, if the results are to be of any value. 

Present traffic on a highway is not necessarily an indication of 
the amount that will use the road when it has been improved. 
It does serve as a basis for making a scientific estimate of the 
traffic that will use the road during its probable life, and that is 
the great value of the traffic census from the standpoint of design. 
It does have a distinct additional value as basis for the compari- 
son of roads actually in service and as a check on the accuracy of 
the assumptions made when the road was designed. For these 
latter purposes the census must extend over a series of years. 

Traffic Zones. In order to estimate the probable increase 
in traffic, it is desirable to ascertain as nearly as may be the extent 
of the territory that will be served by an improved road. It is 
known that when a good road is built out from a town, the general 
effect is to decrease the apparent distance from any point in the 
territory served by the road to the town, and consequently the 
territory tributary to the town is increased. The amount of the 
increase will depend upon many factors, such as the character of 



340 CONSTRUCTION OF ROADS AND PAVEMENTS 

agricultural activities, the topography, the road-building activi- 
ties in the vicinity of nearby towns and the market facilities of 
those towns. All of these when analyzed make the mapping of 
traffic zones possible as a preliminary to highway design. The 
traffic zone is usually understood to be the area of the rural com- 
munity that will be served by a main highway and its branches. 
All of the traffic originating in the zone is expected under normal 
conditions to use the improved highways of the zone for business 
purposes and to a large extent for pleasure driving. Near the 
market center from which the roads radiate, the territory in the 
zone will be confined to a narrow strip along each side of the 
road. Farther out from the city the road and its branches will 
serve a larger area so that the outline of the zone usually is the 
familiar balloon shape. 

Traffic zones will change with the extension of the road or 
with the extension of roads from nearby cities. They serve as 
a valuable guide in the selection of the type of surface needed and 
in estimating the increase in traffic to be provided for. The 
traffic zone also indicates the adequacy of the proposed system 
of main roads, by showing the extent of the territory served and 
the convenience of the proposed system to the residents of the 
outlying parts of the district. 

The statistics relative to traffic will in the ordinary community 
inadequately represent the conditions to which an improved road 
will be subjected within a few years after it is opened to public 
use. Experience shows that when a road is improved the travel 
on it immediately becomes much larger than it was before. Ulti- 
mately, when all the main roads in the community have been 
improved, the travel will be equalized, but in the meantime the 
first sections built will have been subjected to much greater 
traffic than would be shown by a traffic census taken before the 
roads were improved. 

ANALYSIS OF THE TRAFFIC CENSUS 

The object of the traffic census has been set forth, and it now 
becomes pertinent to note how the traffic census is taken and the 
analysis by which the various deductions are obtained from the 
tabulated census data. 

The width of road is dependent upon the gross amount of 
traffic that will probably use the road, or the frequency with 
which vehicles must turn out in passing. Knowing the number 



SELECTION OF TYPE OF SURFACE 



341 



of vehicles of each class and the probable average speed of travel, 
it is easy to compute the average number of passings per mile. 
If this number exceeds five and is less than ten, the side road 
probably should be of fairly substantial material so as to sustain 
this passing. If the number of passings per mile exceeds about 
ten, the road should doubtless be double-track width. 

The type of surface is dependent not only on the amount of the 
traffic but the character and weight of the individual loads. In 
the last analysis the two important factors are total number of 
vehicles of each class and the load on the pavement per foot or 
yard of width or some similar designation that will have the 
same significance. 

Various methods of taking the traffic census are employed, and 
forms convenient for recording the number of vehicles are 
prepared. These differ in detail and in the classification of the 
vehicles. The following examples serve to illustrate a few of the 
methods. 



THE COMMONWEALTH MASSACHUSETTS 

IteousETO HIGHWAY COMMISSION 

TRAFFIC RECORD 
1912 



STATION No. ._ 



TOWN-CITY 

DATE 

LOCATION STATIOM. 



(AT OR NEAR STA.. t .-,. . .,.. M.M.C NOTATION ) 



KINO or VEHICLE 


7AM. 
9 A*M 


9 A.M 
I| T A M 


II A.M. 
1 ^M 


p b M - 

3PM 


3PM. 
5P.M. 


5 T f O M 

7PM. 


7 T R J M - 

9 RM 


TOTALS 


SINGLE HWw^Si 


r 


r 


r 


r 


r 


r 


r 








SINGLE HOR5EJ V H TLE 


r 


r 


r 


r 


r 


r 


r 








TWO-MORE HOttE5J^ 


r 


r 


r 


r 


r 


r 


r 








TfrMKNOHBJMMu 


r 


r 


r 


r 


r 


r 


r 








AUTOMOBILE JRUNASWT 


r 


r 


r 


r 


r 


r 


r 








AUTOMOBILE JSSST 


r 


r 


r 


r 


r 


r 


r 








MOTOR JJJSJSJ,, 


r 


r 


r 


r 


r 


r 


r 








TOTALS 






















WEATHER CONDITIONS 






















OBSERVER Wiu. NQT 



Form used by Massachusetts Highway Commissions. 



342 CONSTRUCTION OF ROADS AND PAVEMENTS 
FORM USED BY MILWAUKEE COUNTY, WISCONSIN 





12-1 a.m. 


1-2 a.m. 


2-3 a.m. 


etc. 


Touring cars 










Roadsters and runabouts 










Auto trucks 
Motorcycles and bicycles 
Single-horse vehicle 
Light team .. .... 










Heavy team 










Pedestrians on walk or road 











This information is variously tabulated for purposes of 
comparison but such tabulation must show weight as well as 
quantity and the following are examples employed for the 
purpose : 



TRAFFIC CENSUS FORM RECOMMENDED BY SPECIAL COMMITTEE A. S. C. E. 



Horse-drawn vehicles 


Number 
empty 


Number 
loaded 


Est. max. 
load per 
inch of 
width of 
tire in Ib. 


Passenger 
vehicles 


One-horse vehicles 










Two-horse vehicles 
Three-horse vehicles 
Four-horse vehicles . . 










Five-horse vehicles 










Six or more horse vehicles 

Motor-vehicle traffic 

Motorcycles 










]Motor runabouts .... 










Motor touring cars (4 or 5 seats) . . 
Motor touring cars (6 or 7 seats) . . 
Motor wagons or drays 











It is exceedingly important to use the proper factors in arriv- 
ing at the weights of the various kinds of vehicles and tables 
27 and 28 show practice in England and in the United States. 



SELECTION OF TYPE OF SURFACE 



343 



MASSACHUSETTS HIGHWAY COMMISSION RECORDS. BOSTON SOUTH SHORE 
ROAD, STATION No. 403, WIDTH 32 FT. 



Motor vehicles 



Average 

number per 

day 



Assumed 
average, 
weight 
in tons 



Total tons 
per yard 
of width, 
per day 



Runabouts 114.0 1.43 15.3 

Touring cars 467.0 2.23 97.6 

Trucks 38 . 5 6 . 25 22 . 6 

Horse-drawn vehicles 

Light vehicles, one-horse 45 . . 36 1.5 

Heavy vehicles, one-horse 216 .5 1.12 22 . 7 

Light vehicles, two or more horses . . 0.5 . 54 

Heavy vehicles, two or more horses . 104 .5 2 . 46 24 . 1 

TABLE 27. UNITED STATES OFFICE OF PUBLIC ROADS CATEGORIES 

Tons 

1. Loaded one-horse wagon . 88 

2. Unloaded one-horse wagon . 28 

3. Loaded two-horse wagon 1 . 57 

4. Unloaded two-horse wagon . 47 

5. Loaded four-horse wagon 3 . 88 

6. Unloaded four-horse wagon (gears) . 54 

7. One-horse pleasure vehicle . 28 

8. Two-horse pleasure vehicle . 47 

9. Rubber-tired horse vehicle 0. 28 

10. Saddle horse . 50 

11. Motorcycle 0.20 

12. Excessively heavy vehicle 3 . 94 

13. Motor runabout 1 . 68 

14. Motor touring car 2 . 00 

15. Loaded motor dray 2 . 43 

16. Unloaded motor dray 1 . 23 

(Draught horses) 0. 50 

TABLE 28. ENGLISH ROAD BOARD CATEGORIES 

Tons 

1. Heavy vehicle, one-horse 1 . 25 

2. Light vehicle, one-horse . 40 

3. Heavy vehicle, two-horse (or more) 2. 50 

4. Light vehicle, two-horse . 60 

5. Horse lead or driven . 50 

6. Motorcycles 0.13 

7. Omnibuses, two or more horses 3. 00 

8. Motor cars 1 . 60 

9. Motor van, covered 2 . 50 

10. Horses, drawing vehicles 0. 50 



344 CONSTRUCTION OF ROADS AND PAVEMENTS 

Having obtained the traffic information and made suitable 
allowances for the probable increase, the type of surface necessary 
is to be selected in accordance therewith. No great amount of 
data is available for use in making the selection, but the follow- 
ing table is probably one of the best that has been prepared: 



TABLE 29. AVERAGE DAILY TRAFFIC LIMITS IN MASSACHUSETTS 

Table showing results of observations of traffic on different types of road surfaces in 
Massachusetts. Standard road, 15 ft. in width; gravel or waterbound macadam, 5 or 6 
ins. in thickness, with adequate drainage and proper foundation, with 3 ft. gravel shoulder 
on each side. 



Type of surface 


Light 
teams, 
carriages, 
wagons 


Heavy 
teams, 
one-horse 


Heavy 
teams, 
two or 
more 
horses 


Automobiles 


A good gravel road will wear reasonably well 
and be economical with 


50-75 


25-30 


10-15 


50 to 75 












Needs to be oiled with 


50-75 


25-30 


10-15 


Over 75 












Oiled gravel, fairly good, heavy cold oil, J> 
gal. to the sq. yd. applied annually with . . . 


75-100 


30-50 


20 


500 to 700 
or more 


Waterbound macadam will stand with .... 


175-200 


175-200 


60-80 


Not over 50 










at high speed 


Cold oil or tar will prove serviceable on such 


175-200 


175-200 


60-80 


50-500 












Macadam will then stand, but the stone wears, 
of course, with 


175-200 


175-200 


60-80 


500 or more 












Waterbound macadam with hot asphaltic oil 


100-150 


50-75 


25-30 


1 , 500 and 










more with 
fewer teams 










50 trucks 












But will crumble and perhaps fail with over. . 
(On narrow tires, ice, farm and wood teams, 
etc.) 


150 


75 


30 




Waterbound macadam with a good surface 
coating of tar ( l /$ gal. to the sq. yd.) will 
stand with 


100-150 


50-75 


25-30 


1,500 or more 


(But requires to be recoated annually with J4 
gal. of tar per sq. yd.) 











It is assumed that all road surfaces are kept constantly patched, that before applying 
bitumen the road surface is cleaned and patched, and the bitumen covered with pea 
stone and sand or gravel and kept covered so that it never picks up. 



SELECTION OF TYPE OF SURFACE 



345 



til 



Is* 







II 



aaqtuna ajqX 



e-drawn 
hicles 



-Mt:.> 

^nao jaj 



jnoq 
aA jo 



J 



aaoui 
jo jnoj jo aaqran^ 



AV^ jo 



O^TXB jo 



sat88nq 



-JBO jo 



-3BM 



uondtjosap 
l(v jo sno 



-jasqo jo 



punoq 



ssss 



^ *O CD t* t* 



,H T}< 10 CO O 



00 cD CO O ^* 00 
T!< t> CC CQ O ^ 
O5 00 i-i "3 N 1-1 
*<X)CO 



I- ?! i- ^J X 



OON NCO 
OOO'* 
CO.-IM CC 



OOOOCOOOOOJ 




treet 
treet 
Water St. 
Water St. 
igan St. 
igan St. 



E. 
E. 



. 
Mich 
Mich 



346 CONSTRUCTION OF ROADS AND PAVEMENTS 



It is highly desirable to have at hand a tabulation showing 
the wearing value of the several types of pavement in terms of 
tons of traffic per yard of width, and the aim of the traffic census 
should be to adduce such data. 

The following table is such a tabulation : 

TABLE 32. TRAFFIC STATISTICS FROM SHEFFIELD, ENGLAND 



Type 


Traffic in tons 
per yard with 
per year 


Initial cost 


Probable life, 
years 


Cost per square 
yard per year 


6-in. granite block 


73,180 


$3.66 


27 


$0.15 


Redwood blocks 


44,983 


2.40 


14 


0.23 


Tar macadam No. 1.. . 


69,762 


0.66 


21 


0.12 


Tar macadam No. 2. . . 


35,939 


0.46 


21 


0.06 



TABLE 33. TRAFFIC STATISTICS FOR LIVERPOOL, ENGLAND 



Type 


Life 

in 
years 


Life tonnage 
per yard 
width 


Cost per 
square 
yard 


Total 
mainte- 
nance per 
square 
yard in- 
cluding 


Ton 

miles 
a yard 
width 
for 1 ct. 


Cost of 
mainte- 
nance per 
100 ton- 
miles 










interest 






6-in. granite block .... 


18 


9,432,000 


2.40 


0.175 


17 


0.06 


Soft wood 


.18 


3,672,000 


2.04 


0.15 


8 


0.13 


Pitch macadam 


11 


1,320,000 


0.72 


0.066 


10 


0.096 


Tar spray macadam . . 


2 


240,000 


0.24 


0.12 


5.7 


0.18 


Water-bound ma- 














cadam 


1 


120,000 


0.18 


0.18 


3.8 


0.264 

















OTHER FACTORS INFLUENCING SELECTION OF TYPE 

Increase in Traffic. It becomes highly important to estimate 
the probable increase in traffic when a road is improved. This 
increase may result from a diversion of traffic from other roads 
which are parallel or lead in the same general direction as the 
one to be improved. A study of such roads and the amount of 
traffic that may be diverted from them is a guide in determining 
the probable increase in traffic. This becomes very significant if 
a nearby parallel road is a logical through route between populous 
centers, because a detour of a few miles is not a serious deterrent 
to tourists who are traveling across country and they will usu- 
ally take the route that insures the greatest comfort and speed. 



SELECTION OF TYPE OF SURFACE 347 

The increase in traffic may come from new industries that are 
purposely located on the improved road. Such a development 
cannot ordinarily be foreseen and yet may prove to be a most 
important factor in the maintenance of the road. 

Another very important factor is the probable change in char- 
acter of traffic. It is assured that as the highways of a com- 
munity are improved, the transportation methods will undergo 
a change. Heavier loads will be hauled and in many instances 
motor vehicles will be substituted for horse-drawn. This is 
particularly true of the roads in the vicinity of the larger centers 
of population. It is doubtful if even the most visionary pre- 
dictions of these developments during a decade will be anywhere 
near up to the actual facts as time reveals them. 

Not only will traffic change due to new methods of transpor- 
tation, but new agricultural methods are sure to result. Dairy- 
ing, truck farming, and similar activities will be substituted for 
farming methods requiring less frequent use of the highways. 

Probably no factor has had so much bearing on the desire for 
road improvement as the development of the motor vehicle used 
for pleasure, and its use has just begun. Without doubt the 
automobile and fnotor truck will become much more widely used 
in the rural communities as time goes on, and the number of 
city-owned cars using the highways is also certain to increase 
enormously. This most important fact must be recognized in 
deciding upon the type of road. 

Provision for Maintenance. The provision for maintenance in 
the community where the road is to be built has a bearing on the 
type of road that is to be built. The maintenance work may be 
done under skilled supervision, but the unit of control may be 
so large that only seasonal maintenance can be expected, in which 
circumstance a type of road must be selected that will have 
reasonable life under such conditions. 

If the maintenance is under unskilled supervision, there are 
very few types of road that can be expected to remain in good 
condition for any length of time. The most durable type pos- 
sible to construct could be recommended in such circumstances, 
thus relying on the durability of the surface to obviate the 
necessity for maintenance except at long intervals. The other 
alternative would be to build the cheapest form of road, such as 
gravel, which can be repaired by an unskilled superintendent 
with fair results. 



348 CONSTRUCTION OF ROADS AND PAVEMENTS 

If a road is to be a part of a system which is regularly inspected 
and maintained under constant and skilled supervision, then the 
type of road may be selected without any limitations from the 
standpoint of maintenance methods. 

Local Materials. If local materials of any kind are available, 
that will be a factor to consider before choosing the type of road. 
The kind, quality, and cost of local materials relative to the 
same properties of shipped-in materials, will determine which is 
ultimately the most economical. If the local materials are of 
poor quality even though low in price, it will often pay to bring 
in more durable materials of another kind rather than to utilize 
the local materials and construct a road that will be expensive to 
maintain. 

Foundations. When the soil upon which the road is to be built 
affords a good foundation, no modification of the type will be 
made necessary by a consideration of this factor, but in those 
instances where poor foundation is encountered which cannot be 
corrected by drainage, a type of roadway must be selected that 
will distribute the load sufficiently to secure stability. Such 
foundations are encountered occasionally. 

The following table gives the results of some French experi- 
ments on the transmission of pressure through macadam to the 
subgrade. The test was made with a wheel load of 4 tons with 
a 5-in. tire. 



TABLE 34. SHOWING TRANSMISSION OF PRESSURE THROUGH MACADAM 

On macadam alone: 
Thickness of crust, inches ............. 1 . 97 3 . 94 5 . 91 7 . 87 11 . 81 

Pressure on subsoil, pounds per square 

inch ............................... 102.5047.7027.4017.40 9.10 

On T elf or d foundation alone: 
Foundation thickness, inches ....................... 5.91 7.81 11 .81 

Pressure on subsoil, pounds per square 

inch ....................... ..................... 56.00 37.40 20.70 

On combined foundation and macadam: 
With foundation thickness of, inches .......... 5.91 7. 87 9. 84 11. 81 

3.94 in. of stone, pressure on subsoil, 

pounds per square inch ..................... 19 . 30 14 . 70 12 . 60 10 . 20 

5.91 in. of stone, pressure on subsoil, 

pounds per square inch ..................... 13.2010.90 9.10 7.70 

7.87 in. of stone, pressure on subsoil, 

pounds per square inch ..................... 9.70 8.20 6.80 6.10 



SELECTION OF TYPE OF SURFACE 349 

"The pressure on the subsoil through a 12-in. bed of simple 
macadam is apparently the same as the pressure through a 6-in. 
bed of macadam laid over a 10-in. stone foundation. A good 
soil well drained will safely withstand a pressure of 30 Ib. per 
square inch. 

"It is considered that poor soil required at least a 12-in. 
macadam layer or its equivalent. 

"The pressure transmitted by well-constructed gravel will 
be about the same as with macadam of equal thickness. The 
pressure will be much more widely distributed by concrete 
monolithic foundations and will be relatively much less per square 
inch in consequence." 

Aesthetic Considerations. Some attention should be paid to 
the appearance of a highway, and when the road lies in thickly 
populated suburban territory, dusty, sticky or noisy surfaces 
should be eliminated when possible. Every effort should be 
made to preserve any natural beauty of the roadside and to 
encourage the growth of shrubs and harmless wayside grasses. 
Apparently the washings from none of the commonly used 
materials affect the plant life, but excessive dust is a menace to 
plant beauty, and is to a small extent detrimental to plant 
life. 

Making the Selection. The selection of the type of surface 
suitable for a known set of conditions involves a knowledge of 
the characteristics and the cost of the various types of surfaces 
and the materials necessary in their construction. These factors 
will be discussed in succeeding chapters. 

The financial considerations are purposely left for discussion 
in connection with the selection of type of pavement surface, 
since better data on the costs and length of useful life of types 
of pavements are available than on costs and useful life of the 
same surfaces when employed on rural highways. 



CHAPTER XVIII 
SELECTION OF TYPE OF PAVEMENT SURFACE 

The selection of the type of pavement involves the con- 
sideration of many factors that need not be taken into account in 
selecting the surface for a rural highway. Cost and durability, 
factors that are of such importance in selecting the type for rural 
highways, also weigh heavily in the selection of street paving, 
but many other things must be considered also. It is perhaps 
unfortunate that many cities and especially those having a 
population of 10,000 or less, select their pavements without 
having made any scientific study of the question, the result 
being that pavements entirely unsuited to conditions are con- 
stantly being constructed to the great loss of the property owners 
who pay for the improvement. This condition is occasioned by 
two commonly recognized weaknesses in our American system 
of administration of highway construction. 

First of all the administration is political rather than technical, 
with ever changing personnel, so that continuity of policy and 
systematic records of the service value and cost of maintenance 
of pavements have not been possible. 

In the second place American communities are developing 
with phenomenal rapidity so that conditions of traffic in the 
cities do not remain constant long enough to permit conclusions 
to be drawn without the most minute records and these have 
not been kept except in a very few cities. 

It is not at all agreed as to what qualities in a pavement 
should be considered as of most importance in any case. A 
great deal depends upon the individual making the selection, 
since some qualities weigh more heavily with one person than 
they do with another. The tendency, however, is toward an 
exact analysis, regardless of personal preferences. 

In general the problem of selection of the type of pavement 
resolves itself into a special study for each case, yet a great many 
streets have identical characteristics and a type suitable to one 
will be suitable for all. The following discussion of the char- 
acteristics of pavements will serve to indicate in a general way 
the factors that should be taken into account. 

350 



SELECTION OF TYPE OF PAVEMENT SURFACE 351 



Durability. Obviously the life of any type of pavement is 
dependent upon the class and amount of traffic to which the 
street is subjected, and the character of workmanship secured 
in its construction. There are not as yet any considerable exact 
data as to the wear-resisting properties of the various types of 
pavement, in terms of tons of traffic per foot of width or any 
similar unit. To be of value, such data should be susceptible 
of application to a type of pavement when the character of 







Maximum life reported 


Type of pavement 


No. of cities 
reporting 












Business street 


Residence street 


Sheet asphalt 


14 


15 years or more 






32 


10 to 14 years 






18 


5 to 9 years 






2 




25 years or more 




15 




20 to 24 years 




30 




15 to 19 years 




14 




12 to 14 years 




12 




10 to 11 years 


Brick 


3 


25 years or more 






14 


10 to 24 years 






34 


15 to 19 years 






17 


12 to 14 years 






20 


10 to 11 years 






10 


less than 10 






6 




30 years or more 




25 




25 to 29 years 




16 




20 to 24 years 




22 




15 to 19 years 




12 




10 to 14 years 


Wood block 


1 


30 years or more 






1 


21 to 25 years 






2 


16 to 20 years 






4 


11 to 15 years 






3 


10 or less 






2 




26 to 30 years 




1 




21 to 25 years 




4 




16 to 20 years 




1 




15 or less 


Bitulithic and tar 


4 


15 years or more 


10, 15 or more 


treated of various 


12 


10 to 14 years 


13, 10 to 14 years 


kinds 


6 


5 to 9 years 


5 less than 10. 




3 


less than 5 





352 CONSTRUCTION OF ROADS AND PAVEMENTS 

the materials, and the thoroughness with which the construction 
was carried out, were known. 

Illustrating the extreme variation of estimates of life of 
pavements in American cities the foregoing table is given. 

Slipperiness. This characteristic is distinguished from the 
condition of surface that gives a poor foothold for horses although 
the two characteristics often go together, and will be considered 
together in the comparisons made here. The condition of 
slipperiness is of significance to motor-driven traffic and is a 
characteristic of most sheet pavements, and of wood-block pave- 
ments and to some extent of stone-block pavements, when 
they are wet or frosty. Skidding and poor traction are the 
result of slipperiness and these introduce an element of danger 
into the use of pavements having this property. 

Character of Foothold for Horses. This property depends 
upon there being joints or some roughness to afford foothold. 
Sheet asphalt affords rather poor foothold when wet and the 
asphaltic concretes are much the same but more so when finished 
with the seal coat of asphaltic cement and stone chips than when 
finished without such a seal coat. Granite blocks wear to a 
polished and rounded surface and each block is slippery when 
wet but the joints between blocks serve to give shod horses a 
foothold. 

Appearance. In some locations the appearance of the pave- 
ment will be of no significance, in others it is desirable to have a 
pavement that will harmonize with the surroundings. Several 
factors combine in the appearance of the pavement such as 
color, reflection of light, the presence or absence of joints between 
the units of the surface, irregular cracks and the texture of the 
surface. 

Dust. Dust in appreciable quantities resulting from the wear 
on a pavement surface, is an accompaniment of excessive wear 
and is particularly a characteristic of macadam and gravel 
surfaces. It is undesirable for city pavements in any location. 

Sanitariness. This is a characteristic of minor importance since 
the types suitable for most city streets do not differ greatly in 
sanitary qualities. If the type is such that street liquids can 
penetrate the surface and produce odors and breed disease it is 
undesirable, but no high-class pavement is of such a nature. 

Susceptibility to Cleaning. This characteristic is important 
because it is a factor in the cost of keeping the street clean, and 



SELECTION OF TYPE OF PAVEMENT SURFACE 353 

because a type that is hard to clean or expensive to clean may be- 
come insanitary from neglect. The ease with which a street 
may be cleaned depends upon the texture of the surface and the 
number of joints or cracks in the surface. 

Noise. The degree of the noise of traffic on a street depends 
very largely on the character of the pavement. This frequently 
becomes an important factor in the selection of type. Under 
modern traffic conditions in our cities it is very desirable to 
eliminate noise as much as possible. Undoubtedly the con- 
struction of the less noisy pavements will become more and 
more general for congested city districts. 

Tractive Resistance. This factor is of minor importance 
since the high-grade pavements do not differ greatly in tractive 
resistance. Taken in connection with other characteristics it 
may be the determining factor in the selection in some instances, 
but in general it has little bearing on the selection of type. It 
would be a more significant factor if the amount of tractive re- 
sistance for the several types of pavements were more variable. 
No very reliable data on tractive resistance are available but the 
following composite table indicates average values. 

TABLE 35. AVERAGE TRACTIVE RESISTANCE OF SURFACES 1 

Surface Tractive force 

per ton 

Earth packed and dry 100 

Earth dusty 106 

Earth muddy 190 

Sand loose 320 

Gravel good 51 

Gravel loose 147 

Cinders well-packed 92 

Oiled road dry 61 

Oiled road wet 108 

Macadam very good , 38 

Macadam average 46 

Sheet asphalt 38 

Asphaltic concrete 40 

Vitrified brick new 56 

Wood block good 33 

Wood block poor 42 

Cobblestone 54 

Granite tramway 27 

Asphalt block 2 52 

Granite block 2 47 

1 Municipal Engineering, January, 1913. 

J Other source, not in original table. 



354 CONSTRUCTION OF ROADS AND PAVEMENTS 



Maintenance. Some types of low-cost pavement might prove 
economical under constant maintenance, but in many locations 
the continual disturbance of the street for making repairs and 
the interference with traffic make it undesirable to employ such 
surfaces. Ease of maintenance so that streets can be repaired 
quickly with little disturbance to traffic is desirable. 

The characteristics enumerated above are the ones of greatest 
significance in the selection of type for which purpose the relative 
values of the several characteristics is of more use than is an 
arbitrary valuation of each. The following table is a comparison 
of these characteristics for each of the common types of pave- 
ment assuming each to be in first-class condition. No. 1 indi- 
cates the first choice so far as each characteristic is concerned 
and higher number a lower degree of desirability. 

TABLE 36. COMPARISON OF PAVEMENTS 



Type 


Initial cost 


Durability 


Sanitary 
qualities 


1 


Slipperiness 


Dustlessness 


Appearance 


o-S 

1J 


Tractive 
resistance 


Ease of 
maintenance | 


Gravel 


1 


8 


6 


3 


2 


4 


8 


7 


7 


5 


Water-bound macadam 
Bituminous macadam. 
Portland-cement con- 
crete 


2 
3 

4 


9 

7 

6 


6 
3 

1 


3 
2 

5 


2 
5 

3 


4 
1 

2 


9 
3 

5 


7 
4 

2 


7 
4 

1 


4 
6 

4 


Stone-filled sheet as- 
phalt 


6 


5 


1 


1 


7 


1 


1 


1 


4 


? 


Sheet asphalt 


7 


5 


1 


1 


8 


1 


1 


1 


4 


?, 


Asphalt block. 


8 


5 


3 


1 


5 


1 


1 


1 


4 


5 


Vitrified brick; grouted 
Wood block 


9 
10 


4 
3 


4 


5 
1 


3 
4 


2 
1 


4 
2 


3 
1 


1 

2 


6 
1 


Sandstone block.. 


11 


2 


5 


4 


1 


3 


6 


5 


5 


4 


Granite block. 


12 


1 


5 


6 


3 


2 


7 


6 


6 


4 


Bituminous concrete . . 


5 


5 


1 


1 


6 


1 


1 


1 


3 


3 



FACTORS DETERMINING SELECTION 

The relative characteristics of pavements are of value only 
as a guide in selecting the type for known conditions. For some 
locations one characteristic is much more important than it is 
for other locations, and sometimes the selection must be made 
entirely on the basis of one or two desired characteristics. Just 
what characteristics will be the determining ones in the selection 



SELECTION OF TYPE OF PA VEMENT SURFACE 355 



will depend upon the traffic on the street and the location of the 
street and its surroundings. 

Location. The location in the city and the character of the 
abutting property are first to be considered. Obviously some 
things would be pertinent for a street in a congested business 
district that would not apply in a warehouse or freight-house 
district, although the traffic might be very much the same. In 
the first instance, appearance, absence of noise, sanitariness, 
ease of cleaning, and ease of repairing, would be important factors 
to consider in addition to freedom from slipperiness and dura- 
bility. In the latter case durability and freedom from slipperi- 
ness and ease of repairing would be the principal characteristics 
desired. Generally it would be unnecessary in either instance 
to consider initial cost. 

For a boulevard system, appearance, sanitariness, ease of 
cleaning, durability and freedom from noise would be considered. 

For high-class residence streets the factors considered for a 
boulevard system would be pertinent. 

For poorer residence districts initial cost would be the most 
important consideration. Noiselessness, sanitariness, ease of 
cleaning and dustlessness would also be important. 

Traffic. The traffic is always a very important consideration 
in selecting the type of pavement. The traffic census and its 
analysis is explained on page 330. 

TABLE 37. RELATIVE IMPORTANCE OF CHARACTERISTICS IN SELECTING 
PAVEMENTS FOR LARGER CITIES 



Order of 
importance 


Office and 
retail 
district 


Wholesale 
district 


Warehouse 
and dock or 
railroad 
district 


Boulevards, 
high-class 
residence 
district 


Poorer 
residence 
district 


1 


Noiselessness 1 


Durability 1 


Durability 1 


Noiselessness 1 


Cost 


2 


Appearance 


Noiselessness 


Slipperiness 


Appearance 


Durability 


3 


Durability 


Slipperiness 


Tractive re- 


Slipperiness 


Maintenance 








sistance 






4 


Sanitariness 


Ease of clean- 


Ease of 


Durability 


Dustlessness 






ing 


maintenance 






5 


Ease of clean- 


Sanitariness 


Cost 


Ease of clean- 


Sanitariness 




ing 






ing 




6 


Slipperiness 


Maintenance 


Ease of clean- 


Cost 


Ease of clean- 








ing 




ing 


7 


Maintenance 


Tractive re- 


Sanitariness 


Sanitariness 


Appearance 






sistance 








8 


Tractive re- 


Cost 


Noiselessness 


Maintenance 


Tractive re- 




sistance 








sistance 


9 


Cost 


Appearance 


Appearance 


Tractive re- 


Slipperiness 










sistance 





1 Other requirements eliminate the dusty types. 



356 CONSTRUCTION OF ROADS AND PAVEMENTS 



The foregoing table indicates in order the relative importance 
of the several characteristics for various classes of streets in the 
larger cities (50,000 population and upward). 

TABLE 38. RELATIVE IMPORTANCE OF CHARACTERISTICS IN SELECTION 
OF PAVEMENT FOR SMALLER CITIES 



Order of 
importance 


Business streets 


Boulevards and high- 
class residence streets 


Poorer residence 
streets 


1 


Durability 1 


Cost 1 


Cost 


2 


Cost 


Durability 


Durability 


3 


Noiselessness 


Noiselessness 


Dustlessness 


4 


Appearance 


Appearance 


Ease of repairs 


5 


Ease of repairs 


Ease of cleaning 


Ease of cleaning 


6 


Ease of cleaning 


Ease of repairs 


Sanitariness 


7 


Sanitariness 


Slipperiness 


Noiselessness 


8 


Slipperiness 


Sanitariness 


Appearance 


9 


Tractive resistance 


Tractiveresistance 


Slipperiness 



Apparently it is not possible to lay down exact rules for the 
selection of the type of pavement because of the great variety of 
conditions that are encountered. Several of the types are so 
nearly alike in their more important characteristics that the 
final selection may be based principally on cost which is a variable 
depending upon locality. 

Cost of Pavements. In discussing the cost of pavements it 
is customary for the layman to take only the initial cost into 
account, rather than the annual cost for the life of the pavement. 
This is wholly illogical because the ratio of the annual costs may 
be very different from the ratio of initial costs. It should not 
be inferred that the pavement having the lowest annual cost is 
always the best since the cost may be in part increased by the cost 
of keeping the particular type clean or it may be based on effec- 
tive and continual expert maintenance, a condition not found in 
many cities of less than 50,000 population. Obviously the initial 
cost, which is a variable in the cities of America, is a factor in the 
annual cost. The first cost can always be determined for any 
locality with a considerable degree of accuracy and the annual 
cost can then be estimated for comparative purposes. 

Annual Cost. Annual cost is a somewhat illusive item and one 
may easily be misled in calculating it. It should be assumed that 
the construction of a pavement represents a justifiable investment 

1 Other requirements eliminate the dusty types. 



SELECTION OF TYPE OF PAVEMENT SURFACE 357 

upon which the community will receive adequate returns. These 
returns are not susceptible of exact valuation, consisting in part 
of increased facility of communication, increased comfort of 
travel, better appearance, better returns from abutting property 
and similar clearly denned benefits. Having invested money in 
a pavement, these returns are accepted in lieu of interest on the 
money so invested, and since money is willingly so invested it 
may be assumed that the return is adequate to compensate for 
the loss of interest. As the pavement is used it must be main- 
tained and the cost thereof is a direct contribution for insuring 
that the pavement will have normal life. Interest should never 
be charged against a pavement in a comparison unless at the same 
time the direct return is considered and evaluated, which is 
impossible. A high interest charge would be necessary for a 
pavement of high initial cost but such a pavement might produce 
a high economic return because of low tractive resistance and 
general usefulness. The pavement of low initial cost would be 
charged with a low interest but might also represent a lower 
economic usefulness. Obviously it is exceedingly difficult to 
evaluate the relative usefulness and for that reason interest on 
initial investment will not be considered in the comparisons made 
herein. 

Economical Life. A pavement will eventually wear to a con- 
dition where it has ended its economical life. It must then either 
be rebuilt in entirety or be resurfaced. When it reaches this 
stage it will likely have some value left in it. It may have a 
foundation suitable for a new surface or the entire pavement may 
be covered with a new wearing surface. Some of the materials 
of the old surface may be utilized in the new. In determining 
the economical life of a pavement surface the two factors that 
need to be taken into account are the total cost of maintenance 
and the cost of renewal of the surface. The base, curbs and drain- 
age structures will ordinarily last so long a time that their cost 
is negligible in determining economical life, and has no bearing 
on comparison of surfaces. 

As the pavement ages, the cost of maintenance will increase 
and consequently the average cost of maintenance per year will 
gradually increase. The quotient obtained by dividing the initial 
cost of the surface by the years of life will decrease as the pave- 
ment increases in age. At first this quantity will be greater than 
the average annual cost of repairs so that the sum of the two 



358 CONSTRUCTION OF ROADS AND PAVEMENTS 



quantities will decrease from year to year. Eventually, how- 
ever, the average annual cost for repairs will increase more 
rapidly than cost divided by years of life will decrease and the sum 
of the two will begin to increase each year. Hence a pavement 
has reached its economical life when 

total cost of repairs to date + cost of renewal of surface 

years of life 
becomes a minimum. 

Residual Value. It has been previously pointed out that a 
pavement has some value left in it at the end of its economical 
life. The base may be used again, or the pavement as a whole 
may be used as a base for a new surface. Some of the materials 
of the worn-out surface may be usable. As an example, the old 
surface material from a sheet-asphalt pavement may be utilized 
for the binder course for the new pavement; old stone blocks 
may be redressed and reset. The residual value is the difference 
between the initial cost of the original pavement and the cost of 
a new surface that will be suitable for the pavement at the end 
of the economical life of the first surface. 

That the various factors entering into the annual cost and 
especially the wear of traffic are susceptible of fairly exact 
analysis has been demonstrated by British highway engineers 
and some excellent estimates have been made by American 
engineers and the following tables are inserted as indicating the 
kind of information that should be available when selecting the 
type of pavement. 

TABLE 39. SHOWING ESTIMATED ANNUAL COST OF PAVEMENTS 
FOR A PERIOD OF 40 YEARS I 



Type 


Life, years 


First cost 


Annual cost 
per square yard 


Macadam .... 




10 
20 
15 
10 
15 
10 


1.00 
3.25 
3.00 
2.65 
3.75 
1.25 


$0.179 
0.200 
0.240 
0.284 
0.292 
0.296 


Granite block, 
Brick, grout ft 
Bitulithic 


grout filler 
Her 




Wood blocks. . 
Tar macadam 









Engineering and Contracting, Dec. 20, 1911. 



SELECTION OF TYPE OF PAVEMENT SURFACE 359 



FOR A PERIOD OF 50 YEARS 1 



Type 


Initial cost 


Average cost 
per year for 
50 years 


Assumed life 


Granite block 


3 50 


27 


25 


Asphaltic 


2.00 


0.164 


18 


Wood block. 


3 50 


0.274 


20 


Brick 


2.25 


0.199 


15 











Recapitulation. The selection of types of pavement involves 
the following analysis, as has been already outlined. 

1. The selection of those types that possess physical charac- 
teristics suitable to the location. 

2. The elimination from pavements complying with the 
requirements (1) of those that obviously do not have the 
necessary durability. 

3. The elimination of pavement types surviving the selection 
in (2) for which suitable materials cannot be obtained at reason- 
able cost. 

4. An estimate of the economical life of each type remaining 
under consideration is then made. This estimate will be possible 
only after an analysis of traffic on the street to be paved. 

5. A financial comparison of the types remaining under 
consideration is made, based on the probable initial cost in the 
community and the following factors would enter into such a 
tabulation : 

Initial cost residual value 

economical life 

(6) Average annual cost of maintenance. 
(c) Average annual cost of cleaning. 

's Street Pavements and Paving Materials. 



CHAPTER XIX 
THE DESIGN OF PAVEMENTS 

The primary requirement for a pavement is that it serve as a 
trackway for vehicles, and this fact must be given first con- 
sideration in the design. The convenience and comfort of the 
user are to be insured regardless of other factors that enter for 
secondary consideration. 

Other things are often of importance and have considerable 
bearing on the design. These are drainage of abutting property, 
appearance, effect on value of abutting property, cost and 
problematical future traffic needs. 

Grades. The principles discussed as applying to the grades 
suitable for rural highways should apply equally to grades on 
streets, but topographical features often limit the application of 
those principles, and a few general rules have been gradually 
established to guide in the determination of the grade line for 
streets. 

I. The top of the curb on residence streets should always be 
lower than the lawns or parkings on either side. It is usually 
necessary to carry storm water and water resulting from melting 
snow from residence property to the pavement in order to dis- 
pose of it. This requires that the sidewalk shall slope slightly 
toward the curb and that the parking between the walk and curb 
line shall also slope toward the curb. 

Sometimes the drainage may be carried to a side street, or to 
an alley and thus permit a curb higher than the lawns alongside, 
and in other instances utility requires the street to be filled to a 
considerable height above the adjacent property for short dis- 
tances, but these are special cases. 

Occasions also arise where the curb is very much lower than 
the lawns of residences along the street. In such instances the 
sidewalk is ordinarily lowered so that a slope of about 34 in. 
per foot is obtained from the walk to the top of the curb. The 
lawn is then graded back so as to slope sharply to the walk, or a 
long sodded slope is constructed. In those cases where the 

360 



THE DESIGN OF PAVEMENTS 



361 



lawns must be 5 or more ft. above the sidewalks, retaining 
walls are often constructed at the property line of sufficient 
height to retain the lawns. 

In a business district the top of the curb must be enough 
below the floor line of the buildings along the street to permit 



Residence Street 60 Ft. Wide 




Retail Business Street 



60' 



Wholesale Business Street 




''W/M 

.'...._&..... 20- & 
Boulevard for a Small City 




fc -32' - 

Elaborate Boulevard through High Class Residence District 

FIG 87. Typical designs for streets. 

constructing the walk with a slope toward the curb. Here again 
special cases may arise where the curb will be higher than the 
floor line, but these are unusual and must be considered as 
exceptions. 

On business streets those buildings that have a floor line 



362 CONSTRUCTION OF ROADS AND PAVEMENTS 

considerably above the sidewalk must be provided with steps at 
the door to facilitate entrance This is exceedingly undesirable 
and if the condition exists throughout a block the sidewalk is 
more frequently placed at the floor line and steps are provided 
at the curb, an arrangement that seems to be much more 
satisfactory. 

Since the sidewalks in a retail district are used by large numbers 
of pedestrians, the design of the street ought to include suitable 
facilities for pedestrians. Ramps can be provided instead of 
steps whenever room will permit, and every precaution be taken 
to insure convenience and safety of those who use the walks. 

II The grades should be held to as low a per cent, as possible, 
but the necessity of connecting with intersecting streets and 
fitting to existing sidewalks and buildings will largely determine 
the grades. 

It is comparatively easy to show that a great saving in energy 
will result from grade reduction on busy city streets, and doubt- 
less instances constantly occur where large sums of money may 
wisely be expended to reduce grades. On the other hand, 
property lines have long been established and buildings have 
been erected in accordance with existing grades and lines, and 
any considerable change is likely to result in heavy damage to 
property. It is not uncommon to encounter grades as high as 
8 per cent, on city streets, and sometimes grades as high as 15 
per cent, exist and people endure them. 

III. The grade line should be broken only at streets or at 
alleys. Often it is possible to provide a continuous grade for a 
full block or for a greater distance, and this should be done wher- 
ever feasible. If occasion demands, the grade may be changed 
at any street or alley intersection. The object of having the 
grade continuous for an entire block is one of appearance and of 
convenience to those using abutting property, and cannot be 
laid down as an inflexible rule. 

IV. The type of surface to be used must be considered in 
determining the limiting grades or, if topographical conditions 
preclude grade adjustments, the streets must be paved with a 
material suitable to the grade. If it is necessary or desirable 
to use a certain type of pavement, such as creosoted wood block* 
then the grades must not exceed that which experience has shown 
to be the maximum permissible for that type. 

The following table gives safe limits of grade for the various 



THE DESIGN OF PAVEMENTS 363 

types of surface where subjected to mixed traffic but as may be 
expected there is little uniformity in practice in this respect. 

TABLE 40. ORDINARY MAXIMUM GRADES FOR VARIOUS TYPES OF 

SURFACE 

Per cent. 

Wood block 3 

Asphalt block 6 

Brick 10 

Sheet asphalt 5 

Bituminous macadam 8 

Bituminous macadam without seal coat 10 

Concrete 8 

Hillside brick 12 

Granite block open joint (sand or pitch filler) 12 

Bitulithic, asphaltic concrete 7 

Width of Pavement. The width of the pavement is directly 
dependent upon the number of vehicles that will use it, and the 
width of the sidewalk upon the number of pedestrians. It is 
customary to allow a width of 8 ft. for each line of vehicles and 
a width of 2 ft. for each line of pedestrians. The minimum width 
for a residence street is usually 24 ft. and is based on the assump- 




Pipe 

FIG. 88. Pavement with a low curb. 

tion that at times a vehicle may be standing at the curb on one 
side of the street and two others may pass at the same point. 
For convenience, then, the width must provide for three lines of 
traffic or 24 ft. Fig. 87 shows a cross-section typical of such a pave- 
ment. This will not always apply to little-used streets in small 
cities where the width may be reduced to 18 ft. Since a vehicle 
cannot readily turn around in that width, narrow pavements are 
constructed with a low curb so that a wheel can readily pass over 
it on occasion. Fig. 88 shows a cross-section typical of those used 
for this class of pavement. 

If a residence street is closely built up and serves a large 
territory with many vehicles constantly passing, the width must 
be greater than 24 ft. It will be common to find vehicles stand- 
ing at opposite curbs and there must be room between for two 



364 CONSTRUCTION OF ROADS AND PAVEMENTS 



vehicles to pass. The total width required is then 32 ft. In 
practice this is frequently reduced to 30 ft. Similarly a street 
may be encountered upon which, in addition to vehicles standing 
at opposite curbs, there may be fast or auto traffic and some horse- 
drawn traffic. It will frequently happen under these conditions 
that three vehicles will be passing at the point at which vehicles 
are standing at the curb, and a width of 40 ft. will be required. 
This is sufficient width for the most heavily traveled residence 
streets, except boulevards that carry a large amount of pleasure 
traffic. 



xo 

9 
8 

7 

I. 



Crown 



CITY OF WASHINGTON RULE 

FOR 

CLASS A SURFACES 
of PaVtx 



Class A Surfaces 

Sheet Asphalt 

Asphaltic Concrete 

Wood Blocks 

For other Types add 

1 Inch to Crown 

Omit Car Track Space 

in Measuring Width 




1 



20 30 40 

Width of Pavement in Feet 

FIG. 89. 

On boulevards it is not uncommon to have two distinct lines 
of traffic moving in each direction and the vehicles in each line 
constantly turning out to pass those in front. In addition, two 
lines of vehicles may be standing at the curbs, making in all 
eight lines of traffic to provide for and 64 ft. of paved width is 
the minimum that will be adequate. 

If the street has a car line, 10 ft. of width should be added for 
a single track, and 16 ft. for a double track. 

On business streets the same general principles are observed 
except that where the street is too narrow to provide both ample 



THE DESIGN OF PAVEMENTS 



365 



carriage way and ample walkway, preference is given to the 
carriage way to some extent. 

In a wholesale district the walkway is of secondary importance 
and the carriage way must be very wide. This is due to the 
necessity of trucks backing up to the curb to load and unload. 
This requires at least 16 ft. of width on each side or a total of 
32 ft. for vehicles standing at each curb. If, in addition, pro- 
vision is made for two lines of traffic and a double-track car 
line, a total width of 64 ft. is necessary. Often it is desirable to 



Class A Surfaces 
Sheet Asphalt 
Asphaltlc Concrete 
Wood-Block 
Grouted Brick 

Class B Surfaces 
Concrete 
Stone Block 
Bitulithic 
Pitch Filled Brick 




30 40 

Width of Pavement in 

FIG. 90. 



provide for four lines of moving vehicles or a total width 
of 80 ft. 

In every instance the width of a pavement should be deter- 
mined only after a careful traffic census has been taken and 
analyzed. To be too conservative as to the needs of the traffic 
is to insure congestion on the improved street and to restrict the 
movements of vehicles so as to seriously hamper the handling 
of commodities. 

Cross-slope. The cross-slope of a pavement is provided to 
cause the water to flow to the gutters. If the surface is rigid 



366 CONSTRUCTION OF ROADS AND PAVEMENTS 

and dense and exceedingly regular, a very slight cross-slope is 
sufficient. If the surface is somewhat elastic and apt to become 
slightly uneven, a greater cross-slope is required. 

The slipperiness of any pavement is somewhat increased by an 
increase in the cross-slope; hence with those types of pavement 
that tend to become slippery, it is customary to use as slight a 
cross-slope as is consistent with drainage. 




ROSEWATER RULE 

FOR 
ALL SURFACES EXCEPT 

SHEET ASPHALT 
Crown= Width (100-4 s % Grade) 



30 40 

Width of Pavement in Feet 




30 40 50 

Width of Pavement in Feet 



FIG. 91. 



On hills the drainage is taken care of without regard to the 
cross-slope, and, consequently, in order to avoid an increase in 
slipperiness, only enough cross-slope should be used to insure 
that the water will work gradually to the curb. 

Since the amount of water flowing on the pavement will in- 
crease toward the curbs, it is desirable to gradually increase the 
cross-slope as the curb is approached. This is accomplished by 
making the finished surface parabolic in form with the vertex at 
the crown line of the pavement. 



THE DESIGN OF PAVEMENTS 



367 



The total crown to be used for various types of pavements may 
be determined from the diagrams shown in Figs. 89, 90, 91 and 
92. These are well-known and frequently used rules, and, 
although they do not agree very closely, there are no data to 
indicate conclusively which is the best. Undoubtedly modifica- 
tions of the amount of crown shown by the diagrams are 
frequently necessary to accommodate the pavement to local 
conditions, but the diagrams are satisfactory under average con- 



BALTIMORE RULE 

FOR 

BRICK, STONE AND 
WOOD BLOCKS 

-% Grade) 





BALTIMORE RULE 

FOR 
SHEET PAVEMENTS 



20 



30 40 50 60 70 
Width of Pavement in Feet 



/ 



20 



30 40 50 60 70 
Width of Pavement in Feet 



FlG. 92. 



ditions. When the total crown has been decided upon, points 
on the cross-section can be readily determined from the parabolic 
formula. Usually if four points are determined that will suffice 
except on very wide streets. At one-fourth the distance from 
the center line to the curb the drop is one-sixteenth the total 
amount of crown; at one-half the distance from the center line 
to the curb the drop is one-fourth the total amount of crown. 
This is commonly referred to as the quarter point. At three- 



368 CONSTRUCTION OF ROADS AND PAVEMENTS 

fourths the distance from the center line to the curb the drop is 
nine-sixteenths the total crown. 

If there are car lines on the street, the width between the 
outside rails should be deducted from the width between curbs 
in computing the crown, and the cross-section should be laid 
off from the outside rails instead of from the center line of the 
street. 

Unsymmetrical Streets. Many instances are encountered 
where the gutter lines of streets are not at the same elevation. 
This should be avoided so far as possible but sometimes it is the 
only design practicable; and if the property on opposite sides of 
the street differs more than 1 or 2 ft. in elevation, a symmet- 
rical cross-section will appear to be unsymmetrical, an optical 
illusion that has been quite generally encountered by engineers. 
The unsymmetrical cross-section not only has a better appear- 
ance than the symmetrical but also simplifies the design at the 
intersection with other streets. When an unsymmetrical sec- 
tion cannot be avoided and the street does not have car tracks, 
the crown line or highest part of the pavement should be shifted 
to the high side of the street so that the cross-slope will be alike 
on both sides of the crown line. This is accomplished as follows: 




FIG. 93. 

First determine the street that would have a crown equal 
to y f y (Fig. 93) which, for illustration, may be assumed to 
be 9j/ in. This is the crown of a 50-ft. street, if sheet asphalt 
is used. See Fig. 89 (Washington, D. C., rule). Half of this is 
25 ft. The difference between this width and that of the street 
shown in Fig. 93 is 35 ft. Determine the proper crown for a 
street 35 ft. wide which is 6% in. The crown line would then be 
25 plus 17 % equals 42.5 ft. from the low curb (x 1 ', Fig. 93), and 
the total crown on the low side of the pavement would be 9J^ 
plus 6% equals 16>i in. (y f , Fig. 93), while on the side next the 
high curb the crown would be 6% in. (y, Fig. 93). 

It is apparent that 15% in. is not exactly the theoretical 
crown for a street of a half width of 42.5 ft. (85 ft. wide) since, 



THE DESIGN OF PAVEMENTS 



369 



according to the formula used the crown would be 16J^ in. The 
exact width for which 15% in. is the proper crown can be com- 
puted and a second approximation can be made and thus arrive 
at very nearly the ideal crown for the portion of the pavement on 




.V/.I-T? 

4' Tar Sand 



'^^^S^o/^e Edqincj 



<-8'Hand Packed Rubble 



IZ'*8'Curb.\ .IZ'*6'Gutter 

?TTT7 
4 Tar Sand 



?-- oo-u - +*-. ll-v.. .*....+* 

Street Car Tracks*.... 6'Tqr Macadam? \-6'4'Sett t 



-6' Concrete 



8' Rubble ' 



i 



4'Tar-Sand -7 



- 15-0'- -i 

'-~ 9-0- *i 



2T-0'- 

,6'Tar Macadam ~~- oiw - *c -ir - 

_6*4 m Setf-y \ I j j 

f'i''Tirv^''i^T-i::'j^)';'i';^ 



! ../2' 2- 'Edging ' <' -Q' Rubble 




-d'Rubbie '-8-RubbJe 

Courtesy Engineering-Contracting. 

FIG. 94. English practice in street layouts. 

the low side, but since all of the rules are empirical it is un- 
necessary to go to that refinement in general practice. 

Car Tracks on Unsymmetrical Streets. If a single car track is 
to be provided for on an unsymmetrical street, it should be placed 
at the crown line and not at the middle of the street. If the 

24 



370 CONSTRUCTION OF ROADS AND PAVEMENTS 

street is too narrow to permit this, then the crown line must 
coincide with the rails and the slope in the high side of the pave- 
ment reduced to the lowest possible amount, so as to hold 
down the necessary slope on the low side of the pavement. If a 
double-track car line is to be provided for, each track should be 
placed with the outside rail at the elevation determined for that 
point on the cross-section by the preceding paragraph. This 
will necessitate sloping the pavement sharply between the tracks, 
but since that part of the street is little used by vehicles and the 
portion outside the tracks is, it is the best solution to a very 
unsatisfactory condition. At street intersections the tracks 
would be brought to the elevation of the intersecting pavement. 

Here again the lack of room or other conditions may force 
the tracks to the middle of the street and necessitate a steep 
slope on the low side of the pavement. This is dangerous 
when the pavement is slippery and unsatisfactory at any time. 

Intersections. In the design of intersections three factors 
must be considered; the safety of traffic, the comfort and con- 




FIG. 95. Showing false curb and cover plate over the gutter at the 

cross-walk. 



venience of pedestrians, and the proper disposition of storm 
water. 

Since vehicles will be constantly turning the corners, the 
slope of the pavement ought not to be too great and should 
preferably be in the direction that will favor traffic. In the 
ideal case the pavement will slope upward from each of the four 
curb corners to the crown line. Every possible effort should be 
made to establish the grades so as to bring about that con- 



THE DESIGN OF PAVEMENTS 



371 



dition, but when it is impossible the departure should be only so 
much as demanded by the conditions. 

For the comfort and convenience of pedestrians the sidewalks 
are commonly raised only a short step above the gutter, and are 
constructed with a moderate slope upward from the curb. In- 
numerable special conditions arise to modify the ideal plan, but 
the departure from the ideal should be no greater than necessary. 
The maximum allowable cross-slope for a sidewalk is % in. per 
foot, but a much lower slope is decidedly preferable. The ideal 
slope is about Y in. per foot. 

Storm water should be disposed of by means of manholes and 
catch-basin inlets so constructed that they d,o not inconvenience 
traffic and without danger of flooding the intersection. 




FIG. 96. Showing intersection pavement warped up to the top of the curb 

at the cross-walk. 

In residence districts the plan shown in Fig. 95 is commonly 
employed. The pavement at the crosswalk is warped up to the 
elevation of the curb, a false curb and cover provided at each 
gutter and one catch-basin constructed at each corner. The 
sidewalk is thus made continuous across the pavement and the 
water flows between the false curb and the true curb, but under 
the cover plate. The width of the channel between the curb 
and the false curb is usually 6 in., but 8 or 10 in. is sometimes 
necessary. This type of intersection has the disadvantage of 
being uncomfortable for vehicles turning the corner, particularly 
if they "cut in." But on residence streets where traffic is light, 
it is a satisfactory type of intersection and takes care of the 
drainage without inconvenience to pedestrians. A modification 
of this type of intersection is shown in Fig. 96. The pavement is 



372 CONSTRUCTION OF ROADS AND PAVEMENTS 

warped up to the top of the curb at the crosswalk and thus the 
walk is continuous across the street. The catch-basin for the 
street water is placed some distance from the crossing and 
the gutter is sloped away from the crossing. The water from 
the intersection is taken care of by four catch-basins placed at the 
four curb corners, each taking the water from one-fourth of the 
intersection area. 

Not infrequently the intersection is constructed without pro- 
vision for pedestrians to cross the gutters without wading when 
storm water is flowing, but this is poor practice, especially in 
residence districts. 

The two types of intersection mentioned above are entirely 
unsuited to business streets or other streets where traffic is heavy, 




FIG. 97. Showing special gutter design for streets where automobiles regu- 
larly stand at the curb. 

because of the inconvenience to traffic caused by the warped-up 
pavement at the crosswalk. 

For business streets two general methods of caring for drainage 
are in common use. These are designed with many variations 
as to detail, but the essential points are alike. At the walk 
corners the pavement is warped up to the level of the curb 
entirely around the corner, and drainage is provided as in- 
dicated by the arrows in the figure. A variation in this plan 
is to provide catch-basins as shown but to continue the 
gutter around the corner so that pedestrians must step up or 
down at the curb. 

The other general plan is to provide a single water inlet at each 
curb corner with the gutter continuous around the corner. When 



THE DESIGN OF PAVEMENTS 373 

any considerable amount of water is flowing, pedestrians must 
wade across and this is, of course, undesirable. 

Central Gutter Pavements. From time to time engineers have 
advocated the construction of pavements with the gutter at the 
middle. This is the common practice for alley pavements and, 
in a few instances, street pavements have been so constructed. 
The practice has never become general because some of the 
objections such as numbers 1, 2 and 3 in the following, apply to 
fundamental characteristics and probably cannot be entirely 




FIG. 98. Showing conventional intersection design for a business street. 

overcome. The following categorical statement is believed to 
fairly represent present opinion in the matter. 

ADVANTAGE OF A CENTRAL GUTTER* 

Some of the principal advantages of such a pavement are as 
follows: 

1. The capacity of the pavement to carry storm water is many 
times that of the pavement constructed in the old way. 

2. It will keep the dirt and filth in the center of the street 
where it was made and where it can be easily cleaned or washed 
away. 

3; With this construction it will be easier and more convenient 

1 W. G. Kirch offer, in The Municipality for January, 1916. 



374 CONSTRUCTION OF ROADS AND PAVEMENTS 

to establish street grades to conform to existing conditions than 
it is with the present method of street construction. 

4. It will be more economical in the cost of catch-basins and 
sewers, as one or possibly two catch-basins will take the place 
of four or more. 

5. No need of deep gutters with costly covers for sidewalks, 
which are an obstruction to the street. 

6. Lower curbs or none at all in the residence sections, except 
such as might be formed of sod. 

7. Greater convenience in driving up to the curb. No mess 
of water, filth, paper, cigar stubs, etc., to alight into from a 
carriage or auto. 

8. More sanitary because storm water, or water from street 
washing, would be more concentrated and therefore wash the 
street cleaner. 

9. The appearance of the street will be improved from the 
esthetic point of view. 

10. Less crown (or anti-crown) in this case will be needed. 

11. Street will be more easily cleaned, as the debris will be 
concentrated in one windrow in place of two as now. 

12. This form of street pavement will tend to divide traffic 
to right and left side of the street. 

13. Great advantage on boulevarded streets where four gutters 
are now necessary. 

14. Where concrete is used as a paving material the tendency 
to crack along the center line will be reduced because the expan- 
sion of the pavement, due to temperature changes, will put com- 
pression stresses in the pavement at the center line instead of 
tension stresses as is now the case when the street is crowned 
at the center. 

DISADVANTAGES OF PAVEMENT 

Some of the disadvantages to such a form of street are: 

1. On a narrow street with car tracks, the gutter would be 
between the rails which would cause debris to accumulate in the 
wheel grooves. This objection could be eliminated on a wide 
street by making a low point each side of the car tracks. 

2. During heavy storms the stream of water in the center of 
the street might be too deep to walk through. 

3. Where the grade is slight and where there is freezing and 



THE DESIGN OF PAVEMENTS 375 

thawing weather, water may collect in pools 4 to 6 ft. wide, 
freeze and make traffic in the center of the street difficult. 

4. If pavement is made thick at the curb and thin at the center, 
fear has been expressed that the pavement would crack along 
the center line. 

5. Fear has been expressed that rapidly moving vehicles at 
street intersections would tend to skid toward the center of the 
pavement instead of toward the curb, as would be the case of 
a crowned street. This contention would be true in case of 
vehicles turning around a corner to the right, but if the vehicle 
was turning to the left the new form of surface would tend 
to keep the vehicle in the street and right side up, while with 
the crowned surface, as at present, the vehicle has a tend- 
ency to skid down the crown toward the curb and possibly 
overturn. 

The Design of Street Intersections. One of the most trouble- 
some problems encountered in street design is the establishment 
of grades at intersections. So many and diverse are the con- 
ditions encountered that no simple rules can be laid down 
covering all cases. Moreover, practice has not been anywhere 
nearly standardized, nor can it be. The design of inter- 
sections is therefore a matter for special study every time it 
presents itself. A few fairly well defined principles may be laid 
down that will serve as a guide in working out most of the 
cases that occur. 

Streets with Grades less than 2 per cent. (a) The center- 
line grade is carried without a break across the intersection 
and the curbs on opposite sides of the street are not at the 
same elevation. The difference in elevation on a 40-ft. street 
with a 2 per cent, grade will be 0.8 ft. and this can readily be 
taken care of by either varying the height of the curb so as to 
keep the gutters at nearly the same elevation, or by using 
an unsymmetrical cross-section for the street, or by both means. 
It may be desirable to keep the curbs and the pavement cross- 
section symmetrical on the more important of two intersecting 
streets, and have a break in the grade line of the other at the 
curb line of the first. This is frequently done where one street 
is a main thoroughfare and the other a cross street. 

As a general rule difficulty is experienced in securing a safe 
and properly drained intersection if the difference in elevation 
of the opposite curbs is much greater than 1 ft., i.e., on a 50- 



376 CONSTRUCTION OF ROADS AND PAVEMENTS 





5' 


< 2' x 


k' 


< 2' > 


5' 










Crown .45' 














1 












50.09 






50.09 . 


. 50.40 






51.23 


in 




1 


0.0 jt 


50 

49.94 . 
50 


r 30 
JU 


3.08 




S 






n Curb Height 0.5' 




49.36 


50.93 





a 49.00 49.63 


50.00 ,50.37 51.00 < 2.5&Dowa 




4D.18 


49.80 49 - 


85 50 ' 16 


50.78 






'**! ~"\ 




> w 




s, 












C-l 




To 




Q 




4.28 ^ 








49.90 






49 


70 






51.08 



Fia. 99. Design of intersection for residence street with light grades. 



100.11 



0.46* 



A)- 



Grown 0.75' 

1,1 

f 

100.04 -UOO.W 100.04 



100.64 



^99.95 



29.71 



99.66 100.00 



99.71 



1.8* 



2* 



99.66 



100.00 99.95^ 



Curb Height 0.6' 



100.29 



100.00 100.00 100.34 



^99.95 --100.00 99.95-?* 



100.29 



99.81 99.66 



5.5^ 



2% 



100.49 



FIG. 100. Design of intersection for grades less than 3 per cent. 



THE DESIGN OF PAVEMENTS 377 

ft. pavement when the grade of the intersecting street is 2 
per cent. When such is the case, method (6) may be used. 
Fig. 99 shows the design of an intersection for a residence street 
with slight grades. 

(6) The other method of designing intersections for streets 
of light grades is to make the elevations of the four curb corners 
the same. The grade lines of each street will then break at the 
curb lines of the intersection. This design is generally easily 
carried out on residence streets, but may be difficult in a business 
district on account of the established building-line elevations. 
From the standpoint of securing an intersection that is safe for 
vehicles, it is to be commended. It has the disadvantage 
of putting the curb line somewhat below the level of the lots on 
the uphill side of the street, but this is a secondary considera- 
tion; Fig. 100 shows the design of an intersection for a busi- 
ness street with slight grades. 

Streets with Grades Over 2 Per Cent. If streets are on grades 
greater than 2 per cent, and especially if they reach 5 per cent, 
or more, it is frequently impossible to carry the grades con- 
tinuously across intersections because of the difference in height 
of curb that would result, although it should be done if possible, 
The grade cannot always be broken at the curb line because of 
the difficulty of securing reasonable grades to the sidewalks, es- 
pecially on business streets. On residence streets it is some- 
times possible to adjust the grades of walks if the street grades 
do not exceed about 4 per cent., and make the break in street 
grade at the curb line of the intersecting street. When that is 
possible it is the best solution of the problem as it usually increases 
the grades on the remainder of the block less than any other 
method of treatment. Figs. 101 and 102 show designs of inter- 
sections for grades in excess of 2 per cent. 

For business streets satisfactory grades at the intersection are 
secured by flattening the street grade across the intersection, 
making the break in the grade line at the property line of the 
intersecting street. It will easily be seen that this increases the 
grade along the remainder of the block. 

This emphasizes the desirability of flattening the grade only 
so much as is necessary to secure a satisfactory intersection. 
This can only be determined by repeated trial for any given 
intersection. On account of the variation of width of paving and 
sidewalk, no uniformity exists in the procedure, but whatever 



378 CONSTRUCTION OF ROADS AND PAVEMENTS 

modification is made looks to one end, viz., to secure an inter- 
section with reasonable slope and sidewalks that fit to the curb 
grade without undue cross-slope. This cross-slope may be as 
great as 6 per cent, and in exceptional cases 10 per cent., but 
for ordinary cases should be held as low as 2 per cent. 

For the intersection of streets crossing at excessive grades or 
for streets intersecting at acute angles, the problem becomes 
very complicated and the procedure outlined by Mr. Vernon S. 
Moon in a paper read before the Municipal Engineers of the 
City of New York has been widely quoted and commended. 
It is given as one of the examples of good practice at the end of 
this chapter. 



J 

CM' 

3 

i_5 

6* 

50.12 


< 14 V 




5 


r . 


< 14 > 


50.73 300' P.L.to P.L. 


n 

O.S5- 
*) 




I 

50.00 3 


ro\ 



* 
o> 
^- 


n 0.8' 

50.60 50.50 
50.40 50.30 
50.00 50.51 


2% 

2% 
} 


s ; 


^ v 

N 


ts. 
"* Curb Height 0.6 




49.52 49.80 

^. 

* 49.20 49.50 


50.58 
61 Down 
) .50.80 New 6.53* 




1 

49.12 


49.40 

-49.20 




43.60 49.90 
49.40 49.70- 


5D.1S 


o j 

^ 


I 

N e. 


\ *} 

' 2% 

1% 


fc 

4.1* 

2% 


* 
^i 


49.43 


50.28 



FIG. 101. Design of intersection with steep grades. 

Curbs. Curbs are used at the edge of the pavement except 
in those cases where the street is in the outskirts of the city 
and in reality serves the purpose of a country road. The curb 
defines the edge of the pavement and thus adds somewhat to the 
appearance of the street; it retains the soil and sod on the park- 
ing so that it will not wash onto the pavement ; it serves to confine 
traffic to the paved area thus protecting the grass plots or side- 
walks from the encroachment of traffic and it serves as one side 
of the drainage channel directing the water into the proper 
outlets. Thus the curb serves a utilitarian as well as an 



THE DESIGN OF PAVEMENTS 



379 



ornamental purpose. Both appearance and utility' must be 
considered in the design and construction. 

Height of Curbs. The height of curb is dependent partly 
upon securing good appearance and partly upon having ample 
height to prevent traffic encroaching on the grass plots or side- 
walks. In special cases it may also depend upon the amount of 
storm water carried in the gutter. A uniform height of curb is 
desirable because of the appearance and in residence districts 
this height is usually either 6 or 8 in. In business districts the 
height of the curb is usually either 6, 8 or 10 in., but the tendency 
is to have it somewhat higher on the average than in residence 




FIG. 102. Design of intersection for diagonal streets. 

districts. At corners the curb should never be less than 6 in. 
high so as to prevent vehicles cutting in on the grass plots or 
walks in turning the corner. 

In cities where the street grades are very light, it is frequently 
necessary to secure drainage by sloping the gutter independent 
of the grade of the crown line of the pavement, which results in 
the curb height varying along the block. This does not look as 
well as if it were of the same height, but is not otherwise ob- 
jectionable. 

In hilly cities many special conditions arise requiring a varia- 
tion in the height of the curb from point to point along the 



380 CONSTRUCTION OF ROADS AND PAVEMENTS 



street or on opposite sides at the same point. These conditions 
are unavoidable and are objectionable only on account of the 
appearance. 








. ft 



Mixed Dry 



Granite Curb & Vitrified Block 
Gutter Used in Washington, D.C. 



/,'S.'ff Concrete-- 

/4*- *4 

Combined Curbs, Gutter 
Used in Washington.D.C. 



Curb and False Curb 
for Cross Walks 



u 

Two Course Curb with Batter 



Porous Foundation 
2 "Porous Tile. 




Stone Curb Setting j wo Course Combined Curba Gutter 

FIG. 103. Designs of curbs and combined curb and gutter. 

Stone Curbs. Sandstone, granite and limestone are used for 
curbs, the latter less commonly than the other kinds. The size 



THE DESIGN OF PAVEMENTS 381 

of the blocks used is variable but for residence streets and for 
ordinary business streets it is usually 5 in. thick and from 4 
to 8 ft. long. The depth will depend upon the thickness of the 
pavement and the amount of exposed face desired. 

For streets where heavy trucks are likely to back in against the 
curb, granite should be used if it is advisable and the thickness 
should be at least 6 in. and 8 in. is better. 

The curbstones should extend to the bottom of the pavement 
base and the total height of the stones will, therefore, depend 
upon the kind of pavement and is usually between 16 and 20 in. 

Radius Curbs. The curb is curved at the corners where streets 
or alleys intersect. The radius at alley corners may be 3 or 4 ft. 
and at street corners 6 to 9 ft. on business streets, and 6 to 12 ft. 
on residence streets. The longer the radius the easier for traffic 
to round the corner, but this cuts in on sidewalk space on busi- 
ness streets and that limits the possible radius to about 9 ft. 
Radius stone are more expensive than straight curbs, and the 
longer the radius, of course, the more expensive. For that reason 
the radius is held as low as consistent with reasonable convenience 
at the corners. The curved portion of the curb is formed with 
stone that have one face dressed to the prescribed radius, while 
the back may be either dressed to a corresponding radius or may 
be a chord. Usually the corner is formed with two radius stones, 
but on the curves of a radius exceeding 6 ft., more than two stones 
are commonly employed. The ends of radius stone are dressed 
to a radial line so that the joints will be of uniform width. 

Concrete Curbs. Portland-cement concrete curbs are quite 
extensively used, especially where suitable stone curbing is 
expensive. The concrete curb is usually made 6 in. thick and 
deep enough to reach to the bottom of the pavement base. The 
aggregates used are sand and broken stone passing a %-in. ring 
and retained on a J^-in. ring. Where it may be secured, granite 
or some equally hard stone is desirable, but a good quality of 
limestone may be used satisfactorily. Graded and bank-run 
gravel are also widely used. The mixtures employed are 1 part 
cement, 2 parts sand, and 3 parts stone, or 1 part cement, 2J^ 
parts sand and 4 parts stone, the former being preferable. The 
general principles already discussed as applying to the selection 
and testing of concrete materials apply to curb work as well as 
to any other kind of concrete construction. 

The exposed face of the curb and the top is finished with a wood 



382 CONSTRUCTION OF ROADS AND PAVEMENTS 

float to give a rough or granular appearance not unlike that of 
sandstone. This is accomplished by 'tamping the concrete in 
place and allowing it to set sufficiently to permit the removal of 
the forms. The forms are removed as soon as possible and the 
curb is scoured with a wood float and water until the desired 
surface is obtained. This cannot be carried out successfully 
if the finishing is delayed too long. 

In other instances the concrete is placed between metal forms 
or smooth plank forms, and the top is finished with a steel float. 
The face receives no special finish, but if the forms are smooth 
the face will be smooth and not unsightly. 



Curb capable of adjustment 
'' """ '< 



4'to7 



Grate 17x22' 360*Cover 














1 T 

^-1 




= 






/ 


/ 




- 




Branch Same -Size . 


^ 


^= 


" > 
Xl 


~ 




as Main Pipe 




g 


<o 
jr 







< 4'-o" 
Brick-\ 


I 





Outlet 



(Vitrified 




FIG. 104. Catch basins without trap. 



In every case the upper edge of the curb next the pavement is 
struck off with an edging tool to a radius of about 1 in. 

The curb is constructed in sections about 6 ft. long to take 
care of expansion, and to give an appearance resembling stone. 
The sections are separated from each other during construction 
by means of a metal platen J- in. thick which is set in the forms 
and serves as a partition to separate the sections. Cutting the 
sections with a trowel does not answer the purpose. After the 
concrete sets the platen is removed, leaving a joint between the 
sections. 

Much difficulty is experienced at curb corners unless adequate 
provision is made for expansion. It is good practice to provide 
an expansion joint 1 in. wide between the last straight section of 
curb and the first section of radius curb at the corner. It is 



THE DESIGN OF PAVEMENTS 



383 



usually unnecessary to fill this joint, but if a filler is used it should 
be some kind of elastic felt. 

Like the stone curb, the concrete curb should be placed on some 
substantial foundation such as hard-tamped clay, stone, gravel 
or cinders. Fig. 103 shows settings used for curbs. 

Armored Curb. The curved portion of the curb at corners and 
sections where trucks are likely to back in against it are protected 
by a metal plate which is built into the curb. Fig. 103 shows 
three types of protection commonly employed, but many others 
are used. 

For severe service the concrete curb should be made 8 in. thick 
and should have a heavy protection plate. 

With concrete pavements the curb is often made integral with 
the pavement, as discussed elsewhere. 



Top of Cur b^\. 




Vertical Section 

FIG. 105. Catch basins with trap. 

Curbs on Country Brick Roads. The curb on a brick country 
road is made integral with the base and with the top level with 
the surface of the pavement (see Fig. 50). It is usually made of 
a better mixture of concrete than the base because it will be sub- 
jected to some wheel wear and is constructed after the base has 
been completed but before it has had time to set. 

Concrete Combined Curb and Gutter. This type of curb is 
used on residence streets where a smooth gutter is desired or 
where the appearance of such a curb is deemed superior to that 
of the straight curb. It is commonly constructed of a rather lean 
base and with a rich mortar coat of about H m - thickness, for 
the surface. The size varies considerably and Fig. 103 shows a 
few of the commonly used designs for this type of curb. Formerly 



384 CONSTRUCTION OF ROADS AND PAVEMENTS 

it was deemed impractical to build this curb of varying height, 
but methods of construction have been perfected that make it 
possible to do so, and maintain a constant width of gutter slab. 
The base is usually made of 1-2^-5 mixture and the surface a 
1 to 2 mortar. The forms are set and the concrete for the base 
which is mixed with but little water is tamped in place and struck 
off. The front form board for the curb is then removed and the 
mortar coat is applied and struck off by means of a templet 
drawn along the side form boards. If the curb is not of uniform 



Siancfarcf Manhole 
Cover. 




Omrffedin Hard pan 



FIG. 106. Typical manhole designs. 

height the templet for the top of the curb is omitted, and that is 
finished by means of the trowel or steel float. Care must be used 
in the construction to insure a neat and workmanlike finish, and 
the mortar coat must be applied before the base has taken a set. 
If dust from the street settles on the base before the top is applied, 
or if the base has taken a set, it will prevent the mortar coat from 
adhering and later it will scale off. 

As with straight curbs the combined concrete curb and gutter 
is made in sections separated by metal platens set in the forms 



THE DESIGN OF PAVEMENTS 385 

and same provisions for expansion are necessary as are employed 
with straight curbs. The combined* curb and gutter must be 
placed on a substantial foundation of well-tamped gravel or 
cinders. The grade and alignment must be carefully maintained 
for the sake of appearance, and to insure good drainage. 

In recent years this type of curb has been built of one course 
of 1-2-4 concrete in the manner already described for the straight 
curb. This is particularly desirable if it appears that traffic 
will get out on the gutter slab to any extent. 

The concrete combined curb and gutter should not be used for 
business streets because the constant use of the gutter slab as a 
pavement will wear the slab so that it will become rough and 
uneven. It is also quite likely to wear into a groove at the line 
where the pavement proper joins the gutter slab. 

Special Gutter Designs. With most types of sheet pavements 
it is desirable to provide a gutter of some inelastic material for 
some traffic conditions. If vehicles stand at the curb on a sheet 
pavement, the wheels will form depressions that will hold water 
and thus interfere with drainage. It is good practice to provide 
a gutter slab about 18 in. wide made of concrete, vitrified brick 
or creosoted wood blocks. Either the concrete or stone curb may 
be used. 

Where the streets are on grades exceeding 3 per cent, some 
difficulty is experienced in starting the load on wood-block and 
sheet pavements because of the poor footing afforded for horses. 
Horse-drawn trucks that stop at the curb to deliver goods are 
thus inconvenienced. If vehicles stand continually along the 
curb it is desirable to provide an inelastic slab in this area. 
The gutter slab for such locations is sometimes made about 6 
ft. wide, constructed of vitrified brick or stone blocks. The 
remainder of the pavement may be creosoted wood blocks or a 
sheet surface. This type of gutter slab is undesirable for sheet 
surfaces on heavy traffic streets because of the tendency for a 
rut to form at the edge of the slab. Fig. 97 shows a special design 
of curb and gutter. 

Catch-basins. Storm water from pavements is ordinarily 
disposed of by means of storm-water sewers or by means of 
sewers carrying both storm water and sewage, but the former is 
the more common method. 

The street water will carry miscellaneous rubbish, manure, and 
often considerable quantities of soil. If this material gets into 

25 



386 CONSTRUCTION OF ROADS AND PAVEMENTS 



the sewer it is likely to become lodged on some obstruction and 
finally the accumulation will clog the sewer. For that reason 
the street water is first taken into a catch-basin and from the 
catch-basin the water, freed of most of the detritus, flows into the 
sewer. The catch-basin is so designed that it can be cleaned 
out as occasion demands. 



/7 ~ "^-Surface of Pav/nff 




mmmrn 



1-3 -5 Concrete 



J 




" 

6 > 



onnnn 
ccnnn 
cnnnn 
nnnnn 
ncnnn 
onncc 





Transverse Section 



FIG. 107. Typical curb inlet designs. 

Catch-basins may be constructed beneath the gutter, entirely 
under the paved area or they may be constructed just back of the 
curb in the sidewalk area or in the sodded space of residence 
streets. The catch-basins are of a wide diversity of design, a 
few of which are shown in Fig. 104. If the storm water is taken 
into a combination sewer, it is necessary to provide a water seal 
or trap so that odors will not reach the street from the sewer. 
Fig. 105 shows the design of catch-basins of this type. 



THE DESIGN OF PAVEMENTS 387 




FIG. 108. Types of inlet castings. 



388 CONSTRUCTION OF ROADS AND PAVEMENTS 

Manholes. At the junction of the pipe from a catch-basin 
and the sewer, the connection is made by means of a manhole. 
The drains from several catch-basins often lead to the manhole 
through which the sewer is carried. Fig. 106 shows a few types 
of manholes. 

Curb Inlets. Sometimes street water is taken directly to the 
sewer instead of through an intervening catch-basin, and when 
such is the case the curb inlet is employed instead of the catch- 
basin. The curb inlet differs from the catch-basin only in that 
it has no receptacle for collecting the street refuse carried by 
the water. Several types of curb inlets are shown in Fig. 107. 

Catch-basins and Curb -inlet Covers. The perforated covers 
through which the water flows into the catch-basin or inlet are of 
great variety, and the particular type employed in any case will 
depend, to some extent upon local conditions and to a greater 
extent upon cost. A simple perforated or slotted cover is to be 
avoided if any considerable quantity of paper, leaves or other 
similar material is likely to be washed to the catch-basin, as the 
opening will clog readily. The type that provides a slotted 
grating for the gutter and a false curb with a large opening is 
to be preferred in this case. Fig. 108 shows a few of the many 
types of castings that are in use. 

CAR TRACK PAVING 

Types of Pavement for Car Tracks. Whether the car-track 
paving shall be of the same material as that used on the re- 
mainder of the street depends upon several conditions. Any 
street that carries a large amount of heavy truck traffic must 
have a very durable type of pavement and the car-track paving 
may be of the same type as the remainder of the street. Streets 
that are paved with stone blocks, wood blocks or vitrified brick 
generally have car tracks paved with the same material. 

If the traffic is mixed and not as heavy as indicated in the 
preceding paragraph the car track paving may be of some more 
durable material than is used for the remainder of the street 
It will readily be seen that in turning on to the car track, or in 
crossing it, there is a tendency for the steel-tired wheels to slide 
along the rail for a distance, thus bringing severe wear on the 
paving next the rail. At crossings where the tracks curve around 
corners or the trackwork is otherwise complicated the paving is 



THE DESIGN OF PAVEMENTS 



389 



likely to be cut up into small areas that receive severe service. 
In such cases it is good practice to provide a very durable 
car-track pavement. Thus we often find that streets that are 
paved with sheet pavements (sheet asphalt, asphaltic concrete, 
bitulithic, etc.) have car tracks paved either with wood blocks, 
granite blocks, or vitrified brick. 

Even for moderate-traffic streets paved with sheet surfaces it- 
is common to use a " toothing" along each rail. This consists 




FIG. 109. Illustrating need of expansion joints in curbs and walks. 

of one or two rows of wood blocks or vitrified brick laid along the 
rail with the long dimension parallel to the center line of the 
track. 

Types of Car-track Rails. The type of the rail is an important 
factor in the life of the car-track paving. Three types or modi- 
fications of them are employed. If a car track is not adequately 
supported the continual vertical motion of the rail as the cars pass 
will gradually loosen the paving blocks adjacent to the rail. 
Once loosened, water enters and softens the supporting soil 



390 CONSTRUCTION OF ROADS AND PAVEMENTS 

under the ballast and hastens the deterioration of both track 
and pavement. 

The effect of any movement of the track is increased if the 
paving blocks extend under the head of the rail. 

T-rails. The T-rail is of the form that is used for steam roads 
except that the rail is higher so as to permit the pavement being 
placed above the ties and to afford a more rigid support for cars. 
Where the rail is of this type a special-shaped paving block is 



Special Rail Block 



; Brick or Stone Block Surface lf 

\. Joints Grouted .<-/ of 1-4 Mortar 



$ 



>v->- >'.:'&>**;.'' ^?^r^APi*>'-<^' -' ffl ^ 'V^' ' ' 
: V > : ?v- : > Concrete or Ballast- rVvX--;?/^'.''*^ * *? 8 V * ^ 

-'' 



firick or Stone Block Surface 



^,,,,,,,^^\\\\\v^)S/Q>eJ:perr~f. ';, Joints Grouted 



-^ ...... -^ 



^^^yiy^^/^^^f^'^^ 
l^^'^^W^iy:-^^;^'^] 



-p'~'jw&r:i<^ 

VT^y&'v 1 ^ 

\^-^^>;:or^fe^ : ^^-->'f> 



i 




Ouluth Method Superior Method 

Concrete Paving for Car Tracks 
FIG. 110. Paving along T rails. 

often employed to form a groove for the car-wheel flanges. This 
is not a satisfactory type of car-track paving for streets of heavy 
vehicular traffic because drivers will permit the wheels of vehicles 
to travel in the groove next the rail and the concentration of 
traffic soon wears out the paving. Fig. 110 shows the arrange- 
ment of the paving along rails of this kind. The T-rail is most 
economical for the street car company. 



THE DESIGN OF PAVEMENTS 



391 



Grooved Rails. The shape of this rail is best shown by 
Fig. Ill which also shows the arrangement of the paving along 
tracks of this kind. Since the top of the rail is even with the 
pavement surface there is no tendency to guide the wheels of 
vehicles along the track. 

Lipped Rails. This rail is similar to the grooved rail as will 
be seen by reference to Fig. 112. 



Block or Two Rows Blocks ,.Wooc/or 

Sheet.Pavemenf ^'Parallel toRaiJ_ jStoneBfoc. 
H 



2" Wearing /Ix" Binder Course 
s j'Course 




.>: A* .^Vf. f3-- ; :'-'ii>'-A- ^' ''?''?" Concrete, or,Ba//<7sr i^*"'^f.'.\-V>l*6'/<?5^.-<-''.-4A* 4 *.^ 
FIG. 111. Paving along grooved rails. 

Track Construction. Regardless of the type of rail used, in- 
creasing attention is being paid to the track construction and 
especially to the foundation construction. The thickness of the 
ballast under the ties varies with soil conditions but is rarely less 
than 6 in. and often is more than 1 ft. The difficulties en- 
countered with car-track paving are generally due to insufficient 



Slope 



Two Rows of Blocks 
/to4Morfa{ {Parallel to Rai/ 
'per foot .-4'Wooct Block Surface - 



.y > .^'. A. . A; **' ' -^ '- ---o- />-. -.4 ) -- -e.\ > w .; 

, - ' A- . c>: . . Concrete or Ballast A * JE'' 'A* % ^' " ^ i 

. . r.- A . t A . . . > : A . ; A*. . ^ . . / jy. ; A '. . ^ . ? '^ .' .>.'.' ^/ 

FIG. 112. Paving along side-bearing rails. 

stability of the track. Figs. 110, 111, 112 show the recom- 
mended practice for car-track construction on paved streets 
and represent the minimum requirements permissible. 

Pavement Foundations. The design of the foundation is one 
of the neglected factors in pavement design, probably because 
foundation failures are not always immediately apparent or are 
readily explained by "unforseen contingencies." It is apparent 



392 CONSTRUCTION OF ROADS AND PAVEMENTS 



that the foundation is the vital part of the pavement and should 
be carefully designed. The function of the pavement is to trans- 
mit the load from the wearing surface to the earth subgrade and 
in so doing to distribute the load over sufficient area that the 
subgrade will not be distorted by the pressure. The necessary 
thickness depends upon the nature of the earth foundation, the 
bearing power of the soil, the weight of the loads that the pave- 
ment will carry and the rigidity of the wearing surface. 

For any known soil condition the foundation thickness needed 
for a sheet surface is greater than for a block-pavement sur- 
face carrying the same traffic. Likewise the macadam or gravel 
foundation for a given surface must needs be thicker than a 
Portland-cement concrete foundation for the same pavement. 
Soils of low-bearing power require greater thickness than stable 
soils. 

The proper thickness should be determined only after an 
examination of the soil that will form the subgrade and the special 
considerations of foundation thickness has been discussed for 
each type of surface in the preceding chapters. The following 
table of average thickness of foundation for good soil conditions 
will be of interest for comparison. 

TABLE 41. COMPARISON OF THICKNESS OF PAVEMENT FOUNDATIONS 



Type of surface 


Thickness of foundation 
for residence streets 


Thickness of foundation 
for business streets 


Gravel or 
macadam, in. 


Concrete, 
in. 


Gravel or 
macadam, in. 


Concrete, 
in. 


Granite blocks 
Wood blocks 




4 
5 
5 
5 


8 to 10 
6 to 8 


6 to 8 
6 to 8 
5 to 6 
6 
6 
6 


Brick (grouted) 


6 

8 

6 


Bitulithic 


Sheet asphalt 
Asphalt blocks 


8 



EXAMPLE OF GOOD PRACTICE 1 

1. Definition of Platforms. The center-line intersection shall 
be deemed to be the point of intersection of the center lines, except 
for cases where the center lines do not meet at a common point 

1 Mr. Vernon S. Moon in the proceedings of the Municipal Engineers of 
the City of New York, 1911. 



THE DESIGN OF PAVEMENTS 393 

when it shall be the area included within the center lines at their 
intersection. 

The curb-line platform shall be deemed to comprise the area 
included within the lines connecting the points on intersection of 
the curb tangents, or in the case of a street terminating at another 
street it shall comprise the area within the prolongations of the 
curb lines across the intersection and a line joining the curb 
tangents. 

The building-line platform for rectangular intersections shall 
be deemed to include the area bounded by the prolongations of the 
building lines of both streets across the intersection so as to 
comprise the greatest platform area. In the case of other than 
right-angled intersections, it shall comprise the area bounded by 
the respective lines of each street and by lines at right angles 
or normal to the center lines and passing through acute-angled 
building line corners, or the corners giving the greatest platform 
area. If the intersection of the center lines falls without the 
building-line platform, as above described, the said platform shall 
be increased sufficiently to include the said intersection. When 
the building-line corner is turned with a curve the platforms above 
defined shall be indicated upon the map unless herein definitely 
fixed. 

2. Definitions of Elevations Fixing Grades. Unless otherwise 
indicated on the map, the elevations shown at a street intersec- 
tion shall be deemed to be that fixed for the point of intersection 
of the center lines of both streets affected, or for the center line 
intersection. 

3. Treatment of Center-line Intersection. The center-line 
intersection, when it comprises an appreciable area and unless 
otherwise shown on the map, shall have a uniform elevation at its 
boundaries, and in determining the elevations for the other plat- 
forms herein described, the center-line intersection referred to 
as a basis of calculation shall be deemed to be the nearest point 
on the center line of each street at the boundary of the said 
platform. 

4. Treatment of Platform for Streets Having a Light Grade. 
If the grade of each of the intersecting streets is 3 per cent, or 
less, as determined by calculating the rate between the es- 
tablished elevations, the elevation of the center lines of each 
street within the limits of the curb-line platform shall be the same 
as that fixed for the center-line intersection. The elevation of 



394 CONSTRUCTION OF ROADS AND PAVEMENTS 





FIG. 113. Showing design and use of guard fences. 



THE DESIGN OF PAVEMENTS 395 

the curbs shall be determined as indicated in Paragraph 8. 
Provided, however, that the difference in the elevation of points 
on the center lines opposite any building-line corner, shall not 
provide a greater transverse sidewalk slope than that fixed as 
the maximum in Paragraph 7, in which latter event the building- 
line platform shall be used and the grades of that portion of the 
streets adjoining the said corners shall be flattened between the 
boundaries of the building-line platform and the center-line inter- 
section, as provided in Paragraph 5 (a). 

5. Treatment of Platform for Streets Having a Steep Grade 
or Meeting at an Acute-angled Intersection. (a) If the grade of 
any portion or portions of intersecting streets ad joining a building- 
line corner is over 3 per cent., as calculated between the estab- 
lished elevations, or if a further flattening of the platform grade is 
required to provide proper sidewalk slopes, for any part of an 
intersection described in Paragraph 4, the grades of the said 
portion or portions of each street shall be reduced between 
the- boundaries of the building-line platform and the center- 
line intersection as follows: If the intersecting streets are of 
the same width, the grade of the street traversing the shorter 
block length adjoining the intersection shall be reduced one- 
third and that of the street traversing the longer block shall be 
reduced two-thirds. In case the streets have different widths, 
the grade of the wider street shall be reduced one-third and that 
of the narrower street two-thirds between the above limits. 
All grades less than 3 per cent, which are not herein required to 
be flattened shall be applied at the same rate as originally com- 
puted between established elevations. Provided, that in no 
case shall the maximum platform and sidewalk slopes fixed in 
Paragraphs 6 and 7 be exceeded. 

Any excess in grade over that allowed in Paragraph 7 shall be 
removed by further flattening, as follows: 

(6) Special flattening of platform grades for extreme cases of 
steep grades or acute-angled intersections. If the difference in 
elevation tentatively fixed for points on the center lines of 
intersecting streets opposite any building-line corner, after 
applying the minimum and up to the maximum transverse 
sidewalk slope on the higher and lower sider respectively, exceeds 
the maximum transverse sidewalk grades hereinbefore described, 
the elevation of each street at the boundary of the building-line 
platform shall be adjusted to remove the excess, the adjustment 



396 CONSTRUCTION OF ROADS AND PAVEMENTS 

of each of the said elevations being directly proportional to the 
grade of each as originally flattened or applied. 

For all cases covered by Paragraphs (a) and (6) the elevations 
at the intersections of the center line of each of the narrower 
streets or at the streets traversing the longer blocks, if they 
are of equal width, with the curb-line platform of the inter- 
sected street shall be the same as the elevation of a point on the 
center line of the intersected street immediately opposite the 
first-named intersection, except that the elevation at this point 
shall be abandoned when the grade along the center line between 




FIG. 114. A patrolman on a Maryland road. 

the curb-line platform and the building-line platform exceeds 
the grade as originally computed. 

The grades of the center line of the wider street or of the 
street traversing the shorter block, if they are of equal width, 
shall be uniform between the exterior boundaries of the building- 
line platform and the center-line intersection, except that the 
maximum platform slope hereinafter fixed shall not be exceeded. 
The grades of the center line of the narrower street or of the 
street traversing the longer block, if they are of equal width, 
shall be uniform between the elevations fixed at the exterior 
boundaries of the curb-line platform, and also between the 
latter point and the center-line intersection. 



THE DESIGN OF PAVEMENTS 



397 



6. Maximum Platform Grades. The maximum allowable 
grade along the center line between the curb-line platform and 
the center-line intersection shall be at the rate of 4 per cent., 
unless otherwise indicated on the map. 





it** 



FIG. 115. Patrol outfits Illinois State Highway Department. 

The grades along the center line between elevations estab- 
lished within the limits of a building-line platform shall be 
uniform, subject only to the flattening provided for in Para- 
graph 5 (6). 

7. Transverse Sidewalk Grades. Whenever practicable, the 
sidewalk shall slope upward in a direction at right angles to the 
curb toward the building line at the rate of 2 per cent. 



398 CONSTRUCTION OF ROADS AND PAVEMENTS 

The elevation of the sidewalk at the building-line corner shall 
be determined by applying this rate to the elevation of the curb 
giving the higher building-line elevation, at a point immediately 
opposite the corner, unless the resulting grade on the lower side 
exceeds 6 per cent., in which case the sidewalk shall be level on 
the higher side and a greater transverse sidewalk slope up to the 
maximum shall be used on the lower side. 

The maximum transverse sidewalk slope shall be 6 per cent., 
except in those cases where the street grade as originally com- 
puted on any street adjoining a building corner is more than 6 
per cent., when the maximum slope shall be 10 per cent, for 
either street, opposite the said corner. In no case shall the side- 
walk at the building line be lower than that of a point im- 
mediately opposite it on the curb. 

If the transverse sidewalk slope at the building-line corner 
is more or less than 2 per cent., it shall be made to agree with this 
latter rate at a point distant 25 ft. from the building-line corner. 

8. Curb Elevations. The relation between the elevation of 
the center lines and of the top of the curbs at points immediately 
opposite it at the boundary of and outwardly from the building- 
line platform shall be as follows: For roadway widths of 24 ft. 
or less the top of the curbs shall be 0.1 ft. higher than the center 
line. For roadway widths ranging from 24 ft. up to and includ- 
ing 34 ft. the top of the curbs and the center line shall be at the 
same elevation. For roadway widths ranging from 34 ft. up 
to and including 44 ft. the top of the curbs shall be 0.1 ft. lower 
than the center line. For roadway widths ranging from 44 ft. 
up to and including 54 ft. the top of the curbs shall be 0.2 ft. 
lower than the center line, and for roadway widths ranging from 
54 ft. up to and including 64 ft. the top of the curbs shall be 
0.3 ft. lower than the center line. 

The elevation of the intersection of the curb tangents shall be 
determined from a point immediately opposite on the center line 
of the wider street or the street traversing the shorter block, if 
they are of equal width, subject, however, to the same correction 
in elevation between the top of the curbs and the center line as 
herein provided. 

9. Depth of Gutters. Whenever practicable a standard depth 
of gutter of 0.4 ft. shall be used. 

10. Curb Grades at Corners. The tangents in the curbs shall 
be graded uniformly between the elevations established for them 



THE DESIGN OF PAVEMENTS 



399 



at the boundaries of the building-line platform and at the inter- 
section of the curb tangents. The curve formed in the curb 
joining the tangents shall follow a uniform grade between the 
elevations of the curb tangents at the points of. curve. 




FIG. 116. Camp for convicts on highway construction. 

11. Grades between Platforms. The grades of the center line 
and of the curbs between the elevations computed at platform 
intersections, or between a platform and an intermediate estab- 
lished elevation, shall be uniform. 



CHAPTER XX. 
MAINTENANCE. 

Maintenance of a highway consists in performing such repair 
operations as are needed from time to time to keep the surface 
up to maximum servicability and to prevent abnormal deteriora- 
tion of supplementary appurtenances such as guard rails and sign 
posts. In some instances maintenance becomes so extensive and 
elaborate as to really constitute reconstruction, but such work is 
not included under the ordinary interpretation of maintenance. 

When a roadway surface of any kind is completed for traffic, 
it is assumed to possess the maximum servicability for that type of 
construction. Deterioration will begin immediately and progress 
at an accelerated rate until the surface reaches its economical 
life. During this period the wearing surface should be kept in 
good repair by the operation of a system of maintenance in order 
to insure the maximum economical life. The amount and kind of 
maintenance work needed will depend upon the kind of surface, 
the volume and character of the traffic, the climate and the age 
of the road surface. 

It is an established practice in many cities to require the con- 
tractor who constructs a roadway surface to maintain that surface 
for a period varying from 5 to 7 years. This is sometimes indi- 
rectly through a guarantee clause. Compliance with the guaran- 
tee or maintenance provision is enforced through a bond filed by 
the contractor and drawn to cover the specification requirements 
relative to maintenance. This system originated when certain 
new types of pavement were being developed and public officials 
did not have a means of judging as to the probable serviceability of 
the proposed types. The promoters were willing to guarantee the 
product in order to secure contracts and the system thus developed. 

At present the requirement that the contractor must construct 
the pavement in accordance with the engineers' specifications and 
then guarantee the results, works a manifest injustice which is re- 
flected in the price paid for the work. It is believed that a guaran- 
tee should cover only a short period of time, such as one year, and 

400 



MAINTENANCE 401 

should be drawn to protect the public from dishonesty in the con- 
struction. It should not include a maintenance provision. 

The cost of maintenance cannot be predicted with any degree 
of certainty for several reasons. The most important item in 
establishing the cost of maintenance is the volume and character 
of the traffic that will use the highway, but it is almost impossible 
to foresee the traffic developments on a paved surface. The cost 
of labor also fluctuates greatly, and cannot usually be estimated 
several years in advance. The same is true of the cost of materials. 
For these reasons, to require a contractor to include in his bid a 
provision that he will maintain the surface for a period of years 
after its construction, usually results either in inadequate mainte- 
nance during the period or in loss of money to the contractor. 

After a pavement has passed beyond the guarantee period the 
city must maintain it and this work may be done by contract or 
by force account. Both methods are used but force account 
maintenance is growing in favor. 

The guarantee method of maintenance has never been exten- 
sively employed in connection with rural highways, and force 
account maintenance is being generally adopted. For some classes 
of maintenance work it has proven advantageous to employ the 
contract method. 

MAINTENANCE OF RURAL HIGHWAYS 

Organization. Nearly all state highway organizations include 
a maintenance department which has general supervision of all 
maintenance activities in the state. The highways to be main- 
tained are divided into patrol districts including from five to fifteen 
miles of highway, and a patrolman is employed to perform all 
maintenance work on the highways in his district. The amount 
of road that one man can care for will vary with the type of sur- 
face, the amount of traffic and the climatic conditions. 

In addition to the work done by the patrolmen, there will be 
some general repair work that requires a crew of several men and 
extensive equipment. For work of this latter class maintenance 
gangs are organized with the proper personnel and suitable equip- 
ment for each class of work that is performed by the gang. 

Patrol Maintenance. This system of maintenance is regularly 
employed for every type of roadway surface that is constructed 
on rural highways. The patrolmen need not be experienced in 
highway work when they begin their work, but must have some 

26 



402 CONSTRUCTION OF ROADS AND PAVEMENTS 

knowledge of the way road machinery is handled, and must be 
wide awake and possess a reasonable amount of initiative and 
common sense. They are usually employed for about 7 months 
in the year in the northern states and one to two months longer 
in the south. For earth, sand-clay and gravel surfaces, a team is 
necessary for dragging and grading, as there are rainy times when 
work should be done when the tractor cannot be used. The patrol- 
man must furnish his own team if one is to be used. If the road 
surface is bituminous macadam, asphaltic concrete, sheet asphalt, 
brick or concrete, it is entirely practicable to employ motor trucks 
for hauling all supplies and for dragging the earth shoulders. The 
patrolman may also use a light truck for travelling over his dis- 
trict but that would not be an efficient use of the truck. 

Equipment of Patrolmen. For earth, sand-clay and gravel 
roads the patrolman would be equipped with the following tools 
and machinery: 

1. A light road grader suitable for one team. 

2. One or two steel or split log drags. 

3. One or two road planers, such as the Minnesota planer. 

4. One slip scraper. 

5. One wheel scraper. 

6. One plow (sometimes) . 

7. One team with dump wagon. 

8. Picks, shovels, grubbing hoe, axe, scythe, measuring tape, paint brushes, 
sign stencils. 

9. Small kit carpenter tools. 

10. Manual of instructions and report blanks. 

For broken stone macadam, which is being maintained without 
a bituminous treatment, the following would be required : 

1. A light road grader suitable for one team. 

2. One split log or steel drag. 

3. One slip scraper. 

4. One team with dump wagon. 

5. Picks, tampers, napping hammer, grubbing hoe, axe, scythe, measuring 
tape, paint brushes, sign stencils. 

6. Small kit carpenter tools. 

7. Manual of instructions and report blanks. 

For maintenance of roads upon which the wearing surface is one 
of the types of bituminous surfaces, or surfaces upon which bi- 
tuminous materials are employed for filling cracks, the following 
equipment would be required : 



MAINTENANCE 403 

1. A light grader suitable for one team. 

2. A split log or steel drag. 

3. One slip scraper. 

4. One team with dump wagon. 

5. One portable kettle for heating bituminous material. 

6. One pouring pot for bituminous material. 

7. Picks, shovels, rakes, tampers, grubbing hoc, axe, scythe, measuring 
tape, paint brushes and sign stencils. 

8. Small kit carpenter tools. 

9. Manual of instructions and report blanks. 

The lists of equipments given above are intended to provide 
for the care of the side road and ditches, guide posts, guard rails, 
bridge floors and the wearing surface. Some items are omitted in 
specific cases and others added, but the lists show the ordinary 
equipment. Everything is provided of such a character that one 
man can do all of the work on his section of road. In some cases 
where the patrol district is made up entirely of earth roads, the 
patrolman is permitted to employ assistants to aid in the dragging 
under proper restrictions. The patrolman may also be permitted 
to rent a mowing machine to use in cutting weeds. 

Patrolling Earth Roads. The first duty is to maintain a smooth 
surface for traffic. This is accomplished by first smoothing with a 
light grader and then by dragging repeatedly with a plank or steel 
drag. Usually the grader must be used when the roads are settling 
after the spring rains, and after that the drags are adequate. 
The whole problem is to keep the surface smooth and free from 
depressions that will hold water. 

The ditches must be kept clear of obstructions so that they will 
drain freely. This is done by cleaning out with a blade grader 
and then cutting the weeds two or three times a year. Small ob- 
structions can be removed with the shovel. Where erosion of 
storm water has removed a part of the side road or the berm on 
fills, the earth is returned with the slip or wheel scraper and care- 
fully placed and tamped. 

The waterway at the ends of the culverts is cleared of weeds 
or trash two or three times a year, and the catch basins on the tile 
lines are also cleared twice a year. 

Weeds are cut at least twice a year and if this is adhered to good 
sod will usually replace the unsightly weeds. Where the topog- 
raphy permits, a mowing machine is employed for this purpose, 
but in many places the scythe will have to be used. Brush, weeds 
or low hanging limbs to trees that might obstruct the view at the 
turns, should be cut frequently. 



404 CONSTRUCTION OF ROADS AND PAVEMENTS 

Guard rails, warning signs and road signs or markers should be 
painted as required to keep them in a good state of preservation 
and any repairs required should be made promptly. 

Patrolling Surfaced Roads. The duties of the patrolmen are 
similar to those imposed upon patrolmen on earth roads except 
that the methods differ so far as upkeep of the wearing surface is 
concerned. On gravel and sand clay surfaces the principal work 
will be done with the light blade grader and the drag and planer, 
but new surfacing will be required in places. This is added while 
the road is wet so that it will bond to the old surface. In order 
to keep such surfaces up to the maximum serviceability continual 
work is required. 

With surfaces consisting of a bituminous carpet coat, the patrol- 
men patch the surface with bituminous material whenever a break 
occurs in the surface. The spot is thoroughly cleaned, new ma- 
terial heated and spread and the patch covered with stone chips 
to keep the new material from sticking to wheels. In some cases 
it may be necessary to remove depressions by adding stone to a 
small area of the surface. When this is to be accomplished the 
area effected is loosened with a pick to secure a bond between the 
old and the new material. The new stone is placed and tamped, 
coated with bituminous material and covered with chips. If the 
patch is thin, it is well to thoroughly coat the bottom of the de- 
pression with bitumen before the new material is placed. 

For repairing surfaces such as sheet asphalt or asphaltic concrete 
it is desirable to have available the equipment for preparing the 
proper mixtures of aggregates and bitumen at suitable tempera- 
tures. This sort of equipment cannot be furnished to patrolmen, 
and repair work on hot mixed pavements is usually carried out 
by special gangs. 

Temporary repairs are often accomplished by mixing small 
quantities of stone and a suitable binder by means of a shovel. 
Sometimes the binder is used cold and sometimes hot, but the 
material after mixing is stored until required and is placed and 
tamped cold. 

In order to insure that a patch will not be displaced by traffic 
it is necessary to remove the old wearing surface over the area 
affected, down to the base course. The sides and bottom of the 
hole, which should be roughly circular in form rather than square 
or rectangular, should be coated with the bituminous material 
before the new material is placed. The hole is filled and the 



MAINTENANCE 405 

material thoroughly tamped. The surface is coated with bi- 
tuminous material and covered with stone chips. 

The principal maintenance work on brick or concrete wearing 
surfaces consists in filling the cracks with a suitable bituminous 
filler. This is necessary once or twice a year and may be done 
either by the patrolman or by special gangs. The work consists in 
carefully removing dust or sand from the cracks, if they contain 
such material, and then filling with a bituminous filler. 

With all types of surfaced roads the side roads, ditches, guard 
rails, bridges, signs and waterways must be cared for in the same 
manner as with earth roads, and this work is most readily accom- 
plished by patrolmen. 

GANG MAINTENANCE 

Some classes of repair work can most economically be accom- 
plished by special gangs, and this is especially true of those opera- 
tions requiring several men to insure rapid and efficient work. 
The size of the gang and equipment provided depends entirely upon 
the work to be done. 

Gang Maintenance on Earth Roads. The work outlined in 
Chapter V, as involved in the construction of an earth road, is 
for administrative purposes sometimes classed as grade reduction 
work or construction and other times as grader work or mainte- 
nance. The grader maintenance is accomplished by special 
gangs organized and handled as described in the chapter referred 
to. For this work a tractor, one or two graders, a team and wagon 
and about four men constitute the gang. 

Gang Maintenance on Gravel and Macadam Roads. When it 
becomes necessary to resurface roads of this character, special 
gangs are employed. The equipment consists of the following: 

1. One macadam roller. 

2. One sprinkling cart. 

3. One scarafier. 

4. One heavy harrow. 

5. One light grader suitable for one team. 

6. Teams and dump wagons for hauling material. 

7. Shovels, picks, stone forks, rakes as needed. 

The work consists in thoroughly loosening the old material by 
means of the scarafier, harrowing to bring up the coarser material, 
adding new material to give the desired thickness, and rolling and 
bonding the surface with water. 



406 CONSTRUCTION OF ROADS AND PAVEMENTS 

If the maintenance consists in applying a bituminous carpet 
coat to the surface, special equipment will be required for that work. 

Oil Storage. If any regular use of road oil is made it will be 
advisable to provide one or more tanks for storage of oil, and these 
should be of sufficient capacity to hold a tank car of oil. The 
tank may be on the ground or under ground, or it may be elevated 
so that the distributing tank can be filled by gravity. If heavy 
oils are used the tanks must be equipped with steam coils for heat- 
ing the oil. 

For distributing the oil, motor driven tank trucks or horse 
drawn trucks are suitable. If the oiling operations cover a large 
mileage the motor truck is necessary in order to speed up the work. 

The surface of the road will be cleaned with a rotary broom street 
sweeper, supplemented by hand sweeping. 

Teams with dump wagons will be needed for hauling the chips 
used for dressing the surface. 

The work consists in thoroughly cleaning the surface by sweeping 
first with the power broom and then finishing with the hand broom 
to remove pockets of dust missed by the power broom. The bi- 
tuminous oil is then spread and covered with coarse chips. 

Gang Maintenance on Sheet Surfaces. When extensive repairs 
become necessary on sheet asphalt or asphaltic concrete surfaces, 
it is necessary to have a plant for mixing the materials comprising 
the surface. The equipment would consist of the following : 

1. A small plant for preparing bituminous mixtures. 

2. One tamden roller. 

3. Wagons or trucks for hauling the hot mixture. 

4. Axes, shovels, rakes, smoothing irons and tool heater. 

5. Portable kettle for heating bituminous cement. 

The road is inspected and the area to be repaired at each break 
in the surface is marked. The existing surface is removed down to 
the base. New material is mixed, spread in the holes and rolled. 
If it is an asphaltic concrete the surface is painted with asphalt 
cement and covered with stone chips or sand. 

Gang Maintenance on Brick and Cement Surfaces. Sometimes 
gangs are organized to fill the cracks in these surfaces instead of 
requiring it to be done by the patrolman. The equipment re- 
quired is the same as that furnished the patrolmen for similar 
work. The crew generally consists of a foreman and three or four 
laborers. One team will be required to haul materials. The work 
done is identical with that of the patrolman on similar surfaces. 



MAINTENANCE 407 

SNOW REMOVAL 

In areas of considerable snow fall an increasing amount of at- 
tention is being paid to removing the snow from the travelled part 
of the road or packing it down so that traffic will not be impeded. 
No one method has as yet been adopted for this work, but the 
following methods have been used with some success. 

Snow Plows. One type of snow plow is a V-shaped drag drawn 
by a tractor. It removed the snow for a width of about twelve 
feet, but several trips are required where the snow has drifted 
and laborers are required to pile back the snow from the cut in 
deep drifts. 

Another type of snow plow is pushed ahead of a truck and by 
making successive trips a track of any desired width can be made. 
Usually a track about fifteen feet wide is cleared. 

Still a third type of snow plow is built after the design of the 
rotary plow used in railroad service and is identical in operation, 
but of course much smaller. It is pushed by a truck or tractor. 

Usually there is combined with each of these methods a certain 
amount of hand shovelling to clear the heavy drifts. The use of 
snow fences is also being adopted to some extent. 

MAINTENANCE OF STREETS 

The maintenance of streets involves the upkeep of the pavement, 
where the street is paved, the maintenance of unimproved streets, 
the cleaning of the streets including the removal of snow in those 
cities where snowfall is of sufficient volume to impede traffic, and 
the inspection and cleaning of the inlets and catch basins in the 
storm sewer system. In many cities the removal of ashes and other 
refuse is accomplished by the organization that is responsible for 
the other activities mentioned, but that problem will not be dis- 
cussed herein. 

Pavement Repairs. Pavement repairs are sometimes made by 
the contractor who constructed the pavement, under a mainte- 
nance provision of his contract, and while such repairs are usually 
performed under the supervision of the city engineering depart- 
ment, the methods of actually doing the work vary with the con- 
tractor. The discussion herein refers more specifically to the re- 
pairs made after the city takes over the pavements for maintenance. 

Nearly all cities use the gang system rather than the one man 
patrol system in making pavement repairs, due primarily to the 
fact that the types of pavements that predominate do not lend 



408 CONSTRUCTION OF ROADS AND PAVEMENTS 

themselves so readily to patrol methods, and due also to the 
fact that as a rule it is desirable to expedite the work so as to 
occasion the minimum inconvenience to traffic. The maintenance 
gangs are usually organized for work on a particular type of pave- 
ment and work the entire season on that type. This simplifies 
supervision and the problem of equipping the gangs. 

Repairs are made in the manner described in the discussion of 
the construction of the several types in proceeding chapters. 

For the bituminous sheet pavements the prepared mixtures 
for the patching may be purchased under a contract or they may 
be prepared at a municipal plant. Cities that have a large area 
of sheet pavements to maintain generally find it advisable to 
operate a municipal plant as it gives the city better control over 
the time and rate at which the work is done. 

It is the usual practice to begin the repair work as soon as the 
season will permit and to continue at a rate that is estimated to 
insure completion of the projected work during the season. Open- 
ings made in pavements to reach service pipes are usually repaired 
by the utility company making the opening, but the replacement 
is under the supervision of the street department. In order to 
control the work, permits are required before openings can be made. 
This applies to plumbers as well as to public utilities. 

Unimproved streets are also maintained by gangs and the work 
consists in smoothing the streets two or three times a year by 
means of blade graders, and in maintaining the smooth condi- 
tion as well as may be by the use of the drag. The methods follow 
very closely those adopted for similar work on rural highways. 

Dust Suppression. The suppression of dust has become an 
important problem for sanitary reasons and for reasons of cleanli- 
ness. On unimproved streets one or the other of the following 
methods are usually followed: suppression by sprinkling with 
water and suppression by means of light petroleum oil. 

Street Sprinkling. Water sprinkling has been widely practiced 
for years both on unimproved streets and on gravel, macadam and 
even on high class pavements. When the cost of the water is con- 
siderable this method is expensive, and in any case it is of low 
efficiency. The effect of sprinkling lasts but a few hours in hot 
weather and is never entirely satisfactory. Immediately after 
sprinkling, the streets is likely to be sloppy and in a few hours, dusty. 

Sprinkling with oil, or road oiling, has been fully discussed in a 
previous chapter. 



MAINTENANCE 409 

Cleaning. It has come to be generally recognized that the 
best prevention of dust is through efficient cleaning, but this 
method is only available where the streets are paved with a fairly 
smooth pavement. 

STREET CLEANING 

Sweeping. One method of cleaning is to sprinkle and sweep 
the streets at frequent intervals. The work may be done nightly, 
as would be necessary on busy streets, or it may be done less fre- 
quently on residence streets. Sometimes the interval between 
cleanings is as great as two weeks or even a month. The street is 
sprinkled and immediately swept by a power sweeper, the sweepings 
being left in the gutter to be picked up by another gang. In busy 
districts the work is done at night and the cleanings are all re- 
moved before daylight. In residence districts the work is done 
by day. 

For smooth pavements such as wood block and sheet pavements 
a rubber squeegee is used instead of the broom on a power ma- 
chine. This method results in a cleaner pavement than can be 
secured with the broom but the method cannot be used on block 
pavements because the squeegee will not remove dirt from the 
cracks and uneven places. 

Recently a power cleaner operating on the principle of the 
vacuum cleaner has been developed and seems to be preferable 
to any other method devised, because the sweepings are entirely 
removed from the street at one operation. 

Flushing. Cleaning by flushing with water is widely employed 
and the method consists in washing the pavement with a stream of 
water from a pressure tank, or a stream from a pump connected 
to a tank. The jet of water flushes all of the dirt to the gutters 
and most of it is carried into the storm sewers and thus disposed of. 

Hand Sweeping. In order to preserve through the day the 
cleanly condition of the streets, patrols, the familiar " white 
wings," go over the pavement repeatedly, removing papers, trash 
and droppings and placing them in iron receptacles placed at con- 
venient points. These are emptied daily. Each patrolman works 
in a fixed area and usually works alone. 

CLEANING DRAINAGE ACCESSORIES 

The catch basins and inlets to the storm sewers are cleaned 
several times a season, or as often as refuse accumulates therein. 
The amount of labor involved in this task is enormous in a city of 



410 CONSTRUCTION OF ROADS AND PAVEMENTS 

any size, and the tendency in the design of these accessories is 
toward a type that is self-cleaning. 

SNOW REMOVAL 

The problem of snow removal is a serious one on the busier 
streets of those cities that experience considerable snowfall. 

The snow is removed by special gangs recruited for the purpose, 
supplemented by the work of the regular street cleaning forces. 
The snow is scraped to the gutters by snow plows and loaded onto 
trucks, or is shoveled directly from the street into wagons or trucks. 
It is then hauled to vacant lots or streams and dumped. In a few 
cities the snow is dumped into special traps connected with the 
sewers and thus disposed of. In other instances the snow is re- 
moved from the busy streets and stacked in the side streets where 
it is expected to melt and thus be disposed of. In cities such as 
New York and Chicago elaborate and comprehensive plans are 
worked out for removing the heavy snowfall to which those cities 
are subjected. Trucks, snow plows, snow-loaders and enormous 
forces of snow fighters are recruited for the work and the organiza- 
tion for handling the forces is complete and effective. 

EXAMPLES OF GOOD PRACTICE 

PATROL SYSTEM FOR PENNSYLVANIA ROAD MAINTENANCE 1 

Each patrolman will be supplied with tools and equipment neces- 
sary for his work and each one will have a small red flag which is 
will be required to place in a conspicuous position on the road when, 
for any reason, he is required to leave the roadside during working 
hours. Hence, either the presence of the patrol man at work or of 
his flag, indicating temporary absence, will be noticeable during 
the working hours. 

Great care is being exercised in the selection of these patrolmen 
and State Highway Commissioner Cunningham is determined to 
have none but sober, honest and industrious men in these responsi- 
ble positions. If it is found that the patrolmen are neglecting their 
work instant dismissal will follow. 

The manner in which the caretakers will work is as follows: 
Along the side of the highway at frequent intervals will be placed 
small piles of stone chips and gravel, which will be used in patching 

1 Engineering and Contracting, September 10, 1917. 



MAINTENANCE 411 

holes as they are found in the roadway. Barrels, or drums, of bi- 
tuminous material, containing approximately 45 gal. each, will be 
placed at intervals of from J^ to H mile along the roadside. When 
the caretaker finds a spot in the road which shows signs of wear 
he will place the stones and bituminous material on it, tamping 
it down carefully and making the surface of the road smooth and 
even. The caretaker also will look after the edges of the road and 
will keep the berms clear of weeds and grass and will protect the 
shoulders of the road to prevent water from getting underneath. 

Each patrolman will be supplied with the following outfit: A 
small combination melting and pouring pot on wheels, a hand- 
pouring pot, aa asphalt tamper, a wheelbarrow, a push brush, a 
pick, a short-handled and a long-handled shovel, a scythe and a 
snath, a mattock, a rake and a brush hook. 

As the patrolmen will be under the constant watch of the county 
superintendent, it will be necessary for them to devote their entire 
time and attention to the territory to which they are assigned. It 
is the intention, ultimately, that no man shall have more than 6 
miles of roadway to patrol, and this only in sections where the 
character of the road is such that he can cover it easily and con- 
veniently in a day. In mountainous districts, and in places where 
peculiar formations make the care of the road more onerous, the 
patrol distance will be diminished. 

SPECIFIC DUTIES OUTLINED 

The following list of the general duties of the patrolmen has 
been prepared by the State Highway Department and each man, 
as he is engaged, will be furnished with a copy of it and will have his 
duties explained to him in detail. 

Keep drains and ditches open at all times. 

Special attention must be given to defects in planking and condition of 
bridge floors. 

Repair all defects in the surface of the road, maintaining same in a true and 
even condition. 

Repair and whitewash guard rails. 

Provide protection and red lights in cases of flood washouts, or other emer- 
gency conditions. 

Remove brush from along the sides of the road, giving special attention to 
this condition at curves, approaches to railroad crossings, bridges, cross- 
roads, etc. 

Keep the berms or shoulders of the road trimmed up, in that the surface 
water may be discharged freely from the road surface to the side ditches. 

Remove all advertising signs from within the legal limits of the highway. 



412 CONSTRUCTION OF ROADS AND PAVEMENTS 

Paint and keep in first-class condition all department direction and warning 
signs. 

Inspect culverts, head- walls, cribbing, retaining walls, etc., and report de- 
fects immediately to the superintendent. 

Whitewash large rocks and the bases of poles on narrow sections of highway 
and at sharp curves. (Spring and fall.) Poles to be whitewashed to a height of 
6 ft. above ground. 

All equipment, tools and material placed in the charge of each caretaker 
must be accounted for by him at all times, and tools and equipment kept in 
thorough repair. 

Economic and workmanlike results will be the most important factor recog- 
nized by the department. 

Attention must be given to the entire section allotted to the caretaker, and 
work not confined to special and convenient portions. 

Daily report postal card must be mailed every evening to the superintendent. 

When working on the road caretaker must have flag, which will be provided, 
displayed at all times near where work is being performed. 

When conditions require additional help, team hire, or material of any 
character, permission must be first secured from the superintendent. 

All additional help and team hire must be carried on foreman's daily report 
form, together with regular pay roll form, etc. 

All bills for materials, etc. in amounts less than $10, must be covered by 
superintendent's purchase order; larger amounts by requisition of superinten- 
dent and department purchase order. 

Caretakers must be courteous and considerate of the interests of the public 
at all times, and conduct themselves in a manner becoming representatives 
of the commonwealth. 

Sobriety, honesty, industry, good character, and ability are the essentials 
required, and a failing in any of these will be met by dismissal. 

METHODS OP SNOW REMOVAL FROM HIGHWAYS* 

The insistent demands of modern traffic have made necessary 
the removal of snow from the surface of highways in industrial 
and commercial areas. Efficient methods of keeping these high- 
ways open in winter were outlined by Charles J. Bennett, State 
Highway Commissioner of Connecticut, in a report submitted 
Feb. 28 at the annual convention of the American Road Builders' 
Association 

In order to make a study of snow removal, the general conditions 
which govern the amount and character of the snow to be removed 
must be carefully considered. These may be classed as follows : 

Geographical Location of the Section. This determines the 
amount of annual snowfall, and the approximate greatest fall per 
storm which must be taken care of; also the usual moisture con- 

1 Engineering-Contracting, March 5, 1919. 



MAINTENANCE 413 

tent, which is a large factor in determining the amount of equip- 
ment needed. In defining this general class further, for convenience 
we may consider three sub-divisions: 

(a) Locations where the total depth of any one storm is not 
over 9 in., and the total snowfall not over 3 ft. 

(6) Locations where the total depth of any one storm is not 
over 18 in., and the total snowfall not over 3 ft. 

(c) Any location where conditions are more severe. 

Local Conditions. These are the usual cause of excessive ac- 
cumulations of snow at any given point. The general direction of 
the road combined with the prevailing direction from which the 
snow drives, causes much difference in the depth of snow to be re- 
moved. A side-hill location, or location of a road in a cut, will 
cause the accumulation of snow in the traveled path. Stone walls, 
fences and untrimmed brush hedges which may run along the 
roadway, form the most usual cause of drifts. A study should be 
made with the purpose of eliminating, as far as possible, any 
special accumulation from these causes. Hedges may be trimmed, 
walls removed, and snow fences installed. This work, properly 
carried out, will eliminate the formation of many drifts. If 
nothing can be done to prevent the formation of drifts, special ef- 
forts should be made to handle this accumulation locally, without 
leaving it to the equipment which handles the bulk of the work. 

The removal of snow in particularly congested districts, such as 
city streets, is a special problem which requires an entirely dif- 
ferent equipment from the general snow removal on highways. 
Under these conditions special studies should be made of local 
conditions, as the bulk of the snow has to be picked up and moved 
away from the streets themselves. 

The location on the travel-way of the trolley tracks, from which 
the traction companies remove the snow by plows, necessitates 
about double the amount of snow removal from the remaining 
portion of the road surface. This usually occurs in thickly popu- 
lated districts, but often occurs on interurban lines between towns. 
Equipment necessary to handle this class of work will have to be 
about double that of the ordinary work. Arrangements should be 
made to have extra equipment at these points to assist the regular 
snow removal equipment, so that it will travel at approximately 
the same rate of speed as if the trolley tracks were not there; 
similar to the local arrangements made where drifts cannot be 
prevented. If this is done, the problem is simplified and resolves 



414 CONSTRUCTION OF ROADS AND PAVEMENTS 

itself into the selection of equipment suitable to handle the greatest 
average fall in any one storm, for the section in question. 

Classification of Roads for Snow Removal Purposes. After 
determining the amount and character of snow liable to occur, 
it is then necessary to classify the roads as to the speed at which 
the work must be handled; the amount of snow to be left on the 
road and the width to which the snow should be removed, so that 
the prevailing class of traffic may use the highway with safety. 
For this purpose there are, roughly, three classes into which the 
roads may be divided : 

1. Those which carry heavy motor vehicle traffic. 

2. Those which carry a small percentage of motor vehicles and 
a large percentage of horse-drawn traffic. 

3. Those which carry a negligible amount of motor traffic, the 
delay to which should not cause serious hardships. 

Under the first class, the snow must be removed as rapidly as 
possible from the complete width of the roadway surface. The 
local conditions in this class of road are almost always bad. They 
usually run through fairly well built-up sections, where snow 
fences are not practicable, and where under the most severe con- 
ditions some snow must be moved. Under these conditions, any 
snow which must be moved clear of the roadway should be handled 
by a local organization, allowing the regular equipment to proceed 
with their work, which should be limited to taking care of the 
free passage of traffic. 

In the second class the snow need not, necessarily, be completely 
removed, and the speed necessary for the first class need not be 
maintained. About 4-in. depth of snow can be left on the road to 
take care of the horse-drawn traffic, and the width should be 
sufficient for the safe passage of vehicles, with the possible excep- 
tion of deep drifts, where the removal to this width would cause 
an unnecessary expense. 

Selection of Snow Removal Equipment. In selecting the equip- 
ment to be used, it is necessary to bear in mind the general classifi- 
cations as well as the classifications according to traffic. In general 
Class A, which includes storms up to 9 in. in depth, it has been 
found that the use of a plow attached to the front of a motor truck 
will operate to advantage, and is almost absolutely necessary 
where speed is the deciding factor, as on the roads carrying a 
heavy auto traffic. These trucks may be also used to supplement 
the equipment used on the secondary roads, should they not be 



MAINTENANCE 415 

sufficiently clear by the time the main roads are finished. Road 
machines and plows operated with horses may be successfully used 
on the secondary roads, supplemented as above, by trucks. 

The remaining class of roads carry little motor traffic, and it is 
usually sufficient to open up the drifts so that sleighs may be safely 
used. This may be done with teams and a bob sled or drag. 

In general, Class B, which includes storms up to 18 in. in depth, 
the use of motor trucks with plows is usually satisfactory, provided 
enough equipment is at hand and the work is carried on continu- 
ously with speed enough to keep ahead of the storm. High powered 
tractors may be used to good advantage, and the outlying roads 
may be taken care of, as under the first general head. 

Under the more severe conditions where the storms of more than 
18 in. are liable to occur, the removal of snow is a difficult problem, 
and should only be undertaken where it is absolutely necessary. 
In these locations removal by hand is practically the only suc- 
cessful method, and considerable snow must be moved from the 
roadway proper, as in the case of the removal of snow from city 
streets. Snow rollers should be used upon the secondary roads, and 
in the outlying sections the roads simply broken open. 



CHAPTER XXI 
ROAD MATERIALS TESTING 

Considerable progress is being made in the development of 
Standard tests for the various materials employed in highway con- 
struction and the various tests described in the previous edition of 
this book have undergone more or less revision since the book 
appeared. Early in 1920, a conference of testing engineers was 
called by the Committee on Tests and Investigations of the Amer- 
ican Association of State Highway Officials. The following 
methods of testing were adopted as standards at that conference. 
It will be noted that many of the tests had been previously adopted 
as standards by the American Society for Testing Materials. 

1. NON-BITUMINOUS MATERIALS 

ABRASION TEST FOR GRAVEL 

The aggregate is screened first through screens having circular 
openings 2 ins., 1 J^ ins., 1 in., % in. and % m - m diameter. The 
sizes used for this test are divided equally between those passing 
the 2-in. and retained on a 1^-in. screen, passing a IJ^-in. screen 
and retained on 1-in. screen, passing a 1-in. screen and retained 
on a 24-in. screen, passing a %-in. screen and retained on a J/- m - 
screen. The material of these sizes is washed and dried. The 
following weights of the dried stone are then taken: 1,250 grams 
of the size passing the 2-in. and retained on the lJ4-in. screen, 
1,250 grams of the size passing the 1^-in. and retained on the 
1-in. screen, 1,250 grams passing the 1-in. screen and retained on 
the %-in. creen, and 1,250 grams passing the %-in. screen and 
retained on the H-in. screen. This material is placed in the 
cast-iron cylinder of the Deval machine, as specified for the 
standard abrasion test on stone. Six cast-iron spheres 1.875 ins. 
in diameter and weighing approximately 0.95 pound (0.45 kg.) 
each, are placed in the cylinder as an abrasive charge. The 
spheres are the same as those used in the standard paving brick 
rattler test. 

416 



ROAD MATERIALS TESTING 417 

After the cast-iron spheres have been placed in the cylinder 
the lid is bolted on and the cylinder mounted in the frame of the 
Deval machine. The duration of the test and the rate of rotation 
are the same as specified for the standard test for stone, namely, 
10,000 revolutions at the rate of 30 to 33 revolutions per minute. 
At the completion of the test the material is taken out and screened 
through a 16-mesh sieve. The material retained upon the sieve 
is washed and dried and the percent loss by abrasion of the ma- 
terial passing the 16-mesh sieve calculated. 

When the materials have a specific gravity below 2.20 a total 
weight of 4,000 grams, made up of the four groups of sizes described 
above, instead of 5,000 grams shall be used in the abrasion test. 

ABRASION TEST FOR BROKEN STONE 

(A. S. T. M. Standard Method Serial Designation D 2-08, slightly modified) 
The machine shall consist of one or more hollow iron cylinders, closed at 
one end and furnished with a tightly fitting iron cover at the other ; the cylinder 
to be 20 cm. in diameter and 34 cm. in depth, inside. These cylinders are to 
be mounted on a shaft at an angle of 30 deg. with the axis of rotation of the 
shaft. 

The rock to be tested shall be broken from large pieces to as nearly uniform 
size as possible, and as nearly 50 pieces as possible shall constitute a test 
sample. No pieces having edges or faces that have been rounded by wear 
shall be included. The total weight of rock in a test shall be within 10 g. of 
5 kg. All test pieces shall be washed and thoroughly dried before weighing. 
Ten thousand revolutions, at the rate of between 30 and 33 per minute, shall 
constitute a test. Only the percentage of material worn off which will pass 
through a 0.16 cm. (Xe m -) mesh sieve shall be considered in determining the 
amount of wear. This shall be expressed as the percentage of the 6 kg. used 
in the test. 

For materials having a low specific gravity the quantity used for the test 
shall be adjusted on a volume basis retaining the specified number and size 
of pieces. For such materials a volume of 4000 cu. cm. of the broken stone 
or broken slag shall be used. 

STANDARD TEST FOR TOUGHNESS OF ROCK 
(A. S. T. M. Standard Method, Serial Designation: D 3-18) 

Toughness, as applied to rock, is the resistance offered to fracture under 
impact, expressed as the final height of blow required of a standard hammer to 
cause fracture of a cylindrical test specimen of given dimensions. 

Quarry samples of rock from which test specimens are to be prepared shall 
measure at least 6 in. on a side and at least 4 in. in thickness, and when possible 
shall have the plane of structural weakness of the rock plainly marked thereon. 
Samples shall be taken from freshly quarried material, and only from pieces 
which show no evidences of incipient fracture due to blasting or other causes. 
27 



418 CONSTRUCTION OF ROADS AND PAVEMENTS 

The samples should preferably be split from large pieces by the use of plugs 
and feathers and not by sledging. Commercial stone-block samples from 
which test specimens are to be prepared, shall measure at least 3 in. on each 
edge. 

Specimens for test shall be cylinders prepared as described hereafter 
25 mm. in height and from 24 to 25 mm. in diameter. Three test specimens 
shall constitute a test set. The ends of the specimen shall be plane surfaces 
at right angles to the axis of the cylinder. 

One set of specimens shall be drilled perpendicular and another parallel to 
the plane of structural weakness of the rock, if such plane is apparent. If a 
plane of structural weakness is not apparent, one set of specimens shall be 
drilled at random. Specimens shall be drilled in a manner which will not 
subject the material to undue stresses and which will insure the specified 
dimensions. 1 The ends of the cylinders may be sawed by means of a band or 
diamond saw, 2 or in any other way which will not induce incipient fracture, 
but shall not be chipped or broken off with a hammer. After sawing, the ends 
of the specimens shall be ground plane with water and carborundum or 
emery on a cast-iron lap until the cylinders are 25 mm. in length. 

Any form of impact machine which will comply with the following essentials 
may be used in making the test : 

(a) A cast-iron anvil weighing not less than 50 kg., firmly fixed upon a solid 
foundation. 

(6) A hammer weighing 2 kg., arranged so as to fall freely between suitable 
guides. 

(c) A plunger made of hardened steel and weighing 1 kg., arranged to slide 
freely in a vertical direction in a sleeve, the lower end of the plunger being 
spherical in shape with a radius of 1 cm. 

(d) Means for raising the hammer and for dropping it upon the plunger 
from any specified height from 1 to not less than 75 cm., and means for deter- 
mining the height of fall to approximately 1 mm. 

(e) Means for holding the cylindrical test specimen securely on the anvil 
without rigid lateral support, and under the plunger in such a way that the 
center of its upper surface shall, throughout the test, be tangent to the spherical 
end of the plunger at its lowest point. 

The test shall consist of a 1-cm. fall of the hammer for the first blow, a 
2-cm. fall for the second blow, and an increase of 1-cm. fall for each succeeding 
blow until failure of the test specimen occurs. 

The height of the blow in centimeters at failure shall be the toughness of the 
test specimen. The individual and the average toughness of three test speci- 
mens shall be reported when no plane of structural weakness is apparent. In 
cases where a plane of structural weakness is apparent, the individual and 
average toughness of the three specimens in each set shall be reported and 
identified. Any peculiar condition of a test specimen which might affect the 
result, such as the presence of seams, fissures, etc., shall be noted and recorded 
with the test result. 



The form of diamond drill described in Bulletin No. 347 U. 8. Department of Agri- 
culture, pp. 6-7, is recommended and should prove satisfactory if the instructions are strictly 

'Note. A satisfactory form of diamond saw is described in Bulletin No. 347 U. S. Depart- 
ment of Agriculture, pp. 7-9. 



ROAD MATERIALS TESTING 419 

WEIGHT PER CUBIC FOOT AND VOID TESTS ON 
COARSE AGGREGATE 

The weight per cubic foot of coarse aggregate shall be determined as follows : 

A cylindrical measure of at least M cu. ft. capacity with inside diameter 
approximately equal to inside height, or a box approximately cubical in shape 
and of not less than Y^ cu. ft. capacity should be used. 

Ordinarily, the determination should be made on aggregate in air-dry 
condition. When the aggregate contains an appreciable amount of moisture, 
the percentage of water by weight should be determined and recorded. 

About J4 of the total amount of aggregate necessary to fill the measure is 
first introduced in such manner as to avoid separation of sizes. This material 
is then shaken down by rocking the measure from side to side until no further 
settlement takes place. The process, is repeated until the measure has been 
filled to overflowing, after which it is struck off level with the top with a straight 
edge and weighed. 

The percentage of voids in the aggregate may be determined from the weight 
per cubic foot and specific gravity in the usual manner. 

METHOD OF DETERMINING THE WEIGHT OF FINB 
AGGREGATE PER CUBIC FOOT 

For tests on fine aggregate use a cylindrical metal measure having inside 
diameter equal to inside depth. A measure of capacity of % to % cu. ft. is 
suggested, but a measure as small as Ko cu. ft. capacity may be used. 

Ordinarily the weight per cubic foot should be determined on air-dry 
material. When the aggregate contains an appreciable amount of moisture 
the percentage of water by weight should be determined and recorded. 

Fill the measure one- third full, puddle with 25 to 30 strokes from a H-in. 
round steel bar 20 in. long, pointed at the lower end. Continue filling and 
puddling in like manner until the measure is full, then strike off the top by a 
rolling motion with the bar. Determine the weight of the contents of the 
measure and calculate the weight in pounds per cubic foot. 

SPECIFIC GRAVITY AND ABSORPTION TESTS ON 
STONE OR OTHER COARSE MATERIALS 

The apparent specific gravity is obtained by weighing the water displaced 
by a sample of the material weighing approximately 1,000 grams, broken 
into pieces about 1 % ins. in diameter. A special type of vessel is used. It 
consists of a galvanized iron cylinder closed at one end, and measuring 
5 in. in diameter by 8 in. high. A brass spout J^-in. in diameter is soldered 
into the side of the cylinder 6 in. from the bottom. The spout is inclined 
at an angle of 2 with the horizontal and is 2^ in. long. A notch is filed 
across its lower end, as shown, to stop the drip from the displaced water. 
In determining the specific gravity, the dried and cooled sample is weighed 
to the nearest 0.5 gram and immersed in water for 24 hours. The pieces are 
then individually surface-dried with a towel, the sample reweighed and 
immediately placed in the cylinder, which has been previously filled to over- 
flowing with water at room temperature. 

The weight of water displaced by the sample is used to calculate its apparent 
specific gravity. The difference between the original weight of the sample 
and its weight after 24 hours, is used to determine the absorption. 



420 CONSTRUCTION OF ROADS AND PAVEMENTS 

STANDARD METHOD FOR MAKING A MECHANICAL ANALYSIS OF 
BROKEN STONE, BROKEN SLAG, OR GRAVEL PEBBLES 

(A. S. T. M. Standard Method, Serial Designation: D 18-16, slightly 

modified.) 

The method shall consist of drying at not over 110C. (230F.) to a constant 
weight a sample weighing in pounds six times the diameter in inches of the 
largest holes required; passing the sample through such of the following 
size screens having circular openings as are required or called for by the 
specifications, screens to be used in the order named: 8.89 cm. (3)^ in.), 
7.62 cm. (3 in.), 6.35 cm. (2^ in.), 5.08 cm. (2 in.), 3.81 cm. (1 ^ in.), 3.18 cm 
(\Y in.), 2.54 cm. (1 in.), 1.90 cm. (% in.), 1.27 cm. (Y 2 in.), and 0.64 cm. 
(}4 in-)j determining the percentage by weight retained on each screen; 
and recording the mechanical analysis in the following manner: 

Passing 0.64 cm. (^ in.) screen per cent. 

Passing 1.27 cm. (% in.) screen and retained 

on a 0.64 cm. (% in.) screen per cent. 

Passing 1.90 cm. (% in.) screen and retained 

on a 1.27 cm. (3^ in.) screen per cent. 

Passing 2.54 cm. (1 in.) screen and retained 

on a 1.90 cm. (% in.) screen. . per cent. 

. per cent. 

100.00 per cent. 

STANDARD METHOD FOR MAKING A MECHANICAL ANALYSIS 

OF SAND OR OTHER FINE HIGHWAY MATERIAL 
(A. S. T. M. Standard Method, Serial Designation: D 7-18, slightly 

modified.) 

Adopted, 1919. Revised 1916, 1918. 

The method shall consist of drying at not over 110C. (230F.) to a constant 
weight of a sample weighing of from 100 grams to 500 grams; passing the 
sample through each of the mesh sieves (American Society for Testing Materi- 
als standard sieves) specified in Table I 1 ; determining the percentage by 
weight retained on each sieve, the sifting being continued on each sieve until 
less than 1 per cent, of the weight retained on each sieve shall pass through 
the sieve during the last minute of sifting; and recording the mechanical 
analysis in the following manner: 

Passing 200-mesh sieve per cent. 

Passing 100-mesh sieve and retained on a 200- 
mesh sieve per cent. 

Passing 80-mesh sieve and retained on a 100- 
mesh sieve per cent. 

Passing 50-mesh sieve and retained on a 80- 
mesh sieve per cent. 

per cent. 

100.00 per cent. 

^ote. The order in which the sieves are to be used in the process of sift- 
ing is immaterial and shall be left optional, but in reporting results the order 
in which the sieves have been used shall be stated. 



ROAD MATERIALS TESTING 



421 



TABLE 1. A. S. T. M. STANDARD SIEVES 



Mesh 
Designation 


Unit of 
Measure 


Actual 
Mesh 


Opening 


Wire 
Diameter 


Permissible 
Variations 


Mesh 


Diameter 


10* 


cm. 
in. 
cm. 
in. 
cm. 
in. 
cm. 
in. 
cm. 
in. 
cm. 
in. 
cm. 
in. 
cm. 
in. 


3.9 
9.9 
8 
20.3 
12.0 
30.5 
16 
40.6 
20 
50.8 
31 
78.7 
39 
99.1 
79 
200.7 


0.200 

0.079 
0.085 
0.0335 
0.050 
0.0197 
0.036 
0.0142 
0.029 
0.0114 
0.017 
0.0067 
0.014 
0.0055 
0.0074 
0.0029 


0.056 
0.022 
0.040 
0.0157 
0.033 
0.0130 
0.026 
0.0102 
0.021 
0.0083 
0.015 
0.0059 
0.0116 
0.0046 
0.0053 
0.0021 


0.04 
0.1 
0.2 
0.5 
0.4 
1.0 
0.6 
1.5 
0.8 
2 
1 
3 
1 
3 
3 
8 


0.005 
0.002 
0.0015 
0.0006 
0.0012 
0.0005 
0.0010 
0.0004 
0.0010 
0.0004 
0.0008 
0.0003 
0.0008 
0.0003 
0.0005 
0.0002 


20* 


30 


40* < 
50 


80 


100* 


200* 



* It is recommended that for routine tests except for fine aggregate for 
hot mixed bituminous surfaces, the /4-in. screen and these sieves be used. 



MAKING A MECHANICAL ANALYSIS OF MIXTURES OF SAND OR 

OTHER FINE MATERIAL WITH BROKEN STONE, BROKEN 

SLAG OR GRAVEL PEBBLES 



(A. S. T. M. Standard Method, Serial Designation: D 19-16.) 

The method shall consist of drying at not over 110C. (230F.) to a constant 
weight a sample weighing in pounds six times the diameter in inches of the 
largest holes required;, separating the sample by the use of a screen having 
circular openings 0.64 cm. (^-in.) in diameter; examining the portion retained 
on the screen in accordance with the Standard Method for Making a Mechan- 
ical Analysis of Broken Stone or Broken Slag, except for Aggregated Used 
in Cement Concrete (Serial Designation: D 18) of the American Society 
for Testing Materials; examining the portion passing this screen in accordance 
with the Standard Method for Making a Mechanical Analysis of Sand or 
Other Fine Highway Material, except for Fine Aggregates Used in Cement 
Concrete (Serial Designation D 7) of the American Society for Testing Ma- 
terials; and recording the mechanical analysis in the following manner: 



422 CONSTRUCTION OF ROADS AND PAVEMENTS 

Passing 200-mesh sieve per cent. 

Passing 100-mesh sieve and retained on a 

200-mesh sieve per cent. 

Passing 80-mesh sieve and retained on a 100- 
mesh sieve per cent. 

Passing 10-mesh sieve and retained on a 20- 

mesh sieve per cent. 

Passing 0.64 cm. (J^-in.) screen and retained 

on a 10-mesh sieve per cent. 

Passing 1.27 cm. (^-in.) screen and retained 

on a 0.64 cm. (%-in.) screen per cent. 

Passing 1.90 cm. (%-in.) screen and retained 

on a 1.27 cm. (3^-in.) screen per cent. 

per cent. 



100.00 per cent. 
TEST FOR AMOUNT OF CLAY AND SILT IN SAND OR FINE AGGREGATE 

The sample as received shall be moistened and thoroughly mixed, then 
dried to constant weight at a temperature between 100C. (212F.) and 110C. 
(230F.). 

Five hundred (500) grams representative of the dried sample shall be 
placed in a dried and accurately weighed pan or vessel having vertical sides 
and provided with a pouring lip. This pan shall be substantially 22.9 cms. 
(9 in.) in diameter by not less than 10.2 cms. (4 in.) deep. Pour sufficient 
water in the pan to cover the sand (about 225 c. c.). Agitate vigorously 
for fifteen (15) seconds and then pour off the water into a tared evaporating 
dish, taking care not to pour off any sand. Repeat until the wash water is 
clear, using a glass rod to stir the material for the last few washings. 

Thoroughly dry the pan and washed sand in an oven at between 100C. 
(212 F.) and 110 C. (230 F.), weigh and determine net weight of sand. 

Compute the per cent, of clay and silt as follows: 

Original weight - weight after washing 

- X 100 = per cent, of clay and silt. 
Original weight 

For a check on the results, evaporate the wash water to dryness and weigh 
the residue. 

Weight of residue 



Original weight 



X 100 = per cent, of clay and silt. 



TEST FOR AMOUNT OF CLAY AND SILT IN GRAVEL 

The sample as received shall be moistened and thoroughly mixed, then 
dried to constant weight at a temperature between 100 C. (212 F.) and 
110 C. (230 F.). 

A representative portion of the dry material, weighing not less than 50 
times the weight of the largest stone in the sample, shall be selected from the 
sample, and placed in a dried and accurately weighed pan or vessel. The pan 



ROAD MATERIALS TESTING 423 

shall be 30.2 cms. (12 in.) in diameter by not less than 10.2 cms. (4 in.) 
deep, so nearly as may be obtained. Pour sufficient water in the pan to 
cover the gravel and agitate vigorously for fifteen (15) seconds, using a 
trowel or stirring rod. Allow to settle for fifteen (15) seconds, and then pour 
off the water into a tared evaporating dish, being careful not to pour off any 
sand. Repeat until the wash water is clear. 

Dry the washed material to constant weight in an oven at between 100 C. 
(212 F.) and 110 C. (230 F.), weigh and determine net weight of gravel. 

Compute the per cent, of clay and silt as follows: 

Original weight weight after washing 

- X 100 = per cent, of clay and silt. 
Original weight 

TEST FOR CLAY IN SAND-CLAY, Top-SoiL AND SEMI-GRAVEL 

Dry 500 grams of the material at a temperature below 350F. (176.6C.) 
to a constant weight. Gently pulverize to break down soft clods or masses, 
but not to grind or break hard material. Pass through a 10-mesh sieve, 
weigh the coarse residue and record as "coarse material." Use the material 
passing through the 10-mesh sieve as the starting point of a percentage analysis 
as follows: 

Weight out two samples of 50 grams of this material for duplicate analysis. 
Place each in a tared wide mouth bottle (5 to 6 cm. diameter and about 12 to 
15 cm. high). Add about 5 c. c. of dilute ammonia water and about 200 c. c. 
of water. Close with a cork or glass stopper and shake thoroughly for 20 
minutes. Allow the sample to settle eight minutes and decant carefully or 
siphon off the supernatant liquid to a depth of 8 cm. below the surface of the 
liquid. (The depth of the liquid in the bottle should be sufficient to leave 
about 4 cm. below the point of siphoning). Fill the bottle again with water, 
shake for three minutes, allow settlement, and siphon off as before. Repeat 
the process until the supernatant liquid is clear. Be careful to wash the 
stopper and neck of the bottle free from coarse material before decanting. 

Dry bottle and washed material to constant weight at between 100 C. 
(212 F.) and 110 C. (230 F.), weigh and determine net weight of washed 
material. 

Original weight washed weight 

- X 100 = per cent, clay and silt. 
Original weight 

As a check the washings drawn off shall be collected and evaporated to 
dryness for direct recovery of the fine sediment classed as clay and silt. 

Weight of residue 

- X 100 - per cent. clay. 
Original weight 

The determinations on the two samples shall check within one per cent, 
to be acceptable. 

TESTS FOR SEMI-GRAVEL, TOP-SOIL AND SAND-CLAY 

Wash the contents of the bottle cleanly into a porcelain evaporating dish 
and carry to dryness on a water bath. The dried residue should be carefully 
scraped from the dish and passed through a nest of 20-, 60-, 100- and 200-mesh 



424 CONSTRUCTION OF ROADS AND PAVEMENTS 

sieves. The residue retained on each sieve is weighed and recorded as sand 
of the respective sizes. Their sum constitutes the total "sand." The residue 
passing the 200-mesh sieve and caught in the pan is weighed and recorded as 
"silt." Duplicate samples should check within 1 per cent. 

(a) The coarse material should be examined for hardness and with the 
magnifying glass to identify its character as quartz, hard iron compounds, 
feldspar, schistose material, or indurated clay. Hard quartz or iron gravels 
are valuable in themselves and as indicating the quality of the finer aggregate. 
Feldspar, mica, and clay nodules are worthless and indicate that the accom- 
panying soil is poor for road building. 

(6) The sands should be examined with the magnifying glass for identifica- 
tion as quartz and for the presence of mica scales or feldspar needles. If mica 
or feldspar is present in appreciable amounts the sample should be rejected. 

(c) When the clay is recovered by evaporation it can be examined for 
tenacity by cementing together two glass plates, each 1 inch wide, set at 
right angles, with a layer of clay whose thickness is fixed by a fine bent wire 
laid between the plates. The moist clay covers the wire on one plate, and the 
other plate is squeezed down tightly on the wire. After drying, the one plate 
held firmly against cleats, wire slings are run symmetrically from the ends 
of the upper plate to one arm of a beam balance, and the tension necessary 
to separate the plates is given by shot or weights in the other pan of the 
balance. This test is tedious and is of service chiefly on low-grade samples 
which are of doubtful efficiency, but which represent the only available 
material for local construction. 

(d) Approximate tests for tenacity of mixture can be made as follows: 
Make cylinders from the material passing the 10-mesh sieve, 25 mm. by 

25 mm. The material is worked into a stiff mud and molded under 132 kg. 
per sq. cm. pressure. Dry thoroughly at 100C. (212 F.) and break by the 
small Page impact machine for testing cementing value, using a 1 kg. hammer 
and 1 cm. drop. Record the number of strokes as the relative measure of 
tenacity. 

Usually the plastic character and adhesiveness of a good road soil can be 
judged by the feeling of the mud made from this material, its adherence to the 
hands, and its stretch under light pulling. 

COLORIMETRIC TEST ON CONCRETE AGGREGATE 

The test to be used is described in the "Proceedings of the 
American Society for Testing Materials, Philadelphia, Pennsyl- 
vania, Volume XIX, Par. 1, 1919. Appendix to Report of Com- 
mittee C-9 on Concrete and Concrete Aggregates," and is as 
follows : 

The test as usually made consists of shaking the sand thoroughly in a 
dilute solution of sodium hydroxide (NaOH) and observing the resultant color 
after the mixture has been allowed to stand for a few hours. Fill a 12-oz. 
graduated perscription bottle to the 4^ oz. mark with the sand to be tested. 
Add a 3 per cent, solution of sodium hydroxide until the volume of the sand 
and solution, after shaking, amounts to 7 oz. Shake thoroughly and let stand 



ROAD MATERIALS TESTING 425 

for 24 hours. Observe the color of the clear liquid above the sand. A good 
idea of the quality of the sand can be formed earlier than 24 hours, although 
this period is believed to give best results. 

If the solution resulting from this treatment is colorless, or has a ligh^ 
yellowish color, the sand may be considered satisfactory in so far as organic 
impurities are concerned. On the other hand, if a dark colored solution of a 
color deeper than that indicated is produced, the sand should not be used in 
high grade concrete such as that required in roads and pavements, or in 
building construction. 

Color Values. While it is not practicable to give exact values for the 
reduction in strength corresponding to the different colors of solution, the 
tests made thus far show this relation to be about as follows: 

Reduction in 
Compressive Strength of 

Color 1.3 Mortar at 7 and 

Number 28 days. 

per cent. 

Fig. 1 none 

Fig. 2 10-20 

Fig. 3 15-30 

Fig. 4 25-50 

Fig. 5 50-100 

Washing dirty sands has the effect of greatly reducing the quantity of 
organic impurities. However, even after washing, sands should be examined 
in order to determine whether the organic impurities have been reduced to 
harmless proportions. 

The following list includes sufficient apparatus for making five field tests 
at a time: 

Five 12-oz. graduated prescription bottles; Stock of 3 per cent, solution 
of sodium hydroxide (dissolve 1 oz. of sodium hydroxide in enough water 
to make 32 oz.) 

This test does not give satisfactory results when lignite is present in the sand. 



PROPOSED TEST FOR PERCENTAGE OF SHALE IN GRAVEL 

It is suggested that for the separation of shale and other light unsatisfactory 
pieces from concrete aggregate, a solution of zinc chloride (ZnCl 2 ) or some 
other satisfactory liquid having a specific gravity of approximately 1.95 be 
used. A sample of the pebbles should be first dried to constant weight at 
not over 110 C., then placed in a container of suitable size partially filled 
with the solution. Agitate for five minutes, skim off the lighter materials and 
then pour the solution through a sieve which will retain the pebbles. Repeat 
operation until entire sample has been separated. Dry to constant weight, 
measure the volume of retained material and compute the percentage by 
volume of shale or other soft material. 



426 CONSTRUCTION OF ROADS AND PAVEMENTS 

SLUMP TEST FOR CONSISTENCY OF CONCRETE 

For the determination of the consistency either in the field or in the labora- 
tory the committee proposed the use of the 4x8x12 conical frustum. 

In making the test, the thoroughly cleaned frustum should be placed on a 
level non-absorbent surface and filled with 3-inch layers of concrete. During 
filling, the mold should be held down by the operator placing his toes on the 
lip at the bottom of the mold. As each layer of material is introduced it should 
be puddled, with a Y% in. rod to uniformly distribute the material. 

After the upper layer has been placed the top shall be struck off and the 
mold removed by slowly pulling it vertically upward. The height of the 
frustum shall be measured and the slump calculated from the difference of 
the height of the mold and the frustum. 

In making the slump test in the laboratory or in the field it is recommended 
that the form be filled immediately after mixing and withdrawn three minutes 
after mixing has been completed. 

When central mixing plants are used, slump tests shall be made at the 
plant and at the end of the haul. At the plant the sample of concrete shall 
be taken after the entire batch has been discharged from the mixer. At the 
end of the haul the slump sample shall be taken from the batch after it has been 
dumped on the sub'grade. The slump at the points of deposition shall be 
suitable for the particular type of finish employed. 

PROPOSED ABRASION TEST FOR FINE AGGREGATE 

The following is suggested as a tentative method for determining the 
resistance of the fine aggregate to abrasion. The fine aggragate is washed and 
dried at a temperature not exceeding 110 C. All material retained on the 
^ in. sieve, and all material passing a standard 50-mesh sieve is discarded. 
Five hundred (500) grams of the portion passing a % in- screen and retained 
on a 50-mesh sieve are placed in a Deval abrasion cylinder with a charge of 
250 grams of %y-m. commercial steel bearing balls (21 balls weigh practically 
250 grams). The weight of the balls is to be within 1 per cent, of the required 
250 grams. The charge in the Deval abrasion cylinder is rotated for 2,000 
revolutions at the rate of 33 R. P. M. The sample of sand is removed and 
sieved over a 100-mesh sieve. The sample is preferably divided in three 
portions for sieving, the sieving being completed over a white sheet of paper, 
and is continued until practically no dust passes the sieve when shaking for 
one minute. The portion retained on the 1 00-mesh sieve is weighed. Five 
hundred (500) grams minus the weight of the samples retained on the 100- 
mesh after abrasion, is taken as the loss on abrasion. This weight divided 
by 5 gives the percentage of wear. 

PROPOSED TEST FOR CONSISTENCY OF CONCRETE 

For the determination of the consistency either in the field or 
in the laboratory the committee proposed the use of the 4x8x12 
conical frustum. 



ROAD MATERIALS TESTING 427 

In making the test, the thoroughly cleaned frustum should be 
placed on a level non-absorbent surface and filled with 3-in. 
layers of concrete. During filling, the mold should be held down 
by the operator placing his toes on the lip at the bottom of the 
mold. As each layer of material is introduced it should be puddled, 
with a J^-in. rod to uniformly distribute the material. 

After the upper layer has been placed the top shall be struck 
off and the mold removed by slowly pulling it vertically upward. 
The height of the frustum shall be measured and the slump cal- 
culated from the difference of the height of the mold and the 
frustum. 

In making the slump test in the laboratory or in the field it is 
recommended that the form be filled immediately after mixing and 
withdrawn three minutes after mixing has been completed. 

When central mixing plants are used slump tests shall be made 
at the plant and at the end of the haul. At the plant the sample 
of concrete shall be taken after the entire batch has been dis- 
charged from the mixer. At the end of the haul the slump sample 
shall be taken from the batch after it has been dumped on the 
subgrade. 

H. BITUMINOUS MATERIALS 
FIXED CARBON 

This determination is made in accordance with the method described for 
coal in the Journal of the American Chemical Society, 1899, volume 21, page 
1116. One gram of the material is placed in a platinum crucible weighing 
from 20 to 30 grams and having a tightly fitting cover. It is then heated for 
seven minutes over the full flame of a Bunsen burner. The crucible should 
be supported on a platinum triangle with the bottom from 6 to 8 centimeters 
above the top of the burner. The flame should be fully 20 centimeters high 
when burning freely, and the determination should be made in a place free from 
drafts. The upper surface of the cover should burn clear, but the under 
surface should remain covered with carbon, excepting in the case of some of 
the more fluid bitumens, when the under surface of the cover may be quite 
clean. 

The crucible is removed to a desicator and when cool is weighed, after 
which the cover is removed, and the crucible is placed in an inclined position 
over the Bunsen burner and ignited until nothing but ash remains. Any 
carbon deposited on the cover is also burned off. The weight of ash remain- 
ing is deducted from the weight of the residue after the first ignition of the 
sample. This gives the weight of the so-called fixed or residual carbon, which 
is calculated on a basis of the total weight of the sample, exclusive of mineral 
matter. If the presence of a carbonate mineral is suspected, the percentage 
of mineral matter may be most accurately obtained by treating the ash with 



428 CONSTRUCTION OF ROADS AND PAVEMENTS 

a few drops of ammonium carbonate solution, drying at 100 C., then heating 
for a few minutes at a dull red heat, cooling and weighing. 

An excellent form of crucible for this test has a cover with a flange 4 milli- 
meters wide, fitting tightly over the outside of the crucible, and weighs com- 
plete about 25 grams. Owing to sudden expansion in burning some of the 
more fluid bitumens, it is well to hold the cover down with the end of the tongs 
until the most volatile products have burned off. 

Some products, particularly those derived from Mexican petroleum, show 
a tendency to suddenly expand and foam over the sides of the crucible in 
making this determination, and no method of obviating this trouble without 
vitiating the result has thus far been forthcoming. Recent experiments in 
the laboratory of the Office of Public Roads and Rural Engineering indicate 
that the difficulty may be overcome by placing a small piece of platinum 
gauze over the sample and about midway of the crucible. The gauze should 
be so cut or bent as to touch the sides of the crucible at all points, and is of 
course weighed in place in the crucible before and after ignition. 

DUCTILITY 

A briquette of the material to be tested shall be formed by pouring the 
molten material into a briquette mould. The dimensions of the briquette 
shall be: 1 cm. (1.181 in.) in thickness throughout its entire length; distance 
between the clips or end pieces, 3 cm. (1.181 in.); width of asphalt cement 
section at mouth of clips, 2 cm. (0.787 in.); width at minimum cross-section 
half way between clips, 1 cm. (0.394 in.). The center pieces are removable, 
the briquette mould being held together during moulding with a clamp or wire. 

The moulding of the briquette shall be done as follows: The two center 
sections shall be well amalgamated to prevent the asphalt cement from adher- 
ing to them, and the briquette mould shall then be placed on a freshly amal- 
gamated brass plate. The asphalt cement to be tested, while in a moulten 
state, shall be poured into the mould, a slight excess being added to allow 
for shrinkage on cooling. When the asphalt cement in the mould is nearly 
cool, the. briquette shall be cut off level, with a warm knife or spatula. When 
it is thoroughly cooled to the temperature at which it is desired to make the 
test, the clamp and the two side pieces are removed, leaving the briquette 
of asphalt cement held at each end by the end by the ends of the mould, which 
now play the part of clips. The briquette shall be kept in water for 30 min. 
at 4 C. (39 F.) or 25 C. (77 F.) before testing, dependent on the tempera- 
ture at which the ductility is desired. The briquette with the clips attached 
shall then be placed in a "ductility test machine" filled with water at one of 
the above temperatures to a sufficient height to cover the briquette not less 
than 50 mm. (1.969 in.). This machine consists of a rectangular water-tight 
box, having a movable block working on a worm-gear from left to right. The 
left clip is held rigid by placing its ring over a short metal peg provided for 
this purpose; the right clip is placed over a similar rigid peg on the movable 
block. The movable block is provided with a pointer which moves along a 
centimeter scale. Before starting a test, the centimeter scale is adjusted to 
the pointer at zero. Power is then applied by the worm-gear pulling from 
left to right at the uniform rate of 5 cm. (1.969 in.) per min. The distance, in 



ROAD MATERIALS TESTING 429 

centimeters, registered by the pointer on the scale at the time of rupture of 
the thread of asphalt cement shall be taken as the ductility of the asphalt 
cement. 

PENETRATION OF BITUMINOUS MATERIALS 
(A. S. T. M. Standard Method, Serial Designation: D 5-16) 

I. DEFINITION 

Penetration is defined as the consistency of a bituminous material, expressed 
as the distance that a standard needle vertically penetrates a sample of the 
material under known conditions of loading, time and temperature. Where 
the conditions of test are not specifically mentioned, the load, time and temper- 
ature are understood to be 100 g., 5 seconds, 25 C. (77 F.), respectively, and 
the units of penetration to indicate hundredths of a centimeter. 

II. APPARATUS 

The container for holding the material to be tested shall be a flat-bottom, 
cylindrical dish, 55 mm. (203 /16 in.) in diameter and 35 mm. (1 Y$ in.) deep. 1 

The needle 2 for this test shall be of cylindrical steel rod 50.8 mm. (2 in.) 
long and having a diameter of 1.016 mm. (0.04 in.) and turned on one end to 
a sharp point having a taper of 6.35 mm. ( l / in.). 

The water bath shall be maintained at a temperature not varying more 
than .1 C. from 25 C. (77 F.). The volume of water shall be not less 
than 10 liters and the sample shall be immersed to a depth of not less than 10 
cm. (4 in.) and shall be supported on a perforated shelf not less than 5 cm. 
(2 in.) from the bottom of the bath. 

Any apparatus which will allow the needle to penetrate without appreciable 
friction, and which is accurately calibrated to yield results in accordance with 
the definition of penetration will be acceptable. 

The transfer dish for container shall be a small dish or tray of such capacity 
as will insure complete immersion of the container during the test. It shall 
be provided with some means which will insure a firm bearing and prevent 
rocking of the container. 

III. PREPARATION OF SAMPLE 

and stirred thoroughly until it is homogeneous and free from air bubbles. 
It shall then be poured into the sample container to a depth of not less than 
15 mm. (% in.). The sample shall be protected from dust and allowed to 
cool in an atmosphere not lower than 18 C. (65 F.) for one hour. It shall 
then be placed in the water bath along with the transfer dish and allowed 
to remain one hour. 

The sample shall be completely melted at the lowest possible temperature 

'Note. This requirement is fulfilled by the American Can Company's Gill style ointment 
box, deep pattern, 3 oz. capacity. 

'Note. Until a standard needle that is generally procurable is developed, it is recommended 
that the Roberts No. 2, Parabola Needle be employed. 



430 CONSTRUCTION OF ROADS AND PAVEMENTS 

IV. TESTING 

(a) In making the test the sample shall be placed in the transfer dish 
filled with water from the water bath of sufficient depth to completely cover 
the container. The transfer dish containing the sample shall then be placed 
upon the stand of the penetration machine. The needle, loaded with specified 
weight, shall be adjusted to make contact with the surface of the sample. 
This may be accomplished by making contact of the actual needle point with 
its image reflected by the surface of the sample from a properly placed source 
of light. Either the reading of the dial shall then be noted or the needle 
brought to zero. The needle is then released for the specified period of time, 
after which the penetration machine is adjusted to measure the distance 
penetrated. 

At least three tests shall be made at points on the surface of the sample 
not less than 1 cm. (% in.) from the side of the container, and not less than 1 
cm. (iMs in.) apart. After each test the sample and transfer dish shall be 
returned to the water bath and the needle shall be carefully wiped toward 
its point with a clean, dry cloth to remove all adhering bitumen. The reported 
penetration shall be the average of at least three tests whose values shall not 
differ more than four points between maximum and minimum. 

(6) When desirable to vary the temperature, time and weight, and, in order 
to provide for a uniform method of reporting results when variations are made, 
the sample shall be melted and cooled in air as above directed. They shall then 
be immersed in water or brine, as the case may require, for one hour at the 
temperature desired. The following combinations are suggested: 

At C. (32 F.) 200-g. weight, 60 seconds. 
At 46 .1 C. (115 F.) 50-g weight, 5 seconds. 

DISTILLATION OF CREOSOTE OIL 

(A. S. T. M. Standard Method, Serial Designation: D 38-18) 

(a) Report: This shall be a tubulated glass retort with a capacity of 250 
to 290 cc. The capacity shall be measured by placing the retort with the 
bottom of the bulb and the end of the offtake in the same horizontal plane, 
and pouring water into the bulb through the tubulature until it overflows 
the offtake. The amount remaining in the bulb shall be considered its 
capacity. 

(6) Condenser Tube: The condenser tube shall be a suitable form of tapered 
glass tubing of the following dimensions : 

Diameter of small end 12. 5 mm., permissible variation 1.5 mm. 

Diameter of large end 28.5 mm., permissible variation 3.0 mm 

Length 360.0 mm., permissible variation 4.0 mm. 

(c) Shield: An asbestos shield shall be used to protect the retort from air 
currents and to prevent radiation. This may be covered with galvanized 
iron, as such an arrangement is more convenient and more permanent. 

(d) Receivers: Erlenmeyer flasks of 50 to 100 cc. capacity are the most 
convenient form. 



ROAD MATERIALS TESTING 431 

(e) Thermometer: The thermometer shall conform to the following re- 
quirements : 

The thermometer shall be made of thermometric glass of a quality equivalent 
to suitable grades of Jena or Corning make. It shall be thoroughly annealed. 
It shall be filled above the mercury with inert gas which will not act chemically 
on or contaminate the mercury. The pressure of the gas shall be sufficient 
to prevent separation of the mercury column at all temperatures of the scale. 
There shall be a reservoir above the final graduation large enough so that the 
pressure will not become excessive at the highest temperature. The thermo- 
meter shall be finished at the top with a small glass ring or button suitable 
for attaching a tag. Each thermometer shall have for identification the 
maker's name, a serial number and the letters "A. S. T. M. distillation." 

The thermometer shall be graduated from to 400 C. at intervals of 1 C. 
Every fifth graduation shall be longer than the intermediate ones, and every 
tenth graduation beginning at zero shall be numbered. The graduation 
marks and numbers shall be clear-cut and distinct. 

The thermometer shall conform to the following dimentions: 

Total length, maximum. . . .385.0 mm. 

Diameter of stem 7.0 mm., permissible variation 0.5 mm. 

Diameter of bulb, minimum 5.0 mm., and shall not exceed diameter of 

stem. 

Length of bulb 12.5 mm., permissible variation 2.5 mm. 

Distance, to bottom of 

bulb 30.0 mm., permissible variation 5.0 mm. 

Distance, to 400 295.0 mm., permissible variation 10.0 mm. 

The accuracy of the thermometer when delivered to the purchaser shall 
be such that when tested at full immersion the maximum error shall not 
exceed the following: 

From to 200 C .5 C. 

From 200 to 300 C 1 .0 C. 

From 300 to 375 C 1 .5 C. 

The sensitiveness of the thermometer shall be such that when cooled 
to a temperature of 74 C. below the boiling point of water at the barometric 
pressure at the time of test, and plunged into free flow of steam, the meniscus 
shall pass the point 10 C. below the boiling point of water in not more than 
six seconds. 

The retort shall be supported on a tripod or rings over two sheets of 20- 
mesh gauze, 6 in. square. It shall be connected to the condenser tube by a 
tight cork joint. The thermometer shall be inserted through a cork in the 
tubulature with the bottom of the bulb % in. from the surface of the oil in the 
retort. 

The exact location of the thermometer bulb shall be determined by placing 
a vertical rule graduated in divisions not exceeding % 6 in. back of the retort 
when the latter is in position for the test, and sighting the level of the liquid 
and the point for the bottom of the thermometer bulb. The distance from 
the bulb of the thermometer to the outlet end of the condenser tube shall 



432 CONSTRUCTION OF ROADS AND PAVEMENTS 

be not more than 24 nor less than 20 in. The burner should be protected 
from draughts by a suitable shield or chimney. 

Exactly 100 g. of oil shall be weighed into the retort, the apparatus assembled 
and heat applied. The distillation shall be conducted at the rate of at least 
one drop and not more than two drops per second, and the distillate collected 
in weighed receivers. The condenser tube shall be warmed whenever neces- 
sary to prevent accumulation of solid distillates. Fractions shall be col- 
lected at the following points: 210, 235, 270, 315 and 355 C. The receivers 
shall be changed as the mercury passes the dividing temperature for each 
fraction. When the temperature reaches 355, the flame shall be removed 
from the retort, and any oil which has condensed in the offtake shall be 
drained in the 355 fraction. 

The residue shall remain in the retort with the cork and the thermometer 
in position until no vapors are visible; it shall then be weighed. If the residue 
is to be further tested it shall then be poured directly into the brass collar 
used in the float test or into a tin box and covered and allowed to cool to air 
temperature. If the residue becomes so cool that it cannot be poured readily 
from the retort, it shall be re-heated by holding the bulb of the retort in hot 
water or steam, and not by the application of flame. 

For weighing the receivers and fractions, a balance accurate to at least 
0.05 g. shall be used. 

During the progress of the distillation the thermometer shall remain in 
its original position. No correction shall be made for the emergent stem 
of the thermometer. 

When any measurable amount of water is present in the distillate it 
shall be separated as nearly as possible and reported separately, all results 
being calculated on a basis of dry oil. When more than 2 per cent, of 
water is present, water-free oil shall be obtained by separately distilling 
a larger quantity of oil, returning to the oil any oil carried over with the 
water, and using dried oil for the final distillation. 



SPECIFIC VISCOSITY DETERMINATION 

As all viscosity determination should be compared with that of water at 
25 C., the apparatus should be previously calibrated as follows: The cup 
and outlet tube should first be scrupulously cleaned. A piece of soft tissue 
paper is convenient for cleaning the latter. The stopper is then inserted in 
the tube and the cup rilled with water at 25 C. to the top of the projections 
The measuring cylinder should be placed directly under the outflow tube so 
that the material, upon flowing out, will not touch the sides, and the stopper 
may then be removed. The time required both for 50 and 100 cubic centi- 
meters to run out should be ascertained by means of a stop watch and the 
results so obtained should be checked a number of times. The time required 
for 50 cubic centimeters of water should be about 11 seconda and for 100 
cubic centimeters about 22.8 seconds. 

Bituminous road materials are tested in the same manner as water and the 
temperature at which the test is made is controlled by the bath. The material 
should be brought to the desired temperature and maintained there for at 



ROAD MATERIALS TESTING 433 

least three minutes before making the test. The results are expressed as 
specific viscosity compared with water at 25 C., as follows: 

Specific viscosity at _ seconds for passage of given volume at A C. 

A C. seconds for passage of same volume of water at 25 C. 

FLOAT TEST 

The float apparatus consists of two parts, an aluminum float or saucer and 
a conical brass collar. The two parts are made separately, so that one float 
may be used with a number of brass collars. 

In making the test the brass collar is placed with the small end down on the 
brass plate, which has been previously amalgamated with mercury by first 
rubbing it with a dilute solution of mercuric chloride or nitrate and then with 
mercury. A small quantity of the material to be tested is heated in the metal 
spoon until quite fluid, with care that it suffers no appreciable loss by volatiliza- 
tion and that it is kept free from air bubbles. It is then poured into the collar 
in a thin stream until slightly more than level with the top. The surplus 
may be removed, after the material has cooled to room temperature, by 
means of a spatula or steel knife which has been slightly heated. The collar 
and plate are then placed in one of the tin cups containing ice water main- 
tained at 5C., and left in this bath for at least 15 minutes. Meanwhile, the 
other cup is filled about three-fourths full of water and placed on the tripod, 
and the water is heated to any desired temperature at which the test is to be 
made. This temperature should be accurately maintained, and should at no 
time throughout the entire test be allowed to vary more than one-half a degree 
centigrade from the temperature selected. After the material to be tested 
has been kept in the ice water for at least 15 minutes, the collar with its 
contents is removed from the plate and screwed into the aluminum float, 
which is them immediately floated in the warmed bath. As the plug of 
bituminous material becomes warm and fluid, it is gradually forced upward and 
out of the collar, until water gains entrance to the saucer and causes it to sink. 

The time in seconds between placing the apparatus on the water and when 
the water breaks through the bitumen is determined by means of a stop 
watch and is taken as a measure of the consistency of the material under 
examination. 

FLASH POINT TEST 

The open-cup oil tester consists of a brass oil cup, of about 100 cubic centi- 
meters capacity. The outer vessel serves as an air jacket. No glass cover 
is used in the open-cup method. A suitable thermometer is suspended from 
the wire support directly over the center of the cup so that its bulb is entirely 
covered with oil but does not touch the bottom of the cup. The testing 
flame is obtained from a jet of gas passed through a piece of glass tubing, and 
should be about 5 millimeters in length. 

The test is made by first filling the oil cup with the material under examina- 
tion to within about 5 millimeters of the top. The Bunsen flame is then 
applied in such a manner that the temperature of the material in the cup is 
raised at the rate of 5 C. per minute. From time to time the testing flame 

28 



434 CONSTRUCTION OF ROADS AND PAVEMENTS 

is brought almost in contact with the surface of the oil. A distant nicker or 
flash over the entire surface of the oil shows that the flash point is reached 
and the temperature at this point is taken. It will usually be found that 
the flash point as determined by the open-cup method is somewhat higher 
than by the closed-cup method, for the same material. 

The burning point of the material is obtained by continuing the test and 
noting that temperature at which it ignites and burns. The flame should 
then be extinguished by means of a metal cover supplied with the instrument. 

VOLATILIZATION TEST 

An oven is used that will give a uniform temperature throughout all 
parts where samples are placed. A gas oven or an electric oven of proper 
design may be used. The bulb of one of the thermometers is immersed in a 
sample of some fluid nonvolatile bitumen, while the other is kept in air at the 
same level. The first thermometer serves to show the temperature of the 
samples during the test, while the latter gives prompt warning of any sudden 
changes in temperature due to irregulatities in the heat. 

Before making the test the interior of the oven should show a temperature 
of 163 C. as registered by the thermometer in air. A tin box 5^ centimeters 
in diameter and 3J^ centimeters deep (American Can Company, gill type, 
deep pattern ointment box) is accurately weighed after carefully wiping with 
a towel to remove any grease or dirt. About 50 grams of the material to 
be tested is then placed in the box. The material may then be weighed or a 
rough balance, if one is at hand, after which the accurate weight, which 
should not vary more than 0.2 gram from the specified amount, is obtained. 
It may be necessary to warm some of the material in order to handle it con- 
veniently, after which it must be allowed to cool before determining the accur- 
ate weight. 

The sample should now be placed in the oven where it is allowed to remain 
for a period of five hours, during which time the temperature as shown by 
the thermometer in bitumen should not vary at any time more than 2 C. 
The sample is then removed from the oven, allowed to cool and reweighed. 
From the difference between this weight and the total weight before heating, 
the percentage of loss on the amount of material taken is calculated. 

The general appearance of the residue should be noted, especially with 
regard to any changes which the material may have undergone. Some 
relative idea of the amount of hardening which has taken place may be ob- 
tained from the results of a float or penetration test made on the residue, 
as compared with the results of the same test on the original sample. It 
is also frequently desirable to make the specific gravity and other test on the 
residue for the purpose of identifying or ascertaining the character of the 
base used in the preparation of cut-back products. Before any tests are made 
on the residue, it should be melted and thoroughly stirred while cooking. 

Highly volatile and nonvolatile materials should not be subjected to this 
test at the same time in the same oven, owing to a tendency on the part of 
the latter to absorb some of the volatile products of the former. 



ROAD MATERIALS TESTING 435 

BITUMEN INSOLUBLE IN PARAFFIN NAPHTHA 
This determination is made in the same general manner as the total bitumen 
determination, except that 100 cubic centimeters of 86 to 88 B. paraffin 
naphtha, at least 85 per cent, distilling between 35 C. and 65 C., is employed 
as a solvent instead of carbon disulphide. Considerable difficulty is some- 
times experienced in breaking up some of the heavy semi-solid bitumens; 
the surface of the material is attacked, but it is necessary to remove some of 
the insoluble matter in order to expose fresh material to the action of the 
solvent. It is, therefore, advisable to heat the sample after it is weighed, 
allowing it to cool in a thin layer around the lower part of the flask. If dif- 
ficulty is still experienced in dissolving the material, a rounded glass rod will 
be found convenient for breaking up the undissolved particles. Not more 
than one-half of the total amount of naphtha required should be used until 
the sample is entirely broken up. The balance of the 100 cu. centimeters 
is then added, and the flask is twirled a moment in order to mix the contents 
thoroughly, after which it is corked and set aside for 30 minutes. 

In making the filteratiou the utmost care should be exercised to avoid 
stirring up any of the precipitate, in order that the filter may not be clogged 
and that the first decantation may be as complete as possible. The sides of 
the flask should then be quickly washed down with naphtha and, when the 
crucible has drained, the bulk of insoluble matter is brought upon the felt. 
Suction may be applied when the filtration by gravity almost ceases, but should 
be used sparingly, as it tends to clog the filter by packing the precipitate too 
tightly. The material on the felt should never be allowed to run entirely 
dry until the washing is completed, as shown by the colorless nitrate. When 
considerable insoluble matter adheres to the flask no attempt should be made 
to remove it completely. In such cases the adhering material is merely 
washed until free from soluble matter, and the flask is dried with the crucible 
at 100 C. for about one hour, after which it is cooled and weighed. The 
percentage of bitumen insoluble is reported upon the basis of total bitumen 
taken as 100. 

The difference between the material insoluble in carbon disulphide and in 
the naphtha is the bitumen insoluble in the latter. Thus, if in a certain instance 
it is found that the material insoluble in carbon disulphide amounts to 1 
per cent, and that 10.9 per cent, is insoluble in naphtha, the percentage of 
bitumen insoluble would be calculated as follows: 

Bitumen insoluble in naphtha _ 10.9-1 9.9 
Total bitumen ~T5o~ = 99 = 

BITUMEN INSOLUBLE IN CARBON TETRACHLORIDE 
This determination is conducted in exactly the same manner 

as described under " Determination of Bitumen Soluble in Carbon 

Disulphide," using 100 cu. centimeters of chemically pure carbon 

tetrachloride in place of carbon disulphide. 

The percentage of bitumen insoluble is reported upon the basis 

of total bitumen taken as 100, as described under "Determination 

of Bitumen Insoluble in Paraffin Naphtha." 



436 CONSTRUCTION OF ROADS AND PAVEMENTS 

BITUMEN SOLUBLE IN CARBON BISULPHIDE 

This test consists in dissolving the bitumen in carbon disulphide 
and recovering any insoluble matter by filtering the solution 
through an asbestos felt. The form of Gooch crucible best 
adapted for the determination is 4.4 centimeters wide at the top, 
tapering to 3.6 centimeters at the bottom, and is 2.5 centimeters 
deep. 

The asbestos is cut with scissors into pieces not exceeding 1 
centimeter in length, after which it is shaken up with just enough 
water to pour easily. The crucible is filled with the suspended 
asbestos, which is allowed to settle for a few moments. A light 
suction is then applied to draw off all the water and leave a firm 
mat of asbestos in the crucible. More of the suspended material 
is added, and the operation is repeated until the felt is so dense 
that it scarcely transmits light when held so that the bottom of 
the crucible is between the eye and the source of light. The 
felt should then be washed several times with water, and drawn 
firmly against the bottom of the crucible by an increased suction. 
The crucible is removed to a drying oven for a few minutes, after 
which it is ignited at red heat over a Bunsen burner, cooled in a 
desiccator and weighed. 

From 1 to 2 grams of bitumen or about 10 grams of an asphalt 
topping or rock asphalt is now placed in the Erlenmeyer flask, 
which has been previously weighed, and the accurate weight of 
the sample is obtained. One hundred cubic centimeters of 
chemically pure carbon disulphide is poured into the flask in small 
portions, with continual agitation, until all lumps disappear and 
nothing adheres to the bottom. The flask is then corked and 
set aside for 15 minutes. 

After being weighed, the Gooch crucible containing the felt 
is set up over the dry pressure flask, and the solution of bitumen 
in carbon disulphide is decanted through the felt without suction 
by gradually tilting the flask, with care not to stir up any precipi- 
tate that may have settled out. At the first sign of any sediment 
coming out, the decantation is stopped and the filter allowed to 
drain. A small amount of carbon disulphide is then washed down 
the sides of the flask, after which the precipitate is brought upon 
the felt and the flask scrubbed, if necessary, with a feather or 
"policeman," to remove all adhering material. The contents of 
the crucible are washed with carbon disulphide, until the washings 



ROAD MATERIALS TESTING 437 

run colorless. Suction is then applied until there is practically 
no odor of carbon disulphide in the crucible, after which the outside 
of the crucible is cleaned with a cloth moistened with a small 
amount of the solvent. The crucible and contents are dried in the 
hot-air oven at 100C. for about 20 minutes, cooled in a desiccator, 
and weighed. If any appreciable amount of insoluble matter 
adheres to the flask, it should also be dried and weighed, and any 
increase over the original weight of the flask should be added to 
the weight of insoluble matter in the crucible. The total weight 
of insoluble material may include both organic and mineral matter. 
The former, if present, is burned off by ignition at a red heat until 
no incandescent particles remain, thus leaving the mineral matter 
or ash, which can be weighed on cooling. The difference between 
the total weight of material insoluble in carbon disulphide and 
the weight of substance taken equals the total bitumen, and the 
percentage weights are calculated and reported as total bitumen, 
and organic and inorganic matter insoluble, on the basis of the 
weight of material taken for analysis. 

This method is quite satisfactory for straight oil and tar products, 
but where certain natural asphalts are present it will be found 
practically impossible to retain all of the finely divided mineral 
matter on an asbestos felt. It is, therefore, generally more 
accurate to obtain the result for total mineral matter by direct 
ignition of a 1-gram sample in a platinum crucible or to use the 
result for ash obtained in the fixed carbon test. The total bitu- 
men is then determined by deducting from 100 per cent, the sum 
of the percentages of total mineral matter and organic matter 
insoluble. If the presence of a carbonate mineral is suspected, 
the percentage of mineral matter may be most accurately obtained 
by treating the ash from the fixed carbon determination with a few 
drops of ammonium carbonate solution, drying at 100C., then 
heating for a few minutes at a dull red heat, cooling and weighing 
again. 

When difficulty in filtering is experienced for instance, when 
Trinidad asphalt is present in any amount a period of longer 
subsidence than 15 minutes is necessary, and the following method 
proposed by the Committee on Standard Tests for Road Materials 
of the American Society for Testing Materials is recommended: 

From 2 to 15 grams (depending on the richness in bitumen of 
substance) is weighed into a 150-cubic centimeter Erlenmeyer 
flask, the tare of which has been previously ascertained, and 



438 CONSTRUCTION OF ROADS AND PAVEMENTS 

treated with 100 cu. centimeters of carbon disulphide. The 
flask is then loosely corked and shaken from time to time until 
practically all large particles of the material have been broken up, 
when it is set aside and not disturbed for 48 hours. The solution 
is then decanted off into a similar flask that has been previously 
weighed, as much of the solvent being poured off as possible with- 
out disturbing the residue. The first flask is again treated with 
fresh carbon disulphide and shaken as before, when it is put away 
with the second flask and not disturbed for 48 hours. 

At the end of this time the contents of the two flasks are care- 
fully decanted off upon a weighed Gooch crucible fitted with an 
asbestos filter, the contents of the second flask being passed 
through the filter first. The asbestos filter shall be made of 
ignited long-fiber amphibole, packed in the bottom of a Gooch 
crucible to the depth of not over one-eighth of an inch. After 
passing the contents of both flasks through the filter, the two 
residues are shaken with more fresh carbon disulphide and set 
aside for 24 hours without disturbing, or until it is seen that a 
good subsidation has taken place, when the solvent is again de- 
canted off upon the filter. This washing is continued until the 
filtrate or washings are practically colorless. 

The crucible and both flasks are then dried at 125C. and 
weighed. The filtrate containing the bitumen is evaporated, the 
bituminous residue burned, and the weight of the ash thus obtained 
added to that of the residue in the two flasks and the crucible. 
The sum of these weights deducted from the weight of substance 
taken gives the weight of bitumen extracted. 

TESTS OF PREMOLDED JOINT FILLERS 

The bituminous material before manufacture into premolded 
joint fillers should be subjected to the tests as for poured expansion 
joint fillers. 

TESTS OP EMULSIONS 

The essential tests on emulsions are percent, of water and quality 
of bitumen. 

The percentage of water may be obtained as given under the 
methods of water determinations as given under bituminous 
materials without the addition of naphtha or benzol. The emul- 
sion can be broken down by the addition of a ten percent, solution 
of calcium chloride. The separated bituminous material is then 



ROAD MATERIALS TESTING 439 

kneaded by hand to separate all contained water and then sub- 
jected to the usual quality tests. 

DETERMINATION OF PARAFFIN SCALE 

It is recommended that the paraffin scale determination should 
be omitted on account of difficulty encountered in obtaining de- 
pendable results due to the inaccuracy of any methods which have 
heretofore been introduced. 

DETERMINATION OF WATER IN BITUMINOUS MATERIALS 
The apparatus consists of copper still, 6 in. by 3J^ in. Ring 



burner to fit still. Connecting tube. Condenser trough. Con- 
denser tube. Separatory funnel. Thermometer 0-250C. 

In case of coal tar material, 50 c. c. of coal tar naphtha, or light 
oil shall be measured into a 250 c. c. graduated cylinder, and 200 c. c. 
of the material to be tested should be added. In the case of 
petroleum products, petroleum naphtha may be used. The con- 
tents should be transferred to the copper still and the cylinder 
should be washed with 100 to 150 c. c. more naphtha, and the 
washings added to the contents of the still. The condenser 
trough should be filled with water. Heat should be applied by 
means of the ring burner, and distillation continued until the vapor 
temperature has reached 205C. (401F.). The distillate shall 
be collected in the separatory funnel, in which 15 to 20 c. c. of 
benzol or naphtha have been previously placed. This effects a 
clean separation of the water and oil. The reading shall be made 
after twirling the funnel and allowing to settle for a few minutes. 
The percentage shall be figured by volume. 

When fresh supplies of naphtha or light oil are obtained, they 
shall be tested to determine freedom from water. 

We recommend that further investigation be made on this 
method by using a water saturated solution of naphtha. This 
criticism has been made on the method due to the fact that naphtha 
possibly possesses an affinity for water. 

DISTILLATION OF BITUMINOUS MATERIALS SUITABLE FOR ROAD 

TREATMENT 

(A. S. T. M. Standard Method, Serial Designation: D 20-18) 
The sample as received shall be thoroughly stirred and agitated, warming, 
if necessary, to insure a complete mixture before the portion for analysis is 
removed. 



440 CONSTRUCTION OF ROADS AND PAVEMENTS 

If the presence of water is suspected or known, the material shall be de- 
hydrated before distillation. About 500 c. c. of the material are placed in an 
800-c. c. copper still provided with a distilling head connected with a water- 
cooled condenser. A ring burner is used, starting with a small flame at the 
top of the still, and gradually lowering it, if necessary, until all the water has 
been driven off. The distillate is collected in a 200-c. c. separatory funnel 
with the tube cut off close to the stopcock. When all the water has been 
driven over and the distillate has settled but, the water is drawn off and the 
oils returned to the residue in the still. 

The contents of the still shall have cooled to below 100 C. before the oils 
are returned, and they shall be well stirred and mixed with the residue. 

The apparatus shall consist of the following standard parts : 

(a) Flask: The distillation flask shall be a 250 c. c. Engler distilling flask, 
having the following dimensions: 

Diameter of bulb 8.0 cm. 

Length of neck 15.0 cm. 

Diameter of neck 1.7 cm. 

Surface of material to lower side of tubulature 11.0 cm. 

Length of tubulature 15.0 cm. 

Diameter of tubulature 0.9 cm. 

Angle of tubulature 75 deg. 

A variation of 3 per cent, from the above measurements will be allowed. 

(6) Thermometer: The thermometer shall conform to the following require- 
ments: 

It shall be made of thermometric glass of a quality equivalent to suitable 
grades of Jena or Corning make. It shall be thoroughly annealed. It shall 
be filled above the mercury with inert gas which will not act chemically on 
or contaminate the mercury. The pressure of the gas shall be sufficient to 
prevent separation of the mercury column at all temperatures of the scale. 

There shall be a reservoir above the final graduation large enough so that 
the pressure will not become excessive at the highest temperature. The ther- 
mometer shall be finished at the top with a small glass ring or button suitable 
for attaching a tag. Each thermometer shall have for identification the 
maker's name, a serial number, and the letters "A. S. T. M. Distillation." 

The thermometer shall be graduated from to 400 C. at intervals of 1 C. 
Every fifth graduation shall be longer than the intermediate ones, and every 
tenth graduation beginning at zero shall be numbered. The graduation 
marks and numbers shall be clear-cut and distinct. 

The thermometer shall conform to the following dimensions: 

Total length, maximum 385.0 mm. 

Diameter of stem 7.0 mm., permissible variation. . . .0.5 mm. 

Diameter of bulb, minimum. ... 5.0 mm., and shall not exceed diameter of 

stem. 

Length of bulb 12.5 mm., permissible variation. . . .2.5 mm. 

Distance from to bottom of 

bulb 30.0 mm., permissible variation. . . .2.5 mm. 

Distance from to 400 295.0 mm., permissible variation. . .10.0 mm. 



ROAD MATERIALS TESTING 441 

The accuracy of the thermometer when delivered to the purchaser shall be 
such that when tested at full immersion the maximum error from to 200 C. 
shall not exceed the following: 

From to 200 C .5 C. 

From 200 to 300 C 1 .0 C. 

From 300 to 375 C. . . . 1 .5 C. 

The sensitiveness of the thermometer shall be such that when cooled to 
a temperature of 74 C. below the boiling point of water at the barometric 
pressure, at the time of test, and plunged into free flow of steam, the meniscus 
shall pass the point 10 C. below the boiling point of water in not more than 
6 seconds. 

The thermometer shall be set up as for the distillation test, using water, 
naphthalene and benzophenone as distilling liquids. The correctness of the 
thermometer shall be checked at and 100 C. after each third distillation 
until seasoned. 

(c) Comdenser: The condenser tube shall have the following dimensions: 

Adapter 70 mm. 

Length of straight tube 185 mm. 

Width of tube. 12-15 mm. 

Width of adapter end of tube 20-25 mm. 

(d) Stands: Two iron stands shall be provided, one with a universal clamp 
for holding the condenser, and one with a light grip arm with a cork-lined 
clamp for holding the flask. 

(e) Burner and Shield: A Bunsen burner shall be provided with a tin 
shield 20 cm. long by 9 cm. in diameter. The shield shall have a small hole 
for observing the flame. 

(/) Cylinders: The cylinders used in collecting the distillate shall have a 
capacity of 25 c. c., and shall be graduated in 0.1 c. c. 

The apparatus shall be set up, the thermometer being placed so that the 
top of the bulb is opposite the middle of the tubulature. All connections 
should be tight. 

One hundred cubic centimeters of the dehydrated material to be tested 
shall be placed in a tared flask and weighed. After adjusting the thermometer, 
shield, condenser, etc., the distillation is commenced, the rate being so regu- 
lated that 1 c. c. passes over every minute. The receiver is changed as the 
mercury column just passes the fractionating point. 

The following fractions should be reported : 

Start of distillation to 110 C. 

110 to 170 C. 

170 to 235 C. 

235 to 270 C. 

270 to 300 C. 

Residue. 

To determine the amount of residue, the flask is weighed again when dis- 
tillation is complete. During the distillation the condenser tube shall be 
warmed when necessary to prevent the deposition of any sublimate. The per- 
centages of fractions should be reported both by weight and by volume. 



GLOSSARY 

The following words and terms are employed in highway engineering 
and have been defined by a special committee of the American Society 
of Civil Engineers or by the American Society for Testing Materials. For 
many of the words both have agreed on the definition. 

Asphalts. Solid or semi-solid native bitumens, solid or semi-solid 
bitumens obtained by refining petroleum, or solid or semi-solid bitumens 
which are combinations of the bitumens mentioned with petroleums or 
derivatives thereof, which melt upon the application of heat and which 
consist of a mixture of hydrocarbons and their derivatives of complex 
structure, largely cyclic and bridge compounds. 

Native Asphalt. Asphalt occurring as such in nature. 

Asphalt-block Pavement. One having a wearing course of previously 
prepared blocks of asphaltic concrete. 

Asphalt Cement. A fluxed or unfluxed asphalt specially prepared as 
to quality and consistency for direct use in the manufacture of bituminous 
pavements, and having a penetration at 25C. (77F.) of between 5 and 
250, under a load of 100 grams applied for 5 sec. or, 

Asphalt Cement. A fluxed or unfluxed asphaltic material, especially 
prepared as to quality and consistency, suitable for direct use in the manu- 
facture of asphaltic pavements, and having a penetration of between 5 
and 250. 

Asphaltenes. The components of the bitumen in petroleums, petro- 
leum products, malthas, asphalt cements and solid native bitumens, which 
are soluble in carbon disulphide but insoluble in paraffine naphthas. 

Asphaltic. Similar to. or essentially composed of, asphalt. 

Base. Artificial foundation. 

Binder. A foreign or fine material introduced into the mineral portion 
of the wearing surface for the purpose of assisting the road metal to retain 
its integrity under stress, as well as, perhaps, to aid in its first construction. 
(2) The course in a sheet-asphalt pavement, frequently used between the 
concrete foundation and the sheet-asphalt mixture of graded sand and 
asphalt cement. 

Bitumens. Mixtures of native or pyrogenous hydrocarbons and their 
nonmetallic derivatives, which may be gases, liquids, viscous liquids, or 
solids, and which are soluble in carbon disulphide. 

Bituminous. Containing bitumen or constituting the source of bitumen. 

Bituminous Cement. A bituminous material suitable for use as a binder 
having cementing qualities which are dependent mainly on its bituminous 
character. 

Bituminous Concrete Pavement. One composed of stone, gravel, sand 
shell, or slag, or combinations thereof, and bituminous materials incor- 
porated together by mixing methods. 

Bituminous Emulsion. A liquid mixture in which minute globules of 
bitumen are held in suspension in water or a watery solution. 

442 



GLOSSARY 443 

Bituminous Macadam Pavement. One having a wearing course of 
macadam with the interstices filled by penetration methods with a bitu- 
minous binder. 

Bituminous Material. Material containing bitumen as an essential 
constituent. 

Bituminous Pavement. One composed of stone, gravel, sand, shell, 
or slag, or combinations thereof, and bituminous materials incorporated 
together. 

Bituminous Surface. A superficial coat of bituminous material with 
or without the addition of stone or slag chips, gravel, sand, or material of 
similar character. 

Blanket. See "Carpet." 

Bleeding. The exudation of bituminous material on the roadway 
surface after construction. 

Blown Petroleums. Semi-solid or solid products produced primarily 
by the action of air upon liquid native bitumens which are heated during 
the blowing process. 

Bond. The combined action of inertia, friction, and of the forces of 
adhesion and cohesion which helps the separate particles composing a 
crust or pavement to resist separation under stress. Mechanical bond is 
the bond produced almost wholly, in a well-built broken-stone macadam 
road, by the interlocking of angular fragments of stone and the subsequent 
filling of the remaining interstices with the finer particles. 

Bound. Bonded. 

Brick Pavement. One having a wearing course of paving bricks, or 
blocks. 

Bridge. A structure for the purpose of carrying traffic over a gap in 
the roadbed measuring 10 ft. or more in the clear span. 

Camber of a Bridge. The rise of its center above a straight line through 
its ends. 

Camber of a Road. See "Crown." 

Carbenes. The components of the bitumen in petroleums, petroleum 
products, malthas, asphalt cements and solid native bitumens, which a^e 
soluble in carbon disulphide but insoluble in carbon tetrachloride. 

Carpet. A bituminous surface of appreciable thickness, generally formed 
on top of a roadway by the application of one or more coats of bituminous 
material with gravel, sand, or stone chips added. 

Cement An adhesive substance used for uniting particles of other 
materials to each other. Ordinarily applied only to calcined "cement 
rock," or to artificially prepared, calcined, and ground mixtures of limestone 
and siliceous materials. Sometimes used to designate bituminous binder 
used in bituminous pavements, when the expression "bituminous cement" 
is 'understood to be meant. 

Cemented. Bonded. Referring to water-bound macadam, the term 
"cemented" is used to designate that condition existing when, after rolling 
the stone forming the crust, the remaining voids have been filled with the 
finer sizes, and the stone dust or "flour" has, under the action of water, 
taken a "set," as does cement itself. 

Cement-concrete. An intimate mixture of gravel, shell, slag, or broken 



444 GLOSSARY 

stone particles with certain proportions of sand or similar material, cement, 
and water, made previous to placing. 

Cement-concrete Pavement. One having a wearing course of hydraulic 
cement-concrete. 

Chert. Compact siliceous rock formed of calcedonic or opaline silica, 
or both. 

Chips. Small angular fragments of stone containing no dust. 

Clinker. Generally a fused or partly fused byproduct of the combustion 
of coal, but also including lava and Portland-cement clinker, and partly 
vitrified slag and brick. 

Coal Tar. The mixture of hydrocarbon distillates, mostly unsaturated 
ring compounds, produced in the destructive distillation of coal. 

Coat. See "Carpet." (1) The total result of one or more single-surface 
applications. (2) To apply a coat. 

Coke-oven Tar. Coal tar produced in byproduct coke ovens in the 
manufacture of coke from bituminous coal. 

Consistency. The degree of solidity or fluidity of bituminous materials. 

Course. One or more layers of road metal spread and compacted sepa- 
rately for the formation of the road or pavement. Courses are usually 
referred to in the order of their laying as first course, third course, etc. 
Also a single row of blocks in a pavement. 

Crown. The rise in cross-section from the lowest to the highest part of 
the finished roadway. It may be expressed either as so many inches (or 
tenths of a foot), or as a rate per foot of distance from side to center, i.e., 
"the crown is 4 in.," or "the crown is ^ in. to the foot." 

Crusher-run. The total unscreened product of a stone crusher. 

Crusher-run Stone. The product of a stone crusher, unscreened except for 
the removal of the particles smaller than remaining on about a /4~ m - screen. 

Crust. That portion of a macadam or similar roadway above the foun- 
dation consisting of the road metal proper with its bonding agent or binder. 

Culvert. A structure for the purpose of carrying traffic over a gap in 
the roadbed, measuring less than 10 ft. in clear span. 

Cut-back Products. Petroleum, or tar residuums, which have been 
fluxed, each with its own or similar distillates. 

Dead Oils. Oils with a density greater than water which are distilled 
from tars. 

.Ditch. The open-side drain of a roadway, usually deep in proportion 
to its width, and unpaved. 

Drainage. Provision for the disposition of water. Side drainage. 
That along the sides of the roadway. Sub- or under-drainage. That 
below the surface. Surface drainage. That on the roadway or ground 
surface. V-drainage. That provided by the construction of troughs in 
the subgrade of the roadway, which troughs are like a " V," with flat sloping 
sides, and are filled with stone. 

Dust Layer. Material applied to a roadway for temporarily preventing 
the formation or dispersion under traffic of distributable dust. 

Earth Road. A roadway composed of natural earthy material. 

Emulsion. A combination of water and oily material made miscible with 
water through the action of a saponifying or other agent. 



GLOSSARY 445 

Expansion Joint. A separation of the mass of a structure, usually in 
the form of a joint filled with elastic material, which will provide oppor- 
tunity for slight movement in the structure. 

Fat. Containing an excess. A fat asphalt mixture is one in which the 
asphalt cement is in excess and the excess is clearly apparent. 

Fixed Carbon. The organic matter of the residual coke obtained upon 
burning hydrocarbon products in a covered vessel in the absence of free 
oxygen. 

Flour. Finely ground rocks or minerals pulverized to an impalpable 
product. 

Flushing. (1) Completely filling the voids. (2) Washing a pavement 
with an excess of water. 

Flush Coat. See "Seal Coat." 

Flux. Bitumens, generally liquid, used in combination with harder 
bitumens for the purpose of softening the latter. 

Footway. The portion of the highway devoted especially to pedestrians. 
A sidewalk. 

Foundation. The portion of the roadway below and supporting the 
crust or pavement. 

Artificial Foundation. That layer of the foundation especially placed 
on the subgrade for the purpose of reinforcing the supporting power of the 
latter itself, and composed of material different from that of the subgrade 
proper. 

Natural Foundation. The natural earthy material below and supporting 
the artificial foundation or, if there is no artificial foundation, the crust or 
pavement. 

Free Carbon in Tars. Organic matter which is insoluble in carbon 
disulphide. 

Gas-house Coal Tar. Coal tar produced in gas-house retorts in the 
manufacture of illuminating gas from bituminous coal. 

Grade. (1) The profile of the center of the roadway, or its rate of rise 
or fall. (2) Elevation. (3) To establish a profile by cuts and fills or earth- 
work. (4) To arrange by sizes, broken stone, gravel, sand, or combinations 
of such materials. 

Granite.. A granitoid igneous rock consisting of quartz, orthoclase, 
more or less oligoclase, biotite and muscovite. 

Granitoid. A textural term to describe those igneous rocks which are 
entirely composed of recognizable minerals. 

Gutter. The artificially surfaced and generally shallow waterway 
provided usually at the sides of the roadway for carrying surface drainage. 
Occasionally used synonymously with "ditch," but incorrectly so, as 
"gutters" are always paved or otherwise surfaced, and ditches are not. 

Haunches. The sides or flanks of a roadway. Sometimes also called 
"quarters." 

Highway. The entire right of way devoted to public travel, including 
the sidewalks and other public spaces, if such exist. 

Layer. A course made in one application. 

Liquid Bituminous Materials. Those having a penetration at 25C. 
(77F.), under a load of 100 grams applied for 5 sec., of more than 10, 



446 GLOSSARY 

and a penetration at 25C. (77F.), under a load of 50 grams applied for 1 
sec., of not more than 350. 

Macadam. A road crust composed of stone or similar material broken 
into irregular angular fragments compacted together so as to be interlocked 
and mechanically bound to the utmost possible extent. 

Mastic. A mixture of bituminous material and fine mineral matter 
suitably made for use in highway construction and for application in a heated 
condition. 

Mat. See "Carpet." 

Matrix. The binding material or mixture of binding material and fine 
aggregate in which the large aggregate is embedded or held in place. 

Mesh. The square opening of a sieve. 

Metal. See "Road Metal." 

Mortar. A mixture of fine material such as sand, .cement, and water or 
other liquid suitably proportioned and incorporated together for the purpose 
for which it is used. 

Mush. A greasy mud sometimes found on bituminous crusts. 

Normal Temperature. As applied to laboratory observations of the 
physical characteristics of bituminous materials, is 25C. (77F.). 

Oil -gas Tars. Tars produced by cracking oil vapors at high temperatures 
in the manufacture of oil gas. 

Palliative. A short-lived dust layer. 

Patching. Repairing or restoring small isolated areas in the surface of 
the metaled or paved portion of the highway. 

Pavement. The wearing course of the roadway or footway, when con- 
structed with a cement or bituminous binder, or composed of blocks or 
slabs, together with any cushion or "binder" course. 

Penetration. The consistency of a bituminous material expressed as 
the distance that a standard needle vertically penetrates a sample of the 
material under known conditions of loading, time and temperature. Where 
the conditions of test are not specifically mentioned, the load, time and 
temperature are understood to be 100 grams, 5 sec., 25C. (77F.) and the 
units of penetration to indicate hundredths of centimeters. 

Penetration Method. The method of constructing a bituminous maca- 
dam pavement by pouring or grouting the bituminous material into the 
upper course of the road metal before the binding of the latter has been 
completed. 

Petroleum. Liquid bitumen occurring as such in nature. 

Pitches. Solid residues produced in the evaporation or distillation of 
bitumens, the term being usually applied to residues obtained from tars. 

Hard pitch. Pitch showing a penetration of not more than ten. 

Soft pitch. Pitch showing a penetration of more than ten. 

Pocket. A hole or depression in the wearing course. 

Pot-hole. A hole extending below the wearing course. 

Profile. A longitudinal section of a highway, generally taken along 
the center line. 

Quarters. The four sections of equal width which, side by side, make 
up the total width of a roadway. 

Raveling. The loosening of the metal composing the crust. 



GLOSSARY 447 

Refined Tar. Tar freed from water by evaporation or distillation which 
is continued until the residue is of desired consistency; or a product pro- 
duced by fluxing tar residuum with tar distillate. 

Renewals. Extensive repairs over practically the whole surface of the 
metaled or paved portion of the highway. 

Repairs. The restoration or mending of a considerable amount of the 
metaled or paved portion of the highway, but not usually of a majority 
of the surface area. More extensive than " Patching" but less so than 
".Renewals." 

Resurfacing. The renewal of the surface of the crust or pavement. 

Road. A highway outside of an urban district. 

Roadbed. The natural foundation of a roadway. 

Road Metal. Broken stone, gravel, slag, or similar material used in road 
and pavement construction and maintenance. 

Roadway. That portion of a highway particularly devoted to the use of 
vehicles. 

Rock Asphalt. Sandstone or limestone naturally impregnated with asphalt. 

Rock-asphalt Pavement. A wearing course composed of broken or 
pulverized rock asphalt with or without the addition of other bituminous 
materials. 

Rubble. Rough stones of irregular shapes and sizes, broken from larger 
masses either naturally or artificially, as by geological action, in quarrying, or 
in stone cutting or blasting. 

Sand-clay Road. A roadway composed of an intimate mixture of sand 
and clay. 

Scarify. To loosen and disturb superficially. 

Seal Coat. A final superficial application of bituminous material during 
construction to a bituminous pavement. 

Setting Up. The relatively quick change such as takes place in a bitumi- 
nous material after its application to a roadway, indicated by its hardening 
after cooling and exposure to atmospheric and traffic conditions, as opposed 
to the slower changes later occurring gradually and almost imperceptibly. 

Shaping. Trimming up and preparing a subgrade preparatory to apply 
ing the first course of the road metal or artificial foundation. 

Sheet-asphalt Pavement. One having a wearing course composed of 
asphalt-cement and sand of predetermined grading, with or without the 
addition of fine material, incorporated together by mixing methods. 

Sheet Pavement. A pavement free from frequent joints such as would 
accompany small slabs or blocks, and which has an appreciable thickness 
(say in excess of 1 in. on the average) for its wearing course. 

Shoulders. The portion of the highway between the edges of the road 
metal or pavement and the gutters, slopes, or watercourse. 

Side Drain. See " Drainage." 

Sidewalk. The portion of the highway reserved for pedestrians. 

Slag. Fused or partly fused compounds of silica in combination with 
lime or other bases, resulting in secondary products from the reduction of 
metallic ores. 

Soil. A mixture of fine earthy materials with more or less organic matter 
resulting from the growth and decomposition of vegetation or animal matter. 



448 GLOSSARY 

Solid Bituminous Materials. Those having a penetration at 25C. 
(77F.), under a load of 100 grams applied for 5 sec., or not more than 10. 

Spalls. Fragments broken off by a blow, irregular in shape, and of suffi- 
cient size to be comparable to the original mass. 

Squeegee. A tool with a rubber or leather edge for scraping or cleaning 
hard surfaces, or for spreading and distributing liquid material over and into 
the superficial interstices of roadways. 

Squeegee Coat. An application by means of the squeegee. 

Stone Chips. Small angular fragments of stone containing no dust. 

Straight -run Pitch. A pitch run to the consistency desired, in the initial 
process of distillation, without subsequent fluxing. 

Street. A highway in an urban district. 

Subgrade. The upper surface of the native foundation on which is 
placed the road metal or the artificial foundation, in case the latter is 
provided. 

Superficial Coat. A light surface coat. 

Surface Coat. See "Carpet." 

Surface Treatment. Treating the finished surface of a roadway with 
bituminous material. 

Tailings. Stones which after going through the crusher do not pass 
through the largest openings of the screen. 

Tars. Bitumens which yield pitches upon fractional distillation and 
which are produced as distillates by the destructive distillation of bitumens, 
pyrobitumens or organic materials. 

Dehydrated Tars. Tars from which all water has been removed. 

Telford. Properly, an artificial foundation advocated by Thomas Tel- 
ford (1757-1820), and consisting of a pavement of stone about 8 in. thick, 
laid by hand, and closely packed and wedged together. The individual 
stones were desired to be about 16 sq. in. in section, and about 8 in. in length. 
They were set close together on the prepared subgrade, their longest dimen- 
sion vertical and on their larger ends, their interstices chinked with smaller 
stones, and the whole rammed (or rolled) until firm and unyielding. 

Telford Macadam. Macadam with an artificial foundation of Telford. 

Topped Petroleum. Petroleum deprived of its more volatile constituents. 

Under-drain. See "Drainage." 

Up-keep. Maintenance. 

V-drain. See "Drainage." 

Viscosity. The measure of the resistance to flow of a bituminous mate- 
rial, usually stated as the time of flow of a given amount of the material 
through a given orifice. 

Volatile. Applied to those fractions of bituminous materials which will 
evaporate at climatic temperatures. 

Water-bound. Bound or bonded with the aid of water. 

Water-gas Tars. Tars produced by cracking oil vapors at high tempera- 
tures in the manufacture of carburetted water gas. 

Wearing Coat. The superficial layer of the crust or pavement exposed 
to traffic. 

Wearing Course. The course of the crust or pavement exposed to traffic. 

Wood-block Pavement. One having a wearing course composed of wood 
paving blocks, generally rectangular in shape. 



INDEX 



Absorption test for brick, 178 
Acute angle intersections, 378 
Administration of paving, 14 
of rural highways, 6 
systems of, 14 
Administration authorities, county, 

9 

municipal, 12 
national, 10 
state, 9 
township, 9 

^Esthetic considerations, 348 
Aggregates for asphaltic concrete, 

316 

mixed macadam, 289, 291, 297 
Portland cement concrete, 141 
sheet asphalt, 305, 306, 307 
Aid, national, 12 

state, 11 
Analyses, fluxes, 309 

of pavement costs, 356 
traffic census, 340, 343 
Annual cost of pavement, 356, 358, 

359 

Appearance of pavements, 352 
Applying bituminous materials, car- 
pet coats, 269 
dust layer, 262 
penetration macadam, 279 
Portland cement concrete pave- 
ments, 275 

Applying screenings, 130 
Area, method of assessment, 17 
Armored curbs, 380, 383 
Asphalt, 229, 240 

Bermudez, 243 

Asphalt, cement, 249, 253, 256, 257 
Cuban, 243 
European, 244 
geological source, 239 
Mexican, 243 
natural, 242 
nature of, 239 
29 449 



Asphalt, petroleum, 245 

refining, 244 

rock, 249 

Trinidad, 242 

typical analyses, 249 

specification, 249 
Asphalt blocks, composition of, 315 

manufacture of, 315 

size of, 315 
Asphalt block pavements, 315 

bedding course, 316 

characteristics of, 316, 354 

composition of blocks, 315 

cost of, 316 

cross section for, 303 

foundation for, 316 

laying, 316 

sand bedding course, 316 

sand filler, 316 

size of blocks, 315 

subgrade, 315 

tamping blocks, 316 
Asphalt cement, 249 
Asphalt cement for asphaltic con- 
crete, 253, 256 

binder course, 253, 256 

consistency of, 257 

melting tank for, 326 

proportioning, 312, 330 

sheet asphalt, 257 
Asphalt fillers for brick, 257 

expansion joints, 257 

stone block surfaces, 228, 236 
Asphalt fillers for wood surfaces, 

214, 219, 257 

Asphalt paint coat for binder, 305 
Asphalt plants, 311 
Asphalt wagons, 326 
Asphaltic concrete pavements, 316, 
330 

asphalt cement for, 253, 256 

bitulithic, 317, 320 

characteristics of, 324 



450 



INDEX 



Asphaltic concrete pavements, cross 

sections for, 303 
dressing the surface of, 323 
foundation for, concrete, 319 

macadam, 321 

good practice, examples of, 327 
grading, Bitulithic, 318 
sand, 317, 327 
Topeka, 319 
stone, 316, 327 

storage bins for aggregates, 325 
suburban roads, 323 
thickness of, 321 
types of, 317, 319 
Topeka type, 318 
warrenite, 319 
Washington, D. C. practice, 

331, 333 
Assessments for pavements, 16 

rural highways, 13 
Automobile licenses, 12 

Balancing quantities of earthwork, 

75,81 

Base with integral curbs, 185 
Base course for asphalt block pave- 
ments, 316 
asphaltic concrete roads and 

pavements, 319, 334 
brick roads and pavements, 182 
Base course for sheet asphalt pave- 
ments, 302 

stone block pavements, 226 
wood block pavements, 212, 216 
Bedding course, asphalt blocks, 316 
brick, 186 
stone blocks, 316 
wood blocks, 214, 218 
Berm, 73 

Bermundez asphalt, 243 
Binder course, asphalt paint coat 

for, 305 

asphalt cement for, 253, 256 
character of materials for, 305 
Chicago specification for, 327 
close, 304 

for sheet asphalt, 304, 305, 327 
made of old surface mixtures, 
305 



Binder course, mixing, 308, 309 

open, 304 

proportioning, 304, 327 

rolling, 309 

spreading, 309 

temperature suitable, 308 

thickness of, 304 
Bitulithic, 317 

definition, 240 

determination of amount in 
pavement, 402 

nature of, 240 

proportioning, 312 

tests of, 400 
Bituminous binders, 239 

for asphaltic macadam, 251, 253 

for carpet coats, 250 

for penetration macadam, 251, 
285, 290 

for Portland cement concrete, 
158 

for sheet asphalt pavements, 
253 

typical specifications, 253 
Bituminous carpets on gravel, 267 

on macadam, 267 

on Portland cement concrete, 

158, 275 

Bituminous concrete, 316 
Bituminous filler for brick pave- 
ments, 257 

for expansion joints, 214, 257 

for stone block pavements, 228, 
236, 257 

for wood block pavements, 214, 
219,. 257 

requirements for, 257 

typical specification, 257 
Bituminous road and paving mate- 
rials, 239 

asphalt, nature of, 239 

Bermundez asphalt, 243 

bitumen, 240 

blown oils, 246 

cement, 249, 256 

coal tar, 246 

Cuban asphalt, 243 

cut-back pitches, 247 

fluxes, 247 



INDEX 



451 



Bituminous road and paving mate- 
rials for asphalt blocks, 315 

for bituminous concrete, 253 

for carpet coats on concrete, 158 
on gravel, 250 
on macadam, 251 

for dust laying on earth roads, 

249 

on gravel, 249 
on macadam, 249 

for expansion joints, 257 

for filler for block pavements, 
257 

for mixed macadam, 253 

for penetration macadam, 251 

for sheet asphalt, 253, 257 

Gilsonite, 244 
products, 245 

Mexican asphalt, 243 

mixtures, 247 

natural asphalt, 242 
rock asphalt, 244 

petroleum asphalt, 245 

properties of, 258 

refining asphalts, 254 

residual asphalts, 245 

sources of, 242 

tar, 246 

tests of, 416 

Trinidad asphalt, 242 

petroleum, 243 

water-gas tar, 247 
Bituminous surface on concrete, 158 

on gravel, 267 

on macadam, 267 
Blade brader work, 85 
Bleeding of wood blocks, 210 
Blind drains, 128 
Blocks, asphalt, 315 

granite, 223 

grooved, 224 

sandstone, 223 

traprock, 223 

vitrified brick, 176 

wood, 204 
Blocks, stone, 223 

quality of, 223 

recut granite, 229 

regularity of, 225 



Blocks, size of, 223 

tests for, 225 
Blocks wood, bleeding of, 210 

kinds of wood used, 204 

manufacture of, 211 

preservative treatment, 205 

quality of, 205 

regularity of, 205 
Blown oil, 246 

Bonding properties of broken stone, 
118 

gravel, 103 
Bonds, 13 
Brick pavements, 176 

appliances used in construc- 
tion, 196 

base with integral curbs, 185 

bituminous filler for, 191 

characteristics of, 197 

concrete base for, 182 
for thin sections, 184 

construction of, 180 

cost of, 197 

cross sections for, 179 

design, 194 

earth subgrade for, 181, 201 

examples of good practice, 197 

expansion joints, 192 

grout filler, 189, 198 
Brick, vitrified, 176 

absorption test for, 178 

county roads, 194 

cross breaking test, 178 

culling, 188 

kinds of, 176 

non-repressed, 177 

physical characteristics, 178 

regularity of shape, 180 

repressed, 176 

size, 179 
Brick, vitrified, vertical fiber, 176 

wearing qualities, 178 

wire-cut-lug, 177 

inspection, 202 

kinds of brick used, 176 

laying the brick, 187, 200 

macadam base, 185 

monolithic, 194 

mortar cushion, 186 



452 



INDEX 



Brick, vitrified, physical character- 
istics of, 178 
rolling brick, 188, 198 

sand cushion, 187 
sand cushion, 187 

filler, 188 

two course pavements, 185 
typical cross sections, 179 

Carriers for brick, 196 
Catch basins, 385 
Clay, 61, 94 

slaking, 87 
Cleaning, ease of, 352 
Characteristics of soil, 60 
City streets, 14, 360 
Coal tar, 246 
Coarse aggregate for concrete roads, 

142, 165 

Comparison of pavements, 354 
Computing quantities of earthwork, 

81 
Concrete, asphaltic, 316 

bithulithic, 317 

Topeka, 318 

warrenite, 319 
Concrete, Portland cement, 141 

base for pavement, 182 
thin section, 184 

characteristics of, 157, 344 

combined curb and gutter, 383 

cross sections for, 146, 147, 148, 
152 

culverts, 37 

curing, 154 

expansion joints for, 155 

foundation for, 149 

machinery used for, 152, 160 

maintenance of, 157 

mixers, 152 

mixing and placing, 150, 152 

one course, 142 

plaining concrete, 165 

proportioning, 143, 144 

reinforced, 156 

roads and pavements, aggre- 
gates for, 141, 170 

rolling the foundation, 150, 169 

stresses in, 141 



Concrete, thickness of, 171 

top coating of bit. mat., 158 
two courses, 143 

Construction of asphalt block sur- 
faces, 316, 
asphaltic concrete surfaces, 316, 

330 

bituminous macadam, 291 
Construction of brick rattler, 77 
brick roads and pavements, 176 
concrete roads and pavements, 

149 

country brick roads, 194 
curbs, and curb and gutter, 383 
earth roads, 76 
gravel roads, 105 
macadam roads and pavements, 

121 
methods, elevating grader, 82, 

83 
monolithic brick pavements, 

194 

penetration macadam, 276 
sand clay roads, 94, 96 
sheet asphalt surfaces, 308 
stone block pavements, 323 
suburban roads, 323 
wood block pavements, 212, 217 
Country brick roads, 194 
County, administrative authorities, 

9 

bonds, 13 
roads, 8 
Creosote oil, 206 

and tar mixture, 207 
for paving blocks, 207, 209 
Creosote oil, source and composition, 

206 

specification, 207 
treatment, 211 
Cross breaking test, 178 
Cross section for asphalt block pave- 
ments, 303 
asphaltic concrete pavements, 

303 

brick roads and pavements, 179 
concrete roads and pavements, 

146, 148, 151, 152 
curbs, curb and gutter, 350 



INDEX 



453 



Cross section for earth roads, 71, 72 

gravel roads, 107 

macadam roads and pavements, 
126 

penetration macadam, 277 

sand clay roads, 95 

stone block pavements, 226 

wood block pavements, 213 
Cross sections, 28, 35 
Crossing stones, 228 
Crown, diagrams, for, 364 
Crusher run stone, 120 
Cuban asphalt, 243 
Culling brick, 188, 202 
Culverts, concrete, 64, 65, 66 

pipe, 64, 69 

purpose of, 37 

types of, 64, 70 

Curb and gutter, combined con- 
crete, 383 

construction of, 384 

design of, 380 

expansion of, 382, 389 

foundation for, 380 

gravel aggregate for, 384 

one course, 385 

two course, 384 

types of, 380 
Curb grades, 398 

inlets, 387 

purpose of, 388 
Curb inlets, types of, 386 
Curbs, armored, 383 

concrete, 380 

construction of, 381 

country brick roads, 383 

design of, 380 

expansion of, 382, 389 

height of, 379, 398 

integral, 380 

materials for, 381 

purpose of, 378 

radius, 381 

settings for, 380 

stone, 380 

Curing concrete roads, 154, 174 
Cut-back pitches, 247 
Cuts, side slope for, 77 
Cutting wood blocks, 211 



Definitions of elevation fixing plat- 
form grades, 393 
platforms, 392 

terms employed in highway en- 
gineering, 407 
Design of asphalt block pavements, 

315 
asphaltic concrete pavements, 

303 

brick roads and pavements, 176 
culverts, 62 
curbs, 380 
drainage, 39 
gravel roads, 106 
macadam roads, 117 
rural highways, 60 
sheet asphalt pavements, 314 
stone block pavements, 226 
street intersections, 375, 392 
wood block pavements, 213 
Design of pavements, 360 
car track paving, 388 
catch basins for, 382, 385 
central gutter pavements, 373 
combined concrete curb and 

gutter, 380, 383 
cross slope, 364, 367 
crown, 365 
Design of pavements, curb inlets, 

386, 387, 388 

curb, armored, 380, 383, 389 
concrete, 380, 381, 383 
height of, 379 
radius, 381 
stone, 380 

design of intersections, 375 
foundations, 348, 391, 392 
grades, 360 

ordinary maximum for vari- 
ous surfaces, 363 
intersections, 370, 371, 373 
manholes, 384, 388 
special gutter designs, 372, 385 
unsyinmetrical streets, 369 

car tracks on, 369 
width, 361, 363, 369 
Direct taxes, 11 

Distributers for bituminous ma- 
terials, 282 



454 



INDEX 



Ditches, 40 
Drag, road, 91 

use of, 86 

Drain tile, loads on, 67 
Drainage, 39, 40, 43 
Drains, broken stone, 128 

tile, 41 

Dump cars, 133 
Dump wagons, 91 
Durability of pavements, 351 
Dust layers and bituminous carpets, 
260, 267 

applying to new road, 269 
worn road, 271 

bituminous materials used, 250, 
275 

cost of, 263 

dust suppression on earth roads, 
260 

grading, 261 

kind of oil to use, 249, 261 

on concrete roads, 273, 275 

results to be had, 263 

unloading oil from cars, 263 
Dust layers and dust suppression on 
gravel or macadam, 264 

examples of good practice, 273 

oil on hard pavements, 266 

palliatives, 267 

Earth roads, computing quantities 
of earth work, 81 

construction of, 76, 80 

cost of, 84 

cross sections for, 73 

design of, 60 

dragging, 86 

grades for, 73 

maintenance of, 85, 86, 403 

oiling, 260 

overhaul, 78 

plans for, 33, 34, 35 

protection of slopes, 78 

shrinkage, 79 

side slopes, 77 
Earth work, 76 

computing quantities, 81 

cost of, 82, 84, 85 

shrinkage, 79 



Earth, tools and appliances, 88 
Economical life of pavements, 357 
Elevating grader, 81, 83 

work, 83 

Elevations, curb, 398 
Equipment for maintenance, 402 
Erosion, 44 

Examples of good practice, asphaltic 
concrete roads and pave- 
ments, 327 

brick roads and pavements, 197 
concrete roads and pavements, 

163 

design of intersections, 392 
drainage of highways, 50 
earth work maintenance, 85 
gravel roads, 111 
Koch investigations of sand- 
clay, 100 

macadam roads, 135 
mixed macadam roads, 295 
penetration macadam roads and 

pavements, 283 
plans for roads and pavements, 

34,35 

sand clay roads, 98 
Examples of good practice, sheet 

asphalt pavements, 327 
stone block pavements, 231 
use of road oils, 273 
wood block pavements, 215 
Excavation, steam shovel, 81, 82 
Expansion joints for brick pave- 
ments, 192, 198 
concrete pavements, 155, 172 
curbs, 389 
fillers for, 193 
protection plates for, 155, 157, 

172 
wood block pavements, 214 

Factors determing selection of type, 

346, 354 
Filler for sheet pavements mixtures, 

306 
Fillers, asphaltic, 214, 219, 228, 236, 

257 

bituminous, 193 
for brick surfaces, 193 



INDEX 



455 



Fillers, for stone block pavements, 
236 

for wood block surfaces, 214, 219 

mastic, 193 

tar, 258 

Filling expansion joints, 193 
Fills, earth, 77 

layer method, 76 

preparation of site, 76 

rolling, 76 

side slope, 77 

sodding, 78 
Finance, 11 
Finishing bridge, 154 

floats, 162 

Floats, finishing, 162 
Fluxes, analysis of, 247 

nature of, 247 

source of^ 248 

specification for, 255 

use of, 247 

Foothold for horses, 352 
Forks, stone, 132 
Foundation, 348, 391, 392 

for asphalt block pavements, 
316 

for asphaltic concrete surfaces, 
319 

for brick roads and pavements, 
182 

for concrete roads and pave- 
ments, 149 

for mixed macadam, 292 

for penetration macadam, 277 

for sheet asphalt pavements, 
302 

for stone block pavements, 226 

for water bound macadam, 123, 
130 

for wood block pavements, 212, 

216 
Front foot rule for assessments, 17 

Gang maintenance, 405 
Gilsonite, 244 
Gilsonite products, 245 
Glossary of road terms, 408 
Graders, blade, 85, 90 
elevating, 81, 90 



Giaders, Maney, 90 
Grades at curb corners, 398 

between platforms, 399 

for pavements, 350, 360, 363 

for earth roads, 73 

for rural highways, 73 

maximum, 74 

minimum, 75 

reduction of, 76 

ruling, 74 

safety considerations, 75 

undulating roads, 75 
Grading, appliances, 81, 85, 90 

balancing quantities, 75 

earth roads, 76 

for Bitulithic, 318 

methods of, 81 

rural highways, 76 

standard for sheet asphalt, 317 

tables of, for asphaltic concrete, 

319, 333 

Grading, tables of, for sheet asphalt, 
307 

Topeka, 319 
Gravel, bonding properties, 103 

gravel roads, 103 

mixed macadam, 297 

typical bank gravel, 104 

wearing properties, 103 
Gravel coated earth roads, 110 
Gravel roads, carpet coats for, 269 

characteristics of, 109 

constructions of, 104 

cost of, 110, 116 

crown, 106 

cross sections for, 107 

dust layers for, 264 

example of good practice, 111 

foundation for, 105 

ideal materials, 103 

harrow for, 111 

maintenance of, 110 

placing gravel, 108 

preparation for, 105 

rolling, 108 

selection of gravel, 105 

surface method, 106 

trench methods, 106 

wearing properties, 103 



456 



INDEX 



Gravel, well built gravel roads, 109 
width and thickness of gravel, 
106 

Gravity distributing wagons, 281 

Grooved rails, 391 

Grooved stone blocks, 224 

Ground water, 41 

Grout filler for brick, 189 
for stone blocks, 229 
wood blocks, 214, 220 

Grout, mortar box for, 189 

Gumbo, 93 

Gypsum roads, 94, 97 

Harrows, 96, 111 

Heaters, sand and stone, 294 

Height of curbs, 379, 398 

Highway engineering, 20 

Highway systems, development of, 1 

cost of hauling, 5 

county authorities, 9 

educational systems, 2 

energy saving, 5 

expenditures justifiable, 13 

local traffic, 4 . 

municipal authorities, 14 

national authorities, 10 

public highways, 4 

social consideration, 1 

state authorities, 9 

through motor traffic, 5 

township authorities, 9 

transportation systems, 3 

Improved granite block pavements, 

230, 236 

Industrial railway hauling, 133 
Inspection of brick, 188 

wood blocks, 202 
Integral curbs, 185 
Intersections, 375, 392 

Joint fillers for brick pavements, 188 
expansion joints, 192 
stone block pavements, 236 
wood block pavements, 214, 219 

Laying asphalt blocks, 316 
asphalt concrete, 322 
brick, 187 
sheet asphalt, 308, 309 



Laying stone blocks, 227 

wood blocks, 213, 217 
Licenses, automobile, 12 
Life of pavements, 351, 357 
Lipped rails, 391 
Loading devices for road materials, 

133 

Loads on drain tile, table, 67 
Loam, 62 
Local materials, 347 

traffic, 4 

Location of pavements, 355 
Longitudinal cracks, 157, 165 

joints, 155 

Macadam base, construction of, 185 

for asphalt block pavements, 316 

for asphaltic concrete, 321 

for brick pavements, 185 

for stone block pavements, 226 
Macadam, penetration, characteris- 
tics of, 279, 354 

construction of, 277, 286 

cost of, 281 

cross sections for, 277 

foundation for, 277 

maintenance of, 280 

materials for, 251, 276, 283, 290 
Macadam, waterbound, 117, 118 

applying screenings, 130, 138 

blind drains, 128 

carpet coats on, 261 

characteristics of, 344 

cross sections for, 126 

construction of, 121, 122 

dust layers for, 254 

examples of good practice, 135 

maintenance of, 127, 131 

materials required, quantity, 

123, 135, 136 
used, 117 

mixed, 281 

placing stone, 125, 137 

puddling, 130, 139 

quality of rock, 117 

road-bed and shoulders, 123, 130 

rolling, 128 

size of stone, 118, 119 
crusher run, 120 



INDEX 



457 



Macadam, size of stone, lower 

course, 119, 137 
Telford, 119 
upper course, 118 
thickness of, 121 
tools and machinery, 120, 124, 

129, 132 

Macadam, wearing properties, 130 
Machinery, asphalt plants, 324 

for brick roads and pavements 

constructions, 196 
for concrete road and pavement 

construction, 160 
for earth road construction, 88 
for grading, 81 
for hauling materials, 132 
for macadam and gravel road 
construction, 124, 129, 132 
for penetration macadam, 281 
for mixed macadam, 273 
Maintenance, 354, 400 

influence on selection, 347 

methods of, earth roads, 88 

of asphaltic concrete surfaces, 

324 

of concrete roads and pave- 
ments, 157 
of earth roads, 85 
of gravel roads, 110 
of macadam roads, 131 
of sheet asphalt surfaces, 325 
of wood block pavements, 215 
Making the selection of type, 349 
Maney grader, 90 
Manholes, design of, 384 

purpose of, 388 

Manufacture of wood blocks, 211 
Material for sheet asphalt, 304, 305, 

312, 327 

for stone blocks, 223, 228, 229 
for wood blocks, 204, 215, 217 
Materials, bituminous, 239 

tests for, 416 

Materials for asphalt blocks, 315 
for asphaltic concrete, 253, 256, 

316, 317, 327 
for brick pavements, 176 
for concrete base, 182 

roads and pavements, 141 



Materials for curbs and curb gutter, 
380, 384 

for gravel roads, 103 

for macadam, 117 

for mixed macadam, 253, 297 

for penetration macadam, 251, 
276, 283, 290 

for sand clay roads, 93 
Maximum grades for pavements, 
360, 363 

roads, 74 

Melting tanks for bituminous ma- 
terials, 292, 294 
Mexican asphalt, 243 
Mixed bituminous macadam, 291 

cement, for, 253 

characteristics of, 294, 354 

construction of, 292 

foundation, 292 

gravel aggregate for, 297 

mechanical appliances used, 
292, 293, 294 

precautions, 300 

proportioning, 300 

seal coat, 300 

stone for, 291 

weather conditions, 300 
Mixers for bituminous concrete, 324 

macadam, 293, 295 

Portland cement concrete, 152 

sheet asphalt surfaces, 324, 326 
Mixing asphaltic concrete, 321 

bituminous macadam, 292 

plants for sheet surfaces, 311 

Portland cement concrete, 152 

sheet asphalt, 308, 309 
Mixtures, bituminous, 247 

of tar and creosote, 207 
Monolithic brick pavements, 194 
Mortar box for grout, 196 
Mortar cushion for brick, 186 

stone blocks, 227 

wood blocks, 212, 221 
Motor trucks, 133 

Narrow gage car for hauling, 133 
National aid, 12 

National conference on concrete road 
building, conclusions of, 169 



458 



INDEX 



National Highway system, 7 
Natural asphalts, 242 

refining of, 243 

rock asphalts, 244 

sand clay mixtures, 94 
Noise from pavements, 353 

Ohio experience with road oils, 273 
Oil on hard pavements, 266 
Oiles earth roads, 260, 262 
Open binder, 304 
Ordering pavements, 15 
Organization, maintenance, 401 

of Illinois Highway Dept., 10 
Overhaul, 78 

Palliatives other than oil, 267 

Pat test, 310 

Patrol maintenance, 401 

Paved fords, 69 

Pavements, assessments for, 16 

Pavements, asphalt block, 315 

asphaltic concrete, 316 

brick, 176 

concrete, 141 

cost of, 356 

design of, 391 

drainge of, 391 

life of, 351, 357 

macadam, 117 

monolithic brick, 194 

ordering, 15 

reinforced concrete, 156 

selections of, 350 

sheet asphalt, 302 

stone block, 223 

wood block, 204 
Pavements foundations, 348, 391, 

392 
Paving blocks, stone, 213 

kinds of stone used, 213 

sizes of, 213, 216, 227 

uniformity of, 213, 215 
Paving brick, 176 

sizes of, 1 79 

tests of, 180 

types of, 176 

uniformity of, 180 
Paving plans, 36 
Paving, surveys, for, 36 



Peculiarities of traffic, 338 
Penetration and mixed macadam 
roads and pavements, 276, 
284 
Penetration macadam, 276, 284 

applying bituminous binder, 
279 

bituminous material for, 251, 
290 

characteristic of, 279, 354 

construction of, 277, 286 

cost of, 281 

cross-sections for, 277 

foundation, 277 

examples of good practice, 283 

maintenance of, 280 

rolling, 278 

size and kind of stone, 276, 283 

thickness, 277 

wearing course, 278 
Petroleum asphalts, 245 
Physical characteristics of brick, 178 
Pitch fillers for brick pavements, 
188, 191 

expansion joints, 192 

stone blocks, 228 

wood blocks, 214, 200 
Pitches cut back, 247 
Placing sand cushion, 187 
Placing sand mortar bedding course, 

186 

Plan view, 33 
Plans, paving, 35, 36 
Plans, road, 33, 34, 35 
Plants asphalt, 311 
Plates, protection, 155 
Platform grades, 399 
Platforms definition of, 392 
Portable stone crushing plants, 135 
Portland cement filler, 189 
Pouring bituminous filler, 191 
Pouring cans, 281 
Present traffic, 337 
Preservative treatment for wood 
blocks, 205 

character of, 205 

quantity of, 209 

Pressure distributing wagons, 282, 
283 



INDEX 



459 



Profile, 33, 37 

Proportioning asphalt cement, 312, 
326 

asphaltic concrete mixtures, 326 

Bitulithic, 317 

grout filler, 189 

mixed macadam, 300 

Portland cement concrete for 
roadway surfaces, 143, 173 

sheet asphalt mixtures, 326 
Protected joints, 155 
Protection of slopes, 78 
Puddling, 130, 139 

Quality of rocks for Bitulithic, 316, 

327 

for asphaltic concrete, 316, 327 
for macadam, 117 
for mixed macadam, 291 
for Portland cement concrete 

surfaces, 141 
Quantity of bituminous for asphaltic 

concrete, for asphalt blocks, 

315, 318, 319 
for Bitulithic, 319 
for mixed macadam, 282, 292 
for sheet asphalt, 297, 307 

Radius curbs, 381 

Rakes for sheet surfaces, 326 

stone, 132 

Reconnaisance survey, 22 
Recut granite blocks, 229 

in Baltimore, 235 

in New York, 233 
Reduction of grades, 76 
Refined asphalt specifications, 254 
Refining asphalts, 244 
Reinforced concrete culverts, 64, 65, 
66 

roads and pavements, 156 
Repressed vitrified brick, 176 
Residual asphalts, 245 

value, 358 
Rewards, state, 11 
Roadbed, 123 
Road drags, types of, 91, 92 

use of, 86 
Road graders, 90 
Road planer, 92 



Road plans, 33, 34, 35 
Roads, asphaltic concrete, 303, 323, 
330 

brick, 176, 194 

carpet coats on, 267 

design of, 60 

earth, 76 

gravel, 103 

gypsum, 97 

local, 4 
Roads, macadam, 117 

mixed macadam, 291 

penetration macadam, 276 

Portland cement concrete, 141 

rural, design of, 60 

sand clay, 93 

state, 8 

town, 8 

township, 8 
Roller, horse drawn, 134, 196 

tandem, 129, 134 

three wheeled, 129, 134, 196 
Rolling asphaltic concrete, 322 

Bitulithic, 320 

brick surfaces, 188 

earth fills, 76, 77 

gravel, 108, 111, 113, 114 

macadam, 128 

penetration macadam, 278 

sheet asphalt, 309 

Telford, 129 

wood blocks, 214 
Rooter plow, 89 
Ruling grade, 74 
Runoff, 39, 43 
Rural highways, design of, 60 

Safety considerations, 75 

Sand bedding course for brick, 186 

for stone blocks, 226 

for wood blocks, 212, 218 
Sand-clay construction on clay, 94 

for gumbo, 94 

for loam, 94 

for sand, 96 

Sand-clay roads, characteristics of, 
97 

construction of, 94, 95, 96 

cross sections for, 95 



460 



INDEX 



Sand cushion, 186 

Sand for asphaltic concrete, 317 

bedding course, 186 

filler for block surfaces, 189 

Portland cement concrete sur- 
faces, 141 

sand-clay roads, 94 

sheet asphalt, 306, 327 
Sand filler for block surfaces, 188 

mortar bedding course, 186 
Sanitariness, 352 
Scarafiers, 135 

Screens for sheet asphalt plants, 326 
Seal coat, 285, 300 
Seasoning wood blocks, 211 
Selection of gravel for gravel roads, 
104 

of surface for rural highways, 
337 

of type of pavements, 20 
Sheet asphalt pavements, 302 

asphalt cement for, 312 
paint coat for binder, 305 
plants, 311 

base course, 302 

binder course, close, 304, 327 
open, 304 

characteristics of, 312, 354 

concentrated traffic on, 310 

construction of, 308 

design for, 314 

earth foundation, 302 

fillers for, 306 

foundation for, 302 

material for binder course, 305 

mixing plants for, 311 

old surface mixtures for binder, 
305 

pat. test. 319 

proportions of materials, 306, 
312, 327 

rolling, 309 

sand for, 306 

Sheet asphalt pavements, specifi- 
cation for, 328 

standard gradings for, 306, 307 
Shrinkage of earthfills, 79, 81 
Side ditches, 39 

on fills, 77 



Side ditches, slope cuts, 77 
Sidwalk grades, transverse, 371 
Sieve analysis, method, 71, 74, 75 

tables, 307, 318, 319, 333 
Sieves, standard for road materials, 

72 

Size of asphalt blocks, 315 
brick, 179 
coarse aggregate for asphaltic 

concrete, 316, 327 
for bitulithic, 317 
for concrete base, 182, 194 
for concrete roads and pave- 
ments, 141, 170 
crusher run stone, 120 
curb expansion joints, 382, 389 
sand for asphaltic concrete, 317, 

327 

for bedding course, 186 
for concrete roads and pave- 
ments, 141, 170 
for sheet asphalt, 306 
stone blocks, 223 
stone for mixed macadam, 291, 

300 
for penetration macadam, 

276, 283 
for Telford, 118 
for waterbound macadam, 

118, 119 

wood blocks, 205 
Slip scrapers, 89 
Slipperiness, 352 
Slope in cuts, 77 

fills, 77 

Smoothing irons, 326 

Soils, clay, 61, 93, 94 

loam, 62, 94 

sand clay, 94 

Sources of bituminous materials, 

242 

Specification for asphalt blocks, 315 
asphalt cement, 256 
binder course, 296, 318 
bituminous binders, 249 

fillers for block pavements, 

257 

macadam, 295 
creosote oils, 207 



INDEX 



461 



Specification, flux, 255 

grout filler, 189 

paving brick, 180 

refined asphalt, 254 

road oil for use on concrete, 275 
Standard gradings sheet asphalt, 307 
State aid, 11 

bonds, 13 

rewards, 11 

roads, 7, 8 

Stationary crushing plants, 135 
Steam shovel excavation, 81, 82 
Stone block pavements, 223 

asphaltic fillers for, 229 

characteristics of, 230, 354 

cost of, 234, 236 

cross-section for, 226 

examples of good practice, 231 

foundation for, 226 

grout filler for, 229 

kinds of stone used, 223 

laying blocks, 227, 237 

mortar bedding course for, 227 

pitch filler for, 228 
Stone block pavements, recut blocks, 
229 

requirements for stone blocks, 
223, 225 

sand cushion for, 226 
filler for, 228 

size of blocks, 223, 226, 237 

special kinds of, 224 

tamping the blocks, 227, 238 
Stone for asphalt blocks, 315 

asphaltic concrete, 306, 316, 327 

foundations, 182 

macadam, 117 

Portland cement concrete road 

surfaces, 141 

Stone blocks for pavements, 223 
Stone crushing plants, 135 

cubes, 224 

curbs, 380 

drains, 41 

for asphalt blocks, 315 

for asphaltic concrete, 316, 327 

for mixed macadam, 291 

for penetration macadam, 276, 
283 



Stone for Portland cement concrete 

foundations, 183, 302 
roadway surfaces, 142 
Storage bins for hot aggregates, 

325 
Street intersections, design of, 375, 

392 
Street paving, administration of, 14 

design of, 360 

Stresses in concrete roadway sur- 
faces, 141 
Strike boards for concrete roadway 

surfaces, 153, 154 
Subgrade, 169, 289, 315 
Suburban asphaltic concrete roads, 

323 

Surface drainage, 52 
Surface mixtures for asphaltic con- 
crete, 316 
bitulithic, 317 
bituminous macadam, 291, 297 

299 

mixed macadam, 291, 297, 299 
sheet asphalt, 306 
Warrenite, 319 
Surface oiling, 250 
Surveys and plans for roads and 

pavements, 22 
complete detailed, 23 
for earth roads, 23 
Iowa directions, 24 
paving, 36 
reconnaissance, 22 
Systems of administration of high- 
ways, 6 
county, 9 
municipal, 14 
national, 10 
state, 9 
town, 9 
township, 9 

Table of average gradings, asphaltic 
concrete, Washington, 
D. C., 333 

asphalt plant operating statis- 
tics, 335 

block quarries, available to 
New York, 233 



462 



INDEX 



Table of cement, amount to use with 
bank gravel, 144 

comparison of light and heavy 
creosote oils, 209 

composition of brick rattler 
shot, 80 

cost of concrete roads, Mil- 
waukee Co., Wis., 163 
Illinois contract work, 163 

of oiling, 264 

English Road Board categories 
of weights, 343 

life of pavements, 351 

linear feet of road per cubic yard 
of stone, 136 

pavements, 254 

pavements, general, 358 

report on pavements, Cam- 
bridge, Mass., 354, 358 

superficial area of fine aggre- 
gates, 307 
Table of loads on drain tile, 67 

maximum grades for pave- 
ments, 363 

office of Public Roads weight 
categories, 343 

properties of bituminous mate- 
rials, 258 

quantity of stone for roads, 136 

relative importance of charac- 
teristics of pavements, 355 

sieve analysis, asphalt con- 
crete, 319 
bitulithic, 318 

standard sheet asphalt grading, 
307 

statistics, Liverpool, Eng., 359 
Sheffield, 346 

stone blocks, sizes of, 226 

thickness of pavement founda- 
tions, 392 

Topeka grading, 319 

tractive resistance of roadway 
surfaces, 353 

traffic summary, city of Buffalo, 

345 
Chicago, 345 

U. S. office of Public Roads, 
343 



Table of waterways for culverts, 63 

weight categories, English Road 

Board, 343 

Talbot's formula for waterways, 63 
Tampers for sheet surfaces, 326 
Tamping asphalt blocks, 316 

stone blocks, 227 
Tar, gas house, 246 

water gas, 247 
Taxes, direct, 11 

special, 11 

Testing bituminous road and paving 
materials, 427 

non-bituminous road materials, 

416 
Tests, abrasion, 416, 417, 426 

asphaltenes, 435 

bituminous road and paving 
materials, 427 

burning point, 433 

carbenes, 435 

clay and silt, 422 

colorimetric, 434 

consistency of concrete, 426 

Deval, 416 

distillation, 430, 439 

ductility, 428 

Engler, 432 

fixed carbon, 427 

flash point, 433 

float test, 433 

loss on heating, 434 

penetration, 429 

shale, 425 

sieve analysis, 420, 421 

specific gravity, 419 

bituminous material, 392 
coarse aggregate, 419 
fine aggregate, 419 

toughness, 417 

viscosity, 432 

voids, 419 

Thin-section concrete base for pave- 
ments, 184 

Through motor traffic, 5 
Tile culverts, 64 
Timber for wood blocks, 204 
Time for mixing concrete, 173 
Topeka asphaltic concrete, 318 



INDEX 



463 



Town roads, 9 

Township roads, 8 

Traction hauling, 132 

Tractive resistance, 353 

Traffic census, 216, 337, 339, 342, 343 

analysis of, 340 

forms for, 341 
Traffic on pavements, 355 

zones, 339 
T-rails, 390 
Traveled way, 71 
Treating wood blocks, 211 
Treatment of center line intersec- 
tions, 393 
Trinidad asphalt, 242 

petroleum, 243 . 
Two-course brick pavements, 185 
Two-course concrete roadway sur- 
faces, 143 
Types of asphaltic concrete, 317 

of car track paving, 389 
Types of car track rails, 391 

of culverts, 64 

of soils, 60 

Underdrainage, 51 

Uniformity of stone paving blocks, 

225 

of paving brick, 180 
Unsymmetrical streets, car tracks 

on, 369 
cross-slope, 368 

Vertical fiber brick, 177 

Vitrified brick roads and pavements, 

176 
Voids; determination of in coarse 

aggregate, 70 
Jackson methods, 70 

Wagons, dump, 91 

for traction hauling, 132 
Warrenite, 319 
Waterbound macadam, 117 
Water for concrete roads, 170 

gas tar, 247 

soluble materials, 404 

supply equipment, 155, 162 
Wearing course specification for 
asphaltic concrete, 330, 331 



Wearing couise specification for 
bituminous macadam, 295 

sheet asphalt, 328 

Weights of macadam materials, 136 
Western wheat grass, 46 
Wheel scrapers, 89 
Wire-cut-lug brick, 177 
Wood block pavements, asphalt 
cleaning, filler for, 215 

Heading, 210 

case of cleaning, 354 

characteristics of, 210, 354 

construction of, 212, 217 

cost of, 215 

creosote, oils employed, 205, 206 
Wood blocks pavements, cross- 
section for, 213 

durability of, 215, 216 

expansion joints, 214, 219 

foundation for, 212, 216 

maintenance of, 205, 215 

manufacture of blocks, 211 

mastic bedding course, 215, 218 

mortar bedding course, 212, 
218, 221 

preservative treatment of 
blocks, 205, 211, 217 

quality of blocks, 205, 217 

sand bedding course, 212, 218 

sand filler, 214, 220 
Wood block pavements, samtariness, 
cutting, 215 

size and kind of blocks, 194, 
195, 207 

slipperiness, 215, 220 

tar filler, 210, 214 
Wood blocks, cutting, 211 

inspection of treatment, 212 

manufacture of, 211 

preservative treatment, 205, 
217 

quality of, 217 

seasoning, 211, 217 

size of, 195, 217 

timber used, 204, 217 

Zone and Area method, 17 
Zone and benefit method, 18 
Zones, traffic, 339