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Fundamentals of Construction 

and Maintenance of 
Secondary Type Highways 




Published by Purdue University at LaFayette, Indiana 

Entered at the Post Office at LaFayette as second class matter under 
the Act of July 16, 1894. 



Purdue University recognizes its opportunity for public 
service by carrying the benefits of its teaching and research 
activities to those in the State who are interested in engineering 
problems, but who are unable to be benefited by the regular 
courses of resident instruction which are offered at the Uni- 

The Engineering Extension Service of Purdue University is 
carried on in the following ways : 

1. Conferences are held at Purdue University and at other 
places in Indiana for the benefit of road builders, canners, elec- 
trical workers, power plant men, foundrymen and for others 
engaged in manufacturing and in public utility industries. 

2. Groups of lectures are delivered by engineering experts 
of Purdue University for the benefit of industrial workers and 
executives. Talks are also given on subjects related to engineer- 
ing before civic, commercial and manufacturing organizatio; 

3. Publications in the form of bulletins and circulars are 
issued containing up-to-date information on engineering subjects. 

Address communications concerning Engineering Extension 
Service to 

Purdue University, Lafayette, Indiana. 



Fundamentals of Construction 

and Maintenance of 
Secondary Type Highways 


Professor of Railway Civil Engineering 
In Charge of Highway Engineering 



OCTOBER, 1922 


Civil l-:iii;iii;MTiii; 



CHAPTER I. Introduction ....'. . 5 

CHAPTER II. Elements of Road Construction 7 

CHAPTER III. Elements of Earth Road Maintenance 13 

CHAPTER IV. Construction of Sand-Clay, Cinder and Shale Roads 18 

CHAPTER V. Maintenance of Sand-Clay, Cinder and Shale Roads 21 

CHAPTER VI. Gravel Road Construction 21 

CHAPTER VII. Gravel Road Maintenance 25 

CHAPTER VIII. Macadam Road Construction 27 

CHAPTER IX. Macadam Road Maintenance 31 

CHAPTER X. Dust Prevention 32 

CHAPTER XL Bituminous Carpets 35 


Frontispiece Civil Engineering Building. 

Fig. 1. Cross-section of an Earth Road 8 

Fig. 2. Determining Crown with Level Board .'.. 8 

Fig. 3. Shaping Earth Subgrade and Side Ditches with Blade Grader 9 

Fig. 4. Washout along Hillside Road 10 

Fig. 5. Lowering Ground Water with Tile Drains 10 

Fig. 6. False Ditch between Roadway and Berm 11 

Fig. 7. A Good Sign to Follow, Allen County 11 

Fig. 8. A Good Highway with Flat Curves and Light Grades 12 

Fig. 9. Details of a Plank Drag 14 

Fig. 10. An Earth Road before Improving 15 

Fig. 11. An Earth Road after Improving 15 

Fig. 12. Small Culvert Clogged with Weeds 16 

Fig. 13. Water Held in Side Ditches Softens the Subgrade 16 

Fig. 14. An Earth Road in Poor Condition 17 

Fig. 15. Improperly Drained and Shaped Road on Steep Hill 18 

Fig. 16. Clay Hill with Sand Spread and Harrowed 19 

Fig. 17. Hill with Consolidated Sand-Clay Surface 19 

Fig. 18. Washed Gravel for Road Construction < 21 

Fig. 19. A Poorly Constructed Gravel Road 23 

Fig. 20. A Good Gravel Road 23 

Fig. 21. Poor Drainage and Insufficient Depth of Surface Material 

Caused this Gravel Road to Break Up 24 

Fig. 22. Dangerous Point on Road Caused by Short Culvert 26 

Fig. 23. Safe Road with Extended Culvert 26 

Fig. 24. Suggested Cross-section of a Macadam Road 28 

Fig. 25. Sprinkling Macadam Prior to Last Rolling 29 

Fig. 26. A Properly Shaped and Maintained Macadam Road 30 

Fig. 27. Crushed Stone for Maintenance Along Highway 31 

Fig. 28. Spreading a Thin Covering of New Material with Truck 32 

Fig. 29. Oiling a Macadam Surface to Prevent Dust 33 

Fig. 30. Spreading Cover Material on a Bituminous Carpet 35 

Fig. 31. A Bituminous Surface That Has Been Neglected 36 

Fig. 32. A Good Bituminous Surface Highway 36 


This bulletin of information is prepared in order to bring 
the best practice in road work to the attention of the county 
and township road officials of Indiana. It is also believed that 
city street commissioners, highway contractors and others in- 
terested in road problems may find herein material of value to 
them. This is not intended to be a complete treatise of the sub- 
jects of road building and maintenance under all conditions, but 
it is an explanation of the fundamental problems particularly ap- 
plicable to Indiana. 

A portion of the information in this volume has appeared 
in newspaper articles and in mimeograph form. 

Special credit is due B. H. Petty, Assistant Professor of 
Highway Engineering, for constructive criticism in the prepara- 
tion of the manuscript. 

September, 1922. C. C. ALBRIGHT. 




In recent years the improvement of the highways has come 
to be one of the most important problems of the times. The 
daily press and the technical publications have contained much 
discussion about the development of the so-called higher types 
of highways. This is important and desirable since less than 
10 percent of the rural highways will probably carry 85 percent 
of the total traffic. Notwithstanding this fact, 90 per cent of 
the highway mileage must carry the remaining 15 percent of 
the traffic to and from the individual rural dweller and these 
secondary roads are absolute esssentials as connecting links be- 
tween the more or less remote rural home and the main high- 
ways. The health, happiness, contentment, advancement and 
prosperity of those who dwell in the country are largely depend- 
ent upon transportation over these roads which are frequently 
impassable for periods varying from a few days to several 
months per year. 

In view of these conditions it appears that too little stress 
has been placed on the development of the simple types of roads. 
Heavy expenditure of money is not warranted for light traffic, 
but it is possible to construct roads of a type that, will answer 
practically all the purposes of light traffic for a fraction of the 
cost of a hard surfaced road. 

The 1914 statistics of the United States Bureau of Public 
Roads gave a total of 2,445,760 miles of road in the United States. 
Of this amount 257,291 miles, or 10.5 percent, had improved sur- 
faces. The statistics of 1919, the latest available, show a cor- 
responding total mileage of 2,478,552 with 299,135 miles, or 12.1 
percent, improved. The average improvement rate in this period 
is, therefore, only three-tenths of one percent per year. This 
period was during the World War when little work not absolutely 
essential was performed. At the present time the rate of prog- 
ress is probably double the above, but the actual construction and 
maintenance must be further increased to meet the traffic de- 
mands. To illustrate these conditions the following figures are 
given : The total production of all kinds of motor vehicles in- 
creased from 25,000 in 1905 to over 2,000,000 in 1920 while the 
registration of motor vehicles increased from 1,009,513 in 1912 

to 9,750,000 in 1921. It will thus be seen that the production of 
vehicles increased 8000 percent in 16 years and the registration 
increased 900 percent in 10 years. Leading highway engineers 
and traffic experts have estimated the desirable rate of increase 
in highway improvement to accomodate the traffic demands as 
one percent and that this rate is desirable for the next ten or 
fifteen years. In 1921 about $420,000,000 were expended for new 
construction and $180,000,000 for maintenance, but to meet the 
desirable increase of improvement over $1,000,000,000 would be 
necessary per year. This places highway work as one of the 
leading industries of America and the huge sum of money in- 
volved indicates the desirability of expert knowledge on the 

Much study has been given to the road surface, but the sub- 
grade factors have been largely neglected. The latter conditions 
as well as the surface are now receiving intensive study at the 
Bates Experimental Road in Illinois under the direction of the 
Illinois Department of Roads and the United States Bureau of 
Public Roads. Other tests of importance are being conducted 
at Pittsburg, California, and Arlington, Virginia. The data ob- 
tained from these experiments with that secured from numerous 
others of less importance will be of great value in future high- 
way plans. 

It seems almost unnecessary today to demonstrate the neces- 
sity of road improvement, however, a simple problem in elemen- 
tary highway economics may be of some value. The tractive 
force required to pull a load on a common farm wagon over un- 
improved earth roads is 100 to 300 pounds per ton of load. The 
average is 200 pounds per ton. It has been demonstrated that 
this can easily be reduced to one-half the value on a properly con- 
structed and maintained surface. An estimate for the value of 
this improvement, as given by the United States Bureau of Pub- 
lic Roads, is 2 to 10 cents per ton mile. The average is 6 cents. 
Assume a traffic so light that only ten tons per mile per day is 
averaged for 300 days per year. The saving is 300x10x6 or $180 
per mile per year. This sum is sufficient to maintain an earth 
road in excellent condition for twenty times the assumed tarffic. 
$180 also represents the interest at 6 percent on $3000. There- 
fore this would justify an expenditure of $3000 per mile for 
permanent improvement, i. e., grading, drainage, culverts, bridges, 
guard fences, signs, etc. The cost of grading the average road 
in a suitable manner for present or future permanent improve- 
ment will be $1,000 to $4,000 per mile. 

Since the motor vehicle is found in all rural communities and 
predominates in many, this discussion would not be complete 
without some reference to the economies of motor transport. 

There is very little reliable data available concerning the 
cost of motor traffic ; but in 1918 some valuable tests were con- 

ducted in the vicinity of Cleveland, Ohio. These experiments 
dealt entirely with the fuel consumption of trucks running over 
various road surfaces. The gasoline consumed on gravel and 
macadam roads was 60 to 80 percent of that on earth roads ; 
while on the best type of brick and concrete roads it was only 
50 percent. On a basis of fuel alone the gravel road would give 
a saving, at 23 cents per gallon, of 1.4 cents per mile. In addi- 
tion the better classes of roads offer a saving in time of travel, 
repairs, wear on tires, oils, other lubricants and depreciation. 

Assuming a daily tarffic of 20 trucks per mile for 300 days, 
we have a yearly saving per mile on the gravel road of 300x20x 
$0.014 or $84. This is 6 percent on a capital charge of $1,400. 
It has been stated that the results of these tests were largely 
responsible for the success of a $60,000,000 bond issue for hard 
surfaced roads in Illinois. 

First class gravel and macadam roads with 18 foot wearing 
surfaces, exclusive of sub-grade and structures, capable of carry- 
ing several hundred average vehicles per day can be constructed 
for $8,000 to $14,000 per mile. The total cost in any individual 
case will vary with many local factors. 


At the present time the public roads of Indiana have been 
largely laid out or as commonly stated have been constructed. 
On many of the secondary roads the latter word is greatly mis- 
leading as practically no construction work has been done other 
than plowing a shallow side ditch and scraping some of the sod 
and surface material to the center of the road. Indiana has 
84,400 miles of rural highways, about 35,000 miles of which have 
been surfaced. Of the total mileage 50,000 have no surface ma- 
terial other than the local soil. Little or no attention has been 
paid to adequate grading, drainage or improving much of this and 
in wet weather these roads are continuous mud holes while in 
dry weather they are rough and dusty trails. 

Construction and maintenance both vary with soil condi- 
tions. Typical soils of Indiana are the heavy clays of the Mau- 
mee Valley, the light shifting sands of the Dunes region along 
lake Michigan, the gravel and sandy loams of the north central 
region, the black soil near a part of the Illinois line, the clays of 
the southern Knobs and the silts of the lower Wabash and Ohio 
River Valleys. 

Proper drainage is the essential basis of all highway im- 
provement. No road can be properly built or kept in good con- 
dition unless provision is made for the elimination of all free or 


excess water. In the sandy soils previously mentioned this is 
easily accomplished, but particular care must be taken in order to 
secure favorable results with clay or gumbo soils. If the soil is a 
light, fine sand, a flat crown and shallow side ditches will usu- 
ally suffice. The sand will have less tendency, under these condi- 
tions, to shift or drift. Any rain except the very heaviest will be 
rapidly absorbed by the sand or quickly carried away by the 
shallow ditches. 

/7/se /e C 

Fig. 1. Cross-section of an earth road. 

Fig. 2. Determining crown with level board. 

In a clay or dense soil the side ditches should generally be 
eighteen inches or more below the crown of the road. This will 
vary with the steepness of the grade across and parallel to the 
road, the width of the road and the average intensity of the 
rainfall. The ditch section may be V shaped or flat bottomed. 
The former shape is gaining favor as it can both be constructed 
and maintained with the common road grader or scarper which 
reduces the labor cost. If a flat bottom is used it should not be 
less than 24 to 30 inches in width so that a slip or drag scraper 
can be used for construction and cleaning purposes. 

Water should be taken from the side ditches at frequent 
intervals and carried away in natural drainage channels to pre- 
vent danger of "washouts" along the side of the road from the 
larger volume of water. It will also be necessary to enlarge the 
ditch section if water is to be carried more than 150 to 200 yards. 

Fig. 3. Shaping: earth subgrrade and side ditches with blade grader. 

When the road is located on a steep hillside, it is often desir- 
able to put tile drains on the upper side of the road to intercept 
ground water flow. The tile should be placed from 30 to 60 
inches below the surface of the ground and always below the 
frost line. The trench should be back-filled with gravel or 
crushed stone. At the present time some engineers do not be- 
lieve such drains are of any value in heavy dense soils. There 
can be no question, however, as to their value in intercepting 
ground water and lowering the water table under the road in 
porous soils. In all cases rainfall and free water should be car- 
ried from the travelled way as quickly as conditions will permit. 
This applies equally to hard surfaced and to inferior types of 
roads. Wet spots in the road can be drained by running a line 
of small tile, not less than 4 inch, to the side ditch. If good 
coarse gravel or crushed stone is available, a French or blind 
drain can be used. This is constructed by digging a narrow 
trench and back-filling with coarse aggregate. The grade of 
these drains should be not less than one inch in five feet and 
the top should be covered with at least six inches of compact soil 
in order to prevent rapid clogging of the aggregate. These drains 
are quite effective and are often much cheaper than the tile drain. 


The only purpose in crowning a roadway is to carry surface 
water quickly to the side ditches. Too much crown is objection- 
able to traffic and will cause vehicles to travel in the same line 
at the center of the road. This results in ruts, increases the 
danger of collision of passing vehicles and causes loose surface 
material to roll to the side of the road. A flat surface would be 
the ideal condition as the vehicles would travel over the entire 
surface causing uniform wear with less danger of collision and 
little displacement of material. 

Fig. 4. Washout along hillside road. 

Fig 5. Lowering ground water with tile drains. 

The crown of a road in heavy soil should be from one-half 
to one inch per foot and should seldom exceed three-fourths of 
an inch per foot. Thus for a sixteen foot roadway the crown 
would be 24x8 or 6 inches. The crown should be carried as a 


smooth surface to the ditch line. An inferior road will invariably 
result if a false ditch is formed .between the roadway and the 
berm or shoulder. 

Fig. 6. False ditch between roadway and berm. 

The width and grade of a road are also important factors. 
It is usually advisable on main roads to have the traveled way 
wide enough for two vehicles to pass. This together with a 
low crown will result in a more even distribution of traffic, will 

Fig. 7. A good sign to follow, Allen County, 


lessen the maintenance work and contributes to the safety of 
travel over the road. The total width of the road should include 
the traveled way, the shoulders, the side ditches and at least a 
narrow berm between the ditch and adjacent property line. The 
latter is necessary for the protection of the property line fence. 
The shoulders protect both the roadway and the ditch and under 
normal weather conditions, when necessary, will carry passing 
vehicles. A sure indication that the traveled way is too narrow 
is that the maintenance of the shoulders is excessive because of 
use by vehicles. Frequent traffic accidents may also indicate 
the same thing. 

The longitudinal grade of all roads should be as flat as pos- 
sible without excessive cost. A rise of one foot in a distance of 
one hundred feet adds twenty pounds to the tractive force re- 
quired to move a ton of load. A rise of five feet in a hundred 
foot distance, therefore, doubles the force required to move this 
load on a well graded and maintained earth road. The effect of 
grade is more serious in the case of a slow moving animal drawn 
load than for a motor vehicle moving at higher speeds. The 
momentum of the rapidly moving motor vehicle is of material 
assistance in overcoming the grade while this factor is practically 
negligible in a horse drawn vehicle. For motor traffic short, 
straight grades of a maximum of ten percent may be used, but are 
not desirable as the maximum safe speed on descending prob- 
ably would be exceeded. On sharp curves or on long tangents 
the grades should be kept within three to five percent where 

Fig. 8. A good highway with flat curves and light grades. 

Short or sharp curves in the alignment of the road should 
be avoided as they are a source of danger to passing vehicles. 
On main line highways curves should seldom have a radius of 


less than 300 to 500 feet. Obstructions to sight such as trees 
or high banks on the inside of curves should be removed when- 
ever possible. There should be a clear view across the inside 
of the curve for at least fifty yards on secondary roads and one 
hundred yards on main traveled highways. 

The methods of construction described in this chapter could 
be easily applied, without excessive cost, on a majority of the 
highways of Indiana. The funds required for the work would 
yield large dividends as the general character and appearance of 
the roads would be improved from twenty-five to one hundred 
percent, the work of maintenance would be reduced, the cost of 
transportation would be lowered and the pleasure of the passing 
traveler would be greatly increased. 


Assuming that the sub-grade of a road has been properly 
constructed, shaped and drained the next step is the actual main- 
tenance of the surface. Weather and traffic iDoth tend to destroy 
the finished road and these influences must be met with proper 
maintenance. There are normally two main periods of intensive 
maintenance, viz., in the early spring just after the frost has 
left the ground and in the late autumn just before the final 
"freeze up." Immediately after the frost has left the ground is 
the best time to use the grader. This should be used to form a 
new well defined ditch. At this time also extra material should 
be moved to the road surface in order to fill ruts and depressions. 
While the road is soft and moist this new material will unite with 
the original road top to form a new surface. All sod and loam 
or decayed vegetable matter should be removed from the road, 
as otherwise it forms a prospective point of failure. This ma- 
terial can be used to fill low places along the road or hauled to 
adjoining farms as a fertilizer. No loose material should be 
placed on the road surface after it has become thoroughly dry 
and settled. Loose earth will not unite with the hard top of the 
road, but will be stirred up as dust by the vehicles in dry weather 
and will form a slop after a rain. The only excuse for adding 
loose earth in the summer is because of a washout or other 
emergency repair. 

The next step is to grade and shape the surface that has 
been eroded and scarred by the action of weather and vehicles 
during the winter. This can first be accomplished by the steel 
bladed grader. The formation of a false ditch at the edge of the 
traveled way should be prevented by occasionally passing the 
grader or planer over the edge of the shoulder. Good sod is a 
material aid in maintaining the shoulders. It also holds loose 



material washed from the surface of the road and may in time 
build up the shoulder higher than the road surface. When this 
condition occurs the sod must be cut off with the blade grader 
or small ditches opened up at frequent intervals across the 
shoulders, so that water falling on the surface of the road will be 
carried quickly to the side ditches. 

Figr. 10. An earth road before improving. 

Fig. 11. An earth road after improving, 

After the initial grading the road grader, drag or planer 
should be used after every rain that is sufficiently heavy to soften 
the surface thoroughly. The drag and planer are very inex- 
pensive pieces of equipment and are very effective for the minor 
work of maintenance during the greater part of the working 


season. If they are properly used a continual improvement of 
the road surface during the season will be effected. By the 
intelligent use of simple road machinery it is possible, under fa- 
vorable conditions, to produce a surface that will rival for 
smoothness a city boulevard. This condition can be maintained 
until freezing begins. Certain faults in the road, as wet spots 
due to springs or to excessive shade, bad material, etc., should 
be studied as they appear and properly corrected. 

Fig. 12. Small culvert clogged with weeds. 

Fig. 13. Water held in side ditches softens the subgrade. 


To secure the best drainage conditions, weeds, high grass 
and brush along the shoulders and in the side ditches should be 
cut and burned as often as necessary. The frequency of this 
work will depend upon the weather and local conditions, but 
usually once or twice a year is sufficient. Small culverts and 
bridge openings should be cleaned as often as necessary to insure 
unobstructed waterways. 

Fig:. 14. An earth road in poor condition. 

When freezing begins in the autumn the surface will break 
up under heavy traffic unless the road has practically perfect 
drainage. No earth road will safely carry any but the lightest 
traffic during a prolonged rainy season or during alternate freez- 
ing and thawing of the ground. At this time the road should 
again receive particular attention. Advantage should be taken 
of days when the frost is out of the ground to go over the road 
with the blade grader or preferably the drag or planer and smooth 
out the ruts and wheel tracks. Free water from rainfall and 
melting snow will quickly drain from the smooth crowned sur- 
face while if held in rough spots it will be absorbed by the road. 
In the latter instance mud holes will rapidly develop under traffic 
and the road may become impassable. If the road freezes with 
a smooth surface it will be agreeable for traffic and will go 
through the winter with a minimum amount of damage. 

The main points of earth road maintenance may thus be 
briefly summarized and are sufficiently important to be placed 


in the note book of every one who has anything to do with the 
work of highway maintenance. 

1. Poperly drain the road. 

2. Properly shape the road. 

3. Use the flattest permissible crown. 

4. Prevent the formation of false ditches. 

5. Do heavy grading only in early spring. 

6. Remove all pockets of inferior material from road 

7. Use grader, drag or planer after all hard or prolonged 
rainfall and at such other times as necessary. 

8. Patrol road as often as necessary and correct specific 
faults as soon as they appear. 

9. Keep ditches and culverts free from obstructions. 

10. Grade road surface immediately before the winter 
"freeze up." 

11. During winter weather take advantage of mild, warm 
days to smooth out ruts and wheel tracks. 

12. Be vigilant at all times and remember the homely 
maxim, "An ounce of prevention is worth a pound of 




Sand-clay roads are the next higher type of development 
above natural earth. They are satisfactory for a moderate 
traffic of animal drawn vehicles and a light traffic of automobiles. 
They may be satisfactory for a light traffic of heavy trucks 
where the sub-grade is sand, but are seldom satisfactory where 
the sub-grade is clay. 

Fig. 15. Improperly drained and shaped road on steep hill. 


The road surface should be shaped and graded as indicated 
in a previous chapter. A light crown should be used. If the soil 
is sand about two inches of clay should be added in one applica- 
tion. These should then be thoroughly mixed, using a disc or 
spike tooth harrow. The object is to mix the materials so com- 
pletely that the particles of sand and clay are uniformly distrib- 
uted. If this is not accomplished certain parts of the surface 
will become muddy and rutted in wet weather while other parts 
will be loose and sandy in dry weather. 

Fig:. 16. Clay hill with sand spread and harrowed. 

Fig. 17. Hill with consolidated sand-clay surface. 

Where a clay soil is found it should be shaped as before de- 
scribed. The surface is then plowed or scarified to a depth of 
two or three inches and the clay pulverized by rolling, discing 


or harrowing. About three or four inches of sand should then 
be applied and mixed with the clay after which two or three 
inches of additional sand should be applied and thoroughly 
mixed. It might be possible to mix as much as six inches of 
sand with the pulverized clay surface at one operation, but the 
chances are that the mixing will not be uniform. 

In both of the above cases it will require about one-third as 
much clay as sand. The amount will vary with individual cases 
and must be determined to suit local conditions. 

Regular use of the grader and planer will improve the sur- 
face of a sand-clay road and keep it in excellent condition for 
light traffic. 

Cinders, Cinders and coarse ashes may also be used with 
fair results on a clay soil. The use of cinders as a surface for 
clay roads is rapidly growing around the industrial districts of 
some eastern states. Very good results have been obtained 
where the cinders were carefully selected, rolled in place and 
surface treated with asphaltic oil or refined tar. The best cinders 
are obtained from large industrial works and are prepared by 
passing over screens to eliminate the fine ashes. If this superior 
quality of material is not available an improvement in the clay 
surface of the road will be effected by using straight run cinders. 
In addition to their use as a surface material cinders are also 
valuable as a base for gravel and macadam roads. They can 
usually be obtained at little cost other than the labor of hauling 
and placing. 

Shale. Shale is found in some localities in southern Indiana. 
This material varies in quality from a hard clay to a soft stone. 
The former is but little better than common clay and probably 
not worth the labor of hauling and placing on the road. Some 
of the harder varieties give good results for light traffic when 
placed on a well shaped sub-grade. 

The cost of these improvements, in addition to the initial 
shaping of the sub-grade and side ditches will vary from $500 
to $2,000 per mile, or a total cost per mile for all work and ma- 
terials of $800 to $5,000. 




These roads, constructed of inferior materials, require fre- 
quent attention to keep them in good condition and should be 
maintained in a somewhat similar manner to earth roads. There- 
fore the maximum intensity of maintenance .will occur in the 
spring. They are easily softened by water and consequently re- 
quire frequent use of the grader, drag or planer. New material 
of the same character as that in the road surface should be added 
where necessary after the road has been softened by rain. These 
surfaces require less maintenance work than an earth road and 
carry traffic much better. They can be maintained in good 
condition for a cost of $75 to $150 per mile per year for light 



A decade or more ago before the extensive use of the auto- 
mobile and motor truck Indiana was noted for its excellent 
gravel pikes which formed the greatest mileage of improved 
roads. Motor vehicles are particularly destructive to the roads. 
Fifteen years ago 85 to 95 percent of the vehicles were horse 
drawn while at the present time 90 to 95 per cent are motor 
powered. The total number of vehicles passing over the roads 
has increased many fold. As a consequence of these changed 
conditions the roads have been badly worn and in some cases 
nearly destroyed. Improved standards of construction are there- 
fore necessary to meet the changed traffic conditions. 

Fig. 18. Washed gravel for road construction. 

Well built gravel roads will carry satisfactorily a heavy traf- 
fic of horse drawn vehicles, a medium traffic of pleasure automo- 
biles and a light traffic of trucks. Two hundred to five hundred 
vehicles per day can be carried economically under favorable 

An ideal gravel for road building should be well graded, 
hard, tough and should possess good bonding qualities. Gravel 
having these qualities in a large degree is found widely distrib- 
uted over the northern two-thirds of the state. It is obtained 
from glacial deposit banks and from the beds of streams. 

There should be from 10 to 25 percent of bonding material 
such as clay in the gravel. River or washed gravels do not, 
as a rule, contain sufficient bonding material and it may there- 
fore be necessary to add some clay to such gravel. The clay 
should be spread on top and harrowed into the gravel after it 
has been spread on the road. A better bonding material is lime- 
stone screenings. 

Washed and screened gravel can be used successfully on a 
clay sub-grade. After a short time the clay will work up into the 
gravel and act as a binder. Washed gravel, however, should 
not be placed on a sandy sub-grade. The two readily mix under 
traffic but do not bind. 

All large rocks should be removed from the gravel by screen- 
ing if necessary. The maximum size will vary with the char- 
acter of the material, but should not be larger than will pass a 
2^2 or 3 inch circular mesh screen. Pebbles in the wearing sur- 
face should not exceed a diameter of 1^ inches. The maximum 
size of particles may be larger when the gravel is well graded 
from coarse to fine. In all cases the largest pebbles used should 
constitute a fair proportion of the material. This will give a 
more stable road since the larger particles are not so easily dis- 
placed by traffic. If there is a large percentage of the oversize 
pebbles not passing the maximum screen, it may be economical 
to put them through a crusher. The crusher product is then 
mixed with the screened gravel giving a superior product. 

There are two general methods of construction, the feather 
edge and the trench. In both cases the sub-grade should be 
properly graded and drained as explained in Chapter II. 

The feather edge method is the older and the one most 
commonly used. The gravel is dumped in the center of the sub- 
grade and is then spread and crowned by the grader or is flat- 
tened out under traffic. With this type of construction the outer 
edges of the gravel surface are too thin to carry the vehicles in 
wet weather. As a result the edges soon become badly rutted. 
The road will also have too heavy a crown. 


A better method of construction is by trenching. On a flat 
subgrade or on one that has not been improved the trench may 
be formed by plowing the center of the road and moving the 
loose earth to each side by a grader. On an old road that has 
some crown, it is advisable to form shoulders by pulling the 
earth in from the side ditches with a grader. Following the 
completion of the trench, gravel may be placed as previously 

Fig. 19. A poorly constructed gravel road. 

Fig. 20. A good gravel road. 

The gravel should be placed in layers of not more than 4 to 
6 inches in thickness with the larger pebbles and the coarse gravel 
confined to the bottom layer. The top layer should be well 
graded and should not contain any oversize pebbles. Each layer 

should be compacted separately. While it is not necessary to 
roll the gravel it is desirable if heavy traffic is to be turned on 
the road immediately after construction. Loose, dry gravel is 
objectionable to traffic and if the material is not well graded the 
large pebbles will work to the top. Rolling with about a ten ton 
roller hastens the consolidation of the gravel. If the gravel is 
very dry it should be sprinkled during the rolling. The com- 
pleted road should have a crown of not to exceed y 2 inch per 
foot which should be carried across the shoulders to the ditch 

Modern traffic with its heavy, fast moving loads requires a 
heavier surface than was formerly necessary. Not less than 8 
inches of gravel should be used and 10 to 12 inches may be nec- 
essary on an inferior subgrade or for very heavy traffic. These 
values may be reduced one-third on the edges of the roadway. 
To provide for shrinkage the thickness of loose gravel should 
be approximately 20 percent greater than the compacted thick- 

" ' 

Figr. 21. Poor drainage and insufficient depth of surface material caused this 
gravel road to break up. 

A small mileage of roads has been constructed in the fol- 
lowing manner. The large oversize pebbles and small boulders 
are placed on the subgrade to a depth of 6 to 12 inches, the voids 
between the larger stones being filled with smaller ones until a 
fairly uniform surface is secured. This is then rolled after which 
the gravel is added as described above. Such a road should be 
somewhat superior to the common type of gravel road. 

Minnesota and Iowa have developed the following method 
of constructing gravel roads which gives very satisfactory re- 
sults when properly applied. The same method can also be 


used when applying maintenance gravel. The gravel is deposited 
on the shoulders of the road and then carried to the surface with 
a blade grader. As traffic compacts the loose material, additional 
amounts are added until the entire quantity has been used. An 
advantage of this method is the small amount of loose material 
on the road at any time. There is also no necessity of a roller 
or other costly equipment. The method probably originated in 
Minnesota where the material was hauled and placed along the 
road during the winter for the sake of cheaper haul costs at a 
time when labor and teams were available. 

The cost of a gravel road varies greatly with the cost of 
labor, material and other conditions. Roads similar to those de- 
scribed could probably be constructed nearly anywhere in Indiana 
for $7,000 to $10,000 per mile. 


Under favorable conditions a gravel road will be smooth, 
resilient, comfortable to travel and will afford good traction to 
all kinds of vehicles, but in order to preserve these conditions 
systematic maintenance is necessary. 

During the first few months after construction, the road 
should be carefully maintained. Ruts, holes, wheel tracks and 
weak spots should have new material added which should be of 
the same kind as that in the road. It should only be added after 
a rain or when the road is wet as it will not bond with the old 
gravel when dry. During the period of seasoning the drag, 
planer and grader should be used to bring the surface to a uni- 
form, smooth contour. 

The characteristic failure of an old gravel road under high 
speed traffic is a pitting of the surface. This is caused by the 
loosening of the surface particles and the pulverizing of the bind- 
ing material under traffic. The fine binding material is then 
picked up by the air currents and suction caused by the moving 
vehicles and the greater part of it is blown away from the road. 
As a result the pebbles have nothing to hold them together and 
are easily thrown out by the wheels of the vehicles. 

A road planer is one of the best pieces of machinery to be 
used for the constant maintenance of a gravel road. By its use 
the road can be kept entirely free from waves or large irregu- 
larities. With heavy traffic and several weeks of dry weather 
some pitting of the surface can not be avoided. A light dressing 
of fine gravel with a minimum of binding material is very useful 
in maintenance. This material is carried to the low spots by the 
planer and gradually becomes consolidated with the road surface 


When the road becomes thickly and deeply pitted a partial 
reconstruction is the only remedy. The surface should be scari- 
fied to a depth of not more than two or three inches; it should 
then be shaped with the blade grader and a few inches of new 
material should be added. 

Fig. 22. Dangerous point on road caused by short culvert. 

Fig. 23. Safe road with extended culvert. 

Highway officials are often compelled to improve and main- 
tain old gravel roads that are too narrow or too highly crowned 
for present traffic. The first step is the preparation of the shoul- 
ders with a blade grader by cutting away the sod on both sides 
of the traveled way. New gravel may then be added on both 


sides of the center of the road, leaving the hard surface at the 
center to carry vehicles while the ne,w material is gradually being 
compacted. This method has been used successfully on many of 
the state roads of Indiana. 

The cost of maintenance of a gravel road varies from $100 
to $500 per mile per year for average traffic, but on heavily 
traveled trunk lines it may reach the sum of two or three thous- 
and dollars. The latter values are two or three times a desirable 
maximum and indicate the annual maintenance of the road 
amounts to a partial reconstruction. Under these conditions the 
road is used beyond its economical capacity and it should be 
replaced with one of higher type. 


A stone or macadam road was one of the first types to be 
developed in America. In the early part of the last century the 
travel between Boston, New York, Baltimore, Washington and 
Philadelphia was principally by stage coach. The old stage 
routes were hoof deep with dust when dry and hub deep with 
mud when wet. In order to improve traveling conditions broken 
stone was dumped on the surface. The result was not entirely 
satisfactory, but was a material improvement over previous con- 
ditions. Travel was lifted out of the mud and dust which was 
the chief object of the improvement. As a result of this early 
work, road building was stimulated and for over one hundred 
years the mileage of stone and macadam roads has steadily in- 
creased. Macadam roads are suitable for about the same char- 
acter of traffic as gravel roads. 

There are two types of stone roads, the unbound and the 
water-bound macadam. In the first type the broken stone is 
spread on the earth sub-grade and is then compacted by the 
action of the weather and vehicles. In the second type the 
broken stone and screenings are cemented into a solid mass by 
means of water and rolling. 

Limestone is the principal material used in the construction 
of stone or macadam roads although granite, trap, slag and some 
other materials are used to a lesser extent. Limestone is widely 
distributed in a suitable quality for road work. The stone should 
be well graded in sizes between y\ inch and 3 inches, although 
some late specifications allow a maximum size passing a 3^ 
inch circular mesh screen. The stone dust and all particles of 
stone smaller than l /\. or y inch in diameter should be removed 
by screening at the crusher. The latter product is commonly 
termed screenings. 

Because of the uniformity of quality and grading the prod- 
uct of some commercial crusher is desirable although this may 


not be practicable on account of excessive transportation costs. 
In that event if a good local ledge of rock or a supply of field 
boulders in sufficient quantity is available a portable crushing 
and screening plant can be installed. These plants will produce 
50 to 125 tons of crushed stone per day while a large commercial 
plant may turn out as much as 1000 tons per day. Before de- 
veloping a local supply the stone should be submitted to a repu- 
table laboratory to determine its fitness for use. Caution should 
be used in the installation of a portable plant to crush field 
boulders, as they may be so hard as to be beyond the capacity 
of any but the largest size crushers. 

All rules for grading, alignment, drainage and construction 
of sub-grade as detailed in previous chapters apply to macadam 
road construction. The sub-grade may or may not be trenched. 
The trench method is of course the superior method. 

The unbound macadam. road is constructed by placing the 
crushed stone on the previously prepared sub-grade. It is usually 
roughly spread to the desired thickness. Screenings are then 
spread over the top to bind the material together. A greater 
quantity of screenings is required than in a water-bound mac- 
adam. Crusher run material containing the screenings is some- 
times used. The road is then left to the action of weather and 
traffic. Such a road may after a time of seasoning give good 
service for light traffic but it usually does not wear evenly. The 
chief argument for this type of construction is low first cost due 
to the absence of sprinkling and rolling. While the first cost will 
be less than a water-bound macadam, a large amount of mainte- 
nance is necessary to put it in good condition after construction 
and in the end the results will seldom be entirely satisfactory. 

A water-bound macadam road should be at least 8 inches 
thick to carry heavy traffic. In some cases 10 inches or more 
will be economical and necessary. In computing quantities about 
20 per cent should be allowed for shrinkage during rolling and 
for the stone that will be rolled into the sub-grade. There will 
be required in addition 10 to 15 per cent of screenings. If the 
sub-grade is flat the edges of the road may be thinner than the 
center by the total amount of the crown slope which should not 
exceed ]/2 inch per foot. 



k- J"-l # 

Fig. 24. Suggested cross-section of a macadam road. 

It is necessary that the stone be confined between solid 
shoulders so that it will be thoroughly compacted by the roller. 


The stone may be placed on a flat sub-grade but a light crown 
in the base gives a superior condition as suface water is more 
easily eliminated. The stone should never be placed until the 
base has been thoroughly weather seasoned or rolled with a 
heavy roller to remove all shrinkage. 

Some of the eastern states build water-bound macadam 
roads only on top of Telford bases. This consists of large irreg- 
ular blocks of stone laid by hand on the sub-grade, the open- 
ings being filled with spalls and small stones and the whole 
rolled. This makes a stronger road but also adds materially to 
the cost. 

After the base has been prepared the stone is dumped from 
wagons or trucks and evenly spread to the desired loose depth. 
Not over 5 to 6 inches in depth of loose stone should be placed 
at one time as more cannot be compacted under the roller. A 
simple way to control the depth is by means of wood blocks of 
the desired thickness placed on the base. These are moved for- 
ward as the work progresses. Delivery should be made in such 
a manner that the vehicles will not pass over the freshly spread 

A 10 or 15 ton roller should be used to roll the stone. Roll- 
ing ceases when the stone no longer shifts under the roller or 
when it begins to crush. Another layer should then be applied 
and rolled in a similar manner. The shoulders should also be 
rolled with this course so that the stone and shoulder will pre- 
sent an unbroken surface. 

Fig:. 25. Sprinkling: macadam prior to last rolling. 

The last step is to apply and roll the screenings into the 
surface. They should be applied by casting from a shovel. To 
insure an even distribution the loose screenings may be swept 


into the surface. The surface is then sprinkled and this followed 
with the roller. The rolling is continued adding more screenings 
as they work into the spaces between the stone and sprinkling 
until completed. The rolling should be stopped when a light 
wave of mortar forms as the roller passes over the surface. No 
more screenings should be used than is necessary to bind the 
surface, since the most even wear occurs when the traffic is 
carried on the larger particles of stone. 

The road may now be closed to traffic for two or three days 
until the mortar has time to set up ; although there is no particu- 
lar objection to opening it to traffic immediately. It should be 
carefully watched for a few weeks as some spongy spots will 
appear under traffic. Screenings should be placed on these spots 
and broomed into the surface. They should then be sprinkled 
and rolled. A road of this kind well constructed will carry 300 
to 800 vehicles per day with proper maintenance, providing not 
more than fifty to seventy-five per cent are motor vehicles. For 
motor traffic heavier than seventy-five per cent the road should 
have a bituminous carpet. 

Fig 1 . 26. A properly shaped and 

<l:im road. 

In 1920 an eastern state rebuilt 18 foot water-bound maca- 
dam surfaces 5 inches thick on Telford bases for $10,000 per 
mile. This included the cost of cleaning off the old worn ma- 
cadam surface which was used for widening and building up 
narrow shoulders. It is estimated that the present cost of an 
8 inch water-bound macadam road in Indiana would be $8,000 
to $15,000 per mile. 



When a macadam road is in a perfect condition the sensa- 
tion of traveling over it is very pleasant. It also offers small 
resistance to travel ranking close to some hard surfaced types 
in this factor. Unfortunately these high qualities are rapidly 
destroyed under fast moving automobile traffic. The fine stone 
dust that acts as a binder of the larger particles is picked up by 
the traffic and blown away. The surface presents a coarse, 
rough appearance and finally becomes deeply pitted similar to 
an old gravel road. 

Fig. 27. Crushed stone for maintenance along highway. 

Here again the methods of maintenance are similar to those 
of a gravel road. A mulch of fine stone screenings on the sur- 
face is useful to supply the deficiencies and fill small holes. 
Eventually under constant and heavy traffic this will not be 
sufficient and pot holes will appear. If the pitting is not too 
deep or extensive about two inches of clean, coarse sand or fine 
gravel may be added. When the irregularities become too great 
nothing remains to be done but a general scarifying and reshap- 
ing of the surface together with the addition of new material. 
This should be followed by rolling. 

The addition of a gravel wearing surface to a crushed stone 
base is finding increased favor in some localities for secondary 


roads. The combination gives the stability of crushed stone for 
the base with the wearing qualities of gravel for the surface. 

Fig. 28. Spreading: a thin covering: of new material with truck. 

The cost of maintenance of a macadam road will vary with 
the amount of traffic, climate and other conditions. A rather 
large investment is involved in the first cost of a macadam road 
and it is therefore economy to conserve this investment by care- 
ful maintenance. When the maintenance charge becomes too 
large it will be economical to give the road a surface treatment 
of bituminous material after which it is maintained as a bitumin- 
ous road. 


Water, oils, tars and other substances are applied to the sur- 
faces of earth, gravel and macadam roads for the purpose of re- 
ducing or preventing dust and lessening the maintenance ex- 
pense by rendering the surface more stable. 

Dust is formed on a road by disintegration or loosening of 
the surface, by earth from the shoulders, by material carried by 
the wheels of vehicles from other roads, by the droppings of 
horses and by other causes. Dust is not only disagreeable to 
the traveler but is also a menace to health as many of the respira- 
tory diseases are directly traceable to dust arising from the roads 
and streets. Dust injures the fine finish of vehicles, increases 
wear of bearings and is a cause of motor troubles. It is carried 
away by the wind and may result in the ultimate failure of the 
road. Because of the conditions enumerated a reasonable ex- 
penditure of money for its suppression is true economy. 


Water is used largely in the cities to allay the dust but it 
is never entirely satisfactory. In {Jie summer frequent applica- 
tion is necessary, and if too much is used a sloppy surface will 
result. In the case of rural roads the cost of application is pro- 
hibitive, i 

Calcium chloride may be used in place of water with im- 
proved results. This was formerly applied, after dissolving in 
water, by a common sprinkling wagon. It is now applied more 
successfully in the dry form. The dry chloride is prepared in an 
improved flake which is easily spread by a grain or fertilizer 
drill. The virtue of calcium chloride lies in its affinity for water. 
Moisture is absorbed from the atmosphere at night thereby 
keeping the road damp during the day. Two applications of the 
chloride are sufficient in an average season although in excep- 
tional cases more will be necessary. The first application will 
require 1 to \ l / 2 pounds per square yard. This should be followed 
a few weeks later by half that quantity. The cost will vary from 
2 to 4 cents per square yard of surface per season. 

The advantages of calcium chloride are that it is odorless, 
is not injurious to the hoofs of animals and does not stick to the 
wheels of vehicles. A road treated with it can be maintained in 
the usual manner with drag, planer or scraper. 

Fig-. 29. Oiling a macadam surface to prevent dust. 

Tars and oils have been used more largely for dust suppres- 
sion than other substances. For this purpose the lighter and less 
viscous grades of oils and tars are used. They may be applied 
either hot or cold from gravity or pressure distributors. The 
best results are generally obtained when the material is applied 
hot with a pressure distributor. The cost of this method is a 


little greater than gravity distribution unless there is a large 
amount of surface to be covered. For gravel and macadam roads 
the material should be somewhat heavier than is suitable for 
earth surfaces. From % to */> gallon per square yard is applied 
but to obtain the best results not more than y 2 gallon should be 
applied at one time. As a rule tars have not been entirely satis- 
factory for earth road treatment and their use for this purpose 
is not recommended. 

The oil or tar should be of a quality that will harden or "set 
up" within 24 to 48 hours after application. Some oils act as a 
lubricant with a consequent tendency to disintegrate the road 
surface. It is therefore important that only good grades of 
asphaltic or semi-asphaltic oils or suitable tars should be used. 
Where oils are used the asphaltic content will vary from 30 to 
65 per cent. 

Suitable preparation of the road is as essential as good oil or 
tar. The surface, should be carefully shaped. All holes or de- 
pressions should be filled with new material similar to that in 
the original surface. This should be tamped or rolled. The road 
should not be oiled immediately but, if possible, traffic should 
pass over it for at least one week. A longer period would be 
preferable. The traffic will find the weak spots which should 
again be repaired. The object of this careful preparation is to 
secure a smooth surface with a uniform texture. Just prior to 
oiling, the dust should be brushed from the surface. This can be 
accomplished in the quickest and most economical manner with 
a street sweeper or power broom. The sweeping should be done 
with just sufficient pressure to remove the dust. If too much 
pressure is used the binder in the road suface will be loosened 
with resulting damage to the surface. In the event that a 
sweeper is not available the oiling should be done following a 
heavy rain. No oil should be applied, however, until the surface 
is completely dry. In applying the oil one-half of the road should 
be treated at a time. Traffic should be kept off the fresh oil from 
24 to 48 hours after which the other half of road may be treated 
in like manner. Any excess of oil should be covered and ab- 
sorbed with a small amount of coarse sand or stone grit. The 
total cost of labor and material will vary from three to twelve 
cents per square yard per season. 



Prior to the application of a bituminous carpet the road sur- 
face should be repaired and put in the best possible condition 
as just described for oiling. It is even more essential that the 
dust should be removed. Bituminous carpets are not applied to 
earth roads. They are placed with good success on macadam 
surfaces but with only partial success on gravel surfaces. The 
latter surfaces will break up to some extent in the spring and 
must be reshaped and retreated. Highway engineers are work- 
ing on the problem of applying bituminous carpets to gravel 
surfaces and it is probable that their efforts will be successful in 
the near future. In Maine fairly good results have been attained 
by treating the gravel surfaces with refined tar. In general the 
best results have been secured where bituminous carpets have 
been applied on macadam roads having a minimum of fine bind- 
ing material. 

Fig. 80. Spreading cover material on a bituminous carpet. 

The hot bitumen should be applied to the clean, dry surface 
with a pressure distributor, and should be covered immediately 
with a light dressing of pea gravel or stone chips. The covering 
material should be hard and tough so that it will not be easily 
broken or disintegrated. Pea gravel well graded from l /\. inch to 
^8 inch is desirable while the stone chips may vary from T 4 to 
Y^ inch. Under average conditions, after the first season, about 
l /4 gallon of bitumen and 15 pounds of pea gravel or 20 pounds 
of stone chips will be required per square yard of surface. At 
present prices of labor and materials the cost would be 8 to 14 
cents per square yard per year. 


A bituminous carpet when properly applied gives good trac- 
tion, is pleasing to the eye, is waterproof, protects the material 
underneath from wear, is quiet and dustless. We therefore find 
that it has many of the excellent qualities of the best grade of 
hard surface pavements. 

Fig:. 31. A bituminous surface tlmt has been neglected. 

Fig. 32. A good bituminous surface highway. 

Pennsylvania, New York, Connecticut, Rhode Island and 
other eastern states have thousands of miles of old macadam 
roads with bituminous carpet surfaces that carry successfully 
500 to 2000 vehicles per 24 hours. 

Lafayette, Indiana 

A collegiate institution founded upon an act of Congress of 
July 2, 1862, maintained by appropriations from the State of 
Indiana and the United States, aided by numerous private and 
public gifts and named in honor of John Purdue, a citizen of La- 
fayette; offers instruction in both undergraduate and graduate 
courses in Engineering, Science, Agriculture and Pharmacy. 

The institution possesses superior resources for conducting 
the courses of instruction, viz : 

An instructional corps of over two hundred persons. 

An estate of over one thousand acres. 

Twenty-six principal buildings. 

Extensive laboratories of Chemistry, Physics, Botany, Zo- 
ology* Bacteriology, Electrical Engineering, Steam Engineering, 
Gas Engineering, Locomotive Engineering, Hydraulics, Mater- 
ials Testing, Practical Mechanics, Pharmacy, Soil Physics, Dairy- 
ing, Horticulture, Veterinary Science, Animal Industry and Ex- 
perimental Fields and Orchards. 

An equipment of laboratory apparatus and materials in all 
departments of unusual extent and varied character. 


RETURN TO the circulation desk of any 
University of California Library 

or to the 


University of California 
Richmond Field Station, Bldg. 400 

1301 South 46th Street 
Richmond, CA 94804-4698 


To renew or recharge your library materials, you may 

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DEC 12 

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