Location, Constraction 
 
 and 
 
 Maintenance of Roads 
 
 GOODELL 
 

The Location, Construction 
 and Maintenance of Roads 
 
 BY 
 
 JOHN M. GOODELL 
 
 Reprinted from 
 
 GOOD ROADS YEAR BOOK 
 1917 
 
 
 NEW YORK 
 
 D. VAN NOSTRAND COMPANY 
 
 25 PARK PLACE 
 
 1918 
 
COPYBIGHT 1917 
 BY 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 COPYRIGHT 1918 
 
 BY 
 D. VAN NOSTRAND COMPANY 
 
 COMPOSED AND PRINTED AT THE 
 
 WAVERLY PRESS 
 
 BY THB WILLIAMS & WILKINS COMPANT 
 
 BALTIMOEE, U. S. A. 
 
PREFACE 
 
 In the summer of 1916, several State highway engineers re- 
 ported to the American Highway Association that there was 
 need of a concise explanation of the best current practice in locat- 
 ing, constructing and maintaining country roads, not combined 
 with information about city pavements. It was found by these 
 engineers that the information in many excellent engineering 
 treatises proved confusing to rural road officials because they 
 did not have sufficient technical knowledge to draw a line be- 
 tween what was applicable to country highways and what was 
 restricted to urban conditions. Inquiry showed that such an 
 outline of road-building would be welcomed by the road officials 
 of other States, and the preparation of this book was accordingly 
 begun. 
 
 Highway engineers in all parts of the country generously con- 
 tributed material and advice. Special attention was paid to 
 ascertaining reasons for unusual methods, in order to avoid the 
 publication of anything useful only in restricted localities and 
 possibly leading to trouble if tried generally. The purpose was 
 to furnish information of a national value rather than an expres- 
 sion of the views of a few individuals, who inevitably have per- 
 sonal preferences and prejudices. As each section was finished 
 it was submitted for criticism to engineers or chemists with 
 special knowledge of the subjects discussed, and most of the chap- 
 ters formed by combining these revised sections were sent out 
 to other engineers for further criticism. Some of the chapters 
 were revised a number of times before they were finally ap- 
 proved. As a consequence, although my name appears as the 
 author on the title page, the book is rather the product of the 
 cooperation of over fifty of the leading American highway engi- 
 neers and the patient and intelligent handling of the details of 
 the work by Miss Isabelle Stockett, at the time chief clerk of the 
 American Highway Association. 
 
 This book appeared originally as Part II of the 1917 Good 
 Roads Year Book. Its wide circulation, the many references to 
 it in technical journals, and its use as a textbook by engineering 
 colleges, indicating that the volume had won a distinct position 
 in technical literature, led the Directors of the American High- 
 way Association to assign the copyright to the D. Van Nostrand 
 Company, when the Association was dissolved a few days ago. 
 By this action the results of the cooperative labors of so many 
 specialists will remain available to the public. 
 
 iii 
 
IV PREFACE 
 
 Added to the text as it appeared in the Good Roads Year 
 Book is a chapter on the reasons for improving roads. This is 
 part of a "good roads manual" for public officials, not techni- 
 cally educated, which had considerable circulation in manu- 
 script form among road commissioners applying to the American 
 Highway Association for such information. It is printed here 
 as a concise justification of the expenditure of public funds for 
 road improvements, a subject which highway engineers must 
 frequently discuss at public meetings. 
 
 JOHN M. GOODELL. 
 
 Upper Montclair, N. J., March, 1918. 
 
CONTENTS 
 
 Location, Grades, Widths and Cross-Sections of Rural Roads 1 
 
 Regulations of the California Highway Commission Regarding Surveys 
 
 and Plans 12 
 
 Drainage, Culverts and Bridges 19 
 
 Earth and Sand-Clay Roads 37 
 
 Gravel Roads 51 
 
 Water-Bound Macadam Roads 64 
 
 Road-Building Rocks 75 
 
 Concrete Roads 90 
 
 Standard Specifications for Portland Cement 107 
 
 Petroleum and Residuums 109 
 
 Asphalt and Native Solid Bitumens 117 
 
 Asphaltic Materials for Roads 124 
 
 Tar and Tar Products 132 
 
 Bituminous Roads 138 
 
 Bituminous Surface Applications 150 
 
 Brick Roads 157 
 
 A Brick Pavement on a One-inch Concrete Base 178 
 
 Highway Bonds 180 
 
 Resistance of Roads to Traction 189 
 
 Rural Public Roads in the United States 192 
 
 Money Spent on Roads in the United States 193 
 
 Extent of Surfaced Roads in the United States 194 
 
 Motor Car Statistics 195 
 
 Vitrified Paving Brick Production 196 
 
 Broken Stone Production 198 
 
 Gravel and Paving Sand Production 199 
 
 The Reasons for Improving Roads 200 
 
 Manufacturers and Constructors Cards . 215 
 
LOCATION, GRADES, WIDTHS AND CROSS- 
 SECTIONS OF RURAL ROADS 
 
 The improvement of any road or system of roads must begin 
 with a study of its location and grades, for unimproved roads 
 are often bad in both respects. The purpose of relocation is to 
 enable the road to carry the anticipated traffic with the least 
 effort and loss of time. It is impracticable to relocate all roads 
 and improve their grades at the present time, and highway offi- 
 cials must be satisfied with gradually eliminating or at least 
 reducing the defective conditions. In order to carry on this 
 work efficiently, however, the entire system of roads under a 
 board or commission must be studied as a whole, so that the 
 whole body of taxpayers may be benefited as uniformly as 
 practicable by the work done annually. The work should be 
 planned in a broad way several years in advance, if possible, for 
 it is only in this way that the needs of all parts of the district can 
 be met without favor or prejudice. This is particularly important 
 where the needs are great, the road funds meager, and property 
 has been developed along locations where roads should never have 
 been laid out. The situation in such cases has been summed up 
 as follows by W. S. Keller, State highway engineer of Alabama: 
 
 The genuine bad roads cannot be maintained for the reason that they 
 have never been constructed. The great amount of work necessary to 
 keep them in passable condition disheartens the man who is by law com- 
 pelled to work them. Until these roads are relocated, avoiding heavy grades 
 and marshy bottoms, sharp angles and useless twists, and are graded so 
 they will have good drainage, we may expect them to be bad. 
 
 Location. It is evident that the road should be as nearly 
 straight between the points it connects as the configuration of the 
 country traversed will permit. It is desirable, however, to re- 
 strict grades to 6 per cent and to avoid expensive cuts, fills 
 and bridges. To locate the road properly and meet all local 
 conditions in the best manner requires competent engineering 
 services; if they are not obtained there is a strong probability 
 that after the country develops new locations must be made to 
 meet the increased transportation needs and the expenditures 
 for new rights-of-way will be far greater than to-day. But if, 
 for the present, engineering services are out of the question, the 
 road authorities can at least relocate roads that are plainly un- 
 
;-'=.. 
 
 2 AMERICAN HIGHWAY ASSOCIATION 
 
 necessarily low and marshy and unnecessarily steep and high. 
 This is particularly the case where roads have been laid out on 
 the section lines of the government land surveys. However 
 desirable the rectangular parceling of unoccupied land may 
 have been in attracting settlers, it has proved a heavy handicap 
 on transportation by introducing many right-angle turns and 
 causing needless length in the roads of these regions. The fol- 
 lowing comment on this condition was made by W. S. Gearhart, 
 State engineer of Kansas: 
 
 A 60-foot road on two sides of a section of land occupies 14.55 acres, 
 while a road 60 feet wide in a diagonal direction through the section occu- 
 pies 10.28 acres. Thus there is a saving in the diagonal road of 4.27 acres 
 and 0.587 mile of distance. The saving in the cost of right of way, assum- 
 ing that the land along the section line is as valuable as on the diagonal 
 line, is $85.40 if the land is worth only $20 per acre. This amount in most 
 cases would be sufficient to grade the 1.413 miles of diagonal line in first- 
 class condition. If a man lives 4 miles north and 4 miles east of his market- 
 place he is 5.657 miles on the diagonal line from it; that is, on the section- 
 line road he must travel 4.686 miles farther in making the round trip than 
 on the diagonal line. 
 
 The same official has reported that a county commission built 
 a mile of road on a section line, which crossed the same stream 
 three times. By adopting a somewhat different location and 
 making the road 1J miles long, the stream would be crossed but 
 once and the road become of greater service to the community. 
 "More than $3,000 worth of steel bridges were bought, it will 
 cost not less than about $2,500 for the abutments to set these 
 three structures on, and an expenditure of $2,500 will be neces- 
 sary to make the road passable, or a total of about $8,000 to 
 accommodate four men whose property is reported as probably 
 not worth as much as the cost of the road." Instances of this 
 nature prove the desirability of having roads located by engi- 
 neers without interference from political or personal influences. 
 The assertion that such services are unnecessary in connection 
 with such relatively inexpensive highways as dirt roads is best 
 answereo! by pointing to the action of the Utah State road com- 
 mission in substituting an entirely new location about 15 miles 
 long for an old route in Beaver County. This was done by the 
 engineers because the new line had better alignment, grades and 
 road materials. 
 
 The influence of soil conditions and the presence or absence of 
 road materials may not be given due consideration in locations 
 made by persons who are not engineers. The following comments 
 on this point were made by A. N. Johnson in a report on the high- 
 ways of Maryland: 
 
LOCATION AND GRADES OF RURAL ROADS 3 
 
 Should it happen that two locations are possible with about equal ad- 
 vantages and disadvantages, except that one was over a different soil from 
 the other, that location should be taken which traverses the soil best cal- 
 culated to insure a good road-bed. For example, if it were possible to 
 avoid going through a clay section when a more open soil could be had 
 close at hand, much would be saved both in the cost of construction and 
 in the subsequent maintenance by going over the more open soil. It is 
 hardly necessary to state that crossing soft, boggy soil should be avoided 
 whenever the expense of going around such a place would be no more than 
 for crossing it. If possible it is always well to locate a road in the vicin- 
 ity of good road-material, either a suitable stone or gravel, for the prox- 
 imity of such material lessens for all time the cost of maintenance of the 
 road, and when this point is considered such a location would be war- 
 ranted even at an increased first cost. 
 
 PROFILE OP ROAD IN BALTIMORE COUNTY, MD. 
 
 Showing How Relocation Saved a Large Sum in the Improvement of the 
 
 Road. 
 
 Value of Engineering Services. Few persons realize that the 
 expense of engineering services in relocating old roads is gener- 
 ally more than offset by the saving in the cost of construction 
 of a properly located road over one improperly located. The 
 engineer knows how to fit the road to the ground in hilly country 
 so that the material from the cuts may be used in making near- 
 by embankments and costly rock excavation will be reduced to 
 the lowest practicable amount. On the Maryland State high- 
 ways, the expense of moving 100 to 150 cubic yards of earth is 
 from $50 to $75, which is equal to the cost of making a mile of 
 careful surveys that may be reasonably expected to save more 
 than 150 cubic yards of such earthwork. The accompanying 
 illustration shows the saving in excavation expenses on a road in 
 Baltimore County, Md. The hilly character of the old road 
 made necessary heavy reductions in grade to give a highway prop- 
 erly accommodating the traffic. The heavy cutting to give suit- 
 
4 AMERICAN HIGHWAY ASSOCIATION 
 
 able grades along the old location is shown by the diagram, 
 while the light excavation and filling required on the new loca- 
 tion is also indicated. Such savings of cost can only be made by 
 competent engineers. The amount of detail which the engineers' 
 survey must furnish depends on the character of the road to be 
 built and the nature of the country. Less detail is necessary 
 for an earth road in a flat country than a brick road in a hilly 
 district, for example, but enough should be obtained to make 
 sure that the final location is along the line on which the cost of 
 transportation plus the interest on the first cost plus the cost of 
 maintenance of the road will be the minimum for the available 
 funds for first cost. The last point is important, for the best 
 location is often governed by the amount of money which can 
 be spent on construction. 
 
 In carrying out extensive work by contract, experience shows 
 that low bids from responsible contractors are best secured when 
 full information is obtained for their use in preparing estimates. 
 For instance, in carrying out road improvements in Vermilion 
 County, Illinois, under a $1,500,000 bond issue, about 1800 draw- 
 ings of plans, profiles and cross-sections were prepared in the 
 first two months of the work. These were plotted on Plate 
 A 4 by 20 profile paper cut into 32-inch lengths. The longitu- 
 dinal scale of the plans was 80 feet to 1 inch and the tranverse 
 scale 40 feet to 1 inch. The horizontal scale of the profiles was 
 80 feet to 1 inch and the vertical scale 4 feet to 1 inch. The 
 plans show all section corners, bench marks, fence lines, shade 
 trees, farm entrances, property owners' names, drains and cul- 
 verts to be built, and any other data necessary for a complete 
 knowledge of the working conditions. The cross-sections are 
 plotted on a scale of 4 feet to 1 inch. An 11 by 8J-inch map was 
 made of the location of 14 sources of sand and gravel, the plants 
 furnishing paving brick and the railways running from them to 
 the district where the roads were to be built, and 24 by 20-inch maps 
 were made showing the roads, railways and sidings available for 
 contractors' use. The existing road grades were shown on small 
 maps, and other small maps showed the location and size of pro- 
 posed bridges and culverts. 
 
 Grades. The effect of grades on hauling is usually stated in 
 the following manner: If a horse can pull 1,000 pounds on a 
 level road, he can pull 810 pounds with the same effort on a 2 
 per cent grade, 720 pounds on 2f per cent grades, 640 pounds on 
 3J per cent grades, 540 pounds on 4 per cent grades, 400 pounds 
 on 5 per cent grades and only 250 pounds on 10 per cent grades. 
 These figures are only approximate but they show the impor- 
 tance of reducing grades as much as possible where traffic is heavy. 
 Where traffic is not heavy, the cost of reducing grades below 3 
 
LOCATION AND GRADES OF RURAL ROADS 
 
 or 4 per cent, if it must be done by expensive construction or 
 considerable lengthening of the road, is generally considered an 
 unwarranted expense. 
 
 A thoroughly consolidated roadbed is a valuable public asset 
 and in planning grade improvements it is sometimes undesirable 
 to cut 6 to 12 inches into such a road for a long distance in order 
 to secure a theoretically perfect profile. 
 
 Where a road will probably have considerable automobile 
 traffic the grades up a hill should be flattened somewhat at the 
 top if necessary, so the driver can see an approaching car when 
 it is 300 feet from him. When the change in grade at the sum- 
 mit is not more than 6| per cent, no flattening is necessary. If 
 the change is 10 per cent a vertical curve about 200 feet long 
 should be employed; for a 13 per cent change, a curve 292 feet 
 long and for a 16 per cent change, a curve 360 feet long. 
 
 Widths. Highway commissions in many parts of the country 
 are reporting that their roads are often too narrow to accommo- 
 date the traffic coming on them as soon as they are improved. 
 State Highway Commissioner Everett of New Hampshire re- 
 ports that the standard width of 21 feet from ditch to ditch 
 is not wide enough on many of the roads under his jurisdiction, 
 and the experience of the Wayne County road commission, in 
 Michigan, shows that the minimum width of hard-surface road- 
 way in the district around Detroit should be 16 feet and 18 feet, 
 and should be adopted wherever practicable. These comments 
 relate to double-width roads. A width of 8 feet, previously used 
 for single-width roadways, is now generally considered too nar- 
 row and 9 and 10 feet are advocated. 
 
 Many of the State highway departments have established 
 standard cross sections for earth roads. The present standards 
 in Wisconsin are shown in the diagrams on the next page. They 
 are also the standards for macadam and gravel roads having 
 a hard surface 9 feet in width. Where the slopes are not indicated 
 they are made in accordance with the accompanying table. 
 Guard rails are used when the vertical distance from the edge 
 of the shoulder to the top of the ditch is more than 4 feet. 
 
 Slopes Required by Wisconsin Commission in Road Work in Different 
 Kinds of Soil 
 
 SOIL 
 
 ALL CUTS 
 
 FILLS LESS THAN 
 FOUR FEET 
 
 FILLS OVER FOUR 
 FEET 
 
 Sand and sandy gravel 
 
 2 to 1 
 
 3 to 1 
 
 2 to 1 
 
 Loam 
 
 H to 1 
 
 3 to 1 
 
 1$ to 1 
 
 Clay and clay gravels 
 Hard pan 
 
 1 tol 
 
 5 to 1 
 
 3 to 1 
 3 to 1 
 
 Utol 
 1 to 1 
 
 Solid rock 
 
 As it stands 
 
 3 to 1 
 
 As it stands 
 
 
 
 
 
AMERICAN HIGHWAY ASSOCIATION 
 
 omourtt of vratev HI 
 drtchas nil I b great 
 
 cuton intfrciC'f ing ditch 
 of top OT Mtn* 
 
 Mot 3ctK>n in Cuts on K fit to moderotsly heovy 3ofa 
 
 JitCh beyona toe of stone rrnen 
 ground slopes toward till 
 
 Section on fills less t nan 4 feet above urroundmg land 
 
 . NO-* Section on Fills more tnon A teet above BO r rounding lono 
 
 "Dftcft bvyond toe otMop 
 rhn ground Slope? tovioitltUl 
 
 ing to 
 
 Slope occowfftg 
 to tools 
 
 No 7 Section for side hill or dug out AoadS 
 
 STANDARD EARTH ROAD SECTIONS, WISCONSIN 
 
LOCATION AND GRADES OF RURAL ROADS 7 
 
 The Wisconsin sections are wide enough to carry a 16-foot 
 roadway. It is now generally held that the distance from ditch 
 to ditch should be 24 feet, even for a single-width road, if local 
 conditions permit. In some States, where the legal right-of-way 
 is only 30 feet, it is impracticable to secure 24 feet between 
 ditches and have proper fences and banks along the road where 
 it is in cuts. It is necessary to obtain extra wide rights-of-way 
 in such cases or to make the road narrow. 
 
 It has been claimed that if a hard surface is placed on a road- 
 bed, the width of this pavement need not be so great as when 
 the traffic is carried by a less durable surface, and consequently 
 a smaller width between ditches and less earthwork are required. 
 This argument ignores the fact that a narrow roadway concen- 
 trates the travel and may cause the improved surface to carry 
 a volume of traffic for which it is unsuited. For this reason 9 
 and 10 feet for a single-width surfaced roadway and 16 or 18 feet 
 for a double-width roadway are generally favored. In recent 
 years a new factor has become important in determining the prop- 
 er width of hard surfacing. Heavy motor trucks and omni- 
 buses are now in regular service on many roads. If they turn 
 off a hard surface on to a soft shoulder they may become mired 
 or unmanageable and crash through fences or guard rails before 
 the brakes stop them. The driver is usually on the left hand of 
 such a truck where he cannot easily see the edge of the hard 
 paving, and consequently he keeps his truck well toward the 
 center of the road in order to avoid trouble on the shoulders, 
 although the driver of a lighter vehicle would keep farther over 
 to the side. 
 
 Where the road is used by carts or trucks that make a loaded 
 trip in one direction only, as well as in other sections where funds 
 are not available at present for a double-width paved roadway, 
 an 8 to 10-foot pavement has been laid on half the road, with one 
 side along the center line, as though a similar pavement were 
 to be laid at once on the other side of the road. 
 
 Rights-of-way. The width of the road is restricted in the older 
 parts of the country by narrow rights-of-way, which are trouble- 
 some limitations on road improvements. Cuts and fills of more 
 than a few feet widen the strip occupied by the road, ditches and 
 side slopes. Telephone poles and trees along the road require 
 space, and provision for both is desirable. As a result of long 
 experience in Massachusetts and California, reinforced by ob- 
 servation in many other States, Austin B. Fletcher, state high- 
 way engineer of California, recommmends securing a minimum of 
 50 feet for right-of-way, and 60 feet wherever practicable. 
 
 Acquiring rights-of-way is an annoying feature of the work of 
 highway commissions, and in any extensive undertaking expe- 
 
8 AMERICAN HIGHWAY ASSOCIATION 
 
 rience shows that the best results are obtained if the business is 
 handled by one man, with whatever assistance is needed. Dip- 
 lomatic methods are best but legal warfare is sometimes neces- 
 sary, and whatever means must be used should be employed 
 promptly in order to have the right-of-way available for construc- 
 tion as soon as it is time to begin work. In some States, it is un- 
 necessary for the authorities to pay for private property taken 
 for public use in advance of actually taking possession. If 
 the property owner is dissatisfied with the original offer of pay- 
 ment or the award made to him by the public authorities, he 
 may pursue his remedy in the appropriate court, even though his 
 land has already been occupied by the public. In other States 
 no rights-of-way can be taken before they have been acquired, 
 after a vast amount of red tape, by donation, purchase or condem- 
 nation. The western States are particularly oppressed by such 
 roundabout methods of entering upon private property to carry 
 on improvements for the benefit of the entire community. 
 
 It has been Mr. Fletcher's experience that the expense of ob- 
 taining abstracts of title to ascertain the ownership of land is 
 unnecessary. The method he has employed in securing rights- 
 of-way for hundreds of miles of California highways is the fol- 
 lowing: When the field parties are making the original surveys, 
 the chiefs of party usually inquire from the occupants of the land 
 surveyed who the owners or those interested in the property may 
 be. This gives a clue to the ownership. Thereafter one of the 
 staff visits the proper county officers and ascertains from the 
 assessment rolls or the records who purport to be the owners. 
 Deeds or agreements are then prepared, containing the proper 
 descriptions, and it is very rare, indeed, that any objection has 
 been made to the accuracy of the instrument submitted. By 
 thus performing its own title searches, even though thay may 
 not have always been the most exact from a title lawyer's stand- 
 point, the authorities have saved thousands of doUars and have 
 never had an injunction or ejectment proceeding instituted 
 against them by objecting land owners. 
 
 Curves. Sharp curves and right-angle intersections are danger 
 places where vehicles move rapidly. The width of the roads 
 should be increased on sharp curves, except where it is already 
 wide, and the right-of-way at right angle intersections should be 
 widened and cleared so as to give drivers on the crossing roads 
 a good view of approaching vehicles. This is not always prac- 
 ticable, unfortunately, but road commissions should keep in 
 mind that these places are dangerous, that it js their duty to 
 reduce the dangerous conditions on the roads under their charge 
 and that it is less expensive to improve these places now than it 
 will be later. 
 
LOCATION AND GRADES OF RURAL ROADS 9 
 
 On curves on a road with a uniform cross-section there is a 
 tendency for the drivers of motor vehicles to stay on the inside 
 of the curves because the centrifugal effect of passing on the 
 outside is unpleasant. In order to make motor travel equally 
 agreeable on any part of the cross-section of curving roads, it is 
 now the practice to superelevate the outside of the road, as is 
 done on railways. Experiments with different angles of super- 
 elevation on California roads have led the highway department 
 of that State to adopt a slope of f-inch rise to each foot of width 
 of the roadway on all curves having radii of 300 feet or less. 
 The transition from the standard crowned cross-sections to the 
 uniform transverse slope stated is made in a distance of about 
 80 feet. In passing from the straight to the curved road, the 
 outside of the road is gradually made horizontal and then grad- 
 ually tipped up until there is the same slope throughout the sec- 
 tion from the inside to the outside edge. In this transition the 
 inside edge remains at the same elevation it would have if the 
 ordinary crowned cross-section were maintained; the change 
 is made by adding to the height of the other parts of the standard 
 section, so the improvement is generally called "banking the 
 curves." 
 
 Grade Crossings. The elimination of grade crossings is a prob- 
 lem that frequently complicates the location or relocation of 
 highways. The usual method of carrying the road under or over 
 the railroad tracks is so costly that its general use on rural roads 
 is impracticable. Some of the narrow underpasses with sharply 
 curving approaches that have been built on roads used by numer- 
 ous automobiles at high speed are almost as dangerous as the 
 grade crossings they replace. Attention is therefore being given 
 more and more to comprehensive relocation as a means of re- 
 ducing the number of grade crossings and making those remain- 
 ing less dangerous than before. For example, there was a Wis- 
 consin road 23.9 miles long with 16 grade crossings and 15 
 such crossings on branch roads feeding it, in addition to 3 under- 
 passes and 2 overhead bridges. A careful study by the State 
 highway commission showed that by reasonable relocation the 
 total number of crossings could be reduced to 16 at grade, 4 
 underpasses and 2 overhead bridges, and the 16 grade crossings 
 would be on the branch roads, none remaining on the main road. 
 The total cost of right-of-way and construction for such an im- 
 provement was estimated at $35,000, much less than the cost of 
 elimination in the usual manner. 
 
 The New York State highway department has had a long 
 experience in treating grade-crossing problems and as a result 
 has adopted the following general rules for location at such 
 crossings : 
 
10 AMERICAN HIGHWAY ASSOCIATION 
 
 1. The alignment should be laid out so that approaches are 
 on a tangent which is at least 400 feet long, 200 feet on each side 
 of the crossing. The angle that the highway makes with the 
 railroad should not be less than 60 degrees. The grade of the 
 approaches should not be greater than 6 per cent, and there 
 should be a portion level or nearly so for a distance of not less 
 than 100 feet on each side of the crossing. 
 
 2. On the highway within 200 feet of the railroad, on each 
 side, traffic should have a clear view of approaching trains for a 
 distance of 1,000 feet. (See Rule 5.) 
 
 3. The width of the planked crossing shall not be less than 
 24 feet, measured at right angles to the center line of the high- 
 way. The ends of the pavement should be protected by an edg- 
 ing of stone or concrete placed at a sufficient distance from the 
 ends of the ties to allow for replacing them. 
 
 4. A standard danger sign should be placed at each side of 
 the crossing along the highway in a prominent location at least 
 400 feet from the crossing. 
 
 5. When the view of the railroad either way, as required in 
 2, is less than 1,000 feet, or when there is a great deal of traffic 
 on either the highway or railroad, or when vision may be 
 blocked by cars or trains as in the case of a railroad with two 
 or more tracks, a flagman should be employed to warn highway 
 traffic. 
 
 The New York State highway department's rules for the elim- 
 ination of grade crossings are as follows: 
 
 1. Subways shall have a clear head-room of not less than 13 
 feet and a clear width between abutments of not less than 26 feet. 
 The approaches when in a cut shall have a minimum width of 
 28 feet between bottoms of slope. When a highway passes over a 
 railroad the clear height over said railroad shall be not less than 
 21 feet and the approaches when on embankment shall be not 
 less than 28 feet wide across the shoulders. 
 
 2. The alignment and grade of approaches shall be such 
 that traffic at any point within the limits of the elimination 
 will be able to see that approaching it for a distance of 300 feet. 
 The maximum allowable grade shall be 6 per cent. 
 
 3. Bridges carrying railroads over highways shall be of a 
 solid-floor, ballasted type. Drainage of such floors shall be 
 such that water will not drop upon the roadway. Bridges car- 
 rying highways over railroads shall have solid concrete floors 
 with a minimum width of roadway of 18 feet. 
 
 4. When an elimination is made on a highway already im- 
 proved, the pavement shall be of the same type as the existing 
 pavement. If the highway is not improved the pavement shall 
 be the same as that contemplated. 
 
LOCATION AND GRADES OF RURAL ROADS 11 
 
 5. Subways shall be drained in a thoroughly satisfactory 
 manner. 
 
 6. The limits of an elimination shall be taken as the points of 
 intersection of the approach grades of the elimination with the 
 grade of the existing highway. 
 
REGULATIONS OF THE CALIFORNIA HIGH- 
 WAY COMMISSION REGARDING 
 SURVEYS AND PLANS 1 
 
 Part 1. Surveys 
 
 (a) Note Books. Survey note books will be furnished to the 
 chief of party by the Division engineer. No survey note book 
 other than the standard book so furnished shall be used, and 
 the use of loose sheets is prohibited. The notes placed therein 
 shall be the "original" notes of the survey and shall not be copied 
 from sheets or from other books. 
 
 The standard book shall be used for alignment, topography 
 and levels, and for all other information which the survey parties 
 are required to secure; all notes shall begin at the bottom of the 
 page and read upward. 
 
 On beginning a survey the chief of party shall see that a proper 
 entry of the Division, county and route, is made upon the label 
 pasted to the inside of the front cover of the note book. 
 
 Attached to the back cover of each book are several pages 
 showing the "standards" required in all surveys. All survey 
 notes shall conform in so far as possible to such "standards" to 
 the end that all surveys and the manner of taking the notes thereof 
 shall be uniform throughout the work. 
 
 At the beginning of each day's work the following data shall 
 be entered in the book: Date; weather conditions; names of 
 members of party and duties of each. 
 
 When no notes are taken on a working day or portion of a 
 day, the date shall be entered and the reason for the loss of time 
 shall be stated clearly and concisely. 
 
 All survey and other notes shall be suitably indexed on the first 
 ruled page of the note book. 
 
 Every day at the close of the work the notes shall be copied 
 neatly upon specially printed sheets furnished by the division 
 engineer and numbered consecutively, and after careful check- 
 ing such sheets shall be forthwith forwarded to the division 
 engineer. 
 
 No note book shall contain notes relating to more than one 
 route or to more than one county. 
 
 1 From Austin B. Fletcher, State Highway Engineer of California. 
 
 12 
 
REGULATIONS OF THE CALIFORNIA HIGHWAY COMMISSION 13 
 
 (b) Alignment Notes. The base line of the survey shall be 
 referred to the true meridian, which shall be determined by ob- 
 servation on polaris. The chief of party before beginning a sur- 
 vey shall procure all tables and other data needed for such deter- 
 mination and observations shall be made from time to time to 
 ensure the accuracy of the work. The line shall also be checked 
 by magnetic bearings taken at each transit point. All angles 
 in the base line shall be azimuth angles read from the back sight 
 and repeated with the telescope reversed. 
 
 Complete traverses shall be run in all surveys and computed 
 in the field. If the error of closure exceeds 1 : 5000 the division 
 engineer shall be notified and the party shall not move camp until 
 he has authorized such moving. The closures shall be completed 
 and computed in such lengths as the division engineer shall 
 prescribe. 
 
 The base line shall be as nearly as may be in the center of the 
 proposed road. When it is apparent that a tangent base line will 
 not follow the approximate center of the proposed road, a curve 
 of suitable radius shall be run. Curves shall be measured by 
 computing the length of the arc and not by chords. 
 
 If the survey follows an existing road, wire nails not less than 
 5? inches in length shall be driven flush with the traveled way at 
 all angle points in the base line, at the beginning and ending of 
 all curves and on long tangents at intervals not exceeding 1000 
 feet. 
 
 When the base line does not follow a traveled way or when the 
 roadway is so soft that nails will not hold their position, wooden 
 stakes driven flush with the ground shall be used and the transit 
 point indicated thereon by a small nail. 
 
 All transit points shall be properly referenced as provided 
 under the caption "Stakes." 
 
 Stations shall be established every 100 feet on the base line 
 and indicated by short wire nails driven through bits of red 
 cloth into the ground to serve as temporary markers during the 
 survey. The stations and half stations shall be also permanently 
 marked by stakes set on both sides of the proposed road suffi- 
 ciently far removed from the base line to prevent their being dis- 
 turbed during the building of the road. 
 
 (c) Stakes. All stakes which are to be used for establishing 
 grades shall be made from 2x3 inch scantling, from 24 to 30 
 inches in length, laid flat and sawed diagonally into two wedges, 
 with the sharp ends approximately J inch thick. The lumber 
 from which the stakes are made shall be sound, reasonably free 
 from knots, and planed on all sides. These stakes shall be driven 
 into the ground to about one-half of their length with the 2-inch 
 face parallel to the base line. On the right side of the road the 
 
14 AMERICAN HIGHWAY ASSOCIATION 
 
 station number shall be marked plainly on the side of the stake 
 facing Station 0, and on the opposite side of this stake shall be 
 marked to the nearest tenth, the offset from the base line. The 
 face toward the road must be reserved for marking during con- 
 struction. On the left hand side of the road, the offset from the 
 base line shall be marked on the side of the stake facing Station 
 O and the station number on the opposite side. 
 
 All stakes used to mark monuments and for transit points shall 
 be wedge shaped, not less than 1 foot in length nor less than f x 
 2-inch at the top. Such stakes shall be driven flush with the 
 ground unless they are so located as not to endanger the travel- 
 ing public. Short nails driven into the tops of these stakes shall 
 indicate the monument and transit points. 
 
 All monument and transit points shall be referenced by three 
 ties to natural objects or, if such do not exist, to stakes, as shown 
 by the "standards" at the back of the note book. 
 
 (d) Topography. All objects, such as houses, barns, fences, 
 gates, field entrances, trees, telephone and telegraph poles, power 
 lines, railroad and railway tracks, within a distance of 150 feet 
 on either side of the base line shall be located by offsets from the 
 base line and recorded in considerable detail, and the limits of 
 the "traveled way" on all existing roads shall be indicated. 
 Separate sketches, with levels and dimensions of all essential 
 features, shall be made in the note book of all bridges, large cul- 
 verts and other appurtenances of the road, and plainly refer- 
 enced in the topography notes. 
 
 The azimuth from the back sight to the boundary lines of all 
 incorporated cities and of all counties shall be ascertained and 
 recorded. The azimuth of the boundary lines of all entering 
 and intersecting highways, of township lines, and of division 
 lines between property holdings shall be ascertained and re- 
 corded with reasonable accuracy, and when feasible the names 
 of the owners of property abutting on the proposed road shall 
 be recorded. 
 
 When it is desirable to locate topographic features from a 
 sub-tangent, the station will be measured from the nearest end of 
 the curve. 
 
 (e) Levels Whenever there is a known government bench 
 within 3 miles of the survey, the datum plane of such bench shall 
 be adopted for the work. If no such bench is available, a datum 
 plane shall be assumed at such an elevation as will be low for all 
 parts of the survey. 
 
 Benches shall be established during the progress of the work 
 at each end of the survey, at city and county lines, and at other 
 convenient points not more than 1000 feet apart, and at shorter 
 intervals on grades. 
 
REGULATIONS OF THE CALIFORNIA HIGHWAY COMMISSION 15 
 
 Where no permanent objects or structures exist, a long, sub- 
 stantial stake shall be driven firmly into the ground and prop- 
 erly referenced. 
 
 On bench marks, at turning points, and on construction stakes, 
 elevations shall be determined to hundredths of a foot. 
 
 Cross section levels shall be taken to tenths of a foot at each 
 100-foot station and at half stations, at entering and intersecting 
 roads, for not less than 200 feet from the base line, at driveways 
 and field entrances and wherever the surface of the ground changes 
 abruptly. The elevation of the center of the traveled way of 
 an existing road shall be taken and properly noted when it does 
 not coincide with the base line. The cross sections shall include 
 the whole width between fences, and where the grade is likely to 
 be changed substantially the cross sections shall cover a width 
 sufficient to include all ground likely to be affected. 
 
 Sections shall be taken at all culverts and water crossings, and 
 elevations shall be taken a sufficient distance up and down all 
 streams to afford data for designing new structures. 
 
 (f) General Data. The survey notes shall contain data con- 
 cerning: 
 
 1. The location of outcropping boulders and bedrock, suitable 
 for road metal or concrete. 
 
 2. The location of all quarries near the proposed road. 
 
 3. The location and approximate quantity of field stone 
 available in the vicinity of the road. 
 
 4. The location of all gravel pits. 
 
 5. The location of points where good river sand can be obtained. 
 
 6. The available points where water for sprinklers and steam 
 rollers can be obtained. 
 
 7. The location of all railroad spur tracks or sidings within rea- 
 sonable haul of the proposed highway and the name of the railroad. 
 
 8. The most advantageous locations for rock crushing plants 
 along the road. 
 
 9. The current wages paid to teamsters and laborers in the 
 locations through which the road will pass. Amount paid for 
 hire of mules or horses (without driver) per day. Amount paid 
 for man and two-horse team per day. 
 
 10. The locations where special underdrains should be in- 
 stalled due to the existence of unstable sub-soil conditions. In- 
 quiry should be made of residents and local officers regarding 
 spots that break up badly in wet weather. 
 
 11. The approximate area of the watershed at each stream 
 crossing if it can be readily obtained. All high-water marks 
 should be noted and inquiry as to whether or not water over- 
 flows the road. 
 
 12. All general information that may prove of value in the con- 
 struction of the highway. 
 
16 AMERICAN HIGHWAY ASSOCIATION 
 
 Part II. Plans 
 
 (a) Drafting. All drafting so far as possible shall be done in 
 the division offices. At the Sacramento headquarters, the draft- 
 ing shall be limited to work of a general nature, such as the de- 
 sign of standards, general maps and to such revision work of 
 the plans made in the division offices as may be necessary. No 
 drafting shall be done in the survey party camps except such as 
 '*s immediately needed in the mountainous country to facilitate 
 il:^ choice of lines and grades. 
 
 '!;? plans, profiles and cross-sections shall be plotted in the 
 division offices from the copies of the survey notes sent in daily 
 by the survey parties as required under the rules for surveys. 
 
 (b) Warkinn Plans. The plan and profile of every road survey 
 shall be plottt, 1 on detail paper 30 inches in width and of such 
 length as may be found convenient, the plan to be plotted above 
 the profile, and such drawings shall be known as the "Working 
 Plans." 
 
 Plans and profiles shall be plotted from left to right, the plan 
 on the scale of 1 inch to 100 feet and the profile to the same hori- 
 zontal scale and to the vertical scale of 1 inch to 20 feet. 
 
 The base line of the survey shall be plotted by coordinates 
 obtained from the traverse sheets which have been made and 
 calculated in the survey camps and said base line shall be inked 
 in red before the topography is plotted. All angles and curve 
 points shall be marked by small circles, and the even stations by 
 a line | inch in length drawn at right angles across the base line. 
 
 The even stations and the plus distance of all angle and curve 
 points shall be numbered below the base line. The calculated 
 bearings of the base line, together with the tangent and curve 
 lengths and the radii of the curves, shall be indicated above the 
 line. The right-of-way lines shall be shown hi red. They shall 
 be properly referenced to the base line and land corners. Where 
 they are not parallel to the base line their bearings and lengths 
 shall be indicated. The topography and lettering other than 
 that relating to the base line shall be done neatly and so as to 
 permit of tracing easily but such details shall not be inked. 
 
 All drafting details shall conform to the conventions shown on 
 the specimen sheet furnished to each drafting office. 
 
 The north point shall be indicated at intervals of not more 
 than fifty stations. 
 
 The datum line of the profile shall be drawn inch from the 
 bottom of the sheet and inked in black. Perpendiculars shall be 
 erected at each even station and inked in black. The even sta- 
 tions and plus distances shall be numbered below the datum line 
 and the elevations of the present surface of the ground shall be 
 
REGULATIONS OF THE CALIFORNIA HIGHWAY COMMISSION 17 
 
 shown above the datum line and to the left of the perpendiculars. 
 The elevations of the proposed finished road surface shall be 
 shown in red and to the right of the perpendiculars. 
 
 The present ground surface shall be drawn in black, and the 
 proposed finished surface of the road and proposed rates per 
 cent of grade in red. Points of change in the rate of the finished 
 grade and the beginning and end of vertical curves shall be in- 
 dicated by small circles. 
 
 No title need be placed on the working plans; they shall be 
 identified by the file number, and such plans shall bear the sig- 
 natures of the employees concerned in their preparation and the 
 date. 
 
 (c) Cross Sections. The cross sections shall be plotted to the 
 scale of 1 inch to 5 feet vertical and horizontal on specially ruled 
 sheets, 20 by 30 inches in size, furnished by the highway engi- 
 neer. They shall be plotted from the bottom of the sheet up- 
 ward and so as not to interfere with one another more than is 
 necessary. The station numbers shall be placed directly below 
 the datum line and across the base line. The present ground 
 surface, the elevation at the base line and the station number 
 shall be inked in black. The proposed finished surface, together 
 with the elevation at the center of the proposed roadway, shall 
 be shown in red. 
 
 (d) Layout Plans. The layout plans shall be on tracing cloth 
 20 by 30 inches in size and the first sheet shall carry the title, 
 small index or key maps, conventions, and the necessary certifi- 
 cates and signatures, and such sheet will be prepared in Sacra- 
 mento. The subsequent sheets shall be traced from the working 
 plan, shall be authenticated by the signatures of the division 
 engineer and the highway engineer, shall state the whole num- 
 ber of sheets in the set and the number of the individual sheet, 
 the file number, and on each sheet shall be shown the true North 
 Point. These plans shall conform as closely as is practicable in 
 workmanship and appearance to the specimen sheet hereinbefore 
 referred to. 
 
 (e) The Grade Line. The grade shall be established tenta- 
 tively on the profile under the direction of the division engineer 
 and transferred to the cross-sections and the proposed finished 
 surface of the roadway and slopes shall be drawn on the sections 
 with the aid of templets to be furnished by the highway engineer. 
 If it appears to be desirable to shift the center of the roadway 
 from the base line, the new alignment shall be located on the 
 working plan by a dotted redline. The limits of earth work 
 shall be shown on the plan by a dotted red line where they ex- 
 tend beyond the fences or known right-of-way lines. 
 
 After the grade line has been so tentatively established and 
 
18 AMERICAN HIGHWAY ASSOCIATION 
 
 the estimates have been completed, the working plan, cross-sec- 
 tions and estimates, together with sketches of special structures, 
 shall be submitted to the highway engineer for his scrutiny. 
 
 (f) Accessions. Every plan made in a division office and which 
 is to remain there after it has been signed by the division engi- 
 neer, shall be entered in the "Accession Book" and described as 
 required by the captions therein. All other plans and maps re- 
 ceived at such offices, and which are to remain there, shall be 
 likewise entered in said book. 
 
 (g) Filing of Plans and Note Books. All plans shall be filed 
 flat in drawers in the division offices but during their prepara- 
 tion the working plans may be rolled and folded afterward. 
 
 When completed, the layout plans shall be filed at Sacramento 
 headquarters and on the completion of a contract the cross- 
 sections shall be likewise filed at Sacramento, blue prints thereof 
 being furnished to the division offices. 
 
 All note books shall be filed at Sacramento when the contract 
 relating to the surveys therein is completed. 
 
 All documents, whether plans, books or papers, which relate 
 to road contracts shall be stamped with the file mark adopted. 
 
DRAINAGE, CULVERTS AND BRIDGES' 
 
 In most parts of the country water is one of the most destructive 
 influences on roads. When it collects on the surface it tends to 
 inj ure the roadway unless the latter is paved with some hard, im- 
 pervious material. The mudholes on earth, gravel and broken 
 stone roads become soft, so that traffic increases their area and 
 depth rapidly. The impervious crust is finally broken through, 
 allowing water to reach the roadbed, which gives way under heavy 
 loads and the condition of the roadway becomes very bad. If 
 water collects in the ditches, it percolates sideways into the road- 
 bed, softening it and eventually causing subsidence which produces 
 marked irregularities in the surface, so that mudholes form there. 
 If the subgrade on which the roadbed is carried is soggy, a road 
 can not be maintained on it. Charles J. Bennett, State highway 
 commissioner of Connecticut, has reported an instance of this in a 
 city where a 7-inch broken stone roadway was placed on a poorly 
 drained clay subgrade. The roadway broke up when frost came 
 out of the ground and became so impassable that stringers were 
 laid on it and covered with crossplank to furnish a driveway. 
 This heaving action of frost will eventually destroy any roadbed 
 in which water is allowed to collect. The water expands every 
 time it freezes. The expansion opens up the earth, so that gradu- 
 ally more water enters it and finally there is so much in the pores 
 and cracks that its expansion throws up the roadway. 
 
 Troubles with water are particularly noticeable on grades. The 
 water is not shed so quickly from the roadway on steep slopes as 
 it is on fairly level roads, but runs toward the side ditches at an 
 acute angle with them. If there is any check to the flow at the 
 side of the roadway, such as irregularities of the surface or vege- 
 tation offer, some scouring will eventually take place, and it is for 
 this reason that the good condition of the shoulders of steep roads 
 is important. The scouring of ditches on steep grades is a com- 
 mon occurrence after heavy rains, and experienced maintenance 
 men regard it as an injury that must be repaired immediately. 
 If the road is on a fill and also on a grade, the handling of water 
 requires special care if heavy gullying of the slopes is to be 
 avoided. A gully may be cut a quarter of the way across a new 
 
 1 Revised by W. F. Childs, Jr., Resident Engineer, Maryland State Roads 
 Commission. 
 
 19 
 
20 AMERICAN HIGHWAY ASSOCIATION 
 
 road in such a location by a single heavy rain. An unusual case 
 of the effect of water on slopes has been mentioned by Mr. Ben- 
 nett. A road which led up a steep hill was originally only wide 
 enough for one vehicle and was the drainage channel for the sur- 
 face water of the hillside. The surfacing was washed away by 
 every heavy rain. A new road was built by filling in stone to a 
 depth of 4 feet, with an open box culvert at the bottom to carry 
 whatever water might penetrate beneath the road from the sides. 
 This stone fill extended the entire width of the road, from shoulder 
 to shoulder, and very deep, wide ditches were provided at each 
 side. There has been no trouble with this road since it was re- 
 constructed in this way, showing what good drainage can do even 
 in an exceptionally bad place. 
 
 In any drainage work it is necessary to allow for the different 
 water-holding capacities of different materials. Experiments by 
 the United States Office of Public Roads and Rural Engineering 
 show that with the same condition of dryness, clay will take up 
 more water than sand, but will not part with so much. The rate 
 of drainage from saturated sand is almost twice as fast as from 
 saturated clay during the first twenty-four hours after the mate- 
 rials are allowed to drain. Silt is the slowest material to drain 
 and the loams come between sand and clay. While silt and clay 
 absorb more water than sand, they allow water to percolate very 
 slowly indeed in comparison with sand, and it is for this reason 
 that they form water-tight barriers when confined so their grains 
 can not flow away. When in a loose condition silt permits the 
 smallest amount of percolation, and calling the rate with this 
 material 1 the rate with loose clay is nearly 3, loose sandy loam 
 nearly 28 and loose sand nearly 54. With compacted materials, 
 however, such as exist in a well-built roadbed, the lowest rate of 
 percolation is with clay; calling it 1, the rate with compact silt is 
 2, compact sandy loam 15, and compact sand 93. The experi- 
 mental investigations make clear the reason for particularly care- 
 ful drainage of clay and silt subgrades. 
 
 General Methods of Drainage 
 
 Road drainage is chiefly a matter of, first, climate; second, 
 topography; and third, soil. It may be treated separately under 
 two heads, surface draining and sub-surface or under-drainage. 
 
 In the case of surface drainage, the surface water may be shed 
 in four ways, first, by cross-slope or crown in construction; sec- 
 ond, by longitudinal grade after the crown is determined; third, 
 by discharge into natural water-courses; and fourth, by discharge 
 into artificial outlets. 
 
 The crown should be determined by, first, character or type of 
 
DRAINAGE, CULVERTS AND BRIDGES 21 
 
 road; second, the locality; and third, by grade. The crown for a 
 natural earth road or a shell road should be made from 1 to 2 
 inches higher in construction than that which is ultimately de- 
 sired. This opinion is based on the fact that these types of roads 
 are more susceptible to consolidation and displacement under 
 traffic than most other roads. 
 
 In thickly populated districts a high crown is dangerous to 
 traffic and the cross-slope of roads constructed through towns or 
 other thickly populated districts should be reduced to that which 
 is just sufficient to shed water to the gutter line. In such dis- 
 tricts high crowns cause a sliding motion of vehicles and bring 
 an extra strain upon lower portion of the wheels which is objec- 
 tionable and causes public criticism, which, if not considered, 
 brings about a certain amount of prejudice against modern road 
 construction. Finally, in considering crowning of roads the ques- 
 tion of grades must not be overlooked. Ordinarily the practice 
 is to increase the crown as the grades become steeper. For all 
 grades up to and including 5 per cent, the crowns mentioned in 
 the next paragraph are considered sufficient. When the grade is 
 in excess of 5 per cent the crown should be so increased that the 
 water will be shed to the side of road rather than run down its 
 surface or, at least, make a curve in its course of final dis- 
 charge. 
 
 The minimum and maximum crowns which it is desirable to 
 use may be determined by multiplying half the width in feet of 
 the hard-surfaced roadway by ^ to 1 inch for gravel roads, \ to 
 f inch for macadam, J to \ inch for roads with a bituminous sur- 
 face, and \ to f inch for brick and concrete. Formerly curved 
 cross-sections were used with impervious pavements, which were 
 quite flat at the center and increased in curvature toward the 
 sides, with the result that there was a wholly needless slope at the 
 latter. This has been changed of late, and there is a tendency to 
 use uniform slopes from the sides toward the center, where an 
 angle is avoided by introducing a very flat curve. The unpaved 
 shoulders are often given a slope of 1 inch per foot of width. 
 
 There are two general methods of draining the roadbed, by side 
 ditches and by underdrains, which will be explained in more detail 
 later. In flat country, the roadbed is best kept dry by raising it 
 above the neighboring land, just as railway roadbeds are raised. 
 If this is not done, it is very difficult to keep roads in good condi- 
 tion. 
 
 In undeveloped swamp country, George W. Cooley, State en- 
 gineer of Minnesota, has found the most permanent roadbeds can 
 be built by constructing the embankment of material dredged from 
 a drainage ditch on the upper side of the road and a smaller ditch 
 on the lower side. When the swamps have soundings of 2 to 5 
 
22 AMEKICAN HIGHWAY ASSOCIATION 
 
 feet, he considers that the elevation of the bottom of the dredged 
 ditch may be disregarded except that it should not be above the 
 suitable theoretical grade line. This is because the surrounding 
 land is swampy at all times and the subgrade can not be drained 
 by any means short of draining the whole swamp. 
 
 In ordinary flat prairie country, the elevations recommended by 
 H. E. Bilger, road engineer of the Illinois highway department, 
 vary with the kind of soil used in the roadbed, as follows: with 
 dense clay or gumbo, where the obtainable grade of the side ditch 
 is less than 0.4 per cent, not more than 800 feet of earth road in 
 one stretch should have its crown less than 12 inches above the 
 adjacent fields, unless the road is along a ridge or on a side hill so 
 that culverts will deliver the water from the uphill ditch to nat- 
 ural outlets on the downhill side. In partly impervious soils, 
 such as loams, the same elevation should be maintained, when 
 the side ditches have a slope of less than 0.2 per cent. With sand, 
 gravel or very loose soil, the crown should be 6 inches above the 
 adjacent fields. 
 
 It is troublesome enough to care for the surface and under- 
 ground water on the right-of-way, without having the work ag- 
 gravated by water from adjacent property. On hillsides, there- 
 fore, the water flowing down the slopes toward the road is often 
 intercepted by ditches along the crest of the cuts, as shown in 
 Cross-Section 2 on page 6, and carried away to suitable outlets. 
 Such ditches are sometimes called "berm ditches." In sections 
 where irrigation is practiced, considerable trouble is sometimes 
 experienced as a result of the overflowing of the road, and to pre- 
 vent this the following law has been enacted in Colorado: 
 
 No person or persons or any corporation shall cause waste water, or the 
 water from any ditch, road drain or flume, or other place, to flow in or upon 
 any road or highway so as to damage the same, and any such person, or 
 persons or corporation so offending or violating any of the provisions of 
 this section for which there is no specific penalty provided shall pay a fine 
 of not less than $10 nor more than $300 for each offense, and a like fine of 
 $10 for each day that such obstruction shall be suffered to remain in said 
 highway, and shall also be liable to any person, or persons or corporations 
 in a civil action for any damages resulting therefrom; and it shall be the 
 duty of the road overseer in the district in which such violation shall occur 
 to prosecute any person, persons or corporation or corporations violating 
 the provisions of this act. 
 
 The water accumulating in the ditches should be discharged as 
 quickly as possible into neighboring outlets. After light rainfalls, 
 this may not seem important, but when a heavy rain occurs in the 
 early spring while the roadway is impervious the need of numer- 
 ous outlets is evident. This is particularly true on slopes, where 
 a large quantity of water in the ditches is liable to scour them 
 
DRAINAGE, CULVERTS AND BRIDGES 23 
 
 badly. As it is not always practicable to find natural drainage 
 channels on each side of the road, culverts must be built to carry 
 the water under the roadway from one ditch to the other, as well 
 as to provide adequate channels for the brooks crossing the rights- 
 of-way. 
 
 Although properly designed and well-built culverts protect a 
 road-bed from injury, it is sometimes desirable to avoid the use 
 of large structures of this class if it can be done by relocating the 
 road. This is particularly the case where the beds of the streams 
 are in alluvial soil which is readily eroded by swiftly moving flood 
 waters. In such cases there is uncertainty whether unpaved 
 channels to and from the culvert will not become so eroded that 
 the structure will settle. Culverts of large size in such localities 
 are comparatively expensive, and if there are many of them it is 
 always well to ascertain if the number can not be reduced by chang- 
 ing the position of the road. In a few cases winding brooks have 
 had straight channels dug to accomplish the same purpose. This 
 is particularly the case in districts where the roads follow straight 
 section lines without regard to topography. 
 
 The most elaborate investigation of surface and underground 
 roadbed drainage that has been made in this country was under- 
 taken by a committee of the American Railway Engineering Asso- 
 ciation, which reached the following conclusions: 
 
 Side ditches should be provided in cuts, whether the subgrade 
 be in rock or earth. The minimum side ditch should be 1 foot 
 wide on the bottom and 1 foot deep below subgrade. The mini- 
 mum grade for side ditches should be 0.30 per cent If the rate 
 of grade of the track in any cut is less than 0.30 per cent, the cut 
 may be widened to permit side ditches to be constructed on 0.30 
 per cent grades, or drain pipes may be laid to proper grades below 
 the ditches to any available outlet. 
 
 Efficient subdrainage of wet cuts and of saturated soil upon 
 which embankments rest may be attained by the use of pipe 
 drains. They should be laid immediately below the center of the 
 side ditch in cuts and about 10 feet from the toe of the slopes of 
 embankments and on grades of not less than 0.20 per cent. Care 
 should be taken to locate the pipe at such depths that no dis- 
 placement will be made in its alignment by the subsidence of the 
 roadway under traffic. To this end the trench in which the tile 
 is to be laid should be dug down into a motionless stratum under- 
 lying the saturated material which it is desired to drain. The 
 trench above the pipe should be completely filled with cinders or 
 other porous material which filters the water and aids its passage 
 to the pipe and prevents the intrusion of the saturated material 
 under pressure of traffic. 
 
 A water pocket beneath the track may be drained by small 
 
24 AMERICAN HIGHWAY ASSOCIATION 
 
 cross drains laid in cinder-filled trenches, or by trenches filled 
 with cinders, gravel or similar material. 
 
 The committee recommended that no pipe be used with an in- 
 side diameter of less than 6 inches, except for cross drains. It 
 will rarely be necessary to use larger sizes than 12 inches. The 
 trench should not be wider than is needed for digging it economi- 
 cally and laying the pipe. 
 
 Surface intercepting ditches should be constructed on the up- 
 hill side of all cuts where they may be opened without causing 
 slides. Open ditches should be dug along, and about 10 feet from, 
 the toes of embankments resting on soil liable to become unstable 
 if saturated, to divert water flowing toward the embankment. 
 Where an open ditch may endanger such an embankment, a drain 
 pipe may be laid along the toe of its slope. In constructing ditches 
 on slopes above cuts, they should not be larger than necessary in 
 order that they may not become the notch or score from which a 
 slide will start. They should be 10 to 25 feet from the crest of 
 the cut, and the material excavated from them should be deposited 
 on the side nearer the roadbed. 
 
 Side Ditches 
 
 The cross-section of side ditches should be such that they can 
 be formed and maintained by road machines, if practicable, for the 
 use of such equipment in places for which it is suitable gives the 
 desired results at lowest cost. The sections shown on page 226 
 illustrate the capabilities of road machines. In the final shaping 
 of the road, care must be taken not to dig the ditches too deep at 
 any place, leaving a depression to hold water. The purpose of a 
 ditch is to carry water away without retaining any of it. If any 
 depressions exist they must be remedied in some effective manner. 
 
 Very good results can be had by making side ditch 2 feet wide 
 on the bottom with a 4 : 1 slope on the road side and a slope on 
 the back side equal to the angle of repose of the particular mate- 
 rial encountered in the excavation. The 4:1 slope on the road 
 side is not dangerous to traffic, the slopes can be grassed with a 
 good texture of grass and the slope is not so steep as to become 
 gullied by water shed into the ditch from the surface of the road 
 where the crown is excessive or the grade steep. The slopes can 
 also be made and maintained with a road machine. 
 
 The grade of the flow-line of the ditch should be 0.5 per cent if 
 possible, rather more than the recommendation for railway ditches 
 previously quoted, but in flat country it is sometimes impracticable 
 to secure such a grade. Under such conditions the grade lines for 
 the ditches should be given by a surveyor, and the excavation 
 made to conform exactly to the lines. When finished, these flat 
 
DRAINAGE, CULVERTS AND BRIDGES 25 
 
 ditches must be maintained on the true grades, or water will fail 
 to run off quickly. Flat ditches are often made wide and shallow, 
 so as to expose as much water to evaporaton as possible, and on 
 well-maintained level roads care is taken that these shallow ditches 
 are not unduly shaded by trees and shrubs, so that evaporation 
 will be checked. 
 
 Where there are two convenient outlets with a side ditch run- 
 ning from one to the other, the grade may be improved and a 
 deep, unsightly ditch avoided by selecting a good intermediate 
 summit and drawing water both ways to the outlet. This summit 
 may be regulated by the grades desired or by holding them from 
 6 to 12 inches below the sub-grade at the summit and running 
 straight flow-line grades each way to the outlets. 
 
 Deep, narrow ditches with steep sides have two defects fre- 
 quently observed where roads are not maintained properly. One 
 defect is the danger they offer to vehicles which may be crowded 
 into them for any reason. The records of the Iowa State high- 
 way commission for September, October and November, 1916, 
 show that in that State alone 353 automobiles turned turtle, re- 
 sulting in 5 deaths and 451 injuries. Just how many of these ac- 
 cidents were due to ditching the cars is not stated, but this is gen- 
 erally regarded as the usual cause of overturning. Where the 
 ditches are deep or the road is on an embankment with steep 
 slopes, substantial guard rails should be provided. During Sep- 
 tember, October and November, 1916, the Iowa records show that 
 167 cars went over embankments, killing 7 persons and injuring 
 234. Such a list points more clearly than general arguments to 
 the great importance of guard rails that will act as real guards. 
 
 The second defect is the relatively high velocity which water 
 may acquire in a deep, narrow ditch. If the latter is protected 
 against erosion high velocity may cause no trouble, but such pro- 
 tection is not common and when the water rushes through an 
 earth ditch the latter will become eroded and both the roadbed 
 and the bank may be severely injured. 
 
 The maintenance of ditches cut in earth on slopes is hardly 
 possible unless water-brakes are constructed in them. These 
 are usually heavy timbers placed across the ditch and projecting 
 several inches above it. They check the flow of the water at 
 intervals down the hill, and thus prevent a velocity which will 
 be destructive. The ditches where they are used must be cleaned 
 out after every rain or the bottoms will become filled to the top 
 of the timbers and later storms will gully the road and the banks 
 at their ends. In some cases, the water-brakes are heavy con- 
 crete beams. Where the water attains an erosive velocity in 
 ditches paving protects them better than the waterbrakes. 
 
 Wherever practicable ditches in earth on grades exceeding 
 
26 AMERICAN HIGHWAY ASSOCIATION 
 
 5 per cent should be paved. This adds somewhat to the first 
 cost, even when field stone suitable for the purpose can be ob- 
 tained in the vicinity, but the first cost is offset by the reduced 
 expense for maintenance. 
 
 The outlets from the ditches should receive careful attention, 
 because they are frequently a source of needless expense for 
 maintenance. There should be a paved channel of sufficient size 
 leading from the ditch to the waterway into which the water 
 is discharged. If field stone for such a pavement can not be 
 obtained, it will be advisable to employ concrete. 
 
 The protection of the embankments by grass or other vege- 
 tation is a remedy for scouring used on many railways and 
 some highways. Witch grass is a good species for the purpose, but 
 must not be used near cultivated land. Bermuda grass and red 
 top have been recommended for some localities and other varie- 
 ties are probably better suited for different local conditions. 
 On the Southern Railway the banks have been held by planting 
 the volunteer or Japanese honeysuckle in parallel horizontal 
 rows about 10 feet up the slopes. Where the slopes stand satis- 
 factorily except during heavy rains, and the material is such that 
 vegetation will not grow on them, they are sometimes held in 
 place by covering them with coarse cinders and gravel. This 
 prevents the water from coursing down them unchecked and 
 thus checks erosion. 
 
 At every driveway from a road into adjoining property, there 
 is likely to be an obstruction of the ditch crossed by this drive. 
 If the ditch is shallow with gently sloping sides, the best drive 
 from a drainage viewpoint is a paved strip from the roadway 
 across the ditch into the property. Unfortunately this is not 
 often practicable and rarely adopted when it is. The usual 
 driveway is formed by filling dirt over a flimsy plank drain or 
 a line of 4-inch tile on an insecure foundation, and this affords 
 wholly inadequate drainage. A culvert with an ample water- 
 way should be provided, with a substantial facing or headwall 
 at each end. Sometimes culverts under driveways can be omitted 
 in the case of shallow side ditches, by locating a summit at the 
 entrance and running the grade down in both directions from it to 
 well-defined outlets. 
 
 At such drives attention should be paid to the amount of 
 water they may discharge into the side ditches. Sometimes on 
 a hillside a driveway will discharge a large volume of water at 
 such a high velocity that, unless properly led away, part of it 
 will flow across the road to the other side, which does the 
 shoulders and roadway no good and may cause serious injury. 
 
DRAINAGE, CULVERTS AND BRIDGES 27 
 
 Underdrainage 
 
 The usual method of repairing a wet place adopted by an 
 untrained roadbuilder is to dump stone over it. After the stone 
 has been forced into the mud by the traffic, more stone is dumped 
 there, with the result that a mudhole is formed at each end of 
 the stone fill. The water is in the earth and must find an outlet 
 somewhere. Instead of trying to seal it up, the proper remedy 
 is to carry it off by some kind of underdrainage. The problem 
 of caring for underground water is, first, a matter of soils ; second, 
 a matter of topography; and third, one of temperature. There 
 are many soils of a gravelly, sandy, or similar character, which 
 ordinarily are self-draining to a degree and do not require par- 
 ticular attention. The difficulty is with those highways built on 
 clayey or loamy soils which are more or less retentive and do not 
 drain readily. 
 
 When the entire roadbed is somewhat damp or soggy it was 
 formerly the general practice to lay a foundation of large stones 
 wedged together by small stones and thoroughly rammed. This 
 is called a Telford foundation and is 6 inches or more thick. 
 It is still used extensively for the purpose but there are sub- 
 stitutes for it which have come into use. In some cases from 
 6 to 12 inches of coarse gravel or small field stone are placed 
 on the subgrade and rolled. Still another type of drainage foun- 
 dation, developed first in Massachusetts, is formed by excavating 
 the subgrade to a V-shape cross-section, 6 to 8 inches deep 
 at the sides and 12 to 18 inches deep at the center, and 
 filling this with field stones, the largest at the bottom. With 
 any of these types, there should be an outlet every 50 feet or so 
 from the lowest part of the foundation, formed by cutting a 
 trench through the shoulders to the side ditches and backfilling 
 it with coarse gravel or stone. Even when the road is not on 
 wet land, many engineers build cross drains filled with stones at 
 50-foot intervals in the top of the subgrade of gravel and mac- 
 adam roads. They are 5 or 6 inches deep at the center and 
 are at right angles to the ditches except on hills, where they in- 
 cline slightly downhill from the center. 
 
 In many parts of the country stone or gravel is unavailable 
 for such drainage work and drain tile has been employed. It 
 has proved successful and economical, even when stone could be 
 obtained, provided it was laid properly. Many engineers recom- 
 mend using drains whenever water remains in the ground for a 
 considerable period of time within 3 feet of the surface. The 
 reason for this is that the maintenance of a well-drained road 
 is easier work than if the subgrade is soggy. If a heavy rainfall 
 soaks the top of a road which is already soft below the surface, 
 
28 AMERICAN HIGHWAY ASSOCIATION 
 
 heavy loads are liable to rut it seriously, because it will take much 
 longer to dry out than a well underdrained road. In the early 
 spring, when the water in the ground freezes and thaws alter- 
 nately, good underdrainage is particularly useful in preventing 
 the upheaval of parts of the road. 
 
 The influence of a well-laid line of drain tile upon the position 
 of the upper surface of the ground-water, called the "water table" 
 by many engineers, is greater than many persons realize. Prof. 
 Ira O. Baker has reported the following experimental proof 
 of the extent of this influence. Lines of drain tile were laid 
 50 feet apart and 2J feet deep in a field notoriously soggy 
 and heavy on account of the presence of hardpan which held 
 the water "like a jug." Where the field was without drainage 
 the water rose to within 6 inches of the surface. Where it 
 was drained, the water level midway between the drains was 
 18 inches below the surface, showing that even in such 
 very heavy soil, the top surface of the ground-water 25 feet 
 from the drain was only 1 foot above the tile. It is this wide 
 influence of good drains which makes the effect of a single line of 
 deep-laid tile along one side of a road greater than that of shal- 
 low lines along both sides. The general rule of agricultural 
 drainage experts is to place drains 100 feet apart and at a depth 
 of 3| to 4 feet. 
 
 The drain is best laid in a trench below the ditch at the side 
 of the road from which the greatest amount of ground-water is 
 expected. Although a large number of drains laid perfectly 
 horizontal for long distances have given satisfactory service, it is 
 desirable to give them a uniform slope of at least 2 inches per 
 100 feet if possible. This is a somewhat lower minimum grade 
 than some engineering books recommend, but is warranted by 
 experience. The tile should not be smaller than 4-inch, and if 
 the ground contains a large amount of water and the outlets 
 of the drains are far apart, larger sizes may be desirable, partic- 
 ularly in level country. 
 
 Tile should not be laid except from grade lines given by the 
 engineer, and they must be laid accurately to line and grade. 
 The trench to receive them should be no larger than is necessary 
 to lay them properly at the least expense, but in opening a trench 
 it is sometimes less expensive to make it wider than required for 
 the tile, because of the extra cost of digging in a very narrow 
 trench. In any case the bottom should be cut very carefully 
 so as to have it exactly on the right grade. If there is any prob- 
 ability that the bottom will settle and throw the tile out of align- 
 ment, a 4 by 1-inch plank is sometimes laid to support the 
 tile. The ends of the tile are laid touching. Some engineers 
 recommend covering the top half of the joint with tar paper or 
 
DRAINAGE, CULVERTS AND BRIDGES 29 
 
 burlap, but this is probably unnecessary if the trench is back- 
 filled with clean gravel or broken stone from 1 to 4 inches 
 in size, which is the best material to use. In any case the fill- 
 ing should be porous and placed carefully so as not to move the 
 tile. When the gravel or stone filling is within 12 inches of 
 the surface, some engineers coyer it with about 3 inches of 
 hay or straw before the earth filling is placed to form the bottom 
 of the side ditch. 
 
 The outlets of the drains should be constructed with special 
 care, because they are particularly liable to injury. They are 
 preferably made of stronger pipe than agricultural tile, firmly 
 supported and protected at the end by a substantial wall or 
 facing. A drain with its end stopped is of little value. 
 
 Pipe drains are the most serviceable type, but there are vari- 
 ous substitutes. One of these is a covered trough of rough stone, 
 another is a similar plank trough, and another is merely a mass 
 of gravel and stones, with the largest pieces at the bottom. The 
 drawback of all of these is that they tend to break down or be- 
 come clogged with fine material, which can not enter a properly 
 laid tile drain. 
 
 Where the side ditches are on very flat grades, they are some- 
 times drained into the underdrains at intervals of about 0.1 mile 
 by blind catch-basins. These are merely masses of coarse gravel, 
 stone or brickbats reaching from the bottom of the ditch to the 
 tile, and covered at the top by a low pile of similar material 
 which acts as a screen. By this means the side ditches need 
 not be cut so deep as to be dangerous. Where the side ditches 
 carry large quantities of water which must be drained off in this 
 manner, large drain tiles are needed and open brick or concrete 
 inlets like those used on sewerage systems may be used. 
 
 Where an embankment is built on a wet side hill, the latter 
 must first be underdrained thoroughly to prevent slipping of the 
 embankment. When an embankment in such a locality begins 
 to slip, the trouble may sometimes be remedied by digging large, 
 deep intercepting ditches on the high side, leading to the nearest 
 culverts. These ditches are usually filled with stone. Any 
 pockets in the ground near the uphill toe of the embankment, in 
 which water may collect and soften the neighboring earth or clay, 
 should be filled. 
 
 Size of Culvert Openings and Bridge Waterways 
 
 The waterway to be provided for large culverts and bridge 
 openings depends upon many conditions, which have been stated 
 as follows by Prof. A. N. Talbot: 
 
30 AMERICAN HIGHWAY ASSOCIATION 
 
 1. The variation of the rainfall in different localities. 
 
 2. The meagreness of rainfall data, since records are gener- 
 ally given as so much per day and rarely per hour, while the du- 
 ration of the severe storms is not recorded. 
 
 3. The melting of snow with a heavy rain. 
 
 4. The permeability of the surface of the ground, depending 
 upon the kind of soil, condition of vegetation and cultivation, etc. 
 
 5. The degree of saturation of the ground and the amount 
 of evaporation. 
 
 6. The character and inclination of the surface to the point 
 where the water accumulates in the watercourse proper. 
 
 7. The inclination or slope of the watercourse to the point 
 considered. 
 
 8. The shape of the area drained and the position of the 
 feeders. 
 
 The importance of this item will be seen in comparing a spoon- 
 shaped area where the main watercourse is fed by branches from 
 both sides so arranged that water from the whole area reaches the 
 culvert at the same time, with a long, narrow basin in which, 
 before the water from the upper part reaches the opening, the 
 rainfall from the lower portion has been carried away and the 
 severe part of the storm is past. 
 
 While there are three formulas giving the size of waterways 
 for drainage areas of different sizes, it is generally agreed by 
 engineers that it is best to find out by examination and inquiry 
 if possible the flood heights of any stream that is crossed. The 
 condition of neighboring culverts and bridge openings during 
 floods should be investigated, and the nature of the channel of 
 the stream and the character of its drainage basin ascertained. 
 Such records are not only helpful in determining the size of the 
 structure under consideration but are of value in showing the 
 degree of reliance that can be placed on a waterway formula. 
 
 A formula widely used in the Central States was proposed in 
 1887 by Prof. A. N. Talbot. The area in square feet of the net 
 waterway is found by multiplying the three-fourths power of the 
 acres drained by a coefficient. This coefficient was taken by 
 Professor Talbot as 0.33 for rolling farming land subject to floods 
 when snow melts and the valley drained is three or four times as 
 long as it is wide, 0.16 to 0.2 in districts not affected by snow and 
 with the valleys several times longer than wide, and from 0.67 to 
 1.0 for steep, rocky ground. The waterways given by this for- 
 mula are stated in the table on the next page. 
 
DRAINAGE, CULVERTS AND BRIDGES 
 
 31 
 
 Square Feet of Waterway Required by Talbot's Formula for Passing the Runoff 
 from Areas Stated of Different Classes of Land 
 
 ACRES 
 DRAIN- 
 ED 
 
 LEVEL 
 LAND 
 
 ROLL- 
 ING 
 LAND 
 
 HILLY 
 LAND 
 
 MOUN- 
 TAINOUS 
 
 ACRES 
 DRAINED 
 
 LEVEL 
 LAND 
 
 ROLLING 
 
 LAND 
 
 HILLY 
 LAND 
 
 MOUN- 
 TAINOUS 
 
 10 
 
 1.1 
 
 2.3 
 
 3.4 
 
 4.5 
 
 180 
 
 9.8 
 
 19.7 
 
 29.5 
 
 39.3 
 
 20 
 
 1.9 
 
 3.8 
 
 5.7 
 
 7.6 
 
 200 
 
 10.6 
 
 21.2 
 
 31.8 
 
 42.5 
 
 30 
 
 2.6 
 
 5.1 
 
 7.7 
 
 10.2 
 
 240 
 
 12.2 
 
 24.4 
 
 36.6 
 
 48.8 
 
 40 
 
 3.2 
 
 6.4 
 
 9.5 
 
 12.7 
 
 280 
 
 13.7 
 
 27.4 
 
 46.1 
 
 54.8 
 
 50 
 
 3.8 
 
 7.5 
 
 11.3 
 
 15.0 
 
 320 
 
 15.1 
 
 30.3 
 
 45.4 
 
 60.5 
 
 60 
 
 4.3 
 
 8.6 
 
 12.9 
 
 17.2 
 
 360 
 
 16.5 
 
 33.1 
 
 49.6 
 
 66.1 
 
 70 
 
 4.8 
 
 9.7 
 
 14.5 
 
 19.4 
 
 400 
 
 17.9 
 
 35.8 
 
 53.7 
 
 71.6 
 
 80 
 
 5.4 
 
 10.7 
 
 16.1 
 
 21.4 
 
 440 
 
 19.2 
 
 38.4 
 
 57.6 
 
 76.9 
 
 90 
 
 5.8 
 
 11.7 
 
 17.5 
 
 23.4 
 
 480 
 
 20.6 
 
 41.2 
 
 61.8 
 
 82.3 
 
 100 
 
 6.3 
 
 12.6 
 
 19.0 
 
 25.3 
 
 520 
 
 21.8 
 
 43.6 
 
 65.3 
 
 87.1 
 
 120 
 
 7.3 
 
 14.5 
 
 21.8 
 
 29.0 
 
 560 
 
 23.0 
 
 46.0 
 
 69.1 
 
 92.1 
 
 140 
 
 8.1 
 
 16.3 
 
 24.4 
 
 32.6 
 
 600 
 
 24.2 
 
 48.5 
 
 72.7 
 
 97.0 
 
 160 
 
 9.0 
 
 18.0 
 
 27.1 
 
 36.1 
 
 640 
 
 25.4 
 
 50.9 
 
 76.3 
 
 101.8 
 
 About 1880 the Santa Fe system began to measure accurately 
 the area of the waterways of streams during floods in Missouri, 
 Kansas, Indian Territory and Texas. The work was done as 
 carefully as possible and in 1897 the results were summarized 
 and a table of waterway areas issued by James Dun, chief engi- 
 neer of the system, for the use of his engineers. The collecting 
 of such information was continued after that date, and in 1906 
 an enlarged table was printed for public use, which is extensively 
 employed by railway and highway engineers in the section of the 
 
 Square Feet of Waterway Given by Dun's Table for Passing the Runoff from 
 Areas Stated; Applicable to Missouri and Kansas 
 
 Area, square mile 
 
 Waterway, square feet. 
 
 Area, square mile 
 
 Waterway, square feet. 
 
 Area, square mile 
 
 Waterway, square feet. 
 
 Area, square mile 
 
 Waterway, square feet. 
 
 Area, square mile 
 
 Waterway, square feet. 
 
 Area, square mile 
 
 Waterway, square feet. 
 
 Area, square mile 
 
 Waterway, square feet. 
 
 0.01 
 2.0 
 
 0.100.150.200.250.300.350.400.45 
 
 16 
 
 0.550.600.650.700.750.800.850.90 
 
 70 
 
 1.0 
 
 100 
 
 1.9 
 190 
 
 3.6 
 357 
 
 6.0 
 509 
 
 0.020.030.040.050.060.070.080.09 
 
 4.0 
 
 25 
 
 74 
 
 1.1 
 110 
 
 2.0 
 200 
 
 3.8 
 373 
 
 6.5 
 533 
 
 6.0 
 
 32 
 
 78 
 
 1.2 
 120 
 
 2.2 
 220 
 
 4.0 
 
 388 
 
 7.0 
 556 
 
 7.5 
 
 38 
 
 81 
 
 1.3 
 130 
 
 2.4 
 
 240 
 
 4.2 
 403 
 
 7.5 
 
 579 
 
 9.0 
 
 44 
 
 85 
 
 1.4 
 
 140 
 
 2.6 
 260 
 
 4.4 
 417 
 
 8.0 
 601 
 
 10.5 
 
 51 
 
 1.5 
 150 
 
 2.8 
 280 
 
 4.6 
 430 
 
 8.5 
 622 
 
 12.0 
 
 56 
 
 91 
 
 1.6 
 160 
 
 3.0 
 300 
 
 4.8 
 443 
 
 9.0 
 641 
 
 62 
 
 94 
 
 1.7 
 170 
 
 3.2 
 321 
 
 5.0 
 
 455 
 
 9.5 
 660 
 
 15 
 
 0.50 
 66 
 
 0.95 
 97 
 
 1.8 
 180 
 
 3.4 
 340 
 
 5.5 
 
 483 
 
 10.0 
 679 
 
32 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 country mentioned. A portion of the table is reproduced here. 
 Mr. Dun stated that it did not give waterways large enough for 
 the floods that occurred at very long intervals and were of un- 
 precedented severity, for which he did not consider it advisable 
 for provision to be made. He recommended waterways 60 to 
 80 per cent as large as those tabulated for culverts and bridge 
 openings in Illinois, about 5 per cent larger waterways for Texas 
 when the areas drained exceeded 1 square mile, and from 1 \ to 6J 
 per cent smaller waterways in New Mexico for areas exceeding 
 1 square mile. 
 
 About thirty years ago, C. C. Wentworth, of the engineering 
 staff of the Norfolk & Western Railway, made a careful study 
 of the area of the culverts which had proved of sufficient size on 
 that road, and found that for drainage basins of one acre and 
 upward, the square feet of culvert cross-section should be equal 
 to the two-thirds power of the number of acres drained. This 
 formula has been used for many years on that railway and found 
 entirely satisfactory. The accompanying table gives the areas 
 computed by it for a number of drainage districts. These re- 
 lations hold good quite generally over the area between the Blue 
 Ridge and the Ohio River, and have been found to agree with 
 flood discharges in Maine, Connecticut, and New York. It 
 has been suggested that with rainfalls of less intensity or flatter 
 slopes than those of the section which furnishes the data on which 
 the formula is based, the areas of necessary waterways may be 
 taken at some percentage of those given by the formula. 
 
 Square Feet of Waterway Required to Discharge the Runoff from Areas of 1 
 to 99 Acres, Computed by the Wentworth Formula 
 
 
 
 
 1.0 
 
 2.0 
 
 3.0 
 
 4.0 
 
 5.0 
 
 6.0 
 
 7.0 
 
 8.0 
 
 9.0 
 
 
 
 
 1.0 
 
 1.6 
 
 2.1 
 
 2.5 
 
 2.9 
 
 3.3 
 
 3 7 
 
 4 
 
 4.3 
 
 10 
 
 4.6 
 
 4.9 
 
 5.2 
 
 5.5 
 
 5.8 
 
 6.1 
 
 6.3 
 
 6.6 
 
 6.9 
 
 7.1 
 
 20 
 
 7.4 
 
 7.6 
 
 7.9 
 
 8.1 
 
 8.3 
 
 8.5 
 
 8.8 
 
 9.0 
 
 9.2 
 
 9.4 
 
 30 
 
 9.7 
 
 9.9 
 
 10.1 
 
 10.3 
 
 10.5 
 
 10.7 
 
 10.9 
 
 11.1 
 
 11.3 
 
 11.5 
 
 40 
 
 11.7 
 
 11.9 
 
 12.1 
 
 12.3 
 
 12.5 
 
 12.7 
 
 12.8 
 
 13.0 
 
 13.2 
 
 13.4 
 
 50 
 
 13.6 
 
 13.8 
 
 13.9 
 
 14.1 
 
 14.3 
 
 14.5 
 
 14.6 
 
 14.8 
 
 15.0 
 
 15.1 
 
 60 
 
 15.3 
 
 15.5 
 
 15.7 
 
 15.8 
 
 16.0 
 
 16.2 
 
 16.3 
 
 16.5 
 
 16.7 
 
 16.8 
 
 70 
 
 17.0 
 
 17.2 
 
 17.3 
 
 17.4 
 
 17.6 
 
 17.8 
 
 18.0 
 
 18.1 
 
 18.3 
 
 18.4 
 
 80 
 
 18.6 
 
 18,7 
 
 18.9 
 
 19.0 
 
 19.2 
 
 19.3 
 
 19.4 
 
 19.6 
 
 19.8 
 
 19.9 
 
 90 
 
 20.1 
 
 20.2 
 
 20.4 
 
 20.5 
 
 20.7 
 
 20.8 
 
 21.0 
 
 21.1 
 
 21.3 
 
 21.4 
 
 Culverts 
 
 As the amount of water to be carried across the roadway by a 
 culvert is usually small, the majority of such structures are made 
 of some kind of pipe. The defects which such culverts develop 
 
DRAINAGE, CULVERTS AND BRIDGES 33 
 
 at times are generally due to lack of attention to features essen- 
 tial for good construction. The pipe must be laid on a perfect- 
 ly firm support. If the trench for it is cut too low and must be 
 leveled by replacing some of the material, the latter should be 
 consolidated thoroughly before the pipe is laid, and as it takes 
 considerable time to do this properly, it pays to be careful to 
 excavate in the first place to the exact grade. 1 After the pipe 
 has been laid and the joints filled if it is made of bell-and-spigot 
 lengths, the backfilling should be done with the same care used 
 in good sewerage work. The earth should be rammed thorough- 
 ly around the sides of the pipe, taking care not to disturb it in 
 doing this, and not more than 6 inches of earth should be spread 
 without ramming. The 2 feet of fill immediately over the 
 pipe should be similarly placed in 6-inch layers and rammed, 
 and while the material above this need not be placed so carefully 
 it should be thoroughly consolidated. 
 
 The inlet and outlet of the pipe should be at the bottom of the 
 ditches it connects or at the level of the bed of the brook that it 
 carries across the road. Each end should have a wall or facing 
 resting on an absolutely firm foundation far enough below the 
 surface to remain unaffected by frost and heavy enough to hold 
 back the bank resting against it. Concrete makes the best 
 facing, but substantial masonry and heavy planks have given 
 good service when properly used. By locating and protecting 
 the ends of the pipe in this way two important advantages are 
 gained, first, the thorough drainage of the side ditches and, 
 second, the prevention of undercutting of the ends of the pipe. 
 If the bottom of the ditch or bed of the brook is soft, it should be 
 payed for some feet above and below the culvert to prevent 
 serious erosion during severe storms. At irregular intervals 
 several years apart the ditches and brooks are exceptionally 
 flooded and the water is liable to rise above the top of the pipe. 
 If the culvert has been constructed as just recommended no 
 danger need be feared, for the road will act as a dam for a few 
 hours until these excessive quantities of water are discharged. 
 A poorly built culvert is likely to be washed out, however, and 
 carry part of the road with it. Standard plans for culvert head- 
 walls can be obtained from most State highway departments and 
 from the United States Office of Public Roads and Rural Engineer- 
 ing at Washington. 
 
 Where a pipe culvert is carried across a side-hill road, dis- 
 charging on the outer slope, some form of channel is often neces- 
 sary for carrying the water down the side of the embankment 
 
 1 If the sub-grade is soggy it is well to lay the pipe on a concrete floor 
 running from the foundation of one headwall to that of the other. Belt 
 joints should be laid up-hill. 
 
34 AMERICAN HIGHWAY ASSOCIATION 
 
 without causing erosion. Gutters of rough stone paving, con- 
 crete channels and metal troughs have all been used for this 
 purpose. 
 
 When a culvert is formed of two pipes laid side by side, which 
 is desirable where the grades are very flat, or the bed of the brook 
 is wide and the depth of water shallow even after heavy rains, 
 particular care must be exercised in consolidating the filling be- 
 tween the pipes. 
 
 In a few places, where timber is abundant and cheap, cul- 
 verts of heavy plank are used, but at the best, they are only 
 temporary structures, and it is unwise to put temporary works 
 which are costly to replace in a roadway graded to permanent 
 lines. The same is true of box culverts of dry masonry, with 
 unpaved bottoms. Masonry culverts laid carefully in cement 
 mortar are rarely so cheap as permanent pipe or concrete cul- 
 verts. Plans and instructions for building concrete culverts 
 can be obtained on application from most State highway de- 
 partments and from the United States Office of Public Roads 
 and Rural Engineering. 
 
 Any type of concrete culvert should be built carefully or 
 frost will cause trouble with it. The sand and gravel or broken 
 stone must be clean and graded so as to give a dense mixture, 
 and the mixing of the mortar must be thorough. The forms 
 must be strong and tight and located so that the structure will 
 be true to grade. The headwalls in particular should be carried 
 down to a secure foundation, and piling or a substantial timber 
 platform should be used to carry the concrete in case there is 
 any doubt whatever of the supporting power of the underlying 
 material. 
 
 The general tendency of rapidly flowing streams is to lower 
 their beds. This results in time in leaving the culvert floor 
 rather high for the natural bed of the stream and the water finds 
 its way underneath. A substantial cross wall at the outlet end of 
 the culvert, carried well below possible wash, is effective in stop- 
 ping this class of under-cutting, A frozen earth floor will some- 
 times act like a plank floor in causing such undercutting, and 
 hence good cross-walls are advisable in all culverts, whether 
 floored or not. If the channels leading to or from a culvert are 
 in soft material liable to erosion, they should be paved or pro- 
 tected by brush and heavy stones. 
 
 Bridges 
 
 Structures with a clear span exceeding 6 feet are generally 
 classed as bridges and should be permanent improvements on any 
 road brought to final grade and alignment. There has been 
 
DRAINAGE, CULVERTS AND BRIDGES 35 
 
 such great waste of money in past years on the bridges on rural 
 roads that the highway departments of most states have prepared 
 standard plans and specifications which cover most needs of 
 local road officials, and similar standards have been prepared 
 by the United States Office of Public Roads and Rural Engi- 
 neering. Structures of this character should only be built under 
 competent engineering supervision, both as to substructures and 
 superstructures. There is an unfortunate tendency on the part 
 of highway commissions to endeavor to save money by omitting 
 desirable precautions such as piling, which insure the safety of 
 the bridges under conditions which an engineer recognizes as 
 dangerous. For example, an unusually heavy rainfall in north- 
 eastern Iowa in June, 1916, washed out 163 bridges. Some were 
 old structures that needed replacing at an early date, but others 
 were expensive new structures of good design and construction 
 except for the fatal omission of the piling under the founda- 
 tions which was recommended by the engineers but left out to 
 reduce the cost. Not a bridge built according to the standards 
 of the State highway commission was damaged. 
 
 There are many bridges which have been in service for a long 
 period of time without suffering any injury, although their sub- 
 structures are in streams with an easily eroded bottom and banks. 
 For example, the Walhouding aqueduct on the Ohio canal system, 
 built about 1830, has four piers and two abutments in a stream 
 with a fairly swift current, rising suddenly to a great height. 
 Both its banks and bed near the aqueduct are rapidly eroded 
 unless protected. The piers and abutments rest on double plat- 
 forms of hewn timbers, laid crosswise and carried by piles driven 
 close together near all four sides of each base. Brush and heavy 
 stone were placed on the river bed around each foundation and 
 a row of strong piles was driven across the river bed just below 
 the aqueduct to prevent the removal of the brush and stones by 
 the current. Such a record of endurance made by structures 
 built before the beginning of the present era of scientific engi- 
 neering shows how needless are most of the washouts of expen- 
 sive bridges that occur every year. 
 
 As bridges on improved roads should be permanent struc- 
 tures, they should be designed to carry a heavy roller followed 
 'by a trailer loaded with coal. A bridge capable of supporting 
 a 15-ton roller will carry any of the heaviest field guns now 
 used in Europe. 
 
 Money is saved by having the plans and specifications for 
 bridges of reinforced concrete or steel prepared by an expe- 
 rienced engineer, so that all bidders on its construction will base 
 their estimates on the same structure and that structure will be 
 adapted to the locality and service. If each bidder must prepare 
 
36 AMERICAN HIGHWAY ASSOCIATION 
 
 his own plans, the expense of doing so is added to the cost of the 
 fabrication of the steel and the erection of the structure. This 
 makes a general increase in the cost of bridges in a district where 
 the practice is followed, for many unsatisfactory plans must 
 be prepared for one that is satisfactory. Furthermore the com- 
 mission awarding the contract must not only pick out the lowest 
 bidder but also decide which is the best plan, which may not 
 be that offered at the lowest price. 
 
 In level country where a stream overflows its banks during 
 heavy floods and bridges above the flood level require long expen- 
 sive approaches, what are known as overflow bridges are coming 
 into quite extensive use. They are structures designed to be 
 submerged by the floods and to offer as little obstruction as pos- 
 sible to the water passing over them. If the floods are likely 
 to carry large quantities of brush, the bridges are kept partic- 
 ularly low so the brush will pass freely over them when they are 
 submerged. The roads leading to a number of such bridges 
 have concrete pavements extending to the limits of the sub- 
 merged areas, for earth, gravel and broken stone roads are liable 
 to serious injury from water flowing across them. As the injury 
 to overflowed embankments generally starts at the top of the 
 downstream slope, the latter is often protected against scouring 
 by covering it with heavy stone. Stone with rounded edges is 
 less suitable for this purpose than stone of an angular shape, 
 because the former is rolled about more easily. 
 
 Fords 
 
 Where money is limited, the cost of building even a submerged 
 bridge is heavy, and the stream to be crossed is shallow, a ford 
 is sometimes constructed as a serviceable temporary expedient. 
 In Washington County, Utah, for example, there is a stream with 
 a sandy bottom which is dry at some seasons and dangerous 
 during floods on account of the treacherous nature of the wet 
 sand. A ford has been constructed which consists of two rubble 
 walls 4 feet deep and 2 feet wide, with a 2-foot rubble fill between 
 them. The entire width of this rubble fill from one wall to the 
 other is 20 feet, and the stones of which it is made were laid in 
 a dense mixture of sand and clay, which is not easily washed out 
 of the voids between the stones. The upstream wall was laid 
 dry but had 16 inches of clay puddled against the entire depth 
 of its outer face. The downstream wall was laid in lime mortar. 
 
 Near Shelbyville, Tennessee, fords have been made passable 
 at all times by constructing a number of parallel culverts close 
 together to carry the usual flow of the stream and building a 
 concrete roadway over these culverts to give a safe footing for 
 horses and a secure roadway for automobiles during high-water 
 when the roadway is submerged. 
 
EARTH AND SAND-CLAY ROADS 1 
 
 As a very large proportion of our country roads must be earth 
 roads for many years and the basis for any type of surfaced high- 
 way is a properly located, drained and graded earth road, the rela- 
 tive importance of this type is very great. If earth roads were 
 properly constructed and maintained, and their culverts and 
 bridges were permanent structures, a large part of the road taxes 
 now wasted would produce useful returns. It is proper for both 
 highway commissions and engineers to devote a large part of 
 their time and money to the improvement of the main roads 
 which are of service to the largest number of taxpayers, but there 
 is a deplorable lack of efficiency in the care of the local dirt roads in 
 many parts of the country. In some States, of which New York, 
 Illinois and Iowa are examples, these roads are under some super- 
 vision, directly or indirectly, by the State highway department, 
 but generally the local authorities do as they please. For in- 
 stance, in 1916 there were 71,000 miles of roads in Wisconsin in 
 sole charge of local officials, who spent about $4,500,000 on them. 
 The work was subdivided among nearly 13,000 road districts, 
 each with a road supervisor, and there were 3750 members of town 
 boards with general control over road work. Of these 16,750 
 officials, about one-fifth drop out of office annually. During 
 the ten years ending December 31, 1916, nearly 50,000 men 
 were in charge of local road work and over $40,000,000 spent by 
 them, with few perceptible lasting improvements. A system 
 giving such results is manifestly wrong, and should be replaced 
 by one with a smaller number of road officials having greater 
 authority and responsibilities and serving longer terms. It will 
 seem from the following notes that the construction and mainte- 
 nance of earth roads calls for executive ability and skill that can- 
 not be obtained unless fair permanence in office is assured. 
 
 The construction of earth roads falls into two general classes, 
 that where there are cuts and fills and that where the road is 
 formed by building a low embankment on the surface. Except 
 where the length of road is great enough to use elevating graders 
 with economy, these two classes are generally built by different 
 methods. 
 
 1 Revised by W. S. Keller, State Highway Engineer of Alabama. 
 
 37 
 
38 AMERICAN HIGHWAY ASSOCIATION 
 
 Cuts and Fills 
 
 In grubbing roots and breaking hard ground to a shallow depth, 
 a rooter plow is often used, which is a heavy type of subsoil plow 
 made for the purpose. The road plow is a heavy form of turning 
 plow used in hard ground where the cuts are shallow. Either 
 type is drawn by four to eight horses or a tractor. Plows are 
 also specially made for pushing soil already loosened from ditches 
 toward the center of the road. 
 
 When the cut is more than a few feet in depth and the mate- 
 rial loosened with difficulty, it is often blasted. The fastest and 
 most economical method of doing this is to sink holes across the 
 cut on a line back from the face a distance about one-fourth 
 greater than the depth of the cut and about the same distance 
 apart. When the cut is 6 feet or more deep, the line of holes 
 is kept about 6 feet from the face and the holes are sunk about 
 6 feet apart. They are loaded with a low-strength explosive 
 and care must be taken not to loosen the ground below the fin- 
 ished grade line. The use of explosives in road grading in other 
 material than rock has been extending rapidly on account of its 
 low cost and the rapid progress that can be made under suitable 
 conditions, for the blasts leave the clay or hardpan in a broken 
 up condition making it easy to handle. On side-hill cuts in heavy 
 ground, where the slope is steep and there is some question about 
 the security of an embankment to carry the outer part of the 
 road, a safe roadway can often be blasted out of the hill at a cost 
 comparing favorably with a road partly supported by a retain- 
 ing wall. Even on easier slopes, where a long side-hill cut in 
 heavy ground must be made and the excavated material can be 
 employed as an embankment to carry the outer part of the road- 
 way, the excavation is often made by blasting. Blasting is 
 also an effective method of breaking up stumps and boulders. 
 
 Where the material is easily handled and can be dumped within 
 100 feet of the cut, slip scrapers are generally regarded as the 
 least expensive equipment. The Fresno scraper is regarded as 
 better than the slip scraper for hauls exceeding 100 feet. If the 
 haul exceeds 100 feet and is under 1000 feet, wheel scrapers are 
 ranked highly. The large sizes are most desirable for econ- 
 omy on hauls over 600 feet. The material is usually plowed so 
 the wheelers can be loaded easily, and it is necessary to have 
 about one of them for every 100 feet of haul in order to work 
 most economically. Bottom-dump wagons can be made to give 
 very low hauling costs if enough are provided so that while one is 
 being loaded at the cut, the driver and team which brought it in 
 can be used in hauling a loaded wagon. 
 
 In recent years traction steam shovels have been growing stead- 
 
EAKTH AND SAND-CLAY EOADS 39 
 
 ily in favor for road grading. They make shallow cuts as easily 
 as deep cuts, and have taken out earth and rock at very low 
 figures when the equipment for removing the excavated mate- 
 rial was properly selected and used so as to keep the shovel work- 
 ing most of the time. The economy of steam shovel operation 
 depends upon the proportion of the working day that it is ac- 
 tually digging, and this depends upon having wagons or cars 
 ready to receive the excavated material. The wagons or cars 
 may often be run along the top of the bank of a shallow cut 
 and kept moving in a continuous line, saying the delay of turn- 
 ing and backing up to the shovel, which is necessary when 
 they move over the graded cut. The utility of a shovel on road- 
 work is increased if it can be employed in a gravel pit or quarry 
 when not grading. 
 
 The bottom of the cut should be carried down approximate- 
 ly parallel to the finished cross-section, and care should be taken 
 not to disturb the material below the grade line. In very heavy 
 ground, the final trimming is sometimes done by hand, but gen- 
 erally a road machine can be used to advantage. 
 
 Where a fill is made, the surface must be cleared. Stumps 
 should be grubbed out 1 and all large material liable to decay 
 should be removed, for if left in place the fill will settle as it rots 
 or have loose places likely to retain moisture. If the fill is on 
 a steep side-hill, the latter should be cut into a series of level 
 benches or steps and the drainage should receive careful atten- 
 tion. If the hill has a gentle slope, it is usually sufficient to plow 
 parallel furrows, which will furnish a sufficiently uneven surface 
 to hold the fill. The object in any case is to unite the material 
 in the bottom of the embankment with that of the hillside. 
 
 If the road will be maintained as an earth road for several 
 years, so it will have ample time to become consolidated under 
 traffic before any surfacing is applied, there is usually little rea- 
 son for limiting the thickness of the layers in which the embank- 
 ment is built. But if a surfacing is to be given the road at an 
 early date, the layers should not exceed 2 feet for high fills and 
 1 foot for low fills. The teams and scrapers moving over the 
 fill compact it to some extent. Formerly little attention was 
 paid to smoothing the surface of the layers, but of late this has 
 been considered important in some states and drags are kept 
 at work on a bank a large part of the time. George W. Cooley, 
 State engineer of Minnesota, has explained this leveling work 
 as follows: 
 
 1 It is not customary in the South to require green stumps and roots to 
 be grubbed where the fill over their tops is as much as 18 inches. Any 
 matter in process of decay must be removed but a green stump sealed in a 
 fill so that air will not reach it lasts forever. 
 
40 AMEEICAN HIGHWAY ASSOCIATION 
 
 In Minnesota the plan has been adopted in the construction of earth 
 roads to require the continual use of a drag or planer on grade building. 
 This latter plan has been found very efficient and renders future work on 
 the surface less expensive, besides tending to produce a more compact 
 road bed. The tool found most satisfactory in this work is that known 
 as the "Minnesota road plane," which consists of the two blades of an ordi- 
 nary road drag, fixed between a pair of runners about 14 feet long, the blades 
 set at an angle of about 60 degrees to the runner and made rigid or adjust- 
 able as may be deemed best. The planer is hauled on a line parallel with 
 the axis of the road and its operation is similar to that of the ordinary drag, 
 with the additional advantage of making a smoother surface. The old 
 style drag without runners has a tendency, especially on new work, to 
 increase the waves or undulations frequently occurring on road construc- 
 tion, while the planer eliminates these faults and as a general maintenance 
 tool has proved the most satisfactory. 
 
 All embankments settle or "shrink" for some time after they 
 have been built. If the material is broken into small pieces and 
 trampled by teams, the shrinkage will be less than if it is dumped 
 in large masses. There is little shrinkage in a well-built earth 
 dam to impound water, but road embankments need not be 
 built so carefully, and it is probably desirable to allow for at 
 least 10 per cent shrinkage of embankments over 3 feet high and 
 at least 15 per cent for those under 3 feet. If loamy material is 
 used in the embankments the shrinkage will probably be greater 
 than this. 
 
 Grader Work 
 
 A large part of the earth roads now built or reconstructed are 
 made with road machines. These are built in many sizes for 
 both horse and tractor hauling, and serve a variety of purposes 
 in an economical manner. They are not adapted for making 
 cuts and fills, although frequently employed in shaping a road 
 after the grading has been done. The method of using the 
 machine on construction is explained in the following instruc- 
 tions prepared by W. S. Gearhart, State engineer of Kansas: 
 
 In building new roads with a road grader the dead weeds and grass 
 should first be burned off before any grading work is done, and the width 
 of the road to be graded should be staked so the ditches can be properly 
 lined up. Then plow a light furrow with the point of the grader blade, 
 carrying the rear end of the blade well elevated. 1 On the second round 
 drive the wheels in line with the point along the hollow made the first 
 round, plowing a full furrow with tne advance end of the blade, dropping 
 the rear end somewhat lower than before. The third time mova toward 
 the middle of the road the earth previously plowed, then return to the 
 ditch and plow it out deeper, moving the earth toward the middle when- 
 ever as much has been plowed as the machine will move at once. Repeat 
 this process until the ditches are the proper depth, and then cut off the 
 outer slopes of the ditches by placing one wheel of the grader in the bot- 
 tom of the ditch and the other one on the bank. This can be done easily 
 
 1 A plow is necessary in breaking up the ground except in light soils. 
 
EARTH AND SAND-CLAY ROADS 41 
 
 if the bank is not more than 30 inches above the bottom of the ditch. Then 
 trim the earth to the true cross-section. Thoroughly harrow the loose 
 material with an ordinary straight-tooth harrow if there are no clods, going 
 over it until the bumps have been leveled off, the low places filled up and 
 the material well compacted. If there are sods or tough lumps of earth 
 in the road a disk harrow should be used to pulverize this material, and 
 the disk harrow should be followed by a drag or a straight-tooth harrow 
 to level and smooth the road. No newly graded road can be finished in 
 good shape without using either the harrow or the drag, or both. 
 
 In the later rounds of a road machine, in the final shaping 
 of the road, part of the loose material in the center of the road 
 is pushed back to the shoulders. The settlement on fills will 
 result in losing about 2 feet in the width of the roadway, and the 
 fills should be made wider than the standard sections to allow 
 for this loss. In doing this final work, the blade of the grader 
 is set at an angle of about 45 degrees with the direction of travel, 
 its ends adjusted to the slope of the road, and lowered as a whole 
 on successive rounds. 
 
 If the work is on a scale large enough to warrant the use of two 
 graders hauled by a tractor or roller, a trained grading crew is 
 often able to build a good roadbed at very low cost. Mechani- 
 cal traction has resulted in the development of methods of con- 
 struction impracticable when teams of four to eight horses were 
 employed, and as a general proposition mechanical traction is 
 most economical when the sections to be graded are a quarter 
 of a mile or more long, and there is enough work in the vicinity 
 to keep a tractor busy most of the time. 1 Time lost in standing 
 idle or moving long distances from one grading job to another 
 reduces the economical advantage of a tractor on work not well 
 organized. In many cases the hauling is done by a road roller. 
 Tractors and rollers are particularly good investments where 
 labor and teams are hired at high rates and not always obtainable. 
 Mechanical traction is so much more powerful and rapid than 
 horse traction, that its total saving on road work can only be 
 figured by including the saving in labor charges due to speedy 
 construction. 
 
 Where road grading is carried on by day labor by district offi- 
 cials, preparation is sometimes made for it in late fall or early 
 spring by plowing up the ground along the lines of the ditches 
 and slopes. This disintegrates the sod and prevents the roots 
 of grass and weeds from forming clods which must be broken 
 up by disk harrows or thrown out of the road with forks. While 
 it is allowable to build an embankment on good sod after it has 
 been burned over, neither sod nor any other organic material 
 
 1 Traction grading with heavy road machines is better adapted for some 
 conditions than others, and the advice of an experienced engineer should be 
 obtained before purchasing expensive equipment 
 
42 AMERICAN HIGHWAY ASSOCIATION 
 
 should be allowed in the embankment unless reduced to small, 
 disconnected bits. If clods are left in a fill, particularly in the 
 top, it is very difficult to maintain by dragging a hard, uniform 
 surface free from depressions and waves. 
 
 Grading by machines is often followed up immediately by 
 hand trimming and the removal of loose stone. Easing upon 
 work by leaving steep, untrimmed slopes and uneven ditches 
 results in heavier maintenance expense. 
 
 In organizing grader work, it is desirable to keep on hand re- 
 pair parts of the machines, such as blades and whiffletrees, as 
 well as plow points and other parts of the equipment likely to 
 wear out. The small tools should be selected with care, for 
 observation by efficiency specialists has shown that the shape 
 of a shovel, for example, has considerable effect on the amount 
 of shoveling a man can accomplish in a day. Hard earth cannot 
 be dug economically by the shovel best adapted for loose earth, 
 and neither is best for gravel and broken stone. 
 
 On extensive work the elevating grader has proved an eco- 
 nomical and rapid machine when a mile or more of road can be 
 traversed without turning the outfit. Such a grader is often 
 hauled by a traction engine, which rolls the material it passes 
 over and thus assists materially in making a compact road. The 
 method of using the grader depends upon the nature of the work 
 to be done. In cuts, the grader often discharges the excavated 
 material into wagons driven beside it until full. These wagons 
 haul the material to the nearest fills. In light cuts, the material 
 is deposited on the roadway and moved to the nearest low places 
 in the road by slip or wheel scrapers. The cut is usually started 
 at the shoulder and the grader moves toward the roadside on 
 successive rounds, so that the excavated material is deposited 
 nearer and nearer to the center of the road by the elevating and 
 discharging device. The road should be dragged during con- 
 struction, and as soon as the rough grading is finished it should 
 be shaped at once. In this connection attention is called to 
 the following comment by the Iowa highway commission: 
 
 The impassable condition to which some contractors and county road 
 crews reduce their roads while cuts, fills and other improvements are being 
 carried out, is absolutely inexcusable. The worst conditions usually 
 arise at leveling or smoothing up while dumping is in progress. The dirt 
 of the fill so dumped packs in humps so that sometimes it is impracticable 
 to eradicate the unevenness for years. A little care in spreading the dirt 
 evenly at the time of dumping results in the fill packing in thin, even lay- 
 ers instead of humps. Such a road is travelable during construction, 
 and when the fill is completed the job is done. A Marshall County road 
 crew solved the problem by keeping a light road drag at hand. From time 
 to time a team was unhooked from a scraper and hitched to this. A few 
 minutes work put the freshly dumped material into thin layers instead 
 of humps. 
 
EAKTH AND SAND-CLAY ROADS 43 
 
 The utility of a road roller on earth roads is generally under- 
 estimated. After the earth has been given as much crown as 
 the road can have and still enable the traffic to use its entire sur- 
 face readily, any further improvement of the surface drainage 
 must be attained by decreasing the porosity of the earth. This 
 can be done by oiling the road as described later in the section 
 on Surface Applications, and by reducing the pores of the earth 
 by rolling. The latter is particularly useful in compacting places 
 of a yielding character. Many counties have purchased rollers, 
 placed them in charge of competent men, and rent the outfits 
 to the townships as the latter need them. In some cases, a roller 
 is bought by a number of townships, acting as a whole. The 
 work of a roller outfit is likely to be unnecessarily expensive if 
 it is not carefully planned so as to avoid long journeys to do small 
 jobs. 
 
 Dragging 
 
 Earth roads under light traffic can be kept in good condition 
 during a large part of the year by dragging and proper care of 
 the ditches. It is an axiom in road maintenance that defects 
 in the surface of a road should be remedied as soon as they 
 appear, because traffic will develop them quickly. The earth 
 road is particularly subject to injury because it does not have 
 hard stone locked in place to resist the destructive effect of horses' 
 shoes, narrow tires and pneumatic tires. On the other hand it 
 is more easily repaired than any other road, because as soon as 
 its surface is wet by rain the ruts and holes can be filled by haul- 
 ing a drag over the surface. This scrapes material from the 
 high points into the depressions and rubs down the whole sur- 
 face. The following explanation of the nature of the improve- 
 ment has been given by A. R. Hirst, State highway engineer 
 of Wisconsin: 
 
 If a sample of moist earth is taken from the traveled portion of a road 
 over a gumbo, clay or black prairie soil, it will be found practically imper- 
 vious to water, as may be proved by forming a roughly shaped dish of damp 
 earth and filling it with water. It will be noticed that the dish is practi- 
 cally water-tight. Earth in this condition is what the clay workers call 
 puddled. It has been worked and reworked by the carriage wheels and 
 animals' hoofs until nearly all the traveled portion of a sticky muddy 
 road is covered with a layer of this impervious, puddled earth. As usually 
 found on most of the roads, this puddled earth is full of holes and ruts, 
 which are filled with water that cannot escape through the impervious 
 soil. As long as the water remains the soil cannot dry out and the road 
 is kept in a most uncomfortable if not impassable condition. It is also 
 a matter of observation that this puddled earth when compressed and dried 
 becomes extremely hard. On these two facts, the imperviousness of pud- 
 dled earth and its hardness when dried, rests the theory of road dragging. 
 
44 AMERICAN HIGHWAY ASSOCIATION 
 
 f When the road drag is properly used it spreads out the layer of imper- 
 vious soil over the surface of the road, filling up the ruts and hollows until 
 a smooth surface is secured. As a small amount of material is always to be 
 pushed to the center, a slightly rounded effect will be given to the road, 
 which may be increased or decreased as desired by subsequent dragging. 
 By forcing the mud into the hollows and ruts it is evident that the water 
 must go out, which it does by running off to the side of the road. The 
 drying out of the road is thus much facilitated and the road is made imme- 
 diately firmer because the water is squeezed out. The effect of traffic 
 over the road tends to press down and thoroughly compact each thin 
 layer of puddled earth which the drag spreads over the surface every time 
 it is used. After the first few draggings it will be noticed that the road is 
 becoming constantly smoother and harder so that the effect of a rain is 
 scarcely noticeable, the water running off the surface which is so smooth 
 and hard as to absorb but little of it. 
 
 The drag is an old implement. It was described in a book by 
 William Gillespie published in 1851 and widely used by stu- 
 dents of engineering and public officials, yet the drag did not 
 come into favor until about 1900. Even today it is not used on 
 more than a small percentage of the roads where it should be 
 employed regularly. It has a number of forms, the essential 
 feature being two parallel blades held vertically or nearly so 
 about 2J feet apart by a frame of some sort. The bottom of 
 each blade scrapes over the surface of the road. The rear blade 
 projects 12 to 16 inches to one side of the front blade so that 
 when the drag is pulled at an angle of 30 degrees, the ends of the 
 blades will be on a line parallel with the center of the road. The 
 drag is hauled by a chain, to which the team can be hitched at 
 points that will make the drag lie diagonally on the road as it is 
 pulled along. The manner of its use has been described sub- 
 stantially as follows by the United States Office of Public Roads. 
 
 Under ordinary circumstances the position of the hitching link on the 
 draw chain should be such that the runners will make an angle of from 
 60 degrees to 75 degrees with the center line of the road, or in other words, 
 a skew angle of from 15 degrees to 30 degrees. It is apparent that by 
 shifting the position of the hitching link the angle of skew may be in- 
 creased or diminished as the conditions require. When dragging imme- 
 diately over ruts or down the center of the road after the sides have been 
 dragged, it is usually preferable to have the hitching link at the center of 
 the chain and to run the drag without skew. When the principal pur- 
 pose of the dragging is to increase the crown of the road, the drag should 
 be sufficiently skewed to discharge all material as rapidly as it is collected 
 on the runners. On the other hand, if depressions occur in the road sur- 
 face, the skew may perhaps be advantageously reduced to a minimum, thus 
 enabling the operator to deposit the material which collects in front of the 
 runners at such points as he desires by lifting or otherwise manipulating 
 the drag. It is impracticable to prescribe even an approximate rule for 
 fixing the length of hitch, because it is materially affected by the height 
 of the team and the arrangement of the harness, as well as by the condi- 
 tion of the road surface. Experience will soon teach the operator, however, 
 when to shorten the hitch in order to lessen the amount of cutting done 
 
EAETH AND SAND-CLAY ROADS 45 
 
 by the front runner and when to lengthen it in order to produce the oppo- 
 site effect. Care should be taken that a ridge, often called a ''potato 
 ridge," is not left in the center of the road. 
 
 When the road surface is sufficiently hard or the amount of material 
 which it is desired to have the drag move is sufficient to warrant the oper- 
 ator standing upon the drag while it is in operation, he can greatly facili- 
 tate its work by shifting his weight at proper times. For example, if it is 
 desired to have the drag discharge more rapidly, the operator should move 
 toward the discharge end of the runners. This will cause the ditch end 
 of the runners to swing forward and thus increase the skew angle of the 
 drag. The operator may, of course, produce the opposite effect by moving 
 his weight in the opposite direction. In the same way, he can partially 
 control the amount of cutting which the drag does by shifting his weight 
 backward or forward, as the case may be. 
 
 The rule frequently cited, that all earth roads should be dragged 
 immediately after every rain, is in many cases entirely imprac- 
 ticable and is also very misleading because of the conditions 
 which it fails to contemplate. It is true that there are many 
 road surfaces composed of earth or earthy material which do 
 not become very muddy under traffic, even during long rainy 
 seasons, and since such surfaces usually tend to harden very 
 rapidly as soon as the weather clears up, it may be desirable to 
 drag roads of this kind immediately after a rain. Such roads, 
 however, would not ordinarily need to be dragged after every 
 rain, because of the strong tendency that they naturally possess 
 of holding their shape. On the other hand, many varieties of 
 clay and soil tend to become very muddy under only light traffic 
 after very moderate rains, and it is evident that roads constructed 
 of such materials could not always be successfully dragged imme- 
 diately after a rain. Sometimes, in fact, it may be necessary 
 to wait until several consecutive clear days have elapsed after 
 a long rainy spell before the road is sufficiently dried out to keep 
 ruts from forming almost as rapidly as they can be filled by drag- 
 ging. In many cases of this kind, however, it is possible greatly 
 to improve the power of the road to resist the destructive action 
 of traffic during rainy seasons by repeatedly dragging it at the 
 proper time. 
 
 Maintenance by dragging is most successful when well organ- 
 ized. The results obtained by good management in Hopkins 
 County, Kentucky, are frequently cited as indications of this, 
 and for this reason the following account of the work there is 
 quoted from a report by the Kentucky department of highways. 
 
 In 1912 a county engineer was appointed. The county roads were 
 measured under his supervision and 2-mile sections designated, and in 
 January, 1913, drags were started on about 100 miles of the county roads. 
 This original contract was only for dragging the roads, which work was 
 to be done four times between January 1 and April 1, at a cost of $10 to 
 $12 per mile. As the sections dragged were not continuous, the citizens 
 
46 AMERICAN HIGHWAY ASSOCIATION 
 
 at once appreciated the difference between the maintained road and that 
 which was not maintained. Consequently the next contract, which 
 called for dragging and also for cleaning the ditches for six months, until 
 November, 1913, resulted in contracts for 150 miles of road and at a re- 
 duced cost. In November, 1913, a contract substantially like that now 
 in use was adopted and the time of the contract was for one year, or until 
 November, 1914. Over 200 miles were maintained this year at an average 
 cost of $28 per year per mile. For the year from November, 1914, to No- 
 vember, 1915, the benefit of the maintained roads was so well understood 
 by the citizens that 560 miles were under contract at an average cost of 
 $24.35 per mile per year. 
 
 In November, 1915, a two-year contract was entered into, which the 
 county may revoke for non-performance of the obligation at the end of 
 the first year. About 520 miles are now under contract, at prices ranging 
 from $12 to $40 per mile per year, the average being $22. 10. It is expected 
 this mileage will soon be increased. Originally a contractor was allowed 
 to have charge of 8 miles, but now he is not allowed to contract for more 
 than 4 miles of road. Under the 1915 contracts the contractor must trim 
 the branches which overhang and interfere with travel on the roadway; 
 keep the roadway between ditches free from shrubbery and weeds; keep 
 the ditches clean, free from obstructions, and at all times capable of car- 
 rying the water. ' 'He shall by June 1 each year grade the roads with dump 
 scraper, grader, drag and ditcher, or in any way he may see fit, so that the 
 center of the roadway shall be crowned so that the water will flow from the 
 center of the road to the side ditches, and at no place will the water stand 
 on the road or run down the road. The road shall be dragged from ditch 
 to ditch at each dragging, when the road is wet, but not sticky." 
 
 A record of the number of draggings is kept by the county engineer 
 on cards which, before mailing by the contractor, are countersigned by the 
 rural route carrier or a reliable citizen. The contractor also hauls ma- 
 terial and constructs all culverts and bridges of 10-foot span or under, and 
 keeps the approaches to and the floors and abutments of all bridges and 
 culverts on his road in good traveling condition. An analysis of these 
 contracts shows that where the contract has been faithfully executed 
 there is a decrease each year in the cost per mile, mainly because the far- 
 mer contractor has learned from experience that continuous maintenance 
 makes a lower cost of time and labor each succeeding year. 
 
 In the semi-arid regions, the soil is often of a very light nature, 
 so lacking in adhesive qualities that strong winds or flowing 
 water erode it and travel abrades it rapidly into fine dust. It is in 
 its best condition to carry travel when it is moist, but if it be- 
 comes saturated with water it is almost impassable. Chuck 
 holes a foot deep are formed in dry weather in an earth road 
 through such soil, and as they become filled with light dust they 
 are a serious impediment to easy travel. Clay or gravel con- 
 taining clay improves the roads when worked into them. The 
 ditches should be wide and shallow, rather than deep, and the 
 crown should be rather low for an earth road, in order to retain 
 moisture in the roadbed. For the same reason, all grading and 
 ditching are best done just before or during the rainy season, 
 in order to have plenty of water to pack the soil. On account 
 of the pulverulent nature of the material, the ends of all culverts 
 
EARTH AND SAND-CLAY ROADS 47 
 
 must be planned carefully and riprap or some other material 
 placed to prevent erosion about the inlets and outlets. The main 
 problem with earth roads in such soils is to keep the roadbed 
 damp and to incorporate with it adhesive or fibrous material 
 which will act as a binder. 
 
 Sand-Clay Roads 
 
 The grains of which sand is composed are usually hard and 
 tough and able to resist abrasion if held securely in place. In 
 an asphalt pavement they are held by the asphalt and a wearing 
 surface of great resistance to abrasion results. In a sand-clay 
 road they are bound together by clay in a less firm manner but 
 one giving excellent results on well-drained roads carrying light 
 traffic. The aim of the builder of such a road is to employ just 
 enough of the stickiest clay at his command to fill the pores of 
 the sand and to mix these materials together so thoroughly that 
 there are neither lumps of clay nor pockets of loose sand left in 
 the surfacing. This gives the maximum amount of hard sand 
 to carry the traffic and the minimum amount of clay to bind it. 
 More sand makes a less durable road and more clay makes one 
 which becomes soft more rapidly when wet. 
 
 There is a great difference in the value of different clays for 
 such work. Some of them become dough-like when mixed with 
 a certain amount of water and can be molded into objects which 
 retain their shape after drying. If these molded objects are im- 
 mersed in water they will retain their form for a long time. These 
 varieties are called "plastic clays" and the most plastic are 
 called "ball clays." There are other varieties which fall to pieces 
 more or less quickly when wet, as quicklime does, and they are 
 therefore called "slaking clays." They are more easily mixed 
 with sand than the plastic clays but they have much less bind- 
 ing power and a road built with them is less durable when dry 
 and more easily rutted when wet. The amount of clay to be used 
 can be determined by a simple field test described as follows 
 by Andrew P. Anderson: 
 
 From typical samples of each of the available clays, test mixtures, 
 varying by one-half part, are made with the sand so that each clay is rep- 
 resented by a set of mixtures ranging by successive steps from one part 
 sand and three parts clay to four parts sand and one part clay. These 
 are worked up with water into a putty-like mass and from each mix 
 two equal quantities are taken and rolled between the palms of the hands 
 into reasonably true spheres, labeled and placed in the sun to dry. When 
 thoroughly baked, a set of spheres representing any one clay is placed in 
 a flat pan or dish and enough water poured gently into the pan to cover 
 them, care being taken not to pour the water directly on the samples. Some 
 samples will begin to disintegrate immediately. Those breaking dowo 
 
48 AMERICAN HIGHWAY ASSOCIATION 
 
 most slowly contain most nearly the proper proportion of sand and clay 
 for the particular materials. The relative binding power of the various 
 clays may then be determined by comparing the hardness and resistance 
 to abrasion of the various dry samples having the correct proportion of 
 sand and clay, as determined by the water tests. 
 
 In February, 1917, representatives of 21 state highway depart- 
 ments and of the U. S. Office of Public Roads recommended the 
 following mixtures for hard, medium and soft classes of sand-clay 
 roads. 
 
 Hard class: Clay, 9 to 15 per cent; silt, 5 to 15 per cent; total 
 sand 65 to 80 per cent; sand retained on a 60-mesh sieve, 45 to 
 60 per cent. 
 
 Medium class: Clay, 15 to 25 per cent; silt, 10 to 20 per cent; 
 total sand, 60 to 70 per cent; sand retained on a 60-mesh sieve, 
 30 to 45 per cent. 
 
 Soft class: Clay, 10 to 25 per cent; silt, 10 to 20 per cent; 
 total sand, 55 to 80 per cent; sand retained on a 60-mesh sieve, 
 15 to 30 per cent. 
 
 By clay is meant material separated by subsidence through water 
 and possessing plastic or adhesive properties ; it is generally below 
 0.01 mm. in diameter. By silt is meant the fine material other 
 than clay which passes a 200-mesh sieve and is generally from 0.07 
 to 0.01 mm. in diameter. By sand is meant the hard material 
 which passes a 10-mesh sieve and is retained on a 200-mesh sieve, 
 and is generally from 1.85 to 0.07 mm. in diameter. 
 
 The larger part of the following explanation of the construc- 
 tion of sand-clay roads was prepared by W. S. Keller, State 
 engineer of Alabama, where many miles of sand-clay roads have 
 been built and are giving good satisfaction: 
 
 Every farmer who lives in a section of country where both sand and 
 clay are prevalent, is more than likely traveling over a section of natural 
 sand-clay road but is ignorant of the fact. He can call to mind some 
 particular spot on the road he travels, though it may not be more than 100 
 feet in length, that is always good ana rarely requires the attention of the 
 road hands. Good drainage will be noticed at this place and if he takes 
 the trouble to investigate, he will find that a good mixture of sand and 
 clay forms the wearing surface. If this 100 feet of road is always good 
 then the entire road can be made like it provided man will take advantage 
 of the lesson taught by nature and grade the road so that the drainage 
 will be good and surface the balance of the road with the same material. 
 If it is not possible to find this ready mixed surfacing material convenient 
 to the road it may be possible to find the two ingredients in close proximity. 
 In case the road after grading shows an excess of sand, clay should be 
 added, or in case clay predominates, sand should be added to produce 
 good results. There are four general ways in which sand-clay roads may 
 be built: 
 
 1. Ready mixed sand and clay placed on clay, sand or ordinary foun- 
 dation. 
 
 2. Sand and olay placed on soil foundation and mixed. 
 
EARTH AND SAND-CLAY ROADS 49 
 
 3. Clay hauled on a sand foundation and mixed with the sand. 
 
 4. Sand hauled on a clay foundation and mixed with the clay. 
 Taking up the various methods in order: 
 
 1. A natural mixture of sand and clay can often be found where the 
 two materials are found separate. The most important point is to know 
 the natural mixture when seen. The very best guide to this is to find a 
 natural piece of good road. A sample from the best of this good section 
 will, by comparison, indicate what is required, close to the road to be sur- 
 faced. This natural mixture of sand and clay can be noticed where red 
 clay and sand crop out, usually well up in the hills, having in ditches and 
 cuts the appearance of red sandstone. A good stratum of well mixed 
 sand and clay will otand perpendicular in cuts and ditches, resisting ero- 
 sion almost as well as sandstone. A test of the best natural sand-clay 
 mixtures will show the sand forms about 70 per cent of the whole. The 
 test is very simple. Take an ordinary medicine glass, measure 2 ounces 
 of the mixture into the glass and wash out the clay. Dry the remaining 
 sand and measure again on the medicine glass. The loss will be the amount 
 of clay originally contained in the mass. 
 
 Before placing any sand-clay on the road, the road should be graded 
 to the desired width. The surface of the graded road should be flat or 
 slightly convex. The sand-clay should be put on from 8 to 12 inches in 
 thickness, depending on the character of the subgrade or foundation. 
 With a hard clay for foundation, 8 inches of sand clay will suffice. If the 
 subgrade is sand it is well to put on as much as 12 inches of the surfacing 
 material. After a few hundred feet of surfacing material has been placed, 
 a grading machine should be run over it to smooth and crown the road 
 surface before the top becomes hard and resists the cutting of the blade. 
 It is a good plan to turn the blade of the machine so as to trim the edges 
 of the surface part, discharging the excess sand and clay onto the earth 
 shoulders. After one round trip with the blade turned out, the remaining 
 dress work with the machine should be with the blade turned in, with the 
 exception of one trip down the center of road with the blade at right angles 
 to the axis of the road for the purpose of distributing any excess of mate- 
 rial left in the center. 
 
 After the machine work, it is well to follow with a drag, which smooths 
 any rough places left by the machine and leaves the road with a smooth, 
 even surface. A sand-clay road, unlike other roads, cannot be finished 
 in a short space of time. It can be left in an apparently finished condi- 
 tion with a hard smooth surface, but it will be found on close examina- 
 tion that the hard surface is in reality only a crust, below which there are 
 several inches of loose material. After the first hard rain the crust soft- 
 ens, the road becomes bad and the work appears to be a failure. This, 
 however, is just what is needed to make it eventually good. After the 
 surface has dried until the mass is in a plastic state, it should be dragged 
 until the surface is once more smooth, with proper crown, and should be 
 kept this way by dragging at least once a day until the sun has baked it 
 hard and firm. The mistake of keeping traffic off during this process of 
 resetting should not be made. The continuous tamping of the wheels of 
 wagons and hoofs of horses is just what is needed to compact the sand- 
 clay into a homogeneous mass. The ordinary roller is not very effective 
 in this work, but corrugated rollers have given excellent results. One 
 type which is widely used has 18 cast-iron wheels weighing 300 pounds 
 each, which compress the bottom of the mixture first. As the material 
 becomes more and more compact the wheels ride higher and higher and 
 finally the surface is so hard that the roller does not sink into it at all. A 
 drag is an indispensable machine in the construction of any kind of sand- 
 olay road. 
 
50 AMERICAN HIGHWAY ASSOCIATION 
 
 2. Sand and clay placed on a soil foundation and mixed. This is nec- 
 essary where the old road has neither a sand nor clay foundation and it 
 is impossible to find the two ingredients ready mixed, but possible to get 
 both in separate state near at hand. The clay should first be placed 
 on the road to a depth of 4 inches and the required width. It is not 
 wise to place more than a few hundred lineal feet of clay before the 
 sand is hauled, as the clay rapidly hardens and makes the mixing process 
 difficult. After, say, 400 feet of clay has been placed, the clay should be 
 broken by means of a plow and harrow, if it has become hard, and sand to 
 a depth of 6 inches placed on it. This should be plowed and harrowed in 
 thoroughly. This is best done immediately following a rain, as the two 
 can be more satisfactorily mixed. The traffic aids the mixing and should 
 be encouraged on the road. After the mass appears to be well mixed, the 
 road should be properly shaped, as previously explained. The road should 
 be given watchful attention and should sand or mud holes appear, a second 
 plowing and mixing should be given it. 
 
 3. Clay hauled on a sand foundation and mixed with the sand. The 
 mixing process is similar to that described under second head. It is only 
 necessary to add that as the foundation is sand, a little more clay will be 
 necessary than where the foundation is of clay or soil. 
 
 4. Sand hauled on a clay foundation and mixed with clay. The clay 
 foundation should be plowed to a depth of 4 inches and harrowed with a 
 disk or tooth harrow until the lumps are thoroughly broken or pulver- 
 ized. Sand should then be added to a depth of 6 inches and mixed as be- 
 fore described. 
 
 Sand and clay can be mixed best when wet, but as most road construc- 
 tion is done in the summer months, it is necessary to do most of the mix- 
 ing dry and keep the road in shape after the first two or three rains, while 
 the passing wagons and vehicles give the road a final wet mixing. A sand- 
 clay road is the cheapest road to maintain, for the reason that it can be 
 repaired with its own material. With a drag or grading machine ruts 
 can be filled with material scraped from the edges, whereas on gravel or 
 macadam roads, this is not possible. The repairing of these roads can be 
 done almost exclusively with the drag, only enough hand work being re- 
 quired to keep the gutters open and the growth of weeds cut on the should- 
 ers. Holes are repaired by adding more sand-clay, and when many of them 
 appear fresh sand-clay should be spread over the surface of the road. If 
 the road gets into really bad condition, the roadbed should be plowed up, 
 reshaped and fresh sand-clay added. This is unnecessary where the road 
 is maintained properly and the travel is not too heavy for the type of 
 construction. 
 
GRAVEL ROADS 1 
 
 At the close of 1914, 45 per cent, of the surfaced roads in the 
 United States were gravel roads, as shown in detail in a table in 
 Part III of this volume. The presence of good gravel in many 
 parts of the country and the low cost of constructing and main- 
 taining gravel roads will make them a leading type for many 
 years to come. 
 
 Some gravels are much better for road construction than 
 others. In Michigan, where three-fifths of the surfaced roads 
 are built of gravel, the value of this material for the purpose 
 is held to vary with the percentage of pebbles in it, the road- 
 building value of the rock of which the pebbles are composed, 
 and the cementing properties of the fine material mixed with the 
 pebbles. In this State at least 60 per cent by weight of the 
 gravel for state reward roads must be pebbles larger than J-inch. 
 No pebbles larger than 2J inches are used in the bottom of the 
 road and none larger than 1J inches in the top. The binder 
 required for holding the pebbles together is clay, uniformly mixed 
 with the pebbles, free from lumps, and amounting to not over 
 10 per cent of the total weight of the gravel. 
 
 There is a large mileage of gravel roads in New Jersey, and 
 as a result of experience with them, the State highway depart- 
 ment rejects gravel with over 5 per cent retained on a Ij-inch 
 circular opening and over 35 per cent retained on a ^-inch cir- 
 cular opening. Three grades are recognized. Grade A is a 
 pebble gravel with a clay binder with not less than 25 nor more 
 than 35 per cent retained on a J-inch circular opening, not less 
 than 40 nor more than 60 per cent retained on a 10-mesh sieve, 
 not less than 8 nor more than 20 per cent passing a 200-mesh 
 sieve, and the balance a fairly well graded sand. Grade B is a 
 sandy gravel depending upon oxide of iron for its cementing 
 properties, with 20 to 40 per cent retained on a 10-mesh sieve 
 and 10 to 25 per cent passing a 200-mesh sieve. Of this material 
 passing a 200-mesh sieve, at least 40 per cent must be soluble 
 in a 1:3 dilution of hydrochloric acid. Grade C is gravel which 
 does not fall under either of the previously mentioned grades but 
 is approved by the engineer for the bottom part of gravel roads. 
 
 1 Revised by Frederic E. Everett, State Highway Commissioner of New 
 Hampshire. 
 
 51 
 
52 AMERICAN HIGHWAY ASSOCIATION 
 
 In Illinois, the State highway department requires the gravel 
 to be rather uniformly graded in size from fine material to peb- 
 bles that will just pass a 3^-inch ring, and not over 15 per cent 
 of the mass (exclusive of clay) passing a f-inch ring. It must 
 not contain over 5 per cent of loam but it must have 15 to 25 
 per cent of clay by dry measure. If a local gravel does not form 
 a good bond, the contractor must supply a bonding gravel for the 
 top f-inch of the road. All of this material must pass a 1-inch 
 screen and contain 40 per cent of pebbles retained on a J-inch 
 screen and from 20 to 30 per cent of clay and loam, not more 
 than 5 per cent being loam. 
 
 The variations in these specifications show the range of prop- 
 erties of the materials found useful by experience. Few attempts 
 have been made to prepare a general specification for road gravel 
 on this account. The following requirements were adopted by the 
 American Society of Municipal Improvements in 1916 and re- 
 commended by the Committee on Materials for Road Con- 
 struction of the American Society of Civil Engineers: 
 
 Two mixtures of gravel, sand and clay shall be used, hereinafter desig- 
 nated in these specifications as No. 1 product (for top course) and No. 2 
 product (for middle and bottom courses.) 
 
 No. 1 product shall consist of a mixture of gravel, sand and clay, with 
 the proportions of the various sizes as follows: All to pass a 1^-inch screen 
 and to nave at least 60 and not more than 75 per cent retained on a J-inch 
 screen; at least 25 and not more than 75 per cent of the total coarse aggre- 
 gate (material over i-inch in size) to be retained on a f-inch screen; at 
 least 65 and not more than 85 per cent of the total fine aggregate (mate- 
 rial under J inch in sizo) to be retained on a 200-mesh sieve. 
 
 No. 2 product shall consist of a mixture of gravel, sand and clay, with 
 the proportions of the various sizes as follows : All to pass a 2 J-inch screen 
 and to have at least 60 and not more than 75 per cent retained on a J-inch 
 screen; at least 25 and not more than 75 per cent of the total coarse aggre- 
 gate to be retained on a 1-inch screen; at least 65 and not more than 85 
 per cent of the total fine aggregate to be retained on a 200-mesh sieve. 
 
 It is evident that the most useful information concerning the 
 value of any gravel for road work is obtained by examining a 
 road built of it. If there is a good gravel road and the source 
 of this gravel is not known, a sample of the gravel can be analyzed 
 mechanically by a portable sand tester, and the gravel deposits 
 in the vicinity tested by the same instrument until one is found 
 showing about the same properties. An exact agreement should 
 not be expected. Tests of the gravel in a satisfactory road in 
 the State of Washington and of the material in the pit from 
 which it was obtained gave the following variations: 
 
GRAVEL ROADS 
 
 53 
 
 Mechanical Analyses of Identical Gravel Sampled at Pit and in the Road 
 
 PASSING 
 
 PIT 
 
 ROAD 
 
 PASSING 
 
 PIT 
 
 ROAD 
 
 PASSING 
 
 PIT 
 
 ROAD 
 
 200 sieve 
 100 sieve 
 80 sieve 
 50 sieve 
 40 sieve 
 
 per cent 
 
 4.1 
 8.0 
 6.6 
 16.3 
 13.1 
 
 per cent 
 
 6.4 
 8.1 
 4.7 
 7.4 
 6.9 
 
 30 sieve 
 20 sieve 
 10 sieve 
 8 sieve 
 4 sieve 
 
 per cent 
 
 10.2 
 14.7 
 14.5 
 2.6 
 5.2 
 
 per cent 
 
 6.5 
 12.1 
 12.7 
 3.4 
 9.5 
 
 2 sieve 
 f inch 
 1 inch 
 1J inch 
 1? inch 
 
 per cent 
 
 3.5 
 1.2 
 
 j*r cent 
 
 8.3 
 5.7 
 1.9 
 6.4 
 
 
 
 
 
 Where coarse gravel is composed of rock pebbles giving a 
 cementitious powder some engineers consider it unwise to use 
 enough clay binder to fill the voids. If roads of coarse gravel 
 bound with a large amount of clay are used by many automobiles 
 the pebbles become dislodged and the road does not become hard, 
 it is claimed. Consequently these engineers prefer to use a 
 smaller amount of clay and to allow the traffic to wear down the 
 road and produce the necessary binder by attrition and internal 
 disintegration of the mass of gravel. This process makes it neces- 
 sary to maintain the road carefully for some time after its com- 
 pletion, but is stated to give a better road eventually with some 
 classes of gravel. 
 
 In New England, where gravel roads have been built extensive- 
 ly, it is generally considered safe to use on roads for light traffic 
 the gravel from any pit where the face stands vertical and has 
 to be loosened before it can be shoveled. Other gravels usually 
 have to be supplied with a binder. It is always desirable to make 
 a careful search for all deposits of gravel and an examination 
 of the quality of each before deciding upon the deposit to use. 
 In Dubuque County, Iowa, for instance several months were 
 spent in such an investigation because the local limestone was 
 too soft for road use. Finally a satisfactory pit was found 1J 
 miles from the road to be improved, and by transporting it on 
 a light narrow-gauge railway :to the road and then distributing 
 it by branches of this railway and by motor trucks and dump 
 wagons, its cost on the road was kept down to a satisfactory 
 figure. 
 
 Preparing the Gravel 
 
 The management of the gravel pit should receive enough study 
 and attention to make sure that the material is delivered to the 
 wagons or cars at the lowest cost. The organization for the 
 purpose will depend upon the location of the pit, the quality of 
 the gravel and the quantity of material to be taken out. Where 
 there is only a small percentage of the gravel which is over size, 
 
54 AMERICAN HIGHWAY ASSOCIATION 
 
 and the remainder runs a uniformly good mixture, the large 
 stones can be removed by a flat gravel screen, or, on small works, 
 can be forked out during loading. It is not always necessary to 
 go to the expense of screening. With a good foreman in the pit 
 it may be possible to get a proper mixture of the material from 
 a pit where the gravel lies in strata of different sized pebbles, 
 provided there is also a good foreman on the road, so that the 
 strippings, if any, will be placed on the shoulders and the over- 
 large material will be used for foundations in low places. 
 
 Where there is a considerable proportion of overlarge stone 
 in the gravel it is customary to set up a crushing and screening 
 plant at the pit. For example, Kane County, Illinois, has an 
 outfit consisting of a jaw crusher, screen, elevator and storage 
 bin holding 15 cubic yards. The gravel is first screened, because 
 by taking out the material of suitable size for road work only the 
 large stone is fed to the crusher and its capacity is thereby much 
 increased. The presence of the small stone in the crusher tends 
 to clog it and retard the breaking of the large stone. The screened 
 and crushed material is discharged by gravity from the bins into 
 the 5-yard motor trucks which are used for delivering it. The 
 pit material is delivered to the screen by a belt conveyor, 18 
 inches wide and 40 feet long. One end of the belt is under a plat- 
 form having a hopper over the belt. The gravel is brought by 
 slip scrapers to the platform and dumped through the hopper 
 onto the conveyor. 
 
 In some plants of this character the gravel is run over a bar 
 screen or "grizzly" which holds back all oversize stone and delivers 
 it to the crusher. This keeps the large stone entirely out of the 
 screen. In Wisconsin work the screen has $-inch perforations 
 for the first half of its length and If -inch perforations for the 
 second half, giving three sizes of gravel. The jaws of the crusher 
 are set to give about equal parts of the two coarser sizes separated 
 by the screen. 
 
 As the pebbles composing gravel are rounded and do not lock 
 together as well as broken stone, it is customary to use somewhat 
 smaller sizes of gravel than of crushed stone. Gravel obtained from 
 beaches and rivers is usually more rounded than that from pits 
 and consequently may not be so good for roads, unless suitable 
 binding gravel can be used for a wearing surface or limestone 
 screenings or other good binding material can be used with it. 
 
 Pit-run Gravel Roads 
 
 Many miles of gravel roads have been built by dumping the 
 gravel on the roadbed, spreading it roughly and allowing 
 traffic to consolidate it. The consolidation is a tedious process, 
 
GRAVEL ROADS 
 
 55 
 
 but good roads often result in the end, particularly if the road 
 is kept well dragged so that ruts and holes are prevented. Bet- 
 ter results are obtained, however, if the gravel is rolled after it 
 is spread. The loads of large stone should be dumped at the low 
 or soft places on the roadbed. In deep, mealy sand, the sub- 
 grade is sometimes covered with marsh hay, wet sand or fine 
 
 Cubic Yards of Loose Gravel Required to make One Mile of Road of Dif- 
 ferent Widths and Thicknesses. Based on Table of Commissioner of Pub- 
 lie Roads of New Jersey. 
 
 WIDTH 
 
 THICKNESS OF ROAD AFTER CONSOLIDATION, INCHES 
 
 
 
 7 
 
 8 
 
 9 
 
 10 
 
 11 
 
 12 
 
 feet 
 
 
 
 
 
 
 
 
 6 
 
 880 
 
 ,027 
 
 1,173 
 
 1,320 
 
 1,467 
 
 1,613 
 
 1*760 
 
 7 
 
 1,027 
 
 ,198 
 
 1,369 
 
 1,540 
 
 1,711 
 
 1,882 
 
 2,054 
 
 8 
 
 1,173 
 
 ,369 
 
 1,564 
 
 1,760 
 
 1,956 
 
 2,151 
 
 2,346 
 
 9 
 
 1,320 
 
 ,540 
 
 1,760 
 
 1,980 
 
 2,200 
 
 2,420 
 
 2,640 
 
 10 
 
 1,467 
 
 ,711 
 
 1,956 
 
 2,200 
 
 2,444 
 
 2,689 
 
 2,934 
 
 11 
 
 1,613 
 
 ,882 
 
 2,151 
 
 2,420 
 
 .2,689 
 
 2,958 
 
 3,226 
 
 12 
 
 1,760 
 
 2,053 
 
 2,346 
 
 2,640 
 
 2,933 
 
 3,227 
 
 3,520 
 
 13 
 
 1,807 
 
 2,224 
 
 2,542 
 
 2,860 
 
 3,178 
 
 3,496 
 
 3,614 
 
 14 
 
 2,054 
 
 2,396 
 
 2,738 
 
 3,080 
 
 2,422 
 
 3,764 
 
 4,108 
 
 15 
 
 2,200 
 
 2,567 
 
 2,933 
 
 3,300 
 
 3,667 
 
 4,033 
 
 4,400 
 
 16 
 
 2,346 
 
 2,738 
 
 3,128 
 
 3,520 
 
 3,912 
 
 4,302 
 
 4,692 
 
 17 
 
 2,493 
 
 2,909 
 
 3,324 
 
 3,740 
 
 4,156 
 
 4,571 
 
 4,986 
 
 18 
 
 2,640 
 
 3,080 
 
 3,520 
 
 3,960 
 
 4,400 
 
 4,840 
 
 5,280 
 
 19 
 
 2,787 
 
 3,250 
 
 3,716 
 
 4,180 
 
 4,644 
 
 5,109 
 
 5,574 
 
 20 
 
 2,933 
 
 3,422 
 
 3,912 
 
 4,400 
 
 4,888 
 
 5,378 
 
 5,866 
 
 Cubic Yards of Crushed Stone or Gravel Required to Give Different Depths 
 when Lying Loose on One Mile of Roadways of Different Widths. Based 
 on Table of Wisconsin Highway Commission. 
 
 DEPTH OF LOOSE MATERIAL, INCHES 
 
 SURFACE 
 
 1 
 
 ii 
 
 ti 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 feet 
 
 cu. yds. 
 
 cu. yds. 
 
 cu. yds. 
 
 cu. yds. 
 
 cu. yds. 
 
 cu. yds. 
 
 cu. yds. 
 
 cu. yds. 
 
 8 
 
 130 
 
 160 
 
 195 
 
 260 
 
 391 
 
 521 
 
 652 
 
 782 
 
 9 
 
 147 
 
 180 
 
 220 
 
 294 
 
 440 
 
 587 
 
 734 
 
 880 
 
 10 
 
 163 
 
 200 
 
 244 
 
 326 
 
 489 
 
 652 
 
 816 
 
 977 
 
 12 
 
 196 
 
 240 
 
 293 
 
 392 
 
 587 
 
 783 
 
 980 
 
 1,171 
 
 14 
 
 218 
 
 280 
 
 342 
 
 436 
 
 684 
 
 913 
 
 1,141 
 
 1,369 
 
 15 
 
 244 
 
 300 
 
 366 
 
 488 
 
 733 
 
 979 
 
 1,222 
 
 1,466 
 
 16 
 
 261 
 
 325 
 
 391 
 
 522 
 
 782 
 
 1,043 
 
 ,304 
 
 1,565 
 
 18 
 
 294 
 
 367 
 
 440 
 
 588 
 
 880 
 
 1,174 
 
 ,468 
 
 1,760 
 
 20 
 
 326 
 
 400 
 
 488 
 
 652 
 
 978 
 
 1,304 
 
 ,632 
 
 1,954 
 
 22 
 
 359 
 
 440 
 
 537 
 
 718 
 
 1,076 
 
 1,434 
 
 ,796 
 
 2,148 
 
 24 
 
 392 
 
 480 
 
 584 
 
 784 
 
 1,174 
 
 1,564 
 
 ,960 
 
 2,342 
 
56 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 Weight in Pounds Per Cubic Yard of Sand and Gravel. From 
 Resources of the United States, 1915." 
 
 'Mineral 
 
 BTATB 
 
 o 
 E 
 
 4 
 
 OB 
 
 ORAVEL 
 
 STATE 
 
 a 
 
 5 
 
 GRAVEL 
 
 STATE 
 
 a 
 
 03 
 
 3 
 
 
 o 
 
 Alabama 
 California 
 Florida 
 
 2505 
 2645 
 2605 
 2820 
 2700 
 2720 
 2580 
 
 2790 
 
 2895 
 2680 
 3005 
 2945 
 2850 
 2830 
 
 Massachusetts 
 Michigan 
 Minnesota 
 Missouri 
 New Jersey. . . 
 New York .... 
 Ohio. . 
 
 2710 
 2895 
 2865 
 2680 
 2600 
 2590 
 2700 
 
 2810 
 
 2985 
 2880. 
 2840 
 2730 
 2760 
 2830 
 
 Oregon.. . 
 
 2620 
 2500 
 2695 
 2930 
 2570 
 2800 
 2665 
 
 2880 
 2680 
 2910 
 3065 
 2780 
 2970 
 2820 
 
 Pennsylvania 
 Texas 
 Washington. . 
 W.Virginia.. 
 Wisconsin... . 
 Average.. 
 
 Illinois.. 
 
 Indiana. . 
 
 Iowa.. . 
 
 Kentucky 
 
 
 
 NOTE: The average weights were obtained from 670 producers of sand 
 and 560 producers of gravel in all parts of the country; the range was 
 from 2200 to 4000 pounds for sand and from 2200 to 4200 pounds for gravel. 
 The weights given for each state are the averages of the reports from ten 
 or more producers in that State. 
 
 brush to hold the gravel. The stone should be well raked and 
 no stone larger than 2 inches should be allowed in the top of the 
 road. 
 
 It is best to lay the gravel in two courses, each 5 or 6 inches 
 thick when loose. The spreading of the first course begins at the 
 place on the road where the gravel reaches it and in this way 
 the material is consolidated by the teaming over it. When this 
 is very hard work enough clay is sometimes added to pack the 
 gravel. Some engineers require this course to be harrowed. 
 It is desirable to shape this course with a grading machine and 
 roll it, but if the equipment is not available it can be improved 
 by using a drag or a road plane, as described on page 266. 
 
 After a considerable stretch of the bottom course has been 
 finished, the second course can be started, beginning at the end 
 farthest from the gravel pit, so as to have the teaming do as much 
 consolidation work on the bottom course as possible. Some 
 engineers require the entire bottom course to be finished before 
 the second is started. It is best to harrow the second course be- 
 cause pit-run gravel usually needs good mixing and the harrow 
 will bring the large stones to the surface, so they can be thrown 
 aside. If the gravel needs a binder the harrowing will help to 
 distribute it evenly. If too much clay is added the road is likely 
 to rut in wet weather and be dusty in dry weather. After the har- 
 rowing, the surface is shaped with a grader, if one is available, or 
 with a drag or plane. It should then be rolled, and with some 
 gravel the rolling gives the best results if the road is first wet. 
 
 Gravel is a surfacing material, it will not make a defective 
 roadbed good, although it may temporarily improve it. Con- 
 
GRAVEL ROADS 57 
 
 sequently it is best to allow a new roadbed to be used as an earth 
 road for a year, so it will have a chance to settle. If it is kept 
 well dragged during this seasoning period, it will become hard 
 enough to sustain the gravel. If it is known that gravel will be 
 placed after a year's use, the earth road should be dragged to a 
 very flat crown, in order to prevent too much crown in the gravel 
 road. When gravel must be placed on a fresh roadbed, it is 
 sometimes advisable to lay a 6-inch course and allow that to 
 become consolidated by traffic before the second course is laid. 
 If there are any defects in the roadbed they will become apparent 
 during the early use of the road and can be repaired before the 
 completion of the surfacing. If only the bottom course is laid 
 the first season it should be well dragged, for inequalities in the 
 bottom course are usually reproduced in the upper course, no 
 matter how carefully the latter is laid and shaped. 
 
 There are two methods of placing gravel. That usually em- 
 ployed on pit-run gravel roads is called the feather-edge method. 
 The roadbed to receive the gravel is graded to a very small crown 
 and the gravel is spread on it to a nearly uniform thickness until 
 within about 12 inches of the edge, when the bed is sloped off to 
 a mere row of pebbles at the edge. In the second method of con- 
 struction, a shallow trench, sometimes called a "gravel bed" 
 or a "box," is excavated in the top of the roadbed, and the gravel 
 deposited in it. If it rains this trench is likely to become muddy 
 and to prevent this drainage channels should be cut through 
 the shoulders to the side ditches. Bank gravel will become con- 
 solidated and shed water more quickly than stream gravel and 
 it is better suited for the trench method in consequence. The 
 feather-edge method is less expensive and more easily carried 
 on if traffic must be permitted on the road during construction. 
 
 The following explanation of the construction of a two-course 
 feather-edge gravel road was written by H. E. Bilger, road engi- 
 neer of the Illinois Highway Department: 
 
 When the bonding material in the gravel is not entirely satisfactory 
 with respect to both quality and quantity, it is usually advisable that 
 two-course construction be adopted. Whether or not the work is to be 
 done by contract, it is important that there be used some positive and 
 accurate method of determining the volume of gravel delivered upon the 
 roadbed. There are several methods by which this can be accomplished, 
 but experience seems to indicate that by the use of temporary side- 
 board forms the desired results can be assured and this method is not 
 uneconomical. 
 
 Upon the satisfactory completion of the roadbed there should be set 
 thereon, true to line and grade, temporary side forms having a width 
 equal to the depth of the loose gravel, which should be shown on the plans. 
 These boards should be held in place by stakes at such intervals as will 
 prevent lateral deflection greater than about 3 inches from the true align- 
 ment. Whether the gravel is hauled by wagons, motor trucks, industrial 
 
58 AMERICAN HIGHWAY ASSOCIATION 
 
 railways, or other vehicles, it may be dumped directly upon the subgrade. 
 After there has been placed upon the subgrade a sufficient quantity of 
 gravel for the lower half of the road, it should be distributed to a uniform 
 depth by the use of a blade grader, drag scraper, or otherwise. While 
 this course is being spread, all the larger stone should be raked or other- 
 wise placed directly in contact with the subgrade. Upon this course of 
 gravel there should be placed such an amount of bonding clay as may be 
 necessary in order that the gravel will comply with the specifications. 
 
 After the gravel has been spread it should be thoroughly harrowed 
 several times over until the cores formed by dumping it have been entire- 
 ly loosened up to a density equal to that in the other portions of the gravel. 
 The importance of this thorough harrowing can scarcely be overestimated, 
 for in order to secure the results it is essential that the voids in the gravel 
 be reduced to a minimum, which means that a maximum density of mate- 
 rial must be obtained, and this density is closely approached by harrowing 
 until the pebbles of the several sizes become so placed as to occupy the 
 spaces between those of a large size. The cost of this harrowing as com- 
 pared with the results obtained is practically negligible, and if necessary 
 it would actually be more advisable to do away with the rolling and retain 
 the harrowing than to do away with the harrowing and retain the rolling. 
 The harrow should be of the stiff tooth type, and should have metal teeth 
 at least 1-inch in diameter, extending about 6 inches below the frame. 
 The spacing of the teeth should be such as will admit of the free passage 
 of the stones between them, and yet so displace them as to produce the 
 density desired. The design of the harrow should provide a weight of 
 from 8 to 12 pounds upon each tooth. 
 
 After the second course of gravel has been placed, it should be spread 
 until its upper surface comes flush with the top of the side forms and its 
 cross section conforms to that desired. The forms should then be removed 
 and the gravel allowed to take its natural position. Upon this second 
 course there should be distributed the necessary quantity of bonding 
 clay. It should then be thoroughly harrowed several times, as before, 
 until the cores formed by dumping the gravel have been entirely loosened 
 up and the clay has been uniformly distributed throughout. The har- 
 rowing should continue until a uniform density of material is obtained 
 throughout the upper course. 
 
 Having done this, the earth shoulders should be shaped by the nec- 
 essary cutting and filling until the cross section conforms approximately 
 to the finished work. Material other than the natural earth should not 
 be used in forming these shoulders, and all vegetable matter should be 
 strictly prohibited from entering into the work. Upon having shaped the 
 shoulders, the graded roadway over the entire width should be rolled sev- 
 eral times over until it is thoroughly compacted, forming a firm, smooth 
 surface, free from waves and according to the requirement of the plans. 
 The rolling should begin at the extreme outer edges of the shoulders and 
 should work toward the center, at each rolling of the gravel allowing an 
 overlap of one-half of the width of one of the rear wheels, and each wheel 
 should cover the entire gravel surface. 
 
 Should the condition of the gravel or its bonding material be such as 
 not to compact readily under the action of the roller, sprinkling or other 
 means should be employed to compact the gravel as the engineer may 
 direct. The speed of the roller should not exceed about 100 feet per min- 
 ute. It is quite probable that after rolling there will appear either on 
 the shoulders or the gravel certain depressions and other irregularities. 
 To correct these defects suitable material should be added or removed 
 and they should then be rerolled. The finished surface should conform 
 to the cross section shown on the plan and should present a smooth and 
 
GRAVEL ROADS 59 
 
 even appearance. Should the gravel, with its natural or artificial mixture 
 of bonding clay, for the upper 4 inches of the road, be of such character 
 that it will not insure a satisfactory wearing surface with a dense body 
 and uniform texture, a 1-inch coating of bonding gravel should be applied 
 uniformly over the entire surface of the gravel road. This bonding gravel 
 should then be raked and rolled into the road surface until all the inter- 
 stices are filled and the surface is smooth, of a uniform texture and free 
 from waves. 
 
 Screened Gravel Roads 
 
 In some States, preference is given to gravel roads built like 
 macadam roads, the gravel being screened so that the courses 
 will be composed of material of different sizes. This is the case in 
 Wisconsin, for instance. In that State, except on sandy road- 
 beds, construction is started at the end of the road farthest from 
 the gravel supply, when screened gravel is used, because the 
 roller can be run continuously without interfering with the teams 
 bringing the gravel. The first course consists of material from 
 If to about 3 inches in size spread to a loose depth of 6 inches. 
 The voids are filled with gravel under ^-inch in size and the road 
 is then rolled. This course is laid for a distance of about 400 
 feet, and the second course is then started. This consists of 
 about 5 inches of $ to IJ-inch stone with the voids filled like 
 those of the bottom course. The surface is shaped with a grader 
 and rolled and flushed like a macadam road. 
 
 In many instances better results are obtained, according to 
 J. T. Donaghey, chief inspector of the Wisconsin highway com- 
 mission, by crushing the gravel fine enough for practically all 
 the material to pass a If-inch ring. The screen is partly jack- 
 eted so that just enough of the material passing the -inch open- 
 ings is carried into the } to If-inch size to fill the voids in the 
 latter. This mixture is used in both the bottom and top courses 
 and results in a type of road which Mr. Donaghey considers 
 more easily built, more satisfactory and more cheaply maintained 
 than any other gravel type. Where clay is added to assist in 
 binding or there is naturally an excessive amount of clay in the 
 gravel, it is advisable to place a covering of sharp sand or gravel 
 on the finished surface to protect it until the excess clay has worked 
 to the surface and washed off. 
 
 In the work in Kane county, Illinois, to which reference has 
 already been made, George N. Lamb, county superintendent cf 
 highways, places the lower course in a trench or box and rolls it 
 and the shoulders until there is no difference of elevation where 
 they meet. The second course is then placed with the edges 
 feathering out a foot or two over the shoulders. 
 
 The following instructions for preparing the subgrade were 
 issued in 1914 by the Wisconsin highway commission: 
 
60 AMERICAN HIGHWAY ASSOCIATION 
 
 Starting at the desired point, set two stakes opposite the reference 
 stake, the distance between them being the width of the new road. To 
 do this, refer to the grade sheet, which gives the distance from the side 
 stake (placed when the survey was made) to the center of the new road. 
 Subtract from this distance one-half the desired width of road and 
 put in a stake with inside edge at this distance from the reference stake. 
 Opposite this stake place another with its inside edge distant the width 
 of the road from the inside edge of the first one. All stakes forsubgrade 
 should be made of -inch round iron about 24 inches long, and about twenty- 
 five should be kept on each surfacing job. Stake out 700 or 800 feet at a 
 time. Be sure that the stakes are in line, except at bends or on curves. 
 Usually curves will have to be staked out by eye to get good results. 
 
 With a road plow cut as close to the inside edge of stakes as possible 
 withour disturbing them, turning the furrow toward the center of sub- 
 grade. Plow about 5 inches deep. One furrow on each side is generally 
 sufficient. Plow should be equipped with shoe or wheel and coulter. If 
 a rooter is used, three furrows on each side will usually be necessary. Make 
 first cut about 5 inches deep as close to stakes as possible, the next 6 inches 
 nearer the center of the road. Drop the shoe down so rooter will run 
 about 3 inches deep for the third cut, working 6 inches nearer center of 
 subgrade than previous furrow. 
 
 A light grader that can be handled with two horses is best for shaping. 
 Use with the blade so set as to move the plowed ground from the center 
 of trench or subgrade on to the bank outside of stake line. This work 
 cannot be accomplished neatly with the grader alone, as some of the earth 
 will roll back into the trench under the best of conditions. Make the 
 trench deep enough. The depth at the sides should be at least the total 
 loose depth of the two courses of material and more than this on sandy 
 soils. It is much easier to throw out excess material with the road grader 
 after the surface is laid than it is to bring extra material up from the 
 ditches or to haul it in by wagons during the finishing when the trench has 
 not been made deep enough to hold the stone. Nothing is more essential 
 than a good solid shoulder, and the time to get it is before material is 
 placed in the trench. In clay soils after making the trench, plow drains 
 through the shoulders every 50 feet on both sides and every 25 feet at low 
 points between hills and immediately clean them out so they will drain 
 the subgrade in case of rain. 
 
 The following procedure is not advised, as it is usually the most expen- 
 sive way of getting shoulders. If the road has once been covered with 
 crushed stone or gravel, and it is not desired to tear up the old surface, 
 shoulders can be brought up to the stakes by bringing in dirt with the 
 road machine from the side banks or from the ditches (if the latter mate- 
 rial is fit to use), or can be hauled in with wagons. If the old road has a 
 crown of one inch to the foot, it will take approximately 1,100 cubic yards 
 of compacted material per mile to build up 6-inch shoulders and retain the 
 minimum width of 20 feet on top. The cost of hauling and placing this 
 material is usually very much greater than the value of the stone or gravel 
 saved. As a matter of fact, no material is wasted if the subgrade or trench 
 is cut in the old surface, the stone or gravel thrown out making an excel- 
 lent shoulder. Failure is inevitable if an attempt is made to build a gravel 
 or stone road with a heavy roller without first getting proper shoulders 
 to support the material while it is being rolled. 
 
 Straighten up stakes and drive them firmly. Tie a chalk or binder 
 twine line to stakes on each side so line will draw on inside faces of stakes, 
 drawing it tight. It is usually best to put in additional stakes at 50-foot 
 points so this line will not sag. These lines ae to guide the laborer in 
 trimming the shoulders so the edges will be straight and the grade uni- 
 
GRAVEL ROADS 
 
 61 
 
 form. On a 9-foot road, if these lines are set 7 inches above center of 
 subgrade, they will be 1 foot higher than the bottom of trench at the 
 shoulder. On a 15-foot road set lines 6 inches above center of subgrade. 
 They will then be one foot higher than the bottom of trench at the shoulder. 
 The blade of an ordinary square point dirt shovel is 1 foot long and can be 
 used by the laborer to tell when trench is deep enough at sides by setting 
 blade of shovel up to line. When trench is finished, it should run with a 
 uniform slope from center to edge. Clean out drainage trenches through 
 shoulders, so that they really drain out from the trench. This will keep 
 the trench from filling up in case it rains. It is well to widen the trencn 
 and road on the inside of curves, and to elevate the outer edge of curves. 
 After the subgrade has been properly shaped to the same crown (or, 
 better, a slightly greater crown) than the finished road is to have, it should 
 be rolled until hard, especially if recently filled. Any hollows that devel- 
 op during the rolling snould be filled. Roll enough, but stop before the 
 top layer of earth starts to slip. Wet spots in the subgrade should be 
 shoveled out, filled with good earth or cinders and rolled. Don't leave 
 sink holes with the expectation of filling them with crushed stone. They 
 must be dug out and refilled with good material if a firm surface is to ever 
 be gotten at that point. 
 
 In spreading gravel or broken stone many engineers place on 
 the subgrade wood or concrete blocks of the desired loose depth 
 of the course. In Wisconsin, however, the material is spread by 
 requiring a load to cover a certain length and width of surface. 
 The foreman is given a table of the length of 9-foot road which 
 loads of different sizes will cover and the spreader is required to 
 
 Length of Road in Linear Feet Which a Load of Stone of Given Size will 
 Cover to the Given Loose Depths. Based on Table of Wisconsin Highway 
 Commission. 
 
 WIDTH 
 
 or ROA.D 
 
 LOOSE 
 DEPTH 
 
 SIZE OF LOAD IN CUBIC YARDS 
 
 1 
 
 1} 
 
 ij 
 
 1! 
 
 2 
 
 2* 
 
 2* 
 
 2! 
 
 8 
 
 ftet 
 
 inches 
 
 feet 
 
 feet 
 
 feet 
 
 feet 
 
 feet 
 
 feet 
 
 feet 
 
 feet 
 
 feet 
 
 8 
 
 3 
 
 13.5 
 
 16.9 
 
 20.2 
 
 23.6 
 
 27.0 
 
 30.4 
 
 33.7 
 
 37.1 
 
 40.5 
 
 
 4 
 
 10.1 
 
 12.6 
 
 15.2 
 
 17.7 
 
 20.2 
 
 22.6 
 
 25.3 
 
 27.8 
 
 30.3 
 
 
 5 
 
 8.1 
 
 10.1 
 
 12.1 
 
 14.1 
 
 16.2 
 
 18.2 
 
 20.2 
 
 22.3 
 
 24.3 
 
 
 6 
 
 6.75 
 
 8.4 
 
 10.1 
 
 11.8 
 
 13.5 
 
 15.2 
 
 16.9 
 
 18.5 
 
 20.3 
 
 9 
 
 3 
 
 12 
 
 15 
 
 18 
 
 21 
 
 24 
 
 27 
 
 30 
 
 33 
 
 36 
 
 
 4 
 
 9 
 
 11.25 
 
 13.5 
 
 15.75 
 
 18 
 
 20.25 
 
 22.5 
 
 24.75 
 
 27 
 
 
 5 
 
 7.2 
 
 9 
 
 10.8 
 
 12.6 
 
 14.4 
 
 16.2 
 
 18 
 
 19.8 
 
 21.6. 
 
 
 6 
 
 6 
 
 7.5 
 
 9 
 
 10.5 
 
 12 
 
 13.5 
 
 15 
 
 16.5 
 
 18 
 
 10 
 
 3 
 
 10.8 
 
 13.5 
 
 16.2 
 
 18.9 
 
 21.6 
 
 24.3 
 
 27 
 
 29.7 
 
 32.4 
 
 
 4 
 
 8.1 
 
 10.1 
 
 12.2 
 
 14.2 
 
 16.2 
 
 18.2 
 
 20.2 
 
 22.3 
 
 24.2 
 
 
 5 
 
 6.5 
 
 8.1 
 
 9.7 
 
 11.3 
 
 13.0 
 
 14.6 
 
 16.2 
 
 17.8 
 
 19.4 
 
 
 6 
 
 5.4 
 
 6.7 
 
 8.1 
 
 9.4 
 
 10.8 
 
 12.1 
 
 13.5 
 
 14.8 
 
 16.2 
 
 12 
 
 3 
 
 9 
 
 11.2 
 
 13.5 
 
 15.8 
 
 18.0 
 
 20.2 
 
 22.5 
 
 24.7 
 
 27.0 
 
 
 4 
 
 6.7 
 
 8.4 
 
 10.1 
 
 11.8 
 
 13.5 
 
 15.1 
 
 16.9 
 
 18.5 
 
 20.2 
 
 
 5 
 
 5.4 
 
 6.7 
 
 8.1 
 
 9.4 
 
 10.6 
 
 12.1 
 
 13.5 
 
 14.8 
 
 16.2 
 
 
 6 
 
 4.5 
 
 5.6 
 
 6.7 
 
 7.8 
 
 9 
 
 10.1 
 
 11.2 
 
 12.3 
 
 13.5 
 
62 AMERICAN HIGHWAY ASSOCIATION 
 
 make the loads cover just this length. When this method is 
 followed it is convenient to have the loads hauled of the same 
 size. The man placed in charge of the spreading should be se- 
 lected carefully, because a large amount of money can be wasted 
 by placing too much material on the road. The depth of the 
 loose material should be checked as often as possible on this 
 account. 
 
 When the gravel is bought by weight it is the Wisconsin rule 
 to take the weight of a cubic yard of pit gravel at 3000 pounds 
 and of crushed gravel at 2650 pounds. If the material is wet 
 it will weigh more than when it is in a normal condition and al- 
 lowance should be made for this. 
 
 Special Binders 
 
 Gravel roads are now being built for quite heavy traffic with 
 binders giving greater toughness to the road than clay or rock 
 powder will afford. Examination of many roads after several 
 years of use has shown that there is less large stone and more 
 small stone in them than when they were built. This change 
 is considered due to the internal disintegration of the stone by 
 the loads coming upon it, part of the reduction taking place when 
 the road is heavily rolled during construction and part later under 
 heavy travel. The special binders are used to hold the stone so 
 firmly together that after the rolling of the road there will be no 
 further internal disintegration. The method of using bituminous 
 binders for this purpose is explained in the chapter on bitumi- 
 nous roads, and the method of using glutrin in the chapter on 
 broken stone roads. 
 
 Maintenance 
 
 The maintenance of gravel roads must begin immediately 
 after the road is thrown open to travel. A small hole in a gravel 
 road, unless immediately repaired, soon becomes a large hole. A 
 few large holes mean a ruined road and a large expense for resur- 
 facing. Furthermore a gravel road, no matter how well rolled, 
 cannot be considered finished until traffic has gone over it and 
 tested every part. For this reason, some engineers allow traffic 
 on the road before the roller has left it, so that any weak places 
 may be revealed and repaired at once while the equipment is 
 still at hand. The rounded pebbles of pit gravel do not inter- 
 lock like pieces of crushed stone but are usually held together 
 by a clay binder which is not so strong as the cementitious pow- 
 der from some classes of rock. Until travel has broken down 
 the pebbles and furnished rock powder which will act with the 
 clay and form a rigid mass, a gravel road is not so firm as a crushed 
 stone road and needs more maintenance. 
 
GRAVEL ROADS 63 
 
 The gravel roads of New Hampshire are used throughout the 
 summer by a heavy automobile traffic, particularly on Satur- 
 days and Sundays. They are nevertheless kept in good condition 
 by the patrol system of maintenance at very low cost, consider- 
 ing the destructive use to which they are subject. Each patrol- 
 man has a section for which he is responsible, and a number of 
 sections are united in a division under the general supervision 
 of a maintenance foreman, who is in immediate charge of all main- 
 tenance work and reports to the division engineer. Each patrol- 
 man must supply a horse and dump cart, shovel, pick, hoe, 
 rake, stone-hook, axe, iron bar, iron chain and tamp. Special 
 tools are furnished by the State highway department. The meth- 
 ods of maintainance are indicated in the following quotations 
 from the instructions issued to the patrolmen: 
 
 One dragging in the spring is worth two in the summer. It is better 
 to drag a mile of road several times and get it in good condition, than to 
 drag 2 or 3 miles and not finish any part of it. Don't drag a soft section 
 when it is so wet that the first vehicle to pass will rut it all up. First 
 fill the holes and ruts with new material and then drag as the surface dries 
 out. Every patrolman should have material dumped in small piles along 
 the side of his section so that on a rainy day he can at once fill all holes 
 and ruts in which water is collecting. 
 
 When the weather is unsuitable for dragging, as during a dry spell, all 
 patrolmen should cart on all the new material possible in order to fill all 
 ruts and holes and resurface worn-sections. Carting is very essential 
 during dry periods and should never be neglected. Whenever a patrolman 
 is in doubt as to what to do next the general rule is to cart new material, 
 for all roads are wearing out under travel and it is necessary that the 
 surface be continually renewed to take the place of the old material that 
 is thrown out as mud or blown away as dust. 
 
 Save all the sods, leaves, rubbish, stones and refuse that you clean off 
 your road and dump this waste material in places where the bank is steep 
 so that by flattening the side slope there will be no need of a guard-rail, 
 or dump the material back of a present guard-rail so that later this guard- 
 rail can be removed. 
 
 Oiling gravel roads generally requires careful preparation of 
 the surface because the large amount of clay binder has a ten- 
 dency to interfere with the formation of a satisfactory oiled 
 surface. Consequently the surface should be thoroughly cleaned 
 and a comparatively light oil used. The first applications are 
 likely to be disappointing, but if holes and ruts are filled promptly, 
 two or three applications on carefully cleaned surfaces during 
 the first year will eventually give a good wearing surface, pro- 
 vided the roadbed and gravel have been thoroughly consolidated 
 and the traffic is not too heavy for this type of road. It is the 
 general opinion at present that surface applications should not 
 be made until a gravel road has had at least one year's service. 
 The methods of doing the work are given in a later chapter. 
 
WATER-BOUND MACADAM ROADS 
 
 Water-bound macadam roads are adapted to highways carry- 
 ing moderate traffic, for experience shows that even when a large 
 part of the traffic is motor-driven this type of construction can 
 be maintained successfully by surface applications, as described 
 in a later chapter. Where a gravel road is not quite able to carry 
 the traffic, a macadam top course on a gravel base has been 
 adopted as a standard type by the highway departments of a 
 number of States. The following statements give the views 
 regarding water-bound macadam held by three State highway 
 departments having a large mileage of it under their charge: 
 
 New York: The department is still building a large mileage of water- 
 bound macadam. Because of the presence of local material and other fa- 
 vorable conditions this is, in cost, the cheapest durable road which can be 
 built; and it is the belief of the department that on all roads of ordinary 
 or light traffic this type is still a satisfactory one for general use. Of 
 course this type must have surface treatment with oil, and this is planned 
 for in all cases. (Edwin Duffey, State commissioner of highways, 1916. ) 
 Michigan: During the early existence of the department, macadam 
 roads constituted as much as 50 per cent of the mileage constructed. As 
 the use of the automobile became more widespread, the percentage of 
 macadam roads built each year decreased, owing to the excessive cost of 
 maintaining this type under the automobile traffic. Within the past two 
 years, however, waterbound macadam roads have been again growing in 
 favor, because it has been found possible with a bituminous surface treat- 
 ment to maintain them in a condition comparable in the point of service 
 to the higher types of roads. The first treatment, which is made after 
 the road has been seasoned by opening it to traffic for three or four months, 
 is essentially a part of the initial cost of construction. (Frank F. Rogers, 
 State highway commissioner, 1916.) 
 
 Wisconsin: It is not at all an economical type of surfacing unless in- 
 tensely maintained with surface treatments and a patrol system, but when 
 so maintained gives economical service even on heavily traveled roads. 
 (Wisconsin highway commission, 1916.) 
 
 Stone 
 
 The roadbuilding properties of different rocks are explained in 
 the next chapter. The following notes on the selection of stone 
 were prepared by Prevost Hubbard and Frank H. Jackson, Jr. 1 
 The ideal rock for the construction of a water-bound macadam 
 
 1 "The Results of Physical Tests of Road-building Rock," Bulletin 370, 
 United States Department of Agriculture. 
 
 64 
 
WATER-BOUND MACADAM ROADS 
 
 65 
 
 road resists the wear of traffic to which it is subjected to just 
 that extent which will supply a sufficient amount of cementitious 
 rock dust to bind or hold the larger fragments in place. It is 
 generally admitted that the ordinary macadam road is not well 
 suited to any considerable amount of automobile traffic, because 
 such traffic rapidly removes the binder without producing fresh 
 material to take its place. 
 
 Cementing value is a necessary quality for rocks used in mac- 
 adam road construction. As determined by test, cementing 
 values below 25 are called low; from 26 to 75, average, and above 
 75, high. In general, the cementing value should run above 25. 
 For rocks which show a low French coefficient of wear, however, 
 a relatively high cementing value is more necessary than for 
 those which have a high French coefficient. Interpretation of 
 results of the cementing value test is subject to a number of 
 influencing considerations. For instance, it has been found that 
 certain feldspathic varieties of sandstone give excellent results 
 in this test, while experience has shown that they do not bind 
 well when used in the wearing course of macadam roads. In 
 the case also of certain varieties of the trap group, low results 
 are frequently shown by laboratory tests for rocks which bind 
 quite satisfactorily upon the road, provided traffic is sufficiently 
 heavy to supply the requisite amount of fine material. Certain 
 granites, gneisses, and schists which are not suitable for use as 
 binding material give good results in this test. In such cases 
 it is usually found that the highly altered nature of the material 
 reduces its toughness and resistance to wear to such an extent 
 as to condemn it for use. 
 
 Experience has shown that in general the following table of 
 limiting values for the French coefficient of wear, toughness, and 
 hardness may be used in determining the suitability of a rock 
 for the construction of the wearing course of a macadam road: 
 
 Limiting Values of Physical Tests of Rock Suitable for Water-bound 
 
 Macadam 
 
 TRAVEL 
 
 FRENCH 
 COEFFICIENT 
 
 PERCENTAGE 
 OF WEAR 
 
 TOUGHNESS 
 
 HARDNESS 
 
 Light 
 
 5 to 8 
 
 5 to 8 
 
 5 to 9 
 
 10 to 17 
 
 Moderate 
 
 9 to 15 
 
 2 7 to 5 
 
 10 to 18 
 
 14 or over 
 
 Heavy 
 
 16 or over 
 
 Under 2 7 
 
 19 or over 
 
 
 
 
 
 
 
 With relation to the limitations for hardness it may be noted 
 that when any given value for toughness falls within certain 
 limits which define the suitability of the material for macadam 
 road construction under given traffic conditions, the 
 
 corre- 
 
66 AMERICAN HIGHWAY ASSOCIATION 
 
 spending value for hardness will fall within similar limits for hard- 
 ness. In this connection it will be seen in the table that a max- 
 imum limit for hardness is only given in the case of light traffic. 
 It has been found that the great majority of samples having a 
 French coefficient of wear of from 5 to 8 and a hardness of over 
 17 are granites, quartzites, and hard sandstones, which are unsuited 
 for use in the wearing course of water-bound macadam roads 
 due to their lack of binding power. 
 
 The weight of a cubic yard of crushed stone varies consider- 
 ably, depending upon the rock, the size to which it is broken 
 and the amount of shaking the sample receives before its volume 
 is measured. The range in weight of a cubic foot of solid rock 
 is 162 to 221 pounds for trap, 165 to 200 pounds for schist, 156 
 to 175 pounds for felsite, 156 to 193 pounds for quartzite, 125 
 to 193 pounds for limestone, and 125 to 187 pounds for granite. 
 The total range from the lightest limestone to the heaviest trap 
 is over 75 per cent and the crushed rock will show the same varia- 
 tions. Consequently, when broken stone is bought by weight 
 it should be actually weighed before estimating the quantity re- 
 quired for good work. 
 
 Crushed stone is the most important branch of the stone in- 
 dustry. The production of this material for road building in 
 the different states is given in a table on page 198 of this book. 
 The requirements for railroad ballast and concrete as well as for 
 road work are so large that commercial broken stone is avail- 
 able in many parts of the country at a lower price than the cost 
 of quarrying and crushing local material. It is sometimes eco- 
 nomical, even at a greater initial cost, to import stone from a 
 distance if thereby a more durable road may be had than is pos- 
 sible with the use of local stone. 
 
 Much of the stone is crushed locally, usually in portable plants. 
 These comprise a crusher with an engine and boiler, revolving 
 screens, portable bins and an elevator to lift the stone after it 
 is crushed into the screen and sometimes into the bins. The 
 capacity of a crusher should be adjusted to the road roller ca- 
 pacity. If the crusher furnishes more stone than the roller can 
 consolidate, it is too large to work economically. If the crusher 
 can not supply enough stone to keep the roller at work, the lat- 
 ter will operate uneconomically. Furthermore the arrangements 
 for supplying stone from the crusher to the road must be such 
 that the expensive equipment at each end of the line will be 
 kept operating all the time. There is some difference of opin- 
 ion as to the proper capacity of a crusher, for in some sections 
 of the country it is held that from 60 to 80 cubic yards of 
 broken stone is as much as a single roller will consolidate properly, 
 while in other sections it is held that a roller which does not con- 
 solidate 75 tons per day is not doing good service. 
 
WATER-BOUND MACADAM ROADS 67 
 
 Where the stone supply is limited to ledges at infrequent inter- 
 vals but little choice in the location of the crushing outfit is pos- 
 sible. If field stone or ledges are available alongside the road 
 at frequent intervals a crusher can serve about two miles of 
 road most economically. Local conditions, however, affect the 
 proper arrangement of the plant so greatly that no precise rules 
 can be drawn up. It occasionally happens that the availability 
 of water for the boiler is of more importance than any other 
 factor in determining the location of the outfit. 
 
 If possible, the crusher should be set low enough so that a plat- 
 form can be built at the level of the opening into which the stone 
 is dumped. The carts are driven onto this platform and the ma- 
 terial is handled most economically in this manner. The men who 
 set up the plant should have had experience in this work. Much 
 depends on the proper alignment of the several parts and the 
 delays in operation will be avoided if the work is done properly 
 in the first instance. 
 
 The screens in such portable plants have three sections about 
 4 feet long and 30 inches in diameter. The first section has per- 
 forations which are ^-inch in diameter. The perforations of the 
 second section are generally If inches in diameter where com- 
 paratively hard stone is used and 1% inches in diameter where 
 softer stone is employed. With the very soft stone used in some 
 of the Central States, the perforations are sometimes 2 inches, 
 and the third section of the screen is omitted. The perforations 
 in the third section are from 2 to 2$ inches in diameter as a rule, 
 depending upon the maximum size of the stone which is allowed 
 in the road, but this maximum size varies widely in different 
 States. In New York stone up to 3| inches in size is used in the 
 bottom course and in Ohio pieces of sandstone as large as 6 inches 
 in their longest dimensions are permitted in the bottom course 
 of some roads. Stone passing a 4-inch circular opening is also 
 permitted under some conditions. In Wisconsin the bottom 
 course is usually made of stone 2 to 3J inches in size; in this case 
 the perforations in the screen are , 2 and 3^ inches. 
 
 The stones too large to pass through the openings in the third 
 section of the screen drop out and are run through the crusher 
 again. There is sometimes a conveyor to carry these tailings 
 from the end of the screen to the crusher. The jaws of the crusher 
 should be set to give as few tailings as possible and the length 
 of the screen sections should be adjusted to accomplish the same 
 purpose. The operation of the screens should be observed from 
 time to time in order to make sure that material which should 
 pass the openings in each section does not flow along the screen 
 so rapidly that there is a failure to separate it out by the right 
 section of the screen. If the screen revolves too rapidly fine 
 
68 AMERICAN HIGHWAY ASSOCIATION 
 
 material will be carried into the coarser grades. Stone purchased 
 from commercial crusher plants is often observed to run small, 
 the best separation occurring in the product which is obtained 
 during a time of minimum demand. This is because more time 
 is then given to the stone in its passage through the screens. 
 It is impracticable to obtain a complete gradation of the sizes 
 of stone and for this reason highway engineers often permit vari- 
 ations from the nominal maximum and minimum dimensions 
 of any size. For instance the f-inch stone specified in New 
 Jersey may contain up to 5 per cent of material larger than 1 J inch 
 and up to 8 per cent smaller than f inch, although the nom- 
 inal range of size is from f to 1J inch. 
 
 There is no uniformity in the designation of the sizes of crushed 
 stone; what is termed as No. 1 stone in Ohio is entirely different 
 from No. 1 stone in New York. 
 
 Drainage 
 
 The investment in a macadam road is so great that every pre- 
 caution should be taken to have the roadbed thoroughly drained. 
 The methods of doing this were explained in the chapter on 
 drainage. If they are not employed wherever necessary the road 
 will inevitably become rutted and marked by holes during pro- 
 longed wet weather, and the maintenance of such places will 
 entail an annual expenditure far greater in the end than the cost 
 of proper drainage work. 
 
 Formerly Telford foundations were used in all wet, soggy 
 ground under well-built broken stone roads but experience has 
 shown that with good underdrainage equally satisfactory foun- 
 dations can be built of coarse gravel. This is dumped on the 
 bottom of the road after the soft material has been excavated 
 to a considerable depth. The mass of gravel should be drained 
 into the side ditches by constructing blind drains through the 
 shoulders at intervals of not over 50 feet. 
 
 Where suitable field stone is available for a Telford foundation 
 it is still sometimes used. The New York requirements for 
 stone for this purpose are a thickness of not less than l inches, 
 a depth equal to the depth required for the foundation, from 6 
 to 8 inches, and a length not more than one and a half times 
 the depth. The New Jersey specifications require stone 5 to 
 10 inches long, 2 to 4 inches wide and at least 6 inches deep. 
 Some engineers advise placing this stone on a bed of gravel, while 
 others believe that if gravel is available it is best to make the 
 entire base of it and not employ Telford, since the latter is quite 
 expensive. The stone must be set on their broader base, length- 
 wise across the road, and wedged by driving small stone into 
 
WATER-BOUND MACADAM ROADS 69 
 
 the interstices. The projecting points should be broken off 
 with a stone hammer, the depressions in the top filled with stone 
 chips, and the foundation rolled. 
 
 The V-shaped drain described on page 27 is a substitute for 
 a Telford foundation which has received much favor in some 
 states. 
 
 Sub-Grade 
 
 It is necessary to place the stone for a macadam road in a box 
 or trench in order to roll it successfully. The method of exca- 
 vating the sub-grade was described on page 60. The bot- 
 tom must be slightly crowned. This is for two reasons; first to 
 shed any water which may sink through the macadam, and 
 second, to keep the amount of stone required for the road to the 
 minimum actually necessary. The sub-grade must be rolled 
 until hard in order, first, that the stone placed on it can not be 
 driven into it and thus serve no useful purpose, and second, to 
 turn toward the sides of the road, into the blind drains leading 
 to the ditches, any water which may penetrate the courses of 
 stone. 
 
 The depth of the box or trench is fixed by the desired 
 depth of the macadam roadway. This is rarely less than 6 
 inches at the center and is sometimes considerably more, al- 
 though there is a question whether a greater thickness than 8 
 inches after rolling serves any useful purpose. The harder and 
 tougher the stone, the less need be the thickness of the road, 
 provided the sub-grade is firm. Usually the sides of the macadam 
 roadway are 1 to 2 inches thinner than the center. 
 
 On very sandy soils, to keep the sand from working up through 
 the stone, a covering of clay, hay, straw, or fine brush is spread 
 over the subgrade. 
 
 Placing the Broken Stone 
 
 It is customary to begin placing the broken stone as soon as 
 a few hundred feet of the subgrade has been prepared to receive 
 it, because it is undesirable to expose the rolled earth surface to 
 the danger of drenching by rains for a longer period than is 
 necessary. 
 
 The first course is rarely if ever spread to a greater depth than 
 6 inches when loose, because a roller cannot compact a deeper 
 course of stone in a satisfactory manner. The thickness is sel- 
 dom less than 4 inches. The largest size of the screened stone 
 is used. In some states it is forbidden to dump the stone di- 
 rectly on the subgrade, on the ground that this leaves a mass of 
 consolidated small stone in the center of the heap which remains 
 
70 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 almost intact when the pile is leveled. Accordingly the stone 
 must be deposited on dumping boards about 6 feet long and 3 
 feet wide, from which it is shoveled to the subgrade. This is no 
 longer a generally adopted requirement, however, but it is not 
 unusual to require a load to be deposited in several dumps 
 so that the least amount of shoveling and raking will be required. 
 
 Costs Per Mile Corresponding to Different Costs Per Square Yard. Based on 
 Table Published by Commissioner of Public Roads of New Jersey 
 
 Width, feet 
 
 Square 
 yards, 
 per mile 
 
 8 
 4,693* 
 
 10 
 
 5.866J 
 
 12 
 7,040 
 
 14 
 8,213* 
 
 16 
 9,386} 
 
 18 
 10,560 
 
 20 
 11.7331 
 
 Cost per sq. 
 
 
 
 
 
 
 
 
 yd. 
 
 
 
 
 
 
 
 
 $0.25 
 
 $1,173.33 
 
 $1,466.67 
 
 $1,760.00 
 
 $2,053.33 
 
 $2,346.67 
 
 $2,640.00 
 
 $2,933.33 
 
 0.30 
 
 1,408.00 
 
 1,760.00 
 
 2,112.00 
 
 2,464.00 
 
 2,816.00 
 
 3,168.00 
 
 3,520.00 
 
 0.35 
 
 1,642.67 
 
 2,053.33 
 
 2,464.00 
 
 2,874.67 
 
 3,285.33 
 
 3,696.00 
 
 4,106.67 
 
 0.40 
 
 1,877.33 
 
 2,346.67 
 
 2,816.00 
 
 3,285.33 
 
 3,754.67 
 
 4,224.00 
 
 4,693.33 
 
 0.45 
 
 2,112.00 
 
 2,640.00 
 
 3,168.00 
 
 3,696.00 
 
 4,224.00 
 
 4,752.00 
 
 5,280.00 
 
 0.50 
 
 2,346.67 
 
 2,933.33 
 
 3,520.00 
 
 4,106.67 
 
 4,693.33 
 
 5,280.00 
 
 5,866.67 
 
 0.55 
 
 2,581.33 
 
 3,226.67 
 
 3,872.00 
 
 4,517.33 
 
 5,162.67 
 
 5,808.00 
 
 6,453.33 
 
 0.60 
 
 2,816.00 
 
 3,520.00 
 
 4,224.00 
 
 4,928.00 
 
 5,632.00 
 
 6,336.00 
 
 7,040.00 
 
 0.65 
 
 3,050.67 
 
 3,813.33 
 
 4,576.00 
 
 5,338.64 
 
 6,101.33 
 
 6,864.00 
 
 7,626.67 
 
 0.70 
 
 3,285.33 
 
 4,106.67 
 
 4,928.00 
 
 5,749.33 
 
 6,570.67 
 
 7,392.00 
 
 8,213.33 
 
 0.75 
 
 3,520.00 
 
 4,400.00 
 
 5,280.00 
 
 6,160.00 
 
 7,040.00 
 
 7,920.00 
 
 8,800.00 
 
 0.80 
 
 3,754.67 
 
 4,693.33 
 
 5,632.00 
 
 6,570.67 
 
 7,509.33 
 
 8,448.00 
 
 9,386.67 
 
 0.85 
 
 3,989.33 
 
 4,986.69 
 
 5,984.00 
 
 6,981.33 
 
 7,978.67 
 
 8,976.00 
 
 9,973.33 
 
 0.90 
 
 4,224.00 
 
 5,280.00 
 
 6,336.00 
 
 7,392.00 
 
 8,448.00 
 
 9,504.00 
 
 10,560.00 
 
 0.95 
 
 4,458.67 
 
 5,573.33 
 
 6,688.00 
 
 7,802.67 
 
 8,917.33 
 
 10,032.00 
 
 11,146.67 
 
 1.00 
 
 4,693.33 
 
 5,866.67 
 
 7,040.00 
 
 8,213.33 
 
 9,386.67 
 
 10,560.00 
 
 11,733.33 
 
 1.05 
 
 4,928.00 
 
 6,160.00 
 
 7,392.00 
 
 8,624.00 
 
 9,856.00 
 
 11,088.00 
 
 12,320.00 
 
 1.10 
 
 5,162.67 
 
 6,453.33 
 
 7,744.00 
 
 9,034.67 
 
 10,325.33 
 
 11,616.00 
 
 12,906.67 
 
 1.15 
 
 5,397.33 
 
 6,746.67 
 
 8,096.00 
 
 9,445.33 
 
 10,794.67 
 
 12,144.00 
 
 13,493.33 
 
 1.20 
 
 5,632.00 
 
 7,040.00 
 
 8,448.00 
 
 9,856.00 
 
 11,264.00 
 
 12,672.00 
 
 14,080.00 
 
 NOTE: When the cost per square yard is greater than $1.20, the corre- 
 sponding cost per mile can be found by adding to the tabulated cost for a rate 
 of $1.00 per square yard, the tabulated cost for a rate equal to the difference 
 between the given rate and $1.00. The costs per square mile for widths 
 greater than 20 feet are found by adding together the costs for two of the 
 tabulated widths which will give the desired width. 
 
 The easiest method of distributing the stone is by using an auto- 
 matic spreader wagon which deposits it in a layer of approxi- 
 mately the right thickness. The methods of determining the 
 thickness are explained on page 61. 
 
 When a hundred feet or so of the first course has been spread, 
 the rolling should begin. A roller weighing about 600 pounds 
 
WATER-BOUND MACADAM ROADS 71 
 
 per inch of width of roll is usually recommended for rolling hard 
 rock, but one of three-fourths this weight will probably do bet- 
 ter work with soft limestone. The roller starts at the edges of 
 the stone and care should be taken that the shoulders are not 
 crushed during the trips near the sides of the trench. The roller 
 should not be run much faster than 100 feet per minute. After 
 both sides are moderately firm, the roller should move gradually 
 toward the center until the whole lower course is thoroughly 
 compacted. The rolling should be stopped as soon as the 
 pieces of stone begin to break. Sometimes it is found that 
 a wavy motion continues and the stone will not compact. 
 This may be due to a wet subgrade, which will probably give 
 no trouble if allowed to dry for a day or two, or it may be due 
 to the use of a very hard stone, when the application of a little 
 sand or fine gravel may remedy the difficulty. With some 
 soft, coarse, gravel stones a crawling motion may be noticed, 
 which can be prevented by a light sprinkling of coarse sand, 
 stone screenings and sometimes by water. The rolling is con- 
 tinued until the stone has no movement when the men walk over 
 it. If depressions develop during the rolling they must be 
 filled with stone of the same size as that used in the course 
 and rolled until firm. 
 
 Some engineers advise harrowing the loose stone with a spike- 
 tooth harrow in order to mix the stone thoroughly and to save 
 a part of the rolling. This would be of advantage if full loads of 
 stone were dumped directly on the subgrade, for it would break 
 up the cores of small stone in the center of the piles. Other 
 engineers recommend using a blade grader to shape the loose 
 stone just before rolling. 
 
 It is not customary to apply a binder of gravel or screenings 
 to the bottom course in some states and it is required in others. 
 It is apparently a detail depending considerably upon the hard- 
 ness of the stone used. If the stone is relatively soft and the 
 bottom course is constructed of a large size of stone, a binder 
 may prevent the internal disintegration of the stone under loads 
 to some extent, but with the somewhat smaller, hard trap rock 
 used in Massachusetts, for instance, screenings are unnecessary. 
 
 After about a hundred feet of the bottom course has been 
 rolled, the second course is spread. This consists of the size from 
 J to li or 1| inches, and the loose depth is 3 to 5 inches. Large 
 loads should not be dumped directly on the bottom course. The 
 top course is usually given its final shaping with rakes. This 
 course is rolled commencing on each outer edge with the rear 
 wheel half on the stone and half on the shoulders; the roller is 
 gradually worked toward the center. If depressions are devel- 
 oped during this work, they must be filled, and the rolling should 
 continue until the surface is hard and uniform in contour. 
 
72 AMERICAN HIGHWAY ASSOCIATION 
 
 The surface is then covered with the binder. The material 
 used for this purpose varies with the character of the stone in 
 the top course. Generally screenings are employed, but in states 
 where the top course is composed of rather large sizes of stone 
 the screenings have small stone mixed with them. In Mary- 
 land limestone screenings are not permitted with trap rock with- 
 out the consent of the engineer. A. R. Hirst, State highway engi- 
 neer of Wisconsin, advises using a clayey pea gravel or disinte- 
 grated granite with crushed quartzite or granite, and if these 
 are unavailable he prefers a bituminous binder. 
 
 Screenings are rarely if ever permitted to be dumped on the 
 road. They should be placed in piles along the road at such 
 intervals that they can be distributed readily and enough mate- 
 rial will always be available. In Massachusetts it is not cus- 
 tomary to place the screenings to a greater depth than 1 inch. 
 In Michigan the depth is about } inch and in Wisconsin about 
 J inch on State roads. 
 
 Although the screenings are sometimes rolled dry, after being 
 spread, the usual practice is to sprinkle the road with water 
 before rolling. The road must be sprinkled until the screenings 
 are thoroughly wet and do not stick to the wheels of the roller. 
 Where hard, small stone is used in the top course more water 
 is generally employed than where the stone is larger, and an 
 attempt is made to flush the screenings into the interstices be- 
 tween the stones. If the screenings are picked up by the roller 
 at any time, more water must be applied. The sprinkling and 
 rolling are continued until water is carried along in front of the 
 roller wheels at every point of the road. 
 
 Rolling must be done carefully for the appearance of the road 
 will depend upon this work. 
 
 After the road has dried sufficiently, the shoulders should 
 be smoothed off with a road machine, if one is available. The 
 shoulders should be trimmed so the water can flow from the 
 center of the road to the ditches along every foot of the way. 
 All surplus material should be removed, and the shoulders should 
 be rolled as far out as it is safe to run the roller. 
 
 Glutrin Binder 
 
 For a number of years, glutrin has been used extensively as 
 a binding material for both gravel and broken stone roads. It 
 is an adhesive binding liquid whose base is the lignin derived 
 from the sulphite pulp wood process. It is sold in a concentrated 
 state and should be diluted with water before use. 
 
 It should be understood that when the road material to be 
 treated is other than stone, it should contain at least 10 per cent 
 
WATER-BOUND MACADAM ROADS 73 
 
 of clay. When this is lacking in the original road material, it 
 should be evenly added as the road material is put in place. 
 When used on gravel or sand-clay roads, glutrin should be di- 
 luted with water in the proportion of one part glutrin to not 
 less than three parts water. This mixture should be applied 
 by means of any distributor which will spread it uniformly. 
 The application should be continuous, so that the road is kept 
 moist, but not so rapidly as to permit the forming of pools or 
 the flowing off to the sides. Penetration must be secured, and 
 consequently the distributor should make at least four trips 
 over the road in applying the amount of glutrin called for in the 
 specifications. This is usually about | gallon of glutrin to the 
 square yard. 
 
 When used in the construction of broken stone or slag roads, 
 the glutrin should be applied during the process of puddling 
 the top course. The puddle should be begun as usual with plain 
 water, but as soon as the screenings are thoroughly saturated, 
 glutrin should be placed in the sprinkler in the proportion of one 
 part glutrin to five parts water, and the puddling completed 
 with this mixture. The specifications usually call for | gallon 
 of glutrin to the square yard to be used in this process. A still 
 stronger bond can be secured if, after the road has been pud- 
 dled in this manner, it is allowed to dry out and a surface ap- 
 plication is then made over the center 80 per cent of the width 
 of the road, of 0.2 gallon of glutrin, diluted in the proportion of 
 one part glutrin to three parts water. As soon as the road is 
 dry, it can be opened to traffic. 
 
 There have been many miles of glutrin-bound roads con- 
 structed in Connecticut and New York, which have been given 
 a bituminous top course, or even an oil treatment, the purpose 
 being to bind the mass of stones thoroughly together with glu- 
 trin to prevent the internal disintegration of the gravel or stone 
 by traffic and to protect the glutrin from surface water. 
 
 Glutrin should not be used with a pure siliceous material like 
 quartz, unless at least 10 per cent of clay is added. With broken 
 stone, the fine material produced in rolling, furnishes a substi- 
 tute for the clay required with gravel. 
 
 Maintenance 
 
 Where there is very little automobile traffic the old-fashioned 
 methods of maintenance are still applicable. If the road was 
 built late in the fall, particularly if trap rock was used, it is pos- 
 sible that loose stone will appear on the surface in the spring. 
 They should be removed and need cause no apprehension. Holes 
 and ruts should be filled with small stone and screenings, prefer- 
 
74 AMERICAN HIGHWAY ASSOCIATION 
 
 ably during a rain so the traffic will begin to bind the patch as 
 soon as the weather clears. When the top course has been worn 
 down so that the large stone of the bottom course show in places, 
 the road should be repaired. If the top course is to be less than 
 3 inches thick the stone can be spread on the road and treated 
 like the top course of a new road. If the course is to be made 
 of 3 inches or more of loose stone, it is generally best to loosen 
 up the road by means of spikes placed in the wheels of the roller 
 or by the use of a scarifier. 
 
 This method of maintenance is practically obsolete on account 
 of motor traffic. The shearing action of the wheels of an auto- 
 mobile on a water-bound road speedily loosens the stones of the 
 top course and it is necessary to protect the surface by a tenacious 
 mat of bituminous material and stone. Experience shows that 
 this should not be applied until the road has seasoned for a few 
 months. If the road is finished late in the fall, so that no oppor- 
 tunity will be afforded for it to season before winter closes down 
 construction work, the surface can be bound with calcium chlo- 
 ride to hold it until spring, when the bituminous mat can be 
 applied. 
 
 The ordinary method of maintaining the road is to clean it 
 thoroughly and then apply a road oil uniformly over the surface. 
 Some of these oils are so thin that they soak into the surface 
 while others must be covered with sharp sand or screenings free 
 from dust. The methods of doing the work are explained in 
 the chapter on surface applications. 
 
ROAD BUILDING ROCKS 
 
 Mineral Composition. 1 Reports of geologists and mineralo- 
 gists on road-building rocks classify them according to their 
 origin as igneous, sedimentary and metamorphic. 
 
 Igneous rocks are those which have solidified from a very hot 
 liquid condition and their physical condition, technically termed 
 "structure," depends largely on the rate of cooling of the fused 
 material. The "intrusive" or "plutonic" type of igneous rocks 
 cooled slowly at great depths below the earth's surface, and the 
 minerals composing it are usually in large and well developed 
 particles. This type includes granite, syenite, diorite, gabbro, 
 and peridotite. The "extrusive" or "volcanic" types of igneous 
 rocks cooled more rapidly upon the earth's surface and are finer 
 grained. They frequently show a so-called "porphyritic" 
 structure on account of the presence of larger crystals in a fine- 
 grained, dense mass forming the main mass of the rock. This 
 type includes rhyolite, trachyte, andesite, basalt and diabase. 
 
 Sedimentary rocks are made up of fragments of minerals or 
 shells that were moved about, mainly by water, and finally de- 
 posited on the beds of lakes or seas in more or less parallel layers. 
 There they became cemented together by the pressure upon them 
 and changes in the composition of a part of their constituents. 
 This last change is of the same general nature as that occurring 
 far more quickly in the case of plaster or mortar. This class 
 includes calcareous types of rock like limestone and dolomite, 
 and siliceous types like shale, sandstone, and chert (flint). Both 
 types are usually distinctly bedded or stratified. 
 
 Metamorphic rocks were produced from the two classes just 
 mentioned by pressure and heat. The long-continued shearing 
 and compressive forces sometimes produced a "foliated" or 
 "schistose" character, with a parallel arrangement of the minerals 
 composing them, or a "massive" or "nonfoliated" character. 
 Gneiss, schist and amphibolite are foliated metamorphic rocks, 
 and slate, quartzite, eclogite and marble are nonfoliated meta- 
 morphic rocks. 
 
 1 Abridged from Bulletin 348, U. S. Department of Agriculture, "Rela- 
 tion of Mineral Composition and Rock Structure to the Physical Prop- 
 erties of Rock Materials," by E. C. E. Lord, petrographer, Office of Public 
 Roads and Rural Engineering. 
 
 75 
 
76 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 
 
 4,991 
 
ROAD BUILDING ROCKS 
 
 77 
 
 ::::::::::::::::::::::::::::::: I:R:::::::::::::::::::::::::::::::;::N: 
 
 i 
 
 12 .1 
 
78 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 *r s 
 
 493^ uoicojqv 
 
 4**1 
 
ROAD BUILDING ROCKS 
 
 79 
 
 O 
 
 4 S9 1 
 
 s 
 
 SS9I 
 
80 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
ROAD BUILDING KOCKS 
 
 81 
 
 O ir, O 
 
 J.S3"! uoisoaqy 
 
 .-^TTv::;:::::;:::::.r:iM::^7i:;:;;;:::::;::;:::::;:;;;;;;n:rri::::::::::: 
 
82 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
ROAD BUILDING ROCKS 83 
 
 The original mineral components of igneous rocks and the 
 essential part of metamorphic schists are quartz, plagioclase, 
 orthoclase, augite, hornblende, muscovite, biotite, rock glass, 
 magnetite and garnet. These are called primary minerals. 
 Rock glass, included among them, is a mineral of variable com- 
 position found in certain volcanic rocks which cooled very rapidly. 
 It is extremely brittle and when present in appreciable quantities 
 has a tendency to lower the wearing properties of the rock. Orth- 
 oclase and plagioclase are usually called " feldspar" by engineers 
 and biotite and muscovite are called "mica." 
 
 Quartz is the most widely distributed mineral known. It has 
 a specific gravity of 2.66 and a hardness of 7 in Mohs' scale. 1 
 When present in large quantities, especially when finely consoli- 
 dated, as in fine-grained, igneous and massive metamorphic 
 rocks, the resulting material is extremely hard and offers great 
 resistance to wear. 
 
 Orthoclase and plagioclase are among the principal ingredients 
 of igneous and metamorphic rocks and some sandstones. Their 
 specific gravity is 2.54 to 2.76 and their hardness 6 to 6.5. Many 
 coarse-grained feldspathic rocks break down readily under im- 
 pact on account of the cleavage of these minerals. In fine- 
 grained rocks the effect of this cleavage is less marked, and some 
 of them are extremely hard and tough. 
 
 Augite and hornblende are the chief iron-bearing or dark silicate 
 constituents of basic igneous rocks, commonly called "trap 
 rocks," and the crystalline schists derived from them. Their 
 specific gravity is 2.93 to 3.71 and their hardness 5 to 6.5. Their 
 crystalline shape is such that they interlock very compactly with 
 other minerals, which is one of the reasons for the marked dura- 
 bility of trap rocks. 
 
 Biotite and muscovite occur chiefly in granite, gneiss and mica- 
 ceous schist. Their specific gravity is 2.7 to 3.2 and their hard- 
 ness is 2 to 3. The flaky character of mica is well known and is 
 largely responsible for the foliated character of many metamor- 
 phic rocks and their resulting inferior wearing properties in roads. 
 
 Magnetite has a specific gravity of 5.18 and a hardness of 5.5. 
 Garnet has a specific gravity of 3.15 and a hardness of 7.5. They 
 occur in only two road-building rocks, peridotite and eclogite, 
 and in some cases materially increase the wearing properties of 
 the rock. 
 
 Secondary minerals are produced by the alteration of rocks, 
 mainly by the chemical action of water and carbonic acid on 
 primary rock constituents. The chief secondary minerals are 
 
 1 Mobs' scale of the relative hardness of minerals is as follows: 1, Talc; 
 2, gypsum; 3, calcite; 4, fluorite; 5, apatite; 6, orthoclase; 7, quartz; 8, 
 topaz ; 9, corundum ; 10, diamond. 
 
84 AMERICAN HIGHWAY ASSOCIATION 
 
 calcite, dolomite, kaolin, chlorite, epidote, limonite, serpentine, 
 talc, zeolite and opal. 
 
 Calcite has a specific gravity of 2.6 and a hardness of 3. Dolo- 
 mite has a specific gravity of 2.9 and a hardness of 3.5. These 
 two minerals are the chief constituents of limestones and dolo- 
 mites, and cannot be distinguished microscopically. They 
 cleave freely and hence many calcareous rocks break down readily 
 when used in roads. 
 
 Kaolin is derived to a large extent through the decomposition 
 of orthoclase. It sometimes occurs in small crystal flakes re- 
 sembling white mica (muscovite), and sometimes as minute 
 grains of very indefinite composition. In the latter form, called 
 "amorphous," kaolin has a great effect on the binding property 
 of rock powders, for it becomes glue-like when wet, and when 
 dry it binds together firmly the other mineral particles with 
 which it is associated. 
 
 Chlorite and epidote are derived from augite, hornblende, 
 biotite and plagioclase and are most abundant in trap rocks and 
 dark crystalline schists. Chlorite is a soft green mineral which 
 occurs either in mica-like flakes or as very fine scales and fibers of 
 indefinite composition. In the latter form it has cementing 
 properties like those of amorphous kaolin. Epidote (specific 
 gravity, 3.25-3.5; hardness, 6-7) occurs as yellowish green crystals 
 which, when present in appreciable quantities, apparently in- 
 crease the wearing properties of rocks. 
 
 The results of a study of several hundred road-building rocks 
 indicate that the effects of their mineral composition on their 
 value for highway purposes are probably as follows : 
 
 Igneous and nonfoliated metamorphic rocks, owing to a pre- 
 ponderance of hard silicate minerals combined with greater uni- 
 formity in structure, are more durable than other road-making 
 materials, finer-grained varieties offering greater resistance to 
 abrasion than coarse-grained types. 
 
 The resistance to wear of igneous and metamorphic rocks, 
 containing an abundance of quartz, hornblende, augite, epidote, 
 and garnet, is greater than that of similar rocks rich in mica, 
 chlorite, serpentine, and calcite. 
 
 Foliated metamorphic rocks, owing to the parallel arrange- 
 ment of their mineral constituents, are, as a rule, deficient in 
 toughness and therefore not well adapted to road construction. 
 
 Sedimentary rocks are usually deficient in wearing properties, 
 except in the case of highly indurated sandstones, containing a 
 moderate amount of siliceous clay, cement, and limestones or 
 dolomites rich in quartz and having very little clay. 
 
 Rocks for road making break down under impact into frag- 
 ments, the shape and physical character of which are conditioned 
 by mineral composition and structure. 
 
ROAD BUILDING ROCKS 85 
 
 The effect of weathering is generally to lower the resistance to 
 wear of road materials, owing to the development of soft, in 
 part glue-like (colloidal) products of alteration. Where the 
 secondarjr minerals are harder and more crystalline the wearing 
 properties of the rocks are proportionately increased. 
 
 The cementing value of road materials is conditioned chiefly by 
 the glue-like (colloidal) products of rock decay and increases in a 
 general way proportionately with these products, reaching a 
 maximum in rocks free from quartz. 
 
 The slaking property of rock powders is dependent in the case 
 of siliceous igneous and metamorphic rocks chiefly on the physical 
 character of the primary mineral components, whereas in basic 
 igneous rocks and sandstones it is caused to a large degree by 
 glue-like (colloidal) products of rock decomposition. 
 
 Physical Properties. 1 The success or failure of a rock for road 
 building depends largely upon the extent to which it will resist 
 the destructive influences of traffic. The three most important 
 physical properties are hardness, toughness, and binding power 
 Hardness is the resistance which the rock offers to the displace- 
 ment of its surface particles by abrasion; toughness is the resist- 
 ance which it offers to fracture under impact; and binding power 
 is the ability which the dust from the rock possesses, or develops 
 by contact with water, of binding the large rock fragments to 
 gether. In order to approximate as closely as possible in the 
 laboratory the destructive effects produced by traffic, climatic 
 agencies and faulty construction, certain physical tests have 
 been developed. 
 
 Hardness is determined by subjecting a cylindrical rock core 25 
 millimeters in diameter, drilled from the specimen to be examined, 
 to the abrasive action of quartz sand fed upon a revolving steel 
 disk. The end of the specimen is worn away in inverse ratio to 
 its hardness, and the amount of loss is expressed in the form of a 
 coefficient as follows: 
 
 Coefficient of hardness = 20 w/3, where w equals the loss in 
 weight after 1,000 revolutions of the disk. 
 
 Toughness is determined by subjecting a cylindrical test speci- 
 men 25 by 25 millimeters in size to the impact produced by the 
 fall of a 2-kilogram hammer upon a steel plunger whose lower 
 end is spherical and rests upon the test piece. The energy of 
 the blow delivered is increased by increasing the height of fall 
 of the hammer 1 centimeter after each blow. The height of 
 blow in centimeters at failure of the specimen is called the tough- 
 ness. 
 
 Abstracted from Bulletin 370, U. S. Department of Agriculture, "Re- 
 sults of Physical Tests of Road Building Rock/' by Pre"vost Hubbard, 
 chemical engineer, and Frank H. Jackson, Jr., assistant chemical engineer, 
 Office of Public Roads. 
 
86 AMERICAN HIGHWAY ASSOCIATION 
 
 A test devised by the French and sometimes called the Deval 
 test, for measuring the combined action of abrasion and impact, 
 is as follows: Five kilograms of freshly broken rock between 2 
 and 2| inches in size is tested in a special form of cylinder so 
 mounted on a frame that the axis of rotation of the cylinder is 
 inclined at an angle of 30 with the axis of the cylinder itself. 
 The fragments of rock forming the charge are thus thrown from 
 end to end twice during each revolution, causing them to strike 
 and rub against each other and the sides of the cylinder. After 
 10,000 revolutions the resulting material is screened through a 
 -j^-inch sieve and the weight of the material passing is used to 
 calculate the percentage of wear. The French coefficient of 
 wear is calculated from the per cent of wear as follows: 
 
 French coefficient of wear = 40 H- percentage of wear 
 
 To determine the binding power, or cementing value, as it is 
 usually called, 500 grams of the material to be tested is crushed 
 to pea size and ground with water in a ball mill until it has the 
 consistency of a stiff dough. It is then molded into cylindrical 
 briquettes 25 by 25 millimeters in size, which, after thorough 
 drying, are tested to destruction in a special form of impact 
 machine. A 1-kilogram hammer falls through a constant height 
 of 1 centimeter upon an intervening plunger, which in turn rests 
 upon the test piece. A graphic record of the number of blows 
 required to destroy the specimen is obtained. The number of 
 blows producing failure is called the cementing value of the 
 material. 
 
 The specific gravity, weight per cubic foot, and the water 
 absorption in pounds per cubic foot are obtained on samples of 
 rock which are tested to determine their road-building qualities. 
 The weight per cubic foot is calculated from the specific gravity 
 of the material obtained on a 10-gram sample by the usual dis- 
 placement method. The gain in weight of this fragment after 
 four days' continuous immersion in water is used to calculate 
 the water absorption in pounds per cubic foot of the solid rock. 
 
 Results of Tests. Because of the fact that the various rock 
 families, when subjected to the tests outlined, give results which 
 are more or less distinctive of a group or type, these results can 
 best be discussed in many cases collectively. There are 14 fam- 
 ilies of rock which are more or less commonly used in macadam- 
 road construction. The variations which have been found to 
 exist in the three principal tests for each of these are shown in 
 graphic form in the diagrams on pages 76-82. The values of 
 the tests are arranged as abscissae, with the zero points to the 
 left and the values numerically increasing toward the right. 
 
ROAD BUILDING BOCKS 87 
 
 The ordinates or vertical lines represent the percentages of the 
 total number of samples having values corresponding to the 
 abscissae on which they are plotted. The figures in parentheses 
 hi the upper right-hand corner of each block represent the total 
 number of determinations from which these percentages were 
 calculated. 
 
 Andesite, Basalt, Diabase, Diorite, Gabbro, and Rhyolite 
 comprise the well-known group of road-building rocks commonly 
 known as "trap." The average toughness of all the traps, with 
 the exception of gabbro, which runs somewhat lower, is about 18. 
 This is a considerably higher average than that shown by any 
 of the other types or groups. The same relationship holds true 
 in the abrasion test, the average French coefficient of wear run- 
 ning from about 13 to 15. Comparatively slight variations in 
 hardness are noted for any family or for the group as a whole, 
 the average hardness for which is about 18. The binding power 
 of the traps varies through wide limits, depending largely on the 
 degree of weathering they have undergone. The specific gravity 
 of this group averages about 2.9, giving an average weight per 
 cubic foot of 180 pounds. Individual samples are seldom less 
 than 2.7 nor more than 3.2 specific gravity. Water absorption 
 may vary from a few hundredths of 1 per cent to over 7 per cent. 
 
 Granite is characterized by low toughness and high hardness. 
 The average value for the former is about 8, while that for the 
 latter runs as 18.5. The abrasion test develops an average 
 French coefficient of wear of about 11. Cementing values run 
 low, the only exceptions being very highly weathered material 
 which usually shows low toughness and resistance to wear. The 
 specific gravity averages 2.7. The weight per cubic foot aver- 
 ages 168 pounds. Water absorption has been found to run from 
 about 0.04 to 3 per cent. 
 
 The limestones and dolomites, or magnesium limestones, are 
 undoubtedly the most widely used road-building rock. The 
 average French coefficient of wear is about 8, toughness 7, and 
 hardness 15. The cementing values are usually good, about 75 
 per cent of all samples tested running over 25. The specific grav- 
 ity of the limestones and dolomites averages close to 2.7. In 
 general, the weight per cubic foot will average about 168 pounds 
 for the limestones and 170 pounds for the dolomite. Absorption 
 may vary from a few hundredths of 1 per cent to over 13 per 
 cent. 
 
 The sandstones are characterized by wide variations in the 
 results of all tests. The average French coefficient of wear is 
 about 12, average toughness about 10, and average hardness 
 about 16. The cementing value of sandstones varies widely, 
 depending upon their composition. Their specific gravity aver- 
 
88 AMERICAN HIGHWAY ASSOCIATION 
 
 ages 2.62. The weight per cubic foot averages 164 pounds. 
 Absorption runs from a few hundredths of 1 per cent to about 2 
 per cent. 
 
 The average toughness of marble is about 5 and the v average 
 hardness is less than 14. Marbles usually show good cementing 
 value tests, with about the same range as the limestones and 
 dolomites. The specific gravity ordinarily falls between 2.7 and 
 2.9 and the weight per cubic foot averages 173 pounds, which is 
 somewhat higher than the average for either limestone or dolo- 
 mite. The maximum absorption is under 2.5 per cent. 
 
 Quartzites show an average toughness of 15. The quartzites 
 invariably show a low cementing value. Their specific gravity 
 usually lies between 2.6 and 2.8 and their average weight per cubic 
 foot is about 167 pounds. Their water absorption runs from a 
 few hundredths of 1 per cent to nearly 3 per cent. 
 
 Gneiss and schist show similar physical properties. The 
 average French coefficient of wear for the gneiss samples is about 
 9. Their average hardness, toughness, specific gravity, weight 
 per cubic foot, and absorption are approximately the same as for 
 granite. 
 
 The schists show an average French coefficient of wear of about 
 12. Their average hardness is about 17.5 and their toughness 
 averages 11. The toughness test for both gneiss and schist is 
 made perpendicular to the plane of foliation. If taken hori- 
 zontal to the plane of foliation much lower results would be ob- 
 tained, as failure would then occur along these natural lines of 
 cleavage. The specific gravity of schists usually lies between 
 2.65 and 2.90 and the average weight per cubic foot is about 181 
 pounds. Water absorption is seldom over 2 per cent for this 
 family. 
 
 With the exception of the highly altered varieties, both gneisses 
 and schists show a rather low cementing value. 
 
 Chert is a very hard material, but frequently shows a low re- 
 sistance to wear, owing to its tendency to fracture along lines 
 which have developed as shrinkage cracks in the rock structure. 
 For this reason it is extremely difficult to test for toughness. The 
 cementing value of pure chert is usually low, but some highly 
 weathered deposits develop in service good cementing value, 
 especially if a high-binding clay is associated with it. The 
 French coefficient of wear has usually been found to average 5, 
 toughness 16, and the hardness coefficient between 19 and 20. 
 Specific gravity usually lies between 2.4 and 2.65 and the aver- 
 age weight per cubic foot is about 160 pounds. Water absorp- 
 tion may run from a few tenths of 1 per cent to over 8 per cent. 
 
 Shales and slates are highly laminated rocks that tend to break 
 into flat plates not suitable for road-building purposes. They 
 
ROAD BUILDING ROCKS 89 
 
 are seldom used in road construction, except perhaps as a filling 
 for sub-foundations. They vary greatly in nearly all of their 
 physical properties. 
 
 Many varieties of slag resemble in certain outward respects 
 the common road-building rocks. However, in general, they 
 are more porous and glassy, and vary so greatly in physical 
 properties that with reference to their physical characteristics 
 from the standpoint of road construction they cannot well be 
 considered as a single class with definite limits or general average 
 numerical values. 
 
CONCRETE ROADS 
 
 Although concrete pavements were laid at Belief ontaine, Ohio, 
 in 1893 and 1894, the type did not attract general attention until 
 fifteen years later. During 1913, over 10,000,000 square yards 
 were laid, eight times as much as in 1911. This rapid develop- 
 ment was accompanied by marked differences in methods of con- 
 struction, which aroused some apprehension that poor results 
 from inferior methods would retard the logical adoption of the 
 type in places for which it was suited. Accordingly road and 
 street engineers and contractors from all parts of the country 
 met in February, 1914, for a three-day discussion of concrete 
 road building. The report of this conference exercised a standard- 
 izing influence on methods of construction, as had the somewhat 
 earlier adoption by the American Concrete Institute of stand- 
 ard specifications for concrete roads and pavements. Some of 
 the methods of construction presented features which required 
 detailed investigation, and committees were appointed for such 
 work. In February, 1916, a second national conference was 
 held, at which the reports of these committees were received 
 and discussed. This chapter summarizes the information pre- 
 sented at that conference. 
 
 Foundation and Subgrade 
 
 The following opinions regarding foundations and subgrade 
 were adopted by the 1916 conference: 
 
 When roadways are constructed over fills, extreme care should be ob- 
 served to insure the use of proper materials in layers of such thickness 
 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 pave- 
 ment is placed thereon. Deep fills should be allowed to settle through 
 one winter wherever such procedure is possible. Puddling will be found 
 advantageous in compacting deep fills. Wetting and rolling shall be per- 
 formed when making a fill in order to secure thorough compactness. Fills 
 should never be made with frozen materials nor with lumps greater than 6 
 inches in their greatest dimension. 
 
 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 intelli- 
 
 90 
 
CONCRETE ROADS 91 
 
 gent care and painstaking labor than the preparation of the subgrade. The 
 slight additional cost necessary to insure good results is abundantly jus- 
 tifiable. When the pavement is constructed on virgin soil, care should 
 be taken to remove all soft spots so as to insure a 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 cen- 
 ter than at the sides. An old roadbed should be scarified, reshaped and 
 rolled. The subgrade adjacent to curbs should be hand-tamped. 
 
 The importance of a uniformly firm support for the concrete 
 slab was not fully appreciated by all roadbuilders. There was an 
 opinion among some that the concrete would act as a beam and 
 distribute the loads coming on it over such a wide area that inequali- 
 ties in the sustaining power of the earth would prove unimportant. 
 The number of cracks in concrete pavements attributable to un- 
 warranted confidence in this beam action is beyond proof, but 
 today the opinion is generally held that the money spent in se- 
 curing a firm foundation is a wise outlay to insure low mainte- 
 nance charges. This is particularly the case where an old road 
 is used for a foundation. It is unlikely that a concrete pavement 
 will be laid on it until the old road needs repairs. If the sur- 
 face is then merely leveled by a thin course of stone or gravel, it 
 is possible that there will be weak places, particularly along the 
 sides of the road. 
 
 Drainage 
 
 The 1916 conference adopted the following statement of the 
 principles which should govern the drainage of the roadbed sup- 
 porting a concrete slab: 
 
 The drainage of the roadbed is of vital importance. If the subgrade 
 is not well drained there is danger of unequal settlement and of frost action, 
 which will cause cracks. The method of drainage to be used will depend 
 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. 
 
 There is an objection to the use of cross-drains under thin 
 concrete roads which is not serious in most cases but may be 
 under some conditions. It is practically impossible to compact 
 the material over a blind drain as thoroughly as that of the main 
 portion of the subgrade, and each blind drain is likely to be a weak 
 place in the foundation. An alternative for them which some 
 engineers have advised is the construction of a blind drain just 
 outside each edge of the concrete slab and extending 8 or 10 
 inches below the subgrade. These drains are connected every 
 50 feet with the side ditches by blind drains. All drains under 
 
92 AMERICAN HIGHWAY ASSOCIATION 
 
 the roadway should have a covering of sand or fine gravel on 
 top to prevent the mortar in the wet concrete from passing into 
 the broken stone or gravel of the drain. 
 
 Cross-section of Roads 
 
 The following statements were adopted by the 1916 conference 
 regarding the section of the concrete pavement : 
 
 The thickness of a concrete road or pavement is controlled by many 
 factors, each of which should be given consideration. In view of the in- 
 creasing use of the heavy motor truck and bus, it seems unwise to build 
 pavements with a thickness of less than six inches at any point. In gen- 
 eral, pavements should be thicker at the center than at the sides. Alleys 
 with an inverted crown, and narrow one-slope roads, should have a uni- 
 form thickness. Wherever the thickness can be increased without excess- 
 ive cost, to secure a flat subgrade, or one nearly flat, such increase is 
 advisable. 
 
 The desirable width for single-track roads is 10 feet. The desirable 
 width of double-track roads is 18 feet. The total width of the roadway 
 should not be less than 20 feet for single-track roads and not less than 26 
 feet for double-track roads. 
 
 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 un- 
 usual cases, one one-hundredth will be sufficient for country roads and one- 
 fiftieth will be considered satisfactory for alley pavenents. For city 
 streets an average crown of one -seventy-fifth will generally be found 
 sufficient and should not be reduced, except on grades. 
 
 Single-track concrete roads are occasionally built on the right- 
 hand side of the roadway going in the direction of the heavy 
 traffic. This gives the loaded wagons the better surface. The 
 templet used in determining the section of the road is the same 
 as for a double-track road but only one-half the road is concreted. 
 In Huron and Medina Counties, single-track roads have been 
 built as one-slope roads instead of half the section of double-track 
 roads, and this construction is preferred by some engineers. 
 
 In Wayne County, Michigan, it has been decided to make 
 concrete roads 18 feet wide wherever possible, and never less 
 than 16 feet. Near Detroit the width will be 20 feet. While 
 this increase in width from 10, 12, 15, and 16 feet will add 
 materially to the first cost, it is expected to prove economical 
 in the long run, because the expense of maintaining heavy broken 
 stone or gravel shoulders will be avoided. This maintenance is a 
 large sum on comparatively narrow roads with heavy traffic. 
 
 There is a decided difference of opinion regarding shoulders 
 for concrete roads. Some engineers hold that the natural soil 
 should be used, and where satisfactory shoulders cannot be 
 made of it the width of the concrete should be increased. Other 
 engineers recommend gravel or broken stone shoulders after 
 
CONCRETE ROADS 93 
 
 experience with them. The difference of opinion is probably 
 due to differences in the quality of the earth which must be 
 used for earth shoulders and to differences in the character of the 
 traffic, upon which the opinions are based. There is no question, 
 however, that if traffic makes frequent use of shoulders of clay 
 or clayey loam, they are speedily ruined, and if heavy traffic makes 
 frequent use of macadam shoulders, the junction between the 
 concrete and broken stone becomes a long rut. In either case the 
 proper maintenance of the shoulders will be expensive. If two 
 macadam or gravel shoulders wider than 4 feet are considered 
 necessary, it is advisable in every case to consider the alternative 
 of an increased width of concrete. The construction of gravel 
 and macadam shoulders should be postponed, if practicable, until 
 a month after the concrete road has been finished, and they should 
 be left slightly higher than the concrete to facilitate turning 
 out on them. 
 
 In cuts, where the grades are over 5 per cent, it is usually neces- 
 sary to pave the ditches and to use gravel or macadam shoulders. 
 The maintenance of these ditches and shoulders is expensive, 
 and it is possible that money will be saved in the end, even on 
 single-track roads, by increasing the width of the concrete and 
 adding a concrete ditch and curb at each side. The ordinary 
 construction will call for a 10-foot concrete road, 8 feet of shoul- 
 ders and 8 feet of ditches, a total of 26 feet width of cut at the 
 bottom of the excavation. For this can be substituted a concrete 
 roadway 16 feet wide with two integral curbs bringing the total 
 width to 17 feet 8 inches. The curb acts as an abutment for the 
 toe of the slope. 
 
 On fills over 5 or 6 feet high, where turning out on a soft shoulder 
 may cause a serious accident, it is desirable to widen a single- 
 track pavement to 16 feet unless the top of the fill is so wide that 
 an overturned car will not roll down the slope. In any such case, 
 the safety of the public requires a more careful study of the 
 dangers on embankments than was given to the subject before 
 automobiles became numerous. Attention is called to the 
 record of deaths and injuries on page 25. 
 
 Materials 
 
 Cement is bought for most road work under the standard 
 specifications of the American Society for Testing Materials, 
 which were revised in 1916. They are printed in the next chapter. 
 
 The following statements regarding fine and coarse aggregate 
 were adopted by the 1916 conference: 
 
 The selection of proper aggregates for concrete road construction is 
 of utmost importance. Clean, hard, well-graded materials are absolutely 
 
94 AMERICAN HIGHWAY ASSOCIATION 
 
 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 
 should never be placed on the subgrade but on planks or some other means 
 provided to keep them free from dirt. When aggregates are placed di- 
 rectly on the subgrade care should be used by the shovelers to avoid get- 
 ting 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. 
 
 Investigations to determine the usefulness of the rattler test 
 to show the value of different concrete mixtures for road work 
 indicate that it may prove of value. For the present, however, 
 the older practice of relying on tests of the stone is being followed 
 wherever any testing is done. Generally the best clean, hard and 
 tough crushed rock or gravel is used, provided it will give a con- 
 crete harder than the mortar used with it. It is desirable to 
 use stone having a French coefficient of wear of at least 8. 
 
 Experience indicates that cracks occur more often in gravel 
 concrete than in stone concrete. Probably this is largely due 
 to the very fine material on the surface of most gravel pebbles, 
 which must be washed off carefully to make the material fit for 
 road work. 
 
 Fine aggregate, or "sand," is generally required to pass a J- 
 inch screen. Not more than 25 per cent must pass a 50-mesh 
 sieve and not more than 5 per cent a 100-mesh sieve. It must 
 contain no vegetable or other deleterious matter and not over 3 
 per cent by weight of clay or loam. The sand should be tested 
 frequently in the field by shaking a sample with water in a grad- 
 uated glass and allowing it to settle for an hour. If there 
 is more than about 5 per cent of very fine material showing on the 
 top of the sand, samples should be sent to the laboratory. Nat- 
 ural sand or screenings from hard, tough, durable rock may 
 be used. Natural sand sometimes contains vegetable acids 
 which reduce its value for good concrete. Their presence is 
 determined by making similar briquettes of the natural sand 
 and of standard Ottawa sand, and no natural sand should be used 
 in road work which does not give a strength at least equal to 
 that obtained with Ottawa sand. The best sand is that in which 
 the coarse particles predominate. Improvements can sometimes 
 be made by mixing two natural sands or a fine sand and screenings. 
 
 The standard specifications for coarse aggregate, or "stone" 
 call for material passing a 2-inch round opening, with not more 
 
CONCRETE ROADS 95 
 
 than 5 per cent passing a screen having four meshes per inch 
 and without any intermediate sizes removed. 
 
 The water used in making the concrete must be free from oil, 
 acid, alkali or vegetable matter. 
 
 Proportions 
 
 The 1916 conference adopted the following statements of the 
 principles governing the proportions of the materials: 
 
 The method of measuring materials for the concrete, including water, 
 should be one which will insure accurate proportions of each of the in- 
 gredients at all times. It is recommended that a sack of Portland ce- 
 ment, containing 94 pounds net, be considered the equivalent to 1 cubic 
 foot. 
 
 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. 
 
 The standard specifications for one-course country roads call 
 for one sack of cement to not more than 2 cubic feet of fine aggre- 
 gate and not more than 3 cubic feet of coarse aggregate, with 
 the volume of fine aggregate never less than half that of the 
 coarse aggregate. A cubic yard of the mixed concrete must 
 contain at least 1.7 barrels of cement. The amount of water 
 used must be enough to produce concrete holding its shape 
 when struck with a template. Concrete which has partly hard- 
 ened must never be used. 
 
 The standard specifications for two-course pavements call 
 for a base mixed in the proportions of 1 sack of cement to not 
 more than 2J cubic feet of fine aggregate and not more than 4 
 cubic feet of coarse aggregate, with at least half as much fine as 
 coarse aggregate. Two grades of top aggregate are specified 
 for the top course; No. 1 must pass a $-inch screen and have not 
 over 10 per cent passing a J-inch screen, and No. 2 must pass a 
 1-inch screen and have not over 5 per cent passing a J-inch 
 screen. Two mixtures are specified for the top course. Mix- 
 ture 1 consists of one sack of cement to not more than 1 cubic 
 foot of fine aggregate and not more than 1^-cubic feet of No. 
 1 top aggregate. Mixture 2 consists of one sack of cement 
 to not more than 1J cubic feet of fine aggregate and not more 
 than 2J cubic feet of No. 2 top aggregate. The volume of fine 
 aggregate must equal half the volume of top aggregate in either 
 mixture. 
 
 The quantities of cement, sand and gravel required to build 
 a mile of road of different widths and thicknesses are given in the 
 accompanying tables, supplied by the Portland Cement Associa- 
 tion. They are based on the assumption that a barrel of cement is 
 
96 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 equivalent to 4 cubic feet and the voids in the stone are 45 per 
 cent. Variations from the tabulated quantities may amount 
 to 10 per cent either way. 
 
 The proportions of cement, sand and stone should be such 
 that the concrete will have the properties desired for a rpad. 
 Where good stone is expensive but softer stone is cheaper, a two- 
 course pavement utilizing the poor stone in the base and the hard 
 stone in the top may prove more economical than a thinner one- 
 
 Quantities of Cement, Sand and Stone Required for One Mile of Single- 
 Course Concrete Road of Different Widths and Thicknesses 
 
 (Furnished by the Portland Cement Association) 
 
 1 
 
 THICK- 
 NESS 
 
 AREA 
 CROSS 
 SECTION 
 
 SUPER- 
 FICIAL 
 AREA 
 
 VOLUME 
 CON- 
 CRETE 
 
 MIX; 1:2: 4 
 
 MIX; 1:2: 3 
 
 MIX; 1: 1}: 3 
 
 I 
 
 I 
 
 Cement 
 
 T3 
 
 1 
 
 1 
 
 j 
 
 I 
 
 02 
 
 Cement 
 
 I 
 
 OQ 
 
 ft. 
 
 ins. 
 
 ins. 
 
 sq. yds. 
 
 sq. yds. 
 
 cu. yds. 
 
 bbls. 
 
 CU. 
 
 yd,. 
 
 cu. 
 yds. 
 
 bbls. 
 
 cu. 
 
 yds. 
 
 CU. 
 
 yds. 
 
 bbls. 
 
 cu. 
 ydt. 
 
 CU. 
 
 yds. 
 
 10 
 
 5 
 
 61 
 
 0.540 
 
 5,867 
 
 951 
 
 1436 
 
 428 
 
 856 
 
 1654 
 
 494 
 
 732 
 
 1818 
 
 405 
 
 809 
 
 10 
 
 6 
 
 7 
 
 0.633 
 
 5,867 
 
 1113 
 
 1680 
 
 496 
 
 991 
 
 1938 
 
 578 
 
 856 
 
 2124 
 
 473 
 
 946 
 
 12 
 
 5 
 
 & 
 
 0.667 
 
 7,040 
 
 1173 
 
 1771 
 
 521 
 
 1043 
 
 2040 
 
 610 
 
 903 
 
 2240 
 
 498 
 
 997 
 
 12 
 
 6 
 
 7 
 
 0.778 
 
 7,040 
 
 1369 
 
 2067 
 
 608 
 
 1218 
 
 2382 
 
 710 
 
 1054 
 
 2614 
 
 582 
 
 1164 
 
 14 
 
 5 
 
 ft. 
 
 0.799 
 
 8,213 
 
 1407 
 
 2125 
 
 625 
 
 1250 
 
 2448 
 
 732 
 
 1084 
 
 2685 
 
 597 
 
 1195 
 
 14 
 
 5 
 
 7 
 
 0.821 
 
 8,213 
 
 1445 
 
 2182 
 
 650 
 
 1298 
 
 2514 
 
 751 
 
 1113 
 
 2760 
 
 607 
 
 1228 
 
 14 
 
 6 
 
 7f 
 
 0.929 
 
 8,213 
 
 1635 
 
 2469 
 
 728 
 
 1455 
 
 2845 
 
 850 
 
 1259 
 
 3121 
 
 695 
 
 1390 
 
 14 
 
 6 
 
 8 
 
 0.951 
 
 8,213 
 
 1673 
 
 2526 
 
 753 
 
 1504 
 
 2911 
 
 870 
 
 1288 
 
 3195 
 
 703 
 
 1422 
 
 16 
 
 5 
 
 7 
 
 0.938 
 
 9,387 
 
 1651 
 
 2493 
 
 735 
 
 1469 
 
 2873 
 
 859 
 
 1271 
 
 3153 
 
 702 
 
 1403 
 
 16 
 
 6 
 
 8 
 
 1.083 
 
 9,387 
 
 1912 
 
 2887 
 
 851 
 
 1702 
 
 3327 
 
 994 
 
 1472 
 
 3652 
 
 813 
 
 1625 
 
 18 
 
 5 
 
 71 
 
 1.083 
 
 10,560 
 
 1907 
 
 2880 
 
 849 
 
 1697 
 
 3318 
 
 992 
 
 1468 
 
 3642 
 
 810 
 
 1621 
 
 18 
 
 6 
 
 81 
 
 1.250 
 
 10,560 
 
 2200 
 
 3322 
 
 979 
 
 1958 
 
 3828 
 
 1144 
 
 1694 
 
 4202 
 
 935 
 
 1870 
 
 20 
 
 5 
 
 7* 
 
 1.235 
 
 11,733 
 
 2173 
 
 3281 
 
 967 
 
 1934 
 
 3781 
 
 1130 
 
 1673 
 
 4150 
 
 924 
 
 1847 
 
 20 
 
 6 
 
 8 
 
 1.420 
 
 11,733 
 
 2499 
 
 3773 
 
 1112 
 
 2224 
 
 4348 
 
 1300 
 
 1924 
 
 4773 
 
 1062 
 
 2124 
 
 22 
 
 5 
 
 5 
 
 1.019 
 
 12,907 
 
 1794 
 
 2709 
 
 798 
 
 1597 
 
 3122 
 
 933 
 
 1381 
 
 3426 
 
 762 
 
 1525 
 
 22 
 
 6 
 
 6 
 
 1.222 
 
 12,907 
 
 2151 
 
 3248 
 
 957 
 
 1914 
 
 3743 
 
 1119 
 
 1656 
 
 4108 
 
 914 
 
 1828 
 
 24 
 
 5 
 
 5 
 
 1.111 
 
 14,080 
 
 1955 
 
 2952 
 
 870 
 
 1740 
 
 3402 
 
 1017 
 
 1505 
 
 3734 
 
 831 
 
 1662 
 
 24 
 
 6 
 
 6 
 
 1.333 
 
 14,080 
 
 2346 
 
 3543 
 
 1044 
 
 2088 
 
 4082 
 
 1220 
 
 1806 
 
 4482 
 
 997 
 
 1994 
 
 30 
 
 5 
 
 5 
 
 1.389 
 
 17,600 
 
 2444 
 
 3690 
 
 1087 
 
 2175 
 
 4253 
 
 1271 
 
 1882 
 
 4670 
 
 1038 
 
 2077 
 
 30 
 
 6 
 
 6 
 
 1.667 
 
 17,600 
 
 2934 
 
 4430 
 
 1305 
 
 2611 
 
 5105 
 
 1526 
 
 2259 
 
 5603 
 
 1247 
 
 2494 
 
 course pavement of the harder stone. In any case the amount 
 of mortar used should be about 10 per cent in excess of the voids 
 in the stone. There is so much variation in the grading of sand 
 and stone that a 1:2:4 mixture in one place may be equal to a 
 1:2:3 mixture in another. As the work progresses, the quality 
 of the concrete must be watched carefully, and the proportions 
 shifted so that the greatest density will be obtained. Attention 
 to this feature of the work is considered very important by ex- 
 perienced concrete road builders. 
 
CONCKETE ROADS 
 
 97 
 
 Quantities of Cement, Sand and Stone ^ in One Mile of Two-Course Concrete Road of 
 Different Widths and Thicknesses 
 
 (Furnished by the Portland Cement Association) 
 
 
 BASE 
 
 
 
 BASE MIX; 1: 2$: 4 
 
 BASE MIX; 1:2: 4 
 
 TOP 
 
 1 
 
 TOP MIX; 1$: 2$ 
 
 TOP MIX; 1: 1: 1} 
 
 
 
 
 
 
 
 
 W 
 
 
 
 
 Thick- 
 
 g 
 
 
 
 
 
 
 
 Thick- 
 
 o 
 
 
 
 
 
 
 
 
 
 ness 
 
 8 
 
 
 
 
 
 
 
 ness 
 
 8 
 
 
 
 
 
 
 
 w 
 
 1 
 
 
 
 a 
 
 02 
 
 1 
 
 1 
 
 VOLUME 
 
 1 
 
 1 
 
 02 
 
 02 
 
 I 
 
 O 
 
 I 
 
 1 
 
 1 
 
 3 
 
 VOLUME 
 
 6 
 
 I 
 
 OQ 
 
 6 
 
 I 
 
 1 
 
 ft. 
 
 ins. 
 
 ins. 
 
 cu. 
 yd*. 
 
 bbls. 
 
 CU. 
 
 yds. 
 
 CU. 
 
 yds. 
 
 bbls. 
 
 CU. 
 
 yds. 
 
 CU. 
 
 yds. 
 
 ins. 
 
 ins. 
 
 CU. 
 
 yds. 
 
 bbls. 
 
 CU. 
 
 yds. 
 
 Ctt. 
 
 yds. 
 
 bbls. 
 
 CU. 
 
 yds. 
 
 CU. 
 
 yds. 
 
 30 
 
 5 
 
 5 
 
 2445 
 
 3399 
 
 1247 
 
 2005 
 
 3692 
 
 1100 
 
 2176 
 
 2 
 
 2 
 
 977 
 
 2043 
 
 454 
 
 756 
 
 2902 
 
 429 
 
 644 
 
 10 
 
 4 
 
 5J 
 
 787 
 
 1094 
 
 401 
 
 645 
 
 1188 
 
 354 
 
 700 
 
 2 
 
 2 
 
 326 
 
 682 
 
 152 
 
 253 
 
 968 
 
 143 
 
 215 
 
 10 
 
 5 
 
 6| 
 
 951 
 
 1322 
 
 485 
 
 780 
 
 1436 
 
 428 
 
 846 
 
 2 
 
 2 
 
 326 
 
 682 
 
 152 
 
 253 
 
 968 
 
 143 
 
 215 
 
 12 
 
 4 
 
 5| 
 
 977 
 
 1358 
 
 498 
 
 801 
 
 1475 
 
 440 
 
 870 
 
 2 
 
 2 
 
 391 
 
 819 
 
 182 
 
 303 
 
 1161 
 
 172 
 
 258 
 
 12 
 
 5 
 
 6 
 
 1173 
 
 1630 
 
 598 
 
 962 
 
 1771 
 
 528 
 
 1044 
 
 2 
 
 2 
 
 391 
 
 819 
 
 182 
 
 303 
 
 1161 
 
 172 
 
 258 
 
 14 
 
 4 
 
 5f 
 
 1177 
 
 1636 
 
 600 
 
 965 
 
 1777 
 
 530 
 
 1048 
 
 2 
 
 2 
 
 456 
 
 955 
 
 212 
 
 354 
 
 1355 
 
 200 
 
 303 
 
 14 
 
 5 
 
 e! 
 
 1407 
 
 1956 
 
 718 
 
 1154 
 
 2125 
 
 633 
 
 1254 
 
 2 
 
 2 
 
 456 
 
 955 
 
 212 
 
 354 
 
 1355 
 
 200 
 
 303 
 
 14 
 
 4 
 
 6 
 
 1216 
 
 1690 
 
 620 
 
 997 
 
 1836 
 
 547 
 
 1082 
 
 2 
 
 2 
 
 456 
 
 955 
 
 212 
 
 354 
 
 1355 
 
 200 
 
 303 
 
 14 
 
 5 
 
 7 
 
 1445 
 
 2009 
 
 737 
 
 1185 
 
 2182 
 
 650 
 
 1286 
 
 2 
 
 2 
 
 456 
 
 955 
 
 212 
 
 354 
 
 1355 
 
 200 
 
 303 
 
 16 
 
 4 
 
 6 
 
 1392 
 
 1935 
 
 710 
 
 1141 
 
 2102 
 
 626 
 
 1239 
 
 2* 
 
 2 
 
 523 
 
 1091 
 
 243 
 
 404 
 
 1546 
 
 228 
 
 346 
 
 16 
 
 5 
 
 7 
 
 1651 
 
 2295 
 
 842 
 
 1354 
 
 2493 
 
 743 
 
 1469 
 
 2 
 
 2 
 
 523 
 
 1091 
 
 243 
 
 404 
 
 1546 
 
 228 
 
 346 
 
 18 
 
 4 
 
 6i 
 
 1612 
 
 2241 
 
 822 
 
 1322 
 
 2434 
 
 725 
 
 1435 
 
 2 
 
 2 
 
 586 
 
 1226 
 
 272 
 
 454 
 
 1739 
 
 257 
 
 390 
 
 18 
 
 5 
 
 7J 
 
 1906 
 
 2649 
 
 972 
 
 1563 
 
 2878 
 
 858 
 
 1696 
 
 2 
 
 2 
 
 586 
 
 1226 
 
 272 
 
 454 
 
 1739 
 
 257 
 
 390 
 
 20 
 
 4 
 
 61 
 
 1846 
 
 2566 
 
 941 
 
 1514 
 
 2787 
 
 831 
 
 1643 
 
 2 
 
 2 
 
 651 
 
 1362 
 
 302 
 
 504 
 
 1935 
 
 286 
 
 429 
 
 20 
 
 5 
 
 7* 
 
 2174 
 
 3022 
 
 1109 
 
 1783 
 
 3283 
 
 978 
 
 1935 
 
 2 
 
 2 
 
 651 
 
 1362 
 
 302 
 
 504 
 
 1935 
 
 286 
 
 429 
 
 20 
 
 4 
 
 4 
 
 1304 
 
 1813 
 
 665 
 
 1069 
 
 1969 
 
 587 
 
 1161 
 
 2 
 
 2 
 
 651 
 
 1362 
 
 302 
 
 504 
 
 1935 
 
 286 
 
 429 
 
 20 
 
 5 
 
 5 
 
 1630 
 
 2266 
 
 831 
 
 1337 
 
 2461 
 
 734 
 
 1451 
 
 2 
 
 2 
 
 651 
 
 1362 
 
 302 
 
 504 
 
 1935 
 
 286 
 
 429 
 
 22 
 
 4 
 
 4 
 
 1434 
 
 1993 
 
 731 
 
 1176 
 
 2165 
 
 645 
 
 1276 
 
 2 
 
 2 
 
 716 
 
 1498 
 
 333 
 
 555 
 
 2128 
 
 315 
 
 472 
 
 22 
 
 5 
 
 5 
 
 1793 
 
 2492 
 
 914 
 
 1470 
 
 2707 
 
 807 
 
 1596 
 
 2 
 
 2 
 
 716 
 
 1498 
 
 333 
 
 555 
 
 2128 
 
 315 
 
 472 
 
 24 
 
 4 
 
 4 
 
 1563 
 
 2173 
 
 797 
 
 1282 
 
 2360 
 
 703 
 
 1391 
 
 2 
 
 2 
 
 781 
 
 1634 
 
 363 
 
 605 
 
 2322 
 
 343 
 
 515 
 
 24 
 
 5 
 
 5 
 
 1955 
 
 2717 
 
 997 
 
 1603 
 
 2952 
 
 880 
 
 1740 
 
 2 
 
 2 
 
 781 
 
 1634 
 
 363 
 
 605 
 
 2322 
 
 343 
 
 515 
 
 30 
 
 4 
 
 4 
 
 1955 
 
 2717 
 
 997 
 
 1603 
 
 2952 
 
 880 
 
 1740 
 
 2 
 
 2 
 
 977 
 
 2043 
 
 454 
 
 756 
 
 2902 
 
 429 
 
 644 
 
 Mixing 
 
 The principles that should govern mixing were stated as fol- 
 lows by the 1916 conference: 
 
 The ingredients should be mixed in a batch mixer. The mixing should 
 be continued for at least one minute 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. 
 
 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. 
 
 The reason for fixing one nvnute as the minimum time for 
 mixing is that tests have shown that water is not worked through 
 
98 AMERICAN HIGHWAY ASSOCIATION 
 
 the mass as it should be in less than a minute. A smaller quan- 
 tity of wat r can be used with long-time mix ng than with short- 
 time mixing and the same degree of fluidity obtained. On ac- 
 count of the desirability of keeping the amount of water as close 
 as possible to 1 gallon per cubic yard of concrete, at least one 
 minute nrxing time is desirable. If a large quantity of water 
 is used and the mixing time is less than a minute, the product 
 may appear uni orm to the eye when it actually is not well mixed. 
 The reason for restricting the speed of the mixer to 16 revolu- 
 tions per minute is that at a higher speed some of the material 
 sticks to the drum and there is considerable splashing as the 
 concrete is discharged. At least 10 revolutions are necessary 
 to mix the aggregate. 
 
 Placing 
 
 The principles governing placing were stated as follows by the 
 1916 conference: 
 
 If the subgrade has been disturbed by teaming or other causes, it should 
 be brought to its former surface, and thoroughly moistened with water. 
 The concrete should be deposited rapidly to the required depth and width. 
 The section should be completed to a transverse joint, with 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 embedded in the concrete before the concrete has begun 
 to harden; the concrete above the reinforcement should be placed within 
 20 minutes after the placing of the concrete below. 
 
 In two-course pavements the top should be placed within twenty min- 
 utes after the placing of the bottom. 
 
 The standard specifications allow forty-five minutes as the 
 maximum time between the laying of the bottom course and the 
 placing of the top course. 
 
 Practically all concrete roads are built with special paving 
 mixers which discharge the concrete on the road where it is to 
 be used by means of chutes or buckets hauled along a boom that 
 can be swung from one side of the road to the other. The pitch 
 of the chute should be steep enough to deliver concrete of a 
 proper consistency readily. In the attempt to cover consider- 
 able area, contractors sometimes set the chute at a flat angle 
 and use too much water, in order to make the concrete flow 
 readily. Tests have shown that the least angle of the chute 
 should be 20 degrees. If the chute is new or rusted, concrete 
 with a proper amount of water will flow rather slowly down a 
 20 degree slope until the metal surface has been smoothed by the 
 wet mass. For this reason the chute may need a steeper slope 
 at the outset than later. 
 
CONCRETE ROADS 99 
 
 Forms 
 
 The 1916 conference adopted the following statement of the 
 principles that should govern the use of forms to retain the con- 
 crete at the sides of the roadway: 
 
 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-inch stock and capped with a 2-inch 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 edges of forms are clean so as to avoid un- 
 evenness 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. 
 
 They must be set firmly and the topes must be true to grade, 
 because they support the templets, bridges and other appliances 
 used in finishing the surface. The steel angles on wood forms 
 are necessary to enable the finishing work to proceed in a satis- 
 factory manner. By having the angles project 3 or 4 inches 
 beyond the end of the wood at one end and set back the same 
 distance at the other, the alignment of the forms will be facili- 
 tated. Painting wood forms will prevent warping and add to 
 their life. Where a power-driven striking and finishing machine 
 is used, specially heavy forms securely held in place are needed. 
 
 Joints 
 
 While transverse joints are omitted on some work, they are 
 generally required because of the prevailing opinion that they 
 reduce the cracking of the concrete. They are constructed by 
 placing across the road a strip of prepared filler made for the 
 purpose. This filler is usually held in place by a steel templet 
 until the concrete is deposited against it. The templet is then 
 removed and the concrete settles against the filler. The joints 
 are of two types, with and without metal protection plates. The 
 following statements regarding them were adopted at the 1916 
 conference : 
 
 Transverse joints should be placed across the pavement perpendic- 
 ular to the center line about 50 feet apart. There seems to be a tendency 
 to lengthen 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 perpendicularly to the surface of the 
 pavement to avoid the possibility of one slab rising above the other. 
 
 The tendency of present practice is toward the omission of metal 
 protection plates for joints. It is possible that the value of metal pro- 
 tection plates is dependent somewhat on the character of the aggregate 
 used, and it is considered that they are more essential in street pavements 
 than in country highways. 
 
100 AMERICAN HIGHWAY ASSOCIATION 
 
 The standard specifications call for J-inch transverse joints 
 at intervals of not more than 36 feet. The filler must project 
 at least f-inch above the concrete during construction, and after 
 the completion of the pavement it is trimmed off f-inch above 
 the surface. The traffic flattens out the projecting material and 
 hardens the top of the joints. Experience shows that it is very 
 desirable to have the joints form a plane surface perpendicular 
 to the surface of the road. 
 
 Measurements of the expansion and contraction of concrete 
 roadway slabs have been made by R. J. Wig, C. S. Laubly and 
 W. A. Mclntyre, from which they drew the following conclu- 
 sions: Contraction and expansion are caused by both temper- 
 ature changes and changes in moisture conditions, and under 
 climatic conditions similar to those at Washington, D. C., the 
 effects from these two factors in concrete road surfaces are ap- 
 proximately of the same magnitude. In concrete roads, ex- 
 pansion and contraction are sufficient to cause frequent trans- 
 verse cracks unless joints are provided. The actual movement 
 in any particular case depends upon the character of the concrete 
 and of the subgrade. A sloppy concrete shows greater movement 
 than a concrete mixed only moderately wet. 
 
 Organization of the Work 
 
 In order for the work to proceed economically, it is necessary 
 for the mixer to be kept running most of the time. This can 
 only be accomplished if repair parts are kept on hand and mate- 
 rials are supplied as needed. If the materials are delivered by 
 rail it often pays to keep men at the sand and stone plants to see 
 that the railroads furnish cars as needed and the shipments are 
 made on time. If the contractor operates his quarry he must 
 see that precautions are taken to reduce delays due to break- 
 downs or other causes to a minimum. The delivery of mate- 
 rials along the road calls for careful planning of both plant and 
 organization. In any case, provision should be made against de- 
 lays due to insufficient materials by storing supplies of cement, 
 sand and stone on the work. The cement can be stored in a shed 
 at the railroad siding or in tents with raised wood floors along the 
 road. The sand can also be stored along the road. The stone is 
 best stored at the railroad siding, because it is costly to rehandle 
 and by doing the work at one place mechanical appliances can be 
 used which will reduce the expense materially. The organiza- 
 tion should be arranged to avoid all unnecessary handling of 
 materials, not only because this involves a labor charge but also 
 because transportation equipment is doing no useful work while 
 being loaded or unloaded. Tractors with trailers, motor trucks 
 
CONCRETE ROADS 101 
 
 and industrial railways are generally used for hauling, and by 
 having competent repairmen to keep them in order and running 
 them with two shifts so as to use them about eighteen hours a 
 day, very low unit costs are often obtained in comparison with 
 the expense of hauling by horses or mules. 
 
 The water supply must be planned to wet the subgrade, sup- 
 ply the mixer and keep the concrete wet for a number of days 
 after it is laid. While it has been delivered along the road in 
 tanks, it is usually pumped through a pipe, generally 2 inches in 
 diameter. As the water which must be used sometimes con- 
 tains sand which will score the cylinders or plungers of a high 
 pressure pump so as to put it out of service, it is often lifted by a 
 centrifugal pump in such cases into a storage tank where the sand 
 has an opportunity to settle before the water is drawn by the 
 high-pressure pump. If the tank has two chambers separated 
 by a partition running nearly up to the water level, the separa- 
 tion of the sand will be improved, for the stream water can be 
 delivered into one chamber where most of the sedimentation 
 will occur and be drawn from the other. There should be a relief 
 valve in the pipe line near the pressure pump so as to prevent 
 breaking the pipe if all the gates on it are closed. If no valve is 
 used the pump should be belt driven, so that in case the pressure 
 rises the belt will slip. The friction head in a 2-inch pipe when 
 discharging 50 gallons per minute is about 85 feet per 1000 feet 
 of its length, and when discharging 60 gallons per minute the fric- 
 tion head is about 115 feet. Consequently the pump must have 
 power to overcome a considerable pressure due to friction as well 
 as that due to the highest elevation to which the water must 
 be raised. 
 
 The size of the paving gang will depend upon the size of the 
 mixer, which should depend in turn upon the rate at which mate- 
 rials can be delivered to it. There are two 1 sizes of mixers, one 
 in which two sacks of cement are used in each batch of concrete 
 and the other taking a three-sack batch. The smaller machine 
 requires about two men handling cement, two shovelers and two 
 wheelers for sand, three shovelers and three wheelers for stone, 
 a helper at the mixer and a man to bundle the cement sacks. 
 The larger machine requires about two men to handle cement, 
 three shovelers and three helpers for sand, four shovelers and 
 four wheelers for stone, a helper at the mixer and a man to bundle 
 sacks. In addition the crew requires a foreman, a mixer oper- 
 ator, a fireman, two men setting forms, a pump tender, three or 
 four men spreading and floating the concrete, two finishers, and 
 one or two attending to the curing of the concrete. To keep 
 
 8 During 1916, four-sack mixers were used on several roads, so it is prob- 
 able that there will be three sizes of mixers in regular use soon. 
 
102 AMERICAN HIGHWAY ASSOCIATION 
 
 such a gang working efficiently in the comparatively small area 
 occupied by a concreting job it is necessary to have the mate- 
 rials deposited so they can be handled expeditiously and without 
 confusion. 
 
 Finishing 
 
 The principles which should govern the finishing of concrete 
 were stated as follows by the conference: 
 
 The surface of the concrete should be struck off by means of a templet 
 moved with a combined longitudinal and transverse motion. The excess 
 material accumulated in front of the templet should be uniformly distrib- 
 uted over the surface of the pavement except near the transverse joint, 
 vrhere 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 com- 
 position as the body of the work. After being brought to the established 
 grade with a templet, the concrete should be finished, from a suitable 
 bridge, with a wood float to true surface. A metal float should not be 
 used. 1 
 
 Brooming of the surface is not necessary and grooves are objectionable 
 even on grades. 
 
 For country roads the templet or strikeboard is often made 
 of two 2 by 10-inch planks 1 foot longer than the road is wide. 
 The lower edge is cut to the desired crown of the road and shod 
 with a strip of J by 4-inch steel fastened with countersunk screws. 
 It has a handle on each side at each end, so it can be moved along 
 easily with a kind of sawing motion. This motion fills all de- 
 pressions with concrete and has no tendency to drag out the 
 large stone. A slight excess o .'concrete is always kept ahead 
 of the strikeboard, and a workman often walks in front of the 
 board to spread the concrete and take care of any excess that 
 may accumulate in front of it. It is usually necessary to run the 
 Btrikeboard over the surface three times; with very angular stone 
 it may be necessary to go over it four times. 
 
 Finishing is now regarded as very important. At Sioux City, 
 Iowa, where the concrete streets are unusually free from cracks, 
 the success with this type of roads is attributed to the special care 
 spent in the finishing. A wood float is preferred to a steel trowel 
 for finishing because it is believed to make a more dense surface 
 which is not slippery. The bridge from which the men work 
 is a 2 x 12-inch plank, trussed to prevent deflection and supported 
 by the side forms. No finishing should be done while there is 
 free water on the surface. For finishing at unprotected joints a 
 float split lengthwise, so as to fit over the joint filler, is used. 
 
 1 Owing to the rapid development of belt finishing it is probable that finish- 
 ing by wood floats will not be considered essential by many engineers after 
 this year. 
 
CONCRETE ROADS 103 
 
 Power finishing machines are now used to some extent as a 
 substitute for hand finishing. They operate by rapidly increas- 
 ing and decreasing the weight on the area of concrete on which 
 they rest. These vibrations of load joggle the concrete, increas- 
 ing its density and leaving a satisfactory finish when the con- 
 crete has a suitable consistency and the work is conducted 
 carefully. 
 
 During 1915 and 1916, an increasing use has been made of 
 belt finishing. The work is done with canvas belts from 12 to 
 24 inches wide. In Wayne County, Michigan, where the method 
 has been used for the longest time, a 12-inch belt about 1 foot 
 longer than the width of the road, is preferred. It has a handle 
 at each end and is pulled gently back and forth across the surface 
 after the latter has been shaped by the strikeboard. After the 
 surface is finished in this way, it is gone over a second time with 
 another belt, and sometimes a third time with a third belt. The 
 belts are washed at the close of each day. 
 
 When belts are used for finishing it is desirable to shape the 
 concrete with a strikeboard having a face about 8 inches wide and 
 long handles like those of a plow at each end. With such a strike- 
 board the men can tamp as well as shape the concrete, and thus 
 leave the surface in better condition for the belt than is the case 
 with a thin strikeboard. 
 
 Curing 
 
 The protection and curing of the concrete must be carried on 
 carefully because the best concrete may be seriously damaged 
 by too rapid drying out of the surface in hot or windy weather, 
 by exposure to low temperature or by being opened to traffic too 
 soon. The principles which should govern the work were stated 
 as follows by the 1916 conference: 
 
 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 pavement for at least two 
 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. 
 
104 AMERICAN HIGHWAY ASSOCIATION 
 
 Placing concrete in roads and pavements in temperatures at or near 
 freezing is not advisable, and if in special cases, such work is unavoidable, 
 the water and aggregate should be heated and precautions taken to pro- 
 tect the concrete from freezing for at least ten days. 
 
 Chemicals to lower the freezing temperature of the mixture should not 
 be used. Concrete should not be deposited on a frozen subgrade. 
 
 The canvas provided for protection during hot and windy 
 weather, should be sufficient to cover at least half the surface 
 laid during a day. Strips 2 yards wide are used and they are 
 about a yard longer than the width of the pavement so that each 
 end can be weighted. They are supported on frames so as not 
 to touch the concrete, and are kept in place until the concrete 
 has hardened. 
 
 The curing of concrete by ponding is not only more econom- 
 ical in many cases than the use of wet earth but it has a greater 
 advantage in permitting the inspector to determine at a glance 
 if the curing is proceeding properly. It is difficult to make cer- 
 tain that an earth covering is kept properly wet, but there can 
 be no question whether water is standing on the concrete. Banks 
 of earth are constructed along each edge of the pavement and 
 transverse banks at each expansion joint and more frequently 
 where the grades make them necessary. The water is kept at 
 least 2 inches deep over the center of the road. 
 
 If there is danger of a heavy storm which will pit the surface 
 of fresh concrete it must be protected by canvas. Contractors 
 are advised to request the nearest forecasting station of the United 
 States Weather Bureau to send its daily bulletin of the prob- 
 able weather conditions during the next thirty-six hours. 
 
 The standard specifications require both water and aggre- 
 gates to be heated if the temperature drops to 35 degrees or is 
 likely to do so within twenty-four hours, and the concrete laid 
 under these conditions must be specially protected from freezing 
 for at least ten days. A canvas cover will be sufficient to pro- 
 tect the concrete against frost during the first night and after 
 that about 3 inches of straw or marsh hay held down securely 
 will probably serve. If a sharp lowering of the temperature is 
 anticipated the straw should be covered with canvas. It is 
 cheaper to take all necessary precautions than to tear out and 
 replace damaged concrete. Even a light freezing of the top 
 will make the surface scale. 
 
 Maintenance 
 
 The following explanation of methods of maintenance was 
 prepared by A. H. Hinkle, L. C. Herrick, John W. Mueller and 
 Maurice Hoeffken for the 1916 conference: 
 
CONCRETE ROADS 105 
 
 Joints and cracks can be successfully treated by thoroughly cleaning 
 them and filling when dry, and preferably during warm weather, with hot 
 tar, then covering with dry sand or screenings. The tar should be per- 
 mitted to lap over the spalled edges of the crack, but not to exceed 1 inch. 
 The most desirable covering is clean, coarse sand or cleans creenings of stone, 
 slag or gravel, that will pass a $-inch circular opening, and be retained 
 on a ^-inch mesh screen. The tar should be poured when hot enough to 
 run readily into the crevices of the pavement (about 200 to 250 F.). 
 It is believed that no large excess of the tar should be used as the frequent 
 use of such an excess might eventually build up an elevation on the sur- 
 face which would be objectionable to traffic. The covering of screenings 
 or sand should be put on immediately after pouring the tar so that while 
 in the liquid state it will unite with the screenings or sand in sufficient 
 degree to prevent the tar from sticking to wheels of vehicles or melting 
 during hot periods and running from the cracks. 
 
 The use of a mastic consisting of a mixture of hot tar and sand, in place 
 of pure tar, for filling the cracks and joints, gives promise of excellent 
 results; but perhaps it is too soon to give definite specifications for this 
 mixture. The filling of the larger and more open cracks or joints with 
 the mastic, and the use of the pure tar for filling the minor openings in 
 the pavement and such as are made necessary by settlement after the 
 joints have been originally filled with the mastic, may be found to be most 
 satisfactory. 
 
 A pouring can with a round or vertical spout is very satisfactory for 
 pouring tar in filling cracks and joints. Inasmuch as it is desired that 
 the tar shall lap over the edges of the crack or joint, the use of a conical 
 pouring can would be of doubtful economy. 
 
 Small holes and shallow depressions can be successfully treated as fol- 
 lows: Clean surface thoroughly. Where the surface is disintegrated it 
 should first be thoroughly swept with a steel broom in order to remove 
 all loose spalls or foreign matter; afterward, the dust must be removed 
 by sweeping with a rattan or house broom. The hot tar is then applied 
 to the dry concrete and rubbed well with a squeegee or stiff broom to se- 
 cure a good bond to the surface of the concrete. The tar is then covered 
 with coarse sand or screenings (^ to Yg inch) of stone, slag or gravel. The 
 amount of tar used will vary from \ to 1 gallon per square yard, depending 
 upon the depth of the depression to be filled. When more than \ gallon 
 per square yard is used, it should be applied in two coats and the excess 
 screenings swept off before the second coat is applied. The more tar 
 that is applied to the surface, the more desirable it is to have the coarser 
 material for a covering. In filling small holes the application of the tar 
 in two layers would, of course be unnecessary. 
 
 To repair larger holes and deeper depressions than those discussed 
 above : Thoroughly clean and paint the surface with tar. Fill the hole 
 or depression with broken stone, preferably of such size that they will 
 not exceed in diameter one-half the depth of the depression to be filled 
 nor exceed in size stone suitable for an ordinary tar macadam. The stone 
 should be levelled off and compacted as well as may be by tamping 
 or rolling so as to conform to the true surface of the road. The voids are 
 then filled with the hot tar and screenings applied to the surface, which 
 is again compacted and treated as in building a tar macadam. 
 
 The use of a cold mix consisting of clean, hard stone chips coated with 
 a coal tar cutback, for filling such holes and depressions, as described 
 under the above paragraph, has been followed to some extent with very 
 promising results. The stone chips are first thoroughly coated with the 
 cold tar preparation by turning with shovels after the tar has been 
 sprayed upon them, as in mixing ordinary cement concrete. The mixture is 
 
106 AMERICAN HIGHWAY ASSOCIATION 
 
 then permitted to stand a few days until the lighter oils vaporize from the 
 tar, which leaves the stone coated with the heavy tar. The coated chips 
 are then well tamped into the hole or depression to be filled, the shallower 
 depressions being first painted with the pure tar. Coarse sand or fine 
 screenings are then spread over the surface. If the voids appear quite 
 open after the coated chips have been thoroughly tamped, a light appli- 
 cation of the tar is made to seal up the voids before the surface screenings 
 are applied. 
 
 Where the pavement is disintegrated badly or broken clear through so 
 as to require rebuilding, it should be cut away with vertical edges. After 
 the subgrade is levelled and compacted and the edges and subgrade thor- 
 oughly dampened (but the foundation not made muddy), the part cut 
 away is replaced with new concrete conforming in quality as nearly as 
 possible to the concrete of the surrounding pavement. It is well to coat 
 the edges of the old concrete with cement grout. Care should be taken 
 that the surface of the new concrete conforms to the surface of the adja- 
 cent concrete. The new concrete should be kept well dampened for about 
 seven days, and protected from traffic (ten days in warm weather and 
 much longer in cold weather) until thoroughly hardened. If the replace- 
 ment is over an excavation the concrete should be properly reinforced. 
 
STANDARD SPECIFICATIONS FOR PORT- 
 LAND CEMENT' 
 
 1. Portland cement is the product obtained by finely pul- 
 verizing clinker produced by calcining to incipient fusion, an 
 intimate and properly proportioned mixture of argillaceous and 
 calcareous materials, with no additions subsequent to calcination 
 excepting water and calcined or uncalcined gypsum. 
 
 2. Chemical Properties. The following limits shall not be 
 exceeded: 
 
 Loss on ignition, per cent 4.00 
 
 Insoluble residue, per cent 0. 85 
 
 Sulfuric anhydride (SO 3 ), per cent 2.00 
 
 Magnesia (MgO), per cent 5.00 
 
 3. Physical Tests. The specific gravity of cement shall be not 
 less than 3.10 (3.07 for white Portland cement). Should the test 
 of cement as received fall below this requirement a second test 
 may be made upon an ignited sample. The specific gravity test 
 will not be made unless specifically ordered. 
 
 4. The residue on a standard No. 200 sieve shall not exceed 22 
 per cent by weight. 
 
 5. A pat of neat cement shall remain firm and hard, and show 
 no signs of distortion, cracking, checking, or disintegration in 
 the steam test for soundness. 
 
 6. The cement shall not develop initial set in less than forty- 
 five minutes when the Vicat needle is used or sixty minutes when 
 the Gillmore needle is used. Final set shall be attained within 
 ten hours. 
 
 7. The average tensile strength in pounds per square inch of 
 not less than three standard mortar briquettes composed of one 
 part cement and three parts standard sand, by weight, shall be 
 equal to or higher than the following: 
 
 1 Adopted by the American Society for Testing Materials in 1904 and re- 
 vised in 1908, 1909 and 1916. These specifications are the result of several 
 years' work of a special committee representing a United States Govern- 
 ment Departmental Committee, the Board of Direction of the American 
 Society of Civil Engineers and Committee C-l on Cement of the American 
 Society for Testing Materials, in cooperation with Committee C-l. The 
 specifications as here printed are but the first part of the Society's "Stand- 
 ard Specifications and Tests for Portland Cement," as officially published. 
 
 107 
 
108 AMERICAN HIGHWAY ASSOCIATION 
 
 AGE AT 
 
 TEST 
 
 STORAGE 07 BRIQUETTES 
 
 TENSILH 
 STRENGTH 
 
 day, 
 
 7 
 
 1 day in moist air, 6 days in water 
 
 lb. per sq.in. 
 200 
 
 28 
 
 1 day in moist air, 27 days in water 
 
 300 
 
 
 
 
 8. The average tensile strength of standard mortar at twenty - 
 eight days shall be higher than the strength at seven days. 
 
 9. Packages, Marking and Storage. The cement shall be de- 
 livered in suitable bags or barrels with the brand and name of 
 the manufacturer plainly marked thereon, unless shipped in 
 bulk. A bag shall contain 94 pounds net. A barrel shall con- 
 tain 376 pounds net. 
 
 10. The cement shall be stored in such a manner as to permit 
 easy access for proper inspection and identification of each ship- 
 ment, and in a suitable weather-tight building which will protect 
 the cement from dampness. 
 
 11. Inspection. Every facility shall be provided the purchaser 
 for careful sampling and inspection at either the mill or at the 
 site of the work, as may be specified by the purchaser. At least 
 ten days from the time of sampling shall be allowed for the com- 
 pletion of the 7-day test, and at least 31 days shall be allowed for 
 the completion of the 28-day test. The cement shall be tested 
 in accordance with the methods hereinafter prescribed. The 
 28-day test shall be waived only when specifically ordered. 
 
 12. Rejection. The cement may be rejected if it fails to meet 
 any of the requirements of these specifications. 
 
 13. Cement shall not be rejected on account of failure to meet 
 the fineness requirement if upon retest after drying at 100C. 
 for one hour it meets this requirement. 
 
 14. Cement failing to meet the test for soundness in steam 
 may be accepted if it passes a retest using a new sample at any 
 time within 28 days thereafter. 
 
 15. Packages varying more than 5 per cent from the specified 
 weight may be rejected; and if the average weight of packages 
 in any shipment, as shown by weighing 50 packages taken at 
 random, is less than that specified, the entire shipment may be 
 rejected. 
 
PETROLEUM AND RESIDUUMS* 
 
 A large part of the materials used as dust preventives and 
 binders to hold together the mineral constituents of roads are 
 obtained from petroleum. Petroleum is a term which covers 
 mineral oils of a great variety of characteristics, all alike in being 
 composed of a great variety of complex chemical compounds 
 called hydrocarbons, of which there is a very large number. 
 The investigation of the properties of these hydrocarbons and 
 their derivatives requires a knowledge of organic chemistry which 
 few roadbuilders possess, and because some of them have at- 
 tempted to tread the veritable mazes of this extremely compli- 
 cated domain of chemistry, no little confusion has arisen. The 
 main facts regarding petroleum and the other hydrocarbons used 
 in roadbuilding are definitely known, but the details of any group 
 of these compounds are best left for the chemical specialist, who 
 is making steady progress in his researches concerning them. 
 
 Paraffin and Asphaltic Oils 
 
 The roadbuilder's interest in petroleum is largely in its base, 
 a term used to designate a part of oil left after distilling off the 
 more volatile portions. The base is sometimes made up of com- 
 pounds of the paraffin group or series, as chemists term such 
 allied compounds. Marsh gas is a member of the paraffin series, 
 and its least complex representative. A few other members are 
 gases but most of them are liquids or solids, and their number is 
 legion. The base of other petroleums is made up of compounds 
 called polycyclic polymethylenes by the chemist, and as these 
 compounds occur in native asphalts such a base is called asphaltic. 
 The base of other petroleums is made up of both paraffin and 
 asphaltic compounds and such petroleums are called semi- 
 asphaltic. 
 
 The gaseous hydrocarbons are of no interest to the roadbuilder. 
 The liquid and solid hydrocarbons are what determine the value 
 of petroleum for his purposes. The liquid and solid paraffins are 
 greasy materials without binding properties, while the asphaltic 
 materials are sticky. Consequently the roadbuilding value of 
 petroleum depends upon the asphaltic compounds in its base. 
 
 1 Revised by PreVost Hubbard, chief of road materials tests and re- 
 search, United States Office of Public Roads. 
 
 109 
 
110 AMERICAN HIGHWAY ASSOCIATION 
 
 Paraffin oils have been used successfully as dust preventives 
 when sprinkled in small quantities on a clean road, but if used in 
 large quantities they form a greasy, dirty surface and seem to 
 lubricate the pieces of stone in the road, which becomes rutted 
 rapidly. 
 
 Petroleum is obtained from many districts, which are called 
 fields in the industry. The leading fields which supply or have 
 supplied materials for roadbuilding in the United States are 
 discribed substantially as follows by John D. Northrop in Mineral 
 Resources of the United States, 1915: 
 
 1. The Appalachian field embraces all oil pools east of central 
 Ohio and north of central Alabama, including those of New York, 
 Pennsylvania, West Virginia, southeastern Ohio, Kentucky, 
 Tennessee, and northern Alabama. The oils of the Appalachian 
 field are in the main of paraffin base, free from asphalt and prac- 
 tically free from sulphur, and they yield by ordinary refining 
 methods high percentages of gasoline and illuminating oils the 
 products in greatest demand. 
 
 2. The Lima-Indiana field embraces all areas of oil production 
 in the northwestern part of Ohio and in Indiana. The petroleum 
 of the Lima-Indiana field contains some asphalt, though con- 
 sisting chiefly of paraffin hydrocarbons with sulphur compounds. 
 
 3. The Illinois field lies in the southeastern, south-central and 
 western parts of the State, comprising about 16 counties. Illinois 
 oils contain varying proportions of both asphalt and paraffin 
 and differ considerably as to specific gravity and distillation 
 products. Sulphur is generally present. 
 
 For commercial purposes it is customary to group under the 
 title "Mid-Continent field" the areas of oil production in Kansas, 
 Oklahoma, northern and central Texas, and northern Louisiana. 
 Mid-continent oils vary in composition within wide limits, rang- 
 ing from asphaltic oils poor in gasoline and illuminants, to oils 
 in which the asphalt content is negligible and the paraffin con- 
 tent relatively high and which yield correspondingly high per- 
 centages of the lighter products on distillation. Sulphur is pres- 
 ent in varying quantities in the lower grade oils. 
 
 5. The term "Gulf field" includes that portion of the gulf 
 coastal plain of Texas and Louisiana in which petroleum is found 
 in domes, associated with rock salt and gypsum. Oils from the 
 Gulf field are characterized by relatively high percentages of 
 asphalt and low percentages of the lighter gravity distillation 
 products. Considerable sulphur is present, much of which, how- 
 ever, is in the form of sulphureted hydrogen and is easily removed 
 by steam before refining or utilizing the oil as fuel. 
 
 6. The California field is mainly located in Kern, Fresno, 
 Orange, Santa Barbara and Los Angeles Counties. The Cali- 
 
PETROLEUM AND RESIDUUMS 
 
 111 
 
 fornia oils are generally characterized by much asphalt and little 
 or no paraffin and by small proportions of sulphur. The chief 
 products are fuel oils, lamp oils, lubricants, and oil asphalt. 
 
 Oils from Wyoming and Colorado are in the main of paraffin 
 base, suitable for refining by ordinary methods. Heavy asphaltic 
 oils are also obtained in certain of the Wyoming fields. 
 
 7. Mexican field. This extends along the Gulf of Mexico from 
 the vicinity of Tampico to the vicinity of Tuxpan, and produces 
 asphaltic and semi-asphaltic petroleum. 
 
 8. Trinidad field. A large amount of asphaltic petroleum is 
 produced on the island of Trinidad. 
 
 Clifford Richardson gives the following explanation of the rela- 
 tion between this petroleum and Trinidad asphalt: 
 
 Rising from the sands in which it occurs and coming in contact with the 
 colloidal clay forming a portion of the mud existing below the crater or 
 depression which holds the asphalt, it is emulsified with it and converted 
 into the material which we recognize as Trinidad lake asphalt. 
 
 Refining Petroleum 
 
 Crude asphaltic petroleum has been used as a dust preventive 
 and as a binder, but generally the petroleum is refined to obtain 
 a number of valuable materials occurring in it. The crude oil 
 is first allowed to settle in tanks in which the mineral matter 
 
 Petroleum Marketed in the United States in 1915 by Fields 
 (John D. Northrop, in Mineral Resources of the United States, 1915) 
 
 FIELD. 
 
 QUANTITY (BAR- 
 EELS OF 42 GAL- 
 LONS) 
 
 VALUE 
 
 AVERAGE PRIOB 
 PER BARREL 
 
 Appalachian 
 
 22,860,048 
 
 $35 468,973 
 
 $1 552 
 
 Lima-Indiana 
 
 4 269 591 
 
 4 114 228 
 
 964 
 
 Illinois 
 
 19 041 695 
 
 18 655 850 
 
 980 
 
 Mid-continent 
 
 123 295 867 
 
 72 437 701 
 
 588 
 
 Gulf 
 
 20 577 103 
 
 9 802 901 
 
 476 
 
 California.. . 
 
 86 591 535 
 
 36 558 439 
 
 422 
 
 Colorado and Wyoming 
 
 4 454 000 
 
 2 400 503 
 
 539 
 
 Other fields 
 
 14 265* 
 
 24 295* 
 
 1 703 
 
 
 
 
 
 
 281,104,104 
 
 $179,462,890 
 
 $0.638 
 
 * Includes Alaska, Michigan, and Missouri. 
 
 NOTE : The Barber Asphalt Company reports that the importation of 
 crude petroleum from Trinidad has been as follows: 1914, 140,438 barrels; 
 1915, 330,022 barrels; 1916, 372, uOO barrels. The imports of crude petro- 
 leum from Mexico are reported by John D. Northrop as follows: 1914, 
 16,245,975; 1915, 17,478,472 barrels. 
 
 A preliminary estimate by J. D. Northrop of the 1916 production in the 
 United States is 292,300,000 barrels. 
 
112 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 Degrees Baume, Specific Gravities, Weights in Pounds per Gallon and Volume 
 
 in Gallons per Pound of Petroleum at 60F. 
 
 (From "United States Standard Tables for Petroleum Oils," United States 
 Bureau of Standards) 
 
 D EGREE8 
 BAUMri 
 
 SPECIFIC 
 GRAVITY 
 
 POUNDS PER 
 GALLON 
 
 GALLONS 
 PER POUND 
 
 DEGREES 
 
 BAUM 
 
 SPECIFIC 
 GRAVITY 
 
 POUNDS PER 
 GALLON 
 
 GALLONS 
 PER POUND 
 
 10.0 
 
 1.0000 
 
 8.328 
 
 0.1201 
 
 19.6 
 
 0.9358 
 
 7.793 
 
 0.1283 
 
 10.2 
 
 0.9986 
 
 8.317 
 
 0.1202 
 
 19.8 
 
 0.9346 
 
 7.783 
 
 0.1285 
 
 10.4 
 
 0.9972 
 
 8.305 
 
 0.1204 
 
 20.0 
 
 0.9333 
 
 7.772 
 
 0.1287 
 
 10.6 
 
 0.9957 
 
 8.293 
 
 0.1206 
 
 20.2 
 
 0.9321 
 
 7.762 
 
 0.1288 
 
 10.8 
 
 0.9943 
 
 8.281 
 
 0.1208 
 
 20.4 
 
 0.9309 
 
 7.752 
 
 0.1290 
 
 11.0 
 
 0.9929 
 
 8.269 
 
 0.1209 
 
 20.6 
 
 0.9296 
 
 7.742 
 
 0.1292 
 
 11.2 
 
 0.9915 
 
 8.258 
 
 0.1211 
 
 20.8 
 
 0.9284 
 
 7.731 
 
 0.1293 
 
 11.4 
 
 0.9901 
 
 8.246 
 
 0.1213 
 
 21.0 
 
 0.9272 
 
 7.721 
 
 0.1295 
 
 11.6 
 
 0.9887 
 
 8.234 
 
 0.1214 
 
 21.2 
 
 0.9259 
 
 7.711 
 
 0.1297 
 
 11.8 
 
 0.9873 
 
 8.223 
 
 0.1216 
 
 21.4 
 
 0.9247 
 
 7.701 
 
 0.1299 
 
 12.0 
 
 0.9859 
 
 8.211 
 
 0.1218 
 
 21.6 
 
 0.9235 
 
 7.690 
 
 0.1300 
 
 12.2 
 
 0.9845 
 
 8.199 
 
 0.1220 
 
 21.8 
 
 0.9223 
 
 7.680 
 
 0.1302 
 
 12.4 
 
 0.9831 
 
 8.188 
 
 0.1221 
 
 22.0 
 
 0.9211 
 
 7.670 
 
 0.1304 
 
 12.6 
 
 0.9818 
 
 8.176 
 
 0.1223 
 
 22.2 
 
 0.9198 
 
 7.660 
 
 0.1305 
 
 12.8 
 
 0.9804 
 
 8.165 
 
 0.1225 
 
 22.4 
 
 0.9186 
 
 7.650 
 
 0.1307 
 
 13.0 
 
 0.9790 
 
 8.153 
 
 0.1227 
 
 22.6 
 
 0.9174 
 
 7.640 
 
 0.1309 
 
 13.2 
 
 0.9777 
 
 8.142 
 
 0.1228 
 
 22.8 
 
 0.9162 
 
 7.630 
 
 0.1311 
 
 13.4 
 
 0.9763 
 
 8.131 
 
 0.1230 
 
 23.0 
 
 0.9150 
 
 7.620 
 
 0.1313 
 
 13.6 
 
 0.9749 
 
 8.119 
 
 0.1232 
 
 23.2 
 
 0.9138 
 
 7.610 
 
 0.1314 
 
 13.8 
 
 0.9736 
 
 8.108 
 
 0.1233 
 
 23.4 
 
 0.9126 
 
 7.600 
 
 0.1316 
 
 14.0 
 
 0.9722 
 
 8.096 
 
 0.1235 
 
 23.6 
 
 0.9115 
 
 7.590 
 
 0.1318 
 
 14.2 
 
 0.9709 
 
 8.086 
 
 0.1237 
 
 23.8 
 
 0.9103 
 
 7.580 
 
 0.1319 
 
 14.4 
 
 0.9695 
 
 8.074 
 
 0.1239 
 
 24.0 
 
 0.9091 
 
 7.570 
 
 0.1321 
 
 14.6 
 
 0.9682 
 
 8.063 
 
 0.1240 
 
 24.2 
 
 0.9079 
 
 7.561 
 
 0.1323 
 
 14.8 
 
 0.9669 
 
 8.052 
 
 0.1242 
 
 24.4 
 
 0.9067 
 
 7.551 
 
 0.1324 
 
 15.0 
 
 0.9655 
 
 8.041 
 
 0.1244 
 
 24.6 
 
 0.9056 
 
 7.541 
 
 0.1326 
 
 15.2 
 
 0.9642 
 
 8.030 
 
 0.1245 
 
 24.8 
 
 0.9044 
 
 7.531 
 
 0.1328 
 
 15.4 
 
 0.9629 
 
 8.019 
 
 0.1247 
 
 25.0 
 
 0.9032 
 
 7.522 
 
 0.1330 
 
 15.6 
 
 0.9615 
 
 8.007 
 
 0.1249 
 
 25.2 
 
 0.9021 
 
 7.512 
 
 0.1331 
 
 15.8 
 
 0.9602 
 
 7.997 
 
 0.1250 
 
 25.4 
 
 0.9009 
 
 7.502 
 
 0.1333 
 
 16.0 
 
 0.9589 
 
 7.986 
 
 0.1252 
 
 25.6 
 
 0.8997 
 
 7.493 
 
 0.1335 
 
 16.2 
 
 0.9576 
 
 7.975 
 
 0.1254 
 
 25.8 
 
 0.8986 
 
 7.483 
 
 0.1336 
 
 16.4 
 
 0.9563 
 
 7.964 
 
 0.1256 
 
 26.0 
 
 0.8974 
 
 7.473 
 
 0.1338 
 
 16.6 
 
 0.9550 
 
 7.953 
 
 0.1257 
 
 26.2 
 
 0.8963 
 
 7.464 
 
 0.1340 
 
 16.8 
 
 0.9537 
 
 7.942 
 
 0.1259 
 
 26.4 
 
 0.8951 
 
 7.454 
 
 0.1342 
 
 17.0 
 
 0.9524 
 
 7.931 
 
 0.1261 
 
 26.6 
 
 0.8940 
 
 7.445 
 
 0.1343 
 
 17.2 
 
 0.9511 
 
 7.921 
 
 0.1262 
 
 26.8 
 
 0.8929 
 
 7.435 
 
 0.1345 
 
 17.4 
 
 0.9498 
 
 7.910 
 
 0.1264 
 
 27.0 
 
 0.8917 
 
 7.425 
 
 0.1347 
 
 17.6 
 
 0.9485 
 
 7.899 
 
 0.1266 
 
 27.2 
 
 0.8906 
 
 7.416 
 
 0.1348 
 
 17.8 
 
 0.9472 
 
 7.888 
 
 0.1268 
 
 27.4 
 
 0.8895 
 
 7.407 
 
 0.1350 
 
 18.0 
 
 0.9459 
 
 7.877 
 
 0.1270 
 
 27.6 
 
 0.8883 
 
 7.397 
 
 0.1352 
 
 18.2 
 
 0.9447 
 
 7.867 
 
 0.1271 
 
 27.8 
 
 0.8872 
 
 7.388 
 
 0.1354 
 
 18.4 
 
 0.9434 
 
 7.856 
 
 0.1273 
 
 28.0 
 
 0.8861 
 
 7.378 
 
 0.1355 
 
 ' 18.6 
 
 0.9421 
 
 7.846 
 
 0.1275 
 
 28.2 
 
 0.8850 
 
 7.369 
 
 0.1357 
 
 18.8 
 
 0.9409 
 
 7.835 
 
 0.1276 
 
 28.4 
 
 0.8838 
 
 7.360 
 
 0.1359 
 
 19.0 
 
 0.9396 
 
 7.825 
 
 0.1278 
 
 28.6 
 
 0.8827 
 
 7.351 
 
 0.1360 
 
 19.2 
 
 0.9383 
 
 7.814 
 
 0.1280 
 
 28.8 
 
 0.8816 
 
 7.341 
 
 0.1362 
 
 19.4 
 
 0.9371 
 
 7.804 
 
 0.1281 
 
 29.0 
 
 0.8805 
 
 7.332 
 
 0.1364 
 
 NOTE: Tables for oils of greater specific gravity than 1.000 and of the 
 comparative volumes of oils at 60 and other temperatures are given on 
 pages 129 and 131. 
 
PETEOLEUM AND RESIDUUM8 113 
 
 and water are separated from the oil. The latter is drawn off 
 into cylindrical stills set horizontally in brickwork like boilers. 
 There is a furnace below the still, and the latter contains steam 
 coils and sometimes steam jets at the bottom of the stills. The 
 heating by means of the furnace and the steam coils and jets 
 should be conducted very carefully, if the final products are to 
 be used for road work, and careless heating has resulted in very 
 undesirable materials being sold for highway purposes. The 
 vapors from the stills are removed to condensers and liquefied. 
 
 The distillate that is obtained until the temperature reaches 
 about 300F. and the specific gravity of the product is about 0.73 
 is refined to furnish gasoline and naphtha. While the tempera- 
 ture is increased from 300 to 575F., the specific gravity of the 
 distillate increases to about 0.82, and the oil produced during 
 this stage is treated to supply kerosene. If it is desirable to pro- 
 duce as much kerosene as possible the furnace is heated and the 
 sides of the still kept as cool as possible, so that some of the 
 heavy vapor driven off in the bottom of the still will condense 
 in the top and fall back into the much hotter material at the 
 bottom, "cracking" these heavy vapors into lighter compounds. 
 One result of such cracking is often the liberation of free carbon, 
 which settles into the material in the bottom of the still. As- 
 phaltic oils can be cracked at a lower temperature than paraffin 
 oils. 
 
 If road oils for surface treatment are desired, the distilling 
 process is stopped after the light distillates are driven off. The 
 thick oil left in the still is called the residuum, and some people 
 look upon it as a by-product and the name "residuum" as having 
 a somewhat derogatory signification. As a matter of fact the 
 residuum obtained in distilling some petroleums is by far the most 
 important product obtained from them. Some Calif ornian and 
 Mexican oils contain such a large amount of asphaltic compounds 
 and so little light oils that by stopping the refining process when 
 the residuum has the consistency desired for some classes of 
 paving materials, it is unnecessary to add any other bitumen to 
 fit it for use. 
 
 In the patented Trumbull process, the oil is heated and then 
 allowed to flow down the inner surface of a large vertical heated 
 cylinder. The vapors are drawn from the top of the cylinder 
 and the asphaltic residuum is collected at the bottom. The 
 temperatures used and the rate at which the crude oil is fed to 
 the top of the cylinder fix the consistency of the residuum. 
 
 One of the earliest attempts to improve the process of refining 
 petroleum so as to yield the maximum quantity of products useful 
 for paving was made by Dubbs. By adding sulphur to the 
 residuum while it was at a high temperature he produced mate- 
 
114 AMERICAN HIGHWAY ASSOCIATION 
 
 rials which have been widely used as fluxes. About the same 
 time Byerly found that by blowing air through the heated re- 
 siduum asphaltic products were obtained, the oxygen performing 
 the same function as the sulphur used in the Dubbs process. 
 Some of these blown-oil products have been used as fluxes and 
 others have been used for a great variety of purposes. Some 
 asphaltic oils furnish a residuum which does not require blowing 
 to obtain road material but this treatment is generally employed 
 with semi-asphaltic oils when such a product is desired. Appar- 
 ently the hydrocarbons of the paraffin series are little affected by 
 the blowing process, which affects compounds of other series. 
 
 Meaning of Analyses. The characteristics of the residuums 
 from various oils are given in the accompanying table. The fol- 
 lowing notes explain the significance of the information in the 
 table, and are abridged from Pr&vost Hubbard's Dust Preventives 
 and Road Binders. 
 
 Specific Gravity. The mark "25/25C." indicates that the 
 determination was made at 25C. (77F.) and the result expressed 
 in comparison with water at the same temperature. The test 
 is mainly useful in identifying the material, but also gives a rough 
 indication of the amount of heavy hydrocarbons which give 
 body to the material. Material having a specific gravity exceed- 
 ing 0.93 or 0.94 should be heated before use. 
 
 Flash Point. This test is of value as differentiating between 
 the heavy crude oils and cut-back 1 products, and the fluid re- 
 siduums. It also shows the point to which a refined oil has been 
 distilled and whether it is advisable to heat the material before 
 application. 
 
 Loss at 160C. The loss in weight is an indication of the rela- 
 tive losses by volatilization of different road oils in actual service. 
 It is an empirical test, like the rattler test for paving bricks. The 
 residue should be sticky. If it is desirable for the material to 
 maintain its consistency after application, it should show a low 
 loss. If the material is applied by a method which requires more 
 or less fluidity, a high loss is permissible, in order that the mate- 
 rial may rapidly attain the desired consistency in the road, 
 although a high loss is not necessary in the case of dust preven- 
 tives. The loss is now usually determined at 163C. 
 
 Loss at 205C. The purpose of this test is to show the effect 
 of a high temperature as compared with 160 or 163. It is not 
 often made. 
 
 Bitumen Soluble in 082. The solubility of the bitumen itself 
 is independent of its character and consistency, so the amount 
 and character of insoluble material is of most interest. 
 
 1 A cut-back product is one made by fluxing a dense asphalt with a 
 light oil. 
 
PETROLEUM AND RESIDUUMS 
 
 115 
 
116 AMERICAN HIGHWAY ASSOCIATION 
 
 Inorganic Matter. This indicates in some cases the nature of 
 the dense bitumen. 
 
 Insoluble Organic Matter. This affords an indication of 
 whether oil has been distilled destructively. 
 
 Bitumen Insoluble in 88B. Naphtha. The hydrocarbons in- 
 soluble in paraffin naphtha are termed "asphaltenes" and those 
 which are soluble "malthenes." The former tend to give body 
 and consistency and the latter contribute adhesive properties to 
 a road material. Blown oils contain very high amounts of insol- 
 uble hydrocarbons, sometimes as much as 25 to 30 per cent. The 
 character of the bitumen dissolved in naphtha, after the solvent 
 has evaporated, is instructive, for a sticky residue indicates better 
 road building qualities in the original material than that which 
 is greasy. 
 
 Soluble Bitumen Removed by H2S04 and Saturated Hydro- 
 carbons in Total Bitumen. These tests are mainly of value as 
 indicating the source of the material under examination. Clifford 
 Richardson gives the following explanation of the significance of 
 the tests in The Modem Asphalt Pavement: 
 
 Hydrocarbons in general are divided into those which are saturated 
 and those which are unsaturated, the former being stable and the latter 
 reactive and very susceptible to change, combining with or being con- 
 verted into other hydrocarbons by the action of sulphuric acid and other 
 reagents. The saturated can be separated from the unsaturated hydro- 
 carbons by strong sulphuric acid, and this will be found to be a very impor- 
 tant means of differentiating the oils and the solid bitumens among them- 
 selves, by determining the relative proportions of these two classes of 
 hydrocarbons which they contain. 
 
 Solid Paraffin. This test confirms the information obtained 
 from an inspection of the residue after the test of the loss at 
 160C. The heavy liquid hydrocarbons of the paraffin series are 
 probably more detrimental in road oils than are the solid paraffins. 
 
 Fixed Carbon. Fixed carbon is the coke resulting from the 
 ignition of the bitumen in the absence of oxygen. 
 
 Fluxes 
 
 Fluxes are petroleum products which are mixed with harder 
 bituminous materials to soften them to any desired consistency. 
 Petroleum with a paraffin base furnished the first flux used in 
 the asphalt paving industry. 
 
 Asphaltic or semi-asphaltic flux is the residuum left on distilling 
 petroleum having an asphaltic or semi-asphaltic base to a point 
 where the residuum is a dense liquid when cool but any further 
 distillation will produce a solid residuum when cold. It is char- 
 acterized by a relatively low amount of saturated hydrocarbons. 
 While it resembles natural maltha in some respects, it differs in 
 remaining soft after heating to 400F., most malthas becoming 
 hard pitches after such treatment. 
 
ASPHALT AND NATIVE SOLID BITUMENS' 
 
 The following definition of "asphalt" has been adopted by the 
 American Society for Testing Materials: 
 
 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. 
 
 This definition is dependent upon the same society's definition 
 of "bitumens," which is: 
 
 Mixtures of native or pyrogenous hydrocarbons and their non-metallic 
 derivatives, which may be gases, liquids, viscous liquids, or solids, and 
 which are soluble in carbon disulphide. 
 
 These definitions were prepared after numerous conferences of 
 road engineers and producers of materials, and while adopted by 
 the society are not accepted by all specialists. 
 
 The following definitions are given by Clifford Richardson in 
 The Modern Asphalt Pavement: 
 
 Native bitumens consist of a mixture of native hydrocarbons and their 
 derivatives, which may be gaseous, liquid, a viscous liquid or solid, but, 
 if solid, melting more or less readily on the application of heat, and solu- 
 ble in turpentine, chloroform, bisulphide of carbon, similar solvents, and 
 in the malthas or heavy asphaltic oils. Natural gas, petroleum, maltha, 
 asphalt, grahamite, gilsonite, ozocerite, etc., are bitumens. Coal, lignite, 
 wurtzelite, albertite, so-called indurated asphalts, are not bitumens, be- 
 cause they are not soluble to any extent in the u^ual solvents for bitumen, 
 nor do they melt at comparatively low temperatures nor dissolve in heavy 
 asphaltic oils. These substances, however, on destructive distillation 
 
 1 Revised by Provost Hubbard, chief of road materials tests and re- 
 search, United States Office of Public Roads. 
 
 2 Solid bituminous materials are those having a penetration at 25C. 
 (77F.) under a load of 100 grams applied for five seconds, of not more than 
 10. The significance of " penetration" is explained on page 121. 
 
 Semi-solid bituminous materials are those having a penetration at 25C. 
 (77 F.) under a load of 100 grams applied for five seconds, of more than 
 10 and a penetration under a load of 50 grams applied for 1 second of not 
 more than 350. 
 
 Liquid bituminous materials are those having a penetration at 25C. 
 (77 F).) under a load of 50 grams applied for one second or more than 
 350.. 
 
 117 
 
118 AMERICAN HIGHWAY ASSOCIATION 
 
 give rise to products which are similar to natural bitumens, and they have 
 been on this account defined by T. Sterry Hunt as "pyro-bitumens," 
 which differentiates them very plainly from the true bitumens." 
 
 Asphalt is a term used industrially to cover all the solid native bitu- 
 mens used in the paying industry and specifically to include only such as 
 melt on the application of heat, at about the temperature of boiling water, 
 are equally soluble in carbon bisulphide and carbon tetrachloride and to 
 a large extent in 88 naphtha, those hydrocarbons soluble in naphtha 
 consisting to a very considerable degree of saturated hydrocarbons, yield- 
 ing about 15 per cent of fixed carbon and containing a high percentage of 
 sulphur. Under this definition it can be seen that grahamite is not an 
 asphalt, since it is not largely soluble in naphtha and yields a very high 
 percentage of fixed carbon on ignition. It is also less soluble in carbon 
 tetrachloride than in carbon bisulphide. Gilsonite is not an asphalt, 
 since the saturated hydrocarbons contained in the naphtha solution are 
 very small in amount and quite different in character from those found 
 in asphalt. 
 
 Roadbuilders use the term "natural asphalts" to designate 
 the native solid or semi-solid asphalts, and "oil asphalts" to desig- 
 nate the corresponding materials prepared from petroleum or 
 maltha. Some producers of oil asphalts object to the term on 
 the ground that the material obtained by distilling away the 
 lighter parts of asphaltic petroleum is as "natural" as that 
 obtained by refining native asphalts. By "rock asphalt" is 
 meant sandstone and limestone impregnated with asphalt or 
 maltha. "Asphaltic sands" are mixtures of asphalt or maltha 
 and sand, the latter in loose grains which fall apart when the 
 bitumen is extracted; many of them are called rock asphalts 
 because in their natural condition the maltha cements them into 
 a rock-like mass. 
 
 The sources of the asphalts used in the United States are given 
 in the accompanying table. The quantities of materials there 
 stated were not all used for road and street purposes, as there are 
 many other uses to which some of them are put. 
 
 Trinidad Asphalt. Trinidad asphalt comes from the island of 
 that name. The main source is on La Brea Point, about 28 miles 
 from Port of Spain, the chief town. Here there is a circular pitch 
 lake of nearly 115 acres extent, between which and the sea are 
 other pitch deposits more or less mixed with sand. The former 
 furnishes the "lake asphalt" and the latter the "land asphalt" 
 of the paving industry. 
 
 The material in the lake is described by Clifford Richardson 
 as an emulsion of water, gas, bitumen, fine sand and clay. It is 
 in constant motion owing to the evolution of gas, and for this 
 reason, whenever a hole is dug in the surface, whether deep or 
 shallow, it rapidly fills up and the surface resumes its original 
 level after a short time. Although soft it can be readily flaked 
 out with picks in large conchoidal masses weighing 50 to 75 
 
ASPHALT AND NATIVE SOLID BITUMENS 
 
 119 
 
 pounds. It is honey-combed with gas cavities and resembles a 
 Swiss cheese in structure. It is of uniform composition, as 
 follows: Water and gas volatilized at 100C., 29 per cent; bitumen 
 soluble in cold carbon disulphide, 39 per cent; bitumen absorbed 
 
 American Production and Importation of Asphaltic Materials, 1915 
 
 (Compiled from report by John D. Northrop in Mineral Resources of the 
 
 United States, 1915. Output stated in tons of 2000 pounds, except 
 
 in case of imports, which are in tons of 2240 pounds) 
 
 
 19 
 
 15 
 
 19 
 
 14 
 
 
 Tons 
 
 Value 
 
 Tons 
 
 Value 
 
 American bituminous rock .... 
 Wurtzelite (elaterite), gilsonite 
 Grahamite 
 
 44,329 
 20,559 
 10,863 
 
 $157,083 
 275,252 
 94,155 
 
 51,071 
 
 19,148 
 9,669 
 
 $162,622 
 405,966 
 73,535 
 
 
 
 
 
 
 Total American natural bitu- 
 minous material 
 
 75751 
 
 526 490 
 
 79 888 
 
 642 123 
 
 American road oils and fluxes. 
 
 417,859 
 
 2,392,576 
 
 171,447 
 
 
 American oil asphalts and 
 pitches 
 
 246,644 
 
 2,323,007 
 
 189,408 
 
 
 
 
 
 
 
 Total American road oils, as- 
 phalts, etc. 
 
 664,503 
 
 4,715,583 
 
 360,855f 
 
 3,016,969 
 
 Mexican road oils and fluxes* 
 
 174,854 
 
 1,325,201 
 
 111,058 
 
 
 Mexican oil asphalts and 
 pitches* 
 
 213,464 
 
 2,405,235 
 
 202,729 
 
 
 
 
 
 
 
 Total Mexican road oils, as- 
 phalts, etc* 
 
 388,318 
 
 3,730,436 
 
 313 787 
 
 4 131,153 
 
 Imports of asphalt 
 Trinidadf .. 
 
 92,107 
 
 498,900 
 
 61,708 
 
 334,635 
 
 Bermudez 
 
 28,659 
 
 144,595 
 
 58,755 
 
 295,765 
 
 Cuba 
 
 391 
 
 9,243 
 
 458 
 
 11,407 
 
 Barbados 
 
 64 
 
 6,426 
 
 71 
 
 6,592 
 
 Mexico 
 
 56 
 
 755 
 
 140 
 
 2,048 
 
 Switzerland 
 
 200 
 
 1 637 
 
 620 
 
 3 706 
 
 Italy 
 
 492 
 
 3,438 
 
 247 
 
 1 477 
 
 France 
 
 
 
 100 
 
 1,317 
 
 England ... . . 
 
 774 
 
 9,801 
 
 628 
 
 6,269 
 
 Germany ... 
 
 658 
 
 4,854 
 
 1,354 
 
 10,856 
 
 
 
 
 
 
 * Refined in the United States from imported Mexican petroleum, 
 f There are discrepancies in the figures in the report. 
 
 by mineral matter, 0.3 per cent; mineral matter, 27.2 per cent; 
 water of hydration in clay and silicates, 4.3 per cent. 
 
 Trinidad land asphalt reached the places where it is found 
 either by overflowing from the lake or by intrusion into the soil 
 from the same subterranean source that supplies the lake asphalt. 
 
120 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 Its character is much affected by the effect of the weathering to 
 which it has been subjected. Clifford Richardson states that 
 refined land asphalt of good quality differs from the lake supply 
 byits higher specific gravity due to the larger amount of mineral 
 matter it contains, by a higher softening or melting point, and 
 a somewhat lower percentage of bitumen and, in consequence of 
 these facts, a much greater hardness at all temperatures. Land 
 asphalt requires much more paraffin flux than lake asphalt, and 
 asphaltic oil fluxes offer certain advantages over paraffin fluxes 
 for use with land asphalt. 
 
 Composition of Refined Trinidad and Bermudez Asphalts 
 (Clifford Richardson) 
 
 
 TRINIDAD 
 
 BERMTTDEZ 
 
 Specific gravity at 77F. (25C.) . . . 
 
 1 40 
 
 1 08 
 
 Streak 
 
 Blue black 
 
 Black 
 
 Lustre 
 
 Dull 
 
 Bright 
 
 Structure 
 
 Homogeneous 
 
 Uniform 
 
 Fracture 
 
 Semi-con- 
 
 Semi-con- 
 
 Hardness 
 
 choidal 
 2 
 
 choidal 
 Soft 
 
 Melts .. 
 
 235F.(113C.) 
 
 183F.(84C.) 
 
 Penetration at 77F. (25C.) 
 
 4 
 
 20 
 
 Loss at 325F. (163C.), 7 hours 
 
 1.1% 
 
 3% 
 
 Character of residue 
 
 Smooth 
 
 Smooth 
 
 Loss at 400F (205C ) 7 hours 
 
 4 0% 
 
 8 2% 
 
 Character of residue 
 
 Blistered 
 
 Wrinkled 
 
 Bitumen soluble in CSg 
 
 56 5% 
 
 94.4% 
 
 Bitumen retained by mineral matter 
 
 3% 
 
 
 Mineral matter 
 
 38.5% 
 
 3.6% 
 
 Water of hydration 
 
 4 2% 
 
 
 Vegetable matter 
 
 
 2 0% 
 
 Bitumen soluble in 88 naphtha 
 
 35 6% 
 
 62 2% 
 
 Percentage of total bitumen which above is 
 Soluble bitumen removed by HjSO^ 
 
 63.1% 
 61.3% 
 
 65.4% 
 62.4% 
 
 Saturated hydrocarbons in total bitumen. . 
 Pure bitumen soluble in C Cl^ 
 
 24.4% 
 100 0% 
 
 24.4% 
 99 5% 
 
 Fixed carbon 
 
 10 8% 
 
 13.4% 
 
 
 
 
 Bermudez Asphalt. Bermudez asphalt comes from a pitch lake 
 in Venezuela about 30 miles from the coast in an air line. The 
 lake is about 1J miles long, 1 mile wide, of irregular shape and 
 covers about 900 acres. It is covered with a crust from a few 
 inches to 2 feet thick, having some grass and shrubs, with a few 
 palms, and the pitch is visible on the surface in but few places. 
 It is very wet, so that excavations fill with water and it is diffi- 
 cult to excavate the pitch, which has an average depth of 4 feet. 
 The deposit is probably formed by the exudation of a large quan- 
 tity of soft maltha. The asphalt from the lake varies greatly in 
 
ASPHALT AND NATIVE SOLID BITUMENS 121 
 
 the amount of water it contains, which fluctuates between 11 
 and 46 per cent. This water is not emulsified with the bitumen 
 but is adventitious surface water. The material for industrial 
 use is selected, and when refined has the composition given in 
 the accompanying table, which also gives the -composition of refined 
 Trinidad asphalt. 
 
 Meaning of Analyses. The significance of most of the terms 
 used in this table are explained in the section on Petroleum. The 
 new terms are the following: 
 
 Streak is the color of a rubbed or scratched surface. 
 
 Hardness is stated in terms of Mohr's scale, in which 1 is the 
 hardness of talc, 2 that of rock salt, 3 that of calcite, 4 that of 
 fluorite, etc. When a bitumen is softer than I on this scale its 
 hardness is stated by its behavior in a penetration test, explained 
 below. 
 
 Melting point is determined by an arbitrary test, because 
 bituminous materials are made up of a mixture of hydrocarbons 
 and their derivatives and can not have a true melting point, such 
 as a definite compound possesses. 
 
 Penetration is determined by the distance that a needle of 
 specified size loaded with a specified weight will penetrate into a 
 sample of the material in a specified time. Usually a No. 2 
 needle loaded so that the total weight is 100 grams and a time 
 period of 5 seconds is employed, but a 50-gram weight and a 
 1-second time period are used with liquid bitumens. Prevost 
 Hubbard makes the following statement regarding this test: 
 
 The penetration test is a convenient one to employ for identification 
 and control, and is often indicative of the value of an oil or asphalt product 
 for construction work. While the test for bituminous road materials is 
 made in the same manner as in asphalt paving work, the standards for 
 road purposes are somewhat different. No oil product should be employed 
 in macadam construction with a penetration higher than 25 mm. when 
 tested at 25C. with a No. 2 needle for five seconds under a weight of 100 
 grams, unless it possesses the property of hardening considerably when 
 subjected to the volatilization test. On the other hand, it is rarely neces- 
 sary to require a penetration as high as that for asphaltic cement used in 
 the topping of an asphalt pavement, for the reason that the upper course 
 of a macadam road has much greater inherent stability than the sand 
 course of the asphalt pavement. A penetration of from 10 to 15 mm. is 
 usually considered sufficient for road work. If a material having a much 
 lower penetration is selected, its susceptibility to temperature changes 
 will have to be considered. 
 
 Organic matter insoluble is a term of uncertain significance 
 which has been explained by Clifford Richardson as follows : 
 
 On adding together the percentages of bitumen soluble in carbon disul- 
 phide and of inorganic matter obtained on ignition, the sum will seldom 
 amount to 100.0. The difference has been considered for many years as 
 
122 AMERICAN HIGHWAY ASSOCIATION 
 
 organic matter not bitumen (insoluble). This maybe true in exceptional 
 cases, but recent investigations have shown that it is not at all so in many 
 bitumens. For example, in Trinidad asphalt it has been found to consist 
 of the water of combination of the clay which the material contains and 
 some inorganic salts which are volatilized on ignition. The amount of 
 organic matter is extremely small. In other cases, it may consist to a 
 considerable extent of grass and twigs, as in the seepages which have run 
 out over sod. On the whole, therefore, it seems desirable not to describe 
 it by any definite name, but merely as an undetermined difference. 
 
 Pure bitumen soluble in CCU (carbon tetrachloride) is not 
 usually determined unless a road oil has been badly cracked or a 
 solid bitumen like grahamite has been added, so that the per- 
 centage of hydrocarbons insoluble in 88 naphtha is high. The 
 bitumens insoluble in carbon tetrachloride but soluble in carbon 
 bisulphide are called "carbenes." 
 
 Other Asphalts. Maracaibo asphalt is found on the Limon 
 River about 50 miles west of Maracaibo, Venezuela. According 
 to Clifford Richardson it is an exudation from maltha springs. 
 When carefully refined it contains from 92 to 97 per cent of 
 bitumen soft enough to be indented by the finger nail. It con- 
 tains a very small percentage of malthenes and has a higher soften- 
 ing point than either Trinidad or Bermudez asphalt. 
 
 Cuban asphalts are found in small quantities in many places 
 on the island and what little use of them is made in the United 
 States is mainly for varnishes. A deposit 18 miles from Havana 
 has furnished material used in street pavements. 
 
 Asphaltic materials are found in many places in Mexico, and 
 some of them have been developed more or less. What is usually 
 known among roadbuilders as Mexican asphalt is prepared from 
 the malthas and petroleums obtained mainly from the Tampico 
 and Tuxpan district. 
 
 Natural asphalt has been obtained in California at several 
 places, but the most noted deposits are no longer worked. 
 
 Refining natural asphalt consists merely in driving off the 
 water it contains by heating the material to about 325F. in 
 large tanks containing coils of pipes through which steam is 
 passed. In the bottom of the tanks are steam jets which agitate 
 the asphalt. The vegetable impurities, if any, are skimmed from 
 the top. The refined asphalt is drawn off while it is liquid into 
 barrels for shipment. When it is to be used, it is melted with a 
 residuum flux. 
 
 Solid Bitumens not Asphalts. Gilsonite is a hard, brittle bitu- 
 men with a reddish brown streak and a conchoidal fracture, 
 obtained mainly from Utah and Colorado. It is sold in two 
 grades, gilsonite selects and gilsonite seconds, the former being 
 the more pure. Gilsonite from different mines varies consider- 
 ably, and some of it is of little value for use in paving mixtures. 
 
ASPHALT AND NATIVE SOLID BITUMENS 
 
 123 
 
 Grahamite is a hard, brittle bitumen with a black streak, 
 otherwise resembling gilsonite in appearance. Its softening 
 point is very high and not yet definitely determined. It is 
 obtained mainly from Oklahoma. 
 
 Properties of Gilsonite and Grahamite 
 (Clifford Richardson, The Modern Asphalt Pavement} 
 
 
 GILSC 
 
 JUTE 
 
 GRAHAMITE 
 
 Specific gravity, 78/78F. . . . 
 Streak 
 
 1.044 
 Brown 
 
 1.049 
 Brown 
 
 1.171 
 Black 
 
 Lustre 
 
 Lustrous 
 
 Lustrous 
 
 Dull 
 
 Fracture 
 
 Sub-con- 
 
 Sub-con- 
 
 Hackly 
 
 Hardness 
 
 choidal 
 
 2 
 
 choidal 
 2 
 
 Brittle 
 
 Softens 
 
 260F. 
 
 300F. 
 
 Intumesces 
 
 Flows 
 
 275F. 
 
 325F. 
 
 Intumesces 
 
 Loss, 325F., 7 hours 
 
 0.9% 
 
 2.3% 
 
 0.1% 
 
 Loss, 400F., 7 hours 
 
 1.2% 
 
 4.0% 
 
 0.5% 
 
 Bitumen soluble in CSz 
 
 99.0% 
 
 99.9% 
 
 94.1% 
 
 Insoluble organic matter .... 
 Mineral matter 
 
 0.0% 
 0.0% 
 
 0.0% 
 
 0.1% 
 
 0.2% 
 
 5.7% 
 
 Bitumen soluble 88 naphtha 
 Soluble bitumen removed by 
 H 2 SO 4 
 
 47.2% 
 87.7% 
 
 15.9% 
 71.8% 
 
 0.4% 
 25.0% 
 
 Total bitumen as saturated 
 hydrocarbons 
 
 5 9% 
 
 4.5% 
 
 0.32% 
 
 Bitumen soluble in 62 naph- 
 tha 
 
 67 4% 
 
 30 3% 
 
 0.7% 
 
 Bitumen insoluble in CCU . . 
 Fixed carbon 
 
 0.0% 
 13 0% 
 
 0.4% 
 13.4% 
 
 68.7% 
 53.3% 
 
 
 
 
 
 Manjak resembles grahamite and is obtained from Barbadoes 
 and South America. Its lack of uniformity and its high price have 
 prevented any large use of it for American pavements, although 
 it is used successfully in preparing other materials. 
 
 Fluxing Solid Bitumens. Paving materials are made from solid 
 bitumens by fluxing them with petroleum residuums by two 
 methods. In the first method the residuum is heated to above 
 the temperature at which the solid bitumen melts and the latter 
 is then added. Grahamite does not melt but intumesces and the 
 residuum to flux it must be raised to an exceptionally high tem- 
 perature. The mixture is agitated until the bitumen is all 
 melted and the combined material is of uniform quality. 
 
 In the second method, the residuum is heated to about 350F. 
 and air is then blown through it for six to forty hours, depending 
 upon the quality of the old and the properties desired in the fin- 
 ished product. As soon as it reaches the proper consistency the 
 blowing is stopped and enough solid bitumen mixed with it to 
 give a paving material having the required properties. 
 
ASPHALTIG MATERIALS FOR ROADS' 
 
 The selection of bituminous materials for road purposes should 
 be based upon the local climatic conditions, the volume and 
 character of the traffic, the character of the stone to be used, 
 and the type of road to be constructed or maintained. Such 
 conditions manifestly call for expert advice. The requirements 
 of several state highway departments are given here merely as 
 indicating the way in which specialists have met the needs of 
 their respective localities. 2 
 
 Some of the requirements for road oils can be met by a few 
 crude asphaltic petroleums. Pre*yost Hubbard gives the accom- 
 panying analysis of a crude California petroleum of this char- 
 acter. This oil contained a small amount of water, and care in 
 heating it would be necessary to prevent foaming. Hubbard 
 says that "this oil is capable of increasing greatly in consistency 
 after application and would serve as an excellent binding medium." 
 
 1 Revised by Pr6vost Hubbard, chief of road materials tests and re- 
 search, United States Office of Public Roads. 
 
 2 Among the engineers to whom this chapter was submitted was F. H. 
 Joyner, Road Commissioner of Los Angeles County, California, who pre- 
 pared the following comment, which illustrates forcibly the necessity of 
 the services of a specialist in extensive road improvements: 
 
 "From a study of the notes you submitted made by my assistants and 
 myself, and from reports of the chemist and chief road oiler, we reached 
 the decision that our study and conclusions on what we call road oils are 
 of value only here in California, where we use only the native oils. While 
 there is much in the notes that would not be applicable to our California 
 oils or asphalts, I do not believe it would be necessary or proper to propose 
 any changes in the notes." 
 
 The following statement by W. Arthur Brown, chemist of the Los 
 Angeles county road department, explains the views mentioned by Mr. 
 Joyner : 
 
 "The desirable constituent of a first-class road is asphalt. The asphalt 
 carpet coat demands an oil that contains the highest grade of asphalt. It 
 also demands that this asphalt be thin enough to spread well. It should 
 enter all the interstices of the road surface. When the lighter constituents 
 of the oil have served their purpose, namely, that of carrier and distribu- 
 tor, they are no longer needed, in fact, they are not needed except, possi- 
 bly, in very small amount. They should then be of such a nature that they 
 will volatilize readily. We do not wish a possible volatile constituent that 
 is solid or nearly so in cold weather but thin and acting as a fluxing agent 
 in hot weather. 
 
 The specification of the Los Angeles county highway department is a 
 departure from, and simpler than, the older ones requiring fixed carbon, 
 asphaltene, viscosity, float test, loss on heating during a certain number 
 of hours at a specified temperature, ductility test, etc. This specification 
 requires that the oil be reduced on the Brown evaporator in a specified 
 time. This test determines the percentage of asphalt and insures the 
 
 124 
 
ASPHALTIC MATERIALS FOB ROADS 125 
 
 Crude California Petroleum Adapted for Road Work 
 (From Provost Hubbard's Dust Preventives and Road Binders) 
 
 Character Black, viscous, sticky. 
 
 Specific gravity 25/25C 0.984 
 
 Flash point, degrees C 160.0 
 
 Loss at 100C., 7 hours, per cent 5.25 
 
 Character of residue More viscous than crude 
 
 Loss at 163C., 7 hours, per cent 16.4 
 
 Character of residue Sticky, very viscous 
 
 Loss at 205C., 7 hours, per cent 30.0 
 
 Character of residue Solid, not brittle 
 
 Soluble in CS 2 , per cent 99.77 
 
 Organic matter insoluble, per cent 0.12 
 
 Inorganic matter, per cent 0.11 
 
 Bitumen insoluble in 86 naphtha, per cent 9.8 
 
 Fixed carbon, per cent 2.05 
 
 Viscosity, mentioned in this table, is explained by PreVost 
 Hubbard as follows: 
 
 If it is desired to apply a rpad binder at a given temperature, as for 
 instance when it is to be heated by means of steam, a determination of its 
 viscosity at that temperature is often of value. The test also serves as 
 a means of identification. When a viscous material is to be cut with one 
 of lower viscosity in order to bring it to a proper consistency for applica- 
 tion, the actual viscosity of the mixture should be ascertained and not 
 calculated from that of the two constituents for the reason that this prop- 
 erty is not additive. 
 
 In reporting the results of the test, the temperature of the 
 material, the quantity used in testing, and the time in seconds 
 taken by the material in flowing through a short tube of standard 
 dimensions in what is called an Engler viscosimeter, are recorded. 
 The longer the period of time taken by the material in flowing 
 through the tube, the greater its viscosity. 
 
 The float test is employed in determining the relative con- 
 sistency of very viscous materials. The results are reported in 
 seconds of time that a float containing the material under test 
 will remain floating in water at a stated temperature. It is con- 
 sidered a very useful test in controlling the preparation of road 
 
 volatile oil being 01 such a nature that it will leave the oil when once it is 
 applied on the road. The percentage of asphalt is also much nearer the 
 actual in the oil than by the methods of heating in an oven at a lower 
 temperature. These specifications also require a stickiness test. This 
 stickiness test, made on the Brown adhesivemeter, when interpreted in 
 accordance with the entire specifications, especially with the time to reduce 
 to asphalt, determine whether the oil has sufficient binding properties to 
 hold the particles from displacement from each other and from the base. 
 The stickiness and loss are standardized against road oils found on the 
 market throughout California. The results of the tests have been carefully 
 compared with actual service results, which are in accord with laboratory 
 results in every case so far known." 
 
126 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 oils from given materials, for by continuing the heating until 
 the residue gives a predetermined result in the float test, a uni- 
 form product will be obtained. 
 
 The ductility test shows the distance in centimeters that a 
 briquette of the material will stretch before breaking, when 
 pulled at the rate of 5 centimeters per minute. The briquette 
 is 1 cm. square at the smallest section and has a cross-section 
 of 2 square cm. at the clips, which are 3 cm. apart. 
 
 State Requirements for Asphaltic Materials for Penetration Roads 
 
 
 ILLINOIS 
 
 OHIO 
 
 NEW 
 YORK 
 
 PENNSYL- 
 VANIA 
 
 Grade A 
 
 Grade B 
 
 Grade 
 A-l 
 
 Grade 
 A 
 
 Specific gravity, 25/25C 
 
 1.000+ 
 163 
 
 50 
 5-12* 
 
 6 
 Smooth 
 
 0.97-1.00 
 200 
 
 15 
 
 5-8 
 
 2 
 
 Smoothf 
 
 99.5 
 
 0.97+ 
 180 
 
 30 
 9-16} 
 
 5 
 
 
 0.97+ 
 190 
 
 40 
 14-19 
 
 5 
 
 
 
 
 Flash point, degrees C., min 
 Ductility at 25C., centimeters, 
 min ... 
 
 
 45 
 9-15 
 5 
 
 Penetration, 100 gr., 5 sec., 
 25C., mm., min 
 Loss at 163C., 5 hrs., per cent, 
 max 
 
 Character of residue 
 
 Bitumen soluble in 82, per 
 cent, min . ... 
 
 99.0 
 
 Pure bitumen products 
 
 99.5 
 95.0 
 80.0 
 65.0 
 
 72-85 
 
 99.5 
 95.0 
 81.0 
 66.0 
 
 72-85 
 98.9+ 
 8-16 
 
 99.5 
 96.0 
 81.0 
 66.0 
 
 70-88A 
 
 Bermudez products 
 
 
 Cuban products 
 
 
 
 Trinidad products 
 
 
 98.5 
 
 Solubility in 86 naphtha, per 
 cent 
 
 72-80 
 99.4+ 
 7-14 
 
 Solubility in CCU, per cent.. 
 
 Fixed carbon, per cent. . . 
 
 8-16 
 
 
 
 * 8-12 for material with 90 per cent total bitumen, 7-10 for material 
 with 80 per cent to 90 per cent bitumen and 5-8 for Trinidad material 
 having less than 80 per cent bitumen. 
 
 t Penetration of residue at least 60 per cent of that of the original 
 material. 
 
 } 9-12 for pure bitumen products, 12-16 for fluxed native asphalts. 
 
 Penetration of residue at least half that of original material. 
 
 A In 76 naphtha. 
 
 NOTE Illinois specifies a brittleness test as follows: "A cylindrical 
 prism of the bituminous binder 1 cm. in diameter, after being maintained 
 at a temperature of 5C. (41 F.) for 20 minutes, shall bend 180 degrees 
 at any point without checking or breaking." New York specifies a tough- 
 ness test as follows: "It (the bituminous material) shall show a toughness 
 at 32F. not less than 15 cm. Toughness is determined by breaking a 
 cylinder of the material If inches in diameter by If inches in height in a 
 Page impact machine. The first drop of the hammer is from a height of 
 5 cm. and each succeeding blow is increased by 5 cm." New York also 
 specifies a maximum of 4.7 per cent of paraffin. 
 
ASPHALTIC MATERIALS FOR ROADS 
 
 127 
 
 
 : 
 
 lO CO CO<?9 
 
 O*O 
 00<M 
 
 00 
 
 o 
 
 fiq 
 
 ^ 
 
 f2 
 
 "e 
 
 1 
 
 e 
 
 ^ 
 
 I 
 
 a, 
 
 co 
 
 i 
 
 0500 CoS 
 
 CiOCQ 1 
 - * 
 
 
 00 
 
 4- 
 
 Oll 
 
 O5 IO r-H CO ,, 00 1 
 05 OS 00 CO 05 00 
 
 >o oo o 
 
 O5 CO i 1 CO 
 O5 O500 CO 
 
 1C OOO 
 
 Oi CO i-H CO 
 
 Oi O5 OO CO 
 
 M-1O 
 <N 00 
 
 8 
 
 
 o 5 
 
 21 
 
 gs 
 
 * *H M 
 
 * O_< 
 S^^ 
 
 .STJ g 
 fecg'Sb 
 
 $ 
 og*S 
 
 I 
 
 2-? si 1 
 
 
 i P ^ - 3 
 ;rgi:s 
 
 1 2 a 9 
 
 O ^.2 ^ o3 -t- 3 03 
 ^ ft'o'S O^^J 
 
 illflllj 
 
 llpIW 
 
 
128 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 State Requirements for Asphaltic Materials for Surfacing 
 
 
 NEW YORK 
 
 OHIO 
 
 Grade 
 H. O. 
 
 Grade 
 C. O. 
 
 Grade 
 H. O. 
 
 Grade 
 M. O. 
 
 Grade C. O 
 
 Specific gravity 25/25C 
 
 0.96 
 
 163 
 
 * 
 
 10 
 
 0.93 
 
 52 
 30 
 
 0.96 
 
 0.93 
 
 0.91 
 
 Flash Point degrees C 
 
 Ductility at 20C cm ... 
 
 
 
 ' ' 30 ' ' 
 
 Sticky 
 99.5 
 
 90-98 
 3 
 
 Loss at 163C., 5 hours, per cent . 
 Character of residue 
 
 5 
 
 25 
 
 Bitumen soluble in CS2, per cent. 
 Solubility in 86 naphtha, per 
 cent 
 
 99.5 
 
 75.90f 
 6^14 
 
 4.7 
 
 99.5 
 
 80-95 f 
 10 
 4.0 
 
 99.5 
 
 80-94 
 6 
 
 99.5 
 
 85-97 
 3.5 
 
 Fixed carbon, per cent 
 
 Paraffin scale per cent 
 
 
 
 
 * The residue after evaporation to 10 mm. penetration at a tempera- 
 ture not exceeding 500F., must amount to 85 to 95 per cent of the original 
 volume and have a ductility of at least 25 cm. 
 
 t In 76 naphtha. 
 
 j The residue after evaporation to 10 mm. penetration at a temperature 
 not exceeding 500F. must amount to 50 to 65 per cent of the original 
 volume and have a ductility of at least 25 cm. 
 
 NOTE New York specifies the following toughness test: Grade H. O. 
 shall show a toughness at 32F. not less than 20 cm. determined by the 
 Page impact test. Ohio requires a viscosity of 10 to 60 at 100C. for 50 cc. 
 for Grade H. O., 40 to 80 at 50C. for 50 cc. for Grade M. O., and 5 to 12 
 at 50C. for 50 cc. for Grade C. O. 
 
 Shipping Road Oil. Small quantities of road oil are shipped in 
 tight wooden 50-gallon barrels, such as are used for shipping 
 molasses, or in steel barrels. These barrels make the oil cost 2 
 to 3 cents a gallon more than the price for the oil itself. Unin- 
 jured empty barrels can generally be resold to the shipper. 
 Heavy oil is troublesome to remove from barrels, and they are 
 usually dumped into the open heating kettles and broken up. 
 When the oil is warm the broken pieces of wood are raked out 
 and used for fuel. If there is no heating kettle on the job, the 
 barrels of heavy oil must be kept close to a fire or in a very warm 
 room before the oil can be poured from them into the distributor. 
 
 Larger quantities of oil are shipped in tank cars, holding 8000 
 or 12,000 gallons. Where a large amount of oil is to be used 
 annually near any railway, it will be desirable for the officials to 
 supply a tank into which the oil can be run as soon as the car 
 arrives. The season for roadwork is limited and during it there 
 is a brisk demand for tank cars. The oil company which loses 
 the service of a car for a week or ten days, while it stands on a 
 siding waiting to be emptied, is obliged to add an equivalent 
 item to its overhead expense, and the road district which provides 
 for prompt discharge of tank cars is in a position to demand, 
 
ASPHALTIC MATERIALS FOR ROADS 
 
 129 
 
 and will probably get, quotations shaded somewhat to recognize 
 its sense of business fairness. 
 
 If oil must be used hot, a f or 1-inch steam connection must 
 be made with the heating coils of the tank car. For this reason, 
 the car is often spotted on a siding near an electric station or 
 mill, but the steam can also be furnished by a road roller, trac- 
 tion engine or other convenient source. It will take from twelve 
 to twenty-four hours to heat a tankful of heavy oil to 150 to 
 170F., which is high enough to allow it to be pumped. The 
 temperature can be increased after that in the distributor. The 
 amount of steam supplied to the heating coils of the car is regu- 
 lated by a valve on the exhaust pipe of the coil, which is adjusted 
 to prevent a waste of steam. As some road' oils have a low flash 
 point, great care must be taken to prevent any oil coming in con- 
 tact with a flame. The temperature of the oil should be tested 
 from time to time with a thermometer, to see that it is not over- 
 heated. If there is any water in the oil it will give a great deal 
 of trouble if heated quickly, and if foaming is detected the rate 
 of heating should be checked at once. 
 
 Specific Gravities, Degrees Baume, Weights in Pounds per Gallon and Volume 
 
 in Gallons per Pound of Oils at 60F. Having Specific 
 
 Gravities Exceeding LOO 
 
 SPECIFIC 
 GRAVITY 
 
 DEGREES 
 BAUME 
 
 POUNDS 
 PER GALLON 
 
 GALLONS 
 PER POUND 
 
 SPECIFIC 
 GRAVITY 
 
 DEGREES 
 BAUME 
 
 POUNDS 
 PER GALLON 
 
 GALLONS 
 PER POUND 
 
 1.00 
 
 0.00 
 
 8.328 
 
 0.1201 
 
 1.15 
 
 18.91 
 
 9.577 
 
 0.1021 
 
 1.01 
 
 1.44 
 
 8.411 
 
 0.1189 
 
 1.16 
 
 20.00 
 
 9.660 
 
 0.1009 
 
 1.02 
 
 2.84 
 
 8.495 
 
 0.1177 
 
 1.17 
 
 21.07 
 
 9.744 
 
 0.0997 
 
 1.03 
 
 4.22 
 
 8.578 
 
 0.1165 
 
 1.18 
 
 22.12 
 
 9.827 
 
 0.0985 
 
 1.04 
 
 5.58 
 
 8.661 
 
 0.1153 
 
 1.19 
 
 23.15 
 
 9.910 
 
 0.0973 
 
 1.05 
 
 6.91 
 
 8.744 
 
 0.1141 
 
 1.20 
 
 24.17 
 
 9.994 
 
 0.0961 
 
 1.06 
 
 8.21 
 
 8.828 
 
 0.1129 
 
 1.21 
 
 25.16 
 
 10.077 
 
 0.0949 
 
 1.07 
 
 9.49 
 
 8.911 
 
 0.1117 
 
 1.22 
 
 26.15 
 
 10.160 
 
 0.0937 
 
 1.08 
 
 10.74 
 
 8.994 
 
 0.1105 
 
 1.23 
 
 27.11 
 
 10.243 
 
 0.0925 
 
 1.09 
 
 11.97 
 
 9.078 
 
 0.1093 
 
 1.24 
 
 28.06 
 
 10.327 
 
 0.0913 
 
 1.10 
 
 13.18 
 
 9.161 
 
 0.1081 
 
 1.25 
 
 29.00 
 
 10.410 
 
 0.0908 
 
 1.11 
 
 14.37 
 
 9.244 
 
 0.1069 
 
 1.26 
 
 29.92 
 
 10.494 
 
 0.0889 
 
 1.12 
 
 15.54 
 
 9.327 
 
 0.1057 
 
 1.27 
 
 30.83 
 
 10.577 
 
 0.0877 
 
 1.13 
 
 16.68 
 
 9.411 
 
 0.1045 
 
 1.28 
 
 31.72 
 
 10.660 
 
 0.0865 
 
 1.14 
 
 17.81 
 
 9.494 
 
 0.1033 
 
 1.29 
 
 32.60 
 
 10.743 
 
 0.0853 
 
 NOTE: For a similar table of oils of specific gravities less than 1.00 
 see page 112. 
 
 Pumping Road Oil. In order to remove the oil from the tank 
 car to the distributors, some form of pump is generally necessary, 
 for it is not often that the car can be placed on a siding or trestle 
 high enough to allow it to be emptied by gravity. 
 
130 AMERICAN HIGHWAY ASSOCIATION 
 
 If a lift pump set in the top of the car is used, it should be a 
 3 or 4-inch size. With it one man can fill a 600-gallon dis- 
 tributor in twenty minutes. 
 
 In many cases a hose or pipe is connected to the bottom of 
 the car and run to an oil pump, operated by a steam or gasoline 
 engine, which forces the oil into the distributor. A 1J or 2-inch 
 power-driven rotary pump will deliver 600 gallons in ten to fif- 
 teen minutes. These pumps work with either hot or cold oil. 
 A water tank pump can be used with cold oil but hot oil will ruin 
 the valves speedily. A 2-inch suction tank pump will fill a 600- 
 gallon tank in thirty to forty minutes. 
 
 The hose used in the connections between the pump and the 
 bottom of the tank car should be as short as possible because the 
 oil often destroys it rapidly. It is desirable to have a cut-off 
 valve in the connection pipe. When everything is coupled ready 
 for use, the discharge valve in the bottom of the car is raised by 
 means of a vertical stem running up to the dome of the car, and 
 the flow of oil is controlled by the cut-off valve, for the manipu- 
 lation of the tank valve is quite troublesome. 
 
 Heating Road Oil. As the fixed and operating charges at an 
 oil storage plant are about the same irrespective of the amount 
 of oil delivered into distributors, it is desirable to load as many 
 carts daily as practicable, in order to reduce the unit cost of such 
 work. In California, where large amounts of oil are used in sur- 
 facing concrete roads, oil stations have been designed with par- 
 ticular attention to effecting such economics. It is considered 
 desirable to have the oil at a temperature of 300 F. when it is 
 applied, so it is heated to 325 for delivery within 10 miles and 
 350 for longer deliveries. 
 
 The oil is discharged from the cars into storage tanks or pits 
 holding 10,000 to 25,000 gallons. These contain steam coils to 
 warm the oil sufficiently to enable it to be pumped into a circu- 
 lating tank holding 2000 to 3000 gallons, where it is heated 
 further by steam coils. The oil is then pumped through a heater 
 and back into the circulating tank until its temperature is about 
 200, after which the temperature of the heater is raised and the 
 oil pumped through it into the distributor. The whole operation 
 takes one and one-half hours. 
 
 The heater resembles a return tubular boiler. The furnace 
 has a fire brick arch and walls and is heated by oil burners. The 
 heated gases pass over the furnace arch in a chamber formed of 
 ordinary brick masonry, and finally escape through a steel stack. 
 The oil is pumped through a multiple grid of 3-inch pipes. The 
 design is made on the assumption that with furnace temperatures 
 of 1800 to 2000, 1 square foot of heating surface will transmit 
 3 British thermal units per hour per degree of change in temperature. 
 
ASPHALTIC MATERIALS FOR ROADS 
 
 13J 
 
 Volume of Oil at 60F. Equivalent to Unit Volume at Stated Temperatures in 
 Fahrenheit Degrees 
 
 0F 
 
 
 
 10 
 
 20 
 
 30 
 
 40 
 
 50 
 
 60 
 
 70 
 
 80 
 
 90 
 
 
 
 
 
 
 
 
 1.000 
 
 0.996 
 
 0.992 
 
 0.988 
 
 100 
 200 
 300 
 400 
 
 0.984 
 0.947 
 0.912 
 0.881 
 
 0.980 
 0.943 
 0.909 
 0.877 
 
 0.977 
 0.940 
 0.906 
 0.875 
 
 0.973 
 0.936 
 0.903 
 0.871 
 
 0.969 
 0.933 
 0.899 
 0.868 
 
 0.965 
 0.929 
 0.896 
 0.865 
 
 0.962 
 0.926 
 0.893 
 0.862 
 
 0.958 
 0.922 
 0.890 
 0.859 
 
 0.954 
 0.919 
 0.886 
 0.856 
 
 0.951 
 0.916 
 0.883 
 0.853 
 
 NOTE : This table is based on the assumption that the volume of oil 
 increases 0.4 per cent for every increase of 10F. above 60. This rule 
 is exactly applicable only to some oils. In Los Angeles County, Cal., the 
 rate of increase in volume is taken at 0.3 per cent in the specifications of 
 the county road department. 
 
 Purchasing Oil. Oil increases in volume from 0.3 to 0.4 per 
 cent for each 10F. rise in its temperature. The oil is bought 
 on the basis of its volume at 60F. and if measured at any other 
 temperature its volume must be computed, or, in the case of an 
 oil having an increase in volume of 0.4 per cent per 10F., the 
 accompanying table will give the volume at 60 with a minimum 
 amount of figuring. To use it, multiply the tabular number 
 for the temperature at which the measurement was made by 
 the measured quantity of oil. For example 1,100 gallons of oil 
 at 375F. multiplied by 0.888 gives 978 gallons as the volume 
 at 60F. If the rate of increase per 10F. was 0.3 per cent, the 
 volume at 60F. would be 995 gallons. 
 
TAR AND TAR PRODUCTS 1 
 
 The tar used in roadbuilding is obtained by refining the crude 
 tar produced in the destructive distillation of coal, in making en- 
 riched water gas and in certain classes of coke ovens. It is a com- 
 plex mixture of many hydrocarbons and is not a simple chem- 
 ical substance. 
 
 In a city gashouse, gas is produced by heating coal in retorts 
 usually about 8 feet long, 15 inches high and 18 inches wide. 
 The tar is driven off with the gas and is collected for the most 
 part in "hydraulic mains" which act as water seals for the gas. 
 The gas is further cooled in a condenser, where more tar is de- 
 posited, and the remaining tar is removed in a tar extractor 
 and scrubbers. The tar obtained at each stage in the process 
 is different from that obtained at the other stages, but all of it 
 is usually run into large wells, where the accompanying ammo- 
 niacal water rises and is drawn off. The character of the tar 
 varies greatly. It is much affected by the temperature at which 
 the coking is conducted, as well as by the character of the coal 
 used. High temperatures result in an increase in the amount of 
 free carbon in the tar, and this increase in free carbon is accom- 
 panied by an increase in specific gravity. The presence of ammo- 
 niacal water with oils distilling below 110C. is stated by Pre- 
 vost Hubbard to be the distinguishing features of all crude coal 
 tars. 
 
 Another class of tar is obtained from by-product coke ovens. 
 The retorts in this case are much larger but are operated in much 
 the same way as the retorts of illuminating gas plants, except 
 that the main endeavor is to produce the maximum amount of 
 coke instead of gas. For this reason the temperatures are lower 
 than those usually employed in coal-gas works and the tar is 
 likely to have a comparatively low amount of free carbon and a 
 comparatively high amount of oils. There are several types of 
 by-product coke ovens, and some produce tars better suited for 
 road work than other types. 
 
 Water gas is made by passing steam over hot coal, in which 
 process no tar is produced. This gas is a mixture of hydrogen 
 and carbon monoxide, and burns with a flame of no value for 
 
 1 Revised by Prevost Hubbard, chief of road materials tests and research, 
 U. S. Office of Public Roads. 
 
 132 
 
TAR AND TAR PRODUCTS 133 
 
 illumination. It must therefore be mixed with hydrocarbons, 
 which are usually obtained by cracking a grade of petroleum dis- 
 tillate called gas oil. In the purification of this enriched or "car- 
 buretted" gas, tar is obtained which is called water-gas tar. 
 It is lighter than coal tar and the water it contains is practically 
 free from ammonia, which is an identifying characteristic of this 
 material. It has a comparatively high amount of heavy oil and 
 a low amount of pitch. 
 
 In some gas works both coal gas and water gas are made and the 
 tar from both processes are collected together, resulting in mixtures 
 which may vary greatly in composition. 
 
 The crude tar is stored in tanks at the refineries, each class 
 by itself. As much water is removed by settling as is possible, 
 since this is the cheapest method of getting rid of it. After set- 
 tling, the tar is pumped into a still. Sometimes the tars from sev- 
 eral sources are mixed so that a product with certain character- 
 istics can be obtained which are unattainable by refining tar from 
 one source. The stills are set in brick like horizontal boiler shells 
 and are heated very carefully at first to prevent the water in the tar 
 from causing foaming. The vapors from the still are liquified in 
 condensers. Water and light oils are first driven off, then inter- 
 mediate oils and finally heavy oils. The road materials are ob- 
 tained from the residuum. The distillation must be stopped 
 early if a light road tar is desired, while the process is carried 
 much further if a binder is desired. In the final stages, the con- 
 tents of the still are agitated by jets of air to prevent coking. 
 
 The composition of several crude tars and of the heavy pitches 
 made by refining them is given in the accompanying table. The 
 figures must not be considered more than representative of gen- 
 eral characteristics, for individual tars in the same class vary 
 greatly. 
 
 Tar products for road purposes are called "straight-run" when 
 they are the residuums left after refining crude tars to the degree 
 which will furnish a material of suitable composition, and "cut- 
 back" when they are made by fluxing a hard pitch with a lighter 
 distillate. 
 
 The effect of free carbon in tar upon its utility for road purposes 
 has been a subject of protracted controversy. Philip P. Sharpies 
 makes this comment: 
 
 Experience has seemed to settle that a moderate amount of free carbon 
 is beneficial in a road tar, thus bearing out the practical experience gained 
 in the use of coal tar materials in other directions. At the same time, an 
 excess of free carbon is not desirable, since it tends to make the material 
 difficult to work and also reduces to a considerable degree the amount of 
 true bitumen available. On the other hand, a certain percentage of free 
 carbon seems to enhance the binding power of the refined tar. The upper 
 
134 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 I 
 
 fl 
 
 c <^ 
 
 2 
 
 1 
 
 AS, 
 OOD 
 
 WAT 
 RAVE 
 
 VERTICAL 
 PROVIDE 
 R. I. 
 
 COKE OVEN, 1 
 LEBANON, PA. 
 
 NTAL 
 , 
 , N. T. 
 
 . 
 
 . co 
 rHrH -O5 -00 O 
 
 -I-H -o 
 
 <jrt< -lO 
 
 -CO 
 rH -<N 
 
 rHOrH -00 -O 
 
 CO -CO 00 
 
 i-HCT> -rH 00 -O 
 
 Sooo -oo -o 
 
 rH OCO -rH 
 
 COOS 
 
 l TfH Tji 
 
 CO -O 
 
 T}J TH 
 rH -<M 
 
 "> :S 
 
 O500 d O 
 
 . 
 
 rHCO 
 TJ4 
 
 
 sifflifMfi 
 Mllff^M 
 
 o oJcs.S QJ- Jg.-S o a> 
 
 Jg_g*:3-5L|i~ 
 
 the 
 whi 
 s the 
 vity 
 ile t 
 les i 
 ed di 
 su 
 ced, 
 e is 
 s of 
 ies. 
 
 tc 
 d 
 e 
 n 
 ec 
 
 soft pit 
 Hubbard 
 coke ove 
 er carbo 
 ce in spe 
 same wa 
 may ha 
 re no ver 
 y. This 
 tar acid 
 eature of 
 mall perc 
 Philip P. 
 
 distille 
 pe Pre 
 Semet-Sol 
 produce 
 great diff 
 omewhat 
 true, an 
 ough the 
 ries inve 
 ated. In 
 one marke 
 which ha 
 f tar acid. 
 
 lf w s- 
 
 oJ. a, rt 03 fl-^^ 1^5^ 
 
 2^-5 ^.2^2 ^-S^Ho 
 
 ^Hiiiyi 
 
 o^^-b.s b g 
 
 O Q Q3 c3 
 
 so 
 ely t 
 ltho 
 va 
 ica 
 e o 
 nd 
 age o 
 
 a; fl ~ a aj 
 
 1-l a^ 
 1.2*1 
 
 n 
 c 
 
 v 
 ria 
 m 
 p 
 
 e 
 
 ed w 
 C 
 ract 
 tto- 
 ted t 
 hat 
 , it is 
 erent 
 d to 
 elded 
 al var 
 les 
 arge 
 
 w 
 th 
 f e 
 
 t 
 o 
 
TAR AND TAR PRODUCTS 135 
 
 limit may perhaps be set at 25 per cent for a binder and perhaps 22 per cent 
 for a tar used for hot surface application. The lower limits on these classes 
 of materials should certainly not be less than 12 per cent for binder mate- 
 rials and 10 per cent for hot surfacing materials. With cold surfacing 
 materials the free carbon is necessarily much lower, as its presence in large 
 quantities reduces the penetration. With cold surfacing materials 4 per 
 cent may be placed as a desirable minimum. 
 
 Prevost Hubbard makes the following comments on free car- 
 bon in his Dust Preventives and Road Binders: 
 
 In tars of the same consistency, those of low carbon contents have a 
 greater inherent binding strength than those of high-carbon contents. 
 In tars whose bitumen contents are of the same consistency those of high 
 carbon contents have a greater inherent binding strength than those of low 
 carbon contents, but the binding capacity of the former is lower. In sand- 
 tar mixtures containing a relatively large amount of high carbon tar, the 
 carbon may act as a filler and add to the mechanical strength of the min- 
 eral aggregate, but better results in this respect can be obtained by the 
 use of a smaller quantity of low carbon tar of the same melting point, 
 together with a mineral filler. The waterproofing value of high-carbon 
 tars is in general less than that of low-carbon tars. Free carbon retards 
 the absorption of tars by porous surfaces. When tar is exposed in 
 comparatively thin films free carbon has little or no effect in retarding 
 volatilization. 
 
 Applying these facts to the use of tar in road treatment the following 
 conclusions are logically deduced: (1) In the treatment of old road 
 surfaces a low carbon tar is to be greatly preferred to a high carbon tar. 
 (2) In ordinary bituminous road construction, both from the standpoint 
 of efficiency and economy, a low-carbon tar is to be preferred to a high- 
 carbon tar whose bitumen content is of the same consistency. 
 
 The distillation test of tars furnishes information regarding 
 their utility for road work. Formerly the test was made on ma- 
 terial which might or might not contain water, but the tend- 
 ency of specialists at present is to remove any water from the 
 samples by preliminary distillation at a low temperature, for no 
 water is permitted in tar for hot application under most speci- 
 fications now. The distillation is carried on in an Engler flask 
 and is conducted in a series of stages. The terminal tempera- 
 tures of the stages have usually been 110C., 170C., 270C. and 
 300C., but recently it has been proposed to make another stage 
 with a terminal temperature of 235C. The test is one which must 
 be conducted with careful observance of the procedure speci- 
 fied for the method followed or the results will not be comparable. 
 The distillate obtained during each stage is called a * 'fraction." 
 
 The 1916 requirements of several State highway departments 
 for different grades of tar are given in the table on pages 136 
 and 137. 
 
136 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 o 
 
 I 
 
 1 
 
 I 
 
 
 + 
 
 
 rH 1C 0} O 
 I <N I O 
 
 ^0~ 
 
 :& 
 
 Illl ; 
 
 S -";-< 03 03 03. !' 
 
 sggaaao : 
 
 fl eVeSSS 
 
 Htib+a'Eb 2Oo<M<MW 
 
 So a? to <u >vP B S I I I 
 
 r-,T3 aJTS^ ^'SrMOpO 
 
 -M ^"S 
 
 ^2^^ 
 
 OQ 
 
s 
 
 
 
 Binder 
 
 TAR AND TAR PROD 
 
 co oo ; ; 
 rH <N <i <N & ; -< ; 
 
 rH ' 
 
 CTC 
 
 At 40C. first 100 cc. S 
 At 25C. 
 At 60C. 
 Residue after carrying distillation to 315C. 
 Determined by ^-inch cube method. 
 First 50 cc. at 40C. 
 r This tar may contain not over 1 per cent of water. 
 5 First 50 cc. at 50C. ; specific viscosity. 
 1 The distillate to 110C. must not exceed 2 per cent. 
 To315C. 
 JOTE. New Jersey limits the naphthalene in the distillate of water gas tars to 2 per cent, and specifies a loss on evap- 
 ion of 28 and 12 per cent of grades UA and U2 respectively. Illinois requires a cylinder of tar 1 cm. in diameter, after t_i 
 aining at 0C. for twenty minutes, to bend into a semicircle of 3 cm. diameter, without checking or breaking. JJ 
 
 2 
 
 1 
 
 q 
 
 W 
 
 ^>oJ(M 00 ;rH 5 S JO 
 
 rH 
 
 
 1 
 
 rH 
 
 o o o 8 jo 
 
 rH C5 t>- 
 
 
 
 
 d 
 
 00 
 
 o oo o 
 
 
 1 
 
 I 
 
 d 
 
 a 
 
 ^ :g - : o 
 
 Ci 
 
 rH CO ^1 Q O 
 rH 
 
 
 Binder 
 
 rH T ~ H 
 
 CO 
 
 O O O O O 
 
 rH (M I> 
 
 rH 
 
 
 S 
 
 j 
 
 o" 
 
 CO o 
 rH 
 
 (MOOCOCO Q 
 
 1 
 
 rH lO 1 O CO 
 IQ OQ rH 
 
 rH 
 
 IO 
 
 co c<i o o 
 
 rH<N CO 
 
 1 
 
 ."> 
 W 
 
 O 
 
 oo -^ 
 
 S 1 ^ 
 
 32 |3 
 
 rH 
 
 .v'i ; 
 
 PQ 
 
 -S if 
 
 CO 
 
 ^ "^ 
 
 o : ^ tl 
 
 CO 
 
 
 
 : " S i 
 
 
 
 : : cs v e 
 
 . . 
 
 a a a-3 -^ -a 
 a " ^ 
 llffa 1 
 
 Iflll's 2 g 
 
 ^ g - - ~ . *H XJ 
 
 r.oddt 5 ^j 
 
 ^d U5^ 0> .S fl 
 
 fe 
 
 3 ot-cob-^d^ g g s 
 
 J -r> rH (N (N '3 rH ' . '^3 C> 
 
 & ll & 
 
 ) OQ S 2 
 
 ) 03 ^ < 
 
 tlj &)^ bb C 
 
 o ^ J 41 +3* g i 
 S "$* 
 
 & r2 .S9S-2 
 
 OQ fa >fad 
 
 
BITUMINOUS ROADS 1 
 
 Bituminous materials are used on gravel and broken stone roads 
 in three ways: (1) thoroughly mixed with the stone or gravel 
 before the latter is placed on the roads; (2) driven into the 
 interstices between the stone after the latter has been placed on 
 the road; (3) applied to the surface of a finished gravel or broken 
 stone road. The first method produces what is now commonly 
 called bituminous concrete and the second method bituminous 
 macadam. These will be described in this section and surface 
 applications will be described in the next section. 
 
 Rock for Bituminous Roads. 2 In bituminous road work obser- 
 vations indicate that in some cases it is advantageous to use a 
 rock of relatively high absorption rather than one with low 
 absorptive qualities, owing to a better adhesion of the bituminous 
 material by a partial surface impregnation of the rock. 
 
 While the binding or cementing value of a rock is a most 
 important consideration from the standpoint of ordinary macadam 
 construction, the same is not true of broken-stone roads which 
 are carpeted or constructed with an adhesive bituminous material. 
 The French coefficient of wear is also of relatively less importance, 
 owing to the fact that the fine mineral particles produced by the 
 abrasion of traffic combine, or should combine, with the bitumi- 
 nous material to form a mastic which is held in place and pro- 
 tects the underlying rock from abrasion so long as it is kept 
 intact by proper maintenance. The toughness of the rock is of 
 more importance, as the shock of impact is to a considerable 
 extent transmitted through the seal coat and may cause the 
 underlying fragments to shatter. It would, therefore, seem that 
 the minimum toughness of a rock for use in the construction of 
 a bituminous broken-stone road or a broken-stone road with a 
 
 1 It is the purpose of this chapter to indicate the methods followed in 
 several sections of the country where bituminous roads have been built 
 extensively rather than to recommend any methods as the best for all 
 conditions. Revised by P. St. J. Wilson, chief engineer, United States 
 Office of Public Roads and Rural Engineering; F. H. Joyner, road com- 
 missioner of Los Angeles County, Cal.; and W. R. Farrington, division 
 engineer, Massachusetts Highway Commission. 
 
 2 From Bulletin 370, United States Department of Agriculture, "Physi- 
 cal Tests of Road-Building Rock," by Prevost Hubbard, chemical engi- 
 neer, and Frank H. Jackson, Jr., assistant testing engineer, OfHce of 
 Public Roads. 
 
 138 
 
BITUMINOUS ROADS 139 
 
 bituminous-rnat surface should, for light traffic, be no less than 
 for ordinary macadam subjected to the same class of traffic. 
 For moderate and heavy traffic, however, the same minimum 
 toughness should prove sufficient, owing to the cushioning effect 
 of the bituminous matrix. No maximum limit of toughness need 
 be considered for any traffic. 
 
 In the case of bituminous concrete roads, where the broken 
 stone and bituminous material are mixed prior to laying and 
 consolidation, it generally appears advisable to set a minimum 
 toughness of 6 to 7 for light-traffic roads, instead of 5, in order to 
 insure that the fragments of rock which have been coated with 
 bitumen shall not be fractured under the roller during consolida- 
 tion; and 12 or 13 for moderate and heavy traffic, instead of 10 
 and 19, as in the case of water-bound macadam roads. 
 
 Bearing in mind the fact that availability, cost, and various 
 local conditions generally control the selection of proper limits, 
 the accompanying table may be used as a general guide for 
 minimum limits of the French coefficient of wear and toughness 
 in connection with bituminous broken-stone roads. 
 
 Bituminous Materials. Climatic conditions, the volume and 
 character of traffic to be carried by a road, the kind of stone to 
 be used, and the methods of construction vary greatly in differ- 
 ent places and have an important influence on the determination 
 of the bituminous materials to be used. For this reason it is not 
 practicable to have a general specification of universal applica- 
 bility. The requirements for bituminous binders of a number 
 of states are given in the tables on pages 126, 127 and 136. 
 
 In most cases the binders are furnished by the contractors 
 under specifications of greater or less detail. In Massachusetts 
 the State highway commission usually purchases its material and 
 furnishes it to the contractors, although contractors are occa- 
 sionally required to supply it. 
 
 Bituminous Macadam. Roads of this type are frequently said 
 to be built by the "penetration" method because the bituminous 
 material is made to penetrate the interstices of the road from the 
 surface. The grading, drainage and rolling of the subgrade are 
 carried out as in the case of waterbound macadam roads. On the 
 subgrade is laid a base or bottom course, then a top course to 
 which the bituminous material is applied, and finally a thin 
 "seal" coat of bituminous material covered with screenings or 
 gravel to protect the main mass of the road from the weather 
 and other deteriorating influences. 
 
 The depth of the bottom course varies with the character of 
 the subgrade, the traffic, the quality of the stone, the character 
 of the top course and the preferences of the highway authorities. 
 Probably 6 inches at the center and 4 inches at the sides are 
 
140 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 Limits of Physical Tests of Rock for Bituminous Roads 
 (Recommended by Pr6vost Hubbard and Frank H. Jackson, Jr.) 
 
 
 LIGHT TO MODERATE TRAVEL 
 
 MODERATE TO HEAVY TRAVEL 
 
 French 
 coefficient 
 
 Percent- 
 age of wear 
 
 Toughness 
 
 French 
 coefficient 
 
 Percent- 
 age of wear 
 
 Toughness 
 
 Broken stone with 
 bituminous car- 
 pet 
 
 At least 
 
 5 
 
 5 
 
 7 
 
 Not over 
 
 8 
 8 
 
 5.7 
 
 At least 
 5 
 
 5 
 
 7 
 
 At least 
 
 7 
 
 7 
 10 
 
 Not over 
 
 5.7 
 
 5.7 
 4 
 
 At least 
 
 10 
 
 10 
 13 
 
 Bituminous macadam 
 with seal coat 
 
 Bituminous concrete . 
 
 Gallons of Bituminous Material per Mile of Road for Different Rates of 
 
 Application 
 
 GALLONS 
 PER 
 SQUARE 
 YARD 
 
 WIDTH OF ROAD IN FEET 
 
 9 
 
 10 
 
 12 
 
 15 
 
 18 
 
 20 
 
 22 
 
 0.20 
 
 1,056 
 
 1,174 
 
 1,408 
 
 1,760 
 
 2,112 
 
 2,347 
 
 2,582 
 
 0.25 
 
 1,320 
 
 1,467 
 
 1,760 
 
 2,200 
 
 2,640 
 
 2,933 
 
 3,227 
 
 0.33 
 
 1,742 
 
 1,936 
 
 2,323 
 
 2,904 
 
 3,484 
 
 3,872 
 
 4,259 
 
 0.40 
 
 2,112 
 
 2,347 
 
 2,816 
 
 3,520 
 
 4,224 
 
 4,694 
 
 5,163 
 
 0.50 
 
 2,640 
 
 2,934 
 
 3,520 
 
 4,400 
 
 5,280 
 
 5,867 
 
 6,454 
 
 0.60 
 
 3,168 
 
 3,520 
 
 4,224 
 
 5,280 
 
 6,336 
 
 7,040 
 
 7,744 
 
 0.67 
 
 3,538 
 
 3,931 
 
 4,716 
 
 5,896 
 
 7,075 
 
 7,862 
 
 8,648 
 
 0.70 
 
 3,696 
 
 4,107 
 
 4,928 
 
 6,160 
 
 7,392 
 
 8,214 
 
 9,035 
 
 0.75 
 
 3,960 
 
 4,400 
 
 5,280 
 
 6,600 
 
 7,920 
 
 8,801 
 
 9,680 
 
 0.80 
 
 4,224 
 
 4,694 
 
 5,632 
 
 7,040 
 
 8,448 
 
 9,387 
 
 10,326 
 
 0.90 
 
 4,752 
 
 5,280 
 
 6,336 
 
 7,920 
 
 9,494 
 
 10,561 
 
 11,616 
 
 1.00 
 
 5,280 
 
 5,867 
 
 7,040 
 
 8,800 
 
 10,560 
 
 11,734 
 
 12,907 
 
 1.25 
 
 6,600 
 
 7,334 
 
 8,800 
 
 11,000 
 
 13,200 
 
 14,668 
 
 16,134 
 
 1.50 
 
 7,920 
 
 8,801 
 
 10,560 
 
 13,200 
 
 15,840 
 
 17,601 
 
 19,361 
 
 1.75 
 
 9,240 
 
 10,267 
 
 12,320 
 
 15,400 
 
 18,480 
 
 20,535 
 
 22,587 
 
 2.00 
 
 10,560 
 
 11,734 
 
 14,080 
 
 17,600 
 
 21,120 
 
 23,468 
 
 25,814 
 
 average depths. 1 In Massachusetts, where the foundation is pre- 
 pared very carefully, sometimes consisting of 12 inches or more 
 of gravel or telford, an 18-foot roadway usually has a bottom 
 course 2 inches thick at the sides and 3 inches thick at the center, 
 after rolling, except on stone foundations, where the standard 
 thickness is 2 inches at all points of the cross-section. These 
 thicknesses are increased in some cases. 
 
 The Massachusetts specifications call for smaller stone than 
 those of most states, and give the engineer the final decision 
 
 1 On roads where the traffic promises to be heavy, it is often considered 
 best to have the same depth the entire width of the road. 
 
BITUMINOUS ROADS 141 
 
 regarding the proportions of the J to IJ-inch size and the 1J to 
 2J-inch size which shall be mixed together for this course, the 
 intention being, where stone is crushed locally, to vary these 
 proportions in order to use the output of the crusher. In New 
 York and Pennsylvania the maximum size of the stone for this 
 course is 3| inches. The Pennsylvania specifications require the 
 stone to have a French coefficient of wear of not less than 10, 
 and permit the use of gravel and of broken slag which weighs 70 
 pounds or more per cubic foot, measured loose. In Ohio, if sand- 
 stone is used in the bottom course, pieces as large as 6 inches are 
 permitted; the maximum size with other rocks is 4 inches. In 
 Illinois and California the maximum size is 3 inches. These 
 variations are due mainly to differences in the average quality 
 of stone available in the different states. 
 
 After the stone has been spread, it is sometimes harrowed. The 
 Illinois specifications call for the use of a tooth harrow weighing 
 10 to 12 pounds per tooth. The course is then consolidated with 
 a roller, one weighing 10 tons or more being generally required. 
 It is next covered with screenings, small gravel and sometimes 
 coarse sand, which are broomed and rolled dry until the inter- 
 stices are filled, but not over-filled. Some engineers consider the 
 course finished at this stage, while others require it to be sprinkled 
 with water and rolled so as to consolidate it still further. 
 
 On the work under a number of State highway departments, 
 the stone for both the top and bottom courses must be shoveled 
 from the carts into place, or be dumped on platforms and shoveled 
 from there into place, or be spread over the road by distributing 
 wagons built for the purpose. In other states the stone for the 
 bottom course may be dumped on the subgrade and shoveled 
 from these piles into its final place. Stone for the top course is 
 never permitted to be dumped in piles on the bottom course. 
 The screenings or other fine material used on the road are gen- 
 erally required to be delivered along the road before construction 
 begins. 
 
 Other types of bottom courses than those made of graded 
 aggregates are occasionally used. Many macadam roads in good 
 condition have had a bituminous macadam top course put on 
 them. Macadam roads when in poor condition are often scari- 
 fied, new material added where needed, and then rolled, thus 
 furnishing a suitable bottom course at minimum expense. If 
 these old roadways are thus used, their drainage should be care- 
 fully examined and all defects remedied before the top course is 
 laid. In the New York state highways, a base of run-of-bank 
 gravel not larger than 3J inches is sometimes used. In this case 
 the material passing a J-inch screen must not be more than 5 per 
 cent in excess of the voids in the remainder of the material after 
 this fine stuff has been removed. 
 
142 AMERICAN HIGHWAY ASSOCIATION 
 
 In Massachusetts the top course is usually 2 inches thick, and 
 as stone from 1J to 2^ is required the largest pieces become im- 
 bedded slightly in the bottom course by the rolling. More than 
 15 per cent of the J to If -inch stone, which is permitted in the 
 bottom course, is not desired in the top course because experi- 
 ence has convinced the Massachusetts engineers that its presence 
 makes a less durable road. More bituminous binder is required 
 with coarse than small stone, but the entire quantity can be 
 applied at one time, while if small stone is used it has been 
 found desirable to construct this course in two layers in order to 
 be certain that the smaller voids existing with such stone are 
 filled. 
 
 The top course in most States is usually from 2 to 3 inches 
 thick. 
 
 The top course of the New York State highways is made of 1J 
 to 2J inches stone, in Pennsylvania 1 to 3-inch, in Ohio If to 1\- 
 inch stone for a course less than 3 inches thick and 2J to 4-inch 
 stone for a course 3 inches or more thick, unless the stone has a 
 loss on abrasion of less than 6 per cent, when the size is reduced 
 to 2 to 3f inches; in Illinois 1 to 2i inches. The Ohio and 
 Illinois specifications require it to be harrowed. 
 
 In rolling this course, it is usually considered desirable to roll 
 adjacent strips of the shoulders as well, so as to unite the shoulder 
 and roadway as completely as practicable. It is also generally 
 considered desirable to roll the stone until it is "locked" in place 
 so the binder distributor can pass without leaving any impres- 
 sion, but not to the maximum density. The reason for this is 
 that the bituminous material is believed to be more uniformly 
 distributed if the course of stone is capable of further compression 
 after the binder has been applied. Some stone hard enough to 
 carry travel should not be rolled heavily, for if heavily rolled the 
 voids will be so reduced that the binder will not penetrate into 
 them properly. 
 
 No bituminous material should be applied except when the 
 stone on the surface is clean and free from dust. The applica- 
 tion is now made in many cases with a pressure distributor, 
 which is required by some State highway departments; it is also 
 applied by gravity distributors and, on small work, by hand 
 pouring cans. 
 
 Distributing wagons often have some kind of fire-box for keep- 
 ing the binder hot. Gravity distributors discharge their contents 
 through nozzles or other spraying devices at their rear about 12 
 inches above the road. The shape and location of the nozzles 
 are so selected that the binder will be distributed uniformly 
 over a strip of the road somewhat wider than the distance be- 
 tween the wheels. The binder flows from the nozzles by gravity, 
 
BITUMINOUS ROADS 143 
 
 and as the contents of the tank are drawn off the pressure on the 
 nozzles decreases and the rate of flow per minute is reduced. 
 In order to maintain a uniform flow, a control valve in the out- 
 let pipe is provided. The rate of application of the material is 
 regulated by this valve and the speed of the distributor. 
 
 Pressure distributors are used where it is desired to have better 
 control over the rate of application of the binder than is practic- 
 able with gravity distributors, and also to obtain the best dis- 
 tribution and penetration. In some types, compressed air or 
 steam is admitted to the top of the tank so that the pressure on 
 the surface of the binder, whether the tank is full or almost empty, 
 is sufficient to drive the material through the nozzles with con- 
 siderable force. In other types, the binder is driven out of the 
 nozzles by a small pump. The nozzles of the pressure distrib- 
 utors are generally about 6 inches from the surface of the road. 
 In some cases the binder is forced through a hose ending in a 
 nozzle which the operator moves along just above the surface of 
 the road. 
 
 Bituminous material is also distributed from tank wagons with- 
 out any suitable piping and nozzles of their own. This is done 
 by attaching to their rear end a light two-wheel sulky having the 
 necessary distributing apparatus, which is connected by piping 
 with the outlet of the tank wagon. Attachments are also made 
 for this purpose which can be bolted to an ordinary tank wagon. 
 
 Pouring cans resemble garden watering cans in appearance. 
 The top is usually partly covered to prevent the binder from slop- 
 ping out, and there is generally a removable screen which intercepts 
 anything likely to clog the nozzle. The nozzle is a slot 6 to 10 
 inches long, which is usually adjustable. A skillful man can 
 apply bituminous material in this way very uniformly, but the 
 expense on large work is greater than with distributors. 
 
 The binder can be heated in portable kettles, usually mounted 
 on wheels, in distributing wagons, oil heating pits, or in tank cars, 
 the method to be followed depending upon the amount of material 
 to be heated. 
 
 The amount of binder used is from li to If gallons per square 
 yard, depending upon the depth and size of the stone. If an 
 asphalt binder is used it must be applied at a temperature of 
 about 300F. and if tar at about 200 to 225F. After it is spread 
 it is covered with small stone, usually from about i to f inches 
 in size; in New York State work stone of f to li inches is speci- 
 fied. In Massachusetts good results have been obtained in 
 some cases with sand. After this dressing has been spread it is 
 often gone over with brooms to make certain that all voids in the 
 surface are filled, and the material unformly distributed, and the 
 brooming should be finished with the brooms working parallel with 
 the line of the road. 
 
144 AMERICAN HIGHWAY ASSOCIATION 
 
 After the top course has become firm under the roller, the 
 surface is swept clean and the seal coat is applied. This is usually 
 spread at the rate of J to } gallon per square yard, and is covered 
 with i to f-inch stone chips or pea gravel. The road is then 
 broomed, using a lock street broom for the purpose, and then 
 given a thorough rolling as to consolidate it as much as possible 
 and the broom can be attached to the roller during this final rolling. 
 A liberal use of both the hand broom and the lock street broom, 
 or the broom fastened to the roller, during the screening and 
 finishing of the road will do much to insure that the dressing 
 is evenly taken up by the oil and a smooth riding surface obtained 
 that will not start the pounding of automobiles and the con- 
 sequent rippling of the surface. 
 
 In the State highway work of Illinois, there are there courses 
 and a seal coat in bituminous macadam construction. The sec- 
 ond course is 1 to 2i-inches stone, harrowed, rolled, and treated 
 with 1 gallon of binder per square yard. This is covered with J 
 to J-inch screenings, which are broomed into the voids and the 
 excess swept off. A second application of binder is then made 
 at the rate of \ gallon per square yard and covered with torpedo 
 gravel ranging in size from f-inch down to fine sand. This is 
 broomed until the voids are filled, when the surplus is removed. 
 Another application of binder is made at the rate of \ gallon 
 per square yard and covered with torpedo gravel at the rate of 
 about 1 cubic yard per 200 square yards of road. The wheels 
 of the roller may be wet to prevent them from picking up the 
 binder; some engineers object to such wetting and require the 
 wheels to be oiled. 
 
 Where the grade is steep, the Massachusetts highway com- 
 mission has recently tried the practice of leaving the surface 
 rather rough, so as to afford a foothold for horses and resistance 
 to skidding for automobiles. 
 
 Bituminous Concrete. When the stone and binder are mixed 
 together thoroughly before they are placed on the road, it is prac- 
 ticable to use both small and large stone and thus reduce the vol- 
 ume of the voids to be filled with bituminous binder. This mate- 
 rial is placed on any of the bottom courses used with bituminous 
 macadam and also on concrete. It is essential for the bottom 
 course to be dry and clean when the inixture is spread over it. 
 
 The size of the stone required by different State highway 
 departments varies somewhat, and some departments have a 
 number of standard proportions. In Massachusetts crusher- 
 run trap from J to 1J inches is specified for some roads, and also 
 crushed gravel, which will be mentioned later. In New York, 
 f to IJ-inch stone is used for a course 2 inches or less in thick- 
 ness, and for thicker courses stone up to 2J inches in size is 
 
BITUMINOUS ROADS 145 
 
 allowed. In both New York and Maryland materials are per- 
 mitted which will give a finished pavement with less than 10 
 per cent passing a 2-mesh screen, 8 to 22 per cent passing a 4- 
 mesh, 25 to 55 per cent passing a 10-mesh, 18 to 30 per cent 
 passing a 40-mesh, 5 to 11 per cent passing a 200-mesh, and 7 
 to 11 per cent of bitumen. In Maryland a mixture is also used 
 containing two parts of J to 11-inch stone and one part of sand 
 with 25 per cent passing a 20-mesh screen and 5 per cent passing 
 80-mesh. To this mixture is added 5 per cent of powdered lime- 
 stone or cement and 7 to 9 per cent of bitumen. In Illinois the 
 proportions are left to the engineer, but the purpose is to obtain 
 the equivalent of a thorough mixture of 1 cubic yard of grit sand 
 passing a f-inch ring with 40 to 80 per cent passing a 10-mesh 
 sieve, and 3 cubic yards of f to l inch stone with 30 to 80 per 
 cent retained on a 1-inch ring. Instead of the stone 3 cubic 
 yards of f to 1-inch gravel with 20 to 70 per cent retained on a 
 f-inch screen may be used. 
 
 The amount of bituminous binder on the Massachusetts work 
 is about 20 to 24 gallons per cubic yard of stone. In New York, 
 for the work with broken stone without fine material, 18 gallons 
 are used per cubic yard of stone and the purpose is to have the 
 finished course contain from 5 to 7J per cent by weight of bitumen. 
 On the Illinois work, from 27 to 30 gallons of binder containing 
 95 per cent or more of bitumen is used per cubic yard of stone or 
 gravel, and if the binder contains less than 95 per cent of bitumen 
 the quantity must be increased proportionately. 
 
 Although stone and tar binder have occasionally been mixed 
 cold, as in Rhode Island, it is customary to mix the stone and 
 bituminous material hot. There is a marked difference of opin- 
 ion regarding the temperature to which the stone should be heated, 
 Massachusetts requiring this to be 180F. or more and Illinois 
 300 to 375. A high temperature will injure some binders and 
 not others, and it is therefore important to have the aggregate 
 uniformly heated to the proper temperature for the binder used, 
 the weather conditions, and the length of haul from the mixing 
 plant to the road. The binder is heated in kettles or tanks. The 
 temperature for asphalt is 275 to 375 and for tar 200 to 275, 
 the limits varying somewhat with the grades used. Special care 
 must be taken to prevent overheating. Sometimes hot stone and 
 cold binder are mixed. The mixing on small work can be done 
 by hand, but is more quickly and thoroughly performed on large 
 work in mixers made for the purpose. 
 
 The best equipment for any contract will depend upon local 
 conditions, among which the transportation of the mixed mate- 
 rial is an important factor. The mixture must be delivered 
 on the site at temperatures of 150 to 280, according to the 
 
146 AMERICAN HIGHWAY ASSOCIATION 
 
 binder used. The maximum permissible drop between the tem- 
 peratures of the material at the mixer and when it reaches the 
 road, freedom from segregation in the mixture, and the practi- 
 cable speed of delivery, fix the maximum length of haul. If the 
 maximum length of haul permits the use of a central plant for 
 the whole work, it is often practicable to locate it at the crusher 
 plant and save some labor charges. Portable plants for use along 
 the road have been greatly improved in recent years and are used 
 extensively. 
 
 The wagons for transporting the mixture should be tight, and 
 under some weather and hauling conditions their contents should 
 be covered with canvas to keep them from becoming chilled. The 
 bodies of motor trucks are sometimes jacketed or insulated for 
 the same purpose. 
 
 The mixture should be shoveled from the wagons, or dumped 
 on wood or metal platforms from which it can be shoveled. The 
 shovels are often heated, as are the rakes used in spreading the 
 mixture. It is considered desirable by some engineers to pro- 
 hibit delivering hot mixture on the road within one hour of 
 sunset. 
 
 When the edges of the pavement are not protected by a stone 
 or concrete curb, the New Jersey highway department requires 
 the contractor to place temporary curbs of 6 or 8-inch planks of 
 the same thickness as the finished top course. 
 
 When it is necessary to lay half of the width of a road so as to 
 allow traffic on the other half, the base of the first half is allowed 
 to project about 2 feet beyond the center line of the roadway. 
 The top course in such cases ends only a few inches beyond the 
 center line, for this will insure all of it resting on a firm base. 
 After the second half of the base has been constructed, the inside 
 edge of the top course already laid is cut back vertically or nearly 
 so along a straight or properly curved line so as to obtain a 
 perfect joint with the second half of this course. 
 
 After the material has been spread, it should be rolled imme- 
 diately. Sometimes an initial compression is given with a 3- to 
 6-ton tandem roller and the final compression with a 10-ton 
 macadam roller, but the usual practice is to use a 7- to 10-ton 
 roller giving 200 to 300 pounds per linear inch of roll. The 
 wheels may be oiled to prevent the binder from sticking to them. 
 This rolling is continued until the roller leaves no marks in pass- 
 ing. Any places which can not be reached by the roller are 
 rammed with a hot iron tamp. 
 
 The road is often given a seal coat at the rate of J to | gallon 
 of binder per square yard, which is at once covered with pea 
 stone or grit. The binder is often the same material used in the 
 bituminous concrete but sometimes it is a more fluid grade. 
 
BITUMINOUS ROADS 147 
 
 Some engineers require it to be applied with a squeegee distributor. 
 The seal coat is rolled until it is thoroughly incorporated with the 
 top course. 
 
 Mixed Gravel-Asphalt Roads. The Massachusetts highway com- 
 mission has built a number of roads with mixed gravel-asphalt 
 surfaces on gravel and broken stone bases. The surfacing with a 
 gravel base is 2J inches thick after rolling. The folio whig notes 
 from its 1915 report describe the construction: 
 
 A road, 18 feet in width with 3-foot shoulders, was built everywhere, 
 the curves being banked and widened to 21 feet. A gravel foundation was 
 put in wherever the bottom was bad, and about 4 inches of local crushed 
 stone was spread and well rolled. 
 
 On this was spread, as evenly as possible, about 3 inches of a bitumi- 
 nous mixture made of gravel that had been run through the crusher and 
 sand or stone dust, mixed with a heavy asphaltic product. The gravel 
 and sand and the asphalt were thoroughly heated and were mixed in a hot 
 mixer, and then carted onto the road and spread. The surface was rolled 
 down to about 2 inches in thickness when the mixture was sufficiently cool 
 not to crawl under the roller. 
 
 Great care is necessary to insure a uniform product, uniformly heated, 
 mixed and spread, and that sufficient asphalt is used and no more than 
 sufficient to bind the mixture properly. The quantity of asphalt has to 
 vary somewhat, according to the amount of voids in the mineral aggre- 
 gate. The variation is usually from 18 to 22 gallons of the hot asphalt to 
 the cubic yard of gravel. When the mixture is right it has about the 
 consistency of brown sugar and compacts under the roller, though when it 
 is first spread and rolled it sometimes has a few hair cracks which the 
 traffic soon irons out. The asphaltic product used in this work has a pene- 
 tration of from 80 to 120 with a Dow penetrometer. 
 
 Sand and Oil Roads. In 1905 the Massachusetts highway 
 commission surfaced a road at Eastham by distributing hot 
 asphaltic oil over the sand which is practically the only material 
 in the vicinity, applying 1J gallons to the square yard in two 
 applications. The results were so encouraging that more sand- 
 oil roads have been built and the experience thus gained has 
 shown what are the requirements for success. They are now 
 built by both the penetration or layer method and by the mixing 
 method. They are considered suitable when the traffic is mostly 
 light teams and automobiles and will not stand up if used daily 
 by many heavily loaded teams. The average daily traffic in 1915 
 on one successful layer road was 20 heavy teams, 17 light teams 
 and 253 automobiles. On a mixed road it was 6 heavy teams, 
 23 light teams and 505 automobiles; on another mixed road 21 
 heavy teams, 38 light teams and 197 automobiles. 
 
 It is desirable for success to use a hard, strong, sharp and well- 
 graded sand, such as is abundant on Cape Cod, where this type 
 of construction has been developed. Many sands are too fine, 
 too uniform in size, too rounded or not strong enough. Fair 
 results have been obtained with some fine sands, however. 
 
148 AMERICAN HIGHWAY ASSOCIATION 
 
 An oil asphalt of good quality that will bind and not lubricate 
 must be used. For the layer type, the preference in Massa- 
 chusetts is for an oil with a viscosity of 150 to 200 seconds at 
 200C., using a Lawrence viscosimeter or about 1038 to 1384 
 with 100 cc. at 100C. in an Engler viscosimeter. From 1J to 
 2 gallons per square yard are used, in two applications, with a 
 covering of sand after application. In the mixed type, oil as- 
 phalts having a penetration of 60 to 135 by the Dow penetrometer 
 have been tried, but that now used ordinarily has a penetration 
 of 90 to 125. From 16 to 22 gallons per cubic yard of sand have 
 been used; the present average is 18 gallons. The Massachusetts 
 commission advises testing each carload of oil before using it. 
 
 In the layer type of construction, the commission spreads clay 
 or loam over the sand subgrade to reduce the rutting of the sur- 
 face by wheels and pitting by horses' hoofs when the oil cart passes 
 over it. The oil is then spread evenly while hot with a dis- 
 tributing cart and immediately covered with sand. This process 
 is then repeated. 
 
 In the mixed type of construction the sand and oil are mixed 
 hot to form a mastic which is spread over the sandy subgrade 
 and rolled. The subgrade is carefully shaped and hardened as 
 in the case of the penetration type. The mastic sheet is about 
 4 inches thick at the center and 3 inches at the edges. The best 
 results have been obtained by keeping the road constantly shaped 
 with a road scraper during rolling, and a seal coat of J gallon of 
 a lighter oil such as is used in layer work improves the surface 
 and decreases maintenance charges. In the early work the sand 
 was heated on sheets of iron, but this overheated parts of it and 
 underheated other parts, so that now the heating is done in rotary 
 heaters. 
 
 If the traffic in the future proves too heavy for these roads, the 
 commission believes they can be greatly improved and strength- 
 ened at a moderate cost by using harder asphalt, greater care in 
 grading the sand, and the addition of cement and stone dust. 
 In this way a sheet asphalt pavement 2 inches thick can be laid 
 on the old sand-asphalt road as a base. 
 
 Asphalt Blocks on Country Roads 
 
 As designed and manufactured for use on country roads, the 
 asphalt blocks are 5 inches wide, 12 inches long, and 2 inches deep, 
 weigh about eleven pounds each, and have a specific gravity of 
 about 2.40. 
 
 The asphalt block was developed and perfected on the theory 
 that crushed trap rock, on account of its preeminent hardness and 
 inherent grittiness, made the best known material for a roadway 
 
BITUMINOUS ROADS 149 
 
 surface, the one thing needed being a cement, or binding material, 
 to keep all of the particles permanently in place. This was accom- 
 plished by the use of an asphaltic cement to bind together the prop- 
 erly graded particles of crushed trap, the hot mixture being con- 
 solidated by tremendous pressure into blocks so dense and free from 
 voids as to be practically non-absorbent. In the asphalt block, 
 therefore, we have an asphaltic concrete, or macadam, mixed, in 
 exact proportions, at a central plant, under conditions insur- 
 ing absolute uniformity, and receiving the compression necessary 
 to produce a dense and non-absorbent material. 
 
 Not only has a special block been produced, but a special method 
 of construction has been worked out, designed to utilize what is 
 left of the worn and rutted macadam road as a foundation for the 
 blocks. This is accomplished by scarifying the surface, if necessary, 
 filling up the deep ruts, rolling with a heavy steam roller, and lay- 
 ing upon the surface of the old macadam, a bed of cement mortar 
 about 1 inch in thickness, to serve the double purpose of forming 
 a firm unyielding bed for the blocks, and binding them securely 
 to the macadam foundation underneath. By this method the 
 material used in the original construction of the road is not thrown 
 away, but used as foundation for a permanent wearing surface. 
 Where the old macadam is too thin, or too badly worn to be safely 
 used as a foundation, it will be necessary to lay a concrete base, 
 but usually there is broken stone enough in the old macadam to 
 supply what is needed for laying concrete. 
 
 A pavement may be laid of any desired width, contour, grade, 
 or crown. It is perfectly feasible to pave one-half of the roadway, 
 or only a narrow strip in the center, and extend the paved area 
 at a later date as traffic necessities require, or as appropriations 
 become available. It is not necessary to set curbstones or head- 
 ing stones to border or define the 
 paved area, since a row of stretcher 
 blocks held firmly in place by a shoulder 
 of mortar, as shown in the sketch, 
 answers the purpose perfectly and 
 leaves the entire roadway surface 
 smooth and uniform. 
 
 A good example of this construc- 
 tion is on the Albany Post Road, through the villages of Hast- 
 ings-on-Hudson, Dobbs Ferry, Irvington, North Tarry town, Town 
 of Mount Pleasant, Briar cliff and Ossining, N. Y., on the Boston 
 Post Road in Pelham Manor and Rye, N. Y., on 9 miles of road- 
 way from Daytona to Deland, Volusia County, Florida, and on 
 Nassau Street, Princetown, N. J., a section of the Lincoln Highway. 
 
BITUMINOUS SURFACE APPLICATIONS 1 
 
 Surface applications vary widely in character, according to 
 their purpose. In most cases such an application is essentially a 
 maintenance measure, but in the case of the bituminous mats or 
 wearing courses used in California, or the mats now laid on new 
 water-bound macadam, the first cost of such work is essentially 
 a part of the first cost of the improvement. The practice in 
 making such surface applications of any general type varies 
 widely in different parts of the country, more widely than the 
 practice in any other branch of road work. Whether greater 
 uniformity will prove desirable or the work can be done success- 
 fully by a wide variety of methods can not be definitely deter- 
 mined until the records of such work and of the traffic on roads 
 are kept with more detail and uniformity than at present. The 
 widespread interest in the subject was one of the leading charac- 
 teristics of highway affairs in 1916, and was an evidence of the 
 conditions mentioned. 
 
 Oiling Earth Roads 
 
 Surface applications on earth roads were made in California 
 many years ago, and a method of incorporating oil and earth by 
 a special form of roller was employed for some time. More 
 recently well built earth roads in Iowa and Illinois have received 
 surface applications as a maintenance measure. The experience 
 in these states shows that while some success follows applications 
 on roads that are not in good condition, it is very desirable to 
 have the surface properly shaped and hard before the oil is applied. 
 The oil binds the grains of earth together and reduces the dust, 
 but it does not give the resistance to attrition which a hard sur- 
 face affords. The treatment is therefore one which must be 
 regarded as adapted only for roads with light traffic and light 
 vehicles. If sand instead of earth is present, the methods of con- 
 struction first used in Massachusetts and described on page 147 
 should be considered. 
 
 If the road has ruts and holes in the surface and is poorly 
 drained, water will collect in puddles, soften the oiled crust at 
 
 1 Revised by George H. Biles, second deputy State highway commissioner 
 of Pennsylvania, and B. H, Piepmeier, maintenance engineer of the Illinois 
 State highway department. 
 
 150 
 
BITUMINOUS SURFACE APPLICATIONS 151 
 
 these places, and seep into the roadbed. The material under the 
 crust will give way under heavy loads and the money spent in 
 oiling will be largely lost, because the oiled material will become 
 mixed with the unoiled material below and dust will be produced 
 about as freely as on an unoiled road. Furthermore, the oiling 
 of a mudhole often aggravates troubles due to such a defect. 
 
 The surface to receive the application must be dry, or the oil 
 will not penetrate the pores, and it must be free from dust, for 
 the oil forms flakes or scales with the dust and these are a worse 
 nuisance than plain dust, being very irritating to the eyes. 
 
 Both cold and hot applications have been used successfully in 
 Iowa, but the State Highway Commission prefers to heat the oil 
 as it apparently gives enough better penetration to justify the 
 additional expense. It is desirable to secure the advice of a 
 specialist in selecting the oil. A light oil must be used and as 
 it may have a low flash point, care should be taken to keep it at 
 a temperature below its flash point and to prevent any of it 
 coming into contact with a flame. The first application is made 
 at a rate of about J gallon per square yard, and later applications 
 at the rate of J to | gallon. The brief experience in such work 
 indicates that two light applications annually for two years and 
 afterward a single application annually will be sufficient on a 
 road adapted for such treatment and not subject to traffic requir- 
 ing a more durable surface. During 1916 the Illinois State high- 
 way department issued the following advice on the work. 
 
 The best results may be secured during the first application, by apply- 
 ing either a cold oil or at least a very thin product that will penetrate the 
 surface of the road several inches and at the same time contain as many 
 binding elements as possible so as to seal all pores in the earth, making it 
 waterproof and at the same time adding some binding qualities that may 
 assist the bond of the soil itself. A suitable product, as is commonly 
 expressed, may vary from 30 to 60 per cent in asphalt. After the surface 
 of the road has been thoroughly saturated, a hot oil or a slightly heavier 
 product may be used. 
 
 If the heavier oils are used for the first application they will not readily 
 penetrate the surface of the road and will consequently form a mat on 
 top. The forming of the mat before the surface of the road is more or less 
 waterproof may be a serious fault as moisture will accumulate beneath the 
 mat and the road will be much slower in drying out than it would had the 
 oil not been applied. The mat surface with a soft subsoil will rut more 
 readily, besides breaking and scaling off in large pieces, making the road 
 surface rough and undesirable. 
 
 The Illinois authorities recommend covering the oiled surface 
 with clean, hard sand, at the rate of a cubic yard to 100 to 150 
 square yards. 
 
152 AMERICAN HIGHWAY ASSOCIATION 
 
 Broken Stone Road Surfacing 
 
 It has been found that a surface application on a new water- 
 bound macadam road may prove unsatisfactory, although if the 
 road is exposed to traffic for three months the desired results are 
 obtained if the treatment is properly carried out. This is prob- 
 ably due to the large amount of fine, lightly-bound dust on the 
 roadway, which is removed by the early traffic, or to the greater 
 stability of the road as a result of its consolidation by traffic. 
 In New York, macadam roads finished so late in the fall that they 
 can not have three months wear before winter, are given a surface 
 application of calcium chloride as a temporary protection against 
 raveling during the months that must elapse before bituminous 
 surfacing can be placed. 
 
 In making thin surface applications to an old road that is thick 
 enough to carry the prospective traffic and has a surface in fair 
 condition, the ruts and holes must first be patched. This is best 
 done several days in advance of the surfacing. Each hole or 
 rut is swept clean, 1 painted with bituminous material and filled 
 with J to 1? inch stone and binder. The stone and binder are 
 often mixed at a central point and carted along the road by the 
 patching gang, for use where required. Just before the surfacing 
 is done, the road is swept thoroughly, often with some type of 
 revolving broom. Sometimes wire brooms are used first and then 
 fiber brooms. The oil is applied hot or cold according to quality 
 at the rate of about J to f gallon per square yard, as the engi- 
 neer considers best, and then covered with clean screenings, granu- 
 lated slag or gravel at the rate of about 60 pounds per square 
 yard. It is advisable to secure the advice of a specialist in 
 selecting the oil. The oil is applied by hand on small work, but 
 usually with a distributor. If the screenings are distributed by 
 hand they should be previously deposited in piles at convenient 
 intervals along the roadside. They are also distributed by 
 spreader carts. The length of time the road should be closed to 
 traffic depends upon the weather, character of the oil, and the 
 amount of screenings used, varying from 1 to 48 hours. 
 
 If the road oil rises through the screenings, or " bleeds," in hot 
 weather, more screenings should be spread over those places. If 
 the road is used mainly by automobiles, a thin covering of screen- 
 ings is sometimes spread first and later a covering of sand or other 
 fine material, to act as a filler and prevent the tires from dislodging 
 the screenings. 
 
 The following rules for the amount of bituminous material to 
 be used in surfacing broken stone roads were prepared by George 
 H. Biles, second deputy highway commissioner of Pennsylvania: 
 
 1 It is desirable to cut the edges of a hole so as to secure vertical faces 
 to which the new material will adhere properly; a patch with a feather edge 
 is liable to be unsatisfactory. 
 
BITUMINOUS SURFACE APPLICATIONS 153 
 
 If the surface of the road is made up of pieces of ballast size stone 
 (3-inch) from which traffic has removed all the fine material, leaving large 
 surface voids between the stone, enough of the bituminous material must 
 be applied so that it will flush up level to the top of the large pieces of stone 
 and firmly bind the chips and gravel which lie in the crevices between the 
 stone. 
 
 If, on the other hand, the surface of the road is equally clean, but traffic 
 has not removed the fine particles between these stones to the same extent, 
 and the crevices between them are consequently smaller, then a somewhat 
 smaller amount of bituminous material should be used, since an excess 
 will again flow off the road. 
 
 In treating a road which has recently been resurfaced, it will be found 
 often that even after all the screenings and fine material have been swept 
 from the top of the road leaving the large stones bare, there will still be a 
 certain amount of dust and fine material between the stones which has 
 not yet been compacted thoroughly by traffic and which will absorb the 
 bituminous material like a blotter, leaving only a brown stain in these 
 spaces. In such cases, the amount of application must be increased until 
 this fine material is well saturated and there is enough of the bituminous 
 material near the surface of the road to bind thoroughly the covering of 
 chips or gravel. 
 
 The first application of a bituminous surfacing to a waterbound 
 macadam road may be disappointing. The hoofs of horses are 
 liable to dislodge the mat and the surface will have a spotted 
 appearance. After several applications, however, the macadam 
 surface will become protected everywhere. 
 
 On the New York State highways which are thick enough to 
 carry the traffic but are too rough to be treated satisfactorily with 
 cold oil and screenings, surfacing with two applications of hot 
 oil is sometimes done. After the old road is patched and cleaned, 
 it is covered with 0.4 to 0.6 gallon of oil to the square yard, over 
 which just enough 1-inch stone is spread to cover the surface. 
 This is rolled lightly and then covered with 0.3 to 0.4 gallon of 
 oil per yard. This is covered with \ inch stone in the thinnest 
 possible layer, which is rolled as soon as the oil is cool enough to 
 permit it. 
 
 On the Illinois highways, when a double application is made, 
 about } gallon per square yard is used on each application, and 
 the preferred covering is torpedo sand, \ to f inch in size, but 
 clean, stone chips are also employed. The total amount of cover- 
 ing material with such a treatment is one cubic yard for each 125 
 square yards of road. When a single application is made \ to 
 J gallon of oil per square yard and a cubic yard of torpedo sand 
 for every 150 square yards of road are employed. 
 
 Bituminous sandstone obtained in Kentucky has been used in 
 parts of that state for re-surfacing old macadam. The latter is 
 scarified, smoothed with a road machine, and enough new stone 
 added to give the desired thickness and contour. This is rolled 
 thoroughly and then covered with pulverized bituminous sand- 
 
154 AMERICAN HIGHWAY ASSOCIATION 
 
 stone to a depth of about If inches, loose, when spread. It is 
 desirable to allow the sun to shine on the loose material for a few 
 hours, until it appears slightly oily, and then roll it, slowly at 
 first and later more rapidly. 
 
 Concrete Road Surfacing 
 
 While surface applications to concrete roads have been em- 
 ployed in a number of states, there is no agreement as to their 
 desirability. They have been used to the greatest extent in 
 California, where both thin wearing surfaces and an asphaltic 
 mixture are used. The following information concerning both 
 types was supplied by Austin D. Fletcher, State highway engineer 
 of California. 
 
 The thin bituminous wearing surface is about half an inch in thickness 
 when completed. After it has been under traffic for a few months it is 
 found to contain a fairly uniform mixture of mineral aggregate and bitumi- 
 nous binder consisting of about 8 to 11 per cent of bitumen and the balance 
 mineral aggregate of a fairly uniform grading running from dust to rock 
 of ^-inch maximum diameter. It shows no tendency to flow or creep and 
 the surface remains true and free from rolling. The concrete base, how- 
 ever, must be finished with a true, smooth surface to make a good riding 
 highway as this type of surfacing is not thick enough to smooth up to any 
 considerable extent a concrete pavement whose surface is uneven. 
 
 The procedure in laying this thin wearing surface is as follows: First 
 the surface of concrete is cleaned of dirt, dust films and any thin coat of 
 laitance. This is best accomplished by opening the bare concrete to 
 traffic for a month or two. The iron shod traffic and the rapidly moving 
 rubber tires are of greatest help in breaking any weak layers of dirt or 
 laitance and exposing the surface of the concrete proper. This "traffic 
 cleaning" is followed by brushing with revolving street brooms and hand 
 brooms. In some cases flushing the surface with water is a help in wash- 
 ing off any thin coat of clay. It is of greatest importance that the asphaltic 
 oil bind to the solid concrete and not to any overlving weak film of dirt. 
 The care taken in getting a clean concrete is without doubt in a large 
 measure responsible for the success of this surfacing because of the strength 
 of the bond between the concrete and the bituminous wearing coat. The 
 few failures where the wearing surface has been stripped from the con- 
 crete have been nearly always easy to trace to a pavement improperly 
 cleaned prior to the application of the road oil. 
 
 After the concrete has been cleaned the asphaltic oil is applied by a 
 pressure distributor at the rate of J gallon per square yard. This oil 
 surface is immediately covered by a layer of either crushed rock screenings 
 or fine gravel of \ to inch. This material may contain some fines and 
 dust but should be fairly clean. 
 
 The screenings are applied by shoveling from piles placed at frequent 
 intervals alongside the road. The shovelers can be taught to so throw 
 the screenings that they will cover the road surface with a fairly uniform 
 thickness. The road can now with advantage be given a light rolling but 
 this is not necessary. Any excess screenings should be swept into piles 
 alongside of the road to be used on the second application of road oil. This 
 is applied on the second application at the same rate and is covered with 
 screenings as before. 
 
BITUMINOUS SURFACE APPLICATION 155 
 
 The road is now thrown open to traffic and during the first two weeks 
 may require further screenings to take up excess oil. The traffic is of great 
 assistance in forcing the screenings into the oil and compacting and mak- 
 ing a homogeneous carpet on the concrete. 
 
 The oil is applied to the road at a temperature of from 250 to 300. 
 It contains approximately 90 per cent of 80 penetration asphalt. In 
 California the road oil companies classify this product as a "90-80" road 
 oil. 
 
 In building the thin bituminous wearing surface for concrete pavements 
 two physical properties of the road oil are of greatest importance. First 
 the oil must be of such a viscosity that when applied to the road it will 
 readily combine with the screenings that are thrown upon its surface. 
 A very viscous oil will form a hard surface and the screenings will lie 
 there without being absorbed and to a large extent be thrown off the road 
 by the passing traffic. Only a small amount will settle or be forced into 
 the oil and the surface will not build up into a satisfactory protecting 
 wearing coat. 
 
 The second physical property of great importance is that the road oil 
 must be cementing or adhesive so that it will bind tightly to the concrete 
 surface and bind together all of the fragments of stone screenings. It 
 should be an active cement and if it is not sticky then the wearing sur- 
 face will not be firm enough to resist the push and pull of the passing 
 traffic. 
 
 The State highway routes leading from the great centers of population 
 have required a higher type of surfacing to meet successfully the demands 
 of heavy traffic. 
 
 After proper curing of the concrete its surface is cleaned of all dirt and 
 dust films and given a paint binder coat composed of asphaltic cement 
 and engine distillate of lightest gravity. The asphalt used has a penetra- 
 tion between 80 and 90, the mix being one part asphalt and one to two 
 parts distillate, the exact proportion of distillate being determined by 
 trial. The satisfactory mixture is one that paints the concrete with a thin, 
 uniform, glossy black film which becomes hard two hours after application. 
 
 The surfacing used has the following composition expressed in per- 
 centages : 
 
 Bitumen soluble in carbon disulphide, 7^10 
 
 Aggregate: 
 
 PASSING REFUSING 
 
 200 sieve 8-13 per cent. 
 
 80 
 
 40 
 
 10 
 
 4 
 
 2 
 
 200 sieve 14-25 " 
 
 80 " 17-29 " 
 
 40 " 5-11 " 
 
 10 " 15-25 " 
 
 4 " 3-10 " 
 
 100 
 
 The asphaltic cement used has a penetration of from 70 to 90 degrees, 
 District of Columbia standard, and passes the usual requirements for 
 solubility, volatility and ductility. The heating of asphalt, aggregates 
 and dust and mixing and laying follow the usual practice. 
 
 Prior to the laying of the surfacing, the testing laboratory makes grad- 
 ing tests of such sand, limestone dust and rock screenings as will be avail- 
 able for the work and selects such of these that give the desired mix. In 
 this selection the following points are considered important: 
 
 Let a be taken as the percentage of asphaltic cement that will be used 
 in the finished material. Then the dust passing the 200-mesh sieve should 
 at least equal a-1. The fine sand passing the 80 mesh and retained on 
 
156 BITUMINOUS SURFACE APPLICATIONS 
 
 the 200 should be approximately 2a. If the available sand is high on the 
 finer sieves a may be taken as high as 9.5 per cent. If the sand is coarse, 
 a may be as low as 8 per cent for the trial mix. The coarse aggregate pass- 
 ing the No. 2 sieve and retained on No. 10 should be from 28 to 35 per cent 
 of the other mix. If these points are satisfied by the available material 
 the weights of coarse aggregate, fine aggregate, dust and asphaltic cement 
 can be given to the road crew for a trial batch. Under field working con- 
 ditions a trial batch will show if the mix is "wet" or "dry" and by a slight 
 change in the percentage of asphaltic cement a mixture can be made that 
 will rake and roll properly. In this way the mineral aggregate is not 
 changed but kept under known satisfactory grading. As the work pro- 
 ceeds, grading tests should be run at frequent intervals on the different 
 mineral aggregates to insure a uniform grading in the finished pavement. 
 Analysis of samples of the different batches should also be made to check 
 the uniformity of the mix. 
 
 The surface after thorough rolling should have a specific gravity in 
 excess of 2.20 if the sands and crushed rock screenings are of average spe- 
 cific gravities. A sample of the finished pavement taken each day and 
 tested for specific gravity will indicate if there has been insufficient com- 
 pression, either due to method of rolling or to the surface being too cold 
 when rolled. 
 
BRICK ROADS 1 
 
 Brick pavements have been used on the streets of American 
 cities for many years and the United States Bureau of the Census 
 reports that in 1909 they formed nearly 24 per cent of the entire mile- 
 age of paved streets in 158 cities. Some of the early brick pave- 
 ments gave satisfactory service for many years, but others did 
 not. The unsatisfactory early experience was due in part to 
 the use of unsuitable materials, in part to the improper recon- 
 struction of pavements cut to permit laying pipes, and in part 
 to the defective methods of construction employed, just as was 
 the experience with other types of block pavements. It is not 
 possible to build lasting block pavements unless the blocks are 
 prevented from settling, which results in holes in the surface, 
 or from tilting over on their bottom side, called "turtling," 
 which results in a rounding of the upper edges of the blocks, 
 called "cobbling." These defects led to better methods of 
 construction, so that when bricks came into use on country 
 highways success was assured if municipal experience was taken 
 as a guide. There are always communities as well as persons 
 unwilling to profit by the experience of others, however, and con- 
 sequently some brick roads have been built of poor materials 
 and by poor methods with the inevitable unsatisfactory results. 
 Such unfortunate experience was unnecessary then and is un- 
 necessary today; it was largely due to ignorance of the require- 
 ments for good work, carelessness, lack of proper supervision, 
 and a desire to cheapen the cost of such roads below the amount 
 needed for proper construction. 
 
 Paving Bricks 
 
 Paving bricks are made from a great variety of shales and fire 
 clays and consequently bricks of equal worth vary considerably 
 in appearance. Shale contains iron which makes shale bricks 
 red when burned under normal oxidizing conditions and brown 
 
 1 Revised by William W. Marr, chief state highway engineer of Illinois; 
 A. H. Hinkle, deputy highway commissioner of Ohio; P. M. Tebbs, engi- 
 neer of construction of the Pennsylvania State Highway Pepartment; 
 Will P. Blair, secretary of the National Association of Paving Brick Manu- 
 facturers; and W. C. Perkins, chief engineer, R. T. Stull, ceramic engi- 
 neer, and F. A. Churchill, of the Dunn Wire-Cut Lug Brick Company. 
 
 157 
 
158 AMERICAN HIGHWAY ASSOCIATION 
 
 or nearly black when burned under reducing conditions. Fire 
 clays have less iron than shales, the iron being present in a com- 
 bined state, and bricks made from them are buff-colored, unless 
 reducing conditions during burning darken them. The shales 
 and fire clays are often unsuited for making paying bricks as they 
 occur, and then material from one stratum in a pit must be 
 mixed with that from another stratum or that from one pit with 
 that from another, and sometimes with sand or surface clay. 
 
 The raw materials are crushed and ground dry in large revolv- 
 ing pans under heavy rolls, called "mullers." This material is 
 screened to remove pieces of too large size, and is then conveyed 
 to a pug mill, in which the materials are mixed somewhat as 
 concrete is mixed in a continuous concrete mixer. Here enough 
 water is added to convert the material into a thick mud, which 
 is beaten by the revolving blades into a condition of uniform 
 consistency and composition. This mud is fed continuously 
 into a brick machine, where it is forced by an auger through a 
 die, whence it emerges as a fairly hard bar of rectangular section, 
 which is cut mechanically into bricks. This bar of hard clay may 
 be approximately 4 by 4? inches in section, in which case it is 
 cut about every 9 inches, forming "end-cut" bricks, or it may be 
 approximately 9 by 4$ inches in section and cut every 4 inches, 
 forming " side-cut" bricks. These bricks are sometimes sub- 
 mitted to a reshaping process before drying, in which case they 
 are called "re-pressed" bricks, and sometimes they are dried as 
 they are finished by the brick machine, in which case they are 
 called "wire-cut" bricks. For drying, the bricks are placed on 
 cars which are run very slowly through a long, tunnel-like heater, 
 into which hot dry air is admitted continuously. After remain- 
 ing on the cars in the tunnel about twenty-four hours their 
 weight is reduced from 15 to 20 per cent. The bricks are then 
 ready for burning, one of the most important steps in the manu- 
 facturing process. The bricks are stacked in kilns in such a 
 way that the heated air circulates freely around them, and great 
 care must be taken in the regulation of the temperature through- 
 out the entire burning process, from the time the kiln is first 
 warmed until it is cool enough to permit the withdrawal of the 
 bricks. 
 
 In laying paving bricks a space is left between successive rows 
 for the material which forms the joints, and as it is very desir- 
 able for these joints to be of a uniform width, one side of a paving 
 brick has either two or four lugs, which are small projections 
 from the surface of the bricks. 1 These projections serve to keep 
 
 1 There are some bricks which do not have lugs but have raised letters 
 or four projections, one near each corner, on one face. Raised letters are 
 not permitted on bricks for Ohio State roads. 
 
BKICK ROADS 159 
 
 the adjacent faces the proper distance apart when the bricks are 
 forced into contact during the paving operations. These pro- 
 jections extend J to J inch from the side or face. In one class of 
 side-cut bricks the cutting is done by wires which are moved 
 across the bar of clay so as to produce the lugs needed on one side 
 of the brick. These are called "wire-cut lug" bricks. In an- 
 other type of side-cut bricks, 2J, 3 and 4 inches deep, the ribs 
 are moulded on one of the sides as it comes through the die. A 
 wire-cut side is placed on top in laying such bricks, which are 
 called "vertical fiber" bricks in some parts of the country. Other 
 types of projections are made by devices attached to the brick 
 machine. In the case of repressed bricks, the projections from 
 one or both sides are made in the press. 
 
 There is no universal standard size for bricks but the tendency 
 seems to be toward 3J inches width, 4 inches depth and 8^ inches 
 length, with a permissible variation of f inch either way in the 
 width and depth and i inch either way in length. The depth is 
 occasionally reduced as much as an inch for roads having light 
 traffic, when the monolithic and cement-sand cushion types of 
 construction, explained later, are used. 
 
 "Hillside" bricks are made for use on grades of 5 per cent or 
 more. They have one or more grooves cut the full length of the 
 bricks, along their edges, in the case of bricks to be laid in the 
 usual manner, or two grooves cut transversely in the case of bricks 
 to be laid parallel with the curb. These grooves are about f inch 
 deep and are intended to prevent slipping of horses or automo- 
 biles. Bricks with beveled edges are used for grades, notably on 
 the carriage ramps of the Pennsylvania Terminal in New York, 
 where the travel is very heavy, and quite generally on grades ex- 
 ceeding 5 per cent, throughout Ohio. 
 
 Tests of Bricks 
 
 The color of the interior of bricks from the same plant gives 
 an indication of their quality, for generally the color is darker 
 in the bricks burned with the higher temperatures. The color of 
 the exterior of the bricks is a less reliable indication of quality, 
 and even interior color is of little or no value in judging the bricks 
 from different plants. The other features of bricks which can 
 be determined by visual inspection are explained in the follow- 
 ing description of the bricks which may be rejected under the 
 standard specifications of the American Society for Testing 
 Materials : 
 
160 AMERICAN HIGHWAY ASSOCIATION 
 
 All bricks which are broken in two or chipped in such a manner that 
 neither wearing surface remains substantially intact, or that the lower or 
 bearing surface is reduced in area by more than one-fifth. 1 
 
 All bricks which are cracked in such a degree as to produce defects such 
 as are defined in (the previous paragraph) either from shocks received in 
 shipment and handling, or from defective conditions of manufacture, 
 especially in drying, burning or cooling, unless such cracks are plainly 
 superficial and not such as to perceptibly weaken the resistance of the brick 
 to its condition of use. 
 
 All bricks which are so off-size, or so misshapen, bent, twisted or kiln- 
 marked, that they will not form a proper surface as defined by the paving 
 upecifications, or align with other bricks without making joints other than 
 those permitted in the paving specifications. 
 
 All bricks which are obviously soft 5 and too poorly vitrified to endure 
 street wear. 
 
 Formerly a number of different laboratory tests of the properties 
 of paying bricks were required by specifications, but today reli- 
 ance is placed mainly on the rattler test to determine their qual- 
 ity. Its name is derived from the use of a foundry rattler, em- 
 ployed in cleaning iron castings, in making the first tests of this 
 kind on bricks. The rattler used today is constructed specially 
 for the purpose. It is an iron and steel barrel of the cross-section 
 of a 14-sided polygon, about 20 inches long and 28 inches in diam- 
 eter, inside dimensions, with a shaft projecting from each end. 
 This barrel is mounted in a frame with the shafts horizontal and 
 can be revolved by power. 
 
 Ten dry bricks are weighed and placed within the rattler, 
 together with an abrasive charge consisting of 10 cast-iron spheres 
 weighing from 7 to 7J pounds each and a sufficient number of 
 cast-iron spheres from If to 1J inches in diameter and weighing 
 from 0.75 to 0.95 pound each, to make a total charge of 300 
 pounds. The rattler is then revolved 1800 times at the rate of 
 29^ revolutions per minute. In this way the bricks are sub- 
 jected to innumerable blows which are considered to imitate the 
 conditions of service more nearly than any other test yet de- 
 
 1 Mr. Tebbs makes this comment: "The area of a standard brick is about 
 30 square inches and I consider about one-fifth or 6 square inches a very 
 large allowance. I think that a reduction of not more than one-tenth of 
 the area should be permitted." This comment is not approved by Mr. 
 Blair on the grounds that experience has shown no ill effects from the rule 
 of the Society, and to limit the reduction of area to 10 per cent, would in- 
 crease materially the cost of the bricks. 
 
 a Mr. Tebbs advises adding the words, "not uniformly vitrified, badly 
 laminated." The phrasing of the standard specifications was debated at 
 great length before adoption, and uniform vitrification was not adopted 
 as a requirement because no brick is uniformly vitrified, strictly speak- 
 ing. The words "badly laminated" are sometimes used, but objection 
 has been raised to them as not conveying to the inspector the meaning of 
 the engineer, which is to reject bricks having laminations that are separate 
 one from the other, sometimes called "open" laminations. 
 
BBICK ROADS 
 
 161 
 
 vised. When the test is finished, the bricks are taken out, all 
 pieces of them weighing less than 1 pound are discarded, and the 
 remainder are weighed. The loss in weight during the test, 
 expressed as a percentage of the original weight, is the form in 
 which the results are stated. 
 
 The percentage of permissible loss in the rattler test is fixed 
 at different amounts in order to meet the conditions imposed by 
 differences in travel and the experience of different localities with 
 bricks of various grades. The American Society for Testing 
 Materials gives the following scales of maximum permissible 
 losses for different classes of travel : 
 
 CHARACTER OF TRAVEL 
 
 MAXIMUM PER 
 
 MIS8IBLE LOSS 
 
 
 Average 
 
 Single brick 
 
 Heavy 
 
 22 
 
 24 
 
 
 24 
 
 26 
 
 Light 
 
 26 
 
 28 
 
 
 
 
 The New York and Pennsylvania State highway departments' 
 specifications call for the medium-travel grade and Ohio and 
 Illinois for the heavy-travel grade. In Illinois the wire-cut 
 lug bricks are given 1 per cent higher permissible loss than the 
 repressed bricks, which must conform to the tabulated require- 
 ments. In that State there is a minimum permissible loss spec- 
 ified, 17 per cent for wire-cut and 16 per cent for repressed bricks. 
 The average permissible maximum loss may reach 25 per cent 
 for wire-cut lug bricks if no individual brick loses more than 
 28 or less than 20 per cent, and may reach 27 per cent if the 
 range of loss of every individual brick is between 29 and 23 per 
 cent. With repressed bricks, the average loss may reach 24 
 per cent, with a range of 27 to 19 per cent for every individual 
 brick, and 26 per cent with a range of 28 to 22 per cent. These 
 requirements put a premium on uniformity in the bricks, which 
 many engineers regard as of importance in preventing unequal 
 wear of the surface of a brick road. They hold that where soft 
 and hard bricks are laid together indiscriminately, some of the 
 bricks are worn away more rapidly than where a pavement is 
 laid with bricks of a more uniform quality. 
 
 In New York and Ohio 30 bricks form a lot for sampling. 
 These represent the hard, medium and light-burned bricks de- 
 livered on the job, and each grade is tested separately. During 
 testing there is a large percentage of failures in the abrasion test, 
 partially caused by the selection of light and hard-burned brick. 
 The laboratory results obtained on such bricks serve as a guide 
 in throwing out or culling part of the bricks on the job. 
 
162 AMERICAN HIGHWAY ASSOCIATION 
 
 Some years ago the crushing strength and specific gravity of 
 paving bricks were considered properties which should be speci- 
 fied, but experience has shown that it is unnecessary to do so. 
 The specific gravity of fire-clay bricks averages between 2.1 and 
 2.25 and that of shale bricks between 2.2 and 2.4. The crushing 
 strength of good paving bricks ranges from 10,000 to 20,000 
 pounds per square inch, when the test load is applied over the 
 entire top surface of the specimens, and may be higher if only a 
 part of the surface is loaded. This is from five to ten times the 
 probable maximum load on a pavement. 
 
 The capacity of a brick to absorb water was formerly consid- 
 ered an important indication of its porosity, and low porosity 
 was held to be essential for strength and good sanitary proper- 
 ties, which were then considered as particular advantages of 
 brick pavements. With the improvements that have been made 
 in the rattler test and the increased knowledge of the slight in- 
 fluence of a wide range in porosity upon the sanitary value of 
 such pavements, the absorption test has lost much of its former 
 favor among roadbuilders. It affords useful information in 
 comparing bricks made under identical conditions and for other 
 research work, and it is still required by a few State highway 
 departments. In Ohio, the bricks taken from a rattler after 
 testing in that apparatus must not absorb more than 3J per cent 
 of their weight of water during immersion for forty-eight hours. 
 In Pennsylvania, the absorption of thoroughly dried bricks im- 
 mersed in water for twenty-four hours must not exceed 3J per 
 cent. 
 
 Another test, formerly used extensively, probably because the 
 apparatus for making it was available in many schools and easily 
 obtained, is the transverse or cross-breaking test. It is now 
 little used outside of New York and New Jersey. In the former 
 State the test required by the highway department is to place 
 the sample brick on edge on two parallel supports 6 inches apart 
 and load it at the center until it breaks. If the distance in 
 inches between the supports is represented by L, the load in 
 pounds which produces rupture by W, and the width and depth 
 in inches of the brick by b and d respectively, the modulus of 
 rupture will be 3WL/2bd 2 , which must not be less than 2000 
 pounds in bricks for New York state work. 
 
 Curbs 
 
 Curbs are required along the sides and ends of brick pave- 
 ments laid on a sand cushion or laid on natural soil and having 
 sand-filled joints, in order to hold the bricks at those places and 
 also, with some types of base, to hold the material of the base in 
 
BKICK ROADS 163 
 
 place. Planks have been used, but their short life compared with 
 that of the pavement makes them undesirable, for nobody can 
 foretell whether they will be renewed as they wear out. In 
 some places stone slabs can be obtained for the purpose at prices 
 which enable them to be used economically. Vitrified curbs are 
 sometimes used, but require more careful bedding than stone 
 curbs, because their shorter length and lighter weight render 
 them more subject to displacement. Concrete is most gener- 
 ally used for curbs. In country highway work the top of the 
 curb is usually flush with the surface of the pavement. If a con- 
 crete base is used, the curb is usually an integral part of it, and 
 is generally from 6 to 8 inches wide on top. If a concrete base 
 is not used, the depth of the curb must be governed mainly by 
 the character of the subgrade, the frost hazard and the character 
 of the shoulders. In any case it is desirable to have the top 2 
 inches of the concrete curb not leaner than a 1:2:3 mixture, 
 finished with a wooden float, and the outer surface should be 
 spaded. This spading is done by placing a spade in the form 
 against the outer plank and rocking it back and forth so as to 
 force the coarse aggregate of the fresh concrete away from the 
 face. 
 
 Where the bricks are bedded on mortar or green concrete, 
 most engineers believe that curbs are not needed. 1 If they are 
 omitted special care must be given to providing firm shoulders 
 along the marginal bricks. 
 
 The Base 
 
 A brick pavement requires an absolutely firm unyielding sup- 
 port. Ail old macadam road thoroughly underdrained and se- 
 cure against settlement or upheaval ,is considered a satisfactory 
 support by some engineers. But it is rarely possible to find such 
 a road, for usually the drainage is defective, the cross-section has 
 too much crown, or the grades are wrong. It is then necessary 
 to disturb the hard crust of the road and this is very likely to 
 reduce materially its value as a foundation. In some parts of 
 Florida, where frost is not to be feared, if the sand which pre- 
 vails is held in place by curbs or planks and thoroughly rolled 
 while damp, it makes a hard, unyielding support not subject to 
 disturbance if good drainage is assured. On the other hand, the 
 black soil of the prairie States, which absorbs water freely and 
 
 1 Mr. Marr states: "Experience in Illinois demonstrates beyond ques- 
 tion that curbs are not needed under such conditions. We have had sev- 
 eral instances where the edges of the bricks were exposed at intersections 
 to a grinding action of wheels striking them at acute angles, and there 
 seems to be absolutely no danger of the bricks being loosened at the edges 
 under any conditions obtaining in ordinary service. 
 
164 AMERICAN HIGHWAY ASSOCIATION 
 
 parts with it slowly, is an unstable material and a strong con- 
 crete foundation must be provided for brick roads built over it, 
 so that any differences in the supporting capacity of the subgrade, 
 from one season to another or between adjoining places in the 
 road, are equalized by the concrete slab and do not cause waves 
 in the brick surface. 
 
 The methods of constructing the road bed and preparing the 
 subgrade are explained in the chapter on earth roads. It is 
 necessary to have a uniformly firm subgrade, and if there are 
 heavy cuts and fills the grading must be done carefully. It is 
 desirable to allow the subgrade to go through one winter before 
 putting down the pavement, although this is rarely practicable 
 under the usual working conditions. The drainage is particularly 
 important, on account of the difficulty of improving it, if defec- 
 tive, after the pavement is laid. 
 
 If the subgrade is firm and well drained, a 6 to 8-inch base of 
 good gravel, broken stone, vitrified clay 1 or slag, thoroughly 
 consolidated by rolling, may prove sufficient for moderate traffic. 
 Such a base should be built in two courses with all the care given 
 to the best macadam construction. In some cases, second qual- 
 ity paving bricks have been used for a base. The subgrade is 
 covered with enough sand to give a depth of 2 inches after roll- 
 ing with a hand roller. The No. 2 bricks are laid flat on this 
 cushion, parallel with the curb, and the joints are filled with fine 
 sand. 
 
 The best base for general use is concrete. A few years ago 
 there was a general opinion that it should be 6 inches thick, but 
 4-inch bases on well-built subgrades are giving satisfaction where 
 frost action is not serious, and a thickness of only 3 inches or less 
 is under consideration by some engineers. If a secure subgrade 
 is provided, the best thickness is in part determined by the cost 
 of the concrete. A 1 : 3 J : 6 mixture with ordinary materials, 
 laid to form a 5-inch base, may be less expensive than a 1 : 2| : 5 
 mixture of better materials laid to form a 4-inch base. If gravel 
 is used as the aggregate, it is generally economical to screen it and 
 then recombine it, if good concrete is desired. If good concrete 
 is not desired, it will be better to leave out the cement entirely 
 and use the money thus saved in putting down a good base of the 
 
 1 Mr. Hinkle advises eliminating gravel and vitrified clay as materials 
 for a base for this reason: "While fair foundations may be made from 
 these materials, it so frequently happens that poor foundations result 
 from the use of these materials that I think it well to omit referring to 
 them here and hence not encourage their use any more than necessary." 
 Mr. Blair believes that the long experience with gravel foundations in 
 places like South Bend, Ind., warrants their use. 
 
BBICK ROADS 165 
 
 macadam type. 1 The thinner the base, the better the concrete 
 should be. A 4-inch base of poorly graded, dirty aggregate and 
 a pinch of cement is an invitation to early failure. One common 
 defect is insufficient mixing. This should be done hi a batch 
 mixer which should be run between 15 and 20 revolutions per 
 minute, and after all the materials are in the mixer, the process 
 should be continued until the mixer has made at least 15 revo- 
 lutions. The surface of the concrete should be struck off by 
 means of a transverse templet, drawn along the side forms, and 
 be kept well wet for at least three 2 days. No traffic should be 
 permitted on the base for at least seven days after it is laid. On 
 the Illinois state highways, if there are deviations exceeding J 
 inch from the desired shape of the surface, they must be repaired 
 if a sand-cement cushion, described later, is to be employed. 
 
 The Cushion or Bedding of the Bricks 
 
 One of the causes which contributed to limit the serviceability 
 of some early brick pavements was the imperfect way in which 
 the bricks were supported on the base. The latter was covered 
 with loose sand of inferior quality for its purpose, smoothed off 
 roughly without being consolidated, and the bricks laid on it and 
 driven to a bearing with a paver 's tamper. The joints were 
 then filled with sand and the roadway thrown open to travel. 
 The surface was not smooth at the outset, traffic on it soon forced 
 some bricks down more than others, and water percolating in 
 cold weather through the joints into the sand cushion alternately 
 froze and thawed, throwing the bricks into irregular positions. 
 Under such conditions the edges of the bricks became chipped, 
 and finally many of the bricks became broken and dislodged, 
 leaving holes in the roadway. The lesson of this experience was 
 so clear that for a number of years the importance of bedding 
 the brick securely has been generally recognized. Today there 
 are three methods of doing this, termed the sand cushion, sand- 
 cement or dry mortar bed and monolithic or green concrete bed 
 types. The purpose of each is to support the bricks securely at 
 the proper elevation to give the pavement a smooth surface. 
 
 Sand-Cushion Type. A sand cushion is primarily intended to 
 smooth out the inequalities in the top of the base, which were 
 formerly greater than good practice now permits, to provide for 
 the slight variations in the depth of the bricks. Experience 
 
 1 Mr. Tebbs advises the use of concrete exclusively as a base for brick 
 pavements. Mr. Blair holds that experience at Cleveland, Terre Haute 
 and other places shows that under proper conditions a base of other ma- 
 terial will prove satisfactory. 
 
 1 Mr. Hinkle advocates at least five days. 
 
166 AMERICAN HIGHWAY ASSOCIATION 
 
 shows that the sand must be free from large stones, which pre- 
 vent satisfactory consolidation of the cushion, and some engi- 
 neers hold that it must also be free from loam, clay and materials 
 of a greasy nature when wet. 1 Granulated slag is sometimes 
 used instead of natural sand and is believed by some engineers to 
 be superior to ordinary sand. Dry sand must be used, accord- 
 ing to some engineers, on the ground that wet sand shrinks in 
 drying and cannot be relied upon to support the bricks at the 
 desired elevation. Other engineers believe that somewhat damp 
 sand is more easily handled and gives as good results. The 
 thickness of this bed in the case of city streets has usually been 
 2 inches of late, but where a concrete base is used for a country 
 highway and is finished so that no part deviates more than J 
 inch from the. true surface, a thickness of 1J inches is enough. 
 On narrow roads where the concrete base is easily finished to the 
 exact cross-section of the road, 1 inch is probably enough. 2 
 
 The dry sand is cast over the base to a slightly greater depth 
 than the proposed thickness of the cushion. The extra depth is 
 usually about \ inch where a 2-inch cushion is desired. A plank 
 templet, which is often provided with a steel edge, is then drawn 
 over it to smooth it down to the prescribed cross-section. If the 
 roadway is less than about 25 feet wide, this templet is supported 
 at the ends by the curbs. If the roadway is wider than 25 feet, 
 the templet is long enough to reach from one curb to a longitu- 
 dinal plank support at the center of the road. The sand is con- 
 solidated and brought down to grade by rolling it by hand, using 
 a roller weighing 300 to 400 pounds. After rolling the surface 
 is tested with the templet, the high spots reduced and the low 
 places filled, and the rolling repeated. This process is repeated 
 until a uniform surface at the desired elevation is obtained. The 
 extra elevation of the templet in the first stage of the work is 
 
 1 Mr. Tebbs makes the following comments: "Pennsylvania specifica- 
 tions allow 15 per cent of loam and I advocate the use of a sand contain- 
 ing loam, because it helps to bind it, thereby avoiding the shifting about 
 which often occurs with clean dry sand. It has been proved that dry sand 
 occupies less space than wet sand. Dry sand cannot always be obtained 
 without considerable expense, and 1 therefore think it advisable to use 
 reasonably dry sand without requiring that it be dried, and as thin a 
 cushion as it is practicable to use. The cushion should be 1 inch or less. 
 This decrease in the depth of the cushion minimizes the shrinkage due to 
 the drying of sand which was moist when placed." 
 
 2 Mr. Marr states: "It has been well demonstrated that the thinner 
 the sand cushion between the rigid base and the brick wearing surface, 
 the better, and its only function is to assure a smooth surface on the pave- 
 ment. The use of the plain sand cushion is growing less every year and 
 seems to have its greatest advantage in street paving where numerous 
 subsequent openings may be expected and it is necessary to use a soft 
 filler." 
 
BRICK ROADS 167 
 
 obtained by laying strips of wood of the requisite thickness on 
 top of the curbs or other supports of the templet. 
 
 If a road carries only light vehicles, a well consolidated sand 
 cushion is a satisfactory support for the bricks. Heavy vehicles, 
 whether drawn by horses or self-propelled, are believed to jar the 
 road although definite tests with a seismograph or a similar in- 
 strument are needed to determine the correctness of this opinion. 
 It is certain, however, that if the roadway contains a railway 
 track the whole structure will be jarred by the cars traveling along 
 it. The sand cushion is not considered by many engineers to 
 be a satisfactory support for bricks likely to be jarred, on account 
 of the possibility that the repeated minute vibrations in it may 
 cause parts of it to shift their position. This apprehension has 
 led to the use of the sand-cement bed. 
 
 Sand-cement Cushion Type. The cushion consists of a dry 
 mixture of one part of cement with three to five parts of mortar 
 sand. These materials must be thoroughly mixed dry. If the 
 cushion is to be 1 inch thick, as in Pennsylvania state work, the 
 mixture contains less cement than if it is to be f inch thick as 
 in the Illinois State work. The loose material is given about } 
 inch greater depth than the desired thickness of the finished bed. 
 The mortar is spread and shaped like a sand cushion. In Illi- 
 nois, where the sand-cement bed has been used extensively, the 
 shaping of the bed for the brick is considered of prime importance 
 and the State highway department requires the contractor to 
 employ skilled men for this part of the work. 
 
 There is a difference of opinion as to the best method of moist- 
 ening the sand-cement bed to convert it into mortar. Some 
 engineers hold that the bricks should be laid on the dry bed and 
 rolled, and then the pavement should be sprinkled sufficiently 
 to allow water to pass down the joints into the bed. This 
 wetting down should be done as soon as the bricks have been 
 rolled. The Pennsylvania highway department requires the 
 mortar bed to be sprinkled lightly just before the bricks are laid. 
 In any case, the mortar bed should not be laid so far in advance 
 that any of it will remain exposed over night, and if any of it be- 
 comes wet and the cement sets it must be replaced by dry material. 
 
 Monolithic Type. 1 The monolithic or green concrete bed is not 
 actually a cushion, for the bricks are laid on the fresh concrete 
 base as soon as it has been finished. In this type of work steel 
 side forms for the base are generally specified and curbs are 
 
 1 A monolithic brick pavement was laid about 1904 in Terre Haute, Ind., 
 on the recommendation of Street Commissioner Varrelman of St. Louis. 
 It was on a railroad teaming yard and a private street to the warehouse of 
 Hullmann & Company. This is probably one of the earliest uses of the 
 type in this country. 
 
168 AMERICAN HIGHWAY ASSOCIATION 
 
 omitted. The steel forms are considered necessary as supports for 
 the heavy steel templet which is used. 
 
 The concrete is placed in successive batches for the entire 
 width of the pavement in a continuous operation. This concrete 
 as placed has a slightly greater depth than the finished thickness 
 of the base, and the workmen are guided in placing it by a light 
 wood templet which rests on the side forms when in use. When 
 it has been brought to a smooth surface of the desired shape, it 
 is finished with a steel templet. This consists of a 6-inch steel 
 I-beam in front and a 6-inch steel channel at the rear, held 2 
 feet apart by a metal frame at each end. Each frame has two 
 rollers 3 feet or more apart. These rollers rest on the side forms 
 and permit the templet to be moved ahead easily and without 
 jerks. Both beams are bent to the desired crown of the pave- 
 ment. The lower flange of the I-beam is f to -^ inch lower than 
 that of the channel. The space between the two beams is kept 
 filled with dry 1 : 3 mortar, thoroughly mixed. As the templet is 
 moved along, the I-beam shapes the fresh concrete accurately, 
 and the channel leaves a thin, compacted bed of mortar on its 
 surface, so that the bricks have a support which is true to grade 
 in every respect. Experience shows that particular care must be 
 taken in this type of construction to use concrete which will not 
 flow but will quake. If it flows it will not support the bricks 
 and if it does not quake it will be deficient in strength. The 
 bricklaying should follow closely behind the templet before the 
 concrete takes its initial set, and the workmen are required to 
 move with special care over the bricks just laid. Some engineers 
 require boards to be laid for the workmen to walk and stand on. 
 
 Delivering and Laying Bricks 
 
 In case the bricks are not tested at the plant, each carload 
 must be sampled as it is delivered and the lot should not be 
 allowed on the road until the samples have been tested and ap- 
 proved. If this is not done, imperfect bricks are likely to find 
 their way into the road, and the work of roadside inspection is 
 made needlessly expensive and prolonged. 1 
 
 1 Mr. Hinkle calls attention to the following paragraphs in the speci- 
 fications of the Ohio State highway department: "If all the bricks in a 
 shipment or in several shipments of the same make and kind of bricks 
 appear to be uniform in quality two samples of 12 each may suffice^ If 
 in a shipment there appears to be different classes of bricks, such as bricks 
 that appear to be more or less burned than others, a representative lot 
 of 12 bricks is to be secured for each class of bricks, exclusive of the culls. 
 The approximate number of each class sampled should be given on the 
 notification card accompanying the samples. Unless otherwise ordered 
 by the Engineer, at least one lot of samples should be taken for every 
 
BRICK ROADS 169 
 
 Bricks are liable to considerable injury if handled roughly, 
 and to prevent such injury to them after their acceptance by 
 test many engineers specify the manner in which they shall be 
 handled. The requirements of the Illinois highway department 
 are as follows: 
 
 Before the fine grading is finished, the bricks shall be hauled and neatly 
 piled without the edging line in sufficient quantities to complete the brick 
 surface. Clamps and conveyors may be used in connection with the 
 work but the bricks shall not be dumped from industrial cars or vehicles, 
 nor shall they be thrown to piles or to industrial cars or to vehicles. The 
 bricks shall not be piled in any place where they will be likely to be be- 
 aplattered or covered with mud or otherwise injured. In delivering the 
 bricks from the piles for placement in the pavement, no wheeling in bar- 
 rows will be allowed ofc the brick surface, but they shall be carried on 
 pallets. They shall be placed upon the pallets so that when delivered to 
 the dropper they will lie in such order that each brick in the regular oper- 
 ation of placing it upon the foundation as prepared, will bring the lugs in 
 the same direction with the best side uppermost. 
 
 The bricks are laid with the best side up and the projections 
 for spacing all in the same direction; in highway work they are 
 laid in rows or courses at right angles to the curb. Alternate 
 rows commence with a half brick at the curb and the joints in a 
 row must be at least 3 inches from those in the row last laid. 
 When the row reaches the curb towards which it is laid it must be 
 completed with a bat at least 3 inches long. The fractured end 
 of a broken brick must be toward the center of the road. Brick 
 layers generally carry three or four rows across the roadway 
 simultaneously, as this enables them to save considerable walk- 
 ing. The bricks are laid from the bricks already in place, and 
 no walking is permitted on the cushion or dry mortar bed. In 
 order to keep the cross joints of uniform width, after about six 
 or eight rows have been laid, a 4 x 4-inch timber 3 feet long is 
 moved along the face of the last row and tapped lightly with a 
 sledge. 
 
 After the bricks are laid the surface is swept clean and inspected. 
 The soft bricks are replaced by good ones; they are detected by 
 
 100,000 bricks, care being taken to secure bricks from different parts oJ 
 the cars or piles so that the samples submitted will be representative of 
 the bricks to be used. If at any time a shipment of bricks is received in 
 which the quality of the bricks does not appear equal to that of the sam- 
 ples previously submitted, additional samples should be immediately 
 sent to the testing laboratory. A sufficient number of samples in every 
 case should be taken to insure the use of bricks of proper quality, but it 
 should be borne in mind that the charges for transportation are high and 
 only a sufficient number of samples should be submitted for test, which 
 will permit of proper control of the quality of bricks used." 
 
170 
 
 AMEKICAN HIGHWAY ASSOCIATION 
 
 Thousands of Bricks Required to Pave a Mile of Road of Different 
 Widths with Different Numbers of Bricks per Square Yard 
 
 BRICK PER 
 SQUARE 
 YARD 
 
 WIDTH OF STREET 
 
 8 
 
 10 
 
 12 
 
 15 
 
 18 
 
 20 
 
 22 
 
 33 
 
 174.2 
 
 193.6 
 
 232.3 
 
 290.4 
 
 348.5 
 
 387.2 
 
 425.9 
 
 34 
 
 179.5 
 
 199.5 
 
 239.4 
 
 299.2 
 
 359.0 
 
 398.9 
 
 438.8 
 
 35 
 
 184.8 
 
 205.3 
 
 246.4 
 
 308.0 
 
 369.6 
 
 410.7 
 
 451.7 
 
 36 
 
 190.0 
 
 211.2 
 
 253.4 
 
 316.8 
 
 380.1 
 
 422.4 
 
 464.7 
 
 37 
 
 195.3 
 
 217.1 
 
 260.5 
 
 325.6 
 
 390.7 
 
 434.2 
 
 476.9 
 
 38 
 
 200.6 
 
 222.9 
 
 267.5 
 
 334.4 
 
 401.3 
 
 445.9 
 
 490.5 
 
 39 
 
 205.9 
 
 228.8 
 
 274.6 
 
 343.2 
 
 411.7 
 
 457.6 
 
 503.4 
 
 40 
 
 211.2 
 
 234.7 
 
 281.6 
 
 352.0 
 
 422 .4 
 
 469.4 
 
 516.3 
 
 41 
 
 216.5 
 
 240.5 
 
 288.6 
 
 360.8 
 
 432.9 
 
 481.1 
 
 529.2 
 
 42 
 
 221.8 
 
 246.4 
 
 295.7 
 
 369.6 
 
 443.5 
 
 492.8 
 
 542.1 
 
 43 
 
 227.1 
 
 252.3 
 
 302.7 
 
 378.4 
 
 454.1 
 
 504.6 
 
 555.0 
 
 44 
 
 232.3 
 
 258.1 
 
 309.8 
 
 387.2 
 
 464.6 
 
 516.3 
 
 567.9 
 
 45 
 
 237.6 
 
 264.0 
 
 316.8 
 
 396.0 
 
 475.2 
 
 528.0 
 
 580.8 
 
 46 
 
 242.9 
 
 269.9 
 
 323.8 
 
 404.8 
 
 485.8 
 
 539.8 
 
 593.7 
 
 dampening the surface of the road for they absorb moisture 
 more quickly than the others. Bricks which are badly broken, 
 spawled or misshaped are turned over or replaced by good ones, 
 but slight chipping of the corners is not considered serious. 1 
 The surface is then rolled, for which purpose a tandem self-pro- 
 pelled roller weighing 2\ to 4 tons is employed where a sand 
 cushion is used and a hand roller about 2| feet long and 2J feet 
 in diameter, weighing about 600 pounds, is preferred for mono- 
 lithic pavements. The rolling should begin at one side of the 
 road and proceed back and forth on lines slightly inclined toward 
 the center of the roadway. When the center is reached the roller 
 should be used on the other side of the road in the same way. 
 Parts of the pavement which cannot be reached by the roller 
 are rammed with a paver's tamper weighing about 50 pounds, 
 the blows being struck on a 2-inch plank 10 to 12 inches wide 
 and at least 6 feet long. 
 
 After the rolling, the pavement is again inspected and any 
 bricks which have been broken or seriously injured are replaced. 
 The joints are examined, and if the sand-cushion has been forced 
 up into them more than \ inch in the sand-cushion type, the 
 bricks are lifted out, the cushion reshaped, and the bricks relaid. 
 This inspection of the joints is only necessary where a sand cushion 
 is used. 
 
 1 Mr. Hinkle considers that it is very desirable for all defective bricks 
 to be culled out before the bricks are laid in the pavement. This will not 
 only save the expense of replacing the defective bricks with good ones, 
 but will avoid disturbing the cushion. This is more important with the 
 monolithic than with other types of pavement. 
 
BRICK ROADS 
 
 171 
 
 Filling Joints 
 
 Joints between the bricks are filled with sand, cement grout 
 or bituminous material. Sand is objectionable because it gives 
 very little support to the bricks, allows their edges to become 
 chipped, and permits water to percolate down into the cushion. 
 It is no longer employed except for roads for light travel, where 
 the saving in first cost is considered more important than the 
 probability that maintenance expenses will become high at an 
 early date. 
 
 Grout Fillers. The grout filler is strongly advocated by many 
 engineers on the ground that it holds the bricks firmly and does 
 
 I 
 
 -{ 
 
 Height, Z$* 
 
 neignt, 25" 
 
 VtfiHi of Box, f { Depth of 
 
 Height ,29" 
 OepffjofBox, 
 
 I ii* r \*u i 9 f,^ 
 
 A Depth of 
 ' \Box.l2'' 
 
 Box FOR MIXING GROUT 
 
 not wear away more rapidly than the vitrified clay. This claim 
 rests upon the assumption that good grouting is done, for poor 
 joints of this type are chipped out by horses' shoes and thus al- 
 low the edges of the bricks to become broken. If the grouting 
 is properly done this will not happen. 1 It is extremely im- 
 
 1 Mr. Marr states: "The cement-grouted pavement seems to be tbe 
 most satisfactory for country highways, and this has led us in our studies 
 in Illinois to attach great importance to the perfection of the grout filler. 
 We have been working along the line that, theoretically, the earth itself 
 is the foundation for the pavement and is in itself wholly adequate, if it 
 is thoroughly settled and properly drained. In other words, we hold that 
 ordinary dry earth sustains any load which we place upon it while it is 
 
172 AMERICAN HIGHWAY ASSOCIATION 
 
 portant, however, with cement filler that a rigid foundation be 
 secured. 
 
 Grout for filling joints should be made of equal parts of cement 
 and clean, sharp, sand mixed thoroughly while dry. As a gen- 
 eral rule, all of it should pass a No. 10 sieve but not more than 30 
 per cent should pass a screen having 50 meshes to the inch. 
 After the sand and cement are thoroughly mixed dry, water is 
 added to bring the mass to a conolition somewhat thinner than 
 thin cream, so it will flow into the joints without any separation 
 of its ingredients. The mixing is kept up continuously, either 
 in a small batch mixer or the box shown in the accompanying 
 illustration. The tendency on extensive work is to use a batch 
 mixer equipped so it can be used for applying the grout. If the 
 box is used, about 2 cubic feet of the dry mixture is made into 
 mortar in each batch. The best grout is obtained when the 
 water is added slowly. 
 
 The surface of the pavement to be grouted is cleaned, well 
 wet, and then covered with enough grout to about fill the 
 joints. The grout is taken from the mixing box in scoops and 
 after it is poured from them it is swept into the joints, usually 
 with coarse rattan brooms. After a 50-foot section of road has 
 had the joints filled in this manner, and before the grout first 
 poured begins to set, a somewhat thicker grout is made and 
 applied on the same surface. It is brushed into the joints with 
 squeegees having rubber edges where they rest on the pavement. 
 This process of applying the relatively thick grout and brushing 
 it into the joints with squeegees is continued until the joints are 
 completely filled. It is very desirable to apply the grout, so far 
 as possible, to the exact parts of the pavement where it is to fill 
 the joints. If any great excess of grout is applied at one place in 
 the pavement and swept to another place, the cement and sand 
 are liable to become separated and defective grout will result. 
 If the bricks have rounded edges, the squeegees should be pressed 
 
 in this condition, and that the real problem is to keep it in this condition 
 by covering and waterproofing it with some material which will withstand 
 the abrasive action of traffic. This, in turn, leads us to believe that if we 
 use a thin base, such, for instance, as 2 inches of sand and cement mixed, 
 or even 1 inch, or even, theoretically, i inch, the properly grouted bricks 
 will then withstand successfully the action of any such traffic as we have 
 at the present time. 
 
 "The mortar bed has for its prime function the insurance of a perfect 
 grout joint, by preventing earth or other foreign matter from working 
 up into the bottom of the joints during construction. It has a secondary 
 value in enabling us to obtain a smoother wearing surface by facilitating 
 the proper grading of the bed on which the bricks lie by the use of mechan- 
 ical methods such as templets. We have built a 6-mile stretch of brick 
 road 9 feet wide, on a 1-inch mortar bed base, which 1 believe will demon- 
 strate the correctness of the theory we are now holding." 
 
BRICK ROADS 
 
 173 
 
 firmly against them on the last brushing so that no thin edges 
 of grout will remain on the surface, for they break away very 
 soon and are liable to pull a part of the joint filler with them. 
 
 To prevent the grout from flowing through the joints beyond 
 the limits of the section where the filling is being done, strips of 
 fa inch steel 6 inches wide and 3 feet long are inserted in the 
 last transverse joint, to act as a dam until after the initial set of 
 the cement. 
 
 After the surface has been inspected, it is the practice in Illi- 
 nois to cover it with sand, which is kept wet for ten days, and no 
 travel is permitted on the road for three weeks after the grout 
 has been poured. In Ohio and Pennsylvania, the sand is kept 
 damp for at least five and four days respectively, and travel is 
 kept off for at least ten days. In New York travel is kept off 
 for ten days, and the covering must be kept moist for that period. 
 The National Association of Paving Brick Manufacturers ad- 
 vises keeping the covering wet for four days and travel off the 
 road for fifteen days. 
 
 Bituminous Fillers. Bituminous fillers vary greatly in qual- 
 ity, and the experience with some of the materials tried has not 
 been satisfactory. The filler should not become soft during hot 
 weather nor brittle during cold weather, it should adhere to the 
 bricks, and it should not be injured by water. A 1 : 1 bituminous- 
 sand mastic filler has recently been used considerably. Ob- 
 viously climatic conditions should govern the selection of the 
 material in some degree, for a filler suitable for the brick pave- 
 ments of Florida might prove unsatisfactory during a New 
 England winter. 
 
 The Ohio State requirements for asphalt fillers are as follows : . 
 
 Specific gravity, 0.98 to 1.04. 
 
 Solubility in chemically pure carbon disulphide, at least 99^ 
 per cent. 
 
 Matter soluble in 86B. paraffin naphtha, 25 to 40 per cent. 
 
 Limits for penetration 
 
 TEMPERATURE 
 
 NEEDLE 
 
 WEIGHT 
 
 TIME 
 
 PENETRATION 
 
 C. 
 
 
 grams 
 
 
 
 25 
 
 No. 2 
 
 100 
 
 5 sec. 
 
 2.5 to 5 mm. 
 
 4 
 
 No. 2 
 
 200 
 
 1 min. 
 
 2 mm. or more 
 
 46 
 
 No. 2 
 
 50 
 
 5 sec. 
 
 10 mm. or less 
 
 Melting point by cube method, 80C. to 120C. 
 It shall be free from water and not foam when heated to 350F. 
 The Ohio State requirements for coal tar pitch fillers are as 
 follows : 
 
174 AMERICAN HIGHWAY ASSOCIATION 
 
 Specific gravity at 25C., 1.23 to 1.3. 
 
 lYee carbon on extraction with carbon disulphide, 20 to 40 
 per cent. 
 
 Inorganic matter on ignition, 0.5 per cent. 
 
 Melting point by cube method, 57C. to 63C. 
 
 It shall be free from water and not foam when heated to 300F. 
 
 These bituminous fillers are used hot and the bricks should 
 therefore be dry when the joints are poured. If a sand-cement 
 bed is used, the water for it must be applied through the joints, 
 if it is added in that way, long enough before the joints are filled 
 to permit them to become dried out. 
 
 The filler is melted in a kettle, from which it is usually drawn 
 into funnel-shaped pourers terminating in a nozzle having an 
 opening about J inch in diameter, with a valve by which the 
 flow through it can be regulated. This is held over the joint, 
 with the nozzle projecting into it, and carried along slowly. The 
 joints are somewhat overfilled by the pourer, on the theory that 
 the early travel on the pavement will force some of the surplus 
 material into the joint and make it more dense. After the joint 
 is poured, some engineers have it dusted over with sand, and it 
 is customary to keep traffic off the pavement until the filler has 
 cooled. 
 
 A mixture of tar and sand, called a " mastic filler," has been 
 used to some extent. The hot tar and heated sand are mixed 
 in equal volumes. A softer grade of tar is used in the mixture 
 than that called for by the Ohio specification for a tar filler. 
 This mastic filler is flushed into the joints by pouring it onto the 
 pavement and spreading it with a squeegee. 
 
 It is particularly desirable to roll the bricks and fill the joints to 
 within at least 50 feet of the bricklaying work. If rain falls and 
 the cushion becomes saturated, it is impossible to roll the bricks 
 to a firm condition, for the wet sand allows them to rock and the 
 cushion is forced up into the joints. By lifting out a brick here 
 and there, the height of the sand in the joint can be seen and the 
 character of the rolling judged from it. 
 
 Expansion Joints 
 
 In the early days of brick street pavements, the bricks at the 
 crown of a street occasionally rose in summer as a result of the 
 expansion of the pavement by heat. To remedy this, joints 
 filled with some compressible material were laid along one or 
 both curbs, and some engineers used similar transverse expan- 
 sion joints at intervals of 50 to 75 feet. The longitudinal joints 
 have proved useful, but there is some question as to the value of 
 the transverse joints in street pavements. The objection to 
 transverse joints is that they are worn away rather rapidly and 
 
BRICK ROADS 175 
 
 this causes the travel to chip off the edges of the bricks separated 
 by them. Whenever this chipping occurs to any extent, the 
 pavement soon develops a rut or hole. Cracks in a country 
 road, if properly filled when they first open and kept filled after- 
 ward, do not injure it appreciably, and it is generally consid- 
 ered that transverse joints in a brick wearing surface, to prevent 
 transverse cracks, are more likely to cause than prevent trouble. 
 
 Expansion joints are of two types, poured and prepared. The 
 former are made by placing a board filler of the thickness of the 
 joint against the curb and laying the bricks against it. The 
 Maryland rule for the thickness of the joints is as follows: On 
 streets 30 feet or more wide, 1J inches next each curb; on 20 to 
 30-foot streets, 1 inch next each curb; on 12 to 20-foot streets, J inch 
 next each curb; on streets under 12 feet, f inch next one curb. In 
 Pennsylvania a J-inch joint at each curb is specified. On the 
 Illinois brick roads with a sand-cement base a f-inch joint along 
 one curb is used. The plank filler usually consists of two thin 
 6-inch boards of a wedge-shape cross-section, dressed on both 
 sides. One of them is laid against the curb with the thin edge on 
 the base, and the other is placed against it with the thick edge 
 downward. The combined thickness of the two is equal to the 
 thickness of the joint. Handles are attached to their upper 
 edges, so they can be lifted out when the grout filler which has 
 been poured has set. The filler for poured expansion joints should 
 meet the requirements for the filler for other joints of this type. 
 With the monolithic and sand-cement cushion types of pavement, 
 the joints should be filled as far as the bricks are laid, each day. 
 
 Prepared fillers are now extensively used. They are strips 
 of bituminous material or some kind of felt or fabric impreg- 
 nated with bituminous material. They are placed against the 
 curb and the bricks laid against them, thus doing away with the 
 board fillers required with poured joints and making it unneces- 
 sary to provide heating kettles on pavements with grouted 
 joints. 
 
 Experience on the Pennsylvania State highways has shown 
 that a prepared filler extending the full depth of the brick some- 
 times permitted water to penetrate from the road surface into 
 the cushion, where it froze and heaved the bricks. It is there- 
 fore considered advisable on that work to have the prepared 
 filler stop from f to 1 inch below the surface of the road and to 
 fill the top of the joint with hot bituminous material. 
 
 Where a cement-sand bed is used, a | inch prepared expansion 
 joint extending through the entire pavement is recommended 
 by some engineers; it is placed in two strips, the first or bottom 
 strip being placed in the concrete base, and the second strip im- 
 mediately above it when the bed and bricks are laid. 
 
176 AMERICAN HIGHWAY ASSOCIATION 
 
 Small Cubical Bricks 
 
 Shortly after small stone blocks were introduced in Europe for 
 constructing pavements having the trade name of "Durax," the 
 county superintendent of Monroe County, N. Y., J. Y. McClintock, 
 employed cubes measuring 2 to 2 J inches on a side for resurfacing 
 old macadam roads to resist motor traffic. In 1916 he stated that 
 vitrified clay cubes had given better results than those of other 
 materials. Those laid in 1916 were 2J inches in each dimension, 
 weighed about 1 pound each, and were laid 225 to the square 
 yard. The only specification for the cubes is that they must not 
 absorb more than 3 per cent, of their weight when immersed in 
 water. They have been laid on a gravel base, broken slag, broken 
 stone and concrete, and the joints are filled with any local fine 
 material. It is considered advisable to make the base several 
 feet wider than the roadway, so that the gravel or broken stone 
 shoulders adjacent to the cubes shall be supported rigidly and 
 the tendency for the border cubes to become displaced will be 
 minimized. 
 
 Aspha-Bric 
 
 During 1915 and 1916 attention was directed to the possibilities 
 of asphalt impregnated brick. The idea of impregnating brick with 
 bituminous material is not new. In 1893 brick boiled in coal tar 
 were laid in Portland, Ore., and remained in service 17 years. 
 About 1907 nose brick boiled in asphalt were laid along the tracks 
 of the Los Angeles Electric Railway Corporation and 2500 simi- 
 lar brick were laid along tracks in San Francisco about 1912. 
 Brick boiled in bituminous material have also been laid in Nash- 
 ville and Chattanooga. 
 
 The method of treating brick which came into prominence in 
 1915 is designed to fill completely the pores in the brick. As the 
 porosity of different grades and makes varies considerably, the 
 quantity of impregnating material required will range from about 
 6 to 15 per cent of the volume of the brick. As a result of the 
 treatment it is claimed that the brick become impervious to mois- 
 ture, the bituminous jointing material adheres more firmly to the 
 treated than to the untreated brick, and the wearing properties, 
 as indicated by the standard rattler test, are greatly improved. 
 This last advantage is indicated in the accompanying tabulation 
 of tests of untreated and treated "second" brick conducted by 
 Robert W. Hunt & Company. Each test was made with five 
 untreated and five treated brick, 225 pounds of small shot and 75 
 pounds of large shot, the rattler making 1800 revolutions at the 
 rate of 30 revolutions per minute. The increase in wear due to 
 
BRICK ROADS 
 
 177 
 
 Results of tests of untreated and asphalt impregnated brick. Each sample 
 consisted of five untreated and five treated brick 
 
 SAMPLE 
 
 l 
 
 2 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Weight in pounds: 
 Before treatment 
 After treatment. . . 
 
 50.66 
 56.75 
 6.09 
 
 27.02 
 8.38 
 
 53.34 
 
 14.77 
 
 1 
 
 
 48.81 
 54.01 
 5.20 
 
 17.39 
 8.96 
 
 35.63 
 16.59 
 
 
 
 
 46.50 
 48.97 
 2.47 
 
 28.81 
 6.22 
 
 61.96 
 12.70 
 
 3 
 3 
 
 53.35 
 55.77 
 2.42 
 
 17.19 
 10.07 
 
 32.22 
 18.06 
 
 
 1 
 
 45.25 
 47.49 
 2.24 
 
 13.93 
 6.51 
 
 30.79 
 13.71 
 
 
 
 
 48.65 
 51.33 
 2.68 
 
 11.88 
 6.83 
 
 24.42 
 13.31 
 
 
 
 
 49.75 
 54.60 
 4.85 
 
 19.57 
 7.36 
 
 39.34 
 13.48 
 
 
 
 
 47.95 
 49.94 
 1.99 
 
 13.63 
 6.46 
 
 28.43 
 12.94 
 
 
 
 
 50.03 
 54.53 
 4.50 
 
 11.78 
 6.25 
 
 23.55 
 11.46 
 
 
 
 
 Asphalt used 
 
 Loss in weight, pounds : 
 Untreated 
 
 Treated 
 
 Loss in weight, per 
 cent: 
 Untreated 
 
 Treated 
 
 Broken brick: 
 Untreated . . 
 
 Treated. . . . 
 
 
 impregnation will, it is stated, enable manufacturers to stop their 
 burning at a lower temperature than is now customarjr, thus 
 materially reducing the number of poor brick in a kiln, and to 
 obtain the necessary strength by impregnating the brick. It is 
 also claimed that grades of brick unsuitable for pavements may 
 be made into satisfactory pavers by impregnation. For example, 
 impregnating clay building brick with 11.3 per cent of asphalt 
 gave a product showing 9.3 per cent loss in the standard rattler 
 test, although untreated brick showed 100 per cent loss after 500 
 revolutions. Shale building brick which showed 42.4 per cent 
 loss in the rattler test before they were treated, lost only 17 per 
 cent after treatment. Sand-lime brick which showed 100 per 
 cent loss after 400 revolutions lost only 23 per cent after being 
 impregnated with 10 per cent of asphalt. Impregnating clay 
 and shale building brick with 8J per cent of asphalt reduced the 
 loss in the rattler test from 40.9 to 14.2 per cent. The impregna- 
 tion of the brick also reduces their absorption of water to practi- 
 cally nothing. 
 
 The asphalt-impregnating process begins when the brick are 
 removed from the kilns or dryers. They are loaded on small 
 cars which are run into a cylinder. There they are heated to 
 about 300 F., which expands them, and a vacuum is produced 
 in the cylinder to remove all moisture from the brick and leave 
 their pores open. The cylinder is then filled with a special grade 
 of asphalt at a temperature of 350F. and the cylinder put under 
 heavy pressure until the gauges show that impregnation is com- 
 plete. The asphalt is drained off and pressure again applied 
 until the brick have cooled. During cooling they contract some- 
 what, causing the asphalt to become sealed in the pores. 
 
A BRICK PAVEMENT ON A ONE-INCH CON- 
 CRETE BASE' 
 
 A brick pavement was laid in 1917 in Stockland township, 
 Iroquois County, Illinois, on a one-inch concrete base. This 
 pavement is 9 feet wide, and the contract is for about 6J miles, 
 of which about 3 miles has been constructed. The contract 
 price for this work is approximately $8700 a mile, of which about 
 $300 is for bridges and culverts and about $450 for grading. 
 The price for the slab alone is $1.50 per square yard. 
 
 This pavement is being laid on an old gravel road for a foun- 
 dation and, in order to secure the full benefit of this old material, 
 the gradient of the new pavement varies but slightly from that 
 of the present road. By not disturbing the old gravel, it has 
 been possible to secure a very firm subgrade and we have no doubt 
 but the pavement will prove very satisfactory. The concrete 
 base is composed of 1 part cement to 2J parts fine aggregate and 
 4 parts coarse aggregate. The fine aggregate consists of sand 
 all of which passes a J-inch mesh. The coarse aggregate con- 
 sists of material which would be retained on a t-inch mesh and 
 passes a f-inch mesh. As a matter of fact, there is very little 
 of this material which will not pass a f inch mesh and it is the 
 same type of gravel that is commonly used for roofing purposes. 
 
 I have no doubt but this pavement would be practically as 
 good as if the brick had been laid directly on the old gravel road, 
 but in a construction of this kind, it is necessary to have some 
 sort of a concrete base in order to secure a perfectly smooth and 
 uniform surface on which to lay the bricks. 
 
 The subgrade was thoroughly rolled and all soft places, of 
 which there were very few, were removed and the subgrade 
 brought up to a true plane by the addition of fresh material which 
 was thoroughly compacted. Before concrete was placed, the 
 subgrade was well wet; after the concrete was placed, it was 
 struck off by means of a template and the bricks were laid di- 
 rectly on the green concrete. 
 
 Two brick setters were used on this job and by having a brick 
 hammer on each side of the road, the setters not only started but 
 finished the courses, as on a pavement of this width no bats, except 
 
 1 By Rodney L. Bell, Division Engineer, Illinois State Highway De- 
 partment. 
 
 178 
 
BKICK PAVEMENT 179 
 
 one half-sized brick, are required in starting and finishing the 
 courses. Bricks were carried on to the pavement in such a way 
 that the good side of the bricks was always placed up and the 
 lugs all in one direction. By requiring the brick carriers to use 
 some care, a large amount of the culling which ordinarily takes 
 place on a brick road was eliminated. Just as soon as the bricks 
 were culled, the pavement was swept and the rolling started. 
 
 One man did nothing but keep the roller moving the entire 
 time. It was a small hand roller about 30 inches in length and 
 24 inches in diameter and when filled with water weighed about 
 700 pounds. This weight was sufficient to secure a good surface 
 over the entire length of the pavement. The first rolling was 
 begun at the outer edge and the pavement was rolled parallel to 
 the center line of the pavement. After the entire surface had 
 been covered in this way, the pavement was cross-rolled in oppo- 
 site directions, the roller making an angle of about 45 degrees 
 with the center line of the pavement. 
 
 In order to allow plenty of time to secure a thorough job of 
 rolling, the grouting machine was kept about 100 feet behind the 
 brick layer. The grout mixture consisted of one part cement and 
 1 part of sand mixed in a machine designed for this purpose. It 
 was the intention to practically fill the joints at the first appli- 
 cation so that after the grout had had a chance to settle, it would 
 leave from J to f inch to be filled with subsequent applications. 
 
 The second application of the grout was mixed slightly thicker 
 than the first, and was wheeled back over the pavement from the 
 mixing machine rather than bother with moving the machine 
 back over the pavement a second time. This application was 
 worked into the joints by use of a squeegee and on the final going 
 over, the squeegees were pulled at an angle of about 45 degrees 
 with the joints in order to secure a better surface and to keep 
 the grout from being dragged out from between the brick. 
 
 After the grout had set sufficiently, the pavement was covered 
 with 1 inch of loose dirt, which was kept wet for one week. The 
 pavement was opened to traffic after it had been down three 
 weeks. 
 
 This work is being paid for by a bond issue which has been 
 voted by Stockland township, Iroquois County, and is under 
 the general supervision of Benj. Jordan, county superintendent 
 of highways of Iroquois County. 
 
HIGHWAY BONDS 1 
 
 The mathematical theory of interest as applied to bond cal- 
 culations is explained in a section of Bulletin 136 of the United 
 States Department of Agriculture which has tables of much 
 value to those making a detailed examination of the subject. 
 For the usual purposes of highway officials, however, the much 
 simpler tables which are printed herewith are not only sufficient 
 in scope but also more easily used. 
 
 The bonds used almost universally until a few years ago were 
 of the sinking-fund type. Parties issuing them have to provide 
 annually during the term of the bonds the stipulated interest 
 and, theoretically, set aside a sum at interest which will amount 
 at the end of the term to the principal of the bonds. This an- 
 nual sum set aside at interest is called the sinking fund, and the 
 amount which must be raised for such a fund depends upon the 
 interest it bears. This interest is usually quite low in comparison 
 with the interest paid on the bonds. 
 
 Unfortunately the financial methods of public officials do not 
 always remain above criticism and it often happens that the annual 
 payment into the sinking fund is forgotten or neglected. 2 Some- 
 times the money accumulated in the sinking fund is diverted 
 from its purpose. Such departures from sound finance result in 
 a lack of money to pay off the bonds when they become due, as 
 agreed, and it then becomes necessary to issue a new series of 
 bonds to carry this indebtedness. This is a serious matter when 
 the improvements for which the bonds were issued have become of no 
 further use, as in the possible case of a worn-out road surface, 
 or obsolescent, as in the possible case of an overloaded bridge, 
 when the taxpayers who contribute for the second bond issue are 
 obliged to pay for something for which they receive little or no 
 benefit. This is not equitable, and so some states fix the term 
 of bonds which may be issued to pay for certain classes of im- 
 
 1 Revised by B. K. Coghlan, associate professor of highway engineer- 
 ing, Agricultural and Mechanical College of Texas. 
 
 'Baker, Watts & Co., bankers, of Baltimore, make the lollowing com- 
 ment: "We view it as a very serious matter to neglect the sinking fund, 
 regardless of the character of the improvement for which the bonds are 
 issued. We think that public officials cannot be too forcibly impressed 
 with the absolute necessity of managing public funds strictly in accordance 
 with the laws and ordinances authorizing bond issues, and any neglect or 
 diversion of public sinking funds should be summarily dealt with." 
 
 180 
 
HIGHWAY BONDS 181 
 
 provements. In New Jersey, for example, the term of bonds for 
 gravel roads is limited to five years, waterbound or bituminous 
 macadam ten years, bituminous concrete fifteen years, 6-inch 
 concrete twenty years, block pavements twenty years, sheet 
 asphalt on a concrete base twenty years, and stone, concrete 
 and iron bridges thirty years. The useful life of the improve- 
 ment is what must be considered, and this is determined in some 
 cases by obsolescence rather than depreciation, notably in the 
 case of bridges. The attractiveness of bonds for road work 
 would be enhanced in many cases if an equivalent of the fol- 
 lowing statute, in force in Mississippi, were generally adopted: 
 
 The public highway or highways so surveyed and adopted by such com- 
 missioners shall be constructed and maintained out of the proceeds of 
 such bonds; proceeds of such bonds to be used alone in their construction; 
 and the board of supervisors shall levy an annual tax, on the recommen- 
 dation of such commissioners, on all the taxable property in such district 
 or districts of not exceeding 1 mill on the dollar, which shall be used to 
 supplement the general fund of the county in maintaining said road or 
 roads and the culverts, bridges and levees thereon. 
 
 The importance of maintenance of roads is so great that 
 statutes authorizing bond issues for construction should require, 
 as part of the stipulations under which the bonds are issued, an 
 adequate financial provision for the upkeep of the roads during 
 the term of the bonds. This insures a full statement of the 
 financial obligations of the bond issue upon the taxpayers before 
 they vote on the issue. 
 
 The investment of the sinking fund affords an indication of 
 the financial ability of a community. In some sections of the 
 country, the investment is intrusted to special boards of sinking 
 fund commissioners, and appointment to such a board is re- 
 garded as a high honor, so that the positions are filled by men of 
 the highest business standing. In such cases the community 
 not only feels confident of its financial stability but its bond 
 issues are sought so eagerly that it is not necessary to pay high 
 rates of interest. In a few places, sinking funds have been 
 neglected and the financial standing of the community suffers 
 in consequence. 
 
 A second type of bond is known as the annuity bond. An 
 annuity is a fixed sum paid at regular intervals of time for either 
 a definite term or for the life of the beneficiary of the annuity. 
 An annuity bond draws interest at an agreed rate, but at the 
 close of each retirement period stated in the bond, the payment 
 to the bondholders includes both the interest that has accrued 
 during the period since the last payment and enough of the 
 principal to make the full payment a definite, uniform amount 
 at the close of each retirement period. The annual payment at 
 
182 AMERICAN HIGHWAY ASSOCIATION 
 
 the end of the first retirement period is mainly for interest and 
 that at the end of the last period is mainly for retiring the last 
 of the outstanding principal. The advantage of the plan is that 
 it retires some principal annually and thus saves the taxpayer 
 the expense of paying interest on the whole of a bond issue dur- 
 ing its term. This makes annuity bonds less expensive than 
 sinking fund bonds to the county issuing them. 
 
 The annuity bond issue possesses the advantage of requiring 
 the same amount to be raised each year, during its term. The 
 annual payments must be adjusted, however, so that the amount 
 of principal retired will be some multiple of $100, $500 or $1000, 
 or whatever sum is the face value of one bond. Consequently the 
 actual payment on annuity issues at the end of a retirement period 
 is not the uniform theoretical amount given in bond tables but 
 an amount varying slightly from it, sometimes more and some- 
 times less. 1 
 
 The serial bond issue is a type which has found favor with both 
 borrowers and lenders. The farmer finds it desirable because it 
 retires each year a part of the principal, and is thus more econom- 
 ical than a sinking fund bond issue. The purchasers of the bonds 
 like them because there is a strong public sentiment in favor of 
 serial bonds, which gives them standing as a good type of invest- 
 ment security. It is the least expensive method of borrowing 
 money by issuing bonds, as an examination of the accompanying 
 tables will show. 
 
 One defect of serial bonds for certain classes of public im- 
 provements is that the heaviest payments for interest and the 
 retirement of principal must be made in the early years of the 
 term of the bonds, before the work for which they pay has yielded 
 any returns. Consequently what are known as deferred serial 
 bonds are now used to meet such conditions as often arise in 
 road districts. With such a type of bond, no principal is retired 
 until a certain period, usually five years, has elapsed. During 
 this period interest is paid but nothing more. Thereafter the 
 principal is retired by uniform amounts and the interest charges 
 are met just as in the case of straight serial bonds having a term 
 shorter by five years, or whatever is the deferred period. In 
 this way a road district need not pay anything but interest until 
 
 1 The following comment on this type of bond has been received from 
 John S. Harris, of the banking house of Sidney Spitzer and Company, 
 Toledo: "We would not suggest your recommending the installment 
 (annuity) bonds, as they are very hard to figure and hard to dispose of. 
 It is necessary to figure each year when you collect your coupons the 
 amount of principal and the amount of interest. A serial bond answers 
 the same purpose and is much more attractive to the investing public. 
 Road bonds should not be issued in any other way than as serial bonds, as 
 every one knows that issuing long-time road bonds is wrong." 
 
HIGHWAY BONDS 183 
 
 the improvements have begun to yield a return and it need not 
 pay so much for the use of money as when it issues sinking fund 
 bonds. 
 
 The question which taxpayers generally put to public officials 
 regarding a bond issue is what increase such an issue will make in 
 the annual taxes. A series of examples will show how the ac- 
 companying tables can be used to answer such questions. 
 
 What is the tax rate for a $300,000 issue of 5 per cent, 40-year 
 bonds, retired by a sinking fund drawing 3 per cent, when the 
 tax valuation of the road district is $9,300,000? 
 
 The table of the annual cost of sinking fund bonds shows that the 
 annual cost of a $1 bond of this class is 6.326 cents. The annual 
 cost of a $300,000 issue will be $18,978. The additional tax per 
 $100 valuation in the district will be $18,978 + 93,000 = 20.407 
 cents. Any taxpayer can find out what his additional tax will 
 be by multiplying 20.407 cents by the number of hundreds of 
 dollars worth of property for which he is assessed. If his prop- 
 erty is assessed at $2000, for example, his additional tax for 
 roads will be $4.08. 
 
 How much money would be saved by issuing annuity rather 
 than sinking fund bonds in this case? 
 
 The annual cost of a 1-dollar 4-per cent, 40-year annuity bond 
 is shown by the table to be 5.828 cents, so the annual cost of a 
 $300,000 issue will be $17,484. The additional tax per $100 
 valuation will be 18.8 cents, or 1.607 cents less than under the 
 sinking fund system. The man whose property is assessed at 
 $2000 would save 32 cents, and the district as a whole would 
 save $1494.51, which would go a long ways toward paying for 
 the engineering expenses of the road improvement. 
 
 What is the least expensive type of a $300,000 issue of 5 per 
 cent, 40-year bonds to the above district? 
 
 The four accompanying tables show that the straight serial 
 bond is the least expensive type, for the average annual cost of 
 a 1-dollar bond of this type is 5.062 cents. This is equivalent 
 to $15,186 for a $300,000 issue. The additional tax per $100 
 valuation will be 16.329 cents, 4.978 cents less than under the 
 sinking fund type, which will save 81 cents to the man having 
 property assessed at $2000. The saving to the district will be 
 $3792 as compared with a sinking fund issue and $2298 as com- 
 pared with an annuity issue. 
 
 The drawback of a straight serial bond can be seen from the fig- 
 ures of the payment needed at the end of the first and the fortieth 
 years, 7.5 and 2.625 cents respectively on a 1-dollar bond. Road 
 improvements do not yield any benefits until completed, and by 
 deferring payment on the principal for five years, the additional 
 cost to the community will average only $939 a year. The 
 maximum annual amount will be somewhat higher than in a 
 
184 AMEHICAN HIGHWAY ASSOCIATION 
 
 straight 40-year serial issue, because the principal must be re- 
 tired in 35 years instead of 40 years, but this disadvantage may 
 not outweigh the desirability of deferring the repayment of the 
 principal. 
 
 The management of a bond issue requires attention to all the 
 requirements of the laws governing such matters and a knowledge 
 of the conditions which affect the value of bonds. Every step 
 which the law requires to be taken in connection with such bonds 
 must not only be taken properly but recorded fully and clearly. 
 As soon as the voters authorize the issue, a statement of the fact 
 should be drawn up, showing also the area, population and as- 
 sessed valuation of the district, the value of its agricultural and 
 industrial products, its material resources and the extent of their 
 development, the banking and transportation facilities serving 
 it, the existing indebtedness of the district, the condition and 
 number of the schools, and all other information which will indi- 
 cate the resources and character of the community that has de- 
 cided to borrow the money. This information should be sent 
 to banking houses and insurance companies making a specialty 
 of purchasing public bonds and, if the issue is a large one, it 
 should be advertised in financial journals. There should be 
 ample time between the publication of these notices and the sale 
 of the bonds for purchasers to make a full investigation of them. 
 
 1 Private sales of bonds for public works should be discouraged 
 all sales of bonds should be publicly advertised, and bidders 
 should be invited to submit sealed bids on or before a certain 
 date. The bonds should be sold to the highest responsible bid- 
 der who complies with all of the terms and conditions of the sale. 
 The city or county should reserve the right to reject any or all 
 of the bids, as a protection against any effort to pool bids and 
 purchase the bonds at a price considerably less than their value. 
 
 Some cities and counties engage competent attorneys, familiar 
 with the preparation of the legal papers pertaining to bond is- 
 sues, to examine the records prior to the sale and to prepare all 
 necessary forms. The city or county assumes the expense for 
 all such work and furnishes the successful bidder with the approv- 
 ing opinion of the counsel thus engaged and with the executed 
 bonds. Some cities and counties go even further by providing 
 uniform proposal blanks for the bonds and refusing to accept bids 
 not made on such blank. The advantage of these provisions is 
 that the seller knows he is offering a legally and validly issued 
 bond, the buyer has the same assurance, and the value of the is- 
 sue is certainly enhanced thereby. The seller is undoubtedly re- 
 imbursed for the expense incurred in such preparatory work by 
 the price he receives for the bonds. 
 
 and the next paragraph were prepared by Baker, Watts & 
 Company. 
 
Annual cost of a 1-dollar sinking-fund bond for different terms, interest 
 rates and rates of interest on sinking fund 
 
 INTER- 
 EST ON 
 SINK- 
 ING 
 
 FUND 
 
 TERM 
 
 RATE OP INTEREST ON BONDS, PER CENT 
 
 4 
 
 4.25 
 
 4.5 
 
 4.75 
 
 5 
 
 5.25 
 
 5.5 
 
 6 
 
 percent 
 
 years 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 2 
 
 5 
 
 23.216 
 
 23.466 
 
 23.716 
 
 23.966 
 
 24.216 
 
 24.466 
 
 24.716 
 
 25.216 
 
 
 10 
 
 13.133 
 
 13.383 
 
 13.633 
 
 13.883 
 
 14.133 
 
 14.383 
 
 14.633 
 
 15.133 
 
 
 15 
 
 9.783 
 
 10.033 
 
 10.283 
 
 10.533 
 
 10.783 
 
 11.033 
 
 11.283 
 
 11.783 
 
 
 20 
 
 8.116 
 
 8.366 
 
 8.616 
 
 8.866 
 
 9.116 
 
 9.366 
 
 9.616 
 
 10.116 
 
 
 25 
 
 7.122 
 
 7.372 
 
 7.622 
 
 7.872 
 
 8.122 
 
 8.372 
 
 8.622 
 
 9.122 
 
 
 30 
 
 6.465 
 
 6.715 
 
 6.965 
 
 7.215 
 
 7.465 
 
 7.715 
 
 7.965 
 
 8.465 
 
 
 35 
 
 6.000 
 
 6.250 
 
 6.500 
 
 6.750 
 
 7.000 
 
 7.250 
 
 7.500 
 
 8.000 
 
 
 40 
 
 5.656 
 
 5.906 
 
 6.156 
 
 6.406 
 
 6.656 
 
 6.906 
 
 7.156 
 
 7.656 
 
 
 45 
 
 5.391 
 
 5.641 
 
 5.891 
 
 6.141 
 
 6.391 
 
 6.641 
 
 6.891 
 
 7.391 
 
 
 50 
 
 5.182 
 
 5.432 
 
 5.682 
 
 5.932 
 
 6.182 
 
 6.432 
 
 6.682 
 
 7.182 
 
 2.5 
 
 5 
 
 23.023 
 
 23.273 
 
 23.523 
 
 23.773 
 
 24.023 
 
 24.273 
 
 24.523 
 
 25.023 
 
 
 10 
 
 12.926 
 
 13.176 
 
 13.426 
 
 13.676 
 
 13.926 
 
 14.176 
 
 14.426 
 
 14.926 
 
 
 15 
 
 9.577 
 
 9.827 
 
 10.077 
 
 10.327 
 
 10.577 
 
 10.827 
 
 11.077 
 
 11.577 
 
 
 20 
 
 7.915 
 
 8.165 
 
 8.415 
 
 8.665 
 
 8.915 
 
 9.165 
 
 9.415 
 
 9.915 
 
 
 25 
 
 6.928 
 
 7.178 
 
 7.428 
 
 7.678 
 
 7.928 
 
 8.178 
 
 8.428 
 
 8.928 
 
 
 30 
 
 6.278 
 
 6.528 
 
 6.778 
 
 7.028 
 
 7.278 
 
 7.528 
 
 7.778 
 
 8.278 
 
 
 35 
 
 5.821 
 
 6.071 
 
 6.321 
 
 6.571 
 
 6.821 
 
 7.071 
 
 7.321 
 
 7.821 
 
 
 40 
 
 5.484 
 
 5.734 
 
 5.984 
 
 6.234 
 
 6.484 
 
 6.734 
 
 6.984 
 
 7.484 
 
 
 45 
 
 5.227 
 
 5.477 
 
 5.727 
 
 5.977 
 
 6.227 
 
 6.477 
 
 6.727 
 
 7.227 
 
 
 50 
 
 5.026 
 
 5.276 
 
 5.526 
 
 5.776 
 
 6.026 
 
 6.276 
 
 6.526 
 
 7.026 
 
 3 
 
 5 
 
 28.835 
 
 23.085 
 
 23.335 
 
 23.585 
 
 23.835 
 
 24.085 
 
 24.335 
 
 24.835 
 
 
 10 
 
 12.723 
 
 12.973 
 
 13.223 
 
 13.473 
 
 13.723 
 
 13.973 
 
 14.223 
 
 14.723 
 
 
 15 
 
 9.377 
 
 9.627 
 
 9.877 
 
 10.127 
 
 10.377 
 
 10.627 
 
 10.877 
 
 11.377 
 
 
 20 
 
 7.722 
 
 7.972 
 
 8.222 
 
 8.472 
 
 8.722 
 
 8.972 
 
 9.222 
 
 9.722 
 
 
 25 
 
 6.743 
 
 6.993 
 
 7.243 
 
 7.493 
 
 7.743 
 
 7.993 
 
 8.243 
 
 8.743 
 
 
 30 
 
 6.102 
 
 6.352 
 
 6.602 
 
 6.852 
 
 7.102 
 
 7.352 
 
 7.602 
 
 8.102 
 
 
 35 
 
 5.654 
 
 5.904 
 
 6.154 
 
 6.404 
 
 6.654 
 
 6.904 
 
 7.154 
 
 7.654 
 
 
 40 
 
 5.326 
 
 5.576 
 
 5.826 
 
 6.076 
 
 6.326 
 
 6.576 
 
 6.826 
 
 7.326 
 
 
 45 
 
 5'. 079 
 
 5.329 
 
 5.579 
 
 5.829 
 
 6.079 
 
 6.329 
 
 6.579 
 
 7.079 
 
 
 50 
 
 4.887 
 
 5.137 
 
 5.387 
 
 5.637 
 
 5.887 
 
 6.137 
 
 6.387 
 
 6.887 
 
 3.5 
 
 5 
 
 22.648 
 
 22.898 
 
 23.148 
 
 23.398 
 
 23.648 
 
 23.898 
 
 24.148 
 
 24.648 
 
 
 10 
 
 12.524 
 
 12.774 
 
 13.024 
 
 13.274 
 
 13.524 
 
 13.774 
 
 14.024 
 
 14.524 
 
 
 15 
 
 9.183 
 
 9.433 
 
 9.683 
 
 9.933 
 
 10.183 
 
 10.433 
 
 10.683 
 
 11.183 
 
 
 20 
 
 7.536 
 
 7.786 
 
 8.036 
 
 8.286 
 
 8.536 
 
 8.786 
 
 9.036 
 
 9.536 
 
 
 25 
 
 6.567 
 
 6.817 
 
 7.067 
 
 7.317 
 
 7.567 
 
 7.817 
 
 8.067 
 
 8.567 
 
 
 30 
 
 5.937 
 
 6.187 
 
 6.437 
 
 6.687 
 
 6.937 
 
 7.187 
 
 7.437 
 
 7.937 
 
 
 35 
 
 5.500 
 
 5.750 
 
 6.000 
 
 6.250 
 
 6.500 
 
 6.750 
 
 7.000 
 
 7.500 
 
 
 40 
 
 5.183 
 
 5.433 
 
 5.683 
 
 5.933 
 
 6.183 
 
 6.433 
 
 6.683 
 
 7.183 
 
 
 45 
 
 4.945 
 
 5.195 
 
 5.445 
 
 5.695 
 
 5.945 
 
 6.195 
 
 6.445 
 
 6.945 
 
 
 50 
 
 4.763 
 
 5.013 
 
 5.263 
 
 5.513 
 
 5.763 
 
 6.013 
 
 6.263 
 
 6.763 
 
 
 
 
 
 
 
 
 
 1 
 
 
 4 
 
 5 
 
 22.463 
 
 22.713 
 
 22.963 
 
 23.213 
 
 23.463 
 
 23.713 
 
 23.963 
 
 24.463 
 
 
 10 
 
 12.329 
 
 12.579 
 
 12.829 
 
 13.079 
 
 13.329 
 
 13.579 
 
 13.829 
 
 14.329 
 
 
 15 
 
 8.994 
 
 9.244 
 
 9.494 
 
 9.744 
 
 9.994 
 
 10.244 
 
 10.494 
 
 10.994 
 
 
 20 
 
 7.358 
 
 7.608 
 
 7.858 
 
 8.108 
 
 8.358 
 
 8.608 
 
 8.858 
 
 9.358 
 
 
 25 
 
 6.401 
 
 6.651 
 
 6.901 
 
 7.151 
 
 7.401 
 
 7.651 
 
 7.901 
 
 8.401 
 
 
 30 
 
 5.783 
 
 6.033 
 
 6.283 
 
 6.533 
 
 6.783 
 
 7.033 
 
 7.283 
 
 7.783 
 
 
 35 
 
 5.358 
 
 5.608 
 
 5.858 
 
 6.108 
 
 6.358 
 
 6.608 
 
 6.858 
 
 7.358 
 
 
 40 
 
 5.052 
 
 5.302 
 
 5.552 
 
 5.802 
 
 6.052 
 
 6.302 
 
 6.552 
 
 7.052 
 
 
 45 
 
 4.826 
 
 5.076 
 
 5.326 
 
 5.576 
 
 5.826 
 
 6.076 
 
 6.326 
 
 6.826 
 
 
 50 
 
 4.655 
 
 4.905 
 
 5.155 
 
 5.405 
 
 5.655 
 
 5.905 
 
 6.155 
 
 6.655 
 
 185 
 
186 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 Annual cost of a 1-dollar sinking-fund bond for different terms, interest 
 rates and rates of interest on sinking fund Continued 
 
 INTER- 
 EST ON 
 
 
 RATE OP INTEREST ON BONDS, PER CENT 
 
 SINK- 
 ING 
 FUND 
 
 TERM 
 
 4 
 
 4.25 
 
 4.5 
 
 4.75 
 
 5 
 
 5.25 
 
 5.5 
 
 6 
 
 per cent 
 
 years 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 4.5 
 
 5 
 
 22.279 
 
 22.529 
 
 22.779 
 
 23.029 
 
 23.279 
 
 23.529 
 
 23.779 
 
 24.279 
 
 
 10 
 
 12.138 
 
 12.388 
 
 12.638 
 
 12.888 
 
 13.138 
 
 13.388 
 
 13.638 
 
 14.138 
 
 
 15 
 
 8.811 
 
 9.061 
 
 9.311 
 
 9.561 
 
 9.811 
 
 10.061 
 
 10.311 
 
 10.811 
 
 
 20 
 
 7.188 
 
 7.438 
 
 7.688 
 
 7.938 
 
 8.188 
 
 8.438 
 
 8.688 
 
 9.188 
 
 
 25 
 
 6.244 
 
 6.494 
 
 6.744 
 
 6.994 
 
 7.244 
 
 7.494 
 
 7.744 
 
 8.244 
 
 
 30 
 
 5.639 
 
 5.889 
 
 6.139 
 
 6.389 
 
 6.639 
 
 6.889 
 
 7.139 
 
 7.639 
 
 
 35 
 
 5.227 
 
 5.477 
 
 5.727 
 
 5.977 
 
 6.227 
 
 6.477 
 
 6.727 
 
 7.227 
 
 
 40 
 
 4.934 
 
 5.184 
 
 5.434 
 
 5.684 
 
 5.934 
 
 6.184 
 
 6.434 
 
 6.934 
 
 
 45 
 
 4.720 
 
 4.970 
 
 5.220 
 
 5.470 
 
 5.720 
 
 5.970 
 
 6.220 
 
 6.720 
 
 
 50 
 
 4.560 
 
 4.810 
 
 5.060 
 
 5.310 
 
 5.560 
 
 5.810 
 
 6.060 
 
 6.560 
 
 Annual cost of a 1-dollar annuity bond for different terms and rates of interest 
 
 RATE OF INTEREST ON BONDS, PER CENT 
 
 
 4 
 
 4.25 
 
 4.5 
 
 4.75 
 
 5 
 
 5.25 
 
 5.5 
 
 6 
 
 ror 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 cents 
 
 centt 
 
 5 
 
 22.462 
 
 22.621 
 
 22.779 
 
 22.938 
 
 23.097 
 
 23.257 
 
 23.418 
 
 23.740 
 
 10 
 
 12.329 
 
 12.483 
 
 12.638 
 
 12.794 
 
 12.950 
 
 13.108 
 
 13.267 
 
 13.587 
 
 15 
 
 8.994 
 
 9.152 
 
 9.311 
 
 9.472 
 
 9.634 
 
 9.798 
 
 9.963 
 
 10.296 
 
 20 
 
 7.358 
 
 7.522 
 
 7.688 
 
 7.855 
 
 8.024 
 
 8.195 
 
 8.368 
 
 8.718 
 
 25 
 
 6.401 
 
 6.571 
 
 6.744 
 
 6.919 
 
 7.095 
 
 7.274 
 
 7.455 
 
 7.823 
 
 30 
 
 5.783 
 
 5.960 
 
 6.139 
 
 6.321 
 
 6.505 
 
 6.692 
 
 6.880 
 
 7.265 
 
 35 
 
 5.358 
 
 5.541 
 
 5.727 
 
 5.916 
 
 6.107 
 
 6.301 
 
 6.497 
 
 6.897 
 
 40 
 
 5.052 
 
 5.242 
 
 5.434 
 
 5.630 
 
 5.828 
 
 6.029 
 
 6.232 
 
 6.646 
 
 45 
 
 4.826 
 
 5.022 
 
 5.220 
 
 5.422 
 
 5.626 
 
 5.833 
 
 6.043 
 
 6.470 
 
 50 
 
 4.655 
 
 4.856 
 
 5.060 
 
 5.267 
 
 5.478 
 
 5.691 
 
 5.906 
 
 6.344 
 
HIGHWAY BONDS 
 
 187 
 
 Variations in annual cost of a 1 -dollar serial bond for different terms and 
 
 rates of interest, the principal being retired by the same amount at the 
 
 end of each year 
 
 TERM 
 
 PAYMENT 
 
 RATE OP INTEREST, PER CENT 
 
 4 
 
 4.25 
 
 4.5 
 
 4.75 
 
 5 
 
 5.25 
 
 5.5 
 
 6 
 
 years 
 
 5 
 
 10 
 15 
 20 
 25 
 30 
 35 
 40 
 45 
 60 
 
 date 
 
 First year 
 Last year 
 
 cents 
 
 24.000 
 20.800 
 22.400 
 
 14.000 
 10.400 
 12.200 
 
 10.667 
 6.933 
 8.800 
 
 .9.000 
 5.200 
 7.100 
 
 8.000 
 4.160 
 6.080 
 
 7.333 
 3.467 
 5.400 
 
 6.857 
 2.971 
 4.914 
 
 6.500 
 2.600 
 4.550 
 
 6.222 
 6.311 
 4.267 
 
 6.000 
 2.080 
 4.040 
 
 cents 
 
 24.250 
 20.850 
 22.550 
 
 14.250 
 10.425 
 12.337 
 
 10.917 
 6.950 
 8.933 
 
 9.250 
 5.213 
 7.231 
 
 8.250 
 4.170 
 6.210 
 
 7.583 
 3.475 
 5.530 
 
 7.107 
 
 2.978 
 5.047 
 
 6.750 
 2.606 
 4.678 
 
 6.472 
 3.316 
 4.394 
 
 6.250 
 2.085 
 4.167 
 
 cents 
 
 24.500 
 20.900 
 22.700 
 
 14.500 
 10.450 
 12.475 
 
 11.167 
 6.967 
 9.067 
 
 9.500 
 5.225 
 7.362 
 
 8.500 
 4.180 
 6.340 
 
 7.833 
 3.483 
 5.658 
 
 7.357 
 2.985 
 5.171 
 
 7.000 
 2.613 
 4.806 
 
 6.722 
 2.322 
 4.522 
 
 6.500 
 2.090 
 4.295 
 
 cents 
 
 24.725 
 20.950 
 22.850 
 
 14.750 
 10.475 
 12.613 
 
 11.417 
 
 6.984 
 9 200 
 
 9.750 
 5.238 
 7.494 
 
 8.750 
 4.190 
 6.470 
 
 8.083 
 3.491 
 
 5.787 
 
 7.607 
 2.993 
 5.300 
 
 7.250 
 2.619 
 4.934 
 
 6.972 
 2.328 
 4.650 
 
 6.750 
 2.095 
 4.427 
 
 cents 
 
 25.000 
 21.000 
 23.000 
 
 15.000 
 10.500 
 12.750 
 
 11.667 
 7.000 
 9.333 
 
 10.000 
 5.250 
 7.625 
 
 9.000 
 4.200 
 6.600 
 
 8.333 
 3.500 
 5.916 
 
 7.857 
 3.000 
 
 5.428 
 
 7.500 
 2.625 
 5.062 
 
 7.222 
 2.333 
 
 4.777 
 
 8.000 
 2.100 
 4.550 
 
 cents 
 
 25.250 
 21.050 
 23.150 
 
 15.250 
 10.525 
 
 12.888 
 
 11.917 
 
 7.017 
 9.467 
 
 10.250 
 5.263 
 7.756 
 
 9.250 
 4.210 
 6.730 
 
 8.583 
 3.509 
 6.046 
 
 8.107 
 3.007 
 5.557 
 
 7.750 
 2.632 
 5.191 
 
 7.472 
 2.339 
 4.905 
 
 7.250 
 2.105 
 4.677 
 
 cents 
 25.500 
 21.100 
 23.300 
 
 15.500 
 10.550 
 13.025 
 
 12.167 
 7.034 
 9.600 
 
 10.500 
 5.275 
 
 7.887 
 
 9.500 
 4.220 
 6.810 
 
 8.833 
 3.517 
 6.175 
 
 8.357 
 3.014 
 5.685 
 
 8.000 
 2.640 
 5.320 
 
 7.722 
 2.344 
 5.033 
 
 7.500 
 2.110 
 4.805 
 
 cents 
 
 26.000 
 21.200 
 23.600 
 
 16.000 
 10.600 
 13.300 
 
 12.667 
 7.067 
 9.867 
 
 11.000 
 5.287 
 8.144 
 
 10.000 
 4.240 
 7.120 
 
 9.333 
 3.535 
 6.434 
 
 8.857 
 3.028 
 5.942 
 
 8.500 
 2.654 
 5.577 
 
 8.222 
 2.355 
 5.288 
 
 8.000 
 2.120 
 6.060 
 
 Average . 
 
 First year. . . . 
 
 Last year 
 
 Average 
 
 First year. 
 
 Last year 
 
 Average.. 
 
 First year 
 
 Last year. . . 
 
 Average 
 
 First year 
 Last year 
 
 Average.. 
 
 First year. 
 
 Last year 
 
 Average... . 
 
 First year 
 Last year 
 
 Average 
 
 First year 
 Last year 
 Average.. 
 
 First year 
 Last year 
 Average 
 
 First year 
 Last year 
 Average.. . 
 
 
188 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 Variations in annual cost of a 1-dollar deferred serial bond for different 
 terms and rates of interest, the principal being retired by the same amount 
 at the end of each year beginning with the end of the sixth year 
 
 TERM 
 
 PAYMENT 
 
 RATE OF INTEREST, PER CENT 
 
 4 
 
 4.25 
 
 4.5 
 
 4.75 
 
 5 
 
 5.25 
 
 5.5 
 
 6 
 
 years 
 
 10 
 15 
 20 
 25 
 30 
 35 
 40 
 45 
 50 
 
 date 
 
 1-5 years 
 Sixth year 
 Last year 
 
 cents 
 4.000 
 
 24.000 
 20.800 
 13.200 
 
 cents 
 
 4.250 
 24.250 
 20.850 
 13.400 
 
 4.250 
 14.250 
 10.425 
 9.641 
 
 4.250 
 10.917 
 6.950 
 7.762 
 
 4.250 
 9.250 
 5.213 
 6.635 
 
 4.250 
 8.250 
 4.170 
 
 5.883 
 
 4.250 
 7.583 
 3.475 
 5.347 
 
 4.250 
 7.107 
 2.978 
 4.947 
 
 4.250 
 6.750 
 2.606 
 4.630 
 
 4.250 
 6.472 
 2.316 
 4.380 
 
 cents 
 
 4.500 
 24.500 
 20.900 
 13.600 
 
 4.500 
 14.500 
 10.450 
 9.817 
 
 4.500 
 11.167 
 6.967 
 7.925 
 
 4.500 
 9.500 
 5.225 
 6.790 
 
 4.500 
 8.500 
 4.180 
 6.033 
 
 4.500 
 7.833 
 3.483 
 5.492 
 
 4.500 
 7.357 
 2.985 
 5.087 
 
 4.500 
 7.000 
 2.613 
 
 4.772 
 
 4.500 
 6.722 
 2.322 
 4.720 
 
 cents 
 
 4.750 
 24.725 
 20.950 
 13.800 
 
 4.750 
 14.750 
 10.475 
 9.992 
 
 4.750 
 11.417 
 6.984 
 8.088 
 
 4.750 
 9.750 
 5.238 
 6.945 
 
 4.750 
 8.750 
 4.190 
 6.183 
 
 4.750 
 8.083 
 3.491 
 5.639 
 
 4.750 
 7.607 
 2.993 
 5.231 
 
 4.750 
 7.250 
 2.619 
 4.914 
 
 4.750 
 6.972 
 2.328 
 4.385 
 
 cents 
 
 5.000 
 25.000 
 21.000 
 14.000 
 
 5.000 
 15.000 
 10.500 
 10.166 
 
 5.000 
 11.667 
 7.000 
 8.250 
 
 5.000 
 10.000 
 5.250 
 7.100 
 
 5.000 
 9.000 
 4.200 
 6.333 
 
 5.000 
 8.333 
 3.500 
 5.785 
 
 5.000 
 7.857 
 3.000 
 5.375 
 
 5.000 
 7.500 
 2.625 
 5.055 
 
 5.000 
 7.222 
 2.333 
 4.799 
 
 cents 
 
 5.250 
 25.250 
 21.050 
 14.275 
 
 5.250 
 15.250 
 10.525 
 10.342 
 
 5.250 
 11.917 
 7.017 
 8.413 
 
 5.250 
 10.250 
 5.263 
 7.255 
 
 5.250 
 9.250 
 4.210 
 6.483 
 
 5.250 
 8.583 
 3.509 
 5.932 
 
 5.250 
 8.107 
 3.007 
 5.519 
 
 5.250 
 7.750 
 2.632 
 5.198 
 
 5.250 
 7.472 
 2.339 
 4.415 
 
 cents 
 
 5.500 
 25.500 
 21.100 
 14.400 
 
 5.500 
 15.500 
 10.550 
 10.516 
 
 5.500 
 12.167 
 7.034 
 8.575 
 
 5.500 
 10.500 
 5.275 
 7.410 
 
 5.500 
 9.500 
 4.220 
 6.592 
 
 5.500 
 8.833 
 3.517 
 6.079 
 
 5.500 
 8.357 
 3.014 
 5.662 
 
 5.500 
 8.000 
 2.640 
 5.340 
 
 5.500 
 7.722 
 2.344 
 4.530 
 
 cents 
 
 6.000 
 26.000 
 21.200 
 14.800 
 
 6.000 
 16.000 
 10.600 
 10.867 
 
 6.000 
 12.667 
 7.067 
 8.900 
 
 6.000 
 11.000 
 5.287 
 7.715 
 
 6.000 
 10.000 
 4.240 
 5.933 
 
 6.000 
 9.333 
 3.535 
 6.372 
 
 6.000 
 8.857 
 3.028 
 5.199 
 
 6.000 
 8.500 
 2.654 
 5.624 
 
 6.000 
 8.222 
 2.355 
 4.759 
 
 Average.. 
 
 1-5 years 
 Sixth year 
 Last year 
 
 4.000 
 14.000 
 10.400 
 9.467 
 
 4.000 
 10.667 
 6.933 
 7.600 
 
 4.000 
 9.000 
 5.200 
 .6.480 
 
 4.000 
 8.000 
 4.160 
 5.733 
 
 4.000 
 7.333 
 3.467 
 5.200 
 
 4.000 
 6.857 
 2.971 
 4.800 
 
 4.000 
 6.500 
 2.600 
 4.489 
 
 4.000 
 6.222 
 2.311 
 4.240 
 
 Average.. 
 
 15 years 
 
 Sixth year 
 Last year 
 
 Average.. 
 
 15 years. . . . 
 
 Sixth year 
 Last year. . . 
 
 Average 
 
 15 years.. 
 
 Sixth year 
 Last year 
 
 Average 
 15 years 
 
 Sixth year 
 Last year 
 Average.. 
 
 15 years... 
 
 Sixth year. ... 
 Last year 
 Average 
 
 1-5 years 
 Sixth year 
 Last year 
 Average 
 
 15 years 
 
 Sixth year 
 Last year 
 Average.. . 
 
 
RESISTANCE OF ROADS TO TRACTION 
 
 The resistance to traction of a small number of pavements of 
 different types, in different conditions was investigated in 1915 
 by the electrical engineering department of the Massachusetts 
 Institute of Technology. A half-ton electric delivery wagon was 
 used, and each test was made by driving the wagon over the test 
 pavement in one direction and then in the other, so that the ef- 
 fect of the wind, if any, would be neutralized by averaging the 
 results of the runs in both directions. The tests are described in 
 a paper presented to the American Institute of Electrical Engi- 
 neers in June, 1916, by Profs. A. E. Kennelly and O. R. Schurig. 
 The results were summarized in the accompanying illustration. 
 
 Curve 1 is nearly flat, and the authors state that if the effect 
 of air resistance was eliminated from the total resistance to trac- 
 tion, the resistance of a good level asphalt pavement would be 
 about 17 pounds per ton at all speeds. Such a pavement in 
 poor condition had a resistance of about 23 pounds per ton when 
 the wagon ran at 12 miles per hour and 25 pounds at 15 miles. 
 There were no tests of wood block pavements in poor condition; 
 curve 2 gives the results for a good pavement. 
 
 Curve 3 is for a good brick pavement; the effect of slight wear 
 of bricks was to increase the tractive resistance to 25 pounds per 
 ton at 12 miles and about 30 pounds at 15 miles. 
 
 Curve 4 is for a dry, hard water-bound macadam road in fair 
 condition. A similar road in a dusty condition showed an in- 
 crease of 3 pounds in the resistance to traction at all speeds. A 
 poor, damp road in poor condition offered a resistance of 33 
 pounds at 10 miles and 39 pounds at 13 miles. Oiling a good 
 water-bound macadam road increased its resistance to traction 
 about 5 pounds, this increase gradually growing larger as the 
 speed increased. 
 
 Curve 5 is for bituminous macadam in good condition. The 
 curve for another road in good condition began with a resistance 
 of a little under 26 pounds per ton at 9 miles an hour and in- 
 creased to 32 pounds at 14 miles. AJI old road of this type in 
 poorly patched condition offered a resistance of about 29 pounds 
 at 8 miles and 37 pounds at 13 miles. A good road which was 
 recently treated and still soft had a resistance of 33 pounds at 8 
 miles and nearly 36 pounds at 13 miles, as shown in Curve 9. 
 A very poor, soft road with many holes had a resistance of 41 
 
 189 
 
190 
 
 AMERICAN HIGHWAY ASSOCIATION 
 
 pounds at 7 miles and 54 pounds at 12 miles, showing what a 
 rapid increase to resistance follows an attempt to go at even 
 moderate speed over such a road. 
 
 The authors make the following comments of the tests: 
 There are three principal elements which determine the trac- 
 tive-resistance curve for different speeds and a given vehicle, within 
 the range of conditions covered by the tests. 
 
 The first element is a constant resistance, the magnitude of 
 which depends on the lack of resilience of the road surface and 
 the tires, that is to say, on the energy losses due to displacement 
 of tire material and road-surface material. This constant ele- 
 
 (22 44 
 
 14 
 
 16 18 20 
 SPEED- KM. PER HR. 
 10 11 12 13 
 SPEED -MILES PER HR. 
 
 8 i 10 il 12 13 fc l'5 1*6 
 
 CURVES SHOWING RESISTANCE TO TRACTION AT DIFFERENT SPEEDS 
 
 ment would be encountered upon a smooth, level road of the 
 particular type considered, in the absence of impact, air and wind 
 resistance. 
 
 The second element is an increasing resistance with increasing 
 speed due to impact losses. This resistance results from lack of 
 smoothness of the road surface and varies approximately as the 
 second power of the velocity at impact. 
 
 The third element is an increasing resistance with increased 
 speed. It is due to the air pressure against the front of the 
 vehicle and varies approximately as the second power of the 
 speed. 
 
RESISTANCE OF ROADS TO TRACTION 191 
 
 The first element is called the displacement resistance, the second 
 the impact resistance and the third the air resistance. The 
 displacement resistance is very marked in Curve 10, for a granite- 
 block pavement with sand joints. The displacement resist- 
 ance varies, not only with the type and surface quality of the 
 road, but also with the type, dimensions and quality of the tires 
 on the wheels. The same tires were used in the experiments by 
 Kennelly and Schurig. The air resistance of a given vehicle at 
 any given speed is the same for all classes of pavement. The 
 impact resistance of a road depends not only on the type and 
 character of the road surface and the sizes of its irregularities, 
 but also on the type, dimensions and quality of the tires on the 
 wheels, the weight of the truck and the quality of its springs. 
 
 Increasing the gross weight of the vehicle by 12 per cent, 
 through load, was found to have no effect on tractive resistance 
 within the observed speed limits for smooth roads in good con- 
 dition; but on rough roads, a distinct increase in tractive resist- 
 ance with this extra weight was observed. 
 
RURAL PUBLIC ROADS OF UNITED STATES 
 AT CLOSE OF 1915 
 
 Circular 68, United States Department of Agriculture. Prepared by the 
 
 Division of Road Economics, Office of Public Roads and Rural 
 
 Engineering. 
 
 STATE 
 
 TOTAL 
 RURAL 
 ROADS 
 
 TOTAL 
 SURFACED 
 ROADS 
 
 PERCENTAGE 
 OF ROADS 
 
 SURFACED 
 
 CASH 
 EXPENDITURES 
 FOR ROADS 
 IN 1915 
 
 TOTAL STATE 
 FUNDS 
 FOR ROADS TO 
 JANUARY 1, 
 1916 
 
 Alabama 
 
 miles 
 
 55,446 
 
 miles 
 
 5,915 
 
 10.7 
 
 $4,283,207 
 
 $586,405 
 
 Arizona 
 
 12,075 
 
 350 
 
 2.9 
 
 1,076,178 
 
 1 039 388 
 
 Arkansas 
 
 50,743 
 
 1,200 
 
 2.3 
 
 2,803,000 
 
 165 000 
 
 California 
 
 61,038 
 
 13,000 
 
 21.3 
 
 20,753,281 
 
 16,571 091 
 
 Colorado . . . ... 
 
 39,691 
 
 1,750 
 
 4.4 
 
 2,193,000 
 
 1,024,751 
 
 Connecticut 
 
 14,061 
 
 3,200 
 
 22.7 
 
 3,484,944 
 
 17,019,120 
 
 Delaware 
 
 3,674 
 
 300 
 
 8.0 
 
 397,500 
 
 224,695 
 
 Florida 
 
 17,995 
 
 3,500 
 
 19.4 
 
 5,501,135 
 
 1 135 
 
 Georgia 
 
 84,770 
 
 13,000 
 
 15.3 
 
 3,700,000 
 
 
 Idaho. 
 
 23,109 
 
 950 
 
 4.1 
 
 1,974,636 
 
 572 812 
 
 Illinois. ... 
 
 94,141 
 
 11,000 
 
 11.7 
 
 9,263,995 
 
 1 686 627 
 
 Indiana 
 
 63,370 
 
 27,000 
 
 42.6 
 
 13,000,000 
 
 
 Iowa 
 
 106,847 
 
 1,000 
 
 1.0 
 
 13,606,299 
 
 255,935 
 
 Kansas 
 
 111,536 
 
 1,250 
 
 1.1 
 
 5,510,000 
 
 30 000 
 
 Kentucky 
 
 57,916 
 
 13,000 
 
 22.1 
 
 3,122,430 
 
 616,715 
 
 Louisiana 
 
 24,562 
 
 2,250 
 
 9.1 
 
 3,569,709 
 
 606 327 
 
 Maine . . . 
 
 25,528 
 
 3,000 
 
 11.7 
 
 3,293,902 
 
 5 865 209 
 
 Maryland 
 
 16,458 
 
 2,950 
 
 17.9 
 
 5,630,000 
 
 17,583,142 
 
 Massachusetts 
 
 18,681 
 
 8,800 
 
 46.6 
 
 6,557,279 
 
 18,999,992 
 
 Michigan 
 
 74,089 
 
 8,600 
 
 11.6 
 
 10,174,738 
 
 3,182,701 
 
 Minnesota 
 
 93,500 
 
 5,500 
 
 5.9 
 
 8,292,000 
 
 4,288,174 
 
 Mississippi 
 
 45,778 
 
 2,500 
 
 5.5 
 
 2,900,000 
 
 
 Missouri 
 
 96,124 
 
 8,000 
 
 8.3 
 
 8,369,189 
 
 1 791 172 
 
 Montana 
 
 39,204 
 
 775 
 
 2.0 
 
 3,676,318 
 
 34346 
 
 Nebraska 
 
 80,338 
 
 500 
 
 0.6 
 
 3,520,000 
 
 377,850 
 
 Nevada . 
 
 15,000 
 
 75 
 
 0.5 
 
 250,000 
 
 20,000 
 
 New Hampshire 
 
 14,020 
 
 1,800 
 
 12.8 
 
 2,363,414 
 
 3,259,789 
 
 New Jersey 
 
 14,817 
 
 4,600 
 
 31.0 
 
 7,163,584 
 
 8,355,576 
 
 New Mexico 
 
 11,873 
 
 450 
 
 3.8 
 
 584,919 
 
 662,955 
 
 New York 
 
 80,112 
 
 17,500 
 
 21.8 
 
 24,255,648 
 
 96,622,498 
 
 North Carolina 
 North Dakota 
 
 50,758 
 68,000 
 
 6,500 
 1,100 
 
 12.8 
 1.6 
 
 5,510,000 
 2,500,700 
 
 38,500 
 
 Ohio 
 
 86,453 
 
 30,920 
 
 35.8 
 
 12,975,688 
 
 8,566,275 
 
 Oklahoma. . . ... 
 
 107,916 
 
 300 
 
 0.3 
 
 3,410,000 
 
 30,323 
 
 Oregon 
 
 36,819 
 
 7,780 
 
 21.1 
 
 6,182,000 
 
 418,975 
 
 Pennsylvania 
 
 91,556 
 
 9,883 
 
 10.8 
 
 12,541,257 
 
 30,801,211 
 
 Rhode Island 
 
 2,121 
 
 1,246 
 
 58.8 
 
 594,119 
 
 3,907,784 
 
 South Carolina 
 
 42,220 
 
 3,500 
 
 8.3 
 
 1,000,000 
 
 
 South Dakota 
 
 96,306 
 
 850 
 
 0.9 
 
 1,450,000 
 
 
 Tennessee 
 
 46,050 
 
 8,625 
 
 18.7 
 
 3,503,500 
 
 3,500 
 
 Texas 
 
 128,960 
 
 12,000 
 
 9.3 
 
 9,500,000 
 
 
 Utah 
 
 15,000 
 
 1,053 
 
 7.0 
 
 1,213,100 
 
 809,732 
 
 Vermont 
 
 15,082 
 
 3,478 
 
 23.1 
 
 1,475,145 
 
 3,671,564 
 
 Virginia 
 
 53,388 
 
 4,760 
 
 8.9 
 
 4,018,399 
 
 2,713,550 
 
 Washington 
 
 42,428 
 
 5,460 
 
 12.8 
 
 6,670,702 
 
 8,552,789 
 
 West Virginia 
 
 32,024 
 
 1,200 
 
 3.7 
 
 2,759,212 
 
 1 130, 978 
 
 Wisconsin. . 
 
 75,702 
 
 14,050 
 
 18.5 
 
 9,960,980 
 
 4,219,001 
 
 Wyoming . . . 
 
 14,381 
 
 500 
 
 3.5 
 
 441,291 
 
 43,237 
 
 
 
 
 
 
 
 Total. 
 
 2,451,660 
 
 276,920 
 
 11.3 
 
 $266,976,399 
 
 $265,350,824 
 
 
 
 
 
 
 
 1 Of this $118,000 was returned to the counties in 1911 by act of legislature. 
 
 192 
 
REVENUES USED IN 1914 IN EACH STATE FOR 
 PUBLIC ROAD AND BRIDGE PURPOSES AND 
 TOTAL OUTSTANDING BONDS FOR ROADS 
 AND BRIDGES AT CLOSE OF 1914 
 
 From Bulletin 890, U. S. Department of Agriculture, Prepared by the Office 
 of Public Roads and its State Collaborators 
 
 STATE 
 
 PUBLIC ROAD AND BRIDGE REVENUES 
 
 TOTAL STATE AND 
 LOCAL BONDS 
 
 Total 
 
 'Sj'ei 
 
 Is 
 
 
 
 l| 
 %3 
 PH 
 
 Per capita 
 
 Per $100 
 assessed 
 valuation 
 
 Alabama 
 
 $3,949,019.00 
 982,721.22 
 1,522,696.20 
 19,171,984.66 
 1,937,546.23 
 3,640,962:75 
 511628.00 
 2,280,255.09 
 3,688,172.25 
 1,371,468.58 
 8,734,712.77 
 14,233,985.93 
 10,187,507.32 
 5,544,048.00 
 2,474,621.00 
 1,777,572.12 
 2,642,006.79 
 6,000,652.03 
 6,091,875.30 
 9,261,998.00 
 6,458,940.07 
 3,960,377.00 
 5,513,048.71 
 2,888,400.61 
 1,796,277.69 
 245,013.65 
 1,590,464.11 
 7,308,287.08 
 556,398.82 
 23,231,964.02 
 5,2^5,490.78 
 2,402,383.52 
 14,3341245.98 
 2*112,680.80 
 5,310,466.76 
 10,424,580.00 
 446,496.05 
 1,024,480.37 
 1,217,809.42 
 2,370,560.16 
 9,920,079.11 
 803,070.63 
 1,023,941.01 
 3,224,528.82 
 7,944,717.38 
 2,483,747.00 
 9,880,240.50 
 669,661.16 
 
 $71.22 
 81.38 
 30.00 
 314.09 
 48.70 
 258.90 
 139.25 
 126.71 
 45.72 
 56.22 
 91.32 
 194.06 
 97.88 
 49.92 
 42.52 
 72.37 
 112.35 
 364.60 
 326.08 
 124.84 
 69.06 
 86.51 
 57.40 
 73.67 
 22.37 
 20.11 
 113.44 
 486.49 
 46.86 
 2Q2.60 
 102.75 
 34.92 
 165.99 
 19.57 
 144.23 
 113.86 
 205.76 
 24.26 
 12.64 
 51.48 
 76.92 
 91.15 
 71.86 
 60.39 
 187.25 
 77.55 
 130.50 
 44.06 
 
 $77.01 
 8.63 
 28.99 
 123.17 
 18.69 
 755.50 
 20.37 
 41.56 
 62.80 
 16.45 
 155.85 
 394.89 
 183.27 
 67.79 
 61.58 
 39.10 
 88.37 
 603.62 
 758.00 
 161.13 
 79.88 
 85.42 
 80.22 
 19.75 
 23.38 
 2.23 
 176.11 
 959.00 
 4.54 
 467.00 
 107.00 
 34.23 
 351.84 
 30.45 
 55.54 
 232.00 
 418.50 
 33.59 
 15.84 
 56.86 
 37.80 
 9.77 
 112.22 
 80.08 
 118.87 
 103.39 
 178.81 
 6.86 
 
 $1.840 
 4.810 
 0.960 
 8.060 
 2.420 
 3.260 
 2.520 
 3.020 
 1.410 
 4.210 
 1.540 
 5.270 
 4.580 
 3.280 
 1.080 
 1.073 
 3.550 
 4.630 
 1.810 
 3.290 
 3.110 
 2.300 
 1.670 
 7.680 
 1.510 
 2,900 
 3.690 
 2.830 
 1.690 
 2.54Q 
 2.360 
 4.160 
 3.000 
 1.274 
 7.890 
 1.360 
 0.820 
 0.670 
 2.080 
 1.080 
 2.540 
 2.150 
 2.870 
 1.560 
 6.950 
 2.030 
 4.230 
 4.590 
 
 $0.6900 
 0.7000 
 0.3600 
 0.6600 
 0.4600 
 0.3500 
 0.5450 
 1.0700 
 0.4370 
 0.8200 
 0.3700 
 0.7500 
 1.1300 
 0.2000 
 0.2390 
 0.3220 
 0.6330 
 0.4850 
 0.1270 
 0.4000 
 0.4400 
 0.9620 
 0.3000 
 0.8300 
 0.3900 
 0.2400 
 0.3620 
 0.290 
 0.7700 
 0.2030 
 0.6970 
 0.6800 
 0.2200 
 0.1769 
 0.5900 
 0.2050 
 0.0720 
 0.3510 
 0.3400 
 0.3780 
 0.3910 
 0.4000 
 0.4620 
 0.3720 
 0.7900 
 0.2120 
 0.4000 
 0.3700 
 
 $5,418,000.00 
 295,000.00 
 1,467,066.00 
 32,277,000.00 
 90,500.00 
 7000000.00 
 1 280000.00 
 5959 199.00 
 127500.00 
 1,339,000.09 
 798,761.55 
 42,095,357.34 
 1,960,780.00 
 
 Arizona 
 
 Arkansas 
 California.. 
 
 Colorado 
 Connecticut 
 Delaware 
 Florida 
 
 Georgia 
 
 Idaho 
 Illinois 
 
 Indiana 
 
 Iowa 
 
 Kansas . . 
 
 Kentucky. 
 
 705,000.00 
 1,588,835.00 
 785,000.00 
 12*863,700.00 
 10,305,522.82 
 10,389,029.43 
 1,411,889.00 
 8,327,172.00 
 522,500.00 
 2,224,050.72 
 
 Louisiana 
 
 Maine 
 
 Maryland 
 Massachusetts. . . 
 Michigan 
 
 Minnesota 
 
 Mississippi 
 
 Missouri 
 Montana. 
 
 Nebraska 
 Nevada 
 New Hampshire. . 
 New Jersey 
 
 38,000.00 
 675,000.00 
 14,011,337.00 
 157,000.00 
 76,82^,088.00 
 8,955,300.00 
 
 New Mexico 
 
 New York 
 
 North Carolina.. 
 North Dakota.... 
 Ohio 
 Oklahoma 
 Oregon 
 
 31,175,968.53 
 1,440,000.00 
 1,615,000.00 
 127,547,659.00 
 1,800,000.00 
 460,000.00 
 
 Pennsylvania 
 Rhode Island 
 South Carolina... 
 South Dakota 
 Tennessee 
 Texas 
 Utah 
 
 6,898,277.00 
 14,615,017.00 
 541,500.00 
 
 5,650,994.93 
 1,555,000.00 
 1,303,000.00 
 281,078.00 
 
 Vermont 
 
 Virginia 
 Washington 
 
 West Virginia 
 Wisconsin. 
 
 Wyoming 
 
 
 Total or ave . . . 
 
 $240,263,784.46 
 
 $98.22 
 
 $80.79 
 
 $2.620 
 
 $0.3500 
 
 $344,763,082.32 
 
 193 
 
EXTENT OF SURFACED ROADS IN THE UNITED 
 STATES AT THE CLOSE OF 1914 
 
 From Bulletin 890, U. S. Department of Agriculture, Prepared by the Office of 
 Public Roads and its State Collaborators 
 
 STATE 
 
 MACADAM 
 
 BITUMI- 
 NOUS 
 MACADAM 
 
 GRAVEL 
 
 SAND 
 CLAY 
 
 BRICK 
 
 CON- 
 CRETE 
 
 MISCEL- 
 LANEOUS 
 
 TOTAL 
 SURFACED 
 
 miles 
 
 4,988.50 
 253.43 
 1,097.50 
 10,279.73 
 1,193.87 
 2,975.45 
 243.50 
 2,830.47 
 12,342.12 
 679.00 
 11,606.31 
 30,962.40 
 614.57 
 1,148.85 
 12,403.28 
 2,067 62 
 2,762.36 
 2,489.26 
 8,505.89 
 7,828.51 
 3,967.83 
 2,133.35 
 6,712.57 
 609.25 
 1,204.54 
 262.00 
 
 1,659.63 
 5,897.46 
 261.50 
 15,635.90 
 6,003.75 
 955.00 
 30,569.17 
 121.60 
 4,726.40 
 982.88 
 693.42 
 3,270.50 
 363.00 
 8,102.00 
 10,526.79 
 1,253.75 
 1,442 03 
 3,909.57 
 4,922.09 
 1,064.97 
 13,399.47 
 468.50 
 
 Alabama 
 
 miles 
 
 431.00 
 11.23 
 362.50 
 837.40 
 3.00 
 923.42 
 161.50 
 829.16 
 234.00 
 42.50 
 1,675.11 
 10,291.29 
 171.30 
 194.30 
 10,628.00 
 
 miles 
 
 31.00 
 13.50 
 4.00 
 877.90 
 
 '"i28;28 
 35.50 
 42.80 
 87.00 
 12.00 
 121.53 
 168.35 
 
 '"59 '.03 
 
 miles 
 
 2,589.50 
 125.70 
 535.00 
 3,563.59 
 574.25 
 1,057.93 
 21.00 
 42.50 
 1,073.00 
 168.00 
 7,052.30 
 20,264.59 
 413.00 
 151.85 
 1,713.50 
 430.00 
 1,139.36 
 243.95 
 6,289.57 
 5,230.25 
 2,825.25 
 1,281.10 
 3,671.50 
 514.25 
 21.00 
 193.00 
 
 1,013.70 
 2,858.52 
 184.00 
 5,802.97 
 529.00 
 955.00 
 15,385.93 
 6.90 
 3,060.15 
 235.19 
 230.10 
 85.00 
 212.00 
 2,788.00 
 5,258.98 
 685.75 
 1,165.42 
 822.09 
 3,924.48 
 20.50 
 9,597.00 
 52.50 
 
 miles 
 1,916.00 
 45.00 
 175.00 
 582.25 
 450.12 
 840.27 
 
 T,i63!66 
 10,778.00 
 449.00 
 2,467.95 
 150.25 
 23.00 
 758.50 
 
 "i',44^66 
 2.26 
 69.00 
 
 miles 
 
 miles 
 1.00 
 
 miles 
 20.00 
 58.00 
 
 "3, 489! 46 
 164.25 
 
 Arizona 
 Arkansas 
 
 
 21.00 
 929.19 
 2.25 
 24.22 
 
 '"i2!66 
 .40 
 4.50 
 148.80 
 53.17 
 5.77 
 1.35 
 2.50 
 
 California 
 Colorado 
 
 '"iis's 
 
 '256! 24 
 1.72 
 
 "'82i92 
 34.75 
 
 '"i'.io 
 
 .25 
 
 Connecticut 
 Delaware 
 Florida. 
 
 25.50 
 484.77 
 168.00 
 3.00 
 57.70 
 
 '"ilso 
 
 38.75 
 
 '"i89'62 
 1,510.89 
 455.96 
 44.69 
 
 Georgia 
 
 Idaho- 
 
 Illinois 
 
 Indiana 
 Iowa 
 
 Kansas 
 
 Kentucky 
 Louisiana.. 
 
 Maine 
 Maryland.. . . 
 
 55.36 
 488.70 
 834.30 
 1,021.19 
 120.25 
 86.00 
 1,531.05 
 78.00 
 39.21 
 2.00 
 
 61.87 
 1,809.24 
 
 5,7i7!97 
 1,111.00 
 
 12,903 '87 
 6.70 
 1,000.72 
 * 1,881. 80 
 352.92 
 27.50 
 
 43.93 
 1,042.31 
 1,337.33 
 94.50 
 19.00 
 29.58 
 59.00 
 
 .05 
 
 10.51 
 189.34 
 
 Massachusetts.. 
 Michigan 
 Minnesota 
 Mississippi 
 Missouri. . 
 
 
 1,375.27 
 985.33 
 604.25 
 1,442.25 
 14.00 
 1,131.10 
 67.00 
 
 270.90 
 561.40 
 72.50 
 
 ' ' ' .'50 
 
 107.30 
 17.50 
 14.00 
 2.77 
 
 
 118.50 
 5.00 
 3.00 
 2.00 
 
 1.00 
 
 Montana . 
 
 Nebraska 
 Nevada.. 
 
 1.30 
 
 2.40 
 
 7.53 
 
 New Hamp- 
 shire 
 New Jersey 
 New Mexico 
 New York 
 North Carolina. 
 North Dakota.. 
 Ohio- 
 
 154.26 
 417.63 
 5.00 
 3,168.63 
 9.00 
 
 "i',066'.29 
 3.00 
 137.25 
 198.33 
 107.40 
 3.50 
 10.00 
 148.00 
 181.00 
 15.50 
 
 ' '255! 77 
 165.52 
 62.95 
 183.00 
 
 
 7.07 
 
 151.83 
 250.67 
 
 
 
 
 148.53 
 
 244.19 
 1.25 
 
 553.61 
 40.00 
 
 4,313.50 
 
 
 211.00 
 105.00 
 300.00 
 
 640.41 
 
 315.67 
 
 46.00 
 
 Oklahoma 
 Oregon 
 Pennsylvania... 
 Rhode Island... 
 South Carolina. 
 South Dakota.. 
 Tennessee 
 Texas 
 Utah 
 Vermont 
 Virginia 
 
 '"269 '.33 
 
 28.41 
 
 199.87 
 7,398.23 
 3.00 
 53.50 
 12.00 
 
 ii674.08 
 
 
 
 3,101.00 
 129.00 
 613.00 
 3,490.48 
 401.00 
 
 
 
 
 
 4,550.50 
 511.00 
 49.00 
 1.94 
 1,177.89 
 502.82 
 771.92 
 1,408.00 
 
 .50 
 
 2.00 
 11.25 
 2.50 
 
 
 
 274.67 
 142.17 
 140.00 
 70.00 
 72.00 
 416.00 
 
 1,511.65 
 83.50 
 
 
 
 Washington 
 West Virginia... 
 Wisconsin 
 Wyoming. 
 
 26.35 
 121.10 
 2.40 
 
 79.42 
 18.50 
 83.07 
 
 2,054.00 
 
 
 
 
 
 
 
 Total. 
 
 64,898.43 
 
 10,499.79 
 
 116,058.12 
 
 44,154.73 
 
 1,593.88 
 
 2,348.43 
 
 17,738.16 
 
 257,291.54 
 
 
 Percent 
 
 25.22 
 
 4.08 
 
 45.11 
 
 17.16 
 
 0.62 
 
 0.91 
 
 6.90 
 
 100.00 
 
 State roads only. 
 
 194 
 
MOTOR-CAR REGISTRATIONS AND GROSS 
 MOTOR-VEHICLE REVENUES, 1913-1915 
 
 Circular 59, United States Department of Agriculture. Prepared by the 
 
 Division of Road Economics, Office^ of Public Roads and Rural 
 
 Engineering 
 
 
 MOTOK-CAR REGISTRATIONS 1 
 
 TOTAL GROSS REVENUES 
 
 1013 
 
 1914 
 
 1915 
 
 1913 
 
 1914 
 
 1915 
 
 Alabama 
 
 2 5,300 
 
 3,613 
 3,583 
 '100,000 
 13,000 
 
 23,200 
 2,440 
 
 4,000 
 4 3,000 
 2 20,000 
 
 2,113 
 94,656 
 45,000 
 
 70,299 
 34,550 
 
 7,210 
 2 10,000 
 11,022 
 14,217 
 62,660 
 
 54,366 
 46,000 
 2 3,850 
 38,140 
 5,916 
 
 13,411 
 1,091 
 8,237 
 51,360 
 1,898 
 
 134,495 
 10,000 
 15,187 
 86,156 
 a 3,000 
 
 13,975 
 80,178 
 10,295 
 10,000 
 14,457 
 
 8,672 
 5,040 
 5,642 
 123,504 
 17,756 
 
 27,786 
 3,050 
 
 4,833 
 4 3,368 
 20,915 
 
 3,346 
 131,140 
 66,500 
 
 106,087 
 49,374 
 
 11,766 
 2 12,000 
 15,700 
 20,213 
 77,246 
 
 76,389 
 67,862 
 5,694 
 54,468 
 10,200 
 
 16,385 
 1,487 
 9,571 
 62,961 
 3,090 
 
 168,223 
 14,677 
 17,347 
 122,504 
 13,500 
 
 16,447 
 112,854 
 12,331 
 14,000 
 20,929 
 
 11,634 
 
 7,753 
 8,021 
 163,797 
 28,894 
 
 41,121 
 5,052 
 
 8,009 
 '10,850 
 25,000 
 
 7,071 
 180,832 
 96,915 
 
 145,109 
 72,520 
 
 19,500 
 11,380 
 21,545 
 31,047 
 102,633 
 
 114,845 
 93,269 
 9,669 
 76,462 
 14,540 
 
 59,000 
 2,009 
 13,449 
 81,848 
 5,100 
 
 255,242 
 21,000 
 24,908 
 181,332 
 25,032 
 
 23,585 
 160,137 
 16,362 
 15,000 
 28,724 
 
 $83,000 
 27,545 
 17,411 
 75,000 
 60,833 
 
 316,667 
 24,735 
 
 13,228 
 4 6,000 
 12,000 
 
 35,160 
 507,629 
 150,345 
 
 787,411 
 186,066 
 
 52,000 
 2 10,000 
 138,509 
 150,000 
 764,154 
 
 190,329 
 40,000 
 
 $113,202 
 34,077 
 56,420 
 1,338,785 
 80,047 
 
 406,623 
 35,672 
 
 20,147 
 4 6,736 
 104,575 
 
 58,580 
 699,725 
 432,309 
 
 1,040,136 
 268,471 
 
 85,883 
 2 12,000 
 192,542 
 268,231 
 923,961 
 
 ( 8 ) 
 132,398 
 51,146 
 235,873 
 27,000 
 
 34,325 
 4,331 
 185,288 
 814,536 
 19,663 
 
 1,529,852 
 89,580 
 55,964 
 685,457 
 13,500 
 
 77,592 
 1,185,039 
 157,020 
 14,000 
 125,000 
 
 $180,744 
 45,579 
 80,551 
 2,027,432 
 120,801 
 
 536,970 
 55,596 
 
 29,396 
 2 60,000 
 125,000 
 
 121,259 
 924,906 
 587,318 
 
 1,533,054 
 387,588 
 
 117,117 
 75,600 
 268,412 
 386,565 
 1,235,724 
 
 373,833 
 2 160,540 
 76,700 
 323,289 
 33,120 
 
 2 183,000 
 7,875 
 257,776 
 1,062,923 
 29,625 
 
 1,991,181 
 123,000 
 79,245 
 984,622 
 154,892 
 
 108,881 
 1,665,276 
 206,440 
 15,000 
 '180,000 
 
 Arizona 
 
 Arkansas 
 
 California 
 
 Colorado 
 
 Connecticut 
 Delaware 
 
 District of Col- 
 umbia 
 
 Florida 
 
 Georgia 
 
 Idaho 
 
 Illinois . 
 
 Indiana 
 
 Iowa 
 
 Kansas 
 
 Kentucky .... 
 
 Louisiana . . . 
 
 Maine 
 
 Maryland 
 
 Massachusetts. . 
 Michigan 
 
 Minnesota 
 
 Mississippi 
 
 Missouri 
 
 173,510 
 12,000 
 
 26,000 
 3,323 
 152,834 
 661,446 
 15,084 
 
 1,275,727 
 60,000 
 41,961 
 457,538 
 3,000 
 
 56,873 
 841,062 
 129,851 
 10,000 
 89,170 
 
 Montana 
 
 Nebraska 
 
 Nevada 
 
 New Hampshire 
 New Jersey 
 
 New Mexico 
 New York. . . . 
 
 North Carolina. 
 North Dakota. . . 
 Ohio 
 
 Oklahoma 
 Oregon 
 
 Pennsylvania.. . 
 Rhode Island. . . 
 South Carolina 2 . 
 South Dakota... 
 
 195 
 
Motor-Car Registrations Continued 
 
 
 MOTOR-CAB REGISTRATIONS 1 
 
 TOTAL GROSS REVENUE* 
 
 1913 
 
 1914 
 
 1915 
 
 1913 
 
 1914 
 
 1915 
 
 Tennessee.. 
 
 '10,000 
 
 32,000 
 4,000 
 5,913 
 9,022 
 
 24,178 
 5,144 
 34,346 
 1,584 
 
 6 19,769 
 40,000 
 2,253 
 8,475 
 13,984 
 
 30,253 
 6,159 
 53,161 
 
 2,428 
 
 7,618 
 7 40,000 
 9,177 
 11,499 
 21,357 
 
 38,823 
 13,279 
 79,741 
 3,976 
 
 2 9,000 
 
 16,000 
 3,000 
 111,460 
 83,611 
 
 48,356 
 40,000 
 190,770 
 7,920 
 
 39,538 
 20,000 
 4,852 
 154,267 
 120,814 
 
 60,506 
 60,648 
 293,580 
 12,140 
 
 '34,000 
 20,000 
 2 60,000 
 218,480 
 176,875 
 
 238,717 
 128,952 
 431,977 
 19,880 
 
 Texas 1 . 
 
 Utah 
 
 Vermont 
 
 Virginia 
 
 Washington 
 West Virginia. . . 
 Wisconsin 
 
 Wyoming 
 
 
 Total 
 
 1,258,062 
 
 1,711,339 
 
 2,445,664 
 
 8,192,253 
 
 12,381,951 
 
 18,245,711 
 
 1 Does not include motor cycles nor dealers' and manufacturers' licenses. 
 
 2 Estimated. 
 
 3 Registration law declared unconstitutional. 
 
 4 State registrations only. 
 
 6 Total cars registered under perennial system. 
 8 Registrations 1915 only. 
 
 'American Highway Association received report that there were 138,866 
 automobiles licensed on April 1, 1916. 
 
 PRODUCTION OF VITRIFIED PAVING BRICK 
 IN THE UNITED STATES 
 
 (From "Mineral Resources of the United States, 
 
 TEAR 
 
 QUANTITY 
 
 VALUE 
 
 AVERAGE PRICE PER 
 THOUSAND 
 
 
 thousands 
 
 
 
 1895 
 
 381,591 
 
 $3,130,472 
 
 $8.20 
 
 1896 
 
 320,407 
 
 2,794,585 
 
 8.72 
 
 1897 
 
 435,851 
 
 3,582,037 
 
 8.22 
 
 1898 
 
 474,419 
 
 4,016,822 
 
 8.47 
 
 1899 
 
 580,751 
 
 4,750,424 
 
 8.18 
 
 1900 
 
 546,679 
 
 4,764,124 
 
 8.71 
 
 1901 
 
 605,077 
 
 5,484,134 
 
 9.06 
 
 1902 
 
 617,192 
 
 5,744,530 
 
 9.31 
 
 1903 
 
 654,499 
 
 6,453,849 
 
 9.86 
 
 1904 
 
 735,489 
 
 7,557,425 
 
 10.28 
 
 1905 
 
 665,879 
 
 6,703,710 
 
 10.07 
 
 1906 
 
 751,974 
 
 7,857,768 
 
 10.45 
 
 1907 
 
 876,245 
 
 9,654,282 
 
 11.02 
 
 1908 
 
 978,122 
 
 10,657,475 
 
 10.90 
 
 1909 
 
 1,023,654 
 
 11,269,586 
 
 11.01 
 
 1910 
 
 968,000 
 
 11,004,666 
 
 11.37 
 
 1911 
 
 948,758 
 
 11,115,742 
 
 11.72 
 
 1912 
 
 911,869 
 
 10,921,575 
 
 11.98 
 
 1913 
 
 958,680 
 
 12,138,221 
 
 12.66 
 
 1914 
 
 931,324 
 
 12,500,866 
 
 13.42 
 
 1915 
 
 953,335 
 
 12,230,899 
 
 12.83 
 
 196 
 
OUTPUT OF VITRIFIED BRICK IN 1914 AND 
 1915 BY STATES 
 
 (From "Mineral Resources of the United States, 
 
 
 
 1914 
 
 
 
 1915 
 
 
 
 Quantity 
 
 Value 
 
 Aver- 
 age 
 price 
 
 - 
 sand 
 
 Quantity 
 
 Value 
 
 Aver- 
 age 
 price 
 
 thou- 
 sand 
 
 Alabama 
 Arkansas 
 California 
 Colorado 
 Connecticut 
 and Rhode 
 Island 
 
 thousands 
 
 18,679 
 
 * 
 
 1,800 
 
 * 
 
 * 
 
 $248,525 
 * 
 
 39,705 
 
 * 
 
 $13.31 
 12.14 
 22.06 
 11.52 
 
 16 03 
 
 thousands 
 
 29,018 
 * 
 
 3,182 
 
 * 
 
 * 
 
 $374,387 
 * 
 
 66,784 
 * 
 
 * 
 
 $12.90 
 12.00 
 20.99 
 11.59 
 
 12 66 
 
 Florida 
 Georgia 
 
 * 
 16,470 
 
 * 
 234,855 
 
 12.00 
 14.26 
 
 17,193 
 
 166,086 
 
 9.66 
 
 Illinois 
 
 157,176 
 
 2,086,344 
 
 13.27 
 
 142,689 
 
 1,796,350 
 
 12.59 
 
 Indiana 
 
 42,937 
 
 576,892 
 
 13.44 
 
 35,237 
 
 466,873 
 
 13.25 
 
 Iowa 
 
 14,997 
 
 211,905 
 
 14.13 
 
 20,573 
 
 300,785 
 
 14.62 
 
 Kansas 
 
 50,707 
 
 594,229 
 
 11.72 
 
 47,511 
 
 608,599 
 
 12.81 
 
 Kentucky 
 
 * 
 
 * 
 
 12 74 
 
 * 
 
 # 
 
 10 85 
 
 Michigan 
 
 7,733 
 
 120,562 
 
 15 59 
 
 4,420 
 
 62,238 
 
 14 08 
 
 Minnesota 
 Missouri 
 
 * 
 26,217 
 
 424,170 
 
 16.12 
 16 18 
 
 * 
 * 
 
 * 
 
 * 
 
 14.18 
 14 62 
 
 Montana 
 Nebraska . . 
 
 * 
 
 * 
 * 
 
 22.50 
 11 14 
 
 * 
 561 
 
 # 
 8,323 
 
 22.01 
 14 84 
 
 New Jersey. . . . 
 New Mexico 
 New York 
 Ohio 
 Oklahoma 
 Pennsylvania. . 
 Tennessee 
 Texas 
 
 * 
 * 
 
 31,240 
 293,381 
 9,912 
 
 151,200 
 
 * 
 
 1,684 
 
 * 
 * 
 
 515,672 
 3,682,230 
 127,792 
 
 2,052,676 
 
 * 
 
 23,599 
 
 15.00 
 10.40 
 16.51 
 12.55 
 12.89 
 13.58 
 15.26 
 14 01 
 
 * 
 24,154 
 333,288 
 16,537 
 
 124,354 
 
 * 
 
 * 
 
 * 
 
 384,458 
 4,017,758 
 198,387 
 
 1,638,518 
 
 * 
 
 # 
 
 12.00 
 15.92 
 12.05 
 12.00 
 13.18 
 14.47 
 15 45 
 
 Virginia 
 Washington. . . . 
 West Virginia. . 
 Other Statesf . . 
 
 * 
 * 
 
 67,750 
 39,441 
 
 * 
 * 
 
 899,215 
 662,495 
 
 10.00 
 18.99 
 13.27 
 16.80 
 
 14,861 
 69,474 
 59,844 
 
 265,691 
 841,067 
 853,107 
 
 17.88 
 12.11 
 14.26 
 
 Total 
 
 931,324 
 
 $12,500,866 
 
 $13.42 
 
 953,335} 
 
 $12,230,899* 
 
 $12.83 
 
 * Included in "Other States." 
 
 f Includes all products made by less than three producers in one State. 
 
 J In the total quantity and total value of vitrified brick are included, 
 respectively, 824,359,000 vitrified brick sold for paving, valued at $11,114,- 
 427, and 128,976,000 vitrified brick sold for other uses, valued at $1,116,472. 
 
BROKEN STONE FOR ROAD BUILDING PRO 
 DUCED IN THE UNITED STATES IN 
 1914 AND 1915 
 
 (From 
 
 'Stone in 1915," G. F. Loughlin, "Mineral Resources of 
 the United States' 1 
 
 STATE OR TERRITORY 
 
 1 
 
 J14 
 
 1 
 
 915 
 
 
 Quantity 
 
 Value 
 
 Quantity 
 
 Value 
 
 Alabama. 
 
 Short tons 
 
 74,914 
 
 $75 528 
 
 Short tons 
 49 972 
 
 $42 116 
 
 Arizona. 
 
 2,600 
 
 4,000 
 
 
 
 Arkansas 
 
 199,417 
 
 140,442 
 
 113,606 
 
 75044 
 
 California 
 
 1 707 230 
 
 982 321 
 
 1 567 505 
 
 902 462 
 
 Colorado 
 
 6052 
 
 10 100 
 
 5 842 
 
 7 178 
 
 Connecticut. . 
 
 360,443 
 
 216 064 
 
 728 014 
 
 330 174 
 
 Delaware 
 
 53,430 
 
 33 501 
 
 21 742 
 
 21 707 
 
 Florida 
 
 159,524 
 
 84,911 
 
 102 517 
 
 56 381 
 
 Georgia 
 
 57,553 
 
 37,088 
 
 90244 
 
 54 696 
 
 Hawaii 
 
 41,832 
 
 37,049 
 
 34,413 
 
 36366 
 
 Idaho 
 
 
 
 
 
 Illinois .. 
 
 1,838,599 
 
 893889 
 
 1 625 250 
 
 747 718 
 
 Indiana 
 
 2,089,103 
 
 1,065 360 
 
 1 792 261 
 
 910 462 
 
 Iowa 
 
 19,308 
 
 17,438 
 
 32437 
 
 28 397 
 
 Kansas 
 
 27,248 
 
 20,135 
 
 20,046 
 
 15 591 
 
 Kentucky 
 
 545,878 
 
 323,075 
 
 609,995 
 
 379,234 
 
 Louisiana 
 
 
 
 830 
 
 664 
 
 Maine 
 
 5,950 
 
 4 650 
 
 1 747 
 
 1 409 
 
 Maryland 
 
 404,523 
 
 349 833 
 
 334 153 
 
 274 644 
 
 Massachusetts 
 
 649,144 
 
 594 666 
 
 738 015 
 
 599 555 
 
 Michigan 
 
 53Q,823 
 
 267,702 
 
 510,524 
 
 224 734 
 
 Minnesota 
 
 46,944 
 
 36,172 
 
 59,733 
 
 57,286 
 
 Missouri 
 
 466,143 
 
 363,302 
 
 553,049 
 
 383,022 
 
 Montana 
 
 4,590 
 
 1 271 
 
 23 875 
 
 5 186 
 
 Nebraska 
 
 32,137 
 
 27,300 
 
 
 
 New Hampshire . ... 
 
 20,936 
 
 13,745 
 
 14845 
 
 12 416 
 
 New Jersey 
 
 827,705 
 
 674,202 
 
 1,059 749 
 
 822 214 
 
 New Mexico 
 
 
 
 547 
 
 407 
 
 New York 
 
 2,267,264 
 
 1,408,490 
 
 2,900,165 
 
 1,623,570 
 
 North Carolina . 
 
 65700 
 
 65 128 
 
 69 238 
 
 73 404 
 
 Ohio 
 
 3,453,360 
 
 1,748 075 
 
 3 088 599 
 
 1,567 676 
 
 Oklahoma. 
 
 15,802 
 
 7,441 
 
 46430 
 
 29 764 
 
 Oregon.. 
 
 218,379 
 
 157,267 
 
 290,648 
 
 202,580 
 
 Pennsylvania 
 Rhode Island 
 
 1,640,049 
 61,373 
 
 1,110,039 
 72,255 
 
 1,844,626 
 91,872 
 
 1,218,446 
 110,167 
 
 South Carolina 
 South Dakota 
 
 28,425 
 14,120 
 
 27,684 
 11 300 
 
 27,111 
 11 292 
 
 26,566 
 
 8487 
 
 Tennessee.. 
 
 345,765 
 
 264 288 
 
 441 298 
 
 369 296 
 
 Texas 
 
 196,051 
 
 119,218 
 
 269,151 
 
 164,865 
 
 Utah 
 
 16,000 
 
 19,200 
 
 6,500 
 
 3,750 
 
 Vermont 
 Virginia 
 
 17,978 
 1,931,852 
 
 13,563 
 1,185,271 
 
 14,929 
 
 2,193,898 
 
 13,269 
 1,538,149 
 
 Washington. 
 
 162,777 
 
 87 259 
 
 213 039 
 
 111 461 
 
 West Virginia 
 
 197,245 
 
 113 525 
 
 196,068 
 
 129,106 
 
 Wisconsin 
 
 1,000,667 
 
 635,618 
 
 914,295 
 
 555,927 
 
 Wyoming. . 
 
 
 
 
 
 
 
 
 
 
 
 21,786,833 
 
 13,329,365 
 
 22,710,070 
 
 13,735,546 
 
 198 
 
GRAVEL AND PAVING SAND PRODUCED IN 
 THE UNITED STATES IN 1914 AND 1915 
 
 R. W. Stone in "Mineral Resources of the United States, 1915" 
 
 STATE 
 
 PAVING SAND 
 
 ORAVEL, 
 
 1914 
 
 1915 
 
 1914 
 
 1915 
 
 Quantity 
 (short 
 tons) 
 
 Value 
 
 Quantity 
 (short 
 tons) 
 
 Value 
 
 Quantity 
 
 (short 
 tons) 
 
 Value 
 
 Quantity 
 (short 
 tons) 
 
 Value 
 
 Alabama 
 Arizona... . 
 
 5,849 
 
 $4,538 
 
 * 
 
 * 
 
 527,891 
 
 $138,693 
 
 547,656 
 
 * 
 
 831,668 
 2,974,090 
 
 * 
 16,518 
 
 22,848 
 
 * 
 
 * 
 4,424,527 
 2,482,922 
 1,554,199 
 
 448,897 
 * 
 854,180 
 270,906 
 2,457,094 
 935,252 
 991,119 
 1,656,745 
 7,422 
 118,970 
 17,491 
 
 583,200 
 2,112,557 
 
 * 
 
 2,828,887 
 77,241 
 
 * 
 
 2,816,132 
 
 368,797 
 1,814,902 
 
 239,649 
 540,653 
 1,494.421 
 251,216 
 
 * 
 
 519,850 
 478,707 
 114,273 
 1,567,840 
 
 1,551,719 
 
 $116,672 
 
 314,003 
 709,602 
 
 * 
 * 
 
 4,495 
 15,071 
 
 * 
 * 
 
 885,548 
 591,592 
 313,327 
 
 162,524 
 * 
 284,410 
 169,772 
 671,970 
 175,084 
 153,627 
 226,716 
 5,500 
 27,389 
 1,775 
 
 77,760 
 447,388 
 
 989,801 
 23,652 
 
 * 
 
 922,379 
 
 118,960 
 433,223 
 
 * 
 
 * 
 36,826 
 203,867 
 393,121 
 29,772 
 * 
 
 126,801 
 129,016 
 43.016 
 349,941 
 
 443,791 
 
 Arkansas 
 California 
 Colorado 
 
 106,578 
 
 26,714 
 
 
 
 673,924 
 3,258,718 
 7,610 
 
 278,876 
 595,449 
 3,310 
 
 173,985 
 
 $42,841 
 
 * 
 
 Connecticut.. . 
 Florida 
 Georgia 
 Hawaii 
 
 * 
 29,000 
 5,610 
 
 * 
 7,000 
 1,400 
 
 * 
 
 * 
 
 98,435 
 12,244 
 
 10,637 
 7,875 
 
 Idaho 
 
 
 
 
 
 * 
 4,955,219 
 4,184,093 
 1,087,967 
 160,283 
 815,796 
 738,510 
 
 760,204 
 177,642 
 2,140,359 
 637,900 
 1.500,291 
 1,321,839 
 13,310 
 88,026 
 
 670,000 
 
 2,204,880 
 
 * 
 
 2,149,310 
 311,059 
 10,875 
 2,417,805 
 505,737 
 611,821 
 1,766,651 
 
 29,927 
 196,909 
 445,504 
 1,183,646 
 184,763 
 822 
 294,398 
 457,137 
 455,804 
 1,294,893 
 718,441 
 
 142,215 
 
 * 
 
 793,422 
 602,533 
 205,820 
 19,512 
 208,770 
 190,717 
 
 268,338 
 50,795 
 530,338 
 236,704 
 354,855 
 257,827 
 11,970 
 16,435 
 
 112,500 
 672,433 
 
 891,762 
 42,438 
 5,725 
 654,833 
 225,559 
 137,221 
 
 387,845 
 
 * 
 
 4,995 
 25,603 
 183,296 
 433,399 
 45,162 
 390 
 87,379 
 162,183 
 125,618 
 343,230 
 48,245 
 
 26,205 
 
 Illinois 
 
 121,812 
 158,443 
 201,900 
 137,582 
 
 21,653 
 
 * 
 
 39,851 
 55,290 
 64,340 
 37,206 
 14,272 
 
 291,436 
 240,053 
 293,948 
 
 244,103 
 
 * 
 
 73,645 
 66,894 
 97,008 
 
 70,311 
 
 * 
 
 Indiana 
 Iowa 
 Kansas 
 Kentucky 
 Louisiana 
 Maine 
 
 
 Maryland 
 Massachusetts.. 
 Michigan 
 Minnesota 
 
 327,750 
 78,380 
 320,322 
 36,458 
 
 76,212 
 33,161 
 
 74,806 
 15,666 
 
 163,304 
 47,239 
 131,466 
 
 71,517 
 25,444 
 14,021 
 
 Mississippi 
 
 Missouri 
 Montana 
 Nebraska 
 Nevada 
 
 30,327 
 5,259 
 
 6,485 
 
 * 
 
 610 
 
 New Hamp- 
 shire. 
 
 
 
 
 
 New Jersey 
 New Mexico 
 
 110,260 
 
 39,902 
 
 160,256 
 51,363 
 
 53,599 
 
 * 
 
 21,240 
 
 New York 
 North Carolina 
 North Dakota. 
 Ohio 
 Oklahoma 
 
 82,725 
 
 34,148 
 
 
 
 
 
 407,025 
 
 134,370 
 
 501,359 
 
 194,026 
 
 Oregon 
 
 3,368 
 625,171 
 
 2,607 
 235,326 
 
 15,218 
 291,599 
 
 14,174 
 
 106,828 
 
 Pennsylvania. . . 
 Rhode Island... 
 South Carolina. 
 South Dakota. . 
 Tennessee 
 Texas 
 
 
 
 
 
 * 
 
 6,489 
 46,460 
 44,445 
 
 * 
 2,484 
 14,315 
 11,300 
 
 
 13,815 
 11,904 
 
 * 
 
 * 
 3,552 
 
 2,950 
 
 * 
 
 Utah 
 Vermont . 
 
 Virginia 
 
 * 
 
 363,745 
 44,617 
 . 222,298 
 
 * 
 
 86,796 
 17,819 
 71,560 
 
 83,827 
 69,598 
 206,094 
 
 27,628 
 27,230 
 67,340 
 
 Washington 
 West Virginia... 
 Wisconsin 
 Wyoming 
 
 Concealed 
 totals 
 
 36,645 
 
 13,761 
 
 391,150 
 
 97,138 
 
 
 3,580,171 
 
 1,121,999 
 
 3,381,717 
 
 1,077,346 
 
 39,212,858 
 
 9,398,897 
 
 37,972,548 
 
 9.598,391 
 
 Included in "Concealed totals.' 
 
 199 
 
THE REASONS FOR IMPROVING ROADS 
 
 Good roads are desirable for three distinct reasons, which may 
 be called social, business and pleasure reasons. 
 
 Social Benefits from Good Roads. The social reasons for road 
 improvements appeal to persons living in the country. The 
 women who dwell in the country districts know better than any 
 others what bad roads mean to themselves and their sisters on 
 other f atms, and how utterly drab and hopeless is life in the coun- 
 try with inadequate means of communication between themselves 
 and almost their next-door neighbors. The country parson can 
 tell what a handicap bad roads are in his work. Preaching two 
 sermons on Sunday is but a part of his labors. He must visit 
 his parishioners if he is to be the guide, counselor and friend he 
 aspires to be. He knows by hard experience the difficulty of 
 riding or walking over muddy roads and through oceans of slush 
 to those longing for his comforting presence in time of sickness 
 and death, and how hard it is to convey to those who are ill the 
 things necessary for their recovery. The country doctor can 
 likewise bear witness to the restraint and even suffering caused 
 by bad roads. Taking men as they are in the large, the wonder 
 is that there are any who would choose his profession, the most 
 devoted and consecrated of all that serve humanity. He comes 
 when he is called and where. His charity is unmeasurable, his 
 rewards are insignificant. Time with him and with the patient 
 waiting his aid is often the deciding factor between life and death; 
 he knows full well the death rate due to isolation by poor 
 highways. 
 
 We cannot state in percentages the increase in the satisfaction 
 of people with country life which follows the certainty a doctor 
 can be obtained when he is needed. It is not yet possible to 
 state in numerals how much better a man is for attending church 
 regularly or how much better a farmer's wife is for driving over a 
 good road whenever she wishes to call on her neighbors. But 
 there is one thing to which everybody will agree; the schools of 
 our rural territory are one of the great defenses of our national 
 prosperity, and the education of our children is one of our best 
 safeguards for the wise government of our republic. And so 
 everyone will admit the importance of these figures: In eight 
 typical rural counties studied by the U. S. Office of Public Roads 
 during a period of five years, the average school attendance in- 
 creased from 66 out of every 100 pupils enrolled before the roads 
 were improved, to 76 out of every 100 after the improvements. 
 
 200 
 
REASONS FOR IMPROVING ROADS 
 
 201 
 
 Ten per cent more children were helped, therefore, to become 
 better citizens by an increase in taxation for roads amounting to 
 only 9 per cent of the total tax for all purposes. 
 
 Business Benefits from Good Roads. The business advantages 
 of road improvements to the owner of a farm can be stated even 
 more definitely, for they can be measured in dollars and cents. 
 In the investigation by the U. S. Office of Public Roads, just 
 mentioned, the observations were carried out in New York, 
 Virginia, Alabama, Florida and Mississippi, in districts which 
 represent typical dairying, farming, mining and lumbering con- 
 ditions, before and after the construction of roads. The amount 
 of road improvements done in each of them, which produced the 
 improved conditions which will be stated, were as follows: 
 
 COUNTY 
 
 MILES 
 
 P ROADS 
 
 
 Total 
 
 Improved 
 
 Franklin, N. Y.. 
 
 1,370 
 
 369 
 
 Spotsylvania, Va. 
 
 400 
 
 83 
 
 Dinwiddie, Va 
 
 524 
 
 101 
 
 Lee, Va 
 Wise Va 
 
 450 
 300 
 
 105 
 146 
 
 Dallas, Ala 
 Manatee, Fla 
 
 1,000 
 575 
 
 218 
 64 
 
 Lauderdale, Miss 
 
 800 
 
 147 
 
 
 
 
 The investigations by the government's experts were not hasty 
 observations from a buggy or automobile; they were painstaking 
 searches through real-estate transfers, public records, railway 
 reports, school reports and like sources of information, studied on 
 the spot until their accuracy was fully established. They were 
 made from year to year, moreover, to make sure that the local 
 conditions were fully understood and the annual effect of a road 
 improvement was ascertained beyond question. 
 
 Real estate transfers showed that the percentage of increase 
 in the value of rural property along these improved roads in about 
 five years was as follows: Franklin, 9 to 114; Spotsylvania, 63 to 
 80; Dinwiddie, 68 to 194; Lee, 70 to 80; Wise, 25 to 100; Dallas, 
 50 to 100; Manatee, 50 to 100; Lauderdale, 25 to 50. The 
 transfers on which these figures are based are mostly for prop- 
 erty within a mile of the improved roads. 
 
 In each county the extent of the districts sending vehicles to 
 the improved road was carefully determined in much the same way 
 that the drainage area of a stream is ascertained. The products 
 of these districts and the proportion of them hauled over the 
 roads were then ascertained. The railway shipments from and 
 
202 AMERICAN HIGHWAY ASSOCIATION 
 
 into the districts were investigated. In case of doubt the actual 
 travel on the roads was ascertained by counts of the vehicles and 
 their loads. The average length of the haul on the roads was 
 found out. From all these statistics, given in detail in the report, 
 it is shown that the cost of hauling one ton one mile on the roads 
 of these counties was decreased from an average of 33.5 cents 
 before highway improvements were made to 15.7 cents after- 
 ward. This saving of 17.8 cents per ton per mile amounts to 
 $627,409 in all. To accomplish it the additional taxes amounted 
 to only 6.3 cents per ton per mile, leaving a net saving of 11.6 
 cents per ton per mile. 
 
 Roads as Sources of Enjoyment. It is unfair to object to includ- 
 ing the pleasure obtained by riding comfortably through the 
 country as one of the returns we receive from our road taxes. 
 It is just as proper to include that kind of pleasure as a justifiable 
 object of expenditure as the investments for liquors, tobacco, the 
 theatre and confectionery. E. W. James, one of the road experts 
 of the United States government, recently made the following 
 statement on the subject: 
 
 The people of the United States spent in 1915 $2,500,000,000 for spiritu- 
 ous and malt liquors $800,000,000 for tobacco, $450 000,000 for the "mov- 
 ies," $300,000,000 for candy, $200,000,000 for soda water and $50,000,000 
 for chewing gum. The total for these pleasures is $4,300,000,000. So I 
 think it conservative to say that the average man is willing to pay some- 
 thing for pleasure. There can be no question about the pleasure derived 
 from riding on good roads, and that a part of the money invested in such 
 roads can be logically justified on the score of this pleasure. After all, 
 the total annual expenditures on roads in the United States is only equal 
 to our purchase of candy and merely one-eighth of the money spent on 
 liquor. 
 
 The Townsman's Interest in City Roads. When the average 
 townsman dresses in the morning, a large part of the clothes he 
 puts on are made of cotton, which has to be teamed over a good 
 many miles from the plantations to the shipping points. If he 
 has fruit, cereal, eggs and toast for breakfast, let us say, about 
 everything he eats has been hauled over several miles of roads, 
 either to be shipped to him or to the mills where it is prepared for 
 shipment. A large part of the furniture in his home and at his 
 office has been made from hardwood hauled over the roads. 
 These and other things which anybody can list for himself must 
 all vary in price to the townsman with the cost of hauling them 
 from the farms and forests to the mills or railroad stations. Just 
 what this fact means has been stated by J. E. Pennybacker, the 
 highway economist of the United States Office of Public Roads, 
 as follows: 
 
REASONS FOR IMPROVING ROADS 203 
 
 The public roads throughout the country, which constitute the primary 
 means of transportation for all agricultural products, for many millions 
 of tons of forest, mine and manufactured products, and which for a large 
 percentage of farmers are the only avenues of transportation leading from 
 the point of production to the point of consumption or rail shipment, 
 have been improved to only a slight extent. By reason of this fact, the 
 prevailing cost of hauling over these roads is about 23 cents per ton per 
 mile. More than 350,000,000 tons are hauled over these roads each year, 
 and the average haul is about 8 miles, from which it can readily be seen 
 that our annual bill for hauling over the public roads is nearly $650,000,000. 
 The cost per ton-mile for hauling on hard surfaced roads should not exceed 
 13 cents. It is therefore evident that if our roads were adequately im- 
 proved a large annual saving in the cost of hauling would result. 
 
 The difference between 23 and 13 cents is 10 cents, which is 
 the ton-mile tax of poor roa,ds which the city people pay, for most 
 of the hauling is toward markets or shipping points and the cost 
 of this hauling is part of the total expense of products of the land 
 to the consumer. The total is about $280,000,000, which the 
 45,000,000 people living in the cities and towns of the United 
 States pay annually on account of poor roads. This averages 
 over $6 a year per person. 
 
 Poor roads put a much more serious drain on the townsman's 
 pocket-book, however. His food is costing him more every year, 
 and he therefore has a very close, personal interest in having the 
 agricultural lands farmed in such a way that they yield their 
 largest returns at the lowest working cost. This means more 
 than producing milk and vegetables at a low cost; it also includes 
 raising at low expense the wheat and corn from which his flour 
 and meal are made, producing fowls and hogs economically, and 
 reducing the cost of growing cotton. How many intelligent 
 young men, able to earn a good living in a city, will live in the 
 country if they have to travel through miles of mud or dust, at 
 decided physical discomfort, in order to market their products, 
 meet their friends or buy their supplies? How many young 
 women will be willing to live in the country where bad roads 
 isolate them, with only the sparrows for companions, with the 
 doctor almost inaccessible, the schools difficult for the children 
 to reach, and church-going a real labor? Yet if the townsman is 
 to have the things he eats grown for him efficiently and economi- 
 cally he must take his part in making country life agreeable and 
 profitable to these intelligent young people. It means a saving 
 of dollars and cents to him. 
 
 Our American Roads. The length of the rural roads in the 
 United States at the close of 1915 is given in the table on page 
 192. This table shows that only 11.3 per cent of the total mile- 
 age at that time had been surfaced, and that only 2 per cent had 
 
204 AMERICAN HIGHWAY ASSOCIATION 
 
 been built by the state highway departments or with more or less 
 financial or engineering assistance from the states. 
 
 It has been estimated that about 80 per cent of the total travel 
 on these roads is done on about 15 per cent of their total length. 
 The percentages vary in different states. The Iowa Highway 
 Commission found that from 10 to 15 per cent of the roads of each 
 county are main traveled routes, which it is proper to construct 
 and maintain, under the Iowa highway laws, at the expense of 
 the county as a unit. The remaining roads are of less general 
 use and are constructed and maintained by the townships through 
 which they pass. 
 
 This division of our highways into main routes and local roads 
 is of fundamental importance in road administration. Public 
 money must be used so as to yield the greatest good to the great- 
 est number of people. But it is human nature for a man living 
 a mile or more from a main road to complain that he is unfairly 
 treated if he must travel over a dirt road part of the way to town 
 while a neighbor has a good, hard-surfaced road running by his 
 place. As a matter of fact, although the hard road does not 
 reach his farm it does help him materially, as Prof. B. K. Cogh- 
 lan, of the Texas Agricultural and Mechanical College has 
 shown by a recent investigation. He reports: 
 
 Where a farmer lives at a considerable distance from the improved 
 road he will still derive some benefit. In one county, where the gravel 
 roads extend only about 8 miles from town, the farmers living several 
 miles beyond haul wood during the dry spells and pile it at the end of the 
 gravel road; then when bad weather comes and it is impossible to work in 
 the fields they haul this wood to town. In another case two teams are 
 used until the improved road is reached, when one team is unhitched and 
 left with a friend, and the man proceeds to town with the other. In a 
 third instance, where it formerly took two days to haul a load to market, 
 since a good road has been built for about one-half of the distance, two 
 wagons, with two teams each, haul one day until the good road is reached 
 when all the load is put on one wagon, which proceeds to town with one 
 team, the other three teams returning home. 
 
 Our main roads which carry four-fifths of the traffic present 
 problems which are often quite different from those of the local 
 roads. Highways must be built to carry the traffic over them at 
 the lowest possible cost for both construction and maintenance. 
 Where the traffic is light, as on local roads and some main roads, 
 comparatively inexpensive types of construction can be main- 
 tained at small expense and are therefore better than more ex- 
 pensive types because more miles of them can be provided for 
 the same total cost than is the case with expensive types of con- 
 struction. As a rule, however, we are trying to get too much 
 work from inexpensive roads and at the same time we are neglect- 
 
REASONS FOR IMPROVING ROADS 205 
 
 ing to maintain them in a condition for giving the most service. 
 For many years to come, a large part of our roads will be earth, 
 top-soil, sand-clay and gravel. That is no reason, however, for 
 their being mud holes in wet weather or sources of blinding dust 
 in dry weather. Well graded, drained and maintained roads of 
 these types are pleasant to ride over and inexpensive to maintain, 
 unless they are called upon to carry more travel than they are 
 capable of supporting. Then they fail just as a beam fails when 
 it is overloaded. The beam is ajl right for a given loading, but 
 all wrong for a greater one. A road may be all right for a certain 
 travel but all wrong for a greater travel; the failure to recognize 
 this is responsible for a large part of the waste of road taxes 
 today. 
 
 Different Classes of Road Improvements. The improvement of 
 roads comprises a number of classes of work. People who speak 
 of road improvements in Missouri probably refer to grading and 
 draining, while road improvements in Massachusetts usually 
 signify the construction of a hard surface on a road already 
 graded and drained. Such use of the word "improvements' 7 
 indicates how varied are the really pressing highway needs of 
 different parts of the country and the importance of studying the 
 local resources and transportation requirements of a district be- 
 fore planning the improvement of its roads. 
 
 The first thing to be considered in planning good roads is the 
 amount of money which it is wise for a community to spend for 
 them. Most estimates of this nature are based on the existing 
 annual tax receipts available for the purpose. This is not the best 
 basis for a sound judgment. A family of three persons can make 
 an income of $1800 go farther than a family of six persons can. It 
 is the same with rdads. To find out roughly how much money 
 can be devoted to road work it is best to divide the assessed valu- 
 ation of the district by the miles o roads in it. This gives the 
 valuation, or taxable wealth, of the district per mile of road. 
 For instance, Lake County, Mich., has a valuation of only $5420 
 per mile, showing that not even the entire wealth of the county 
 is sufficient to improve all its roads. Wayne County, Mich., on 
 the other hand, has a valuation of $514,931 per mile, indicating 
 its financial ability to carry out any kind of road improvements 
 in reason. In a rich agricultural district like Calhoun County, 
 Mich., the valuation is $52,294 per mile, indicating that it is 
 financially able to construct whatever kind of main roads may 
 be best suited for the travel on them. We look with pity on the 
 young saleswoman who spends all her money on clothes she does 
 not need, and yet we complain when a county with a very low 
 valuation per road-mile is not intersected with roads as smooth 
 
206 AMERICAN HIGHWAY ASSOCIATION 
 
 as the top of a billiard table. This shows that we have our fool- 
 ish ideas, like the flighty saleswoman. 
 
 There is a measure of the need for roads, just as there is a 
 measure of the financial resources for roadbuilding. This meas- 
 ure is the travel the road is carrying now and the probable in- 
 crease in the travel during the next five to ten years. The im- 
 provement of a country road results in the slow development of 
 property along it, so that there is a slow annual increase in 
 what is called the residential travel. If the road is on a through 
 route between important cities some distance apart, there may 
 or may not be a material increase in the foreign travel, by which 
 is meant the travel between these cities. This can only be de- 
 termined by a study of local conditions. The residential travel 
 can be actually counted, however, and this ought to be done. 
 The state highway department or the United States Office of 
 Public Roads and Rural Engineering at Washington will furnish 
 instructions for the work, which can be done by school children 
 under the direction of their teachers. This is a kind of child 
 labor which no reformer will weep over and the efficiency expert 
 will approve. 
 
 The travel over a road wears it out in different ways, according 
 to the number and character of the vehicles, the relative propor- 
 tion of horse-drawn vehicles and automobiles, the climatic con- 
 ditions and the construction of the road. For the same travel, 
 a road adopted for a moist section with cold winters is needlessly 
 expensive for a dry section with little frost. Some types of roads 
 wear out quickly but are easily maintained, other types with- 
 stand travel well but when they need repairs the work is expen- 
 sive. All these things must be considered in determining the 
 annual cost of a road, which is done in the following way. 
 
 The first element of this cost is the first cost of construction per 
 mile of road, including all engineering expenses. Knowing the 
 travel over the road, an expert can estimate the number of years 
 such a road will serve its purpose, if properly maintained, before 
 reconstruction is necessary. This cost divided by the number of 
 years of service gives the annual first cost. To this must be added 
 the annual interest on the first cost per mile. If the construction 
 costs are met by the proceeds of a bond issue, the interest and 
 sinking fund charges on the bonds take the place of the annual 
 first cost and interest just mentioned. The annual cost per mile 
 of maintaining the road in serviceable condition is the last item 
 to be estimated. The sum of all these items is the total annual 
 cost per mile of the road, and this figure is the most important 
 one to the taxpayers. But another unit for measuring cost, 
 which is sometimes very useful, is the cost of the road per vehicle 
 mile. This is obtained by dividing the total annual cost per 
 
REASONS FOR IMPROVING ROADS 207 
 
 mile by the number of vehicles using the road annually. The 
 type of construction which gives the lowest cost per vehicle mile 
 is generally the best to employ. 
 
 While the preceding notes explain the steps to be taken in 
 planning a good road, they cannot supply the good judgment 
 necessary to take the steps wisely. We admire the skill of a 
 slack-rope gymnast but we are not foolish enough to emulate 
 him. The skill and knowledge needed to select the right type of 
 construction for a road are greater than those required by the 
 slack-rope performer, and yet our minds are so warped by con- 
 stant use of roads that we are strongly inclined to think we are 
 able to do the work of road engineers. W e wn ^ ^ e losing money 
 in our road planning until we stop this foolishness. 
 
INDEX 
 
 Absorption of water by earth, 20 
 Accidents, on roads, 25 
 Aggregates for concrete, 93 
 Alabama, road mileage, 192, 193, 194 
 Andesite, 76, 87 
 
 properties, 77 
 Annuity bonds, 187 
 Appalachian oil fields, 110 
 Arid regions, roads, 46 
 Arizona, funds for roads, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Arkansas, funds, 193, 195 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Aspha-bric, 176 
 Asphalt, see Bitumen 
 
 Bermudez, 120 
 
 blocks, 148 
 
 California, 122 
 
 Cuban, 122 
 
 definitions, 117 
 
 Maracaibo, 122 
 
 Mexican, 122 
 
 mixers, 145 
 
 natural, 118 
 
 oil, 118 
 
 Trinidad, 118 
 Asphaltenes, 116 
 Augite, 321 
 
 Automobile accidents, 25 
 Automobile registration, 193 
 
 Banking curves, 230 
 Basalt, 75, 87 
 
 properties, 76 
 Base, see Foundation 
 Belts for finishing concrete, OT 8 
 Berm ditches, 22 
 Bermudez asphalt, 120 
 Binders, bituminous, 124 
 
 clay, 51, 52, 53, 56, 58 
 
 glutrin, 72 
 
 gravel and screenings, 71 , 72 
 
 iron oxide, 51 
 
 rock powder, 53 
 Biotite, 83 
 Bitumen, definition, 117 
 
 ductility, 126 
 
 fixed carbon, 116 
 
 float test, 125 
 
 fluxing solid, 123 
 
 gilsonite, 122 
 
 grahamite, 123 
 
 hydrocarbons, 116 
 
 inorganic matter, 116 
 
 insoluble organic matter, 116, 121 
 
 manjak, 123 
 
 native solid, 117 
 
 paraffin, 116 
 
 penetration, 121 
 
 solid, semi-solid and liquid, 117 
 
 solubility in carbon disulphide, 114 
 
 in carbon tetrachloride, 122 
 
 in naphtha, 116 
 
 viscosity, 125 
 Bituminous fillers for joints, 173 
 
 Bituminous roads, 138 
 
 concrete, 144 
 
 macadam, 139 
 Blasting, 38 
 Blowing oils, 114, 116 
 Bonds, 180 
 Box, 57, 60, 69 
 Brick, paving, 157 
 
 cubical, 176 
 
 impregnated with asphalt, 176 
 
 production, 196, 197 
 Brick roads, 157 
 
 on 1-inch concrete base, 178 
 Bridges, 34 
 
 avoided by relocation of roads, 2 
 
 overflow, 36 
 
 size of waterways, 254 
 Byerly process of blowing oils, 114 
 
 Calcite, 84 
 Calcium chloride, 74 
 California asphalt, 122 
 
 banking curves, 9 
 
 funds for roads, 193 
 
 motor cars, 195 
 
 oil, 110 
 
 regulations regarding surveys and plans, 12 
 
 road mileage, 192, 194 
 Carbon disulphide test for bitumens, 114 
 Catchbasins, 29 
 Cement, standard specifications for Portland, 
 
 107 
 Cementing value of rock powders, 85 
 
 test, 86 
 Chert, 75, 88 
 Chlorite, 84 
 Clay, absorption and retentivity, 20 
 
 for sand-clay roads, 47 
 
 slope in cuts and fills, 5 
 Clearing right-of-way, 39 
 Colorado, funds for roads, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Concrete, cement, curing, 103 
 
 expansion and contraction, 100 
 
 finishing, 102 
 
 mixing, 97, 101 
 
 placing, 98 
 
 proportions, 95 
 
 quantities of sand, cement and stone re- 
 quired for roads of different widths and 
 thicknesses, 96, 97 
 Concrete, bituminous, 144, 155 
 Concrete roads, 90 
 
 surfacing, 154 
 Connecticut, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Contracts, plans for, 4 
 Costs per mile corresponding to different 
 
 costs per square yard, 70 
 Cross-drains, 27, 91 
 Cross-sections of roads, concrete, 92 
 
 influence on drainage, 20 
 
 Wisconsin standards, 6 
 Crown of roads, 21, 92 
 Crushing gravel, 54 
 
 rock, 66 
 
 209 
 
210 
 
 INDEX 
 
 Cuban asphalt, 122 
 Culverts, 32 
 
 avoided by relocation, 23 
 
 driveway, 26 
 
 headwalls, 33 
 
 size, 29 
 Curbs, 162 
 Curves, 8, 9 
 Cushion for brick, 165 
 Cut-back bituminous products, 133 
 Cuts, 38, 42 
 
 Deferred serial bonds, 188 
 Delaware, road mileage, 192, 194 
 
 funds, 193 
 
 motor cars, 195 
 Deval test, 86 
 Diabase, 75, 87 
 
 properties, 77 
 Diorite, 75, 87 
 
 properties, 77 
 Distillation test of tar, 137 
 Distributors of oil, 142 
 Ditches, 24 
 
 accidents by ditching vehicles, 26 
 
 berm ditches, 22, 24 
 
 marsh-road, 21 
 
 outlets, 22, 26 
 
 recommendations of American Railway En- 
 gineering Association, 23 
 
 steep grades, 19, 25 
 
 summits in, 25 
 
 water brakes, 25 
 Dolomite, 84, 87 
 
 properties, 80 
 Dragging, earth roads, 43 
 
 embankments during construction, 40, 43 
 
 gravel roads, 56, 57, 63 
 
 road plane, 40 
 
 sand-clay roads, 49 
 Drainage, 19, 68, 91 
 
 size of culverts, 30 
 Driveway culverts, 26 
 Dubbs process of refining petroleum, 113 
 Ductility test of bitumens, 126 
 Dumping boards, 70, 141 
 Dun's culvert formula, 31 
 Durax pavements, 176 
 
 Earth roads, 32 
 
 oiling, 146 
 Embankments, 39, 42 
 
 accidents on, 25 
 
 building in layers, 39, 90 
 
 drainage, 23, 24, 29 
 
 in flat country, 22 
 
 in marshes, 21 
 
 protection against scouring, 28, 33 
 
 slopes, 5 
 Engineering, bridge, 35 
 
 importance in road work, 3 
 
 regulations of California commission re- 
 garding surveys and plans, 12 
 
 Excavation, 38 
 Expansion joints, 99, 174 
 
 Feather-edge gravel and broken stone roads, 57 
 
 Feldspar, 83 
 
 Fillers for joints, 99 
 
 Fills, see Embankments 
 
 Finishing concrete surfaces, 102 
 
 Flash point of oils, 114 
 
 Float test of bitumens, 125 
 
 Florida, funds for roads, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Fluxes, 116, 123 
 Fords, 36 
 
 Forms for concrete roads, 99 
 Foundations, brick roads, 163 
 
 bridges, 35 
 
 concrete roads, 90 
 
 culverts, 33 
 
 gravel roads, 67, 60 
 
 macadam roads, 68 
 
 on sand, 55 
 
 steep grades, 20 
 
 telford, 27, 68 
 
 French coefficient of wear, 86 
 Funds for road work in the different Stated, 193 
 
 Gabbro, 75, 87 
 
 properties, 78 
 Garnet, 83 
 Georgia, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Gilsonite, 122 
 Glutrin, 62, 72 
 Gneiss, 75, 88 
 
 properties, 82 
 Grade crossings, 9 
 Graders, 40 
 
 elevating, 42 
 
 gravel roads, 56, 58, 60 
 
 sand-clay road uses, 49 
 Grades, 1, 4, 11 
 
 effect on traction, 4 
 
 improved by relocation, 3 
 Grading, 38, 40 
 
 light cuts on hard roads, 5 
 Giahamite, 123 
 Granite, 75, 87 
 
 properties, 79 
 Gravel bed, 57 
 Gravel, crushing, 54 
 
 for concrete roads, 94 
 
 length of road which a load of gravel of 
 given size will cover to given loose depths, 
 61 
 
 mechanical analysis, 53 
 
 production, 199 
 
 quantity of loose gravel for a mile of road of 
 different widths and thicknesses, 55 
 
 quantity required to give different depths 
 when lying loose on a mile of road of 
 different widths, 55 
 
 road-building grades, 51, 57 
 
 screening, 54, 59 
 
 spreading, 61 
 
 weight, 56, 62 
 Gravel roads, 51 
 Gravel^asphalt roads, 147 
 Grout joints for brick, 171 
 Grubbing right-of-way, 39 
 Guard rails, 25 
 Gulfoilfield.llO 
 
 Hardness, test for, 85, 121 
 Harrowing, bituminous macadam, 141 
 
 broken stone roads, 71 
 
 gravel roads, 56, 58 
 
 Heating binders and road oils, 130, 142, 145 
 Highway maintenance, see Maintenance of 
 
 Roads 
 
 Hillside brick, 159 
 Hornblende, 83 
 Hydrocarbons, 109, 116 
 
INDEX 
 
 211 
 
 Idaho, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Illinois, bituminous roads, 141, 142, 144, 145 
 
 brick roads, 161, 167, 169, 178 
 
 funds, 193 
 
 gravel roads, 52, 57 
 
 motor cars, 195 
 
 oil field, 110 
 
 road mileage, 192, 194 
 Indiana, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Inorganic matter in bitumen, 116 
 Iowa, automobile accidents, 25 
 
 funds for roads, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 
 Joints, brick roads, 169, 171 
 
 concrete roads, 99 
 Joint fillers, 99, 175 
 
 Kansas, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Kaolin, 84 
 Kentucky, funds, 193 
 
 motor cars, 195 
 
 organization for road dragging, 45 
 
 road mileage, 192, 194 
 
 Layers in embankments, 39 
 Lima-Indiana oil fields, 110 
 Limestone, 84, 87 
 
 properties, 79 
 Loam, absorption and retentivity, 20 
 
 slopes in cuts and fills, 5 
 Location of roads, 1 
 
 at grade crossings, 10 
 Loss by volatilization of oils, 114 
 Louisiana, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 
 Macadam roads, bituminous, 139 
 
 water-bound, 64 
 
 surface treatment, 152 
 Magnetite, 83 
 Maine, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Maintenance, bad roads, 1 
 
 bituminous roads, 153 
 
 concrete roads, 104 
 
 dragging, 43 
 
 earth roads, 43 
 
 gravel roads, 62 
 
 macadam roads, 73 
 
 sand-clay roads, 50 
 Malthenes. 116 
 Manjak, 123 
 Maps, California commission regulations, 16 
 
 Vermillion County improvements, 4 
 Maracaibo asphalt, 122 
 Marble, 75, 88 
 
 properties, 81 
 Marshes, roads across, 21 
 Maryland, bituminous concrete, 145 
 
 brick roads, 175 
 
 funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Massachusetts, bituminous roads, 140, 144 
 
 funds, 193 
 
 gravel-asphalt roads, 147 
 
 Massachusetts, motor cars, 195 
 
 road mileage, 192, 194 
 Mastic joint fillers, 174 
 Mexican asphalt, 119, 122 
 Mica, 83 
 Michigan, funds, 193 
 
 gravel for roads, 51 
 
 motor cars, 195 
 Michigan, road mileage, 192, 194 
 
 water-bound macadam, 64 
 Mid-continent oil fields, 110 
 Mileage of roads, 192, 194 
 Minerals in road building rocks, 83 
 Minnesota, funds, 193 
 
 motor cars, 195 
 
 water-bound macadam, 64 
 
 road mileage, 192, 194 
 Mississippi, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Missouri, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 
 Mixers for bituminous concrete, 341, 391, 400 
 Mixers for concrete, 97, 101 
 Mohs, scale of hardness, 83 
 Monolithic brick roads, 167 
 Montana, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Motor trucks, road widths needed for, 7 
 Muscovite, 83 
 
 Nebraska, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Nevada, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 New Hampshire, funds, 193 
 
 gravel roads, 63 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 New Jersey, broken stone specification*, 98 
 
 funds, 193 
 
 gravel for roads, 51 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 
 telford specifications, 68 
 New Mexico, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 New York, bituminous roads, 141, 145 
 
 brick roads, 161 
 
 funds, 193 
 
 grade crossing regulations, 10 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 
 telford specifications, 68 
 
 water-bound macadam, 64, 67, 153 
 North Carolina, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 North Dakota, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Note-keeping on surveys, 12 
 Nozzles for road oil, 142 
 
 Ohio, bituminous macadam, 141 
 brick roads, 161, 168, 173 
 funds, 193 
 macadam, 67 
 motor cars, 195 
 road mileage, 192, 194 
 
212 
 
 INDEX 
 
 Oiling roads, 150 
 
 gallons of bituminous material per mile 
 of road for different rates of application, 
 140 
 
 gravel, 63 
 
 macadam, 74 
 Oils, classification, 109 
 
 equivalent volumes at different tempera- 
 tures, 131 
 
 classification, 109 
 
 road, 124, 135 
 
 shipping, 128 
 
 specific gravity, weight and volume at 60, 
 
 129 
 Oklahoma, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Oregon, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Orthoclase, 83 
 Outlets, ditches, 22, 26 
 
 drains, 29 
 
 Paraffin, 109, 116 
 
 Patrol system of maintenance, 297 
 Penetration roads, 126, 139 
 Penetration test of bitumens, 121 
 Pennsylvania, bituminous roads, 141, 153 
 
 brick roads, 161, 167, 175 
 
 funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Petroleum, 109 
 
 specific gravity, degrees Baume 1 , weight 
 
 and volume at 60, 112, 129 
 Pipe culverts, 33 
 Plagioclase, 83 
 Plans, Vermilion C9unty improvements, 4 
 
 California commission regulations, 16 
 Plowing, in grading, 38 
 
 sub-grades, 60 
 
 Ponding concrete roads, 96, 104 
 Pouring cans, 143 
 Pumping road oil, 128 
 Pyro-bitumens, 118 
 
 Quartz, 83 
 Quartzite, 88 
 properties, 81 
 
 Rattler test, 160 
 
 Refining petroleum, 111 
 
 Residuums, 114 
 
 Resistance of roads to traction, 189 
 
 Retentivity of clay, loam, etc., 20 
 
 Rhode Island, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Rhyolite, 75, 87 
 
 properties, 78 
 Rights-of-way, 7 
 
 clearing and grubbing, 41 
 Road machines (graders), 40 
 Roadbed, elevation for drainage, 22; grading, 
 
 38,60 
 
 Road plane, see Dragging 
 Roads, asphalt block, 148 
 
 bituminous, 138 
 
 brick, 157 
 
 concrete, 90 
 
 costs per mile corresponding to different 
 costs per square yard, 70 
 
 dragging, 44 
 
 drainage, 19 
 
 earth, 37 
 
 Roads, grade crossings, 9 
 
 grades, 4 
 
 gravel, 51 
 
 gravel-asphalt, 147 
 
 location, 1 
 
 macadam, bituminous, 138 
 
 water-bound, 64 
 
 maintenance, 1, 43, 50, 62, 73, 104, 153 
 
 mileage, 193, 195 
 
 resistance to traction, 189 
 
 sand-clay, 47 
 
 sand-oil, 147 
 
 sections, 6, 21 
 
 semi-arid regions, 46 
 
 top-soil, see Sand-clay 
 
 widths, 6, 21, 92 
 Rock crushing, 66 
 Rock for roads, see Stone 
 Rolling roads, earth, 43 
 
 gravel, 58 
 
 macadam, bituminous, 62, 63, 146 
 
 sand-clay, 49 
 
 water-bound, 71, 72 
 Runoff, factors influencing, 30 
 
 Sand, absorption and retentivity, 20 
 
 for concrete, 93 
 
 for cushion for brick, 166 
 
 production of paving, 199 
 
 slopes in cuts and fills, 5 
 
 weight, 56 
 
 Sand-asphalt roads, 147 
 Sand-clay roads, 47 
 Sandstone, 75, 87 
 
 properties, 80 
 Schist, 75, 84, 88 
 
 properties, 82 
 Scrapers for grading, 38 
 Screening gravel, 59 
 
 rock, 67 
 
 Seal coats, 139, 144, 146 
 Section-line roads, 2 
 Serial bonds, 187 
 Shale, 75, 88 
 Shoulders, gravel roads, 58 
 
 macadam roads, 72 
 
 concrete roads, 92 
 
 bituminous roads, 142 
 Shrinkage of embankments, 40 
 Silt, absorption and retentivity, 20 
 Single-track roads, 7, 92 
 Sinking fund bonds, 185 
 Slag, 89 
 Slaking clay, 47 
 
 rock powder, 85 
 Slate, 75, 88 
 Slopes of cuts and fills, 5 
 
 protection, 26, 33 
 South Carolina, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 South Dakota, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Specific gravity determinations of oil, 114 
 Steam shovels, 38, 
 Stone, crushed, see Rock 
 
 length of road which a load of stone of given 
 size will cover to given loose depths , 61 
 
 production, 198 
 
 quantity required to give different depths 
 when lying loose on a mile of roadway of 
 different widths, 55 
 
 sizes, 67 
 
 weight, 66 
 Stone, for bituminous roads, 138, 141, 144 
 
INDEX 
 
 213 
 
 Stone, for concrete roads, 93, 96 
 
 for water-bound macadam, 64 
 
 mineral composition, 75 
 
 physical properties and tests, 85 
 Straight-run bituminous products, 133 
 Streak of minerals, 121 
 Sub-grades, brick roads, 163 
 
 concrete roads, 90 
 
 gravel roads, 60 
 
 macadam roads, 69 
 Summits in ditches, 25 
 
 on roads, 5 
 Surfacing roads with bituminous materials, 
 
 150 
 
 Surveys, regulations of California commis- 
 sion, 12 
 Swamp roads, 21 
 
 Talbot's culvert formula, 30 
 Tar and tar products, 132 
 Telford foundations, 27 
 Tennessee, funds, 193 
 
 motor cars, 195 / 
 
 road mileage, 192, 194 
 Texas, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Tile drains, 27 
 
 Top soil roads, see Sand-clay Roads 
 Toughness, test for, 85 
 Traction, effect of grades, 4 
 
 resistance of roads to, 189 
 Tractors, 41, 100 
 Trap, 83, 84, 87 
 
 Trench, for gravel and broken stone, 57, 60, 69 
 Trinidad asphalt, 118 
 Trumbull process of refining petroleum, 113 
 
 Underdrains, 27 
 for embankments, 23 
 size, 24 
 
 Underpasses on New York highways, 10 
 Utah, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 
 V-drains, 27 
 Vermont, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Vertical curves, 5 
 Virginia, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Viscosity of bitumens, 125 
 Volatilization test of oils, 114 
 
 Wagons, 38 
 
 spreader, 70 
 Washington, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Water-bound macadam roads, 64 
 Water-brakes, 25 
 Water for concrete, 101 
 Wear of rocks, test, 86 
 Weathering of rocks, 85 
 Wentworth's culvert formula, 32 
 West Virginia, funds, 193 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 Width of roads, 5, 92 
 
 at grade crossings, 10 
 Wisconsin, funds, 193 
 
 gravel roads, 59 
 
 motor cars, 195 
 
 road mileage, 192, 194 
 
 standard road sections, 5 
 
 water-bound macadam, 64, 67 
 Wyoming, funds, 193 
 
 motor cars, 195 
 
 oil, 111 
 
 road mileage, 192, 194 
 
ANNOUNCEMENTS 
 
 215 
 
INDEX TO ANNOUNCEMENTS 
 
 Asphalts and Allied Substances by Herbert Abraham 226 
 
 Asphalts by T. H. Boorman ... 220 
 
 American Ballast Co 224 
 
 Atlas Portland Cement Co 218 
 
 Barber Asphalt Paving Co., The ... 217 
 
 Barrett Company, The 219 
 
 Boorman, T. Hugh 220 
 
 Clark, Edward A 220 
 
 Granite Paving Block Manufacturers Assn. of the U. S. A. Inc 222 
 
 Hastings Pavement Co. Inc., The 223 
 
 Koehring Machine Co 225 
 
 New York Mastic Works 220 
 
 Robeson Process Co 220 
 
 Societa Sicula per Pesplotazione dell' Asfalto naturale Siciliano. 224 
 
 Spencer, W. B 220 
 
 Union Oil Co. of California 220 
 
 Van Nostrand Co., D 220, 226 
 
 Willite Road Construction Co. of America, Inc. . . .221 
 
 21G 
 
The Standard of Comparison 
 for Paving and Road Materials 
 
 To claim that a paving or road-building material is as good 
 as Trinidad or Bermudez asphalt is considered the strongest 
 endorsement that can be brought forward. 
 
 But the materials for which this claim is made are usually 
 new and untried, and year after year one "Just-as-good-as- 
 lake-asphalt" follows another into oblivion. 
 
 Bermudez Trinidad 
 
 Road Asphalt Lake Asphalt 
 
 Meanwhile the use of the lake asphalts steadily increases, 
 and their position as the standard materials by which all 
 others are judged is more firmly fixed (1) by the continued 
 good service of natural asphalt roads and pavements, some 
 of which, though 30 years old, are in service today; and (2) 
 by the duplication of unfortunate experience with artificial 
 or manufactured asphalt. 
 
 Engineers and officials with reputations to preserve, and 
 taxpayers whose money is to be spent may well consider also 
 that even if there was any material for paving and road- 
 building equaling the lake asphalts in stability, dependability 
 and long life, it would take 30 years to prove it. 
 
 THE BARBER ASPHALT PAVING 
 COMPANY 
 
 PHILADELPHIA PENNSYLVANIA 
 
 217 
 
SEND FOR THIS FREE BOOK 
 
 A practical BOOK for engineers, contractors and 
 public officials. Obtain your copy by writing the 
 Service Department of 
 
 The Atlas Portland Cement Company 
 
 Member of Portland Cement Association 
 
 30 Broad St., New York Corn Exchange Bank Bldg., Chicago 
 
 Phila. Boston St. Louis Minneapolis Des Moines Dayton Savannah 
 
 218 
 
The Company 
 
 Road Materials, Etc. 
 
 The Barrett Company has a record of forty years in fur- 
 nishing paving materials. Its experience and reputation 
 gained through the years are coupled with progressiveness. 
 Its engineers and chemists are constantly at work on the 
 solution of new problems. Each year marks a distinct 
 advance. 
 
 Barrett materials combine knowledge and experience. 
 
 "Tarvia-X" is used as a binder in the construction of mac- 
 adam roads. 
 
 "Tarvia-A" and "Tarvia-B" are used for maintenance on 
 many kinds of roads. 
 
 Barrett's Paving Pitch is used as a filler on stone block, 
 wood block and brick paving. Special grades are made to meet 
 every requirement and a new mastic filler has been developed for 
 use in stone and brick pavements. 
 
 Barrett's Carbosota Creosote Oil is designed for preserv- 
 ing all timber used in highway fences and bridges. 
 
 Barrett's Ever jet Paint is a black paint designed for pro- 
 tecting exposed ironwork. 
 
 Booklets and particulars on request 
 
 The Company 
 
 New York Chicago Philadelphia Boston St. Louis Cleveland 
 
 Cincinnati Pittsburgh Detroit Birmingham 
 
 Kansas City Minneapolis Salt Lake City Seattle Peoria 
 
 THE BARRETT COMPANY, LIMITED: Montreal Toronto Winnipeg 
 
 Vancouver St. John, N. B. Halifax. N. S. Sydney. N. S. 
 
 219 
 
The Literature of 
 
 ROAD MAKING and MAINTENANCE 
 
 On our shelves is the most complete stock of technical, industrial, 
 engineering and scientific books in the United States. The technical 
 literature of every trade relating to road work is well represented, 
 as is every branch of Civil Engineering. 
 
 A large number of these we publish and for an ever increasing 
 number we are the sole agents. 
 
 ALL OUR INQUIRIES ARE CHEERFULLY AND CAREFULLY 
 
 ANSWERED AND COMPLETE CATALOGS AS WELL AS 
 
 SPECIAL LISTS ARE SENT FREE ON REQUEST 
 
 D. VAN NOSTRAND COMPANY 
 PUBLISHERS AND BOOKSELLERS 
 
 25 PARK PLACE 
 
 NEW YORK 
 
 UNION OIL COMPANY 
 of California 
 
 ASPHALT ROAD OILS 
 
 Los Angeles San Francisco 
 
 CALIFORNIA 
 
 GLUTRIN ROAD BINDER 
 
 Particulars from 
 
 ROBESON PROCESS CO. 
 
 18 East 41st Street 
 
 New York City 
 
 EDWARD A. CLARK 
 
 Mining and Drilling Engineer 
 
 Asphalt, Coal, Manganese and Zinc Properties 
 for Sale 
 
 Park Row Building New York City 
 
 T. HUGH BOOKMAN, C. E. 
 
 Consulting Engineer 
 Forti6cations and Military Roads 
 City Pavements and Efficiency 
 Washington Building, New York City 
 
 W. B. SPENCER, C. E. 
 
 SPECIALIST IN 
 
 ROAD MACHINERY 
 
 30 Church Street 
 
 New York 
 
 NEW YORK MASTIC WORKS 
 
 Established 1872 
 Original Importers of Neuchatel and Seyssel 
 
 Rock Asphalt 
 
 War and Navy Departments 
 
 Specialists in Asphalt construction 
 
 T. HUGH BOORMAN, Cons. Eng. 
 
 1 Broadway. New York City 
 
 ASPHALTS 
 
 19t4 Road Edition by 
 T. HUGH BOORMAN, C. E. 
 
 Price, $2.00 
 
 W. T. COMSTOCK CO. 
 23 Warren Street New York City 
 
 220 
 
How to Save Transportation Costs 
 
 is the 
 
 Question of the Hour 
 
 Wl LLITE 
 
 TRADE MARK REG. U. S. PAT. OFFICE 
 
 Pavement for Military Roads 
 and Country Highways 
 
 Patented U. S. A., July 11, 1916 
 
 The Invention of H. P. WILLIS, B.E., M. Am. Soc. C. E., formerly 
 Chief Engineer N. Y. State Highway Department 
 
 Willite has the overwhelming commercial advantage over all other 
 types of pavement (which have to pay 100 per cent, of all material entering 
 into their construction) because about 85 per cent of all the raw material 
 (native mineral aggregate), used in both the WILLITE foundation and 
 WILLITE wearing course costs nothing, as it is obtained right in the road 
 itself or adjacent thereto. This filler can be the run of the road without 
 selection, no matter what the character of the soil may be, such as mixed 
 earth, sand, gravel, shale, sedimentary sand, disintegrated granite, etc. 
 
 Willite Road Construction Co. 
 
 of America, Inc. 
 51 Chambers Street NEW YORK 
 
 221 
 
THE 
 
 FIRST COST 
 ST COST 
 
 No Waste 
 
 Today's Necessity 
 
 State Street, Albany, N. Y. 
 
 "I believe in a paving programme based 
 
 on future needs. I use Improved Granite 
 
 Block Paving once down no more worry." 
 
 The Mayor. 
 
 "I am for Improved Granjte Block Pav- 
 ing every time it gives my horses a good 
 sure footing and saves delay." 
 
 The Driver. 
 
 Present need is for better streets, traffic 
 has never made such demands as now. 
 
 Make your streets permanent, eliminate 
 repairing, speed up transportation in your 
 city, make it safe. 
 
 roved Granite 
 lock Paving 
 
 Longest Life 
 
 No Repairs 
 
 No Maintenance 
 
 "I am always safe from skidding and my 
 brakes hold on Improved Granite Block 
 Paving. The Chauffeur. 
 
 "I am first, last and always for the mayor 
 or the official who puts my money into 
 Improved Granite Block Paving. Once 
 down down forever." 
 
 The Taxpayer. 
 
 Good Material Well Laid is Absolute Economy 
 
 Granite Paving Block Manufacturers' Ass'n 
 
 of the U. S. A., Inc. 
 
 31 State Street 
 
 Boston, Mass. 
 
 Facts , figures and practice 
 of best engineers A 
 
 at your disposal * 
 
 Write for^ 
 our Booklet 
 
 PERMANENT PAVING 
 
 AND LATEST 
 
 SPECIFICATIONS 
 
 FOR LAYING 
 
 222 
 
Asphalt Blocks 
 
 for 
 
 Resurfacing Country Roads 
 
 A REAL PAVEMENT ON A REAL COUNTRY ROAD 
 
 ALBANY POST ROAD, TOWN OF MT. PLEASANT, N. Y. 
 
 LAID 1910 
 Part of an Eight Mile Stretch of Asphalt Blocks 
 
 The Asphalt Block is a composition of Trinidad "Lake" Asphalt, crushed trap rock 
 and inorganic dust, thoroughly mixed at a temperature of 300F., and pressed into 
 block form by hydraulic presses working under the tremendous pressure of 240 
 tons per block. 
 
 The manufacture of Asphalt Blocks is now a national industry with plants in 
 many parts of the country. The use of Asphalt Blocks has reached a total of 
 over fifteen million square yards. 
 
 Asphalt Block Pavements are Durable, Reasonable in Cost, Pleasing in Ap- 
 pearance, not Affected by Extremes of Temperature, Noiseless and Sanitary. 
 
 The field for Asphalt Blocks is by no means limited to their use on public streets 
 and roadways. They are used extensively for the wearing surface of piers, ware- 
 houses, loading platforms, bridges and factory floors. 
 
 Asphalt Blocks have stood the test of time 
 
 For further information address 
 
 THE HASTINGS PAVEMENT CO. 
 
 25 BROAD STREET NEW YORK CITY 
 
ASPHALT FILLER 
 
 Asphaltic Roadway Gravel 
 Roofing Gravel 
 
 (MASCOT) 
 
 LIMESTONE 
 
 AMERICAN BALLAST COMPANY 
 
 12161-1219 Holston National Bank Building 
 
 KNOXVILLE TENNESSEE 
 
 Societa Sicula per 1'esplotazione dell' 
 Asfalto naturale Siciliano 
 
 (Own Mines and Works at Ragusa, Sicily) 
 
 HEAD OFFICE AT PALERMO, VIA GIRGENTI 3 
 
 Cable Address, Rotland, Palermo. A. B. C, 5th Ed., Code used 
 
 Exportation of 
 
 SICILY .NATURAL ROCK ASPHALT 
 SICILY ASPHALT POWDER IN 50 KILO SACKS 
 SICILY ASPHALT MASTIC IN 25 KILO BLOCKS 
 COMPRESSED SICILIAN ROCK ASPHALT SLABS 
 
 MANY MILLIONS OF SQUARE METRES IN BERLIN, PARIS, VIENNA 
 BUCAREST, GLASGOW; CAIRO, EGYPT, AND ATHENS, ALSO IN MONTREAL 
 (CANADA), AND IN NEW YORK, PHILADELPHIA, BOSTON, NEW ORLEANS 
 AND OTHER ATLANTIC PORTS IN THE UNITED STATES HAVE BEEN 
 LAID WITH SUCCESS SINCE 1888. 
 
 T. HUGH BOOKMAN, Consulting Engineer 
 
 1 Broadway, New York 
 
 224 
 
225 
 
600 Pages 6x9 Cloth Illustrated Postpaid $5.00 
 
 ASPHALTS AND 
 ALLIED SUBSTANCES 
 
 Their Occurrence, Mode of Production, 
 Uses in the Arts and Methods of Testing 
 
 By HERBERT ABRAHAM 
 
 B.S. of Chemistry, Member A.C.S.,S.C.I.,A.S.T.M.,I.A.T.M. 
 
 CONTENTS 
 
 Part I. General Considerations 
 
 Historical outline, norrenclature and classi- of bitumens and pyrobitumens. Annual pro- 
 
 fication 9f bituminous substances. Chemistry duction of asphalts, asphaltites and asphalti- 
 
 of bituminous substances. Geology and origin pyrobitumens. 
 
 Part II. Semi-Solid and Solid Native Bituminous Substances 
 
 Methods of refining. Mineral waxes (Ozoker- mineral matter. Asphaltite deposits (Gilsonite 
 ite, Montan Wax, Hatchettite, etc.) Deposits of Glance Pitch and Grahamite). Asphaltic pyro- 
 natural asphalts occurring in a fairly pure state. bitumen deposits (Elaterite, Wurtzilite, Albert- 
 Deposits of natural asphalts associated with ite and Impsonite). Pyrobituminous shales. 
 
 Part III. Tars and Pitches 
 
 Methods of producing tars and pitches. Wood- and water gas tars and pitches; Paraffins wax 
 
 tar, wood-tar pitch and rosin pitch; Peat and and wax tailings ; Petroleum asphalts; Wurtzi- 
 
 lignite tars and pitches; Shale tar and shale lite pitch; Fatty-acid pitches and , bone-tar 
 
 tar pitch; coal tar and coal-tar pitch; oil-gas pitch. 
 
 Part IV. Manufactured Products and their Uses 
 
 Methods of blending. Bituminous dust-pre- Bituminous sheet roofings and floor coverings, 
 
 ventatives. Bituminous road-surt'acings. Bitu- Asphalt shingles. Bituminous waterprcofiing 
 
 minous fillers for stone or concrete pavements. membranes. Asphalt insulating and sheathing 
 
 Sheet asphalt pavements. Asphalt block pave- papers. Asphalt plastic compounds. Bitumi- 
 
 ments. Impregnated wood block pavements. nous waterproofing, compounds for cement. 
 
 Wood preservatives. Asphalt mastic flooring. Asphalt paints, varnishes and japans. 
 
 Part V. Methods of Testing 
 
 Physicalcharacteristics (color, fracture lustre, Naphthalene, Paraffine, Saturated hydrocar- 
 
 streak, specific gravity, viscosity, hardness, due- bons, Sulphonation Residue, Mineral Matter, 
 
 tility and tensile strength tests). Heat tests Saponifiable Constituents, Unsapqnifiable Mat- 
 
 (fusing point, volatile matter, flash point, burn- ter and Glycerol). Analysis of Paving Materials, 
 
 ing point, fixed carbon and distillation tests). Analysis of Asphalt Plastic Compositions, etc. 
 
 Solubility tests (in carbon bisulphide, carbon Analysis of Sheet Roofings, Shingles, Mem- 
 
 tetrachloride , petroleum naphtha and other branes, etc. Analysis of Asphalt Paints, Var- 
 
 solvents). Chemical tests (Water, Carbon, nishes and Japans. 
 Hydrogen, Sulphur, Nitrogen, Free Carbon, 
 
 D. VAN NOSTRAND COMPANY 
 
 PUBLISHERS AND BOOKSELLERS 
 25 Park Place New York 
 
 226 
 
UNIVERSITY OF CALIFORNIA LIBRARY 
 BERKELEY 
 
 THIS BOOK IS DUE~ON THE LAST DATE 
 STAMPED BELOW 
 
 Books not -turned on tim a subject to ^fine. of 
 50c Der volume after the 'third aay o - not in 
 
 ta 
 
 xpiration of loan 
 
 APR 
 
 OCT 12 1927 
 
 1 
 
 50w-7,'16 
 
YC 1330! 
 
 389494 
 
 UNIVERSITY OF CALIFORNIA LIBRARY