Evening Republican, Volume 17, Number 87, Rensselaer, Jasper County, 11 April 1913 — Home Course Road Making [ARTICLE+ILLUSTRATION]

Home Course Road Making

XL—The Relation of Automobiles to Modern Highways.

By LOGAN WALLER PAGE,

Director Office of Public Roach, United States Department of Agriculture. Copyright by American Press Association, 1912.

THE most complex problem now engaging the attention of highway engineers all over the world is the preservation of the crushed stone road under the destructive action of motor vehicles and the devising of new methods of construction adapted to the requirements of this twentieth century traffic. That the automobile has come to stay no one will dispute. It is estimated that there are already about 450,000 ma

chines owned in the United States, and the number is Increasing at a marvelous rate. The fact that must give us concern is that the old methods of construction which have stood every test for more than 100 years are inadequate to meet the conditions of this new form of traffic and that we are in the midst of a transition period which must eventually revolutionize the science and art of the road builder. The highway engineer of today is called upon to ascertain in what way the automobile injures the road, what is the exact cause of the injury, and finally to devise an adequate remedy. When Tresaguet, the great French engineer, made bis report to the council of bridges and roads in 1775 he set -forth the principles of construction which, as modified and added to by John L. Macadam in the early part of the nineteenth century, have proved adequate until the twentieth century. These great road builders and their successors sought to secure a road capable of withstanding thfe wear of iron tired horse drawn vehicles, for the motor driven vehicles had no place in their philosophy. They worked upon the theory that the dust abraded from the crushed, stone would fill the voids between the angular fragments and when wet serve as a cement, thereby making the road surface practically a monolith. The iron shod horses and the iron tired wheels passing over the road from time to time were depended upon to wear off a sufficient amount of rock dust to replace that carried away by wind and water, and this under the action of moisture recemented, thereby automatically renewing the bond of the road surface. ’ The rubber tired wheels, moving at excessive speed, fail to produce any new dust from the rock, but the tremendous shearing effect of the driving wheels loosens this dust, and as the body of the machine displaces a large volume of air the deflected currents carry the rock dust off the road, thereby effecting a permanent loss of the ail essential binder. It follows that the road is soon stripped of its fine binding material, exposing the upper or wearing course of the stone. These stones robbed of the binding material are soon loosened by the shear of the driving wheels, leaving the road badly raveled or disintegrated. It is, of course, apparent that the effects described are greatly Intensified on curves, where skidding is most frequent.

Highway and mechanical engineers have given much study to the action of the automobile on the road surface, and many ingenious theories have been advanced While it is true that _the slipping of the tire, skidding, shape of the car body, suction of the pneumatic tires, all contribute to produce the effect, the most conclusive experiments seem to warrant the assertion that the great tractive force or shear exerted by the driving wheels of motorcars is the main factor of Injury. A series of tests conducted by the United States office of public roads in 1908 produced, some interesting results along this line. Cars of various weights and types were run over a measured course at different rates of speed and right angle photographs taken of each run. A sixty horsepower car stripped for racing, weighing with its driver and mechanician about 2.800 pounds, was driven over this stretch of road at rates of speed varying from fire to sixty miles per hour, the speed being In creased five miles |>er hour tor each trip over the road. Up to fifteen miles an hour little or notffect was produced on the road, but from twenty miles an hour the effect was striking with each Increase tn speed. These demonstrattbns proved that little or no effect is

produced by’xhe^front"wheels and that practically the entire disturbance of the road is produced by the rear or driving wheels, if the effect were produced by suction or vacuum the action of both front and rear wheels should be somewhat similar at least, it seems apparent to the writer, therefore, that the road best adapted to motor traffic is the road which will best resist this powerful tractive shear. It has already been demonstrated that no plain macadam road is capable of resisting this* force. ' y “ The efforts of progressive highway engineers are thus directed primarily toward the preservation of our stone surfaced roads anathe construction of dustless roads by the use of a binder more powerful than stone dust and. secondly, to minimizing or mitigating the dust nuisance. For the purpose of discussing intelligently the experiments thus far conducted with special binders the term “dust preventives” has been applied to all of the various binders having for their main object either suppression or the prevention of dust These may be divided into two classes, temporary and permanent The temporary binders serve merely as palliatives and require frequent renewal. The permanent binders, so called, enter into the structure of the road as a constltutent element and are either incorporated with the other materials at the time of the con--struction or applied later by a surface treatment. In the class of temporary binders may be included water, salt solutions, light oils and tars and oil and tar emulsions, waste sulphite liquors, etc., while the permanent binders include the heavy petroleums and .tars, pitches and .numerous oil, tar and asphalt preparations. The value of salt solutions, which have been used to some extent, lies in the hygroscopic character of the dissolved salt, which, having considerable affinity for water, keeps the road surface in a moist condition long after a surface treated with water alone would have become dry through evaporation.

The light oils and tars as well as the oil and tar emulsions depend for their effect upon a comparatively small amount of true binding base left upon the road surface after the volatile products have evaporated. These materials prove effective only so long as they retain their binding power. When the binding power is destroyed it is necessary to apply more material. The heavy oils and tars differ from the lighter products in that they contain a much greater amount of true binding base. The results are, therefore, of a more lasting character and hence the naffie “permanent binders.” The semisolid and solid preparations usually contain a still greater amount of binder. With some few exceptions all of the true binders are bitumens. The usual method of applying these materials to the road surface is by sprinkling. The temporary binders can usually be applied cold, but the permanent binders because of their much greater viscosity must be heated until sufficiently fluid. In England and France the use of coal tar is practiced to a large extent, and their methods of application have been highly developed. Machines are,in general use which are self propelling and in which the tar is heated and applied to the road surface as a spray under high pressure. /These so called “tar sprayers” are not only very economical in the use of tar, but insure a more even distribution and better penetration of the road surface than it is possible to obtain in almost any other way. In the construction of dustless roads the crucial question is that of cost. The effort must be to develop a form of construction which will withstand fast automobile traffic and at the same time be within the financial resources of the community. This is largely being done at present by the use of a bituminous binder instead of rock dust. The two methods generally employed are known as the penetration and the mixing methods. In the former the hot liquid binder is sprinkled or sprayed over the stone and allowed to penertate through

the voids and coat the stones usually to a depth of two or three inches, in the mixing method the stones and binder are thoroughly mixed either by hand or machine, so that each atone is covered with a thin film of the binder This method in general insures the better and mhre even distribution of the binder throughout the road surface, but tbe cost ig greater than that of the penetration method. One of tbe chief causes of tbe great number of failures which have been recorded in the use of bituminous road □taterlals is the failure of tbe user as well as manufacturer to understand certain fundamental principles. To many a tar is simply a tar and an oil an oil. while tn reality there is a vast difference sometimes even In the tars produced at tbe same works. The oils also range from those of a paraffin base to those almost wholly asphaltic. Specifications for the bitumens should be prepared by an expert and materials should be tested io the laboratory.

AN OILED MACADAM ROAD WITH MACHINE TRAVELING SIXTY MILES PER HOUR—NO DUST.

AN UNTREATED ROAD WITH MACHINE TRAVELING SIXTY MILES AN HOUR—PLEN TY OF DUST.