The Future of Road-making in America

by Archer Butler Hulbert

"There used to be much contention regarding the use of binding material in the making of a macadam road, but it is now conceded by nearly all practical and experienced road-makers, both in Europe and America, that the use of a binding material is essential to the proper construction of a good macadam road. It adds to its solidity, insures tightness by closing all of the spaces between the loose, irregular stones, and binds together the macadam crust in a way that gives it firmness, elasticity, and durability."

Binding material to produce the best results should be equal in hardness and toughness with the road stone; the best results are therefore obtained by using screenings or spalls from the broken stone used. Coarse sand and gravel can sometimes be used with impunity as a binder, but the wisdom of using loam or clay is very much questioned. When the latter material is used for a binder the road is apt to become very dusty in dry weather, and sticky, muddy, and rutty in wet weather.

The character of the foundation should never take the place of proper drainage. The advisability of underground or subdrainage should always be carefully considered where the road is liable to be attacked from beneath by water. In most cases good subdrains will so dry the foundation out that the macadam construction can be resorted to. Sometimes, however, thorough drainage is difficult or doubtful, and in such cases it is desirable to adopt some heavy construction like the telford; and, furthermore, the difficulty of procuring perfectly solid and reliable roadbeds in many places is often overcome by the use of this system.

In making a telford road the surface for the foundation is prepared in the same manner as for a macadam road. A layer of broken stone is then placed on the roadbed from five to eight inches in depth, depending upon the thickness to be given the finished road. As a rule this foundation should form about two-thirds of the total thickness of the material. The stone used for the first layer may vary in thickness from two to four inches and in length from eight to twelve inches. The thickness of the upper edges of the stones should not exceed four inches. They are set by hand on their broadest edges lengthwise across the road, breaking joints as much as possible. All projecting points are then broken off and the interstices or cracks filled with stone chips, and the whole structure wedged and consolidated into a solid and complete pavement. Upon this pavement layers of broken stones are spread and treated in the same way as for a macadam road.

Stone roads should be frequently scraped, so as to remove all dust and mud. Nothing destroys a stone road quicker than dust or mud. The hand method of scraping with a hoe is considered best. No matter how carefully adjusted the machinery built for this purpose may be, it is liable to ravel a road by loosening some of the stones. The gutters and surface drains should be kept open, so that all water falling upon the road or on the adjacent ground may promptly flow away. Says Spalding, a road authority:

"If the road metal be of soft material which wears easily, it will require constant supervision and small repairs whenever a rut or depression may appear. Material of this kind binds readily with new material that may be added, and may in this manner frequently be kept in good condition without great difficulty, while if not attended to at once when wear begins to show it will very rapidly increase, to the great detriment of the road. In making repairs by this method the material is commonly placed a little at a time and compacted by passing vehicles. The material used for this purpose should be the same as that of the road surface and not fine material, which would soon reduce to powder under the loads which come upon it. By careful attention to minute repairs in this manner a surface may be kept in good condition until it wears so thin as to require renewal.

"In case the road be of harder material, that will not so readily combine when a thin coating is added, repairs may not be frequent, as the surface will not wear so rapidly, and immediate attention is not so important. It is usually more satisfactory in this case to make more extensive repairs at one time, as a larger quantity of material added at once may be more readily compacted to a uniform surface, the repairs taking the form of an additional layer upon the road.

"Where the material of the road surface is very hard and durable, a well-constructed road may wear quite evenly and require hardly any attention, beyond ordinary small repairs, until worn out. It is now usually considered the best practice to leave such a road to itself until it wears very thin, and then renew it by an entirely new layer of broken stone placed on the worn surface and without in any way disturbing that surface.

"If a thin layer only of material is to be added at one time, in order that it may unite firmly with the upper layer of the road, it is usually necessary to break the bond of the surface material before placing the new layer, either by picking it up by hand or by a steam roller with short spikes in its surface, if such a machine is at hand. Care should be taken in doing this, however, that only the surface layer be loosened and that the solidity of the body of the road be not disturbed, as might be the case if the spikes are too long."

In repairing roads the time-honored custom of waiting until the road has lost its shape or until the surface has become filled with holes or ruts should never be tolerated. Much good material is wasted by spreading a thick coat over such a road and leaving it thus for passing vehicles to consolidate. The material necessary to replace defects in a road should be added when the necessities arise and should be of the best quality and the smallest possible quantity. If properly laid in small patches the inconvenience to traffic will be scarcely perceptible. If such repairs are made in damp weather, as they ought to be, little or no difficulty is experienced in getting a layer of stone to consolidate properly. If mud fills the rut or hole to be repaired, it should be carefully removed before the material is placed.