MAINTENANCE OF BROKEN-STONE ROADS.
To maintain a broken-stone road in good condition it is necessary first of all that it be frequently cleaned of mud and dust, and that the gutters and surface drains be kept open to insure the prompt discharge of all water that may come upon the surface of the road.
The best method of making repairs that may become necessary to the road-surface depends upon the char acter of the material composing the surface and the weight of the traffic passing over it.
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 the traffic. 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, the repairs may not be so 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 very little, if anything, in the way of 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 in the same manner as in original construction, on top of 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 plac ing the new layer, either by picking it up by hand or, if a steam roller is in use, by means of short spikes in its surface. Care should be taken in doing this, how ever, 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.
The maintenance of macadam roads under trying conditions or under severe traffic has in many instances proven a matter of considerable difficulty and of large expense. The great development of automobile travel has introduced a new element into the problem and greatly increased the difficulties of road maintenance. These vehicles, moving rapidly upon rubber tires, exert a lifting action upon the surface of the road, draw the binder out in the form of dust, and leaving the surface loose. Under ordinary circumstances the destruction of a broken-stone road is greatest in dry and dusty weather. If the road is subject to consider able travel, wear becomes rapid and a certain amount of the road metal is blown away by the wind, washed away in case of rain, or cleaned from the surface as mud. The binding material wearing into dust and being removed from the road loosens the stones of the road-surface, causing the road to " ravel. " Much difficulty has also been experienced in some localities, where the macadam roads connect with earth roads which in wet weather are composed of heavy, sticky mud, on account of the "picking up" of the macadam surface in muddy weather by the wheels of vehicles which are covered with mud. The stones in the surface are loosened and carried off until the road is destroyed.
To protect a broken-stone road against excessive wear and prevent raveling in dry weather, some means of laying the dust must be used. Sprinkling the road-surface with water is often used for this purpose, and has an important effect in reducing the wear and prolonging the life of the road. If the road be systematically sprinkled, the material ground off by the traffic will pack upon the surface, forming a cushion which serves to protect it from further attri tion. In sprinkling, the object should be to keep the surface damp, and not to flood it by applying too large a quantity of water at once.
Oil and tar are also used for laying dust in the maintenance of macadam roads. The use of oil in road construction in California has already been dis cussed in Art. 29, and the surfaces of macadam roads have also been sprinkled with oil in a number of eastern towns for the purpose of laying dust. This usually requires from one to three applications of oil during the season and has been found much cheaper than sprin kling with water. It is probable also that some treat ment of this nature will be found of value in preventing the " picking up " of a road surface by mud. Tar is also frequently used in much the same manner as oil in laying dust and preventing the raveling of the surface. The construction of tar roads will be separately con sidered in Art. 42.