The use of oil for hardening the surfaces of earth and gravel roads originated in California, where it has rapidly extended into common practice. The use of oil was at first intended only for the purpose of laying the dust, and the surface of the road was sprinkled two or three times during the summer with a light coating of oil. The effect of the oil upon the road was such as to very quickly modify both the purpose and the method of the application, and many roads were soon constructed in which oil was used for the purpose of binding together the material of the road surface, and thus forming a crust over the road which would take the wear of traffic. The results in general were satisfactory, giving, in many instances, smooth firm road surfaces, free from dust during the summer, and without mud in winter.
Methods of Construction. Several methods have been employed in the construction of oiled roads. In the earlier construction, the oil was applied to the road when hard and smooth, the surface being sprinkled with the oil, which was absorbed into the surface. The following extract from a paper by T. F. White, in Engineering Record for Feb. 22, 1902, explains this method as commonly practiced: "Oil on roads, besides aiding to make a wearing surface, preserves the road-bed. It follows therefore, that the road-bed should be carefully prepared, well graded and shaped, and the surface smoothed and packed as firmly as the material of which it is composed will permit before the oil is applied. We therefore do our grading during the early part of winter, that the road-bed may have the benefit of the winter rains, and become packed from travel as well as from thor ough rolling. We roll after it has become moistened through.' Then in the spring, while still moist, we go over it with a blade grader or smoother or both, and dress up the surface, crowning it as desired; and as soon thereafter as the surface is dry and the weather is settled and warm, the oil is applied, as much in quantity as the material will absorb and mix with.
This has reference to a road never oiled before.
" It may be desired to put oil on a road that is not in very good shape as to grade and smoothness of surface. It is not recommended to apply oil to such a road, but circumstances may make it seem desirable. In such a road there may be chuck holes full of dust. To oil it we go over the holes first, scraping out the dust, filling them nearly full of oil, and then with hoe and rake, work in the dust, together with sharp sand and fine gravel, which are thrown in from a wagon drawn alongside, until the holes are filled from bottom up with oil, dirt, and gravel, thoroughly mixed together.
When all the holes are filled, we apply a coat of oil to the whole surface of the road. Should the road be very uneven, however, and full of holes, we prefer to haul on gravel, of a kind' that will pack, and fill up the holes and uneven places, saturate with water and roll before applying oil. Should the surface of a road be worked up to a considerable depth of dust, if it is of a nature to pack with water and compression, we drench it thoroughly and roll. But if it will not so pack, being of too sandy a nature, we pour on the oil, attempting to saturate all loose material to the firmer stratum below. The only rule we have as to quantity of oil to be applied is to put on sufficient to saturate all of the loose covering of the road, and secure some penetration into the firm road-bed beneath.
"After the oil is put on in any of these instances some appliance for mixing the oil and loose road materials is run over the surface backwards and for wards until a thorough mixing is accomplished. If the road surface is very loose, a common steel lever harrow, with the teeth slanted back, is useful. This may be dragged to and fro longitudinally along the road, and back and forth spirally across the road, until a thorough mixing is secured. On firmer roads and where there is ,little loose covering, a lighter implement, with numerous dragging fingers suspended from an axle, is better.