Work of Maintenance Broken-Stone Road

If the patch is small and thin, it will usually be thoroughly consolidated by the traffic; but if it is thick, it may be necessary to tamp it. However, as a rule, it is much better to lay succes sively two thin courses than one thick one.

386.

The method of continuous maintenance is a method of constant patching. This method contemplates restoring to the whole length of the road an amount of stone equal to the annual loss by wear, and therefore it is necessary to do more than just fill the holes and depressions as described in the preceding section.

In maintaining the road by patching, it is impracticable to employ a roller, and therefore the patches must be put on in such a manner as to induce travel to consolidate the new stone. The method of accomplishing this is as follows: The first patches are made along the middle of the road at intervals of about 50 yards, without reference to any depressions that there may be between. These patches have the shape of elongated rectangles, about 3 X 8 feet. The whole section having been gone over in this way, the madman commences again at the original starting-point and makes new patches, checker-board fashion, alternately on the right and the left of the first patches and midway in the space between them. On the third trip, he makes new patches be tween the second set; and so on, always observing the checker board arrangement. Thus in five trips the whole central part of the roadway has been covered, while travel has been induced to change direction five times and virtually to pass over nearly the whole surface.

Re-surfacing.

The term re-surfacing is frequently applied to two distinct operations. One consists in smoothing and leveling up the surface of an old road without adding much, if any, new material; and the other consists in adding an entirely new layer of material to an old road. For greater clearness, the first will here be called re-grading, and the second re-coating.

Re-grading.

When the surface of the road has become uneven and rough, and when the broken stone is thick enough not to require much new material, the top of the road is loosened, re-graded, and re-rolled. The loosening is usually done by run ning over the road, one or more times, with a steam stone-road roller having spikes in the rear wheels—see Fig. 66. Of course the roller must be heavy enough to force the spikes into the road metal; but to insure this condition the size of the spikes is usually thus adjusted to the weight of the roller. The amount of rolling required depends upon the hardness of the road and the amount of hand labor used; in one case a 12-ton roller loosened 240 square yards of a hard limestone per hour.* The spikes break up the layer to a depth of 3 or 4 inches, after which men complete the loosening process by breaking up the larger masses with hand picks. Sometimes the old road is broken up by a plow drawn by

a steam roller; but ordinarily this is not as good as using the spikes on the roller, since the road is not broken up to a uniform depth, and since there is danger of mixing the under-material with the top course, thus rendering the latter unfit for use again. Some times a harrow follows plow or the roller.

After the crust is broken up, the surface is leveled off by the use of shovels and rakes; and then it is sprinkled and rolled as in the original construction. Usually no new binding material is re quired, the detritus from the old road being sufficient.

The following tabular statement shows the distribution of the labor and the cost of re-grading a limestone road having an ex ceedingly hard crust: * Re-grading is applicable only when the road wears unexpect edly rough and uneven, or when the road was originally made needlessly thick. It is not economical to spend time and money in consolidating a thick layer part of which must later be loosened and re-consolidated. True economy requires the construction of a road of such a thickness that when the surface is too rough and uneven for further service, the road will be worn so thin as to require a layer of new material—which should be added without materially disturbing the old surface; that is, it is more economical to construct a thin road and give it a new top as occasion may re quire, than it is to build a thick road and re-grade it one or more times before it is worn so thin as to require a new top layer.

Re-coating.

All dust or mud should be removed from the old surface before adding the new material. Where the surface of the old road is very compact and the new material is hard and tough, it may be necessary to loosen the surface with picks to the depth of an inch, to secure a good bond between the old surface and the new material; but usually it is sufficient to score the sur face with a hand pick, making gashes 8 to 12 inches apart, having a maximum depth of 4 of an inch. If the sides of the road need no new material, a shallow groove having its outer face vertical should be cut longitudinally along the edge of the 'portion to be covered, so as to form a buttress for the new top and to secure a good union of the old and the new material. Where water is plen tiful, it is wise to soften the surface by copious sprinkling, to insure a firm bond between the new material and the old road-bed. The new stone is to be spread, rolled, and sprinkled just as in new construction.

The cost of labor to lay 21,908 square yards of a 3-inch course of 2-inch trap rock, bound with trap screenings, in New York City in 1897 was as follows: *