METHOD OF REPAIRING. The repairs necessitated in the maintenance of an asphalt pavement may be classified as follows: (1) those due to a settlement of the subgrade; (2) those due to a disintegration of the pavement in spots; (3) those due to the formation of waves; (4) those due to the formation of cracks; (5) the painting of the gutter; and (6) the remedying of defects next to the street-car rails, crossing stones, man-hole covers, etc.
It is generally conceded that the majority of repairs are necessitated by the settlement of the foundation over trenches. To repair these defects, it is neces sary to remove the wearing coat, the binder, and the foundation, and then, after having consolidated the material in the trench (see § 450), to relay the pavement much as in the original construction. The edges of the binder course and also of the wearing coat should be thoroughly covered with a thin coat of asphaltic cement to secure a perfect union of the old and the new material. The stone in the old concrete should not be used again, since the mortar makes a surplus of fine material and would prevent a firm adhesion of the new cement to the stone. Both the binder course and the wearing coat should be thoroughly tamped or rolled. Owing to the difficulty of fully consolidating the patch, it is left a trifle high to prevent a possible depression.
If the wearing coat disintegrates in spots, or forms "macaroons," from any of the causes described in § 631-53, the affected part must generally be cut out, since it is usually affected to its full depth. If the binder course is the cause of the deterioration (see § 642), it also must be cut out. The new material is to be laid as described in the preceding paragraph. If the disintegration does not extend to the full depth of the wearing coat, the repair may be made by " skimming," as described in the succeeding paragraph.
Formation of Waves. If the wearing coat has shifted under the traffic so as to form waves, i. e., until it is thicker in some parts
than others, or if the wearing coat has crowded towards the gutter, it may be necessary to melt off a portion of the high part, and also to re-surface the thin part. This is called skimming. The asphalt is melted off either with an open grate on low wheels in which coke is burned; or with a special heater having a tank for gaso lene, a hood 'over the burner, and an asbestos mat to protect the adjacent pavement. Fig. 118 shows the form of surface heater in common use. The surface is heated until the affected portion can be raked off; and then new material is added to bring the pavement to its proper thickness. There is considerable differ ence of opinion as to the possibility of doing good work by this method.
When cracks have formed in the wearing coat, all the loose material is cut off, the crack is cleaned out, and hot asphaltic cement is poured in.
Owing to the disintegrating effect of water, asphalt gutters usually require comparatively frequent re pairs either by painting (§ 630) with asphalt rich in bitumen, or by skimming (§ 660), or by removing the wearing coat and re-laying it, using an asphalt richer in bitumen than that in the remainder of the pavement.
The present practice is to make the repairs to asphalt pavements by contract with a guarantee of the work for a number of years; and therefore it is important that a record should be kept of the area and location of the several patches and also of the date when each was made. This is done by dividing the pavement into imaginary squares, of say, 10 feet on a side; and then when a patch is to be made, one or more of these squares should be located by chalk marks on the pavement, and the boundary of the patch should be sketched in a cross-ruled note-book. The records of the individual patches are afterwards platted upon a. single sheet to see that a subsequent patch does not overlap one for which the guarantee has not expired.