After the base course has passed the compactiontest, prime the hole with a light application of asphalt,which can either be sprayed or brushed on. The primematerial must be thin enough so that it can be appliedlightly.NOTE: An excess of asphalt prime coat will flushinto the patch mix and causes bleeding.The final step in the preparation of the hole is toapply a tack coat to the vertical faces, as shown in figure16-26.Bituminous Materials ReplacementThe first step in the replacement of the pavingmaterials is to obtain a sufficient quantity of material tocomplete the project. Use a hot mix if possible becauseit is stronger and lasts much longer.To allow forcompaction when using a hot mix, you should overfillthe area approximately 40 percent of the pavementthickness. When a cold mix is used, it should be spreadand rolled in layers with each layer not to exceed 1 1/2times the maximum aggregate size in the mix. Whencold mix is spread, keep the material as level as possibleto prevent segregation. Both hot and cold mixes can bespread by grader, by paver, or by hand, depending on thesize of the repair.Compaction of bituminous materials is done withsteel-wheel rollers and pneumatic-tired rollers on largerareas, or with vibrator tampers, vibratory patch rollers,and hand tampers on smaller areas. Compaction is animportant part of the patching operation. The rollingoperation on hot mix should begin immediately after thematerial is placed. Cold mix should be rolled afterFigure 16-26.-Tack coat application to the vertical faces.16-22proper aeration of the material. The edges of the patchshould be rolled first. This seals the edges and preventsthe material from dishing out and water frominfiltrating. When cold mix is used, the patch may havea porous surface and require waterproofing. This canbe done by applying a sand seal or by applying a thinlayer of portland cement and tamping it in.Obtaining a smooth riding surface requires care.Too many patches are built as mounds that result asbumps in the road A straightedge should be used as aguide to finish the patch. The patch should not be lowerthan the rest of the pavement. Instead, it should be levelwith or one-eighth inch higher than the surroundingarea. Figure 16-27 shows the steps in patching apothole.Figure 16-27.-Steps in patching a pothole.
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