Bituminous Materials Replacement

The first step in the replacement of the paving materials is to obtain a sufficient quantity of material to complete the project. Use a hot mix if possible because it is stronger and lasts much longer. To allow for compaction when using a hot mix, you should overfill the area approximately 40 percent of the pavement thickness. When a cold mix is used, it should be spread and rolled in layers with each layer not to exceed 1 1/2 times the maximum aggregate size in the mix. When cold mix is spread, keep the material as level as possible to prevent segregation. Both hot and cold mixes can be spread by grader, by paver, or by hand, depending on the size of the repair.

Compaction of bituminous materials is done with steel-wheel rollers and pneumatic-tired rollers on larger areas, or with vibrator tampers, vibratory patch rollers, and hand tampers on smaller areas. Compaction is an important part of the patching operation. The rolling operation on hot mix should begin immediately after the material is placed. Cold mix should be rolled after

Figure 16-26.-Tack coat application to the vertical faces.

proper aeration of the material. The edges of the patch should be rolled first. This seals the edges and prevents the material from dishing out and water from infiltrating. When cold mix is used, the patch may have a porous surface and require waterproofing. This can be done by applying a sand seal or by applying a thin layer of portland cement and tamping it in.

Obtaining a smooth riding surface requires care. Too many patches are built as mounds that result as bumps in the road A straightedge should be used as a guide to finish the patch. The patch should not be lower than the rest of the pavement. Instead, it should be level with or one-eighth inch higher than the surrounding area. Figure 16-27 shows the steps in patching a pothole.

Figure 16-27.-Steps in patching a pothole.

SURFACE TREATMENTS

A surface treatment is an application of asphalt materials to any type of road surface with or without a cover of mineral aggregate. This application produces an increase in thickness usually less than 1 inch. Surface treatments have a variety of uses. They waterproof, provide a nonskid wearing surface, and rejuvenate an old surface.

Purposes

The simplest types of bituminous surfaces that may be placed over prepared surfaces are called surface treatments. Surface treatments are applications of bituminous material to any type of base or pavement surfaces which, together with an aggregate cover, produce a pavement with a thickness of 1 inch or less. In some cases, multiple treatments that produce thicker pavements are used.

Surface treatments are applied for one or more of the following purposes:

1. Waterproof the surface.

2. Provide a wearing surface.

_3. Make the surface nonskid.

4. Prevent hydroplaning.

_5. Rejuvenate an old road or runway.

6. Make permanent improvements.

Types

Surface treatments may be applied to the base course of a new road or to the surface of an old road as a method of repair. Surface treatments are grouped into three categories: sprayed asphalt, sprayed asphalt with cover aggregates, and asphalt-aggregate mixtures.