Disintegration

Disintegration is the breaking up of a pavement into small, loose fragments. This includes the dislodging of aggregate particles. If not stopped in its early stages, disintegration can progress until the pavement requires complete rebuilding. Potholes and raveling are two of the more common types of early stage disintegration.

POTHOLES.- Potholes are bowl-shaped holes of various sizes in the pavement, resulting from localized disintegration under traffic (fig. 16-21). They are usually caused by weakness in the pavement, resulting from too little binder, too thin a surface, too many fines, or poor drainage.

RAVELING.- Raveling is the progressive loss of surface material by weathering or traffic abrasion (fig. 16-22). Usually the fine aggregate wears away first, leaving little pockmarks in the pavement ^surface. As erosion continues, larger particles eventually break free, and the pavement soon has the rough and jagged appearance, typical of surface ^erosion. Raveling is caused by poor construction methods, inferior aggregates, or poor mix design.

Slippery Surfaces

One of the most common causes of a slippery flexible pavement is a thin film of water over a smooth surface. his can cause a vehicle to hydroplane. Other causes of slippery surface in flexible pavements are bleeding and polished aggregates.

Figure 16-21.-Pothole.

Figure 16-22.-Raveling.

BLEEDING AGGREGATES.- Bleeding is the upward movement of bituminous material in a flexible pavement, resulting in the formation of a film of bituminous material on the surface (fig. 16-23). The most common cause of bleeding is too much asphalt in one or more of the pavement layers. This is usually the result of a rich plant mix or a prime or tack coat that is too heavy. Bleeding normally occurs in hot weather.

POLISHED AGGREGATES.- Polished aggregates are those that have been worn smooth under traffic (fig. 16-24). Polished aggregates are caused by using the wrong type of aggregate in the pavement mix.

Figure 16-23.-Bleeding asphalt.

Figure 16-24.-Polished aggregate in pavement surface.