ASPHALT PAVEMENT STRUCTURE

Asphalt pavement is a general term applied to any pavement that has a surface, constructed with asphalt (fig. 16-4). Normally, it consists of a surface course (layer) of mineral aggregate, coated and cemented with

Figure 16-2.-Liquid asphaltic products.

Table 16-1.-Recommended Uses of Various Asphalt Grades

asphalt, and one or more supporting courses, which may be of the following types:

1. Asphalt base, consisting of asphalt-aggregate mixtures (macadam)

2. Crushed stone (rock), slag, or gravel

3. Portland cement concrete

4. Old brick or stone block pavements

Asphalt pavement structure consists of all courses above the prepared foundation. The upper or top layer is the asphalt-wearing surface.

Essential Properties of Asphalt-Wearing Surface

The surface of an asphalt pavement, exposed to vehicular traffic, must be tough to resist distortion and to provide a smooth riding surface. It must be waterproof and sloped to shed surface water to the roadside and protect the entire asphalt pavement structure and the foundation from the erosive effects of moisture. It must resist wear, caused by traffic, and still retain necessary anti-skid properties. It must also be bonded to the layer or course beneath it.

Figure 16-3.-Spread of wheel load through the pavement structure.

Figure16-4.-Asphalt pavement cross sections, showing common and typical asphalt pavement structures.