The surface course is the uppermost structural layer in an asphalt pavement. In most cases it is the top layer of the pavement and also serves as the wearing course. Since it is directly exposed to traffic and environmental forces, it must be produced with highest quality material.
Characteristics of Surface Course
The surface course must provide the following characteristics for an asphalt pavement.
Adequate wet weather friction for safety
High resistance to load-induced rutting, shoving and surface cracking
High resistance to thermally induced cracking
Low permeability to minimize surface-water infiltration
High durability to resist disintegration due to the combined effects of aging, traffic loading and freeze-thaw effects.
Appropriate surface texture for noise control, safety and aesthetics