Q. Function of prime coat in bituminous pavement?

The main function of prime coat in bituminous pavement is to protect the subgrade from weathering andmoisture. Because the presence of moisture affects the strength of subgrade, prevention of water entry at the time of construction is essential to avoid the failure of the pavement. In cold countries, by getting rid of moisture from subgrade, danger of frost heave can be minimized.

Prime coat is an asphalt that, when applied evenly to the surface of subgrade orsub-base, serves to seal the surface to hinder the penetration of moisture into subgrade. Vehicular traffic must be avoided on the surface sprayed with prime coat since the traction and tearing action of vehicles would damage this asphalt layer.

Fig: Position of application of prime coat