Which of the following defines a prime coat?

A prime coat is a crucial layer in the construction and maintenance of asphalt pavements. It is specifically defined as a sprayed application of low viscosity liquid, which is typically a diluted asphalt emulsion. This application serves to penetrate the surface of the underlying material, ensuring a better bond between the base layer and the subsequent asphalt layer.

Applying a prime coat is essential because it enhances adhesion, helps to control dust and stabilize the underlying surface, and prepares the surface for the top layer of asphalt. The low viscosity allows the liquid to thoroughly soak into the subgrade or base material, creating a suitable substrate for asphalt construction.

The other options focus on different aspects of road construction and maintenance, which don’t align with the specific definition of a prime coat. For instance, a thick layer of asphalt over untreated material refers more to the asphalt surface layer, while sealing asphalt pavement relates to maintenance processes rather than the initial bonding layer that a prime coat provides. A compact layer of aggregate material describes the base layer but does not involve the liquid application characteristic of a prime coat.