What comprises an asphalt pavement structure?

An asphalt pavement structure is primarily composed of all layers that are placed above the prepared subgrade or foundation. This encompasses not only the surface layer, which is the topmost layer where traffic directly contacts, but also the base and sub-base layers that provide structural support and drainage. The entire assembly is designed to work together to distribute loads from traffic and ensure longevity and durability under varying conditions.

Considering the options, focusing solely on the subgrade and foundation or restricting the definition to only the surface layer or base layers would omit vital components of the pavement structure. Each part has a crucial role in performance, load distribution, and overall stability of the roadway. Therefore, the comprehensive definition recognizes the importance of all these layers in creating an efficient and effective asphalt pavement system.