Bitumen, or asphalt, is an intricate blend of hydrocarbons obtained mostly by the distillation of crude oil. Due to its adhesive and waterproofing qualities, it is extensively used in road construction, roofing, and many industrial applications. Bitumen has a complex chemical makeup, consisting of many types of molecules that contribute to its distinct features. Depending on its structural behaviour, allweather road pavements may be built in one of the following ways: Rigid pavement, semi-rigid pavement, and flexible pavement are all classifications of the same material. As the name suggests, flexible pavements are so named because of the way they deflect or bend under stress. There are often multiple layers of material used to build flexible pavements. All the loads that are taken from the layer above are distributed and then sent to the layer below. Layers of different materials are commonly layered in decreasing order of load-bearing capacity, with the costliest (and thus most expensive) at the top and cheapest (and thus least expensive) at the bottom to maximise this characteristic. Following are some of the components of a traditional flexible pavement construction covered in this section: The first thing to do is: This is the outermost layer, the one that is most often in contact with passing vehicles. A single HMA sub-layer or a slew of them may go into its construction. The layer directly underneath the HMA that is often made out of aggregate as its primary building block (either stabilised or unsterilized). The third sub-base course is called: Here, we're talking about the layer or layers that are directly below the basic course. In most cases, there is no need for a second base. Soil for the Subsoil: Soil subgrade is a natural soil layer used as a base for the subsequent layers of pavement materials.
Verma et al. (Mon,) studied this question.