A flexible pavement structure is composed of various layers of materials. Due to this, the total pavement structure deflects due to traffic loads, thus these types of pavements are known as flexible pavements.
Asphalt road pavements are defined as asphalt layers built bound over a granular base. In recent years, there has been a rapid increase in using additives in asphalt concrete mixtures to improve its properties. The performance of asphalt mixture is a function of asphalt cement, aggregate, and its volumetric properties. Asphalt cement binds the aggregate particles together, enhancing the stability of the mixture and providing resistance to deformation under induced tensile, compressive, and shear stresses. These distresses reduce the services life of the pavement and elevate the maintenance costs. The serious distresses associated with asphalt pavements are cracking, which occurs at intermediate and low temperatures, and permanent deformation, which occurs at high temperatures. Asphalt concrete (AC) is designed to resist rutting, fatigue, low temperatures cracking and other distresses. The design of asphalt mixture involves the selection and proportioning of materials to obtain the desired properties in the finished product. the bitumen modification provides binders with: Modification/reinforcement of asphalt binder is possible during different stages of its usage, either in between binder production and mix processes or before paving mix production. Thus the difference between the two applications is that the first application is used as measure to overcome the distress failure which already occurred in the pavement, while the second application is used as measure to prevent the existence of such failure. Another application of pavement reinforcement is the use of reinforcement elements in asphalt overlays to provide an adequate tensile strength to the asphalt layer and to prevent failures of the pavement such as reflection cracking. The term reinforced pavements refers to the use of one or more reinforcing layers within the pavement structure. Hence, the task of current asphalt researchers and engineers is to look for different kinds of polymer modified asphalt such as crumb rubber. The dynamic properties and durability of conventional asphalt, however, are deficient in resisting pavement distresses. Rutting and fatigue cracking are among the major distresses that lead to permanent failure of the pavement surface.
In general, road pavement distresses are related to asphalt binder (bitumen) and asphalt mixture properties. However, due to some distresses like fatigue failure, the performance and durability of bitumen are highly affected by changes with time in terms of its characteristics which can lead to the cracking of pavement. In asphalt concrete (AC), bitumen as a binder serves two major functions in road pavement, first, to hold the aggregates firmly and second to act as a sealant against water. To achieve this goal, designers should take into account three fundamental requirements which include environmental factors, traffic flow, and asphalt mixtures materials.
Road construction engineers must consider the primary user's requirements of safety as well as the economy. Roadways are an integral aspect of transportation infrastructure.