Roadways are considered one of the most important elements of infrastructure and they play an essential role in our daily lives. Over the years, road structures have deteriorated more rapidly due to increases in service traffic density, axle loading and low maintenance services. To minimize the damage of pavement surface and increase durability of flexible pavement, it is important to understand the mechanism of complex behaviors of asphalt concrete mixtures in the field of improving the pavement mechanical performance. Aggregate gradation and asphalt cement are two key factors that influence the engineering properties of asphalt concrete mixtures; essentially the asphalt binder is the component that determines the mix viscous behavior and consists of asphalt cement and modifier. Many research works suggest that a specified tyre rubber is a promising modifier to improve the asphalt binder properties and hence to develop the mixture viscoelastic properties.
The use of rubber modified bitumen (RMB) to achieve better pavement performance has been studied for a long time. The properties of RMB are dependent on the rubber gradation, characteristics and content as well as the bitumen nature. Low-temperature, ductility is improved, viscosity is increased, elastic recovery is improved, adhesive and cohesive properties of the pavement are improved. In view of this, the necessity for the use of CRM to improve the performance of local asphalt concrete performance has been arising.There are many modification processes and additives that are currently used in bitumen modifications, such as styrene butadiene styrene (SBS), styrene-butadiene rubber (SBR), and ethylene vinyl acetate (EVA). The use of these other modifiers in road and pavement construction will increase the construction cost as they are expensive materials. However, with the use of CRM, will definitely be environmentally beneficial, and not only it can improve the bitumen binder properties and durability, but it also has a potential to be cost effective (Hamed, 2010).
In recent times, a serious problem that leads to environment pollution is the abundance and the increase of waste tyre disposal. Large amounts of rubbers are used as tyres for cars and trucks. Despite the long run in service, these tyres are not discarded. Although, the rubber as a polymer is a thermosetting material cross linked to processing and moulding, however, it cannot be softened or remoulded by re-heating unlike other types of thermoplastics polymer which can be softened and reshaped when heated. The major approach to solve this issue is the recycle and reuse of waste tyre rubber and the reclaim of rubber raw materials (Adhilkarri et al., 2000). In recent years, researches on applications of rubberised bitumen binders have reported many advantages. These advantages include improved bitumen resistance to rutting due to high viscosity, high softening point and better resilience, improved bitumen resistance to surface initiated cracks, the reduction of fatigue/reflection cracking, the reduction of temperature susceptibility, improved durability as well as the reduction in road pavement maintenance costs (Lu et al., 2009).
Rubber-asphalt mixtures are prepared by a process that typically uses 37- 47 by weight of relatively large (1/16 in. to 1/4 in.) rubber particles to replace some of the aggregate in the mixture. The benefits of adding rubber to the mix, besides elimination of rubber tyre waste, are increased flexibility, resistance to studded tyres, increased fatigue life, reduced noise, and crack reflection control. In addition, the increased elastic response of this material also reportedly causes ice, formed on the pavement during freezing weather, to break under transient vehicle loadings.