Bitumen as a pavement material
The characterization of bitumen and bituminous mix has been discussed in detail in the web-course Transportation Engineering - I
Bitumen is a complex material, its property ranges from viscous liquid to brittle solid. While bitumen shows linear viscoelastic behaviour at small strains, the nonlinear behaviour becomes more prominent at large strains (Monismith and Secor 1962, Pagen 1968, Cheung and Cebon 1997). The deformation of bitumen is loading rate and temperature dependent (Van der Poel, 1955, Deshpande and Cebon 1997).
The bituminous mix is manufactured by mixing bitumen and aggregates of specified size distribution at some specified elevated temperature. Then, the mix is transported to the site, laid and subsequently compacted to pack the aggregate particles together. During the compaction process the air voids are brought down to its desired level. The compacted mix, thus, achieves its strength when it cools down and becomes serviceable as bituminous road . Figure-1 shows a typical cross-section of a bituminous mix sample.
Figure-1 A typical cross-section of a bituminous mix sample
The mechanical behaviour of bituminous mix has been studied extensively through various tests, and empirical relationships have been developed for mix design and prediction of the performance of the mix. However, prediction of response of bituminous mix through mechanics based models, is a difficult task. Various attempts have been made by the researchers, for example based on, linear viscoelastic principle (Lee and Kim 1998, Kim and Little 2004), elastic visco plastic principle (Uzan 2005), discrete element analysis (Sadd 2004, Abbas et al. 2005) etc., so as to capture the complex mechanical behaviour of bituminous mix.