Rheology of Asphalt Binders in Pakistan

This paper describes how asphalt binder rheological properties play a major role in the performance of hot-mix asphalt mixtures (HMA). High temperatures and heavy loads may cause significant premature rutting in asphalt layers if asphalt binder is not characterized properly while designing HMA. Conventional binder characterization (penetration and viscosity grading) can not be related to the expected field performance of an HMA in a given environment. Therefore, performance-based specifications are gaining recognition in the highway community. Six binders that are typically used in highway construction in Pakistan were obtained from the two oil refineries in the country. The binders were subjected to mechanical testing using dynamic shear rheometer (DSR) to determine their critical high temperatures and rheological characteristics. Three models (CA, CAM, and 2S2P1D) were employed for characterizing the rheology of the binders using frequency sweep tests data. The results indicate that the existing asphalt binder grades used in Pakistan are very susceptible to high temperatures.