Abstract:
Asphalt concrete pavements have substantial amount of value at the end of their service lives. Rehabilitation strategies for deteriorated pavements include HMA overlays, in case the underlying old pavement layers can still provide considerable structural support. However, in areas where changes in final pavement grade can adversely affect the performance of storm water drainage and bridge clearances, all or a portion of the damaged HMA layer is milled to match the overlay elevation to that of the existing pavement. Pavement milling is widely used these days, as a result vast quantities of Reclaimed Asphalt Pavements (RAP) are generated. The RAP is either land filled or stockpiled for the later use in other construction projects. To conserve the natural resources and for economic reasons, practice of using RAP in asphalt mixes is gaining popularity as a rehabilitation alternate and RAP material has also been widely used as granular base course material in asphalt and Portland cement concrete pavement constructions.
Recognizing the importance of the flexible asphalt pavement recycling and its potential use in Pakistan specially to mitigate HMA rutting, Superpave guidelines involving RAP are developed for asphalt pavement recycling. Current research work is based on extensive asphalt binder testing to characterize the virgin, extracted and blended binders according to Superpave specifications (PG grading system). Keeping in view the high temperature susceptibility in Pakistan, only high and low temperature performance testing on original binders and Rolling Thin Film Oven (RTFO) residue with Dynamic Shear Rehometer (DSR) and Bending Beam Rheometer (BBR) has been performed to determine the PG grades and to study the rheological properties of the binder blends. Finally, the blending charts and master curves have been constructed for the expected performance of RAP blends in new asphalt mixes. These blending charts, master curves and other rheological data for original, extracted binders and their blends can be used as guideline by the pavement designers to design flexible pavements involving RAP under Superpave specifications.
