Understanding effects of RAP on rheological performance and chemical composition of SBS modified binder using series of laboratory tests

The present study aims to evaluate rutting, fatigue, and rheological performances of a SBS co-polymer modified binder (PMB40) blended with different percentages (i.e., 0%, 15%, 25% and 40%) of reclaimed asphalt pavement (RAP) binder. The change in viscosity, mixing and compaction temperatures, and temperature susceptibility of PMB40 binder mixed with RAP were measured using Brookfield viscometer. Furthermore, linear viscoelastic range (LVE) and time-temperature sweep tests were conducted to characterize binders. The rutting and fatigue performance of PMB40 binder with varying percentages of RAP was evaluated using multi stress creep and recovery (MSCR) and linear amplitude sweep (LAS) tests, respectively. The change in chemical composition of PMB40 binder with addition of RAP was determined by Fourier transform infrared (FTIR) spectroscopy. The results showed that addition of RAP makes PMB40 binder stiff and less temperature susceptible, however, it did not change mixing and compaction temperatures significantly. Furthermore, high temperature performance grade (PG) of PMB40 binder was unaltered with addition of RAP, which is contrary to findings reported in literature. The MSCR test showed significant reduction in recovery and increment in non-recoverable creep compliance of PMB40 binder with addition of RAP, indicating a poor rutting resistance of the binder with inclusion of RAP. The LAS test showed that rate of damage increases and number of cycles to fatigue failure of PMB40 binder decreases with addition of RAP. The FTIR test confirmed increase in sulfoxide and carbonyl content with addition of RAP. A good correlation was found for ICO and ISBS indices obtained from FTIR with rheological properties of PMB40 binder. It is to be noted that the findings presented in this paper are based on one modified binder and one RAP source, thus it is recommended that effects of different RAP sources on performance of SBS modified binder be studied in detail. Further, effects of ageing (short term and long term) should be studied to have insight into characterization of RAP blended binders. It is also recommended that binder’s rheological performance tests be validated by conducting laboratory tests on asphalt mixes.