Influence of RAP sources and proportions on fracture and low temperature cracking performance of polymer modified binder

Abstract

The present study evaluates effects of reclaimed asphalt pavement (RAP) obtained from two different sources on fracture and low temperature cracking resistance of a polymer modified binder (PMB). Two different RAPs, one from urban highway (RAP-A) and other from rural highway (RAP-S) were collected. The binder extracted from RAP-A and RAP-S had different viscosity, rheological and chemical characteristics. The binder extracted from RAP-A was found to have higher viscosity and stiffer nature compared to RAP-S. The PMB binder was blended with different proportions (i.e., 0, 15, 25 and 40% by weight of binder) of RAP-A and RAP-S. The double edge notched tension (DENT) test was conducted to evaluate fracture cracking potential of PMB binder containing different percentages of both the RAPs. Further, low temperature cracking potential of RAPs blended binders was measured using bending beam rheometer (BBR) test. The results from the DENT test showed the second peak in the load-displacement curve for the control PMB disappeared with addition of RAPs, indicating damage to polymer interlinking. Inclusion of RAP-A (urban highway source) in PMB resulted in a smaller critical crack tip opening displacement (CTOD) value compared to RAP-S (rural highway source). The statistical analyses showed that lower percentage of RAPs (i.e., 15% RAP-A and 15% RAP-S) had similar effect on CTOD value of PMB, however, at higher percentage of RAPs (25% and 40%), both RAPs found to behave differently. The BBR test showed that addition of RAPs resulted in increase in stiffness and decrease in m-value, indicating poor low temperature cracking potential of PMB. The addition of RAP-A resulted in lower m-value compared to RAP-S. Based on the DENT and the BBR tests, it can be concluded that the PMB binder with RAP-A could be more fracture susceptible compared to binder with addition of RAP-S. The low temperature performance grade (PG) of PMB did not change significantly with addition of even 40% of both the RAPs, which is contrary to what is being reported in literature. The findings presented in the paper showed that RAP source and its proportions can have different impact on performance of mixes, thus assuming that nature of RAP binders remains same irrespective of change in a source may lead to premature failure of a pavement.