Blending efficiency of reclaimed asphalt rubber pavement mixture and its correlation with cracking resistance

Despite significant number of studies on recycling of conventional reclaimed asphalt pavement (RAP) mixtures into new asphalt mixture construction, research on recycling reclaimed asphalt rubber pavement (RARP) is still quite limited. The special multiphase system of asphalt rubber (AR) binder may cause a more complicated blending condition during the recycling of RARP due to the existence of rubber particles, and the blending efficiency of RARP and virgin AR mixtures is still unclear. The main objective of this study is to investigate the mobilization tendency of aged AR binder during the recycling of RARP mixture considering both the potential mobilizations of bitumen phase and rubber particles, as well as their correlation with the cracking resistance of the RARP mixture. AR mixtures containing 40% RARP were prepared at three different mixing temperatures and one warm mix case with the inclusion of a foam-based additive. A special gradation design was used to track the mobilization of aged AR binder from RARP to virgin coarse aggregates. Mobilization indexes of bitumen and rubber were established based on Fourier transform infrared spectroscopy and thermal gravimetric analysis tests, while the cracking resistance of the RARP mixture was evaluated by the semi-circular bending test. The mobilization indexes indicated that rubber and bitumen were simultaneously mobilized, and a higher mixing temperature led to stronger mobilization tendencies. In addition, a positive correlation was found between both mobilization indexes and the cracking resistance of the RARP mixture. The foam-based WMA additive markedly improved the blending efficiency but compromised the cracking resistance of the RARP.