Macroscopic and Microscopic Mechanisms of Low-temperature Crack Resistance of Hot Mix Asphalt With High Content of Rejuvenated RAP

This paper aimed to study the macroscopic and microscopic mechanisms of modifying and rejuvenating additives for improving low-temperature crack resistance of plant-produced hot mix asphalt (HMA) with high content of reclaimed asphalt pavement (RAP), thereby improving the insufficient low-temperature crack resistance of this material. Three different types of additives (i.e., regenerant #1 of 8%, regenerant #2 of 8%, and regenerant 2 of 4%+high viscosity additive of 4%) were used to prepare HMA-RAP beam specimens for laboratory three-point bending tests. The macroscopic characteristics of fracture behavior were analyzed. The corresponding peridynamics models of laboratory tests were constructed. The micromechanical mechanisms of internal crack initiation and propagation in HMA-RAP specimens and the mechanisms of different additives improving the low-temperature crack resistance were revealed. Results show that the failure strain, stiffness modulus, strain energy density, and other low-temperature fracture performance indicators of HMA-RAP with both modifying and rejuvenating additives outperform those with rejuvenating additive only. The applicability of peridynamics models was demonstrated in accurate simulations of low-temperature fracture behavior of HMA-RAP. The rejuvenating additive significantly improves the interfacial bonding of aged asphalt. Specifically, the rejuvenating additive No. 1 leads to more uniform stress distribution at the bottom of the specimens, while the rejuvenating additive No. 2 better recovers the bonding ability of old asphalt. The modifying additive enhances the overall performance of asphalt binder but works better especially for virgin asphalt binder. As compared to the mere use of rejuvenating additive, its combination with modifying additive can recover the performance of aged asphalt binder and improve the overall viscosity of asphalt binder, which improves the drawback of inadequate low temperature crack resistance of HMA-RAP.