Linear viscoelastic, viscoplastic, and damage characterization of recycled asphalt binders and mixtures containing recycling agents with long-term aging

Recycling agents (RAs) are additives incorporated into recycled asphalt mixtures to mitigate the negative effects of using recycled asphalt materials on the performance. This study evaluates the impact of RAs on long-term aging susceptibility and performance at two scales. At the binder scale, rheological tests are conducted on recycled binder blends to examine the effects of RAs on high- and intermediate-temperature rheological behavior. At the mixture scale, dynamic modulus, cyclic-fatigue tests, and Hamburg Wheel Tracking Tests (HWT) are employed to assess the effects of RAs on linear viscoelastic properties, cracking resistance, and rutting resistance, respectively. In addition, changes in binder and mixture properties with long-term aging are assessed. In both binder and mixture analyses, the RA-modified systems are compared to ‘reference’ systems that reflect the current practice in the state from which the mixtures were sourced. The results indicate that RA-modified binders exhibit somewhat poorer rutting performance compared to the reference systems while the HWT test shows that all systems fulfilled the minimum mixture rutting criterion proposed by NCHRP Project 09-58. The addition of the RAs to asphalt binder yielded decreases in dynamic shear modulus and increases in phase angle compared to the reference systems in all cases. However, the rheological effects of the RAs diminished at the harshest long-term age level considered at both the binder and mixture scales. The cyclic-fatigue performance of mixtures prepared with the RAs were similar to the reference systems at the long-term age level evaluated.