Determining meso-parameters of hot mix asphalt with reclaimed asphalt pavement based on workability

Abstract

The flowability and compaction behaviors of hot mix asphalt (HMA) are critical for the mechanical performance and durability of HMA. When reclaimed asphalt pavement (RAP) is incorporated into HMA, the flowability and compaction would be significantly affected. Since the recycled asphalt mixture consists of virgin aggregate, virgin asphalt, aged asphalt, and RAP, the contact parameters and the related contact relations cannot be directly defined during discrete element modeling. Therefore, this study employed the slump test to measure the flowability of two types of HMAs, HMA with 0 % and 100 % RAP. The angle of repose (AoR) was used to characterize the macroscopic flowability and to determine the mesoscopic parameters used in the discrete element modeling (DEM). The contact parameters inside the asphalt mixture were determined by comparing the actual AoR with the virtual AoR at different asphalt contents. The results of the study showed that the contact relations between particles in the mixtures were directly affected by the RAP and the asphalt content, which leads to the variation of flow behaviors of the uncompacted asphalt mixtures. The macroscopic flow behaviors could be qualitatively explained as a coupling effect of friction and bonding. The friction between particles and the bonding provided by asphalt binder were determined when different binder content was added. By trial calculation, the friction coefficient of the RAP surface was 0.37, which was lower than that of the virgin aggregate. When AoRs reached the maximum values, the bond strength inside the HMA without RAP was 7.5 × 104 Pa. Due to the compatibility of the aged and virgin asphalt, the bond strength inside the HMA with 100 % RAP was only 6.2 × 104 Pa. Then, virtual compaction tests were conducted for HMAs with 0 % and 100 % RAP. Under the same compaction effort, HMA with 100 % RAP presented larger porosity, which was consistent with the actual situation, indicating the parameter calibration method is feasible to characterize the flowability of HMA with or without RAP. In conclusion, this study indirectly realizes the calibration of internal parameters in recycled asphalt mixtures based on the flowability and provide a microscopic mechanism to explain the macroscopic performance variations of recycled asphalt mixtures.