Investigating the Effect of Degree of Blending on Performance of High RAP Content Mixtures

Abstract

The objective of this research was to investigate the effect of degree of blending on the rutting and fatigue performance of 100% reclaimed asphalt pavement (RAP) content mixtures. Recycled asphalt binders were extracted from the mixtures using a stage-extraction technique and evaluated. Five commercially available rejuvenators were evaluated based on a homogeneity index and the aging rate to select the best (RA1) and the worst (RA2) performing rejuvenator, respectively. Five mixtures were designed and tested at three aging levels to evaluate the selected rejuvenators. Mixtures were tested using the loaded wheel tester (LWT) and the Florida indirect tensile test (IDT) for high- and intermediate-temperature performance characterization, respectively. The LWT showed that the short-term aged recycled mix exhibited a better rutting resistance and less moisture susceptibility than the virgin mix when its high-temperature performance grade (HTPG) was 6°C higher than the virgin mix. However, the level of diffusion, as measured by the homogeneity index (Ih), did not seem to be a determining factor in moisture susceptibility or rutting depth. Also, the applied aging levels did not seem to affect the rut depths for RAP mixtures at lower rejuvenator dosage levels (RAP + 7.9% RA1 and RAP+6.5%RA2). IDT results showed that the virgin and 100% RAP mixtures exhibited average energy ratio (ER) values higher than the critical value of 1, indicating satisfactory crack initiation resistance behavior. Mixture R1 (100% RAP mixtures recycled with a low dose of RA1), with the highest Ih, exhibited the best cracking performance compared to the virgin mixture. It is recommended that cracking and rutting performance be plotted against the HTPG to determine the target HTPG of the recycled mix. The target HTPG of the recycled mix can then be obtained by adjusting the rejuvenator amount. In this research, the target HTPG of the recycled mix was 75°C or higher. It should be noted that this type of analysis is mix- and rejuvenator-specific and should be conducted during the mix design until a sufficient degree of confidence and familiarity with the rejuvenator is reached.