Comparison of asphalt rubber-aggregate and polymer modified asphalt–aggregate systems in terms of surface free energy and energy indices

The surface free energy (SFE) is a material property that can be used to identify optimum asphalt–aggregate combinations (i.e., interfaces) for improved design of hot mix asphalt (HMA) and to characterize the HMA performance through the use of micromechanical models. Based on SFE measurements, and subsequent calculation of energy indices, this paper compares asphalt–aggregate interfaces formed with asphalt rubber (AR) and polymer modified (PM) asphalt binders (or asphalts) specified for fabrication of permeable friction course (PFC) mixtures in Texas. Six PM asphalts and four AR asphalts with five different aggregates were assessed. Corresponding results suggest that, in terms of the energy indices computed, the fracture resistance, moisture damage susceptibility, and the wettability of the asphalt over the aggregate of AR asphalt–aggregate systems can be comparable to that developed by PM asphalt–aggregate systems. However, this conclusion is restricted by the variability encountered for both asphalt groups analyzed (i.e., AR and PM). Additional research is recommended to analyze the effect of lime in PM asphalts (since PFC mixtures fabricated with PM asphalts often include lime) and the effect of mineral fillers on both PM- and AR-aggregate systems.

► Surface free energy and energy indices served to characterize asphalt–aggregate systems (AAS).
► Asphalt rubber (AR)- and polymer modified (PM)-asphalts produced comparable AAS.
► The AAS evaluated are representative of permeable friction course (PFC) mixtures.
► The energy indices computed can be used to improve the design of PFC mixtures.