Effects of recycling agents (RAs) on rutting resistance and moisture susceptibility of mixtures with high RAP/RAS content

Abstract

Increasing the content of Recycled Asphalt Materials (RAM) in Hot Mix Asphalt (HMA) requires a comprehensive understanding of the effects of RAM on pavement performance. While there is a significant focus on the benefits of adding the Recycling Agents (RAs) in terms of cracking resistance of high RAM mixtures, limited research is published on the rutting and moisture damage of high RAM mixtures containing significant amounts of Recycling Agents. This study investigates the effects of RAs on the rutting resistance and moisture susceptibility of high RAM mixtures through analysis of analyzing the Hamburg Wheel-Track Test (HWTT) data with current AASHTO method and a modified analysis method separating the dry from the wet behavior. The RAM employed in this study includes Reclaimed Asphalt Pavements (RAP) and Recycled Asphalt Shingles (RAS). Two levels of high RAP mixtures (30% and 50%) and one combination of RAP and RAS (30% + 5%) were used to fabricate test asphalt mixtures and compared to a control mixture with no RAM. One petroleum-based RA (REOB) and two bio-based RAs were used to soften these mixtures using pre-determined dosages. In total thirteen-three mixture combinations were prepared and measured in this study. The HWTT test parameters recommended in the current AASHTO method were calculated and compared with the parameters determined by using a modified analysis method, in which the deformation due to the visco-plastic flow is separated from the deformation induced by moisture in the wet HWTT. The results illustrate that in general high RAM improved the rutting resistance and moisture susceptibility as compared to the virgin mixture, but some of the RAs used, show an alarming increase in the moisture susceptibility potential of the high RAM mixtures. It is therefore concluded that caution should be used in analysis of the HWTT rutting behavior of high RAM mixes as the RA used could result in inferior rutting behavior under wet conditions.