Impact of recycled asphalt materials on asphalt binder properties and rutting and cracking performance of plant-produced mixtures

The use of recycled asphalt materials (RAM), such as Reclaimed Asphalt Pavement (RAP) and Reclaimed Asphalt Shingles (RAS), offers a great benefit in improving the rutting resistance of Hot Mix Asphalt (HMA) due to the changes in the rheological properties of the aged asphalt binder. To improve the HMA crack resistance, soft asphalt binders are typically blended with RAP and/or RAS to modify their rheological properties. However, soft asphalt binders could compromise the HMA rutting resistance, particularly in areas with high pavement temperatures and heavy traffic. Texas has implemented HMA mixtures with addition of RAM in many projects, and several premature field-rutting failures were observed with these mixtures. The addition of stiff aged asphalt binders of RAP and RAS can also decrease the HMA cracking resistance potential. Different from other previous studies, this study used plant-produced mixtures collected from various highway construction sites and projects to investigate the effects of RAM on the asphalt binder properties as well as the rutting and cracking performances of these plant-produced asphalt mixtures that represent actual in-service field applications. Through this study, designers, engineers, and the industry are able to gain a clearer understanding of pavement performance of mixtures with RAM. As theoretically expected, the corresponding results indicated that addition of RAP and RAS significantly improved the Dynamic Shear Rheometer (DSR) high temperature grade of all the extracted asphalt binders, with most of the HMA mixtures exhibiting relatively low Jnr values in the multiple stress creep recovery (MSCR) test. For the HMA rutting performance tests, all the mixtures passed the Hamburg Wheel Tracking Test (HWTT) while some exhibited relatively high permanent deformation in the Repeated Load Permanent Deformation (RLPD) test. By comparison, the MSCR (Jnr)-RLPD correlation was found to be more definitive than the DSR-RLPD correlation. In general, the mixtures with RAP and RAS exhibited comparatively low cracking resistance in the Overlay Tester (OT).