Impact of Recycled Binder Availability on Performance Properties of RAP Asphalt Mixtures

This study evaluated the impact of recycled binder availability (RBA) on the performance properties of asphalt mixtures in Florida, covering two recycled asphalt pavements (RAP) contents (20% and 40%) and two aggregate types (granite and limestone). According to the current state specification, the 20% RAP mixture used a performance grade (PG) 76-22 polymer-modified asphalt binder, and the 40% RAP mixture used a PG 52-28 binder. Each mixture was subjected to a rigorous performance testing plan at two asphalt binder contents: volumetric optimum binder content (V-OBC) and RBA-adjusted optimum binder content (A-OBC) at 80% RBA. The testing plan included the indirect tensile asphalt cracking test (IDEAL-CT), overlay test (OT), Hamburg wheel tracking test (HWTT), asphalt pavement analyzer (APA), and indirect tensile asphalt rutting test (IDEAL-RT). Test results indicated that adding more virgin binders, considering 80% RBA, improved cracking resistance but reduced moisture resistance in RAP mixtures, especially those with 40% RAP. Increasing virgin binder content also reduced rutting resistance in 40% RAP mixtures but had a negligible impact on 20% RAP mixtures. At A-OBC, 40% RAP mixtures had comparable cracking resistance but were more rutting resistant than 20% RAP mixtures. Additional HWTT and IDEAL-CT testing of 40% RAP mixtures showed that grade bumping the virgin binder from PG 52-28 to PG 58-28 and PG 58-22 improved the rutting and moisture resistance of 40% RAP mixtures, but its impact on the cracking resistance varied depending on the virgin aggregate type. Finally, the HWTT, APA, and IDEAL-RT results were strongly correlated, whereas the IDEAL-CT and OT results showed a moderate or weak correlation depending on the mixture aging condition.