Modifying Existing Asphalt Mix Design Procedures for RAP/RAS Surface Mixtures

The use of high Recycled Binder Replacement Percentages (RBRs%) in asphalt surface mixtures is increasing. The asphalt binders in Reclaimed Asphalt Pavement (RAP) and Recycled Asphalt Shingles (RAS) are generally hardened and embrittled from oxidization and may not fully mobilize and blend with virgin materials. Consequently, high recycled content mixtures may be prone to cracking if appropriate measures to consider this effect are not taken during the mixture design process. An in-depth study is needed to systematically evaluate the effects of asphalt content on the cracking and rutting performance of RAP and RAS mixtures to guide refinement of the North Carolina Department of Transportation (NCDOT)'s mixture design procedure to achieve reliable performance. It is imperative that this study encompasses a broad range of recycled material sources because past research has demonstrated that RAP and RAS stockpiles across North Carolina vary greatly with respect to rheological properties. In addition, a review of asphalt plant operations for stockpiling, processing, and characterizing recycled materials is necessary to identify measures that can be imposed in the NCDOT's specifications to reduce the variability in RAP and RAS sources within the state.​ The objectives of the proposed research project are to: (1) Modify the NCDOT's procedures for the design of surface mixtures containing RAP and RAS to improve performance and (2) Modify the NCDOT's specifications to improve the consistency within and across RAP and RAS stockpiles within North Carolina.