Low-Temperature Performance Evaluation of Recycled Binder Blends for Assessing Recycling Agents' Acceptance

The use of high contents of recycled materials in asphalt mixtures has an adverse effect on the low-temperature cracking performance of these mixtures if not accounted for properly due to the high stiffness and poor relaxation properties of the reclaimed asphalt pavement (RAP) binder. This concern has driven some to suggest using recycling agents (RAs) in the asphalt mixture to restore the rheological properties of the RAP binder without compromising the short- and long-term performance of the mixture. However, the relationships between RA type and dosage, virgin and RAP binder characteristics, and low-temperature properties, i.e., creep stiffness and m-value, need to be investigated further to assess the acceptance of RAs. In this study, 26 recycled binder blends from a combination of three virgin binders, four RAP sources, and eight RAs were used to study these relationships. First, the use of a method based on the dynamic shear rheometer to predict low-temperature properties of recycled binder blends successfully is demonstrated. Second, a linear relationship is found to exist between the low-temperature properties and RA dosage of these blends. Third, a parameter based on low-temperature properties is proposed to select an RA that yields a balance in the stiffness and relaxation properties of the recycled binder blends. Fourth, a conceptual framework is proposed to assess the acceptance of RAs based on low-temperature performance-related parameters.