Assessing Recycled Binder Availability, Activity, and Contribution at Different Temperatures

Recycled binder availability (RBA), degree of activity (DoA), and recycled binder contribution (RBC) are distinct properties often used interchangeably in the literature. This study aims to clarify the distinctions among these terms and assess how they vary with temperature, as well as their interrelationships. To achieve this, a reclaimed asphalt pavement (RAP) sieve analysis approach, indirect tensile strength testing of 100% RAP specimens, and tracer-based microscopy are employed to measure RBA, DoA, and RBC, respectively. Three RAP sources are evaluated, and each property is measured at multiple temperatures. Sieve analysis and microscopy measurements indicate that only partial RBA and RBC, respectively, are achieved, and that these properties display minimal susceptibility to changes in temperature. In contrast, DoA significantly increased as the temperature rose from 100°C to 140°C, reaching 100%, and then plateaued from 140°C to 155°C. In most of the cases, the laboratory-mixed asphalt mixture samples evaluated exhibited RBC values comparable to the RBA measurements for the respective RAP source, suggesting that RBC becomes equivalent to RBA when the DoA reaches 100%.