Using Color Measurements to Assess Reclaimed Asphalt Pavement Degree of Activity

Abstract

High reclaimed asphalt pavement (RAP) content mixtures pose a challenge because of uncertainty about the activity level of RAP binder during production. This activity level, termed degree of activity (DoA), influences the integration of RAP binder into the virgin binder matrix of asphalt mixtures. This study proposes a practical method for measuring DoA using light intensity (LI) measurements obtained from the asphalt compatibility tester (ACT). As darker colors reflect less light, it is hypothesized that LI decreases as the activation level of RAP increases. Thus, LI can provide a quantitative measure associated with DoA for RAP samples. Furthermore, this study compares DoA measurements obtained using the ACT with those obtained using a method associating DoA with indirect tensile strength (ITS) of 100 percent RAP specimens. The two methods showed similar trends, but their measurements occasionally diverged. Both methods demonstrated an increase in DoA as temperatures rose from 100°C to 155°C, with DoA values exceeding 70% at standard production temperatures (140°C–155°C) for hot asphalt mixtures. The ACT-based DoA measurement approach holds promise for improving material selection and the design of recycled asphalt mixtures. However, further validation with a broader range of RAP sources is required to confirm its reliability and applicability across varying material sources.