Durability Evaluation of High Recycled Binder Ratio Asphalt Mixtures

The economic and environmental benefits of incorporating recycled asphalt materials (RAMs) into new asphalt mixtures are achieved only if the durability of the asphalt mixtures is maintained. This study, conducted under National Cooperative Highway Research Program project 09-65, aims to evaluate the durability of asphalt mixtures with high RAM contents, considering component materials, mitigation strategies, and balanced performance. The evaluation included existing mix designs with variable RAM contents typically produced in each U.S. climatic zone (north/freeze and south/no freeze). In addition, this study considered alternative binders, partial RAM binder availability, a bio-based recycling agent, a liquid anti-stripping agent, and lime as potential strategies to improve the durability of high RAM asphalt mixtures. Four sets of experiments were selected to address the primary durability issues (surface cracking, moisture susceptibility, and raveling), while verifying rutting resistance for balanced performance. The results indicate that the high RAM strategies required to improve cracking performance can still result in durable asphalt mixtures within the context of a balanced mix design. In addition, the results show that liquid anti-stripping agents and lime are effective in improving the moisture resistance of the recycled mixtures. Finally, two screening tools based on component materials and mix design parameters are proposed to preliminarily evaluate the moisture resistance of high recycled binder ratio asphalt mixtures. Overall, this study provides valuable tools and guidelines for the evaluation and design of durable asphalt mixtures, focusing on those with high RAM contents and balanced performance.