Effects of Immobilized RAP Binder on Asphalt-Aggregate Interaction and Performance of 100% Recycled Asphalt Mixtures

The current trend in the asphalt industry is to increase the utilization of recycled asphalt pavement (RAP). In general, there are two types of RAP binder in RAP aggregates, the mobilized RAP binder and the immobilized RAP binder. The former can be blended into the virgin binder to coat aggregates during asphalt blending, while the latter can be treated as black rocks because they have already become an outer crust of RAP aggregates. Studies have focused on the mobilized RAP binder quantification and the significance of mobilized RAP binder to mixture performances. However, it remains unknown whether the immobilized RAP binder affects mixture performances. This study developed a laboratory procedure for immobilized RAP aggregates preparation and investigated the contribution of immobilized RAP binder to asphalt-aggregate interaction as well as the performance of 100% recycled asphalt mixtures. The work of adhesive energy and the 𝐾-𝐵-𝐺* model were adopted to characterize the asphalt-aggregate interaction for asphalt mortar. Resilient modulus and dissipated creep strain energy were used to evaluate the stiffness and cracking resistance of 100% recycled asphalt mixtures. Results showed that the immobilized RAP binder can strengthen the asphalt-aggregate interaction and improve the cracking resistance of 100% recycled asphalt mixtures by increasing total asphalt content. However, if the total asphalt content remains the same, the immobilized RAP binder increases stiffness but decreases the cracking resistance of 100% recycled asphalt mixtures.