Towards Optimized Use of Asphalt Recycling Agents: Interim Results from RILEM TC 308-PAR Task Group 4

This paper presents the initial outcomes of the coordinated experimental activity conducted by Technical Group 4 of RILEM TC 308-PAR, dedicated to the evaluation of Asphalt Recycling Agents (ARAs). The study aims to assess the effectiveness of the ARAs’ dosage procedure, proposed in the Recommendation document prepared in the previous RILEM effort by the same leading authors, for restoring the rheological performance of recycled asphalt binders while ensuring consistency across multiple international laboratories. Each participating laboratory independently selected its reference asphalt binder, reclaimed asphalt (RA) product, and ARA, following a shared testing protocol. The comparison between reference and recycling binder blends was based on the relative differences in complex modulus (G*) under unaged, short-term aged (STA), and long-term aged (LTA) conditions. Results indicate that most laboratories achieved comparable stiffness levels in the unaged state and adequate rutting resistance after STA. Under LTA conditions, most recycling binder blends exhibited lower stiffness, confirming the rejuvenating effect of the ARAs. Overall, the findings demonstrate the feasibility of the proposed approach and ARAs’ capacity to effectively restore asphalt binder properties. These preliminary results represent an essential step toward establishing standardized evaluation methods and best practices for the use of recycling agents in asphalt pavement applications within the RILEM framework.