Evaluation and classification of recycling agents for asphalt binders

Abstract The economic and environmental benefits of using recycled asphalt materials continue to motivate agencies to increase their proportion in new pavement construction and maintenance and rehabilitation activities, but the resulting reduced cracking resistance remains an engineering performance challenge. The addition of recycling agents is one of the strategies to mitigate this issue caused by the increased stiffness and brittleness of the recycled mixture. This study explored the mechanism by which different types of recycling agents partially restore flexibility and ductility of asphalt binder and mixtures. A binder blend with 50% reclaimed asphalt pavement (RAP) binder was rejuvenated with seven types of recycling agents. Rheological and chemical tools were used to evaluate the binder blends and compare their performance to a control blend without a rejuvenator to study the rejuvenation mechanism. Corresponding asphalt mixtures were also tested to ensure adequate performance. Based on the results, the recycling agents were divided into three categories: (a) Softeners, (b) Replenishers, and (c) Emulsifiers. The results showed that while some agents act only on a physical level, others interact with the blend at a chemical level that affects the physical properties. A novel parameter was developed to compare the effectiveness of various recycling agents.