Use of Alkali–Silica Reaction-Affected Recycled Concrete Aggregate in Hot-Mix Asphalt

Abstract

The effects of using alkali–silica reaction-affected recycled concrete aggregate (ASR-RCA) in hot-mix asphalt (HMA) were investigated. The goal of the study was to determine if the asphalt binder provided sufficient moisture protection to prevent reexpansion of existing ASR gel or occurrence of new ASR. Expansion tests were performed with a dilatometer on RCAs to determine the possibility of new ASR occurring in reactive aggregates in the HMA. Micro-Deval and freeze–thaw tests measure higher mass loss in ASR-RCAs than that in virgin aggregates, which is caused by preexisting aggregate microcracks and ASR gel in ASR-RCAs. Moisture damage testing indicated good moisture resistance of HMA mixtures made with ASR-RCA, especially when compared with virgin siliceous aggregate. Expansion testing indicated that both ASR-RCAs were still reactive with 0.5 N sodium hydroxide (NaOH) solution saturated with calcium hydroxide (CaOH2) at 60°C. Expansion testing of HMA specimens in NaOH + CaOH2 solution at 60°C indicated a reaction between the asphalt binder and the solution, but little ASR. However, expansion testing in deicer solution at the same temperature indicated that some ASR may have occurred along with the primary binder-solution interaction. The volume change characteristics associated with the binder–solution interaction with and without ASR was supported by the change in pH and alkali concentration of the test solution. The potential distress mechanisms are identified, and possible remedial measures as guidelines are recommended for the use of ASR-RCA in HMA.