A mechanistic study on mitigation of alkali-silica reaction by fine lightweight aggregates

Previous studies have shown that fine lightweight aggregate (FLWAs) may be a possible solution for ASR mitigation. However, the mechanisms of mitigation have not yet been fully elucidated. This study investigated how three commonly used FLWAs, expanded slate, shale, and clay can mitigate ASR in concrete using the accelerated mortar bar test (AMBT), concrete prism test (CPT), pore solution analysis and scanning electron microscope (SEM) analysis. The AMBT and CPT results showed that expanded clay was the most effective in reducing the expansion caused by ASR. Pore solution analysis showed that FLWAs, especially expanded shale and clay can reduce the alkalinity as well as increase aluminum content in the pore solution. SEM analysis revealed that infilling reaction products formed in the pores of the FLWAs, whose composition was closer to C-A-S-H, rather than alkali-silica reaction product.