Using Supplementary Cementitious Materials to Mitigate Alkali-Silica Reaction in Concrete with Recycled-Concrete Aggregate

Recycled concrete aggregate (RCA) is a key tool for improving sustainability in the construction and demolition industries. The use of RCA in new concrete is, in part, obstructed by the dearth of research available on the durability of RCA systems. This paper investigates the efficacy of replacing portland cement with supplementary cementitious materials (SCM), known to mitigate alkali-silica reaction (ASR) in concrete with virgin aggregates, as a method for reducing expansions related to ASR from reactive RCA. Fly ash (Class F), silica fume, and metakaolin were all investigated for their ability to mitigate ASR. The results of modified accelerated mortar bar tests are presented for two different RCAs when using 100% portland cement, binary blends of portland cement and fly ash, and ternary blends of portland cement, fly ash, and either metakaolin or silica fume. The results indicated that SCM can mitigate ASR in concrete made with RCA, though not as effectively as for natural aggregate systems. Higher levels of mitigation may be required for some RCAs, compared to the level necessary to mitigate or prevent ASR in concrete made with the original aggregates, depending on composition of the RCA.