Correlation Between the Reactivity of Supplementary Cementitious Materials and Their Efficacy to Prevent Alkali-Silica Reaction

Abstract

Supplementary cementitious materials (SCMs) have been extensively used to partly replace ordinary portland cement to reduce concrete carbon footprint and improve concrete durability. However, SCMs with varying reactivities affect the hardened properties and durability of concrete. Current prescriptive specifications to prevent alkali-silica reaction (ASR) are based only on the chemical composition of SCMs and known past performance test results. SCMs with similar chemical compositions but different reactivities will affect their efficacy to prevent ASR. In this study, SCM reactivities were correlated to their ASR prevention efficacy in mortar and concrete mixtures. SCM reactivities were determined based on the calcium hydroxide consumed by SCM at 50 ℃ in a high pH environment. The accelerated mortar bar test and the miniature concrete prism test were used to monitor the expansion and evaluate the efficacy of SCMs in terms of ASR prevention. A very highly reactive fine aggregate and several SCMs including three fly ashes, a slag, a silica fume, and a natural pozzolan with varying compositions were used. The results showed that the reactivity of SCM in the mixture and their mass fraction in the cementitious material blend was correlated well to the expansion of the mortar and concrete mixtures. The findings showed that the higher the SCM reactivity, the lower the expansion due to ASR. A possible new approach to determine the SCM efficacy in preventing ASR was discussed.