The Efficacy of Calcined Clays on Mitigating Alakli-Silica Reaction (ASR) in Mortar and Its Influence on Microstructure

Abstract

Previous research has shown that using metakaolin is an effective strategy for mitigation of alkali-silica reaction (ASR). Metakaolin reduces the OH⁻, K⁺ and Na⁺ concentrations in pore solution. The high aluminium content in metakaolin has also been shown to contribute to ASR reduction. However, the efficacy of calcined clays from different sources and qualities for ASR mitigation is still limited. This study investigated the mechanisms of ASR suppression by using one known highly reactive fine aggregate and four calcined clays from different sources. The optimum replacement for ASR mitigation was determined by replacing 5 %, 10 %, 15 % and 20 % of portland cement with the different calcined clays and then tested for expansion in the accelerated mortar bar test (AMBT). Results indicated the chemical composition and mineral phase of calcined clays had a significant influence on the efficacy of ASR mitigation. In addition, ASR gel was found in control mixture and the mixture with 10 % calcined clay 1 (CC1). ASR gel composition was investigated into the two mixtures by using energy-dispersive X-ray spectroscopy (EDS) in coupled with scanning electron microscopy (SEM), but no significant differences were found in gel composition between the two mixtures.