Influence of Limestone Mineral Addition in Cements on the Efficacy of SCMs in Mitigating Alkali-Silica Reaction Assessed by Accelerated Mortar Bar Test

Abstract

This study evaluates the effect of limestone mineral addition in cement on the efficacy of supplementary cementitious materials (SCMs) in mitigating alkali-silica reaction (ASR) using the accelerated mortar bar test (AMBT). Mortars with and without SCMs were prepared by substituting portions of 0% limestone general portland (GP) cement with increasing amounts of limestone. Mortars with SCMs (25% fly ash or 65% slag) exhibit negligible expansion regardless of the limestone content in the binder, whereas mortars without SCMs exhibit high and almost identical expansion for all limestone substitutions. The expansion results show that limestone does not aggravate ASR, has no detrimental effect on the efficacy of SCMs in ASR mitigation, and likewise has no observable ASR-mitigating properties under the test conditions. The calcium silicate hydrate (C-S-H) composition is not affected by the amount of limestone, which suggests that limestone has no influence on the alkali uptake in the C-S-H. This is supported by the pore solution analysis results where SCMs (both fly ash and slag) have drastically reduced the pore solution alkali concentration over time, whereas limestone substitution only resulted in an alkali reduction equivalent to the substitution (dilution). Moreover, the carboaluminate phases formed when limestone is present were observed to decompose under AMBT conditions; thus, their influence on ASR mitigation is not possible to discern from this study.