Impact of Alkali Release from Aggregates on Pore Solution of Mortars

When alkali reactive or marginally reactive aggregates are used in concrete, the concrete mixtures are mitigated by using SCMs or by limiting alkali loading. The level of mitigation depends on the reactivity of the aggregate. These mixtures may still undergo low levels of reaction with the alkalis in the binder system without causing deleterious expansion. During this time, the alkalinity of the system normally decreases as the alkalis are bound in the reaction products. However, if an aggregate contributes, or releases, alkalis into the binder system over time, it can drive additional ASR reaction, leading to long-term damage. RILEM has published the AAR-8 method to measure the potential for alkali release of an aggregate but there is no correlation between the results from that test and the impact on the pore solution in the concrete yet. In this study, four either reactive or innocuous aggregates were tested according to AAR-8 and used to make mortar specimens. The impact of these aggregates on the pore solution of mortar was studied by extracting the pore solutions at various ages. The mortar specimens were cured at 60 ℃ to accelerate the ASR reaction and to see if alkali release can impact the pore solution as the alkalis are consumed in the reaction. Results showed that both reactive and innocuous aggregates can potentially release alkalis. However, no impact was observed on the pore solution of mortar made with the aggregates. The two methods used to obtain the pore solution of the mortar showed similar results.