Polymer action on alkali-silica reaction in cement mortar

Abstract

Polymer modification of mortar and concrete leads to reduced water absorption, lower ionic mobility, reduced thickness of the interfacial transition zone, lower availability of Ca(OH)2 and higher tensile strength and ductility and thus may have an inhibiting effect on alkali-silica reaction (ASR) and related damage. However, the existing studies are inconclusive and cover only a limited range of polymers. In this study, polymer-cement mortars (PCMs) based on styrene-butadiene, acrylic and epoxy polymer additions were subjected to an accelerated alkali reactivity test and their expansion compared with that of an unmodified cement mortar (CM). Despite their lower capillary water absorption in standard laboratory climate, the weight increase of PCMs during exposure to the 80 ºC NaOH solution bath of the alkali reactivity test was higher than that of the unmodified CM, promoting higher expansion due to ASR in PCMs. Even though SEM observations confirmed the existence of more extensive ASR in PCMs, microcracking in the cement paste of the unmodified CM was widespread, while little evidence of microcracking was present in the cement paste of PCMs. The potential for polymers to inhibit ASR and reduce related damage may be further evidenced through a more suitable alkali reactivity test at a temperature closer to field temperature, under which PCMs have been shown to have lower water absorption than unmodified CMs.