Alkali-silica reaction in metakaolin-based geopolymer mortar
Résumé
This paper assesses the behaviour of metakaolin-based geopolymers in the presence of alkali-reactive aggregates. Geopolymer mortars were made with flash metakaolin and sodium waterglass solution in presence of six different aggregates, each having different levels of reactivity to alkali-silica reaction (ASR). The behaviour of geopolymer in presence of such reactive aggregates was investigated by monitoring the dimension changes and the dynamic modulus of the specimens placed in accelerated conditions at 60 A degrees C and 95 % RH for up to 250 days. SEM and EDX analyses were also performed at 170 days to visualize the newly formed products. A comparison with an ordinary Portland cement (OPC) was made for all aggregates in order to evaluate how strongly geopolymers were affected by ASR, if at all. Results showed that geopolymers, although they contained high concentrations of alkalis, were more able to resist ASR than OPC was, and no characteristic swelling or any significant loss of rigidity was observed for the geopolymer specimens. An exception was nevertheless noted for the mortar made with crushed glass sand, where a significant drop in rigidity was found, with the presence of a gel layer at the surface of the glass grains but without any swelling.