The role of calcium on the formation of alkali-silica reaction products

Predicting the conditions for alkali-silica reaction (ASR) had been difficult for several decades due to the lack of in-depth knowledge of the ASR products. In this study, thermodynamic data for the synthesized ASR products (i.e., K-shlykovite, Na-shlykovite and ASR-P1) at 80 degrees C are determined. The effect of the initial Ca/Si ratio, from 0 to 0.5, on the formation of ASR products at 80 degrees C is investigated for the samples prepared with an initially fixed K/Si or Na/Si ratio of 0.5. The results show that the amount of ASR products formed first increases and then decreases with increasing the initial Ca/Si ratio. The reduced amount of ASR products at higher Ca/Si ratio is accompanied by formation of C-S-H, suggesting that a conversion of ASR products to C-S-H can occur at high Ca/Si ratio. The solid phases and aqueous chemistry predicted by thermodynamic modelling agrees very well with the experimental results.