The influence of alkali to aluminum ratio in pore solution on alkali-silica reaction and its correlation to aluminate phases

Abstract

This study aims to establish an overall relationship between ASR expansion and Alkali-Al ratio in pore solution. Mortars containing various aluminate hydrates or not were immersed in NaOH solutions for ASR expansion test (38 °C). Solid and aqueous compositions of the corresponding pastes were analyzed using XRD and ICP-OES. The dissolution of reactive silica under different alkali and Al concentrations in pore solution were examined by SEM images. The results indicate that the relationship between ASR expansion and Alkali-Al ratio can be characterized by an S-shape trend consisting of two thresholds (1.8 × 103 & 3.2 × 103). These two thresholds are closely related to various aluminate phases in pastes as their solubility is a key factor influencing Alkali-Al ratio. The presence of strätlingite of high solubility maintains Alkali-Al ratio at very low levels, at which ASR expansion is strongly controlled. In contrast, the absence of aluminate phases leads to very high Alkali-Al ratios, allowing ASR to take place even at alkali concentrations as low as 200 mM. When Al concentration is controlled by ettringite and monosulfate (maybe carbonates), Alkali-Al ratio varies between two thresholds depending on the alkalinity of the pore solution and Al uptake in CSH, and ASR expansion increases with this ratio.