Efficient inhibition of ASR by microbially induced calcium carbonate precipitation on aggregates at a low degree of saturation

Alkali-silica reaction (ASR) is a chemical reaction between alkaline ions (Na+, K+), silicon phases and aluminum phases in the aggregate, causing volume expansion and cracking of the concrete, leading to a deterioration in the mechanical properties of the structure. In previous studies, microbially induced carbonate precipitation (MICP) technology had been demonstrated to be effective in inhibiting ASR. In this study, in order to explore better inhibition effect, MICP treatments of alkali active aggregates under different saturation degrees were tested. The results showed that when treated at a low-saturation degree (35 %), the inhibition effect of ASR was better comparing with that obtained at higher saturation degrees in the presence of same CaCO3 content. When the CaCO3 content was about 6 %, mortar bar specimens made of low-saturation treated aggregates possessed a 75 % reduction in the expansion and a 37 % increase in the compressive strength compared to the control group. In addition, through microstructure and component analysis of the aggregate surface, it was found that under the low-saturation treatment, the CaCO3 layer could be formed on the surface of the aggregate more uniformly and efficiently, with a higher binding strength to the aggregate and a greater Vickers hardness. Thus, it could better block the invasion of external alkaline ions to react with the active SiO2 inside the aggregate, leading to a better inhibition of ASR.