Mitigating alkali-silica reaction in cement mortars through microbial carbonate precipitation technique

Alkali-Silica Reaction (ASR) is a major cause of durability reduction in cement mixtures. This reaction takes place between the reactive silica contained in aggregates and the alkaline elements contained in cement (sodium and potassium), producing a hydrophilic gel known as glass water. This gel swells upon absorbing water, causing a damaging internal pressure in the mortar. This study aimed to investigate the impact of Microbial-Induced Calcite Precipitation (MICP) with Sporosarcina pasteurii on the progress of ASR in cement mortars. The mortars were made using the accelerated mortar bar method (ASTM C1260) by substituting 0, 25, 50, 75, and 100 % of aggregates with waste glass, as the extreme material causing ASR. The glass was treated by two methods named Wet Calcite Precipitation (WCP) and Fixed Calcite Precipitation (FCP), which both involved spraying 0.5 ml/cm2 of bacterial suspension on the glass. After 28 days of exposure to alkaline conditions, the mortars were examined by Scanning Electron Microscopy, X-ray Diffraction spectroscopy, and Energy-dispersive X-ray spectroscopy to verify the occurrence of ASR. The mortars were subjected to the expansion test, the ultrasonic pulse velocity (UPV) test, and the compressive strength test to measure their physical and mechanical properties. Both MCP treatments managed to significantly reduce the adverse effects of ASR (compared to the control) at the 95 % confidence level. Between WCP and FCP, WCP was more effective in improving the results of UPV and expansion tests, and FCP was more effective in improving compressive strength. The findings showed that MICP can effectively inhibit the adverse effects of ASR in cement mortars.