The effect of bacteria Bacillus Cohnii on the synthesised calcium silicate hydrate (C–S–H) with various calcium to silica ratio in nanoscale

Calcium silicate hydrate (C–S–H) is the main cement hydration product, providing the most mechanical strength to concrete structure. As per the previous studies of bacteria-based self-healing concrete using non-ureolytic bacteria, one of the main issues is that the amount of externally added calcium salt was restricted by the properties of carriers, limiting the content of precipitated calcium carbonate. In addition, previous studies barely investigated the potential impact of microbial activities on the individual cement hydration products. Therefore, in this study, for the first time, we investigated the individual impact of bacteria on synthesised C–S–H gel and the potential of biomineralisation of C–S–H gel. In light of results obtained in this study, we evidenced that C–S–H could be biomineralised to produce a considerable amount of calcium carbonate. Decalcification of C–S–H gel and microbial carbon-capture were simultaneously occurred prior to the precipitation of calcium carbonate, resulting in increase of calcium and bicarbonate ions in the solution. The amount of precipitated CaCO3 is closely in response to Ca/Si ratio in C–S–H, higher Ca/Si essentially led to more precipitates, whilst the remaining structure and mass of C–S–H gel that could not be further biomineralised was generally similar.