Aerobic bacteria induced biomineralization: effects of nutrient and calcium content on the nanostructure and chemical composition of simulated cement mixture

During the past two decades, aerobic bacteria induced biomineralization has gained popularity for autonomous sealing of cracks in concrete structures due to its environmentally friendly characteristics of carbon retention. However, the mechanism of the biomineralization induced by aerobic bacteria for concrete crack sealing is still unclear due to the complex chemistry of cement matrix. Also, as the main nutrient for bacterial growth, the effect of yeast extract (YE) on biomineralization should be properly evaluated. For the first time, this study investigates the effects of YE and calcium content on the development of nanostructure and chemical composition of cement matrix during the biomineralization process induced by aerobic bacteria Bacillus cohnii. The effects of calcium content were realized by constructing a simulated cement mixture consisting of calcium hydroxide and synthesised C-S-H with different C/S ratios. The effects of YE content were evaluated by the addition of different amounts of YE into simulated cement mixture with different C/S ratios. Results suggest that 10g/l of YE can cause a high pH value of 10 and an unsuccessful growth of bacteria in simulated cement mixture with C/S ratios 0.6 and 0.8. Upon increasing the YE from 10 g/l to 20 g/l, the pH reduced from 10 to 9 and the bacteria was successfully grown. Higher amounts of bicarbonate ions can cause an enhanced decalcification of synthesised C-S-H rather than calcium hydroxide. The aerobic bacteria Bacillus cohnii showed superior performance on calcium absorption and calcite precipitation, being a promising way for practical concrete crack sealing.