Bio-mineralization induced by Bacillus mucilaginosus in crack mouth and pore solution of cement-based materials

Cement-based Materials have been widely used in the world, and bacteria have a capacity to induce mineral precipitation and can be applied to heal crack and resist efflorescence of cement-based materials. In this paper, Bacillus mucilaginosus was used for inducing mineralization by fixing CO₂ from the air. The calcium-containing substances in cement-based materials that participating in the bio-mineralization were analyzed. Among them, the reaction between C₃S and CO₂ in the air can be ignored, and the mineralized products of Ca(OH)₂ were mainly calcite, while the mineralized products of C-S-H were mainly aragonite. The results of XRD and SEM indicated that products obtained by reaction between C₃S paste and CO₂ were calcite, so the calcium-containing substances participating in bio-mineralization was mainly Ca(OH)₂. The effect of bacteria cells on the formation of carbonate ions was analyzed. The pH value and the concentration of ions indicated that the absorption of CO₂ was accelerated when the bacteria were involved, and more carbonate ions were supplied to bio-mineralization. The experiments of Zeta potential and conductivity showed that bacteria cells had an adsorption effect on Ca²⁺ because of its negatively charged surface. The analysis of nucleation kinetics indicated that calcium carbonate nucleated on the surface of bacteria cells, and its followed heterogeneous model, the rate of nucleation was 3.36 × 10^-4 s^-1-3.38 × 10^-3 s^-1. Analysis of every mineralization step showed that the enzyme-catalyzed reaction rate was the minimum when microorganisms existed, and it was the control step.