Mechanism of bacterial control of mineralisation gradient at the surface layer of cement-based materials

Cement-based composites reinforced with steel bars are the primary material in the construction of infrastructure. Their durability in the service environment is thus a crucial topic. The application of bio-mineralisation technology shows great prospects in improving the properties of cement-based materials (CBMs). In this study, the underlying mechanism was explored by investigating the effects of various factors on the mineralisation gradient at the surface layer of CBMs. Four factors were studied to investigate the process of bacterial action: the absorption of carbon dioxide from the air, the transformation of carbon dioxide into HCO3-, the adsorption of Ca2+ from the pore solution of CBMs and the formation of calcium carbonate in pores, which results in a decrease in porosity. The results of calcium carbonate content and porosity indicated that bacteria could regulate the mineralisation gradient at the surface of CBMs. Numerical calculations and experimental measurements were also conducted for further verification.