Impact of calcium content and pH value on MICP crack healing of geopolymer concrete

In recent years, microbial-induced carbonate precipitation (MICP) is becoming a popular method of soil stabilisation and concrete crack healing. In MICP, calcium is a necessary reactant, and pH value is a crucial factor for living bacteria. Both parameters (i.e., calcium and pH) are adjustable for geopolymer concrete mix design. Given the attractive potential for future applications of geopolymer concrete, understanding the impact of calcium content and pH value of MICP crack healing in geopolymer concrete mix design is of great importance. In this study, it was found that high calcium content in geopolymer concrete mix design is helpful to improve the healing effect. When CaO% in mix design increases from 7.5 % to 18.3 %, the healing degree increases. When Na2O% increases from 4.4 % to 11.6 %, the pH value of geopolymer concrete is improved by around 1, and it was also found that the impact of pH value depends on the way healing is implemented. In the case where bacteria were applied from outside of the healing surface cracks, the effect of pH value was almost negligible. However, when bacteria were used for internal healing, the lower pH value of the geopolymer mix design was beneficial for bacteria to provide a more suitable environment for bacterial activity and thus generate healing products. Therefore, the adjustment of calcium content and pH value in the geopolymer mix design can enhance the effectiveness of MICP crack healing for geopolymer concrete.