Mechanical properties and frost resistance of self-healing concrete based on expanded perlite with different particle sizes as microbial carrier

Microbial mineralization technology enables self-diagnosis and self-healing of concrete cracks, however, with the application of this technology, especially in cold regions, the involvement of water causes damage to concrete in freeze-thaw. Therefore, in this study, the mineralization properties of microorganisms at different low temperatures as well as the adsorption and charge characteristics of expanded perlite with different particle sizes as microbial carrier were investigated. Concrete specimens were prepared using self-healing agents with different particle sizes, and their mechanical and self-healing properties were comprehensively evaluated after freeze-thaw cycles. The results showed that the number of microbial colonies and urease activity decreased with the decline of freezing temperature, and the freeze-thaw cycling process exacerbated the further decrease of urease activity to 12.3% of the original activity. With the decrease of carrier particle size, the adsorption effect increased and the protective effect on microorganisms in alkaline environment was more significant. Concrete freeze-thaw tests showed that the best frost resistance was achieved with a self-healing dose of 0.6 mm-1.2 mm, with a mass loss and relative dynamic elastic modulus of 1.18% and 91.7% at 300 freeze-thaw cycles. Additionally, the self-healing dose in this particle size range showed the best repair performance with a maximum crack repair width of 1.063 mm and an average repair width of 0.512 mm, 0.479 mm, 0.443 mm, and 0.421 mm after 0, 100, 200, and 300 freeze-thaw cycles, respectively.