Salt weathering effects induced by sodium sulfate crystallisation on biocemented materials

As an environmentally friendly technology, microbially induced carbonate precipitation (MICP) provides a novel approach to improve ground and repair concrete cracks. Currently, researchers have indicated that MICP can enhance the resistance of concretes to salt crystallisation; however, the impact of salt weathering on biocemented materials is generally ignored. Therefore, this study deeply investigates the salt weathering effects on biocemented materials by subjecting the biocemented samples to wet–dry (WD) cycles with respect to sodium sulfate (Na2SO4). The experimental results reveal that the biocemented samples exhibit severe degradation after WD cycles, even at a sodium sulfate concentration as low as 5 wt.%. This is because the sodium sulfate crystals precipitate and grow in the pores during WD cycles, generating significant pressure on the pore walls. Thus, the microcracks are formed and enlarged between calcium carbonate (CaCO3) bridges and sand particles. As the cycles progress, the more and larger microcracks ultimately break the calcium carbonate bonds, leading to the detachment of the sand particles and the strength loss in the samples. Overall, this study explores the salt weathering effects on biocemented materials, which may pave the way for MICP applications in saline environments.