Mechanical–microstructural properties of biochar–MICP–cemented sand by particle size

Microbially induced calcium carbonate precipitation (MICP) technology is widely used in soil reinforcement, but it still has challenges in improving cementation uniformity and mechanical properties. In this paper, the effects of biochar content on MICP reinforcement effect were discussed by using calcareous sand with different particle sizes (0.25 mm, 0.5 mm, and 1 mm). The role of biochar in improving cementation uniformity and calcium carbonate deposition distribution was revealed by unconfined compressive strength (UCS) test, bacterial retention rate analysis, scanning electron microscopy (SEM), and X-ray diffraction (XRD) characterisation. The results showed that the incorporation of biochar significantly improved the bacterial retention rate and sand column uniformity and optimised the distribution of calcium carbonate deposition. UCS showed: UCS0.25 mm > UCS0.5 mm > UCS1 mm, and with the increase of biochar content, UCS showed a trend of increasing first and then decreasing, and the optimal content was 4% (0.25 mm), 6% (0.5 mm), and 8% (1 mm), respectively. SEM and XRD analysis showed that biochar promoted the deposition of calcium carbonate by acting as a nucleation site, which significantly improved the bridging effect and pore filling effect between particles, thereby improving the bonding uniformity and mechanical properties.