An efficient bio-stabilization technology with bio‑carbonation of reactive magnesia for soil improvement in cold regions

Low curing temperature conditions (5–15 °C) in cold regions pose major challenges for soil improvement using conventional binders, underscoring the urgent need for solutions to enhance soil strength and ensure engineering safety. This study investigated the feasibility and temperature-dependent behaviors of bio‑carbonation of reactive magnesia (BCRM) technology for soil improvement in cold regions. Unconfined compressive strength tests were conducted to explore the effects of curing temperature (T) and curing age (t) on strength enhancement. Combined with macro- (water content and dry density) and micro- (mineral composition and microstructure) analysis, the underlying mechanisms were elucidated. Experimental results showed that low T retarded the bio‑carbonation reaction of reactive magnesia, resulting in longer t required to obtain stable ultimate strength. However, despite lower increase rates, bio‑carbonized samples achieved higher ultimate strength and secant modulus at lower T. It was primarily attributed to the preferential formation of hydrated magnesia carbonates with higher content and crystallinity at low T, which enhanced the bridging and bonding performance. Comparative analyses with ordinary Portland cement (OPC) highlighted the superior efficiency of BCRM technology in stabilizing soil at low T, showing higher ultimate strength and shorter curing age. Notably at 5 °C, the ultimate strength of the bio‑carbonized sample cured for 12 days was up to 2.94 times that of the OPC-reinforced sample cured for 28 days. This study provides an efficient solution for soil improvement in low-temperature conditions. It is expected to enhance soil stability and hold significant implications for preventing and mitigating geological and geotechnical risks associated with soil deterioration in cold region engineering.