Microbial-induced spherical CaCO₃ enhanced cement hydration produced by a calcium lactate recipe

A microbially induced calcium carbonate precipitation (MICP) recipe utilizing calcium lactate was proposed to investigate its regulation of cement hydration and mechanical properties. At optimal concentrations (0.5 × 10⁹ CFU·mL⁻¹ biomass, 0.3 mol·L⁻¹ urea, 0.08 mol·L⁻¹ calcium lactate), the 28-day compressive and flexural strengths of cement mortar increased significantly by 45.82% and 36.79%, respectively. Compared to Ca(OH)2, calcium lactate produces more amorphous and spherical bio-CaCO3. These spherical particles efficiently fill pores, improving compactness. The calcium lactate-urea synergy accelerates hydration, evidenced by a 14.3% higher heat release rate, enhanced AFt-to-AFm conversion, and increased C-S-H gel polymerization. It also inhibits excessive Ca(OH)2 consumption, improving durability. The microorganism-calcium lactate complex reduces the activation energy for Ca(OH)2 and CaCO3 formation by 29.86% and 10.14%, respectively, facilitating sustained exothermic reactions. In summary, this recipe optimizes MICP by regulating CaCO3 morphology and hydration pathways, enhancing strength.