Synergistic quicklime-microbial stabilization of red-bedded mudstone

To enhance the stabilization performance of red-bedded mudstone subgrade soil, a novel synergistic technique combining microorganisms and quicklime was developed and evaluated through comprehensive physical, mechanical, and microstructural analyses. The results demonstrated that quicklime significantly improved the pore structure by increasing the proportion of pores with diameters in the range of 0.5–50 μm, thereby facilitating microbial migration and calcium carbonate precipitation. The proposed technique effectively enhanced cementitious material production (cementation rate: 6.83 %), unconfined compressive strength (1.63 MPa), and resistance to swelling and deformation (swelling rate: 0.26 %). The observed synergistic effect can be attributed to two primary mechanisms. First, quicklime promotes soil particle agglomeration, resulting in larger pores that enable bacterial mobility and provide optimal microenvironments for microbial activity. Second, during curing, quicklime undergoes hydration and ionization, releasing Ca2+ and OH− ions. The Ca2+ ions serve as calcium sources for microbial-induced carbonate precipitation, while the OH− ions react with SiO2 and Al2O3 to form hydrated gels that develop a skeletal soil structure. Meanwhile, the exothermic reaction further accelerates calcium carbonate deposition within the agglomerated pores.