Influence of Urea Pre-hydrolysis Strategy on Soft Clay Solidification by Microbes and Reactive Magnesia

Substantial quantities of engineering waste soils are generated due to the rapid infrastructure development in China.To alleviate this issue,bio-carbonation of reactive magnesia (r-MgO) technology,utilizing a urea pre-hydrolysis strategy,was employed to solidify soft clay for resource utilization.The effects of solidification methods,pre-hydrolysis duration (T),and urea concentration (C) on soil improvement were systematically investigated through unconfined compressive strength tests,pickling-drainage tests,dry density measurements,and water content assessments.The results show that:(1) The urea pre-hydrolysis strategy significantly enhances the solidification of soft clay,with the 7-day cured bio-carbonized sample exhibiting a 1.5-fold strength increase compared to samples without pre-hydrolysis,matching the strength of Portland cement-treated samples with 28-day curing.(2) Increases in both T and C promote urea hydrolysis and produce more carbonate ions for r-MgO bio-carbonation;however,the strength of bio-carbonized samples shows a change from rise to fall,with optimum T and C at 12 hours and 2mol/L,respectively.(3) A moderate increase in carbonate content produces more hydrated magnesium carbonates (HMCs) to improve the strength of bio-carbonized samples,while excessive carbonate content inhibits strength enhancement by negatively affecting the cementation performance of HMCs.