Influence of Urea Pre-hydrolysis Strategy on Soft Clay Solidification by Microbes and Reactive Magnesia
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摘要: 我国基础设施建设导致产生大量工程弃土，为实现软黏土的固化与资源化利用，提出了基于尿素预水解策略的生物碳化活性氧化镁技术.通过开展一系列的无侧限抗压强度测试、酸洗测试、干密度和含水率测试，重点探究了固化方式、预水解时间和尿素浓度对土体固化性能的影响.研究结果表明：(1)预水解策略可实现软黏土的高效固化，养护7d后生物碳化试样的强度相较于未预水解试样提升了1.5倍，甚至与养护28d水泥固化试样的强度相当；(2)预水解时间和尿素浓度的增加均可提高尿素水解量并产生更多碳酸根参与到活性氧化镁的生物碳化，但固化试样的强度整体呈现出先增后减的趋势，最优预水解时间和最优尿素浓度分别为12h和2mol/L;(3)适当增大碳酸根含量可促进更多胶结产物水合碳酸镁的形成，以提高固化试样的强度；但过高的碳酸根含量反而会影响水合碳酸镁的胶结性能，导致强度降低.Abstract: 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.
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Keywords:
- soft clay /
- reactive magnesia /
- bio-carbonation /
- pre-hydrolysis /
- microbes /
- unconfined compressive strength
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