复合侵蚀对微生物固化建设弃渣土的耐久性影响

Effect of composite erosion on the durability of microbial solidified construction waste soil

  • 摘要: 建设弃渣土在寒旱区等环境中面临冻融-风蚀复合侵蚀威胁,针对微生物诱导碳酸钙沉淀(MICP)技术固化建设弃渣土的耐久性问题,通过冻融-室内风洞试验与微观结构测试,系统研究了复合侵蚀条件下固化建设弃渣土的强度衰减规律与微观损伤机制。结果表明:随着复合侵蚀次数的增加,试样表观形貌整体性降低、表面强度和固化层厚度降低、其风蚀质量损失逐渐增加,但经历9次冻融循环后,其累计风蚀质量损失率仅为0.117%,远低于原状土样的8.12%,表面强度下降8.29%,复合侵蚀下强度损失为19.62%,表明仍具有较高的抗风蚀扬尘能力和抗复合侵蚀耐久性;建设弃渣土的孔隙比越小、固化次数越多其固化改良效果越好,抗复合侵蚀耐久性越强;微观分析发现,随着冻融次数的增加,试样浅表层的孔隙率增加,整体性降低,土颗粒间黏结性降低,对碳酸钙晶体形态影响较小,仍以方解石为主,含少量球霰石和文石;三维结构分析进一步表明,微生物固化后表层碳酸钙含量显著增多,且随着沿径向入渗深度的增加逐渐减少,其孔隙度分布正好相反,沿径向孔隙度明显增加。

     

    Abstract: The construction waste soil is faced with the threat of freeze-thaw-wind erosion in cold and arid areas. In order to solve the durability problem of solidified construction waste soil by microbial induced calcium carbonate precipitation (MICP) technology, the strength attenuation law and micro-damage mechanism of solidified construction waste soil under combined erosion conditions were systematically studied by freeze-thaw-indoor wind tunnel test and microstructure test. The results show that with the increase of the number of composite erosion, the integrity of the apparent morphology of the sample decreases, the surface strength and the thickness of the solidified layer decrease, and the wind erosion mass loss increases gradually. However, after 9 freeze-thaw cycles, the cumulative wind erosion mass loss rate is only 0.117%, which is much lower than 8.12% of the undisturbed soil sample. The surface strength decreases by 8.29%, and the strength loss under composite erosion is 19.62%, indicating that it still has high wind erosion dust resistance and composite erosion resistance durability. The smaller the void ratio of the construction waste soil and the more the curing times, the better the curing improvement effect and the stronger the durability of the composite erosion resistance. Microscopic analysis showed that with the increase of freeze-thaw cycles, the porosity of the shallow surface layer of the sample increased, the integrity decreased, the adhesion between soil particles decreased, and the influence on the crystal morphology of calcium carbonate was small, still dominated by calcite, containing a small amount of vaterite and aragonite. Three-dimensional structure analysis further showed that the content of calcium carbonate in the surface layer increased significantly after microbial solidification, and gradually decreased with the increase of radial infiltration depth. The porosity distribution was just the opposite, and the porosity increased significantly along the radial direction.

     

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