钙源和Ca2+浓度对EICP固化钙质砂效果影响的试验研究

    EXPERIMENTAL STUDY ON THE EFFECT OF CALCIUM SOURCES AND CA2+ CONCENTRATION ON EICP CURED CALCAREOUS SAND

    • 摘要: 酶诱导碳酸钙沉淀技术(EICP)是一种环保高效的土体加固技术,钙源的种类可能会影响其加固效果。为定量化分析钙源对EICP固化钙质砂的影响,本文开展了不同钙源(氯化钙、醋酸钙、乳酸钙、硝酸钙)和不同Ca2+浓度(0.25 M、0.5 M、0.75 M、1 M)的砂柱固化试验和水溶液试验。通过无侧限抗压测试、渗透性测试、碳酸钙生成量测定、SEM微观分析,从宏观和微观角度对EICP固化钙质砂的效果进行探讨和分析。结果表明:在钙离子浓度较高时(Ca2+=1 M),氯化钙作为钙源固化出的强度较高,在钙离子浓度较低时(Ca2+≤0.75 M),硝酸钙作为钙源固化出的强度较高;在减小试样渗透性方面:醋酸钙>氯化钙>硝酸钙>乳酸钙,醋酸钙作为钙源固化出的试样渗透性下降最明显;不同钙源在水溶液中的反应速度大致为:硝酸钙>氯化钙≈乳酸钙>醋酸钙;不同钙源下沉淀产物的晶体类型和微观形貌有区别,氯化钙、醋酸钙作为钙源所形成的碳酸钙晶体形态为菱形,乳酸钙作为钙源生成的碳酸钙晶体形态为三角形且尺寸较小,醋酸钙作为钙源生成的碳酸钙晶体形态呈现多个小球包裹所形成的不规则球状。

       

      Abstract: Enzyme-induced calcium carbonate precipitation(EICP) is an environmentally friendly and efficient soil consolidation technique,and the type of calcium source may affect its consolidation effect. In order to quantify the effect of calcium source on EICP-cured calcareous sands,experiments on sand column curing with different calcium sources(calcium chloride,calcium acetate,calcium lactate,calcium nitrate) and different Ca2+ concentrations(0.25 M,0.5 M,0.75 M,1 M) and aqueous solution experiments were carried out in this paper. The effects of EICP curing of calcareous sands were explored and analysed from macroscopic and microscopic perspectives through unconfined compressive tests,permeability tests,calcium carbonate production measurements,SEM test analyses. The results showed that the strength of specimens cured with calcium chloride as the calcium source is higher at higher calcium ion concentrations(Ca2+=1 M) and calcium nitrate as the calcium source at lower calcium ion concentrations(Ca2+≤0.75 M). In terms of reducing the permeability of the specimen: calcium acetate>calcium chloride>calcium nitrate>calcium lactate,with the most significant decrease in permeability of specimens cured with calcium acetate as the calcium source. The crystal types and microscopic morphology of the precipitation products differ between calcium sources. Calcium chloride and calcium acetate as calcium sources formed rhombic-shaped calcium carbonate crystals. The calcium carbonate crystals formed by calcium lactate as the calcium source were triangular in shape and smaller in size. Calcium acetate as calcium source produces calcium carbonate crystals with irregular spherical shape formed by wrapping several small spheres.

       

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