压实度对MgO碳化土加固效果的影响及其机理研究

活性MgO是一种用于软土加固的新型材料，与土体拌和并经CO₂气体碳化后可使固化土强度在数小时内显著提高。在已有研究的基础上，通过静压法制取86%、87%、89%、91%和92%五种不同初始压实度下活性MgO固化土试样，并对固化土试样进行室内碳化试验。对碳化前后的MgO固化试样进行了含水率、干密度和无侧限抗压强度测试，以研究压实度对MgO碳化土含水率、干密度和无侧限抗压强度的影响规律；最后从无侧限抗压破坏的试样中选取典型样品进行X射线衍射、热重、扫描电镜和压汞试验，根据碳化产物和孔隙特征2个方面分析MgO碳化固化土的微观特征。结果表明：MgO固化土碳化过程中消耗了大量CO₂和水分，生成的主要碳化产物为棒状三水菱镁石和片状水碳镁石/球碳镁石，这些碳化产物具有显著的胶结和填充作用，使氧化镁固化土试样的干密度和强度明显增加；固化土的初始压实度对碳化效果有较大影响，随着初始压实度的增加，碳化试样的含水率呈先减小后增加趋势，而无侧限抗压强度呈先增大后减小趋势；当固化土试样的初始压实度为中等压实度89%时，碳化后试样含水率最低，生成的碳化产物最多，碳化试样的无侧限抗压强度最大，孔隙率最小，说明该压实度为最佳初始压实度，最有利于氧化镁固化土的碳化加固。

Influence and Mechanism of Compaction Degree on Stabilization Effect of MgO-carbonated Soil

Reactive magnesia (MgO)is considered as a novel material used in soft soil stabilization, and the soil strength is significantly improved in several hours when the soil is admixed with reactive MgO and then subjected to carbonation of gaseous CO₂. On the basis of existing studies, reactive MgO-stabilized soil samples were prepared under the conditions of five different compaction degrees of 86%, 87%, 89%, 91%, and 92% using the static pressure method, and then the laboratory carbonation experiments of the MgO-stabilized soil samples were performed. Some tests for those pre-or post-carbonation MgO-stabilized samples were conducted including the tests of the moisture content, dry density, and unconfined compressive strength in order to study study the influence law of the compaction degree on the moisture content, dry density, and unconfined compressive strength of the MgO-carbonated soils. Finally, typical samples were chosen from the broken specimens after the unconfined compression tests, and the micro structural characteristics of the carbonated soils were analyzed from the aspects of the carbonation products and pore characteristics via the X-ray diffraction, thermo gravimetric, scanning electron microscope, and mercury injection tests. The results indicate that a large amount of CO₂ and water are consumed when the reactive MgO-stabilized soils are subjected to CO₂ carbonation, and the main carbonation products are prismatic nesquehonite and flaky dypingite/hydromagnesite, which have significant cementing and filling effects, facilitating the obvious improvement of the dry density and strength of the carbonated reactive MgO-stabilized soils. The initial compaction degree of the MgO-stabilized soils has a significant impact on the carbonation effect. With the increase in the initial compaction degree, the water content of the carbonated soils shows the trend of first increasing and then decreasing, whereas the unconfined compressive strength exhibits the opposite trends. When the initial compaction degree reaches the medium compaction degree of 89%,the water content of the carbonated samples is the lowest and most carbonation products are formed, leading to the largest unconfined compressive strength as well as the smallest porosity of the carbonated samples. Moreover, the compaction degree of 89% is demonstrated to be the best initial compaction degree and most beneficial for the carbonation of MgO-stabilized soil.