CO2碳化矿渣-CaO-MgO加固土效能与机理探索

CO₂碳化联合工业固废协同加固土技术是旨在替代传统水泥固化方法的新型技术尝试。以工业废料——矿渣为主要材料,辅以活性MgO和CaO形成矿渣-CaO-MgO固化体系,将固化土料均匀搅拌制样后进行CO₂碳化试验。通过无侧限抗压强度、扫描电镜和X射线衍射等试验,探究固化剂掺量、配比、碳化时间和初始含水率等因素对碳化加固土效果的影响。结果表明：CO₂碳化对土体加固具有明显改良效果,碳化24 h试样抗压强度最高可提升25.77倍;碳化试样抗压强度与固化剂掺量（6S4L0M除外）、活性MgO占比呈正相关;碳化试样强度随碳化时间先增加后趋于平缓（或略微下降）、最佳碳化时间为6 h左右,随初始含水率增加而先增加后下降、最佳含水率为16%左右;活性MgO碳化效能明显优于活性CaO,矿渣中低活性CaO并不能显著改良自身碳化性能。CO₂碳化作用促使碳酸盐晶体（CaCO₃、MgCO₃）生成,晶体发育程度与碳化时间、固化剂掺量及活性等因素有关;碳酸盐晶体有效填充试样内部孔隙并黏结土颗粒,形成整体骨架结构使试样强度得以大幅提升。

Performance and mechanism of CO2 carbonated slag-CaO- MgO-solidified soils

The proposed technology of CO₂ carbonation combined with industrial solid wastes is a novel attempt to replace the traditional Portland cement for soil stabilization. A series of CO₂ carbonation tests are performed on the soils solidified with slag-CaO-MgO blend, which contains the main material, industrial waste slag, and the supplementary materials, reactive CaO and MgO. The effect of binder dosage, MgO/CaO mass ratio, carbonation time and initial moisture content on carbonated-solidified soils are investigated by the unconfined compressive strength (UCS), scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The results show that the CO₂ carbonation treatment has an obvious improving effect on the mechanical properties of soils, and the compressive strength of solidified samples can be maximally increased by 25.77 times after carbonation of 24 h. The strength of carbonated soils is proved to be positively correlated with the binder content (except 6S4L0M) and proportion of reactive MgO. The prolongation of carbonation time induces an initial increase in strength until the peak, followed by an almost constant or slight decrease, and the optimal carbonation time corresponding to the peak strength is around 6 h. The compressive strength of carbonated samples increases first to the maximum and then decreases as the initial moisture content rises, and the optimal water content at peak strength is about 16%. The carbonation efficiency of reactive MgO is significantly better than that of reactive CaO, while the low reactivity CaO contained in slag cannot largely enhance the mechanical strength of solidified soils by accelerated carbonation. CO₂ carbonation promotes the formation of carbonate crystals (CaCO₃ and MgCO₃), and the growth of these crystals is closely related to the carbonation time, binder dosage and reactivity of components. The carbonate crystals can effectively fill the interparticle pores within samples and bind firmly soil particles together, forming an overall skeleton structure and improving greatly the strength behavior.