摘要:
为减少碳排放、探寻岩土工程的二氧化碳（CO2）利用技术，本研究基于氧化镁（MgO）碳化固化原理，提出了一种固碳轻质土(Carbon sequestration lightweight soil, C-LS)原理，该原理采用MgO和渣土替代水泥作为固化材料、CO2替代空气发泡，将MgO、粉质黏土、水和CO2泡沫按一定比例混合后形成密度<1g/cm3的C-LS。通过无侧限抗压强度、扫描电镜和热重等宏微观试验，研究了不同MgO掺量、设计湿密度、水固比与碳化养护条件对C-LS的流值、凝结时间、干密度、强度、碳化产物及固碳能力的影响规律。结果表明：随MgO掺量和湿密度增加，C-LS流值和凝结时间减小，抗压强度提高，同时其固碳量提高。C-LS的最优配比为50%MgO、50%渣土、湿密度800kg/m3、水固比0.65，在自然养护下，其28d强度达1.18MPa，在外部加速碳化条件下，C-LS强度最高达1.86MPa，满足高速公路路堤填筑和其它填筑材料要求。根据C-LS强度与碳化产物产量及固碳量的内在联系，研究揭示了C-LS强度形成微观机理。C-LS技术能大量消耗CO2和工程渣土，为岩土工程固碳利用提供了崭新的技术途径。
Abstract:
To reduce carbon emissions and explore carbon dioxide (CO2) utilization technologies in geotechnical engineering, this study proposes a novel method for preparing carbon sequestration lightweight soil (C-LS) based on the magnesium oxide (MgO) carbonation mechanism. A mixture of MgO and waste soil is used as a binder instead of cement and CO2 instead of air for foaming. By mixing MgO, silty clay, water and CO2 foam in specific proportions, C-LS with a density of less than 1 g/cm3 is formed. Through unconfined compressive strength tests, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), the effects of MgO proportions, designed wet densities, water-to-solid ratios and carbonation curing conditions on the fluidity, setting time, dry density, strength, carbonation products and carbon sequestration capacity of C-LS were studied. The results show that with the increase in MgO proportion and wet density, the fluidity and setting time of C-LS decrease, while the strength and carbon sequestration efficiency improve. The optimal mix ratio of C-LS is 50% MgO, 50% waste soil, with a wet density of 800 kg/m³, and a water-to-solid ratio of 0.65. Under ambient conditions, the 28-day strength of C-LS reaches 1.18 MPa, with a carbon sequestration rate of 7.56%. Under accelerated carbonation conditions, the strength of C-LS reaches up to 1.86 MPa, meeting the requirements for highway embankment fill and other filling materials. Based on the intrinsic relationship between the strength of C-LS, the amount of carbonation product, and the carbon sequestration rate, the study reveals the strength formation mechanism of C-LS and proposes a microscopic model. The C-LS technology can significantly consume CO2 and engineering waste soil, providing a novel technical approach for CO2 sequestration in geotechnical engineering.
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