Research on the preparation method and physical-mechanical properties of carbon sequestration lightweight soil

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.