Strengthening Comparison of Carbonated Stabilized Soils Under Different Organic Matters

Organic matter is widely recognized as a key factor limiting the effectiveness of conventional cement stabilization of soft soils, thereby affecting the performance of reinforced soil layers used in construction. However, the influence of different organic matter components on reactive MgO carbonation reinforcement remains insufficiently understood. In this study, silty clay containing varying contents (0~8%) of fulvic acid (FA) and HA (HA) was treated using Portland cement (PC) stabilization, MgO stabilization, and MgO carbonation. The engineering performance and microstructural characteristics of the reinforced soils were evaluated through measurements of dry density, unconfined compressive strength (UCS), pH, X-ray diffraction (XRD), scanning electron microscopy (SEM), and pore structure analysis. The results indicate that MgO carbonation exhibited the highest densification efficiency among the three curing methods, resulting in significantly higher dry density and UCS values than those obtained under PC curing and MgO curing. Increasing organic matter content generally reduced the alkalinity of the stabilized soils and adversely affected strength development. The inhibitory effect of FA on stabilization performance was more pronounced than that of HA, as evidenced by a lower minimum UCS and greater sensitivity to organic matter dosage. Carbonation treatment effectively mitigated the negative influence of both FA and HA, producing substantially higher strengths than the other curing methods. XRD analysis revealed that nesquehonite, dypingite, and hydromagnesite were the major carbonation products, while increasing organic matter content reduced the formation of these strength-contributing phases and promoted the retention of uncarbonated brucite. SEM observations further confirmed that organic matter altered the morphology and distribution of carbonate products, resulting in a looser microstructure despite a reduction in pore volume. Overall, the findings demonstrate that reactive MgO carbonation stabilization possesses stronger resistance to organic matter interference than conventional PC stabilization and can effectively improve the engineering performance of organic-rich soft soils while facilitating CO₂ sequestration. This study provides experimental evidence and design-relevant insights for the optimal application of low-carbon MgO-CO₂ stabilization technology in reinforced soil construction.