Strengthening Comparison of Carbonated Stabilized Soils Under Different Organic Matters

Organic matter critically restricts the effectiveness of conventional cement stabilization of soft soils and undermines the performance of reinforced soil layers. However, how different organic matter components affect reactive MgO carbonation reinforcement remains poorly understood. This study adopted Portland cement (PC) stabilization, MgO stabilization and MgO carbonation to treat silty clay with 0~8% fulvic acid (FA) and humic acid (HA). The engineering performance and microstructural features of stabilized soils were investigated via dry density, unconfined compressive strength (UCS) and pH tests, combined with X-ray diffraction (XRD), scanning electron microscopy (SEM) and pore structure analysis. The results show that MgO carbonation achieved the optimal densification effect, delivering distinctly higher dry density and UCS than the other two methods. Increased organic matter content reduced soil alkalinity and hindered strength development, with FA exerting a stronger inhibitory impact than HA due to lower UCS and higher dosage sensitivity. Carbonation effectively mitigated the adverse effects of FA and HA and yielded superior soil strength. XRD identified nesquehonite, dypingite and hydromagnesite as dominant carbonation products; organic matter reduced the formation of these strength-enhancing phases and retained uncarbonated brucite. SEM further verified that organic matter modified carbonate morphology and distribution, forming loose microstructures despite reduced pore volume. Overall, reactive MgO carbonation presents stronger anti-interference capability against organic matter than conventional PC stabilization. It improves the performance of organic-rich soft soils and realizes CO2 sequestration. This study provides experimental support and practical insights for the engineering application of low-carbon MgO-CO2 soil stabilization technology.