The Mechanical Properties and Microstructural Evolution Mechanism of Carbonation-Cured Loess with Varying MgO Content

In alignment with global carbon neutrality goals, this study investigates the regulatory role of magnesium oxide (MgO) content on the macro–micro properties of carbonation-cured collapsible loess from the Hohhot region. While MgO carbonation is established for soil stabilization, the quantitative influence of MgO dosage on the specific phase evolution pathways and mechanical enhancement within the unique macro-porous fabric of aeolian loess remains poorly understood. Addressing this, we systematically examined loess specimens amended with varying MgO contents (10% to 30%) over carbonation periods up to 24 h. Unconfined compressive strength (UCS) tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to correlate mechanical performance with mineralogical and microstructural evolution. Results indicate that MgO content acts as a primary regulator of the carbonation process. Higher MgO dosages substantially increased CO2 uptake, resulting in a significant relative mass gain—up to more than a two-fold difference between the highest and lowest content samples—and culminated in a compressive strength of 10.48 MPa for the 30% MgO specimen. Microstructural analysis revealed a distinct temporal evolution interpreted to be governed by MgO-mediated supersaturation levels. Initially, Mg(OH)2 agglomerates provided early strength, which was subsequently enhanced by the formation of a three-dimensional framework of nesquehonite, followed by the development of an interlocking skeletal network of hydromagnesite crystals. These carbonate phases enhanced loess strength via a combination of pore infilling, particle cementation, and the construction of a reinforcing micro-skeleton. This work elucidates the link between MgO content and the microstructural evolution of carbonated loess, providing new insights for the synergistic integration of soil stabilization and carbon sequestration in loess regions. The findings offer a valuable reference for engineering applications in collapsible soil environments under the context of sustainable development.