Sustainable stabilization of soft soils through reactive MgO-MgCl2 carbonation: Mechanistic insights and performance optimization

Portland cement, a conventional binder for soft soil stabilization, faces limitations in treating specialized soils due to its high carbon footprint and environmental impact during production. This study proposed an eco-friendly alternative using reactive magnesia (MgO) and magnesium chloride (MgCl2) for carbonation treatment of saline soft soils. The mechanical properties, hydrochemical behavior, water stability, and microstructural evolution of carbonation-stabilized soils were systematically investigated under varying salinity levels (MgCl2 content) and initial moisture conditions. Key findings revealed that unconfined compressive strength and modulus decreased with increasing initial water content but exhibited a unique trend under MgCl2 variation&#8212;initial gradual reduction (3&#8211;6% MgCl2) followed by significant enhancement (6&#8211;12% MgCl2). Carbonation efficiency declined from 40% to 10% with rising initial water content, while showing a V-shaped relationship with MgCl2 dosage (minimum at 6%). Post-carbonation pH decreased with higher MgCl2 content and lower initial moisture, whereas electrical conductivity increased proportionally to both parameters. Microstructural analyses identified distinct phase formations: low-MgCl2 (6%) systems produced flower-like hydromagnesite, spheroidal dypingite, and prismatic nesquehonite, while high- MgCl2 (12%) systems generated short-rod chloro-carbonates and acicular magnesium oxychloride crystals (5Mg(OH)2 MgCl2 8H2O). These crystalline phases collectively enhanced soil stabilization. Optimized performance was achieved at a magnesium-chloride molar ratio <6 and a water-chloride ratio of 12&#8211;17, demonstrating the viability of MgOMgCl2 carbonation activation for sustainable soil stabilization.