Mechanical Performance and Microscopic Mechanisms of Silty Clay Solidified by CaO-MgO Activated Ground Granulated Blast Furnace Slag

Offshore wind turbine foundations usually experience long-term scouring erosion in marine environments. Nowadays, fluidized solidified soil serves as an effective scour protection method, especially for soft soil solidification. This study utilized alkali-activated binders doping on ground granulated blast furnace slag (GGBS) for stabilizing excessive high-water-content clayey soil. Series of flowability tests, unconfined compressive strength (UCS) tests, and water stability tests, accompanied with scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR) tests, were conducted to investigate the mechanical performance, construction properties, and microscopic mechanisms. The results indicate that the optimal CaO-MgO doping simultaneously achieves: (1) sufficient workability (flowability≥160 mm) for pumpability requirements; (2) remarkable strength enhancement (226% UCS increase versus cement-solidified soil at 28 days); mechanistic analysis demonstrates CaO dominates early-age performance (7d strength increased by 158%), while MgO enhances later-stage strength development (28d strength improved by 42%) and pore structure refinement; (3) satisfactory water stability coefficient compared to cement-solidified soil, especially in early age; (4) more homogeneous microstructure, showing a 34% decrease in microporous region area (diameter>50 nm) through NMR image analysis; (5) alkali-activated slag solidified soil could save CO2 emissions by 562.24 kg/m3 compared with cement-solidified soil. In general, the alkali-activated slag solidified clayey soil provides carbon-efficient and sufficient mechanical performance and water stability for offshore wind turbine foundation scouring reinforcement.