Three-Dimensional Microstructure Modeling and Mechanical Property Investigation of Pisha Sandstone-Slag Composite Soil Based on GIS

To mitigate the disintegration and erosion of Pisha sandstone and reduce the carbon footprint of traditional cement-based stabilizers, this study employs industrial by-product blast furnace slag to develop an alkali-activated Pisha sandstone–slag composite soil. Utilizing GIS-based 3D modeling, the research systematically examines the influence of varying slag contents (5%–25%) and curing periods (7–60 days) on the material's mechanical properties and microstructure. Results indicate that increasing slag content enhances the unconfined compressive strength (UCS), achieving up to 10.00 MPa at 25% slag and 60-day curing—representing a 46.52% improvement over Pisha sandstone stabilized with 15% cement (5.89 MPa at 28 days). XRD analysis reveals that alkaline conditions facilitate the dissolution of montmorillonite in Pisha sandstone, releasing active silicate and aluminate ions that form amorphous aluminosilicate gels and sodalite phases, establishing a geopolymer network. The hydration products of slag, namely C-S-H and C-A-S-H gels, further fill pores, enhancing structural compactness. SEM image-based 3D reconstructions show a decrease in porosity from 65.02% to 56.25% as slag content increases. A polynomial regression model (R² = 0.993) correlates 28-day UCS with 3D porosity, offering a theoretical foundation for mix design optimization. This research presents an eco-friendly and practical solution for soil erosion control in the Yellow River Basin and the valorization of industrial solid waste.