Abstract
Abstract Silty clay, a low-plasticity fine-grained soil widely used in transportation and municipal infrastructure, often exhibits insufficient bearing capacity and high deformation sensitivity. To enhance its mechanical performance, this study employed calcined coal gangue (CG) and ground granulated blast-furnace slag (GGBS) as precursors, activated by sodium silicate (Na₂O·nSiO₂). A combination of single-factor tests and Box–Behnken response surface methodology (RSM) was used to optimize mix proportions, with unconfined compressive strength (UCS) at 7 and 28 days as evaluation indices. Reaction products and microstructural evolution were further characterized by X-ray diffraction (XRD) and semi-quantitative scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS). The results showed that alkali-activated CG-GGBS binders markedly improved soil strength. The maximum UCS values reached 3.0 MPa at 7 days and 6.5 MPa at 28 days, representing increases of approximately 650% and 1410% compared with untreated soil. The optimal mix identified by RSM consisted of 13.8% CG, 16.4% GGBS, and 6.3% Na₂O·nSiO₂. Microstructural analysis revealed that balancing the calcium and aluminosilicate reactive phases drives the synergistic co-precipitation of C–(A)–S–H and N–A–S–H gels. This interlocking dual-gel network filled soil pores and progressively transformed the soil structure from loose to compact. In conclusion, utilizing this 100% industrial solid-waste precursor provides a potential and promising low-carbon alternative to traditional cement. Drawing on existing life-cycle assessments of similar waste-based geopolymers, it is estimated to offer a potential 40%–70% reduction in CO2 emissions, demonstrating a more sustainable strategy for silty clay stabilization. Graphical Abstract