Performance Study of Alkali-Activated Coal Gangue Powder-Based Geopolymer Flowable Solidified Soil

This study explores the use of alkali-activated coal gangue powder (CGP) as a sustainable stabilizer to improve loess performance, aiming to promote industrial solid waste valorization and low-carbon geotechnical construction. The effects of binder dosage on flowability, unconfined compressive strength (UCS), and water stability were systematically evaluated, and microstructural mechanisms were examined by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that increasing binder dosage reduced the flowability and setting time while maintaining values above 160 mm, ensuring practical applicability. UCS increased with curing age and binder dosage, reaching 2.06 MPa at 28 days with rapid early strength development. Water stability was significantly enhanced, as no disintegration occurred after 24 h of immersion, and high-binder samples exhibited a buoyant mass increase 4.25 times that of low-binder samples, reflecting improved soil compactness and resistance to capillary water absorption. Microstructural analysis revealed that alkaline activation of CaO, SiO₂, and Al₂O₃ promoted calcium silicate hydrate (C-S-H) gel formation, creating a stable spatial network that strengthened particle bonding and minimized porosity. These findings indicate that alkali-activated CGP can effectively stabilize soil for engineering applications, including road subgrades, foundation improvement, and embankments, providing both sustainable material utilization and reliable geotechnical performance.