From solid waste to subgrade stabilizer: lithium slag-calcium carbide residue geopolymer for silty clay subgrade stabilization

• A novel soil stabilizer was developed using lithium slag and carbide residue. • Strength and frost resistance of the stabilized soil were significantly enhanced. • A cumulative strain model considering freeze-thaw effects was established. • SEM and XRD analyses revealed microstructural and mineralogical changes. • The work promotes sustainable reuse of lithium slag in geopolymer applications. In seasonally frozen regions, silty clay subgrades often suffer from frost heave, thaw settlement, and mud pumping, which jeopardize road stability. This study utilizes lithium slag and calcium carbide residue to synthesize a lithium slag-based geopolymer stabilizer for modifying silty clay. A series of laboratory tests, including unconfined compressive strength, freeze-thaw cycles, dynamic triaxial tests, and microstructural analyses, were conducted. Results show that the geopolymer significantly improves both strength and freeze-thaw durability. After 28 days of curing, the UCS of the stabilized soil was 4 times that of untreated soil and 1.1 times that of cement-stabilized soil. Freeze-thaw strength loss was reduced by 60.13%, and accumulated plastic strain under coupled freeze-thaw and dynamic loading decreased by 14%. Microstructural observations indicate that calcium carbide residue provides sufficient alkalinity for the geopolymer reaction, facilitating the formation of aluminosilicate and calcium-aluminosilicate gels. These gels alter the soil structure from loose contact-based to cemented bonding, forming a denser matrix with enhanced mechanical performance. This study offers a sustainable approach for utilizing industrial solid waste and developing low-carbon soil stabilization technologies for cold region infrastructure.