Mechanical behaviour and mechanisms of CCR-enabled alkali-activated UCG-stabilised clay

Uncalcined coal gangue (UCG) is a potential aluminosilicate precursor for soft-clay stabilisation, but its low reactivity limits alkali activation. This study examines calcium carbide residue (CCR)-enabled alkali-activated UCG-stabilised clay using unconfined compression, consolidated undrained triaxial testing, and scanning electron microscopy (SEM). The effects of CCR and alkaline activator (AA) contents, expressed relative to precursor mass, and UCG content, expressed relative to dry-clay mass, were evaluated. Unconfined compressive strength (UCS) increased with curing time and first increased and then decreased with CCR and AA contents, with optima of approximately 60% CCR and 40% AA within the investigated ranges. Increasing UCG from 10% to 30% increased UCS, stiffness, peak deviator stress, and apparent yield stress while reducing excess pore-water pressure. SEM observations showed that CCR and AA promoted particle coating, bridging, and microstructural densification. The mechanism is interpreted as a coupled CCR–AA–UCG process in which CCR supplies calcium and additional alkalinity, AA promotes precursor dissolution, and UCG provides silicon (Si)- and aluminium (Al)-bearing constituents. Compared with calcined coal gangue, UCG produced lower early strength but more sustained later-age strength development. The results indicate that effective use of low-reactivity UCG requires coordinated calcium supply and alkalinity, providing a potential route for soft-clay stabilisation and industrial by-product utilisation.