Mechanical Properties of Carbonation-Enhanced Alkali-Activated Slag-Solidified Shield Muck: Temperature–Humidity Coupling Effects

Efficient resource utilization of shield muck is critical for urban metro construction. This study investigates temperature–humidity coupling effects on the mechanical properties of carbonated alkali-activated slag-solidified shield muck through multi-scale analyses of compressive strength, pore structure, alkalinity, and microproperties. The results show that carbonation product filling in >1000 nm pores governs 28-day strength enhancement. Humidity regulates reactions via dual pathways. High humidity inhibits CO2 diffusion, causing under-carbonation, and low humidity will lead to excessive carbonization under expansion stress, both increasing harmful porosity. Concurrently, low humidity depletes alkalinity, inhibiting C-A-S-H gel formation, whereas high humidity dilutes pore liquid alkalinity. Temperature modulates alkalinity through CO2 diffusion, Ca2+ leaching, and evaporation—low temperatures preserve alkalinity, while high temperatures intensify surface carbonation and internal alkalinity loss. Synergistic temperature–humidity interactions drive calcite and C-A-S-H gel co-generation via CO2 transport control, Ca2+ leaching optimization, and pore water-phase regulation, ultimately determining mechanical performance evolution.