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.

Moisture content significantly influences strength development in solidified sludge. Ground granulated blast-furnace slag (GGBS) has been found to exhibit cementitious properties in alkaline environments. This paper investigates strength development patterns in portland cement (PC) and GGBS solidified sludge with different curing systems. The effects of initial moisture content (%), PC/GGBS ratio, and cementitious material dosage (kg/m3) on unconfined compressive strength were studied for closed system (CS) and open system (OS). X-ray diffraction (XRD), scanning electron microscopy, and thermogravimetric analysis (TG) tests examined strength and microreaction mechanisms. Results show that strength development and reaction mechanisms in CS differ from those in OS. In contrast to OS, where hydration/carbonation dominates, CS exhibits lower strength due to weakened cement reactions. Here, the PC/GGBS ratio becomes critical as the alkali-activated reaction between GGBS and alkali comes from cement hydration, which serves as the primary source of strength. Clay particles in sludge also participate in alkali-activated reactions in CS. XRD and TG results confirm these mechanistic differences. For in situ curing of high-moisture sludge, a PC/GGBS ratio of 7.5:2.5 and ≥100 kg/m3 cementitious material are recommended for optimal field application.