Traditional disposal methods such as landfilling and land reclamation are insufficient to mitigate the environmental impact of construction spoil, making non-sintered blocks a promising approach for resource utilization. This study investigates the production and performance of steel slag soil blocks as an alternative to conventional cement-based materials for non-sintered blocks. The optimal manufacturing parameters were identified as a sodium silicate solution with 6% Na₂O, 30% steel slag content, a liquid/solid ratio of 0.18, and a forming pressure of 10 MPa, achieving a peak compressive strength of 14.46 MPa. Further, the synergistic combination of alkali activation and carbonation enhanced compressive strength to 17.4 MPa, attributed to the development of a compact microstructure characterized by a honeycomb-like C-(A)-S-H gel and well-crystallized, triangular-shaped aragonite. However, durability tests under freeze-thaw and wet-dry cycles revealed that carbonation can detrimentally affect performance. The transformation of C-(A)-S-H gel into calcium carbonate, with relatively weaker cementitious properties, led to internal cracking and surface detachment. Micro-CT analysis confirmed ring-like patterns under freeze-thaw conditions and diagonal cracks during wet-dry cycling, whereas reference blocks incorporating 30% ordinary Portland cement maintained superior compactness with no cracks. These findings suggest that although the alkali activation and carbonation process enhances early strength, further optimization is necessary to improve long-term durability before broader application can be recommended.

Rapid infrastructure development generates large volumes of high-water-content sludge, creating an urgent need for efficient recycling and management strategies. This study introduces the flocculation–solidification–vacuum preloading (FSVP) method to enhance dewatering efficiency and strength development, facilitating subsequent mechanical construction requirements. To enhance solidification and reduce cement consumption, the response surface method was used to determine the optimal composite curing agent, which consists of 53% cement, 32% rice husk ash, and 15% sodium silicate. Vacuum dewatering was applied to sludge samples treated with different flocculants and curing agents to assess their synergistic effects on soil improvement. The mixed flocculant of polyaluminum chloride and anionic polyacrylamide significantly increased the micropore content and compactness, with pore sizes primarily concentrated around 0.01 μm. While the flocculant facilitated efficient drainage, required unconfined compressive strength could only be achieved with the further addition of a curing agent. The optimal composite curing agent formulation induced hydration and pozzolanic reactions, filling larger pores with cementitious materials and enhancing soil strength. As a result, the vane shear strength reached 58 kPa and unconfined compressive strength reached 365 kPa at 7 days, further increasing to 586 kPa at 28 days.

Maintaining stable tunnel face pressure in slurry shield tunneling is critically dependent on the formation of a low-permeability filter cake. However, the knowledge of the filter cake and mud spurt is not specifically understood. Using a modified fluid loss test, this study investigates the formation and hydraulic properties of filter cakes from various slurry mixtures under different pressures. The key findings reveal that CMC-Na (sodium carboxymethyl cellulose) serves as the most effective additive for enhancing slurry performance. A comprehensive database of constitutive model parameters for 15 slurry compositions was established, enabling precise prediction of the filter cake’s hydraulic conductivity and void ratio under any pressure. Analysis of the cyclic formation process revealed that the dynamic filter cake averages two-thirds of the maximum thickness, offering a key parameter for stability control. Furthermore, a practical mud spurt model was proposed that predicts slurry penetration by avoiding the need for site-specific empirical constants or complex column tests, relying instead on standard geotechnical and slurry parameters. The results provide practical criteria for filter cake formation and directly applicable models to optimize slurry design, thereby enhancing the control and safety of shield tunneling.

Converting waste slurry from underground construction into foamed lightweight soil (FLS) offers a route to waste valorization, but its durability under repeated moisture changes requires evaluation. This study compared FLS prepared with ordinary Portland cement (OPC), alkali-activated slag–fly ash (AASF), and hybrid OPC-AASF. Engineering properties and resistance to 18 wetting and drying (W-D) cycles were evaluated alongside pore structure evolution, microstructural changes, and environmental and economic indicators. Increasing soil content reduced unconfined compressive strength (UCS), with OPC-AASF showing a more gradual decline than OPC. All systems exhibited non-monotonic strength evolution during cycling. After 18 cycles, the UCS losses relative to the 28 d baseline were 1.9%–5.8% for OPC-AASF and 12.3%–17.6% for AASF. In selected specimens, X-ray computed tomography showed that lower macroporosity did not necessarily correspond to better strength retention. The greater strength loss in AASF was accompanied by spatial pore enrichment, coarse low-sphericity pores, and local interfacial damage. X-ray diffraction indicated retention of the main crystalline phases, while scanning electron microscopy showed better local pore wall and interfacial continuity in OPC-AASF. On a common dry-solids mass basis, the hybrid mixture containing 40% soil required 76.0% less OPC than a theoretical OPC foam concrete without waste soil. The estimated carbon emissions, energy intensity, and material cost associated with raw material inputs were 72.2%, 68.0%, and 48.1% lower, respectively. These findings support OPC-AASF as a cement-reduced stabilization system for lightweight backfill, combining waste slurry reuse with strength retention under repeated moisture fluctuations.