Mineral-Binder Stabilization of Dredged Sludge for Building Foundation Ground: Strength Development and Skeleton Reconstruction

High-water-content dredged sludge is difficult to reuse in building foundation systems because its loose fabric, high void ratio and low initial bearing capacity may lead to inadequate construction-stage support and excessive service deformation. This study evaluates a self-developed RT mineral-based cementitious binder for converting dredged sludge into an engineered geomaterial for potential foundation-ground improvement materials. Unconfined compressive strength tests, full stress–strain responses, SEM observation, image-based pore-topology quantification and a fractal poromechanics model were integrated to link mix design, microstructural reconstruction and foundation-related performance. The RT binder generated rapid early strength in the high-water-content sludge. At 3 d, UCS increased from approximately 0.9 MPa at 3% binder dosage to 2.15 MPa at 11% dosage; the 8% mixture reached 1.34 MPa, exceeding the 1.0 MPa material-scale screening level adopted for comparing stabilized foundation-ground candidates. Strength at 8% dosage continued to increase with curing age, although the gain rate decreased after 7 d, indicating rapid early skeleton formation followed by slower structural maturation. Microstructural evidence showed that the improvement was not governed by pore filling alone. C-S-H-like gel phases wrapped and cemented soil particles, whereas needle-like crystals consistent with ettringite morphology bridged and interlocked interparticle spaces, transforming the originally loose sludge fabric into a continuous three-dimensional load-bearing skeleton. The pore area fraction decreased from approximately 51% in untreated sludge to 31.2% at 8% dosage, while the fractal dimension increased to 1.85–1.98. The proposed fractal poromechanics model predicted UCS within ±10% of measured values, confirming that skeleton continuity and pore-topology reconstruction are key descriptors of macroscopic hardening. These findings demonstrate that RT-stabilized dredged sludge is a promising material-scale candidate for building-foundation ground improvement, provided that project-specific bearing capacity, settlement, compaction and durability requirements are further verified.