To address the poor engineering performance of sludge-like soft soils, the high carbon emissions associated with conventional cement stabilization, and the unstable alkalinity supply of single-alkali activation systems, this study develops a solid waste-based FA-GGBFS-PS (FASP) stabilization system, in which a precursor consisting of fly ash (FA), ground granulated blast furnace slag (GGBFS), and phosphorus slag (PS) is activated by a dual-alkali activator derived from carbide slag (CS) and alkali residue (AR). Unconfined Compressive Strength (UCS) tests were conducted to examine the effects of binder composition, activator proportion and dosage, initial water content, and binder content on stabilization performance. Durability was further evaluated through wet-dry cycling and chloride exposure tests, while the underlying mechanisms were characterized using X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analyses. The results indicate that the dual-alkali system provides a stable alkaline environment, facilitating the dissolution and reorganization of Si, Al, and Mg species from multiple solid wastes. This process leads to the formation of a composite cementitious structure dominated by calcium silicate hydrate (C-S-H), calcium (alumino) silicate hydrate (C-(A)-S-H), Magnesium silicate hydrate (M−S−H) gel, and ettringite (AFt). These phases interconnect and fill internal pores, resulting in enhanced strength and a denser soil structure. In addition, the stabilized soil exhibits favorable durability under wet-dry cycles and chloride attack, which improves further with increasing binder content. Overall, the proposed system features low carbon impact and stable performance, offering a viable approach for soft ground improvement and the resource utilization of solid wastes.
