Variations in Engineering Performance and Mechanisms of Expansion Stress Generation in Solid Waste–Based Cementitious Materials under Chloride Salt Exposure

Salts in aquatic environments disrupt the structure of cementitious materials, substantially reducing their durability in bank protection projects. To investigate the effects of sodium chloride solutions on cementitious materials prepared from industrial solid wastes (granulated blast furnace slag and desulfurization gypsum) and municipal solid wastes (construction waste powder and municipal sludge), unconfined compression tests and flexible wall permeability tests were conducted to evaluate their engineering performance. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) analyses were used to characterize the microstructure and chemical composition of the cementitious matrices. After 10 days of immersion in sodium chloride (NaCl) solutions ranging from 0.2 to 50 g/L, the unconfined compressive strength of all mixtures increased by 0.3–20.4%. After 90 days, the unconfined compressive strength gradually declined by 1–29.8%. In chloride environments, industrial residues underwent hydration reactions, forming products such as ettringite and Friedel’s salt. However, the continued formation of these phases generated expansive stresses within the matrices, ultimately causing structural damage. The particle size of construction waste and the slag content directly influenced the extent of chloride-induced structural damage. This study provides critical insights for evaluating the durability of solid waste–based cementitious materials in bank protection engineering.