Investigation on strength properties, mechanism, and durability of dredged sludge solidified with ground granulated blast furnace slag, calcium carbide slag, and phosphogypsum

Abstract

Ground granulated blast furnace slag (GGBS), calcium carbide slag (CS), and phosphogypsum (PG) were combined in a mass ratio of 60:30:10 (abbreviated as GCP) to solidify dredged sludge (DS) with high water content. The long-term strength characteristics of solidified DS under varying curing agent dosage and initial water contents, as well as its durability under complex environmental conditions, were investigated via a series of mechanical and microstructural tests. The superior performance of GCP-solidified DS (SDS-G) in terms of strength and durability was demonstrated in comparison to solidified DS using ordinary Portland cement (SDS-O). The results indicated that the unconfined compressive strength (UCS) of SDS-G was approximately 3.0–4.5 times greater than that of SDS-O at the same dosage and curing ages, exhibiting a consistent increase in strength even beyond 28 days of curing. Additionally, the strength and deformation modulus (E₅₀) of SDS-G increased initially and then decreased during wet-dry cycles, with reductions in mass, volume, and strength significantly were smaller than those observed in SDS-O. Furthermore, the reductions in UCS and E₅₀ induced by freeze-thaw cycles were considerably smaller for SDS-G than for SDS-O, with strength losses of 50.7 % and 88.3 %, respectively, after 13 freeze-thaw cycles. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the enhancements observed in SDS-G were attributed to the formation of ettringite (AFt), which effectively fills larger pores between agglomerated soil particles, thereby creating a denser and more stable microstructure in conjunction with hydrated calcium aluminosilicate (C-(A)-S-H) gels.