Physico-mechanical and microstructural behaviour of high-water-content dredged sediment treated by vacuum preloading coupled with alkali-activated materials

High-water-content dredged sediment (HWDS) solidification via the physico-chemical combination method (PCCM) shows potential for land reclamation. Traditional cement-lime-based PCCM demonstrates limitations of high cost and carbon emissions. Fly ash (FA), ground granulated blastfurnace slag (GGBS), and desulfurization gypsum (DG) were chosen for this study to create ternary alkali-activated materials (AAMs), and the HWDS was solidified using combined vacuum preloading (VP). Mechanical tests assessed VP-phase solidification and post-loading properties (load-bearing and vane shear strength) of cemented dredging sediment (CDS). The findings demonstrated that adding AAMs drastically decreased the sediment's water content during VP. Hydration generated AFt and C-(A)-S-H phases through AAMs reactions. Combined mechanisms enhanced CDS strength (378.2 kPa load-bearing and 85 kPa vane shear at 90 days). These values were 35.3% and 27.1% higher than those of the single chemical-solidified sediment (SCS) without VP. Subsequent investigation revealed a linear relationship between CDS's load-bearing strength and vane shear strength following PCCM treatment: y =-4.820+4.599⁎ x ( R 2 =0.985). The C3G3B4 group exhibited better long-term (90-day) strength, while the C2G3B5 group showed superior early-age (14-day) performance. According to the microscopic test results, the CDS under VP exhibits a more compact pore structure. VP treatment reduced porosity (47.7%-38.3%) and created denser pore structures.