Flowable solidified soil derived from dredged marine sediment: Optimization of fresh rheology and hardened strength

Transforming dredged marine sediment (DMS) into flowable solidified soil (FSS) offers a sustainable route for sediment management. This study developed a DMS-based FSS using a binder in which ground granulated blast-furnace slag (GGBFS) partially replaced ordinary Portland cement (OPC) and nano-silica (NS) was incorporated. Fresh FSS exhibited shear-thinning behavior, and increasing the GGBFS replacement level or NS dosage generally increased the yield stress and apparent viscosity. At 28 d, the NS-free mixture with 70% GGBFS replacement achieved a UCS of 2.376 MPa, approximately 4.98 times that of the OPC-only control. When the GGBFS replacement level was ≤50%, NS further increased UCS by up to 29.4% relative to the corresponding NS-free mixtures; however, at 70% GGBFS, NS reduced UCS, which may be partly associated with lower OPC content and competition for limited Ca(OH)2, potentially reducing slag-activation efficiency. Notably, several mixtures in the 70% GGBFS series exhibited higher UCS under seawater curing than under sealed-humid curing, particularly at early ages. Response surface methodology (RSM) identified feasible proportions satisfying the specified yield-stress and 28 d UCS criteria. These findings provide guidance for binder proportioning in DMS-based FSS.