Raw Marine Sediments in Concrete: Mechanical Performance, Durability, Environmental Release, and End-of-Life Behavior

The valorization of raw dredged sediments in concrete requires simultaneous verification of engineering performance and environmental safety during both service life and end-of-life conditions. This work focuses on raw marine sediment collected from a port area as a partial substitute for natural sand, through a global assessment of physical properties, mechanical performance, durability, simulated-rainfall release, and leaching after crushing. Four concretes with 0, 10, 20, and 30% of sediment, with the same contents of cement and effective water, and targeting the same SF2 consistency class, were manufactured. Increasing the replacement rate increased porosity, water absorption, shrinkage, and carbonation depth, while lowering the compressive strength. At 28 days, the compressive strength dropped from 43.91 MPa for the reference to 38.16 MPa at the 20% replacement and 24.63 MPa at the 30% replacement. The apparent chloride migration coefficient decreased by about 31 and 77% for the two replacement rates, respectively; given the initial chloride content of the sediment, this trend is interpreted comparatively and possible mechanisms are discussed cautiously. In the simulated-rainfall test, releases of anions, trace metals, and organic indicators measured from the intact concrete remained below the adopted screening thresholds; however, because only one slab per formulation was tested, these environmental observations are preliminary. After crushing, some sediment-containing mixtures exceeded inert-waste thresholds for chlorides, fluorides, or nickel, showing that stabilization was incomplete under end-of-life conditions. Among the sediment-containing mixtures tested, the 20% replacement provided the best overall balance between natural-resource substitution, technical performance, and the preliminary environmental observations.