Solidification of marine silt with a one-part slag-based binder: underwater performance and microscopic mechanisms

To promote marine silt reuse and protect offshore infrastructure from erosion, this study developed a one-part slag-based binder for solidification. Calcium hydroxide Ca(OH) 2 and sodium silicate Na 2 SiO 3 were used as one-part alkali activators. The binder performance was systematically evaluated by Unconfined Compressive Strength (UCS), flowability, dispersion resistance, and durability under immersion and wet-dry cycling seawater conditions. Compared with existing silt solidification systems, the proposed system is specifically designed for underwater construction and marine exposure conditions. The optimal mixture, with a Ca(OH) 2 to Na 2 SiO 3 mass ratio of 3:7, attained a 7-day UCS of 2135 kPa under standard curing. This strength stems from balanced calcium, hydroxyl, and silicate species. For underwater placement, the mixing water content was identified as the primary control parameter, where a 30% increase in water content led to a 123% increase in flowability. Incorporating 0.35% hydroxypropyl methylcellulose improved dispersion resistance, while adding 0.8% superplasticizer maintained the required flowability. Durability tests under immersion and wet-dry cycling indicate moderate strength loss and pore coarsening under cycling, but continued strength gain and pore refinement under immersion. These results indicate that the developed one-part slag-based binder provides a low carbon, high performance route for in-situ solidification and beneficial reuse of high-water content marine silt. This study demonstrates that marine silt can be converted into a durable clayey geomaterial with sufficient strength and erosion resistance for ground improvement in coastal and offshore environments.