Design of In Situ Caps for the Isolation of Contaminated Sediments

Formulations of bentonite-cement composites are explored as a basis for creating a range of structured, semipermeable layers adapted to in situ capping of contaminated underwater sediments. In addition to being mechanically stable, such composites provide for a possibility to control cap microstructure and transport properties through the fine-tuning of postdepositional hydration processes in the cap. Microscopic studies combined with flowability and setting tests were used to establish relationships between the structure and mechanical properties for designed composites. Also, apparent diffusion coefficients were measured and corresponding porosity values were calculated for the composites formed under different hydration conditions. It is demonstrated that by varying the cement content and liquid-to-solid ratio during composite formation, it is possible to control structural and transport characteristics of the composite material. Analysis of calculated porosity values combined with microscopy data indicates that the particle packing density plays a crucial role in the development of cap’s microstructural features and retardation capacity.