Fundamental study on the effect of an orientation of clay particles on diffusion pathway in compacted bentonite

To evaluate the effects of smectite content and the compacted direction of bentonite on the orientation properties of clay particles and diffusive pathway in compacted bentonite, scanning electron microscope (SEM) observations for micropore structure in compacted bentonite and through-diffusion experiments for non-sorptive tritiated water (HTO) were conducted. The SEM observations and diffusion experiments were performed for axial and perpendicular directions to the compacted direction of bentonite as a function of bentonite's dry density. Two types of Na-bentonites, Kunigel-V1® and Kunipia-F® with different smectite contents were used for both experiments. No orientation of clay particles was found for Kunigel-V1® with 50 wt.% smectite content, while layers of clay particles orientated in the perpendicular direction to compacted direction were observed for Kunipia-F® with approximately 100 wt.% smectite content. This trend is in good agreement with those for HTO's effective diffusivities. This indicates that smectite content in bentonite affects the orientation properties of clay particles and diffusive pathway.