The effect of pore structural factors on diffusion in compacted sodium bentonite

Four kinds of diffusion experiments; (1) through-diffusion (T-D) experiments for diffusion direction dependency to compacted direction, (2) in-diffusion (I-D) experiments for composition dependency of silica sand in bentonite, (3) I-D experiments for initial bentonite grain size dependency, and (4) I-D experiments for the effect of a single fracture developed in bentonite, were carried out using tritiated water (HTO) to evaluate the effect of pore structural factors on diffusion. For (1), effective diffusivities (De) in Na-bentonites, Kunigel-V1® and Kunipia-F®, were measured for densities of 1.0 and 1.5 Mg·m^-3 in the axial and perpendicular directions to compacted one. Although De values in Kunigel-V1® for both directions were similar over the density, De values for perpendicular direction to compacted one in Kunipia-F® were higher than those for the same direction as compacted one. For (2), apparent diffusivities (Da) in Kunigel-V1® with silica sand were measured for densities of 0.8 to 1.8 Mg·m^-3. No significant effect of the mixture of silica sand was found. For (3), Da values for densities of 0.8 to 1.8 Mg·m^-3 were measured for a granulated Na-bentonite, OT-9607®. However, no effect of initial bentonite grain size was found. For (4), Da values in Kunigel-V1®, in which a single fracture was artificially reproduced and immersed in distilled water, were measured. No effect of the fracture on Da was found. Based on this, it may be said that the composition of smectite in bentonite affects the orientation property of clay particle and also affects diffusion. Furthermore, a penetrated fracture formed in bentonite is restored for a short while and does not affect diffusion.