Speaker: Janne T. Yliharyu

Date: Friday 22nd of March 2024, 1:15pm.


In many applications, it is essential to know what happens to the properties of a material if the water content is changed, i.e., if the material is wetted or dried [1]. One such example is bentonite clay, which is planned to be used as a buffer material in the geological final disposal of radioactive waste. Safety assessment of the multibarrier system, including the bentonite buffer, requires modelling and investigating the release barrier over long periods. These models benefit from information on the local water content of the bentonite layer. To facilitate modelling, we have developed X-ray tomographic methods to measure the time evolution of the local water content and applied the methods to bentonite clay samples in various conditions. This approach provides direct experimental data on the wetting and hydromechanical behavior of small-scale compacted bentonite samples, which can be used to validate material models. We present two approaches for measuring local water content. The first one is based on comparing successive tomographic images obtained during the wetting of the bentonite clay sample. This method involves measurement of the internal deformations of the sample, which is vital because, in general, materials will deform if the water content is changed. The second method is based on dual-energy imaging. Energy information is utilized to obtain quantitative information about the spatial distributions of bentonite and water. In both cases, we have applied a nonstandard beam hardening correction and careful calibrations of the mass attenuation coefficients. The deformation measurement method has been applied extensively to bentonite samples with different dry densities. Also, the influence of temperature on water transport has been studied. Based on the observations, the evolution of the water distribution is qualitatively reminiscent of diffusive transport. The first results from the dual-energy CT are promising, but further studies and validations are required before more profound conclusions can be drawn. These results suggest that deformation measurement enables more accurate water content estimates, but dual-energy CT can be applied in a broader range of material combinations.