Free swelling behavior of MX80 bentonite under elevated temperatures up to 200 °C

Abstract

This paper focuses on understanding trends in the swelling potential of MX80 bentonite under temperatures up to 200 °C using a high-pressure cell. The free swelling behavior of expansive clays under high temperature and high fluid pressure conditions that may be encountered in geological repositories for high-level radioactive waste is important as the swelling potential is closely linked with key transition points on the physical and chemical properties of these clays. Free swell tests performed at temperatures ranging from 22 to 200 °C under sufficient pressure to ensure that the pore water remains as a superheated liquid were performed to assess whether the swell index of bentonite follows similar non-monotonic trends with temperature as observed in the literature for the cation exchange capacity. The measured swell indices follow an increasing-decreasing trend with a transition close to 100 °C. The experimental results can be used to guide parameter selection in long-term simulations on the buffer behavior of the buffer material, which requires an understanding of temperature effects on the coupled thermal-hydraulic-mechanical properties governing these processes.