Thermochemical changes on swelling pressure of compacted bentonite

Bentonite has been considered as a potential buffer material in engineering barriers of high-level radioactive waste disposal systems. The intrusion of groundwater and heat from the waste change the temperature and chemical composition of the bentonite, consequently can alter the mechanical properties of the bentonite. In this study, thermochemical effects on the swelling behaviors were observed in compacted Ca-bentonite samples. Laboratory tests were conducted on Korean Gyeongju bentonite blocks that were compacted at different dry densities. Swelling pressure tests at various temperatures between 30 degrees C and 90 degrees C were carried out by supplying de-ionized water, NaCl solution, and CaCl2 solution. The study revealed that at higher temperature the bentonite swells faster, but the final swelling pressure decreases in the higher temperature condition. As for the chemical effect, the final swelling pressure at the same temperature shows an order: CaCl2 > De-ionized water > NaCl. In addition, the swelling behavior of the bentonite during a thermal loading cycle was experimentally investigated. The swelling pressure at the same temperature revealed different values depending on whether the bentonite was heated up or cooled down. The result demonstrated that the temperature change history should be a significant factor in determining the swelling pressure of bentonite buffers. (C) 2020 Elsevier Ltd. All rights reserved.