Swelling pressure response of Bentonil-WRK bentonite under thermal cycling up to 150°C

This study investigates the thermal effects on the swelling pressure response of compacted Bentonil-WRK (Ca-type) bentonite. Swelling pressure tests were conducted under saturated conditions at dry densities ranging from 1.40 to 1.62 g/cm 3 using a high-temperature load cell system capable of operation up to 160°C. To simulate repository thermal environments, the specimens were subjected to two controlled thermal cycles between 30°C and 150°C. Results revealed a temperature-dependent response, characterized by a gradual decrease in swelling pressure during heating. While the absolute pressure reduction was larger at higher dry densities, the swelling pressure normalized by its value at 30°C showed a more pronounced decrease at lower densities, indicating that the lower-density specimens exhibited greater relative thermal sensitivity. During the heating–cooling cycles, all specimens exhibited thermal hysteresis, characterized by partial recovery of swelling pressure upon cooling, whereas the magnitude of hysteresis was markedly reduced in the second thermal cycle. The swelling pressure did not reach equilibrium at temperatures above 90°C during the first heating stage and only at 150°C in the second heating stage. Although higher dry density specimens exhibited larger absolute pressure reductions, their smaller relative decreases indicate enhanced thermal stability, suggesting that such compaction levels are favorable for ensuring long-term barrier performance under repository-relevant thermal loads. • Swelling pressure of BWRK Ca-bentonite measured at 30–150°C and dry densities of 1.40–1.62 g/cm 3 . • Higher dry density caused a larger absolute, but a smaller normalized swelling pressure decrease. • First heating–cooling cycle exhibited pronounced hysteresis, reduced in the second cycle. • Thermal relaxation occurred only during heating: above 90°C in first and 150°C in second cycle.