Wetting and swelling behaviors of unsaturated compacted Korean Ca-bentonite in contact with a cement-equilibrated fluid

This study aims to investigate the wetting and swelling pressure characteristics of unsaturated compacted Ca-bentonite in contact with a cement-equilibrated fluid, focusing on the interface between the bentonite buffer and host rock. Water retention and swelling pressure tests were conducted on unsaturated compacted Ca-bentonite and Ca-converted bentonite specimens with varying initial dry densities and water contents using deionized (DI) water and the 0.02 M Ca(OH)₂ solution as hydrating fluids. The results showed that the total suction decreased as the degree of saturation increased, whereas the degree of saturation increased with higher dry densities. A slight difference in the water retention (absorption) capacity was observed when using either DI water or the 0.02 M Ca(OH)₂ solution as the hydrating fluid, depending on the degree of saturation. The swelling pressure increased with increasing initial dry density but decreased with increasing initial water content at a given dry density. Contact with the 0.02 M Ca(OH)₂ solution slightly lowers the swelling pressure, which could be attributed to an osmotic effect caused by chemical potential differences, indicating the effect of a small fraction of Na in the interlayers. In addition, chemical alterations in bentonite had minimal impact on the swelling pressure because of limited interactions. These findings improve the understanding of swelling behavior at the interface between the bentonite buffer and host rock, emphasizing the significance of hydrating fluids, bentonite properties, and hydration processes.