Moisture Adsorption and Volume Change of Partially Saturated Bentonite Buffer Materials

ABSTRACTWater vapor adsorption characteristics of buffer materials to be used for the geologic disposal of high-level radioactive waste have been investigated. Highly compacted blocks of Japanese Na bentonite were used as the buffer material. Initial dry density of the blocks was 1.8 g/cm3. Volume changes and water contents of the blocks in equilibrium with surrounding moist air were measured. The humidity of the surrounding air was kept constant, and the suction of the block at equilibrium has been determined by the humidity. The temperature of the surrounding air was varied between 20°C and 60°C.The volumetric strain was observed to vary approximately between −3% and 13% depending on the humidity of 0.6% to 95%. Some analytical expressions derived from these experiments on moisture adsorption are presented in this paper. Water vapor adsorption isotherm of the bentonite blocks was also obtained. The swelling pressures calculated from the analytical expressions are compared with literature data for this bentonite.