Quantitative investigation of factors contributing to swelling pressure decrease of bentonite by cementation based on image processing
Ishiwata, Tobimaru*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*; Kawakita, Ryohei
; Takayama, Yusuke
; Mitsui, Seiichiro

Bentonite clay is planned to be used as a buffer material in the geological disposal of high-level radioactive wastes. The swelling property of bentonite is expected to keep low permeability and control the migration of radionuclides thereby ensuring the safety of geological disposal. In the long-term, however, cementation of bentonite may degrade the swelling property where secondary minerals precipitate and adhere to the montmorillonite component of bentonite. In the present study, natural bentonite ores were investigated as analogues to cementation of bentonite in geological disposal. The images of SEM and EPMA were integrated into "mineral map", which could visually illustrate the distributions of individual mineral grains including fine cementitious minerals. Finally, multi regression analysis (MRA) was used to investigate correlation between petrographic parameters and swelling pressure. MRA showed swelling pressure of bentonite increases with the content of montmorillonite, and decreases with the total perimeter of accessary minerals. This suggests that the presence of secondary minerals can inhibit the swelling of montmorillonite and the area of contact between montmorillonite and secondary minerals might be a key parameter.