Water retention and compression behavior of MX80 bentonite pellet

International audienceBentonite pellet/powder mixture has been considered as a possible sealing material in deep geological disposal of radioactive waste. As the hydro-mechanical behavior of such mixture is intimately related to that of single pellet, in this study, water retention tests and compression tests were performed on single MX-80 bentonite pellet to investigate its hydro-mechanical behavior. Mercury intrusion porosimetry (MIP) tests were also conducted to investigate the microstructure change with suction. The water retention test results show that the changes in water content and void ratio are significant in low suctions ( 59 MPa). These significant changes are accompanied by the propagation of cracks. Results from compression tests show that the contact force of pellet rapidly increases in the beginning, reaches a peak and then decreases. Meanwhile, the contact stiffness and the breaking force of pellets show different variation tendencies in different suction ranges. Results from MIP tests indicate that the volume change of pellet upon wetting is attributed to the swelling of bentonite grain, the expansion of inter-grain pores and the generation of large cracks. At the meantime, the changes of pores at micro-scale and macro-scale, especially the wetting-induced cracks, notably affect the compression properties of pellet. These findings provide useful information for better understanding the overall behavior of bentonite pellet/powder mixture