Aging effects on the swelling behavior of compacted bentonite

Due to its favorable low permeability, high swelling potential, and high retention capacity for radionuclides, the compacted bentonite has been considered as suitable buffer/backfill materials for construction of deep geological repository for disposal of high-level radioactive waste (HLW). However, prior to placing the compacted bentonite brick around the canister, several months to several years may elapse, which could affect the swelling behavior. In this study, the aging effect was experimentally investigated by performing a series of swelling tests on the compacted bentonite samples (prepared at both dry and wet sides with different water contents) that had been aged for 0, 7, 14, 30, 60, and 90 days. The microstructure features prior to wetting were also investigated by means of scanning electron microscopy (SEM), together with the determination of the electrical conductivity (EC) value. Results showed the axial strain and the swelling pressure decreased as the aging time increased for samples prepared at both dry and wet sides. Moreover, the EC value decreased as the aging time increased. These phenomena could be explained by the new bonding between soil particles created by aging, which was confirmed by the SEM observations.