During the operation of deep geological repository, the bentonite as a buffer material would be in a high temperature-strong alkaline environment for a long time, and its physical properties would deteriorate with time. Aging effect on physical property of MX-80 bentonite powder at high temperature and strong alkali conditions was investigated in this paper. MX-80 bentonite was subjected to alkali-heat conditions, i. e., T=90 ℃ and C_NaOH=0.5 mol/L for duration of 0, 15, 30, 45, 60, 90 days, respectively. The variation of physical properties such as the specific gravity, specific surface area and swell index of MX-80 bentonite was studied through laboratory experiments. Some representative specimens were selected for X-ray diffraction (XRD) tests and thermogravimetric analysis (TGA) tests to provide a reasonable explanation from microscopic perspective. The results showed that the specific gravity, specific surface area and swell index of bentonite decreased sharply from 0 to 45 days, gradually levelling off after then, finally, the reduction amplitudes were 13.6%, 18.5% and 58.1% after 90 days, respectively. Montmorillonite content decreased and albite content increased. The changes of montmorillonite and albite were -23.3% and +3.7% after 90 days. The content of free water, weakly bound water and strongly bound water decreased, and the content of the three decreased by 2.84%, 0.13% and 0.24% respectively after 90 days. The fundamental reason for the deterioration of bentonite physical properties over time under high temperature and strong alkali conditions was the dissolution of montmorillonite.

To explore the variation of water retention capacity of expansive soil at different temperatures, the calibration curves of Whatman No.42 filter paper were measured by vapor equilibrium method at 5, 25, 40 ℃ and 60 ℃, and the bilinear calibration equation considering temperature effect was established. The results show that the water retention capacity of the filter paper decreases with the increase of temperature, and the effect on the high suction section of calibration curve is weaker than the low suction section. On this basis, Nanning expansive soil is taken as the research object, and the soil-water characteristic curves of Nanning expansive soil at different temperatures are measured by filter paper method. It is found that the water retention capacity of Nanning expansive soil decreases with the increase of temperature, but the influence of temperature depends on matric suction, especially when it is above 40 MPa, the water-retention capacity of Nanning expansive soil remains unchanged with temperatures. To probe into the microscopic mechanism of the change of water retention capacity of Nanning expansive soil under temperature, some samples were selected for mercury intrusion porosimetry test and bound water adsorption test. Based on the test results, the microscopic mechanism of water retention capacity change of Nanning expansive soil was analyzed from the physical mechanism of the interaction between each phase and each phase interface.