Abstract: The MX-80 bentonite powder was pretreated by thermal aging at 200 ℃ for different durations (t =0, 15, 30, 60, 90, 120 d). Then, thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the variations of bound water, mineral composition, and microstructure in MX-80 bentonite with the thermal aging time t. Based on the crystal structure theory of montmorillonite, the micro-mechanism of high-temperature ageing time effect in MX-80 bentonite was revealed. The results show that, 1) the free water, weak bound water, and strong bound water in bentonite have different degrees of desorption with thermal aging time t increasing. The desorption changes significantly from 0 to 15 days and tends to be stable after 15 days. After 120 days, desorption values of three types of water decrease by 82.6%, 68.8% and 96.5%, respectively. 2) With increasing the thermal aging time t, montmorillonite, the main mineral component of bentonite, is transformed into sodium mica with good stability, and it changes significantly from 0 to 15 days, and tends to be stable after 15 days. After 120 days, the changes of montmorillonite and sodium mica are –12.57% and +12.47%, respectively. 3) In the process of high-temperature aging, the distance between crystal layers of montmorillonite decreases, resulting in the contraction and deformation of lamellar minerals, and the microstructure of bentonite changes with the increase of thermal aging time t. 4) Under the condition of high-temperature aging, the fundamental reason for the changes in the macroscopic physical and mechanical properties of bentonite is the interaction and mutual influence among the mineral composition transformation, bound water desorption, and microscopic morphology change of bentonite.

Key words: MX-80 bentonite, high-temperature aging, time effect, micro-mechanism, montmorillonite