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.