Journal Published Online: 25 February 2020
Volume 49, Issue 4

Hydromechanical Performance of Heat-Treated Bentonite

CODEN: JTEVAB

Abstract

As a buffer material in nuclear waste disposal repository, bentonite experiences long-term persistent heating because of thermal energy released from the sealed nuclear waste canisters. There is no conclusive evidence on how high temperature affects the self-sealing capacity of bentonites. To investigate this effect, bentonite was heated in a muffle furnace at a constant temperature (105°C) for different time periods. The free swelling ratio, swelling pressure, permeability, and specific surface area are used to characterize the physical and mechanical properties of the heated samples. Results revealed that with the increase in the heating time, the free swelling ratio and swelling pressure decrease significantly. The X-ray diffraction pattern of the bentonite sample heated for 90 days reveals a shift from 6° to 9° for the angle corresponding to the (001) diffraction peak of montmorillonite, and with the increase in the heating time, the spacing distance decreases from 1.5 to 0.94 nm. Meanwhile, siliceous oxide is formed during heating, resulting in a cluster of bentonite particles. Results obtained from the infrared spectroscopy and thermogravimetric analysis revealed that the water adsorbed on the intralayer and interlayer surfaces is completely evaporated when the temperature approaches 200°C, but only part of the ionic-bonded water vaporizes, while the structural water remains unchanged. Furthermore, during evaporation, sodium and magnesium ions disappear. Scanning electron microscopy images revealed that bentonite particles are aggregated, rather than uniformly dispersed, which confirms the aforementioned inference. In addition, results obtained from the particle size distribution tests of heated bentonite revealed the same conclusion about its microstructure.

Author Information

Tan, Yunzhi
Department of Civil Engineering & Architecture, China Three Gorges University, Yichang, China
Li, Hui
Department of Civil Engineering & Architecture, China Three Gorges University, Yichang, China
Wang, Peirong
Department of Civil Engineering & Architecture, China Three Gorges University, Yichang, China
Sun, De’an
Department of Civil Engineering, Shanghai University, Shanghai, China
Sun, Wenjing
Department of Civil Engineering, Shanghai University, Shanghai, China
Pages: 13
Price: $25.00
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Stock #: JTE20190570
ISSN: 0090-3973
DOI: 10.1520/JTE20190570