Journal of Shanghai University(Natural Science Edition) ›› 2020, Vol. 26 ›› Issue (4): 628-639.doi: 10.12066/j.issn.1007-2861.2066

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Mechanical properties of bentonite-calcium carbonate mixture

QIN Aifang(), FU Xianlei, RUAN Kunlin, JIA Xu   

  1. Department of Civil Engineering,Shanghai University,Shanghai 200444,China
  • Received:2018-05-07 Online:2020-08-30 Published:2020-01-31
  • Contact: QIN Aifang E-mail:qinaifang@shu.edu.cn

Abstract:

Different amounts of CaCO3 are mixed in bentonite for the purpose of simulating the characteristic changes of bentonite mixed with CaCO3 that precipitates from groundwater around high-level radioactive waste (HLW) repositories. In the process of the project, four groups of bentonite-CaCO3 mixtures are prepared with different contents of CaCO3. Then a series of experiments including swell-under-load, compression and direct shear tests are carried out. The permeability coefficient is calculated through Terzaghi consolidation theory. The microstructure changes are photographed by the scanning electron microscopy (SEM). Test results indicate that: (1) The final swelling strains are related to vertical stress and CaCOcontent. While vertical stress and CaCO3 content increase, the final swelling strains decrease. (2) The compression index deceases slightly as the content of CaCO3 crystals increases. (3) The permeability turns worse with increasing CaCO3 content. (4) With the content of CaCOcrystals changing, the shear strength of unsaturated samples will come to its peak value. Contrary to saturated samples, the cohesive of unsaturated samples increases firstly and then increases with the increasing CaCO3 content. (5) The photographs show that the existence of CaCO3 fills the pores which makes the structure denser.

Key words: bentonite-CaCO$_{3}$ mixture, swelling, compression, permeability conductivity, shear strength

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