Laboratory investigation on the membrane behaviour of highly compacted GMZ bentonite under isothermal conditions

The persistence of membrane behaviour of compacted bentonite barriers under thermo-chemical conditions is of significance for their containment performance in high-level radioactive waste repository. To quantify the membrane behaviour of compacted GMZ bentonite under the combined thermo-chemical effects, a series of multi-stage membrane tests were conducted using NaCl solution with different concentrations under controlled iso-thermal conditions of 20 degrees C, 40 degrees C and 60 degrees C, respectively. Results showed that the chemico-osmotic efficiency coefficient, omega, of compacted GMZ bentonite decreased with the increasing NaCl concentrations. Moreover, with elevating temperature, distinct decrease of the induced differential pressure across specimen was observed, indicating the negative impact of temperature on the membrane behaviour of compacted bentonite. By monitoring the variation of hydraulic conductivity of specimens before and after membrane tests under different thermal conditions, the destruction of membrane behaviour of the specimens under thermo-chemical conditions was analysed from the perspective of microstructural rearrangement.