The effects of salt solutions on the properties of bentonite-sand mixtures

ABSTRACT: The swelling behaviour and hydraulic conductivity of Na-bentonite powder and bentonite-sand mixtures (10 and 20 % of bentonite by dry weight) have been measured with distilled water and various alt solutions (0.01, 0.1 and 1 mol/l concentrations), It was found that in dilute solutions, the bentonite in mixtures subjected to small confining stresses swells sufficiently to separate the sand particles and reach a clay void ratio similar to that achieved by bentonite alone. At high stresses, or in strong solutions, the bentonite in a mixture has insufficient swelling capacity to force the sand particles apart and swelling is limited by the sand pore volume. The hydraulic conductivity of a mixture depends on the bentonite void ratio, and the porosity and tortuosity of the sand matrix. A design model is proposed to predict he engineering properties of a mixture over a range of confining stresses from the properties of its constituents and the permeant. Barriers with a low hydraulic conductivity are used as part of waste containment systems to prevent groundwater contamination by leachate from the waste. Where suitable low hydraulic conductivity soils are not locally available, such a material ca