A Thermodynamic Approach on the Effect of Salt Concentration on Swelling Pressure of Water-saturated Bentonite

Abstract

AbstractThe effect of salt concentration on swelling pressure of water-saturated bentonite was modelled based on the thermodynamic data of water at montmorillonite surface and of water in solutions of various salinities coming in contact with the montmorillonite. Activities of water at montmorillonite surface were obtained as a function of water content and temperature at montmorillonite densities of 0.6 and 0.9Mg/m3 by a vapor pressure method, and the relative partial molar Gibbs free energies (dGw) were determined. Water affected from the montmorillonite surface was estimated to be almost all interlayer water. Swelling pressure vs. montmorillonite partial density was estimated for solutions of various salinities and compared to data measured for various montmorillonite contents and different silica sand contents of bentonites. The calculated swelling pressure clearly decreased with increasing salinity. The effect of salinity on swelling pressure was not clear in the measured data and was within the range of the scattering in the measured data. This cause is presumed to be due to the increase of the ionic strength of porewater by dissolution of soluble minerals in the bentonite.