(GRS 615) Project BIGBEN Constitutive Equations for Sodium and Calcium Bentonites

Compacted air-dry bentonite is foreseen in many repository designs to be utilised as a geotechnical barrier since its hydrophilic and thereby swelling properties let it appear to be ideally suited for this purpose. For predicting the re-saturation dynamics of a bentonite barrier, isotherms or the equivalent retention curves form a vital constitutive equation, relating the relative humidity in the pore atmosphere to the water content of the bentonite.
Several retention properties of MX-80 and Calcigel bentonite were investigated in the framework of project BIGBEN1: (1) the hysteresis of adsorption and desorption isotherm, (2) the adsorption and desorption scanlines substituting the isotherms when changing from adsorption to desorption and vice versa under partially saturated conditions, (3) dependence of the isotherms on temperature, (4) changes in the isotherms due to microstructural reconfigurations as a consequence of repeated wetting and drying of compacted specimen under spatial confinement.