Effects of dehydration and grinding on the mechanical shear behaviour of Ca-rich montmorillonite

In order to investigate in detail the effects of dehydration and grinding on the mechanical shear behaviour of Ca-rich montmorillonite, a cycle of specific experimental shear deformation tests were performed on five typology of samples, preliminary controlled by thermal analysis (TG, DTA) and X-ray diffraction (XRD): (1) a natural Ca-montmorillonite containing about 5% of adsorbed water; (2) the same montmorillonite heated at 80 °C for 2 h to remove only the adsorbed water; (3) up to 250 °C for 2 h to remove also the interlayer water; (4) up to 340 °C for 2 h to complete the removal of interlayer water and start to introduce thermo-structural defects, and (5) the starting natural Ca-rich montmorillonite after hard ball-milling for 20 h to induce mechanical deformation and structural defects in the TOT layers. The five typologies of samples have been tested by a specifically designed and built shear box apparatus, under about 20 MPa condition of normal pressure. All samples, before and after the shear test, have been analysed by Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and XRD. A theoretical mechanical analysis based on the Maxwell model is proposed to explain the τ(ε) and τ(ε̇) shear behaviour of the effects of the different type of dehydration and deformation of the material, that was finally discussed in the context of the microstructural OM, SEM and XRD data.