Chemo-mechanical effects in kaolinite. Part 2: exposed samples and chemical and phase analyses

Abstract

Continuing from part 1 of this paper, the results of laboratory tests on chemo-mechanical interactions in kaolinite subjected to the diffusion of inorganic, salt, acid and base solutions under an applied stress state are presented. Chemical analyses on the surnatant and analyses on X-ray diffraction patterns, high-temperature differential scanning calorimetry thermal gravimetry scans and transmission electron microscopy micrographs led to the conclusion that the bulk of kaolinite mineral is probably only slightly affected by the chemical interactions, the chemical attack being concentrated mainly at the particle edges, where it induces a change in the shape of the edges, which become irregular and less sharp. The mechanical behaviour of kaolinite is not affected by pore fluid salinity, but it is significantly affected by pore fluid pH: both acid or base solutions under an applied stress cause significant volumetric compression. Such strains are irreversible and probably related to the particle rearrangement induced mainly by the degradation of the particle edges, in addition to the decrease in basal friction angle (described in the companion paper) and the change of strength at edge-to-face contact points. The mechanical effects are slightly related to the dielectric constant of the pore fluid and this is consistent with the general conviction that interactions between kaolinite particles are mostly mechanical.