Blackwell Publishing Journal Backfiles 1879-2005
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
The relation between physical and mechanical responses and the structure of clay has been studied. Deformation in response to mechanical stress was measured on samples of Wyoming mont-morillonite and Saint Austell kaolinite in solutions of NaCl (0·005; 0·05; 0·5 and 5 M). Salt concentration was expressed in terms of osmotic potential of water and loading in terms of envelope pressure potential of water, and deformation was measured precisely under small mechanical stress. During shrinking and swelling, deformation was small and reversible, and consolidation was related to the largest mechanical stress applied previously in its history. The arrangement of the clay at equilibrium depends foremost on the type of clay mineral and physico-chemical properties of the liquid phase. For Na-montmorillonite suspensions, transition between gels with tactoids and rigid media with quasicrystals is abrupt and occurs at a potential of about −2000 J kg−1, whether the stress is osmotic or mechanical. Swelling indexes obtained under osmotic and mechanical stress are of the same order of magnitude. Deformation of smectite results from modifications of interassemblage and intra-assemblage organization.
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