Sandrine Paumier, Anne Pantet, Philippe Monnet, Nathalie Touze-Foltz
Evaluation of the viscoelastic properties of a clay material using a flow curve
Appl. Rheol. 19:2 (2009) 23824 (11 pages)Abstract: The specific properties of bentonite such as hydration, swelling,water absorption, viscosity, yield stress and thixotropy make it a valuable material in the form of mineral powder for a wide range of uses in agronomy, cosmetics and civil engineering. A flow curve is a quick test used to evaluate the rheological basic properties of a viscous fluid. However, many bentonite dispersions exhibit a complex flow curve, with yield stress and thixotropy area, especially at high concentration. In this study, flow curves from raw and activated bentonites dispersed in water were acquired at 6, 8 and 10% mass concentrations. Five stages along the flow curve were identified.To explain each stage, rheograms obtained from a dispersion made with a model material were studied in depth. The model material was a smectite extracted from a raw bentonite then saturated with calcium or sodium. Many homoionic and bi-ionic dispersions were prepared at various concentrations. The analysis and the modelling of some creep-recovery tests by a Zener model showed the relationship between the initial stage in the flow curve, named AB stage, and the viscoelastic properties of the fluid. The AB stage corresponds to the deformation of the material in the solid state. The τB point corresponds to an intermediate yield stress between the solid state and the start of the heterogeneous fracturation. The study of many bi-ionic dispersions allowed drawing the evolution of the yield stress as a function of concentration and saturation. The composition of the raw bentonites was expressed as an equivalent bi-ionic dispersion by calculating an active smectite percentage. A good correlation was obtained at the highest concentrations between τB from the bi-ionic model dispersions and the raw bentonites dispersions © 2009 Applied Rheology.
DOI 10.3933/ApplRheol-19-23824
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