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Author index ►Alexandre Pierre, Christophe Lanos, Patrice Estelle

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Extension of spread-slump formulae for yield stress evaluation

Appl. Rheol.23:6 (2013) 63849 (9 pages) ►

This paper provides a new model to evaluate the yield stress of suspensions, slurries or pastes, based on the release of a finite volume of material onto a horizontal surface. Considering the height (h) and the radius (R) of the sample at the flow stoppage, two asymptotic regimes, where h > R or h < R, lead to different analytical models that allow the determination of yield stress. Experimental observations show typical sample shape at stoppage between slump (h > R) and spread (h < R). Based on these observations, we have developed a new analytical model to evaluate accurately the yield stress of materials in this intermediate regime. The validity of this model was evaluated from data obtained using various Carbopol(c) dispersions. The yield stress measured with the proposed model was compared with the yield stress evaluated from shear flow curves obtained with roughened plate/plate geometry fitted to the Herschel-Bulkley model. Results show the relevance of the proposed model which that can be applied in the range between models used for the two asymptotic regimes.► Cite this publication as follows:

Pierre A, Lanos C, Estelle: Extension of spread-slump formulae for yield stress evaluation, Appl. Rheol. 23 (2013) 63849.

A high torque vane rheometer is used to measure the yields stress of cement-based materials. It is shown that this apparatus is suitable for the evaluation of the yield stress of various concretes and mortars in the fresh state in comparison with slump tests realized with ASTM Abrams cone. Then, the rheological properties (yield stress and shear flow behaviour) of a homogeneous kaolin clay suspension are studied with the apparatus and favourably compared with other rheometers and geometries.► Cite this publication as follows:

Estelle P, Lanos C: High torque vane rheometer for concrete: principle and validation from rheological measurements, Appl. Rheol. 22 (2012) 12881.

A new method is developed to determine the rheological and tribological behaviour of viscoplastic fluids using a back extrusion test. In back extrusion geometry, the material is forced to flow in the gap between the inner and the outer cylinder. Such a flow is modelled by a Bingham constitutive law under different wall boundary conditions (stick, slip with friction and perfect slip). When steady-state flow is reached, an apparent shear rate is computed. The analysis of the inner cylinder penetration force versus the penetration depth helps us to develop a method to identify the fluid rheological and tribological properties. This method is based on an inverse analysis to identify the fluid behaviour parameters from experiments performed at different ram velocities and with different apparatus geometries. In order to study more complex fluids (Herschell-bulkley rheological behaviour, for example), an equivalent flow curve is plotted from tests characterized by different average shear rates. The tribological behaviour is identified using different wall boundary conditions, varying the surface roughness of the cylinders. The method is applied to oil/sugar suspension and plasticine. Rheological and tribological behaviours are identified and results are compared with those obtained under steady state shear flow. The obtained rheological parameters are close to those provided by the common rheological methods (difference lower than 15 %).► Cite this publication as follows:

Perrot A, Melinge Y, Estelle, Rangeard D, Lanos C: The back extrusion test as a technique for determining the rheological and tribological behaviour of yield stress fluids at low shear rates, Appl. Rheol. 21 (2011) 53642.

The stability of the flow induced by the extrusion forming process of a cement based material is largely influenced by the relative migration between the lubricating liquid phase and the granular skeleton. In the present work,we propose linking rheological concepts and soil mechanics (consolidation theory, Darcy's law) to reach a simple criterion which predicts the extrusion ability of a mortar. Extrusion tests on studied mortar are performed at different ram velocities for criterion validation.► Cite this publication as follows:

Perrot A, Rangeard D, Melinge Y, Estelle P, Lanos C: Extrusion criterion for firm cement-based materials, Appl. Rheol. 19 (2009) 53042.

A new procedure is described to convert the vane torque and rotational velocity data into shear stress vs shear rate relationships. The basis of the procedure consists in considering locally the sheared material as a Bingham fluid and computing a characteristic shear rate from Couette analogy. The approach is first applied to experimental vane data of Newtonian fluid, then used to process vane experimental data of non-Newtonian and yield stress materials. Results, which are favourably compared with torsional flow, show that the approach correctly predicts the rheological behaviour of the materials investigated.► Cite this publication as follows:

Estelle P, Lanos C, Perrot A, Amziane S: Processing the vane shear flow data from Couette analogy, Appl. Rheol. 18 (2008) 34037.

Particle fluid separation is studied in the case of slow squeezing flow of dense clay suspensions. The fluid pressure gradient generated by the test induces heterogeneity in the sample. Experimental water content measurements at different time points through the test allow the quantification of this separation phenomenon. The problem equations are written in the case of purely extensional flow. Based on Terzaghi principle, Darcy.s law and a Cam Clay type constitutive equation, the influence of the permeability function on the predicted void ratio evolution is studied. It is then shown that a certain water amount is strongly linked to the grains and cannot be extracted from the sample using simple compression. This critical water amount is then taken in account in the permeability function in order to predict the compression load through the test.► Cite this publication as follows:

Roussel N, Lanos C: Particle Fluid Separation in Shear Flow of Dense Suspensions: Experimental Measurements on Squeezed Clay Pastes, Appl. Rheol. 14 (2004) 256.

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