Processing the Couette viscometry data using a Bingham approximation in shear rate calculation

The original contribution is available at http://www.sciencedirect.com/science/article/pii/S037702570800013XInternational audienceThis paper presents an approach to computing the shear flowcurve from torque-rotational velocity data in a Couette rheometer. The approximation techniques in shear rate calculation are generally dictated by the radius ratio between coaxial cylinders and the rheological behaviour of fluid tested. Here, the approach consists in analysing the sheared material as a Bingham fluid and computing an average shear rate when the fluid in the cylindrical gap is partially and fully sheared. We focus in particular on the applicability of the Bingham approximation in shear rate calculation. First, the approach is assessed by examining synthetic data generated with Newtonian, non-Newtonian and yield stress materials with known properties, varying the gap radius ratio. The results, which are compared with commonly used techniques in shear rate calculation, prove the relevance of the proposed approach. Finally, its efficiency is examined by applying it to process Couette data of yield stress fluids taken from published works

Rhéologie de pâtes dentaires par extrusion

International audienceL'objectif de ce travail est d'étudier le comportement rhéologique de différentes pâtes de soins dentaires dont le comportement est principalement plastique. Des tests sont réalisés avec une géométrie d'extrusion et par cisaillement direct (géométrie vane). Ces deux types d'essais permettent d'évaluer les seuils de mise en écoulement et de friction du matériau. Il apparaît que ces seuils sont fortement affectés par une modification des conditions cinématiques. Les résultats permettent de sélectionner les formulations les plus pertinentes pour garantir des conditions d'exploitation optimisées

Ram extrusion force for a frictional plastic material: model prediction and application to cement paste

the original publication is available at http://www.springerlink.com/content/pn3034u81144458g/International audienceWe developed a model to predict the ram extrusion force of frictional plastic materials such as cement-based pastes. The extrusion of cement-based materials has already been studied, but the interaction between shaping force and paste behaviour still have to be understood. Our model is based on the plastic frictional behaviour of cement-based materials and integrates the physical mechanisms that govern material extrusion flow and extrusion force increase. When the process starts, a pressure gradient is created in the extruder due to wall friction of the paste that is submitted to plug flow. It induces a consolidation of the material. As a result, a large increase of extrusion force appears. A Coulomb law is used to model cement-based materials, which is considered as consolidating granular media. Such modelling is compared with experimental results. Tests were carried out on extrudible cement pastes. Modelling and experimental results are in good agreement

Processing the vane shear flow data from Couette analogy

The original contribution is available at http://www.ar.ethz.ch/International audienceA 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

Courbes d'écoulement en géométrie Couette par une approximation de Bingham

National audienceUne méthode simple pour identifier la courbe d'écoulement d'un fluide en cisaillement dans une géométrie Couette est développée. Elle consiste à considérer le fluide en écoulement comme étant un fluide de Bingham, et à évaluer la vitesse de cisaillement caractéristique du fluide partiellement et/ou complètement cisaillé. La pertinence et l'intérêt pratique de la méthode sont examinés en analysant les résultats générés par des données numériques en géométrie Couette de fluides de propriétés fixées, en variant la taille de l'entrefer, puis en l'appliquant aux données expérimentales en géométrie Couette et vane d'un fluide visqueux newtonien et d'une suspension de Carbopol

Slipping zone location in squeeze flow

the original publication is available at http://www.springerlink.com/content/f1611lmr64836780/International audienceIn squeeze flow rheometry, the main problem is the boundary condition between the squeezed material and the plates. Therefore, the crucial assumption is to know the location and the shape of the sample part where wall slip may or may not occur. This question is investigated from experimental results. For this, squeeze flow experiments are carried out to visualize the flow pattern at the walls. Influence of boundary conditions is particularly studied using different plate surface condition. As a result, with wall slipping conditions, we propose a flow modelling divided into two zones: a circular central zone of the sample sticks on the plates and, beyond that zone, the sample slips at the plates with friction

Structural build-up of rigid fiber reinforced cement-based materials

International audienceThe structural build-up of rigid fiber reinforced cement-based materials is studied. It has recently been shown that the behaviour of fiber reinforced concrete depends on the orientation of the fibers that has to be optimized during casting. As a result, there is a great interest to study the rheology of fiber reinforced concrete. One of the most important characteristics of modern fresh concretes is the structural build-up which is involved in many recent issues of concrete casting. This characteristic depends on the cement pastes chemical activity. This present work shows that structural build-up modelling used for common concretes can be generalized to fiber reinforced concretes. It can be shown that, if the inclusions percolation threshold is not reached, the structural build-up rate Athix is amplified by the addition of fibers and aggregates. Finally, this amplification of the structuration is estimated using modelling initially developed for spherical inclusions and aggregates

Squeezing Flow of Suspensions: Flow Regime Evaluation from Energy Approach

International audienceThe squeezing flow geometry is here used to investigate the properties of concentrated suspensions. The suspensions consist in idealized system of smooth hard spheres dispersed in a yield stress colloidal gel. During the squeezing action, the material structure evolves with energy variation due to particle displacement and interaction. The goal of our study is to evaluate the energy evolution from a Fourier analysis as a function of solid volume fraction and compression velocity

Caractérisation rhéologique et tribologique d'un matériau viscoplastique à l'aide d'un essai de back-extrusion

National audienceUne nouvelle méthode d'analyse rhéologique et tribologique est développée en exploitant l'écoulement de back-extrusion. L'utilisation des courbes "effort d'extrusion en fonction du déplacement du cylindre intérieur" permet d'identifier les caractéristiques rhéologiques et tribologiques du fluide testé à partir des résultats de tests réalisés avec différentes vitesses de pénétration du cylindre intérieur et différentes configurations géométriques. Dans le cadre de l'étude de fluides complexes incompressibles, tels que les fluides d'Herschell-Bulkley frottant, la méthode aboutit à la construction d'un rhéogramme équivalent tracé à partir d'essais caractérisés par différents taux de déformation moyens. Le comportement tribologique peut être identifié en modifiant les conditions de frottement à la paroi en variant la rugosité des surfaces. La méthode est appliquée aux cas de suspensions concentrées huile/sucre et plasticine. Les comportements rhéologiques et tribologiques sont identifiés et comparés aux résultats obtenus avec la rhéométrie traditionnelle

Extrusion and structural build-up of 3D printing cement pastes with fly ash, nanoclays and VMAs

3D printing technology (3DP) has provided new design and structural opportunities for cement-based systems (CBS) in architectural construction. However, there are still some issues related to extrudability and buildability of CBS, which can be overcome by using components for CBS rheology control. In this study, three types of nanoclays, a bentonite (BEN), a sepiolite (SEP) and an attapulgite (ATT), and two viscosity modifying admixtures (VMAs), a poly-acrylamide (VMA1) and a methylcellulose ether (VMA2), were added to a reference cement-fly ash 3D printing paste to evaluate their impact on CBS rheological properties and their implications in extrusion and buildability for 3DP. A polycarboxylate-ether based high range water-reducing admixture (HRWRA) was used to reach a target stiff consistency. Four laboratory tests were used to assess paste rheology, extrusion and structural build-up. Proper and deficient material extrusion limits were defined considering cohesion and initial yield stress. It was found that the combination of VMA2 and SEP increased cohesion, enhancing extrusion and avoiding water drainage and frictional behavior of pastes, producing properly extrudable paste. SEP by itself also improved structural build-up. Besides, samples with NC and VMAs required larger amounts of HRWRA, delaying cement setting and compressive strength gain.The authors acknowledge the financial support provided by the project Print3Dcement (PID2019-106525RB-I00) funded by the Spanish Ministry of Science and Innovation (MCIN), project CALTHED (grant number TED2021-132585B-100) funded by the Spanish Ministry of Science and Innovation (MCIN/AEI/10.13039/501100011033) and the European Union “NextGenerationEU”/PRTR, the Grant for training of Lecturers (FPU-UAH 2019) and the trainee Research Personnel Mobility Grant (Movilidad PIF-UAH 2020) funded by University of Alcala. Also, the authors acknowledge the experimental laboratory help of Yohan Jacquet of Universit´e Bretagne-Sud. The authors also thank the materials’ supply of the company TOLSA GROUP S.A