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

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

Structuration of natural muds in a rheological point of view.

This paper discusses the filling of estuary problem which can be defined as the accumulation of fine materials that causes the invasion of muds all over the estuary and that has a direct effect on the fauna and flora in the river, fishing, swimming and the beauty of the landscapes. All this consequences have social, environmental and economic impact. In the context of the study of this phenomena, analysis of the structuration mechanisms of sedimentary materials in estuaries is carried out in order to better understand the fillings estuarine areas and specially to consider sustainable solutions of “cleansing” of these areas. The Rance estuary is particularly targeted by the study. The aim is to provide answers on the rheological behavior of natural vessels by distinguishing the most significant scales to detect structural factors influencing the rheological parameters

Energy distribution in the squeezing of particles in concentrated suspension

The original publication is available at http://www.springerlink.com/content/745r568gh452n713/International audienceIn the present work, the squeeze flow geometry is used to investigate the properties of concentrated suspensions. The suspensions consist on hard glass spherical particles dispersed in a viscoplastic fluid. With such a material, following the solid volume fraction, the material rheological behaviour ranges from purely viscoplastic fluid to granular media. During the squeezing action, the material structure evolves with energy variation due to particle displacement and interaction. The goal of our study is to identify the effect of energy evolution on the flowproperties of suspensions and detect granular contact evolution. The proposed study consists on an energy approach based on the analysis of the global squeeze force and sample height with time. The squeeze force is decomposed in a combination of an average force component and a fluctuating one. This local fluctuating component is investigated from Fourier analysis as a function of solid volume fraction and compression velocity. Results show the evolution of the energy distribution during compression and allow the flow regime modification to be evaluated

Structuration of natural muds in a rheological point of view.

This paper discusses the filling of estuary problem which can be defined as the accumulation of fine materials that causes the invasion of muds all over the estuary and that has a direct effect on the fauna and flora in the river, fishing, swimming and the beauty of the landscapes. All this consequences have social, environmental and economic impact. In the context of the study of this phenomena, analysis of the structuration mechanisms of sedimentary materials in estuaries is carried out in order to better understand the fillings estuarine areas and specially to consider sustainable solutions of “cleansing” of these areas. The Rance estuary is particularly targeted by the study. The aim is to provide answers on the rheological behavior of natural vessels by distinguishing the most significant scales to detect structural factors influencing the rheological parameters

One-Dimensional-Time Study of the Dehydration of Plasterboards Under Standard Fire Condition (ISO 834): Thermo-Chemical Analysis

International audienceGypsum materials are often used as a technical solution for passive fire protection in many civil engineering applications. In this study, the dehydration of plasterboard with large thickness, 40 mm, is studied using a one-dimensional (along the thickness) and time methodology analysis. Such materials are subjected on one side to a standard fire curve (ISO 834). The imposed heat transfer directly to the exposed face of the board induces combined actions due to the gypsum dehydration. The thermal barrier efficiency evolves significantly versus time. The local measurement of the temperature field through the sample and the local water content combined with the analysis of the local chemical structure helped us to model and analyze the dehydration processes

Evaluation of Partially Degraded Existing Sewer System : Inspection of Cement Concrete Pipe

International audienceThe laboratory of civil engineering (LGCGM) at INSA Rennes, France, has performed several studies on the durability of cement mortar in several environments. The objective of the present study is to examine the effective state of concrete of Rennes sewer system. The age of those systems can reach and exceed 50 years. During this time, the aggressive environment has evolved: often public buildings have replaced industrial zone, permeability decrease of soils... Such mechanicals and chemicals solicitations induce internal and external damage of concrete pipes. Our investigations, based on SEM micro graphs, X-ray diffractions and micro analysis, were carried out on different samples: some of them suffering hard deterioration and the other with no apparent signs of damage. Simultaneously, mechanical properties were studied: compressive strength, Brazilian test, determination of the depth of reduced alkalinity with phenolphthalein on freshly fractured surface. Those analyses are completed with porosity and capillarity measurements. That experimental analysis showed that the interior deterioration was principally due to the expansive salt gypsum but carbonation is also present: importance of the two phenomena is correlated with the porosity of the mortar. In some cases alkali reaction is present. The formation of a gypsum surface deposit in the sulphuric acid environment creates a layer susceptible to abrasion and removed easily. Consequently, the damage increase rapidly. An exterior deterioration is also observed and is correlated with the soil (carbonation, chlorite, mechanical flexure)

Inspection et diagnostic des ouvrages à base cimentaire du schéma d'assainissement rennais. Cas d'un collecteur du système unitaire.

XXVIIIèmes Rencontres Universitaires de Génie Civil – La Bourboule du 2 au 4 juin 2010 AUGC 2010International audienceEn collaboration avec la ville de Rennes, nous avons entrepris une étude de l'état du réseau d'assainissement de la ville. Celui-ci est composé quasi exclusivement de conduites en béton. Différents protocoles expérimentaux ont été développés afin de mettre en évidence les pathologies majeures des matériaux à base cimentaire placés dans un tel contexte d'agression, mais également pour mettre en évidence certains des facteurs responsables de l'altération des ouvrages. Dans cet article, nous présentons les résultats de l'inspection d'un ouvrage dont les sollicitations prédominantes sont chimiques et abrasives. L'analyse d'un tronçon de conduite permet de distinguer l'endommagement entre le toit et le radier

Réseau d'assainissement de la ville de Rennes

International audienceL'objectif de l'étude est de mettre en évidence l'état du réseau d'assainissement de la ville de Rennes, de manière à pouvoir envisager les opérations de maintenance dans une logique de prévention et non consécutive à un accident. Au cours du temps, les évolutions de la ville ont conduit au déplacement des activités industrielles en périphérie et se sont substituées des zones pavillonnaires. Les effluents circulant dans le réseau d'assainissement ont donc changés de nature. Le but de cette étude est de déterminer l'état actuel des conduites : propriétés des matériaux et des ouvrages sur le plan physique, chimique et mécanique. La passivation des armatures est déterminée, les formations cristallines liées aux différentes attaques sont analysées par MEB, EDX et diffraction X. Les attaques peuvent être au contact du sol, des effluents et des granulats. Ainsi, il est possible d'estimer, la durée de vie de ces conduites, sous réserves que les conditions d'environnement ne varient pas dans le temps