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A question frequently asked by engineers exposed for the first time to geosynthetics is: “how long do they last”. In this presentation, the author gives an overview of the service life of geosynthetics. Service life is analysed versus the design life and the carbon footprint associated to the construction of a structure. Factors affecting the performance of a geosynthetic used for sealing a canal are presented. A distinction is made between failures occurring because the product did not survive its installation, i.e., survivability-related; failures caused by an inadequate design of the product or the structure considering its environment of service, i.e., performance-related; or premature loss of function despite both installation and design were adequate, due to the inadequate choice or inadequate formulation of the material, i.e., durability-related. The various materials commonly used to waterproof a structure are reviewed, and it is shown that geomembranes are indeed the material of choice for waterproofing a geotechnical structure, such as a canal. Methods available to assess the service life which can be reasonably expected from various geosynthetics for a waterproofing function, such as in a canal or a dam. Field experiences are described, where some geosynthetics are still performing well after more than 60 years. Well-accepted predictive methods show that geosynthetics can last well-over a century in water-transport or water storage applications, especially when covered by soil or concrete to avoid UV exposure, to control their temperature, and to avoid accidental damage.

First, a review of important issues that must be addressed when designing the use of geomembrane linings in canals is presented: water flow characteristics affecting exposed geomembranes and mechanisms that could cause failure of geomembrane linings. The reviewed mechanisms include: deformation of the supporting soil; uplift of geomembrane by wind, flowing water, or groundwater; mechanical damage to the geomembrane lining, e.g. by puncture or excessive stresses Recommendations are presented to address these issues. Then, design methods are presented for the sizing of canal components such as geomembrane protection, geomembrane ballasting, and geomembrane anchorage. It is shown that, in many cases, the association of geomembrane watertight lining and concrete protection layer is a successful solution.

Refractory masonry with dry joints is widely used in the steel-making industry for the linings of several high-temperature components (>1500 ∘ C) including steel ladles and furnaces. To properly optimize the design and performance of these linings, thorough numerical models that consider the presence of joints, joints closure and reopening and the nonlinear elastic-viscoplastic behaviour (creep and stress relaxation) of refractories at high temperature are required. The present study reports on the formulation, numerical implementation, and application of a homogenized multi-scale elastic-viscoplastic model for the simulation of refractory masonry linings with dry joints. Refractory bricks are considered to exhibit linear elasticity as well as rate-dependent plasticity. Four joint patterns are predefined based on the state of bed and head joints. The homogenized elastic-viscoplastic behaviour of each joint pattern is determined using finite element based nonlinear homogenization approach. The transition criteria between the four patterns are defined in terms of macroscopic stresses and strains. Verification of the developed homogenized constitutive laws is carried out by comparing the numerical results of the detailed micro models (brick and joints are considered) with the homogeneous equivalent material models. Furthermore, comparisons with experimental results of refractory masonry walls subjected to biaxial compression load at room and high temperature are carried out. Good agreements between the experimental and numerical results are obtained. Then, the validated models are employed to predict the mechanical behavior of refractory masonry structures subjected to different loading conditions. The present numerical model is able to simulate the orthotropic, compressible, rate-dependent homogenized behaviour of mortarless refractory masonry structures, and accounts for joints closure and reopening due to loading and unloading.

Reactive impregnation concerns many science and engineering areas, such as corrosion in the steel-making industry and chemical engineering. Furthermore, reactive impregnation can become dangerous in some applications. Simulating non-reactive impregnation with classical methods is the first step before computing reactive impreg++nation. However, existing numerical methods present problems such as high computational cost and spurious oscillation. To avoid these computational difficulties, we propose the Self-organized Gradient Percolation model. It is a numerical model based on probabilistic approaches and, in particular, on percolation methods. This work aims to present a 2D model based on the 1D developed model. The first results are free from spurious oscillation and drastically reduced the computational cost compared with the classical methods.

The interface between bricks and mortar is often the weakest part of masonry structures. For refractory linings, the interface strength must be measured at high temperature. Adapted slant shear tests and a new dedicated tensile test set up are proposed here for this purpose. To test the ability of the proposed method, it was applied on two representative brick/mortar couples from room temperature up to 1450 °C. Slant shear tests were conducted to measure ultimate compression and shear stresses and to identify temperature dependent parameters of the Mohr-Coulomb failure criterion. Tensile tests were performed to identify the tensile cut-off. Depending on the brick/mortar couples, the failure can appear at the interface or in the mortar. Cohesion and tensile strength decrease sharply over 900 °C.

International audience; Mortarless refractory masonry structures are widely used in the steel industry for the linings of many high-temperature industrial applications including steel ladles. The design and optimization of these components require accurate numerical models that consider the presence of joints, as well as joint closure and opening due to cyclic heating and cooling. The present work reports on the formulation, numerical implementation, validation, and application of homogenized numerical models for the simulation of refractory masonry structures with dry joints. The validated constitutive model has been used to simulate a steel ladle and analyze its transient thermomechanical behavior during a typical thermal cycle of a steel ladle. A 3D solution domain and enhanced thermal and mechanical boundary conditions have been used. Parametric studies to investigate the impact of joint thickness on the thermomechanical response of the ladle have been carried out. The results clearly demonstrate that the thermomechanical behavior of mortarless masonry is orthotropic and nonlinear due to the gradual closure and reopening of the joints with the increase and decrease in temperature. In addition, resulting thermal stresses increase with the increase in temperature and decrease with the increase in joint thickness.

International audience; The lifespan of refractory results from a complex interaction between chemistry, thermal conditions, and mechanics. The development of numerical models able to predict the results of such complex multi-physics couplings requires an intensive use of the thermodynamics of irreversible processes framework. Today, the main barriers to reach fully predictive simulations are: the access to relevant data at high temperature (chemical kinetics, chemical expansion coefficient, etc), the numerical complexity and the computational time. The theoretical framework is briefly illustrated on refractory lining applications with a focus on the impact of the swelling induced by corrosion. Then, the numerical difficulties to ensure the numerical convergence and the accuracy of the results when solving classical partial differential equations are examined. Finally, a new approach to model the capillary impregnation by slag, based on percolation theory, is proposed. The basics of this method and the first numerical results are presented.

International audience; Recent developments in oxygen transport membranes have led to a selection of membrane materials or designs to achieve a judicious compromise between the oxygen flux, chemical stability and mechanical performance of membranes under operating conditions. This paper briefly describes the state of the art in the current understanding of oxygen transport through mixed-conductor membranes for oxygen separation. A better understanding of oxygen transport mechanisms, in particular, oxygen exchange at the membrane surface, leads to the identification of relevant key parameters that control the oxygen semi-permeation performance of the membrane. From a rational approach, key parameters are identified and discussed to identify promising membrane materials.

International audience; The oil sands industry generates large quantities of mineral waste, such as fluid fine tailings (FFT), whose disposal is often challenging. The use of planar electrokinetic geocomposites (eGCPs) in FFT disposal areas could improve in-situ dewatering by allowing water to drain after it is expulsed during consolidation and by permitting the use of electro-osmosis (EO) to displace a significant portion of the remaining water. Four dewatering experiments involving mature fine tailings (MFT) are presented here: in three of them increasing normal stresses are applied on the MFT followed by EO; in the fourth test, EO is applied before the normal stress is increased. The results show that eGCPs adequately filter MFT; the particles did not clog or blind the filter. MFT were significantly dewatered under an applied normal stress followed by EO. EO was very efficient at extracting the more tightly bound water that remained after mechanical dewatering. In one configuration, a significant improvement of the shear strength from nearly 0 kPa to a mean value of 25 kPa was obtained, which is significantly higher than the 10 kPa required by Alberta regulations. The final solids content in that case was about 70%, starting from an initial solids content of 45%. The energy required for that test was 10.6 kW h per dry tonne.

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International audience; Mortarless refractory masonry is widely used in the steel industry for the linings of high-temperature components such as steel ladles and furnaces. Successful design of these large-sized structures requires a proper understanding of the interaction between material discontinuity introduced by the presence of mortarless joints, joints closure and reopening due to loading/unloading, and their effect on the thermomechanical response of the structure. In the present study, 3D thermomechanical models have been developed to analyze the effects of joints reopening on the thermomechanical behavior of mortarless masonry walls. Four joint patterns, with their corresponding equivalent elastic properties, have been defined based on the state of head and bed joints (open or closed). The effective elastic properties of each joint pattern have been calculated with the help of the finite element method and the strain energy-based homogenization technique. The joints reopening and closure criteria have been defined as a function of macroscopic stresses and strains. The developed material model has been implemented in a commercial finite element software and then used to analyze the thermomechanical behavior of refractory masonry walls. The numerical model has been validated by comparing the numerical results with experimental data (biaxial compression test of a flat wall). Both results are in good agreement.

International audience; Aim. - Eating disorders (EDs), disordered eating (DE) and obesity are thought to have overlapping aetiological processes. DE in obesity can jeopardize weight-loss results, and acyl ghrelin (AG) is a hormone that stimulates food intake and reward processes. The main study objective was to determine whether higher-than-expected concentrations of AG in common obesity are associated with DE symptoms. Methods. - The study population included 84 women, aged 20-55 years, free of established EDs: 55 were severely obese (OB) and 29 were of normal weight (NW). OB participants were stratified into two groups according to their median concentration of fasting AG distribution. The OB women with a high fasting plasma ghrelin concentration (HGC) were compared with both OB women with a low fasting plasma ghrelin concentration (LGC) and NW women. Participants were assessed by the Eating Disorder Inventory (EDI-2), Three-Factor Eating Questionnaire (TFEQ) and Hospital Anxiety and Depression Scale (HADS). Fasting glucose, insulin, leptin and ghrelin plasma concentrations were also quantified. Results. - Between the two AG groups of OB women, there was no statistical difference in either anthropometric or metabolic parameters, HADS, TFEQ or fasting hunger scores. However, the HGC group scored significantly higher than the LGC group on the drive-for-thinness subscale of EDI-2 (9.30 +/- 0.99 vs. 6.46 +/- 0.83, respectively; P = 0.033). Conclusion. - Results support the hypothesis of a potential relationship between fasting plasma AG concentrations and ED risk, regardless of mood and anxiety. AG may be considered a potential biomarker of vulnerability for developing EDs. (C) 2018 Elsevier Masson SAS. All rights reserved.

International audience; In order to support the optimization of mortarless brick linings of steel producing furnaces it is proposed in this paper to investigate only the compressibility of dry refractory joints. To this end, optical measurements based on the Digital Image Correlation method were carried out during compression of Magnesia-Carbon brick samples with dry joints. The second main objective is to assess the accuracy of the secant linearization schemes (the classical secant procedure and its modified extension) to reproduce the reference local and global behaviour of refractory mortarless linings accounting for the identified inelastic convex powerlaw behaviour of the Magnesia-Carbon dry joint. The reference nonlinear solution is obtained by means of finite elements method. Under normal compressive loading, unlike for usual (concave) power-law viscoplastic composites for which the secant schemes are known to provide too stiff results, it was found that the modified secant scheme leads to good overall predictions. The classical secant procedure underestimates the reference local and overall behaviour. To improve the latter result, an empirical improved secant formulation was proposed and implemented. It leads to better estimates at local and global levels.

International audience; Mixed Ionic and Electronic Conductors (MIECs) are promising membrane materials for oxygen separation fromair at high temperature. The transient stage is critical due to the stress induced by the chemical strain, combinedwith the oxygen activity field through the membrane. In the literature, permeation models are able to predict theoxygen flux in steady state or to identify the slowest mechanism. In this paper, the proposed model aims topredict the oxygen activity fields through the membrane both in transient stage and steady state. A macroscopicapproach is proposed, the balance of a temporary species is introduced to take into account separately thedissociative adsorption, associative desorption and interface reaction between surface and bulk. New densitiesof probability are proposed to model dissociative adsorption and associative desorption in order to take intoaccount the difference between “classical” catalysis and the MIECs case. This model is implementing in the finiteelement software COMSOL Multiphysics© thanks to the combination of the modules “coefficient form PDE”and “coefficient form boundary PDE”. The results of the model are in good agreement with steady state andtransient stage experimental data. The different kinetics of oxygen release and oxygen intake are wellreproduced.

International audience; This publication presents new advances in the field of refractories characterization. These laboratory methods that combine experiments and numerical analyses and concern both the thermomechanical and thermochemical behaviour are illustrated through different examples: identification of asymmetrical creep, determination of elastic and inelastic properties, measurements of macroscopic deformation, phase transformations or corrosion kinetics. These advanced techniques offer the refractory community new opportunities to improve the knowledge and the prediction of the phenomena of degradation of the refractories.

International audience; In this article, we test a horizontal detect and avoid algorithm for UASs flying in Terminal Control Areas. We have used recorded commercial traffic trajectories and randomly built thousands of conflict scenarios with UASs to check the ability of such an algorithm to ensure the separation with commercial aviation. We consider two different types of UASs, flying at 80kn or 160kn, with six different missions: flying straight or turning and leveled, climbing or descending. We only focus on horizontal maneuvers at constant speed in order to not interfere with the TCASs of aircraft, nor rely on most UASs poor ability to change speed. The article investigates the influence of the various parameters on the separation achieved and the amount of maneuvers required, especially the strategy used to select the best maneuver among the allowed headings. The analysis of our results shows that, amid two basic and “extreme” strategies that favor either minimal heading changes or the robustness of the maneuvers, the combination of both, switching from the first one to the second whenever the distance between the UAS and aircraft falls under a given threshold, gives the best results with very few remaining airproxes, while keeping low the amount and amplitude of maneuvers.

Finite element (FE) computations have been performed to analyze the thermo-chemo-mechanical behavior of SiC-based refractory parts in linings used in waste-to-energy plants. These parts are in contact on one side with smoke and ashes at high temperature, and on the other side with the pressurized vapor pipe. Three multi-layered lining designs have been studied: two with tiles and one with a concrete panel. A coupled model taking into account the transport of dioxygen in the gas through the porosity, the reaction of dioxygen in contact with silicon carbide particles and the formation of solid components gradually clogging the pores, has been implemented in the finite element code ABAQUS ? . These phenomena affect the mass diffusion rate of dioxygen through the refractory layer and induce a macroscopic swelling of the material. The analysis of the numerical results allows for a better understanding of the influence of the lining design and the nature of the ceramics on the lifespan of such refractory parts. HighlightsPaper proposes an analysis of behavior of SiC-based refractory linings which are subjected to a chemical environment.The model takes into account the transport of oxygen in the gas through the porosity.The model takes into account the chemical expansion induced by oxidation.Three designs of the lining are studied.The obtained results allow the highlighting of the design effect in relation with material properties.

International audience; To support optimisation of refractory masonry structures compressibility of dry joints of magnesia-carbon and magnesia-chromite bricks have been investigated. Laboratory scale tests and finite element modelling have been performed. Measurements done in wide temperature range have shown that the exponential form of the joint closure curve results from gradual closure of initially non-parallel surfaces. The stress needed to close the joint was found to be proportional to the material stiffness. Temperature influences the joint closure by changing the stiffness of material and by reducing the initial joint gap due to thermal expansion.

Permeation induced expansion in substoichiometric perovskites is a key point of their mechanical reliability under oxygen activity gradient. This paper proposes a macroscopic modelling of this phenomenon based on the choice of oxygen activity as state variable. This approach helps to underline the asymmetry of the chemical expansion in its dependence on the difference between the actual surrounding atmosphere and the sintering one. It leads to the development of the notion of loading path in terms of surrounding atmosphere change. The investigations show that the intrinsic chemical expansion behaviour is independent of the sintering atmosphere. The apparent chemical expansion behaviour is driven by the loading path. A study of the sensitivity of each parameters of the model helps to better estimate the possibilities and the limits of the proposed approach.

The MRS-100 system combines at the same time the simplicity of a linear sliding gate and the advantages of a round plate. This sliding gate is based on 3 innovating approaches: a sliding gate built around a refractory plate, a mechanism that avoids the cracking of plates and finally, an optimisation of the round plate through a programmable sequential rotation at the ladle stand. This MRS-100 system leads to a safe use, an improvement of the tasks at the working station and a reduction of the user costs.

Some refractory linings of metallurgical vessels consist of masonry without mortar. To describe the mechanical behaviour of these large-sized structures, it is necessary to use an equivalent material instead of a model that comprises all the bricks and joints involved. The properties of the equivalent material depend on the opening and closure mechanism of joints. In this paper, four joint states which are the combination of open/closed states of bed and head joints are identified, and the corresponding equivalent elastic properties are determined accordingly using homogenisation techniques. The transition criterion between these joint states is based on the unilateral contact conditions written in terms of macroscopic strain. The developed model is then compared to an in-plane biaxial compression test. The numerical and experimental results are in good agreement.

Dense mixed ionic conducting membranes are subjected to stresses induced by the oxygen activity gradient under operating conditions. This works proposed a thermomechanical model, taking into account such chemical induced strain. This model permits predictive simulation by the finite element method in transient and steady state to give guidelines for reactor operating conditions optimization. Modelling has shown that the maximum stress on the membrane depends on thermal gradient along the membrane and transient phase's management.

International audience; Degradation in bauxite refractory linings used in steel plants is localized in the slag‐impregnated zone of refractories. It is proposed to estimate the contribution of the pressure of the impregnated liquid on the degradation of refractories. The study of the gradient of chemical composition allows for the evaluation of the liquid content, the oxide content in the liquid phase, and the “slag” viscosity. The thermomechanical analysis of a porous refractory impregnated by slag enables us to propose analytical expressions for a rapid estimate of the maximum “slag pressure” and its location as well as the level of thermoelastic stresses.

Mixed ionic and electronic conductors (MIEC) are promising materials for ion transport membrane (ITM) based technologies. A reliable design of these membranes requires a better knowledge of their macroscopic mechanical properties. These properties are linked to the composition of membrane materials, but also in a large part to the manufacturing process. Then, the mechanical characterization set-up must allow using specimen very similar in term of manufacturing process as the final parts in. The use of the diametric compression test on thin plates is investigated here, combined with full-field measurements. Guideline for sample size, solution for classical artifact and a dedicated I-DIC algorithm are proposed. Then, Young modulus and tensile strength of seven MIEC compositions of the lanthanum-ferrite perovskite series (La (1− x ) Sr x Fe (1− y ) Ga y O 3−δ , La 0.5 Ba 0.5 Fe 0.7 Co 0.3 O 3−δ and La 0.5 Ca 0.5 Fe 0.7 Co 0.3 O 3−δ ) were determined at room temperature and at 900 °C.

International audience; Three-dimensional (3D) fabrics of commingled yarns offer the possibility of a low-cost and fast manufacturing of complex-shaped composite parts. Textile-reinforcement behavior during the forming process is very important since the appearance of defects (for example wrinkles, yarn misalignment or breakage) can significantly affect the mechanical properties of the final part. Experimental characterization of the mechanical behavior of textile-reinforcements is expensive, time consuming, and a large scattering of results is often observed. To overcome this, meso-scale modeling is an interesting method to study and understand the textile behavior at the unit cell level. To perform realistic simulations, an accurate modeling and, therefore, knowledge of the yarn mechanical behavior are needed. In this paper, a simple protocol is proposed and validated in order to investigate the tensile behavior of commingled polypropylene/glass yarns. Influence of specimen length and strain rate are highlighted. A comparison of tensile behavior of yarns before and after weaving is carried out in order to evaluate the weaving damage effect. Finally, a model describing the commingled yarn behavior is proposed. The parameters of the model are defined. Their dependency to strain rate, specimen length, and weaving damage are highlighted.

International audience; The oil sands industry usually leads to the production of large quantities of mineral waste, such as fluid fine tailings (FFT), whose disposal is often challenging. Electrokinetic geocomposites (eGCP) installed into the FFT disposal area could improve in-situ dewatering: they allow draining the water expulsed during FFT consolidation as well as imposing a voltage across FFT to displace water by electro-osmosis. This paper presents a laboratory device specifically developed to evaluate eGCP performance for sludge dewatering. Based on the oedometer principle, the device aims at studying sludge consolidation as a function of boundary conditions (mechanical stress and/or voltage), with drainage and electrical conduction ensured by two eGCPs positioned on both sides of the sludge layer. Preliminary results obtained with one particular eGCP are presented: the solid content was increased from 42% to 66%, which led to a significant improvement of the shear strength from nearly 0 kPa to a mean value of 40 kPa. The energy required for this experiment was 71 Wh (3.5 kWh per m3 of sludge). The filtration performance remained satisfactory; the sludge particles were retained upstream of the filter, with a clean water flowing through.; L'industrie des sables bitumineux produit de grandes quantités de résidus minéraux liquides, sous forme de boues difficiles à stocker. Des géocomposites électrocinétiques (eGCP) installés directement dans les parcs à résidus pourraient en améliorer l’assèchement : les eGCP peuvent à la fois drainer l’eau expulsée durant la consolidation et imposer une ifférence de potentiel électrique aux bornes des couches de boues afin de provoquer la migration de l’eau par électro osmose. Cet article présente un dispositif expérimental développé spécialement pour évaluer les performances des eGCP avec des boues minières. Basé sur les principes d’un ½domètre, le dispositif permet d’étudier la consolidation en fonction des conditions aux limites, le drainage et la conduction électrique étant assurés par deux eGCP positionnés de chaque côté de la couche de boue. Des résultats préliminaires sont présentés : l’expérience a conduit à un assèchement important, la siccité de la boue passant de 42% à 66% et la résistance au cisaillement de 0 kPa à 40 kPa en moyenne. L’énergie consommée durant le traitement a atteint 71 Wh (3,5 kWh par m3 de boue). La filtration a été correctement assurée par l’eGCP : les particules de boue ont été retenues et de l’eau propre s’est écoulée à travers l’eGCP.

Corrosion of refractories results from reactive transport namely, transport of agents and chemical reactions of these agents with impregnated medium. On one hand, the transport involves either diffusion or impregnation depending on the state of the corrosive agents and the microstructure of the host media. On the other hand, chemical reactions may be very numerous and complex. This study focused on the reactive impregnation of Al2O3-CaO slag into porous high alumina refractory.Transport properties of the porous media have been assessed by performing wicking test. Chemical reactions between the solid high alumina skeleton and Al2O3-CaO slag involve successive dissolution/precipitation mechanisms forming aluminates of lime. Contrary to the thermodynamic properties of the binary system, the kinetics of these solid/liquid reactions is not well known. Corrosion tests associated with quenching method, XRD and high temperature XRD were performed for a better understanding of the kinetics.

International audience; The transient stage is critical due to the stress induced by the chemical and thermal strain. In order to predict this strain, the oxygen activity field through the membrane needs to be known. Usually, the membrane is divided into three zones: the bulk where diffusion takes place and the two surfaces where exchanges between atmosphere and membrane take place. Oxygen bulk diffusion is well described by the Wagner theory. A consensus has not yet emerged regarding the surface exchange models proposed in the literature. Moreover, these models describe the permanent state, and cannot be extended to the transient stage. A new macroscopic surface exchange model which allows computing transient stage is proposed. This model assumed that the oxygen flux is governed by the association/dissociation of adsorbed oxygen and by the high energetic cost of oxygen reduction/oxidation. Then, the balance of transient specie only present on the surface is introduced to account for these two phenomena. The oxygen activity fields predicted by the proposed model are in agreement with the measures of chemical potential drop between the membrane and the atmosphere in permanent state. Transient stage measured during isothermal expansion test is partially reproduced.

Damage of SiC oxide bonded refractories in waste-to-energy facilities (WtE) has been characterized. Different phenomena were observed: wear by slag phases, volume expansion of tiles and fracture in different locations. These results are in agreement with laboratory experiments. The role of gas composition and tiles temperature profile on deposit composition, on condensation of gaseous alkali chloride and on formation of liquid phase inside the porosity of the refractories has been emphasized. Gaseous alkali species are involved, not only in the formation of liquid phases, but also as a precursor of cristoballite formation around the SiC grains as well as in the rich alumina-silica matrix. On the hot face of the refractories, oxo-reduction reactions produce the formation of wollastonite. Post-mortem analysis after several thousand hours of operation point to three main corrosion mechanisms

International audience; It is a common practice to design refractory linings with the help of thermal computations, thermochemistry analyses and strong workman know-how. Their mechanical design is often limited to simple thermo-elastic computations. Sometimes computations are refined considering non-linear mechanical behaviour, even if corrosion often induces additional chemical strain and strong change in service of the mechanical behaviour of the refractory. The aim of this presentation is to briefly recast the irreversible thermodynamic framework in order to underline the implications of some basic thermodynamic concepts in term of refractory behaviour modelling. Then, the use of these concepts to develop fully 3D finite element simulations accounting simultaneously for thermal, mechanical and chemistry phenomena will be illustrated on the particular case of SiC-based refractory. Comparison between long duration oxidation test at high temperature and model prediction allows the validation of the proposed approach. Then, an extension to the industrial case of refractory lining in Waste to Energy plant will be illustrated. The interest of taking into account the thermo-chemo-mechanical coupling effects is shown.

International audience; In refractory masonry lining of industrial furnaces the compressibility of mortars is critical for the thermo-mechanical integrity of the structure.Compressive stress-strain behaviour of refractory mortars has been measured during drying at room temperature and in the service temperaturerange of 300-1400◦C. The results have been explained using fractographic analysis and distinct element method computer modelling. The mortarfailure has been shown to occur due to formation of shear bands of micro-cracks. The propagation of cracks preferably follows the shortest pathbetween larger pores and is influenced by grain cohesion and interlocking. Tests with mortars featuring calcium aluminate cement, mono aluminiumphosphate, water glass and bentonite clay binders have indicated that besides increasing the cohesion between the grains the binder reduces theinternal friction that promotes higher compressibility. It has been found that the mortar with clay has the highest compressibility. The mortar withcement shows the most stable behaviour.

International audience; Silicon carbide-based refractory castables (SiC-RC) have high mechanical and chemical resistances at high temperature. Nevertheless when subjected to both high temperature and aggressive oxidizing environment, due to phase transformation, a chemical strain appears that leads to additional stresses in industrial parts and may cause degradation. In this paper, macroscopic constitutive equations are proposed to model the complex relationship between stress, strain, temperature and oxidizing atmosphere in porous SiC-RC. To model the kinetics of the chemical swelling, oxygen content in the porosity of the heterogeneous material is estimated. It depends on both the oxidation reaction of SiC-based grains and the diffusion of oxygen through the connected porosity in the castable. The macroscopic chemical strain associated to the local SiO2 formation takes only place when the local small voids cannot absorb the reaction product anymore. Besides, the reduction of porosity is accompanied by a reduction in the gas permeability and consequently a reduction in the diffusion of oxygen. The multi-physical model is implemented in the finite element code Abaqus . It accounts for heat transfer,reactive oxygen transport and chemically induced strain. A validation test was carried out on a cylindrical sample subjected to high temperature with a thermal gradient in ambient air. Comparison between experimental results, microscopic observations and numerical results showed that the model provides a good description of the main physical phenomena.

Mixed Ionic and Electronic Conductors are promising materials for oxygen transport membranes at high temperature. The mixed conduction leads to oxygen semi-permeation properties. This oxygen transport properties is linked to the ability of the membrane material to reversibly adsorb and desorb oxygen and to diffuse oxygen through the lattice [1]. However, the defect equilibrium with the surrounding atmosphere induces a “chemical” expansion in the same order than the thermal expansion. Mechanically, the transient stage is critical due to the stress induced by the chemical and thermal strain [2]. To predict this strain, the oxygen activity field through the membrane needs to be known. Usually, to model, the membrane is divided into three zones: the bulk, where oxygen bulk diffusion takes place and the two surfaces where oxygen exchanges between atmosphere and membrane take place. Oxygen bulk diffusion is well described by the Wagner theory [3]. The surface exchanges include the adsorption/desorption, dissociation/association and incorporation/exclusion of oxygen. A consensus has not yet emerged regarding the oxygen surface exchange models proposed in the literature. Two categories of models are reported: one corresponds to an extension of the Wagner theory to the surface [4] and the second corresponds to a chemical approach by kinetic laws [1, 5]. Different experiments have been performed to characterize the surface exchange and bulk diffusion parameters. The measures reported by Geffroy et al. on membrane surfaces during steady oxygen flow exhibits a large chemical potential gap between the membrane surfaces and the surrounding gases [6]. From our knowledge, this experimental data cannot be reproduced by a single model from literature. Moreover, although the combination of Wagner extension approach on the high oxygen side and kinetic approach on the low oxygen side makes it possible to reproduce results in steady state, it does not allowed to investigate transient stage. The proposed talk deals with a new macroscopic surface exchange model describing both oxidizing and reducing surface for transient stage. This model assumes that the oxygen flow is governed by the association/dissociation of adsorbed oxygen and by the high energetic cost of oxygen reduction/oxidation. Then, the balance of a transient species at the membrane surface is introduced to account for these two phenomena. The first results obtained are in accordance with oxygen semi-permeation measurements reported by Geffroy et al. [6]. The computation of isothermal expansion tests realized by Adler [7] in transient stage, using the proposed exchange model and the chemical expansion model proposed by Valentin et al. [8], present also a good correlation with experimental results. [1] S.B. Adler et al, Mechanisms and rate laws for oxygen exchange on mixed-conducting oxide surfaces, J Catal, (245), 91-109, 2007. [2] O. Valentin et al, Chemical expansion of La0.8Sr0.2Fe0.7Ga0.3O3-δ, Solid State Ionics, (193), 23-31, 2011. [3] C. Wagner, Equations for transport in solid oxides and sulfides of transition metals, Prog Solid State Ch, (10), 3-16, 1975. [4] H.J.M. Bouwmeester et al, Importance of the surface exchange kinetics as rate limiting step in oxygen permeation through mixed-conducting oxides, Solid States Ionics, (72), 185-194, 1994. [5] S. J. Xu et al, Oxygen permeation rates through ion-conducting perovskite membranes, Chem Eng Sci, (54), 3839-3850, 999. [6] P.M. Geffroy et al, Influence of oxygen surface exchanges on oxygen semi-permeation through La(1-x)SrxFe(1-y)GayO3-δ dense membrane, J Electrochem Soc, (158), 1-9, 2011. [7] S.B. Adler, Chemical expansivity of electrochemical Ceramics, J. Am. Ceram. Soc., (84), 2117-2119, 2004. [8] O. Valentin et al., Thermo-Chemo-Mechanical Modelling of Mixed Conductors in Transient Stages, Adv. Sci. Rech., (65), 232-237, 2010.

International audience; Corrosion tests of oxide-bonded SiC-based refractory cylinders with molten salts (mainly CaSO4, K2SO4) were performed at high temperature to enable better understanding of the corrosion mechanisms operating in these materials. Salt pellets were placed on the upper surface of small refractory cylinders. After they had been melted, the corrosive product soaked into the pores of the refractory cylinders and partially corroded the SiC phase. SEMEDS analyses showed thatCaSiO3 was the mainnewphase formed, growing from SiC aggregates into the pores.Theshapes of the initial and corroded cylinders were measured at room temperature using a 3D coordinate measuring machine equipped with a laser-plane sensor. These measurements enabled monitoring of the evolution of the residual radial deformation versus the depth from the surface in contact with the salt pellets, and consequently the characterisation of the local volume expansion induced by the phase change. Coupling SEM-EDS analyses with 3D digitising revealed the link between the corrosion product and the volume expansion.

International audience; Many bottom linings of refractory structures used in steel making industry are made of masonries with or without mortar. Several designs are possible: parallel, fish bone or radial. To compare the influence of these designs on the level of stress and displacements in the steel shell, the different masonries were modelled by an equivalent homogeneous material. The thermo-mechanical properties of this equivalent material were determined using a periodic homogenization method. They are temperature depending and depend of the joint states (open or closed in the two directions) for masonries with mortarless joints. This masonry model is used to simulate by the finite element method the behaviour of a simplified steel ladle. It demonstrates the influence of different parameters: presence or not of joints, dry joints/mortar joints, thickness of mortar joints, masonry design. It brings a help for the design of refractory masonry linings.

International audience; Many recent studies have focused on the development of perovskite membranes with high oxygen semi-permeation performance. However, the usual experimental setups used to measure oxygen semi-permeation values may lead to significant errors in the actual performance of the membrane materials. In this paper, special attention is paid to the experimental conditions and the associated impacts on oxygen semi-permeation measurements collected from the membrane. Furthermore, the experimental setups described in the literature do not allow the direct identification of the limiting step for oxygen transport through the membrane, i.e., either through bulk oxygen diffusion or oxygen surface exchange on both membrane surfaces. In this work, a specific experimental setup is proposed for the discrimination of oxygen bulk diffusion and surface exchange phenomena

The decrease of the dense layer thickness can lead to increase the internal stresses in the membrane due to the chemical expansion of membrane material under a large gradient of oxygen partial pressure. This chemical expansion due to p O 2 gradient through the membrane leads to important mechanical stresses in the membrane and commonly to the membrane rupture under large range of p O 2 , i.e. air/methane atmosphere. The solution suggested in this paper is the elaboration by tape casting and co-firing process of multilayer membranes with a specific design in order to decrease stresses due to the chemical expansion in working conditions.

International audience

International audience; The coking process is composed of two main stages: drying process and pyrolysis of coal. A heat and mass transfer model was developed to simulate the drying process of coal. The mechanisms of heat and mass transfer described in the model are: conduction through the coal cake; conduction and convection through the gas in pores; generation, flux and condensation of water vapor. The model has been implemented in finite element software. It requires basic data on the coke oven charge properties and oven dimensions as input. These input data were obtained by experiments or from the literature. The proposed model includes condensation and evaporation allowing us to reproduce the temperature plateau observed experimentally.