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La permeabilite, de meme que la diffusion et l'absorption est utilisee dans le but de quantifier la durabilite d'un beton. La mesure de la permeabilite au gaz des betons depend fortement de leur taux de saturation. De plus, la... more
La permeabilite, de meme que la diffusion et l'absorption est utilisee dans le but de quantifier la durabilite d'un beton. La mesure de la permeabilite au gaz des betons depend fortement de leur taux de saturation. De plus, la taille des pores pouvant etre de l'ordre de grandeur du libre parcours moyen des molecules du gaz percolant, on a alors apparition d'un ecoulement de type moleculaire qui ne respecte pas les hypotheses de la loi de Darcy et consequemment la permeabilite varie en fonction de la pression moyenne de l'essai. Afin de prendre en compte ces problemes, nous avons essaye de quantifier les differents types d'ecoulement en presence et nous proposons une methode de calcul de la permeabilite apparente puis du debit gazeux, pour n'importe quel taux de saturation du beton et pour n'importe quel gradient de pression. Pour cela, il convient de determiner la permeabilite intrinseque du materiau qui est independante de la pression d'essai. Pour un composition de beton standard nous etudions les variations de la permeabilite intrinseque et celle de la part d'ecoulement moleculaire en fonction du taux de saturation du materiau. Les permeabilites sont mesurees a l'aide d'un permeametre a oxygene a charge constante de type CEMBUREAU. (A)
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The evolutions of the different physicochemical and mechanical properties as a function of the expansion due to Delayed Ettringite Formation (DEF) in concrete are studied. In comparison of sound materials, some characterizations were made... more
The evolutions of the different physicochemical and mechanical properties as a function of the expansion due to Delayed Ettringite Formation (DEF) in concrete are studied. In comparison of sound materials, some characterizations were made in accordance to the level of expansion: in the initial time, in the latent period, in the accelerating phase and at the end of expansion. The characterization was as follows; SEM analysis was used to observe the presence of DEF. Physical tests linked to transfer properties; gas permeability and electrical resistivity were measured to detect micro-cracks generated by the DEF advancement. To observe the impact of micro-cracks, compressive strength and static modulus were experimentally determined. It was observed that few tests can be used to detect theses pathologies earlier, during the latent period. Gas permeability, electrical resistivity and elastic modulus results were promising. These tests are very sensitive to the development of micro-crack...
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Recent projects specifications are definitively much more focused on the fact that concrete mix designs must be designed to achieve the expected structures durability rather than typical compressive strength classes. European standard EN... more
Recent projects specifications are definitively much more focused on the fact that concrete mix designs must be designed to achieve the expected structures durability rather than typical compressive strength classes. European standard EN 206 is allowing the implementation of performance-based approach for concrete mixes design even if its implementation still need to be further detailed.
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Abstract This paper presents the application of a new test protocol developed for determining chloride threshold values initiating corrosion in reinforced concrete. The experimental set-up was described in previous work and is based on... more
Abstract This paper presents the application of a new test protocol developed for determining chloride threshold values initiating corrosion in reinforced concrete. The experimental set-up was described in previous work and is based on the intrinsic localized aspect of chloride-induced corrosion. The test protocol is also based on the concept of anodic control of corrosion initiation, and therefore independent of the area of passive steel. The test method is applied to mortar and concrete formulations with different binders and steel surface conditions. Chloride-binding isotherms were also determined to allow the transition from total to free chlorides. It is found that the test protocol is rapid and applicable to all formulations. The experimental results provide an understanding of the influence of binder type, w/b ratio and porosity on chloride-induced corrosion initiation. As expected, the steel surface condition is shown to have an important overall effect on corrosion initiation.
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Abstract When dealing with macrocell corrosion, it is crucial to consider the geometry and size of the structure, including the mobilizable cathode–anode distance, which is the maximum distance where passive reinforcement bars exchange... more
Abstract When dealing with macrocell corrosion, it is crucial to consider the geometry and size of the structure, including the mobilizable cathode–anode distance, which is the maximum distance where passive reinforcement bars exchange current with corroding active sites. An application of the mobilizable cathode–anode distance is the corrosion of submerged regions of reinforced concrete structures where very high local anodic current densities were reported with no visual manifestation making this type of corrosion very dangerous. One possible explanation for these observations is that active steel (anode) bars in the submerged region could be coupled with a cathodic aerated zone located far away from the anode. This paper aims to study the influence of cathode–anode distance on the macrocell current. Experimental investigations were carried out on a 10 m long reinforced beam consisting of 20 segments of rebars: an anode where corrosion was initiated with chloride diffusion, and 19 identical cathodes. Different electrical connections were made between cathodes and corrosion currents were measured in order to test the impact of the cathode–anode distance on the evolution of corrosion current and the attenuation of the cathodic reaction in relation to the distance between anode and cathode. The experimental campaign was supported by numerical simulations, which confirmed the experimental results and tested the impact of electrical resistivity on the mobilizable cathode–anode distance. By connecting the anode to each cathode alone, it was found that macrocell corrosion current could be provided by cathode bars at large distances from the anode, the distance being dependent on the electrical resistivity of the structure. It was also found that, when all the cathodes were connected to the anode, the closest bar received the highest proportion of the total current, which increased with electrical resistivity, whereas the most distant bars received very limited amounts of current.
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This study presents the determination of electrochemical properties of active steel in mortar, based on inverse numerical modeling that focuses on their dependency on chloride content. An experimental campaign, consisting of galvanic... more
This study presents the determination of electrochemical properties of active steel in mortar, based on inverse numerical modeling that focuses on their dependency on chloride content. An experimental campaign, consisting of galvanic coupling tests between anode samples contaminated with different chloride concentrations and cathode samples without chlorides, was carried out. Cathode polarization tests allowed for directly determining passive steel electrochemical parameters. Anode polarization tests coupled with a numerical optimization were then performed for quantifying active steel parameters and focusing on chloride's effect on the iron anodic Tafel coefficient. Furthermore, the steel electrochemical properties were successfully used as input parameters to model the galvanic experiments.
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This paper describes the main results obtained jointly by a number of French laboratories within the framework of a group under AFREM (Association Francaise de Recherches et Essais sur les Materiaux et les Constructions). The objectives... more
This paper describes the main results obtained jointly by a number of French laboratories within the framework of a group under AFREM (Association Francaise de Recherches et Essais sur les Materiaux et les Constructions). The objectives of this group were to define a preconditionin g process which would result in a better distinction between the various types of concrete with an acceptable test length, and to draft a recommendation for measuring the gas permeability of concrete. The procedure for measuring the gas permeability of concrete provides good reproducibility. However, the equipment used does not allow the measurement of permeability values greater than 10 -19 m². A conditioning procedure for predrying a test sample before measurement was defined. This conditioning procedure is the result of a compromise among the necessary attributes of a test, which should be easy to apply and as rapid as possible, while not degrading the test sample excessively. A drying temperature of 8...
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Une campagne experimentale sur plusieurs annees a ete entreprise sur des eprouvettes conservees en laboratoire et sur des corps d'epreuve vieillissant en milieu naturel, afin de caracteriser, du point de vue de la durabilite, une... more
Une campagne experimentale sur plusieurs annees a ete entreprise sur des eprouvettes conservees en laboratoire et sur des corps d'epreuve vieillissant en milieu naturel, afin de caracteriser, du point de vue de la durabilite, une gamme de 15 betons allant du B20 au 8120. Ce programme s'inscrit dans le cadre du sous-theme «Etude experimentale sur sites de vieillissement» du theme «Durabilite» du Projet National BHP 2000 et de l'Operation de Recherche des LPC «Durabilite du beton arme et de ses constituants : maitrise et approche performantielle». Cet article est le troisieme de la serie intitulee «Vieillissement des betons en milieu naturel: une experimentation pour le XXI e siecle». Il rassemble les resultats experimentaux obtenus lors des essais realises en laboratoire sur eprouvettes âgees de 28 jours et concernant la permeabilite aux gaz, le coefficient de diffusion apparent des chlorures, le coefficient d'absorption capillaire et la resistance aux cycles de gel-degel avec ou sans sels. Pour chaque niveau de resistance des betons testes, l'influence des parametres de formulation a notamment ete etudiee. En outre, les classements des 15 formules de beton, etablis sur la base des differentes proprietes de durabilite mesurees, ont ete compares. Les resultats experimentaux confirment la meilleure aptitude des BHP sans air entraine a limiter les transferts gazeux ou ioniques au sein du materiau, comparativement aux betons ordinaires. Vis-a-vis de la resistance aux cycles de gel-degel avec ou sans sels, il est necessaire d'atteindre la gamme superieure des betons a tres hautes performances (100 < f c28 ≤ 150 MPa et 0,20 ≤ E/C < 0,32) pour assurer un bon comportement sans qu'il soit necessaire de respecter les specifications sur le facteur d'espacement des bulles d'air. Ain si, dans la serie des 15 betons etudies, seul le beton M120FS presente un bon comportement a la fois lors de l'essai de gel-degel (sans sels) et de l'essai d'ecaillage. Les resultats montrent en outre la complementarite des indicateurs de durabilite permeabilite aux gaz et coefficient de diffusion des chlorures pour evaluer la durabilite potentielle des betons vis-a-vis de la corrosion des armatures. Enfin, en ce qui concerne l'influence des parametres de formulation, si la diminution du rapport E/C contribue a ameliorer les differentes proprietes de durabilite examinees dans cette etude, il s'avere que l'incorporation d'une addition minerale pouzzolanique ou d'un agent entraineur d'air peut avoir un effet positif ou negatif selon la propriete consideree. Par ailleurs, des pistes sont proposees pour les travaux futurs, notamment dans la perspective de selectionner des indicateurs de durabilite specifiques au gel.
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Research Interests: Civil Engineering, Chemistry, Microstructure, Composite Materials and Structures, Solid Mechanics, and 15 moreWaste Management, Comparative Study, Cement, Nuclear Waste, Fly Ash, Ammonium Nitrate, Microstructures, Service Life, Mortar, Blast furnace Slag, Radioactive waste, Mercury Intrusion Porosimetry, Gas Permeability, Chloride Diffusion, and Decalcification
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This article aims to expose a probabilistic methodology for the design of concrete formulations in a marine environment. As defined in the performance-based approach, durability indicators, considered as random variables, will be defined... more
This article aims to expose a probabilistic methodology for the design of concrete formulations in a marine environment. As defined in the performance-based approach, durability indicators, considered as random variables, will be defined by quantifying their variability. Based on elementary models for engineers, a classical probabilistic approach is then proposed: the probability to depassivate the reinforced bars, through a reliability index, is estimated in order to insure the durability of concrete. Moreover, a Bayesian network is used to update the distributions of random variables.Cet article expose une approche probabiliste pour l’élaboration de formulations de béton en environnement marin. Similairement à l’approche performantielle, des témoins de de durabilité, considérés comme des variables aléatoires, sont caractérisés par leur variabilité. Sur la base de modèles simples, une approche probabiliste classique est proposée: la probabilité de dépassivation des aciers passifs, au travers d’un indice de fiabilité, est estimée afin d’assurer la durabilité du béton. De plus, un réseau bayésien est utilisé pour actualiser les lois de ces variables aléatoires.
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Research Interests: Engineering, Civil Engineering, Modeling, Corrosion, Probabilistic Logic, and 15 moreLiterature Review, Reliability, Durability, Design Methodology, Second Law, Application, Reinforced concrete, Bayesian Network, Sea Water, Marine Environment, Probabilistic Method, Alkali Silica Reaction, Indexation, Chemical Composition, and Experimental Data
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To study the permeability of cementitious materials; a procedure of drying out moisture before the actual measurement of this property, normally called preconditioning, is an unavoidable necessity. In this study, the preconditioning... more
To study the permeability of cementitious materials; a procedure of drying out moisture before the actual measurement of this property, normally called preconditioning, is an unavoidable necessity. In this study, the preconditioning procedure developed by the authors earlier, is used to carry out the measurement of permeability to gases of 15 concrete compositions in order to compare the different steps
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The aim of this work is to give an equivalent gas permeability in order to estimate the associated flow through a concrete specimen exposed to drying, for example with a non-uniform moisture distribution inside (equivalent to a saturation... more
The aim of this work is to give an equivalent gas permeability in order to estimate the associated flow through a concrete specimen exposed to drying, for example with a non-uniform moisture distribution inside (equivalent to a saturation profile), and related to the apparent permeability value, calculated for the same dry sample. The chain of reasoning to obtain this permeability for a given drying situation requires estimation of the water content profile via a model of drying, and of the relative permeability (determined for a given constant moisture content in concrete) over the entire saturation field. The method is based on a finite element idealisation of the sample thickness by a discrete approach in one dimension. It is the analogy between Darcy's law and Ohm's law that allows the local relative permeability to be likened to a local conductivity. Then the existing relation between conductivity and conductance leads to the determination of an equivalent conductance t...
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The permeability to gases of cementitious materials is one of the major contenders for becoming a standard parameter for the quantification of the durability of these materials. This coefficient is thought to be closely related to the... more
The permeability to gases of cementitious materials is one of the major contenders for becoming a standard parameter for the quantification of the durability of these materials. This coefficient is thought to be closely related to the compressive strength. It is shown systematically here, by conducting permeability studies as a function of the degree of saturation of concrete on two sets of concrete compositions having the same compressive strength (100 MPa and 25 MPa), that entirely different gas permeability values may exist for different mix compositions which have the same compressive strength. These measurements were carried out on 5 cm thick, 15 cm dia. specimens by using a CEMBUREAU permeameter and oxygen as the percolating fluid. The results emphasize the fact that the 28 day compressive strength alone cannot be a criterion of the durability of concrete unless it is coupled with the quantification of the resistance to the entrance of aggressive chemicals.
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Research Interests: Engineering, Materials Engineering, Civil Engineering, Probabilistic Logic, Building, and 14 moreDurability, Reinforced concrete, Sea Water, Marine Environment, Service Life, Indexation, Chemical Composition, Portland cement, Diffusion Model, Ordinary Portland Cement, Concrete Cover, Probabilistic Approach, Design rules , and Cement concrete
The objective of this work is to simulate the gas flow across a concrete wall of a nuclear power plant internal enclosure. In the laboratory, permeability measurements are generally made on cylindrical samples (15 cm diameter×5 cm height:... more
The objective of this work is to simulate the gas flow across a concrete wall of a nuclear power plant internal enclosure. In the laboratory, permeability measurements are generally made on cylindrical samples (15 cm diameter×5 cm height: ∅ 15×5 cm) with a steady-state experiment. To be able to predict structural behaviour, we studied size effect and steady-state time with
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... Fig. 3. Migration test simulation (D e =2.10 −12 m 2 /s, thickness=1cm, c up =0.564mol/L, U=12V). ... Four different concretes were made in accordance with the French NFP18305 standard, which specifies conditions to observe when the... more
... Fig. 3. Migration test simulation (D e =2.10 −12 m 2 /s, thickness=1cm, c up =0.564mol/L, U=12V). ... Four different concretes were made in accordance with the French NFP18305 standard, which specifies conditions to observe when the concrete structure is located in a ...
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This work documents the effect of different temperature levels on chloride penetration through a saturated CEM-I mortar. The temperatures studied were 5, 21 and 35°C. In addition to experiments, a model based on multi-ionic diffusion is... more
This work documents the effect of different temperature levels on chloride penetration through a saturated CEM-I mortar. The temperatures studied were 5, 21 and 35°C. In addition to experiments, a model based on multi-ionic diffusion is proposed. It is highlighted that the temperature level has no impact on the chloride binding during immersion tests in NaCl solution, for marine environment concentrations. The chloride diffusivity, which is temperature dependent, can be calculated by the Arrhenius equation. Finally, experimental results were compared with good agreement to the numerical concentration profiles obtained by solving the continuity equation for each present ionic species coupled to the current law.
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Durability of concrete structures is often dependant on ion diffusion transport and more particularly on chloride diffusion. The mechanisms of diffusion involved during the transport of chloride ions into saturated concrete are... more
Durability of concrete structures is often dependant on ion diffusion transport and more particularly on chloride diffusion. The mechanisms of diffusion involved during the transport of chloride ions into saturated concrete are classically described by the Fick's laws which supposed that ions are non electrical particles. Nevertheless, some experimental results remain yet unexplained. Starting from this state of the art, a new approach called the multi-species approach has been developed. This approach makes it possible to account for the interactions between the different species present in the solution. The aim of this paper is first, to clarify the scientific basis of ionic diffusion into saturated porous media and second to describe and understand some experimental data, the significance of which had not been fully understood.
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This paper documents the influence of the temperature level (5, 21 and 35°C) on the chloride penetration through cementitious materials. Mortars based on CEM-I and CEM-V type cements are tested. Results on chloride binding, chloride... more
This paper documents the influence of the temperature level (5, 21 and 35°C) on the chloride penetration through cementitious materials. Mortars based on CEM-I and CEM-V type cements are tested. Results on chloride binding, chloride diffusion coefficients together with total chloride concentration profiles after 6 months of immersion are presented. It is shown that the change of total chloride concentration
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This paper focuses on the effect of different temperature levels on the chloride penetration through a saturated CEM I cementitious materials. The temperatures studied were 5, 21 and 35 circC. In addition to experiments, a model based on... more
This paper focuses on the effect of different temperature levels on the chloride penetration through a saturated CEM I cementitious materials. The temperatures studied were 5, 21 and 35 circC. In addition to experiments, a model based on the multi-ionic diffusion is proposed. It is highlighted that the temperature level has no impact on the chloride binding during immersion tests
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ABSTRACT Within the French context of nuclear waste disposal in deep geological formation, concrete will be used as the building material for structures as well as for engineered barrier systems ( EBSs). With regard to the durability that... more
ABSTRACT Within the French context of nuclear waste disposal in deep geological formation, concrete will be used as the building material for structures as well as for engineered barrier systems ( EBSs). With regard to the durability that is necessary to keep the disposal facilities safe and secure, the long-term behaviour of cement-based materials has to be modelled. To assess the long- term evolution of physical and chemical properties of concrete, it is necessary to perform short- term experiments in conditions allowing extrapolations. The aim of this project was to determine the variation of transfer properties ( diffusivity, permeation) with hydrolysis/ decalcification. To simulate the two time phases of the structure life according to the external conditions, transfer properties were examined through two decalcification tests: a dynamic ( temperature between 20 and 80 degrees C, under a hydraulic pressure drop from 2 to 10 MPa) and a static test ( NH4NO3 attack). The results could be used as input data in the long- term modelling of the disposal confinement capacity.