60 research outputs found
Experimental investigation of the variability of concrete durability properties
One of the main objectives of the APPLET project was to quantify the variability of concrete properties to allow for a probabilistic performance-based approach regarding the service lifetime prediction of concrete structures. The characterization of concrete variability was the subject of an experimental program which included a significant number of tests allowing the characterization of durability indicators or performance tests. Two construction sites were selected from which concrete specimens were periodically taken and tested by the different project partners. The obtained results (mechanical behavior, chloride migration, accelerated carbonation, gas permeability, desorption isotherms, porosity) are discussed and a statistical analysis was performed to characterize these results through appropriate probability density functions
Effect of nano-silica on the hydration and microstructure development of Ultra-High Performance Concrete (UHPC) with a low binder amount
A study of multiple effects of nano-silica and hybrid fibres on the properties of Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) incorporating waste bottom ash (WBA)
Variabilité des propriétés du béton : caractérisation expérimentale et modélisation probabiliste de la lixiviation
Evaluating structures durability requires taking into account the variability of material properties. The thesis has two main aspects: on the one hand, an experimental campaign aimed at quantifying the variability of many indicators of concrete behaviour; on the other hand, a simple numerical model for calcium leaching is developed in order to implement probabilistic methods so as to estimate the lifetime of structures such as those related to radioactive waste disposal. The experimental campaign consisted in following up two real building sites, and quantifying the variability of these indicators, studying their correlation, and characterising the random fields variability for the considered variables (especially the correlation length). To draw any conclusion from the accelerated leaching tests with ammonium nitrate by overcoming the effects of temperature, an inverse analysis tool based on the theory of artificial neural networks was developed. Simple numerical tools are presented to investigate the propagation of variability in durability issues, quantify the influence of this variability on the lifespan of structures and explain the variability of the input parameters of the numerical model and the physical measurable quantities of the material.L'Ă©valuation de la durabilitĂ© des modĂ©lisation probabiliste de la lixiviation structures nĂ©cessite de prendre en compte la variabilitĂ© des propriĂ©tĂ©s du matĂ©riau. La thĂšse prĂ©sente deux aspects principaux : d'une part une campagne expĂ©rimentale visant Ă quantifier la variabilitĂ© d'indicateurs du comportement du bĂ©ton ; d'autre part le dĂ©veloppement d'une modĂ©lisation simple de la lixiviation des bĂ©tons afin de mettre en Ćuvre des mĂ©thodes probabilistes pour estimer la durĂ©e de vie de structures liĂ©es notamment au stockage des dĂ©chets radioactifs. La campagne expĂ©rimentale consiste Ă suivre deux chantiers et Ă quantifier la variabilitĂ© de ces indicateurs, Ă©tudier leur corrĂ©lation et caractĂ©riser la variabilitĂ© des champs alĂ©atoires des grandeurs considĂ©rĂ©es (notamment vis-Ă -vis d'une longueur de corrĂ©lation). Afin de dĂ©pouiller des essais de lixiviation accĂ©lĂ©rĂ©e au nitrate d'ammonium en s'affranchissant des effets de la tempĂ©rature, un outil d'analyse inverse basĂ© sur la thĂ©orie des rĂ©seaux de neurones a Ă©tĂ© Ă©laborĂ©. Des outils numĂ©riques simples sont prĂ©sentĂ©s afin d'Ă©tudier la propagation de la variabilitĂ© dans des problĂšmes de durabilitĂ©, de quantifier l'influence de celle-ci sur la durĂ©e de vie des structures et d'expliquer la variabilitĂ© des diffĂ©rents paramĂštres d'entrĂ©e du modĂšle numĂ©rique et des grandeurs physiques du matĂ©riau
Modelling the spatial variability of leaching kinetics parameters: Investigation about the input variability influence on the lifespan distribution of a concrete structure
International audienceThis works aims at studying, through the Monte-Carlo method, the influence of the leaching kinetics parameters spatial variability on the lifespan of a concrete structure. The considered structure is a tunnel for nuclear waste disposal. It is observed that the expected value for the lifespan estimated when considering the material spatial variability is significantly lower than the lifespan estimated with a single simulation considering uniform parameters fields, equal to the expected value for each parameter.Le but de cette Ă©tude est d'Ă©valuer, par la mise en Ćuvre de la mĂ©thode de Monte-Carlo, l'influence de la variabilitĂ© spatiale des paramĂštres les plus influents par rapport Ă la cinĂ©tique de dĂ©gradation en lixiviation sur la vitesse de propagation dans une structure en bĂ©ton du front de dissolution de la portlandite. La structure considĂ©rĂ©e est un tunnel de stockage de dĂ©chets radioactifs. Nous observons que l'espĂ©rance de la durĂ©e de vie estimĂ©e en tenant compte de la variabilitĂ© spatiale des propriĂ©tĂ©s du bĂ©ton est sensiblement infĂ©rieure Ă la durĂ©e de vie estimĂ©e en considĂ©rant des champs uniformes, Ă©gaux Ă l'espĂ©rance des paramĂštres considĂ©rĂ©
Coupling Between Leaching and Mechanical Behaviour of Concrete
International audienceIn the case of a radioactive waste disposal, concrete containment structures must be studied over extended periods during which it is necessary to account for a possible degradation by calcium leaching due to on-site water. This phenomenon affects the microstructure of concrete and then is coupled with the mechanical behaviour of concrete. The effect of leaching on the static behaviour and then the possible influence of cracks on leaching will be considered. But there is also a possible coupling due to tertiary creep. In this case, failure occurs eventually. And finally, a probabilistic approach is used with the leaching and tertiary creep models to evaluate the lifetime of a concrete structure subjected to chemical and mechanical loading
Quantification of Tafel coefficients according to passive/active state of steel carbonationâinduced corrosion in concrete
International audienceStatistical quantification of Tafel coefficients is investigated in this study for isolated steel rebar embedded in concrete. The survey is supported by a wide experimental campaign carried out earlier to characterize the passive and active states of carbonationâinduced corrosion of steel. Electrochemical measurements (polarization resistance, corrosion potential, Tafel coefficients) and gravimetric estimations of iron loss were regularly conducted over 417 days on 108 concrete specimens. The statistical analysis reveals that the mean value of Tafel coefficients, both cathodic and anodic, is higher under active corrosion, which seems to contradict the general tendency found for chlorideâinduced corrosion, while their coefficient of variation is smaller. The statistical inference was based on the first step of distributions fitting the experimental data and then on the second step of goodnessâofâfit tests. The most suitable of the distributions proposed were the Burr, Rayleigh, and Gamma distributions. A similar analysis was made for the corrosion potential and polarization resistance. The findings of the study will be valuable for probabilistic approaches to corrosion where probabilistic distributions are required
Ătude de sensibilitĂ© d'un modĂšle d'alcali-rĂ©action
International audienceThe alkali aggregate reaction (AAR) is a significant deleterious degradation for many concrete structures, particularly those in which the saturation rate of the concrete remains constantly high, such as dams. The approximations associated with the modeling assumptions of AAR on the scale of a representative elementary volume (REV), and the many uncertainties that affect the parameters of the models, make the prediction of AAR phenomenon random, and thus require to operate in probabilistic context. To limit the stochastic dimension for a probabilistic analysis, a sensitivity analysis by the Morris method was conducted on the AAR model developed by LMDC in accelerated conditions. The outputs of model involved were the maximum and intermediate levels of swelling, as well as the time corresponding to each of these levels of swelling. This study helps to remove about half of the model parameters having little influence on the variability of outputs and can therefore be considered as deterministic subsequently. MOTS-CLĂS : alcali-rĂ©action, analyse de sensibilitĂ©, mĂ©thode de Morris.L'alcali-rĂ©action est une dĂ©gradation dĂ©lĂ©tĂšre significative pour de nombreux ouvrages en bĂ©ton, notamment ceux dans lesquels le taux de saturation du bĂ©ton reste Ă©levĂ© en permanence, comme les barrages. Les approximations associĂ©es aux hypothĂšses de modĂ©lisation de la RAG Ă l'Ă©chelle d'un volume Ă©lĂ©mentaire reprĂ©sentatif (VER), et les nombreuses incertitudes affectant les paramĂštres des modĂšles, rendent alĂ©atoire la prĂ©vision du phĂ©nomĂšne de RAG et imposent d'opĂ©rer en contexte probabiliste. Pour limiter la dimension stochastique lors de l'analyse probabiliste, une Ă©tude de sensibilitĂ© par la mĂ©thode de Morris a Ă©tĂ© entreprise sur le modĂšle de RAG dĂ©veloppĂ© au LMDC en conditions accĂ©lĂ©rĂ©es. Les sorties du modĂšle visĂ©es ont Ă©tĂ© le gonflement maximal et ses niveaux intermĂ©diaires, ainsi que les temps correspondant Ă ces gonflements respectifs. Cette Ă©tude permet d'Ă©carter environ la moitiĂ© des paramĂštres du modĂšle comme Ă©tant peu influents sur la variabilitĂ© des sorties et qui pourront donc ĂȘtre considĂ©rĂ©s comme dĂ©terministes par la suite
Ătude de sensibilitĂ© d'un modĂšle d'alcali-rĂ©action
International audienceThe alkali aggregate reaction (AAR) is a significant deleterious degradation for many concrete structures, particularly those in which the saturation rate of the concrete remains constantly high, such as dams. The approximations associated with the modeling assumptions of AAR on the scale of a representative elementary volume (REV), and the many uncertainties that affect the parameters of the models, make the prediction of AAR phenomenon random, and thus require to operate in probabilistic context. To limit the stochastic dimension for a probabilistic analysis, a sensitivity analysis by the Morris method was conducted on the AAR model developed by LMDC in accelerated conditions. The outputs of model involved were the maximum and intermediate levels of swelling, as well as the time corresponding to each of these levels of swelling. This study helps to remove about half of the model parameters having little influence on the variability of outputs and can therefore be considered as deterministic subsequently. MOTS-CLĂS : alcali-rĂ©action, analyse de sensibilitĂ©, mĂ©thode de Morris.L'alcali-rĂ©action est une dĂ©gradation dĂ©lĂ©tĂšre significative pour de nombreux ouvrages en bĂ©ton, notamment ceux dans lesquels le taux de saturation du bĂ©ton reste Ă©levĂ© en permanence, comme les barrages. Les approximations associĂ©es aux hypothĂšses de modĂ©lisation de la RAG Ă l'Ă©chelle d'un volume Ă©lĂ©mentaire reprĂ©sentatif (VER), et les nombreuses incertitudes affectant les paramĂštres des modĂšles, rendent alĂ©atoire la prĂ©vision du phĂ©nomĂšne de RAG et imposent d'opĂ©rer en contexte probabiliste. Pour limiter la dimension stochastique lors de l'analyse probabiliste, une Ă©tude de sensibilitĂ© par la mĂ©thode de Morris a Ă©tĂ© entreprise sur le modĂšle de RAG dĂ©veloppĂ© au LMDC en conditions accĂ©lĂ©rĂ©es. Les sorties du modĂšle visĂ©es ont Ă©tĂ© le gonflement maximal et ses niveaux intermĂ©diaires, ainsi que les temps correspondant Ă ces gonflements respectifs. Cette Ă©tude permet d'Ă©carter environ la moitiĂ© des paramĂštres du modĂšle comme Ă©tant peu influents sur la variabilitĂ© des sorties et qui pourront donc ĂȘtre considĂ©rĂ©s comme dĂ©terministes par la suite
Tertiary Creep: A Coupling Between Creep and Damage â Application to the Case of Radioactive Waste Disposal
International audienceSummary Introduction to Tertiary Creep Modeling of Tertiary Creep Using a Damage Model Coupled to Creep Comparison with Experimental Results Application to the Case of Nuclear Waste Disposal Conclusions Bibliograph
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