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Évaluation de la durée de vie du béton armé : approche numériqueglobale vis-à-vis de la pénétration d’agents agressifs

Abstract : The purpose of this research is to go deeper in the development of a modelling platform, which describes multiphase and multi-species transport within cementitious materials. Reinforced concrete (RC) structures can be deteriorated as a result of chloride-induced and/or carbonation-induced corrosion of the steel rebars. The modelling platform deals with the initiation period of this corrosion by predicting the transport of the deleterious agents through the concrete cover. This phenomenon is dependent on the moisture properties of the material and requires the study of the movement of liquid-water and gas-phase transport in the material. The first step of this thesis focuses on chloride ingress within fully water-saturated concretes. The chloride ingress is limited to a coupled diffusion-binding process. Within this framework, several models have been developed and numerous experimental data are available. A benchmark of these models is performed in order to identify the most reliable engineering models. This also contributes to choose the most relevant chloride binding isotherms. A probabilistic analysis of selected models among the benchmark is carried out. A general framework is proposed to calculate a reliability service life for reinforced concrete structures in the case of immersion in seawater. A sensitivity analysis is also performed in order to define the most influencing input data. Results point out the crucial role of the concrete cover, the critical chloride content and, to a lesser extent, the effective chloride diffusion coefficient. The importance of the non linearity of isotherms is also highlighted whereas this property is still not well-known. Several moisture transport models have been developed. The understanding of the numerous physical phenomena involved is still insufficient for cementitious materials. A reliability sensitivity analysis of the multiphasic model and of the model based on Richards equation is performed, considering the drying of concretes. Results point out the importance of defining a relevant water vapour desorption isotherm and, to a lesser extent, the liquid-water permeability, as a function of saturation. Thereafter, this research focuses on the determination of this permeability. This is performed by inverse analysis considering two different experimental tests: the mass loss monitoring during a drying and the monitoring of saturation profiles during an imbibition. The determined values are compared to measurements of gas permeability and to measurements with direct and indirect methods (in particular, Katz-Thompson methods) of liquid water permeability, assessed in the literature. Among the outlooks of sophistication of predictive models dedicated to the carbonation, a more comprehensive description of the transport of species in the gaseous phase has to be proposed. The last chapter of the manuscript deals with this issue, by considering a ternary diffusion process of the gaseous mix along with a simplified description of the chemical carbonation reactions. A theoretical study is carried out in order to highlight the changes induced by the new description of transfers: the profiles of gas pressure (depression) and the profiles of CO2 pressure are modified, which can impact the progress of the carbonation front. Thereafter, a calibration of the model is performed in order to bring the numerical predictions into line with the experimental results of accelerated carbonation tests. A reliability sensitivity analysis is performed considering a carbonation test for external fractions of CO2 ranging from 0.04 % to 50 %, with constant external relative humidity. Results point out the significance of the bulk porosity, of the initial content of C-S-H (high external fractions of CO2) and the external moisture conditions (atmospheric external fractions of CO2). Finally, atmospheric carbonation involving wetting–drying cycles is simulated for two concretes
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Sylvain Pradelle. Évaluation de la durée de vie du béton armé : approche numériqueglobale vis-à-vis de la pénétration d’agents agressifs. Matériaux. Université Paris-Est, 2017. Français. ⟨NNT : 2017PESC1176⟩. ⟨tel-01781433⟩

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