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Modélisation du couplage chimico-mécanique d'un béton atteint d'une réaction sulfatique interne

Abstract : Internal sulfate attack (ISA) is a pathology which may affect concrete exposed to excessive temperature at early age. The manifestation of ISA in concrete structures is characterized by series of closely spaced, tight map cracks with wide cracks appearing at regular intervals and excessive tensions in rebars. This phenomenon is alarming for affected structure managers as it deals with people safety and structures operation. Moreover, there is no way to stop reaction. Prediction of concrete expansion, structural degradation and assessment of efficiency and periodicity of repair works are crucial issues. The mechanism of ISA is complex and it is a subject of disagree in the researcher community due to the important number of involved parameters influencing the initiation and the evolution of ISA (concrete mix-design, environmental conditions, thermal and hydric history of the concrete). Several modelling approaches have been presented in literature in order to predict the evolution of swelling, some authors proposed empirical models to predict the final expansion of concrete as a function of the composition of the cement used, other proposed chemical model or mesoscopical model to predict the expansion of the reaction. In this thesis, with the aim of supporting owners for the management of affected structure, a phenomenological model has been formulated from a macroscopic level of observation, to predict the swelling evolution of concrete structures affected by internal sulfate attack. The proposed modelling is based on thermodynamic theory describing the delayed formation of ettringite crystals in a porous media. It takes into account the early age temperature history in concrete, environmental conditions (temperature, moisture) and stress influence on ISA expansion. Parameters related to the concrete chemical susceptibility to ISA can be easily identified experimentally. A specific experimental program helped quantifying the coupling between the temperature evolution at early age and the induced chemical potential. This model has been implemented into the finite element code CESAR-LCPC with the name RGIB, this new module is an evolution of ALKA which is a module dedicated to prediction of the consequences of alkali-silica reaction in concrete. We used this module to recalculate two real structures or part of structures affected by ISA. We present the different steps of numerical calculation carried out to predict the evolution of ISA in a progressive way which allows us to distinguish the influence of the different coupling laws. We discuss the role of thermal history at early age, humidity and effect of mechanical loading on swelling. The result of the numerical simulation are presented and compared to data measured in situ. The numerical simulations carried out show a good agreement with in situ monitoring in terms of three-dimensional swelling. These results highlight the need for having a realistic description of the various physical mechanisms which influence ISA. Such calculations can be helpful for the choice of a method to repair ISA affected structures.
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Nizar Baghdadi. Modélisation du couplage chimico-mécanique d'un béton atteint d'une réaction sulfatique interne. Matériaux. Ecole Nationale des Ponts et Chaussées, 2008. Français. ⟨tel-00467845⟩

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