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Contribution à la compréhension des mécanismes de dépassivation des armatures d'un béton exposé à l'eau de mer : théorie et modélisation thermochimique

Abstract : Corrosion is one of the major problems that affect the durability of reinforced concrete structures. Several mechanisms have been proposed in order to explain the corrosion formation. One of them is the chemical reactions of ionic species from outside with the passive rebar layer. Nevertheless, this mechanism is poorly understood and the models are missing. A theoretical and numerical study was conducted to develop a model to simulate the dissolution/precipitation of oxides/hydroxides of the passive layer of concrete steel in the presence of sea water. The dissolution of lepidocrocite with simultaneous precipitation of akaganeite is a first step of depassivation of steel. Other oxides/hydroxides are thermodynamically stable. In addition, threshold concentrations are formulated for initiating this depassivation. The theoretical study demonstrated a theoretical threshold corresponding to the ratio of chemical activities {Cl−}/{OH−} depending on the temperature : it is equal to 0.2 at 25◦C. The model was used to demonstrate a threshold concentration ratio, threshold commonly used in the literature [Cl-]/[OH-] but this threshold has its limits when the temperature increases. Considering all phenomena, the binding of chloride ions in the cementitious matrix was modeled by reactive transport model. The chemical adsorption was first simulated by the formation of Friedel salt but this induces an overestimation of chlorides binding capacity. Using the formation of Kuzel salt, chloride binding capacity is closer to reality. The chemical adsorption of chloride ions is initiated when the concentration of chloride in the pore solution reaches precipitation threshold of Kuzel salt which depends on the temperature. The higher the temperature is, the greater this value is. Nevertheless, precipitated amount remains the same. A calculation time of degradation of the first passive layer was finally made. The numerical results of the chloride profiles were compared with experimental results from the literature and were used to validate the model. Then, the effect of porosity change was studied.
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Submitted on : Sunday, February 25, 2018 - 1:25:58 PM
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van Quan Tran. Contribution à la compréhension des mécanismes de dépassivation des armatures d'un béton exposé à l'eau de mer : théorie et modélisation thermochimique. Matériaux. Ecole centrale de Nantes, 2016. Français. ⟨tel-01716928⟩

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