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Etude expérimentale et numérique de la dégradation d'éléments structurels en béton armé par corrosion sous courant imposé

Abstract : Corrosion of steel in reinforced concrete generates iron oxides which induce tensile stresses at the steel/concrete interface leading to the concrete cover cracking and loss of reinforcing bar cross-section. The evaluation of such pathology remains difficult and consequently limits the assessment of the structure serviceability, the knowledge on the degradation evolution, and the choice of a suitable repair method. The aim of this study is to correlate internal degradations (corrosion products formation and concrete cracking) induced by steel corrosion to external degradations (concrete cracking).The experimental program aims to determine these degradation mechanisms. The accelerated corrosion tests are carried out on reinforced concrete specimens in the presence of chloride ions by applying a constant current using three current densities (50,100 and 200 µA/cm²) during different exposure periods.Electrochemical properties of reinforced concrete specimens are determined before and after the accelerated corrosion tests. The quantitative evaluation of the corrosion products at the steel/concrete interface based on SEM observations (microscopic scale) demonstrates an important heterogeneity in the distribution and thicknesses (between 0 and 1584 µm). This heterogeneity can be explained by the evolution of anodic and cathodic zones due to different factors such as the non symmetric geometry of the specimens, the accelerated corrosion test environment (moisture, chloride ions and oxygen gradients), and the characteristics of concrete (aggregates, porosity).The internal (angular position, width, and length of cracks) and external crack patterns (maximum crack width) induced by the formation of corrosion products are analyzed. One to five internal cracks are identified in the internal crack patterns and they are classified in three groups. The first and second groups contain horizontal and vertical cracks which propagate in the direction of the shortest concrete cover. The third group is constituted of oblique cracks which are located in the opposite side of the horizontal cracks. The widths of the internal cracks range between 0.1 to 0.4 mm and their lengths between 1 to 3 cm. The maximum external crack widths are between 0.1 to 0.7 mm and are located on the shortest cover sides of the specimens.The maximum effort applied during the pull-out tests decreases with increasing levels of corrosion. However, the corrosion levels reach during the tests are too low to affect the steel/concrete interface behavior. The failure mode identified during the testing is concrete splitting failure regardless the corrosion level. A cause/effect scenario is proposed between steel corrosion and the mechanical induced degradation considering all experimental results.Based on experimental results, two models are proposed. The first one is developed to explain corrosion initiation and propagation. This model is able to determine the corrosion initiation time for each current density.The second model analyses the concrete cover mechanical behavior. The numerical results show that taking into account only the thickness of corrosion products (as an experimental input) does not generate a numerical cracking pattern similar to the experimental one. Then, complementary calculations considering a different distribution of the corrosion product’s thicknesses allow enhancing the agreement between experimental and numerical results
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Olfa Loukil. Etude expérimentale et numérique de la dégradation d'éléments structurels en béton armé par corrosion sous courant imposé. Génie civil. Université Paris-Est, 2017. Français. ⟨NNT : 2017PESC1138⟩. ⟨tel-01759295⟩

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