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Durabilité des réparations des ouvrages d'art en béton

Abstract : About half of the repairs carried out on concrete structures conclude with a premature failure. This is mainly due to the debonding of the repair layer, caused by a lack of adhesion on the degraded concrete surface, and by the corrosion of steel rebars in concrete. It is estimated that over 50% of Europe's annual construction budget is spent on the rehabilitation of existing structures. Two types of repair products are mainly offered on the market, hydraulic mortars and polymer-modified mortars. The intrinsic properties of these products have been studied, but few works have been conducted to assess the evolution of these properties, especially when they are applied on a degraded concrete surface. The aim of this work is to better understand the influence of the presence of polymer in mortars on durability of the repair of concrete structures. To carry out this study, polymer-modified mortars were prepared with a controlled formulation based on the analysis of the composition of several commercial products. The intrinsic properties of these mortars were studied at the fresh and hardened state, focusing in particular on the influence of the nature and content of polymers and of the curing applied to these materials. Increasing the quantity of polymer leads to the increase of the mechanical properties of mortars. This effect is especially noticeable in flexion because polymers reinforce the aggregate-binder interface. The curing of mortars at 40°C improves their mechanical performances and reduce their porosity because in these conditions, the formation of polymer films intertwined with cement hydrates is favored. A test has also been developed to measure the adhesion of mortars on a support representing the concrete surface to be repaired. The influence of the presence of polymer and of the surface state of the support on the adhesion was analyzed, as well as the evolution of adhesion during the storage of specimens in different environments. These tests have shown that the addition of polymer can increase the adhesion of polymer-modified mortars comparing to unmodified mortars. After three months of curing, the adhesion is maximum from 10% of polymer. The increase of the roughness and saturation with water of the support did not induce any increase of the adherence comparing to flat and dry surfaces. As for the intrinsic properties of polymer-modified mortars, the curing at 40°C improves the adherence while an immersion in water is unfavorable. Finally, the risk of corrosion of a steel bar embedded in the mortar was studied by characterizing the electrochemical properties of steel and the transfer properties of aggressive species in mortars. The addition of polymers in mortars enhances the protection of rebar thanks to their electrical insulation properties. In most cases, they also limit the diffusion of CO2 and chloride ions in the material
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Inès Leana Tchetgnia Ngassam. Durabilité des réparations des ouvrages d'art en béton. Autre. Université Paris-Est, 2013. Français. ⟨NNT : 2013PEST1142⟩. ⟨tel-00981689⟩

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