Stéphane Poyet

Accelerated leaching of cementitious materials using ammonium nitrate (6M): influence of test conditions

We have focused on the test conditions influence on accelerated degradation of cementitious materials using ammonium nitrate. PH-buffering and renewal of the leaching solution were studied. PH-buffering appeared not to be very important when the renewal pH remains under eight. Renewal appeared to be the most influential feature. Its absence leads to calcium accumulation in the leaching solution inducing aggressiveness fall. Degradation is then less marked in terms of depth, flux and mineralogy. The resulting porosity increase is also smaller. Nous nous sommes intéressés à l’influence des conditions expérimentales sur la dégradation accélérée au nitrate d’ammonium (6M). Le renouvellement périodique et le maintien du pH de la solution lixiviante ont été étudiés. Il en ressort que le maintien de pH n’est pas important lorsque le renouvellement est effectué jusqu’à pH=8. Le renouvellement est l’élément le plus important. Son absence entraine l’accumulation d’ions calcium dans la solution et la diminution de son potentiel agressif. La dégradation est alors moins marquée en termes d’épaisseur dégradée, de flux lixivié et de minéralogie. L’augmentation de porosité correspondante est aussi plus faible.

Modelling the influence of temperature on accelerated leaching in ammonium nitrate

This study proposes two models for accelerated leaching in ammonium nitrate under variable temperature. The first approach assumes a thermoactivated linear relationship between degradation and the square root of time. The second approach introduces, within a phenomenological model, the thermoactivation of diffusion and hydrates solubility. These two approaches enable one to analyse accelerated leaching tests to identify the concrete variability in order to get rid of the influence of temperature. Cette étude consiste à proposer deux modélisations de la lixiviation accélérée au nitrate d’ammonium sous température variable. La première approche suppose une relation linéaire thermoactivée entre la dégradation et la racine carrée du temps. La seconde approche introduit dans un modèle phénoménologique la thermoactivation de la diffusion et de la solubilité rétrograde des hydrates. Ces deux approches permettent de dépouiller des essais de type DANA afin d’identifier la variabilité du béton en s’affranchissant de l’influence de la température.

Visual parameters of chloride-induced corrosion of reinforced concrete structures

ABSTRACT Corrosion is the major cause of reinforced concrete structures degradation: the pressure generated by oxides formation together with section loss can eventually lead to cracking and the fall in the structure bearing capacity and then jeopardize its service life. The first method for the corrosion state characterisation of concrete structures is to check periodically for visual signs of corrosion on the concrete facing (rust stains and cracks). The goal of this study is to assess the ability of visual inspection to detect and quantify reinforcement corrosion in concrete structures. The data acquired in the framework of the “Poutres de la Rance” benchmark were re-analysed to link the visual signs of corrosion to its real internal consequences (section loss, corroded length…etc.). The results show that, in our case (marine environment), visual inspection does not yield efficient assessment of the real corrosion state and that other non-destructive techniques must be used in order to gain confidence in the diagnosis.

Experimental Investigation of Concrete Packages for Radioactive Waste Management: Permeability and Influence of Junctions

We studied the feasibility of a concrete package for radioactive waste management in a joint program involving Andra (the French agency for radioactive waste management) and CEA (the French atomic energy commission). The package’s long-term durability and radionuclides’ containment were the major concerns. The presence of junctions between the prefabricated body and the poured-in-place lids was identified as a major weakness. The first objective of this study was to characterize the permeability of the selected concrete and of the package itself (that is to say accounting for the junctions influence). We used special specimens including a junction, and tested three different surface preparation methods. The second objective was to assess the influence of the manufacturing conditions (laboratory and industrial) on permeability.

Experimental and numerical characterisation of load-induced damage in reinforced concrete members

The durability of the cooling towers of nuclear power plants (NPP) is an up-to-date issue: some of them can be affected by some cracks. Cracks formation is accompanied by some damages at the steel-concrete interface. These load-induced damages accelerate the diffusion of atmospheric carbon dioxide in the concrete and along the damaged steel-concrete interface. Carbonation at the interface induces steel corrosion which could cause the development of further cracks in the structure, thus, threaten its durability. To understand the effect of cracking, both in terms of corrosion initiation and propagation, an accurate experimental procedure leading to cracks and steel-interface damage representative of those existing on the cooling towers should be found. The objective of this paper is to characterize numerically and experimentally the damage induced at steel/concrete interface by the applied load during three point bending test. This would be determinant parameter for carbonation and then corrosion in RC structures as cooling towers of NPP.

Etude expérimentale et modélisation de l'influence de l'eau sur la réaction alcali-silice

ABSTRACT Water is very important for alkali-silica reaction, it is the diffusion medium for ionic species and in the same time it is part of the reaction products. The work presented in the following article deals with a new method which takes into account the effect of water on alkali-aggregate reaction thanks to original laws. The latter have been determined thanks to experimental results. The modelling is validated by the means of numerical simulations of experiments carried out on purpose or taken from litterature.

Modélisation chimique de la réaction alcali-silice: prise en compte de l'influence de la distribution granulaire réactive

ABSTRACT Nowadays, knowledge about ASR mechanisms is good enough to prevent new cases. Nevertheless a numerical tool seems necessary for all affected structures. This article deals with a new modelling based on the description of alkalis and calcium transport within concrete. It takes into account the effect of the size and distribution of reactive aggregates. Results from an experimental campaign and corresponding numerical simulations are presented and compared.