Etude de la dégradation de la couche passive des aciers du béton armé en milieu maritime : modèle thermochimique

International audienceCette étude s'intéresse à la modélisation du processus de dépassivation des armatures d'un béton saturé exposé à de l'eau de mer. En particulier, elle tente de décrire la dégradation de la couche passive des armatures et les conditions dans lesquelles elle n'assure plus son rôle de protection. Afin d'y parvenir, un modèle couplant transport multi-espèces et thermochimie est mis en place. Le modèle prend en compte le transport par diffusion des ions contenus dans l'eau de mer ainsi que les réactions chimiques se produisant au niveau de la couche passive. Il permet d'étudier l'équilibre thermodynamique de l'oxyde de fer dans un béton pollué par l'eau de mer et de quantifier la durée au-delà de laquelle l'initiation de la corrosion peut commencer en fonction de la nature des constituants de la couche passive. Il montre, en outre, les cinétiques de dégradations de la couche passive</p

Numerical Strategy to Simulate Seawater Ingress in RC Concrete Blocks Exposed to Wetting-Drying Cycles in Field Conditions During 19 years

Numerical results are compared to experimental data on concretes exposed in field conditions for 19 years and subjected to wetting/drying cycles in seawater after a couple of curing days. They were obtained thanks to a hydration model assuming fully hydrated concretes (19 years of curing time) and a reactive transport model in saturated conditions taking into account precipitation/dissolution of minerals and their kinetics and adsorption of ionic species on C-S-H. Numerical results show surprisingly rather good results, especially for concretes with fly ash. For OPC, although model considers average bulk porosity modifications, the experimental apparent diffusion coefficient increases much more. For concretes with silica fume, numerical results also show underestimations of total chloride content also experimental apparent diffusion coefficients are constant. Analysis of hydration calculations show that concretes are not fully hydrated after 19 years. Additional chloride content from reactions between anhydrous phases and chloride ingress may appear

Apports à la méthode des éléments finis appliqués aux calculs de structures en dynamique rapide et amortissement numérique

LORIENT-BU (561212106) / SudocSudocFranceF

External sulfate attack of cementitious materials: New insights gained through numerical modeling including dissolution/precipitation kinetics and surface complexation

International audienc

Proposition de scénario de dégradation des matériaux cimentaires exposés aux attaques sulfatiques externes

National audienceLes nombreuses investigations menées dans le cadre de l’étude de la durabilité des bétons ont montré que l’expansion volumique est le principal phénomène responsable de la dégradation des matériaux cimentaires soumis aux agressions sulfatiques. En prenant en compte les cinétiques de dissolution/précipitation des différentes espèces solides, des modèles numériques ont permis de montrer que la précipitation de l’ettringite serait la principale cause de cette expansion. Toutefois, ces études ne présentent pas clairement l’ordre chronologique d’apparition des différents processus conduisant à la précipitation de cette ettringite, bien que ces processus soient relativement bien connus. Dans la présente étude, nous proposons un scénario de dégradation des bétons en se basant sur l’analyse des résultats d’études numériques antérieures, réalisées sur des pâtes de ciment de type CEM 1 en contact avec une solution de sulfate de sodium concentrée à 3g/l et 4g/l. L’analyse comparative des produits de solubilité des différentes réactions montre que les différents processus s’enchaînent suivant un ordre bien déterminé et permet de mieux comprendre l’origine de la dégradation des matériaux cimentaires

Modelisation of chloride reactive transport in concrete including thermodynamic equilibrium, kinetic control and surface complexation

International audienc

A numerical model including thermodynamic equilibrium, kinetic control and surface complexation in order to explain cation type effect on chloride binding capability of concrete

International audienceThe impact of cation type, sulphate and pH on chloride binding is studied using a numerical model combining thermodynamic equilibrium, kinetics and surface complexation. First, the model is validated by comparing numerical and experimental results obtained on a CEM II concrete material exposed to N aCl, KCl, M gCl 2 and CaCl 2 solutions. Then, the numerical results are discussed to improve our understanding of the differences in chloride binding capability generally observed in the literature. A strong coupling between cation, pH and sulfate affecting chloride binding is highlighted. After six months of exposure, chloride binding due to Kuzel's salt formation has little effect on chloride binding capability whatever the chloride salt solution. The results also confirm the existence of a relationship between pH and chloride binding capability previously observed experimentally in the literature. When some sulfate ions are present in the chloride solution, they reduce the chloride binding capability because of the sulfate absorption process on C-S-H

The advantages of using a geochemical transport model including thermodynamic equilibrium, kinetic control and surface complexation to simulate the durability of concretes exposed to chlorides and sulphates

International audienc

Thermodynamic difficulties to determine a critical chloride threshold for breakdown of the protective layer of steel reinforcement in a maritime concrete structure

There is much debate on the expression used for the critical chloride threshold as well as on its value for breakdown of the protective layer of steel for reinforced concrete. In fact, this concept suggests that the breakdown is only driven by dissolution of the protective layer. A reactive transport model including dissolution and precipitation of solid species with their kinetics is then used in order to simulate the ingress deleterious substances in a concrete exposed to seawater and the chemical degradation of the oxides and hydroxides present in the protective layers covering a steel rebar. The numerical results confirm that most of the oxides are thermodynamically very stable even after a long period of exposure, especially in the inner layer. This finding suggests that corrosion initiation depends on protective layer thickness and history. These results also provide a sound explanation why a wide scatter of values of critical chloride threshold values is reported in literature