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

Méningite bactérienne à un âge pré-scolaire entre 1995 et 2005 : devenir de la cohorte pédiatrique du CHU de Reims

REIMS-BU Santé (514542104) / SudocSudocFranceF

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

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

Staphylococcus capitis isolated from bloodstream infections: a nationwide 3-month survey in 38 neonatal intensive care units

International audienceTo increase the knowledge about S. capitis in the neonatal setting, we conducted a nationwide 3-month survey in 38 neonatal intensive care units (NICUs) covering 56.6% of French NICU beds. We demonstrated 14.2% of S. capitis BSI (S.capBSI) among nosocomial BSIs. S.capBSI incidence rate was 0.59 per 1000 patient-days. A total of 55.0% of the S.capBSIs were late onset catheter-related BSIs. The S. capitis strains infected preterm babies (median gestational age 26 weeks, median birth weight 855 g). They were resistant to methicillin and aminoglycosides and belonged to the NRCS-A clone. Evolution was favorable in all but one case, following vancomycin treatment