Alternative methodology for linear polarization resistance assessment of reinforced concrete structure

International audienceFor reinforced concrete structures, several corrosion detection methods exist: concrete resistivity, half-cell potential or linear polarization resistance (LPR) measurement. The LPR value can be linked to the corrosion rate thanks the Stern-Geary equation if strong hypotheses are made. Existing commercial devices use a guard ring to canalize the current on specific steel rebar area and assume that the steel rebar is uniformly polarized. However, recent works reveal that the top part of the steel rebar, right under the counter electrode, is the most polarized point. The particular point is referred as the point of interest (PI). This works belongs to the DIAMOND project which aims to produce a new corrosion rate measurement device. Comsol® software was used to model the influence of concrete cover, resistivity and injected current on the current density at the PI. Moreover, a significant influence of the steel rebars diameter was also demonstrated. Two types of abacus are built. The first one links to polarization measured on the surface to the polarization on the rebar at the PI. The second links the ratio between the current density at the PI and the density of injected current to concrete cover and steel rebar diameter. The Stern-Geary equation can now be used at the PI without using the approximation of a uniformly polarized rebar. The corrosion state of reinforced concrete structure can be controlled more precisely. The methodology is then applied on two concrete slabs in which three metal bars are embedded at different concrete covers. The first slab is prepared with ordinary concrete while the second contain chloride to artificially activate the corrosion process. The results reveal that the rebars embedded on the first slab are not corroding (icorr ≤0.2 μΑ/cm2) while the second rebar are corroding (icorr>0.2 μΑ/cm2)

Apport des moyens d'essais non destructifs à la modélisation du comportement structural d'édifices anciens

Les édifices anciens sont souvent endommagés (fissure, perte de matière, dégradation des matériaux, déformation géométriques…) et nécessitent leur restauration pour leur préservation ou une mise en sécurité notamment dans le cadre du tourisme. Dans les cas les plus sensibles, le recours à des modélisations du comportement structural est nécessaire. Les calculs doivent être alimentés par une base de données numériques sur la géométrie des structures, les caractéristiques physico-chimiques des matériaux en œuvre, etc… Les données géométriques sont obtenues en grande partie d’après les observations visuelles, les mesures topographiques (géométriques) et les documents d’archive s’ils existent. Ce n’est pas toujours suffisant car des défauts internes non suspectés peuvent exister. L’utilisation des méthodes d’essais non destructifs pour apporter des données complémentaires permettant de modéliser leur comportement structural et de définir les principes de conservation et de restauration les mieux appropriés. Certaines de ces méthodes sont précisément adaptées pour détecter et caractériser au mieux la géométrie des discontinuités internes susceptibles de fragiliser les structures et pour, à terme, intégrer ces éléments dans les calculs mécaniques. Deux méthodes d’investigation non destructives ont été mises en œuvre : le radar géophysique et la mesure de la vitesse de propagation des ondes sonores. Deux édifices très différents ont été auscultés dans ce but : le capitole de Dougga en Tunisie et le tombeau des Rois à Jérusalem

A new methodology for concrete resistivity assessment using the instantaneous polarization response of its metal reinforcement framework

International audienceA new methodology is developed to assess concrete cover resistivity using the instantaneous response of the polarization of a metal rebar (galvanostatic pulse method). The instantaneous ohmic drop is linked only with the concrete resistance, which depends on the concrete cover and resistivity, and rebar diameter. A numerical model was developed in Comsol Multiphysics® in order to create a graph linking concrete resistivity to concrete resistance for concrete cover ranging between 1 to 160 mm. This graph and the measured ohmic drop can be used to determine concrete resistivity for any rebar diameter/concrete cover configuration. The theory developed numerically was then confirmed using an experimental setup with controlled water resistivity. The theory is then generalized for counter electrode (CE) diameter ranging from 20 to 70 mm. Finally, the study reveals that the graph developed for a single rebar can be used for any rebar framework density

Monitoring DIAMOND device for corrosion state evaluation of reinforced concrete structures

The corrosion of steel rebars is a major issue with respect to the durability of reinforced concrete structure. Several corrosion evaluation methods exist: half-cell potential, concrete resistivity or linear polarization resistance (LPR) measurement. However, these techniques are employed at a given moment and are not suitable for continuous corrosion evaluation. This works belongs to the DIAMOND project which aims to produce a new corrosion state measurement monitoring device. The monitoring probe consists on a cylindrical probe. A ring shape counter-electrode CE is plated on the probe side. At the centre of the CE, a reference electrode (RE) is placed for potential measurement. The device is embedded in concrete at 25 mm of the inspected rebar. The instantaneous ohmic drop observed at the beginning of the polarization measurement is only linked with the concrete resistance which depends on concrete cover and resistivity. A numerical model was developed on Comsol® to create abacuses graph that link concrete resistivity and concrete resistance. Thus, the ohmic drop measure at the beginning of the polarization can now be used to determine regularly concrete average resistivity between the monitoring probe and steel rebar. Two other series of abacus graphs are then introduced in order to determine the polarization resistance of the rebar in front of the monitoring probe (the point of interest (PI)). Two monitoring probes were placed in two types of concrete (one sound concrete and one concrete with chloride). Corrosion potential, concrete resistivity and rebar corrosion rate were monitored over around 200 days. The experimental results obtained with the monitoring probe are finally compared to the results obtained with the surface DIAMOND probe (introduced in the ICCRRR 2018 paper “Alternative methodology for linear polarization resistance assessment of reinforced concrete structure [1]”)

An alternative method to measure corrosion rate of reinforced concrete structures

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Study of the active/passive corrosion behaviour of reinforced concrete slabs using different devices

Cet article présente les résultats des mesures électrochimiques réalisées sur des dallettes de béton armé. Ces mesures ont été effectuées durant deux années, quatre fois par an. Trois types d'appareils ont été utilisés: un potentiostat de laboratoire Gamry et deux appareils de chantier Gecor6 et Galvapulse. Les résultats mettent en évidence que les trois types d'appareils sont capables de détecter la corrosion à l'état passif. Les résultats sont cohérents pour le diagnostic effectué dans le cas des dallettes subissant la corrosion par les chlorures et les appareils sont sensibles à la dépassivation des armatures dans ces conditions. Ils mettent en évidence la variabilité du temps d'apparition du processus de corrosion à l'état actif due aux chlorures. Par contre, les niveaux de corrosion diagnostiqués par les trois appareils diffèrent dans le cas de processus de corrosion par carbonatation, même si ceux-ci détectent la corrosion à l'état actif des armatures. Les écarts observés dans ce cas indiquent qu'une interprétation quantitative des résultats (en termes de perte d'épaisseur en fer par exemple) est impossible

Corrosion diagnosis of reinforced concrete beams after 40 years exposure in marine environment by non destructive tools

International audienceThis paper describes the detailed experimental program of the French national project “benchmark des poutres de la Rance”. It presents a corrosion diagnosis of prestressed beams after 40 years exposure in natural marine environment. It includes results from non destructive testing tools, complementary laboratory tests and destructive analyses. This project will provide a large database on the corrosion state of reinforced concrete beams after 40 years exposure in a marine environment (mechanical, electrochemical and physico-chemical properties) and will allow studying the sensitivity of NDT tools to evaluate corrosion risk within reinforced concrete structures. These results will be given to the modellers in order to complete their test conditions in the framework of the validation of mechanical models.Cet article decrit le programme experimental mis en place dans le cadre du Benchmark des poutres de la Rance. Il presente le diagnostic vis-a-vis de la corrosion de poutres en beton precontraint ayant sejourne 40 ans en environnement marin. Ce papier inclut les resultats issus des techniques d-auscultation non destructive, les tests complementaires en laboratoire et les analyses destructives. Ce projet permet de beneficier d-une large banque de donnees sur l-etat de corrosion des poutres apres 40 annees (mecanique, electrochimiques et proprietes physico-chimiques) et d-apprecier la sensibilite des techniques non destructives pour evaluer des risques de corrosion au sein de structures en beton precontraint. Ces resultats sont fournis aux equipes de modelisation afin de completer leurs conditions de tests en vue de la validation des modeles de comportement mecanique

The Geotouristic Project “the Geological Adventure” to the Rescue of an Iconic World Heritage Geosite, the Ammonites Slab of Digne-les-Bains (National Geological Nature Reserve of Haute-Provence and Unesco Global Geopark, France)

International audienceProtected under National Nature Reserve, managed by the Departmental Council of the Alpes de Haute-Provence, and labeled UNESCO Geopark, the Ammonites Slab of Digne-les-Bains (SE France) exhibits 1,550 ammonites over a large open-air surface. Despite the virtual absence of special enhancement for the visitors, this spectacular geosite of high scientific and heritage value has played an important role in the years 1990–2000 in the emergence of notions of geological heritage, geological nature reserve, geotourism, and Geopark. Due to its exposure to mountain weather conditions, the Slab suffers from significant conservation issues. Several studies have shown that its condition was much worse than expected. Without major restoration work, the Slab was in danger of collapse in the short term. Given the high cost of the needed rescue work, the geotourism project “The Geological Adventure” was developed under European Interreg ALCOTRA funding. More broadly, this project aims to develop a sustainable experiential geotourism around the geoheritage of the Southwestern Alps cross-border (France–Italy), partly in situ and thanks to digital tools (22 geosites concerned). An important place is given to scientific pedagogy. Concerning the Ammonites Slab, the project consisted of (1) stabilizing and ensuring the sustainability of the fossiliferous layer; (2) planning and developing the overall geosite (parking area, reception area, observation platform); (3) allowing accessibility for people with disabilities; and (4) offering progressive and immersive educational mediation to make scientific culture accessible to as many people as possible

Downregulation of stromal syntenin sustains AML development

Abstract The crosstalk between cancer and stromal cells plays a critical role in tumor progression. Syntenin is a small scaffold protein involved in the regulation of intercellular communication that is emerging as a target for cancer therapy. Here, we show that certain aggressive forms of acute myeloid leukemia (AML) reduce the expression of syntenin in bone marrow stromal cells (BMSC). Stromal syntenin deficiency, in turn, generates a pro‐tumoral microenvironment. From serial transplantations in mice and co‐culture experiments, we conclude that syntenin‐deficient BMSC stimulate AML aggressiveness by promoting AML cell survival and protein synthesis. This pro‐tumoral activity is supported by increased expression of endoglin, a classical marker of BMSC, which in trans stimulates AML translational activity. In short, our study reveals a vicious signaling loop potentially at the heart of AML–stroma crosstalk and unsuspected tumor‐suppressive effects of syntenin that need to be considered during systemic targeting of syntenin in cancer therapy

Bendamustine-based conditioning prior to autologous stem cell transplantation (ASCT): Results of a French multicenter study of 474 patients from LYmphoma Study Association (LYSA) centers

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