Study of an electrochemical chloride extraction treatment on a both carbonated and chlorinated reinforced concrete

EUROCORR 2017, European Corrosion Congress and 20th Internation Corrosion Congress and Process Safety Congress, PRAGUE, TCHÈQUE, RÉPUBLIQUE, 03-/09/2017 - 07/09/2017Civil engineering structures and historical buildings can suffer from corrosion of the embedded reinforcing steel once the concrete cover is totally carbonated and/or when chloride ions reach the steel/concrete interface. On field, these two types of contamination can be encountered separately or combined requiring implementation of proper repair methods. In this study, in a first step, corrosion of both chlorinated and carbonated reinforced concrete specimens were followed during casting and accelerated contaminations. In a second step, electrochemical chloride extraction was performed as a repair treatment (cathodic polarization, 1 A/m² of steel surface during 8 weeks). The efficiency of the treatment and its impact on the cement matrix and at the concrete-steel interface were studied during the treatment, after rebar depolarization and in the long term (several months) in order to evaluate its durability. In order to achieve these aims, three analysis means were used: electrochemical characterization, scanning electron microscopy and Raman microspectroscopy. In this paper, results obtained on specimens cast with CEM III cement (often encountered on reinforced concrete historical monuments) with chlorides addition into the mix water and further accelerated carbonation are presented. Study of rebar's electrochemical characteristics during the artificial aging highlighted an increase of corrosion rate from negligible value of 0.1 µA/cm² after fabrication to about 10 µA/cm² after carbonation. SEM observations confirmed this phenomenon with the identification of a corrosion layer on most of the concrete/steel interface after carbonation. The ECE efficiency was demonstrated by a chloride extraction of about 97% at the rebar level which yields a decrease of chloride ions concentration below the theoretical threshold value of 0.4 % by mass of cement after two weeks. Simultaneously a realkalisation ring was observed on concrete around the reinforcement bar which reached almost 1 cm after 56 days. After depolarization, results showed that a duration of 28 days of ECE treatment allowed the stabilization of the corrosion state of the rebar. Raman microspectroscopy allowed to study in situ, thanks to specific cells, the corrosion products' reduction during the treatment

Towards the Determination of Chloride Profiles by means of Resistivity Measurements in Reinforced Concrete

Reinforced concrete (RC) structures, such wharfs or floating structures, are submitted to chloride ingress which can lead to rebar corrosion. Before the corrosion initiation, in a preventive point of view, engineers can be interested in non-destructive evaluation and inspection methods. In that way, electrical resistivity tomography is a promising tool to access to resistivity profiles then to chloride profiles in real RC structures in the future. We would like to present herein the advances in the necessary research developments to reach this goal, i.e. the resistivity profiles obtained in reinforced concrete slabs submitted to chloride ingress. The 4 slab dimensions are 90x70x13 cm. The specimens are cured, dried during 9 months then submitted to salted water imbibition during 4 months. Electrical resistivity tomography measurements are performed at short terms during 1 week of imbibition. The monitoring show that several phenomena influence the resistivity profiles such as the penetration of water and chloride ions. Meanwhile, steel rebar effect can be considered thus eliminated from electrical resistivity profiles following the method developed by (Alhajj et al. 2019)

Experimental study of corrosion-induced degradation of reinforced concrete elements

Corrosion of steel reinforcement is the main cause of damage for reinforced concrete structures. Iron oxides produced during the corrosion process can induce concrete cracking, loss of adhesion at the steel-concrete interface, loss of reinforcing bar cross-section and even spalling of the concrete cover. In the presented research, the durability problems related to the corrosion of the reinforcement are investigated by combining experimental and numerical studies. However, this paper particularly focuses on the experimental methodology used for the time evolution of damages (steel corrosion products formation and crack patterns) induced by the accelerated corrosion test. The accelerated corrosion tests were carried out by applying a constant current between reinforcement used as an anode and a counter electrode. To control the corrosion process, electrochemical parameters (such as free corrosion potential, polarization resistance, electrical concrete resistance) were measured. The purpose of this paper is to determine the width and length of the cracks and their orientation according to the current density and time

Evaluation de la durabilité du béton armé vis à vis des ions chlorure à l'aide de capteurs noyés dans le béton versus des auscultations en parement

GC'2019, le Génie Civil au coeur des mutations technologiques et numériques , CACHAN, FRANCE, 20-/03/2019 - 21/03/2019L'évaluation du processus de corrosion de structures en béton armé en milieu chloruré a été étudiée en utilisant deux approches complémentaires : l'auscultation non destructive (ND) du béton d'enrobage et la corrosion des armatures. Différentes méthodes d'évaluation non destructives basées, soit sur de l'instrumentation avec des capteurs noyés dans le béton armé, soit sur des auscultations réalisées en parement, ont été utilisées afin de caractériser la phase d'incubation puis la phase de propagation de la corrosion. Dans cette première phase d'étude, les différents objectifs étaient les suivants : 1) Etudier des bétons différents formulés avec du ciment Portland ou des laitiers, en termes de réaction de transfert dans le béton et de réactions électrochimiques armature/béton/environnement, 2) Analyser les résultats des capteurs noyés dans le béton armé (formulé avec du ciment Portland ou des laitiers) qui permettent de suivre en continu l'évolution des phénomènes, 3) Comparer les résultats entre les capteurs noyés et les mesures réalisées sur parement, 4) Démontrer l'intérêt du Corrosion Health Monitoring sur ouvrages neufs et/ou réparés en termes de surveillance (système d'alerte plutôt qu'alarme) dans le temps. Les différentes méthodes basées sur des mesures de résistivité (capteurs noyés et auscultation en surface) permettent d'accéder à des profils traduisant la pénétration d'eau de mer par imbibition. Des méthodologies d'inversion et de calibration ont été consolidées. Une expérience sur les capteurs de corrosion a été capitalisée. Enfin, de nouvelles méthodes ont été explorées (SUSI, radar de fréquence,...) et certaines sont prometteuses. Les interprétations des résultats peuvent s'avérer délicates et il convient de bien énoncer les hypothèses et les limites notamment dans une prise de décision (maintenance et/ou réparation par ex). Enfin, il est nécessaire de poursuivre cette étude sur du plus long terme afin d'affiner les résultats et les applications fortes pour la gestion du parc d'ouvrages vieillissants

Reinforced Concretes of Tomorrow: Corrosion Behaviour according to Exposure Classes

Reinforced concrete is the most widely used building material but its durability in terms of concrete cover performance and corrosion of steel rebar is still a key point to be studied. To address this topic, within the frame of the national project PERFDUB, two series of eleven reinforced concrete specimens (with metric dimensions) were cast with innovative concrete mixes representative of the French experience, two shapes of rebar and two concrete covers. Then, these specimens were exposed in two natural exposure sites, one in Epernon for carbonation (XC4) and a second one in La Rochelle in the Atlantic Ocean in a tidal zone for chloride ions (XS3m). Their corrosion was carried out using non-destructive testing. In addition, in order to follow the corrosion evolution more accurately in a continuous way, two series of three specimens were casted with embedded sensors and were exposed in two other outdoor sites in Marne-la-Vallée (XC4) and in Eqiom facility (XS3e). The first results of this 20-year project in terms of corrosion of these reinforced concrete specimens obtained with laboratory and field equipment and with monitoring are presented in this paper

Traitements électrochimiques de réhabilitation des ouvrages en béton armé dégradés par corrosion

La première cause de dégradation des structures en béton armé est la corrosion des aciers. Habituellement réparées de manière traditionnelle (mise à nu des aciers lorsque le béton n'est plus adhérent, reconstitution des zones de béton), les structures peuvent maintenant être réhabilitées avec des traitements électrochimiques qui offrent comme avantage le traitement complet des aciers de la structure et non plus une réparation par zones ou "patch" à la suite de laquelle la dégradation se produisait "à côté" de la zone réparée après 5 à 10 ans de fonctionnement. La corrosion des aciers dans les bétons après carbonatation ou après pénétration des chlorures peut être diminuée et/ou stoppée par des traitements électrochimiques adéquats, respectivement la réalcalinisation et la déchloruration. Le traitement électrochimique de réalcalinisation consiste à redonner au béton carbonaté dont la valeur de pH est voisine de 9, son pH alcalin (13) autour des aciers (et si possible l'enrobage) dans lequel les armatures ne se corrodent plus. Le traitement électrochimique de déchloruration a pour objectif d'extraire les ions chlorure (issus des sels de déverglaçage, de l'ambiance marine, ) de l'enrobage béton et donc de diminuer le risque de corrosion des armatures. Le LCPC étudie depuis quelques années, les traitements électrochimiques de réalcalinisation et de déchloruration appliqués à des corps d'épreuve en béton armé de différentes dimensions, en utilisant un courant imposé de 1 A/m² d'acier. Il s'agit non seulement d'expliciter le mécanisme de ces traitements et de donner un avis quant à leur efficacité mais également de pouvoir fournir des méthodes de mesures quantitatives de suivi de traitement et de contrôle. Les résultats de ces études devraient permettre d'envisager des valeurs seuils qui pourraient être indiquées dans les cahiers des charges des réhabilitations par exemple. De plus, les résultats sur le long terme permettraient d'appréhender la pérennité de ces nouveaux traitements

Etude de la corrosion des structures en béton armé et de leur réparation par traitements électrochimiques en vue d'une meilleure gestion des ouvrages d'art

Reinforced concrete structures represent the main part of the heritage in the field of transport infrastructure, energy or hydraulics but also in that of buildings and historical monuments. The first cause of degradation of reinforced concrete structures is the corrosion of carbon steel reinforcements which can occur when the concrete cover is completely carbonated or when the chloride ions have reached the reinforcements or when both contaminations are present. This habilitation thesis presents the research carried out to better understand the pathology of corrosion, establish a reliable corrosion diagnosis, predict the evolution of corrosion and propose electrochemical repair solutions (cathodic protection, realkalisation and chloride extraction). The last chapter pursues a research strategy on the medium and long term with in particular the contribution of numerical modeling for cracking and the use of embedded sensors for a monitoring of corrosion as a function of time (data that requires several decades). Some reflections on scientific research and infrastructure management to help managers conclude this habilitation thesis.Les structures en béton armé représentent une part majoritaire du patrimoine dans le domaine des infrastructures de transport, de l'énergie ou de l'hydraulique mais aussi dans celui des bâtiments et des monuments historiques. La première cause de dégradation des structures en béton armé est la corrosion des armatures en acier carbone qui peut survenir lorsque le béton d'enrobage est totalement carbonaté ou bien lorsque les ions chlorure ont atteint les armatures ou bien encore lorsque les deux contaminations sont présentes. Ce mémoire d'habilitation à diriger des recherches retrace les recherches réalisées pour mieux connaitre la pathologie de la corrosion, établir un diagnostic de corrosion fiable, prédire l'évolution de la corrosion et proposer des solutions de réparations électrochimiques (protection cathodique, réalcalinisation et extraction des ions chlorure). Le dernier chapitre poursuit une stratégie de recherche sur le moyen et le long terme avec notamment l'apport de la modélisation numérique pour expliquer la fissuration et l'utilisation de capteurs noyés pour suivre la corrosion en fonction du temps (donnée qui nécessite plusieurs dizaines d'années). Quelques réflexions sur la recherche scientifique et la gestion des infrastructures visant à aider les maitres d'ouvrages viennent terminer ce mémoire

Galvanic anodes for reinforced concrete repair : French experience

This conference will serve as an introduction to the Workshop untitled « Cathodic Protection of Steel in Concrete by galvanic anodes and will present the French state of the art on the use of this type of repair. Galvanic (or sacrificial) anode systems can be applied in many structures like bridges, harbours, industrial silos, buildings, car parks, for example. These structures exist in various environments : carbonated, chlorinated, marine, etc. Galvanic anode systems can be surface installed or embedded within the concrete. The following different key aspects of the galvanic anode systems will be discussed: Galvanic current directly depends on the steel current demand. As corrosion rate varies with weather conditions (humidity, temperature) and with concrete cover components (old concrete, marine salts, de-icing salts, new concrete,), the galvanic current is never constant and can even be nil if the steel is not corroding anymore. Thus the current variations of the electrochemical cell with time needs to be explained. Design of these systems is essential to ensure that the required protection will work efficiently. The number, size, capacity and location of galvanic anodes is dependent on the current demand, the electrolyte resistivity, the structure geometry, etc. In a classical design of cathodic protection in sea water for instance, resistivity of the media is constant whereas concrete is not a homogeneous material. Different design parameters will be considered. Galvanic anode systems monitoring is at the option of the purchaser and this is often understood as an advantage compared to impressed current cathodic protection that obviously needs to be checked all life through. But without monitoring, no evidence of the performance of the system can be achieved. Embedded reference electrodes, special connexion systems, electrical and electronic devices are available for monitoring galvanic current and will be referred to. Performance criteria can be based on potential measurements (current off, on, cartography), polarisation tests (upon time), current density monitoring. Nevertheless, more studies and analysis are necessary to find out or develop proper performance criteria that has been difficult to obtain if we look back over past experiences. Durability of the galvanic anode systems has not been sufficiently and scientifically explored yet. Examinations could be made on old anode systems that are still in service (visual examination, chemical analysis, estimation of the anode consumption rate) in order to estimate it. All these points will be presented and discussed during this introducing conference

Galvanic anodes for reinforced concrete repair : French experience

This conference will serve as an introduction to the Workshop untitled « Cathodic Protection of Steel in Concrete by galvanic anodes and will present the French state of the art on the use of this type of repair. Galvanic (or sacrificial) anode systems can be applied in many structures like bridges, harbours, industrial silos, buildings, car parks, for example. These structures exist in various environments : carbonated, chlorinated, marine, etc. Galvanic anode systems can be surface installed or embedded within the concrete. The following different key aspects of the galvanic anode systems will be discussed: Galvanic current directly depends on the steel current demand. As corrosion rate varies with weather conditions (humidity, temperature) and with concrete cover components (old concrete, marine salts, de-icing salts, new concrete,), the galvanic current is never constant and can even be nil if the steel is not corroding anymore. Thus the current variations of the electrochemical cell with time needs to be explained. Design of these systems is essential to ensure that the required protection will work efficiently. The number, size, capacity and location of galvanic anodes is dependent on the current demand, the electrolyte resistivity, the structure geometry, etc. In a classical design of cathodic protection in sea water for instance, resistivity of the media is constant whereas concrete is not a homogeneous material. Different design parameters will be considered. Galvanic anode systems monitoring is at the option of the purchaser and this is often understood as an advantage compared to impressed current cathodic protection that obviously needs to be checked all life through. But without monitoring, no evidence of the performance of the system can be achieved. Embedded reference electrodes, special connexion systems, electrical and electronic devices are available for monitoring galvanic current and will be referred to. Performance criteria can be based on potential measurements (current off, on, cartography), polarisation tests (upon time), current density monitoring. Nevertheless, more studies and analysis are necessary to find out or develop proper performance criteria that has been difficult to obtain if we look back over past experiences. Durability of the galvanic anode systems has not been sufficiently and scientifically explored yet. Examinations could be made on old anode systems that are still in service (visual examination, chemical analysis, estimation of the anode consumption rate) in order to estimate it. All these points will be presented and discussed during this introducing conference

Electrochemical chloride extraction of a beam polluted by chlorides after 40 years in the sea

A reinforced concrete beam element, casted in 1960's while the construction of the Rance dam, has been naturally polluted by chlorides after 40 years of a marine tidal exposure. The electrochemical chloride extraction treatment (ECE) has been used in order to rehabilitate the beam. The efficiency of the ECE treatment and its durability was studied based on the analysis made before treatment, 2 months after treatment and after 17 months of immersion of the beam in a salted pond. The chloride concentration profiles show that free chlorides are extracted with an efficiency of 70 % close to the steel, 50% in the intermediate cover and 5% at the concrete surface and that there is no redistribution of the chlorides after 17 months. From the electrochemical characterizations, the steel potential values can, somehow, indicate a slow down of the rebar corrosion probability, but, this phenomenon is not confirmed by the corrosion current values. SEM and EDX results show that after the treatment, the concrete close to the steel contains less Friedel'salt and that the shape of the rust has changed