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

Corrosion at low moisture content in both carbonated and chloride polluted concrete – Villa E-1027, a case study

Corrosion in reinforced concrete is generally attributed to either carbonation or chloride presence in the vicinity of the bars. But in the field of cultural heritage, especially for the most ancient monuments, it is not rare to encounter both carbonated and chloride polluted concrete, inducing heavy corrosion, as was the case in the Villa E-1027 in Roquebrune-Cap-Martin, on the French Mediterranean seashore. The villa was designed by Eileen Gray and Jean Badovici between 1926 and 1929. Due to aggressive environmental conditions and a period of dereliction, the concrete of the villa was quite heavily decayed and a deep restoration was led between 2000 and 2006. But after a little more than 10 years, and despite active maintenance, the villa is again facing corrosion induced decay. Prior to the definition of a new restoration protocol, to better evaluate the corrosion activity, in 2017 a permanent monitoring of moisture and temperature both in the air and in the concrete was installed. In the meantime, a series of instant electrochemical measurements was performed from 2017 to 2018. A first analysis of the results of the monitoring and the non-destructive tests clearly evidences that probably due to the conjunction of the carbonation of the concrete and external active chloride pollution, corrosion can happen at quite low moisture content

Evaluation of compatible mortars to repair 19th century natural cement cast stone from the French Rhône-Alpes region

In France, natural cements were extensively produced in the middle of the 19th century. In the French Alps, due to their ochre color, these cements were massively used, notably to produce cast stone, to simulate natural freestone. A preliminary survey revealed an overall good state of preservation of the buildings of this period. Two kinds of decays mechanisms were however identified : erosion affecting the surface of the majority of the buildings, inducing a gradual disappearance of the initial "fake-stone aspect", and a spalling phenomenon often combined with salts crystallization, observed only on a few buildings. Today, due to a lack of appropriate repair materials, the rehabilitation of these buildings mainly consists in the use of gray Portland-cement-based-mortars combined with a painting finishing, which is not satisfactory considering the conservation deontology, as the original appearance is lost. Therefore, the aim of this project was to develop and to test compatible repair materials to restore the culture heritage of this region. Based on the preliminary characterization of a set of representative ancient buildings, combined to a literature review, specifications concerning the composition and the main properties of repair materials, which could assure a compatibility with the ancient concrete of the region were established. Then, three Prompt-cement and one Portland-cement based mortars were selected, two of them being specifically formulated. Firstly, the appearance, the workability and the mechanical and physical properties of those mortars were characterized. Secondly, to evaluate the compatibility of the selected mortars with ancient concrete, Prompt-cement-based slabs were cast using a 19th century concrete formula, and were artificially eroded. After applying the 4 mortars on the slabs, visual observations and pull-out tests will be carried out before and after artificial aging. Finally, the repair mortar presenting the best performances will be tested on site in a monument of Grenoble

Performance evaluation of patch repairs on historic concrete structures (PEPS): Preliminary results from a selection of French case studies

Within the frame of the international research project PEPS, ‘Performance Evaluation of Patch Repairs on Historic Concrete Structures (PEPS)’, dedicated to the durability of patch repairs in the context of culturally significant structure, a series of repaired monuments was examined in detail. Thus, the operational phases of the project are composed of in situ tests and laboratory analysis on samples performed on a selection of representative historic concrete structures in the three countries who are partners in the project: United States of America, United Kingdom and France. In this paper, cases studies and some results obtained on three of the five French sites will be presented: Le Raincy church built by Auguste Perret between 1920 and 1924, and Rezé housing unit and Jaoul houses built by Le Corbusier respectively in 1955 and in 1953. The assessment methodology followed is the one developed between the three institutions partners on the PEPS project: the Getty Conservation Institute (GCI), Historic England (HE) and Laboratory of Research in Historical Monuments (LRMH). All the selected French sites were repaired several decades ago. For Le Raincy church and the Jaoul houses, the conservation campaign of 1991 was considered, while for Rezé housing unit it was the 1995-1997 campaign. All the case study structures have different construction dates and concrete compositions. Various repair materials and application techniques were used. The conditions of exposure differ from one site to another. All these variations make the evaluation highly complex but also fully instructive, and able to meet the objectives of the project: producing practical guidance helpful for companies and conservators repairing historic concrete

New warning sensors to detect corrosion risk in reinforced concrete

Corrosion is the most frequent but also the most deleterious deterioration mechanism affecting reinforced concrete. In addition to the economic impact of the repair works, for historical concrete structures, corrosion can generate irreversible losses of original material of great cultural value. If the usual non-destructive electrochemical methods have highlighted their efficiency in evaluating on-going corrosion activity, they also have pointed out their drawbacks for accurate extrapolation and prevention. To prevent the corrosion phenomenon, by detecting the penetration of aggressive agents, a new warning sensor system has been developed. The principle of the technique is to embed thin metallic sheets (called orphan blades) in the concrete cover, at different distances from the surface to the reinforcing bars. Then the corrosion of those very reactive orphan blades is followed during the propagation of the carbonation front and/or the penetration of chloride ions using stimulated infrared thermography. The corrosion of the sensors at different depths is indicative of the ingress speed of the front and can alert about the risk of corrosion of reinforcing bars in the concrete. The purpose of this study is to present this new technique and the first results obtained in the laboratory on corroded and non-corroded sensors

First historical cements in France from Boulogne sur Mer: investigations on 19th century's manufactured cement- based monuments

International audienceThe Boulogne-Sur-Mer area in the North of France is one of the cradles of the French cement industry (the other main one is Grenoble region due to Joseph Vicat's first cement works). From fast setting (Roman) to Portland, those cements were famous in France and have been used throughout the entire country. The main objective of this study is to give a preliminary insight of the type of binders used since there is currently few and scattered data on those specific structures and to assess the efficiency of traditional analytical techniques [X-ray diffraction (XRD), optical (OM) and scanning electron microscopy (SEM) observations, coupled with EDS analysis] used to differentiate natural and artificial cements

Performance of patch repairs on historic concrete structures: a preliminary assessment

Carrying out patch repairs to historic concrete buildings and structures needs to be done carefully if their cultural value and significance is to be maintained. This often means repairs using custom designed materials and mixes for compatibility with the original concrete, and with great care paid to good workmanship. But with most repairs, commercial mixes are used which are not compatible with the host concrete but are justified because they adhere well, cure quickly and require limited skills to implement. A research collaboration has been established to test the performance of both approaches. The Performance Evaluation of Patch Repairs on Historic Concrete Structures (PEPS) began in 2018 and is a collaboration between the Getty Conservation Institute, Historic England and the Laboratoire de Recherche des Monuments Historiques. Its purpose is also to better understand key design and specification parameters and application methods. The research is based on assessing case studies in USA, England and France within a variety of climatic and environmental conditions, typologies and repair materials. This paper will present the methodology adopted to evaluate the repairs in the first phase. This will also include historical research on the specification and application of the repairs, preliminary field assessment and some testing

STUDY OF THE FIRST BOULOGNE-SUR-MER CEMENTS USED FOR A HISTORIC AQUEDUCT FROM THE 19TH CENTURY

Natural and Roman cements are generally considered as the first binders of the 19th century concrete but their widespread usage was short-lived as they were quickly replaced by artificial cements (Portland), still the most important and predominant today. The Boulogne-Sur-Mer area in the North of France is one of the cradles of the French cement industry where the first French natural cement was produced in 1802 and the first French Portland cement at around 1850. These cements, natural and artificial, quickly gained a national and international fame. This paper presents a case study of a 19th century aqueduct, still in operation, with a focus on identifying the binders of concretes and mortars. Several combined techniques – optical microscopy (OM), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD) – were carried out to characterize and determine the compositions of the binders present in the aqueduct. Phenolphthalein tests were carried out in order to evaluate the depth of carbonation in the concrete. Several concrete and mortar samples, from pinkish to greyish ones, were taken from the outer and inner parts of the aqueduct. Results show several clinker morphologies and compositions, and different types of hydrates. They also reveal important differences in the microstructure between natural and Portland cement, dated from an early period of the cement industry in France. The concomitance of the use of natural and Portland cement, and good durability of these materials highlight the know-how of the engineers in the 1860s on cement performances and characteristics

Performance evaluation of patch repairs on historic concrete structures (PEPS): a methodology for in situ and laboratory analyses

While there have been many studies on the performance criteria of concrete patch repairs, there are few specific studies on the long-term performance of patch repairs designed to preserve the aesthetic significance of the original fabric of culturally significant concrete structures. In order to address this issue, the Getty Conservation Institute (GCI), Historic England (HE) and the Laboratoire de Recherche des Monuments Historiques (LRMH) commenced work on an international collaborative research project, ‘Performance Evaluation of Patch Repairs on Historic Concrete Structures’ (PEPS). Begun in 2018, the PEPS project aims to produce practical guidance that will help those repairing historic concrete through the assessment of case studies in the USA, England and France within a variety of climatic and environmental conditions, typologies and repair materials. The operational phases of the research project consist of in situ tests and laboratory analysis performed on both the original concrete and previous patch repairs. This paper provides an overview of the assessment methodology that has been developed by an inter-disciplinary team of professionals working in the field of concrete conservation, and includes a variety of traditional and non-traditional non-destructive, mechanical, chemical, and electro-chemical characterization and diagnostic techniques