Unpublished data on corrosion in engineering structures

Véronique Bouteiller, département Matériaux et Structures (MAST) et Xavier Derobert, Département Géotechnique, Environnement, Risques naturels et Sciences de la Terre (GERS), Université Gustave Eiffel

Researchers and partners in the DéCoF-Ré project have conducted a major data acquisition campaign on the piers of the Île de Ré bridge with the aim of improving the reliability of corrosion diagnosis in marine engineering structures. Contributing to improvements in assessing the health of engineering structures, this unprecedented work is shared through four datasets.

For over 35 years, the Île de Ré bridge has stood above the Atlantic Ocean. Exposed to sea spray, storms, tides and more than 350,000 vehicles each year, there is nevertheless a more insidious phenomenon that threatens its durability: corrosion of the reinforcing bars, an electrochemical process that is the leading cause of deterioration in reinforced concrete structures. In a maritime environment, this phenomenon is caused by the penetration of chloride ions through the concrete, which can lead to the oxidation of steel reinforcements. The consequences include: the loss of reinforcement cross-sections, cracking or spalling of concrete, and a reduction in steel/concrete adhesion, which reduces the performance of the structure.

Corrosion assessment is therefore a major challenge for the management of civil engineering structures. However, while corrosion diagnosis is well established and reliable in atmospheric environments, this is less often the case in marine environments: “With maritime structures, you can't use the interpretations of a conventional diagnosis.  Environmental effects, particularly tidal phenomena, can distort measurements and indicate an at-risk area when there is not necessarily any corrosion”, explains Véronique Bouteiller, corrosion specialist and research director at the EMGCU (Experimentation and Modelling for Civil & Urban Engineering Laboratory).

With the aim of improving the reliability of reinforced concrete testing in marine environments and assessing the condition of the piers of the Île de Ré bridge, a consortium of partners launched the DéCoF-Ré (Decision, Corrosion, Reliability on the Île de Ré bridge) project in 2015. “Completed in 2021, DéCoF-Ré brought together researchers from the Université Gustave Eiffel, the Nantes Université and its engineering and research development subsidiary (Capacités SAS), Cerema, and the company Sixense-Concrete – as part of a CIFRE thesis – as well as the Charente-Maritime department, which owns the bridge”, explains project coordinator Véronique Bouteiller. DéCoF-Ré comprised more than 30 people and had a budget of around €1 million.

The project involved a major campaign to collect data in situ. Between 2015 and 2018, researchers conducted investigations by boat on 15 of the bridge's 28 piers. The analyses were carried out on two of the eight sides of the piers – side C, which is most exposed to weather conditions, and side G, which is least exposed – and at the tide line, at a height of 3 metres. “This is where the most significant problems are likely to occur”, explains Xavier Derobert, co-director of GéoEND (Geophysics and Non-Destructive Evaluation Laboratory). 

Over the course of three years, researchers carried out a diagnosis of the corrosion of the bridge’s reinforcements using various non-destructive in-situ techniques (radar detection of reinforcements, measurements of concrete resistivity, reinforcement potential and corrosion rate), a study of the durability of the concrete by taking core samples and laboratory analyses (destructive tests) and, finally, visual autopsies of the reinforcements. The results of this work are now available in four datasets, which have been accessible free of charge since September 2024 on the recherche.data.gouv.fr platform.

“This is the first time we have had so much data on so many piers from the same structure”, says Véronique Bouteiller. “With DéCoF-Ré, we have acquired complementary data sets that have validated our interpretations and enabled us to go deeper in our analysis.” For example, the complementary nature of the corrosion diagnosis and durability study results helped to assess the progress of the corrosion process linked to chloride ions, while the visual autopsy of the reinforcements validated the corrosion diagnosis results. This information is rare – it is normally forbidden to core down to the reinforcements – and important for decision-making: “Often, project owners react when there are visible signs of corrosion – rust streaks, cracks, spalling – but the project results show that corrosion occurs before this stage and that with a comprehensive assessment we are able to indicate where the corrosion is located and thus react earlier. ” 

What is another benefit of the data collected? “It is geolocated, which will enable us to reassess these same piles in 10 or 20 years' time and track the progression of corrosion over time, as well as validate whether or not degradation has progressed”, say Véronique Bouteiller and Xavier Derobert.

To promote the reuse and understanding of their data and methodologies, the researchers collaborated with Céline Rousselot, Research Data Management and Open Access Officer at the university. “Céline helped us build our datasets, both in terms of format, to make them accessible, readable and interoperable, and in terms of content, by identifying data that was incorrect or needed further explanation. She was a huge help”, say the two researchers.

Tidal zone: area subject to daily tidal cycles; at high tide, reinforced concrete is below sea level, and at low tide it is above sea level.
 

Bridge piers: supports bearing the deck, located in the middle of the bridge. At the ends, the supports on the banks are called abutments. 
 

The interview was conducted by the Kogito agency.