Ifsttar PhD subject

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Title : How to connect the mechanical degradation of reinforced concrete structures to the corrosion process of the steel/concrete interface: measurements and 3D modelling

Main host Laboratory - Referent Advisor MAST - EMGCU  -  ADELAIDE Lucas      tél. : +33 181668336

Director of the main host Laboratory MARTIN Renaud-Pierre  -

PhD Speciality Matériaux et Structures

Axis of the performance contract 2 - COP2017 - More efficient and resilient infrastructure

Main location Marne-la-Vallée

Doctoral affiliation UNIVERSITE DE MARNE-LA-VALLEE

PhD school SCIENCES, INGENIERIE ET ENVIRONNEMENT (SIE)

Planned PhD supervisor BOUTEILLER Véronique  -  Université Gustave Eiffel  -  MAST - EMGCU

Planned PhD co-supervisor YVONNET Julien  -  Université Gustave Eiffel  -  MSME

Planned financing Contrat doctoral  - Université Gustave Eiffel

Abstract

At the congress Pavement Preservation & Recycling Summit (PPRS) in Nice in 2018, F. Poupard, Director of the DGITM (General Director of Infrastructure, Transport and Sea) indicated that "our heritage is ageing whereas the need in mobility increases" and thus talked about roads, but also structures "which have a life cycle of 80 or 100 years, but the lack of maintenance in the first 50 years of their lives has led to a greater severe degradation". F. Poupard also called for the implementation of a large plan for the regeneration of bridges and viaducts in the coming years, "made mandatory because of the serious problems that are before us".

From the scientific point of view, one of the main causes of deterioration of reinforced concrete structures is the corrosion of reinforcement. The life cycle controls and the durability indicators of the performantial approach have been proven for the design of new structures by qualifying concrete choices according to exposure classes and loads, but they are not sufficient when it is a question of predicting their ageing and thus a probability of failure.

Corrosion of reinforced concrete structures is detected during a visual inspection, annotating the rust spots and the pattern of cracks following the reinforcement locations. If the asset owner needs more information, a detailed inspection allows to assess, on the one hand, the corrosion state of the structure by non-destructive testing (NDT) and on the other hand, the cause of corrosion by destructive tests (chloride ions and/or carbonation). These measurements, which are only significant for a corrosion state at the time of the assessment, unfortunately, do not allow to predict the corrosion evolution. It is therefore complex to link the durability indicators (water porosity, coefficient of chloride ion diffusion, etc.) and the life cycle indicators (chloride ion profiles and/or carbonation front) obtained from on-site measurements to an overall condition of the structure and thus evaluate its residual bearing capacity. To answer this issue, and thus help the asset owner to better manage its structures, we must look for the link between measurements made in laboratory and/or on-site characterizing the progress of corrosion (resistivity concrete, potential and corrosion rate of reinforcement) and the representative indicators at the structural scale; then determine the one between the measurements named previously and the parameters (or state variables) which can feed a thermo-hydro-mechanical modelling of the structure at a given time.

Major progress has been made recently on the phenomenological analysis of measurements carried out over periods of several decades thanks to the projects ANR APPLET (2007-2010), PN PERFDUB (2015-2019), DéCoF-Ré (2014- 2019), ANR MODEVIE (2015-2019) with studies of structures, trials and samples subjected to chloride ion or carbon dioxide environments. The scientific exchanges carried out within the framework of the National PERFDUB project, and also discussed at the international level under the international federation of concrete model code 2020 (fib AG4-TG8.9) aim to evaluate the relevance of certain indicators, qualify their variability and their time evolution.

In the framework of Olfa Loukil's PhD thesis (2014-2017) based on an approach combining experimental and numerical approaches, the results showed the need to take into account the kinetics of corrosion product formation and the 3D modelling of the corrosion product pressure to predict concrete cracking. This first step must be enriched by the set of parameters that characterize the major phenomena related to corrosion.

This new PhD thesis aims to propose a link between the mechanical degradation of the reinforced concrete structural element and the evolution of the steel/concrete interface during the corrosion process. The idea is to study the kinetics of corrosion product formation through the available experimental measurements and define the input parameters of the concrete cover cracking for 3D modelling to estimate the life cycle of a reinforced concrete structure degraded by corrosion.

This work requires triple physico-chemical, electrochemical and mechanical skills. To establish a sufficiently simple and robust model to evaluate an ageing structure and establish a forecast of its life cycle, the work carried out in the National PERFDUB Project will be considered and completed with the results established in O. Loukil's PhD thesis.

From a socio-economic point of view, the results of this approach would allow to prioritize and plan maintenance or rehabilitation balanced actions between the serviceability of the structure with a cost effective goal. The reinforced concrete structures must remain functional despite the constant evolutions of traffic, climate change, etc. with user safety always checked.

To answer this scientific research and societal issues, we propose an approach in four studies:

1/Literature study
This study will report on elements published in the literature on:
- Corrosion process in the presence of chloride and carbon dioxide ions and the physical phenomena involved,
- Data on the state of corrosion and degradation of corroded reinforced concrete from experimental measurements in laboratory and/or on-site,
- Identification of the growth kinetics of corrosion products, the mechanical properties of corrosion products and the concrete cracking pattern,
- Numerical modelling of the corrosion phenomenon in reinforced concrete, its input parameters and its mechanical consequences.

2/ Cause and effect relationship study
The aim is to link the kinetics of corrosion relying on the corrosion product growths (thickness, location and time evolution) to the concrete cracking pattern (width, length and orientation of cracks and cracking pattern). This analysis will allow, on the one hand, to determine the corrosion process and the parameters influencing its evolution with time and on the other hand, to consider the necessary parameters in terms of input data for modelling.

3/ Experimentation and modeling coupling study
The numerical works will aim at the improvement of modelling results from Olfa Loukil's PhD thesis, taking into account not only the corrosion rate and the concrete material parameters but also the physical parameters such as the porosity, the water/cement ratio, the porous zone and the migration of corrosion products in cracks. By considering the different parameters listed above, the dissolution/diffusion/precipitation phenomena of iron in concrete and macrocracks allow to better understand their influence on the evolution of cracking pattern and also on the time of cracking initiation. A comparison of the numerical results with the experimental ones obtained in the framework of study 3) or extract from the literature should validate each stage of progress.

4/ Prediction study
The final ambition of this PhD thesis is to set up a 3D modelling able to answer the questions of the asset owners: when to make repairs and maintenance actions at a reasonable cost. For this, the modelling will have to be confronted and validated on cases of reinforced concrete structures corroded in outdoor conditions.

The PhD student should have a Research Master's Degree in mechanics of materials and/or structures and/or an engineering degree. A good knowledge in solid mechanics is required, as well as numerical simulation skills. Knowledge of civil engineering materials is a plus. The candidate will have to demonstrate autonomy, rigour and good English language skills. A double formation in experimentation and modelling (the more important part) would be welcomed.

This PhD thesis work will be carried out at the Gustave Eiffel University - UGE (university newly created on January 1st 2020 and bringing together the Paris-Est Marne-la-Vallée University and IFSTTAR among others), on the Champs-sur-Marne campus, in the Experimentation and Modeling of Civil and Urban Engineering (EMGCU) and Multi-Scale Modeling and Simulation (MSME) laboratories. The work will be supervised by Véronique Bouteiller (PhD supervisor), Julien Yvonnet (PhD co-supervisor) and Lucas Adélaide

References
- Loukil O. Etude expérimentale et numérique de la dégradation d’éléments structurels en béton armé par corrosion sous courant imposé, Thèse de l'Université Paris-Est, France; 2017.
- Loukil O, Adelaide L, Bouteiller V, Quiertant M, Chaussadent T, Ragueneau F, et al. Corrosion-Induced Degradation of Reinforced Concrete Elements: Preliminary Results. In: Andrade C, Gulikers J, MarieVictoire E, editors. Service Life and Durability of Reinforced Concrete Structures. RILEM Bookseries. 17. Dordrecht: Springer; 2019. p. 129-40.

Contacts
veronique.bouteiller@ifsttar.fr ; lucas.adelaide@ifsttar.fr ; julien.yvonnet@u-pem.fr

Keywords : Reinforced concrete structures, corrosion, electrochemistry, kinetics, steel/concrete interface, cracking, modelling, structural performance, probability of failure

Main host Laboratory - Referent Advisor	MAST - EMGCU - ADELAIDE Lucas tél. : +33 181668336
Director of the main host Laboratory	MARTIN Renaud-Pierre -
PhD Speciality	Matériaux et Structures
Axis of the performance contract	2 - COP2017 - More efficient and resilient infrastructure
Main location	Marne-la-Vallée
Doctoral affiliation	UNIVERSITE DE MARNE-LA-VALLEE
PhD school	SCIENCES, INGENIERIE ET ENVIRONNEMENT (SIE)
Planned PhD supervisor	BOUTEILLER Véronique - Université Gustave Eiffel - MAST - EMGCU
Planned PhD co-supervisor	YVONNET Julien - Université Gustave Eiffel - MSME
Planned financing	Contrat doctoral - Université Gustave Eiffel
Abstract At the congress Pavement Preservation & Recycling Summit (PPRS) in Nice in 2018, F. Poupard, Director of the DGITM (General Director of Infrastructure, Transport and Sea) indicated that "our heritage is ageing whereas the need in mobility increases" and thus talked about roads, but also structures "which have a life cycle of 80 or 100 years, but the lack of maintenance in the first 50 years of their lives has led to a greater severe degradation". F. Poupard also called for the implementation of a large plan for the regeneration of bridges and viaducts in the coming years, "made mandatory because of the serious problems that are before us". From the scientific point of view, one of the main causes of deterioration of reinforced concrete structures is the corrosion of reinforcement. The life cycle controls and the durability indicators of the performantial approach have been proven for the design of new structures by qualifying concrete choices according to exposure classes and loads, but they are not sufficient when it is a question of predicting their ageing and thus a probability of failure. Corrosion of reinforced concrete structures is detected during a visual inspection, annotating the rust spots and the pattern of cracks following the reinforcement locations. If the asset owner needs more information, a detailed inspection allows to assess, on the one hand, the corrosion state of the structure by non-destructive testing (NDT) and on the other hand, the cause of corrosion by destructive tests (chloride ions and/or carbonation). These measurements, which are only significant for a corrosion state at the time of the assessment, unfortunately, do not allow to predict the corrosion evolution. It is therefore complex to link the durability indicators (water porosity, coefficient of chloride ion diffusion, etc.) and the life cycle indicators (chloride ion profiles and/or carbonation front) obtained from on-site measurements to an overall condition of the structure and thus evaluate its residual bearing capacity. To answer this issue, and thus help the asset owner to better manage its structures, we must look for the link between measurements made in laboratory and/or on-site characterizing the progress of corrosion (resistivity concrete, potential and corrosion rate of reinforcement) and the representative indicators at the structural scale; then determine the one between the measurements named previously and the parameters (or state variables) which can feed a thermo-hydro-mechanical modelling of the structure at a given time. Major progress has been made recently on the phenomenological analysis of measurements carried out over periods of several decades thanks to the projects ANR APPLET (2007-2010), PN PERFDUB (2015-2019), DéCoF-Ré (2014- 2019), ANR MODEVIE (2015-2019) with studies of structures, trials and samples subjected to chloride ion or carbon dioxide environments. The scientific exchanges carried out within the framework of the National PERFDUB project, and also discussed at the international level under the international federation of concrete model code 2020 (fib AG4-TG8.9) aim to evaluate the relevance of certain indicators, qualify their variability and their time evolution. In the framework of Olfa Loukil's PhD thesis (2014-2017) based on an approach combining experimental and numerical approaches, the results showed the need to take into account the kinetics of corrosion product formation and the 3D modelling of the corrosion product pressure to predict concrete cracking. This first step must be enriched by the set of parameters that characterize the major phenomena related to corrosion. This new PhD thesis aims to propose a link between the mechanical degradation of the reinforced concrete structural element and the evolution of the steel/concrete interface during the corrosion process. The idea is to study the kinetics of corrosion product formation through the available experimental measurements and define the input parameters of the concrete cover cracking for 3D modelling to estimate the life cycle of a reinforced concrete structure degraded by corrosion. This work requires triple physico-chemical, electrochemical and mechanical skills. To establish a sufficiently simple and robust model to evaluate an ageing structure and establish a forecast of its life cycle, the work carried out in the National PERFDUB Project will be considered and completed with the results established in O. Loukil's PhD thesis. From a socio-economic point of view, the results of this approach would allow to prioritize and plan maintenance or rehabilitation balanced actions between the serviceability of the structure with a cost effective goal. The reinforced concrete structures must remain functional despite the constant evolutions of traffic, climate change, etc. with user safety always checked. To answer this scientific research and societal issues, we propose an approach in four studies: 1/Literature study This study will report on elements published in the literature on: - Corrosion process in the presence of chloride and carbon dioxide ions and the physical phenomena involved, - Data on the state of corrosion and degradation of corroded reinforced concrete from experimental measurements in laboratory and/or on-site, - Identification of the growth kinetics of corrosion products, the mechanical properties of corrosion products and the concrete cracking pattern, - Numerical modelling of the corrosion phenomenon in reinforced concrete, its input parameters and its mechanical consequences. 2/ Cause and effect relationship study The aim is to link the kinetics of corrosion relying on the corrosion product growths (thickness, location and time evolution) to the concrete cracking pattern (width, length and orientation of cracks and cracking pattern). This analysis will allow, on the one hand, to determine the corrosion process and the parameters influencing its evolution with time and on the other hand, to consider the necessary parameters in terms of input data for modelling. 3/ Experimentation and modeling coupling study The numerical works will aim at the improvement of modelling results from Olfa Loukil's PhD thesis, taking into account not only the corrosion rate and the concrete material parameters but also the physical parameters such as the porosity, the water/cement ratio, the porous zone and the migration of corrosion products in cracks. By considering the different parameters listed above, the dissolution/diffusion/precipitation phenomena of iron in concrete and macrocracks allow to better understand their influence on the evolution of cracking pattern and also on the time of cracking initiation. A comparison of the numerical results with the experimental ones obtained in the framework of study 3) or extract from the literature should validate each stage of progress. 4/ Prediction study The final ambition of this PhD thesis is to set up a 3D modelling able to answer the questions of the asset owners: when to make repairs and maintenance actions at a reasonable cost. For this, the modelling will have to be confronted and validated on cases of reinforced concrete structures corroded in outdoor conditions. The PhD student should have a Research Master's Degree in mechanics of materials and/or structures and/or an engineering degree. A good knowledge in solid mechanics is required, as well as numerical simulation skills. Knowledge of civil engineering materials is a plus. The candidate will have to demonstrate autonomy, rigour and good English language skills. A double formation in experimentation and modelling (the more important part) would be welcomed. This PhD thesis work will be carried out at the Gustave Eiffel University - UGE (university newly created on January 1st 2020 and bringing together the Paris-Est Marne-la-Vallée University and IFSTTAR among others), on the Champs-sur-Marne campus, in the Experimentation and Modeling of Civil and Urban Engineering (EMGCU) and Multi-Scale Modeling and Simulation (MSME) laboratories. The work will be supervised by Véronique Bouteiller (PhD supervisor), Julien Yvonnet (PhD co-supervisor) and Lucas Adélaide References - Loukil O. Etude expérimentale et numérique de la dégradation d’éléments structurels en béton armé par corrosion sous courant imposé, Thèse de l'Université Paris-Est, France; 2017. - Loukil O, Adelaide L, Bouteiller V, Quiertant M, Chaussadent T, Ragueneau F, et al. Corrosion-Induced Degradation of Reinforced Concrete Elements: Preliminary Results. In: Andrade C, Gulikers J, MarieVictoire E, editors. Service Life and Durability of Reinforced Concrete Structures. RILEM Bookseries. 17. Dordrecht: Springer; 2019. p. 129-40. Contacts veronique.bouteiller@ifsttar.fr ; lucas.adelaide@ifsttar.fr ; julien.yvonnet@u-pem.fr
Keywords :	Reinforced concrete structures, corrosion, electrochemistry, kinetics, steel/concrete interface, cracking, modelling, structural performance, probability of failure

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