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EURAXESS

MSCA-COFUND-CLEAR-Doc-PhD Position#CD22-48: Risk assessment of concrete expansion due to Delayed Ettringite Formation: benchmarking of the effective thermal energy concept

13/10/2022

Job Information

Organisation/Company
Université Gustave Eiffel
Department
MAST-CPDM
Research Field
Engineering
Engineering » Civil engineering
Researcher Profile
First Stage Researcher (R1)
Country
France
Application Deadline
Type of Contract
Temporary
Job Status
Full-time
Hours Per Week
35
Is the job funded through the EU Research Framework Programme?
H2020 / Marie Skłodowska-Curie Actions COFUND
Marie Curie Grant Agreement Number
101034248
Is the Job related to staff position within a Research Infrastructure?
No

Offer Description

In France and throughout the world, concrete is the most widely used material in nuclear civil engineering structures. It is accepted that concrete can deteriorate after a few years or tens of years. The alterations can be varied and affect either the cement matrix or the reinforcement, or a combination of these two pathologies. The safety requirements for nuclear civil engineering structures do not only concern the mechanical stability of the concrete, but also their ability to maintain containment in the event of an accident. Indeed, concrete containment structures are the third and final safety barrier of the nuclear reactor. Moreover, concrete also stands as the last barrier towards environment in nuclear storage works. The behavior of concrete over time is therefore a very important point for the safety assessment of nuclear installations and this material must meet the required requirements throughout its operating life.

However, among pathologies that can alter the structures, we distinguish several types of degradation of the concrete which can be of chemical origin (chlorides, sulphates, carbonation, ...), thermal (freezing-thawing, ...) or mechanical (creep-shrinkage fatigue, ...). Among the degradations of chemical origin, the internal swelling reactions (ISR), including the delayed ettringite formation (DEF), are at the origin of important degradations in the structures. DEF is an endogenous pathology that can affect cementitious materials that have been subjected to temperatures above about 65°C. At early age and especially in massive parts, this limit temperature is easily reached due to the heat generation during cement hydration. In addition, the rise in temperature on hardened concrete (e.g. due to fire, or radioactive waste storage) also represents a potential case of swelling. When this reaction develops, cracks are formed and mechanical performance is degraded, thus affecting the load-bearing capacity and functionality of structures in service.

Studies by Scrivener et al. (1999), Taylor et al. (2001) and Brunetaud (2005) have contributed to understanding the reaction mechanism of this pathology development, caused by an increase in temperature at early age, based on microscopic observations. Earlier work (Kchakech, 2015) has shown that only the maximum temperature and/or the time beyond this temperature does not predict the swelling potential. Other studies, Pavoine (2003), Baghdadi (2008), Salgues (2013) have been interested in modelling the RSI, however, they require a large experimental database in order to validate the swelling predictions. In addition, some temperature recalculation tools have been developed, such as the RGIB module of the CESAR code (Baghdadi, 2008 ; Seignol et al., 2012), which allow to assess the temperatures reached and their exposure times of concrete in structures.

The objective of the thesis is to quantify the relationship between the thermal treatment of a concrete and the swelling potential related to the DEF of the chemical cement composition (alkalis, sulphates, aluminates, ...). The experimental program aims to deepen the understanding of the early thermal history on the development of expansions, and to enlarge the database of prediction models proposed in the literature. It also aims to quantify the free swelling as a function of time (swelling potential and kinetics) considering the chemical and mineralogical cement nature. The quantification of the heat treatment on concrete will be considered in particular with the concept of effective thermal energy (work initiated by Kchakech, 2015), i.e. by taking the hypothesis that the energy supplied by the system from the threshold temperature of the DEF pathology (approximately 65°C) is responsible for the development of the DEF. In addition, parameters such as the chemistry and mineralogy of the cement will have to be considered for the prediction calculation of the expansion potential as well as the swelling kinetics.

This work will be supported by two external partners: the Institute for Radiation Protection and Nuclear Safety (IRSN) and Saitama University in Japan. The IRSN is leading the ODOBA project (observatory of the durability of reinforced concrete structures), which aims to study concrete pathologies and their consequences on the scale of nuclear structures, with international collaborations (United States, Canada, Belgium, Finland, China, etc.). Including concrete blocks (with different formulations) of metric sizes on an enclosure durability observatory (ODE) on the Cadarache site. In addition, a cooperation program on DEF is underway between the Gustave Eiffel University and the Saitama University in Japan, where reactive DEF concrete blocks are exposed to natural conditions. This thesis will strengthen the collaboration between the Gustave Eiffel University and the Saitama University on the topics of concrete expansions. Both partners will be involved in the follow-up of this thesis and will notably participate in the elaboration of concrete mixes tested in the experimental program including mix-designs already developed and studied by the IRSN (for the French nuclear park) and the University of Saitama. A mobility is planned both at the University of Saitama in Japan (3 months) in order to study the results of swelling of concrete blocks already exposed and also to participate in the implementation of this new experimental program. And at the IRSN site in Cadarache (3 months) in order to study the results of swelling of concrete blocks, equipped with non-destructive testing means allowing the detection of the appearance of pathologies and to follow their evolution. The blocks are subjected to both natural ageing and accelerated testing (controlled hygrometry, temperature and chemical nature of the water). All these results on blocks will be compared with those obtained at the Marne la Vallée laboratory.

From the thesis results, including dedicated tests and revisited literature data to be analyzed, it is expected to get calibrated assessment of the DEF risk (potential expansion amplitude and kinetics). The approach should consider a comprehensive benchmarking of Kchakech’s prediction formulae with due account of chemical reaction modeling, based on the effective thermal energy concept and combined influence of the maximum temperature (if necessary) and of the alkalis, sulphate and aluminate contents. It should imply calibration from specimens monitored in realistic exposure sites such as those from Marne-la-Vallée, Cadarache and Saitama.

Requirements

Research Field
Engineering
Education Level
Bachelor Degree or equivalent
Skills/Qualifications
  • At the time of the deadline, applicants must be in possession or finalizing their Master’s degree or equivalent/postgraduate degree.
  • At the time of recruitment, applicants must be in possession of their Master’s degree or equivalent/postgraduate degree which would formally entitle to embark on a doctorate.
Languages
FRENCH
Level
Excellent
Languages
ENGLISH
Level
Excellent

Additional Information

Benefits
  • High-quality doctoral training rewarded by a PhD degree, delivered by Université Gustave Eiffel
  • Access to cutting-edge infrastructures for research & innovation.
  • Appointment for a period of 36 months based on a salary of 2 700 € (gross salary per month).
  • Job contract under the French labour legislation in force, respecting health and safety, and social security: 35 hours per week contract, 25 days of annual leave per year.
  • International mobility will be mandatory
  • An international environment supported by the adherence to the European Charter & Code.
  • Access to dedicated CLEAR-Doc trainings with a strong interdisciplinary focus, together with a Career development Plan.
Eligibility criteria

Applicants must fulfil the following eligibility criteria:

  • At the time of the deadline, applicants must be in possession or finalizing their Master’s degree or equivalent/postgraduate degree.
  • At the time of recruitment, applicants must be in possession of their Master’s degree or equivalent/postgraduate degree which would formally entitle to embark on a doctorate.
  • At the time of the deadline, applicants must be in the first four years (full-time equivalent research experience) of their research career (career breaks excluded) and not yet been awarded a doctoral degree. Career breaks refer to periods of time where the candidate was not active in research, regardless of his/her employment status (sick leave, maternity leave etc). Short stays such as holidays and/or compulsory national service are not taken into account.
  • At the time of the deadline, applicants must fulfil the transnational mobility rule: incoming applicants must not have resided or carried out their main activity (work, studies, etc.) in France for more than 12 months in the 3 previous years.
  • One application per call per year is allowed.
  • Applicants must be available full-time to start the programme on schedule (November 1st 2023).
  • Application rules are enforced by the French doctoral system which specifies a standard duration of 3 years for a full-time PhD together with the MSCA standards and the OTM-R European rules as follows.
  • Citizens of any nationality may apply to the programme.
  • There is no age limit.
Selection process

Please refer to the Guide for Applicants available on the CLEAR-Doc website: https://clear-doc.univ-gustave-eiffel.fr/how-to-apply/useful-documents/

Additional comments
  • The First step before applying is contacting the PhD supervisor. You will not be able to apply without an acceptation letter from the PhD supervisor.
  • International mobility planned:

The Applicant will have a 3 months mobility at the University of Saitama (Japan).

Please contact the PhD supervisor for any additional detail on job offer.

There are no restrictions concerning the age, gender or nationality of the candidates. Applicants with career breaks or variations in the chronological sequence of their career, with mobility experience or with interdisciplinary background or private sector experience are welcome to apply.

Support service is available during every step of the application process by email: clear-doc@univ-eiffel.fr

Website for additional job details

Work Location(s)

Number of offers available
1
Company/Institute
Université Gustave Eiffel
Country
France
City
Marne-La-Vallée
Postal Code
77454
Street
5, Boulevard Descartes
Geofield

Contact

City
Marne-La-Vallée
Website
Street
5, Boulevard Descartes
Postal Code
77454
E-Mail
tony.pons@univ-eiffel.fr