29 Sep 2023
Job InformationOrganisation/Company
University Gustave Eiffel
Department
MAST
Research Field
Engineering » Civil engineering
Engineering » Materials engineering
Engineering » Mechanical engineering
Researcher Profile
First Stage Researcher (R1)
Country
France
Application Deadline
31 Dec 2023 - 23:59 (Europe/Paris)
Type of Contract
Temporary
Job Status
Full-time
Hours Per Week
38.5
Offer Starting Date
29 Sep 2023
Is the job funded through the EU Research Framework Programme?
Not funded by an EU programme
Is the Job related to staff position within a Research Infrastructure?
No
Offer DescriptionThe distribution of fibers in a fiber-reinforced concrete structural element is a crucial step in the effective development of the reinforcing performance provided by the fibers. The assumption of a uniform and random distribution of fibers within a structural element can only be achieved rarely, due to the negative effects that the fibers themselves have on the workability of wet concrete 12.
For this reason, it is difficult to cast fiber-reinforced concrete elements without external actions, such as manual compaction and vibration, which could compromise the random uniformity of the fiber distribution. By optimising the casting process, the flow direction of the fresh concrete, along which the fibers tend to align, can be adjusted to coincide, as closely as possible, with the expected stress pattern (i.e. the direction of the principal tensile stresses). This would improve the structural efficiency of fiber-reinforced concrete elements.
The doctoral thesis proposal will be developed in the framework of PREFO project, which proposes an innovative process for building diaphragm walls by vertically assembling prefabricated steel fiberreinforced concrete hollow-core 'bricks' to form a panel of the desired depth for excavation retaining structures. Because of the literature review, technical data and a critical review on an engineering development perspective, the first objective will be to identify the best experimental method and the most effective tools for identifying the distribution and orientation of fibers. Then, the final objective will be to develop a casting methodology adapted to the case of pre- cast structural elements, using an optimised and reliable nondestructive testing (NDT) method, and to ensure its control.
Among the experimental methods for identifying fiber orientation and distribution, NDT methods, particularly inductive methods and tomography, are of particular interest because they can be more easily used for production control on precast structural elements. Inductive methods are based on the different electromagnetic properties of metal fibers and the cementitious matrix. In particular, resistivity measurements can be used to estimate density and orientation with respect to the electric field 34. The inductance of a local magnetic field can be also measured 5. However, the application of these methods is limited by the thickness of the elements tested. Secondly, non- destructive methods use X-ray tomography to look at the internal microstructure of a material, and thus determine the orientation and distribution of the fibers 6. Despite the accuracy of the results, it is important to consider the complexity of using the measuring instruments, the post-processing of the data and the risk associated with the use of X-rays. In addition, the tomography can be used just for small elements or samples of structural elements of interest 78. Therefore, although less accurate, inductive methods seem more suitable for use in industry and then in case of pre-cast manufacturing for structural elements such as the pre-cast bricks in the PREFO solution.
The scientific challenges of this scientific work arise from the following questions:
Which of the inductive methods is best suited to precast manufacturing? How can it be adapted and made more reliable? How can the casting method be optimised with the selected NDT method?
The results of the work will be based on comparison and validation with those obtained from modelling fiber-reinforced concrete and analysis of the distribution and orientation of the fibers 8 9.
1 Bayasi MZ, Soroushian P (1992) Effect of steel fiber reinforcement on fresh mix properties of concrete. ACI Materials Journal, 89:369–374 2 Ferrara, L., & Meda, A. (2006). Relationships between fibre distribution, workability and the mechanical properties of SFRC applied to precast roof elements. Materials and Structures/Materiaux et Constructions, 39(4), 411–420. 3 Ozyurt, N., Mason, T. O., & Shah, S. P. (2006). Non-destructive monitoring of fiber orientation using AC-IS: An industrial scale application. Cement and Concrete Research, 36(9), 1653–1660. 4 Lataste, J. F., Behloul, M., & Breysse, D. (2008). Characterisation of fibres distribution in a steel fibre reinforced concrete with electrical resistivity measurements. NDT and E International, 41(8), 638–647. 5 Faifer, M., Ferrara, L., Ottoboni, R., & Toscani, S. (2013). Low frequency electrical and magnetic methods for nondestructive analysis of fiber dispersion in fiber reinforced cementitious composites: An overview. Sensors (Switzerland),13(1), 1300–1318. 6 Vicente, M. A., Mínguez, J., & González, D. C. (2017). The Use of Computed Tomography to Explore the Microstructure of Materials in Civil Engineering: From Rocks to Concrete. Computed Tomography - Advanced Applications. 7 Ponikiewski, T., Katzer, J., Bugdol, M., & Rudzki, M. (2015). Steel fibre spacing in self-compacting concrete precast walls by X-ray computed tomography. Materials and Structures/Materiaux et Constructions, 48(12), 3863–3874. 8 Guenet, T., Modélisation du comportement des bétons fibrés à ultra- hautes performances par la micromécanique : effet de l'orientation des fibres à l'échelle de la structure. Matériaux. Université Paris-Est, 2016. Français. 9 Vu D.T., Modélisation numérique du comportement des bétons de fibres métalliques sous des sollicitations multiaxiales tenant compte de l'effet de l'orientation des fibres Application aux voussoirs du tunnel, PhD Thesis, Université Gustave Eiffel,2022.
RequirementsResearch Field
Engineering » Civil engineering
Education Level
Master Degree or equivalent
Skills/Qualifications
The candidate must be able to work independently and show a spirit of initiative. Good writing skills in French and English are expected (writing articles and papers for journals and conferences). High motivation is highly recommended. Communication skills are also required (exchanges with the management team, presentations at meetings, etc.). The candidate will work as part of the EMGCU laboratory research team, contributing to PREFO research project funded by bpi France. The project is in partnership with GERS Department of the Gustave Eiffel University and NGE Fondations, as project leader and industrial partner as well. The applied research nature of the project means that the work will involve regular exchanges with the company's team, which is a good opportunity for the candidate for future employment in this or related field.
Specific Requirements
The doctoral thesis is for a MSc graduate in Civil, Materials or Mechanical Engineering. The candidate should have a good knowledge of engineering sciences and the mechanics of materials, particularly concrete. The candidate will have a taste for and preferably experience in experimental research, with theoretical and practical skills and an attitude combining curiosity and discipline. Basic knowledge of numerical simulation techniques (in the field of civil engineering or mechanical engineering in general) is appreciated. Proficiency in one or more programming languages will be recommended. Proficiency in standard Microsoft Office tools is essential. Fluency in technical English is also required (reading of publications).
Languages
ENGLISH
Level
Excellent
Languages
FRENCH
Level
Good
Research Field
Engineering » Materials engineering
Number of offers available
1
Company/Institute
Université Gustave Eiffel (MAST/EMGCU)
Country
France
Geofield
Where to applyState/Province
France
City
Champs-sur-Marne
Website
https: // www. univ-gustave-eiffel.fr/
Street
14-20 Boulevard Newton
Postal Code
77454
STATUS: EXPIRED