Experimental study of the chemo-mechanical degradation mechanisms of new binders with reduced carbon impact

The subject of the thesis is part of the ongoing collaboration between LMDC and ANDRA on the chemo-mechanical behaviour of future storage structures for long-lived intermediate-level waste. The concrete used by ANDRA in these structures, which are buried 500 m underground in a geological environment with low mineral content water, will in the long term be subject to chemical degradation caused by the site water, leading to changes in the mechanical properties of the concrete and thus posing a major risk to the stability of the waste repository. The various studies carried out at LMDC as part of this collaboration have led to the development of numerical models for reproducing the chemo-mechanical behaviour of ‘ANDRA’ High Performance Concrete (HPC) within the structures. These models have been developed at the scale of the material considered as homogeneous, and are identified thanks to the acquisition of laws of evolution of the mechanical properties acquired from a large campaign of tests carried out on previously degraded CEM I-based concrete specimens.

In recent years, the need to adapt cementitious materials to the environmental context and the question of the long-term availability of resources have led to the use of new binders for the future construction of concrete structures in these galleries. These developments in materials are leading to questions about the laws of evolution established for ‘historic’ HPC. It therefore appears necessary to develop modelling strategies, by approaching the problems on a microscopic scale, enabling the models to be more easily adapted to changes in material formulation.

The aim of this project will therefore be to study experimentally the chemical and mechanical degradation mechanisms of new binders with reduced carbon impact. The study will focus on degradation under the effect of leaching and carbonation phenomena in a saturated environment, at different temperatures. The adopted approach will combine multi-physics experimental characterisation methods and mechanical analyses at different scales. The study will be broken down into 4 tasks:

• Literature review
• Development of degradation protocols and procedures
• Multi-physical characterisation of degraded specimens and identification of degradation mechanisms and their effects
• Multi-scale assessment of the chemo-mechanical couplings used (and identification of evolution laws)

This thesis will be characterised by a strong experimental component and a methodology based on various advanced analytical techniques for liquids and solids: inductively coupled plasma optical emission spectroscopy, ion chromatography, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy (coupled with energy dispersive X-ray spectroscopy), mercury intrusion porosimetry or microtomography, autoradiography, nuclear magnetic resonance and microindentation in a controlled environment, etc.

From an academic point of view, the Laboratory of Materials and Durability of Constructions (LMDC) is highly-recognised in the field of Civil Engineering, and the training received during the thesis in cement chemistry, microstructural analysis of materials and modelling will provide a range of multi-disciplinary skills that will be of great value. The team supervising this thesis combines skills in the multiphysical behaviour of cementitious materials in aggressive environments, experimental protocols for exposing materials to these environments, and multi-scale and multi-physics characterisation and modelling of cementitious materials.

LMDC is the largest Civil Engineering Laboratory in France. It has a staff of 120, including 60 PhD students every year, providing a dynamic working environment and numerous opportunities for scientific exchange and stimulation. The laboratory has its own range of scientific equipment (SEM-EDS, XRD, ATG, ICP-OES, ion chromatography, etc.) and is a member of research federations (including the Fermat federation), giving its staff access to a large number of cutting-edge facilities.

Finally, the members of LMDC enjoy a very pleasant working environment next to the Canal du Midi in the city of Toulouse. Toulouse is a young and attractive city, ideally located in the middle of south-west France, offering a wide range of tourist attractions.

Candidate profile and selection criteria:

Essential:

The candidate should have a strong scientific curiosity and a taste for experimental work, with the following: (i) an M2 level or master's degree (Engineering degree or university course) in Materials Science, Physical Chemistry or Civil Engineering – Students who are about to graduate can also apply, (ii) a good command of English, and (iii) significant research experience will be an important element. The future PhD student should be motivated and committed, and show initiative and autonomy. They will have various contacts with whom they will need to communicate regularly and act as an interface. They will have to present their results very regularly and report on the progress of their work to various scientific contacts. The PhD student will therefore need to demonstrate good writing skills, as well as an ability to communicate and present their work.

Desirable:

An interest in exploiting data using numerical analysis tools (based on languages such as Python) will be appreciated. Knowledge of techniques for analysing the mineralogical, chemical, microstructural and/or mechanical properties of solids and their theoretical underpinnings would be a plus. Knowledge of cementitious materials would also be an advantage. Speaking French or an interest in learning to speak French could be appreciated in the lab.