Ifsttar PhD subject

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Title : Studying the microstructure of materials to understand their properties: the case of low-carbon cement systems

Main host Laboratory - Referent Advisor GERS - GIE  -  DENEELE Dimitri      tél. : +33 240845802

Director of the main host Laboratory DENEELE Dimitri  -

PhD Speciality Physico-chimie des matériaux

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

Main location Nantes

Doctoral affiliation UNIVERSITE GUSTAVE EIFFEL

PhD school Matière, Molécules, Matériaux et Géosciences (3MG)

Planned PhD supervisor DENEELE Dimitri  -  Université Gustave Eiffel  -  GERS - GIE

Planned financing Contrat doctoral  - Université Gustave Eiffel

Abstract

The use of SCMs (Supplementary Cementitious Materials) has become common practice in the drive to reduce CO2 emissions in the cement industry. Among the various SCMs tested (fly ash, blast furnace slag, glass powder), calcined clays represent a resource of the future, due to their dispersion and availability. However, their complexity, heterogeneity and differences mean that their role in a composite cement, which is expected to perform as well as the benchmark, portland cement, needs to be studied in greater depth.
The calcination of clays tends to increase their dissolution in the cementitious medium through the combined effects of dehydroxylation and modification of the atomic environments of aluminium and silicon. These elements, released at high pH, combine with the portlandite formed during cement hydration to form C-A-S-H, which contributes to increased mechanical strength and a change in transfer properties.
This traditional reaction is supplemented in the presence of carbonates by the precipitation of hemi- and mono- carboaluminates, which prolong the stability of ettringite and help to reduce porosity, thereby increasing the mechanical performance and durability of these ternary systems. The replacement of clinker by metakaolin and limestone has led to the development of LC3 ternary cements.
These composite systems and the reduction in the clinker content of cements represent a real opportunity to meet the objectives of the construction industry, which aims to limit greenhouse gas emissions and optimise the consumption of natural resources. It is therefore necessary to optimise the use of SCMs and to better understand how the hydrates formed in these compound systems contribute to modifying the transfer properties, whether they are binary or ternary.
This requires a detailed study of the microstructure of these composite cements, a crucial step towards understanding the durability mechanisms of these materials. The aim of this thesis is therefore to study these cementitious materials using a variety of approaches to gain a better understanding of the link between the chemical reactivity of these mixed systems, microstructural changes and the evolution of secondary phases, the evolution of porosity and, finally, the evolution of mechanical properties and certain durability parameters.
Scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) will be the investigative technique used initially, as it is easy to analyse the microstructure of materials. It will be supplemented by image analysis in order to identify the distribution of phases and then to quantify the microstructure using quantitative SEM-EDS mapping and the EDXIA method developed recently (Georget et al., 2021, 2022, 2023). The approach developed will use combined mapping analyses from different experimental techniques, which will be compared in order to obtain distributions of mechanical properties (nano-indentation), molecular imaging (Raman spectroscopy) and porosity (backscattered electrons).
By comparing systems based on different SCMs, this work will also implement the multi-scale, multi-technique approach developed in the laboratory over many years, based on expertise in the description of cementitious phases and their evolution (solid state NMR, XRD, ATG, etc.). In addition to these techniques, it is proposed to carry out a complementary and original microstructural description using X-ray tomography. X-ray tomography is one of the most effective methods for visualising, identifying and quantifying the internal 3D structure of material samples. This technique also has the advantage of being non-destructive, leaving the sample unchanged from its initial state. It can therefore be used to monitor internal structural changes over time, which is perfectly suited to the development of properties over time.
This thesis will be carried out under the joint supervision of the "Geomaterials and Environmental Interactions" laboratory of the Gustave Eiffel University (Nantes campus) and the cement and concrete research group of the Civil and Building Engineering Department of the University of Sherbrooke (Canada). Each institution will provide equipment and expertise in the use of analytical and experimental devices.
To carry out this study, we are looking for a student with skills in materials science and a keen interest in the development of materials in line with the energy and ecological transition. Proficiency in petrographic and microscopic observation techniques would be a plus. The candidate will be self-motivated, conscientious and demonstrate curiosity and scientific rigour. The student will have to demonstrate autonomy, curiosity, scientific rigour and a strong ability to adapt to the laboratories in which he or she will be working. Fluency in English is essential in order to ensure that the student's work is given due prominence in international publications.

References :

F. Georget, W. Wilson, K. Scrivener. Simple automation of SEM-EDS spectral maps analysis with python and EDXIA framework, J. Microsc. 2022 May, 286(2), 185-190, doi: 10.1111.jmi.13099

F. Georget, W. Wilson, K. Scrivener. Edxia: microstructure characterisation from quantified SEM-EDS hypermap, Cement and Concrete Research, 141, March 2021, 106327, doi : 10.1016/j.cemconres.2020.106327

F. Georget, J. Schmatz, E. Wellmann, T. Matschei. A critical catalogue of SEM-EDS multispectral maps analysis methods and their application to hydrated cementitious materials, accepted paper in J. Microsc., doi: 10.1111/jmi.13245

Keywords : Cement, low-carbon, microstructure, hydrates, additives, microscopy

Main host Laboratory - Referent Advisor	GERS - GIE - DENEELE Dimitri tél. : +33 240845802
Director of the main host Laboratory	DENEELE Dimitri -
PhD Speciality	Physico-chimie des matériaux
Axis of the performance contract	2 - COP2017 - More efficient and resilient infrastructure
Main location	Nantes
Doctoral affiliation	UNIVERSITE GUSTAVE EIFFEL
PhD school	Matière, Molécules, Matériaux et Géosciences (3MG)
Planned PhD supervisor	DENEELE Dimitri - Université Gustave Eiffel - GERS - GIE
Planned financing	Contrat doctoral - Université Gustave Eiffel
Abstract The use of SCMs (Supplementary Cementitious Materials) has become common practice in the drive to reduce CO2 emissions in the cement industry. Among the various SCMs tested (fly ash, blast furnace slag, glass powder), calcined clays represent a resource of the future, due to their dispersion and availability. However, their complexity, heterogeneity and differences mean that their role in a composite cement, which is expected to perform as well as the benchmark, portland cement, needs to be studied in greater depth. The calcination of clays tends to increase their dissolution in the cementitious medium through the combined effects of dehydroxylation and modification of the atomic environments of aluminium and silicon. These elements, released at high pH, combine with the portlandite formed during cement hydration to form C-A-S-H, which contributes to increased mechanical strength and a change in transfer properties. This traditional reaction is supplemented in the presence of carbonates by the precipitation of hemi- and mono- carboaluminates, which prolong the stability of ettringite and help to reduce porosity, thereby increasing the mechanical performance and durability of these ternary systems. The replacement of clinker by metakaolin and limestone has led to the development of LC3 ternary cements. These composite systems and the reduction in the clinker content of cements represent a real opportunity to meet the objectives of the construction industry, which aims to limit greenhouse gas emissions and optimise the consumption of natural resources. It is therefore necessary to optimise the use of SCMs and to better understand how the hydrates formed in these compound systems contribute to modifying the transfer properties, whether they are binary or ternary. This requires a detailed study of the microstructure of these composite cements, a crucial step towards understanding the durability mechanisms of these materials. The aim of this thesis is therefore to study these cementitious materials using a variety of approaches to gain a better understanding of the link between the chemical reactivity of these mixed systems, microstructural changes and the evolution of secondary phases, the evolution of porosity and, finally, the evolution of mechanical properties and certain durability parameters. Scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) will be the investigative technique used initially, as it is easy to analyse the microstructure of materials. It will be supplemented by image analysis in order to identify the distribution of phases and then to quantify the microstructure using quantitative SEM-EDS mapping and the EDXIA method developed recently (Georget et al., 2021, 2022, 2023). The approach developed will use combined mapping analyses from different experimental techniques, which will be compared in order to obtain distributions of mechanical properties (nano-indentation), molecular imaging (Raman spectroscopy) and porosity (backscattered electrons). By comparing systems based on different SCMs, this work will also implement the multi-scale, multi-technique approach developed in the laboratory over many years, based on expertise in the description of cementitious phases and their evolution (solid state NMR, XRD, ATG, etc.). In addition to these techniques, it is proposed to carry out a complementary and original microstructural description using X-ray tomography. X-ray tomography is one of the most effective methods for visualising, identifying and quantifying the internal 3D structure of material samples. This technique also has the advantage of being non-destructive, leaving the sample unchanged from its initial state. It can therefore be used to monitor internal structural changes over time, which is perfectly suited to the development of properties over time. This thesis will be carried out under the joint supervision of the "Geomaterials and Environmental Interactions" laboratory of the Gustave Eiffel University (Nantes campus) and the cement and concrete research group of the Civil and Building Engineering Department of the University of Sherbrooke (Canada). Each institution will provide equipment and expertise in the use of analytical and experimental devices. To carry out this study, we are looking for a student with skills in materials science and a keen interest in the development of materials in line with the energy and ecological transition. Proficiency in petrographic and microscopic observation techniques would be a plus. The candidate will be self-motivated, conscientious and demonstrate curiosity and scientific rigour. The student will have to demonstrate autonomy, curiosity, scientific rigour and a strong ability to adapt to the laboratories in which he or she will be working. Fluency in English is essential in order to ensure that the student's work is given due prominence in international publications. References : F. Georget, W. Wilson, K. Scrivener. Simple automation of SEM-EDS spectral maps analysis with python and EDXIA framework, J. Microsc. 2022 May, 286(2), 185-190, doi: 10.1111.jmi.13099 F. Georget, W. Wilson, K. Scrivener. Edxia: microstructure characterisation from quantified SEM-EDS hypermap, Cement and Concrete Research, 141, March 2021, 106327, doi : 10.1016/j.cemconres.2020.106327 F. Georget, J. Schmatz, E. Wellmann, T. Matschei. A critical catalogue of SEM-EDS multispectral maps analysis methods and their application to hydrated cementitious materials, accepted paper in J. Microsc., doi: 10.1111/jmi.13245
Keywords :	Cement, low-carbon, microstructure, hydrates, additives, microscopy

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