Etude expérimentale et modélisation thermodynamique du système CaO-SiO2-(Al2O3)-H2O

L objectif de ce travail est de proposer un modèle thermodynamique à 25C qui permette de décrire les principaux produits d hydratation d un ciment Portland ordinaire avec et sans matériaux cimentaires secondaires : les hydrosilicates de calcium. La composition riche en aluminium de ces produits de substitution modifie la nature et la composition des hydrates de la pâte de ciment.Nous avons donc étudié le système simplifié CaO-SiO2-H2O, pour lequel nous avons réalisé différentes synthèses de C-S-H dans des conditions de synthèse et d analyse identiques. Nous avons distingué le cas où la solution d hydratation est sous-saturée de celui où elle est sursaturée par rapport à la Portlandite.Nous avons ensuite étendu le système simplifié précédent au système CaO-Al2O3-SiO2-H2O, pour lequel nous avons réalisé différentes synthèses de C-A-S-H et déterminé le protocole le plus adéquat pour obtenir des hydrates purs.La nature nanoparticulaire et la surface spécifique importante des C-S-H nous ont conduit à développer un modèle thermodynamique qui tiennent compte de réactions de surface. Ainsi, le modèle thermodynamique proposé dans ce travail, inspiré de différents travaux antérieurs du laboratoire, permet de décrire la composition de la solution, la stoechiométrie, et les propriétés de surface des C-S-H à l équilibre. Ce premier modèle a été étendu aux C-A-S-H, en implémentant dans le modèle précédent des réactions de surface qui permettent de décrire l incorporation de l aluminium dans les différents sites possibles.Ce modèle a été appliqué à des cas simples tels que l étude de la rétention d alcalins par les C-S-H, et l évaluation de l impact de l incorporation d aluminium dans les C-S-H sur la répartition minéralogique des hydrates à l équilibre pour un mélange cimentaire avec une forte teneur en aluminiumThe aim of this work is to build a thermodynamic model at 25C to describe the main hydrates of ordinary Portland cement with or without supplementary cementitious materials (SCM) : calcium hydrosilicates. With high aluminium content, SCM in blended cements modify the nature and the composition of the hydrates of cement paste.The simplified model system CaO-SiO2-H2O was studied by synthesising of C-S-H with identical protocol and analysis. We distinguished, hydration solutions undersaturated and supersaturated from Portlandite.This last system has been extended to CaO-Al2O3-SiO2-H2O system. Then, we determined the most suitable protocol to synthesize pure C-A-S-H.The nanoparticular nature and high specific surface of C-S-H lead us to build a surface dependant thermodynamic model. The modelling described in this work, which is inspired from previous works of our laboratory, enables to describe chemistry of solution, solid composition but also surface properties of C-S-H at equilibrium. This first model has been extended to C-A-S-H. Incorporation of aluminium in C-S-H has been taken into account through surface reactions on different titrable sites.Our models were applied to some simple cases such as the study of alkali retention by C-S-H, the evaluation of the impact of aluminium incorporation in C-S-H on hydrates nature and distribution for highly substituted blended cements, i.e. with high aluminium contentDIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Experimental study and thermodynamic modelling of CaO-SiO2-(Al2O3)-H2O system

L’objectif de ce travail est de proposer un modèle thermodynamique à 25°C qui permette de décrire les principaux produits d’hydratation d’un ciment Portland ordinaire avec et sans matériaux cimentaires secondaires : les hydrosilicates de calcium. La composition riche en aluminium de ces produits de substitution modifie la nature et la composition des hydrates de la pâte de ciment.Nous avons donc étudié le système simplifié CaO-SiO2-H2O, pour lequel nous avons réalisé différentes synthèses de C-S-H dans des conditions de synthèse et d’analyse identiques. Nous avons distingué le cas où la solution d’hydratation est sous-saturée de celui où elle est sursaturée par rapport à la Portlandite.Nous avons ensuite étendu le système simplifié précédent au système CaO-Al2O3-SiO2-H2O, pour lequel nous avons réalisé différentes synthèses de C-A-S-H et déterminé le protocole le plus adéquat pour obtenir des hydrates purs.La nature nanoparticulaire et la surface spécifique importante des C-S-H nous ont conduit à développer un modèle thermodynamique qui tiennent compte de réactions de surface. Ainsi, le modèle thermodynamique proposé dans ce travail, inspiré de différents travaux antérieurs du laboratoire, permet de décrire la composition de la solution, la stoechiométrie, et les propriétés de surface des C-S-H à l’équilibre. Ce premier modèle a été étendu aux C-A-S-H, en implémentant dans le modèle précédent des réactions de surface qui permettent de décrire l’incorporation de l’aluminium dans les différents sites possibles.Ce modèle a été appliqué à des cas simples tels que l’étude de la rétention d’alcalins par les C-S-H, et l’évaluation de l’impact de l’incorporation d’aluminium dans les C-S-H sur la répartition minéralogique des hydrates à l’équilibre pour un mélange cimentaire avec une forte teneur en aluminiumThe aim of this work is to build a thermodynamic model at 25°C to describe the main hydrates of ordinary Portland cement with or without supplementary cementitious materials (SCM) : calcium hydrosilicates. With high aluminium content, SCM in blended cements modify the nature and the composition of the hydrates of cement paste.The simplified model system CaO-SiO2-H2O was studied by synthesising of C-S-H with identical protocol and analysis. We distinguished, hydration solutions undersaturated and supersaturated from Portlandite.This last system has been extended to CaO-Al2O3-SiO2-H2O system. Then, we determined the most suitable protocol to synthesize pure C-A-S-H.The nanoparticular nature and high specific surface of C-S-H lead us to build a surface dependant thermodynamic model. The modelling described in this work, which is inspired from previous works of our laboratory, enables to describe chemistry of solution, solid composition but also surface properties of C-S-H at equilibrium. This first model has been extended to C-A-S-H. Incorporation of aluminium in C-S-H has been taken into account through surface reactions on different titrable sites.Our models were applied to some simple cases such as the study of alkali retention by C-S-H, the evaluation of the impact of aluminium incorporation in C-S-H on hydrates nature and distribution for highly substituted blended cements, i.e. with high aluminium conten

Etude expérimentale et modélisation thermodynamique du système CaO-SiO2-(Al2O3)-H2O

The aim of this work is to build a thermodynamic model at 25°C to describe the main hydrates of ordinary Portland cement with or without supplementary cementitious materials (SCM) : calcium hydrosilicates. With high aluminium content, SCM in blended cements modify the nature and the composition of the hydrates of cement paste.The simplified model system CaO-SiO2-H2O was studied by synthesising of C-S-H with identical protocol and analysis. We distinguished, hydration solutions undersaturated and supersaturated from Portlandite.This last system has been extended to CaO-Al2O3-SiO2-H2O system. Then, we determined the most suitable protocol to synthesize pure C-A-S-H.The nanoparticular nature and high specific surface of C-S-H lead us to build a surface dependant thermodynamic model. The modelling described in this work, which is inspired from previous works of our laboratory, enables to describe chemistry of solution, solid composition but also surface properties of C-S-H at equilibrium. This first model has been extended to C-A-S-H. Incorporation of aluminium in C-S-H has been taken into account through surface reactions on different titrable sites.Our models were applied to some simple cases such as the study of alkali retention by C-S-H, the evaluation of the impact of aluminium incorporation in C-S-H on hydrates nature and distribution for highly substituted blended cements, i.e. with high aluminium contentL’objectif de ce travail est de proposer un modèle thermodynamique à 25°C qui permette de décrire les principaux produits d’hydratation d’un ciment Portland ordinaire avec et sans matériaux cimentaires secondaires : les hydrosilicates de calcium. La composition riche en aluminium de ces produits de substitution modifie la nature et la composition des hydrates de la pâte de ciment.Nous avons donc étudié le système simplifié CaO-SiO2-H2O, pour lequel nous avons réalisé différentes synthèses de C-S-H dans des conditions de synthèse et d’analyse identiques. Nous avons distingué le cas où la solution d’hydratation est sous-saturée de celui où elle est sursaturée par rapport à la Portlandite.Nous avons ensuite étendu le système simplifié précédent au système CaO-Al2O3-SiO2-H2O, pour lequel nous avons réalisé différentes synthèses de C-A-S-H et déterminé le protocole le plus adéquat pour obtenir des hydrates purs.La nature nanoparticulaire et la surface spécifique importante des C-S-H nous ont conduit à développer un modèle thermodynamique qui tiennent compte de réactions de surface. Ainsi, le modèle thermodynamique proposé dans ce travail, inspiré de différents travaux antérieurs du laboratoire, permet de décrire la composition de la solution, la stoechiométrie, et les propriétés de surface des C-S-H à l’équilibre. Ce premier modèle a été étendu aux C-A-S-H, en implémentant dans le modèle précédent des réactions de surface qui permettent de décrire l’incorporation de l’aluminium dans les différents sites possibles.Ce modèle a été appliqué à des cas simples tels que l’étude de la rétention d’alcalins par les C-S-H, et l’évaluation de l’impact de l’incorporation d’aluminium dans les C-S-H sur la répartition minéralogique des hydrates à l’équilibre pour un mélange cimentaire avec une forte teneur en aluminiu

Brightness and polarization scattering functions of different natures of asbestos in the visible and near infrared domain

International audienceAsbestos refers to silicate minerals belonging to the serpentine group (chrysotile) and the amphibole group (crocidolite, amosite, tremolite-asbestos, anthophyllite-asbestos and actinolite-asbestos). Such materials have strong effect on health, and real-time instrumentation is on demand to detect asbestos. The current real-time techniques use only some aspects of the optical properties of asbestos, since the scattering properties (brightness and linear polarization scattering functions) of the various natures of asbestos has not been yet fully determined. We present here the brightness and linear polarization scattering functions for 6 natures of asbestos in the 425-1650 nm spectral domain obtained with the PROGRA2 instrument. Although the samples exhibit different shapes, the linear polarization values remain low, bell-shaped as usual for irregular particles, and close to those of mineral particles previously studied with PROGRA2. On the opposite, asbestos brightness curves present strong differences for the different samples. The chrysotile is darker than the other samples in the 80°-150° angle range, probably due to its tubular shape that can act as a light trap for scattering angles greater than a few tens of degrees. Other asbestos particles can be distinguished from building materials such as glass wool or plaster through their brightness curves in some scattering angle ranges. These new laboratory measurements indicate that the optical scattered properties could be used in the future to tentatively detect asbestos particles in a medium generated from building materials

Relationship between composition, rheological and swelling properties of alkali-silica gels produced in cemented waste packages

ACTIInternational audienc

Présentation dans un séminaire au Massachussetts Institute of Technology

AI, ICTSInternational audienc

Influence of the cement composition on the radiolytic behavior under irradiation

International audienceCement based materials are used for the conditioning of Low and Intermediate Level Wastes (LILW)due to their low cost, their ease of making and their ability to immobilize radioelements. Nevertheless,hydrogen gas is produced radiolytically under irradiation. For the safety of nuclear waste disposals, itis important to limit as much as possible the hydrogen gas release.A comparison of the behavior of Portland and Ciment Fondu® cements under irradiation taking intoaccount both real cement pastes and synthetic hydrates was performed to find out the role of the cementcomposition on the radiolytic behavior under irradiation. First, γ-irradiations were performed usinga 60Co source (dose rate: 0.17 - 0.25 Gy.s-1, dose: up to 500×103 Gy). Thermogravimetric analysismeasurements were performed in order to determine the amount and the type of water involved. H2gas production was measured by gas chromatography. Regardless of the water to cement ratio (W/C)chosen (0.2, 0.4 and 0.6), it is shown that Ciment Fondu® pastes produce less H2 under irradiation. Inagreement with a recent study by Kadissy et al. [1], it is shown that the amount of gas produced byportlandite and gibbsite, which are respectively the constitutive hydrates of Portland and Ciment Fondu® cements, strongly depends on the nature of the hydrate. Secondly, portlandite and gibbsite wereirradiated by electrons up to 270 MGy and 3.5 GGy using the LSI SIRIUS accelerator platform. X-RayDiffraction analyses were performed before and after irradiation in order to investigate the structuraldamage. Despite some observed disorder, results show a good structural stability for both hydratesunder irradiation

H2 production under gamma irradiation of a calcium aluminate cement: an experimental study on both cement pastes and its stable hydrates

International audienceThe objective of this paper is to investigate the use of calcium aluminate cements as alternative cements within the context of nuclear waste stabilization by solidification. Using an external 60 Co source, the effect of γ-radiation on H2 gas production of one of the calcium aluminate cement-based materials (cement "Ciment Fondu") and its stable hydrates, was studied. The amount of H2 produced by these cement pastes is found to be much lower (up to five times less) than that of the Portland cement pastes containing the same amount of water, especially in the low range of water to cement ratios (W/C ≤ 0.4) where water is essentially engaged in the hydrates. The H2 production of the two major hydrates of Ciment Fondu, gibbsite AH3 and katoite hydrogarnet C3AH6, is very low compared with that of the main hydrates of other cements (Portland cement, Calcium Sulfo-Aluminate and Magnesium Phosphate cements). The type of water engaged in the hydrates, as hydroxyl groups and/or molecular water, influences significantly the H2 production. Thus, the nature of the hydrate is a key parameter to the aim of optimizing cement matrices with respect to the gas production under irradiation. XRD analysis shows that the crystal structures of gibbsite and katoite are preserved up to very high doses under electron irradiation (3 GGy). This makes calcium aluminate cements (CAC) potential good candidates for nuclear waste conditioning from the point of view of their stability under irradiation

Gallium nitride power devices for power conversion applications

International audienceThis presentation will deal with our work on gallium nitride (GaN) devices for power electronics. The breakdown field of GaN is around 3.3 MV/cm and its mobility can surpass 1000 cm²/V.s, making it an excellent candidate for power switches. The lateral HEMT (High Electron Mobility Transistor) architecture using GaN epitaxy on Silicon is increasingly successful, especially for applications at 650V or below. GaN free-standing wafers are also being used to develop components with a vertical geometry which leads to higher power density due to volume instead of surface conduction.We have developed lateral normally-off GaN-on-Si MOSc-HEMTs (Metal Oxide Semiconductor channel HEMTs). Their advantage comes from the insulated gate technology results in extremely low gate current and a reduced temperature coefficient of its On-resistance, both of which are beneficial for the design of power converters. We will present a full micro inverter using our 100V and 650V MOSc-HEMTs for inclusion on an individual solar panel (DC 45V / AC 230V). The talk will also cover alternative lateral and vertical device architectures that can allow GaN to address new power conversion applications

Gallium nitride power devices for power conversion applications

International audienceThis presentation will deal with our work on gallium nitride (GaN) devices for power electronics. The breakdown field of GaN is around 3.3 MV/cm and its mobility can surpass 1000 cm²/V.s, making it an excellent candidate for power switches. The lateral HEMT (High Electron Mobility Transistor) architecture using GaN epitaxy on Silicon is increasingly successful, especially for applications at 650V or below. GaN free-standing wafers are also being used to develop components with a vertical geometry which leads to higher power density due to volume instead of surface conduction.We have developed lateral normally-off GaN-on-Si MOSc-HEMTs (Metal Oxide Semiconductor channel HEMTs). Their advantage comes from the insulated gate technology results in extremely low gate current and a reduced temperature coefficient of its On-resistance, both of which are beneficial for the design of power converters. We will present a full micro inverter using our 100V and 650V MOSc-HEMTs for inclusion on an individual solar panel (DC 45V / AC 230V). The talk will also cover alternative lateral and vertical device architectures that can allow GaN to address new power conversion applications