Les céramiques transparentes élaborées par cristallisation complète du verre constituent une nouvelle famille de matériaux de qualité photonique en compétition avec la technologie des monocristaux pour les applications optiques. Cette approche verrière offre des avantages considérables par rapport aux monocristaux et aux céramiques polycristallines frittées : un coût réduit, la possibilité d’une production à grande échelle, une large gamme de compositions chimiques accessibles, une mise en forme plus souple et un taux de dopage élevé. Dans le cadre de ce travail, nous avons synthétisé des céramiques polycristallines transparentes de Sr3Al2O6 et Sr3Ga2O6 (structures cubiques) par cristallisation complète du verre de même composition. Les verres d'aluminate de strontium (75SrO-25Al2O3) et de gallate de strontium (75SrO-25Ga2O3) sont élaborés par lévitation aérodynamique couplée à un dispositif de chauffage laser. La transparence de la céramique de Sr3Al2O6 obtenue s’explique par son isotropie optique, ses joints de grains très fins et sa structure totalement dense (non poreuse). Nous avons également développé une nouvelle famille de céramiques transparentes Sr1+x/2Al2+xSi2-xO8 (0<x≤0.4) obtenues par cristallisation complète et congruente du verre. La transmission exceptionnelle de plus de 90% dans la gamme visible et proche infrarouge est expliquée grâce à des études microstructurales et structurales. Cette transparence qui atteint la limite théorique est associée à une biréfringence quasi nulle, des joints de grains très fins et une porosité nulle. Les études par RMN prouvent l'existence d'un désordre chimique qui est à l'origine de la valeur pratiquement nulle de la biréfringence calculée par DFT. Ces matériaux céramiques polycristallins évolutifs et hautement transparents sont des candidats prometteurs pour une large gamme d'applications optiques et photoniques dans les gammes IR et visible. Cette étude a donc conduit à de nouvelles céramiques transparentes, avec des valeurs de transmission jamais atteintes jusqu’à présent pour des oxydes. Elle propose également une nouvelle approche pour l'obtention de céramiques transparentes dans le cas de matériaux anisotropes : introduire un désordre chimique contrôlé au sein du matériau afin d’induire une isotropie optique. Ce concept ouvre la voie à de nouvelles compositions, étendant ainsi le domaine des céramiques transparentes et de leurs applications. / Transparent polycrystalline ceramics elaborated by full crystallization from glass are an emerging class of photonicquality materials competing with single crystal technology, especially for optical applications. This approach provides considerable advantages over single crystals and polycrystalline sintered ceramics represented by cost effectiveness, large scale production, wide range of accessible chemical compositions, easy shaping and high doping level hosting structure. In this work, we show the preparation of transparent cubic Sr3Al2O6 and Sr3Ga2O6 polycrystalline ceramics by full crystallization from the parent strontium aluminate (75SrO-25Al2O3) and strontium gallate (75SrO-25Ga2O3) glasses elaborated by aerodynamic levitation coupled to laser heating system. The transparency of the obtained Sr3Al2O6 ceramics is explained by their optical isotropy, thin grain boundaries and highly dense (non-porous) microstructure. We also show a series of novel Sr1+x/2Al2+xSi2-xO8 (0<x≤0.4) oxide compositions leading to highly transparent and readily scalable polycrystalline ceramics to be obtained by full congruent glass crystallization. The outstanding transparency exceeding 90% in the visible and near IR range is explained through different microstructural and structural (average and local) studies. This transparency, reaching the theoretical limit, is associated to the almost null birefringence, thin grain boundaries and non-porosity. NMR experiments prove the existence of chemical disorder which is at the origin of the relatively zero birefringence value calculated by DFT computations. These scalable and highly transparent polycrystalline ceramic materials are promising candidates for a wide range of optical and photonic applications in the IR and visible ranges. This study besides revealing new ceramic compositions with previously unreported transmission values for micro-scale polycrystalline materials, proposes a new approach for obtaining transparent ceramics in anisotropic materials. This approach consists in inducing a controlled chemical disorder within the material in order to induce optical isotropy. It is anticipated that this proposed concept will open the way to different composition candidates to be elaborated as transparent polycrystalline ceramics, thus extending the ceramic technology domain and its applications.

Les chapes autonivelantes sont souvent composées de ciment alumineux et de sulfate de calcium pour assurer une prise rapide. Le ciment alumineux est généralement à base de monocalcium aluminate (CA). Récemment, un nouveau ciment alumineux riche en mayénite (C12A7) a été conçu pour optimiser l’application des chapes par l’augmentation de la quantité d’ettringite formée. Le développement de l’hydratation au jeune âge (pendant les premières 24 heures) de ce type de produit est pourtant très peu connu. L’objectif principal de cette étude est d’évaluer l’interaction entre l’hydratation au jeune âge et le séchage naturel à travers un modèle de couplage. Ce modèle est appliqué à l’étude d’une pâte pure ettringitique composée de ciment riche en C12A7 et de plâtre alpha. Tout d’abord, un modèle cinétique d’hydratation, initialement développé en système dilué, a été proposé pour étudier l’hydratation d’une pâte pure ettringitique en condition endogène. Il permet de décrire l’évolution en fonction du temps de la porosité, de la teneur en eau, des quantités de phases (réactifs et hydrates). Un modèle de distribution de rayon de pores a été aussi proposé. Ce modèle permet d’obtenir la courbe de pression capillaire au jeune âge nécessaire pour la modélisation des transferts hydriques. Ensuite, une modélisation complète des transferts hydriques a été présentée. Elle a montré que l’hypothèse d’une pression de gaz constante conduit à une surestimation de perte de masse pour des matériaux à faible perméabilité. Pourtant, pour le cas des ciments alumineux, cette hypothèse peut être retenue pour simplifier le couplage avec le modèle cinétique d’hydratation. Enfin, une modélisation des couplages entre l’hydratation et la dessiccation a été développée. L’originalité de ce modèle porte sur l’intégration de la courbe isotherme issue du modèle de distribution poreuse dans la modélisation des transferts hydriques via une fonction Matlab. Le modèle a été capable de reproduire la cinétique de perte de masse d’un échantillon de pâte pure ettringite réactive soumis au séchage précoce. La nécessité de la prise en compte de l’évolution de température a été mise en évidence. De plus, le modèle a prévu un arrêt précoce de l’hydratation à la surface séchante après 10 heures d’hydratation. L’effet de la dessiccation atteint une profondeur de 5 mm sur un échantillon de 3 cm d’épaisseur. / Self-leveling flooring compounds (SLC) are often composed of calcium aluminate cements (CAC) and calcium sulfate to ensure rapid setting. The mineral composition of calcium aluminate cements is usually designed around monocalcium aluminate (CA). Recently, a new cement with the main compound of mayenite (C12A7) has been designed to optimize the application of SLC by increasing the amount of ettringite in the hydration product. However, there is a lack of knowledge related to early-age hydration (during the first 24 hours) of this type of product. The main objective of this study is to evaluate the interaction between early-age hydration and natural drying through a coupling model. This model is applied to the study of an ettringite binder composed of cement rich in C12A7 and plaster First, a kinetic model of hydration, initially developed in a diluted system, has been proposed to study the hydration of an ettringite paste under endogenous conditions. It allows to describe the evolution as a function of time of the porosity, the water content, and the quantities of phases (reactants and hydrates). A model of pore size distribution has also been proposed. This model allows us to obtain the capillary pressure curve at early-age, which is necessary for the modeling of moisture transport. Then, a complete modeling of water transfers was presented. It has shown that the assumption of constant gas pressure leads to an overestimation of mass loss for weakly permeable materials. However, for the case of CAC, this hypothesis can be retained to simplify the coupling with the kinetic model of hydration. Finally, a modeling of the coupling between hydration and desiccation has been developed. The originality of this model concerns the integration of the isothermal curve resulting from the pore size distribution model in the modeling of water transfers via a Matlab function. The model was able to reproduce the kinetics of mass loss of a sample of ettringite binder subjected to early drying. The role of temperature was also elucidated. In addition, the model predicted an early stop of hydration on the drying surface after 10 hours of hydration. The effect of desiccation reaches a depth of 5 mm on a sample with a thickness of 3 cm.

O agregado de trióxido mineral (MTA) tem-se demonstrado aplicável em diversas situações que exigem reparação dos tecidos dentais e periapicais. Contudo, desvantagens relacionadas ao seu elevado custo, propriedades físico-químicas e dificuldade de manuseio têm limitado sua utilização. Neste sentido, um novo cimento de aluminato de cálcio e aditivos (CAC+) foi desenvolvido para superar algumas características negativas do MTA, mantendo, no entanto, suas propriedades satisfatórias. O objetivo deste estudo foi avaliar a progressão de culturas de células osteogênicas e de células indiferenciadas da polpa dental (linhagem OD-21) expostas ao CAC+, utilizando MTA como controle, ou a preparações alternativas do CAC+, com maior conteúdo de cloreto de cálcio (CaCl2) e/ou com substituição do óxido de zinco por óxido de bismuto como radiopacificador. Para isso, células osteogênicas derivadas de calvárias de ratos ou células da linhagem OD-21 foram crescidas sobre Thermanox® por 24 h e expostas, por períodos de até 14 dias, a amostras dos diferentes materiais, posicionadas sobre Transwell®. Em células osteogênicas, apesar de a proximidade com as amostras de CAC+ e MTA inibir o crescimento celular, nas áreas periféricas das lamínulas, foram observados proliferação, viabilidade celular e expressão de marcadores-chave da diferenciação osteoblástica, que precederam a mineralização da matriz extracelular. Culturas expostas ao CAC+, comparativamente ao MTA, exibiram aumentos na viabilidade celular, atividade de fosfatase alcalina e na expressão de marcadores de diferenciação, o que não se repetiu para células OD-21. Além disso, demonstrou-se que os efeitos destes cimentos sobre a osteogênese in vitro variaram de acordo com o período de exposição das culturas, sendo mais favoráveis durante sua fase proliferativa. Entre as preparações de CAC+, verificou-se que o aumento no teor de CaCl2 promoveu maior disponibilização de Ca2+ no meio de cultura, o que correspondeu a maior diferenciação celular e formação de matriz mineralizada em culturas de células osteogênicas e OD-21, e à redução de efeitos negativos da adição de óxido de bismuto sobre osteoblastos. Conclui-se que o CAC+ favorece o desenvolvimento do fenótipo osteogênico, atuando principalmente em células em estágios iniciais de diferenciação e que a adição de CaCl2, independentemente do agente radiopacificador, potencializa os efeitos benéficos sobre células osteogênicas e favorece o desenvolvimento e diferenciação de células indiferenciadas derivadas do tecido pulpar, podendo ser considerado como material alternativo ao MTA. / Mineral trioxide aggregate (MTA) has been successfully applied in endodontic procedures in which dental and periapical tissue repair are required. However, some drawbacks of MTA as high cost, physicochemical properties and difficulty in handling have limited its use. In this context, a novel calcium aluminate cement plus additives (CAC+) has been developed to overcome some negative features of MTA. The aim of this study was to evaluate the progression of either osteogenic cell cultures or undifferentiated dental pulp-derived ones (OD-21 cell line) exposed to CAC+ or to alternative formulations of CAC+ with a higher content of calcium chloride (CaCl2) and/or replacement of zinc oxide by bismuth oxide as radiopacifier agent. Rat calvaria-derived cells or OD-21 cells were grown on Thermanox® coverslips for 24 h and exposed to samples of CAC+ or MTA (control) placed on Transwell® for periods of up to 14 days. In osteogenic cell cultures, the proximity to MTA or CAC+ samples inhibited cell growth, whereas at distance it was observed cell proliferation, cell viability and expression of differentition markers prior to mineralization of the extracellular matrix. Comparatively to MTA, osteogenic cell cultures exposed to CAC+ exhibited higher cell viability, alkaline phosphatase activity and expression of key osteoblast markers, contrary to what was observed for OD-21 cells. Furthermore, it was demonstrated that the effects of these cements on in vitro osteogenesis varied according to the timing of exposure, with a more favorable impact during the proliferative phase of cultures. Among the diverse formulations of CAC+, it was found that the increase in the CaCl2 content promoted greater availability of Ca2+ in the culture medium, which corresponded to higher cell differentiation and mineralized matrix formation in osteoblastic cell cultures and OD-21 cells, while reducing the negative effects of bismuth oxide on osteoblasts. In conclusion, CAC+ supported the acquisition of the osteogenic cell phenotype, mostly for cells in early stages of differentiation. Additionaly, the increase in the CaCl2 content, regardless of the radiopacifier agent, potentiates the beneficial effects on osteogenic cells and promotes the growth and differentiation of OD-21 cells, rendering CAC+ a potential alternative material to replace MTA in endodontic procedures.

Contact mechanical study of layered structures is useful to various fields of engineering, such as - mechanical engineering, civil engineering, materials engineering and biomechanics. Thin hard film coating on a compliant substrate used in cutting tool industry is an example of a layered structure. The protective coating saves the substrate from fracture and wear. However, due to film material brittleness, fracture in the films is of concern. We have developed an analytical model for a film-substrate bilayer system under normal contact loading, which helps us to obtain the stress distribution in the film and fracture behaviour. Our contact model is based on Hankel’s Transform technique, where we assume a Hertzian pressure boundary condition. At each depth of penetration of the indenter in the film-substrate system, we estimate effective modulus of the system based on Gao’s approach. We have validated our analysis by surface strain measurements and photoelastic stress study in the film on a substrate. Experimental observations from literatures show the dependence of different fracture modes in a thin hard film with columnar structure on film thickness and substrate plasticity. We perform fracture analysis, a parametric study of the fracture modes in the film under contact loading. When the film thickness is small and the substrate is relatively hard (e.g. tool steel), the film and the substrate deform conformally under contact loading and the columns of TiN slide against each other into the substrate. On the other hand, when the film is thicker and the substrate is soft (e.g. mild steel or aluminium), the strain mismatch between the film and substrate acts as an added traction at the interface and drives cracks, such as radial tensile stress driven bending cracks that start from the interface at the center of indentation; maximum shear stress driven inclined shear crack that starts inside the film and propagate at an angle to the indentation axis and tensile stress driven edge crack that starts from the free surface outside the contact. We can draw a fracture map based on these calculations which provides a guide to select film thickness depending on the substrate hardness, so that the benign mode of damage, i.e., columnar shear occurs in the film. Apart from generating the fracture map, we can obtain rationale for different fracture phenomenon in the film by studying the indentation stress field. Principal tensile stresses, responsible for driving edge cracks from the free surface outside the contact, become compressive as one approaches the substrate if the substrate is compliant. The cracks therefore do not penetrate deep into the film rather curve away from the axis of indentation. At the transition zone from one mode of damage to other in the fracture map, different modes of fracture may co-exist. The whole column may not shear, rather the shear can start from somewhere in the middle of the film, where the shear stress is maximum and it can end without reaching the interface. The indentation energy is then dissipated in other forms of damage. The contact analysis is further applied to TiN /AlTiN multilayered films having similar elastic properties. Experimental observations suggest that with decreasing layer thickness the fracture resistance of the multilayers increase and some plastic yielding occurs at the top layers of the film. However no substantial change in strain capacity (Hardness/ Young’s Modulus) of the film is observed. Hence we attribute the increase of fracture resistance of multilayers to film plasticity and mimic it by reducing the modulus of the film. The analysis validates the propensity of edge cracking and transgranular cracking as they decrease with increasing number of layers in a multilayer. We next extend our bilayer analysis to a more general trilayer problem where the moduli of the layers vary by several orders. The test system here is a mica-glue-glass system which is used in surface force apparatus experiments. Gao’s trilayer analysis is used to fit the experimental data obtained from surface force apparatus experiments, where a glass sphere indents the trilayer. The parallel spring model used in Gao’s approximation is found to be inadequate to rationalize the experimental data. We have modified Gao’s formulations by reducing the problem to a bilayer problem where the layers are the first layer (in contact) and an equivalent layer which has properties determined by a rule of mixture of the properties of all the layers excluding the top layer set out as a set of springs in series. The modified formulations give a better fit to the experimental data and it is validated from nanoindentation experiments on the same system. The formulation is used to obtain the compression of the glue, which contributes significantly to the deformation of the trilayer system in the SFA experiments. Thus, the analysis can be used to deconvolute the influence of glue in the actual mechanical response of the system in an SFA experiment, which has so far been neglected.

L'objet de ce travail était l'étude de l'oxydation d'un alliage aluminium-5% magnésium à l'état liquide sous oxygène, par analyse thermogravimétrique, en s'appuyant sur celle du magnésium à l'état solide. Dans la plupart des cas, la vitesse absolue d'une réaction est proportionnelle au produit de la réactivité de croissance et de la fonction d'espace caractérisant les dimensions des zones réactionnelles mises en jeu dans le mécanisme de croissance. Nous avons vérifié que c'est le cas de la réaction étudiée ici c'est-à-dire la formation de l'oxyde de magnésium. Les mécanismes de formation de la magnésie dépendent de la pression partielle d'oxygène fixée dans l'enceinte réactionnelle, l'allure des courbes cinétiques ainsi que les morphologies des oxydes formés étant très différentes selon la pression d'oxygène. Sous de faibles pressions partielles, la réaction a lieu en phase gaz après évaporation du magnésium. Dans le cas de l'alliage, un mécanisme de formation de l'oxyde en phase gaz a été proposé. Ce modèle permet de rendre compte de l'influence de la pression partielle sur la vitesse de formation par unité de surface d'évaporation de la magnésie. Dans le domaine de fortes pressions d'oxygène et pour le magnésium solide, une modélisation physico-chimique décrivant les mécanismes de croissance de la magnésie et prévoyant l'évolution au cours du temps de la fonction d'espace a été proposée et validée par confrontation aux résultats expérimentaux. Dans le cas de l'alliage, les courbes cinétiques obtenues dans des conditions isothermes et isobares se sont révélées non reproductibles. Une méthodologie d'étude, basée sur l'utilisation de la méthode des décrochements, a rendu possible la modélisation de la croissance de l'oxyde. En effet, cette méthode a permis de déterminer l'origine de la non reproductibilité des courbes cinétiques, à savoir l'évolution aléatoire de la fonction d'espace, et d'obtenir les variations de la réactivité de croissance avec la pression d'oxygène. En nous appuyant sur la modélisation proposée pour le magnésium, nous avons proposé un modèle physico-chimique décrivant les mécanismes de croissance de l'oxyde et rendant compte de l'influence de la pression d'oxygène

Made available in DSpace on 2014-12-17T14:07:05Z (GMT). No. of bitstreams: 1 YaraFG_DISSERT.pdf: 4146827 bytes, checksum: 3586f66a1b391a184d1b6034e91b85c0 (MD5) Previous issue date: 2012-12-20 / In the ceramics industry are becoming more predominantly inorganic nature pigments. Studies in this area allow you to develop pigments with more advanced properties and qualities to be used in the industrial context. Studies on synthesis and characterization of cobalt aluminate has been widely researched, cobalt aluminate behavior at different temperatures of calcinations, highlighting especially the temperatures of 700, 800 and 900? C that served as a basis in the development of this study, using the method of polymerization of complex (CPM), economic, and this method applied in ceramic pigment synthesis. The procedure was developed from a fractional factorial design 2 (5-2) in order to optimize the process of realization of the cobalt aluminate (CoAl2O4), having as response surfaces the batch analysis data of Uv-vis spectroscopy conducted from the statistic software 7.0, for this were chosen five factors as input variables: citric acid (stoichiometric manner), puff or pyrolysis time (h), temperature (? C), and calcinations (? C/min), at levels determined for this study. By applying statistics in the process of obtaining the CoAl2O4 is possible the study of these factors and which may have greater influence in getting the synthesis. The pigments characterized TG/DSC analyses, and x-ray diffraction (XRD) and scanning electron microscope (SEM/EDS) in order to establish the structural and morphological aspects of pigment CoAl2O4, among the factors studied it were found to statically with increasing calcinations temperature 700?< 800 <900 ?C, the bands of Uv-vis decrease with increasing intensity of absorbance and that with increasing time of puff or pyrolysis (h) there is an increase in bands of Uv-vis proportionally, the generated model set for the conditions proposed in this study because the coefficient of determination can explain about 99.9% of the variance (R?), response surfaces generated were satisfactory, so it s possible applicability in the ceramics industry of pigments / Na ind?stria cer?mica utilizam-se cada vez mais pigmentos de natureza predominantemente inorg?nica. Os estudos nessa ?rea permitem desenvolver pigmentos com qualidades e propriedades mais avan?adas para serem empregados em ?mbito industrial. Estudos de s?ntese e caracteriza??o do aluminato de cobalto t?m sido amplamente pesquisados, o comportamento do aluminato de cobalto em diferentes temperaturas de calcina??es, destacando principalmente as temperaturas de 700, 800 e 900?C utilizando o m?todo de polimeriza??o de complexos (MPC), m?todo este, econ?mico e aplicado em s?ntese de pigmentos cer?micos. O procedimento foi desenvolvido a partir de um planejamento fatorial fracionado 2(5-2) com o objetivo de otimizar o processo de realiza??o do aluminato de cobalto (CoAl2O4), tendo como superf?cies de respostas os dados da an?lise de espectroscopia do Uv-vis realizados a partir do software statistic 7.0, para isso, foram escolhidos cinco fatores como vari?veis de entrada: concentra??es de ?cido c?trico (de maneira estequiom?trica), tempo de puff ou pir?lise (h), temperatura (?C), tempo e taxas de calcina??es(?C/min), em patamares determinados para este estudo. Atrav?s da aplica??o estat?stica no processo de obten??o do CoAl2O4 foi poss?vel estudar entre estes fatores quais possam ter maior influ?ncia na obten??o da s?ntese. Os p?s-precursores foram caracterizados pelas an?lises termogravim?tricas TG/DSC, e os p?s-calcinados (pigmentantes) foram analisados pela difra??o de raios- x (DRX) e microscopia eletr?nica de varredura com energia dispersiva (MEV/EDS) a fim de comprovar os aspectos estruturais e morfol?gicos do CoAl2O4, entre os fatores estudados estaticamente verificou-se que com o aumento da temperatura de calcina??o 700<800<900?C, as bandas do Uv-vis diminuem com o aumento da intensidade da absorb?ncia e que com o aumento do tempo de puff ou pir?lise (h) h? um aumento das bandas do Uv-vis proporcionalmente, o modelo gerado ajustou-se para as condi??es propostas neste estudo, pois o coeficiente de determina??o consegue explicar cerca de 99,9%, da vari?ncia (R?), as superf?cies de respostas geradas foram satisfat?rias, sendo assim sua poss?vel aplicabilidade na ind?stria cer?mica de pigmentos

L'industrie nucléaire est une industrie génératrice de déchets, dont certains sont radioactifs. Ces déchets radioactifs ont des formes et des origines diverses, allant de la paire de gant de manutention faiblement contaminés, à la suspension aqueuse de produits de fissions hautement radioactifs. Dans ce travail, un type de déchet bien particulier a été étudié ; des boues issues de la décontamination d'effluents liquides radioactifs, possédant entre autres les trois particularités suivantes ; * Etre moyennement radioactif, selon les critères de l'ANDRA. * Etre composé d'une forte teneur en eau de constitution (ne pouvant être retirée par simple évaporation) ; * Etre composé d'un sorbant (PPFeNi) dont la stabilité chimique n'est pas assurée pour un pH supérieur à 11. Ces particularités font qu'un enrobage dans une matrice minérale forte consommatrice d'eau, et bas-pH (pH < 11) est envisageable. Le choix c'est alors porté sur le développement d'une matrice ettringitique réalisée à partir d'un mélange de Ciment d'Aluminate de Calcium (CAC) et de sulfate de calcium. Dans un premier temps, la stabilité du sorbant du césium utilisé dans cette étude a été testée dans différents environnements de pH (2 à 14) et de température. Pour cela des analyses chimiques de solution ainsi que des caractérisations du composé par diffraction de rayons X, FTIR et microscopie électronique à balayage-EDS ont permis de fixer les bornes de stabilité que la formulation ettringitique doit avoir. Puis une étude microstructurale (nature et morphologie des produits) de mélanges ettringitiques binaires CAC/sulfate de calcium type hémihydrate et/ou anhydrite a été effectuée afin de caractériser la stabilité de l'ettringite, hydrate fort consommateur d'eau. Les propriétés bas-pH ont été vérifiées notamment par analyse chimique de solutions porales. Certaines limites de ces systèmes concernant le dégagement de chaleur et la possible formation de systèmes expansifs ont été mises en évidence. L'effet de l'augmentation du rapport eau/liant, responsable d'un effet de dilution et permettant de réduire les deux effets précédents, a été également regardé pour ces systèmes binaires. Afin de réduire la chaleur dégagée à court terme tout en permettant le développement de l'hydratation à long terme de systèmes ettringitiques, ces systèmes binaires ont été substitués par des additions minérales à hydraulicité latente type laitier de haut fourneau. Une étude microstructurale de la réactivité du laitier et de la modification de l'assemblage ettringitique a montré une réactivité modérée de ce dernier à jeune âge conformément aux attentes. Pour favoriser sa réactivité à long terme par activation alcaline/sulfatique différentes proportions de sulfate de calcium à dissolution plus lente ont été testés. Les caractéristiques microstructurales de ces systèmes ternaires en présence de différentes teneurs en eau intrinsèquement liée à la nature de type boue du déchet a été étudiée. Enfin, les différentes informations sur l'effet des paramètres de formulation obtenues ont débouché sur la mise en place de tests sur des formulations contenant un déchet simulé inerte et enrichi en chlorures. Des essais systématiques de fluidité, de résistances mécaniques et pour certains d'entre eux d'expansion et de dégagement de chaleur doivent permettre d'identifier une série de mélanges adaptés au test à l'échelle de prototype industriel pour la cimentation de boues. / Nuclear industry generated waste including radioactive wastes, which have different forms and origins. The wastes produced by reprocessing of nuclear fuel are characterized by important water content, by high pH and temperature sensitivity. The cementation in ettringite systems might be a promising solution to solidify radioactive wastes. Mixtures of Calcium Aluminate Cement (CAC) and calcium sulfate are planned to be used, instead of Ordinary Portland Cement (OPC), to form a significant amount of ettringite able to catch water molecules when forming. Moreover, due to the low pH of CAC-based matrices, the latter have a good compatibility with the compounds used to stabilize active elements. Initially, the stability of the sorbent of cesium used in this study was tested in different pH environments (2 to 14) and temperature. Chemical analysis and different microstructural characterizations like X-ray diffraction, FTIR and SEM-EDS have allowed to set stability limits of ettringite systems. Then microstructural study on binary systems composed by mixture of CAC/calcium sulfate (hemihydrate and/or anhydrite) was realized to characterize ettringite stability during the time of hydration. Low pH properties were checked by chemical pore solutions analysis. However, the heat generated by hydration and the possible formation of expansive systems require an increase of e/s ratio and additional components like Ground Granulated Furnace Slag (GGBS). These two parameters were studied subsequently. Microstructural study of GGBS reactivity and the modification of ettringite assemblage were showed that GGBS act as filler at early time of hydration. To promote the GGBS reactivity at long term of hydration by alkaline and sulfate activation, different nature of calcium sulfate was used. Then the microstructural characteristic of this ternary system in presence of different e/s ratio was studied. Finally, different information on the effect of formulation parameters obtained led to the development of tests on formulations containing an inert simulated waste and enriched in chlorides. Systematic tests of fluidity, mechanical strength and for some expansion and heat generation should identify a series of mixtures adapted to test prototype to industrial scale for cementing wastes.

O agregado de trióxido mineral (MTA) tem-se demonstrado aplicável em diversas situações que exigem reparação dos tecidos dentais e periapicais. Contudo, desvantagens relacionadas ao seu elevado custo, propriedades físico-químicas e dificuldade de manuseio têm limitado sua utilização. Neste sentido, um novo cimento de aluminato de cálcio e aditivos (CAC+) foi desenvolvido para superar algumas características negativas do MTA, mantendo, no entanto, suas propriedades satisfatórias. O objetivo deste estudo foi avaliar a progressão de culturas de células osteogênicas e de células indiferenciadas da polpa dental (linhagem OD-21) expostas ao CAC+, utilizando MTA como controle, ou a preparações alternativas do CAC+, com maior conteúdo de cloreto de cálcio (CaCl2) e/ou com substituição do óxido de zinco por óxido de bismuto como radiopacificador. Para isso, células osteogênicas derivadas de calvárias de ratos ou células da linhagem OD-21 foram crescidas sobre Thermanox® por 24 h e expostas, por períodos de até 14 dias, a amostras dos diferentes materiais, posicionadas sobre Transwell®. Em células osteogênicas, apesar de a proximidade com as amostras de CAC+ e MTA inibir o crescimento celular, nas áreas periféricas das lamínulas, foram observados proliferação, viabilidade celular e expressão de marcadores-chave da diferenciação osteoblástica, que precederam a mineralização da matriz extracelular. Culturas expostas ao CAC+, comparativamente ao MTA, exibiram aumentos na viabilidade celular, atividade de fosfatase alcalina e na expressão de marcadores de diferenciação, o que não se repetiu para células OD-21. Além disso, demonstrou-se que os efeitos destes cimentos sobre a osteogênese in vitro variaram de acordo com o período de exposição das culturas, sendo mais favoráveis durante sua fase proliferativa. Entre as preparações de CAC+, verificou-se que o aumento no teor de CaCl2 promoveu maior disponibilização de Ca2+ no meio de cultura, o que correspondeu a maior diferenciação celular e formação de matriz mineralizada em culturas de células osteogênicas e OD-21, e à redução de efeitos negativos da adição de óxido de bismuto sobre osteoblastos. Conclui-se que o CAC+ favorece o desenvolvimento do fenótipo osteogênico, atuando principalmente em células em estágios iniciais de diferenciação e que a adição de CaCl2, independentemente do agente radiopacificador, potencializa os efeitos benéficos sobre células osteogênicas e favorece o desenvolvimento e diferenciação de células indiferenciadas derivadas do tecido pulpar, podendo ser considerado como material alternativo ao MTA. / Mineral trioxide aggregate (MTA) has been successfully applied in endodontic procedures in which dental and periapical tissue repair are required. However, some drawbacks of MTA as high cost, physicochemical properties and difficulty in handling have limited its use. In this context, a novel calcium aluminate cement plus additives (CAC+) has been developed to overcome some negative features of MTA. The aim of this study was to evaluate the progression of either osteogenic cell cultures or undifferentiated dental pulp-derived ones (OD-21 cell line) exposed to CAC+ or to alternative formulations of CAC+ with a higher content of calcium chloride (CaCl2) and/or replacement of zinc oxide by bismuth oxide as radiopacifier agent. Rat calvaria-derived cells or OD-21 cells were grown on Thermanox® coverslips for 24 h and exposed to samples of CAC+ or MTA (control) placed on Transwell® for periods of up to 14 days. In osteogenic cell cultures, the proximity to MTA or CAC+ samples inhibited cell growth, whereas at distance it was observed cell proliferation, cell viability and expression of differentition markers prior to mineralization of the extracellular matrix. Comparatively to MTA, osteogenic cell cultures exposed to CAC+ exhibited higher cell viability, alkaline phosphatase activity and expression of key osteoblast markers, contrary to what was observed for OD-21 cells. Furthermore, it was demonstrated that the effects of these cements on in vitro osteogenesis varied according to the timing of exposure, with a more favorable impact during the proliferative phase of cultures. Among the diverse formulations of CAC+, it was found that the increase in the CaCl2 content promoted greater availability of Ca2+ in the culture medium, which corresponded to higher cell differentiation and mineralized matrix formation in osteoblastic cell cultures and OD-21 cells, while reducing the negative effects of bismuth oxide on osteoblasts. In conclusion, CAC+ supported the acquisition of the osteogenic cell phenotype, mostly for cells in early stages of differentiation. Additionaly, the increase in the CaCl2 content, regardless of the radiopacifier agent, potentiates the beneficial effects on osteogenic cells and promotes the growth and differentiation of OD-21 cells, rendering CAC+ a potential alternative material to replace MTA in endodontic procedures.

L’étude menée s’attache à évaluer le potentiel d’activation du laitier de haut fourneau dans un liant ternaire constitué de ciment alumineux, de sulfate de calcium et de laitier. Dans ce système ternaire, le constituant majoritaire est le sulfate de calcium. Le potentiel d’un tel système n’est pas encore connu mais cette étude vise à renseigner sur les principaux avantages et limites d’utilisation. D’un point de vue des propriétés d’usage de ce liant, la prise, le durcissement rapide et la montée des résistances sont assurés par le liant ettringitique. Ensuite, et uniquement si la dessiccation est évitée, le laitier de haut fourneau réagit et dans ce cas, l’apport du laitier dans de tels systèmes est double. Il contribue à l’augmentation des performances mécaniques à moyen et long terme et à limiter l’expansion sous eau. D’un point de vue de la compréhension des mécanismes d’hydratation, une démarche expérimentale originale est mise en place et dévoile le potentiel du laitier. Elle est basée sur la comparaison des performances obtenues avec différentes cures. Le potentiel d’hydratation du laitier est amplifié lorsque le système subit un séchage puis une réhydratation. Cependant, les techniques utilisées (diffraction des rayons X et calorimétrie différentielle à balayage) ne sont pas adaptées au suivi et à la quantification de laitier consommé. Ainsi, la compréhension de l’hydratation s’appuie sur des techniques dites indirectes. Une semi-quantification par diffraction des rayons X est réalisée pour le suivi et l’évaluation de la mayénite, le sulfate de calcium (anhydre ou dihydraté), la syngénite et l’ettringite, l’analyse thermogravimétrique permet de mesurer le degré d’hydratation du système, et la porosimétrie mercure informe sur les changements microstructuraux. La plus grosse difficulté dans ces travaux a porté sur le suivi et la quantification des phases amorphes (anhydres ou hydratées), telles que le laitier, les gels de C-S-H et d’AH3, et c’est pour cette raison qu’une approche par modélisation a été mise en place afin d’identifier le rôle de chaque constituant du système ternaire [Ciment Alumineux – Sulfate de Calcium – Laitier] et particulièrement du laitier lors de l’essai de réhydratation. L’approche par modélisation permet de mieux identifier les phénomènes chimiques et physiques ayant lieu lors de l’hydratation du liant. Elle est utilisée pour expliquer les observations macroscopiques (comme les performances mécaniques) et aide à déterminer les cinétique d’hydratation dans le milieu poreux. Le modèle utilisé n’est pas encore parfaitement au point mais il a permis d’identifier les différentes séquences d’hydratation (à savoir que le liant ettringitique réagit dans les premiers instants et qu’ensuite, l’hydratation de l’anhydrite entraine la formation de gypse et l’hydratation du laitier est effective à long terme) et de confirmer que la réaction du laitier est lente. / The potential of activation of a Ground Granulated Blast Furnace Slag has been evaluated into a ternary system comprising of a Calcium Sulfate as major component and a Calcium Aluminate Cement. This system is not well known and the main goal of this study is to determine its main advantages and limitations. From the usage properties point of view, fast setting and initial strengths are governed by the ettringitic binder. Then, and only if the dehydration is avoided, slag reacts. In this case, slag contributes to the increase of mechanical performances at medium and long terms and to limit the expansion under water. From an understanding point of view, the original experimental approach reveals the potential of the slag. It is based on a comparison of performances with different types of curing methods. The potential of hydration of the slag is amplified when the system is dehydrated during a few days and then rehydrated. However, slag contribution is complex to establish because analytical methods to follow-up slag consumption (such as X-ray Diffraction and Differential Scanning Calorimetry analysis) are not well adapted. So, to understand the hydration mechanisms, indirect approaches are used. Semi-quantitative methods by X-ray Diffraction to follow-up the mayenite, calcium sulfate, syngenite and ettringite, ThermoGravimetric Analysis to measure degree of hydration and Mercury Intrusion Porosimetry to identify microstructural changes have been carried. The most important difficulty concerns the identification and quantification of amorphous phases such as slag, C-S-H and AH3. That is why a modelling approach is necessary to understand the role of each compound in the ternary mixture and in particular the obvious contribution of slag during rehydration test. This modelling approach increases knowledge of the physical and chemical phenomena in this ternary binder. It is useful to explain the observed macroscopic properties such as strength and helps to determine the kinetics of hydration in porous environment. Even if this model is still under development, it has allowed identifying the sequences of hydration (ettringitic binder reacts at very initial time, then anhydrite transforms into gypsum and slag reacts at long term) and confirms therefore that the reaction of slag is slow.

In theory, this work is devoted to the principles and methods of measurement of volume changes of mortars and concretes. Emphasis is placed on cement self-levelling screeds with initial shrinkage compensation. In the practical part of the work is devoted to the development of prototype measuring system designed for non-contact detection of volume changes hydrating silicate. Using the new measurement method is also practically examined the influence of boundary conditions on hydration volume changes of selected silicate binders, cement mortar and cement levelling compound based on four different connective concepts. In the calculation, this work focuses on the numerical modelling of volume changes of the examined compounds.