1,721,004 research outputs found
Modélisation chemo-mécanique du béton bas-ph : application au calcul des structures de stockage des déchets radioactifs
Full text linkThe purpose of this work concerns to design a tool able to simulate the chemo-mechanical behavior of low-pH concretes used in radioactive waste storage, from early age to a long-term. This tool consists of a phenomenological hydration model and an original chemical evolution model. The first model is used for short-term. It can predict the development of hydration at early age and its consequences. But taking into account that this model has been developed for applications at a young age, it is based on a fixed stoichiometry of hydrates and does not take into account the specificities of low-pHcements (chemical evolution at the long-term by reaction of residual silica). Thus, a chemical evolution model at the long-term is proposed. This model is based on a variable stoichiometry of hydrates. For this, it uses the calcium mass balance for describing calcium exchange between the various hydrates and anhydrous. This equation includes the kinetics of exchanges which are based on the difference in the thermodynamic equilibrium, of the microstructure and temperature. Finally, a coupling with mechanical properties evolution was performed to simulate the mechanical behavior of the radioactive waste storage facility.L’objectif de ce travail de thèse était de concevoir un outil capable de simuler le comportement chemo-mécanique des bétons bas-pH employés dans les structures de stockage des déchets radioactifs, du jeune âge à très long-terme. Cet outil est constitué d’un modèle d’hydratation phénoménologique et d’un modèle d’évolution chimique original. Le premier modèle est utilisé à court-terme. Il permet de prédire le développement de l’hydratation au jeune âge et ses conséquences. Mais compte-tenu que ce modèle a été développé pour des applications au jeune âge, il est basé sur une stoechiométrie fixe des hydrates créés et ne permet pas de prendre en compte les spécificités des liants bas-pH (évolution chimique à long-terme par réaction de la silice résiduelle). Ainsi, un modèle d’évolution chimique adapté pour prédire l’évolution chimique à long-terme est proposé. Ce modèle « long-terme » est basé sur une stoechiométrie évolutive des hydrates. Pour cela, il utilise l’équation de conservation de la masse calcium, qui permet de décrire les échanges de calcium entre les différents hydrates et anhydres. Cette équation intègre les cinétiques d’échanges qui sont fonction de l’écart à l’équilibre thermodynamique, de la microstructure et de la température. Enfin, un couplage de l’évolution chimique et l’évolution des propriétés mécanique a été effectué dans le but de simuler le comportement mécanique de la structure de stockage des déchets radioactifs
Modélisation chemo-mécanique du béton bas-ph : application au calcul des structures de stockage des déchets radioactifs
No full textThe purpose of this work concerns to design a tool able to simulate the chemo-mechanical behavior of low-pH concretes used in radioactive waste storage, from early age to a long-term. This tool consists of a phenomenological hydration model and an original chemical evolution model. The first model is used for short-term. It can predict the development of hydration at early age and its consequences. But taking into account that this model has been developed for applications at a young age, it is based on a fixed stoichiometry of hydrates and does not take into account the specificities of low-pHcements (chemical evolution at the long-term by reaction of residual silica). Thus, a chemical evolution model at the long-term is proposed. This model is based on a variable stoichiometry of hydrates. For this, it uses the calcium mass balance for describing calcium exchange between the various hydrates and anhydrous. This equation includes the kinetics of exchanges which are based on the difference in the thermodynamic equilibrium, of the microstructure and temperature. Finally, a coupling with mechanical properties evolution was performed to simulate the mechanical behavior of the radioactive waste storage facility.L’objectif de ce travail de thèse était de concevoir un outil capable de simuler le comportement chemo-mécanique des bétons bas-pH employés dans les structures de stockage des déchets radioactifs, du jeune âge à très long-terme. Cet outil est constitué d’un modèle d’hydratation phénoménologique et d’un modèle d’évolution chimique original. Le premier modèle est utilisé à court-terme. Il permet de prédire le développement de l’hydratation au jeune âge et ses conséquences. Mais compte-tenu que ce modèle a été développé pour des applications au jeune âge, il est basé sur une stoechiométrie fixe des hydrates créés et ne permet pas de prendre en compte les spécificités des liants bas-pH (évolution chimique à long-terme par réaction de la silice résiduelle). Ainsi, un modèle d’évolution chimique adapté pour prédire l’évolution chimique à long-terme est proposé. Ce modèle « long-terme » est basé sur une stoechiométrie évolutive des hydrates. Pour cela, il utilise l’équation de conservation de la masse calcium, qui permet de décrire les échanges de calcium entre les différents hydrates et anhydres. Cette équation intègre les cinétiques d’échanges qui sont fonction de l’écart à l’équilibre thermodynamique, de la microstructure et de la température. Enfin, un couplage de l’évolution chimique et l’évolution des propriétés mécanique a été effectué dans le but de simuler le comportement mécanique de la structure de stockage des déchets radioactifs
Potential Correlation between Yield Stress and Bleeding
No full textInternational audienceSince both the yield stress and bleeding originate from the network of interacting cement particles, their correlation seems to be possible. The purpose of this paper is to investigate the existence of this correlation by varying solid volume fraction of cement paste. The static yield stress measurements were carried out using a traditional rheological test, and bleeding was determined by turbidimetry measurements. It appears that the correlation between yield stress and bleeding depends strongly on the solid volume fraction
Potential Correlation between Yield Stress and Bleeding
No full textInternational audienceSince both the yield stress and bleeding originate from the network of interacting cement particles, their correlation seems to be possible. The purpose of this paper is to investigate the existence of this correlation by varying solid volume fraction of cement paste. The static yield stress measurements were carried out using a traditional rheological test, and bleeding was determined by turbidimetry measurements. It appears that the correlation between yield stress and bleeding depends strongly on the solid volume fraction
The Effect of Temperature on the Structural Build-Up of Cement Pastes
No full textInternational audienceThe structural build-up of cementitious materials is the subject of more and more attention since it conditions several processes such as formwork pressure and multi-layer casting. However, this phenomenon originating from flocculation and chemical changes is complex and its reversibility is not clearly elucidated. The aim of this paper is to examine the effect of temperature on the reversibility of structural build-up. The results show that irreversible structural build-up remains negligible despite a rise in temperature. It represents between 0.5–7.3% of the total structural build-up. The addition of SCMs allows for a decrease in this irreversible structural build-up. Therefore, a large part of the chemical contribution is expected to be reversible. The effect of temperature can be explained by the increase in the dissolution rate leading to an increase in flocculation and to the bridging effect induced by early hydrates. Finally, the results suggest that the interparticle distance could be the key parameter governing the irreversibility of structural build-up
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Rheological Behavior of Cement Paste: A Phenomenological State of the Art
No full textInternational audienceWith the interest aroused by the development of modern concretes such as printable or self-compacting concretes, a better understanding of the rheological behavior, directly linked to fresh state properties, seems essential. This paper aims to provide a phenomenological description of the rheological behavior of cement paste. The first part is devoted to the most common testing procedures that can be performed to characterize the rheological properties of cement suspensions. The second one deals with the complexities of the rheological behavior of cement paste including the non-linearity of flow behavior, the viscoelasticity and yielding, and the structural build-up over time
Effect of Supplementary Cementitious Materials (SCMs) on the Structural Build-Up of Cement Pastes
No full textInternational audienceThe comprehension of the effect of supplementary cementitious materials (SCMs) on the structural build-up is of great interest, especially for the development of modern concretes. The structural build-up of fresh cement paste describes the evolution of rheological properties with resting time and can be related to the loss of workability. It originates from particle flocculation and chemical changes and is mainly affected by the inter-particle distance and the nucleation of hydrates. The effect of SCMs on this structural build-up is complex and depends on several factors. This study aims to examine the effect of SCMs (fly ash, slag, limestone filler, and metakaolin) on the reversibility of the structural build-up of cement paste. It appears that the addition of slag, fly ash, or metakaolin leads to a decrease in the structural build-up with a negligible irreversible part, while cement paste with limestone filler (LF) exhibits the same trend as Portland cement paste. In addition, it appears that the reversibility of the structural build-up would not depend solely on chemical change
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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