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Durabilité des matériaux cimentaires bas carbone soumis à des phénomènes de dégradation simples et couplés
No full textThe durability of cementitious materials in harsh environments is an important consideration for sustainable construction, especially as the cement industry shifts to low-carbon alternatives. This thesis investigates the resistance of various low-carbon binders, ranging from blended cements to geopolymers, up to key degradation mechanisms such as those due to external sulfate attack, chloride bonding capacity, coupled sulfate-chloride interactions, and other durability issues. A comprehensive experimental program, conducted at the paste scale, was developed to investigate the chemical and microstructural evolution of these materials, linking their composition and curing practices to long-term performance. The first phase of the study assessed the sulfate resistance of blended cementitious materials that included supplementary cementitious materials like blast furnace slag, fly ash, and metakaolin. The study revealed that some of these supplementary cementitious materials significantly improve sulfate resistance by reducing available calcium hydroxide and refining pore structure. Based on these findings, four optimized mixes were chosen for further investigation: a reference CEM I, one binary, one ternary, and one quaternary blend. The second phase of the study investigated the combined effects of sulfate and chloride ions, a common degradation process in marine and harsh environments. Findings revealed a complex interaction: chloride delayed ettringite formation, whereas sulfate destabilized Friedel's salt, allowing chloride ingress. These findings highlighted the need to account for multi-factorial degradation processes when conducting durability assessments. The third phase of the study investigated the role of curing duration in cementitious materials' resistance to coupled sulfate-chloride attack. Extended curing improved chloride binding and overall hydration, but it also exacerbated the production of sulfate-induced expensive products, emphasizing curing's dual role in long-term durability. This study challenged the widely held belief that longer curing times always improve performance, emphasizing the importance of optimizing curing protocols based on environmental exposure conditions. The final phase of the study focused on geopolymers as an alternative low-carbon binder, comparing their durability to standardized low-carbon cement (CEM III). This study examined ambient-cured geopolymers without heat or nanomaterials to determine their viability in practical construction applications. Results confirmed their superiority in carbonation, sulfate, and acid resistance due to their calcium-free composition, but their limitations in chloride binding capacity and freeze-thaw resistance.Overall, this thesis provides a comprehensive framework for understanding the durability of some low-carbon cementitious materials in harsh environments. The findings underscore the importance of mix design, curing strategies, and exposure-specific assessments in optimizing the material performance. Furthermore, the study emphasizes the need to move from cement paste-scale studies to mortar and concrete applications to ensure real-world structural applicability. The findings contribute to the development of more sustainable and durable infrastructure, as well as advance scientific understanding of degradation mechanisms in novel cementitious systemsLa durabilité des matériaux cimentaires dans des environnements agressifs est une considération essentielle pour la construction durable, en particulier à mesure que l'industrie du ciment évolue vers des alternatives à faible empreinte carbone. Cette thèse explore la résistance de divers liants à faible teneur en carbone, allant des ciments composés aux géopolymères, face aux principaux mécanismes de dégradation tels que l'attaque sulfatique externe, la fixation des chlorures, les interactions couplées sulfate-chlorure, ainsi que d'autres problématiques de durabilité. Un programme expérimental mené à l’échelle de la pâte a été mis en place pour étudier l'évolution chimique et microstructurale de ces matériaux, en établissant des liens entre leur composition, leurs conditions de cure et leur performance à long terme. La première phase a évalué la résistance aux sulfates des matériaux cimentaires intégrant des ajouts tels que le laitier de haut-fourneau, les cendres volantes et le métakaolin. Les résultats ont montré que ces ajouts améliorent la résistance aux sulfates en réduisant la quantité d'hydroxyde de calcium disponible et en raffinant la microstructure. Quatre formulations ont alors été sélectionnées pour une analyse approfondie : un ciment CEM I, un liant binaire, un ternaire et un quaternaire. La deuxième phase a permis d’étudier les effets couplés des ions sulfate et chlorure, un processus courant dans les milieux marins et agressifs. Les résultats ont révélé une interaction complexe : les chlorures retardent l’ettringite, tandis que les sulfates déstabilisent le sel de Friedel, facilitant la pénétration des chlorures. Ces observations soulignent la nécessité de prendre en compte les processus de dégradation multifactoriels. La troisième phase a examiné l’influence de la durée de cure sur la résistance des matériaux à l’attaque couplée sulfate-chlorure. Une cure prolongée a amélioré la fixation des chlorures et l’hydratation, mais aussi accentué la formation de produits induits par les sulfates, mettant en évidence le rôle ambivalent de la cure. Cette étude remet en question l’idée selon laquelle une cure prolongée améliore systématiquement les performances, et insiste sur l’optimisation des protocoles selon les conditions environnementales. La dernière phase s’est concentrée sur les géopolymères comme alternative aux liants cimentaires à faible empreinte carbone, en comparant leur durabilité à celle d’un ciment à faible teneur en clinker (CEM III). Contrairement à d’autres travaux basés sur la cure thermique ou l'ajout de nanomatériaux, cette recherche s’est focalisée sur des géopolymères curés à température ambiante. Les résultats ont confirmé leur excellente résistance aux attaques sulfatiques, acides et à la carbonatation grâce à leur matrice aluminosilicatée sans calcium, mais ont révélé des limites concernant la fixation des chlorures et le cycle gel-dégel. Dans l’ensemble, cette thèse propose un cadre détaillé pour comprendre la durabilité des matériaux cimentaires à faible teneur en carbone dans des milieux agressifs. Les résultats mettent en évidence l'importance du choix des formulations, des stratégies de cure et des méthodes d’évaluation adaptées aux conditions d’exposition. Cette étude souligne aussi la nécessité de passer de l’échelle de la pâte à celle du mortier et du béton, pour assurer la validité des résultats en conditions réelles. Les conclusions contribuent au développement d'infrastructures plus durables, tout en approfondissant la compréhension des mécanismes de dégradation des nouveaux systèmes cimentaire
Durabilité des matériaux cimentaires bas carbone soumis à des phénomènes de dégradation simples et couplés
No full textThe durability of cementitious materials in harsh environments is an important consideration for sustainable construction, especially as the cement industry shifts to low-carbon alternatives. This thesis investigates the resistance of various low-carbon binders, ranging from blended cements to geopolymers, up to key degradation mechanisms such as those due to external sulfate attack, chloride bonding capacity, coupled sulfate-chloride interactions, and other durability issues. A comprehensive experimental program, conducted at the paste scale, was developed to investigate the chemical and microstructural evolution of these materials, linking their composition and curing practices to long-term performance. The first phase of the study assessed the sulfate resistance of blended cementitious materials that included supplementary cementitious materials like blast furnace slag, fly ash, and metakaolin. The study revealed that some of these supplementary cementitious materials significantly improve sulfate resistance by reducing available calcium hydroxide and refining pore structure. Based on these findings, four optimized mixes were chosen for further investigation: a reference CEM I, one binary, one ternary, and one quaternary blend. The second phase of the study investigated the combined effects of sulfate and chloride ions, a common degradation process in marine and harsh environments. Findings revealed a complex interaction: chloride delayed ettringite formation, whereas sulfate destabilized Friedel's salt, allowing chloride ingress. These findings highlighted the need to account for multi-factorial degradation processes when conducting durability assessments. The third phase of the study investigated the role of curing duration in cementitious materials' resistance to coupled sulfate-chloride attack. Extended curing improved chloride binding and overall hydration, but it also exacerbated the production of sulfate-induced expensive products, emphasizing curing's dual role in long-term durability. This study challenged the widely held belief that longer curing times always improve performance, emphasizing the importance of optimizing curing protocols based on environmental exposure conditions. The final phase of the study focused on geopolymers as an alternative low-carbon binder, comparing their durability to standardized low-carbon cement (CEM III). This study examined ambient-cured geopolymers without heat or nanomaterials to determine their viability in practical construction applications. Results confirmed their superiority in carbonation, sulfate, and acid resistance due to their calcium-free composition, but their limitations in chloride binding capacity and freeze-thaw resistance.Overall, this thesis provides a comprehensive framework for understanding the durability of some low-carbon cementitious materials in harsh environments. The findings underscore the importance of mix design, curing strategies, and exposure-specific assessments in optimizing the material performance. Furthermore, the study emphasizes the need to move from cement paste-scale studies to mortar and concrete applications to ensure real-world structural applicability. The findings contribute to the development of more sustainable and durable infrastructure, as well as advance scientific understanding of degradation mechanisms in novel cementitious systemsLa durabilité des matériaux cimentaires dans des environnements agressifs est une considération essentielle pour la construction durable, en particulier à mesure que l'industrie du ciment évolue vers des alternatives à faible empreinte carbone. Cette thèse explore la résistance de divers liants à faible teneur en carbone, allant des ciments composés aux géopolymères, face aux principaux mécanismes de dégradation tels que l'attaque sulfatique externe, la fixation des chlorures, les interactions couplées sulfate-chlorure, ainsi que d'autres problématiques de durabilité. Un programme expérimental mené à l’échelle de la pâte a été mis en place pour étudier l'évolution chimique et microstructurale de ces matériaux, en établissant des liens entre leur composition, leurs conditions de cure et leur performance à long terme. La première phase a évalué la résistance aux sulfates des matériaux cimentaires intégrant des ajouts tels que le laitier de haut-fourneau, les cendres volantes et le métakaolin. Les résultats ont montré que ces ajouts améliorent la résistance aux sulfates en réduisant la quantité d'hydroxyde de calcium disponible et en raffinant la microstructure. Quatre formulations ont alors été sélectionnées pour une analyse approfondie : un ciment CEM I, un liant binaire, un ternaire et un quaternaire. La deuxième phase a permis d’étudier les effets couplés des ions sulfate et chlorure, un processus courant dans les milieux marins et agressifs. Les résultats ont révélé une interaction complexe : les chlorures retardent l’ettringite, tandis que les sulfates déstabilisent le sel de Friedel, facilitant la pénétration des chlorures. Ces observations soulignent la nécessité de prendre en compte les processus de dégradation multifactoriels. La troisième phase a examiné l’influence de la durée de cure sur la résistance des matériaux à l’attaque couplée sulfate-chlorure. Une cure prolongée a amélioré la fixation des chlorures et l’hydratation, mais aussi accentué la formation de produits induits par les sulfates, mettant en évidence le rôle ambivalent de la cure. Cette étude remet en question l’idée selon laquelle une cure prolongée améliore systématiquement les performances, et insiste sur l’optimisation des protocoles selon les conditions environnementales. La dernière phase s’est concentrée sur les géopolymères comme alternative aux liants cimentaires à faible empreinte carbone, en comparant leur durabilité à celle d’un ciment à faible teneur en clinker (CEM III). Contrairement à d’autres travaux basés sur la cure thermique ou l'ajout de nanomatériaux, cette recherche s’est focalisée sur des géopolymères curés à température ambiante. Les résultats ont confirmé leur excellente résistance aux attaques sulfatiques, acides et à la carbonatation grâce à leur matrice aluminosilicatée sans calcium, mais ont révélé des limites concernant la fixation des chlorures et le cycle gel-dégel. Dans l’ensemble, cette thèse propose un cadre détaillé pour comprendre la durabilité des matériaux cimentaires à faible teneur en carbone dans des milieux agressifs. Les résultats mettent en évidence l'importance du choix des formulations, des stratégies de cure et des méthodes d’évaluation adaptées aux conditions d’exposition. Cette étude souligne aussi la nécessité de passer de l’échelle de la pâte à celle du mortier et du béton, pour assurer la validité des résultats en conditions réelles. Les conclusions contribuent au développement d'infrastructures plus durables, tout en approfondissant la compréhension des mécanismes de dégradation des nouveaux systèmes cimentaire
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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