Les micropiles à combustibles sont envisagées pour remplacer ou prolonger l’autonomie des batteries dans les dispositifs nomades. Dans ce domaine, la miniaturisation très poussée a abouti à la réalisation de prototypes planaires multi-cellules d’une puissance de 3 à 5 W. La différence d’architecture par rapport aux piles à combustibles « classiques », l’absence d’auxiliaires de fonctionnement et l’utilisation direct de l’air ambiant comme réactif amènent de nouvelles problématiques au niveau de la gestion de l’eau produite. Le travail de cette thèse porte sur la caractérisation de la gestion de l’eau et l’augmentation de la durée de vie d’un système de micropiles à combustible planaire « à respiration », à température ambiante. L’impact prépondérant de la thermique a été mis en avant, au niveau des points de fonctionnement (noyage aux faibles densités de courant et assèchement aux forts courants) comme au niveau local (gradients entre cellules). Les phénomènes d’assèchement et de noyage ont été étudiés grâce à l’imagerie neutronique. Un des principaux phénomènes observé est la rétrodiffusion d’eau vers l’anode suite une condensation au niveau de la cathode, conduisant à une importante perte de puissance. Une étude de la dégradation lors de fonctionnement longue durée a permis de montrer qu’une mauvaise gestion de l’eau favorise la corrosion d’éléments métalliques, conduisant à une diminution des performances. Une solution visant à éliminer ces phénomènes a été développée et implémentée avec succès. L’intégration du microporeux développé lors de cette thèse a permis d’atteindre une dégradation de 0,1 mV/h sur 2500 h de fonctionnement à 3,5 W. / Micro fuel cells have been considered as potential substitute or complement to batteries for nomad systems, in order to enhance their autonomy. Miniaturization of these objects led to the development of multi-cells planar arrays delivering 3 to 5 W. The specificities of this design compared to the “conventionnal” fuel cell stack architecture, coupled to the removal of peripheral components and the use of ambient air as oxidant, comes along with new challenges concerning water management. This work is focused on the characterization of water management and the lifetime improvement of a planar air-breathing fuel cell array at ambient temperature. Thermal effects have been demonstrated to be of first order concerning the operating conditions (flooding at low current density and drying-out at elevated one) and the local heterogeneities (between cells). Drying-out and flooding have been investigated using neutron imaging. One of the major phenomena observed is back-diffusion linked to water condensation on the cathode side, leading to anodic water accumulation and concomitant power decrease. Investigation of the degradation during long term operation pointed out corrosion of metallic elements as the major issue involved in performance decrease. Development and successful implementation of a solution to counter these troubles led to a limited degradation of 0.1 mV/h during a 2500 h operation at 3.5 W.

O aproveitamento de partículas de pneus inservíveis no concreto tem sido objeto de estudo de diversos pesquisadores, pois se justifica como uma alternativa atraente de disposição desses resíduos ao mesmo tempo em que resulta em modificações das propriedades do concreto que podem ser benéficas para certas aplicações, que requerem características específicas, tais como maior capacidade de deformação e comportamento à fratura menos frágil do que o concreto convencional. Essas características do concreto com borracha de pneu (CBP) podem ser interessantes para a redução do risco de fissuração de concretos submetidos a variações volumétricas, caso típico dos concretos massa. Nesta pesquisa se buscou averiguar como a adição de partículas de pneu afeta as propriedades mecânicas, térmicas e viscoelásticas do concreto massa, com o intuito de verificar se era possível obter um compósito menos suscetível aos riscos de fissuração devido a efeitos térmicos. As dosagens de concreto massa com borracha de pneu estudadas foram analisadas em função do teor, da granulometria e do tratamento superficial aplicado às partículas de borracha de pneu. O programa experimental foi desenvolvido em três etapas. A primeira delas envolveu uma ampla faixa de teores de borracha, sendo realizados ensaios básicos para identificar a eficácia dos tratamentos superficiais em proporcionar uma boa interface borracha/matriz do concreto e o maior teor de substituição das partículas de borracha sem prejuízo das propriedades mecânicas. Nessa etapa foram também selecionadas amostras para análise microestrutural por microscopia eletrônica de varredura, a fim de correlacionar a qualidade da interface borracha/matriz do concreto com as características mecânicas. Na segunda etapa foram selecionados os parâmetros que resultaram em melhor desempenho dentre as variáveis analisadas na primeira etapa e buscouse avaliar o efeito da adição de partículas de pneu nas propriedades referentes à tenacidade e à permeabilidade do concreto. Para o desenvolvimento da terceira etapa do estudo foram selecionadas duas composições mais promissoras dentre aquelas utilizadas na primeira e na segunda etapas, a fim de analisar o efeito da borracha de pneu nas propriedades térmicas, elásticas e viscoelásticas do concreto, bem como o comportamento termomecânico. Adicionalmente, algumas amostras foram submetidas a ensaios com vistas à avaliação de características referentes à durabilidade. Os resultados indicaram que o máximo aproveitamento da borracha de pneu no concreto, sem prejuízo considerável das propriedades mecânicas, ocorre para o teor de 10% de partículas de borracha de 1,5mm e 4,8mm em substituição parcial do volume de areia. Teores mais elevados e partículas de menor dimensão levaram a uma contínua redução das propriedades mecânicas e aumento do teor de ar aprisionado. Não houve diferença significativa de propriedades nem na microestrutura das amostras contendo partículas com e sem tratamento superficial. As análises termomecânicas indicaram que o uso de concretos com borracha de pneu pode ser uma alternativa eficiente para minimizar o risco de fissuras de origem térmica, quando comparados a um concreto convencional. Com base nos resultados obtidos até a idade de 2 anos, verifica-se que o consumo de 29 kg/m3 de borracha de pneu no concreto não prejudica as características de durabilidade do material. / The use of waste tire rubber particles in concrete has been studied by several researchers, because it constitute both an attractive alternative for the final disposition of these residues and offers a possibility to modify certain concrete properties that might contribute for a better performance in certain applications that require specific characteristics, such as increased deformation capacity and more ductile behavior than conventional concrete. These characteristics of rubberized concretes might be interesting because they reduce the risk of cracking when concrete is subjected to volumetric changes, as occurs with mass concretes. In this research, it was studied how the introduction of rubber particles would affect the mechanical, viscoelastic and thermal properties of mass concretes, with the aim to check if it is possible to obtain a composite less susceptible to cracking due to thermal effects. The mixtures were analyzed based on the following features: rubber content, granulometry and surface treatment applied to the tire rubber particles. The experimental program was performed in three stages. The first one involved a wide range of mixtures, with varying rubber contents. At this stage, basic tests were carried out in order to identify how effective surface treatments were in generating a good tire rubber/matrix interface as well as how much high tire rubber contents would impact the mechanical properties of the concrete. Samples were selected for microanalysis through scanning electron microscopy to correlate the quality of the rubber/matrix interface with mechanical characteristics. In the second stage, the mixtures that resulted in the best performance in the first stage were further studied. The effects of the addition of tire rubber particles on the properties related to tenacity and permeability of concrete were evaluated. During the third stage, the best two mixtures used in the first and second stages were selected in order to analyze the effect of the addition of rubber particles in the thermal, elastic and viscoelastic properties of concrete, as well as in the thermo mechanical behavior of structures made with this material. Additionally, some samples were subjected to tests for the assessment of features related to the durability of concrete. The results indicated that the best use of tire rubber on concrete, without reducing the mechanical properties, occurs for a 10% content of rubber particles of 1.5mm and 4.8mm, used in partial replacement of the river sand. Higher contents and smaller particles led to greater reductions of the mechanical properties and an increase in the trapped air content. There was no significant difference either in the microstructure or in the properties of the samples containing particles with and without surface treatment. The thermo mechanical analysis indicated that the use of concrete with tire rubber can be an efficient alternative to minimize the risk of cracking due to thermal effects, compared with a conventional concrete. Based on the results obtained until the age of 2 years, the consumption of 29 kg/m3 of tire rubber on concrete did not seem to affect the durability characteristics of the material.

A reação álcali-agregado no concreto é um fenômeno que tem como causa uma reação química que ocorre entre os hidróxidos alcalinos provenientes do cimento e alguns minerais reativos presentes no agregado. Esta reação pode causar a deterioração do concreto, pois os seus subprodutos podem tornar-se expansivos na presença de umidade, originando fissuração, diminuição da resistência, aumento da permeabilidade e, eventualmente, a ruptura da estrutura. O uso de adições minerais em concretos suscetíveis à reação álcali-agregado tem sido apontado como uma alternativa eficiente na prevenção da reação expansiva, juntamente com o uso de agregados não reativos e a limitação dos teores de álcalis no cimento ou concreto. Neste contexto, o presente trabalho teve como objetivo principal a investigação do processo de deterioração do concreto devido à reação álcali-sílica, principalmente no que se refere ao tipo ou mineralogia do agregado e à utilização de cinza de casca de arroz, como substituição parcial do cimento Portland. Desta forma, o programa de pesquisa compreendeu, a realização de ensaios de expansão acelerada em barras de argamassa (ASTM C1260/94) moldadas com cimento Portland tipo CP-I S 32, com teores de 12,5; 25 e 50% de dois tipos de cinza de casca de arroz, em substituição parcial ao cimento, e quatro diferentes tipos de agregados (basalto B, basalto BGO, granito e riodacito). A microestrutura dos materiais utilizados e das barras submetidas ao ensaio acelerado foi avaliada através de técnicas analíticas e experimentais, tais como, petrografia, difração de raios x, porosimetria por intrusão de mercúrio, microscopia eletrônica de varredura e de transmissão (MEV e MET), com microanálise por detecção de energia dispersiva (EDS). Os resultados obtidos no ensaio acelerado comprovaram a potencialidade reativa das rochas analisadas e identificaram uma correlação entre o tipo de rocha e o teor de cinza de casca de arroz. A análise da microestrutura indicou que existe uma reação química da CCA com o meio alcalino utilizado no ensaio que acaba interferindo na formação e na relação C/S dos produtos expansivos resultantes da reação álcali-sílica. / The alkali-aggregate reaction in concretes is a phenomenon caused by a chemical reaction that occurs between alkaline hydroxides from Portland cement and some reactive minerals from aggregates. Such reaction can cause severe concrete deterioration, as its by-products can become expansive in the presence of water, originating fissuration, strength reduction, permeability increase, and eventually, the failure of concrete structures. The use of mineral admixtures in concretes susceptible to the alkali-aggregate reaction has been pointed out as an efficient alternative to prevent concrete expansion, along with the use of non-reactive aggregates and the limitation of the alkali amount in cement or concrete composition. In this context, the main purpose of the present work was the investigation of concrete deterioration due to the alkali-silica reaction, focusing the aspects related to the type or mineralogy of the aggregate and the utilization of rice husk ash as partial substitution of Portland cement. The research program comprised initially accelerated expansion tests carried out in mortar bars (ASTM C 1260/94), which were molded using CP-I S 32 Portland cement, 12.5, 25, and 50% contents of two types of rice husk ash, as partial replacement to the cement, and four different types of rock aggregates (basalt B, Basalt BGO, granite, and rhyodacite). Also, the microstructure of the concrete mixtures investigated, after being submitted to expansion in the accelerated tests, were evaluated through experimental and analytical techniques such as petrography, mercury intrusion porosimetry, x-ray diffraction, scanning and transmission electron microscopy (SEM and TEM), and energy dispersive detection (EDS). The results obtained have proved the reactivity potential of the investigated rock aggregates and identified a correlation between type of aggregate and rice husk ash content. The microstructure analysis indicated that the occurrence of a chemical reaction involving the rice husk ash in the alkaline environment established in the tests, had a significant effect on the amount of expansive by-products as C/S relation resulting from alkali-silica reactions.

The repair of reinforced concrete structures attracts more and more attention of researchers and constructors who see an ever growing number of pathologic phenomenons on several constructions that make use of this widely accepted material. The wrong notion which claims the concrete is an eternal and unchangeable matter has been definitively substituted by the fact that it s a dynamic and complex substance, vulnerable to several aggressive compounds which modify and cause damage to its chemical and physical structure. The present work intended to gather data about the performance of silica fume as a chemical admixture to mortars under the marine atmosphere in the tidal zone, and also evaluate if the magnesium sulfate has any major role in the development of the mortar s properties. To achieve the objectives of the study two groups of mortar were made, one used silica in its composition, and the other didn t. The mortar was cast in cylindrical and prismatic molds to, later, be subjected to natural drying and wetting cycles in the sea coast of Maceió. The cylindrical specimens were 10 x 5 cm and the prismatic ones were 50 x 15 x 4 cm and had reinforcement inside. The tests were conducted in the ages of 14, 28, 91, 135 and 180 days and concerned measuring the compressive, tensile and elastic modulos of the samples and also determine the corrosion potential of the reinforced mortar using the ASTM C 876-91 method. As an addition, X-Ray diffraction tests were conducted to verify if the compounds within the mortars had change and help explain the results from the earlier experiments. Results show that the silica fume mortars developed lower compressive strength than ordinary Portland cement mortars. The tensile strength tests displayed more balanced values for both mortars, with the ordinary exhibiting less strength than its silica fume counterpart at 91 and 135 days, but catching up with it (even slightly surpassing it) at latter ages. X-ray diffraction indicates changes on the phases of the hydrated paste. The analysis of the results suggests that cement mortar with silica fume addition doesn t present the same behavior related to ordinary cement mortar / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O reparo de estruturas de concreto armado atrai cada vez mais a atenção de pesquisadores e construtores que vêem um número crescente de fenômenos patológicos em diversas construções com este material. A noção errônea de que o concreto é um material eterno e imutável foi substituída pelo fato de que ele é uma substância dinâmica e complexa, vulnerável a muitos compostos agressivos que modificam e causam dano à sua estrutura química e física. O presente trabalho propôs-se a coletar dados sobre o comportamento da sílica ativa como uma adição mineral a argamassas expostas ao ambiente marinho, na zona de variação da maré, e também avaliar se o sulfato de magnésio participa de alguma maneira no desenvolvimento das propriedades da argamassa. Para alcançar os objetivos do estudo dois grupos de argamassas foram feitos, um de argamassa convencional e o outro usando sílica em sua composição. Corpos de prova cilíndricos (10 x 5 cm) e prismáticos (50 x 15 x 4 cm com armadura de aço) foram sujeitos a ciclos naturais de molhagem e secagem no litoral de Maceió. Os testes foram feitos nas idades de 14, 28, 91, 135 e 180 dias e compreenderam medir a resistência à compressão, à tração e o módulo de elasticidade das amostras. Ensaios de potencial de corrosão foram conduzidos nas placas de argamassa armada de acordo com a ASTM C 876 91 e análise por difração de raios X foram efetuadas para verificar mudanças nos compostos das argamassas. Resultados mostram que, ao fim do período de testes, a argamassa com sílica desenvolveu resistência à compressão menor quando comparada à argamassa convencional. A resistência à tração mostrou resultados mais equilibrados, com alguma vantagem para a argamassa com sílica. Análise da difração de raios X sugere possíveis mudanças nas fases da argamassa com sílica. Os resultados apontam que o uso de sílica ativa em matriz cimenticia aplicada em ambiente marinho não apresenta o mesmo desempenho quando comparado a matriz cimenticia convencional.

Nas últimas décadas, a busca pelo desenvolvimento sustentável vem influenciando indústrias de diversos setores a procurar uma destinação correta para os seus resíduos, esta ação visa reduzir os impactos ambientais gerados pelas diversas atividades de cada indústria. Neste sentido, a construção civil se mostra um setor potencial para este emprego, visto a elevada quantidade de matéria-prima de origem natural consumida. No estado do Rio Grande do Sul, onde há a terceira maior produção de pedras preciosas do Brasil, as etapas do beneficiamento de pedras, como a ágata, geram resíduos que requerem solução quanto ao seu destino final. O resíduo de ágata apresenta-se sob três formas: pó, com formato mais arredondado; agregado miúdo, alongado, e a terceira no formato de agregado graúdo, também alongado, todos de coloração clara. No entanto, sempre que se almeja empregar um resíduo, inicialmente é preciso avaliar suas possibilidades de aplicação, frente a questões de sua aplicabilidade técnica, ambiental e econômica. O presente trabalho tem por objetivo estimar a influência dos agregados de ágata, quando substituindo o agregado miúdo de calcário, tradicionalmente utilizado em matrizes cimentícias de cimento Portland branco. O estudo foi desenvolvido iniciando-se pela caraterização dos materiais que foram utilizados, passando posteriormente à realização de ensaios de caracterização de argamassas no estado fresco e no estado endurecido. No estado fresco foram avaliados o índice de consistência e a reologia da mistura, através da reometria rotacional e do squeeze flow. No estado endurecido foram avaliadas as propriedades mecânicas, através dos ensaios de resistência à compressão, resistência à tração por compressão diametral, densidade de massa aparente, módulo de elasticidade dinâmico, e de durabilidade, avaliando a absorção de água por capilaridade e a reação álcali-agregado. Verificou-se influências significativas quanto à substituição dos agregados miúdos por pó de rolagem de ágata. No estado fresco observou-se que as argamassas com pó de rolagem de ágata demandaram maior consumo de água e apresentaram maior plasticidade. Já no estado endurecido, as argamassas produzidas com o agregado miúdo de ágata apresentaram uma resistência à compressão e resistência à tração na compressão diametral inferior quando comparadas às argamassas produzidas com calcário, com diferentes relações água aglomerante. Além disso, as argamassas produzidas com agregado miúdo de ágata apresentaram densidade de massa aparente e módulo de elasticidade inferior quando comparada com as argamassas com agregado miúdo de calcário. Quanto à absorção de água por capilaridade, as argamassas produzidas com pó de rolagem de ágata apresentaram menor índice de absorção, com exceção dos traços produzidos sem pó de rolagem de ágata, onde o calcário apresentou uma menor absorção de água por capilaridade. No ensaio de reação álcali-agregado, o agregado miúdo de ágata foi considerado reativo, no entanto a combinação entre este agregado e o pó de rolagem de ágata gerou resultados inócuos. / In recent decades, the demand for sustainable development has been influencing industries from many sectors to seek a proper destination for their waste. The use of waste for other purposes aims to reduce the environmental impacts. In this context, the civil construction industry is a potential sector for this use, since the high amount of natural raw material used, being a viable alternative to reduce their environmental impact. Thus, in the state of Rio Grande do Sul, where there is the third largest production of precious stones of Brazil, processing stages of the stones, such as agate, generate waste that requires solution in relation to its final destination. Agate residues are found in three different forms: powder, with rounded shape; fine aggregate, with elongated shape, and coarse aggregate, also with elongated shape, all light-colored. The use of waste requires knowledge of their application possibilities, trying to evaluate the feasibility of its use in the technical, environmental and economic point of view. The objective of this study was to evaluate the influence of the use of agate aggregates in mortar for white concrete, replacing limestone fine aggregate, usually employed in cementitious matrices of white Portland cement. The study started with the characterization of the materials that were used and conducting to perform the tests in fresh and hardened state. The samples in fresh state were investigated by consistency index and squeeze flow. In the hardened state, samples were subjected to compression tests, tensile strength in diametrical compression, bulk density, dynamic modulus of elasticity, and also durability tests were used to evaluate the absorption of water by capillarity and the alkali-aggregate reaction. The results have shown significant influences in the substitution of fine aggregates by agate powder. In the fresh state it was observed that the mortars with agate powder required higher consumption of water and had better plasticity. In the hardened state, it was observed that mortars with agate fine aggregate showed lower compressive and tensile strength in diametrical compression, bulk density and modulus of elasticity compared to mortars made with limestone. In addition, the mortars produced with agate powder showed lower absorption of water by capillarity, except for mixtures produced without agate powder, where the limestone causes a lower water absorption by capillarity. In the alkali-aggregate reaction the agate fine aggregate can be considered reactive. However, the combination of this aggregate and agate powder can be considered innocuous.

L'objectif de ce travail est de contribuer à la valorisation du métakaolin en substitution du ciment dans les matrices cimentaires en levant certains verrous scientifiques. En effet l'utilisation d'additions minérales modifie les propriétés des bétons, que cela soit à l'état frais, à l'état durcissant ou à l'état durci. A l'état frais, la rhéologie a été étudiée avec l'adaptation et l'application d'une méthode de formulation pour béton auto-plaçant. Cette application a été développée jusqu'à l'échelle industrielle. A l'état durcissant, la phase d'hydratation a été étudiée en s'attardant particulièrement sur l'effet de la nature du ciment substitué sur la réactivité du métakaolin. Enfin à l'état durci deux caractéristiques de durabilité ont été explorées, à savoir l'effet du métakaolin sur la carbonatation dans une première partie, puis sur la diffusion des chlorures dans une deuxième partie. / The objective of the present thesis was to promote the use of metakaolin as substitute for cement in cementitious matrix by unlocking several scientific challenges. The use of mineral additions modifies the properties of concrete in the fresh state, the hardening state and the durability state. In the fresh state, rheology was studied by adapting a formulation method for self-compacting concretes. This application was then further developed to be used at an industrial scale. In the hardening state, the hydration phases were analysed with a focus on the effect of the cement nature on the metakaolin reactivity. Finally in the durability state, two particular features were studied:1) the metakaolin effect on the carbonation kinetic and 2) the effect of the metakaolin on the chloride diffusion.

La fabrication du ciment, par sa phase de clinkérisation, est très énergivore et émet une quantité importante de gaz à effet de serre dans l'atmosphère. En effet, la production d'une tonne de clinker génère environ une tonne de CO2. Afin de réduire ces émissions, une des alternatives est l'utilisation des additions minérales dans la confection des bétons en remplacement partiel du ciment. Cette substitution apparait comme une des solutions les plus efficaces permettant à la fois de diminuer l'énergie consommée et de réduire le dégagement de CO2 dans l'atmosphère. Cette étude s'inscrit dans un projet plus global de développement des bétons de bâtiment à matrices binaires (ciment + additions) s'appuyant sur des critères de propriétés de transfert. En effet, afin de répondre à certaines exigences de durabilité, une campagne expérimentale a été menée sur des bétons confectionnés selon la norme européenne NF EN 206 qui autorise deux méthodes de formulation : * l'approche dite prescriptive, qui porte sur des obligations de moyens, * l'approche dite performantielle, qui consiste à fixer des exigences en terme de performances basées sur des indicateurs généraux ou spécifiques de durabilité. Ce travail de recherche a donc consisté à comparer les propriétés physico-chimiques de bétons à forte teneur en addition minérale (filler calcaire, cendre volante, laitier de haut fourneau et métakaolin), dérogeant à l'approche prescriptive avec celles des bétons de référence répondant à cette même norme. Cette comparaison s'est effectuée au travers d'indicateurs de durabilité généraux (porosité accessible à l'eau, perméabilité à l'oxygène, coefficient de migration des ions chlorure et teneur en Ca(OH)2) et d'indicateurs spécifiques : la résistance à la carbonatation naturelle et accélérée. D'un point de vue méthodologique, les travaux réalisés dans le cadre de cette recherche ont montré l'intérêt de l'approche performantielle pour la formulation des bétons. Mais, à l'heure actuelle, les outils disponibles, c'est à dire les indicateurs généraux et spécifiques, ne sont pas suffisants pour répondre à l'ensemble des bétons couvrant ce texte normatif. A l'échelle du matériau (béton pour une application en bâtiment), les campagnes expérimentales menées ont montré que dans la majorité des cas, les bétons à forte teneur en addition minérale (dérogeant aux spécifications) présentent des comportements proches de ceux observés sur les bétons de référence (répondant à l'approche prescriptive). / The manufacturing of cement, by its clinkering process, is very energy-consuming and emits an important quantity of greenhouse gases in the atmosphere (1 ton of clinker produced 1 ton of CO2 released into the atmosphere). To maximize this latter from an environmental point of view, it is necessary to reduce the cement content. This can be done by replacing part of the cement with mineral additives during the manufacturing phase. This substitution seems one of the most effective solutions allowing, at the same time, to decrease the energy consumed and to reduce the release of CO2 into the atmosphere. This study is part of a more comprehensive development project of concrete building binary matrices (cement + mineral additives) based on transfer properties criteria. Indeed, in order to answer certain sustainability requirements, an experimental campaign was conducted on concrete, made according to the new European standard (EN 206) that allows two methods of formulation: * a traditional prescriptive approach, based on limiting values for the composition (minimum binder content, maximum water to binder ratio, compressive strength class...) of concrete exposed to some aggressive environmental conditions, * an innovative method based on a performance approach for concrete properties. The present work aims at studying the physico-chemical properties of cementitious materials with high substitution rates of cement by mineral additions (limestone filler, fly ash, slag, metakaolin) derogating from the prescriptive approach with reference to concrete corresponding to the same standard. This comparison was made with general durability indicators (water porosity, oxygen permeability, chloride migration coefficient and portlandite content) and specific durability indicators: carbonation in natural and accelerated conditions. From a methodological point of view, the research carried out in the framework of this project has shown the interest of the performance-based approach with regards to the concrete formulation. But at the moment, the available tools, namely the general and specific indicators, are not sufficient to respond to all these types of concrete. However, considering the performance, economic and environmental criteria, laboratory results showed that concrete made according to a performance-based approach had a performance close to reference concrete and the standard prescription could still be reassessed.

Le béton projeté est une méthode de mise en place consistant en la projection pneumatique de béton sur une surface à grande vitesse. Dans le cas de la méthode par voie sèche, le mélange granulats-ciment est introduit sec en machine, l'eau est ajoutée à la fin du transfert. Cette technique, très employée, est néanmoins génératrice de pertes importantes par rebond, pouvant s'élever jusqu'à 40% de la masse projetée. L'enjeu de la réduction des pertes est à la fois économique et environnemental. Les facteurs influents sur le rebond sont liés aux techniques de projection et à la formulation. Ce travail de thèse a pour objectif l'optimisation de la formulation du béton afin de réduire les pertes par rebond, mais également d'améliorer la durabilité. L'étude porte en particulier sur l'influence sur le rebond : du squelette granulaire, de la teneur en eau et de l'emploi d'additifs et/ou d'additions de substitution. Une approche modélisation du phénomène de rebond est également abordée. / Sprayed concrete is a concrete pneumatically projected onto a surface at high velocity. Dry-mix shotcrete is a process in which dry constituents are introduced into the machine and conveyed through a hose to the nozzle, where the water is added. This process is used in various civil engineering or construction projects; unfortunately, it can lead to high losses of concrete due to rebound (up to 40% of the total mass of material). Such losses induce overconsumption of material, which is damaging for the cost of the work and for the environment. Rebound depends on technicals parameters and mix design. The present work focuses on rebound reduction and also on durability enhancement by modification of the mix design. The influence of aggregate size distribution, water content and supplementary cimentitious material is studied. An analytical approach of rebound phenomenon is also implemented.

Entre os produtos confeccionados com polímeros reforçados com fibras, as hastes pultrudadas têm sido utilizadas em um número crescente de aplicações devido a características como baixa massa, elevada resistência mecânica, baixo custo de manutenção e alta resistência à corrosão, em particular quando comparadas com hastes confeccionadas em materiais convencionais equivalentes. Porém, os mecanismos de envelhecimento e de degradação dos compósitos poliméricos reforçados com fibras precisam ser mais bem compreendidos, particularmente os mecanismos de dano em condições de serviço, em aplicações de engenharia civil ou em águas profundas. Neste trabalho, foi avaliada a exposição de hastes pultrudadas produzidas a partir de fibras de carbono e vidro e resinas epóxi e éster-vinílica após 3000 horas em diferentes ambientes, como exposição à radiação UV, exposição à água do mar e exposição à água a 60 °C. Os principais aspectos microestruturais, físicos, térmicos, químicos, mecânicos e de vida útil das hastes foram avaliados antes e após as exposições. As hastes com fibras de carbono apresentaram maior resistência residual de forma geral quando comparadas às hastes de fibra de vidro, as quais perderam mais de 50% da sua resistência original após exposições de curta duração (744 h). Quando expostas à radiação UV, as hastes com fibras de carbono apresentaram maior resistência residual à tração, assim como quando submetidas a esforços combinados nos ensaios de SBS. O ambiente mais agressivo entre os estudados definitivamente foi a imersão em água destilada. Os resultados dos ensaios de short-beam apresentaram melhor relação com os efeitos de degradação do que os ensaios de resistência à tração. Através das análises microestruturais (MO e MEV) foi possível identificar alguns tipos de mecanismos de degradação atuantes em cada condição de envelhecimento acelerado. Após analisar uma combinação de fatores envolvidos, a resina epóxi, dentre as resinas estudas, foi a que apresentou melhores propriedades de interface quando utilizada com fibras de carbono. / Among products made with fiber-reinforced polymers, pultruded rods have been used in an increasing number of applications, due to such features as low weight, high strength, low maintenance costs, and high corrosion resistance, particularly when compared with rods manufactured with equivalent conventional materials. However, the ageing and degradation mechanisms of these polymer composite materials still need to be better understood, particularly the damage mechanisms under various service conditions, such as civil engineering or in deep water applications. This thesis presents an experimental study that evaluates the ageing of pultruded rods produced from reinforced carbon and glass fibers and epoxy and vinyl ester resin matrices when exposed to UV radiation, seawater and distilled water at 60 °C for 3000 hours. The degradation assessment in the different environments was made by analyzing and comparing the microstructural, physical, chemical, thermal and mechanical aspects and the lifespan of the pultruded composite rods before and after accelerated ageing. The carbon fiber rods presented a higher residual resistance considering all the aforementioned aspects when compared to the glass fibers rods, which lost more than 50% of their original resistance after short exposure (744 h) to weathering. When exposed to UV radiation, the carbon fiber rods showed higher residual resistance as compared with other types of degrading conditions. Distilled water was undoubtedly the most aggressive ageing factor in respect to all the evaluated properties and characteristics of the tested rods. The short-beam test results showed higher correlation with the degradation effects than the results of the tensile test. By means of microstructural analysis (SEM and OM), it was possible to identify some types of degradation mechanisms for each kind of applied accelerated ageing. After analyzing a combination of factors involved, it was possible to reach the conclusion that the epoxy resin incorporated with carbon fibers displayed the best overall performance among all possible resin/fiber couples

The study of pathological manifestations in concrete emerges as a valuable tool for understanding the processes involved, in it as long as it makes possible to optimize its use in all stages of the construction process. Under this circumstance it was considerate valid to make a survey about the major damages in Uruguay, for which 93 reports were labeled with 313 assessments on 147 bridges in the period 2004 / 2010. From their analyst’s it was verified of injury "Corrosion of reinforcement", located mainly in the coastal South. Makeover, it was found that "Board" is the most affected of the elements followed by “Side Shields" and "Sidewalks", where "Exposed reinforcement" and "Humidity stains" are the most prevalent problems. / El estudio de las manifestaciones patológicas en el hormigón armado surge como una valiosa herramienta para la comprensión de los procesos involucrados, en la medida que posibilita optimizar su uso en todas las etapas del proceso constructivo. En función de esta circunstancia entendió-se valedero realizar un levantamiento de sus principales daños en el Uruguay, para lo cual fueron catalogados 93 informes con 313 evaluaciones sobre 147 puentes en el periodo 2004 / 2010. De su análisis verifico-se la preeminencia de la lesión “Corrosión de armaduras”, la que se localiza principalmente en la zona costera Sur. A sí mismo, constata-se que “Tablero” es el elemento más afectado de estas estructuras seguido por “Protección lateral” y “Veredas”, donde “Armadura expuesta” y “Manchas de humedad” son las lesiones más relevantes.