Accelerating and mineral admixtures, one of the major ingredients in concrete, are primarily used to modify the properties of both fresh and hardened concrete. Within the scope of this thesis, there were four types of cements having almost identical fineness. The mixes were prepared by using natural pozzolan, blast furnace slag and limestone conforming to TS EN 197-1 and two types of accelerating admixtures, namely triethanolamine (TEA) and calcium formate (CF). The effect of set accelerating admixtures with different cement types on the setting time, water demand and compressive strength has been analyzed by an experimental study in accordance with relevant ASTM standards. Finally, it has been observed that the amount of the accelerating admixtures used is suitable because of their effects on the water demand, setting and strength. Due to the density difference of mineral admixtures and clinker, the normal consistency and 110% flow water content should be considered on a volumetric basis. The effectiveness of the accelerating admixtures on the normal consistency water, 110% flow water content and setting time depends on the type and amount of mineral admixtures. The increase caused by CF in the normal consistency and 110% flow water content is higher than that by TEA. The accelerating effect of TEA and CF on the setting times is more significant for cements incorporating 6% mineral admixture. The effects of accelerating admixtures on the compressive strength change with specimen age, type and amount of mineral admixtures. Generally, for all cement types, early age compressive strengths increase with the increase of TEA, however long term strengths increase by increasing CF.

Estruturas de concreto mais arrojadas têm sido executadas ao longo das últimas décadas, utilizando-se de projetos e técnicas construtivas cada vez mais avançadas, às quais, por sua vez, procuram manter a qualidade na execução da obra e proporcionar maior durabilidade e rapidez na entrega do empreendimento. Dentro deste contexto evolutivo, também se enquadra a tecnologia do concreto, incluindo o estudo dos efeitos de seus materiais constituintes (agregados, aglomerantes, aditivos, adições, etc) sobre as mais diversas propriedades do concreto. Frente a este desafio, a tese se propõe a contribuir de maneira planejada na avaliação de como algumas adições minerais e os aditivos plastificantes podem afetar as propriedades do concreto, com ênfase dada à fluência nas primeiras idades de início de carregamento. A fluência além de ser de difícil obtenção de resultados em laboratório é uma propriedade que possui sua complexidade associada às diversas variáveis intervenientes no fenômeno e ainda ao seu mecanismo de atuação, o qual não é totalmente compreendido. A atual bibliografia sobre o assunto tem se mostrado incipiente e algumas vezes contraditória nos trabalhos disponíveis, principalmente quando se refere aos efeitos na fluência nas primeiras idades, apesar dos esforços depreendidos por pesquisadores consagrados desde a década de 30 do século passado. Assim, surgiu a necessidade de se delimitar a pesquisa a partir de um programa experimental capaz de avaliar, mesmo que ainda restrito a uma amostra de materiais e dosagem limitada, mas que permita uma visão geral de como as adições e os aditivos interagem no comportamento da fluência. O programa experimental compreenderá basicamente na avaliação matricial das possíveis combinações das adições minerais: metacaulim, escória de alto-forno e argila calcinada, associadas aos aditivos plastificantes, base lignossulfonato e naftaleno, sobre a fluência do concreto nas idades iniciais de carregamento de 1, 3 e 7 dias, e ainda sobre outras propriedades mecânicas, elásticas e térmicas, também nas idades de 14 e 28 dias. Os resultados demonstram que tanto as adições minerais estudadas como os aditivos plastificantes e suas combinações, avaliados por meio da análise estatística de variância, interferem decisivamente no comportamento da fluência, mesmo mantendo o proporcionamento dos materiais inalterados em relação à referência. A idéia é de que esta pesquisa contribua para a atualização dos padrões normativos atuais sobre o assunto, e que estimule futuras pesquisas para detalhar o efeito de outras adições e aditivos químicos sobre a fluência e também sobre uma série de traços de concreto e condições além das abordadas nesta tese. / Bolder concrete structures have been performed in the past decade. They use increasingly advanced building projects and techniques which, in turn, aim at keeping work quality and providing higher durability and quicker project completion. Concrete technology also has a role this evolutionary setting. It studies the effects of its component materials (aggregates, binders, chemical and mineral admixtures, etc.) on various concrete properties. In face of this challenge, this thesis aims at contributing to a planned assessment of how some mineral and chemical admixtures can affect concrete properties, mainly regarding creep at early ages at loading. Besides being difficult to assess through laboratorial testing, creep is a property whose complexity is associated to several intervening variables and to its working mechanisms, which are not fully understood. The current relevant literature has shown to be incipient and sometimes contradictory concerning the available studies, mainly those referring to the effects of creep at early ages, despite the efforts renowned researchers have made since the 1930s. This explains the need of limiting the investigations to an experimental program which is able to assess, even if restricted to a sample of materials and limited mix proportion, but also allow an overview of how mineral and chemical admixtures interact creep behavior. For assessing the possible mineral admixture combinations, this experimental program will comprise basically: metakaolin, blast furnace slag, and calcined clay associated to lignosulfonate and naphthalene-based admixtures on concrete creep at ages of loading 1, 3, and 7 days, as well as on other mechanical, elastic, and thermal properties, at ages 14 and 28 days. The results show that both mineral and chemical admixtures and their combinations, assessed in this study through statistical analysis of variance, significantly interfere in creep behavior, even though material proportion remains unchanged compared to the reference concrete mix. The idea is that this research can contribute to update the current standards in this field, and stimulate future studies detailing the effect of other mineral and chemical admixtures on creep and also on other concrete mixes and conditions that have not been approached in this study.

Estruturas de concreto mais arrojadas têm sido executadas ao longo das últimas décadas, utilizando-se de projetos e técnicas construtivas cada vez mais avançadas, às quais, por sua vez, procuram manter a qualidade na execução da obra e proporcionar maior durabilidade e rapidez na entrega do empreendimento. Dentro deste contexto evolutivo, também se enquadra a tecnologia do concreto, incluindo o estudo dos efeitos de seus materiais constituintes (agregados, aglomerantes, aditivos, adições, etc) sobre as mais diversas propriedades do concreto. Frente a este desafio, a tese se propõe a contribuir de maneira planejada na avaliação de como algumas adições minerais e os aditivos plastificantes podem afetar as propriedades do concreto, com ênfase dada à fluência nas primeiras idades de início de carregamento. A fluência além de ser de difícil obtenção de resultados em laboratório é uma propriedade que possui sua complexidade associada às diversas variáveis intervenientes no fenômeno e ainda ao seu mecanismo de atuação, o qual não é totalmente compreendido. A atual bibliografia sobre o assunto tem se mostrado incipiente e algumas vezes contraditória nos trabalhos disponíveis, principalmente quando se refere aos efeitos na fluência nas primeiras idades, apesar dos esforços depreendidos por pesquisadores consagrados desde a década de 30 do século passado. Assim, surgiu a necessidade de se delimitar a pesquisa a partir de um programa experimental capaz de avaliar, mesmo que ainda restrito a uma amostra de materiais e dosagem limitada, mas que permita uma visão geral de como as adições e os aditivos interagem no comportamento da fluência. O programa experimental compreenderá basicamente na avaliação matricial das possíveis combinações das adições minerais: metacaulim, escória de alto-forno e argila calcinada, associadas aos aditivos plastificantes, base lignossulfonato e naftaleno, sobre a fluência do concreto nas idades iniciais de carregamento de 1, 3 e 7 dias, e ainda sobre outras propriedades mecânicas, elásticas e térmicas, também nas idades de 14 e 28 dias. Os resultados demonstram que tanto as adições minerais estudadas como os aditivos plastificantes e suas combinações, avaliados por meio da análise estatística de variância, interferem decisivamente no comportamento da fluência, mesmo mantendo o proporcionamento dos materiais inalterados em relação à referência. A idéia é de que esta pesquisa contribua para a atualização dos padrões normativos atuais sobre o assunto, e que estimule futuras pesquisas para detalhar o efeito de outras adições e aditivos químicos sobre a fluência e também sobre uma série de traços de concreto e condições além das abordadas nesta tese. / Bolder concrete structures have been performed in the past decade. They use increasingly advanced building projects and techniques which, in turn, aim at keeping work quality and providing higher durability and quicker project completion. Concrete technology also has a role this evolutionary setting. It studies the effects of its component materials (aggregates, binders, chemical and mineral admixtures, etc.) on various concrete properties. In face of this challenge, this thesis aims at contributing to a planned assessment of how some mineral and chemical admixtures can affect concrete properties, mainly regarding creep at early ages at loading. Besides being difficult to assess through laboratorial testing, creep is a property whose complexity is associated to several intervening variables and to its working mechanisms, which are not fully understood. The current relevant literature has shown to be incipient and sometimes contradictory concerning the available studies, mainly those referring to the effects of creep at early ages, despite the efforts renowned researchers have made since the 1930s. This explains the need of limiting the investigations to an experimental program which is able to assess, even if restricted to a sample of materials and limited mix proportion, but also allow an overview of how mineral and chemical admixtures interact creep behavior. For assessing the possible mineral admixture combinations, this experimental program will comprise basically: metakaolin, blast furnace slag, and calcined clay associated to lignosulfonate and naphthalene-based admixtures on concrete creep at ages of loading 1, 3, and 7 days, as well as on other mechanical, elastic, and thermal properties, at ages 14 and 28 days. The results show that both mineral and chemical admixtures and their combinations, assessed in this study through statistical analysis of variance, significantly interfere in creep behavior, even though material proportion remains unchanged compared to the reference concrete mix. The idea is that this research can contribute to update the current standards in this field, and stimulate future studies detailing the effect of other mineral and chemical admixtures on creep and also on other concrete mixes and conditions that have not been approached in this study.

Estruturas de concreto mais arrojadas têm sido executadas ao longo das últimas décadas, utilizando-se de projetos e técnicas construtivas cada vez mais avançadas, às quais, por sua vez, procuram manter a qualidade na execução da obra e proporcionar maior durabilidade e rapidez na entrega do empreendimento. Dentro deste contexto evolutivo, também se enquadra a tecnologia do concreto, incluindo o estudo dos efeitos de seus materiais constituintes (agregados, aglomerantes, aditivos, adições, etc) sobre as mais diversas propriedades do concreto. Frente a este desafio, a tese se propõe a contribuir de maneira planejada na avaliação de como algumas adições minerais e os aditivos plastificantes podem afetar as propriedades do concreto, com ênfase dada à fluência nas primeiras idades de início de carregamento. A fluência além de ser de difícil obtenção de resultados em laboratório é uma propriedade que possui sua complexidade associada às diversas variáveis intervenientes no fenômeno e ainda ao seu mecanismo de atuação, o qual não é totalmente compreendido. A atual bibliografia sobre o assunto tem se mostrado incipiente e algumas vezes contraditória nos trabalhos disponíveis, principalmente quando se refere aos efeitos na fluência nas primeiras idades, apesar dos esforços depreendidos por pesquisadores consagrados desde a década de 30 do século passado. Assim, surgiu a necessidade de se delimitar a pesquisa a partir de um programa experimental capaz de avaliar, mesmo que ainda restrito a uma amostra de materiais e dosagem limitada, mas que permita uma visão geral de como as adições e os aditivos interagem no comportamento da fluência. O programa experimental compreenderá basicamente na avaliação matricial das possíveis combinações das adições minerais: metacaulim, escória de alto-forno e argila calcinada, associadas aos aditivos plastificantes, base lignossulfonato e naftaleno, sobre a fluência do concreto nas idades iniciais de carregamento de 1, 3 e 7 dias, e ainda sobre outras propriedades mecânicas, elásticas e térmicas, também nas idades de 14 e 28 dias. Os resultados demonstram que tanto as adições minerais estudadas como os aditivos plastificantes e suas combinações, avaliados por meio da análise estatística de variância, interferem decisivamente no comportamento da fluência, mesmo mantendo o proporcionamento dos materiais inalterados em relação à referência. A idéia é de que esta pesquisa contribua para a atualização dos padrões normativos atuais sobre o assunto, e que estimule futuras pesquisas para detalhar o efeito de outras adições e aditivos químicos sobre a fluência e também sobre uma série de traços de concreto e condições além das abordadas nesta tese. / Bolder concrete structures have been performed in the past decade. They use increasingly advanced building projects and techniques which, in turn, aim at keeping work quality and providing higher durability and quicker project completion. Concrete technology also has a role this evolutionary setting. It studies the effects of its component materials (aggregates, binders, chemical and mineral admixtures, etc.) on various concrete properties. In face of this challenge, this thesis aims at contributing to a planned assessment of how some mineral and chemical admixtures can affect concrete properties, mainly regarding creep at early ages at loading. Besides being difficult to assess through laboratorial testing, creep is a property whose complexity is associated to several intervening variables and to its working mechanisms, which are not fully understood. The current relevant literature has shown to be incipient and sometimes contradictory concerning the available studies, mainly those referring to the effects of creep at early ages, despite the efforts renowned researchers have made since the 1930s. This explains the need of limiting the investigations to an experimental program which is able to assess, even if restricted to a sample of materials and limited mix proportion, but also allow an overview of how mineral and chemical admixtures interact creep behavior. For assessing the possible mineral admixture combinations, this experimental program will comprise basically: metakaolin, blast furnace slag, and calcined clay associated to lignosulfonate and naphthalene-based admixtures on concrete creep at ages of loading 1, 3, and 7 days, as well as on other mechanical, elastic, and thermal properties, at ages 14 and 28 days. The results show that both mineral and chemical admixtures and their combinations, assessed in this study through statistical analysis of variance, significantly interfere in creep behavior, even though material proportion remains unchanged compared to the reference concrete mix. The idea is that this research can contribute to update the current standards in this field, and stimulate future studies detailing the effect of other mineral and chemical admixtures on creep and also on other concrete mixes and conditions that have not been approached in this study.

Yes / Considering the continuous development of sustainable development, energy saving, and emission reduction concepts, it is very important to reduce concrete's cement content in order to improve its environmental impact. Using reactive admixture to replace part of the cement in ultra-high performance concrete (UHPC) can effectively improve the overall performance of the concrete and reduce carbon dioxide emissions (CO2), which is an important aspect of environmental protection. Here, industrial waste residue (fly ash and slag), sea sand (SS), and manufactured sand (MS) were used to produce UHPC under standard curing condition, to reduce the material cost and make the it more environmentally friendly and sustainable. The effects of water-binder ratio, contents of cementitious materials, types of sands, and content of steel fibers on the mechanical performance of UHPC under standard curing were investigated experimentally. In addition, the effects of various factors on the depth under hydraulic pressure and electric flux of UHPC, mass loss, relative dynamic modulus of elasticity, flexural, and compressive strengths of UHPC specimens after freeze-thaw cycles were conducted to evaluate the impermeability, chloride, and freeze-thaw resistance of various UHPCs produced. The obtained experimental results show that the SS-UHPC and MS-UHPC prepared by standard curing exhibit high strength, excellent impermeability, and chloride resistance. The frost resistant grade of all groups of UHPCs prepared by standard curing are greater than F500 and had excellent freeze-thaw resistance, including those produced with local tap water or artificial seawater. The investigation presented in this paper could contribute to the production of new UHPCs of low cost and environmental-friendly and accelerate the application of UHPC in engineering structures.

Concrete experiences volume changes throughout its service life. When loaded, concrete experiences an instantaneous recoverable elastic deformation and a slow inelastic deformation called creep. Creep of concrete is composed of two components, basic creep, or deformation under load without moisture loss and drying creep, or deformation under drying conditions only. Deformation of concrete in the absence of applied load is often called shrinkage. The deformation due to creep is attributed to the movement of water between the different phases of the concrete. When an external load is applied, it changes the attraction forces between the cement gel particles. This change in the forces causes an imbalance in the attractive and disjoining forces. However, the imbalance is gradually eliminated by the transfer of moisture into the pores in cases of compression, and away from the pores in cases of tension. Designs typically use one of the two code models to estimate creep and shrinkage strain in concrete, ACI 209 model recommended by the American Concrete Institute or the CEB 90 Eurocode 2 model recommended by the Euro-International Committee. The ASSHTO LRFD is based on the ACI 209 model. Three other models are the B3 model, developed by Bazant; the GZ model, developed by Gardner; and the SAK model developed by Sakata. The development of concrete performance specifications that limit the amount of compressive creep of concrete mixtures used by the Virginia Department of Transportation, specifically concrete mixtures used for prestressed members (A-5 Concrete) were assessed, along with determining the accuracy and precision of the creep models presented in the literature. The CEB 90 Eurocode 2 model for creep and shrinkage is the most precise and accurate predictor. The total strain for the VDOT portland cement concrete mixtures discussed in this study were found to be between 1200 ± 110 microstrain at 28 days, and 1600 ± 110 microstrain at 97 days, at a five percent significant level. / Master of Science

Yes / Considering the continuous development of sustainable development, energy saving, and emission reduction concepts, it is very important to reduce concrete's cement content in order to improve its environmental impact. Using a reactive admixture to replace part of the cement in ultra-high-performance concrete (UHPC) can effectively improve the overall performance of the concrete and reduce carbon dioxide emissions, which is an important aspect of environmental protection. Here, industrial waste residue (fly ash and slag), sea sand (SS), and manufactured sand (MS) were used to produce UHPC under standard curing conditions to reduce the material cost and make it more environmentally friendly and sustainable. The effects of water-binder ratio, contents of cementitious materials, types of sands, and content of steel fibers on the mechanical performance of UHPC under standard curing were investigated experimentally. In addition, evaluations of the impermeability, chloride, and freeze-thaw resistance of various UHPCs produced were conducted by investigating the effects of various factors on the depth under hydraulic pressure and electric flux of UHPC, as well as the mass loss, relative dynamic modulus of elasticity, flexural strength, and compressive strength of UHPC specimens after freeze-thaw cycles. The obtained experimental results show that the SS-UHPC and MS-UHPC prepared by standard curing exhibit high strength, excellent impermeability, and chloride resistance. The frost-resistant grade of all groups of UHPCs prepared by standard curing was greater than F500 and had excellent freeze-thaw resistance, including those produced with local tap water or artificial seawater. The investigation presented in this paper could contribute to the production of new low-cost and environmentally friendly UHPCs and accelerate the application of UHPC in engineering structures.

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.

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.

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.