The nanostructure, physical properties and mechanical performance of C-S-H, 1.4 nm tobermorite, jennite, and ettringite were studied. C-S-H of variable stoichiometries was examined as a model system in comparison with that produced in the hydration of Portland cement. The current Master’s thesis is comprised of four research papers designed to improve the current understanding of the nanostructure and engineering properties of C-S-H systems and modified C-S-H systems. Many of the controversial issues in cement science were identified and were addressed in a comprehensive research study, which examined the key features of the C-S-H systems at the nano-structure level. In Chapter 4, each paper presented new evidence for a number of mechanical aspects of C-S-H materials. Numerous advanced analytical tools were used in order to verify the observations made in each section. The major achievements of the current work are mentioned briefly as follows: 1. It was determined that microindentation is a useful method for determining the creep behavior of C-S-H of various stoichiometries, 1.4 tobermorite, jennite, and ettringite. 2. Microindentation parameters i.e. creep modulus, indentation modulus and indentation hardness are porosity dependent. 3. Microindentation creep measurements on C-S-H (C/S = 0.80 and 1.20) demonstrated that creep modulus, indentation modulus, and indentation hardness are all dependent on mass-loss from the 11%RH condition. 4. Evidence was presented that the nanostructural role of interlayer water in C-S-H has a significant influence on the creep process.

The diploma thesis is concerned with study of preparation and properties of historic mortars. In theoretical part, there is summarized the historic progress of mortars and their material composition. The experimental part is focused on proposition of mortar mixes. The diploma thesis referring to actual research on Institute of Technology of Building Materials and Components, FCE VUT in Brno. The base mixe of historical mortar came from this research. In experiment, there is the base mixe of historical mortar modified with gypsum. In the first phase of the experimental part the basic technological and aplication properties are assessed. The second phase of the experimental part is focused on the course of hydration of the binder in different environments and subseqeunt determination of the phase composition by X-ray diffraction analysis. The aim of the thesis is to determine the optimal amount of gypsum and to optimize the recipe of historical mortar.

This thesis deals with monitoring the thermodynamic stability of thaumasite and monitoring it is properties in the long term. The aim was to synthesize thaumasite under different conditions and to evaluate it using X-ray diffraction analysis and thermal analysis.

Les sulfates de calcium sont des matériaux économiques et écologiques. Pourtant leur utilisation dans le domaine de la construction est assez limitée du fait de leur sensibilité à l’eau. La capacité des ciments alumineux (CAC) à diminuer la sensibilité à l’eau des sulfates de calcium ainsi que les mécanismes d’insensibilisation ont été étudiés. L’insensibilisation à l’eau des sulfates de calcium a été réalisée par ajout de faibles quantités de ciment alumineux (≤ 30%). Quatre sulfates de calcium de nature différente : gypse, hémi-hydrate α et β, anhydrite synthétique ont été étudiés. L’étude des mécanismes d’insensibilisation à l’eau des sulfates de calcium par ajout du ciment Fondu, menée à différentes analyses de la microstructure : IR, DRX, ATD-TG, MEB, a mis en évidence deux approches : la formation de l’ettringite insoluble et la formation du gel d’AH3 qui colle les grains de sulfate de calcium soluble. La nature des phases cristallochimiques du ciment alumineux a des influences sur les caractéristiques mécaniques, la sensibilité à l’eau ainsi que la durabilité des mélanges [sulfate de calcium / CAC]. L’étude des mélanges [anhydrite synthétique / laitier / CAC] offrent des perspectives intéressantes notamment concernant le développement des liants à faible empreinte CO2. / Calcium sulphate materials are economical and ecological. But their use in the construction is quite limited because of their sensibility to water. The capacity of aluminate cement (CAC) to decrease the water sensibility of calcium sulphate and the mechanisms of insensibilisation were investigated. Waterproofing of gypsum base materials was carried out by addition of small amounts of aluminate cement (≤ 30%). Different nature of calcium sulphates : gypsum, hemihydrate α and β, synthetic anhydrite was studied. The study of mechanisms of insensibilisation to water of calcium sulphate by adding cement Fondu, with different analysis of microstructure : IR, DRX, ATD-TG, MEB, revealed two approaches : formation of ettringite insoluble and formation of gel AH3 that stick soluble grains of calcium sulphate. The nature of phases of aluminate cement has influences on the mechanical properties, sensibility to water and durability of mixtures [calcium sulphate / CAC]. The studies of mixtures [synthetic anhydrite / slag / CAC] offer interesting perspectives for the development of binders with low imprint CO2.

Premature concrete deterioration due to alkali-silica reaction (ASR) and delayed ettringite formation (DEF) is a significant problem all over the world. In cases where these mechanisms were not initially prevented, mitigation is critical to halt expansion and cracking. The main objectives of the research presented herein were to study the effect of ambient relative humidity (RH) on rates of concrete expansion, to determine RH thresholds below which expansion due to ASR and/or DEF may be suppressed, and to evaluate coatings intended to lower the internal RH of concrete and thus minimize future potential for damage. Results from testing showed that the RH threshold for ASR was below 82%, the RH threshold for DEF was below 92%, and the RH threshold for combined ASR and DEF could be about 83% for the materials tested. Furthermore, it was shown that some coatings are effective in reducing ASR- and DEF-related expansion by lowering the internal RH of concrete. / text

La Réaction Sulfatique Interne (RSI) est une pathologie du béton pouvant affecter les matériaux soumis à un échauffement au-delà de 65°C. Elle consiste en une formation d'ettringite dans le matériau durci et conduit à son gonflement. Il s'en suit une fissuration et une dégradation des performances mécaniques pouvant poser des problèmes d'intégrité structurelle à l'instar de la Réaction Alcali-Granulat (RAG) à laquelle elle est fréquemment couplée in situ. Lorsqu'un ouvrage est atteint, il convient de poser un diagnostic, évaluer son aptitude au service, prédire son évolution et mettre en uvre des méthodes de réparation. Ceci nécessite une compréhension fine des effets de la RSI à l'échelle microscopique et à l'échelle de l'ouvrage. De nombreuses études expérimentales et théoriques ont été menées pour déterminer les mécanismes mis en uvre et les paramètres influençant la RSI. Toutefois, la complexité des phénomènes rend délicate la transposition de ces connaissances à l'échelle de la structure. Les approches macroscopiques semblent donc plus adaptées à ce type de problème. Pour mettre au point ces approches, il est nécessaire de comprendre en détail les effets de la pathologie à l'échelle du matériau et de la structure. Cette thèse décrit les résultats d'une étude de laboratoire basée sur des essais sur éprouvettes pour caractériser les couplages entre les gonflements et l'humidité, la température et l'état de contraintes. Ces travaux ont également été l'occasion d'étudier les couplages entre RAG et RSI. En parallèle, des suivis dimensionnels et hydriques de poutres soumises à des conditions d'exposition à l'humidité contrôlées ont permis de constituer une base de données des effets structurels de la RSI. La confrontation de ces essais menés conjointement à l'échelle du matériau et de la structure fournit des données permettant de mettre au point des méthodes de re-calcul des ouvrages et de les valider en confrontant leurs prédictions aux résultats expérimentaux / Delayed Ettringite Formation (DEF) is a reaction that can affect concretes exposed to temperatures higher than 65°C. The corresponding formation of ettringite in the hardened material leads to swellings, cracking and decrease of the mechanical properties. Thus it gives serious concern in terms of structural integrity and serviceability. DEF is often coupled with Alkali-Aggregate Reaction (AAR) in the field. For a structure manager, it is necessary to be able to diagnose the reaction, to assess the serviceability of the structure, to predict its evolution and to repair it. To reach these objectives, it is necessary to understand DEF effects both at the microscopic scale and the structure scale. In the literature, a lot of theoretical and experimental researches have been reported and deal mainly with the chemo-physical mechanisms. These results emphasize the complexity of the microscopic features of DEF and thus can hardly be used to model its structural effects. Thus, macroscopic approaches seem to be more adapted. To develop such approaches, it is necessary to understand the effect of the deleterious process at the scale of the material and of the structure. In this context, this research proposes to quantify the couplings between DEF-induced swellings and moisture, temperature and mechanical loadings thanks to material tests on concrete cylinders. The couplings between DEF and AAR are as well investigated. Moreover the monitoring of dimensions and water content of concrete beams is also performed while being exposed to various controlled water supply conditions. The corresponding results provide a database useful to analyse quantitatively the mechanical effects of DEF (for the material and for the structures) and to validate the numerical models by comparing their predictions to the experimental behaviour

Fosfogesso é um resíduo sólido da produção de ácido fosfórico pelas indústrias de fertilizantes. A produção anual deste material no mundo é de cerca de 180 milhões de toneladas, e isto causa problemas com a sua armazenagem. O fosfogesso tem sido estudado para uso como material de construção de bases e sub-bases de pavimentos. O fosfogesso tem pouca durabilidade frente à ação da água quando sujeito somente à estabilização mecânica. O cimento Portland é então adicionado ao fosfogesso, resultando em misturas mais estáveis. A reação do aluminato tricálcico contido no cimento e dos sulfatos presentes no fosfogesso poderia conduzir à formação de cristais de etringita e à expansão subseqüente. O objetivo desta pesquisa é avaliar a influência do tipo de cimento na expansibilidade das misturas de fosfogesso e cimento para uso na construção de pavimentos. Analisou-se o comportamento expansivo de corpos de prova compactados com diferentes proporções de fosfogesso e cimento, variando-se o tipo de cimento, energia de compactação e período de cura. Para todos os cimentos usados nesta pesquisa, considerando-se o período de 84 dias de cura, a maior parte da expansão ocorreu nos primeiros 28 dias. A influência do tipo de cimento na expansão das misturas de fosfogesso e cimento é significante, mas o teor de aluminato tricálcico não é a única explicação para o comportamento de expansão observado neste estudo, visto que os resultados experimentais indicam que quantidades crescentes de aluminato tricálcico conduzem a menores expansões, fato que contraria a expectativa inicial desta pesquisa. / Phosphogypsum is a solid by-product resulting from the phosphoric acid process for manufacturing fertilizers. The annual worldwide production of this material is about 180 million de tons and it causes problems with its disposal. The phosphogypsum has been studied for use in pavement base and sub-base materials. Phosphogypsum has poor durability when subjected to mechanical stabilization only in wet conditions. The addition of stabilizing materials, such as Portland cement, is one method of overcoming this deficiency. The chemical reaction between tricalcium aluminate present in Portland cement and sulfate ions supplied by phosphogypsum could lead to the formation of ettringite and subsequent expansion. The objective of this research is to evaluate the influence of Portland cement type on the expansion of cement-stabilized phosphogypsum mixtures for use as pavement construction. The expansion behavior was analyzed through compacted specimens composed by different phosphogypsum and cement proportions, varying the cement type, compaction energy and curing period. For all cements used in this research, most of expansion occurred within the first 28 days in relation to the 84 days of curing. There is a significant influence of cement type on the expansion of the cement-stabilized phosphogypsum mixtures, but the aluminate tricalcium content is not the only explanation for the expansion behavior observed in this study. The experimental results show that an increasing amount of tricalcium aluminate yields lower expansion, fact that thwarts the initial expectation of this research.

En géotechnique routière, la technique de la stabilisation des sols à la chaux et aux liants hydrauliques permet la valorisation des sols des déblais. Malgré un encadrement réglementaire strict, cette technique ne donne pas toujours de résultats satisfaisants. Les<br />entreprises utilisatrices des sols traités et productrices des agents de traitement se sont associées pour lancer des travaux de recherches destinés à comprendre les causes des défaillances.<br />Cette étude a tout d'abord établi un modèle de l'enchaînement des mécanismes qui conduisent à une stabilisation des sols :<br />- la chaux permet la floculation des argiles d'où la formation de grumeaux lors du malaxage. Ce grumeau constitue l'entité caractéristique du sol.<br />- le ciment forme une coque enrobant les grumeaux. Le compactage permet la coalescence de ces pâtes en formant un réseau continu. Le durcissement du ciment permet l'acquisition des caractéristiques mécaniques.<br />- l'excès de chaux en milieu basique conduit à la formation d'une seconde génération d'hydrates calciques (C-S-H) par réaction pouzzolanique aux dépens des argiles. Le développement des hydrates permet la rigidification du coeur du grumeau et l'augmentation correspondante des résistances mécaniques sur plusieurs années.<br />Les perturbations rencontrées lors des chantiers peuvent s'interpréter comme des écarts à ce modèle:<br />- écarts d'ordre microstructural ; dans les sols micacés, le comportement mécanique de ces matériaux est contrôlé par la présence de paillettes de micas dans la coque et de<br />fragments aplatis de roche au sein des grumeaux.<br />- écarts d'ordre physico-chimique ; des composés solubles interfèrent avec les liants :<br />- le soufre favorise le développement d'ettringite selon des faciès qui dépendent de la spéciation du soufre et de la perméabilité du grumeau.<br />- les matières organiques ralentissent l'hydratation du ciment et piègent les ions calcium et hydroxyle et sont ainsi responsables des résistances mécaniques insuffisantes<br />Ayant identifié et analysé les mécanismes des perturbations, nous nous sommes attachés à proposer des essais simples et fiables de caractérisation démontrant rapidement la présence de<br />ces agents perturbateurs au sein des sols :<br />- par la caractérisation de la morphologie des particules<br />- par le retard de début de prise de pâtes pures de ciment gâchées avec des jus extraits de sols pour les matières organiques.

Cantilevered reinforced concrete columns with a lap splice of the longitudinal reinforcement near the base can induce high moment demands on the splice region when lateral loads are present on the structure. Code design specifications typically require a conservative splice length to account for these high moment demands and their consequences of bond failure. The required splice length is calculated as a function of required development length, which is a function of the bond between the reinforcement and the surrounding concrete, and a factor depending on the section detailing. However, the effects of concrete deterioration due to alkali silica reaction (ASR) and/or delayed ettringite formation (DEF) may weaken the bond of the splice region enough to overcome the conservative splice length, potentially resulting in brittle failure of the column during lateral loading. This thesis presents the following results obtained from an experimental and analytical program. * Fabrication of large-scale specimens of typical column splice regions with concrete that is susceptible to ASR/DEF deterioration * Measurement of the large-scale specimen deterioration due to ASR/DEF accelerated deterioration * Analytical model of the column splice region based on flexure theory as a function of the development length of the reinforcement and a factor to account for deterioration of the bond due to ASR/DEF * Experimental behavior of two large-scale specimens that are not influenced by premature concrete deterioration due to ASR/DEF (control specimens). This experimental data is also used to calibrate the analytical model. The conclusions of the research are that the analytical model correlates well with the experimental behavior of the large-scale control specimens not influenced by ASR/DEF. The lap splice region behaved as expected and an over-strength in the splice region is evident. To account for ASR/DEF damage, the analytical model proposes a reduction factor to decrease the bond strength of the splice region to predict ultimate performance of the region with different levels of premature concrete deterioration.

Made available in DSpace on 2014-07-29T15:18:22Z (GMT). No. of bitstreams: 1 dissertacao sandra k de melo - parte 1.pdf: 1174678 bytes, checksum: 23084cd61c88de8cd244682ffbc84c82 (MD5) Previous issue date: 2010-07-05 / Delayed ettringite formation (DEF) is a special type of an internal sulfate attack with SO4 2- ions from cement. This process is distinguished by neoformation of ettringite in concrete thermally cured at high temperature levels and exposed to high moisture in service life. This phenomenon can promote expansion and cracking, leading to rupture and spalling, achieving severe deterioration. This research had an experimental approach with the purpose to investigate DEF in concretes with pozzolanic Portland cement containing fly ash. These concretes were undergone to temperature rise by heat of hydration. It was produced two types of pumped concrete with cement content of 350 kg/m3 and 450 kg/m3 containing basaltic aggregate. Two big specimens were cast containing 200 liters of concrete and were immediately submitted to adiabatic temperature rise tests. After that, several specimens were drilled from them in order to evaluate compressive strength and elasticity modulus, as well as microstructural investigations by scanning electron microscopy (SEM) and X Ray diffraction (XRD) along 270 days. In addition, it was cast several cylindrical and prismatic samples with concrete containing 350 kg/m3of cement. Some of them were stored at the same condition of those during the thermal cure and others were conditioned in a moist room as reference, for properties and microstructural investigation. Prismatic ones were submitted to mass variation study, ultrasonic wave tests and also expansion tests. In order to complement this experimental program, a specific study on cement pastes was performed. This involved casting three series of cylindrical samples submitted to different cure cycles followed by evaluation of mass variation, ultrasonic velocity and also microstructure investigation by SEM and XRD. Main results proved that rising internal temperature of concrete by hydration heat above 60ºC promote delayed ettringite formation by microstructural analyses, although this formation had not caused negative consequences on mechanic properties of concretes up to age of 270 days evaluated. The study on the cement pastes confirmed that high temperatures affects the microstructure of cement matrix and also the formed products, collaborating to the formation of hydrated alumina phases besides ettringite. The presence of suggestive thaumasite at advanced ages seems to indicate that this calcium silicate sulfo-carbonate hydrate can accompany DEF process. / A formação da etringita tardia - Delayed Ettringite Formation (DEF) é um tipo especial de ataque por sulfato interno, em que os íons SO4 2- são provenientes do cimento. O processo se distingue pela neoformação da etringita em concretos curados termicamente às elevadas temperaturas e expostos às altas umidades na etapa de serviço. Tal fenômeno pode promover expansão e consequente fissuração, culminando na ruptura e lascamento do material, levando-o à severa deterioração. Este trabalho, de caráter experimental, objetivou investigar a formação da etringita tardia em concretos de cimento Porltand pozolânico, contendo cinza volante, submetido à elevação da temperatura devido ao calor de hidratação do cimento. Para isso, foram produzidos dois concretos bombeados, contendo agregados basálticos, e com consumos de cimento de 350 kg/m3 e 450 kg/m3, com os quais foram moldados dois corpos-de-prova (CPs) de 200 litros, que foram, separadamente, submetidos aos ensaios de elevação adiabática de temperatura. Após o ciclo de cura térmica nestes ensaios, deles foram extraídos corpos-de-prova para a avaliação da resistência à compressão e módulo de elasticidade, além de investigações microestruturais por microscopia eletrônica de varredura (MEV) e difração de Raios X (DRX) durante 270 dias. Adicionalmente, foram moldadas duas séries de corpos-de-prova cilíndricos e prismáticos com o primeiro concreto, sendo que uma foi armazenada na câmara adiabática juntamente com o CP de 200 L e a outra curada continuamente em câmara úmida, servindo de referência para as análises do comportamento mecânico e investigações microestruturais dos CPs cilíndricos. Os CPs prismáticos foram utilizados para a avaliação da variação de massa, velocidade ultrassônica e expansão. Para complementar a pesquisa, realizou-se, também, um estudo específico em pastas de cimento, sendo moldadas três séries de CPs cilíndricos, que foram submetidas a três diferentes ciclos de cura seguidas por uma avaliação da variação de massa e velocidade ultrassônica, além de investigações microestruturais por MEV e DRX. Os principais resultados mostraram que o aumento da temperatura interna do concreto, acima de 60ºC, por calor de hidratação do cimento, propiciou a formação da etringita tardia, constatada pela presença de etringita neoformada durante as análises microestruturais, porém sem efeito negativo sobre as propriedades mecânicas avaliadas até a idade investigada de 270 dias. O estudo de pasta comprovou que as altas temperaturas influem na porosidade da microestrutura da matriz cimentícia e sobre o tipo de produto formado, favorecendo a formação de aluminatos hidratados ao final do ciclo térmico e da etringita durante a estocagem sob alta umidade. A sugestiva presença da taumasita, em idades mais avançadas, parece indicar que este sulfocarbonato de cálcio e sílica hidratado pode acompanhar o processo de DEF.