Submitted by MARCIA ROVADOSCHI (marciar@unifra.br) on 2018-08-20T12:45:35Z No. of bitstreams: 2 Tese_MarceloAdrianoDuart.pdf: 8331452 bytes, checksum: d69e28005ad96f39781d95f4cfc7f7fb (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-08-20T12:45:35Z (GMT). No. of bitstreams: 2 Tese_MarceloAdrianoDuart.pdf: 8331452 bytes, checksum: d69e28005ad96f39781d95f4cfc7f7fb (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-07-31 / Civil construction industry has been developing technologically with the growth in the number of works in various sectors such as housing, transport, industry and infrastructure. This study is intended to contribute to the development of scientific cementitious materials by studying the use of carbon nanomaterials as carbon nanotubes (CNT) and nanoparticles of Hydrated Calcium Silicate (C-S-H) incorporated into the matrix of these materials, which can be categorized as composite, in this case nanocomposites. Materials performance is usually related to the existence of considerable flaws or deficiencies in some properties or characteristics. The incorporation of nanomaterials is a possibility for the amelioration or even create some characteristic and materials property. The use of CNT has already been investigated and the results have shown that though with increase of costs produced materials have positive characteristics such compression and tensile resistance increase and still elasticity modulus increase. Currently steel is used but the fibers and filler materials such as CNT may be an alternative because they can have tensile strength up to 100 times higher than steel, as recent research has shown. The main assumption is that nanoparticles such as C-S-H and oxidized multi walled carbon nanotubes (MWCNT-OX) favor the kinetics of cement hydration and contribute to the nucleation and crystal growth enhancing material characteristics produced as concrete and mortar, for example. In general, it was verified that the combined additions of C-S-H with Ca / Si = 0.8 ratio with nanotubes brought positive results of nanocomposite nanostructure improvements, verified by porosity, permeability analysis and qualitative analysis of electron microscopy images. An increase in the value of the mechanical properties analyzed was shown as a 33% increase in compressive strength, 38% increase in modulus of elasticity and 30% in tensile strength. It is also concluded that using the C-S-H addition with Ca/Si ratio = 0.8 in isolation is a viable alternative to produce relevant results with a lower cost than to opt for mixed additions, since CNT are still materials with high cost and more complex production than C-S-H. / A construção civil vem se desenvolvendo tecnologicamente acompanhando o crescimento do número de obras em vários setores como habitacional, transportes, industrial e infraestrutura. Este projeto pretende contribuir cientificamente para o desenvolvimento de materiais cimentícios através do estudo da utilização de nanomateriais de carbono como nanotubos de carbono (NTC) e também nanopartículas de Silicato de Cálcio Hidratado (C-S-H) incorporadas à matriz destes materiais, que podem ser classificados como compósitos, neste caso nanocompósitos. O desempenho dos materias normalmente está relacionado a existência de falhas ou deficiências consideráveis em algumas propriedades e caracteristicas. A incorporação de nanomateriais é uma possibilidade para o melhoramento ou até mesmo a criação de alguma característica ou propriedade em determinados materiais. A utilização de NTC já vem sendo pesquisada e os resultados têm demonstrado que, embora com elevação dos custos, os materiais produzidos apresentam características positivas como: aumento da resistência à compressão e flexão e também do módulo de elasticidade. Atualmente usa-se o aço e fibras mas a adição de materiais como NTC pode ser uma alternativa, pois estes podem apresentar resistência à tração até 100 vezes maior que o aço, conforme pesquisas recentes já demonstram. A hipótese principal é que nanopartículas de C-S-H e também NTC favorecem a cinética de hidratação de cimentos e contribuem para a nucleação e crescimentos de cristais de produtos hidratados melhorando características dos materiais produzidos como por exemplo: concretos e argamassas. De forma geral, verificou-se que as adições combinadas de C-S-H com relação Ca/Si=0,8 com nanotubos de carbono paredes múltiplas oxidados (NTCPM-OX) trouxeram resultados positivos de melhoria na nanoestrutura dos nanocompósitos produzidos, verificados pela análise da porosidade, permeabilidade e também pela análise qualitativa de imagens de microscopia eletrônica. Veficou-se aumento do valor das propriedades mecânicas analisadas como 33% de aumento da resistência à compressão, 38% de aumento do módulo de elasticidade dinâmico e 30% da resistência à tração. Conclui-se ainda que usar a adição de C-S-H com relação Ca/Si=0,8 de forma isolada é uma alternativa viável produzindo resultados relevantes com um custo mais baixo que optar por adições mistas, visto que ainda os NTC são materiais com custo elevado e produção mais complexa do que o C-S-H.

Concrete is one of the most widely used materials in the world. It is also one of the most versatile while complex materials which human have used for construction. However, an important weakness of concrete (cement-based composites) is its weak tensile properties. Therefore, over the past thirty years many studies were focused to improve its tensile properties using a variety of physical and chemical methods. One of the most successful attempts is to use polymer fibers in the structure of concrete to obtain a composite with high tensile strength and ductility.However, a thorough understanding of the mechanical behavior of fiber reinforced concrete requires the knowledge of fiber/matrix interfaces at the nanoscale. In this study, a combination of atomistic simulations and experimental techniques has been used to study the nanostructure of fiber/matrix interfaces. A new model for calcium-silicate-hydrate (C-S-H)/fiber interfaces is also proposed based on Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDX) analyses. Finally, the adhesion energies between the C-S-H gel and three different polymeric fibers (polyvinyl alcohol, nylon-6 and polypropylene) were numerically studied at the atomistic level, since adhesion plays a key role in the design of ductile fiber reinforced composites. The mechanisms of adhesion as a function of the nanostructure of fiber/matrix interfaces are further studied and discussed. It is observed that the functional group in the structure of polymer macromolecule affects the adhesion energy primarily by changing the C/S ratio of the C-S-H at the interface and further by absorbing additional positive ions in the C-S-H structure. Then the mechanical response of cement paste with added polymeric fibers were studied. A correlation between adhesion energies and the load-displacement curve in split-cylinder test was found. Moreover, as there is a great interest in cellulose-based cement composites, bamboo fibers is added to the cement paste and the fiber/matrix interface and its effect on structure of C-S-H were investigated.

Yes / To realize the sustainable development of concrete, it is vital to mitigate its consumption and environmental footprint (especially CO2 footprint) from prolonging the service life through upgrading mechanical and durable performances of concrete. Incorporating nanofillers can effectively tailor the microstructures and performances of bulk cement paste and cement paste at interfacial transition zone in concrete. The hydrated calcium silicate (C–S–H) gels account for half of the volume of hardened Portland cement pastes, and they are the fundamental source of overall properties of concrete. However, the underlying mechanisms of nanofillers on C–S–H gels remains unclear. Herein, this paper underpinned the role of 5 types of representative nanofillers in tailoring the nanostructure of C–S–H gels in cement composites. The research results demonstrated that through the nano-core effect, nanofillers induce the formation of two new C–S–H gels in outer hydration products, namely nano-core-shell element doped low-density C–S–H (NEDLD C–S–H) and nano-core-shell element doped high-density C–S–H (NEDHD C–S–H). The indentation modulus/hardness of NEDLD and NEDHD C–S–H reaches 25.4/0.80 GPa and 46.7/2.72 GPa, respectively. Such superior performances of NEDLD and NEDHD C–S–H derive from the existence of nano-core-shell elements in C–S–H gels rather than the increase in C–S–H packing density. In a short-range, nanofillers form nano-core-shell elements by adsorbing silica tetrahedrons during the hydration process, improving the mechanical properties of C–S–H basic building blocks. In the long-range, the nano-core-shell elements modify the nano-scale performances of C–S–H gels in outer hydration products due to the increase of C–S–H gels’ integrality. / The authors would like to thank the funding offered by the National Science Foundation of China (52308236, 51978127, 51908103, and 52368031), National Key Research and Development Program of China (2018YFC070560 and 2017YFC0703410), the China Postdoctoral Science Foundation (2022M720648, 2022M710973, 2022M713497). / The full-text of this article will be released for public view at the end of the publisher embargo on 01 Dec 2024.

Dans le cadre du concept français de stockage géologique profond des déchets radioactifs, ilest envisagé de stocker les colis vitrifiés de déchets de Moyenne Activité à Vie Longue au sein de surconteneurs en béton. La chimie de l'eau interstitielle étant susceptible de modifier la durabilité chimique des matrices vitreuses, cette étude a été menée afin d'appréhender la phénoménologie d'altération du verre au contact d'eaux cimentaires. Des solutions représentatives des deux premiers stades de dégradation d'un ciment Portland et d'un ciment bas pH ont été étudiées. Les conditions dans lesquelles le rapport S/V (surface de verre sur volume de solution) et la chimie de la solution pilotent les mécanismes d'altération du verre sont clairement établies.Si le flux d'éléments relâchés par le verre est suffisant pour atteindre et maintenir un état de sursaturation qui permette la nucléation de phases secondaires (C-S-H et zéolithes), alors la précipitation de ces phases pilote la dissolution du verre. Les rôles antagonistes du calcium ont été mis en évidence en fonction du régime d'altération du verre. A faible rapport S/V, l'incorporationdu calcium au sein de la pellicule d'altération augmente ses propriétés passivantes. A l'inverse, àfort rapport S/V, le calcium précipite sous forme de phases cimentaires consommatrices d'élémentsréticulants de la pellicule d'altération, ce qui engendre le maintien d'une vitesse d'altération élevée.Le rôle bénéfique d'un ciment bas pH vis-à-vis de l'altération du verre est expliqué à partir de cesrésultats. Ce travail constitue une première étape visant à la compréhension fine des mécanismesd'altération du verre en milieu cimentaire. / In the French deep geological repository concept, intermediate-level vitrified wastepackages could be disposed of concrete medium. Chemical composition and pH of the interstitialleaching water are expected to influence the chemical durability of glass. Investigations have thusbeen carried out to study glass dissolution mechanisms and kinetics in contact with cement waters.Three cement pore waters were studied: the first two correspond to two stages of the Portlandcement aging and the third corresponds to equilibrium with a low pH concrete. The S/V ratio(glass-surface-area-to-solution-volume ratio) and the chemistry of cement waters are the two mainparameters that control glass alteration mechanisms.If the leaching flow from the glass allows a degree of supersaturation to be reached and maintainedwhich leads to nucleation of secondary phases, then precipitation of these phases drives glassdissolution. At a very low S/V ratio, the calcium uptake into the alteration layer increases itspassivating properties. Conversely, at a high S/V ratio, the calcium precipitates as cementitiousphases consuming elements which form the alteration layer. The glass dissolution is maintained ata high rate.This study contributes to highlighting the beneficial role of low pH cement in glass alteration, andis a first step towards understanding the mechanisms between the glass and the cement medium.

Un modèle de transport réactif est proposé pour simuler la réactivité des matériaux à base de ciment en contact avec une saumure saturée en CO2 et/ou le CO2 supercritique (CO2sc) dans les conditions de stockage géologique du CO2. Un code a été développé pour résoudre simultanément le transport et la chimie par une approche globale couplée, compte tenu de l'effet de la température et de la pression. La variabilité des propriétés du CO2sc avec la pression et la température, telles que la solubilité dans l'eau, la densité et la viscosité sont pris en compte. On suppose que tous les processus chimiques sont en équilibre thermodynamique. Les réactions de dissolution et de précipitation de la portlandite (CH) et de calcite (CC) sont décrites par des lois d'action de masse et des seuils de produit d'activité ioniques. Une cinétique de dissolution de CH est introduite pour faciliter la convergence numérique. La définition d'une variable principale permet de capturer la précipitation et la dissolution des phases solides à base de calcium. Une généralisation de la loi d'action de masse est développée et appliquée aux silicates de calcium hydratés (CSH) pour tenir compte de la variation continue (diminution) du rapport Ca/Si au cours de la dissolution des CSH. Les variations de porosité et de la microstructure induites par les réactions de précipitation et de dissolution sont également prises en compte. Le couplage entre le transport et la chimie est modélisé par cinq équations de bilan de masse écrites pour chaque atome (Ca, Si, C, K, Cl), ainsi que par une équation de conservation de la masse totale et celle de la charge électrique. Les lois de Darcy et de Nernst-Planck sont utilisées pour décrire le transport de masse et d'ions. Les propriétés de transport dépendent du degré de saturation et de la porosité. Le modèle est implémenté dans le code de volumes finis, Bil. Les principes de cette méthode et l'approche de modélisation sont discutés et illustrés sur un exemple simple. Ce modèle est en mesure de simuler les processus de carbonatation des matériaux à base de ciment, dans des conditions à la fois saturés et insaturés, dans une large plage de concentration de CO2, de température et de pression. Plusieurs expériences, rapportées dans la littérature, sont simulées en utilisant divers types de conditions aux limites: (i) solutions saturées ou non en CO2 et carbonate de calcium, (ii) gas supercritique de CO2. Les prédictions sont comparées avec les observations expérimentales. Certains phénomènes observés expérimentalement peuvent être également expliqués par le modèle / A reactive transport model is proposed to simulate the reactivity of cement based material in contact with CO2-saturated brine and supercritical CO2 (scCO2) under CO2 geological storage conditions. This code is developed to solve simultaneously transport and chemistry by a global coupled approach, considering the effect of temperature and pressure. The variability of scCO2 properties with pressure and temperature, such as solubility in water, density and viscosity are taken into account. It is assumed that all chemical processes are in thermodynamical equilibrium. Dissolution and precipitation reactions for portlandite (CH) and calcite (CC) are described by mass action laws and threshold of ion activity products in order to account for complete dissolved minerals. A chemical kinetics for the dissolution and precipitation of CH and CC is introduced to facilitate numerical convergence. One properly chosen variable is able to capture the precipitation and dissolution of the relevant phase. A generalization of the mass action law is developed and applied to calcium silicate hydrates (C-S-H) to take into account the continuous variation (decrease) of the Ca/Si ratio during the dissolution reaction of C-S-H. The changes in porosity and microstructure induced by the precipitation and dissolution reactions are also taken into account. Couplings between transport equations and chemical reactions are treated thanks to five mass balance equations written for each atom (Ca, Si, C, K, Cl) as well as one equation for charge balance and one for the total mass. Ion transport is described by using the Nernst-Plank equation as well as advection, while gas and liquid mass flows are governed by advection. Effect of the microstructure and saturation change during carbonation to transport properties is also considered. The model is implemented within a finite-volume code, Bil. Principles of this method and modeling approach are discussed and illustrated with the help of a simple example. This model, with all the efforts above, is able to simulate the carbonation processes for cement based materials, at both saturated and unsaturated conditions, in a wide CO2 concentration, temperature and pressure range. Several sets of experiments, including sandstone-like conditions, limestone-like conditions, supercritical CO2 boundary and unsaturated conditions reported in the literature are simulated. Good predictions are provided by the code when compared with experimental observations. Some experimental observed phenomena are also explained by the model in terms of calcite precipitation front, CH dissolution front, porosity profile, etc

Le projet du Centre Industriel de stockage Géologique ou CIEGO porté par l’Andra (Agence nationale pour la gestion des déchets radioactifs) permettra de stocker les déchets de moyenne activité à vie longue et haute activité à 500 mètres de profondeur dans des galeries en bétons construites dans une couche d’argilite. L’objectif principal de cette thèse est d’étudier les effets des rayonnements gamma de faible débit de dose sur le comportement physico-chimique et hydrothermo-mécanique du béton. Des expériences à différentes échelles ont donc été réalisées au cours de cette thèse. Des mortiers et des pâtes de ciment ont été irradiés dans un irradiateur gamma (E = 0,667 MeV, LET = 0,23 keV.μm-1) sur le site du cyclotron Arronax (Saint-Herblain,France). La variation des résistances en flexion et en compression a été déterminée pour différents types de matériaux (mortier humide, sec et carbonaté et pâte cimentaire sèche et carbonatée) montrant une importante diminution des propriétés mécaniques. Ces variations on été expliquées par des études physico-chimiques de sillicates de calcium hydratés (C-S-H), phase prédominante du béton, montrant une modification sous rayonnement gamma. Les résultats microscopiques et macroscopiques ont ainsi été comparés afin de comprendre l’évolution d’un matériau cimentaire sous rayonnement gamma de faible débit de dose. / The project of Centre Industriel de stockage Géologique or CIGEO supported by Andra (French Agency for Radioactive Waste Management) will allow storing intermediate level and high-level wastes 500 meters deep inconcrete galleries built in an impermeable argillaceous rock. The main objective of this study is to understand the effects of lower dose rate external gamma irradiations on the physical-chemical and hydro-thermo-mechanical behavior of concrete which could be used in the CIGEO structures and elements. A multiscale and multi-physics experimental protocol has been established during this PhD work. Mortar and cement paste specimens have been irradiated in a gamma irradiator (E = 0.667 MeV,LET = 0.23 keV.μm-1) and subsequently subjected to bending and compressive mechanical stress tests. These irradiations have been performed at the ARRONAX cyclotron facility (Saint-Herblain, France). The variations of compressive and bending strength after irradiation have been measured for different materials (humid, dried and carbonated mortar and cement pastes) showing a high decrease of mechanicals properties. Mechanical variations have been explained by the study of physical-chemical evolution of calcium silicate hydrates (C-S-H), the major phase composing the concrete which can be modified under gamma radiation. Microscopic and macroscopic results were successfully compared to explain the evolution of the cementitious materials under low doserate of gamma radiation.

Le latex est utilisé dans les mortiers industriels dans le but d’améliorer les propriétés de ce matériau, tels que la maniabilité de la pâte à l’état frais, l’adhésion sur le support pour les mortiers-colles et les propriétés mécaniques à l’état durci du matériau. Ainsi l’adsorption du latex sur les phases minérales du ciment a un impact sur la rhéologie et les propriétés mécaniques du mortier frais et durci. Ce comportement résulte des interactions du latex avec les phases cimentaires et de l’avancement des différentes réactions d’hydratation elles-mêmes affectées par la présence de latex. Or, ces interactions ne sont toujours pas bien comprises du fait de la réactivité du ciment. L’objectif de ce travail est de mieux comprendre le rôle du latex en particulier l’influence de ses caractéristiques notamment la taille, le dosage et la densité surfacique de charge du latex, sur le comportement rhéologique du mortier au jeune âge et de ses propriétés à long terme en s’affranchissant de tous les effets liés à l’hydratation du ciment. Pour cela, nous travaillons avec un système modèle inerte qui permet de rendre compte des effets induits par le latex en s’affranchissant de la réactivité du ciment. L’influence des caractéristiques du latex sur les propriétés mécaniques d´une suspension de minéral inerte est estimée par des mesures de rhéométrie dynamique. Les résultats sont corrélés à l’adsorption des particules de latex sur la surface du minéral inerte qui estimée à travers l’établissement des isothermes d’adsorption. Pour ce faire, l’adsorption des différents latex est réalisée sur des surfaces planes de silice (lames de verre) couvertes d’hydrates de silicates de calcium C-S-H (principal hydrate de ciment). L’adsorption du latex sur le minéral inerte est observée directement par microscopie : soit par microscopie optique dans le cas des latex de grande taille (1µm) soit par microscopie à force atomique dans le cas de latex de petite taille (210nm). Les isothermes d’adsorption obtenues des trois latex étudiés, différant soit par la taille soit par la charge, ont montré que, à concentration massique équivalente, le latex chargé s’adsorbe plus que le non chargé, et le latex de petite taille s’adsorbe plus que le gros latex parce qu’il y a plus de particules en interaction avec la surface. La topographie d’adsorption des particules de latex sur la surface est également différente : les latex chargés apparaissent beaucoup plus agrégés que le latex non chargé. La filmification des latex n’est pas observée pour les dosages de latex étudiés. Un accord qualitatif a été obtenu avec les simulations numériques, par méthode Monte Carlo, de l’adsorption des latex. En ce qui concerne les propriétés rhéologiques, les mesures ont été réalisées sur des suspensions de calcite dans une solution saturée d’hydroxyde de calcium. Ces mesures mettent en évidence la contribution des particules de latex au réseau granulaire qui se traduit par l’augmentation de la déformation critique avec la quantité de latex. / Latex is used in industrial mortars to improve the material properties. This behaviour is obviously related to the interactions between cement phases and latex which are still not understood. In this frame, the aim of the present work is to understand the role of latexes in mortar in particular how the various latex characteristics, such as the latex chemistry surface, or the latex size, influence the characteristics of this complex granular system. The major issue concerns the reactivity of the cement: indeed, several parameters are modified during cement hydration which governs the development of the paste mechanical properties. Consequently in order to avoid side effects due to cement hydration, we studied the effect of different latexes on an inert model system able to mimic cement paste. Three different latexes differing from each other in their size and also in their surface charge and surface chemistry were used. The distribution of the different latexes between the interstitial solution and the mineral surface was evaluated using microscopy methods for different latex amounts and correlated to mechanical characteristics of the paste estimated from dynamic rheometry measurements.The adsorption measurements are performed on a flat surface (glass slide) covered by C-S-H in equilibrium with saturated lime solution. The adsorption of latex particles on mineral surface is observed by Atomic Force Microscopy for the smallest latex (210nm) and optical microscopy for the biggest one (1µm). The results obtained show a difference of adsorption latex and how the particles are arranged onto the surface. For the same mass of latex introduced initially, the charged latex are the most adsorbed and appear more aggregated than no charged latex, the small latex is adsorbed more than the big one. The latex filmification is not observed in the case of our study. Qualitatively, the numerical simulations using Monte Carlo simulations are in agreement with experiments.Concerning the rheological measurements, we used calcite suspensions in equilibrium with saturated lime solution. The results report the contribution of different latex characteristics on mechanical properties of mineral particles and latex networks. The critical strain (maximum strain supported by the solid network) increases with the amount of latex.

Le présent travail propose et développe une méthodologie complète d’identification des propriétés mécaniques locales d’un matériau hétérogène à l’échelle des phases constitutives. Il s’agit d’une combinaison de compétences très diverses, à la fois en théorique, en simulation numérique et en expérimentation. Plus précisément, la partie théorique concerne la détermination des relations nano-micro pour le module d’indentation homogénéisé par des techniques de changement d’échelle; la partie numérique basée sur la théorie du calcul à la rupture est réalisée en vue de trouver de ces dernières relations applicables pour la dureté; et la dernière partie est effectuée pour récupérer les propriétés homogénéisées par la voie expérimentale à l’aide de la technique de nano-indentation. L’étude expérimentale de la thèse est pour l’objectif de déterminer des propriétés d’indentation de différents échantillons de pâte de ciment. Un programme expérimental complet, est développé, qui permet de caractériser des phases principales à l’échelle micrométrique de ce matériau, parmi lesquelles nous nous intéressons surtout à celles plus importantes correspondantes à des phases de la matrice C-S-H. La modélisation du problème lié à l’enfoncement d’une pointe d’indentation dans un matériau est étudiée. Pour cela, la première voie, basée sur l’approche cinématique du calcul à la rupture, consiste à tenter de construire des mécanismes de ruine analytiquement, puis à les faire évoluer en fonction du changement de la géométrie initiale, afin d’obtenir la charge de ruine correspondante. La seconde voie consiste ensuite à suivre la même approche, mais en construisant numériquement ces mécanismes de ruine. La charge obtenue dépend naturellement des paramètres de critères retenus, que l’on détermine grâce à la combinaison avec les résultats expérimentaux. Les critères de résistance de Von-Mises et de Tresca valables pour des matériaux purement cohérents ainsi que celui de forme elliptique sont examinés dans ce travail / The present work proposes and develops a complete methodology for identifying the local mechanical properties of a heterogeneous material at the scale of the constitutive phases. It is a combination of very diverse skills in theory, in numerical simulation and in experimentation. More precisely, the theoretical part concerns the determination of the nano-micro relations for the indentation module; the numerical part based on the yield design theory is carried out to find the last relations applicable for the hardness; and the last part is performed to obtain homogenized properties by the experimental way using the nano-indentation technique. The experimental study of the thesis is for the purpose of determining indentation properties of different cement paste samples. A complete experimental program, is developed, which allows characterizing the main phases at the micrometric scale of this material, among which we are mainly interested in the C-S-H matrix phases. The modeling of the problem related to the penetration of an indentation point into a material is studied. For this, the first way, based on the kinematic approach of the yield design theory, consists in trying to construct ruin mechanisms analytically, then to make them evolve according to the change of the initial geometry, in order to obtain the corresponding ultimate load. The second way is then to follow the same approach, but by building numerically these ruin mechanisms. The obtained load depends naturally on the retained criteria parameters, which are determined by the combination with the experimental results. The Von-Mises and Tresca strength criteria for purely coherent materials as well as the elliptical one are examined in this work

Made available in DSpace on 2014-12-17T14:07:05Z (GMT). No. of bitstreams: 1 DiegoBR_DISSERT.pdf: 2561284 bytes, checksum: 728dce6008fc70c37faa4759ea2eba6d (MD5) Previous issue date: 2012-02-16 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Nowadays, the search for new technologies that are able to follow the upcoming challenges in oil industry is a constant. Always trying properties improvements of the used materials, looking for the best performance and greater life time. Besides the search for technologies that show an improvement of performance, the search for materials environmentally correct along the whole production process. In Oil well cementing, this search for new technologies passes through the development of slurry systems that support these requests and that are also environmentally friendly. In this context, the use of geopolymer slurries is a great alternative route to cementing oil wells. Besides having good properties, comparable to Portland cement slurries, this alternative material releases much less CO2 gas in the production of their root materials when compared the production of Portland cement, which releases tons of CO2. In order to improve the properties of geopolymer slurries has been added Calcium Oxide, as observed in other studies that slurries where the Calcium is present the values of compressive strength is greater. The addition has been realized based in the CaO/SiO2 molar ratio of 0.05, 0.10 and 0.15. Have been performed compressive strength tests, thickening time, rheology and fliud loss control test of the slurries, following NBR 9831, as well as the physical chemical characterization of XRD, SEM and TG. Has been observed in most of the tests the slurries follow a tendency until the ratio of 0.10, which inverses in the ratio 0.15. This behavior can be explained by two phenomena that occur simultaneously, the first one is the break of the polymer chains and a consequent increase in molucules mobility, which prevails until the ratio of 0.1, and the second is possible approach of the chains due to the capacity of the calcium ions stabilize the charges of two different aluminum. There is only one linearity in the mechanical behavior that can be attributed to the appereance of the C-S-H phase. Based on this, it is concluded that the phenomenon of breaking the polymer chains predominates until the ratio of 0.1, causing an increase of the filtrate volume, lower rheological parameters and increasing thickening time. From the ratio of 0.15 the approach of the chains predominates, and the behavior is reversed / Nos dias atuais a busca por novas tecnologias que possam acompanhar os desafios que surgem dia a dia na ind?stria do petr?leo ? constante, sempre tentando melhorar as propriedades dos materiais que s?o utilizados, buscando o melhor desempenho e maior vida ?til. Al?m de buscar novas tecnologias ? de fundamental import?ncia o desempenho dos materiais e que estes sejam ambientalmente corretos. No ramo da cimenta??o de po?os de petr?leo, essa procura por novas tecnologias passa pelo desenvolvimento de sistemas de pastas que suportem as solicita??es requeridas pelas normas internacionais e nacionais para esse setor. Nesse contexto, lan?a o desafio de se produzir novos sistemas de pastas para o revestimento de po?os petrol?feros, sejam eles para po?os on shore ou off shore. As pastas geopolim?ricas apresentam-se como uma boa alternativa para a cimenta??o de po?os de petr?leo, pois alem de possuir boas propriedades, compar?veis as pastas de cimento Portland, esse material libera muito menos CO2 na produ??o das suas meterias primas quando comparados ? produ??o do cimento Portland. Com o intu?do de melhorar as propriedades das pastas geopolim?ricas foi adicionado o ?xido de c?lcio, pois foi observado em outros trabalhos que pastas onde o c?lcio esta presente os valores de resist?ncia a compress?o s?o maiores. A adi??o foi realizada baseada na raz?o molar CaO/SiO2 de 0,05, 0,10 e 0,15, foram realizados ensaios de resist?ncia a compress?o, tempo de espessamento, reologia e filtrado das pastas seguindo a NBR 9831, bem como as caracteriza??es f?sico qu?micas de DRX, MEV, TG. Foi observado que na maioria dos ensaios as pastas seguem uma tend?ncia ate a raz?o de 0,10 que se inverte na raz?o de 0,15. Esse comportamento pode ser explicado por dois fen?menos que ocorrem simultaneamente: o primeiro ? a quebra das cadeias polim?ricas com um conseq?ente aumento da mobilidade das mol?culas, que prevalece ate a raz?o de 0,1, e o segundo ? a poss?vel aproxima??o das cadeias devido a capacidade do ?on c?lcio estabilizar as cargas de dois alum?nios diferentes. Existe apenas a linearidade no comportamento mec?nico que pode ser atribu?do ao aparecimento da fase C-S-H. Com base nisso pode se concluir que o fen?meno de quebra das cadeias polim?ricas predomina at? a raz?o de 0,1, provocando o aumento no volume de filtrado, diminui??o dos par?metros reol?gicos e aumento do tempo de espessamento. A partir da raz?o 0,15 a aproxima??o das cadeias predomina e assim o comportamento se inverte

Le processus de l’hydratation de ciment et la microstructure qui en résulte, dépendent de la formulation de la pâte et des conditions d’hydratation. Parmi différents facteurs, la température d’hydratation a un effet important sur la microstructure et les propriétés physiques et mécaniques des matériaux cimentaires. Ceci est particulièrement important pour l’étude du comportement des ciments pétroliers. En effet, dans un puits pétrolier, une gaine de ciment est coulée entre la roche réservoir et le cuvelage en acier pour assurer entre autre la stabilité et l’étanchéité du puits. En raison du gradient géothermique (environ 25°C par km), la gaine de ciment le long d'un puits est exposée à une température d'hydratation qui augmente avec la profondeur menant à une augmentation de perméabilité et une baisse de propriétés mécaniques le long du puits. L'objectif cette thèse est d'étudier l'effet de la température d'hydratation dans la gamme de 7°C à 90°C sur la microstructure d'une pâte de ciment (classe G) et d'établir le lien entre les modifications microstructurales et les propriétés élastiques du matériau. La caractérisation de la microstructure est faite en considérant une combinaison de plusieurs méthodes expérimentales, à savoir, la diffraction des rayons X & l’analyse Rietveld, l'analyse thermogravimétrique, porosimétrie par l'intrusion de mercure, l'évaluation de la porosité par lyophilisation ou par séchage à 11% HR, essais de sorption au Nitrogène et à la vapeur d'eau et finalement, la résonance magnétique nucléaire 1H. L’assemblage de masse des différentes phases de la microstructure a été évalué montrant une légère dépendance à la température d’hydratation. L’étude de la porosité a montré une augmentation de la porosité capillaire et une légère diminution de la porosité totale à 28 jours d’hydratation, ce qui résulte en une diminution de la porosité du gel de C-S-H en augmentant la température d'hydratation. Une méthode d'analyse a été proposée pour évaluer la densité saturée de C-S-H et sa composition chimique en termes des rapports molaires C/S et H/S pour un C-S-H sec et saturé. Les résultats montrent que la densité de C-S-H augmente avec la température d'hydratation expliquant ainsi l'augmentation observée de la porosité capillaire à températures élevées. Les rapports C/S et H/S diminuent avec l’augmentation de la température d’hydratation. La caractérisation de la microstructure a permis d’alimenter un modèle micromécanique destiné à prédire les propriétés élastiques de la pâte de ciment pour différentes températures d’hydratation. Des modèles d’homogénéisation auto-cohérents à deux et trois échelles ont montré que l’augmentation de la porosité capillaire ne suffit pas pour expliquer la baisse des propriétés mécaniques avec la température. En effet, l’augmentation de la densité de C-S-H avec la température d’hydratation annule l’effet de l’augmentation de la porosité capillaire sur les propriétés élastiques. La réduction des propriétés mécaniques pourrait être expliquée en considérant une distribution de porosité au sein de C-S-H sous forme de C-S-H basse densité LD et haute densité HD telle que proposée par Tennis et Jennings (2000). Cette possibilité est investiguée par une combinaison de techniques de porosimétrie : porosimétrie par l'intrusion de mercure, adsorption d'azote et désorption de vapeur d'eau et par un calcul inverse à l’aide de la modélisation micromécanique. Les résultats montrent que la porosité intrinsèque LD augmente légèrement tandis que la porosité intrinsèque HD diminue de manière significative avec l'augmentation de la température d'hydratation. La diminution des propriétés élastiques des matériaux cimentaires avec l’augmentation de la température d'hydratation s’avère être due à l’action combinée de l'augmentation de la porosité capillaire et des changements de porosités intrinsèques à l’intérieure de C-S-H / The cement hydration process and the resulting microstructure are highly dependent on the cement formulation and the hydration conditions. Particularly, the hydration temperature has a significant influence on the cement paste microstructure and its mechanical properties. This is for instance important for understanding the behaviour and properties of oil-well cements which are used to form a cement sheath between the casing and the surrounding formation for stability and sealing purposes. This cement sheath is hydrated under a progressively increasing temperature along the depth of a well due to the geothermal gradient (about 25°C/km). It results generally in a decrease of the mechanical properties and an increase of permeability along the well. The aim of the present thesis is to investigate the effect of the hydration temperature in the range of 7°C to 90°C on the microstructure of a class G cement paste and to establish the link between these temperature dependent microstructure and the elastic properties of the material. The microstructure characterization is done by combining various experimental methods, including X-Ray diffraction associated with the Rietveld analysis, thermogravimetric analysis, mercury intrusion porosimetry, porosity evaluation by freeze-drying or drying at 11% RH, Nitrogen and water vapour sorption experiments and finally 1H nuclear magnetic resonance. The mass assemblage of microstructure phases at different curing temperatures has been evaluated and showed a slight dependence on the hydration temperature. The porosity evaluations show an increase of the capillary porosity and a slight decrease of the total porosity at 28 days, resulting in a decrease of the gel porosity by increasing the hydration temperature. An analysis method has been proposed to evaluate the C-S-H saturated density and chemical composition in terms of H/S and C/S molar ratios. The C-S-H bulk density is increasing with increasing hydration temperature which explains the observed increase of the capillary porosity for higher curing temperatures. The C/S ratio and H/S ratio for both solid and saturated C-S-H are decreasing with increasing curing temperature. The provided quantitative characterization of cement paste microstructure is used in a micromechanical modelling for evaluation of the elastic properties at various hydration temperatures. Two and three-scale self-consistent micromechanical models have shown that the increase of capillary porosity with increasing hydration temperature cannot fully explain the drop of elastic properties. This is mainly due to the increased elastic properties of C-S-H being denser at higher temperature that cancel the effect of increasing capillary porosity on the overall elastic properties. Another way to fully account for the decrease of the mechanical properties of cement paste is to consider the porosity distribution inside the C-S-H in the form of two distinguished C-S-H types, High Density (HD) and Low Density (LD) C-S-H, as proposed by Tennis and Jennings (2000). This possibility is probed by a combination of various porosity evaluations: Mercury intrusion porosimetry, nitrogen adsorption and water vapour desorption and by a back calculation using micromechanical modelling. The results show that the LD intrinsic porosity is slightly increasing while the HD intrinsic porosity decreases significantly with increasing hydration temperature. The decrease of the elastic properties of cement based materials with increasing hydration temperature is therefore a combined action of the increase of capillary porosity and the changes of intrinsic C-S-H porosities