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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
891

Etude des principaux modes d’action de systèmes accélérateurs des ciments Portland / Study of the main modes of action of Portland cement accelerator systems

Jachiet, Marie 24 November 2017 (has links)
Les accélérateurs sont des adjuvants couramment employés dans les matériaux cimentaires afin d’accélérer leur prise et/ou leur durcissement. Leur ajout permet d’accélérer les cadences de production de béton préfabriqué ou encore de compenser le retard d’hydratation induit par l’emploi d’ajouts minéraux cimentaires ou par des conditions hivernales. De nombreuses espèces chimiques, molécules ou ions, connues pour leur pouvoir accélérateur ont été étudiées dans la littérature. Néanmoins, souvent leur mode d’action est associé à une simple activation chimique, se caractérisant par l’accélération de l’hydratation de certaines phases cimentaires. Or au sein de la pâte cimentaire, ces adjuvants peuvent aussi avoir une action physique et modifier l’état de dispersion des grains de ciment, ce qui pourrait indirectement influencer la réactivité chimique.L’objectif de ce travail est donc d’étudier les modes d’action de différents systèmes accélérateurs en combinant l’analyse de la réactivité chimique du ciment et de l’organisation mésostructurale. Plusieurs amines de structures moléculaires différentes et plusieurs sels sodiques ont été employés seuls ou de manière combinée dans des pâtes cimentaires et des mortiers normalisés. Ces matériaux ont alors été étudiés de l’échelle nano/microscopique, puis mésoscopique à macroscopique, sur une période de temps s’étalant des premières minutes d’hydratation jusqu’à 28 jours. L’analyse du liquide interstitiel des pâtes cimentaires a permis d’évaluer les capacités de sorption et de complexation des adjuvants. Via des suivis d’hydratation par calorimétrie isotherme, diffraction des rayons X et analyse thermogravimétrique, l’impact des accélérateurs sur la dissolution des phases cimentaires anhydres et la précipitation d’hydrates a été déterminé. En parallèle, l’organisation mésostructurale des suspensions cimentaires adjuvantées a été analysée de manière directe par microscopies et granulométrie laser. Le comportement rhéologique et le suivi de sédimentation ont aussi permis d’appréhender indirectement l’état de dispersion des pâtes cimentaires. Pour finir, à l’échelle du mortier, des mesures de résistance à la compression ont été réalisées et la microstructure des échantillons a été étudiée par porosimétrie mercure et surface spécifique BET.La combinaison de ces caractérisations chimiques, physico-chimiques et granulaires a permis de mettre en évidence les principaux modes d’action des différentes familles d’accélérateurs. En particulier l’influence sur l’accélération de la structure moléculaire des amines et des espèces ioniques présentes dans le sel a été appréhendée. Enfin, l’emploi de combinaisons d’accélérateurs a permis de moduler l’accélération d’hydratation du matériau cimentaire et d’obtenir des effets synergiques. / Accelerators are common cement additives used in order to accelerate setting and/or hardening. Their addition allows accelerating production rates of precast concrete or compensating hydration retardation induced by the use of supplementary cementitious materials or by winter conditions. Several chemical species, molecules or ions, known for their accelerator power have been studied in the literature. However, their mode of action is often simply associated to chemical activation, which is characterized by hydration acceleration of particular cement phases. Yet, inside the cement paste, these additives can also have a physical action and modify the dispersion state of cement grains, which might indirectly influence chemical reactivity.Therefore the objective of this work is to study the modes of action of different accelerator systems by combining the analysis of cement chemical reactivity and mesostructural organization. Some amines with different molecular structures and some sodic salts were used individually or in a combined way in cement pastes and normalized mortars. These materials were then studied from nano/microscopic to mesoscopic and macroscopic scale over a period of time ranging from the first minutes of hydration till 28 days. The analysis of the pore solution allowed evaluating the additive sorption and complexation ability. Cement hydration was followed by isothermal calorimetry, X-ray diffraction and thermogravimetric analysis in order to determine the impact of accelerators on anhydrous cement phase dissolution and hydrate precipitation. In parallel, mesostructural organization of admixtured cement suspensions was analyzed indirectly by microscopy and laser granulometry. Rheological and sedimentation behavior also allowed apprehending indirectly the dispersion state of cement paste. Lastly, at mortar scale, compressive strength measurements were performed and sample microstructure was studied by mercury intrusion porosimetry and BET specific surface.The combination of these chemical, physicochemical and granular characterizations allowed highlighting the main modes of action of the different accelerator systems. In particular, the influence on acceleration of amine molecular structure and salt ionic species was apprehended. Finally, the use of combinations of accelerators allowed modulating the hydration acceleration of cementitious materials and obtaining synergetic effects.
892

Hydration, pore development and chemical resistance of Metakaolin-fly ash-Portland cement (MK-PFA-PC) blends

Snelson, David Geoffrey January 2005 (has links)
The aim of the project is to utilise fly ash (PFA), a waste material/industrial byproduct, with metakaolin (MK), as a partial replacement for Portland cement (PC) in mortar and paste. The influence of various compositions of MK-PFA-PC blends on the resistance to the action of sulphate and synthetic seawater solutions, setting time and heat of hydration will be examined. MK is calcinated clay and is a relatively new pozzolanic material. Although it is a very effective pozzolan it is also very expensive. Using FA, which is a much less expensive material, as a PC replacement material, is problematic, as there is slow and low early strength development whereas MK enhances early strength development. Combining these materials in ternary blends should therefore produce a high performance material at an acceptable cost for use as a pozzolan. However the properties and performance of such a material still need to be fully established. The results of the research show, for the initial and final setting time of binary MK-PC pastes there is a substantial increase at 5% MK and then decreases at 10 and 15% MK before increasing again at 20% MK replacement level. However, with PFA there are different trends to those observed when using MK alone. The initial and final setting time of binary PFA-PC pastes shows a slight increase at 10% PFA and then systematically increases with increase in PFA content up to 40% PFA. Evaluation of sample preparation for porosimetry found that, overall, the compression tested samples show a lower proportion of 'fine pores' (volume (%) 0.05) jam than the cored and cut paste disks. It is deducted that this is due to the widespread microcracking during failure of the cubes under compressive loading thus modifying the pore structure present in the compressive tested samples. In strength development of mortar there is very little advantage in using MK over binary PFA-PC mortar blends when exposed to sulphate solution for up to 2 years. The strength behaviour in seawater is however quite different from that observed in mortar exposed to sulphate solution. As the MK replacement levels increase relative to the PFA levels the resistance to seawater attack improves significantly. In mortar exposed to sulphate solution the durability is greatly improved at high replacement levels in both binary and ternary blends. The durability of mortar exposed to seawater is greatly improved at 30 and 40% total replacement in ternary blended mortars.
893

[en] EXPERIMENTAL STUDY COMPARING NATIONAL BRANDS OF ORTHOPAEDICAL CEMENT / [pt] ESTUDO EXPERIMENTAL COMPARATIVO DOS CIMENTOS ÓSSEOS NACIONAIS

RENATO MENDES 25 April 2007 (has links)
[pt] O cimento ósseo ou acrílico, também conhecido por polimetilmetacrilato (PMMA), é um biomaterial empregado em cirurgias. Utilizado principalmente na fixação de próteses, além do preenchimento e reconstrução de segmentos ósseos, o cimento ósseo é colocado nos espaços vazios entre o implante e a superfície óssea endosteal, endurecendo em pouco tempo e assegurando a firme colocação da prótese ao preencher por completo o espaço vazio entre o implante e o osso. Avaliou-se a qualidade de cinco marcas de cimento ósseo comum (sem adição de antibióticos), de viscosidade normal, comercializadas no mercado brasileiro, sendo três de fabricação nacional e duas importadas, de acordo com os parâmetros da norma ABNT NBR ISO 5833. Realizou-se a inspeção visual dos componentes a fim de verificar requisitos de aparência, embalagem e rotulagem, aferição de conteúdos (massa e volume), e os seguintes ensaios para obtenção das propriedades físicas e mecânicas do material: estabilidade do componente líquido, temperatura máxima, tempo de colocação, tempo de formação de massa, intrusão, resistência à compressão e resistência e módulo de flexão. Todas as marcas foram reprovadas no item 9.1- Rotulagem da referida norma, e duas marcas, sendo uma nacional e outra importada, reprovadas nos testes de intrusão. Nas demais verificações e ensaios todas as marcas avaliadas obtiveram resultados satisfatórios. / [en] The bone or acrylic cement, also known for polymethylmethacrilate (PMMA), is a biomaterial used in surgeries. Used mainly in the fixation of prostheses, beyond the fulfilling and reconstruction of bone segments, the bone cement is placed in the empty spaces between the implant and the endosteal bone surface, hardening in little time and assuring the firm rank of prostheses when filling completely the empty space between the implantation and the bone. Quality of five marks of common bone cement (without antibiotic addition), of normal viscosity, commercialized in Brazil, was evaluated, being three of brazilian manufacture and two imported, in accordance with the parameters of norm ABNT NBR ISO 5833. They had become fullfilled it visual inspection of the components in order to verify requirements of appearance, packing and labelling, gauging of contents (mass and volume), and the following tests for attainment of the physical and mechanical properties of the material: stability of the liquid component, maximum temperature, setting time, doughing time, intrusion, compressive strength, bending modulus and bending strength. All the marks had been disapproved in the item 9.1-Labelling of the related norm, and two marks, being national and other imported, disapproved in the intrusion tests. In the too much verifications and assays all the evaluated marks had gotten resulted satisfactory.
894

Characterization of a refractory cement and sensor development for temperature measurements in molten steel

Sandin, Pierre January 2018 (has links)
In steel manufacturing, temperature control is a critical parameter,as it is extremely important for the steel quality. In general,disposable sensors are regularly immersed in the melt for temperaturemeasurements. There are commercially available sensors for continuoustemperature measurements. In this study, a refractory cement is used for encapsulation andcarrier of a resistive temperature detector, for continuoustemperature measurements in molten steel. This cement is normallyused for manufacturing of steel melt crucibles. The work in thisstudy is mostly experimental and consist of characterization of thecement and development of the sensor. The characterization includesthe mechanical properties, the thermal shock resistance, the steelmelt resistance and obtainable surface roughness, for differentpowder fractions, water-to-cement ratio, firings and mixing method.Process developments were also done for the manufacturing of thesensor element and its carrier system. The end goal for continuous temperature measurement in molten steelfor more than 60 minutes was not reached. However, functional sensorswere developed where temperatures up to 1000 °C were measured duringcalibrations, and the cement was well characterized. This work has been carried out within the Strategic innovationprogram "Smartare Elektroniksystem", a joint investment of Vinnova,Formas and Energimyndigheten.
895

Estudo do comportamento hidráulico, mecânico e químico de barreiras hidráulicas verticais, compostas por solo residual, bentonita e cimento sob ação de substâncias agressivas / Study of the hydraulic, mechanic and chemical behavior of verticals hydraulic barriers composed by sandy soil, bentonite and cement under aggressive substances’ action

Lemos, Rosemar Gomes January 2006 (has links)
Este estudo tem como objetivo analisar os comportamentos hidráulico, mecânico e microestrutural de misturas compostas, por solo residual arenito Botucatu e bentonita sódica, com e sem adição de cimento, quando permeadas por água (H2O), soda cáustica (NaOH), na concentração de 5% e ácido sulfúrico (H2SO4) na mesma concentração para sua possível utilização em barreiras de contenção de contaminantes do tipo slurry wall. O arenito, solo areno-siltoso característico da região de São Leopoldo/ RS, compõe a matriz das misturas, sendo que a bentonita sódica confere a estas características impermeabilizantes, imprescindíveis às barreiras hidráulicas de contenção. O cimento, além de fazer com que a mistura adquira resistência, interfere na reatividade da barreira, mediante os contaminantes utilizados. A estimativa da eficiência destas misturas baseou-se na comparação entre os valores do coeficiente de condutividade hidráulica, resistência à compressão simples e parâmetros de compressibilidade determinados através dos ensaios de compressão confinada, apresentados nos ensaios com e sem contaminação, conjuntamente com a análise microestrutural das misturas nas mesmas situações. Foram feitas análises químicas por Difração de Raios-x, Microscopia Eletrônica de Varredura (SEM) e Análise Química Elementar (EDS) visando à explicação ordinária das causas microestruturais que levam as misturas a determinado comportamento sob percolação de contaminantes. Na busca do efeito de cada componente sobre o comportamento final de determinada mistura, houve a necessidade de realizar análises químicas e microscópicas individuais, também sob interferência ou não de substâncias agressivas. A partir deste estudo foi possível inferir que a mistura solo-cimentobentonita, é adequada à utilização como barreira vertical quando o contaminante for ácido sulfúrico, por no mínimo 20 semanas, já que a eficiência da mesma foi comprovada pela realização de ensaios no permeâmetro de parede rígida, considerado adequado para este tipo. O uso da mistura solo bentonita para barreiras verticais pode ser emergencial visto que quando o contaminante for soda cáustica a mistura resiste por 4 dias. / The objective of this study is to analyze the hydraulic, mechanical and micro-structural conduct of composite mixtures of Botucatu residual soil and sodic bentonite, with and without cement addition, when permeated by water (H2O), caustic soda (NaOH) in a concentration of 5% and sulfuric acid in the same concentration to their possible utilization in contention of contaminant barriers of the slurry walls type. The sandy soil constitutes part of the matrix of the mixtures. The sodic bentonite confers to these mixture essential waterproof characteristics of hydraulic barriers of containment. The cement interferes on the barrier reactivity moreover add resistance to the mixture by the contaminants that were utilized. The efficiency estimation of these mixtures was established by comparison between hydraulic conductive coefficient, unconfined compression strength and one dimensional compressibility presented on the tests with or without contamination, with the mixture micro-structural and chemical analysis on the same situations: X-ray diffraction, scanning electronic microscopy, Elemental Chemical Analysis (EDS), they want to explain the micro-structural causes that make the mixtures to determinate behavior by percolating of contaminants. Searching the effect of all components about the final behavior of determined mixture there was the necessity to carry out chemical and microscopically individual analysis also by aggressive or non-aggressive substances interference. After completed the study, it is possible to affirm that the soil-cement-bentonite mixture, is good for using as a vertical barrier when the contaminant is sulfuric acid, based on the results of rigid wall permeameter, adequate for this kind of mixture. The use of soilbentonite mixture as vertical barrier for caustic soda could be done just in emergency cases and for a short period of time, once that after some time the barrier reduces drastically its efficiency.
896

Avaliação das restaurações atraumáticas em pré-escolares

Barreto, Vanessa Constant January 2007 (has links)
Proposição: o objetivo deste trabalho foi avaliar, após doze meses, qualitativamente o desempenho clínico e o tempo gasto na execução de 86 restaurações atraumáticas realizadas em pré-escolares de creches comunitárias do município de Porto Alegre, utilizando o cimento de ionômero de vidro de alta viscosidade (Vitro- Molar/DFL). Metodologia: foram selecionadas 42 crianças com necessidades restauradoras, inseridas em um programa educativo-preventivo. As respectivas restaurações foram avaliadas seguindo os critérios USPHS modificado e analisadas estatisticamente pelo teste não paramétrico Mann- Whitney (p<0,05). Resultados: encontrou-se 94,2% de retenção das restaurações envolvendo uma ou mais superfícies em dentes decíduos. O tempo médio despendido para execução da restauração foi de 4,47 minutos segundo análise de variância. Conclusão: concluí-se que as restaurações atraumáticas são indicadas para serem utilizadas em pré-escolares, por apresentarem um bom desempenho clínico e agilidade no atendimento. / Objective: the aim of the present study was to qualitatively assess the clinical performance, after 12 months, of 86 atraumatic restorations bonded with highviscosity glass ionomer cement (Vitro-Molar/DFL), in preschoolers from Porto Alegre-based day care centers, in southern Brazil, and also to assess the length of the treatment. Methods: a total of 42 children who required restorative treatment were selected from a preventive educational program. The restorations were assessed using the modified USPHS criteria and statistically analyzed by the nonparametric Mann-Whitney test (p<0.05). Results: the restorations on one or more surfaces of deciduous teeth had a retention rate of 94.2%. According to the analysis of variance, the length of restorative treatment averaged 4.47 minutes. Conclusion: atraumatic restorations are recommended in preschoolers, since they have a good clinical performance and allow prompt treatment.
897

Estudo de remediação de solo contaminado por borra oleosa ácida utilizando a técnica de encapsulamento / Study for repairing soil contaminated with acidic oily sludge using the encapsulation technique

Jiménez Rojas, José Waldomiro January 2007 (has links)
Este trabalho tem como objetivo aplicar a técnica de encapsulamento, conhecida também como solidificação/estabilização, em um solo contaminado com crescentes quantidades do resíduo industrial borra oleosa ácida, utilizando como agente encapsulante o cimento Portland CP-V ARI. O programa experimental consistiu na realização de estudos pré e pós-tratamento, analisando fisicamente o solo através de ensaios de caracterização geotécnica, compactação, resistência à compressão simples, durabilidade e condutividade hidráulica. Quimicamente foram realizados ensaios de lixiviação em coluna e análises químicas e físico-químicas do lixiviado. Devido às elevadas temperaturas detectadas no momento das misturas de solo/cimento e borra oleosa ácida, foram realizados ensaios para o monitoramento da temperatura e o tempo de hidratação do cimento. Os resultados apontam que quanto maior a quantidade de borra oleosa ácida presente no solo tratado, maior é a temperatura de hidratação do cimento e mais rápido atinge o pico máximo, resultando em menor resistência à compressão simples e maior perda de massa. Em amostras sem cimento, a condutividade hidráulica diminui com o aumento de borra oleosa ácida, quando adicionado cimento a condutividade hidráulica inicialmente diminui com o acréscimo de borra oleosa ácida, mas volta a aumentar com quantidades maiores de contaminante. A técnica de encapsulamento mostrou-se eficiente quanto à redução dos metais pesados, devido, principalmente, ao aumento do pH e a precipitação de tais elementos. Porém não se mostrou eficiente quanto ao sulfato, condutividade elétrica e demanda química de oxigênio. / The objective of this study is applying the encapsulation technique, also known as solidification/stabilization, in soil contaminated with increasing amounts of acidic oily sludge industrial residues, using Portland cement CP-V ARI as the encapsulating agent. The experimental program consisted of studies pre and post-treatment, in which the soil was physically analyzed through geotechnical characterization testings, compactation, unconfined compressive strength, duration and hydraulic conductivity tests. In chemical terms, column leach testings were conducted, along with chemical and physical-chemical analyses of the leachete. Due to the high temperatures detected upon mixing soil/cement and the acidic oily sludge, tests were conducted to monitor the temperature and the hydratation rate of the cement. The results show that the greater the amount of acidic oily sludge in the treated soil, the higher the temperature necessary to hydrate the cement and the faster it reaches the maximum peak, which results in less unconfined compressive strength and greater mass loss. In samples without cement, the hydraulic conductivity reduced upon increasing the amount of acidic oily sludge. When cement is added, the hydraulic conductivity initially decreases with the acidic oily sludge, but it increases again with greater amounts of the substance. The encapsulation technique proved to be efficient in the reduction of heavy metals, due mainly to the pH increase and the precipitation of such components. However, the technique did not prove to be efficient in relation to sulphate, and to the electrical conductivity and the chemical oxygen demand.
898

Influência do teor de calcário na carbonatação de argamassas de cimento branco / On the influence of limestone content on the carbonation of white cement mortars

Wolf, Jairo January 2010 (has links)
Este trabalho visa à quantificação da carbonatação em argamassas de cimento branco em comparação à carbonatação de argamassas de cimento cinza convencional. O estudo experimental foi dividido em 2 fases distintas. Na primeira foram produzidos 12 cimentos pela substituição de 0, 5, 10 e 20% de 3 clínqueres de diferentes procedências por um calcário calcítico. Nesta etapa do trabalho o clínquer e o calcário foram moídos conjuntamente, de forma que não havia controle sobre a granulometria do calcário e do clínquer individualmente. Na segunda fase foram produzidos 21 cimentos, os quais foram constituídos pela adição ao clínquer de 0, 5 10 e 20% do mesmo calcário da primeira fase e de um fíler quartzoso moído de forma a possuir a mesma granulometria do calcário. Nesta etapa os materiais foram previamente moídos, de forma que sua granulometria inicial era controlada, constituindo-se, portanto, 21 cimentos com a mesma finura e 21 argamassas com a mesma relação água/aglomerante. Os resultados dos ensaios de carbonatação, resistência à compressão, porosimetria, termogravimetria, difração de raios-X e análise do pH da solução aquosa dos poros indicam que o calcário tem um efeito potencializador da hidratação das argamassas, com efetivo refinamento da estrutura porosa. Entretanto, a comparação entre os resultados de ambas as fases do estudo mostra que a melhora do desempenho de cimentos acrescidos de calcário não se deve apenas ao efeito de fíler desta adição, mas a uma melhora na eficiência dos cimentos compostos, possivelmente pelo maior moabilidade da mistura clínquer-calcário induzida pelo calcário, isto é, o calcário, quando co-moído com o clínquer, faz com este atinja uma maior superfície específica, aumentando, desta forma, a sua reatividade. Argamassas feitas com cimentos brancos apresentaram menor carbonatação do que argamassas feitas com cimentos cinzas, considerando uma mesma relação água/aglomerante e uma mesma superfície inicial. Os resultados indicam algum tipo de interação química do calcário com a pasta que aumenta a carbonatação, mas este efeito é perceptível para teores elevados de adição. / The present study aims to quantify white cement mortars carbonation when compared to carbonation of conventional gray cement mortars. In the first part of the research, 12 cements were produced by substitution of 0, 5, 10 and 20% of 3 different clinkers by limestone. Clinker and limestone were ground together, so that there was no control over the fineness of limestone and clinker individually. In the second stage of the research 21 cements were produced, which were formed by adding to clinker 0, 5, 10 and 20% of limestone and a crushed quartz filler with the same fineness of limestone. In this second part of the research the materials were first milled, so that their initial particle size was controlled, criating therefore 21 cements with the same finess and 21 mortars with the same water / binder ratio. The test results of carbonation and porosimetry show that limestone has a potentiating effect on mortars hydration with effective refinement of the porous structure. However, the results show that the performance improvement of cement with limestone is not only due to the limestone effect as a filler, but also due to an improvement in the efficiency of blended cements, possibly due to greater efficiency of the clinkers that were milled together with limestone. White cement mortars showed less carbonation than gray cement mortars, assuming the same water / binder ratio and the same initial specific surface. The results show a possible chemical interaction between limestone and the cement paste that eventually increase carbonation depth. This effect was only observable with high addition contents.
899

Efeito do estado de tensões de cura no comportamento de uma areia artificialmente cimentada / Effect of curing stress state on the behaviour of an artificially cemented sand

Dalla Rosa, Francisco January 2009 (has links)
O estudo em laboratório do desempenho mecânico de solos artificialmente cimentados está normalmente vinculado à simulação do comportamento de geomateriais naturalmente formados em campo. Por outro lado, o estudo desses novos materiais pode ser também ferramenta útil na previsão do comportamento de aterros de solos artificialmente melhorados. O comportamento de solos cimentados possui considerável influência da densidade e do estado de tensões a que estes materiais estão submetidos durante a fase que compreende a cimentação dessas partículas. Uma alternativa ao estudo da cimentação nestes solos, é a elaboração de um meio em que as amostras possam ser cimentadas sob um estado de tensões específico, e que ao mesmo tempo em que se promove uma redução do índice de vazios do respectivo material. Seguindo nessa analogia, o presente estudo visa apresentar resultados de ensaios triaxiais realizados em amostras de um solo artificialmente cimentado, curadas sob diferentes níveis de tensão e estado de tensões. São abordados os resultados do ponto de vista da rigidez e deformabilidade encontrados para o material. Os resultados demonstraram que a alteração dos estados de tensões de cura, bem como a magnitude das tensões confinantes durante a cura, apresentaram influência no comportamento tensão-deformação-dilatância das amostras artificialmente cimentadas. / The laboratory study of mechanical performance of artificially cemented soils is normally associated with the mechanical behaviour of geomaterials that were created in field. The behaviour of artificially cemented soils has substantial influence of density and the stress state that these materials have been submitted during the particles cementation. Thus, an alternative to the understanding of cement effects in these soils is the preparation of a similar environment where the specimens can be submitted the cementation while a specific stress state is applied, promoting the respective void ratio reduction. Following this approach, this study aims to show the results of triaxial tests carried out in an artificially cemented soil, which was cured at different stress states. The results have shown that the changing of stress state of curing, as well as the intensity of the confining stress during the cure, presented considerably influence in the stress-strain-dilatancy of the artificially cemented samples.
900

Fluidização de solo arenoso associada à injeção de agente cimentante para ancoragem de estruturas offshore / Fluidisation of sandy soils associated to the injection of cementing agent for applying in offshore structures

Stracke, Fernanda January 2012 (has links)
A instalação de estruturas offshore em grandes profundidades demanda avanços na área da Engenharia, principalmente quanto ao desenvolvimento de novas tecnologias associadas à ancoragem destas estruturas. O objetivo deste trabalho é analisar os mecanismos e conceitos associados à fluidização de solos arenosos com jatos de água, associando a técnica ao melhoramento do solo com agente cimentante, com a finalidade de futuramente aplicar estas técnicas em campo, na instalação e fixação de fundações e âncoras para plataformas e estruturas offshore. O trabalho é fundamentado nas pesquisas de Niven (1998) e Mezzomo (2009). O estudo foi desenvolvido através de ensaios em laboratório, sendo os ensaios de fluidização executados em tanque de acrílico de 45 x 45 cm e altura de 110 cm. Foram realizados ensaios em areia fina de granulometria uniforme (d50 = 0,18 mm). Quanto aos ensaios de fluidização, foi avaliada a influência dos parâmetros do jato (vazão e velocidade) na geometria da zona fluidizada, verificando as equações empíricas para determinar a geometria da zona fluidizada através do número de Froude das partículas (Frp) - desenvolvidas por Mezzomo (2009) - e ampliando o banco de dados dos ensaios de fluidização. Foi avaliada a influência dos parâmetros do jato (vazão) e do solo (permeabilidade e diâmetro das partículas), sobre a profundidade crítica T3. Foi definida a relação entre a profundidade crítica T3 de ensaios executados no centro e na lateral do tanque de ensaios (T3centro/T3lateral = 0,5 a 0,8). Complementarmente, foram realizados ensaios de fluidização associados à injeção de agente cimentante, através dos quais foi possível compreender a forma geral de comportamento da injeção de agente cimentante em solos arenosos. Finalmente, foram executadas provas de carga estáticas à tração em solo arenoso fluidizado e não fluidizado, e em ensaios com injeção de calda de cimento. Através destes, verificou-se uma perda de capacidade de carga entre 30 e 50% devido à fluidização do solo. Além disso, a injeção de agente cimentante resultou em aumento da capacidade de carga entre 11 e 15 vezes, em relação aos ensaios sem injeção de agente cimentante. / The installation of offshore structures in deep water demands advances in Engineering, particularly for the development of new technologies associated with the anchor of these structures. The aim of this paper is to analyze the mechanisms and concepts associated with fluidization of sandy soils with water jets, combining the technique of improvement of the soil with cementing agent in order to implement these techniques in the field for installing and arrest offshore foundations and anchors of platforms and structures, in the future. The work is based on Niven (1998) and Mezzomo (2009) researches. The study was developed through laboratory tests designed for fluidization tests carried on into acrylic tank of dimensions 45 x 45 cm and height of 110 cm. The tests were performed with uniform fine sand (d50 = 0.18 mm). About fluidization tests the influence of jet parameters (rate and speed) on the geometry of fluidized zone was evaluated, verifying empirical equations to determine the geometry of the fluidized zone through the Froude number - developed by Mezzomo (2009) - expanding the database of fluidization tests. The influence of the jet and soil parameters (rate, permeability and d50) on critical depth (T3) was carefully investigated. The relation of critical depth of the tests ran in the center and side position in the tank was found to be from 0.5 to 0.8. In addition, fluidization tests associated with injection of cementing agent were carried out to improve the understanding of the general behavior of the injection of cementing agent (cement grout) in sandy soils. Finally, static tension load tests on fluidized and no fluidized sand were performed, complemented by tests with injection of cement grout. Through these, it was found that there is a 30 to 50% loss in load capacity due to the fluidization of the soil. Furthermore, tests with injection of cement agent resulted in increasing load capacity about 11 up to 15 times, in relation to the tests without cement agent injection.

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