Dissertations / Theses on the topic 'Silica fume'
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Brew, Daniel Robert Mitchell. "Impact of silica fume on cement performance." Thesis, University of Aberdeen, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369734.
Full textAl-Eesa, Azmi Sami Said. "Silica fume concrete in hot and temperate environments." Thesis, Loughborough University, 1990. https://dspace.lboro.ac.uk/2134/6829.
Full textPun, Pierre Che Ho. "Influence of silica fume on chloride resistance of concrete." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq28837.pdf.
Full textKashi, Mohsen Gholam-Reza. "Freeze-thaw durability of high strength silica fume concrete." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53942.
Full textPh. D.
Shehata, Medhat H. "The effects of fly ash and silica fume on alkali-silica reaction in concrete." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58597.pdf.
Full textEl-Khatib, Jamal M. "Durability related properties of PFA, slag and silica fume concrete." Thesis, University of Aberdeen, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315418.
Full textTank, Suresh Bhagwanji. "The use of condensed silica fume in Portland cement grouts." Thesis, University College London (University of London), 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307794.
Full textClaisse, Peter Arnold. "The properties and performance of high strength silica fume concrete." Thesis, University of Leeds, 1988. http://etheses.whiterose.ac.uk/3256/.
Full textGans, Ira. "The production of ultrafine silica particles through a transferred arc plasma process /." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65464.
Full textBoddy, Andrea M. "The effect of product form and silica content of silica fume on its ability to control alkali-silica reaction." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0028/MQ50329.pdf.
Full textPristavita, Ramona. "Transferred arc production of fumed silica : rheological properties." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99787.
Full textIn the present work, we studied the changes in the powder quality by varying the quench conditions used for the production of the powder and by agglomerating the obtained particles. The fumed silica was agglomerated by conveying in a length of tubing with sharp bends. The powder was characterized using BET, Viscosity tests, FT-IR, TEM, SEM and XRD. The product was compared to both a commercial product (Aerosil 200) and the material previously produced by Addona. Tests were done before and after the agglomeration experiments.
The experimental results showed that the agglomeration had no effect on the powder's rheological properties. We concluded that the smaller viscosity values obtained for the plasma produced fumed silica were due to the lack of the free hydroxyl groups from the surface of the particles.
Konduru, Sathish Kumar Raju. "Performance evaluations of latex-modified and silica fume modified concrete overlays for bridge decks." Morgantown, W. Va. : [West Virginia University Libraries], 2009. http://hdl.handle.net/10450/10559.
Full textTitle from document title page. Document formatted into pages; contains xv, 235 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 212-216).
Bajja, Zineb. "Influence de la microstructure sur le transport diffusif des pâtes, mortiers et bétons à base de CEM I avec ajout de fumée de silice." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLN054/document.
Full textThanks to its high mechanical strength and its potential containment capacity conferred by a compact microstructure, concrete is considered as the most suitable material to compose the engineered barrier of some radioactive waste storage structure. Knowledge of diffusion properties and microstructure of these cementitious materials is then essential to study their long-term durability. In a more specific context of low and intermediate waste management, the use of formulations containing silica fume (SF) appears of great importance. The experimental approach consists in selecting many formulations of pastes and mortars to test by the HTO through-out diffusion test. Their initial compositions (water to binder ratio, SF content, sand content and particle size) were varied in order to browse different microstructures and diffusion properties, and to see the influence of each parameter (water, SF, content and grain size of sand) on the evolution of diffusivity within these materials. The microstructure was investigated to interpret the obtained values of diffusion coefficients. Different complementary techniques have been used to characterize the porous structure (water and mercury intrusion porosimetry, nitrogen adsorption), to verify SF reactivity (TGA, SEM associated to EDS) or to determine the profile porosity at ITZ (SEM combined with image analysis).The relationship between microstructure and diffusion coefficients (DeHTO) was then discussed. The ultimate goal was to find a link between microstructure properties and transport parameters to estimate from a simple characterization, the DeHTO of concrete, difficult to get from HTO diffusion cells test. Other attempts have also been made to try to assess the concrete diffusion coefficient, such as the multi-scale modeling approach (the scale of hydrates 3D model), or the diffusion of other elements ( like oxygen or nitrogen).This study shows that silica fume agglomerates (slurry) observed in cement paste and mortar with low standardized sand content (10%), impact the filler and pozzolanic roles of the SF and therefore sustainability parameters of these materials. On the other side, the presence of high aggregates content (> 30%) during mortar’s mixing greatly improves the dispersion of SF particles and helps shearing these agglomerates by providing better homogeneity of the mixture and enhancing microstructural and diffusional properties. It was also shown that the use of the SF as a slurry form in a cementitious mixture is still significantly better than the use of the densified FS, commonly used in the literature. Relations between the DeHTO and the critical pore radius, or the DeHTO and mercury porosity have been established and helped to estimate more or less the HTO diffusion coefficients of two concretes with or without SF
Nacer, Samir. "Optimization of silica fume content and water to enhance performance of concrete /." Available to subscribers only, 2005. http://proquest.umi.com/pqdweb?did=1079666031&sid=7&Fmt=2&clientId=1509&RQT=309&VName=PQD.
Full textAsili, Mostafa. "The fracture toughness of silica fume concrete using experimental and numerical techniques." Thesis, University of South Wales, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265719.
Full textDESHINI, AMARENDRANATH. "FINENESS OF DENSIFIED MICROSILICA AND DISPERSION IN CONCRETE MIXES." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1186774530.
Full textKatzer, Jacek. "Special waste fine aggregate concrete modified by silica fume and dispersed reinforcement : doctoral dissertation." Rozprawa doktorska, [s.n.], 1999. http://dlibra.tu.koszalin.pl/Content/1220.
Full textLi, Jieren. "The combined effect of silica fume and fly ash on microstructure and properties of high-strength concrete." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0035/NQ38485.pdf.
Full textAlam, Sameer Alam. "Plastic and Slag as a Potential Aggregate Replacement in Concrete with Glass Fibers and Silica Fume Admixtures." Youngstown State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1544787269399169.
Full textAlshammari, Talal. "A STUDY ON BEHAVIOR OF NATURAL AND RECYCLED AGGREGATE CONCRETES PREPARED WITH META-KAOLIN AND SILICA FUME." OpenSIUC, 2017. https://opensiuc.lib.siu.edu/theses/2272.
Full textHrout, Ghassan. "Investigate the Effect of Nano SIO2 on Porosity, Compressive and Flexural Strengths of Concrete Has 2% Fly Ash and 2% Silica Fume." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1608296326325322.
Full textJustice, Joy Melissa. "Evaluation of Metakaolins for Use as Supplementary Cementitious Materials." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6936.
Full textStundebeck, Curtis J. "Durability of ternary blended cements in bridge applications." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/5082.
Full textThe entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on November 6, 2007) Includes bibliographical references.
Yılmaz, Altan Karaşahin Mustafa. "Ferrokrom ve silikoferrokrom cürufları ile silis dumanının yol üstyapısında kullanımının incelenmesi /." Isparta : SDÜ Fen Bilimleri Enstitüsü, 2008. http://tez.sdu.edu.tr/Tezler/TF01152.pdf.
Full textAl-Ghamdi, Hamed A. "Effect of curing and mix design parameters on durability of Portland cement and Portland cement-silica fume mortars in a hot-marine environment." Thesis, University of Aberdeen, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301075.
Full textDe, Milito Jose Antonio. "Avaliação do desempenho de aglomerante a base de gesso com cimento portland de alto forno e silica ativa." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/258270.
Full textTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo
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Resumo
Resumo: O gesso é um aglomerante que tem sido muito empregado em revestimento de paredes. Apresenta um bom desempenho, é econômico e de fácil aplicação, mas limitado ao uso interno devido a sua sensibilidade à água. Algumas tentativas têm sido realizadas para melhorar a sua utilização em ambientes sujeitos à umidade. Neste sentido, pesquisas avançam na tentativa de empregar diferentes adições como resinas epóxi, polímeros, cimentos, escórias, impermeabilizantes, entre outros. O objetivo desta tese foi avaliar o desempenho das misturas de gesso com cimento Portland de Alto Forno e sílica ativa nos revestimentos internos e externos sujeitos à umidade. Para isso verificaram-se as propriedades macroscópicas das misturas por meio de ensaios físicos, químicos, físico-químicos e também a avaliação microestrutural utilizando a microscopia eletrônica de varredura. As misturas foram aplicadas em revestimentos de painéis de alvenaria de blocos de concreto e observados visualmente por um período de cinco anos. Além da observação visual foi verificada a resistência de aderência das misturas aplicadas internamente e externamente. Dos resultados obtidos observou-se uma possível coexistência entre o gesso e o cimento e que a adição de sílica ativa na mistura reduz a formação de etringita, principalmente nos revestimentos externos, sujeitos à umidade. A adição de cimento Portland melhora na abrasão e perda de massa, mesmo em idades mais avançadas. Assim, devido ao elevado custo de algumas adições, e as dificuldades de trabalhar com outros tipos de adição na obra, a adição de cimento Portland e sílica ativa ao gesso permitem uma melhoria de resistência, obtendo um revestimento de baixo custo e de fácil manuseio.
Abstract
Abstract: Plaster of Paris is a binding material being used in masonry as a plaster finish coat. Despite being economical, having good performance as and ease with wich it is applied in building, its use is limited to indoors. Some attempts has been made to improve its performance in external environment. In that sense, researches advance in the attempt at using several admixtures like epoxy resins, polymers, cements slags, waterproofing materials among other things. The objective of this thesis is to assess the performance of certain mixtures of rendering material containing plaster of Paris, slag cement and condensed silica fume when applied in the internal and external plaster finish coat. The macroscopic properties of the mixtures were analyzed through physical and chemical tests and also in SEM. Mixtures were applied on coatings of brick and mortar and visually inspected within five years. Bond strengths of the mixtures were measured, both in internal and external walls. Results showed compatibility between plaster of Paris and slag cement and that presence of condensed silica fume in the mixture reduced the formation of etringite, especially in the external coatings. The addition of Portland blastfurnace slag cement reduced the abrasion and the loss of mass, even in older ages. Therefore, due to the high cost of some admixtures, and the difficulty in working with other kinds of admixtures in the construction sites, the mentioned additions to the plaster rendering allow a mechanical strength improvement, thus resulting in low cost and good workability of the plaster finish coat.
Doutorado
Edificações
Doutor em Engenharia Civil
Gao, Xiang, and S3090502@student rmit edu au. "Mix Design and Impact Response of Fibre Reinforced and Plain Reactive Powder Concrete." RMIT University. Civil, Environmental and Chemical Engineering, 2008. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080424.150722.
Full textGrande, Fernando Mazzeo. "Fabricação de tijolos modulares de solo-cimento por prensagem manual com e sem adição de sílica ativa." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/18/18141/tde-07072003-160408/.
Full textIn this work, several aspects of modular bricks composed by binary and ternary mixtures of soil-cement and soil-cement-silica, produced by manual press model SAHARA, were analyzed by means of an experimental methodology, with the purpose of obtaining parameters and guidelines to aim a better performance of the material. During the work, tests in cylindrical samples were executed in an accessory way, what resulted in the support for theoretical basement of several evaluations about the compositions of proportions used in brick's production. Wall panels were constructed with the objective of verifying the masonrys behavior in relation to the compressive strength and walls strain, promoting correlation with the tests results in prisms, bricks and mortar. The researchs contributions allow to relate the technology of the production of soil-cement bricks with the context of sustainable construction and the use of industrial residues in the production of construction materials, besides systematizing information for the elaboration of a technological project with the modular bricks
Possan, Edna. "Contribuição ao estudo da carbonatação do concreto com adição de sílica ativa em ambiente natural e acelerado." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2004. http://hdl.handle.net/10183/8524.
Full textNew researches has been appeared with the concern of reinforced concrete structures durability, standing out the service life prediction. These studies creates some models that establish the concrete performance when exposed to an aggressive environment. There are several ways to modeling this performance: with results obtained in previous tests; with accelerated degradation tests; or deterministic and stochastic methods. The concrete structures service life prediction using short term test data are recommended by ASTM E-632 (1996) since these are correlated with long term test results. The correlation among these tests makes possible the acceleration coefficient determination, which express how the accelerated tests represents the natural degradation phenomenon. In this sense, this work evaluate the concrete carbonation with and without silica fume exposed to natural and accelerated test, verifying the influence of silica fume tenor in this material and water – binder ratio in the carbonation. In addition to this, were determined the carbonation (kc) and acceleration coefficients (αa). The concretes studied has a 0,30; 0,35; 0,45; 0,60 and 0,80 water-binder ratio and 0; 5; 10; 15 and 20% addition tenor. The samples natural carbonation was analyzed after 7 years of CO2 exhibition from Porto Alegre city environment degradation. The accelerated carbonation data were obtained in 7, 28, 63 and 98 days of CO2 exhibition with 5% concentration, temperature of 20°C and humidity of 60%. In accelerated tests, based on statistical analysis through nonlinear estimation multiple regression, the results showed that the silica fume addition in high water-binder ratio mixtures increases the concrete carbonation depth. For water-binder ratio 0,80 with silica fume addition of 0 and 20%, the acceleration coefficients obtained were 31,15 and 35,49, respectively.
Trindade, Guilherme Hoehr. "Influência da incorporação de cinza da casca do arroz e sílica ativa no cimento Portland frente à reação álcali-sílica : desenvolvimento de uma nova proposta de método para avaliação da RAS em materiais suplementares ao cimento Portland." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/131343.
Full textSome materials, consisting almost exclusively for silica, are employed, supplementary form to Portland cement, for promoting improvements to concrete, due to their physical and pozzolanic effects and environmental issues. However, this silica may generate unwanted products in presence of alkalis. This phenomenon is known as alkali-silica reaction (ASR). In the presence of water, these products are able to expand inside concrete, generating internal and external cracks and, in severe cases, structural element degradation. In order to prevent this pathologic manifestation, the aim of the present study was to evaluate reactive potential in ASR of fume silica and two types of rice husk ash (RHA), a manufacturing and residual. Levels of 5 to 50 % were used as partial replacement to standard Portland cement. In the present study, accelerated method in mortar bars according to NBR 15577 - 4/5 and two new accelerated methods (pastes cubes and prisms) were used. Accelerated method in paste cubes evaluated compressive strength, while method in paste prims evaluated dimensional change. Results in mortar bars demonstrated, both RHA, were reactive to ASR. However, level of 50 %, both RHA, was innocuous to ASR. Fume silica was innocuous to ASR at all levels evaluated. Superplasticizer additive was not effective to reduce to expansion caused by RHA. In the cubes assay was possible to evaluate the reactive potential to ASR by analysis of variation coefficient. Results demonstrated a positive correlation between expansion in paste prism and standard method in mortar bars. In the paste prism with 25 % of RHA manufacturing were identified compounds of franzinite, chessexite and thaumasite. These compounds presented morphology of needles sometimes tortuous and sometimes thin and straight in all samples. Thermogravimetric analysis showed the high adsorbent power of water in this paste. In conclusion, paste prims assay at 48ºC with Na2Oeq 1.25 % demonstrated to be a practical laboratory method and presented a great potential to evaluate additional material to Portland cement in front of ARS, and this assay facilitates the identifications of products that cause expansion.
Almeida, Alessandra Etuko Feuzicana de Souza. "Estudo da influência das adições de sílica ativa e copolímero estireno acrílico nas propriedades de argamassas para assentamento de porcelanato." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-15122010-095113/.
Full textDespite the excellent characteristics of porcelain tiles, their application in building facades requires special attention, since this material differs from conventional ceramics and facades are exposed to weathering, which can damage ceramic revetments. The lower water absorption of porcelain tiles is the main cause of the poor adherence between them, as it prevents the mechanical interlocking adherence mechanism that occurs when more porous ceramic materials are applied. The present thesis aims to investigate the effect of silica fume and acrylic polymer together on the properties of mortars employed to install porcelain stoneware tiles to avoid detachment problems due to lack of adherence. An experimental investigation evaluated the fixing properties of the mortars, and a microstructural study including thermal analysis, X-ray diffraction, mercury intrusion porosimetry, infrared spectroscopy and scanning electron microscopy was performed. The results showed that silica fume and acrylic polymer addition to the mortar resulted in improved properties to fix porcelain stoneware tiles, mainly adherence strength, as a consequence of the microstructural improvement due to the decrease in the porosity and the pore mean diameter, and the decrease in the calcium hydroxide to form hydrated calcium silicate
Fagury, Samir Costa. "Concretos e pastas de elevado desempenho: contribuição aos estudos de reparos estruturais e ligações entre concretos novo e velho, com tratamento da zona de interface." Universidade de São Paulo, 2002. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-17012011-092136/.
Full textThe bonding among Portland cement concrete of different ages, compositions and resistances is one of the technological problems of structural concretes. The continuity of this connection is harmed by a several factors from the re−starting of a casting (cold joint) to the recovery of deteriorated concrete structures. From this point of view this paper presents an analysis of the behavior of a repair system applied to the recovery of structures, new−to−old concrete bonding (amplification cases) and casting continuities. One of the most fragile points of a concrete structure is the interface zone, of both materials that compose it and the transition among the different concretes. Prismatic specimens executed with concretes (fck=15MPa, 18MPa, 21MPa, 25 MPa, 30 MPa, 40 MPa and 50 MPa), were used as substratum after a previous complete rupture through a flexural strength test for a further connection, with repair concrete as a bond link, and cylindrical specimens of conventional concretes presenting intentionally \"holes\". High−performance concretes with Portland cement CP V ARI RS (NBR 5733⁄NBR 5737 − ABNT), small quartz aggregates, basaltic coarse aggregates with Dmáx ≤ 6,3mm, silica fume (Fe−Si) additions of 5%, 10% and 15%, and normal setting superplasticizer with contents of 1,5%, 1,8% and 2,0% were used as repair system to improve the transition zone mentioned. Such materials were used after the specimens had been treated superficially and primed with High−performance Portland cement paste. The effectiveness of the connection is noticed mainly by the fact that in results of the flexural strength test of recovered prismatic specimens, the rupture occurred in almost 100% of the cases in the area of the old concrete. In axial compression tests with cylindrical specimens presenting recovered \"holes\", the rupture way demonstrated that the transfers of tensions usually occurred through the repair system, with no tension deviation, and there was a resistance increase in some cases.
Oda, George Akira. "Estudo da atividade pozolânica da sílica da casca de arroz em matrizes de cimento Portland." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-11072017-154356/.
Full textThe use of mineral additions in concrete in order to partially replace Portland cement helps to protect natural resources by saving raw material, reducing energy consumption in cement production and recycling industrial waste that could otherwise cause environmental and public health hazards. One mineral addition that has drawn considerable attention due to its high reactivity is silica fume (SF), a byproduct of the manufacturing process of metallic silicon or iron-silicon alloys and considered by many researchers as a superpozzolan. Silica fume is characterizated by high fineness, high specific area and high content of vitreous silica. The sum of these factors provides SF high reactivity with calcium hydroxide, which is transformed into hydrated calcium silicate. Rice husk ash has also been investigated as an alternative source of silica fume. The silica from rice husk ash contains a high percentage of SiO2 and, depending on the extraction process, has adequate properties to be employed in the manufacturing of high-performance concrete. The objective of this work is to study the pozzolanic activity of silica from rice husk ash produced at the Laboratório de Materiais Avançados à Base de Cimento. In order to evaluate the characteristics of silica samples from rice husk, assays were performed to determine their physical properties as well as their chemical composition and pozzolanicity. The assays performed were: chemical composition,pozzolanicity (modified Chapelle method), B.E.T. surface area method, granulometric distribution, particle size distribution by Scanning Electron Microscope (SEM), amorphicity by X-ray diffractometry (XRD), specific mass and pozzolanic activity index determination with Portland cement (NBR-5752). The characterization assays showed that the silica from rice husk ash has a high amorphicity level and a high surface area, which yield higher reactivity at initial ages. However, at advanced ages it pesented the same efficiency as that of silica from iron-silicon.
Vanderlei, Romel Dias. "Análise experimental do concreto de pós reativos: dosagem e propriedades mecânicas." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-23082006-095043/.
Full textThe technology of Portland cement materials has developed quickly, where the improvement of the mechanical properties has been reached, eliminating the coarse aggregates and studying the granular mixture, in order to fill the emptiness with fine and ultra-fine materials, like crushed quartz and silica fume. The present paper aimed: develop reactive powder concrete with compressive strength close to 200 MPa and module of elasticity above 45 GPa; propose a strength x strain relationship in compression for the material considering the volume of fibers; specify the maximum strain in the traction and in the compression; and to verify the influence of the fibers in the compression strength and in the bending strength. It went using the method of packing of the solid particles to define the grain size distribution, and necessary techniques were developed for the preparation and thermal cure. The experimental analysis understood the study of the following properties: compression strength, module of elasticity, bending strength, strain and ductility. The metallic fibers improved the mechanical properties and they increased the ductility of the concrete. The cure temperature and the time of submission to the thermal treatment, improved the compression strength. The maximum strain in the compression was defined experimentally as 4,3%. The elastic limit for the traction strain was 0,28%. A strength x strain relationship in compression was proposed, and can be used in reactive powders concrete, with compression strength of around 200 MPa and rate of fibers of up to 4% of volume. The results indicate that the reactive powders concrete developed presented excellent compression strength and bending strength, and the material presented a microestrutura with low porosity. The technology developed in this research can be considered a great progress in the technology of materials with Portland cement, and the application of that material is expected in situations that use advantage of the excellent mechanical properties and durability
Almeida, Marina Augusta Malagoni de. "Contribuição ao estudo da durabilidade e do transporte de fluidos em concretos contendo adições minerais." Universidade Federal de Goiás, 2016. http://repositorio.bc.ufg.br/tede/handle/tede/7271.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Brazil's current water crisis, generated by the low level of reservoirs, has threatened the national energy production. Faced with this problem, the wind towers present themselves as a viable solution. It is known that these towers are constructed in regions of high aggressiveness and therefore, it is necessary to develop high performance concretes that are able to withstand environmental action to which they are submitted, so that these structures reach the lifespan previously defined in project, ensuring the viability of the towers. In this sense, the present study evaluates the mass transport mechanisms (permeability and absorption) that takes place inside the concrete containing mineral pozzolanic admixtures of high performance, in order to evaluate the influence of the presence of these additions in these properties. Three different study mixes were prepared containing, respectively, 9% of silica fume in composition with 1% of nanossílica, 5% of a metakaolin with high fineness in composition with 5% of a metakaolin slightly less fine, both with high pozzolanic activity, a mix containing only 10% of the metakaolin with higher fineness, and a reference proportioning. The analysis presented in this work involve the scanning electron microscope (SEM) to characterize the internal structure of the material, the trace reconstruction test to analyze the aggregate/binder ratio in the regions of the cover and the interior of concrete, and the analyzes related to the mass transport: water absorption by immersion and capillarity and the air permeability obtained by the Figg’s method, in addition to the mechanical characterization. The concrete with addition of pozzolanic admixtures showed significant improvements in compressive strength, in the modulus of elasticity, in the air permeability and in the refinement of pores. Furthermore, the evaluation of the microstructure by scanning electron microscope showed that the use of mineral admixtures may cause an improvement in the adhesion and in the densification of the transition zone between aggregate and cement paste. The trace reconstitution test showed that the concrete cover has lower ratio aggregate/binder, which corroborates the results of the capillary absorption test in which it was found that the cover of concrete presents a mean capillarity absorption lower than the interior region. Thus, it was concluded that the incorporation of the different mineral admixtures studied in this work significantly alter the properties of concrete, with positive emphasis on the properties related to the durability, in which the benefits of using mineral admixtures is more pronounced and, in addition, it was also concluded that the concrete cover presents itself more favorable to the durability than the interior region.
A atual crise hídrica brasileira, gerada pelo baixo nível dos reservatórios, tem ameaçado a produção energética nacional. Frente a esse problema, as torres eólicas se apresentam como uma solução viável. Sabe-se que essas torres são construídas em regiões de alta agressividade e, portanto, faz-se necessário o desenvolvimento de concretos de alto desempenho que sejam capazes de resistir às ações ambientais às quais são submetidos de maneira que essas estruturas atinjam a vida útil de projeto previamente definida, garantindo a viabilidade das torres. Nesse sentido, o presente trabalho avalia as propriedades mecânicas e os mecanismos de transporte de massa (permeabilidade e absorção) que ocorrem no interior dos concretos que contêm adições minerais pozolânicas de alto desempenho, com o intuito de avaliar a influência da presença dessas adições nessas propriedades. Foram elaborados três diferentes proporcionamentos de estudo contendo respectivamente, 9% de sílica ativa em composição com 1% de nanossílica, 5% de um metacaulim de elevada finura em composição com 5% de um metacaulim um pouco menos fino, ambos de elevada pozolanicidade e um proporcionamento contendo exclusivamente 10% do metacaulim de maior finura, além de um proporcionamento de referência. São apresentadas análises em microscópio eletrônico de varredura (MEV) visando à caracterização da estrutura interna do material, reconstituição de traço com vistas à análise do teor de agregado/ligante nas regiões do cobrimento e do interior do concreto, análises relacionadas ao transporte de massa: absorção de água por imersão e por capilaridade e permeabilidade ao ar pelo método de Figg, além da caracterização mecânica. Os concretos com incorporação de adição pozolânica apresentaram melhorias significativas na resistência à compressão, no módulo de elasticidade, na permeabilidade ao ar e no refinamento dos poros. Além disso, a avaliação da microestrutura por meio de microscopia eletrônica de varredura mostrou que o uso das adições minerais pode ter causado densificação e melhoria na aderência da zona de transição entre os agregados e a pasta de cimento. O ensaio de reconstituição de traço mostrou que a região do cobrimento apresenta menor relação agregado/ligante, o que corrobora o resultado do ensaio de absorção capilar, em que se constatou que a região do cobrimento apresentou absorção capilar média inferior à região do interior. Assim, se concluiu que a incorporação das diferentes adições minerais estudadas no presente trabalho alterou significativamente as propriedades do concreto, com destaque positivo para as propriedades associadas à durabilidade, nas quais os benefícios do uso da adição mineral são mais pronunciados e, além disso, também se concluiu que a região do cobrimento se apresenta mais favorável à durabilidade que a região interna.
Silva, Fernanda Giannotti da. ""Estudo de concretos de alto desempenho frente à ação de cloretos"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-26072006-135429/.
Full textNowadays, one of the main problems in reinforced concrete structures is steel corrosion, especially due to the action of chloride ions. Its incidence among the main pathologies is quite significant, reaching indexes of 50% in some Brazilian areas. Besides, the cost of repair or rehabilitation of deteriorated structures, in some cases, can be higher than a new structure. To increase the service life of concrete structures and reduce the occurrence of steel corrosion, this work verifies the behavior of concretes with mineral additions in protecting the steel against the corrosion induced by chloride ions, in comparison to concretes without addition. For the production of high performance concretes (HPC), two addition types were used: silica fume (SF), already commercially available, and silica extracted from rice husk (SRH), produced in laboratory. Thus, besides providing a physical barrier to the aggressive agents in the concrete cover, the use of such concretes contribute to decrease the environmental pollution, since the additions studied are residues. Mechanical and durability tests were accomplished, such as water absorption, chloride penetration resistance, chloride penetration depth and concentration and electric resistivity of concretes. In the analysis of corrosion process, two techniques were used: open circuit potential and electrochemical impedance spectroscopy. Regarding the microstructure, tests of mercury intrusion porosimetry, X-ray diffraction, termogravimetry and scanning electron microscopy were conducted. The results obtained in the control of steel corrosion by chloride ions were favorable to the use of the additions in substitution to the portland cement. Both concretes with additions showed better performances than the concretes without silica, indicating high capacity of HPC to protect against the steel corrosion in reinforced concrete structures. Concerning the types of cement used, CP V ARI RS showed to be more efficient than CP V ARI Plus and presented better synergy with SRH. The electrochemical impedance spectroscopy technique can be used in HPC, however the effects of the high resistivity of the material should be minimized, especially when silica fume is used.
Prokopec, Zdeněk. "Mechanické aktivace příměsí do betonů a ověření dopadů na fyzikálně-mechanické vlastnosti čerstvých a zatvrdlých betonů." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2012. http://www.nusl.cz/ntk/nusl-225684.
Full textAlmeida, David Costa de. "Desempenho de argamassas com sílica ativa em ambiente marinho." Universidade Federal de Alagoas, 2007. http://repositorio.ufal.br/handle/riufal/387.
Full textCoordenação de Aperfeiçoamento de Pessoal de Nível Superior
O reparo de estruturas de concreto armado atrai cada vez mais a atenção de pesquisadores e construtores que vêem um número crescente de fenômenos patológicos em diversas construções com este material. A noção errônea de que o concreto é um material eterno e imutável foi substituída pelo fato de que ele é uma substância dinâmica e complexa, vulnerável a muitos compostos agressivos que modificam e causam dano à sua estrutura química e física. O presente trabalho propôs-se a coletar dados sobre o comportamento da sílica ativa como uma adição mineral a argamassas expostas ao ambiente marinho, na zona de variação da maré, e também avaliar se o sulfato de magnésio participa de alguma maneira no desenvolvimento das propriedades da argamassa. Para alcançar os objetivos do estudo dois grupos de argamassas foram feitos, um de argamassa convencional e o outro usando sílica em sua composição. Corpos de prova cilíndricos (10 x 5 cm) e prismáticos (50 x 15 x 4 cm com armadura de aço) foram sujeitos a ciclos naturais de molhagem e secagem no litoral de Maceió. Os testes foram feitos nas idades de 14, 28, 91, 135 e 180 dias e compreenderam medir a resistência à compressão, à tração e o módulo de elasticidade das amostras. Ensaios de potencial de corrosão foram conduzidos nas placas de argamassa armada de acordo com a ASTM C 876 91 e análise por difração de raios X foram efetuadas para verificar mudanças nos compostos das argamassas. Resultados mostram que, ao fim do período de testes, a argamassa com sílica desenvolveu resistência à compressão menor quando comparada à argamassa convencional. A resistência à tração mostrou resultados mais equilibrados, com alguma vantagem para a argamassa com sílica. Análise da difração de raios X sugere possíveis mudanças nas fases da argamassa com sílica. Os resultados apontam que o uso de sílica ativa em matriz cimenticia aplicada em ambiente marinho não apresenta o mesmo desempenho quando comparado a matriz cimenticia convencional.
Pédèches, Jean-Michel. "Etude des proprietes mecaniques et du retrait de betons de haute performance." Toulouse 3, 1988. http://www.theses.fr/1988TOU30061.
Full textSilva, Monique Pafiadache da. "RETRAÇÃO TOTAL E PENETRAÇÃO DE CLORETOS DE CONCRETOS COMPOSTOS COM CINZA DE CCA DE DIFERENTES TEORES DE CARBONO GRAFÍTICO." Universidade Federal de Santa Maria, 2012. http://repositorio.ufsm.br/handle/1/7791.
Full textThe use of agro-industrial by-products with pozzolanic properties has become an alternative in the cement industry because of the increasing consumption of cement, aiming at the rational use and sustainability of the mines that produce raw materials for the production of clinker and longer life of concrete structures. This research investigates the influence of the curing period and of the use of rice husk ash with different contents of graphitic carbon on the compressive strength, total shrinkage and chloride penetration of concretes with high early age strength cement. The levels of replacement of Portland cement adopted were 0%, 5%, 10%, 20% and 30%, the water/binder ratios of 0.35, 0.50 e 0.65 and the wet curing periods of 3 and 7 days. A mixture containing 10% of silica fume to replace Portland cement was used as benchmark. Compressive strength was obtained by a compressive test using cylindrical specimens (Ø 100 mm x 200 mm) according to NBR 5738 and 5739 standards for the ages of 28 and 91 days. The determination of shrinkage was made according to the recommendations of ASTM C-157 (ASTM, 2006) and ASTM C-490 (ASTM, 2004) in test specimens with 100 mm x 100 mm x 285 mm evaluated at the ages of 7, 14, 21, 28, 35, 56, 91 and 182 days. Before being immersed in saline, the test specimens were dried for 91 days. Based on the findings, it has been found, for all mixtures investigated, that the increase in the wet cure period led to higher compressive strength values, lower shrinkage values and reduced chloride penetration for the investigated mixtures. The opposite behavior was observed with the increase of w/b ratio. The mixtures containing rice husk ash of lower contents of graphitic carbon (light-colored) showed the highest values of compressive strength. However, analysis at equal content of replacement shows that this behavior varies according to the a/agl ratio, age at test and curing period, not indicating a general tendency. This behavior is also valid for analysis of mixtures with rice husk ash and silica fume. In the test of shrinkage and chloride penetration following shrinkage, the mixtures of rice husk ash of lower contents of graphitic carbon have shown, in general, better performance, with lower shrinkage values and reduced chloride penetration.
A utilização de subprodutos agroindustriais com características pozolânicas tem sido uma das alternativas encontradas diante do crescente consumo de cimento, visando à racionalidade e à sustentabilidade das jazidas fornecedoras de matérias-primas para produção do clínquer e à maior vida útil das estruturas de concreto. Nesta pesquisa, investiga-se a influência do período de cura e da utilização de cinza de casca de arroz com diferentes teores de carbono grafítico na resistência à compressão axial, retração total e penetração de íons cloreto de concretos com cimento Portland de alta resistência inicial. Os teores de substituição ao cimento Portland adotados foram de 0%, 5%, 10%, 20% e 30%, as relações água/aglomerante de 0.35, 0.50 e 0.65 e os períodos de cura úmida de 3 e 7 dias. Uma mistura com 10% de sílica ativa em substituição ao cimento Portland foi empregada como parâmetro de comparação. A resistência à compressão axial foi avaliada em corpos de prova cilíndricos (Ø 100 mm x 200 mm) segundo as normas NBR 5738 e 5739, para as idades de 28 e 91 dias. A determinação da retração foi feita conforme recomendações da ASTM C-157 (ASTM, 2006) e ASTM C-490 (ASTM, 2004) em corpos de prova de dimensões 100 mm x 100 mm x 285 mm avaliados nas idades de 7, 14, 21, 28, 35, 56, 91 e 182 dias. A avaliação de penetração de íons cloreto (imersão em solução salina) foi realizada nas idades de 7, 14, 28, 56 e 91 dias. Antes de serem imersos em solução salina, os corpos de prova foram submetidos a um período de secagem de 91 dias. Dos resultados obtidos, constatou-se, para todas as misturas investigadas, que o aumento do período de cura úmida resultou em maiores valores de resistência à compressão, menores valores de retração e menor penetração de íons cloreto para as misturas investigadas. Comportamento contrário foi observado com o aumento da relação a/ag. As misturas compostas com CCA de menor teor de carbono grafítico (clara) apresentaram os maiores valores de resistência à compressão, contudo, quando se analisa em igualdade de teor de substituição, esse comportamento varia em função da relação a/agl, idade de ensaio e prazo de cura, não apresentando uma tendência geral. Esse comportamento também é válido quando se analisa as misturas com CCA e SA. No ensaio de retração e de penetração de cloretos após retração, as misturas compostas com CCA de menor teor de carbono grafítico apresentaram, no geral, melhor desempenho com menores valores de retração e de penetração de cloretos.
Martins, Alex Mizael. "Transporte de cloretos em concretos com adições minerais e o desempenho em relação à corrosão das armaduras." Universidade Federal de Goiás, 2016. http://repositorio.bc.ufg.br/tede/handle/tede/7887.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The introduction of wind energy into the brazilian energy matrix is of paramount importance for national energy policy. In this context, the viability of wind towers is a fundamental issue. In Brazil, these towers are built mainly in reinforced concrete, in regions of high aggressiveness (coastal regions, because of their greater wind potential) and, therefore, it is necessary to develop high performance concretes that are able to withstand environmental actions to which they are subjected, mainly the action of the chlorides, so that these structures reach the previously defined project life, thus guaranteeing the viability of the towers. In this sense, the present work evaluates the mechanical properties, the mechanisms of transport of chlorides and the performance in relation to the corrosion of the reinforcement, in concretes that contain high performance pozolanic mineral additions, in order to evaluate the influence of the presence of these additions in these properties. Three different study mixes were developed containing respectively, 9% of silica fume in composition with 1% of nanosilica, 5% of a high fineness metakaolin in composition with 5% of a slightly less fine metakaolin, both with high pozzolanic activity and a mix containing only 10% of the finest metakaolin, in addition to a reference mix. Analyzes related to the chloride transport are presented: penetrability and diffusion; analyzes related to the corrosion of reinforcement: induction of corrosion by aggressive solution wetting cycles and air drying, surface electrical resistivity of concrete and corrosion potential, besides the mechanical characterization. The concretes with incorporation of pozzolanic addition showed, in general, improvements in the mechanical properties. In the chloride transport properties and corrosion performance of the reinforcements, the improvements from the mineral additions were significant. Thus, it was concluded that the incorporation of the different mineral additions studied in the present work significantly altered the properties of the concrete, with a positive highlight for the properties associated with durability, in which the benefits of using mineral addition are more pronounced.
A introdução da energia eólica na matriz energética brasileira é de suma importância para a política energética nacional. Nesse contexto, a viabilidade das torres eólicas é questão fundamental. No Brasil essas torres são construídas, principalmente, em concreto armado em regiões de alta agressividade (regiões litorâneas, por terem maior potencial eólico) e, portanto, faz-se necessário o desenvolvimento de concretos de alto desempenho que sejam capazes de resistir às ações ambientais às quais são submetidos, principalmente à ação dos cloretos, de maneira que essasestruturas atinjam a vida útil de projeto previamente definida, garantindo assim a viabilidade das torres. Nesse sentido, o presente trabalho avalia as propriedades mecânicas, os mecanismos de transporte de cloretos e o desempenho em relação à corrosão das armaduras, de concretos que contêm adições minerais pozolânicas de alto desempenho, a fim de avaliar a influência dessas adições nessas propriedades. Foram elaborados três diferentes proporcionamentos de estudo contendo respectivamente, 9% de sílica ativa em composição com 1% de nanossílica, 5% de um metacaulim de elevada finura em composição com 5% de um metacaulim um pouco menos fino, ambos de elevada pozolanicidade e um proporcionamento contendo exclusivamente 10% do metacaulim de maior finura, além de um proporcionamento de referência. São apresentadas análises relacionadas ao transporte de cloretos: penetrabilidade e difusão; análises relacionadas à corrosão das armaduras: indução da corrosão por meio de ciclos de molhagem em solução agressiva contendo cloretos, medidas de resistividade elétrica superficial do concreto e potencial de corrosão, além da caracterização mecânica. Os concretos com incorporação de adição pozolânica apresentaram, em geral, melhorias em suas propriedades mecânicas. Já nas propriedades de transporte de cloretos, as melhorias advindas das adições minerais foram mais significativas, assim como no desempenho em relação à corrosão das armaduras. Desse modo, concluiu-se que a incorporação das diferentes adições minerais estudadas no presente trabalho alterou significativamente as propriedades do concreto, com destaque positivo para as propriedades associadas à durabilidade, nas quais os benefícios do uso da adição mineral são mais pronunciados.
Munhoz, Flávio André da Cunha. "Efeito de adições ativas na mitigação das reações álcali-sílica e álcali-silicato." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/3/3146/tde-10012008-100734/.
Full textThe alkali-aggregate reaction is a pathologic manifestation that can induce the premature distress and loss in serviceability of concrete structures affected. It is directly associated to the selection of materials (cement, coarse and fine aggregates, water and additives), as the interaction between these materials and environmental condition will grant the concrete some of the properties related to its service life. The slow reaction between alkali hydroxides soluble in the liquid phase within concrete pores and reactive aggregates gives rise to a gel that piles up within concrete voids and the aggregate-paste interface. In presence of water, the gel expands and exerts internal pressure in the concrete. When the internal pressure exceeds the tensile strength, cracking may come up as result. The alkali-aggregate reaction requires the action of water, reactive aggregate and alkalis altogether. Prevention can be carried out by eliminating one of these factors, i.e. employing either inert aggregates or lowalkali cements, or keeping the concrete away from moisture. Otherwise, preventive measures must be taken when reactive aggregates are used in civil construction works, such as the use of low-alkali cements or composite cements bearing alkaliaggregate- reaction mitigating admixtures: blast-furnace slag, fly ash, metakaolin and silica fume, which are the object of the present research. The experimental work included the analysis of two potentially reactive aggregates to alkali hydroxides: basalt and granite milonite. The igneous basalt carries deleterious constituents such as glass, chloropheite (cryptocrystalline silica), that will give rise to the DONDOL_VLOLFD type reaction while the metamorphic granite milonite carries micro granular, recrystallized, undulate-extinction-bearing quartz and deformed feldspar grains, that give rise to DONDOL_VLOLFDWH type reaction. Aiming at evaluating how efficient in mitigating these reactions the active admixtures are, these aggregates were mixed with 16 composite cements. The contents of admixtures followed those usually found in Brazilian industrial cements for blast-furnace slag (15%, 30%, 45%, 60%) and fly ash (10%, 15%, 25%, 35%), and those generally added directly to concrete for metakaolin (5%, 10%, 15%, 20%) and silica fume (5%, 10%, 15%). All materials were characterized for their chemical composition, physical properties and mineralogy. Petrography was carried out on the aggregates. The mortar bars were analyzed at the scanning electronic and transmitted-light optical microscopes. Mercury-intrusion porosimetry and thermal analyses were carried out to quantify residual portlandite. The alkali content within the bars was determined in order to verify migration of Na+ ions. The results show that the efficiency of active admixtures varies according to their chemical and mineralogical composition and proportioning in cement, and to the aggregate reactivity.
Haniche, Rachid. "Contribution à l’étude des bétons portés en température / Evolution des propriétés de transfert : Etude de l’éclatement." Thesis, Lyon, INSA, 2011. http://www.theses.fr/2011ISAL0155/document.
Full textThe study of the behaviour of concrete at high temperatures is of great importance to determine the stability and strength of concrete structures in fire conditions. Spectacular fires, these last years, showed that the concrete could be very strongly solicited. Thus it appears that to ensure a very good behaviour of the concrete at temperature it is saved people and reduced the expenses of immobilisation and repair of the damaged structures. The aims of the present work, by the experimental study, are to provide a better comprehension of the involved phenomena during the exposure to the high temperatures of the high performance concretes (HPC). It focuses, in particular, on the fluids transfers (permeability) and the study of the thermal instability (spalling) of high performance concrete. The thesis work was conducted on high-performance concrete (80 MPa) with 5% silica fume (low permeability material to improve durability), and different amount of polypropylene fibres. The use of polypropylene fibres (PP) is regarded as an effective technical solution to improve the behaviour of the HPC at fire conditions, in particular thanks to the physical phenomena appearing at the temperatures lower than 200°C. Our work is concerned, initially, on the characterization of the evolution of physical properties (porosity, mass loss), thermal properties (conductivity and diffusivity) and mechanical properties (compressive strength and tensile) and the sorption isotherms. The second part concerns the study of the evolution of the permeability, as a main property characterising the hydrous transfers inside the concrete exposed to temperature. An experimental study is conducted concerning the evolution of the permeability of concrete as a function of temperature (up to 200 ° C). The studied parameters are: the type of concrete (with and without fibres), two types and geometry of fibres, the nature of the fluid (air and vapour) and the measurement methods (residual and under temperature). The experimental results shows that the existing fibres generate a most important permeability beyond 150°C and that the obtained results, by residual or under temperature measurements, may be related to the operating procedures. Finally, in the last part an investigation on the spalling phenomenon related to the material compositions is conducted. A new experimental method of investigation of the sensitivity of the formulations to thermal instability is proposed: the study of spherical specimens exposed in high temperatures. This method will be compared to the traditional methods of investigation. The analysis of the test results makes to discuss the thermal instability causes and to characterize the concrete properties at high temperatures, important data to modelling
Janča, Martin. "Zlepšení dispergace křemičitého úletu ve vysokohodnotných betonech." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2017. http://www.nusl.cz/ntk/nusl-295699.
Full textBach, Thi thuy ha. "Evolution physico-chimique des liants bas PH hydratés : influence de la température et mécanisme de rétention des alcalins." Thesis, Dijon, 2010. http://www.theses.fr/2010DIJOS085/document.
Full textBecause of their high alkalinity, Portland cement (OPC)-based materials may have deleterious effects in an underground waste repository. A solution would be to use low-alkalinity cements (also referred as low-pH cements) generating interstitial solutions with a reduced pH (11 instead of 13.5 for OPC), and thus showing an improved chemical compatibility with the repository environment. In this work, the investigated formulations were based on binary (OPC / silica fume) or ternary (OPC / silica fume / slag or fly ash) blends, with high substitution levels of CEM I (from 30% to 80%). This research project met two main objectives: (i) study the chemical evolution of low-pH cements at 50°C or 80°C, since such temperatures could be encoutered in certain zones of the waste repositories, and (ii) determine the mechanisms of alkali retention by hydrated low-pH cements. (i) Investigation of low-pH cement pastes with ongoing hydration over one year showed that increasing the temperature from 20°C to 80°C accelerated cement hydration and favoured the depletion of portlandite. A lengthening of the C-A-S-H silicate chains was also detected by 27Al and 29Si NMR analyses. Besides, ettringite precipitated at 20°C, but was destabilised at higher temperature. The released sulphates were partly adsorbed on the C-A-S-H and dissolved in the interstitial solution. The pH of this solution was reduced from 1.7 to 2.2 units depending on the formulations. The soluble fractions of alkalis did not significantly change with temperature. Among the five investigated blends, ternary binder T1 (37.5% CEM I, 32.5% silica fume, 30% fly ash) was the only one giving a pore solution pH lower than 11 at 20, 50 and 80°C (curing time of 6 months and 1 year). Its long-term evolution was simulated by model systems reproducing its chemical composition with reactive oxides. At equilibrium, the hydrate assemblage comprised C-A-S-H (Ca/Si and Al/Si ratios of 0.75 and 0.15 respectively), amorphous silica and aluminium hydroxide. It led to a pH of 10.3 at 20°C. (ii) C-A-S-H hydrates played a major role in the retention of alkalis. Sorption of potassium was higher than that of sodium and mainly resulted from electrostatic interactions with C-A-S-H. Monte Carlo modelling of these interactions showed that the difference of solvated radii between these ions could not explain by itself the sorption selectivity experimentally observed
Moraes, Mayara Queiroz. "Contribuição aos estudos da influência da nanossílica nas propriedades mecânicas e na trabalhabilidade de concretos para produção em centrais e para fabricação de pré-moldados." Universidade Federal de Goiás, 2012. http://repositorio.bc.ufg.br/tede/handle/tede/3429.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Unlike the silica fume, whose benefits on the properties of the concretes are already widely known, little is known regarding nanosilica. This research offers an analysis of the contribution of different types of nanosilica in mechanical characteristics and workability maintenance of concretes, as well as an evaluation of the behavior of these additions when subjected to steam curing. For this, there were compared among themselves laboratory test results in concretes with different characteristics and different purposes (one of them suitable for production at batching plants and the other for metering precast elements). The results confirmed advantages for the simple addition of nanossílica at mechanical properties of concretes for batching plants with strengths above 40 MPa (a/c<0.52), but showed that the most advantageous situation consists in adding it together with sílica fume, since the concrete with both additions exceeded the reference concrete above 36 MPa (a/c<0.615), which highlights the importance of combining pozzolanic effect of silica fume, the creation of nucleation sites caused by nanossílica and better packaging mix, size distribution generated by the two additions give the folder.Regarding the maintenance of workability, the nanosilica dispersed in superplasticizer demonstrated satisfactory performance. In the analysis of concretes for precast elements, the addition of nanosilica dispersed superplasticizer and silica fume together was also the one which showed the best results in terms of resistance in 28 days of conventional curing. However, with steam curing, a great improvement was noted in the behavior of nanosilica dispersed in water, which had not achieved good results with the conventional cure, while nanosilica dispersed in superplasticizer did not respond well to the process, possibly due to the shape of the polycarboxylate used in the dispersion of the particles. Probably, the nanosilica dispersed in water showed no significant pozzolanic activity levels, but with the rise of temperature and the agitation of the particles, the formation of nucleation sites was intensified. As the development of resistance in early ages, all additions had positive effects, but the best performance was observed on the concrete with the simple addition of nanosilica dispersed in superplasticizer. With this addition, the concrete has reached 40 MPa after only 12 hours of steam curing, within about four times lower than the reference concrete (44 hours), which suggests that its addition to the concrete could result in na almost four times greater productivity of a precast elements factory.
Ao contrário da sílica ativa, cujas vantagens nas propriedades do concreto já são amplamente conhecidas, pouco se sabe em relação à nanossílica. Esta pesquisa contempla uma análise da contribuição de diferentes tipos de nanossílica nas características mecânicas e de manutenção do abatimento de concretos, bem como uma avaliação do comportamento destas adições frente à cura térmica. Para isto, compararam-se entre si resultados de ensaios laboratoriais em concretos com diferentes traços e diferentes finalidades (produção em centrais dosadoras e fabricação de pré-moldados). Os resultados confirmaram vantagens para a adição simples de nanossílica quanto à resistência à compressão dos concretos para centrais com resistências acima de 40 MPa (a/c<0,52), mas mostraram que a melhor situação consiste na adição conjunta de sílica ativa e nanossílica, já que o concreto com a adição conjunta superou o de referência a partir de 36 MPa (a/c<0,615). Isso deixa clara a importância de aliar o efeito pozolânico da sílica ativa, a criação de pontos de nucleação ocasionada pela nanossílica e o melhor empacotamento da mistura, gerado pela distribuição granulométrica que as duas adições juntas conferem à pasta. Quanto à manutenção do abatimento, a nanossílica dispersa em aditivo superplastificante demonstrou desempenho satisfatório. Em relação aos concretos para pré-moldados, foi a adição conjunta de sílica ativa e nanossílica dispersa em superplastificante a que apresentou melhores resultados de resistência aos 28 dias de cura convencional. No entanto, com a cura térmica, notou-se melhora substancial do comportamento da nanossílica dispersa em água, que não havia atingido bons resultados com cura convencional, enquanto a nanossílica dispersa em superplastificante não respondeu bem ao processo, possivelmente por influência da forma do policarboxilato usado na dispersão das partículas. Provavelmente, a nanossílica dispersa em água não apresentou atividade pozolânica relevante, mas com a elevação da temperatura e a agitação das partículas, a formação de pontos de nucleação foi intensificada. Quanto ao desenvolvimento de resistências nas idades iniciais, todas as adições apresentaram efeitos positivos, mas o melhor desempenho foi observado no concreto com adição simples da nanossílica dispersa em superplastificante. Com ela, o concreto atingiu 40 MPa com apenas 12 horas de cura térmica, prazo quase quatro vezes menor do que o do concreto de referência (44 horas), o que leva a crer que sua adição ao concreto poderia implicar em uma produtividade quase quatro vezes maior de uma fábrica de elementos pré-moldados.
Bardella, Paulo Sergio. "Avaliação das propriedades fisicas e mecanicas de concretos produzidos com os cimentos Portland de alta resistencia inicial e de alto-forno aditivados com silica ativa curados termicamente." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/257816.
Full textDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo
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Resumo: A durabilidade das estruturas de concreto depende da estrutura porosa e da impermeabilidade do concreto, uma vez que a entrada de água e de agentes deletérios iniciam os processos patológicos que diminuem a vida útil de uma estrutura de concreto. Dessa forma, o objetivo deste trabalho foi avaliar a resistência mecânica, permeabilidade, absorção e carbonatação natural de concretos submetidos a diferentes condições de cura. Os procedimentos de cura adotados são normalmente utilizadds em canteiros de obra e na produção de estruturas pré-moldadas de concreto: cura imersa até a idade de 7 dias, cura ambiente e cura térmica. A cura térmica foi realizada na temperatura de 60°C. Foram empregados concretos produzidos com cimento Portland de Alta Resistência Inicial (CP V ARI) e cimento Portland de Alto Forno (CP III) sem e com sílica ativa (em substituição ao cimento na proporção de 10% em massa) para cada um dos diferentes tipos de cura utilizados. Os resultados evidenciaram que o tipo de cura afeta o desempenho do concreto. A mudança do tipo de cura aplicada proporcionou variações nas propriedades mecânicas e na durabilidade dos concretos, principalmente no que diz respeito à sua estrutura porosa. Assim, um regime de cura adequado é essencial para garantir a resistência mecânica e a durabilidade dos concretos. A utilização de sílica ativa em substituição ao cimento melhorou o desempenho dos concretos, tanto para a resistência mecânica quanto para a durabilidade, independente do tipo de cura empregado
Abstract: The durability of concrete structures depends on porous structure and its impermeability. The entrance of water and deleterious agents begin the damage processes and reduce the life of the concretestructure. ln that way, the aim of this work was to evaluate the mechanical resistance, permeability, absorption and natural carbonation of concretes submitted to different curing procedures. The curing procedures adopted were usually used in civil construction and in the production of precast structures: moist curing until the age 6f 7 days, curing in air, and steam curing. The maximum temperature of steam curing was 60°C. All concretes were produced with High Early Strength Portland cement (CP V ARl) and Blastfurnace Portland cement (CP TIl) without and with silica fume (10% of replacement, by mass, of Portland cement) for each one of the different curing procedure used. The results showed that the curing procedure affects the concrete performance, providing variations in their mechanical properties and in their durability, mainly in porous structure. Therefore, the curing process used is essential to guarantee the mechanical resistance and the durability of the concretes. The use of silica fume improved the performance of the concretes, as for the mechanical resistance as for its durability, independent of the curing procedure used.
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Mestre em Engenharia Civil
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Full textKodešová, Monika. "Vliv aktivních příměsí a jejich dávkování na CHRL ve stáří 28 a 90 dnů." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2017. http://www.nusl.cz/ntk/nusl-265291.
Full textZakani, Behzad. "Rheological characterization of fumed silica lubricating greases." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/63863.
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