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1
Zakani, Behzad. "Rheological characterization of fumed silica lubricating greases". Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/63863.
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Lubricating greases have been widely used for rail lubrication systems. For an efficient grease pump design, it is important to study grease shear viscosity and it is also crucial to analyze grease yielding behavior to determine its consistency on rail surface. Among all rheological properties measured through experiments, yield stress is an ill-defined property, which investigation of a reproducible method for its determination can be invaluable. As the flow properties of a material will be usually influenced by the changes in environment temperature, studying the effects of temperature on the rheological properties of grease are important.
In this study, different rheological measurements and visualization techniques, previously developed to study a wide range of materials, have been performed to characterize fumed silica based lubricating greases manufactured by L.B. Foster Rail Technologies Corp. Using commercial rheometers and different approaches to determine the yield points of these materials, it was revealed that the values obtained by curve fitting on steady-state flow curves, creep, amplitude sweep crossover and stress ramp-up were roughly similar. The microstructure of this grease was analyzed using Scanning Electron Microscope (SEM) on Cryo and non-Cryo modes. Besides visualizing a new thickener microstructure, it was shown that the heterogeneous structures developed by small fumed silica agglomerates lead to the formation of greases with higher shear viscosities. Finally, thermo-rheological analysis of these samples revealed that these materials follow neither Arrhenius equation nor time-temperature superposition principle.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
2
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.
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Organic ion exchanger resin beads are widely used in nuclear waste technology for pond water cleanup. They accumulate radioactive Cs and Sr in service. For disposal, the beads are encapsulated in cement but their stabilisation in cement has been difficult to achieve. The ion exchangers uptake calcium and inbibe water, as a result of which they swell, cracking the cement. Nuclear Electric had previously commissioned work on non-swelling formulations. These consist of mixtures of sulfate-resisting Portland cement, calcium hydroxide and silica fume. However, concerns have been expressed about cement durability in contact with brines. This thesis had as part of its objectives, (i) determination of the probable stability of the non-swelling matrix in MgSO4 brines and (ii) the corrosion potential of stainless steel in contact with the non-swelling cement. In addition, synthesis, characterisation work was performed on the reaction product of objective (i), M-S-H gel. Its alkali sorption capacity was determined as a function of both Mg/Si ratio and alkali concentration to assess its immobilisation potential.
3
Pristavita, 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.
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The thermal plasma production of fumed silica in a transferred arc consists of the decomposition of quartz to SiO (g) and oxygen followed by an oxidizing quench back to SiO2. The particles formed have diameters of the order of 10 to 20 nm and are linked in a three dimensional branched chain aggregate. Previous work by Addona and Munz (1999) demonstrated the technical feasibility of producing fumed silica using this method, but was unable to demonstrate the special rheological properties of the powder. The most important characteristic of fumed silica is the presence of hydroxyls on the surface of the particles, in the form of isolated hydroxyl groups, hydrogen-bonded hydroxyl groups and siloxane groups.In 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.
4
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.
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Au regard de son importante résistance mécanique mais surtout de ses capacités de confinement potentielles conférées par une microstructure compacte, le béton s’avère le matériau le plus adapté pour composer la barrière ouvragée de la structure de stockage et l’enrobage de certains déchets radioactifs. La connaissance des propriétés de diffusion et de microstructure de ces matériaux cimentaires sont donc des éléments indispensables à l’étude de leurs durabilités à long terme. Dans un contexte plus particulier de confinement des déchets de faible à moyenne activité, l'utilisation des formulations avec ajout de fumée de silice (FS) s'avère d'une grande importance. La démarche expérimentale consiste d’abord à sélectionner des formulations de pâtes et de mortiers à tester en diffusion HTO. Leurs compositions initiales (rapport e/liant, teneur en FS, teneur en sable et granulométrie du sable) ont été variées de telle façon à balayer des microstructures et des propriétés diffusives différentes, et à voir l’influence de chaque paramètre (eau, FS, teneur et granulométrie du sable) sur l’évolution de la diffusivité au sein de ces matériaux. La microstructure a été investiguée afin d’interpréter les valeurs des coefficients de diffusion obtenus. Différentes techniques complémentaires ont été utilisées pour caractériser cette structure poreuse (porosimétrie à l’eau, au mercure, l’adsorption d’azote,), pour vérifier la réactivité de la FS (ATG, MEB associé à l’EDS), et pour déterminer le profil de porosité au niveau de l’ITZ (MEB associé à l’analyse d’images).Le lien entre les propriétés de la microstructure et le coefficient de diffusion a ensuite été discuté. L’objectif ultime étant de trouver un lien entre les propriétés de la microstructure et les paramètres de transport nous permettant, in fine, à partir d’une simple caractérisation, d’estimer le DeHTO du béton, très difficile à obtenir par l’essai en cellules de diffusion HTO. D’autres tentatives ont également été faites pour essayer d’évaluer ce coefficient de béton, comme la démarche de modélisation multi-échelle (de l’échelle des hydrates au modèle 3D), ou la diffusion d’autres éléments (en l’occurrence ici de gaz O2 et N2).La présente étude montre que des agglomérats de fumée de silice (slurry) observés dans la pâte de ciment et dans le mortier à faible teneur volumique en sable normalisé (ici 10%), impactent les rôles filler et pouzzolanique de la FS et par conséquent les paramètres de durabilité de ces matériaux. Cependant, la présence d’une forte teneur en granulats (>30%) pendant le malaxage du mortier améliore considérablement la dispersion des particules de FS et aide à cisailler et à briser ces agglomérats en fournissant une meilleure homogénéité du mélange et en améliorant les propriétés microstructuraux et diffusionnels. Il a également été montré que l’utilisation de la FS sous forme slurry dans un mélange cimentaire est malgré tout nettement meilleure que la FS densifiée, communément utilisée dans la littérature. Des relations DeHTO et rayon critique, ou DeHTO et porosité accessible au mercure ont était établies et ont permis d’approcher plus ou moins des coefficients de diffusion HTO de bétons avec et sans ajout de FSThanks 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
5
Al-Eesa, Azmi Sami Said. "Silica fume concrete in hot and temperate environments". Thesis, Loughborough University, 1990. https://dspace.lboro.ac.uk/2134/6829.
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his investigation deals with the influence of hot and temperate curing environments on the hardened properties of concrete and mortar mixes. Condensed silica fume was blended with OPC as a potential alternative cementitious material to plain OPC for use in the hot Iraqi climate, in an attempt to find a cement combination that would overcome some of the durability problems experienced when using a plain OPC concrete in such an environment. Throughout the investigation two curing environments were used: the first simulating the UK temperate climate and the second simulating the hot Iraqi climate. Temperature and humidity were varied to simulate day and night time. The first stage of the experimental study was the development of a mix design method capable of producing an OPC-CSF cement concrete of a medium workability and a specific 28-days compressive strength ranging between 25 to 55 MPa, both with and without superplasticizer. Three grades of concrete strength were chosen (25,40 and 55 MPa) and the effect of four cement replacement levels (5,10,15 and 20%) of silica fume on concrete compressive strength was assessed. Test results showed that CSF was relatively more effective in lean mixes than in rich ones. Compressive strength of CSF concrete increased with increasing CSF percentages for both normal and superplasticized mixes up to an optimum levels of 10-15% and 15-20%, respectively. The amount of OPC (kg/m`3) necessary to bring a change in compressive strength of 1MPa was also determined and the theoritical blend proportions of OPC-CSF necessary to produce 28-day compressive strength equivalent to the plain OPC mixes were determined from the produced data above. The theoretical blend proportions were examined experimentally and the data were used to establish the relationship between strength and water/cementitious ratio for the blend mixes with and, without superplasticizer. Results showed that this basic relationship had changed quantitatively but not qualitatively when CSF was used. A cost study using current OPC and CSF material costs -was performed in an attempt to determine'the- most economic blend proportions. A total of eleven different concrete -mixes were selected to study the effect of curing environment (hot and temperate), initial curing time (0,1,3 and`-7 days) and curing method (water and polythene sheeting) on the compressive strength, permeability and absorption properties of the CSF concretes. Tests were carried out at 3,7, '14, 28,56,90 and 180 days of age. In addition five different mortar, mixes were used to examine the effect of curing environment (temperate and hot) an the *permeability, pore size distribution and durability to magnesium sulphate attack. Test results showed that hot Iraqi curing environment was favourable to the early-age strength, absorption and permeability of plain OPC mixes. However, - the later-age properties were significantly lower than those obtained for concretes cured in a temperate UK environment. For plain OPC mixes a critical curing period of 3 days was found under both temperate and hot environment. For the CSF blend mixes critical curing periods for the temperate and hot environment were found to be 3 and 1 day respectively. Results also reveal the importance of curing specimens immediately after casting for one day. Research work has also confirmed the superiority of water curing over polythene sheeting in a temperate environment for the rich plain OPC and CSF mixes. However, there was no significant difference between water and polythene for lean mixes. The reduction in , permeability and absorption properties of CSF mixes cured in a both temperate and hot environments is thought to be due to the changes in the pore structure brought about by the use of silica fume. Combining CSF with OPC was found to increase the percentages and volume of fine pores at the expense-of coarse pores. This effect may be described as a "refining" effect. Finally, the performance of CSF mortar mixes cured in a temperate and hot environment and their resistance to magnesium sulphate attack was significantly better than the plain OPC ones.
6
Gans, 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.
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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.
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Thesis (M.S.)--West Virginia University, 2009.Title from document title page. Document formatted into pages; contains xv, 235 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 212-216).
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Pun, 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.
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Kashi, 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.
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Specimens from 27 batches of concrete with water to cementitious (cement plus silica fume) ratio of 0.25 to 0.32, with and without entrained air, were tested for freeze-thaw durability in accordance with ASTM C666, procedure A (freezing and thawing in water). In addition, another set of similar specimens were moist cured for 28 days instead of 14 days and tested in accordance with ASTM C666 , Procedure A to determine the effect of curing time on the freeze-thaw durability of high strength concrete. Results show that non air-entrained high strength concrete with water cementitious ratio of less than 0.30, regardless of the length of curing time, is frost resistant. Non-air-entrained concrete with water-cement ratio of 0.32 is also durable if silica fume is not used.Ph. D.
10
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.
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Boddy, 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.
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El-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.
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Concrete has the largest production of all man-made materials. Compared with other construction materials, it possesses many advantages including low cost, general availability of raw materials, low energy requirement and utilization under different environmental conditions. Therefore, concrete will continue to be the dominant construction material in the foreseeable future. However, durability of concrete and reinfored concrete structures are still of worldwide concern, so producing a good quality concrete which impedes the ingress of harmful substances into it is of paramount importance. Cement replacement materials have been introduced into concrete mixtures for the purpose of improving the durability performance. Hence, the aim of the present investigation is to study the durability of concrete with and without cement replacement materials under various initial curing conditions. In this thesis various concrete mixes with and without cement replacement materials were considered. The cement replacement materials were, pulverised fuel ash, condensed silica fume, and ground granulated blast furnace slag. Superplasticiser was added to the majority of the mixes considered and air entraining agent to some of the mixes. Various curing regimes were employed which comprised hot dry curing to simulate concrete in the hot arid areas in the world and curing at normal temperature. Curing involved air curing, membrane curing and moist curing for fourteen days followed by air curing. A number of tests were conducted at either one particular age or at various ages. These included tests on porosity and pore structure of pastes obtained by mercury intrusion porosimetry technique, water absorption which covers the water absorption of concrete obtained by shallow immersion and the water absorbed by capillary action when the concrete surface is in contact with water, sulphate resistance of concrete which is performed by immersing the concrete specimens in sulphate solution, and monitoring the change in length at various periods of immersion, chloride penetration profiles of concrete at various ages of exposure. In addition to these tests on durability related properties, tests on compressive strength were also performed. Throughout the study a correlation between pore structure and durability related properties is investigated. A comprehensive compilation of chloride penetration data is made and an empirical expression is derived for the prediction of long term diffusion coefficients. At the end of the investigation, limitations of the present study, conclusions and suggestions for future research are made.
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Tank, 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.
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Claisse, Peter Arnold. "The properties and performance of high strength silica fume concrete". Thesis, University of Leeds, 1988. http://etheses.whiterose.ac.uk/3256/.
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Silicafume (SF) has been used as a partial replacement for cement in concrete and experiments have been carried out to measure the durability of the mixes. The SF mixes were made with 20% SF replacement of cement and waterlcement (wlc) ratios of 0.3 and 0.46. Three different curing conditions were used to simulate different site conditions and tests were carried out at 3,28 and 90 days after casting. The following properties were measuredfor the two SF mixes and the two control (OPC) mixes for each of the ages and curing conditions: corrosion rate of embedded steel by linear polarisation, electrical resistivity, carbonation depth, water vapour permeability, chloride permeability, oxygen permeability and porosity from helium and mercury intrusion. Samples were also investigated by thermogravimetric analysis. The resulting data matrix was analysed by using the method of analysis of variance to quantify the effect of the SF on the properties tested and their sensitivity to age and curing. It was also analysed by multiple regression to identify major effects of one property on another. It was concluded that SF will reduce the corrosion rate and that the major contributing factor is the substantial increase in resistivity that the SF causes. This increase in resistivity was found to be highly sensitive to cold curing in the short term but this effect was not permanent. The cause of the increase in resistivity is believed to be the depletion of calcium hydroxide which is caused by the pozzolanic activity of the SF. The analysis also indicated that the SF reduces the porosity in the .01-.15)1m size range and that this has a major influence on the durability.
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DESHINI, AMARENDRANATH. "FINENESS OF DENSIFIED MICROSILICA AND DISPERSION IN CONCRETE MIXES". University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1186774530.
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Cruz, Jimenez Juan Carlos. "Hydrolases on fumed silica : conformational stability studies to enable biocatalysis in organic solvents". Diss., Manhattan, Kan. : Kansas State University, 2010. http://hdl.handle.net/2097/3648.
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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.
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Asili, 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.
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LAJNEF, MONA. "Etude des fumees de silice microstructure, microtexture et influence sur mortier". Paris 6, 1993. http://www.theses.fr/1993PA066399.
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Les fumees de silice (sf) sont de fines poudres legeres qui se forment lors de la fabrication du silicium ou de silico-alliage. Elles constituent un sous-produit encombrant de l'industrie electrometallurgique et pour chaque tonne de silicium fabriquee, 1/4 de tonne de fumee de silice est egalement produit. Additionnees dans le beton, elles ameliorent les proprietes rheologiques et mecaniques des betons. Le but de ce travail a ete de caracteriser, dans un premier temps, d'un point de vue structurale (chimique) et d'un point de vue textural (physique), les sf dans differents etats et environnements. Dans un second temps, les caracteristiques physico-chimiques ont ete correlees aux comportements rheologiques et mecaniques des mortiers dans lesquels elles ont ete incorporees. Dans leur etat de poudre, nous avons identifie en rmn les particularites structurales de certaines sf. En milieu alcalin, la reactivite des sf, exploree par rmn en etudiant l'hydratation de la silice et etudiee par mesure de l'hydrogene produit par les sf, a ete correlee a la presence des elements calcium, silicium libre et carbone libre contenus dans la sf. L'approche texturale a permis de distinguer, par des observations microscopiques directes a differentes echelles, un double niveau d'organisation des sf a l'etat de poudre: le niveau du grain et le niveau de la particule spherique elementaire (dont les agregats constituent le grain). Cette organisation presente un caractere fractal de masse avec des exposants compris entre 1. 54 et 1. 87. Elle a ete quantitativement confirmee en comparant la densite apparente microscopique de la poudre (observee) a la densite calculee a partir des compacites des grains dans le lit de la poudre et des particules elementaires a l'interieur du grain. Il en resulte que les sf peuvent presenter des aspects texturaux les differenciant les unes des autres, a l'echelle de la poudre, mais egalement a l'echelle intragranulaire par l'organisation des particules elementaires a l'interieur des agregats. En milieu mortier, la microtexture des sf a ete demontree comme etant a l'origine des comportements rheologiques des mortiers frais. Dans le mortier durci, les variations des teneurs en elements minoritaires des sf (ca, si et c) ne perturbent pas notablement les proprietes mecaniques. Si a ce stade, les sf sont desagregees a l'etat de particules elementaires, les proprietes mecaniques du mortier sont identiques
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Brooke-Devlin, Wayne. "Novel Shear-Thinning of Aged PDMS/Fumed Silica Admixtures and Properties of Related Silicone Elastomers". VCU Scholars Compass, 2012. http://scholarscompass.vcu.edu/etd/443.
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Fumed silica filler has long been used to structurally reinforce silicone elastomers. Unfortunately, the combination of as little as a few weight percent of untreated fumed silica nanoparticles [uFSN] with a siloxane polymer, such as PDMS, forms a difficult to process waxy solid admixture that even long periods of high shear mixing will not thin. In the course of the current work it was noted that after a period of storage certain solid admixtures would become viscous liquids when subjected to additional high shear mixing. It was further found that the required aging period could be decreased if the admixture storage temperature were increased. The only known interaction of PDMS and uFSN at moderate conditions is the adsorption of polymer on filler, and this interaction is also known to occur more quickly at higher temperature. This study examines the relationship between polymer adsorption and admixture liquefaction. Further, the mechanical properties of cured elastomers containing liquefied admixtures are examined to assess the degree of reinforcement that these materials afford.
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Addona, Tony. "The study of a novel thermal plasma process for the production of fumed silica". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0017/NQ44335.pdf.
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Chu, Qingli. "Texture, proprietes de surface et comportement en suspension des fumees de silice". Orléans, 1995. http://www.theses.fr/1995ORLE2037.
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Les fumees de silice (fs) sont des sous-produits formes lors de la fabrication du silicium et de silico-alliages. Leurs caracteres particulaires et cristallochimiques en font un bon additif pour les betons en ameliorant les proprietes rheologiques et mecaniques de ces derniers. Cependant, ces ameliorations ne sont obtenues que si la desagglomeration et la dispersion des fs est complete. L'objectif de ce travail vise a une meilleure comprehension des phenomenes et parametres conduisant a une amelioration de l'etat de dispersion des fs afin d'ameliorer encore la microstructure et les proprietes des beton. Dans ce but, en fonction de la composition initiale des fs, leurs caracteristiques physico-chimiques a l'etat de poudre et leurs proprietes colloidales en milieu aqueux ont ete etudiees et reliees a leurs proprietes structurales et rheologiques. A l'etat de poudre, les fs contiennent en majorite de la silice sous forme quasi-amorphe de cristobalite mal-cristallisee (pseudo-cristallites d'une dizaine d'angstrom), ainsi qu'une faible quantite de quartz, de cristobalite ii cristallisee et de carbure de silicium. L'observation par meb a montre que le traitement de densification influence fortement la morphologie des grains. L'analyse des images de met nous a permis d'obtenir la distribution de taille des particules elementaires pour les fs etudiees, dont les diametres varient de 0,007 a 0,54 m. En milieu aqueux, le traitement de densification modifie la dispersabilite des fs. Les fs densifiees sont plus difficiles a disperser que les fs non-densifiees. Pour les suspensions de fs, les mesures de la vitesse et du volume de sedimentation, les mesures de la charge de surface des particules ainsi que l'analyse granulometrique ont montre que la dispersabilite et la presence de cations, comme ca#+#2, jouent un role tres important dans l'agglomeration des fs. Il n'est donc pas judicieux de former des coulis avec des fs riches en calcium qui engendrent la formation d'agglomerats mecaniquement stables. Le mecanisme d'agglomeration est lie a l'evolution de la charge de surface des particules. Il a ete etudie quantitativement par la methode d'electrophorese et de titrage d'electrolyte. L'etude rheologique des suspensions de fs (viscosite, seuil d'ecoulement et thixotropie) a montre l'importance de la dispersabilite des fs et de leur teneur en impuretes. L'intervention chimique des impuretes est responsable des augmentations de viscosite et de ph au cours du temps, ainsi que de l'evolution de l'agglomeration et de la charge de surface. Une relation quantitative entre la viscosite apparente et la fraction en solide a pu etre demontree en utilisant l'equation de krieger-doupherty et en introduisant un coefficient qui traduit l'influence de l'agglomeration sur la viscosite
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Katzer, 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.
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Addona, Tony. "The effect of quench conditions on the properties of fumed silica produced using an arc process". Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=26108.
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The effect of quench conditions on the properties of fumed silica generated using an arc process was studied. The process consisted of vaporizing quartz particles in a batch transferred arc reactor using the radiative energy from an Ar/NH$ sb3$ thermal plasma. Ammonia was used to increase the vaporization rate of quartz. The hot gas stream exiting the reactor contained a mixture of the decomposition products of NH$ sb3$ and SiO$ sb2$. This included SiO$ sb{ rm (g)}$, O$ sb2$, H$ sb2$ and N$ sb2$. Rapid quenching of this gas stream with steam resulted in the production of a fumed silica aerosol. Collection of the product took place in a baghouse filter. The quench conditions studied included pre-quench temperature, T$ sb{ rm q}$, and supersaturation, P$ sb{ rm s}$, quench rate, R$ sb{ rm q}$, and quench stoichiometry, S$ sb{ rm q}$. P$ sb{ rm s}$ was defined as the molar ratio of SiO$ sb{ rm (g)}$ flow, calculated from the quartz weight loss during an experiment, to the SiO$ sb{ rm (g)}$ flow predicted at equilibrium. S$ sb{ rm q}$ was the molar ratio of steam to SiO$ sb{ rm (g)}$ flow.In general, high pre-quench temperatures, high quench rates, and low pre-quench supersaturation ratios, produced high surface area powders. Quench stoichiometry did not have an effect here, but the use of a large excess of steam in the quench caused the degree of surface hydroxylation to be high. In all cases, the characteristic chain-like aggregate shape and an amorphous morphology were produced. The thickening and thixotropic ability of the powders was found to be significant compared to commercial brands of fumed silica. The best fumed silica produced during the study was found to be 46% as effective as Aerosil$ sp circler$ 200 and 60% as effective as Cab-O-Sil$ sp circler$ M-5. The experimentally generated powders were not equivalent to the commercial brands due to a lack of surface area. (Abstract shortened by UMI.)
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Pédèches, Jean-Michel. "Etude des proprietes mecaniques et du retrait de betons de haute performance". Toulouse 3, 1988. http://www.theses.fr/1988TOU30061.
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Etude des betons avec resistance a la rupture en compression simple entre 30 et 130 mpa a 28 jours, realises par introduction de fumee de silice condensee et de fluidifiant. Dosage optimal de la fumee de silice (autour de 10% du poids du liant); variation des proprietes mecaniques, plus forte pour la resistance a la compression, avec fragilisation. Influence du fluidifiant sur la faible resistance a la compression aux jeunes ages et sur le retrait (moindre retrait avec la fumee de silice qu'avec les betons classiques d'egale resistance, fortement doses en ciment et/ou fluidifiant)
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Oudjit, Mohamed Nadjib. "Reactivite des fumees de silice condensees en presence de chaux ou de ciment portland". Toulouse, INSA, 1986. http://www.theses.fr/1986ISAT0001.
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Etude de la reactivite de sept varietes differentes de fumees de silice condensees (csf). L'activite pouzzolanique depend de la nature et de la teneur des impuretes qua'ellesrenferment. On montre que: le carbone imbrule retarde le phenomene pouzzolanique; le carbone imbrule, en forte teneur, peut provoquer un important retard d'hydratation du ciment portland; l'incorporation de csf a un ciment portland permet d'obtenir un ciment ayant une resistance en compression comparable ou superieur a celle d'un ciment portland mitral, toutefois des impuretes dans une csf peut conduire a rejeter son utilisation.
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Yin, Quanyi. "Thiol-para-fluoro modified PPFS as building blocks for the design of silica-based nanocomposite and layer by layer self-assembled thin films". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI025/document.
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Ce travail de thèse décrit la préparation de deux types de films de polymères : i) des films nanocomposites à base de silice pyrogénée aux propriétés superhydrophobes et ii) des films LbL auto-assemblés, incluant tous deux des dérivés de poly(2,3,4,5,6-pentaflurostyrene) (PPFS), utilisés comme briques élémentaires. La stratégie utilisée ici consiste à exploiter les nombreux avantages que présente la réaction de substitution du fluor en position para du PPFS avec un thiol, pour générer de nouveaux dérivés aux propriétés ajustables. Ainsi, le premier volet de la thèse a consisté à introduire des chaînes de PPFS de façon covalente à la surface de silice pyrogénée par une stratégie dite de «grafting through» en utilisant la polymérisation radicalaire contrôlée par le voir nitroxydes, en présence de PS-DEPN comme macroamorceur. La cinétique de polymérisation du PFS avec et sans particules silice a été étudiée dans divers solvants, différentes particules hybrides de silices modifiées en surface par une couronne de PPFS ont été préparé. Ensuite, un thiol perfluoré (perfluorodecanethiol:PFDT) a été utilisé pour modifier le PPFS, considéré dans ce cadre comme matrice hôte pour la préparation des nanocomposites et pour modifier le PPFS présent à la surface des particules de silice. A partir de là, un large panel de films nanocomposite a été préparé à partir des différentes combinaisons possibles de polymère hôte (PPFS ou PPFS-PFDT) et de charges inorganiques de silice (modifiées par le PPFS ou par le PPFS-PFDT). Les propriétés de mouillabilité ainsi que la morphologie de surface de chaque film ont été analysées et il en résulte que certains films présentent un caractère superhydrophobe. Le deuxième volet de la thèse a porté sur la modification du PPFS par des thiols porteurs de fonctions acide carboxylique, toujours par la réaction de substitution décrite précédemment. Différents dérivés de PPFS carboxylés de DS variés ont été synthétisés. Leur habilité à développer des liaisons hydrogène avec un polymère modèle accepteur de liaison H (la poly(4-vinyl pyridine) (P4VP)) a été étudiée. Il en ressort que dépendamment de la nature du solvant, des mélanges miscibles ou des complexes interpolymères ont ensuite été formés. Des solutions de complexes préformés ont été successivement déposées par spin-coating pour construire des films. De plus, des films multicouches LbL stabilisés par des liaisons H entre le PPFS carboxylé et la P4VP ont été élaborés and il a été démontré que la nature du solvant de dépôt, ainsi que le taux de modification du PPFS, impactent fortement le mécanisme de croissance, l’épaisseur du film et les caractéristiques de surface, en termes de topologie et de mouillabilitéThis work describes the preparation of two kinds of thin polymer films : i) self-cleaning silica-based (nano)composites films and ii) LbL self-assembling films, both including poly(2,3,4,5,6-pentaflurostyrene) (PPFS) derivatives, as building blocks. The cornerstone of the approach is to exploit the thiol-para fluoro substitution reaction to PPFS chains in order to generate derivatives with tailored properties. In this frame, PPFS chains were anchored onto the surface of vinyl-functionalized fumed silica nanoparticles by nitroxide-mediated polymerization (NMP) in presence of PS-DEPN as macro-initiator via a “grafting through” strategy. The kinetics of NMP of PFS were investigated in presence and without silica in various solvents and well-characterized hybrid silica particles containing different polymer grafting weight were declined. Then, perfluorodecanethiol (PFDT) was employed to modify PPFS, considered as the host polymer matrix, and to functionalize PPFS chains tethered to silica particles. A large panel of (nano)composite films from the different possible host matrix/silica particles combinations was prepared. The wettability and the surface morphology of each film were discussed, as a function of the host structure (PPFS or PPFS-PFDT with different DS) and silica (modified with PPFS or PPFS-PFDT), as well as the silica content. It results that superhydrophobic features can be reached. Subsequently, PPFS was modified by using carboxylic acid mercapto modifier via the thiol-para fluoro coupling. Various carboxylated PPFS derivatives differing in the degree of substitution (DS) were prepared and their ability to develop H-bonds in solution with a model strong H-bond acceptor partner (poly(4-vinyl pyridine) (P4VP)) was investigated. Dependently on the nature of the solvent, a miscible blend or interpolymer complexes (IPC) were achieved. IPC-containing solutions were used to successfully fabricate spin-assisted films. Furthermore, H-bonds mediated LbL self-assembly multilayer films involving carboxylated PPFS and P4VP were prepared and it was evidenced that the nature of the deposition solvent as well as the extent of the modification (quantified by the DS), impact the growth mechanism, the thickness and the surface features, in terms of topology and wettability
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Li, 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.
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Alam, 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.
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Alshammari, 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.
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Construction and demolition waste concrete has dramatically increased worldwide in the last decade. The social and environmental concerns on recycling of these wastes have consequently increased substantially. Recent technology has greatly improved the recycling process for construction and demolition waste concrete. The current study presents the results of a laboratory study on the performance of portland cement concrete prepared by incorporating different mineral admixtures i.e., silica fume (SF) and meta-kaolin (MK) with natural coarse aggregate (NCA) from quarry and recycled coarse aggregate (RCA) from old concrete pavements. The silica fume (SF) and meta-kaolin (MK) were used as a partial replacement of ordinary portland cement. Natural aggregate was replaced with 100% recycled concrete coarse aggregate by volume. In the present investigation, silica fumes (SF) and meta-kaolin (MK) replacement were 0%, 5.0% individually and few combination of SF and MK. A fixed air entraining admixture (AEA) i.e., 5% and water to cement (w/c) ratio of 0.42 was used to study the effect of the SF and MK on concrete mix. To maintain a desired slump for workability of the concrete mix, a super plasticizer (SP) was also used. All the concrete mixes used 605 lb. of ordinary portland cement per cubic yard. Concrete mix specimens were tested for compressive strength after curing periods of 7, 14, 28 days; splitting tensile strength after curing for 28 days; and flexural strength test after curing for 14 and 28 days. The aim of the study was to design a concrete mix with 100% recycled concrete aggregate with the addition of meta-kaolin (MK) and silica fumes (SF) that has strength equal or greater than the strength of concrete prepared with 100% natural aggregate. Among all tests performed, a combination of 5% meta-kaolin (MK) and 5% silica fumes (SF) mixture with 100% natural coarse aggregate showed better results as compared with the mixture used 100% recycled concrete aggregate. For the same combination of MK and SF, 100% recycled concrete showed highest strength. Results also show that the use of 5% meta-kaolin (MK) and 5% silica fumes (SF) with natural or recycle aggregate showed highest compressive, tensile, and flexural strength compared with concrete mixes prepared without meta-kaolin (MK) and silica fume (SF). With different percentages of SF and MK, the compressive strength for NCA and RCA concrete has increased in the range between 7 to 17% and 4 to 12%, respectively after curing for 28 days. The increase of tensile strength with different percentages of SF and MK ranged between 3 to 10% for NCA concrete and 1 to 4% for RCA concrete after curing for 28 days. Also, the flexural strength result has increased with different percentages of SF and MK in the range between 19 to 40% for NCA concrete and 14 to 25% for RCA concrete after curing for 28 days. Hence, by using mineral admixture or supplementary materials i.e., MK and SF, it was possible to achieve higher mechanical properties of the recycled concrete aggregate containing 100% recycled aggregate.
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FRYDA, HERVE. "Piegeage du cesium dans des materiaux a base de ciment alumineux et de fumee de silice". Paris 6, 1995. http://www.theses.fr/1995PA066326.
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La cure d'une pate constituee de ciment alumineux, de fumee de silice et d'une solution aqueuse de cesium conduit au piegeage du cesium au sein d'une phase solide hydratee. Une premiere etape d'immobilisation du cesium intervient au debut de la cure, par adsorption au sein d'une phase amorphe microporeuse, riche en aluminium, entourant les particules de fumee de silice. La prolongation de la cure, alors que le ciment est deja hydrate, mene a la cristallisation d'une zeolite: la chabazite. Le cesium se retrouve alors immobilise dans le reseau de ce cristal. Un test de lixiviation severe prouve l'efficacite de cette immobilisation. La chabazite se forme egalement lorsqu'un melange ciment alumineux-fumee de silice, pre-hydrate sans cesium, est mis au contact d'une solution de cesium. La formation de la chabazite est favorisee par la stabilisation de sa structure cristalline par un cation alcalin de taille suffisante. Le cesium et le potassium sont efficaces, mais pas le sodium. Un traitement thermique a haute temperature (1350c) du melange ciment alumineux-fumee de silice hydrate en presence de cesium conduit a la formation d'une phase cesiee tres stable ; la pollucite. La volatilisation du cesium due au traitement thermique est faible et le piegeage du cesium par la pollucite est extremement efficace
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Lafaurie, Arnaud. "Etude des propriétés de surface des fumées de silice : application à la dispersion dans le polypropylène". Montpellier 2, 2003. http://www.theses.fr/2003MON20049.
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Alam, Mahmood. "Development of vacuum insulation panel with low cost core material". Thesis, Brunel University, 2015. http://bura.brunel.ac.uk/handle/2438/11658.
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Buildings consume around half of the UK's total energy consumption and are responsible for almost 50% of UK's total carbon dioxide (CO2) emissions. Use of high thermal resistance insulation in buildings is critical to save the substantial amounts of space heating energy lost through building fabric. Conventional building insulation materials have higher thermal conductivity values ranging from 40 mWm-1K-1 (Glass fibre) - 26 mWm-1K-1 (Polyurethane foam) and require larger thicknesses to achieve stringent building regulation requirements which may not be feasible due to techno-economic constraints. Vacuum Insulation Panel (VIP) is a relatively new insulation for building applications that offers 5-8 times higher thermal resistance and can achieve significant space savings in buildings. VIPs are produced as a rigid panel comprising inner core board laminated in an outer high barrier envelope under evacuated conditions (< 5mbar). However, the main challenge for large scale acceptance of VIPs in building applications is their higher cost. VIPs have been shown to have an approximately 10 times longer payback compared to conventional EPS insulation due to their high initial cost. Expensive materials currently being used for VIP manufacturing such as fumed silica contribute to high cost of VIPs and it is critical to identify alternative low cost materials for VIP components to overcome the challenge of high cost. The aim of this thesis was to develop an alternative low cost material and investigate its suitability for use as VIP core. Expanded perlite, a low cost material was identified as a replacement of expensive fumed silica in a VIP core. Composite samples containing expanded perlite, fumed silica, silicon carbide (SiC) and polyester fibres were developed by dry mixing of the constituents in different mass ratios and their different properties were experimentally measured to identify optimum composition of composite. Gaseous thermal conductivity at different pressures was calculated from the pore size data obtained using Mercury Intrusion Porosimetry (MIP), gas adsorption and electron microscopy. Radiative conductivity of composite samples was measured using Fourier Transform Infrared (FTIR) to ascertain the opacifying effect of expanded perlite and opacifier (SiC). Centre of panel thermal conductivity of core boards of size 100mm x 100mm made of composite material at atmospheric pressure was measured by using a small guarded hot plate device. Average pore diameter values of expanded perlite decreased with the partial filling of fumed silica aggregates and was found to be in the range of 150-300 nm yielding lower gaseous conductivity values of 1.2-2.1 mWm-1K-1 at 100mbar and became negligible upon further decreasing pressures below 10 mbar. Core boards made of optimised composite containing 30% expanded perlite and 50% fumed silica along with SiC and polyester fibres was found to achieve centre of panel thermal conductivity of 28 mWm-1K-1 at atmospheric pressure and the average radiative conductivity of 0.67 mWm-1K-1 at 300K with its gaseous thermal conductivity at 1 mbar being 0.016 mWm-1K-1. According to the results of the thesis VIP prototypes consisting of core made with optimised composite consisting (50 mass% of fumed silica, 30 mass% of expanded perlite along with 8 mass% of fibre and 12 mass% of SiC) yielded centre of panel thermal conductivity of 7.4-7.6 mWm-1K-1 at pressure of 0.53-0.64 mbar. Opacifying properties of expanded perlite were observed and quantified. Expanded perlite reduced the radiative conductivity of the composite requiring smaller quantities of high density opacifiers such as SiC. For sample containing no expanded perlite, average radiative conductivity was calculated to be 1.37 mWm-1K-1 and radiative conductivity values decreased to 1.12 mWm-1K-1, 0.67 mWm-1K-1, 0.63 mWm-1K-1 and 0.50 mWm-1K-1 with mass ratio of expanded perlite 20%, 30%, 40% and 60% respectively. It was concluded that the solid conductivity of prototypes VIPs was 1.8-2 times higher compared to those of commercially available VIPs and is the main reason for higher centre of panel thermal conductivity.
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Ersu, Dilek. "Preparation And Characterization Of Nanocomposites With A Thermoplastic Matrix And Spherical Reinforcement". Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/3/12607447/index.pdf.
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The aim of this study is to investigate the effects of compatibilizers, fumed silica and mixing order of components on morphological, thermal, mechanical and flow properties of LDPE/Fumed silica nanocomposites. As compatibilizer(Co)ethylene/n-butyl acrylate/maleic anhydride (E-nBA-MAH), ethylene/glycidyl methacrylate (E-GMA) and ethylene/methyl acrylate/glycidyl methacrylate (E-MA-GMA) Lotader®
resins
as silica Cab-o-sil®
M5 fumed silica were used. All samples were prepared by means of a lab scale co-rotating twin screw extruder and injection molded into standard samples. In the first step, individual effects of filler and compatibilizers were studied in binary systems with LDPE. Then, keeping the amount of compatibilizer constant at 5%, ternary nanocomposites were prepared by adding 2 or 5% of fumed silica using different component mixing orders. Among investigated mixing orders, mechanical test results showed that the best sequences of component addition are FO1 [(LDPE+Co)+M5] and FO2 [(LDPE+M5)+Co] mixing orders. Considering the compatibilizers, E-nBA-MAH terpolymer showed the highest performance in improving the mechanical properties, E-GMA copolymer also gave satisfactory results. According to the DSC analysis, since addition of fumed silica and compatibilizer does not influence the crystallization behavior of the compositions, it is concluded that, neither fumed silica nor any of the compatibilizers have nucleation activity on LDPE. MFI test results showed that, addition of fumed silica increases the melt viscosity, decreasing MFI values of samples. This change seems to be directly proportional to fumed silica amount.
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Justice, Joy Melissa. "Evaluation of Metakaolins for Use as Supplementary Cementitious Materials". Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6936.
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Two metakaolins were evaluated for use as supplementary cementitious materials in cement-based systems. The metakaolins varied in their surface area (11.1 v. 25.4 m2/g), but were quite similar in mineralogical composition. Performance of metakaolin mixtures was compared to control mixtures and to mixtures incorporating silica fume as partial replacement for cement at water-to-cementitious materials ratios of 0.40, 0.50, and 0.60. In this study, the early age properties of fresh concrete and the mechanical and durability properties of hardened concrete were examined. Early age evaluations aimed to determine the reactivity of metakaolin (heat of hydration) and its effect on mixture workability (slump, setting time, unit weight). In addition, three types of shrinkage were monitored in metakaolin-cement systems: chemical, autogenous, and free. Compressive, tensile, and flexural strength and elastic modulus were measured at various concrete ages. The influence of metakaolin addition on durability was assessed through accelerated testing for sulfate resistance, expansion due to alkali-silica reaction, and through rapid chloride permeability measurements.
To further quantify the underlying mechanisms of metakaolin's action, the microstructure of pastes was examined. Calcium hydroxide (CH) content was determined using thermogravimetric analysis and verified using differential thermal analysis. Surface area and pore size distribution were evaluated via nitrogen adsorption. These analyses yielded information about the pozzolanic reactivity of metakaolin, associated CH consumption and pore structure refinement, and resulting improvements in mechanical performance and durability of metakaolin-concretes.
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Stundebeck, Curtis J. "Durability of ternary blended cements in bridge applications". Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/5082.
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Thesis (M.S.)--University of Missouri-Columbia, 2007.The 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.
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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.
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Moustachi, Om Elkhaïat. "Influence de la microstructure des mortiers de ciment portland armes de fibres sur leur comportement mecanique en flexion". Toulouse, INSA, 1986. http://www.theses.fr/1986ISAT0002.
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Analyse des modifications de la structure interne du mortier induites par l'introduction des fibres et determination de leur influence sur les proprietes mecaniques du mortier en flexion. Des fiches en paquets introduites dans le mortier se dispersent lors du malaxage en fibres individuelles espacees de quelques microns. Ces espaces, tres peu accessibles aux particules anhydres du ciment sont partiellement remplis par des hydrates. Ils rendent le mortier tres permeable aux fluides et influent directement sur son module d'elasticite en flexion qui diminue avec le pourcentage de fibres. L'effet d'armature des fibres se traduit par une augmentation de la resistance et de l'allongement a la rupture du mortier. De la fumee de silice dispersee a l'aide d'un fluidifiant reduit la porosite entre les fibres et augmente ainsi le module d'elasticite et sa resistance a la rupture
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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.
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Alguns materiais, constituídos quase que exclusivamente por sílica, são empregados, de forma suplementar ao cimento Portland, por promoverem melhorias ao concreto, devido aos seus efeitos físicos e pozolânicos, além de atenderem a questões ambientais. No entanto, essa sílica pode gerar produtos indesejados na presença de álcalis, sendo este fenômeno conhecido como reação álcali sílica (RAS). Na presença de água, esses produtos são capazes de expandir no interior da massa de concreto, provocando fissuras internas e externas e, em casos mais graves, a degradação do elemento estrutural. Com a finalidade de evitar essa manifestação patológica, o presente trabalho propõe-se avaliar o potencial reativo frente à RAS da sílica ativa e dois tipos de cinzas da casca do arroz (CCA), uma comercial e outra residual. Nessa investigação foram adotados os teores de 5 a 50 %, utilizados como substituição parcial ao cimento Portland padrão. Os métodos de ensaio adotados nesta pesquisa foram o método acelerado em barras de argamassa segundo a NBR 15577 - 4/5, e dois novos métodos acelerados (cubos de pasta e prismas). O métodos acelerado em cubos de pasta avaliou a resistência à compressão, enquanto o método em prismas de pasta avaliou a variação dimensional. Os resultados obtidos em barras de argamassa apontaram que ambas as CCA investigadas, foram reativos frente à RAS. No entanto, o teor de 50 %, em ambas as CCA, se mostrou inócuo para essa reação. A sílica ativa foi considerada inócua em todos os teores avaliados. O aditivo superplastificante empregado não foi eficiente em reduzir a expansão provocada pela CCA. Os ensaios que avaliaram a expansão em prismas de pasta apresentaram uma ótima correlação positiva com o método normalizado em barras de argamassa. Nos prismas de pasta com 25 % de CCA industrial foram identificados os compostos franzinite, chessexite e thaumasite. Estes compostos apresentaram morfologia de acículas ora tortuosas ora delgadas e retilíneas compondo todas as amostras coletadas dessa pasta. A análise termogravimétrica apontou o alto poder adsorvente de água dessa pasta. Em conclusão, o ensaio em prismas de pastas a 48°C com 1,25 % de Na2Oeq demonstrou ser um método prático laboratorialmente e apresentou um grande potencial para avaliar os materiais suplementares ao cimento Portland frente a RAS, além de facilitar identificação dos produtos que provocaram expansão.Some 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.
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Gao, Xiang, i 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.
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Concrete is the most broadly used material in construction worldwide and Reactive Powder Concrete (RPC, a type of ultra high performance concrete) is a relatively new member of the concrete family. In this work the critical parameters of RPC mix design are investigated and the mix design is explored through a program of concrete casting and testing. Owing to the enhanced microstructure of RPC, porosity and permeability can be significantly decreased in the concrete matrix. This benefits the durability characteristics of RPC elements resulting in a longer service life with less maintenance costs than conventional concrete. It has been used for high integrity radiation waste material containers because of its low permeability and durability. Fibre reinforced RPC is also ideal for use in long span and thin shell structural elements without traditional reinforcement because of its advantageous flexural strength. Moreover, due to improved impact resistance, RPC can be widely employed in piers of bridges, military construction and blast protection. There is no standard approach to assessing the impact resistance of concrete. This investigation utilises relatively well accepted impact equipment to evaluate the mechanical properties of RPC under dynamic loading. The compressive and flexural tensile strengths of plain and fibre reinforced RPC are investigated using a variety of specimens and apparatus. The dynamic increase factor (DIF) is evaluated to indicate the strain rate sensitivity of the compressive and flexural strength.
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Grande, 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/.
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Neste trabalho, por meio de uma metodologia experimental foram analisados vários aspectos de tijolos modulares compostos por misturas binárias e ternárias de solo-cimento e solo cimento-sílica produzidos em prensa manual modelo SAHARA, com a finalidade de se obter parâmetros e diretrizes que visam um melhor desempenho do material. Realizaram-se ensaios em corpos-de-prova cilíndricos de maneira acessória no decorrer do trabalho, o que resultou no suporte para fundamentação de diversas avaliações sobre as composições de traços utilizados na fabricação dos tijolos. Foram executados painéis de parede com o objetivo de verificar o comportamento da alvenaria em relação à resistência à compressão e à deformabilidade das paredes, possibilitando correlações com os resultados dos ensaios de prismas, tijolos e argamassa de assentamento. As contribuições da pesquisa permitem relacionar a tecnologia da fabricação de tijolos de solo-cimento com o contexto de construção sustentável e o aproveitamento de resíduos industriais, além de sistematizar informações para a elaboração de um projeto tecnológico com os tijolos modularesIn 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
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CHITRANK. "ENHANCING CONCRETE PROPERTIES BY ADDING SILICA FUMES : Compressive Strength". Thesis, 2018. http://dspace.dtu.ac.in:8080/jspui/handle/repository/16366.
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Due to over increasing population and limited resources of land we have to look to the sky to accommodate this increasing population and for that we are so much focused on making high rise buildings and other mega structures to utilise the resources of land to its fullest, but this cannot be achieved without improving our construction technique and materials. As we know that Concrete is one of the most widely used structural material hence its property and quality influence the construction a lot. Here in my project I have tried to evaluate those properties of concrete and the improvement in those properties by adding silica fume. Silica fume act as a filler material and fills the pores between cement particles, making it more dense and improving the microstructure of concrete and thus improving the mechanical properties of concrete, such as strength, impermeability, durability, elastic modulus and so on. It also improve the concrete by chemically reacting with hydration precipitation of Ca(OH2) and producing hydrated calcium silicate in alkaline conditions thus improving the consistency of concrete and workability. Compressive strength of concrete is the most important property of concrete, because other properties like stress-strain relationship, tensile strength, bond strength, modulus of elasticity, density, impermeability, durability etc. can be inferred from the compressive strength using established correlations. Therefore in this project I have focused on observing the improvement in compressive strength of concrete by adding silica fumes and finding the most optimum proportion of silica fume which gives us the best result. Different mix design are prepared following IS code and different proportion of silica fume (i.e. 0%, 5%, 10%, 15%, 20%) are added and the results of 7 and 28 days compressive strength are found and compared. The result shows a progressive increase in compressive strength of concrete (corresponding to 28 days strength) till 15% of silica fume and then it slightly decreases hence we can correlate that the most optimum proportion of silica fume that should be added in concrete is about 15% of total cementitious material. Adding silica fume also improves the early strength of concrete (i.e. 7days strength), durability etc as discussed in the project.
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Liu, Yen-Yu, i 劉彥佑. "Effect of Various Silica Fumes on the Property of Cement-based Material". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/87663527820982435396.
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碩士國立臺灣海洋大學
河海工程學系
101
Past studies have shown that substitution mineral admixture for Portland cement would affect the cement-based composite material properties. This study was aims to investigate the effect of type of silica fume, substitution percentage, and water-binder ratio on the properties of cement-based composite materials such as mechanical properties, physical properties, abrasion resistance and permeability. Test variables include (1) two different sources of silica fume; (2) four silica fume substitutions and (3) two water-cement ratios. The results showed that (1) various silica fume replacements can enhance compressive strength, reduce wear coefficient and permeability; (2) even use of different sources of silica fume, 10% addition (compared to 5%, 15% and 20%) specimens have best compressive strength, abrasion coefficient and permeability and (3) higher fineness of silica fume would have higher improvement.
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Sadique, Sarder. "Production and Purification of Silicon by Magnesiothermic Reduction of Silica Fume". Thesis, 2010. http://hdl.handle.net/1807/25788.
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A new approach is discussed for the generation of high purity silicon from silica fume (SF), which is a waste by-product from the manufacture of metallurgical grade silicon. Process steps were developed and optimized including purification of SF, reduction by magnesium, and post-reduction leaching. Reduction was carried out successfully with initial HCl leached SF in a sealed chamber with varying Mg/SF ratios, temperature and time. These variables affected the production of silicon from SF. Suitable reduction conditions were found to be within the temperature range 750-850C and at approximately 2:1 ratio of Mg/SF. Reduction products were treated using a three-stage acid leaching. XRD, QXRD and ICP analyses of the final silicon powder product indicated that silicon with low impurity levels (low boron content) can be produced. Therefore, silicon produced by magnesiothermic reduction can be an attractive source for the production of solar grade silicon.
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Smith, William E. "Gelation kinetics of fumed silica-alcohol suspensions /". 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3242997.
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Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6576. Adviser: Charles F. Zukoski. Includes bibliographical references (leaves 68-71) Available on microfilm from Pro Quest Information and Learning.
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張銀濃. "An investigation into the effect of silica fume adding procedure on the physical properties of silica-fume concrete". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/92655296218264134093.
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碩士建國科技大學
土木與防災研究所
98
Proper introduction of silica fume in concrete can improve both the mechanical and durability characteristics of concrete had been proved in many reports. Since the silica fume has high hydrophilicity and will become very sticky after it gets wet, it is difficult to add the silica fume with pipeline through air pressure transports. Generally, an artificial broken bag method is employeed. The dry silica fume is measured and then threw into the concrete directly. However, this method has the shortage of low efficiency, high pollution, and artificial measurement error, which becomes a barrier against proper utilization of silica fume concrete. Silica fume can induce pozzolanic reaction only under the stimulation of the calcium hydroxide produced in the hydration of portland cement and some other chemical compound. It will not have any hydration with water. Therefore the mixing silica fume with water will not affect the chemical reaction between silica fume and concrete. This research try to use wast water recovery equipment in Ready-Mixed Concrete Plant to make liquefied silica fume first, and then pumped it into concrete mixer to produce silica-fume concrete. A series of tests show that better performance can be obtained both in workability of fresh concrete and the hardened properties when using liquefied silica fume to produce silica-fume concrete rather than using dry silica fume. In addition, actual practice had shown that about 25% of the productivity of silica-fume concrete can be increased after adopting the liquified procedure. Thus the liquefied procedure is worthwhile to promote in the industry. Key words：liquified silica fume, silica-fume concrete
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Chou, Ching-Hsi, i 周清溪. "Impedance Properties of Paste Incorporating with Silica Fume and Waterproof MaterialImpedance Properties of Paste Incorporating with Silica Fume and Waterproof MaterialImpedance Properties of Paste Incorporating with Silica Fume and Waterproof Material". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/75265758985808171661.
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碩士東南科技大學
防災科技研究所
98
Impedance Properties of Paste Incorporating with Silica Fume and Waterproof Material Student：Ching-Hsi Chou Advisor：Ping-Ju Lin Graduate School of Technology for Hazards Mitigation Tung Nan University ABSTRACT This paper is to study the engineering properties of cement paste with silica fume and waterproof material addition, using AC impedance and Vicat needle penetration. The research including the setting time and the impedance behavior of cement paste incorporating with silica fume and waterproof material is implemented. The results shows that the higher water-to-binder ratio, the higher initial and final setting time of paste; with the increase in silica fume and waterproof material addition, the initial and final setting time of paste decreases. At a fixed-frequency (10 kHz), the impedance value of silica fume and waterproof material paste increases with increasing curing age. The impedance value of paste increases with increasing addition of silica fume and waterproof material at 28-d age. From Nyquist plots of silica fume and waterproof material pastes, the impedance values of silica fume and waterproof material pastes increase with increasing curing age. By equivalent circuit simulation of silica fume and waterproof material pastes, the analysis of equivalent circuit model with interface effect is more accurate than that without interface effect.
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"Effect of Silica Fume on Moisture Flow and the Advective-Dispersive Transport of Ionic Species in Unsaturated Concrete". Thesis, 2013. http://hdl.handle.net/10388/ETD-2013-04-977.
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Under unsaturated conditions, both moisture flow and the transport of ions strongly depend on the degree of saturation in concrete. In the current literature, most theories and empirical models describe moisture flow and the transport of ions in concrete based on the assumption that concrete is fully submerged in a liquid phase. This simplistic assumption often leads to a systematic underestimation in the amount of ions, such as chlorides, especially in the case of concrete applications subjected to cyclic wetting and drying conditions. In this study, an experimental program was established to determine the key hydraulic parameters needed for modeling the moisture flow and the transport of ions in five types of concrete mixes under unsaturated conditions.
The required hydraulic parameters of the five concrete mixes include the saturated hydraulic permeability, the moisture retention function, and the dependency of the relative diffusion coefficient on degree of saturation. A centrifuge technique was used to determine the saturated hydraulic permeability of the five concrete mixes. The moisture retention data of all concrete mixes were determined using a vapour equilibrium technique. The moisture retention data were then used to determine the van Genuchten empirical parameters for an analytical characterization of the capillary pressure-degree of water saturation and the relative permeability-degree of saturation relationships. The dependency of the relative diffusion coefficient on the degree of water saturation was characterized for each type of concrete mix indirectly using an electrical resistivity technique. The experimental results of this study were used in different empirical models that have been originally developed for soils to examine whether they could be applied for concrete
The five concrete mixes used in this study were characterized by the usage of a different proportion of dry densified silica fume in each concrete mix. Those mixes were used to determine the effect of silica fume on the experimental and the empirical key hydraulic parameters considered in this study.
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Cunningham, EA. "A study of nanoparticles : silica fume and woodsmoke". Thesis, 2003. https://eprints.utas.edu.au/19782/7/Cunningham_whole_thesis_ex_pub-mat.pdf.
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The research studies described herein were undertaken in order to characterize the particulate matter comprising the inorganic pollutant silica fume emitted by an electrometallurgical process and the organic emission of woodsmoke from residential woodheaters. These two emissions were selected in view of their suspected influential contribution to air pollution in Hobart, Tasmania, Australia. Their size characterization was seen as a necessary step for a better understanding of the nature of their toxicity within the human respiratory system.
Their sizing was carried out using a Transmission Electron Microscope, the primary particle size (CMD) for 'silica fume being found to vary from a minimum of 34nm (0.034µm) to a maximum of 500nm (0.050µm) depending on sampling site at the smelter, while the aggregate size (VMD) varied from a minimum of 124nm (0.124µm) to a maximum of 180nm (0.18µm). Some 16,593 particles were involved. Sizes such as these place the primary particles of silica fume within the definition of nanometre particles. Similar results for the primary particles of silica fume have been recorded by other workers in the field when the technique of electron microscopy has been used.
On the other hand, woodsmoke organics was shown to vary in primary particle size from a minimum CMD of 21nm (0.021µm) to a maximum of 23.5nm (0.023µm), depending on wood and heater type, while the aggregate size varied from a minimum VMD of 35nm (0.035µm) to a maximum of 58n (0.058µm). Similar sizes were found with a woodsmoke contaminated ambient air sample, with CMD for primary particles of 16run (0.016µm) and VMD for aggregates of 45nin (0.045µm). The woodsmoke sizing represented the analysis of some 10,194 particles and permits both the primary particles and almost all aggregates of woodsmoke to be defined as nanoparticles. This was in contrast to previous work in the field which was at least a factor of ten larger than the present study for both primary particles and aggregates, a fact which has raised come concern with regard to sizing limitations.
Recent research has demonstrated the peculiarly high toxicity of particles in the nanometre size range. Other recent published work has postulated that this might explain the phenomena of health effects of nanoparticles on the human cardiopulmonary systems. It would seem, therefore, plausible to expect that the primary particles of silica fume and both the primary particles and aggregates of woodsmoke may subscribe to such hypotheses, being considered to be classified with the primary mediators of cardiopulmonary
mortality and morbidity.
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Mallick, Jagadish. "Effect of Silica Fume on Steel Slag Concrete". Thesis, 2010. http://ethesis.nitrkl.ac.in/2019/1/JAGADISH_MALLICK.pdf.
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Concrete is the most versatile construction material because it can be designed to withstand the harshest environments while taking on the most inspirational forms. Engineers are continually pushing the limits to improve its performance with the help of innovative chemical admixtures and supplementary cementitious materials. Nowadays, most concrete mixture contains supplementary cementitious material which forms part of the cementitious component. These materials are majority byproducts from other processes. The main benefits of SCMs are their ability to replace certain amount of cement and still able to display cementitious property, thus reducing the cost of using Portland cement. The fast growth in instralisation has resulted in tons and tons of byproduct or waste materials, which can be used as SCMs such as fly ash, silica fume, ground granulated blast furnace slag, steel slag etc. The use of these byproducts not only helps to utilize these waste materials but also enhances the properties of concrete in fresh and hydrated states. Slag cement and fly ash are the two most common SCMs used in concrete. Most concrete produced today includes one or both of these materials. For this reason their properties are frequently compared to each other by mix designers seeking to optimize concrete mixtures. Perhaps the most successful SCM is silica fume because it improves both strength and durability of concrete to such extent that modern design rules call for the addition of silica fume for design of high strength concrete. To design high strength concrete good quality aggregates is also required. Steel slag is an industrial byproduct obtained from the steel manufacturing industry. This can be used as aggregate in concrete. It is currently used as aggregate in hot mix asphalt surface applications, but there is a need for some additional work to determine the feasibility of utilizing this industrial byproduct more wisely as a replacement for both fine and coarse aggregates in a conventional concrete mixture. Replacing all or some portion of natural aggregates with steel slag would lead to considerable environmental benefits. Steel slag aggregate generally exhibit a propensity to expand because of the presence of free lime and magnesium oxides hence steel slag aggregates are not used in concrete making. Proper weathering treatment and use of pozzolanic materials like silica fume with steel slag is reported to reduce the expansion of the concrete. However, all these materials have certain shortfalls but a proper combination of them can compensate each other’s drawbacks which may result in a good matrix product with enhance overall quality.
In the present work a series of tests were carried out to make comparative studies of various mechanical properties of concrete mixes prepared by using ACC brand Slag cement , Fly ash cement and their blend (in 1:1 proportion ). These binder mixes are modified by 10% and 20% of silica fume in replacement. The fine aggregate used is natural sand comply to zone II as per IS 383-1982.The coarse aggregate used is steel making slag of 20 mm down size. The ingredients are mixed in 1: 1.5: 3 proportions. The properties studied are 7days, 28days and 56 days compressive strengths, flexural strength, porosity, capillary absorption.
The main conclusions drawn are inclusion of silica fume increases the water requirement of binder mixes to make paste of normal consistency. Water requirement increase with increasing dose of silica fume. Water requirement is more with fly ash cement than slag cement. The same trend is obtained for water binder ratio while making concrete to achieve a target slump of 50-70 mm. The mortar strength (1:3) increases with increasing percentage of silica fume. Comparatively higher early strength gain (7-days) is obtained with fly ash cement while later age strength (28 days) gain is obtained with slag cement. Their blended mix shows comparatively moderate strength gain at both early and later ages. Mixing of silica fume had made concrete sticky ie more plastic specifically with fly ash cement. The porosity and capillary absorption tests conducted on mortar mixes show decrease in capillary absorption and porosity with increase in silica fume percentage with both types of cements. The decrease is more with fly ash cement than slag cement. But the reverse pattern is obtained for concrete i.e. the results show decrease in 7days,28 days and 56 days compressive strength of concrete due to inclusion of silica fume in the matrix. The increasing dose of silica fume show further decrease in strength at every stage. Almost same trend is obtained for flexural strength also. The specimens without silica fume had fine cracks which are more visible in concrete made with slag cement than fly ash cement.