Global ETD Search

141	Vysokohodnotné betony na bázi druhotných surovin / High-performance concretes based on the secondary raw materials Sáček, Josef January 2008 (has links) This work is devoted to study of physical-mechanical properties and structure of high performance concretes (HPC) based on portland cement. The attention is focused on possibility of substitution of economic high-cost components of concrete with utilization of secondary raw materials or cheaper components. Properties of raw materials and their influence on whole quality of concrete were tracked by various methods. Mechanical properties of prepared HPC samples were tested especially (compression and flexural strength) with further microscopic study of structure. Isoperibolic calorimetry and X-ray powder diffraction method were also used for concrete characterisation. These methods allowed to determine the influence of raw materials on prepared HPC and to carry out a certain optimization among price and quality of this material.
142	Vliv použitého kameniva na vlastnosti vápenných malt / The effect of aggregate type on the properties of lime mortar Žižlavský, Tomáš January 2017 (has links) The thesis is focused on the comparison of the role of different types of aggregates and the binder-aggregate ratio on the properties of lime mortars. The theoretical part of the thesis deals with the effect of properties of aggregate, a binder-aggregate ratio and a use of calcareous aggregate, especially limestone, on the properties of mortars. It also deals with the utilization of limestone as aggregate in a history of masonry. In the practical part of the thesis there is a comparison of physically-mechanical and microstructural properties of mortars prepared with different type of aggregate (siliceous sand and limestone aggregate), with varying binder-aggregate ratio and also with a partial substitution of the aggregate by limestone fines. It was found that the usage of limestone instead of quartz sand produces the mortar of comparable properties. The partial substitution of the aggregate with limestone fines caused noticeable growth of strength, especially in mortars with higher binder-aggregate ratio.
143	Propuesta de uso de cenizas de cáscara de arroz y fibras de polipropileno en diseños de mezclas de concreto para el control de fisuras en losas macizas entrepiso in-situ en la ciudad de Lima / Proposal for the use of rice husk ash and polypropylene fibers in concrete mix designs for the control of cracking in concrete structures in the city of Lima Cano Duplex, Bryan Alexander, Galarza Mateo, Edwin Jean Marco 30 November 2020 (has links) La presente investigación fue elaborada con el fin de estudiar la influencia que tiene el agregar cenizas de cascara de arroz (CCA) y fibras de polipropileno (FPP) en la fisuración por contracción plástica del concreto. El estudio de investigación tuvo lugar en la ciudad de Lima, donde nos enfocamos a investigar las propiedades plásticas y mecánicas de un concreto f´c=210 kg/cm2, que se utiliza comúnmente en la fabricación de losas macizas, con reemplazo parcial del cemento por CCA en porcentajes de 5%, 10% y 15% respecto a su peso, y FPP en rendimiento de 900 gr/m3. Las principales propiedades en estado endurecido fueron investigadas, la resistencia a la compresión y la resistencia a la flexión y la propiedad en estado plástico que se desarrolló fue la fisuración debido a la contracción plástica a través del ensayo ASTM C1579. Teniendo en cuenta que no existe un acuerdo relativo al ancho de fisura máxima en un elemento estructural, se decidió utilizar límites entre 0.2 a 0.4 mm, para ambientes normales, sugeridos por el Mg. Ing. Gianfranco Ottazzi. De los resultados obtenidos, la mezcla adicionada con CCA en reemplazo parcial del cemento en 5%, 10% y 15% junto con las FPP en rendimiento de 900 gr/m3, podemos inferir que las CCA reducirán, no de manera significativa, las propiedades de la resistencia de un concreto f´c= 210 kg/cm2, sin embargo, reducen el promedio de apariciones de fisuras producidas en las losas macizas debido la contracción plástica del mismo. / The present investigation was elaborated with the purpose of studying the influence of the addition of rice husk ash (RHA) and polypropylene fibers (PPF) on the plastic shrinkage cracking of concrete. The research study took place in the city of Lima, where we focused on investigating the plastic and mechanical properties of a concrete f´c = 210 kg / cm2, which is commonly used in the manufacture of solid slabs, with partial replacement of the cement by RHA in percentages of 5%, 10% and 15% respect to its weight and PPF in yield of 900 g / m3. The main properties in the hardened state were investigated, the compressive strength and flexural strength and the property in the plastic state that developed was cracking due to plastic shrinkage through the ASTM C1579 test. Taking into account that there is no agreement regarding the maximum width in a structural element, it was decided to use limits between 0.2 to 0.4 mm, for normal environments, suggested by Mg. Eng. Gianfranco Ottazzi. According to the results obtained, the mixture added with RHA in replacement of cement in percentages of 5%, 10% and 15% together with PPF in yield of 900 gr / m3, we can infer that the RHA will reduce, not significantly, the strength properties of a concrete f´c = 210 kg / cm2, however, reduce the average occurrence of cracks produced in solid slabs due to the plastic shrinkage of the same. / Tesis Ceniza de cáscara de arroz Fibra de polipropileno Fisuras Losas Resistencia a la compresión Resistencia a la flexión Rice husk ash Polypropylene fiber Slump Compressive strength Flexural strength
144	Propuesta de un concreto para pavimentos rígidos con adición de polvo de vidrio en reemplazo parcial del cemento y agregado fino, afín de reducir la contaminación producida por la construcción de la capa de rodadura en la carretera Mayocc-Huanta, tramo Allccomachay-Huanta departamento de Ayacucho / Proposal of a concrete for rigid pavements with the addition of glass powder in partial replacement of cement and fine aggregate, in order to reduce the pollution produced by the construction of the wearing course on the Mayocc-Huanta highway, Allccomachay-Huanta section, department of Ayacucho Dávila Estrada, Herbert Arnold 02 February 2022 (has links) La cantidad de residuos se ha incrementado con el paso del tiempo, siendo actualmente una amenaza grave para el medio ambiente; tal es el caso del vidrio, además también el sector construcción aporta mucho a la contaminación ambiental, un sector que va a seguir en crecimiento constante. Uno de los sectores constructivos que va a crecer mucho más con el paso del tiempo son las vías. En nuestro país la mayoría de carreteras pavimentadas son de asfalto caliente, componente que contamina mucho y necesita mucho mantenimiento, es por eso que esta investigación planteo el uso masa común de los pavimentos rígidos, porque son más eco amigables, más resistentes y mucho más baratos a largo plazo, pero el inconveniente que se tiene con estos pavimento es su uso masivo de cemento componente que contamina mucho en su elaboración, es por eso que para hacer más sostenible con el medio ambiente se ha reemplazado parte del cemento y agregado fino para obtener un concreto ecológico que funciona adecuadamente para pavimentos rígidos, los reemplazos del cemento fueron de 20. 15 y 10%, del agregado fino fueron 15, 10 y 5% porcentajes obtenidos de la investigación de otros resultados, siendo estos los más favorables mecánicamente, los resultados obtenidos arrojan que un concreto con 15% de remplazo funciona correctamente, además reduce costos de realización y disminuye en un 11% la emisión de CO2 respecto de un concreto convencional. / The amount of waste has increased over time, currently being a serious threat to the environment; Such is the case of glass, and the construction sector also contributes a lot to environmental pollution, a sector that will continue to grow constantly. One of the construction sectors that will grow much more with the passage of time are the roads. In our country, most of the paved roads are made of hot asphalt, a component that pollutes a lot and needs a lot of maintenance, that is why this research proposed the common use of rigid pavements, because they are more eco-friendly, more resistant and much cheaper in the long term, but the disadvantage that these pavements have is their massive use of component cement that pollutes a lot in its preparation, that is why to make it more sustainable with the environment, part of the cement and fine aggregate have been replaced to obtain an ecological concrete that works adequately for rigid pavements, the cement replacements were 20, 15 and 10%, of the fine aggregate were 15, 10 and 5%, percentages obtained from the investigation of other results, these being the most favorable mechanically, the The results obtained show that a concrete with 15% replacement works correctly, also reduces production costs and reduces the e by 11%. CO2 mission compared to conventional concrete. / Tesis Polvo de vidrio Pavimentos rígidos Resistencia a la compresión Resistencia a la flexión Medio ambiente Concretos con reemplazo Glass powder Rigid flooring Compressive strength Flexural strength Environment Concrete with replacement
145	Implementation of Superabsorbent Polymers for Internally Cured Concrete Caitlin Jamie Adams (15300313) 17 April 2023 (has links) <p>Hydrated portland cement provides the solid adhesive matrix necessary to bind aggregate (sand and gravel) into concrete. The hydration reaction requires water, however the products of the reaction limit further diffusion of water to unreacted cement. Superabsorbent polymer (SAP) hydrogel particles absorb mixing water, then subsequently desorb when the relative humidity drops, serving as internal water reservoirs within the cement matrix to shorten diffusion distances and promote the hydration reaction in a process called internal curing. Internally cured cementitious mixtures exhibit an increased degree of hydration and reduced shrinkage and cracking, which can increase concrete service life. Increased service life can, in turn, reduce overall demand for portland cement production, thereby lowering CO2 emissions.</p> <p>This dissertation addresses practical implementation questions key to the translation of SAP hydrogel internal curing technology to from the benchtop to the field in transportation applications, including: (1) What effects do mix design adjustments made to increase mixture flow when using SAP have on cementitious mixture properties? and (2) What effect do cementitious binder characteristics have on SAP performance?</p> <p>The addition of SAP to a cementitious mixture changes the mixture’s flow behavior. Flow behavior is an important aspect of concrete workability and sufficient flow is necessary to place well consolidated and molded samples. Often, additional water is added to mixtures using SAP to account for the absorbed water, however cementitious mixture workability is often tuned using high range water reducing admixtures (e.g., polycarboxylate ester-based dispersants). Fresh and hardened properties of mortars were characterized with respect to flow modification method (using the mortar flow table test; compressive strength at 3, 7, and 28 days; flexural strength at 7 and 28 days; and microstructural characterization of 28-day mortars). At typical doses, it was found that the addition of extra water lowers the resulting compressive and flexural strength, while high range water reducing admixtures administered at doses to achieve sufficient mortar flow did not compromise compressive or flexural strength.</p> <p>The SAPs used in cement are generally poly(acrylamide-acrylic acid) hydrogels and are not chemically inert in high ionic-load environments, such as cement mixtures. The behavior of an industrial SAP formulation with characterized across five different cement binder compositions with respect the cement hydration reaction (using isothermal calorimetry, thermogravimetric analysis of hydration product fraction, and scanning electron microscopy (SEM)/energy dispersive x-ray spectroscopy (EDS) microstructural analysis), the absorption behavior of the SAP, and the fresh and hardened properties of SAP-cement composites (mortar flow and compressive and flexural strength). The change in properties induced by the addition of SAP was similar across ASTM Type I cements from three manufacturing sources, suggesting that SAP internal curing can be implemented predictably over time and geography. Excitingly, in analysis of cement systems meeting different ASTM standards (Type III and Type I with 30% replacement by mass with ground blast furnace slag), synergistic and mitigating reaction behaviors were observed, respectively, in Type III and slag cement, suggesting that further study of SAP with these cement systems could be of particular interest.</p> Construction materials Composite and hybrid materials Polymers and plastics superabsorbent polymers hydrogels internal curing concrete mortar cement paste flow table test compressive strength flexural strength microstructure workability cracking tendency binder characteristics alkalinity of pore solution Type I cement Type III cement slag cement
146	Wheat Straw-Clay-Polypropylene Hybrid Composites Sardashti, Amirpouyan 23 September 2009 (has links) The preparation of polymeric hybrid composite consisting of organic and inorganic fillers is of interest for industries like automotive, construction and packaging. In order to understand and predict the physical and chemical properties of these hybrid composites, it is necessary to fully understand the nature and properties of the employed fillers. In this study, the preparation of polypropylene hybrid composite consisting of wheat straw and clay was investigated. A detailed study was performed on wheat straw from South Western Ontario region. The effect of grinding the straw and compounding it with polypropylene was investigated. Experiments were carried out to identify the thermal stability of the ground wheat straw with respect to their size and composition. It was important to identify a correlation between these properties in order to minimize the straw degradation by processing and also to improve the final properties of the hybrid composite. The composite samples were prepared through melt blending method using a co-rotating twin-screw extruder. Sample test bars were prepared by injection moulding. The composition of the constituents of the hybrid composite; percentages of wheat straw, clay and coupling agent, were varied in order to investigate their influence on thermal stability, water resistance and mechanical properties. The results of the study indicated that grinding the wheat straw with a hammer mill produced particles with different sizes and shapes. It was found that through the grinding system all particles, regardless of their size, had a multi-layered structure similar to the plant structure. Further hammer milling did not produce plant particles with long aspect ratios that would be expected in a defibrillation process. Analysis of the chemical composition of wheat straw particles of different sizes and shapes was used to measure the ratio of hemicelluloses: lignin and the ash content. It was found that the large particles contained more amount of lignin whereas smaller particles had larger amount of ash content. The thermal stability of the particles was found to be a function of particle size rather than the lignin content. Particle size analysis on the wheat straw particles after the extrusion process indicated a reduction in the particle length and aspect ratio. The thermal stability of the composites was found to be enhanced by the addition of clay particles at higher temperature and the addition of coupling agent at lower temperatures. Increasing the amount of wheat straw and clay content increased the flexural modulus and reduced the resistance for water absorption. Increasing the amount of coupling agent also increased the flexural modulus and resistance for water absorption. The morphological study by scanning electron microscopy revealed that coupling agent increased the interfacial interaction between the particles and the polymer matrix. Biocomposite Biodegradable Natural Fiber Natural Filler Wheat Straw Polypropylene Clay Coupling Agent Automotive Construction Extrusion Injection Molding Particle Size Solvent Extraction Particle Density Scanning Electron Microscopy Thermo Gravimetric Analysis Differential Scanning Calorimetry Flexural Strength Flexural Modulus Water Absorption Melt Flow Index X-Ray Diffraction Chemical Engineering
147	Wheat Straw-Clay-Polypropylene Hybrid Composites Sardashti, Amirpouyan 23 September 2009 (has links) The preparation of polymeric hybrid composite consisting of organic and inorganic fillers is of interest for industries like automotive, construction and packaging. In order to understand and predict the physical and chemical properties of these hybrid composites, it is necessary to fully understand the nature and properties of the employed fillers. In this study, the preparation of polypropylene hybrid composite consisting of wheat straw and clay was investigated. A detailed study was performed on wheat straw from South Western Ontario region. The effect of grinding the straw and compounding it with polypropylene was investigated. Experiments were carried out to identify the thermal stability of the ground wheat straw with respect to their size and composition. It was important to identify a correlation between these properties in order to minimize the straw degradation by processing and also to improve the final properties of the hybrid composite. The composite samples were prepared through melt blending method using a co-rotating twin-screw extruder. Sample test bars were prepared by injection moulding. The composition of the constituents of the hybrid composite; percentages of wheat straw, clay and coupling agent, were varied in order to investigate their influence on thermal stability, water resistance and mechanical properties. The results of the study indicated that grinding the wheat straw with a hammer mill produced particles with different sizes and shapes. It was found that through the grinding system all particles, regardless of their size, had a multi-layered structure similar to the plant structure. Further hammer milling did not produce plant particles with long aspect ratios that would be expected in a defibrillation process. Analysis of the chemical composition of wheat straw particles of different sizes and shapes was used to measure the ratio of hemicelluloses: lignin and the ash content. It was found that the large particles contained more amount of lignin whereas smaller particles had larger amount of ash content. The thermal stability of the particles was found to be a function of particle size rather than the lignin content. Particle size analysis on the wheat straw particles after the extrusion process indicated a reduction in the particle length and aspect ratio. The thermal stability of the composites was found to be enhanced by the addition of clay particles at higher temperature and the addition of coupling agent at lower temperatures. Increasing the amount of wheat straw and clay content increased the flexural modulus and reduced the resistance for water absorption. Increasing the amount of coupling agent also increased the flexural modulus and resistance for water absorption. The morphological study by scanning electron microscopy revealed that coupling agent increased the interfacial interaction between the particles and the polymer matrix. Biocomposite Biodegradable Natural Fiber Natural Filler Wheat Straw Polypropylene Clay Coupling Agent Automotive Construction Extrusion Injection Molding Particle Size Solvent Extraction Particle Density Scanning Electron Microscopy Thermo Gravimetric Analysis Differential Scanning Calorimetry Flexural Strength Flexural Modulus Water Absorption Melt Flow Index X-Ray Diffraction Chemical Engineering
148	Vlastnosti betonů s přídavkem plazmatem upravených polypropylenových vláken / Properties of concrete with the addition of plasma modified polypropylene fibers Vorel, Pavel January 2013 (has links) Master‘s thesis focuses on concrete combined with polypropylen fibres produced commercially, fibres without surface modifications and fibres modificated by plasma. Most important topic of the thesis is experimental verification of influence of plasma modificated fibres on attributes of fresh concrete and physical-mechanical attributes of solidified concrete. Based on the results of the tests perfomed on examin units compares results and anylyses applicability of different fibre surface modifications.
149	Characterization of Corn Fibres for Manufacturing Automotive Plastic Parts Riaz, Muhammad 04 January 2013 (has links) The study examined the properties of stalk and cob fibres from recombinant inbred corn lines and their parents, grown at two locations, in a polylactic acid (PLA) matrix. The objectives were to: determine fibre compositions; evaluate the effects of fibres on the functional properties of biocomposites and identify quantitative trait loci (QTLs) and gene markers for fibre performance in biocomposites. Significant GenotypeLocation effects were observed. Composites had lower strength (impact, tensile, and flexural) but higher tensile/flexural modulus values than pure PLA. The latter were positively affected by cellulose and hemicellulose but negatively affected by free phenolic levels and 93 fibre QTLs and 62 composite markers were detected. This study identified fibre traits and markers for genes that may be important for the use of corn fibres in biocomposites. / Ontario BioCar Initiative Project funded by Ontario Ministry of Research and Innovation, Agriculture and Agri-Food Canada, The Natural Sciences and Engineering Research Council, The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) and Ontario Public Sector Corn stalk/cob fibre Automotive plastic parts Quantitative trait loci (QTLs) Fibre genes Polylactic acid (PLA) Composite markers GenotypeLocation interaction effects Thermogravimetric analysis (TGA) Biplot analysis, correlation Microcompounding and injection molding Transgressive segregants Fibre chemical composition Composite mechanical properties
150	Gesteinsmechanische Versuche und petrophysikalische Untersuchungen – Laborergebnisse und numerische Simulationen Baumgarten, Lars 26 May 2016 (has links) (PDF) Dreiaxiale Druckprüfungen können als Einstufenversuche, als Mehrstufenversuche oder als Versuche mit kontinuierlichen Bruchzuständen ausgeführt werden. Bei der Anwendung der Mehrstufentechnik ergeben sich insbesondere Fragestellungen hinsichtlich der richtigen Wahl des Umschaltpunktes und des optimalen Verlaufs des Spannungspfades zwischen den einzelnen Versuchsstufen. Fraglich beim Versuch mit kontinuierlichen Bruchzuständen bleibt, ob im Versuchsverlauf tatsächlich Spannungszustände erfasst werden, welche die Höchstfestigkeit des untersuchten Materials repräsentieren. Die Dissertation greift diese Fragestellungen auf, ermöglicht den Einstieg in die beschriebene Thematik und schafft die Voraussetzungen, die zur Lösung der aufgeführten Problemstellungen notwendig sind. Auf der Grundlage einer umfangreichen Datenbasis gesteinsmechanischer und petrophysikalischer Kennwerte wurde ein numerisches Modell entwickelt, welches das Spannungs-Verformungs-, Festigkeits- und Bruchverhalten eines Sandsteins im direkten Zug- und im einaxialen Druckversuch sowie in dreiaxialen Druckprüfungen zufriedenstellend wiedergibt. Das Festigkeitsverhalten des entwickelten Modells wurde in Mehrstufentests mit unterschiedlichen Spannungspfaden analysiert und mit den entsprechenden Laborbefunden verglichen. Gesteinsprobe Prüfkörper Postaer Sandstein Laborprüfungen Petrophysikalische Untersuchungen Einaxialer Druckversuch Dreiaxialer Kompressionsversuch Einstufentest Mehrstufentechnik Spannungspfad Kontinuierliche Bruchzustände Continuous-Failure-State-Triaxial-Test Zugfestigkeitsprüfungen Scherversuch Spaltzugversuch Biegezugversuch Belastungsrichtung Ultraschalllaufzeitmessung Dehnwellen-Resonanzverfahren Kathodolumineszenz-Mikroskopie Gesteinkenngrößen Gesteinsmechanische Parameter Rohdichte Reindichte Porosität Dünnschliffanalyse Sphärizität Korngrößenverteilung Festigkeitskennwerte Höchstfestigkeit Spitzenfestigkeit Restfestigkeit Anisotropie Arbeitskurven Spannungs-Dehnungs-Verhalten Nachbruch Bruchbilder Verformungskennwerte Statischer Elastizitätsmodul Dynamischer Elastizitätsmodul Verformungsmodul Querdehnungszahl Impuls-Laufzeit Wellen-Ausbreitungsgeschwindigkeit Numerische Modellierung Simulationsrechnung PFC-3D Kugelmodell Clump Partikelarrangement Parameterkalibrierung Parallel Bond Mikrobruch Rissausbreitung elastische Wellen rock sample test specimen sandstone uniaxial compression test triaxial compression test unconfined compression test multiple failure state test continuous failure state test tensile splitting strength shear test bending test pulse velocity ultrasonic elastic constants Young’s modulus of elasticity modulus of deformation Poisson’s ratio post failure stress-strain behaviour real density apparent density grain-size distribution porosity flexural strength peak strength residual strength anisotropy fracture pattern micro-crack pulse-propagation velocity clump sphere model parallel bond crack propagation numerical modelling simulation elastic wave PFC-3D parameter calibration particle arrangement ddc:624 Posta Sandstein Gesteinsprobe Mechanische Eigenschaft Petrophysik Elastizität Werkstein Druckversuch Zugversuch Kennzahl Experiment Numerisches Modell

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