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Lightweight mortars with content of alternative raw materials and resistant to adverse effects
Morkusová, Kristýna ; Jakubík, Aleš (referee) ; Bydžovský, Jiří (advisor)
This diploma thesis describes research and following development of lightweight cement mortars with alternative raw materials. Attention was focused on study of the effects of extreme influences such as high temperature (up to 1200 °C), freeze-thaw and agressive sulfur dioxide. Verification of durability of developed mortars was realized using physical and mechanical tests (density and strength), physical and chemical methods (computed tomography) and scanning electron microscopy. Assessment of durability was realized in a longer period of time (90 days).
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ASSESSMENT OF REINFORCED CONCRETE STRUCTURES EXPOSED TO ELEVATED TEMPERATURES
Rozsypalová, Iva ; Kolář,, Karel (referee) ; Vítek,, Jan (referee) ; Daněk, Petr (advisor)
Doctoral thesis is focused on the assessment of concrete structures after fire exposure and extends the knowledge in view of the main aims of the research defined in the objectives of his work. Thanks to the performed fire tests of full-scale concrete specimens, material characteristics corresponding to actual fire load have been assessed for different temperature levels. Resulting from presented research, main steps of assessment procedure have been recommended for both destructive and non-destructive tests of concrete after exposure to fire. Furthermore, behaviour of FRP reinforcement at elevated temperatures have been investigated. Aiming to determine the effects of fire exposure on reinforced concrete structures, experimental program have been defined and performed, including concrete beams reinforced with either steel, or composite reinforcement with glass or carbon fibres and subjected to experimentally simulated fire load. After cooling, bending test have been executed. Above mentioned experimental program was further complemented by extensive numerical analysis. Finally, presented work provides guidelines regarding further investigations required in this field of research.
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Study of the effect of the addition of the cellulose fibers on the selected properties of concrete
Blaha, Lukáš ; Hela, Rudolf (referee) ; Bodnárová, Lenka (advisor)
This dissertation desribes the behavior of cellulose fiber reinforced concrete. In the theoretical section one can find basic information on cellulose fiber and its methods of production and usage in concrete structures. One can find the information about the effect of high temperature on the mechanical and physical attributes of cellulose fiber reinforced concrete, and also a comparison with other fibers used in concrete based on the research done using scientific literature. Furthermore the details about particular cellulose fibers are provided. In the experimental section the formulas for CHRYSO and GREENCEL concrete are designed. The influence of the addition of various types of cellulose fibers into both liquid and solid states of concrete was researched. Tests were also done on the effect of high temperatures (600 °C and 800 °C) on the firmness and densitiy of concrete, its deformations and visual changes. Furthermore, the resistance of cellulose fibers was monitored by monitoring the development of the pH environment (from pH 4 to pH 12) with long-term deposition of different types of cellulose fibers in these environments.
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Study of the properties of fillers to the composites requiring high temperature resistance
Vovesný, Václav ; Gross,, Tomáš (referee) ; Bydžovský, Jiří (advisor)
The diploma thesis is focused on the behaviour of natural and synthetic aggregates and their behaviour in polymer – cement composites, while being exposed to high temperature. The processes, happening in aggregates and mortar under the thermal load, were described in the theoretical part of the thesis same as the testing of heat effects on the aggregates and mortar. Further, the influence of high temperature on each component of concrete was described, followed by the suggestion of the appropriate components for concrete exposed to high temperature. Various aggregates were tested in the experimental part of the thesis. The basic physical and mechanical properties of aggregates were examined same as their mineralogical composition with using XRD, DTA and SEM methods. At the mortar, the influence of high temperature on the concrete density, compressive strength and tensile strength was defined. The gained knowledge was evaluated in the final part of the thesis
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Fracture tests of selected specimens with special aggregates: experiments and numerical simulation
Majda, Tomáš ; Malíková, Lucie (referee) ; Keršner, Zbyněk (advisor)
The diploma thesis deals with selected fracture tests and evaluation of fracture parameters of cement-based composite. One part of the thesis deals with cement-based composite with glass spherical aggregate of a single fraction of 2 mm. After production, the beams with dimensions of 20×40×200mm exposed to temperatures in the range from 100 to 1000 °C for one hour. Using the non-destructive ultrasonic pulse method, the degree of damage caused by termal load was determined. Selected specimen with central edge notch were then tested in three-point bending and fragments after these tests were tested in compression. In the second part, attention was paid to the evaluation of fracture tests conducted on specimen from drill-cores taken from selected objects located at the former Transgas Gas Control Center in Prague. The specimen were provided with a chevron notch before being tested in three-point bending. The measured data was modified by the GTDiPS program and in the case of the glass composite the StiCrack program was used to evaluate fracture parameters.
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Design of synchronous reluctance motor with permanent magnets
Knebl, Ladislav ; Huzlík, Rostislav (referee) ; Ondrůšek, Čestmír (advisor)
V dnešní době je kladen vysoký nárok na účinnost elektrických zařízení a to jak ze strany provozovatele, tak i legislativy. Nejlepší účinnosti dosahují synchronní motory s permanentními magnety umístěnými na povrchu rotoru (SMPM), se kterými lze i u malých motorů dosáhnout účinnosti nad 90%. Nicméně tyto motory jsou z důvodů použití magnetů ze vzácných zemin, např. NdFeB, drahé a jsou schopny provozu pouze s frekvenčním měničem. Z cenových důvodů jsou hledány levnější alternativy k SMPM motorům. Jedním z typů motorů, kterým lze SMPM nahradit je synchronní reluktanční motor s permanentními magnety (PMASR). Tento motor je cenově výhodnější, protože používá menší množství magnetů, při zachování podobných, mnohdy i lepších vlastností, nicméně neodpadá potřeba použití frekvenčního měniče. Navíc je zde možnost použití levnějších feritových magnetů a tím ještě výrazněji snížit cenu motoru. V této práci bude PMASR topologie popsána důkladněji včetně elektromagnetického návrhu metodou konečných prvků. Bude provedena i mechanická analýza zvoleného optimálního modelu. Výsledky dosažené metodou konečných prvků budou následně porovnány s analytickým modelem. Z navrženého modelu bude vyroben prototyp a naměřené výsledky budou porovnány s výpočty.
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High temperature conductivity measurements of ceramic materials
Grochal, Peter ; Kazelle, Jiří (referee) ; Novák, Vítězslav (advisor)
The aim of this work is to get acquainted with the detailed structure of yttrium-stabilized zirconia, focusing mainly on conductivity. Coating platinum electrodes by screen printing. Solution of complexity of conductivity segregation by electrode geometry. Measurement of the conductivity of macroscopic samples of ceramics by impedance spectroscopy to determine the electrical behavior of the system. Creating equivalent circuits to measured data. Detect system behavior when excited by different AC voltage and electrode geometry values.
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Response to abiotic stress in plants growing in green façades of temperate urban environment
Hrochová, Růžena ; Lhotáková, Zuzana (advisor) ; Havelková, Lenka (referee)
With increasing urbanization the temperature of cities is increasing and an effect of urban heat island arises. Vegetation, particularly vertical greenery systems: facades and walls, is mitigating urban heat island and reducing temperature. The aim of this work was to define these systems, their effects on the urban microclimate, to create an overview of the most used plants for greenery systems and to summarize their reactions to abiotic stresses of cities in a temperate region. Mediterranean studies were used in this work due to the scarcity of temperate climate research, which results could become valuable with climate change. Selecting proper vegetation can be done using habitat template, plants that are acclimated or adapted to the urban environment. Plants affect the urban microclimate through shading and transpirational cooling, which ideally contribute to reducing the heat island effect with optimal irrigation. Stressors followed in this work were drought, high temperature and irradiance, air pollution and salinity. To all these stressors plants reacted with limiting physiological functions and reducing growth. The common reaction was a decrease photosynthesis rate and chlorophyll content. Ractions of plants of vertical greenery systems to different stressors and their combinations are...
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Study of resistance of selected aggregates to high temperatures
Holanec, Aleš ; Sitek,, Libor (referee) ; Bodnárová, Lenka (advisor)
The thesis deals with the monitoring of changes taking place in natural stones and aggregates under high temperatures. The theoretical part of the work provides information about basic groups of rocks, the technology of processing the natural stone and primarily about the study of behavior of natural stone and aggregates at high temperatures. Also some findings from different research works aimed at monitoring the behavior of rocks at high temperatures are presented. In the experimental part a selection of rocks with a higher expected resistance to high temperatures is made, including detailed information and description. Further in this section we provide the comparison of the properties of individual rocks. Later we describe the most important methods of testing, the procedure of preparation of rock samples and we design an experiment to use for evaluation of resistance of rocks and aggregates under high temperatures.
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Use of organic fibers in fine-grained cement composites and their influence on the monitored properties
Mazán, Tomáš ; Ondráček, Michal (referee) ; Křížová, Klára (advisor)
The diploma thesis describes the possibilities of using organic fibres to improve the properties of cement composites at high temperatures. The theoretical part of the thesis deals with the behaviour of the different components of concrete and concretes in fire. A substantial part is devoted to the types of fibres, the method of dosage and the effect of their use on selected parameters. The practical part of the thesis is based on the developed methodology. On the basis of the results obtained, a summary of the behaviour and transformations of different types of organic fibres when exposed to temperatures from 20 to 800 °C was compiled. Furthermore, the observed parameters and the effect of the fibres, especially on the strength of the composite loaded at high temperature, are evaluated. The final of thesis concludes with recommendations for fibre dosage and the suitability of using recycled fibres.
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