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Study of the dependence of concrete composition on the values of elasticity modules
Křížová, Klára ; Kolář,, Karel (referee) ; Adámek, Jiří (referee) ; Ďurica,, Tibor (referee) ; Hela, Rudolf (advisor)
The modulus of elasticity is one of the basic characteristics of concrete defining elastic deformation of concrete and it plays a significant role in the static design of structures. Due to current trends in concrete technology, offering a wide variability in the proposals of the composition of concrete, there are changes not only in strength characteristics but also in the modulus of elasticity of concrete. The aim of this doctoral thesis is to study the dependence of different compositions on modulus of elasticity of concrete. Design of concrete composition is prepared with respect to the use of different types of cement, mineral admixtures, types and fractions of aggregates. The work is mainly focused on the determination of static modulus of elasticity in compression with the addition of dynamic modules. In the first phase determined modulus of elasticity are compared with tabulated values according to Eurocode 2, which are derived for the specific strength class of concrete. Part of this work is the compilation of the main technological aspects of concrete which can favorably affect the modulus of elasticity.
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The study of the influence of the composition of the lightweight fiber concrete physical and mechanical properties
Šindelek, David ; Bodnárová, Lenka (referee) ; Hela, Rudolf (advisor)
This bachelor thesis deals with a study of light construction concrete with an addition of steel fibre which monitors its impact of the physical mechanical properties. The work is divided into two parts, theoretical and practical. The theoretical part is focused on characteristics and a design of light concrete within the class 35MPa and over with the density within the class of D1,8. Furthermore, it focuses on the increase of toughness of cementitious composites with the form of application of steel fibre in different doses and lengths. In the practical part, formulas of two strength classes 35/38 D 1,8 and 45/50 D1,8 were designed with the help of the steel fibre Krampeharex in doses of 25 and30 kg/m3, and where there were both its impact of the working diagram as well as the compressive strength monitored for the duration of twenty-eight days
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Analysis of volume changes of cement composites with respect to optimizing the dosage of fine components
Meruňka, Milan ; Ťažký, Tomáš (referee) ; Hela, Rudolf (advisor)
The diploma thesis deals with the determination of the influence of the maximum density of the cement matrix on the volume changes of concrete, the influence of different admixtures or their combinations on the development of hydration temperatures and on the water separation of concrete. The theoretical part describes the various types of volume changes of concrete, the effects of individual input components and mineral admixtures on water separation, hydration heat development and concrete microstructure. The experimental part is focused on monitoring not only the volume changes of concrete mixtures made using different types of admixtures or their suitable combination until the age of 60 days of maturation, but also the influence of their use on selected mechanical parameters of concrete such as compressive strength, concrete in its fresh state and monitoring changes in the microstructure from long-term aging mixtures.
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Development of abrasion resistant concrete
Procházka, David ; Darebník, Zdeněk (referee) ; Hela, Rudolf (advisor)
The resistance of concrete to abrasion is an important feature particularly for transport and water management structures where the surface is exposed to abrasion. Bachelor thesis deals with individual influences on improvement of abrasion resistance of concrete surface. Furthermore, the search of test methods used for testing abroad. In the practical part, we assess the effect of curing agents on resistance to abrasion, water jet and tensile strength by tear-off test.
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Determining the possibilities of increasing binding potencial of fly ash for the usage in cement composites
Jančaříková, Denisa ; Ďurica,, Tibor (referee) ; Klečka,, Tomáš (referee) ; Kulísek, Karel (referee) ; Hela, Rudolf (advisor)
The deliberate use of fly ash in the production of concrete has been used for decades, but recent trends tend to maximise its utility properties. These are different types of activations from chemical through thermal to mechanical. An alkaline agent is added to chemical activation which, by etching the glass structure of the ash grain, promotes its reactivity. Mechanical activation is mainly focused on granulometry and particle size distribution curve. In this thesis three mechanical activation methods are compared: separation the ash into fractions by grain size, mixing these fractions to achieve the ideal particle size distribution curve and grinding. Four types of ash were collected from the Tušimice power plant – ash from individual electrostatic separators (I, II and III) and SESYP ash which represents the total volume of production. Ash from individual separators differ not only in the particle size but also in the chemical composition and reactivity. Better properties generally have smaller ash particles. This is used by mechanical activation by sorting. When mixing the individual ash fractions, the aim is to achieve an optimal grading curve of either the ash itself or the fine particle set in the concrete. In this work, ash is only used to calculate the mixing ratio and the grading curve according to Funk was selected as optimal. The last compared option of activation was grinding ash. Grinding was carried out in an industrial mill for 15, 30, 45, 60 and 75 minutes. The efficiency of the modified ash was monitored for cement paste in terms of rheology and for concrete in terms of consistency, strength and durability. Based on the results we can say that mechanical activation by sorting is suitable for special purposes, but it’s necessary to realise that coarser ash fractions remain unused. When mixing the fractions to ensure matrix density, the efficiency was shown mainly on the durability characteristics. Grinding cause positive effect.
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Reactive powder composites and cement composites without macropores
Panenková, Monika ; Hela,, Vlastimil (referee) ; Hela, Rudolf (advisor)
This diploma thesis deals with the design principles and manifacture of ultra performance concrete (UHPC), reactive powder composites (RPC) and other fine-grained materials, such as Macro defect free (MDF) or Densified systems with small particles (DSP). Theoretical part of this work is focused on the requirements of properties and composition UHPC and RPC and methodology of their design principles. Experimental part describes design principles RPC, manufacture of test specimens, testing of certain physical and mechanical properties, such as tensile strenght, bending strenght and compressive strenght and determination chemical character X-ray and thermal analysis.
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The issue of concrete resistance to high temperatures
Krejčík, Jakub ; Hela, Rudolf (referee) ; Bodnárová, Lenka (advisor)
Bachelor´s thesis deals with resistance of cement concrete to high temperatures. Theoretical part of bachelor´s thesis describes changes that occures in concrete at thermal loading and behavior of each component of concrete. Next there were discribed ways to improve resistance of concrete to high temperatures, by choosing the right component or by adding fibre reinforcement. In experimental part composites with bassalt and polypropylen fibre and with bassalt aggregates were tested. In these composites changes of compressive strenght and changes of density were mesured according to the thermal loading. Next individual fibre reinforcement polypropylen, celulose and bassalt fibres were exposed to the thermal loading and their changes were observed.
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Architectural concrete
Novosad, Petr ; Ďurica,, Tibor (referee) ; Dulenčín, Juraj (referee) ; Klečka,, Tomáš (referee) ; Hela, Rudolf (advisor)
In the development of concrete structures and its finishes we are constantly looking for new ways to highlight the aesthetic value of the concrete. With all the possibilities of shapes, textures and colours, an architectural concrete in the hands of an architect and designer becomes a material, which can be used to express different individual and specific ideas. It is necessary to recognize and cope with these possibilities, but also the limits, which determine the properties of concrete as the proper design and implementation creates excellent finishes that are otherwise inaccessible to other materials and technologies. The theoretical part includes an extensive summary carries out a research on issues of architectural concrete and its production. From this research comes a new definition of architectural concrete and the newly redesigned and determined classes of architectural concrete with respect to the continuous development of technologies and production possibilities, rendering and surfacing. The aim of the thesis is to verify the possibilities of producing quality architectural concrete and additional treatment of the surface with respect to the desired aesthetic quality.
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The issue of the use of carbon nanotubes in cement composites
Pacltová, Klára ; Hela, Rudolf (referee) ; Bodnárová, Lenka (advisor)
The bachelor thesis deals with the analysis of the efficiency of carbon nanoparticles in cement composites. The theoretical part of the bachelor thesis is focused on the research of information about carbon nanotubes and their influence on cement composites. The practical part follows the research of the theoretical part, where is verified the effectiveness of carbon nanotubes in cement composites at different dosages.
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