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Fracture of selected building composites in the vicinity of aggregate-matrix-interface
Vyhlídal, Michal ; Malíková, Lucie (referee) ; Keršner, Zbyněk (advisor)
The interface between aggregate grains and matrix in cementitious composites is their weakest element. The topic is particularly significant in the case of high performance and high strength concrete technology for which the eliminination or reduction of these weak links are necessary. The aim of this thesis is to determine the influence of the interface on the fracture behaviour of the cementitious composites. The fracture experiments were performed for this purpose and were complemented by the nanoindentation’s results and scanning electron microscopy results. Numerical model was created in ANSYS software on the basis of these data and the fracture toughness values of the interface were evaluated by means of the generalized fracture mechanics principles. Conclusion of the thesis is proof that the interface properties have a significant influence on the fracture behaviour of cementitious composites.
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Study of the influence organic fibres on the fire resistance of concrete
Klobása, Jan ; Přikryl, Jan (referee) ; Sedlmajer, Martin (advisor)
The master thesis is focused on current issues of concrete behaviour under high temperatures. In the theoretical part, a search of knowledge about changes in concrete, which take place when exposed to thermal loads, which simulates the effect of fire, is performed, and summarized. It is also important to summarize the changes in the individual components that are used to produce concrete. This work describes the effect of high temperatures on mechanical and physical properties as well. There is an information about the most used fibres and their function in concrete. Emphasis is placed on describing the possibility of using recycled PET or cellulose fibres due to the positive environmental impact. In the experimental part, recipes with different types and amounts of fibres are proposed. The subject of the research was to determine how individual types and amounts of fibres affect the physical mechanical properties of concrete and their suitability for use at high temperatures. Microscopic scanning and study of changes in the structure of concrete was also performed.
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Durability of repair materials with higher fire resistance for concrete structures
Počekajlo, Václav ; Dohnálek,, Pavel (referee) ; Bydžovský, Jiří (advisor)
This dissertation deals with the study of durability and degradation repair mortars for reinforced concrete structures. In its theoretical part, there are the research findings on the behavior of repair mortars exposed to corrosive environments with different exposure time and selected high temperatures. Processes occurring in repair mortars during their loading at high temperatures or when exposed to chemically aggressive environments are described, We can find recipes designed for cementitious binder based with a specific replacement using slag or fly ash in its practical part. The object of the research was to determine the durability of the proposed repair mortars, and determine their suitability for use on concrete structures, which may be exposed to a synergistic effect of chemically aggressive environments with high temperatures simulating fire.
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Effect of moisture on the electrical properties of silicate composites
Karlíková, Helena ; Kusák, Ivo (referee) ; Rovnaník, Pavel (advisor)
This work deals with study on the dependence of electrical properties on the moisture content in silicate composites. The theoretical part contains information about the electrical properties of cement-based and alkali-activated binders, as well as knowledge on moisture parameters and the presence of moisture in the material structure. Samples of cement-based mortars and alkali-activated slag with a graphite powder in the range of 0–18 per cent by weight were produced and quartz sand was used as filler in the experimental part. The samples were provided with copper electrodes and saturated with water after hardening. The electrical properties of the mortars were monitored by means of impedance spectroscopy during the gradual drying of the samples. The effect of microstructure has been studied using scanning electron microscopy and mercury intrusion porosimetry. The results indicate that a significant increase in electrical resistance occurs only when the relative sorption humidity content is below 20 per cent in the 40–5000 Hz frequency range.
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Porušování jemnozrnného cementového kompozitu v blízkosti rozhraní plniva a matrice
Vyhlídal, Michal ; Kabele,, Petr (referee) ; Profant, Tomáš (referee) ; Keršner, Zbyněk (advisor)
The Interfacial Transition Zone (ITZ) between the aggregate grain/reinforcement bar and the matrix is considered to be the weakest element in cementitious composites and is, according to some authors, directly responsible for the nonlinear (more precisely, quasi-brittle) behavior of the composites. The aim of this work is verification of the generally accepted paradigm of the weakest element by means of fracture experiments and corresponding numerical simulations. In the experimental part, in addition to traditional fracture tests, modern methods of 3D scanning, scanning electron microscopy, chemical analysis using an electron microprobe and nanoindentation were used. In the numerical part, models based on generalized linear elastic fracture mechanics as well as modern models intended for the simulation of cement composites, namely crack band model with smeared cracks and the Microplane model, were used. Based on the results, the numerical part was complemented by the Cohesive Zone Material model simulating the behavior of the interface. All results are discussed and put into context with already published work. The main conclusion of the work is that the properties of the ITZ do not have such an influence on the behavior of cement composites as the adhesion between the inclusion and the ITZ, i.e. the matrix.
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Development of materials for 3D printing of elements meeting the requirements of transport structures
Romanová, Dorota ; Melichar, Jindřich (referee) ; Žižková, Nikol (advisor)
This bachelor thesis deals with the use of supplementary cementitious materials as a partial replacement of Portland cement in cement composites, focusing on the requirements of transport constructions. The theoretical part consists of a description of the input raw materials as well as cement substitutes, the studied properties of the 3D printed mixtures and a description of the characteristics of the technology. The practical part is focused on the experimental testing of the selected properties with monitoring of the influence of polymer and bio-polymer additive dosage in the proposed formulations and subsequent analysis of the most convenient one for 3D printing.
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Study of the influence of fillers and external conditions on the resistivity of cement composites
Kejda, Dalibor ; Melichar, Jindřich (referee) ; Černý, Vít (advisor)
The progress of new materials is important for the construction industry. Modern materials include cement composites with reduced resistivity. This is achieved by adding suitable electrically conductive fillers. If there is enough of these fillers, the so-called percolation threshold occurs. Suitable fillers (Condufit C4 and Supragraphite C300) have been proposed. Recipes have been designed to be before and after the percolation threshold. The tests were performed on beams measuring 40x40x160 mm with built-in electrodes for measuring their resistivity. The aim of the work was the research of influencing external conditions on cement composites. The effect of temperature was verified. The lowest values of resistivity were evaluated at temperatures of 50 ° C and the resistivity increased with decreasing temperature. The effect of humidity on the resistivity was then verified. Reference samples and samples with a smaller proportion of graphite powder showed larger differences in resistivities with increasing humidity. The samples above the percolation threshold were not much affected by increasing humidity. Finally, the effect of loading on the resistivity of the samples was verified. Almost all samples with increasing compressive stress showed an increasing value of resistivity.
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Study of the influence organic fibres on the fire resistance of concrete
Klobása, Jan ; Přikryl, Jan (referee) ; Sedlmajer, Martin (advisor)
The master thesis is focused on current issues of concrete behaviour under high temperatures. In the theoretical part, a search of knowledge about changes in concrete, which take place when exposed to thermal loads, which simulates the effect of fire, is performed, and summarized. It is also important to summarize the changes in the individual components that are used to produce concrete. This work describes the effect of high temperatures on mechanical and physical properties as well. There is an information about the most used fibres and their function in concrete. Emphasis is placed on describing the possibility of using recycled PET or cellulose fibres due to the positive environmental impact. In the experimental part, recipes with different types and amounts of fibres are proposed. The subject of the research was to determine how individual types and amounts of fibres affect the physical mechanical properties of concrete and their suitability for use at high temperatures. Microscopic scanning and study of changes in the structure of concrete was also performed.
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Effect of moisture on the electrical properties of silicate composites
Karlíková, Helena ; Kusák, Ivo (referee) ; Rovnaník, Pavel (advisor)
This work deals with study on the dependence of electrical properties on the moisture content in silicate composites. The theoretical part contains information about the electrical properties of cement-based and alkali-activated binders, as well as knowledge on moisture parameters and the presence of moisture in the material structure. Samples of cement-based mortars and alkali-activated slag with a graphite powder in the range of 0–18 per cent by weight were produced and quartz sand was used as filler in the experimental part. The samples were provided with copper electrodes and saturated with water after hardening. The electrical properties of the mortars were monitored by means of impedance spectroscopy during the gradual drying of the samples. The effect of microstructure has been studied using scanning electron microscopy and mercury intrusion porosimetry. The results indicate that a significant increase in electrical resistance occurs only when the relative sorption humidity content is below 20 per cent in the 40–5000 Hz frequency range.
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