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Possibilities of using different types of admixtures in shotcrete technology
Berčík, Martin ; Brožovský, Jiří (referee) ; Hubáček, Adam (advisor)
The Bachelor’s thesis is conceived in the form of research findings on current knowledge of inert and active ingredients and their effects on the shotcrete. It focuses mainly on the composition of individual ingredients, their function executing in the concrete mix and explains how they affect the selected physical and mechanical properties. The work enlightes the importance of using co-products from the industry production as an additive to concrete in terms of both ecological and partly economical.
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BEHAVIOUR OF CEMENTITIOUS COMPOSITES EXPOSED TO HIGH TEMPERATURES
Nováková, Iveta ; Chobola, Zdeněk (referee) ; Sitek,, Libor (referee) ; Wallevik, Ólafur Haralds (referee) ; Pimienta, Pierre (referee) ; Bodnárová, Lenka (advisor)
Fire resistance is becoming increasingly important along with the development of new concrete types with high strength and dense structure with reduced porosity. Such concrete types are susceptible to fire spalling and extensive crack formation. At the moment, there are a limited number of methods for enhancement of fire resistance of existing structures, which could be applied in underground structures with restricted space and limited air exchange, such as tunnels, underground garages or nuclear powerplants. This work is focused on the development of two methods, and both are dealing with porous structure modification. The first method is intentional heat treatment (IHT) method, suitable for the enhancement of fire resistance of existing structures. The second method emphasized the design of air-entrained concrete (AeA-FiResCrete) with the use of “new generation” air-entraining agents suitable for enhancement of fire resistance of newly designed concrete. Testing of compressive strength, porous structure modification was completed by the analysis of “moisture clog,” which contributes to explosive spalling and extensive cracking. The efficiency of developing methods was verified during large-scale testing according to modified ISO834 (m-ISO) curve. No extensive crack formation or explosive spalling was observed during the exposure period during the large-scale testing of slabs with the applied IHT method. The total thickness of the IHT method with configuration IHT200/2, composed of IHT zone and IHT transition zone, penetrated to the depth of 25,5 to 43,0 mm depending upon various concrete types. Moisture clog in AeA-FiResCrete was more significant than in the case of slabs with applied IHT method, and it could be concluded that the IHT method enhances fire resistance of concrete exposed to elevated temperatures without influencing its compressive strength and durability. Results from AeA-FiResCrete testing showed only a slight improvement of its fire resistance.
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Optimizing the composition of micro concrete admixtures.
Juříková, Denisa ; Křížová, Klára (referee) ; Hela, Rudolf (advisor)
The aim of this paper is to summarize knowledges related to the use of fine-grained admixtures in cement composites. By utilizing of these admixtures it is possible to achieve extreme properties, especially high strenght and durability of concrete. These properties can be achieved by optimizing the density of the binder and filler in range of 0 to 0,25 mm. Therefore, large part of thesis is focused on admixtures and its effect on concrete. The experimental part of the thesis deals with optimization od selected admixtures in combination with cement to achieve the minimum of the voids and their compressive strenght were determined at 1, 3, 7, 28 and 60 days.
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Improving of dispersion of silica fume in high performance concrete
Janča, Martin ; Koutný, Ondřej (referee) ; Šiler, Pavel (advisor)
The goal of this work was to create a method for improving the dispersion of silica fumes for use in high performance concrete. Traditional methods used to design and manufacture high performance concrete emphasize the removal of coarse aggregates. Use of specially sorted fine aggregates at relatively low doses, the use of super-plasticizers and siliceous excrement. The low water content was achieved by using superplasticizer on a polycarboxylate basis. The standard ultrasound technology found in each laboratory was selected for the dispersion of silica fume. For experiments were we used dry silica fume powder and aqueous stabilized suspension. For comparison, were prepared different mixtures which showed the effects of the treatment prior to the use of silica fume.
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Development of high-strength concrete defined properties with the use of secondary raw materials
Ondráček, Michal ; Vítek,, Jan (referee) ; Ďurica,, Tibor (referee) ; Vymazal, Tomáš (referee) ; Hela, Rudolf (advisor)
Civil engineering development is connected with the application of new construction methods and the development of new building materials. Concrete, as one of the basic building materials, is part of this development. A major turning point in the development of concrete and its properties occurred with the use of new, more efficient plasticizing additives. This allowed to produce concrete with lower water cement ratio, while increasing the strength of concrete. Gradually, the compressive strength of concrete boundary has moved by several levels, when there are currently commonly used concrete with strength of about 100 N/mm2 and with the special methods of concrete production strength range from 250 to 300 N/mm2. A negative aspect of the development of (ultra) high-strength concrete is their energy and economic demands. A characteristic feature of high-strength concrete is a high content of cement and very fine admixtures, especially silica fume. One way to improve the economics of these types of concrete is the application of cheaper admixture based on industrial waste. The content of this work is the observation and description of the properties of high-strength concrete and reactive powder concrete, in which the admixtures were based on industrial waste were applied. Part of this work is the comparison of economic parameters for individual types of concrete.
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ultra-high-strength concretes
Ambruz, Pavel ; Hubáček,, Adam (referee) ; Hela, Rudolf (advisor)
Thesis deals with summarizing knowledge about production methods of ultra – high – strength concrete (UHSC) and their possible use in practice, which is documented on the existing building. Further work shows suitable raw materials for production UHSC and their availability on the Czech market. The practical part results an experiment whose outcome should be concrete with a compressive strength of 150 MPa.
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High performace cement composites with increased abrasion resistance
Baranov, Dmitry ; Šuleková, Nikola (referee) ; Novotný, Radoslav (advisor)
The bachelor thesis deals with the effect of addition of potassium hydroxide solutions of different concentrations to HPC composites. The study focused mainly on parameters important for the abrasion of the composite such as surface hardness, which was measured in two ways. The first is by using of a manual hardness tester, the second is by a notching method through a drill with a tungsten carbide crown. The samples with the highest concentration of potassium hydroxide had the best results. It was assumed that the cause could be a very thin (400 1000 nm) dense layer on the surface with a predominant content of sulfur and potassium compounds, which was shown on an electron microscope. In addition to the hardness of the surface, other mechanical properties important for cements were monitored. Samples with different KOH concentration were tested for compressive and flexural strength.
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