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Pozzolanic Activity of Silicon Dioxide
Barek, Jaroslav ; Žižková, Nikol (referee) ; Rovnaníková, Pavla (advisor)
The aim of this bachelor's thesis is to investigate and identify the present status of resources with dominant amorphous silicon dioxide content and summarize feasible test methods to assess pozzolanic activity. The use of pozzolan as a partial replacement of Portland cement reduces the carbon dioxide emitted per tonne of product and can also improve various physical properties of the resulting cementitious composites. Assessment of the pozzolanic activity of cement replacement materials is increasingly important because of the economic sustainability of cementing materials. The pozzolanic activity of wheat straw ash, silica fume, nanosilica, two diatomites, glass powder and expanded perlite have been investigated and compared using the strength activity index test, the modified Chapelle test and the pozzolanicity test in accordance with the European Standard EN 196-5. From an experimental investigation of seven different pozzolans, the following main conclusions can be drawn. In the case of an acid-base titration (determination of [OH–], the procedure specified in EN 196-5) is better to use Tashiro (mixed indicator) instead of required methyl orange, Tashiro changes color at the endpoint of a titration distinctly. Strength activity index: the procedure used was based on EN 450-1. In its current form, this procedure is misleading because of two other significant properties of the pozzolan, namely its density and its water-reducing/increasing capabilities. Based on the results of our experimental investigation, the current testing procedure is evaluated against an alternative in which the 25% pozzolan replacement for cement is performed on a volumetric basis and the volume fraction of water is held constant.
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The admixtures which are influencing setting time of portland cement
Hlaváček, Jaroslav ; Kalina, Lukáš (referee) ; Opravil, Tomáš (advisor)
During the production of concrete is important the careful selection of raw materials. Nowadays, we are trying in the production to minimize the economic burden and to maximize the use of secondary raw materials. This work is focused on the use of secondary raw materials from the energy industry in construction for the preparation of hydraulic binders. As the main raw materials were used different power plant fly ash from fluidized combustion. The composition of these secondary materials is quite different from conventional high-temperature ash, due to mixing with water they solidify and harden. Experiments were performed with three lodge fly ash from electrostatic precipitators of the fluidized combustion and one high-temperature fly ash. This work is focused on the possibility of monitoring the use of these secondary materials in construction, especially when tests were evaluated characteristics of strength and speed of setting and hardening.
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Synthetic Preparation and Properties of Thaumasite
Klásková, Silvie ; Dvořák, Karel (referee) ; Fridrichová, Marcela (advisor)
This thesis continues in the monitoring of thaumasite thermodynamic stability. It mainly deals with mineral properties and possible ways of its synthetic preparation. Mineralogical composition determined using X-ray diffraction analysis as well as possible impact of sample storage conditions can help further property identification. Based on the obtained radiographs, thaumasite mineral can be well distinguished from the very similar ettringite mineral.
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Infusorial Earth - Reactive Admixture for Cement Composites
Zimmermann, Štěpán ; Žižková, Nikol (referee) ; Rovnaníková, Pavla (advisor)
The aims of this bachelor´s thesis are the properties and the use of diatomaceous earth as a partial replacement of cement in concrete. It provides information about the origin of diatomaceous earth, sedimentation of dead diatoms and variety of algae, including chemical and physical properties of the diatoms according to origin. The paper also contains information about significant deposits of diatoms, the manner and intensity of mining, including treatment of raw diatomaceous earth for further use. The main use of diatomaceous earth is in the filtration, which represents more than half of total consumption. An important factor for use in building is a high content of amorphous SiO2 and associated pozzolana activity of diatomaceous earth. The experimental part was carried out research on the influence of diatomaceous earth as pozzolanic admixtures on the properties of cement mortars. Tested specimens were obtained by adding 10% diatomaceous earth by weight of cement in the cement mortars. As admixtures were use three diatomaceous earth of different chemical composition, particle size and pozzolanic activity. The evaluated parameters were mortar density, flexural and compressive strength. The microsture of mortars were also observed. Test results were compared with those determined by reference mortars.
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Study of alkali-silica reaction in hybrid systems
Bradová, Lada ; Bílek, Vlastimil (referee) ; Kalina, Lukáš (advisor)
This study evaluates question of alkali–silica reaction (ASR) in hybrid system, which was designed in the bachelor's thesis, to meet the requirements of EN 197-1 and classified to the Blastfurnace CEM III/C cements. The durability of this system is a great unknown. For this reason, the same methods (ASTM C1260, ASTM C289 and ASTM C856) were used to observer the ASR effects as the ones used to observer the Portland cement based concrete. Supplementary methods include determination of compressive strengths according to EN 196-2 and scanning electron microscopy to observe the microstructure. Hybrid system results were compared to two different types of cements, CEM I and CEM III/B. From the results of the ASR evaluation assays, it was found that the hybrid system (CEM III/C-HB) and CEM III/B showed the lowest tendency to ASR. The results of the supplementary methods showed that CEM III/C-HB compressive strength increases after 14 days within NaOH by 43 % in comparison to 28 days strength. Based on those results, it is sure that the CEM III/C-HB shows little susceptibility to ASR.
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Recyclation of dust from production of dry mortar blends
Ondrůšková, Nela ; Novotný, Radoslav (referee) ; Šoukal, František (advisor)
The work deals with the problem of disposal of ever-increasing waste (dust) from the production of building materials and examines the possibility of recycling dust dust into cement repair mortar. The aim of this work was to determine the composition of individual dust particles from the production of cement mixtures and to determine their mechanical properties, as well as to determine the ideal ratio of dust particles to each other when mixing the dust mixture and its mechanical properties. This mixture consisted mainly of dust from products based on Portland cement, aluminous cement, gypsum and lime hydrate. The mixture further replaced part of the cementitious mortar and the impact of the additive on the mechanical properties of the cementitious mortar was determined. X-ray fluorescence spectrometry was used to determine the elemental composition, and X-ray diffraction analysis was used to determine the mineralogical composition. Test specimens were prepared according to the ČSN EN 12390 standard. Mechanical strength tests were performed on the test specimens. A large part of the test specimens could not be subjected to mechanical tests because the test specimen did not solidify even after a long time. The individual measurements that could be made show that the mechanical properties of the dust samples show values which have shown that the dust cannot be recycled into the product due to its instability. Dust particles have too diverse composition and in combination with cementitious repair mortar do not have the required properties. The problem is especially the sampling from the data, which did not solidify at all and thus excluded the remaining samples with already good properties of the same sample. When designing the method of recycling, it was necessary to take into account which product of the company is most in demand, where recycling would also make economic sense, which is also an important indicator for the operation of the company today. Dust particles could prove successful in another product, but it would not be advantageous for the company now, so now the recycling of dust particles will not start and they will be further disposed of in the same way.
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Characterization of portland cement hydration products by thermal dilatometric analysis
Dvořáková, Tereza ; Švec, Jiří (referee) ; Šoukal, František (advisor)
The paper presents the results of thermal dilatometric analysis of cement pastes during the heating at high temperatures. Volume changes were observed in samples of cement paste at selected time intervals during the hydration. Based on the measured data the dTDAc urves course has been described and the results have been compared with the curves of differential thermal analysis. To characterize the microstructure of the cement paste during the considerable shrinkage at higher temperatures the images by scanning electron microscope have been acquired.
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