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Influence of short para-aramid fibers addition on the properties of ultra-high performance cement composite
Tandlich, Dávid ; Šoukal, František (referee) ; Bocian, Luboš (advisor)
In this bachelor's thesis, the use of p-aramid fibers in ultra-high performance cementitious composites was investigated. These fibers were used as a separate reinforcement, but also as a hybrid reinforcement in combination with steel fibers. The surface of both types of fibers was analyzed by SEM. In addition to the composite with p-aramid fibers and the hybrid composite, a reference composite with steel fibers and a matrix without fibers were also prepared. The prepared objects were tested in compressive strength and flexural tensile strength. Furthermore, the fracture surface on the selected bodies was analyzed by SEM. It turned out that it is not possible to clearly determine the composite with the best mechanical properties, as the standard deviations of hybrid and reference composite overlap. However, based on average values, the hybrid composite showed the best mechanical properties. The composite that contained only p-aramid fibers showed significantly lower compressive and flexural strength both compared to the reference composite. Results showed that p-aramid fibers alone did not exceed the effect of steel fibers. A problem was the tendency of p-aramid fibers to decrease a spillage and to form clusters in the matrix, which negatively affected the resulting properties of the composite. However, the use of p-aramid fibers in combination with steel fibers appeared to be advantageous, as it was found out that thanks to p-aramid fibers there was a slight reinforcement of the matrix and an improvement of the mechanical properties within the standard deviations.
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Reactive powder concretes (RPC) with redispersible polymer powders
Ondrůšková, Nela ; Másilko, Jiří (referee) ; Šoukal, František (advisor)
The thesis entitled "Reactive Powder Concretes (RPC) with Redispersible Powder Polymers" deals with the description, design and development of a material with increased ballistic resistance, i.e. with increased resistance to high-speed dynamic stresses due to interaction with a projectile. The high mechanical properties of RPC are achieved mainly by reducing the water coefficient, using a large dose of superplasticizers and high strength aggregates to achieve the densest possible structure. The aim of this work is to investigate the effect of addition of redispersible powder polymer to RPC composite and to find the optimum type and amount of polymer to form a co-matrix, thus improving material properties such as flexural tensile strength and toughness. The preparation, procedure and processing of each formulation are described in each chapter, and the properties of these materials and observations of their behaviour under ballistic loading are described. Experimentally, the thesis focused on monitoring the effect of polymer type and amount, particularly on the change in bulk density and on compressive and flexural tensile strength. The results obtained for the different formulations were compared with each other and related to a reference. SEM analysis was performed to monitor the polymer film formation in the matrix. Based on the tests, two formulations with the best comprehensive properties were selected. These two formulations were subjected to DOP ballistic test.
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Reactive powder concretes (RPC) with polymer latexes
Petrů, Ludmila ; Koplík, Jan (referee) ; Šoukal, František (advisor)
This thesis deals with the effect of polymeric latexes on the properties of concrete based on reactive powders. Three types of commercial latexes were used for the preparation of the samples, namely Revacryl, Duvilax and Plextol. Revacryl AE 2091 is an aqueous dispersion of styrene-acrylate copolymer with a high content of solids. Duvilax BD-20 is a homopolymer polyvinyl acetate dispersion that does not contain fillers with plasticizers. Plextol X 4002 is an aqueous, self-setting acrylic emulsion with a high content of solids. These latexes were added to the samples at concentrations of 0,20; 0,40; 0,60; 1,20 and 2,50 %. To determine the effect of latex on processability, the flow rate of the fresh mixture was measured. The main objective was to determine the ballistic resistance of modified concretes based on reactive powders. The DOP test was used for the determination. Furthermore, the change in mechanical properties was determined by adding a polymer to concrete based on reactive powders. The improvement in properties is expected to be due to the formation of a polymer film and a polymer-cement co-matrix. To demonstrate the film formation, the microstructure of the samples was observed by a raster electron microscope.
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Influence of calcium sulphate type on hydration of Portland cement
Šimčíková, Ivana ; Šiler, Pavel (referee) ; Šoukal, František (advisor)
My bachelor thesis deals with the study of the influence of calcium sulphate types on the hydration of Portland cement. Hydration is performed at 15 °C, 25 °C and 40 °C. In the theoretical part we find a description of the hydration of Portland cement and the influence of the type and amount of gypsum on the hydration period. The experimental part contains the preparation of samples for measurement and the principle of calorimetry including a description of the calorimetric curve. The data obtained from the calorimetric curve was processed into ternary diagrams for illustration. The diagrams show that the more calcium sulphate is soluble, the shorter the induction period, the times of reaching the minimum heat flow and heat flow at the maximum silicate peak will have. Further, the diagrams showed that as the amount of water in sulphate increases, so does the amount of hydration heat released.
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Study of alkali metals ions diffusion in hardened cement
Doležal, Martin ; Janča, Martin (referee) ; Šoukal, František (advisor)
This master thesis is aim to study alkali diffusion (sodium, potassium) in hardened cement paste body. It´s deal with impact of various sorroudings (hydroxide, nitrate and carbonate) in various concentrations and temperature effect. This work is also deal with changes in cement paste and medium. Teoretic part is talking about cement production and cement chemistry, alkali-silica reaction, plasticizer, diffusion an cement testing metods. This work is aimed to white (Aalborg CEM I 52,5 R – SR 5) and road (Mokrá CEM I 42,5 R – sc) cement. Experimental part describes constitution of tested cement pastes, conservation of them and sampling. Diffusion is study by ICP-AES which affected the loss of alkali from the solution and SEM which affected alkali migration (diffusion) in cement paste. In several cases, the formation of a saturated alkali edge was observed, followed by steady diffusion. In the case of potassium there was very slow diffusion through the body mass. The influence of medium and temperature was evaluated as the most significant. The effect of medium concentration wasn´t significant. Also changes in the porosity on the body were observed. The diffusion itself was affected by secondary products gorwing on the surface of body and in the medium. The work deals with them in the last part.
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Possibilities of reducing zinc losses during heat treatment of ferrite ceramics
Buday, Patrik ; Šoukal, František (referee) ; Ptáček, Petr (advisor)
The diploma thesis is focused on the study of the influence of sintering temperature on the evaporation of zinc from Mn-Zn-ferrite ceramics. The main focus of the study is on the reaction kinetics of the zinc evaporation process, at the same time the aim of this work is to propose and verify a method that would limit the evaporation of zinc. The theoretical part summarizes the basic knowledge about the properties, classification, application, and production of Mn-Zn-ferrites. The end of the theoretical part describes the loss of zinc and a possible solution to this undesirable phonomenon. The beginning of the experimental part contains a summary of the principles of infrared spectroscopy, electron scanning microscopy, and X-ray crystallography. The experimental part of the diploma thesis is focused on the description of the production of ferrite samples, the characterization of the input material and the determination of the reaction kinetics of the sintering, and its comparison with the kinetics of the sample treated with a protective layer.
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Mapping the potential of secondary products from the production of titanium white
Nehéz, Samuel Emil ; Šoukal, František (referee) ; Opravil, Tomáš (advisor)
This bachelor’s thesis deals with the use of secondary products from the production of titanium white and its subsequent use during cement production. Secondary products from the production of TiO2 could be regarded as several kinds of sulphate waters, where by their successive neutralization gypsum by-products are prepared. The aim of the bachelor’s thesis was to experiment whether it is possible to use some of these gypsum by-products as solidification retarder in Portland cement. Cement pastes were prepared and subjected to mechanical and analytical examinations. During the mechanical examinations, strength in pressure during bending and strength in pulling for the duration of 60 days were monitored. The material from tested bodies of pastes was reviewed by x-ray difraction analysis after 7 and 28 days. Just as was determined the optimum W/C, initial and final setting time. The prepared samples with the gypsum by-product as their content had some features comparable with commercially used cement.
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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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Influence of zinc loss during the sintering on permeability/inductance of ferrite ceramics
Kvapilová, Vendula ; Ptáček, Petr (referee) ; Šoukal, František (advisor)
The diploma thesis is focused on the investigation of the effect of zinc release during ferritic sintering on the permeability/inductance of ferrite ceramics. The theoretical part deals with the position of ferrites among other ceramic materials. It describes the basic characteristics of ferrites, their crystal structure and finally the problems that are directly related to their production and which fundamentally affect the magnetic properties of ferrites. In the second part of the work, the influence of the temperature and time of sintering and the position of the cores in the furnace during firing on the loss of zinc from the sample and subsequently on the electromagnetic properties of the prepared test specimens from industrial raw material mixtures was investigated. These are initial experiments, which will be followed by further research aimed at eliminating the problem of zinc loss in the production of Mn-Zn ferrites.
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On the efficiency of plasticizing admixtures in alkali-activated slag based system
Flídrová, Michaela ; Šoukal, František (referee) ; Kalina, Lukáš (advisor)
Alkali-activated materials (AAM) are construction materials with great potential, especially for their environmental friendliness, but also due to their mechanical properties. Therefore, it is appropriate to pay further attention to these binders. This diploma thesis deals with monitoring the effectiveness of plasticizers in connection with the surface chemistry of the alkali-activated slag system. Sodium hydroxide and sodium water glass were used as alkaline activators for the preparation of alkali-activated blast furnace slag-based systems. To study the effectiveness of the lignosulfonate plasticizer, yield stress, heat flow, adsorption and zeta potential were monitored depending on the amount and time that the plasticizer was added to the system. The results show that the type of activator used in the mixtures plays an important role. NaOH-activated samples revealed the best efficiency of lignosulfonate plasticizers. A key factor in studying the behavior of the studied mixtures was the measurement of the zeta potential, which provided insight into the surface charge of blast furnace slag particles related to the ability of lignosulfonate to adsorb on grains of alkali-activated slag.
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