National Repository of Grey Literature 15 records found  1 - 10next  jump to record: Search took 0.00 seconds. 
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.
A study of the hydration of calcium aluminate cement in an excess of silica fume
Nehéz, Samuel Emil ; Švec, Jiří (referee) ; Novotný, Radoslav (advisor)
This thesis deals with the effect of silica fume (microsilica) on the hydration process of alumina cement (CAC). During the preparation of the samples, the effect of the amount of microsilica and the effect of the hydration temperature on the formation of hydration products were investigated. Microsilica was always in excess compared to alumina cement. The characterization of the raw materials was carried out using particle size measurement and calorimetry. In the case of the samples themselves, calorimetric measurements showed that the hydration process is divided into two separate events. Thanks to this, it was possible to stop the hydration at the desired time and examine the emerging hydration products. The presence of silica fume caused the formation of characteristic hydration products - strätlingite (C2ASH8). It was found that as the temperature of hydration increases, the resulting products form more quickly. Increased hydration temperature had a negative effect on mechanical properties. The properties and characterization of the prepared samples were further investigated using XRD, TG-DTA and scanning electron microscopy (SEM).
Influencing the hydration of high-performance composites using zinc ions
Všetečka, Tomáš ; Hajzler, Jan (referee) ; Novotný, Radoslav (advisor)
The bachelor thesis is focused on the influence of hydration of high-performance cementitious composites, more specifically reactive powder composites. Zinc ions were supplied by the compounds of zinc oxide and zinc sulphate heptahydrate. Zinc ions were added by weight content to cement at concentrations of 0.2; 0.5 and 1.0 wt. %. The development of properties depending on the content of zinc ions and the type of compound used was monitored in this work. The measured values were compared with reference values that did not contain zinc ions. The highest compressive strengths were obtained with a sample containing 1.0% Zn in the form of zinc oxide. However, this sample is associated with a longer setting time due to the retarding effect of zinc ions on hydration. The retardation effect was monitored using isothermal calorimetry. For samples containing zinc ions, a negative effect on the brass layer of steel fibers, which was used as reinforcement, was observed. Due to the addition of zinc ions, dezincification and subsequent removal of brass from the surface of the fibers took place. Therefore, these specimens had lower tensile strengths. A positive effect on the differential ballistic protection efficiency factor was observed for a sample containing 1% Zn in the form of zinc oxide.
Influence of anticorrosive surface treatment of steel reinforcement fibers on the properties of ultrahigh-performace cement composite
Bocian, Luboš ; Ptáček, Petr (referee) ; Novotný, Radoslav (advisor)
This thesis characterized surface layer of brass on commercially available steel microfibers. Subsequently, it was studied how to remove this surface layer of brass off these microfibers. Additionally, this thesis investigated influence of removal of brass surface layer on mechanical and ballistic properties of RPC composites. It was also studied how previously mentioned surface layer of brass influences interface between steel microfibers and matrix. It was found out that the surface layer of brass on commercially available steel microfibers is uneven and that the brass fills scratches present on steel underneath the surface layer of brass. It was also found out that conc. HNO3 and mixture of NH3 and H2O2 in volume proportion of 3 : 1 can be used to remove the surface layer of brass. The only thing to consider is that steel microfibers from conc. HNO3 corrode. Flexural strength of composite made with fibers from mixture of NH3 and H2O2 is higher than flexural strength of composite made with commercially available steel microfibers with surface layer of brass after 28 and 95 days. Compression strength wasn’t significantly affected in any composite used in this thesis after 28 and 95 days. Composite made with fibers from mixture od NH3 and H2O2 showed slightly better ballistic resistance than composite made with commercially available steel microfibers with surface layer of brass. In terms of SEM analysis of interface between matrix and steel fibers of certain composite, it was found out that there was no evidence of infiltration of components of brass into matrix.
Influence of fumed silica on the properties of ultra-high performace cement composite
Hrbáčová, Markéta ; Švec, Jiří (referee) ; Novotný, Radoslav (advisor)
This diploma thesis deals with the properties of concrete based on reactive powdered materials. Pyrogenic nanosilica (Aerosil 200, Aerosil 380) was added to the concrete in various volume ratios. The aim was to design and prepare a series of samples in order to determine their basic properties, and to determine the behavior of selected samples during penetration by a high-speed projectile compared to the reference sample. In order to determine the strength of the samples, compression and tensile bending tests were performed. The so-called multihit test was used to determine ballistic resistance. The differential effect factor was also determined experimentally and compared with the reference sample. An electron microscope was used to monitor the behavior of the fibers in the binder as well as the binder itself. Hydration curves for individual samples were generated using calorimetric measurements. The bulk density of the samples and the spills during their preparation were also monitored. The resulting strength of the nanosilica samples did not show higher values compared to the reference sample. The results of the multihit test did not show considerable changes compared to the reference composite.
Issues of stopping the hydration of alkali-activated slag using organic substances
Chadima, Jan ; Novotný, Radoslav (referee) ; Bílek, Vlastimil (advisor)
This thesis deals with the stopping of hydration of alkali activated slag by organic solvents and investigates to what extent the selected organic solvent affects the results of the analyses. The solvents used were acetone, diethyl ether, ethanol, isopropanol and methanol, and this is because these are the most commonly used organic solvents in practice. Thermogravimetric analysis along with differential thermal analysis was used to assess the degree of influence of organic solvents on the alkali activated slag and Portland cement samples. Methanol and acetone affected the samples the most and the longer the sample was stored in the solvent, the more it reacted with the organic solvent. The adverse interaction of organic solvent was greatest for the Portland cement samples. Samples that were rinsed with diethyl ether prior to analysis had lower mass losses than samples that were not rinsed. In the case of alkali activated slag, it was found that the way in which the thermogravimetric results were affected by organic solvents was highly dependent on the activator used, with the smallest effect observed for Na2CO3 activation, while the largest effect was observed for NaOH activation at temperatures below 600 °C, and for higher temperatures for water glass activation.
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.
The study of sulfate depletion in cement binders
Jurko, Michal ; Švec, Jiří (referee) ; Novotný, Radoslav (advisor)
This bachelor thesis deals with the study of sulfate depletion in cement binders. Basic knowledge about cement binders is summarised at the beginning of the theoretical part. The theoretical part goes on to describe the hydration of Portland cement (PC) and to briefly describe the influence of different types of milling on PC particle size. In the experimental part, PC fractions of various average particle sizes were prepared on a planetary ball mill for wet conditions. On the prepared cement, their hydration was studied using isothermal calorimetry; especially sulfate depletion, portlandite precipitation, heat flow rate and induction period interval. n the thesis were also used analyzes for autogenous shrinkage, XRD and STA. The input raw materials are cement CEM I 42,5 R (grey, Českomoravský cement, a.s. – Mokrá, Czech Republic) and sulfate-resistant cement CEM I 52,5 R (white, Aalborg Portland, a.s. – Aalborg, Denmark). On the basis of the results analysis, a proposal was made to correct the presence of sulfate ions by adding gypsum in these cements. In the case of CEM I 52,5 R the correction is recommended and in the case of CEM I 42,5 R the correction is necessary.
Utilization of fluidized bed combustion solid residues in the production of refractories
Tvrdý, Michal ; Novotný, Radoslav (referee) ; Opravil, Tomáš (advisor)
The thesis deals with the preparation, study and analysis of refractory ceramics, namely fireclay mortars for stove purposes with the addition of fluid ash. The mixtures for preparation of refractory ceramics were doped with different content of fly and bed fluid ash in order to reduce the consumption of the original raw materials for the preparation of these materials. Fired slate clay, refractory clay, fly and bed fluid ash were used for preparation the samples. Input raw materials and fired fireclay mixtures were characterized by XRD, TG-DTA-EGA, TDA, SEM-EDS, heat microscopy, isothermal calorimetry, ICP-OES. The mechanical properties, i.e. compressive strength and tensile bending, were also determined on fired fireclay mortars. The results showed that the properties of the fireclay mortar containing fly ash are comparable to the starting mortar to a specific ash dosage. It has also been found that bed fluid ash is not suitable for the production of refractory materials.

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