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    Properties of cement pastes with zeolite during early stage of hydration
    (Elsevier, 2016-08-04) Boháč, Martin; Kubátová, Dana; Nečas, Radovan; Zezulová, Anežka; Rybová, Alexandra; Novotný, Radoslav
    Properties of cement pastes with various replacement levels of natural zeolite were tested by isothermal calorimetry and rotational rheology. Zeolite from the Eastern Slovakia region was used for tests. Kinetics of exothermic reaction during early stage of hydration were monitored by calorimetry. The role of different replacement level of zeolite on main rheological parameters is discussed in the paper. The onset point of formation of C-S-H products and the main calorimetric peak move to earlier times with increased zeolite content. Zeolite causes acceleration of hydration before the heat flow peak time and the following deceleration proportionally to its content. Zeolite in cement promotes the AFt formation, which increases the elastic response of fresh paste at the beginning of hydration. Trends of G’ and phase angle show that zeolite accelerates the hydration of C3S and early C-S-H formation.
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    Hexavalent chromium reduction by ferrous sulphate heptahydrate addition into the Portland clinker
    (Elsevier, 2016-08-01) Mončeková, Miroslava; Novotný, Radoslav; Koplík, Jan; Kalina, Lukáš; Bílek, Vlastimil; Šoukal, František
    Nowadays, hexavalent chromium and its content in Portland cement is very actual and often discussed topic. The goal of this study was to observe the influence of different ways of addition of ferrous sulphate heptahydrate on the reduction of hexavalent chromium at the hydration of Portland clinker. Ferrous sulphate heptahydrate was added as crystalline powder and also in an aqueous solution. Obtained experimental results clearly showed higher reduction ability of a liquid form compared to the solid substance. The influence of the grain size on the reduction of hexavalent chromium was inve stigated immediately after mixing clinker with water and also during the first days of hydration process. New oxidation layer containing Fe3+species forms around the non- oxidation part of sulphate species. That is why larger grain size showed lower reduction ability of chromium. In this case the additional chromium reduction effect was observed during the first days of hydration. The results were acquired by UV/VIS method according to STN EN 196-10.
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    Influence of Active Alumina on the Hydration Process of Portland Cement
    (Elsevier, 2016-08-04) Novotný, Radoslav; Bartoníčková, Eva; Švec, Jiří; Mončeková, Miroslava
    The work is interested in the study of the hydration process by means of the isothermal calorimetry method. The Portland cement hydration process led to gradual consumption of contained calcium sulfate. This sulfate depletion is observed on the calorimetry curve as a shoulder of main silicate peak. The addition of hydratable alumina to Portland cement was studied in order to determine its influence on hydration process. Experimental results showed the shifted position of this shoulder according to alumina and calcium sulfate content. It was also observed that the overall hydration process was almost unaffected by alumina addition.
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    Impact of organic and integrated pest management on the elemental composition of wine and grapes in a season with high fungal pressure
    (Polish Society for Magnesium Research and UWM in Olsztyn, 2021-12-01) Pořízka, Jaromír; Diviš, Pavel; Štursa, Václav; Punčochářová, Lenka; Slavíková, Zuzana; Křikala, Jakub
    The aim of this study was to compare organic and integrated pest management systems in terms of the influence of the application of specific pesticides on the elemental composition of grapes and wine. Samples of wine and grapes were obtained from an experimental vineyard estate running both viticulture systems. A comparison of agricultural techniques was carried out under identical climatic and soil conditions. Another important aspect of this study was the comparison in the 2019 season with high fungal disease pressure in the South Moravian Region, which forced the winegrower to use limited doses of protective agents, mainly based on Cu. The work focuses on the determination of 15 elements (Na, Mg, Al, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Pb) in soil, grapes and wine selected according to plant nutrition, toxicology and human diet. Elemental analysis of samples was carried out by inductively coupled plasma mass spectrometry (ICP-Q-MS). Differences in the elemental composition of samples from organic and IPM production were observed in all types of tested samples. The most fundamental differences were found in the case of Cu. Due to the higher application dose of copper fungicides in organic vineyard, the concentration of copper in organic wine (Sauvignon blanc) was almost 3 times as high (774 ± 35 g.l-1) as in wines from IPM (259 ± 27 g.l-1). This study also demonstrated a direct effect of mancozeb application in IPM on elevated Zn an Mn levels in grapes and wine. However, none of the investigated elements exceeded the limits set by national, European or OIV regulations for wine.
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    Modelling of packing density for particle composites design
    (Elsevier, 2016-08-03) Koutný, Ondřej; Kratochvíl, Jiří; Švec, Jiří; Bednárek, Jan
    Effective packing of solid particles is one of the main topics in the field of ceramics, powder metallurgy and concrete technology. In these material sectors it is necessary to maximise or optimise the packing density of particles. Therefore, it is necessary to obtain the ability not even to measure the packing density effectively but especially to predict it and affect it with sufficient accuracy. Despite of large experiences in field of metallurgy and ceramics technology, it is still relatively difficult to predict packing density in the concrete technology. Prediction is based on de Larrard linear packing theory expanded by third parameterincluding wedging effect of particles to the form of 3-parameter packing model. In this paper the model is calibrated for fillers using in Particle composites technology with respect to their granulometry, mainly aimed on UHPC technology. Calibration is based on correlation with experimentally determined values of packing density of model particles mixtures. Successful optimization of particular system composition in concrete technology then could lead not even to decrease of final price but it has also a beneficial influence mainly on mechanical properties and durability of final product.