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    Long-term Observation of Yeelimite Clinker Hydration in Environment of Saturated Water Vapour
    (Elsevier, 2016-08-03) Pekárková, Jana; Kulísek, Karel; Gazdič, Dominik; Fridrichová, Marcela
    Due to ecological overloading decrease, industrial by-products are utilized. Fly ash also belongs among these by-products. In Portland-composite cements, the high-temperature fly ash is applied nowadays, but fluidized bed combustion fly ash (FBC fly ash) is not used. The reason is that the FBC fly ash hydrates to form an undesirable ettringite, C3A.3CaSO4.32H2O. Decomposition temperature of ettringite in ambient conditions is most often mentioned in a range of 50 °C to 110 °C. In order to assess the ettringite long-term stability, ettringite was synthesized by hydration of mineral yeelimite, 3CaO.3Al2O3.CaSO4. The aim of this paper is long-term observation of the hydration of yeelimite in environment of saturated water vapour and examination of how stable the products of hydration are under given conditions. Raw materials for preparation of yeelimite were gypsum, limestone and corundum, weighed according to stoichiometric ratio of yeelimite. The mixture was heated at temperature of 1200 °C, soak 3 hours. After quenching and grinding, yeelimite was hydrated with a water-yeelimite ratio of 0.3. The system was cured as pastes and stored in conditions at laboratory temperature and in settings of saturated water vapour (100% R.H.). In order to follow the progress of synthesis regularly, namely up to age of 180 days of hydration, X-ray diffraction (XRD) was chosen using diffractometer Empyrean PANalytical (CuK-alpha). Based on the XRD patterns, only minor part of ettringite was formed, whilst a majority of yeelimite was preserved. It has been found that ettringite was not the only one product of yeelimite hydration. From an age of 20 days of hydration, a small amount of monosulfate was identified, whose quantity rose gradually. Especially at later ages of hydration, transformation of ettringite into monosulfate was observed.
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    Possibilities of using of alkali-activated mortars in aggressive environment
    (Elsevier, 2016-08-04) Válek, Jaroslav; Jarolím, Tomáš; Labaj, Martin
    In the article the incipiental experimental works about using of alkali-activated mortars in aggressive environment are introduced. Several types of mortars with different composition were prepared and examined. Observed properties of alkali-activated mortars were: resistance of cement concrete's surface to water and defrosting chemicals, resistance against crack formation and development, adhesion to the concrete base and frost resistance. The purpose of this experiment was to propose a mixture of alkali-activated material that would be suitable for application in the form of a screed for concrete and other materials. The pilot tests were performed with several mixtures with different combinations of initial materials. They were also tested in different mixing ratios, depending on the rheological properties of the respective individual mixtures.
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    Immobilization of Heavy Metals in Natural Zeolite-blended Cement Pastes
    (Elsevier, 2016-09-26) Vyšvařil, Martin; Bayer, Patrik
    This paper deals with the investigation of efficiency of natural zeolite-blended cement pastes for the immobilization of heavy metals. Natural zeolite was used to partially replace ordinary Portland cement (OPC) at rates of 0% and 20% by weight of a binder and soluble heavy metal salts were added to a mixing water in an amount of 1% and 5% by weight of the binder. The flexural and compressive strength of the cement pastes were investigated, while the leachability of the heavy metals was determined. Additionally, scanning electron microscopy was performed to investigate the microstructure of the cement pastes, while the pore size distribution was analyzed with mercury intrusion porosimetry. The results indicated that the flexural and compressive strengths of the pastes containing 20 wt.% of natural zeolite were higher than those with OPC alone. It was also found out that the effectiveness in reducing the leachability of Ba, Cd, Cu, Ni and Pb was better for the natural zeolite-blended cement pastes.
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    Carbon Nanotubes in Cementitious Composites: Dispersion, Implementation, and Influence on Mechanical Characteristics
    (Hindawi, 2016-06-14) Jarolím, Tomáš; Labaj, Martin; Hela, Rudolf; Michnová, Kamila
    In article were descibed possibilities of CNT's dipersion. Implementation CNT to the cements matrix and it's influence to the mechanical properties
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    Optimization of heavy weight concrete composition and process of prefabrication for prefabricated shielding cladding tiles
    (IOP Publishing, 2018-06-15) Hela, Rudolf; Jančaříková, Denisa; Louda, Pavel; Jobánek, Jaromír
    The aim of experimental research was to verify the possibility of the prefabrication of the thin shielding cladding tiles from heavy weight concrete with fine.