Centrum AdMaS - VP1 - TSH

Browse

Now showing 1 - 5 of 12

Variability in cement properties - influence on bleeding of cement paste
(IOP Publishing, 2018-06-15) Jančaříková, Denisa; Hela, Rudolf; Netsvet, Daria Dmitrievna; Peřina, Tomáš
The aim of this study is to find relation between cement properties and tendency of cement paste (concrete) to bleeding. We tested 19 cement samples collected from different batches.
The mechanical activation of fly ash
(Elsevier, 2013-09-03) Hela, Rudolf; Jančaříková, Denisa
One of the main options in looking for the new building materials is using of wastes from an industry as a replacement of the existing ingredient. This way is used in the concrete production too. Basic effort is to find a suitable replacement for economically and ecologically unfavorable cement by another component or components. As one of these components can be used fly ash – by-product of coal-fired electric power stations. The using of the fly ash as an additive into concrete is quite old, nevertheless this component offers a lot of new possibilities today too. Mechanical activation is one of them. As mechanical activation is known sorting or grinding of fly ash. Activation by sorting brings some disadvantages as is not using of all production and the high price for rebuilding the plants. Much more effective option provides grinding of the fly ash. This practice also comes to Czech Republic and submitted publication summarizes existing knowledge and presents result from first tests done on Czech fly ashes.
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.
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.
Utilization of by-products for vacuum insulation panels production
(IOP Publishing, 2018-07-12) Zach, Jiří; Peterková, Jitka; Novák, Vítězslav
The paper deals with the possibilities of utilization of alternative raw materials from the textile industry for the production of vacuum insulation panels with extremely low thermal conductivity value. The paper presents current research findings on the behavior of fibrous structures on an organic basis at extremely low pressure. In addition, the paper presents the practical findings and results of experimental work in the production area and the behavior of vacuum insulation panels with an alternative core insulator based on organic fibers.

Browse

Recent Submissions