Igor Medveď

Determination of a partial phase composition in calcined gypsum by calorimetric analysis of hydration kinetics

A calorimetric method for the determination of a partial phase composition in calcined gypsum is presented. The method is based on the separation of the reaction heat of the transformation of β-anhydrite III to β-hemihydrate from the main hydration reaction transforming β-anhydrite III to dihydrate. Using the known hydration heats of β-anhydrite III to dihydrate and β-hemihydrate to dihydrate, the content of β-calcium sulfate anhydrite III and β-calcium sulfate hemihydrate as well as the amount of non-hydrating parts in gypsum can be determined. Practical application of the method is illustrated on three industrial products.

Seebeck effect influence on joule heat evolution in electrically conductive silicate materials

In general, silicate building materials are non-conductive matters that are not able to evolve heat when they are subjected to an external voltage. However, the electrical conductivity can be increased by addition of electrically conductive admixtures in appropriate amount which leads to generation of conductive paths in materials matrix. Such enhanced materials can evolve Joule heat and are utilizable as a core of self-heating or snow-melting systems. In this paper, Joule heat evolution together with Seebeck effect in electrically conductive silicate materials was taken into consideration and the model based on heat equation with included influence of DC electric field was proposed. Besides, a modeling example of heating element was carried out on FEM basis and time development of temperature in chosen surface points was expressed in order to declare ability of such system to be applicable.

Influence of various amount of diatomaceous earth used as cement substitute on mechanical properties of cement paste

Active silica containing materials in the sub-micrometer size range are commonly used for modification of strength parameters and durability of cement based composites. In addition, these materials also assist to accelerate cement hydration. In this paper, two types of diatomaceous earths are used as partial cement replacement in composition of cement paste mixtures. For raw binders, basic physical and chemical properties are studied. The chemical composition of tested materials is determined using classical chemical analysis combined with XRD method that allowed assessment of SiO2 amorphous phase content. For all tested mixtures, initial and final setting times are measured. Basic physical and mechanical properties are measured on hardened paste samples cured 28 days in water. Here, bulk density, matrix density, total open porosity, compressive and flexural strength, are measured. Relationship between compressive strength and total open porosity is studied using several empirical models. The obtained res...

Varying coefficients of diffusion of 133Ba2+ and 137Cs+ in granite

Diffusion coefficients, D, of radionuclides in porous media are usually calculated as single values. The reason is that experimental concentration profiles are fitted with theoretical models in which D is constant. This approach could be rather inadequate. For example, potentially large discrepancies may arise when predicting radionuclides penetration through encasements in radioactive waste repositories at long timescales. In this paper we present an inverse approach based on the Bolztmann-Matano method to calculate the apparent diffusion coefficient of a sorbing radionuclide in saturated porous materials that is not constant but is a function of the radionuclide concentration. We apply our results to the diffusion of 133Ba2+ and 137Cs+ in two types of granite.

Young’s modulus of alumina ceramics during isothermal heating

The Young’s modulus is studied in dehydroxylated alumina ceramic samples in the solid-state sintering region. The initial composition is 35.5 wt.% of kaolin, 35 wt.% of Al2O3, and 29.5 wt.% of feldspar. Since solid-state sintering and dehydroxylation run simultaneously, the samples are preheated at 490 °C for 40 h to reach a complete transformation of kaolinite into metakaolinite. Afterwards, the samples are studied by the modulated force thermomechanical analysis in the isothermal regime at the temperatures 500, 600, 700, 800, 900, 1000, and 1050 °C when no liquid phase is created. The Young’s modulus is measured for 8 h. For temperatures 500, 600, 700, and 800 °C only a small increase (2 – 8 %) of the Young’s modulus is observed, and after 4 h the samples became stabilized. On the other hand, for temperatures higher than 1000 °C the increase of the Young’s modulus continues during the whole time period and reaches over 90 %.The Young’s modulus is studied in dehydroxylated alumina ceramic samples in the solid-state sintering region. The initial composition is 35.5 wt.% of kaolin, 35 wt.% of Al2O3, and 29.5 wt.% of feldspar. Since solid-state sintering and dehydroxylation run simultaneously, the samples are preheated at 490 °C for 40 h to reach a complete transformation of kaolinite into metakaolinite. Afterwards, the samples are studied by the modulated force thermomechanical analysis in the isothermal regime at the temperatures 500, 600, 700, 800, 900, 1000, and 1050 °C when no liquid phase is created. The Young’s modulus is measured for 8 h. For temperatures 500, 600, 700, and 800 °C only a small increase (2 – 8 %) of the Young’s modulus is observed, and after 4 h the samples became stabilized. On the other hand, for temperatures higher than 1000 °C the increase of the Young’s modulus continues during the whole time period and reaches over 90 %.

Building ceramics with an addition of pulverized combustion fly ash from the thermal power plant Nováky

Pulverized combustion fly ash (PFA) from the Power plant Novaky (Slovakia) is analyzed for its potential use in the production of building ceramics. Three materials are used to prepare the mixtures: illite-rich clay (IRC), PFA and IRC fired at 1000 °C (called grog). The mixtures contain 60 % of IRC and 40 % of a non-plastic compound (grog or PFA). A various amount of the grog is replaced by PFA and the effect of this substitution is studied. Thermal analyses (TGA, DTA, thermodilatometry, and dynamical thermomechanical analysis) are used to analyze the processes occurring during firing. The flexural strength and thermal conductivity are determined at room temperature after firing in the temperature interval from 800 to 1100 °C. The results show that an addition of PFA slightly decreases the flexural strength. The thermal conductivity and porosity are practically unaffected by the presence of PFA. Thus, PFA from the Power plant Novaky is a convenient non-plastic component for manufacturing building ceramics.

A Contribution to the Treatment of Salt Damage in Historical Buildings

Salts and water may cause serious damage to historical masonries. Therefore, numerous conservation treatments have been developed by research teams for the consolidation and protection of porous building materials affected by salt attack. Here the focus is on methods for obtaining an effective desalination of historical masonry, indicating their advantages and disadvantages. It is pointed out that cellulose is a favourite material added to poultices used in desalination.

Application of Thermally Treated Sewage Sludge in Blended Cements

Chemical, physical, morphological, and mineralogical analysis of sewage sludge originating from a waste water treatment plant in Patras, Greece, is presented in the paper. The sewage sludge is firstly dried at 70°C, then oven-burned at 700°C for two hours and milled. The thermally treated material is analyzed using XRF and XRD, the particle size distribution is determined by a laser diffraction method. A potential use of sewage sludge in blended cements is investigated on the basis of the measurement of mechanical and basic physical properties of pastes containing the sludge in an amount of up to 60% of the mass of cement. Experimental results show that the thermal treatment of pre-dried sewage sludge and its grinding provides a material that can be successfully applied as a partial replacement of Portland cement. At a production of blended cements for high strength concrete, an up to 20% cement replacement level can be recommended.