Advanced Materials Research Vol. 1126

Abstract: The thermal behaviour of different oil shale samples (Estonia, Jordan, Israel, Morocco) were studied using a Setaram Setsys 1750 thermoanalyzers coupled to a Nicolet 380 FTIR Spectrometer. The experiments were carried out under non-isothermal heating conditions up to 1000 °C at different heating rates in an oxidizing atmosphere. A model-free kinetic analysis approach based on the differential isoconversional method of Friedman was used to calculate the kinetic parameters. The thermooxidative decomposition of oil shale samples proceeded in three steps. Firstly, thermooxidation of volatile organic compounds occurred – depending on the heating rate, up to 460 °C. Secondly, thermooxidation of heavier part of organic matter (kerogen) and fixed carbon as well as thermooxidation of pyrite proceeded up to 580 °C. Finally, carbonates contained in oil shale samples decomposed up to 870 °C. The combined TG-FTIR study of thermooxidative decomposition of samples made it possible to identify in addition to CO2 and H2O as major gases evolved a number of gaseous species like CO, SO2, COS, methane, ethylene, etc. formed and evolved at that. The value of activation energy E in the low-temperature oxidation region was for Estonian and Jordanian oil shale samples lower than that in the high-temperature region which was contrary for Israeli and Moroccan oil shale samples. Therefore, the results obtained indicated the complex multi-step character of the thermooxidative decomposition of the oil shale samples studied.

Abstract: This paper offers a comparison of two different approaches aimed at the identification of moisture diffusivity of porous building materials as a function of moisture content. The approaches are represented by a traditional deterministic approach using the Boltzmann-Matano method and novel stochastic approach by genetic programming. The results of the comparative analysis show that genetic programming may be used as an alternative to the traditional approaches. On the basis of the very good agreement between experimental data and optimized output of genetic programming, the validation of the genetic programming method may be considered as successful.

Abstract: The laboratory measurement of water vapour adsorption/desorption curves is a standard tool for determination of the moisture capacity of porous building materials in hygroscopic region. However, in case of cementitious materials, additional processes like carbonation can occur during the measurement. Generally, process of carbonation affects the pore structure of the material and results in an increase of its bulk density. Therefore, for determination of correct sorption curves the carbonation caused bulk density increase has to be eliminated. In this work the both mentioned effects of carbonation on the measured water vapour sorption isotherm were quantified for autoclaved aerated concrete (AAC). Within the monitored 9-year period, the carbonation caused noticeable changes in microstructure of the tested AAC samples, namely a decrease of the specific surface area of pores and the portion of very small pores. These microstructure changes affected the moisture storage capacity too – the obtained equilibrium moisture contents of the partly carbonated AAC were lower than the ones of the AAC close to the original state. It was also confirmed that in case of continuous measurement of the water vapour sorption curve the carbonation induced bulk density increase could result in an overestimation of the equilibrium moisture contents.

Abstract: An effect of the presence of sodium chloride on water vapour adsorption/desorption loop was quantified for two types of commonly used ceramic bricks with different hygroscopic ability. The measurements were carried out for salt free materials and saline materials contaminated with sodium chloride solutions of two different concentrations. It was found out that at relative humidity higher than deliquescence point, the hysteretic effects of the saline bricks were similar or less significant as the ones of the salt free bricks. In this range of relative humidity the desorption moisture contents did not exceed the values predicted using the simply additive model. However, for the relative humidity lower than deliquescence point the hysteretic effects of the saline bricks were more significant than the ones of the salt free bricks. The effect was of importance in the case of hygroscopic ceramic brick where obtained desorption moisture contents of the saline bricks were noticeably higher than for the salt free brick.

Abstract: Historical monuments are most often built from materials (plaster, walls, rocks, etc.), which have a porous structure. The porous structure is characterized by a set of parameters that control its response to environment. In such structures, depending on the environmental conditions, we encounter with processes like vapor diffusion, adsorption, pore surface diffusion, capillary transport, etc. The processes are accompanied with the transport of heat energy and moisture. When monitoring of thermal - moisture regime of such structures we can find a wide range of effects such as wetting, drying, freezing and thawing. We have monitored several cultural objects localized in different environments, namely the Duomo Cathedral in Florence, the tower of St. Martin in Bratislava and pillar of the St. James Church in Levoča. Building components of the mentioned objects are of different nature such as masonry composed of bricks and plaster, Gioia marble and sandstone. Moisture sensors were used to monitor the thermal – moisture regime based on the hot-ball method for measuring thermal conductivity. The thermal conductivity is a function of the pore content. In the pores, depending on the thermodynamic conditions, air, vapor, water or ice can be found. Collected data are correlated with meteorological conditions.

Abstract: An brief overview of the selected thermo-physical measurements realized in the VILA laboratories for the glass industry and for the fundamental research of glass is presented. Among the routine measurements realized for the glass industry the thermodilatometry for measuring the glass transition temperature, and linear thermal expansion coefficients of glass and metastable glassforming melt are described in detail. The fact that the glass transition temperature is not a single valued physical quantity is stressed in connection with the measurement time temperature schedule. The probably most important quantity related to the glass production technology is the viscosity. Its measurement in the range extending ten orders of magnitude is described. The combination of the falling ball method, the rotation viscosimetry and the thermomechanical analysis is needed to cover the above viscosity range. Among the methods used in the fundamental research of glass structure and properties the study of structural relaxation is overviewed. Here the own method of combined viscous flow and structure relaxation TMA measurement is described in detail.

Abstract: The presented paper aims at thorough uncertainty analysis of combined experimental and computational approach for determination of equivalent thermal conductivity of highly perforated bricks. The thermal conductivity is determined using experimental guarded hot plate method. However, due to large dimensions of analyzed specimens, the measurement is influenced by experimental errors due to abnormal heat leakage. Therefore, numerical modeling of heat transfer is performed in order to quantify this leakage and the resulting value of thermal conductivity is subsequently corrected. The uncertainty analysis is essential part of presented approach leading to its justification. It involves statistical errors, measurement errors as well as results of merged sensitivity analysis. Within the frame of this paper, highly perforated clay brick without cavity fillings was investigated. The results indicated that accuracy of presented approach is very sufficient and combined standard uncertainty is lower than 10 %.

Abstract: Various models of the water vapour sorption isotherms were analysed from the aspect of their applicability for silicate-based building materials like calcium-silicates, burnt clay bricks, plasters and mortars. The analysis included the assessment of the various sorption hysteresis models. They were compared and calibrated with experimental data, consisting of the main adsorption and the scanning curves. For the silicate-based building materials as a fundamental the Brunauer–Emmett–Teller (BET) and Frenkel–Halsey–Hill (FHH) models of adsorption in a combination together with Kelvin-Cohan (KC) model of desorption, with the Independent Domain Model of hysteresis can be applied due to their satisfactory universality.

Abstract: An analytical approach to the determination of a varying salt diffusion coefficient is discussed. It is argued that the approach is fast and reliable and can be very convenient in various civil engineering applications dealing with the transport of salts in porous building materials. The advection-diffusion model of Bear and Bachmat is used to describe the salt transport, and the Bolztmann-Matano inverse analysis is applied to calculate the salt diffusion coefficient. Possible extensions to other models of transport are pointed out. The results are applied to a sandstone from the Msene quarry, Czech Republic.

Abstract: The temperature dependence of the electrical DC conductivity of fly-ash and illite-based ceramics was measured in the temperature range of 20 – 1050 °C. The measurements were done for illite samples with no fly-ash and fired illite added and illite samples containing 10 wt. %, 20 wt. %, 30 wt. %, and 40 wt. % of fly-ash and 0 wt. %, 10 wt. %, 20 wt. %, and 30 wt. % of fired illite. Addition of fly-ash substantially influences temperature dependences of the DC conductivity and introduces a temperature region with a high conduction activation energy which precedes the dehydroxylation. At the lowest temperatures, the main charge carriers are H⁺ and OH⁻ ions, while at higher temperatures K⁺ and Na⁺ ions also play a role. The phase transformation metaillite -> Al-Si spinel is characterized with a current peak at 940 °C.