An experimental and theoretical analysis of the water vapor adsorption in several types of porous building materials is presented. For the measurement of adsorption isotherms, a DVS-Advantage water sorption device is used. The experimental data is analyzed using theoretical formulas based on the BET, BSB, BDDT, and FHH isotherms, assuming a monoas well as multi-layer water vapor adsorption. The BSB equation is found to provide a good approximation for the relative humidities below 0.6-0.7, whereas the FHH equation shows a sufficient accuracy for the relative humidities above 0.4-0.5. Based on a combination of BSB and FHH isotherms, a semi-empirical formula is proposed that allows one to obtain a very accurate approximation of experimental data for all analyzed materials and all values of the relative humidity.Keywords Water vapor adsorption · Porous building materials · Theoretical adsorption isotherms · Experimental measurements Abbreviations c BET constant (-) C s Surface concentration (mol m −3 ) C sat s saturation surface concentration (mol m −3 ) D Fractal dimension (-) H a Molar heat of adsorption (J mol −1 K −1 ) H c Molar heat of condensation/vaporization (
A Boltzmann transformation method that allows determination of water vapor transport properties of building materials as functions of relative humidity during a single experiment is presented. The method is tested at the laboratory measurements on autoclaved aerated concrete. Determination of diffusion coefficient by standard steady-state cup method is done as well, for the sake of comparison. The measured results are discussed with regard to the practical application of the method in materials research and building practice.
Service life assessment of three historical building envelopes constructed using different types of sandstone is presented. At first, experimental measurements of material parameters of sandstones are performed to provide the necessary input data for a subsequent computational analysis. In the second step, the moisture and temperature fields across the studied envelopes are calculated for a representative period of time. The computations are performed using dynamic climatic data as the boundary conditions on the exterior side of building envelope. The climatic data for three characteristic localities are experimentally determined by the Czech Hydrometeorological Institute and contain hourly values of temperature, relative humidity, rainfalls, wind velocity and direction, and sun radiation. Using the measured durability properties of the analyzed sandstones and the calculated numbers of freeze/thaw cycles under different climatic conditions, the service life of the investigated building envelopes is assessed. The obtained results show that the climatic conditions can play a very significant role in the service life assessment of historical buildings, even in the conditions of such a small country as the Czech Republic. In addition, the investigations reveal the importance of the material characteristics of sandstones, in particular the hygric properties, on their service life in a structure.
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