Assessment of suitability of some chosen functions for describing of sorption isotherms in building materials

Abstract

This paper presents results of tests and studies conducted on six common building materials, used for constructing and finishing of external walls. These included: ceramic brick, silicate brick, autoclaved aerated concrete, cement mortar, cement–lime mortar and cement mortar modified with polypropylene fibers. Each of these materials is distinguished by the other structure of porousness, affecting both the course of sorption processes and the isotherms obtained. At first, measurements of moisture sorption kinetics at temperatures of 5, 20 and 35 °C were performed, each time at six levels of relative humidity. Then, when the sorption processes expired, equilibrium moisture sorption values were determined for the materials in 18 individual temperature and humidity conditions. The experimental data were used to determine the sorption isotherm courses for each material at the three temperatures. Then, theoretical analysis was performed in order to determine, which of the models available in the literature described the sorption isotherms of the concerned building materials the best. For each material and each of the three temperature values, twenty-four equations were tested. In each case, those of them were identified which ensured the best matching between the theoretical courses and the experimental data. The obtained results indicate that the Chen’s model proved to be the most versatile. It ensured a detailed description of the sorption isotherms for each material and temperature tested.