Study of the Equilibrium Sorption Humidity of the Materials of the Enclosing Constructions of Buildings at a Temperature -20 °C

Abstract

Equilibrium sorption humidity (further: sorption humidity) together with the thermal conductivity is the most important thermo-technical property of building materials, since itlargely determines the course of the process of heat- and moisture transfer through the enclosing constructions of buildings and, consequently, also the thermo-technical properties of these constructions. The isotherms of the absorption of vapors of water for foam concrete, cellular concrete, expanded-clay lightweight concrete, expanded-clay-pearlite lightweight concrete, expanded-shungizitlightweight concrete and arbolit were experimentally (by exiccator method) determined at temperatures -20, -10,4, +1,2, +20 and +35 °С. The analysis of the obtained results showed that the sorption humidity of all investigated materials increases with the temperature decrease from +35 °C to -10,4 °C. However, at a temperature -20 °С sorption humidity decreases, and what is more, that, it becomesless than the sorption humidity of these materials at a temperature of +20 °С. The reasons for the decrease of the sorption humidity of building materials at a temperature -20 °С in comparison with the values of this property at a temperature of +20 °C appears:

• with the relative humidity of air φ< 80%: the sharp decrease of the mobility of water molecules of the first adsorbed monolayer at a certain temperature, which belongs to temperature range from -10,4 to -20 °С, and, as a result, a sharp increase of thelifetime of a water molecule in the first adsorbed monolayer;


• with the relative humidity of air φ> 80% appears the second reason for the decrease of the equilibrium sorption humidity of building materials at a temperature -20 °C, namely, the freezing of some share of the capillary-condensed water and blocking by formed fixed ice the access of water vapor into the internal pore volume of material.