THE EFFECT OF TEMPERATURE DEPENDENCE OF THE SORPTION ISOTHERM AND MOISTURE CONDUCTIVITY COEFFICIENT ON THE MOISTURE TRANSFER IN THE WALL OF AERATED CONCRETE

Subject: calculation of heat and moisture regimes of enclosing structures made of aerated concrete taking into account the transfer of liquid moisture, which is determined by the values of moisture transfer coefficients. The results of calculations of the thermal and moisture characteristics of walls made of aerated concrete, carried out with the use of generally accepted regulatory methods, require confirmation since a physically unacceptable result can be obtained. Research objectives: the goal of the study was to determine the effect of temperature dependence of the sorption isotherm and the moisture conductivity coefficient on the moisture transfer in the enclosing structures of aerated concrete. Materials and methods: numerical modeling of nonstationary heat and moisture transport processes in a flat homogeneous wall made of aerated concrete D400 for climatic conditions of Tomsk city was performed. The proposed model reflects the movement of moisture due to the gradient of partial pressure of water vapor for the entire range of values of relative humidity in air or moisture content in the material, and for large values of relative humidity - due to a gradient of moisture content. In the calculations, we took into account the dependence of sorption moisture not only on the relative humidity of air but also on its temperature. To determine the coefficient of moisture conductivity, we used an approximation formula constructed on the basis of known experimental data. Interpolation formulas are presented that reflect the change in temperature and humidity of the outside air in accordance with the data of the normative literature. Results: when carrying out special test calculations, it was established that moisture transfer through the inner surface of the wall is practically insensitive to the temperature dependence of the sorption isotherm and coefficient of moisture conductivity. The moisture flow through the outer surface is also not sensitive to the temperature dependencies of these parameters. However, the dependence calculated with allowance for the temperature in the sorption isotherm differs significantly from the dependence without taking temperature into account, and in addition, the position of a maximum of the average overall humidity is displaced from November to December. From the above analysis it follows that taking into account the temperature dependence of the coefficient of moisture conductivity does not lead to a significant change in the characteristics of moisture transfer, both at the stage of removal of construction-generated moisture and in the process of further operation. The temperature dependence of the sorption isotherm only affects the moisture content of the outer surface, but the discrepancy does not exceed 1 % in absolute value. Conclusions: the use of the sorption isotherm and the coefficient of moisture conductivity without taking into account their dependence on temperature is permissible for calculating the heat and moisture regime in homogeneous structures made of aerated concrete under conditions of sorption moistening or drying.