Influence of Temperature on the Sorption Isotherms of Building Materials

Building materials are porous and interact with moisture in the ambient air through sorption phenomena. However, under real world using conditions, the temperature of these materials varies constantly. The problem is that this temperature variation influences the materials' ability to adsorb or desorb moisture, which can distort the assessment of their hygrothermal performance. It is therefore necessary to analyze and model the effect of temperature on these isotherms in order to better predict the behavior of materials under real conditions. The aim of this study is to carry out experimental analysis and modelling of the sorption isotherms of construction materials, in particular cement bricks. The equilibrium desorption and adsorption water contents of the materials were determined at 35°C, 40°C and 50°C using the static gravimetric method. Equilibrium was obtained between 28 and 30 days for desorption and between 21 and 27 days for adsorption at all three temperatures. The results show that the isotherms obtained have a sigmoidal shape and are classified according to International Union of Pure and Applied Chemistry (IUPAC) in the category of type II isotherms. The effect of temperature on sorption isotherms was evaluated. The moisture content of the materials decreases with increasing temperature. The effect of hysteresis is observed for all three temperatures. The experimental points were approximated by the GAB (Guggenheim - Anderson - Boer), Henderson and Oswin models to describe all the isotherms for all the ranges of relative humidity and temperature used. A comparison of these three models shows that the Henderson model is the most appropriate for describing the sorption isotherms of our materials.