Experimental investigation of the influence of the relative humidity of air on the drying process of porous building materials

The paper presents the experimental analysis of influence of the relative humidity of drying air on the drying process of porous building materials. Investigations were conducted by applying the stand which worked in a closed-loop flow and equipped with the following elements: the cooler (condenser), fan with variable rotation speed, throttle, humidifier, heater and control and acquisition systems. During experiments the temperature and velocity of air were equal to 40 degrees C and 3 m/s, respectively, while its relative humidity was varied in the range from 16 to 40%. Two different materials were investigated, i.e., the red brick and mortar. Specimens were placed in the duct and had the top surface exposed to flowing air. Variations of the moisture content and temperature in considered building materials were measured by system of two force meters and thermocouples, respectively. The relative humidity of drying air significantly influenced on the drying process of building materials. The increase of the relative humidity of drying air resulted in the rise of the drying duration, the decrease of the drying rate and the increase of the level of temperature plateau (i.e., equilibrium temperature) which resulted from evaporation in the medium. Moreover, for the mortar drying rates were found much slower than for the red brick.