Effect of wetting time in the sorption and in the thermal conductivity of the most commonly used structural materials

During the thermal assessment of buildings, proper understanding and knowledge of the thermal behavior of the materials is required. Certain indoor and outdoor conditions can cause moisture transfer and could change the thermal properties of buildings (e.g. thermal conductivity, resistance, thermal diffusivity, specific heat capacity, etc.). In this technical note, a research report can be found on the measured thermal conductivity after drying and wetting the samples. For the measurements, we used a dry-heat laboratory oven (Venticell 111) apparatus to dry the samples and a climatic chamber (Climacell 111) to wet the materials in order to get the values. By applying these two chambers, we were able to reach the moisture content of different humidity levels and create the kinetic wetting curves for each sample. To measure the thermal conductivity, a heat flow meter type Holometrix 2000 was used. During the measurements, five different types of materials were used (solid brick, lightweight and foam concrete, plasterboard, corkboard). In order to reach acceptable accuracy, three measurement series were carried out on the samples at each wetting times. During one series, the thermal conductivity was measured 10 times, and the average of the 13 thermal conductivity results gave the final value. Moreover, from the measurement results, new equations and functions were created to show the relationship between the thermal conductivity and the moisture content of the materials. Our results showed that after wetting the samples in a climatic chamber at 293 K and at 90% relative humidity, the kinetic function (time dependence) of adsorbed water increased in the cases of all the materials used; however, thermal conductivity only increased considerably in the cases of the two different types of concrete and of the plasterboard.

Practical application: The role of insulation materials in the building energy and moisture balance is more significant compared to the other materials of the building structures. The high moisture load will require the change of the thermal parameters of the materials. Moisture is a common cause of building degradation. In fact, much of what we know about applied building science today originates from early work investigating moisture impact on buildings, while the severity of moisture problems varies greatly depending on climate. These estimations based on the laboratory measurements of these values of the insulating materials are very important either for the manufacturers or the contractors, planners, and designers.