Experimental investigation of moisture intake/release of CLT in rapidly changing climate

This study investigates cross-laminated timber (CLT) and its response to rapid changes in ambient relative humidity. The experimental research is motivated by the increasing use of CLT in Sweden, driven in part by growing focus on environmentally sustainable construction. This trend has created a need for greater understanding of the material to ensure long-term building quality. The studied CLT element consists of three lamella layers, each 40 mm thick, and is equipped with multiple sensors measuring relative humidity and temperature at the center of each layer. The element is placed in a controlled climate chamber where the relative humidity is rapidly altered weekly between high (85%) and low (35%) levels. Thereafter the relative humidity changes after every two weeks (four-week relative humidity cycle). The temperature is maintained at 20°C throughout the experiment. The study aims to evaluate the effects of short-term rapid relative humidity changes on the moisture absorption and desorption in CLT. It investigates the hysteretic loss or retention of moisture within the CLT element after each full relative humidity cycle. The rapid transition from wetting to drying or vice-versa is analysed to see how the moisture content profile develops at each of the CLT layers. Additionally, moisture gradients are calculated to estimate when and where there is a potential risk of crack formation in the CLT element. The results indicate an expected variation in the moisture content profiles of the inner and outer lamella layers of the CLT to the rapid changes in ambient humidity, with variations also observed along the length of the CLT element. Due to their exposure to the changing climate, the absorption and desorption rates of moisture content of the outer top and bottom layers of the CLT were observed to be similar, however, during drying for example, the moisture content lost from the inner layer has an influence to the relative humidity recorded by the measuring system at the outer layers. The moisture gradient highlights the areas most prone to cracking due to climate changes, with the highest risk observed during desorption, particularly at the outer edge between the top and middle lamella.