The Impact of Hygrothermal Aging on Stability and Water Pressure Resistance of Building Envelope Membranes

Building membranes, specifically those designed as water-resistive barriers (WRBs), play a pivotal role in construction, serving as protective barriers against moisture infiltration from environmental stresses like wind-driven rain, thereby influencing the durability of buildings. As these materials age, changes in their structure can significantly affect their performance in resisting water ingress, with potential implications for the durability of building structures. Therefore, this research investigates the transformative effects of hygrothermal aging on the water-resistance performance, hydrophobicity, chemical integrity, and thermal resistance of the WRBs with a specific focus on non-woven polyethylene, self-adhesive polyethylene, and asphalt-saturated kraft paper, which represent a diverse array of materials commonly used in the construction industry. Two distinct combinations of hygrothermal conditions were designed to age the sample which are 90% RH at 70°C and 40% RH at 40°C, over different time spans of up to eight months. Water pressure resistance was evaluated using a hydrostatic head tester to assess the membranes' ability to withstand water pressure under various aging conditions. Hydrophobicity, a critical characteristic influencing moisture management, was determined through contact angle measurements. Additionally, Fourier Transform Infrared Spectroscopy (FT-IR) was used to detect chemical changes in membrane composition. The thermal stability of the WRBs was also analyzed by thermal gravimetry analysis (TGA). The study shows that aging leads to a slight reduction in the average of water pressure resistance, indicating slight decreases in barrier effectiveness. For contact angle, no significant change is observed in the hydrophobicity of building paper but a very slight decrease in Spun-bonded Poly Olefin film (SPBO) and self-adhesive film. FTIR analysis reveals subtle oxidation changes in building paper, while TGA indicates only minor thermal stability degradation on this membrane and no significant alternation in the chemical integrity of SBPO and self-adhesive film.