Resilience of silicone barrier in building envelopes: From conventional concrete to hempcrete

Long-term performance of silicone-based, fluid-applied membranes used as moisture barriers on conventional concrete and the emerging bio-based building material, hempcrete, was evaluated under a controlled accelerated aging program for up to one year. A combination of thermal Thermogravimetric Analysis and Differential Scanning Calorimetry; chemical Fourier Transform Infrared Spectroscopy; and microstructural Scanning Electron Microscopy coupled with Dispersive X-ray Spectroscopy analyses was employed to examine the influence of temperature, moisture, and substrate chemistry on membrane degradation. Under dry conditions, the membranes showed no substantial thermal, chemical, or microstructural degradation on either substrate, indicating that temperature alone, up to 90 °C, was insufficient to compromise membrane structure. Under wet conditions, however, degradation strongly depended on chemistry generated by the adjacent substrate. In contact with wet concrete, the membrane showed pronounced degradation at elevated temperatures, particularly at 70 and 90 °C, where high alkalinity and enhanced leaching of alkaline, calcium-bearing, and other cementitious species led to reduced thermal stability, loss of polymer integrity, and chemically heterogeneous mineral-rich surface deposits. In contrast, under wet hempcrete exposure, the membrane showed comparatively stable thermal and chemical behavior at 70 and 90 °C. Localized Ca–O–C-rich deposits and surface discoloration were observed, but the primary silicone-related thermal and chemical signatures remained largely unchanged. Long-term assessment at room temperature and 50 °C was not feasible because mould growth caused early termination of these conditions. An Arrhenius-based thermal degradation analysis indicated temperature and pH coupling as the primary factor governing degradation. In wet concrete, increasing temperature increased alkalinity and accelerated degradation, whereas in wet hempcrete, increasing temperature reduced alkalinity, likely due to enhanced release of hemp-derived soluble organic compounds. These results highlight the distinct substrate–membrane interactions in hempcrete versus conventional systems and emphasize the need to consider coupled thermal–chemical effects when designing durable moisture barriers for sustainable building envelopes.