Comparative Hygrothermal Performance of a Mortar Wall with Micronized Miscanthus Fibers versus a Reference Wall: Experimental and Numerical Analysis

Miscanthus fibres are regarded as a sustainable, eco-friendly material with high hygroscopicity and low thermal conductivity. Although promising at the material scale, further wall-scale evaluations are needed. This study investigates the hygrothermal performance of a biobased mortar wall containing micronized miscanthus fibers, compared to a conventional mortar wall. An experimental bi-climatic device was used to simulate distinct outdoor and indoor environments by exposing each side of both walls to different hygrothermal conditions. Temperature and relative humidity (RH) data were collected using a network of sensors, enabling a thorough analysis of the walls' hygrothermal response at various depths under both dynamic and steadystate regimes. Additionally, a numerical model based on the Künzel approach was employed to predict and compare temperature and humidity behavior within the biobased wall. Results showed good agreement between experimental data and numerical predictions, with a maximum temperature deviation of 4 • C at 5 cm depth. However, RH predictions revealed discrepancies, notably a 5 % deviation at 7.5 cm depth. Statistical validation indicated model accuracy. Furthermore, tests involving cyclic moisture changes under isothermal conditions demonstrated that the miscanthus wall acts as an effective hygric regulator, maintaining stable indoor condition as outdoor relative humidity increases. Higher prediction errors observed at boundary depths (0 and 10 cm) were attributed to external airflow during experiments. Overall, the numerical model reliably predicted temperature variations, and RH estimations were acceptable considering material heterogeneity. These findings confirm the potential of miscanthus fiber-reinforced materials for improving hygrothermal performance in building construction.