Hygrothermal behavior of cement mortar containing bio-based phase change materials and miscanthus fibers: Multiscale experiments and numerical modeling

The integration of bio-based phase change materials (PCMs) and natural fibers in building materials offers significant potential for improving hygrothermal performance and energy efficiency. This study investigates a novel hybrid mortar combining microencapsulated bio-based PCMs and miscanthus fibers (MF) using a multiscale experimental and numerical approach. Key hygrothermal properties, including thermal conductivity, effective heat capacity, water vapor permeability, capillary suction, free saturation, and sorption/desorption isotherms, were characterized at the material scale. The results demonstrate that the simultaneous incorporation of microencapsulated PCMs and MF reduces thermal conductivity by up to 67.5% but diminishes the effect of moisture transport enhancement typically provided by MF, leading to lower water vapor permeability and reduced moisture content. A representative wall specimen was tested under controlled bi-climatic conditions to evaluate its response to temperature and relative humidity cycling. Experimental data were compared the numerical simulations based on the Künzel model, showing strong agreement and highlighting the wall's robust thermal and hygric buffering capacities. Overall, this hybrid material provides enhanced thermal insulation and limits moisture diffusion, offering a promising solution for energy-efficient building envelopes.