Résumé
The development of low-embodied carbon materials incorporating bio-aggregates is attracting increasing attention as a sustainable alternative to mineral and fossil derived materials. This interest is driven by growing awareness of waste management challenges and sustainability policies aimed at decarbonizing the building sector. This study explores the valorization of rice husk and rice straw with distinct sizes and morphologies as aggregates for the development of hybrid husk-straw concretes with enhanced hygrothermal performance. Hybrid formulations were produced using rice husk (RH), milled straw (ST), and cylindrical cut straw particles (RSBC). Two formulation strategies were considered: binary mixtures comprising 50 wt% RH and 50 wt% ST with varying straw particle sizes, and ternary mixtures in which RSBC partially replaced milled straw at rates of 25–33 wt%. Results showed that thermal conductivity decreases linearly with increasing straw particle size, from 0.122 W/m·K for concretes containing the finest particles to 0.101 W/m·K for those incorporating elongated particles. Furthermore, substituting 25% of milled straw with cut particles RSBC reduced thermal conductivity by 15%, whereas a 33% substitution yielded reductions of up to 25%. Additionally, hybridization significantly improved hygric properties, with moisture buffering capacity and water vapor permeability reaching 2.19 g/(m²·%RH) and 1.81 × 10 cut particles ⁻¹ ¹ kg/(m·s·Pa), respectively, for the best-performing formulation. Consistently, concretes containing RSBC exhibited higher sorption capacity across the entire relative humidity range. Moreover, compressive strength measured at 5% strain ranged from 0.19 to 0.35 MPa, confirming suitability of these concretes for non-load-bearing building applications.