Influence of Water Content and Porosity on the Thermal Conductivity of Earthen-Straw Composites

Abstract

In the context of sustainable construction, bio-based materials such as earthen–straw composites are gaining increasing interest due to their thermal and environmental properties. This study aims to evaluate the influence of porosity and water content of the raw earthen matrix on the effective thermal conductivity of the earthen–straw composite. The thermal conductivity of the earthen matrix is first estimated using several analytical models (Johansen, Côté and Konrad, and Yang and al.), by considering different porosities (0.35, 0.37, 0.40, and 0.45) and water contents (0–20 %). The Côté and Konrad model has been selected for its ability to predict accurately the thermal conductivity of soils with low water content, providing a more realistic representation of the thermal behavior of the earthen matrix. Then the effective thermal conductivity of the earthen–straw composite is calculated using the Hashin-Shtrikman theoretical method and has been compared with numerical simulations for various straw volume fractions (5 %, 10 %, 15 %). The results show a strong sensitivity to water content and matrix porosity, confirming the consistency between analytical and numerical approaches. This work represents a step toward optimizing the thermal performance of earthen composite materials.