Relationship between hygrothermal and acoustical behavior of hemp and sunflower composites

Abstract

The experimental characterization of most of the hygrothermal properties of bio-based porous materials, which are characteristic for their double-scale porosity, requires for the samples to stabilize their liquid water content. Furthermore, such measurements often take several weeks to several months. In contrast, acoustical measurements can be realized very quickly by using simple and relatively inexpensive test benches such as Kundt's tube. In this article, we investigate the existence of relationships between the hygrothermal and acoustical parameters of the porous media (porosity, resistivity, tortuosity, etc.), in order to provide ways to by-pass hygrothermal measurements by performing an indirect characterization of the material properties using acoustical measurements. Two expressions have been found to properly estimate the thermal conductivity and the water vapor permeability of the studied hemp and sunflower pith composites from acoustical measurements. However, further tests will be needed in order to establish the limits of these estimations (for which materials and in which conditions are they applicable) and further research will be made to shed light on the cause of these relationships. These two properties are capital in the conception of new eco-responsible building materials since a low thermal conductivity helps to improve energy efficiency, and the water vapor permeability plays a major role on thermal inertia, moisture regulation and on comfort inside the building. With further research, these results are expected to accelerate the development of sustainable construction materials and to better consider the complex hygrothermal behavior of such materials.