Hygric properties and adsorption characteristics of simple and dual coblayers of bio-sourced building materials

Abstract

With the world's population increasing and energy demand on the rise, innovative materials are becoming one of the most important solutions for building designers. This paper focuses on the hygrometric properties of bio-sourced materials, specifically new cob mixes used for insulation and load-bearing wall elements, those materials consist of various mixes of French soils and fibers with different water contents. Experiments are conducted using the isothermal sorption and the one-sided moisture transmission tests in transient and steady states. The hygrometric properties of the homogeneous bio-sourced samples (a thermally insulating material, and a structurally mechanical material), and composite bio-sourced materials (both structural and insulating materials) were investigated. Five salt solutions were used to measure distribution of the relative humidity in each material. The moisture content and moisture transfer resistance of the insulating material is more important than the structural material. The composite material has the lowest moisture flux and the adsorption is influenced by the multilayers. Results show that as much as the material contains fibers, as much as its impermeability increases and its diffusivity decreases. Diminution of the bio-sourced material density increases its resistance to the moisture transfer. Using the Freundlich isotherm model, the volumetric water content, sorption capacity and water content were correlated for all the tested samples. The Moisture diffusivity for the studied bio-sourced materials drops strongly in the dry region where the relative humidity is lower than 30%. In the wet state, the moisture diffusivity decreases slightly.