Hygric properties of wheat straw biocomposite containing natural additives intended for thermal insulation of buildings

Straw concrete is a biobased composite developed for thermal insulation of new buildings and thermal rehabilitation of old buildings. It is made of the combination of wheat straw, lime or plaster binder and natural additives (hemoglobin, casein, gelatin). The natural additives are used to improve the thermal and mechanical properties of the material. The characterization of these composites has shown an attractive thermal conductivity and an acceptable mechanical strength. The present paper focuses on the hygric characterization of these materials which have different constituents (straw aggregates, binder and additives). Three properties were experimentally determined, namely, sorption-desorption curves, water vapor permeability and moisture buffer value (MBV). These hygroscopic properties are of great importance when it comes to the comfort of the building. The isothermal water vapour diffusivity was also estimated from the sorption curve and the water vapor permeability. The impact of the sample thickness on the moisture buffer value (MBV) was also highlighted. The results showed that the studied composites have excellent hygric properties which can contribute significantly to ensure hygrothermal comfort in buildings. These hygric performances are competitive with those of other insulating bio-based materials studied in the literature and better than those of conventional materials used in construction.