The use of pith in the formulation of lightweight bio-based composites: Impact on mechanical and hygrothermal properties

Abstract The use of bio-based concretes or renders is rapidly developing. These sustainable materials present many advantages such as their acoustical and hygrothermal properties. These bio-sourced composites are made of vegetable aggregates, associated with a hydraulic binder. One of the most common aggregates is hemp shiv, which is an agricultural waste. However, hemp shiv is not available in big quantities nor in all geographical areas, so it seems interesting to introduce other bio-sourced aggregates in order to increase the availability. Sunflower and maize pith are unexploited agricultural by-products which can have a great potential as insulation materials. To use these aggregates, it is essential to assess first their interactions with different binders. In the present paper, the impact of density and type of aggregate (either hemp shiv or pith) on several key physical parameters was evaluated. These parameters were the uniaxial compressive strength test, the thermal conductivity, the sorption isotherms and the water vapor permeability, as well as the moisture buffering value (MBV). The use of pith shows promising results in terms of thermal and hygroscopic performances, the results also indicate that specific precautions should be taken to preserve the porosity of the soft pith material to optimize the hygrothermal performances.