Preliminary study of the mechanical and hygrothermal properties of hemp-magnesium phosphate cements

The use of bio-based materials in the construction field is of great interest to society and the scientific community because of its highly sustainable character. They are formed by plant fibres and a binder, usually cement, lime or pozzolanic additives. Among the new vegetable fibres used, hemp-based biomaterials have attracted great attention in the recent years due to its excellent thermal and hygroscopic properties. However, they present a very low mechanical performance, which has intensified the search for better alternatives. In this research, the use of magnesium phosphate cement (MPC) as binder with different hemp additions (8%, 12%, 16% and 20% by weight) was evaluated. Thus, a new material made of hemp and MPC (heMPC) was developed. According to the results obtained, the heMPC could be used in floor or pre-cast structural applications since it presented enhanced mechanical (σmax = 0.714 ± 0.11 MPa with a 20 wt.% of hemp content) and thermal (λD = 0.103 W · m−1 · K−1, density = 600 kg · m−3) properties with respect other lime-based hemp biomaterials. Furthermore, the material exhibited good hygroscopic properties (water absorption by capillarity). Accordingly, this preliminary study allowed opening a new research line in the use of hemp bio-composites, in which other important properties are currently under investigation. The MPC used as a binder in this study was formulated with a by-product from the MgO industry, which increases the sustainability and recyclability criteria of the material developed.