Magnesium phosphate cement incorporating sheep wool fibre for thermal insulation applications

The increasing use of synthetic fibres in clothing and the high quality of sheep wool fibre (SWF) from the Australian and New Zealand market leads to a decline in the interest in SWFs produced in European countries, considering them as waste that could be valorised within the framework of a circular economy. The use of natural fibre in cement-based composites presents the main issue of durability due to the alkaline pH media of conventional cement. The use of a low-pH cement could improve the viability of combining natural fibres in this low-pH cement as matrix for developing composites. One of these low-pH cements is magnesium phosphate cement (MPC). As a ceramic material the MPC presents high thermal conductivity (similar to 1 W m(-1) K-1) to be used as isolating material. The present work combines MPC formulated with an industrial by-product (low-grade magnesium oxide; LG-MgO) and Spanish SWF, to develop new sustainable cementbased materials (Sust-MPC-SWF) for thermal building insulation applications. The physical, thermal, and mechanical properties of Sust-MPC-SWF were evaluated to determine the optimal formulation through a design of experiments (DoE). Thirteen formulations designed by DoE were conducted with different sheep wool fibre/cement (SWF/C) and sheep wool fibre/extra water (SWF/EW) ratios. A statistical model was obtained and the optimal formulation (SWF/C = 0.36 and SWF/EW = 0.25) was validated. The increase in SWF content led to an enhancement of thermal and acoustic insulation properties of Sust-MPC-SWF, with similar results to other building materials commercialized with these features.