Influence of the spruce strands hygroscopic behaviour on the performances of wood-cement composites

In wood wool cement composites, the influence of natural fibres is the main factor leading to the instability of the final product. During the manufacture, small variations in wood properties result in inhomogeneous density and strength of the boards. Among the accountable factors, the hygroscopic behaviour of the wood can deeply affect the cement hydration. However, the competitive water absorption mechanism between wood strands and cement is not fully understood. This paper will address the absorption behaviour of wood wool strands in combination with cement. A model for calculating the water to binder ratio of the paste in presence of wood is proposed and validated by NMR and isothermal calorimetry. Finally, the mechanical performances of the composites are tested for different water amounts, verifying the proposed model and defining the conditions for the optimal bending strength.