Hemp fibres/cement interactions: influence on the mechanical properties of the composite

Hemp fibres introduced in a cement paste confer interesting properties to the composite. To understand the mechanical interactions between hemp fibres and the cement matrix it is necessary to have a better knowledge of the mechanical properties of the composite. By a high pectin content, these fibres can fix calcium and hydroxyle ions on their surface. Pectin and consequently fibres, by their calcium adsorption, will prevent the precipitation of calcium silicate hydrates (CSH), which implies a delay of setting time. By the alkaline medium of the cement paste some of sugars or acids contained in the compounds of hemp fibres are degraded, which increase the surface roughness of the fibres. However, the quantity of lixiviated sugars or acids is too low to have an influence on a such environment. The calcium coating on fibres surface involves a strong adhesion between fibres and the cementitous matrix. It results in a high increase of the mechanical properties for an optimal fibre content. Such composites have a highest stiffness and tensile strength than cement paste, and could be consequently interesting in building applications.