On the mechanical behaviour of cement paste reinforced with natural sisal fibres

As the construction industry is always in search of stronger and more sustainable materials, the use of natural fibres as reinforcement has been considered for both enhancing mechanical properties and decreasing carbon dioxide footprints. Sisal fibres (Agave sisalana) have a tensile strength up to 880 MPa, with cellulose as the main constituent. The addition of sisal fibres of varying lengths and concentrations was explored as reinforcement in cement paste. A composite mechanics approach was applied to estimate the minimum volume fraction and fibre critical length, which was further characterised by water uptake, flexural modulus of rupture (MOR) and compressive strength. It was found that 1.0% (vol.%) of 20 mm long fibres could increase the MOR by up to 150.71% with a decrease of almost 25% in compressive strength. In contrast, 1.0% (vol.%) of 5 mm long fibres produced a 103.42% increase in the MOR while reducing the compressive strength by only 9.67%. Therefore, it was concluded that lower fibre concentrations are more beneficial concerning mechanical performance. Ultimately, some sort of fibre treatment is suggested to avoid water absorption, which can affect the overall workability of fresh cement paste and long-term durability aspects such as alkaline hydrolysis and mineralisation.