On the mechanical behaviour of natural sisal fibre reinforced cement paste

As the construction industry is always in seek of stronger and more sustainable materials, the use of natural fibres as a reinforcement agent has been considered, for both enhancement of mechanical properties and decreasing carbon footprint. Specifically, sisal fibres (agave sisalana) present a tensile strength up to 880 MPa, as having cellulose as the main constituent. Hence, the addition of varying lengths and fibre concentrations have been explored as reinforcements in cement paste. A composite mechanic's approach has been applied to estimate the minimum volume fraction and fibre's critical length, which was further characterized by water uptake, as it directly influences cement consistency. Furthermore, the flexural modulus of rupture (MOR) and compressive strength were also assessed. It was found that 1.0% (vol.%) of 20 mm length could increase the MOR up to 150.71% while giving up almost 25% in compressive strength. On the other hand, 0.5% (vol. %) of 5 mm length reached a 103.42% increase in the MOR while reducing only 7.25% in compressive strength. Therefore, it was concluded that shorter fibres were 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 mineralization.