Microstructural Characterization and Mechanical Performance of Sisal Fibre-Reinforced Concrete

Concrete’s brittleness and limited tensile resistance necessitate reinforcement strategies, and natural fibres such as sisal have emerged as sustainable alternatives to synthetic fibres due to their biodegradability, availability, and tensile strength. This study investigated the microstructural behavior and static load performance of sisal fibre-reinforced concrete (SiFRC) with varying fibre contents (0.1–0.5% by weight) and aspect ratios (100, 150, 200). Microstructural analysis was conducted using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX), while mechanical performance was evaluated through compressive, flexural, and split tensile strength tests in accordance with BS EN and ASTM standards. The findings revealed that fibres with 30 mm length and moderate dosages enhanced fibre–matrix bonding, reduced porosity, and promoted effective crack bridging, resulting in superior microstructural integrity and strength performance. At 28 days, the 0.1% fibre content with aspect ratio 200 achieved compressive strength of 30 N/mm² and split tensile strength of 3.40 N/mm², while flexural strength peaked at 4.73 N/mm² in the 0.1/150 mix. Excessive fibre content (≥0.5%) reduced compressive strength due to clustering and void formation, although modest improvements in flexural and tensile properties were observed. The study concludes that optimal fibre dosage and aspect ratio are critical for achieving durability and strength balance in SiFRC. It is recommended that future structural applications adopt fibre lengths of 30–40 mm at dosages not exceeding 0.3–0.4% by weight to maximize bonding efficiency while maintaining workability.