Influence of fibre length and content on mechanical and cyclic behaviour of FRC

Fibre-reinforced concrete (FRC) mitigates brittle failures, but effectiveness depends on the type and physical properties of the fibre. In this study, the mechanical performance of concrete reinforced with short and long glass fibres (GF), polypropylene fibres (PPF) and steel fibres (SF) was evaluated. Two fibre volume fractions were considered (0.25% and 0.50%). After 28 days of curing, specimens were tested for compressive and tensile strength under static loading, and flexural strength under static and cyclic loading. The GF and PPF reduced the compressive strength compared with the control concrete (without fibre), whereas SF improved it by ∼7%. All FRCs exhibited enhanced tensile strength. In the concretes reinforced with GF (GFRC), tensile strength decreased with increasing fibre length and content. In the concretes reinforced with PPF (PPFRC), longer fibres reduced the tensile strength, while a higher content improved it. Flexural strength increased with fibre length and content for all FRCs, with SF resulting in the greatest improvement (79% increase compared with the control). Under cyclic flexural loading, the concretes reinforced with SF (SFRC) exhibited the highest peak load, with increases of 76% and 53% at different loading rates relative to the control. SFRC and PPFRC also demonstrated superior resistance to load drop compared to GFRC.