Synergistic performance of steel-polypropylene fibres in shrinkage and chloride resistance

This study investigates the effects of steel fibres (SF), polypropylene fibres (PP), and their hybrid blends (B1 and B2) on plastic shrinkage cracking and chloride ingress in early-age and hardened concrete. Plastic shrinkage cracking was evaluated using an image processing technique, showing that fibre reinforcement significantly mitigates cracking by enhancing crack-bridging capabilities and reducing shrinkage-induced stresses. Among the fibre mixes, the hybrid blends demonstrated superior performance, with B2, containing a higher proportion of PP, offering more effective crack-width control and minimising early-age cracking risks. Chloride ingress was assessed through volumetric and colorimetric methods. The results showed that fibre-reinforced concrete exhibited enhanced resistance to chloride penetration, with hybrid blends outperforming individual fibre mixes. PP promoted better crack dispersion, while SF more effectively resisted crack propagation and chloride ingress. The synergistic interaction between SF and PP not only improved the concrete’s microstructure but also enhanced its chloride-binding capacity. These combined mechanisms led to significantly improved durability, particularly in hardened concrete, where prolonged hydration further refined the microstructure and reduced permeability. The findings demonstrate hybrid fibre reinforcement as a cost-effective solution to enhance concrete durability, providing valuable insights for resilient infrastructure design in aggressive environments.