Flexural Toughness and Synergy Assessment of Pozzolanic and Non-pozzolanic Concrete Containing Steel Fibers With Varying Geometry

Brittleness poses a significant threat to the durability of cement-based materials over time. The simultaneous addition of pozzolans and fibers offers a novel and eco-friendly approach to tackle concerns regarding brittleness and environmental impacts associated with conventional cement concrete. This paper investigates the effects of pozzolanic substitutions such as silica fume (SF) and metakaolin (MK) for Ordinary portland cement on the mechanical and toughness performances of steel fiber reinforced concrete (SFRC). In the first part of the study, reference plain concrete mix with a water-to-binder ratio of 0.4 is mixed with different percentages of steel fibers with varying geometry, such as crimped steel (CS) and straight steel (SS) fibers, both as individual and hybrid combinations, to determine the mechanical properties. In the second part, the study evaluated how combining CS and SS fibers influence flexural toughness, aiming to identify combinations that may synergistically enhance performance. The study also examined the influence of pozzolans on the flexural toughness of hybrid steel fiber reinforced concrete (Hy-SFRC). An increase in workability was observed due to the hybridization of steel fibers. The increase in compressive strength, modulus of rupture, and modulus of elasticity was greater in pozzolanic SFRC compared to non-pozzolanic SFRC. The ternary mix of SF and MK showed 18.5%, 91%, and 18.7% improvement in 28-day compressive strength, flexural strength and modulus of elasticity compared to the reference mix. The hybrid combination of CS 1.5% and SS 0.5% was considered the best in terms of mechanical properties. The equivalent flexural toughness results indicated that, both binary and ternary pozzolanic Hy-SFRC was higher compared to non-pozzolanic Hy-SFRC, which can only be mapped to the stronger fiber-matrix bond. Also, the synergy quantification revealed that hybridization was most effective in the post-cracking stages. Hy-SFRC containing the ternary mixture of SF and MK provided a maximum toughness of 61.49 J measured up to L/150. Hy-SFRC mix containing a ternary pozzolanic combination of SF 10% and MK 10% gave the best results in flexural toughness, and the corresponding synergy values were found to be the maximum.