Effect of Steel Fiber on Flexural Toughness and Fracture Mechanics Behavior of Ultrahigh-Performance Concrete with Coarse Aggregate

The present study investigated effect of fiber type and hybrid modes on flexural toughness and fracture mechanics behavior of ultrahigh-performance concrete (UHPC) with coarse aggregates was investigated. Results showed that with inclusion of coarse aggregate, UHPC had a higher compressive strength and elastic modulus, and that different fiber types and hybrid modes act similarly. Coarse aggregate brought a disadvantage to bonding strength, dispersion coefficient, and orientation factor of steel fiber. For UHPC mixtures with coarse aggregates, the effect of fiber type and hybridization was slight on the first cracking strengths, but it was significant on the ultimate flexural strengths. In addition, compared with UHPC beams with smooth fiber, those with hooked-end fiber blended with smooth fibers had a better flexural performance, i.e.,flexural toughness values, fracture energy, and characteristics length. Therefore, fiber hybridization was one of most effective alternatives to improve the flexural toughness and fracture mechanics behavior of the UHPC incorporating coarse aggregates. (C) 2018 American Society of Civil Engineers.