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ABSTRACT Strain rate-dependent shear behavior of ultra-high-performance fiber-reinforced concretes (UHPFRCs) with confining pressure was investigated using a new shear test setup in an improved strain energy impact machine (I-SEFIM). Different [...]

ABSTRACT This study investigates the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) with single and hybrid steel fibers. To do this, three different types of steel fibers, i.e., hooked, twisted, [...]

This study investigates the implications of fiber hybridization on the flexural behavior of ultra-high-performance concrete (UHPC). To do this, we considered three straight steel fibers with different lengths, If, of 13 mm (short), 19.5 mm (medium-length), and 30 mm (long) at various volume fractions. Test results indicated that the hybrid use of long and medium-length fibers effectively improved the flexural performance in terms of post-cracking strength, deflection capacity, toughness, and cracking behavior, whereas the hybrid use of long and short fibers generally decreased the performance. To verify this observation, a micromechanical analysis was performed for obtaining the fiber bridging curve, which most significantly influences the post-cracking properties. The hybrid use of long and short (or medium-length) fibers provided negative synergy values in toughness due to several detrimental effects. The complementary energy in the fiber bridging curve increased with an increase in the fiber length, so that an increase in the proportion of short (or medium-length) fiber clearly decreased the complementary energy. Based on a proposed equation for the relationship between the normalized modulus of rupture and the fiber reinforcing index, we found that it is possible to produce deflection-hardening behavior of UHPC with straight steel fibers when the fiber reinforcing index is higher than 0.5. Keywords: Ultra-high-performance concrete Fiber hybridization Flexure Toughness Fiber bridging capacity, 1. Introduction The excellent mechanical strength of ultra-high-performance concrete (UHPC) results in a great decrease of structural weight. Overall, the weight of structures made of UHPC is only 1/3 or [...]

ABSTRACT The direct tensile stress versus strain responses of ultra-high-performance fiber-reinforced concretes (UHPFRCs) at high strain rates (10-150 [s.sup.-1]) were investigated using an improved strain energy frame impact machine. The [...]

ABSTRACT Recently, ultra high performance fiber reinforced concrete (UHPFRC) with compressive strength over 180 MPa and tensile strength of 10 MPa has been developed. Since UHPFRC not only has superior [...]