Effect of Aspect Ratios of Hooked End and Straight Steel Fibers on the Tensile Strength of UHPFRC

Ultra-high-performance fiber reinforced concrete (UHPFRC) exhibits strain hardening and multiple cracking behaviors when subjected to tension load. There are limited studies on the effect of steel fiber aspect ratios on the tensile performance of UHPFRC. Also, tensile testing of cementitious materials and composites is challenging due to the lack of a standardized direct tensile testing method with wide variation. This study experimentally investigated the effect of hooked end and straight steel fiber aspect ratios on the tensile behavior of UHPFRC with a 2% fiber volume fraction. A direct tensile test setup was first developed to obtain good alignment and desirable experimental data in an attempt to overcome some of the difficulties with other tensile tests. UHPFRC failure modes, stress-strain relationships, initial cracking strength, and peak strength, as well as stress-crack width relationships, were characterized and analyzed. The developed tensile test results showed that, as the aspect ratio of the hooked end fiber increased, the ductility ratio and the characteristic stress increased. However, the effect of the straight fiber aspect ratio on tensile behavior was not more significant than that of the hooked end fiber aspect ratio. Over-large straight fiber aspect ratios led to a reduction in characteristic stress and ductility ratio and an acceleration of crack propagation in the early softening phase. In comparisons of the developed direct tensile test and other test methods in terms of peak strength, the small-scale briquette tensile test showed the potential to become an alternative to conservatively evaluate UHPFRC composition strength of.