The Effect of Fiber Content on the Post-cracking Tensile Stiffness Capacity of R-UHPFRC

Concrete cracking can be controlled by adding fibers to concrete, with the expected desirable behavior under serviceability conditions due to narrower close space cracks compared to similar concrete without fibers. Using fibers to produce Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) has enhanced the post-cracking tensile capacity of composite material and increased the related energy absorption capacity for the cracked member. Accordingly, the amount and type of fiber in the matrix affect post-cracking behavior. In this experimental study, specimens reinforced by conventional steel rebars with a constant cross-sectional dimension and reinforced steel ratio were tested. The tested variables were: 1) type and length of fibers; 2) fiber content. The Direct Tensile Test was conducted, and the tensile behaviour of specimens was obtained. The results showed that the increment in fiber content (80 kg/m³ to 160 kg/m³ in this research) or the combination of micro and macro steel fibers with the same content (80 kg/m³ for each fiber type) had no significant effect on the post-cracking stiffness capacity. Moreover, all the R-UHPFRC specimens provided the full tension stiffening with the quasi same post-cracking stiffness capacity close to the bare bar axial stiffness.