Uniaxial tensile behavior of ultra-high performance fiber-reinforced concrete (uhpfrc): Experiments and modeling

Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) is considered a promising material for many structural applications where high strength and high energy absorption capacity are required. The purpose of this work is to study the uniaxial tensile behavior of soft cast (flowable at casting time) UHPFRC by varying the amount of hooked steel fibers (30-mm long) from 0% up to 2.55% by volume. Direct tensile tests have been performed on dog-bone shaped specimens and Digital Image Correlation (DIC) has been used to measure displacements and deformations and to monitor the evolution of cracks. Then, a phase-field model has been implemented in a FE code and numerical simulations have been performed to better understand the effects of different fiber dosages on the mechanical behavior of UHPFRC composites and on their post-elastic evolution. Concrete matrix and fiber reinforcement have been modeled as brittle and elasto-plastic phases of a mixture, whose internal energies are enriched by non-local damage and plasticity contributions. The different failure mechanisms observed in experiments have been reproduced, including the ductile failure experienced by specimens with sufficiently high fiber dosage, which distinguishes for a strain-hardening phase of matrix multi-micro-cracking that anticipates material failure.