Fiber orientation distribution and tensile mechanical response in UHPFRC

In this study, the crucial effect of the fiber orientation distribution on the tensile mechanical response of ultra high performance fiber reinforced concretes (UHPFRC) is discussed. A direct tension test method was used to characterize the tensile response of a UHPFRC material as well as to assess the actual tensile response along the principal directions in a real-scale UHPFRC structural element. Moreover, the actual fiber orientation distribution was evaluated in representative sections through an image analysis technique. The experimental results validated the anisotropy in the fiber orientation distribution and, consequently, in the tensile mechanical properties as a consequence of the casting process and the flow pattern. The concept of the fiber orientation factor was discussed as well as the approaches currently adopted to implement robust and reliable safety factors accounting for the fiber orientation distribution impact on the design methodologies for UHPFRC. Finally, the need of a comprehensive design framework for UHPFRC structures was highlighted in order to allow for fully exploitation of the material properties.