Experimental evaluation of the effectiveness of fiber orientation methods on the mechanical performance of UHPFRC

The effectiveness of the use of fibers in Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) can be limited by their random orientation in the cementitious matrix. Oriented steel fibers, on the other hand, show significant promise in enhancing the tensile and flexural properties of UHPFRC specimens when the principal tensile stresses predominantly align in a single direction. Despite various proposed methods for orienting steel fibers in UHPFRC, their comparative impact on mechanical properties remained unclear. To bridge this gap, three different strategies were examined in this study, namely: i) chute with vibration table, ii) L-shaped device, and iii) electromagnetic field with vibration table, aiming at controlling the steel fibers orientation in UHPFRC specimens. Uniaxial tensile, four-point flexural, and compressive tests were conducted to examine the influence of different orientation methods on mechanical properties. The experimental findings revealed that compared to randomly oriented fibers, oriented steel fiber UHPFRC had superior tensile, flexural, and compressive strength. Additionally, fiber orientation led to improved consistency of the UHPFRC properties as well as thinner, more densely distributed cracks, regular fracture surfaces, and lower elastic modulus and Poisson's ratio. Electromagnetic field orientation proved to be the most effective orientation method, L-shaped device method the least effective due to heightened fluidity demands in the mixture, and the chute with vibration method ranked in between. This research represents a thorough investigation into the comparative efficacy of different methods for orienting steel fibers in UHPFRC, shedding new light on the optimal approach to enhance mechanical properties.