Effect of Fiber Orientation on Compressive Strength of Ultra-High-Performance Fiber-Reinforced Concrete

The structural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) is mainly affected by the fiber volume fraction, the fiber distribution, and the fiber orientation. Fiber orientation especially may vary (locally) in structural members depending on their geometry, the consistency of the fresh concrete, and the way of placing and compacting the concrete. As a result, UHPFRC may behave anisotropically in both tension and compression. To quantify the effect of fiber orientation on the behavior of UHPFRC in compression, tests on cylinders and differently fabricated cubes made of fine- and coarse-grained UHPFRC mixtures were performed. Especially for high fiber volume fraction, specimens with predominantly unidirectional fiber orientation perpendicular to the loading direction showed significantly higher compressive strengths than specimens with predominantly unidirectional alignment of the fibers parallel to the loading direction. Unlike for ultra-high-performance concrete without fibers, a noticeable difference between cylinder and cube compressive strength could be observed in case of UHPFRC.