Relationship between fiber orientation/distribution and post-cracking behaviour in ultra-high-performance fiber-reinforced concrete (UHPFRC)

The relationship between fiber orientation/distribution and post-cracking behaviour in ultra-high-performance fiber-reinforced concrete (UHPFRC) was quantitatively evaluated. A circular UHPFRC panel was cast from its center and prismatic specimens were cut at angles of 0, 30, 60 and 90° between the specimen axis and the radial direction of the panel. The post-cracking behaviour was assessed with three-point bending tests, and fiber orientation/distribution throughout the panel was then evaluated using image analysis and 3D visualization of fiber orientation based on X-ray computed tomography (CT) data. The post-cracking flexural strengths of the specimens cut at angles of 60, 30 and 0° were 80, 40 and 10% of that for the specimens cut at an angle of 90°, indicating perfect linear dependence on the contribution of fibers near the fracture surfaces. Two rectangular UHPFRC panels with a 1:2 width/length ratio were cast, and similar fiber orientation characteristics were found for the circular and rectangular panels.