Effects of fiber content, inclination angle, and casting point on the fiber-matrix interaction of High-Strength Fiber-Reinforced Self Compacting Concrete

This experimental study examines the pullout behavior of aligned and inclined steel fibers embedded in High-Strength Fiber-Reinforced Self Compacting Concrete (HSFRSCC). The effects of four fiber contents (0, 0.25, 0.50, and 0.75%), three inclination angles (0°, 30°, and 45°), and three concrete casting points on the formwork were investigated. The analyses were performed based on load-slip relationships, maximum pullout load, dissipated energy, failure mode, and spalling area. The fiber pullout behavior evidenced the importance of the presence of fibers in the concrete matrix. The pullout loads and pullout energy presented a better performance than the unreinforced matrix when the fiber content was increased to 0.75%; the confinement effect of the fibers in the matrix explains this mechanism. Regarding the failure mode, some inclined fibers at 30° and 45° presented rupture during pullout, more recurrent for 45° and for the matrices that offered greater confinement (0 and 0.75%). Furthermore, the spalling area increased with the inclination angle; it was found that the presence of fibers in the matrix influences the propagation of cracks during the matrix spalling. In some cases, these can increase the susceptibility of fiber rupture during the pullout. Finally, it was inconclusive that the pulled fibers' position relative to the casting point and, consequently, the fiber orientation influences the pullout load.