Fiber-Matrix Interfacial Behavior of Hooked-End Steel Fiber-Reinforced Concrete

Abstract

Concrete has inherent low tensile strength and fails at low tensile strains. These drawbacks have been bypassed by the introduction of discontinuous randomly distributed fibers to the concrete. The fiber-matrix interfacial behavior is of critical importance to the properties of fiber-reinforced concrete (FRC), which is usually assessed by fiber pullout tests. In this paper, a rigorous pullout test setup was developed with 50-mm-diameter × 100-mm-height cylindrical concrete specimens and utilized to investigate fiber-matrix interfacial behavior of hooked-end steel FRC with two fiber sizes and various embedment depths. The relation of fiber pullout load-end slip displacement and its average curves established the efficiency of the utilized fiber pullout test setup concerning the repeatability and reliability. Four components of the fiber matrix interactions were observed for hooked-end steel fibers. These include the elastic fiber-matrix bond, partial fiber-matrix debonding, full fiber-matrix debonding, and fiber (softening, hardening, and frictional) pullout components. Results showed that the ultimate pullout load of the fiber increases with an increase in size of fiber and embedment depth. Moreover, the hook of the fiber that has a 45-degree bending angle and a 2.5- or 3.0-mm length governs the overall pullout characteristics of hooked-end steel fibers.