Fracture Toughness Investigations of Aligned Steel Fiber-Reinforced Cement-Based Composite Considering Crack Deflection Angle

The fracture process of fiber-reinforced concrete is typically accompanied by a deflected crack propagation trajectory that could influence the fracture mode. In this study, an external magnetic field was applied to rotate the steel fibers within the cement matrix in the designed direction. The aligned steel fiber reinforced cement-based composite (ASFRC) samples with different fiber volume contents (0.8%, 1.2%, and 2.0%) were prepared. The mixed-mode fracture toughness KI+II of ASFRC was studied primarily through fracture tests. The full-field displacements and strains were obtained using the digital image correlation method. The crack resistance KR curves were analyzed based on the measured crack mouth opening displacement and load, and a comparison between KI+II and the mode-I fracture toughness KI was made. The calculated KR curves show an increasing tendency with the crack propagation length. Higher stress intensity factors are observed after aligning the steel fibers. In addition, the fiber volume content has no obvious influence on the initial fracture toughness. Moreover, KI+II gradually increases with fiber volume content, and higher values of KI+II are observed rather than mode-I fracture toughness KI. Compared with ASFRC, 0.8% (ASFRC samples with a fiber volume content of 0.8%), the mixed-mode fracture toughness KI+II for ASFRC, 1.2%, and ASFRC, 2.0%, are both increased. The fracture toughness KI of the ASFRC is greater than those of the samples with steel fibers randomly distributed within the cement matrix, indicating that the steel fibers perpendicular to the crack surface have a better bridging effect, which greatly improves the crack resistance ability of the composite. This investigation provides a comprehensive analysis of the fracture behaviors of ASFRC, which is beneficial for its practical applications.