Fracture properties and mechanisms of steel fiber and glass fiber reinforced rubberized concrete

Utilizing waste rubber as a replacement for natural aggregates in concrete presents a viable solution for mitigating environmental pollution. The unique physical properties of rubber introduce more intricate fracture properties and mechanisms in rubber concrete (RC) compared to conventional concrete. In this paper, hybrid fibers composed of steel fibers (SFs) and glass fibers (GFs) were introduced to improve the toughness and deformation resistance of RC. Through the notched three-point bending beam test, the fracture properties of hybrid fiber reinforced RC were investigated. The fracture properties of RC were assessed by considering the crack propagation configuration and the test results of several fracture parameters, including load-deflection curves, load-crack mouth opening displacement (CMOD) curves and fracture energy. Meanwhile, the fracture toughness and failure criteria of hybrid fiber reinforced RC were analyzed using the double-K fracture model. The results demonstrate that the inclusion of rubber particles in concrete can decrease its flexural properties. However, it has a positive impact on enhancing the toughness and strain capacity of the concrete. Moreover, the addition of hybrid fibers in RC can further enhance its toughness and result in a higher fracture energy. When the total hybrid fiber content is 0.8% and the ratio of SF to GF is 3:1, the peak load value of load-deflection and load-CMOD curves can reach 8.57 kN, and achieve the maximum fracture energy of 4682 J/m2. According to the analysis of double-K fracture model, the hybrid fibers enhance the crack resistance and initiation and unstable fracture toughnesses of RC, and this strengthening effect is most pronounced when the total hybrid fiber content exceeds 4%. This paper provides fundamental information on the fracture properties and mechanisms of hybrid fiber reinforced RC that can be applied to bending members in concrete structures.