SIMULTANEOUSLY DETERMINING FRACTURE TOUGHNESS AND TENSILE STRENGTH OF STEEL FIBER HIGH-STRENGTH CONCRETE

Considering the influence mechanism of steel fiber high-strength concrete specimens meso heterogeneity on macroscopic fracture, the calculation formula for fictitious crack growth of teel fiber high-strength concrete macroscopic fracture model is improved by accounting for steel fiber characteristic parameters at meso level of steel fiber content, length, diameter and steel fiber tensile strength, which provides the model and the method to consider steel fiber characteristics for simultaneously determining the fracture toughness and tensile strength of steel fiber high-strength concrete. Based on the proposed model, the fracture toughness and tensile strength of steel fiber high-strength concrete are simultaneously determined by using three point bending specimens with different steel fiber content and water cement ratio of concrete, which are in good agreement with the tensile strength obtained by experiment and the fracture toughness from the SEM. Based on the fact that the discreteness of the test data is the inherent property of steel fiber high-strength concrete, the ±20% complete curves of steel fiber high-strength concrete describing different structural fracture modes of plastic, quasi-brittle and linear elastic are established by using the determined material parameters (fracture toughness and tensile strength), which can cover all test data under laboratory conditions. The model and the method proposed in this paper are applicable to steel fiber high-strength concrete and high-strength concrete, and can provide a basis for the determination of real fracture toughness and tensile strength of composite materials such as steel fiber high-strength concrete, the prediction of fracture failure of individualized structures and other key scientific and technological issues. © 2023 Tsinghua University. All rights reserved.