Mechanical Responses of Steel Fiber–Reinforced Concrete after Exposure to High Temperature: Experiments and Mesoscale Discrete Modeling

The mechanical responses of steel fiber–reinforced concrete (SFRC) thermally damaged at high temperature needs a deeper evaluation via a mesoscopic model that explicitly treats the fibers. For this demand, the lattice discrete particle model for SFRC after high temperature (LDPM-F-HT) is formulated. A series of experimental tests for SFRC with 0%, 1%, and 2% of steel fiber volume fraction with different heating treatments are performed to calibrate and validate the LDPM-F-HT. It is found that the nonmonotone decreasing of the macroscopic compressive strength up to 400°C is caused by the slower thermal degradation of shear strength than that of tensile strength at the mesoscale. The good matches between the experimental and numerical results demonstrate that LDPM-F-HT can capture also this phenomenon. In the numerical simulation of three-point bending tests, it is observed that the dimension of the fracture process zone (FPZ) at load peak increases with the increase of fiber content and heating temperatures. However, the FPZ width in SFRC reaches its maximum value after the thermal treatment of 450°C rather than 600°C.