Mechanical properties and microstructures of Steel-basalt hybrid fibers reinforced Cement-based composites exposed to high temperatures

Steel-basalt hybrid fibers reinforced cement-based composites (SBFRCC) have excellent mechanical properties at ambient temperature. Conducting research on the behavior of SBFRCC at high temperatures is beneficial for applications in structures which may be exposed to fires. In this study, the physical properties of fibers and mechanical properties of SBFRCC exposed to high temperatures were assessed through appearance, mass loss, and compressive, flexural, and splitting tensile strength tests. The deterioration mechanism was studied by X-ray diffraction (XRD), simultaneous thermal analysis (STA), and scanning electron microscopy (SEM). The results show that the color and mass of steel and basalt fiber change significantly with temperature. The addition of steel fiber and basalt fiber can improve residual flexural strength and splitting tensile strength. High basalt fiber content is harmful for compressive strength. The compressive, flexural, and splitting tensile strength of SBFRCC essentially decreases with temperature. Models were established to describe the quantitative relationship between relative strength and fiber content, temperature. The addition of steel fiber and basalt fiber can effectively inhibit cracks generation and propagation by multi-stage cracking resistance. High temperature deterioration of hybrid fibers can only reduce the reinforcement, but steel fiber and basalt fiber can still play a role in bridging cracks at 900°C.