Experimental Study on High Temperature Performance of Hybrid Fiber Reinforced Ultra-High Performance Concrete
In this work,the physical and mechanical properties of hybrid steel fiber(SF)-polypropylene fiber(PPF)-calcium sulfate whisker(CSW)reinforced ultra-high performance concrete(UHPC)were investigated before and after exposed to 200～800℃.The morphologies of hybrid SF-PPF-CSW reinforced UHPC were observed with optical microscope and scanning electron microscope,respectively.And the action mechanism of multi-scale fibers in the process of fracture development in matrix was discussed.The results show that with the increase of temperature,the mass loss of UHPC increases while the ultrasonic pulse velocity decreases.Meanwhile,the SF-PPF-CSW has a certain slowing effect on the decrease of ultrasonic pulse velocity of matrix.The hybrid SF-PPF-CSW reinforced UHPC shows slight change(＜5％)in flexural strength below 400 ℃,while sharply decreases above 400℃.After exposure to 800 ℃,the residual flexural strength of UHPC is about 19.2％～24.7％of initial value.With the increase of temperature,the residual compressive strength increases first and then decreases.The residual compressive strength reaches the maximum value at 400 ℃,which is 48.9％～62.0％higher than that at normal temperature.The hybrid SF-PPF-CSW can effectively improve the physical and mechanical properties of UHPC at all of tested temperatures,and mechanical property enhancement is optimal with 1.7％(volume fraction)SF、0.3％(volume fraction)PPF and 1.0％(volume fraction)CSW.
hybrid fiberultra-high performance concretehigh temperaturephysical and mechanical propertymicrostructure
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