Experimental Study on Uniaxial Tensile Properties of Hybrid Fiber UHPC

To explore the uniaxial tensile properties of hybrid fiber-reinforced ultra-high performance concrete (UHPC),the effects of fiber type and fiber volume fraction on the axial tensile curve,mechanical indexes,fracture energy,and toughness ratio of UHPC were studied through the axial tensile test of dog-bone shaped specimen.The tensile toughness ratio was used to evaluate the tensile toughness.The tensile damage mechanism of hybrid fiber UHPC was analyzed by using the scanning electron microscope (SEM).The results show that:steel fiber combined with non-metallic fibers is more conducive than steel fiber only in improving the tensile strength and peak tensile strain of UHPC,and the increase is 4.64%~39.32% and 26.98%~65.35%,respectively;hybrid fibers can give full play to their synergistic load-bearing,crack-blocking and energy-consuming toughening effects,improving the tensile toughness ratio and fracture energy of UHPC.Steel fiber combined with glass fiber or polyolefin fiber has the most significant effect on improving the tensile toughness ratio,which is 15.0% and 12.5% higher than steel fiber only,respectively;at equal volume fraction,the increase in fracture energy of non-metallic fibers are higher than that of steel fiber,in which,basalt,glass fiber or polyolefin fiber have significant improvement in fracture energy.Based on the axial tensile test,the stress-crack width (σ-ω) relationship between single-doped steel fibers and steel-PVA blended UHPC exponentially was given,and the theoretical curves were in good agreement with the test curves,providing a reference for numerical simulation and engineering application.