Study On The Tensile Properties Of Ultra High Performance Fiber Reinforced Concrete With High Flowability

Ultra high performance fiber reinforced concrete with high flowability(UHPFRC)is a new improvement of UHPC,with more than 190 MPa compressive strength and 180 mm fluidity tested by micro slump cylinder.Owing to the high strength and extremely large flow state of this advanced cementitious material,it can take a profound role in bridge design and construction.In this paper,mechanical properties and deformation were investigated by uniaxial direct tensile test and four-point bending indirect tensile test.The parameters of accumulated energy and number were monitored by acoustic emission test in order to identify the damage revolution under tensile load.For better understand the efficiency contributed by steel fibers,bond properties between matrix and steel fiber with different embedment length and angle were studied by single fiber pullout test.Finally,the damage constitutive model is established according to Weibull distribution and AE damage revolution model.The conclusions are as follows:(1)Different failure modes and processes were studied through uniaxial tensile tests with different steel fiber contents mixed.The matrix and the specimens with different steel fiber contents showed different failure modes respectively.Tensile stress-strain curve was acquired and fitted by polynomial function and rational fraction.Character of stress-strain curve was transforming from no slant curve to stress descend suddenly and strain softening,strain hardening respectively.(2)When the steel fiber volume content increases to 5%,the initial crack strain and peak strain increases 2.8 times and 22 times respectively compared with the matrix,while the initial crack stress and peak stress both increase 3.6,4.4 times respectively.The uniaxial tensile strength can be finely predicted by the analysis of bond stress between single steel fiber and matrix through pullout test,and the deviation is within 8%.(3)The constitutive model under uniaxial tension is achieved according to the Weibull distribution to simulate ascend part of stress strain curve.The relationship between acoustic parameters and tensile strain were detected,and the damage evolution model is fitted.The constitutive model is established by this model to simulate descend part of stress strain curve.(4)The indirect tensile properties were studied by four-point bending experiments,bending strength is nearly 3 times than that of tensile strength.The bending strength,toughness,bending compression ratio and tension compression ratio with 5% steel fiber contents increases 3.2,23,5.9,2.0 times respectively compared with the matrix.