The Study On Fiber Treatment And Tensile Performance Of(Reinforced) UHPC

This paper proposes specific measures to improve the tensile performance of ultrahigh performance concrete(UHPC).Firstly,the surface of steel fiber is modified by zinc phosphate to improve the bonding performance of the fiber-matrix interface;secondly,the orientation of the fiber is oriented by the fiber aligning casting,and the tensile performance of UHPC in specific direction is further improved.In order to observe the specific effect of the fiber treatment mentioned above,the fiber orientation distribution in UHPC was calculated by image analysis,and the microstructure of the steel fiber surface was analyzed by SEM-EDX.Meanwhile,on the one hand this influence of two kinds of fiber treatment on the tensile properties of UHPC or reinforced UHPC was studied by flexural tests and direct tensile tests.On the other hand,this paper also adopts the direct test to study the influence of different reinforcement ratio and steel wire mesh on the tensile performance of reinforced UHPC.Lastly,based on the traditional single crack constitutive model,the stochastic distribution model of spatial strength based on Gauss process is added in this paper,and the tensile constitutive relationship of UHPC is attempted to be predicted.The key work and corresponding key conclusions of this paper are as follows:(1)In this paper,vibration is proposed to improve the directional effect of the fiber,and the test phenomenon and image analysis shows that vibration can effectively help the fiber aligning casting process,and fiber aligning casting has a significant impact on the fiber orientation and distribution uniformity of UHPC.(2)Zinc phosphate is used to modify the surface of steel fibers to make modified steel fibers.SEM-EDX analysis shows that zinc phosphate modified steel fiber improves the bonding performance of the fiber-matrix interface at both physical and chemical levels,and leads to a decrease in the chemical bonding and an increase in the friction bonding at the fiber-matrix interface.(3)The results of flexural tests and direct tension tests show that zinc phosphate modification had no significant effect on the tensile properties of UHPC and reinforced UHPC before cracking,but significantly improved the ultimate bearing capacity and ductility after cracking.Fiber orientation affects the cracking behavior of UHPC and reinforcement UHPC,and can simultaneously improve the cracking load,ultimate load and ductility of UHPC and reinforcement UHPC.(4)The results of direct tension tests of reinforced UHPC with different reinforcement ratio show that,with the increase of reinforcement ratio,the stiffness,ultimate bearing capacity,ductility and durability of ribbed UHPC after cracking will all increase,and it is found that the nominal ultimate tensile strength of UHPC will be significantly different from that of UHPC.(5)The results of direct tension tests of reinforced UHPC with steel wire mesh show that,the addition of steel wire mesh with reinforcement UHPC can significantly improve the initial crack load of reinforcement UHPC,but also reduce the ductility of reinforcement UHPC,at the same time,the reinforcement UHPC with steel wire mesh in the softening stage shows dynamic or "quasi-dynamic" failure characteristics.(6)By establishing and analyzing the force model of UHPC based on random distribution,it can be found that parameters related to the random distribution of spatial strength will affect the fracture distribution characteristics in the UHPC strain hardening process.With the help of this model,the tensile constitutive relation of UHPC can be accurately predicted theoretically.