Study On Tensile Properties Of Reactive Powder Concrete And Its Reinforced Members

The tensile strength of traditional concrete is weak,so it is often ignored when applied to the structure.A large number of steel fibers are uniformly distributed in the RPC matrix,which makes it retain a high tensile strength after being pulled apart and cracked.Therefore,the axial tensile property of RPC should be regarded as an important index in its structural design and should not be neglected.The reinforced RPC can be regarded as the RPC member reinforced by the combination of steel fiber and steel bar.Its tensile performance is affected by the joint influence of steel fiber,steel bar and RPC matrix.In this paper,the direct tensile properties of RPC and reinforced RPC are systematically analyzed from the material level to the component level by combining experimental research and theoretical analysis.Main work contents include:(1)The direct tensile test(DTT)was carried out on the unreinforced RPC and the RPC with HRB500 steel bar by independently designing the axial tensile test device.The test variables include curing mode and curing age,steel fiber volume content and reinforcement ratio.According to the test results,the tensile total stress-strain curves of standard curing RPC and steam curing RPC were obtained.Two axial tensile constitutive models of RPC are proposed.(2)Compared with the common steam curing,the standard RPC can also obtain quite high tensile strength and ultimate tensile strain.This conclusion lays a certain theoretical foundation for the extensive application of RPC materials in the field of engineering by casting on site and natural curing.The elastic modulus of standard curing RPC at 28 d was basically the same as that of steam curing RPC.The deformability of 28 d standard curing RPC was even slightly higher than that of steam curing RPC.According to the test data,the effect of standard curing age on the axial tensile properties of RPC was analyzed.A method for calculating the characteristic ages of RPC is proposed.The function of steel fiber in RPC is analyzed.According to the test data,the tensile and deformation relationship curves of RPC with different steel fiber content were given,and the tensile characteristic curves of RPC were summarized,and the curve characteristics were analyzed.According to the concept of unloading modulus of damage mechanics,a relationship between the deformation of RPC member and crack width is given.Through the analysis and fitting of the test data,the calculation method of estimating the peak stress and peak strain of RPC is obtained according to the volume content of steel fiber.Based on the macroscopic crack mechanics model of fiber reinforced concrete,a macroscopic crack mechanics model suitable for RPC is obtained by modifying it.(3)The tensile load-deformation curves of reinforcement RPC with different steel fiber content and reinforcement ratio were obtained by direct tensile test,and the characteristic curves were summarized,and the whole process of characteristic curves was analyzed.The method of "k? value" is summarized as a method to distinguish tensile hardening and tensile softening of reinforced RPC members after cracking.Where k = the flexion ratio of the steel bar /RPC tensile strength,? is the reinforcement ratio of the member.When k? ?0.8%,the component shows tensile softening characteristics,showing single crack failure;When k>0.8%,the component exhibits tensile hardening characteristic,showing multi-cracks failure.The tensile characteristic values of reinforced RPC members are given,including initial crack load,initial crack strain,visible initial crack load,visible initial crack strain,peak load and peak strain.The effects of reinforcement ratio and steel fiber content on the characteristic values are analyzed.The influence of different crack failure types,steel fiber content and reinforcement ratio on the tensile hardening effect of reinforced RPC members is analyzed.The characteristic curves of the load-deformation relationship of the RPC after crack were summarized.The curves could be divided into three types: the type with low k? value for single crack failure;The type of high k? value of single crack failure;Multi-cracks failure type.Based on the cracking mechanism of ordinary reinforced concrete members and fiber reinforced concrete members,the crack width calculation formula of reinforced RPC is derived,and the iterative method for calculating the crack width of members is given.Based on the test data,the relationship curve between d/? and average crack spacing is drawn.By analyzing the cracking mechanism of reinforced RPC tensile member and verifying the test data,a concept of minimum fiber content is obtained.(4)Based on the pull-out test results of HRB500 steel bars and RPC,various factors affecting RPC bond strength of high strength steel bar are analyzed:(1)casting direction of RPC;(2)bonding length;(3)RPC compressive strength;(4)steel fiber content;(5)Thickness of protective layer.Combined with the calculation method of the code,the suggestion of the formula for calculating the critical anchorage length is given.