Research Of Hybrid Fiber Ultra-High Performance Concrete In Anchorage Zone Of Bridge Expansion Joint

In order to obtain UHPC which is suitable for bridge expansion joint anchorage zone and relatively low price,polyvinyl alcohol fiber(PVA fiber)and polypropylene fiber(PP fiber)were used to replace part of steel fiber while the total fiber volume content was 2%.The effects of synthetic fiber substitution rate(0%～30%)on the working performance,basic mechanical properties,fracture toughness and impact toughness of UHPC under different fiber mixing modes(steel fiber and PVA/PP fiber binary hybrid or ternary hybrid),as well as the effects of synthetic fiber substitution rate and interface treatment methods on the bond splitting tensile strength of UHPC and C40 concrete were studied,and the economic applicability was analyzed.The main contents of this paper are as follows:(1)The effects of synthetic fiber substitution rate on the expansion,compressive strength,tensile strength,flexural strength and elastic modulus of UHPC were studied.It was shown that the substitution rate of synthetic fiber had little effect on the elastic modulus.When the fiber was binary mixed,with the increase of the substitution rate of synthetic fiber,the expansion and compressive strength showed a decreasing trend,while the tensile and flexural strength first increased and then decreased.When the same amount of PVA fiber and PP fiber were used to replace 30%steel fiber,the expansion of UHPC mixture was good(530mm),and the compressive strength decreased slightly,the tensile strength increased,and the flexural strength increased significantly.(2)The effects of synthetic fiber substitution rate on the double-K fracture toughness,fracture energy and bridging toughness increment of UHPC under different fiber mixing modes,and the effects of ternary hybrid fiber(synthetic fiber substitution rate 30%)on the impact toughness of UHPC were studied.It was indicated that the initiation load,initiation toughness and the frature energy of UHPC can be effectively ameliorated by using PVA fiber for replacing part of steel fiber,but the instability toughness decreased obviously when the replacement rate was 30%.The fracture energy of UHPC can be increased by replacing part of steel fibers with PP fibers,but the effect on fracture initiation,cohesion and instability toughness is not significant,and the effect on fracture energy is not as good as PVA fibers.The fracture properties and impact resistance of UHPC can be effectively optimized by replacing 30%steel fiber with equal amount of PVA fiber and PP fiber.(3)The influence of synthetic fiber substitution rate on the bond splitting tensile strength of UHPC and C40 concrete under different interface roughness,interface binder type and fiber mixing mode was studied.It was demonstrated that the increase of interface roughness can significantly improve the bond splitting tensile strength.When the interface roughness was 10mm to 11mm,the bonding splitting tensile strength close to the overall splitting tensile strength of C40 concrete can be obtained only by wetting the bonding interface.With the increase of synthetic fiber substitution rate,the decrease of bond splitting tensile strength was leaded by the decrease of UHPC expansion and steel fiber content,and the decrease trend of expansion and bond splitting tensile strength were roughly the same.(4)Aiming at the anchorage zone of bridge expansion joint,the economic applicability of ternary hybrid UHPC used in this paper was analyzed.It was found that the performance of the tested ternary hybrid UHPC was much better than that of concrete commonly used in bridge anchorage zone,and it was more economical than UHPC with only steel fiber.It is suggested that the tested ternary hybrid UHPC could be used in expansion joint anchorage zone of heavy or extra heavy traffic bridge.