Experimental Investigations Of Hybrid Fiber Concrete And Its Application In Shield Segment

Today the subway shield segment is mainly reinforced concrete pipe inengineering applications, as the concrete is a brittle material, the tensile properties ispoor, making it prone to breakage and cracking during transportation and installation,segment damage and cracks will be adversely affected on tunnel safety and durability,these problems are difficult but must be solved in the shield. In view of the manydefects of the ordinary reinforced concrete shield segment, using the hybrid fiberreinforced concrete prefabricated subway shield segment will provide an effectiveway to improve the safety and durability of the subway tunnel.But the domestic fiber concrete segment in shield tunnel belongs to the pilotstage, there are no full specifications and technical documents to guide theengineering design of fiber reinforced concrete shield tunnel. Hybrid fiber reinforcedhigh-strength concrete used in the subway segment also require a lot of research, thisarticle experimental study of hybrid fiber concrete mixing technology and the steel-polypropylene fiber performance of concrete workability, mechanical properties anddurability.This study found that:(1)Mixing process of concrete mixture into a group of bundles phenomenon bywater mixed method is low, and the dispersion of fiber is the largest coefficient, themixing homogeneity of the fiber concrete fiber is best. The slump also decrease withthe increase of steel fiber, when steel fiber is the same, with the increase of thepolypropylene fiber content, the slump of fiber reinforced concrete also showed adecreasing trend, but the hybrid fiber can effectively inhibit the segregation andbleeding of concrete. Made the amount of steel fiber within a certain range can notsignificantly increase the bulk density of concrete.(2)The analysis of compressive strength shows that, hybrid fiber reinforcedconcrete＞steel fiber reinforced concrete＞plain concrete＞polypropylene fiberreinforced concrete, but the addition of fiber to improve the compressive strength ofconcrete is slightly. The splitting tensile strength and flexural strength of concreteincreased with the increase of steel fiber, the ratio of the splitting tensile strength for fiber reinforced concrete to plain concrete can reach108.36%, ratio of flexuralstrength for hybrid fiber reinforced concrete to plain concrete can reach41.78%. The7days and28days of toughness index of hybrid fiber reinforced concrete is higherthan the plain concrete, steel fiber reinforced concrete or polypropylene fiberreinforced concrete, its toughness index compared to plain concrete is about1.5times,polypropylene fiber-the observation of the substrate interfacial transition zonemicrostructure can be found around; steel fiber, polypropylene fiber and matrix arenot closely linked together, there are still certain clear ance; polypropylene fiber-interfacial transition zone of the substrate than the steel fiber-substrate interfacetransition zone is loose, and its surface should be smooth compared to steel fibersmany mechanical meshing with the paste role than steel fiber.(3)The study on durability of hybrid fiber reinforced concrete show that, theresistance to chloride ion penetration will reduce when only having steel fiber inconcrete, the steel fibers and polypropylene fibers will slightly reduce the resistanceto chloride ion penetration of concrete, but the decrease slightly.NEL methodevaluation that the chloride ion penetration of hybrid fiber reinforced concrete, steelfiber reinforced concrete and polypropylene fiber reinforced concrete is still at a verylow level.(4)According to the experimental comparison results of mechanical propertiesand durability, to select SPFC2for the best optimum mixture ratio, based on theexperimental material parameters of hybrid fiber concrete, proposing the reasonableconfiguration design of reinforced bar of hybrid fiber reinforcement concrete segment,and verify the security and reasonableness of the configuration design of reinforcedbar, the reinforcement can be used8Ф12reinforced (As=A's=884mm2), unworthyof stirrups by the numerical simulation to hybrid fiber reinforced concrete segmentson ANSYS software. The economic efficiency of hybrid fiber reinforced concretesegment also was confirmed.