Investigation Of The Bond Properties Between BFRP Bar And Hybrid Fiber Recycled Concrete Under Freeze-thaw

There are two forms of fiber reinforced composites as a new type of composite materials for implementing in concrete structures: one type of FRP reinforcing bar to replace steel bar due to the corrosion resistance,light weight and high strength of fiber materials,which solve the problem of the durability and safety of steel corrosion effectively;the other type that fiber chopped yarn is mixed in the concrete for increasing the crack resistance of concrete structure due to good mechanical performance of fiber chopped yarn.With the development of society,the environment impacts of these practices are considerable.The use of recycled aggregate concrete(RAC)reduce not only environmental pollution,but also that of the exploitation of natural stone.However,the mechanical property of recycled aggregate concrete lower than the nature aggregate concrete,then combination of fiber materials and RAC due to the satisfactory performance of the fiber materials for taking merits of them.In addition,there is still a lack of research of fiber recycled concrete in domestic which in the freezing resistance of concrete especially.The effect on the bond behavior between basalt-polypropylene hybrid fiber RAC and BFRP bars after freezing and thawing have been investigated.According to the pull-out test which analysis the effect to the bond performance of BFRP bars and hybrid fiber RAC by different freeze-thaw cycles,volume content of single fiber and hybrid fiber.The major contributions as follows:(1)The mechanical property of hybrid fiber RAC after freeze and thaw is analyzed according to the compressive strength test,tensile splitting strength test,elastic modulus test and axial compressive strength test.In one hand,enhancing tensile splitting strength and reduce the other three mechanical property in the single fiber mix;in the other hand,the mechanical performance indexes of hybrid fiber RAC is improved whether normal temperature or after freezing-thawing.The combination of 0.3% volume content of basalt fibers give better performance with respect to mechanical property of hybrid fiber RAC.(2)According to the pull-out test,the influence of bond behavior between BFRP bars and recycled concrete in three factors have been researched.Adding single fiber to the recycle concrete can enhance the ductility of bond behavior,even though reduce the bond strength.In addition,0.3% volume content of basalt fiber has the best result for the bond strength.Hybrid fiber RAC can enhance the bond property and the ductility of bond behavior respectively and the same of freezing and thawing on the hybrid fiber RAC bond behavior.But excessive total of fiber volume content will weaken the improvement of bond strength.(3)The bond-slip constitutive model of BFRP bar and hybrid fiber RAC with freeze-thaw parameters is established and offer a reference for further research due to better simulation effect with the test result.