Research On Flexural Performance Of CFRP Mesh Reinforced ECC Permanent Formwork-GFRP Reinforced Concrete Composite Beam

Carbon fiber reinforced polymer(CFRP)grid reinforced engineering cement-based composite(ECC)formwork is a new type of sheet with CFRP grid embedded inside ECC.This kind of plate material can not only give full play to the plasticity of ECC,which is convenient for pouring and molding,but also give full play to the characteristics of light weight,high strength,and especially durability and corrosion resistance of CFRP.On the other hand,due to the excessive limit of the crack width of GFRP reinforced concrete beams,large cracks will appear in the normal service state of this kind of structure,and the structure is prone to brittle failure,causing excessive psychological burden on the public.Limiting the width of the crack will cause the FRP bar to not fully exert its high tensile performance and cause material waste.In this paper,FRP grid reinforced ECC plate was used as a permanent formwork in GFRP reinforced concrete structure,in order to improve the toughness of the internal concrete structure,improve the crack control ability of the structure,and achieve harmless dispersion of concrete cracks.It can effectively solve the problems of easy cracking and poor ductility of concrete materials,improve the mechanical performance of the structure and prolong the service life of the structure.It has very important theoretical guiding significance and practical engineering application value.This paper studied the mechanical properties of CFRP grid-enhanced ECC plate,and explored its feasibility in permanent formwork.On the basis of self-prepared CFRP grid,the research on flexural performance of CFRP grid reinforced ECC permanent formwork-GFRP reinforced concrete composite beam was carried out,mainly including the following aspects:(1)Uniaxial tensile tests of ECC composite members reinforced with CFRP grids were carried out to study the effects of FRP grid reinforcement ratio and reinforcement material types(CFRP and carbon fiber)on the mechanical properties of ECC composite members reinforced with CFRP grids.It mainly discussed the mechanical properties and failure modes of CFRP mesh-enhanced ECC components.At the same time,the cracking mode and crack development mode of the CFRP-ECC composite plate were clarified through experiments.(2)The flexural behavior of CFRP grid reinforced ECC permanent formwork GFRP reinforced concrete composite beams was tested.The U-shaped permanent formwork and the bottom permanent formwork were used to strengthen the beams respectively.The study focused on the influence of CFRP mesh volume ratio,ECC configuration strength,GFRP reinforcement ratio and permanent template thickness on the bending performance of the test beam.The test results show that the test beam mainly has three types of crushing failure of the concrete in the compression zone,GFRP failure in the tension zone,and peeling failure at the end of the CFRP mesh reinforced ECC permanent formwork.Compared with ordinary GFRP reinforced concrete beams,the cracking load and ultimate load of CFRP grid reinforced ECC permanent formwork-GFRP reinforced concrete composite beams are increased by26.9%-92.3% and 7.4%-34.4%.The deflection of the test beam when it fails is also significantly reduced,and the ductility of the structure increases significantly.When the maximum crack width reached the crack limit of 0.5mm,the bearing capacity is increased from 0.26 Mu to 0.45Mu?0.95 Mu,and the crack control ability increases significantly.(3)According to the "Code for Design of Concrete Structures","Code for Design of Reinforcement of Highway Bridges" and other specifications,the theoretical calculation model of flexural capacity and deflection of concrete composite beams strengthened by CFRP grid and ECC permanent formwork was established.The results indicate that the theoretical formula calculated in this paper agrees well with the experimental values and the data dispersion is small,which can effectively predict the bending capacity and deflection of CFRP grid reinforced ECC permanent formwork-GFRP reinforced concrete composite beams.(4)On the basis of experimental research,the formulas of average crack spacing and maximum crack width were revised,and the formulas were verified with the data obtained from the experiment.The results show that the average crack spacing and the larger crack width obtained by the modified calculation formula in this paper are in good agreement with the experimental values,and the data dispersion is small,which can effectively predict the average crack spacing and maximum crack width of CFRP grid reinforced ECC permanent formwork GFRP reinforced concrete composite beam under normal service condition.