Experimental Study On Compressive Behavior Of Fiber Reinforced Sea Sand Recycled Concrete Filled GFRP Tube Columns

With the continuous growth of population and the expansion of cities,the demand for concrete increases year by year.It is of great social and economic value to apply sea sand and recycled brick aggregate to concrete structures.Recycled concrete has many natural defects such as higher porosity,higher water absorption and weaker interface transition zone.Sea sand concrete has the problems of being easily corroded and having poor durability due to its high chloride ion content.In view of these problems,this paper proposes a composite structure of GFRP confined chopped fiber reinforced sea sand recycled concrete.The mechanical performance and post-crack deformation performance of concrete could be improved effectively by adding chopped fibers into recycled concrete.FRP(fiber reinforced composite)has been widely used in civil engineering due to its advantages of light weight,high strength,corrosion resistance,strong designability and so on.The combination of the two can effectively avoid the corrosion of steel reinforcement and greatly improve the bearing capacity and deformation capacity of specimens.The main research contents are as follows:(1)Experimental study on basic mechanical properties of sea sand recycled concrete reinforced with glass fiber.Taking water-cement ratio,fiber content and replacement ratio of recycled coarse aggregate to natural coarse aggregate as variables,the cubic compression test,splitting tensile test and axial compression tests of 24 groups(a total of 216 specimens)of sea sand concrete were carried out,and the stress-strain curves were obtained.(2)Theoretical study on basic mechanical performance of s ea sand recycled concrete reinforced with glass fiber.The conversion coefficient between the cubic compressive strength and the prism compressive strength is 0.84 through fitting,which is slightly higher than that of ordinary concrete.The stress-strain model suitable for fiber reinforced sea-sand recycled concrete of different fiber contents and different replacement ratio is proposed based on the Guo Zhenhai model.The compressive toughness is analyzed by using the stress cut-off method.(3)Basic theoretical research on mechanical properties of composite materials and experimental research on properties of GFRP tube materials.It mainly includes the calculation of the five engineering elastic constants and the five basic strength mechanics indexes of the single layer plate,the transformation of the stress-strain relation of the single layer plate in different directions,the strength failure criterion of the single layer plate and the calculation of the ultimate strength of the FRP laminated plate.The tensile test of GFRP tube was carried out by means of split-disk method,and the basic material properties such as elastic modulus and tensile strength were measured.(4)Experimental study on axial compression test of GFRP confined fiber reinforced sea sand recycled concrete column.The axial compression test was carried out on 42 circle-section columns with concrete strength grade,GFRP layer number and fiber orientation as variables.The results show that the strength and ductility of GFRP confined fiber reinforced sea sand recycled concrete are greatly improved with the increase of the number of GFRP layers.The failure patterns of specimens with different fiber winding angles is quite different.Compared with the 80° specimens,the ultimate stress of the specimens with a winding angle of 60° is reduced,but the ductility is increased by 1.04 times.(5)Theoretical analysis of GFRP confined fiber-reinforced sea sand recycled concrete short columns under axial compression.The theoretical calculation resul ts and experimental values of each typical FRP confined ordinary concrete models are compared and analyzed from three aspects:ultimate stress,ultimate strain,and constitutive relationship.Finally,limit state equation and constitutive equation applicable to GFRP confined sea sand recycled concrete are established based on the classic model.The formula for calculating the axial bearing capacity of constraining specimens is established by using the unified theory method considering the variable of fiber winding angle.