Study On Mechanical Properties Of SFCB And Its Bond With Concrete Under The Coupling Of Chloride Salt Erosion And Load

Steel-FRP Composite Bar(SFCB)is a new type of reinforced composite material with steel bars as the inner core and longitudinal fibers.The outer fiber mainly includes basalt fiber,carbon fiber and glass fiber.It also has the characteristics of high strength,good ductility,high elastic modulus,stable secondary stiffness and excellent corrosion resistance.However,there are few domestic durability performance tests on the mechanical properties of SFCB tendons,which cannot provide an effective test data reference for the popularization of SFCB tendons in practical engineering applications:(1)Tensile properties are the most important mechanical properties of SFCB bars,so this paper studies the tensile durability of SFCB bars in harsh environments.This paper studies the degradation of tensile properties of SFCB bars(S6B20,S8B30,S6G24),BFRP bars and HRB400 threaded steel bars under the erosion environment of 3.5%sodium chloride solution and 7%sodium chloride solution,and also designs a set of effective Load-bearing device to study the degradation law of tensile performance of SFCB bars under the coupling effect of long-term load and chloride corrosion.The degradation rules of different types of SFCB tendons under the action of chloride salt erosion environment are obviously different,and the tensile strength retention effect of S6B20 tendon is the best.Under the action of chloride salt erosion and load coupling,the tensile strength of all types of SFCB tendons decreased significantly.The retention rate of tensile strength of S6B20 tendon was greater,while the tensile strength of S6G24 tendon decreased more.At the same size,the tensile mechanical properties of the cladding SFCB reinforcement with basalt fiber is stronger than that of the SFCB reinforcement with continuous glass fiber.The stress-strain curve of SFCB tends to have a significant plastic strengthening stage under the action of a large long-term load and chloride salt erosion environment.This paper refers to the tensile strength when it initially enters the secondary stiffness as the secondary stiffness.At the same time,according to the test results,the formula of the ultimate tensile strength degradation of SFCB bars under the coupling action of chloride salt corrosion and load is fitted.(2)Through compression test,the degradation of SFCB's compressive performance under the environment of chloride salt corrosion and long-term load was analyzed.This paper studies the degradation of compressive performance of SFCB bars(S6B20,S8B30,S6G24)and BFRP bars under the erosion environment of 3.5%sodium chloride solution and 7%sodium chloride solution.At the same time,an effective load-bearing device is designed to The degradation law of compressive performance of SFCB bars under the coupling effect of long-term load and chloride salt corrosion was studied.The research results show that:with the increase of the number of erosion days,the high-concentration chloride salt environment weakens the ultimate compressive strength of S6B20 tendons more than low-concentration.Comparing various types of SFCB tendons under the action of chloride salt corrosion,it can be concluded that S6B20 tendons have the best compression resistance and S8B30 tendons are poor.At the same load level,the compressive strength under the attack of 3.5%chloride chloride is higher than that under the attack of 7%chloride chloride.Increasing the concentration of sodium chloride weakens the compressive strength of SFCB and BFRP bars More obvious.(3)In this paper,the unidirectional pull test is used to study the durability of the bonding performance between SFCB bars and concrete.This paper studies the degradation of the bonding properties of SFCB bars(S6B20,S8B30,S6G24),BFRP bars,and HRB400 threaded steel bars under the erosion environment of 3.5%sodium chloride solution and 7%sodium chloride solution.At the same time,a set of effective Load-bearing device to study the degradation of the bonding performance of SFCB bars and concrete under the coupling effect of long-term load and chloride corrosion.The increase of the chloride salt concentration has a significant effect on the early bond strength degradation of S6B20 bars.The main reason for the change in the bonding properties of SFCB bars and BFRP bars is that the FRP surface of the bars is eroded by the chloride salt,and the bond strength of bars is degraded.The main reason is that the steel bar is severely corroded by chloride salt corrosion.(4)Based on the test results and existing research in this paper,the basic anchor length formula and bond-slip constitutive relationship of SFCB tendon under chloride erosion and long-term load are proposed.