Reserach On Durability Of GFRP Bars Reinforced Seawater Sea Sand Concrete Beam

As the global population grows,the demand for infrastructure inevitably rises,the construction industry’s demand for concrete and steel,two major building materials,increases,and the overconsumption of river sand and freshwater resources causes serious environmental problems.China is rich in marine resources,and the shortage of river sand and freshwater resources can be effectively alleviated if seawater marine sand resources can be used locally.However,the high chloride ion content in seawater marine sand concrete accelerates the corrosion process of reinforcing steel in concrete structures and reduces the durability of reinforced concrete structures.In order to solve the corrosion problem of steel reinforcement in concrete,Fiber Reinforced Polymer(FRP)bar has become an alternative to steel reinforcement with its excellent resistance to chloride ion attack.In recent years,scholars at home and abroad have conducted extensive research on FRP-reinforced seawater sea sand concrete members.The research on their durability is mainly focused on artificially simulating the natural environment to accelerate aging,usually by placing the members in specific aging conditions(salt solution,alkali solution,freeze-thaw and wet-dry cycles)to study the effect of single environmental factors on the durability of the members.In contrast,the actual field environment where the members are in service is complex and variable,and the durability of the members is influenced by the coupling of multiple natural environmental factors(UV radiation,sunlight,rain,and temperature).In view of this,this paper investigates the flexural durability of GFRP-reinforced seawater sea sand concrete beams and GFRP-reinforced normal concrete beams exposed to natural environment and accelerated weathering chamber simulating the natural environment,natural environment including indoor and outdoor environments under subtropical monsoon climate.The duration of exposure is one year.In order to simulate the service condition of the members more realistically,different levels of sustained loads were applied to the members.The specific research contents include:1.Six GFRP-reinforced normal concrete beams and six GFRP-reinforced seawater sea sand concrete beams were designed and fabricated,and sustained loads(no sustained load /cracking load / double cracking load)were applied to the beams placed in different environments(indoor environment / outdoor environment / accelerated weathering chamber)for one year.The changes in the surface morphology of the beams and the crack widths produced by sustained loads were observed before and after environmental exposure.2.Four-point bending tests were conducted on beams subjected to one year of environmental exposure to analyze and compare the effects of different environments,sustained load and concrete types on the long-term bending performance of GFRP-reinforced seawater sea sand concrete beams.The damage modes,characteristic points of load-deflection curves,crack width,flexural stiffness and ductility of GFRP-reinforced concrete beams were mainly analyzed and compared.3.Based on the GB50608-2020,considering the influence of environments on GFRP reinforcement in this test,the ultimate tensile strength of GFRP bars is reduced,and the flexural capacity of GFRP-reinforced concrete beam after environmental exposure is calculated and compared with the test results.4.The flexural performance data obtained from the four-point bending test,including deflection,maximum crack width and average crack spacing,are compared and analyzed with the calculation formulae of the existing codes of various countries to obtain the calculation formulae of flexural performance applicable to GFRP reinforced concrete beams under different environments.