Experimental Study On The Deterioration Of Bonding Properties Between GFRP Bars And Concrete Under Aggressive Environment

As we all know,the performance degradation analysis of the reinforced concrete structure in the life cycle has been widely concerned by scholars at home and abroad.Among them,the problem of rebar corrosion has always been the main contradiction that affects the periodic energy degradation of structure.In order to solve this contradiction effectively and improve the whole life cycle performance of the structure,it is an effective method to replace the common steel bar with high performance fiber reinforced polymer bars(referred to as FRP bar).Therefore,it is necessary to study the durability of FRP bars and the bonding property between FRP bars and concrete to popularize the application of FRP bars in concrete structure.This paper is based on the design and properties of FRP reinforced concrete members based on National Natural Science Foundation “Design and performance of reinforced concrete members with FRP bars and common reinforcement with durability(51578267)”,the mechanical properties of Glass Fiber Reinforced Polymer the bars and the degradation of the bonding properties between GFRP bars and concrete under aggressive environment are studied by theoretical analysis and experimental research,the main tasks are:1.Experimental study on the erosion of GFRP bars and GFRP bars and concrete bonded specimens.A total of three batches of erosion test specimens were prepared:(1)tensile specimens,in this paper,three different diameters(8,12 and 16mm)of GFRP bars were soaked with 180 d erosion solution,(2)bending and shearing specimens were tested 12,36 and 72 d corrosion solution of GFRP bars with three different diameters.(3)Bonding performance specimens,the test specimens of GFRP bar-concrete bonded specimens were soaked in 150,210 and 270 d erosion solutions.Three kinds of aggressive environment,such as water,alkali solution and salt solution,were used to analyze the effect of different aggressive environment and soaking time on the apparent deterioration of specimen.The results show that the alkali environment has great damage to the rib material,the surface has the appearance of fiber,peeling,and so on,with the increase of soaking time,the original smooth surface of the rib material becomes coarse and uneven,after the salt aggressive environment,the GFRP bar-concrete bonded member surface is whitish,and a layer of salt is attached to the concrete surface.2.Experimental study on the degradation of tensile mechanical properties of GFRP bars after erosion.Through the tensile test of 34 GFRP bars subjected to erosion,the failure mode of the rib was studied,and the influence of diameter and aggressive environment on the tensile strength and elastic modulus of the rib was analyzed.The tensile test results show that: the larger the diameter of the rib material,the more dispersed the destruction;the aggressive environment has little influence on the elastic modulus of the rib,but the effect on the tensile strength is obvious,the performance is the most lower under the alkali environment,the second is the salt environment,the least is the clear water environment.And size effect it has a lot to do with its length-diameter ratio.3.Experimental study on flexural and shearing mechanical properties of GFRP bars after erosion.The flexural and shear tests were performed on 22 bending specimens and 44 shear specimens subjected to erosion,and the influence of soaking time,aggressive environment and diameter on the flexural and shearing properties of GFRP bars was analyzed mainly.The results show that the aggressive environment and the soaking time have little influence on the flexural modulus and the maximum strain;the larger the diameter of the shear specimen,the more faults the ends of the fracture are,and the more serious the overall damage is.The erosion environment has different degrees of degradation to the flexural and shear strength of the specimen.The shear strength of the specimen decreases with the increase of soaking time,and the shear strength of the previous 36 d decreases faster and the decreasing speed decreases after 36 d.4.Experimental study and theoretical analysis on the degradation of GFRP bars and concrete bond performance.The influence of the aggressive environment,soaking time and size on the bond strength and bond-slip relationship of the specimen was analyzed by the pull-out test of 36 bonded specimens subjected to erosion.The experimental results show that the aggressive environment has obvious influence on the bond strength,the salt environment is the most sensitive to its influence,followed by the water environment,the less influential is the alkali environment;the bond performance decreases with the increase of time,the basic appearance is first steep and then slow down,the bond-slip curve is mainly divided into micro-slip stage,linear ascending stage,the hyperbolic descending stage and the periodic fluctuating residual stress stage,etc.,the bond strength theory model of GFRP bars and concrete is established based on the elastic mechanical thick-walled cylinder model,combining with the relevant test results from domestic and foreign scholars,the experimental values and theoretical values are compared and analyzed,The mean value is 1.02 and the coefficient of variation ? is 0.09,which indicates that the experimental value is in good agreement with the theoretical value,thus verifying the accuracy of the theoretical model of bond strength deduced in this paper.