Degradation Of Interfacial Bond Between BFRP Bars And Concrete Under Freeze-thaw Cycles

As a new type of concrete component,BFRP reinforced concrete is gradually used in the field of civil engineering,especially in Northeast China.Under the freeze-thaw cyclic load,in order to make the concrete structure with BFRP bars more suitable for engineering,it is necessary to study the interfacial bonding performance between BFRP bars and concrete matrix.Therefore,this paper studies the degradation law of the interface bonding performance between BFRP reinforcement and concrete under freeze-thaw cyclic load,which provides theoretical support for evaluating the service condition of BFRP reinforcement concrete members in northern China,and then guides the practical engineering application,which is of great significance to improve the durability of BFRP reinforcement concrete members and their structures.The main research work and achievements are as follows:Firstly,the surface condition,quality,cube compressive strength,splitting tensile strength,maximum tensile strength and elastic modulus of concrete with three kinds of strength and 10 mm diameter BFRP bars subjected to 0,100,200 and 300 freeze-thaw cycles were studied by experiments.The test results show that with the increase of freezethaw cycles,the surface shedding of concrete specimens is obvious,and the mass loss is negligible;With the increase of freeze-thaw cycles,the cube compressive strength and splitting tensile strength of concrete specimens decrease continuously.With the increase of concrete strength grade,the adverse effect of freeze-thaw cyclic loading is less obvious;With the increase of the number of freeze-thaw cycles,the axial tensile strength of BFRP bars decreases,but the elastic modulus increases,which indicates that BFRP bars become more and more brittle after freeze-thaw cycles.Secondly,the degradation law of interfacial bond between BFRP and concrete under freeze-thaw cyclic loading is studied by pull-out test.Based on the test results,the bond slip relationship curve of the interface between BFRP and concrete under freeze-thaw cyclic loading is established.Finally,the influence of freeze-thaw cyclic loading,BFRP diameter,embedded depth and concrete strength grade on the interfacial bond between BFRP and concrete is analyzed The influence of the bond strength and the bond slip curve on the bond strength is discussed.The test results show that the peak bond stress of BFRP reinforcement and concrete increases with the increase of concrete matrix strength;the peak bond stress of BFRP reinforcement concrete decreases with the increase of BFRP reinforcement diameter;the peak bond stress of BFRP reinforcement concrete decreases with the increase of BFRP reinforcement embedded depth;The peak bond stress of BFRP reinforced concrete decreases with the increase of freeze-thaw cycles.Thirdly,based on the pull-out test results of BFRP reinforced concrete under freezethaw cyclic loading,a bond slip constitutive model suitable for this test is proposed.By comparing the bond slip constitutive model with the experimental data,it is found that the fitting effect is better.Finally,based on the finite element method,the pullout process of BFRP reinforcement from concrete matrix is simulated,and the numerical simulation results,experimental results and fitting results are compared.