Study On Interfacial Bonding Performance Of CFL-Concrete With End HB Anchorage In Hygrothermal Environment

Fiber reinforced polymer（FRP）is widely applied in externally bonded reinforcement（EBR）of reinforced concrete（RC）structures due to its advantages of light weight,high strength,corrosion resistance and designability.However,the EBR method will lead to FRP-concrete interface bonding prematurely,and the high tensile performance of FRP cannot be fully utilized.Moreover,the FRP-concrete interface has always been the weakest part of the whole structure,which is sensitive to humidity and temperature.So its bonding performance determines the durability of the whole reinforced strucutre to a great extent.Therefore,it is of great scientific and engineering significance to design an hybrid-bonded（HB）anchorage at the end that can improve the strength of FRP-concrete interface and the utilization rate of FRP tensile strength,and to explore the bonding performance of FRP-concrete interface under this anchoring method in the hygrothermal environment.By taking the bonding interface between carbon fiber laminate（CFL,which was invented by our research group）and concrete as the research object,this study here designs a reinforcement method of end-HB anchorage to strengthen CFL reinforced concrete structure.The failure mechanism and bonding performance of CFL-concrete interface are investigated in the influence of HB anchorage at the end and hygrothermal environments.The main research contents and conclusions of this study are as follows:（1）A kind of double-shear specimen with end-HB anchorage and full-bonded CFL is designed.Through the double-shear tests,the effect of different torque on the ultimate bearing capacity of the specimen is explored,and the prediction model of ultimate bearing capacity is established.It is found that platform load Pp in the load-slip curve and load increment ΔP are controled by chemical bond force and mechanical anchoring force,respectively.Also,the torque is linear with the load increment.（2）The failure modes,load-slip curves,CFL strain distribution,shear stress evolution and local bond-slip curves of double-shear specimens are analyzed according to the full-field interface displacements obtained by DIC technology.It is found that when the load exceeds the platform load Pp,the mechanical anchorage at the end takes part of the interface stress,which leads to a great increase in the bearing capacity of the interface.（3）By designing a non-bonded zone at the loading end of double-shear specimen,the effect of mechanical anchorage on the ultimate bearing capacity of specimens with different bond lengths is explored,and the stress transfer characteristics of the interface with different bond lengths are discussed.It is concluded that the bond length has little effect on the load increment provided by end anchorage,but the CFL strain with shorter bond length is transferred faster and the length of the debonding zone is longer.（4）Based on the bilinear interfacial bond-slip constitutive model,the whole process theoretical model of interfacial debonding between end-anchored CFL and concrete is established.The calculation formulas of end slip,interfacial shear stress and normal stress of CFL are established.The calculation method for evaluating load-slip curves and ultimate bearing capacity of CFL-concrete interface is established.The theroretical results are in good agreement with the experimental results.（5）The damage process and failure modes of end-HB anchored double-shear specimens are analyzed through the hygrothermal environment pretreatment（design temperature is 10℃,23℃,50℃ and 60℃,design relative humidity is 50%,78%and 95%）and the hygrothermal environment-load coupling test.It is found that the hygrothermal environment will change the failure mode of the specimens,that is,the failure mode of the specimens will change from the shear failure of the concrete surface and severe concrete wear in the anchorage area in the indoor environment to the debonding failure mode of the epoxy resin adhesive and no concrete wear in the anchorage area in the high temperature and humidity environment.（6）Based on strain distribution,shear stress evolution and local bond-slip curves of double-shear specimens,the bonding performance of CFL-concrete interface and the effect efficiency of end anchorage under hygrothermal environment are discussed.The expressions of five characteristic values（k₁,k₂,τ_u,s₀ and S_f）in the bond-slip model in 50℃ and 78%RH environment are given respectively.