CFRP-Steel Interface Modification And Durability Under Freeze-Thaw Environment

Carbon Fiber Reinforced Polymer(CFRP)externally bonded steel structure is considered as a potential steel structure strengthening technology because of its superior material properties and convenient construction.It was found that the longterm durability of the interface of CFRP-steel decreased greatly in the corrosion environment,which is mainly due to the deterioration of the interface structural adhesive in the corrosion environment,which leads to the premature and serious peeling off of the reinforced interface.Therefore,how to improve the durability of CFRP-steel interface in corrosion environment is the key to ensure the long-term service performance of CFRP strengthened steel structure system.Based on the damage mechanism of bond interface of CFRP-steel under freeze-thaw environment,two interface modification lifting methods are proposed in this paper,and the bonding properties of modified interface in room temperature and freeze-thaw environment are studied systematically.Main research contents are as follows:(1)The structural adhesive was modified by liquid rubber(QS-BE),and the influence of QS-BE content(0%,5%,10%and 15%)and adhesive layer thickNess(0.5mm,1 mm and 2mm)on the interfacial adhesion was studied by CFRP-steel double shear specimen system.Three-Dimensional Digital Image Correlation(3D-DIC)was used to test the displacement field and strain field of the interface.Scanning Electron Microscope(SEM)was used to analyze the damaged interface,which revealed the mechanism of QS-BE on interface modification.The results showed that when QS-BE content was constant,with the increase of adhesive layer thickNess,the interface failure mode changed from adhesive layer failure to mixed failure.the interfacial maximum strain,maximum slip and fracture energy gradually increased.When the adhesive layer thickNess was constant,with the increase of QS-BE content,the interfacial fracture energy showed a trend of first unchanged and then decreased.When QS-BE content is too much,the rubber particles dispersed in the interface agglomerate in a certain area,which leads to the decrease of interfacial adhesion.On this basis,the bond-slip relationship of the modified interface was determined,and the double-fold-line bondslip model of CFRP-steel modified interface was established by studying the variation of key parameters of bond-slip with adhesive layer thickNess and QS-BE content.(2)The interface of CFRP-steel was treated with silane coupling agent to enhance the adhesion of steel adhesive interface.The effect of silane coupling agent on the interfacial bonding properties of CFRP-steel was systematically studied by adding silane coupling agent into structural adhesive or smearing on the surface of steel plate.It was found that the ultimate load and interfacial fracture energy increased slightly when silane coupling agent of 2%was added to the structural adhesive.When silane coupling agent was applied on the surface of steel plate,the failure mode of the specimen was steel-adhesive interface failure.The bearing capacity and maximum peeling strain were greatly reduced,and The operation was more tedious,which was not conducive to practical engineering application.(3)The durability performance of CFRP-steel specimens modified by QS-BE was used to study the durability under freeze-thaw environment.The results showed that after 200 freeze-thaw cycles,the mechanical properties of the unmodified structural adhesive decreased significantly,while the performance of the modified structural adhesive decreased slightly.With the increase of freeze-thaw cycles,the interface failure mode of the specimens without QS-BE gradually changed from the adhesive layer to the adhesive-steel interface.The interface ultimate load and maximum peeling strain both decreased.The interface failure mode of the specimens modified with QSBE were adhesive layer,the ultimate load and the maximum peeling strain were basically unchanged at first and then decreased with the increase of freeze-thaw cycles.On this basis,the bond-slip relationship of the modified interface was determined after the freeze-thaw environment,and the degradation model of the key parameters of the bond-slip relationship was established by introducing the freeze-thaw damage factor.Finally,the key parameter degradation model was established.The bond-slip degradation model of modified interface under freeze-thaw environment was established by introducing the bond-slip relationship of the double-broken line.