Experimental Study On The Bond Performance Of Epoxy-coated Rebars And Seawater Sea-sand Concrete Under CFRP Confinement

The use of seawater and sea-sand for concrete mixing can effectively solve the shortage problems of fresh water,river sand and other constructional materials in marine engineering.However,the corrosion of steel rebars could easily occur because of the large amount of sulfate and chloride contents in seawater sea-sand concrete.The corrosion problems can be effectively alleviated by using epoxy-coated rebars instead of the ordinary black steel rebars due to the excellent corrosion-resistance of the external coating.However,the bond strength between epoxy-coated rebars and concrete is lower than the ordinary black steel rebars due to the smooth surface of the coating.Besides,the externally bonded CFRP(Carbon Fiber Reinforced Polymer)sheets can constrain the concrete cracking and hence improve the bond performance between seawater sea-sand concrete and epoxy-coated rebars.The bond performance between concrete and rebars is the basis of deformation compatibility.Evaluating the bond behavior between seawater sea-sand concrete and epoxy-coated rebars under CFRP confinement is relatively important,and it has a great significance to practical applications.In this paper,a total of 112 specimens were fabricated and tested under uniaxial tensile load to investigate the effect of CFRP confinement on the bond performance between epoxy-coated rebars and seawater sea-sand concrete.The main contents of this paper are listed as follows:(1)Based on the test results of epoxy-coated rebars and seawater sea-sand concrete under CFRP confinement,the failure modes and the characteristics of each loading stage were analyzed.The effects of the type of concrete and bars,concrete cover,number of stirrups and CFRP on bond performance were analyzed.The results show that the bond strength of rebars and seawater sea-sand concrete is higher than normal concrete.Same as the previous research,bond performance is slightly weakened due to the external epoxy coating.It can be found from the specimens confined with CFRP sheets that the failure modes change from the concrete splitting failure to the pull-out failure,and the confinement of CFRP sheets can significantly improve the bond behavior between concrete and bars.Moreover,the bond strength is increased with the concrete cover,the number of stirrup and CFRP layer.(2)Based on the previous research,the ultimate bond strength between two types of rebars and seawater sea-sand concrete without CFRP was analyzed.The confining pressure of CFRP was used to evaluate the effect of CFRP on the ultimate bond strength of the specimens.Moreover,the theoretical formulas in calculating the ultimate bond strength between two types of rebars and seawater sea-sand concrete under CFRP sheets were established.(3)According to the bond-slip curves of seawater sea-sand concrete and rebars under the CFRP confinement,an appropriate shape was selected in the fitting process.A new bond-slip model was also proposed based on fitting results for seawater sea-sand concrete under CFRP confinement.Good agreement can be achieved for the test results,which can provides the valuable reference for the applications of CFRP confined epoxy-coated rebars reinforced seawater sea-sand concrete structures.