Study On Constitutive Relation Of The Interface Between CFL And Concrete In Hot-wet Environment Under Fatigue Loads

As the outstanding characteristics such as light weight, designability, high strength,good fatigue resistance, corrosion resistance, fiber reinforced plastic (FRP) was widelyapplied to strengthen reinforced concrete structures in civil engineering. The interfacebetween FRP and concrete was the transition layer which transferring the stress from FRPto structures. Recent researches showed that main failure mode was debonding. Therefore,the behavior of the interface layer directly affected the load capacity and fatigueperformance of the strengthened structures. So to study on the bond stress–slip relationshipbetween FRP Sheet and concrete under fatigue load and wet-thermal condition wasimportant in science and application.The study here focused on the interface between the carbon fiber laminate (CFL)which invented by our research group and concrete. Taking consideration of the servingcondition of highway bridges influenced by hot-wet environment, we explored thebond-slip relation of carbon fiber laminate (CFL)-concrete interface under hot-wetenvironment and fatigue load, based on experiments and theory analysis. The main contentsand conclusions based on experimental study were as followed:(1) Conditions for the hot-wet environment were set basing on the characteristics ofsubtropical climate. After accelerating simulation, the specimens were carried out withdouble-shear experiments. The fatigue life, load-deflection relationship, the relativedisplacement between two blocks and the progress for the strains on CFL under peak loadwere analyzed in the paper. Results showed that high temperature and humidity caused anincreasing deformation, a larger ultimate displacement and a significant reduction of fatiguelife.(2) Through whole observation during the test showed that the evolution of fatiguefailure process of CFL-concrete interface appeared obviously3-stages after ot-wetenvironmental pre-treatment. It included the early cracking of concrete, stably debonding ofthe interface and the unstably debonding of the interface.(3) A preliminary study on the evolvement of bond stiffness for the interface wascarried out based on the experimental results. Besides, we proposed a constitutive relation of the interface between CFL and concrete in hot-wet environment under fatigue loads byusing the Popovics functional form.