Experimental Study On Bond Properties Between Corroded Steel Bar And Concrete Under High Temperature

With the rapid develop ment of infrastructure constr uction,the durability proble m of reinforced concrete structure is becoming more and more serious,especia lly the durability deterioration caused by reinforce ment corrosion.Moreover,fire disaster of build ing as lo became to a serio us proble m around the world,and this ma y happ ened more frequrently on aging structures whic h possib ly suffer ing the reinforceme nt corrosion.The reinforceme nt corros ion lead to volume expens ion o f steel bar whic h could cause concrete cover crack and the steel bar exposed to the atmosphere.Therefore,the bond perfor mance between steel bar and concrete deteriorated severely when reinforced concrete with corrosion cracks exposure to high te mperature or fire.However,previo us studies genera lly cons idered either steel corrosio n or high temperature effect on concrete-steel bond perfor mance,and the research on the coup ling effect of steel corrosio n and high temperature was few.In this study,pull-out test of corroded steel bar embedded in concrete under high te mperature was carr ied out on a specia lly designed apparatus which can e liminate the influe nce of high temperature on the load ce ll.The coup ling effect of corrosion and high temperature on steel-concrete bond perfor mace was stud ied systematically.The ma in effort and achievement include the following aspects:(1)A simp lified method for pull-out test under high temperature was proposed and a pull-out test apparatus for eliminating the influe nce of high te mperature on load ce ll was designed.The pull-out test of the steel bar embedded in concrete under high temperature was carried out on the specia lly designed apparatus us ing the s implified method.(2)The influence of steel corrosion on tangentia l bond stiffness was stud ied.Meanwhile,the influe nce of corrosion on pull-out force energy be fore peak force and bond stress release rate of pull-out specime n was also stud ied.A simplified three-stage test method and conservative model of bond strength degeneration were proposed by regressive analys is of the data of the previo us studies and current experiment.Fuether more,a three-stage bond-s lip constitutive model was proposed cons idering influe nce of corrosion o n resid ua l bond strength in the perspective of the release rate of bonding stress.(3)The degradation law of reinforcement strength,tensile splitting strength o f concrete and the bond performa nce between rebar and concrete at high temperature were investigated.Further more,the relatio n between steel-concrete bond perfor mance and concrete mechanica l properties under high te mperature was ana lyzed.Meanwhile,the influence of high temperature on tangential bond stiffness was studied.(4)The variation trend of bond perfor mance between steel bar and concrete under the coup ling effect of high temperature and corrosio n was syste matically studied.Furthermore,the variation law of bond strength with the ele vated temperature at same corrosion rate was stud ied,as well as bond strength with increasing corrosion leve l at sa me temperature.The bond strength model under ele vated temperature was proposed.Moreover,a simplified three-stage bond-slip constitutive relation between corroded bar and concrete under high te mperature was proposed based on bond strength model.