Experimental Study And Theoretical Analysis About Bond Of Corroded Reinforcement In Concrete Confined With CFRP

Reinforced concrete structure is one of the most commonly used structures inthe world at present. The reinforcement and concrete can work together which dependon the bond at the interface. The reinforced concrete structure would be affected bycoupling effect of environmental pollution and various loading damage during theservice life. Therefore, the reinforcement is more prone to corrosion, and deteriorationeffect is happened, and the safety, serviceability and durability of the reinforcedconcrete structure are drastically reduced. To improve the life and serviceability of thereinforced concrete structure, various technologies are used to strengthen the damagedbuildings. Carbon fiber reinforced polymer (CFRP) composites have manyadvantages, for example, high tensile strength, resistance to corrosion, high strengthto weight ratio and high stiffness. Therefore, CFRP sheets have been used forrehabilitation and strengthening of corroded reinforced concrete structures widely, butthe problem is that theoretical research lags behind the engineering application，andmany strengthen mechanism and phenomenon need more research. The existingproblems about the bond of corroded reinforcement and concrete confined with CFRPhave been studied experimentally and analyzed theoretically in this paper. Anelectrolyte corrosion technique was used to accelerate the corrosion of the steel bar incylindrical concrete specimens. The specimens were divided into two types: withstirrup and without stirrups. Bond of corroded reinforcement and concrete wrappedwith CFRP has been studied, and the main research contents and conclusions are asfollows:1. Twenty-eight specimens were experimentally studied to investigate theinfluence of CFRP confinement on the bond between corroded reinforcement andconcrete under monotonic loading. Three confinement methods of CFRP were used asfollows:(a) un-wrapped specimens;(b) post-wrapped specimens;(c) pre-wrappedspecimens. Experimental results indicate that:(1) the bond of corroded reinforcementand concrete was improved significantly by the CFRP, especially the pre-wrapped specimens;(2) the reinforcement corrosion rate was reduced because of CFRPconfinement;(3) CFRP confinement could change the bond failure from the concretesplitting to bar pull-out;(4) based on the test results, theoretical bond models weresetup for the bond strength under different confinement conditions．2. Thirty-eight specimens were experimentally studied to investigate theinfluence of CFRP confinement on the bond between corroded steel bars and concreteunder fatigue loading. Two confinement methods were used as follows:(a)un-wrapped specimens;(b) post-wrapped specimens. Loading levels were0.65,0.75and0.85. Experimental results indicate that:(1) the fatigue life is affected greatly bythe corrosion rate of reinforcement and the fatigue loading stress level.When thespecimens with the same corrosion rate, the fatigue bond life is reduced greatly as thestress level increased. When the specimens with the same stress levele, the fatiguebond life is reduced greatly as the corrosion rat increased;(2) the CFRP confinementcould improve the bond fatigue life effectively when the specimens with the samecorrosion rate and stress level;(3) the fatigue bond failure criteria is that, when thebond is equal to the upper limit fatigue loading because of cumulative damage, thebond failure is happened;(4) the fatigue bond failure is brittle failure, and the steel barwith greater slip when the specimens wrapped with CFRP, and CFRP confinementcould change the fatigue bond failure from concrete splitting to bar pull-out.(5) Testresults revealed that the fatigue loading cycles has no affection to the residual bond ifthe loading level is less than the0.5.3. Sixteen specimens were experimentally studied to investigate the influence ofCFRP confinement on the bond between corroded steel bars and concrete under cyclicloading. Two confinement methods were used as follows:(a) un-wrapped specimens;(b) post-wrapped specimens. Experimental results indicated that:(1) the bond ofwrapped specimens and unwrapped specimens are degraded gradually due to cyclicloading, especially the first cycle loading;(2) CFRP can reduce the bond degradationrate effectively;(3) CFRP confinement could change the bond failure from theconcrete splitting to bar pull-out;(4) the steel bar was pull-out under monotonicloading after ten cycle loading, and test results reveal that the residual bond strengthdegradation is more greatly than the fatigue loading;(5) based on the experimentalresults, theoretical bond models were setup for the bond under cyclic loading.4. Ten specimens were wrapped with none-layer, one layer, two layers, threelayers and four layers CFRP respectively. The affection of different layers of CFRP to the corrosion rate and bond were studied experimentally. Test results indicated that:(1) the mechanism of CFRP repair reinforced concrete structures could reduce thecorrosion rate of reinforcement is that: epoxy could decrease permeability of theoxygen, water and chloride in the concrete, CFRP wraps is able to confine concrete,slowing deterioration from cracking and spalling;(2) CFRP confinement could reducethe corrosion rate significantly, but when the CFRP more than two layers, theaffection is little;(3) the bond strength was improved greatly by the CFRPconfinement, two layers of CFRP confinement could reach the best strengthen effectwhen the specimens without stirrups, but when specimens with stirrups, one layer ofCFRP confinement could reach the effect;(4) time-variant corrosion rate models ofunwrapped specimens and wrapped specimens were setup according to the current.