Experimental Study On Degradation Of Mechanical Behavior Of Corroded Reinforcement Concrete Material And Pier Models In Marine Environment

Reinforced concrete steel are vulnerable to corrosion due to presence of Cl-1 in marine environment.The corrosion will reduce the cross-sectional area of reinforcement,degrade bond action between steel and concrete,and introduce tensile stress due to rust expansion and eventually lead to cracking/spalling of concrete cover.These material and interface degradation will inevitablely result in corrosion damage of reinforced concrete structures and reduction of load-bearing capacities.However,due to the stochastic nature of the steel corrosion,it is still hard to quantify the reduction just by the limited information of steel corrosion mass(area)loss in laboratory or cover crack opening in engineering practice.This paper tries to address the above input-output puzzle in the following three aspects: axial load test of bearing capacity of concrete cylinders conctraint by corroded stirrups and statistical analysis of mechnical performance of corroded steel,test of load-bearing capacity of corroded piers.Firstlly,15 stirrups confined concrete cylindrical specimens were made and the stirrups were artificially corroded with different corrosion level.The specimens were axial loaded in compresson and the force,the axial deformation and the expansion in lateral direction were recorded.Test results showed that the width and length of concrete cover cracks with high concrete strength are relative larger than that of low concrete strength at the same corrosion level.The ultimate compressive force,the initial stiffness,the ductility coefficient and the energy dissipation of the corroded specimens decreased with the increase of corrosion level.The ultimate compressive force,the initial stiffness of specimens with lower concrete strength decreased more seriously than that of higher concrete strength.Three factors that affected ultimate compressive force of specimens were simluated and analyzed,the reduction of stirrups cross-sectional area,the cracking of concrete cover due to corrosion and the degradation of bond performance.Test results showed that the peak load,initial stiffness and energy dissipation of debonding specimens and deprotection specimens were lower than that of intact specimen.The reduction in the cross-sectional area of the stirrups is a major factor in the degradation of the ductility coefficient and energy dissipation.Secondly,29 natural corroded steel bars and 13 plain bars obtained from an existing bridge located in eastern of Shenzhen.The change of residual cross-sectional area of corroded steel bars along the length was tested using the drainage method,and then tensile test.Meanwhile,the parameters of mechanical behavior of corroded steel bars were analyzed and compared with other test results.And finite element simulation analysis was used to study the effect of pitting corrosion on mechnical behavior of corroded reinforcement.Test results showed that the dimensionless yield strength,the dimensionless ultimate strength and the dimensionless elongation of the corroded specimens are negatively correlated with the corrosion level;however,the dimensionless ratio of ultimate strength to yield strength is hardly affected by the corrosion.Moreover,12 reinforced concrete bridge pier models were made based on the demolished bridge in the eastern of Shenzhen as a prototype,and pier models were artificially corroded.6 pier models with different corrosion level were axial loaded while other 6 pier models were tested under reversed low cycle loading till failure.The test results showed that the failure modes of the members with 20% target corrosion level are significantly different from that of other members,no matter the compressive test or cyclic loading test.For small corrosion level,the peak load,ductility coefficient and initial stiffness of the axial compression members all increased slightly.For serious corrosion,these parameters were smaller than that of intact pier member,but the energy dissipation of corroded pier models always decreased.For cyclic loading,the secant rigidity is gradually reduced with the progress of the test,but the energy dissipation is gradually increased.And the degradation rate of corroded members is larger than that of intact specimen,while the growth rate of corroded members is smaller.The plastic hinge of the severely corroded pier model is transferred.