| Chloride ion in marine environment will transport and concentrate in reinforced concrete structures,this will lead to durability problem as it triggers corrosion of reinforcement.Steel corrosion will induce serious consequences: cracking and spalling of concrete protective layers,weakening of the stirrups confinement and bonding between steel and concrete.The bonding between steel and concrete is the key to keep the two materials work together.It is essential to study the degradation of bond behavior after steel corrosion.There are numerous literatures available in this topic;however,the variation of the bond behaviors after steel corrosion was still not fully understood.In this paper,the concrete strength and stirrups were studied,and a total of 180 concrete cube specimens were produced.The concrete strengths are C20,C40 and C50 respectively.The target corrosion ratio of the stirrup is 0%,5%,10%,15% and 20%,respectively,and 12 test pieces for each working condition.In this paper,the research is carried out from two aspects.On the one hand,the stirrups are accelerated corrosion in laboratory,and the tested specimens are subjected to dry-wet circulation(Power on for 5 days and dry for 2 days).In the constant temperature and humidity environment,the initial state and each cycle state of the specimens were tested.The corrosion potential of the steel bars with different corrosion ratios was collected by the potential automatic recorder,while the PARSTAT 4000 electrochemical workstation was used to measure the linear polarization resistance in each period.Through the splitting test of all the test pieces,the actual corrosion ratio of the stirrups was calculated,and the quantitative relationship between the corrosion potential,the polarization resistance(corrosion current density)and the actual stirrups corrosion ratio were studied.The results show that the corrosion potential and linear polarization resistance of the same batch of specimens tested in the same period have little change;With the increases of the number of electricity circulation,the corrosion potential of the same number of steel bars in each test shows a significant first sudden drop,and then tends to decrease slowly;The corrosion current density of the steel bar tended to increase rapidly and keep a increasing slowly with the corrosion ratio of the stirrup;Regression analysis was performed based on all data points to obtain a nonlinear relationship between corrosion potential,corrosion current density and actual corrosion ratio of stirrups.On the other hand,the bond-slip test of corroded stirrup constrained concrete eccentric specimens was studied.The effects of different stirrups corrosion ratios on cracking of concrete protective layer were studied.The effects of the stirrups with different corrosion ratios on the bond-slip performance between the rebar and the concrete were studied under different concrete strength and placement positions.Finally,the test results were verified by mercury intrusion method.The results show that the specimens with different concrete strengths,both the crack width and the crack length,with the increase of the actual corrosion ratio of the stirrups,have the linear increase trend;In the case of the same target corrosion ratio,as the strength of the concrete increases,the maximum width,average width and total length of the crack increase.The porosity at the upper end of the specimens with concrete strengths of C20 and C40 is large,and the peak bond stress,initial stiffness,residual bond stress,mechanical bite force and energy consumption level are all firstly increased and then decreased gradually with the actual corrosion ratio of the stirrups.The lower end of the specimen with concrete strength of C20 and C40 and the upper and lower ends of the C50 concrete strength specimen,the peak bond stress,initial stiffness,residual bond stress,the mechanical bite force and energy consumption level all tend to decrease with the increase of the actual corrosion ratio of the stirrup. |
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