Study On Passivation And Re-corrosion Characteristics Of Corroded Steel Bar Embedded In Concrete

Reinforced concrete is one of the most widely used building materials in the world,and it is widely used in the construction of engineering structures such as buildings,bridges and roads.However,due to the influence of materials and environment,concrete has a greater durability problem.Among them,steel corrosion is the most important factor affecting the durability of concrete,and it is also the focus of concrete durability research.The production,transportation and storage process of steel bars have always been in the atmosphere,and may encounter construction accidents,etc.,which makes the steel bars inevitably have some initial corrosion before they are buried in concrete.These corrosions will definitely affect the steel bars.The passivation and rust behavior in the concrete has an effect,which in turn affects the service life of the concrete structure.In this paper,the corrosion behavior of steel bars with different initial rust surfaces in concrete under chloride environment is studied,and the influence of initial corrosion of steel bars on the corrosion process in concrete is revealed.In this paper,the steel bars with different initial corrosion degree were made by simulating the dry and wet rusting of the natural environment.The dynamic potential scanning anodic polarization test was combined with electrochemical test,acoustic emission monitoring and microscopic observation to study the corrosion of steel bars.Passivation and rust behavior.The results show that when the area ratio of steel corrosion is less than 20.52%,the corrosion steel can still passivate,but the stability of the passivation film gradually decreases with the initial corrosion degree.When the corrosion area rate reaches 46.58%,the steel bar can not be passivated;Corrosion causes weak spots on the surface of the steel bar.Corrosion of the steel bar is more likely to occur at the weak point,forming local corrosion.The frequency of the pitting signal is between 25 and 55 k Hz during the rusting process,and the frequency of the cracked acoustic signal of the hot-rolled skin is between 100 and 300 k Hz.The degree of corrosion increases the amount of pitting signals.The rust corrosion process of corroded steel bars in concrete was studied by using dry and wet cycles to accelerate corrosion of corroded reinforced concrete specimens under chloride environment.Electrochemical test and acoustic emission monitoring were used.The results show that the corrosion characteristics of slightly corroded steel bars with initial rust area ratio of 5.06% in concrete are almost the same as those of uncorroded steel bars.However,the initial corrosion degree of steel bars is further increased,and the re-corrosion start time of concrete in concrete will be advanced.When the rust area rate reaches 46.58%,the steel corrosion process continues.The main frequency of the acoustic emission signal in the rust process is about 25～75k Hz,100 k Hz and 175 k Hz.With the rust process,the high frequency signal is weakened and the low frequency signal is increased.