Study On Corrosion Behavior And Difference Between Low Alloy Corrosion Resistant Reinforcement Bar And Common Reinforcement Bar In Concrete

The structural performance deterioration caused by steel-bar corrosion is related to the safety,applicability,economy and other requirements of the structure.On the one hand,the steel-bar corrosion reduces its mechanical properties,on the other hand,it makes the protective layer expand and spall along the steel-bar,which leads to the decrease of the bond performance between steel-bar and concrete,and finally leads to the early failure of the performance of reinforced concrete structure.How to improve the structural performance is a problem that scholars pay close attention to all over the world.It is an effective method to improve the structural performance starting with the performance of materials and using low alloy corrosion-resistant steel-bar.Therefore,the development and research of low alloy corrosion-resistant steel-bar is of great significance to improve the service life of the structure Based on the National Natural Science Foundation of China(NSFC)project "Study on the evolution and difference of service performance between corrosion-resistant steel-bar and ordinary reinforced concrete columns in marine environment"(No.:51678513),the corrosion resistance of HRB400 ordinary low carbon steel,5Cr low alloy corrosion resistant steel-bar and 5Cr1Ni low alloy corrosion resistant steel-bar in concrete was studied comparatively.The corrosion behaviors of three kinds of steel-bar were studied by means of electrochemical method,X-ray diffraction and SEM scanning.The differences of critical chloride ion concentration,corrosion rate,corrosion products and morphology among the three kinds of steel-bar were revealed.The main research work is as follows:(1)The depassivation critical chloride ion concentration of common low carbon steel-bar and low alloy corrosion resistant steel-bar in concrete was studied by the method of chloride ion natural infiltration.The open-circuit potential and anodic polarization current were used to judge the depassivation condition of steel-bar,and the polarization curves before and after depassivation were studied.Finally,the surface powder of steel-bar depassivation was ground,and the critical chloride ion concentrations of three kinds of test steel-bar were obtained by RCT chloride ion measurement method.The results show that the depassivation time of low alloy corrosion-resistant steel-bar is longer,and critical chloride ion concentration ratio of common steel-bar to 5Cr steel-bar and 5Cr1Ni steel-bar is 1:1.06:1.19.(2)The corrosion rate of common low carbon steel-bar and low alloy corrosion resistant steel-bar in concrete was studied by natural penetration of chloride ion and accelerated corrosion by dry and wet cycles.The self-corrosion potential and corrosion current of steel-bar were fitted by Tafel extrapolation method in weak polarization region.The corrosion rate of steel-bar was characterized by corrosion current density.The difference of corrosion rate of three kinds of steel-bar in concrete was analyzed.The results show that the corrosion rate of the three steel-bar in concrete increases firstly,then decreases and finally stabilizes with time.The corrosion rate of common steel-bar is the fastest,that of 5Cr steel-bar is the second,and that of 5CrlNi steel-bar is the slowest,the ratio is about 4:2:1.(3)The corrosion morphology and composition of corrosion products of low carbon steel and low alloy corrosion resistant steel in concrete were studied by means of immersion dry-wet cycle and energizing corrosion in laboratory.The composition of corrosion products and the microscopic appearance after corrosion were analyzed by means of X-ray diffraction and SEM scanning.The results show that there are many corrosion products in common steel,among which Fe2O3 and Fe3O4 are the most,and contain ?-FeOOH and ?-FeOOH.After rust,the surface is corroded in bulk,with more gullies,wider cracks and deeper cracks.The corrosion products of 5Cr steel-bar are less than that of common steel,and there is no instable ?-FeOOH.The surface of rust steel is rich in Cr grains,and the cracks are narrower and shallower than that of common steel.The corrosion process of 5CrlNi steel-bar is the slowest and the corrosion products are the least.The surface of steel-bar after rust is a dense small corrosion pit and the cracks are shallow.