Effect Of Corrosion Inhibitors On Steel Bars And Microstructure Of Passivation Film In Carbonated Concrete

Reinforced concrete still plays an irreplaceable role in the application of civil engineering.At present,incorporating corrosion inhibitor is the most economical and effective way to solve the durability problem of reinforced concrete.The passivation film is the main barrier to prevent corrosion of steel bars,thus the ultimate cause of corrosion of steel bars can be attributed to changes in the composition and structure of the passive film.As the content of CO₂in the atmosphere increases year by year,carbonization is receiving increasing attention.Therefore,it is of great significance to investigate the effect of corrosion inhibitor on the microstructure of passivation film under carbonization aiming at improving the dull environment on the surface of steel bars in concrete and developing new and efficient corrosion inhibitors.In this paper,carbonization is used as a corrosive environment,takes the cement paste test specimens with built-in steel bars,reinforced concrete test pieces,and simulated steel bars in carbonized solutions as research objects.The immersion test,XRD,SEM and XPS,combining with half-potential method,polarization curve method and electrochemical method with AC impedance spectroscopy,weight loss rate of steel bars and corrosion area rate,were used to investigate the effect of internal corrosion inhibitors on the composition and microstructure characteristics of rebar passivation film under carbonization conditions,and to clarify the relationship between corrosion inhibitors and electrochemical corrosion,which can also provide a theoretical basis for optimizing the amount and proportion of rust inhibitors and the composition of the oxide scale on the surface of the steel bar to improve the corrosion resistance of the steel bar.The main research results are as follows:1.Under the condition of carbonization,the test block without rust inhibitor began to corrode in the early stage of carbonization,and the resistance of the blunt steel bar gradually decreased with age.The incorporation of a corrosion inhibitor can have a wonderful rust inhibition effect,increasing the electrochemical impedance and corrosion potential of the test piece,slowing down the decline rate and speed of the natural potential of the steel bar in concrete,and reducing the corrosion area and weight loss of the steel bar.The corrosion inhibition effect of cathode-type and composite-type corrosion inhibitors will increase with the increase of the amount of corrosion inhibitors,while anode-type corrosion inhibitors will cause pitting of reinforcing steel at a certain concentration and promote the corrosion of the steel bar.2.Comprehensive corrosion resistance performance:composite type>anode type>cathode type,the corrosion inhibition effect in anode type rust inhibitor:sodium molybdate>sodium chromate,sodium molybdate can form Fe-MoO₄-Fe₂O₃ on the surface of steel bars,so the surface passivation film can effectively slow down the corrosion of the steel bar.The corrosion resistance effect of the cathode type corrosion inhibitor:BTA>DMEA.Among the composite corrosion inhibitors,sodium molybdate+BTA has the best corrosion resistance effect,the natural potential,corrosion rate and weight loss rate are all can be kept in a good range;which has a superior engineering application prospects to a certain extent.3.In simulated carbonized solution,the steel bars in the test group doped with 0.5%and1.0%corrosion inhibitors had different degrees of corrosion,and the surface of the steel bars did not rust in the test group with 2.0%corrosion inhibitors.The iron peak analysis was performed on the surface of the steel bars by using XPS technology,the main component of the passivation film on the surface of the steel bar was FeOOH,followed by Fe₂O₃,Fe²⁺,and Fe°,the content of FeOOH is always the highest in any conditions,reaching more than 50%.The incorporation of corrosion inhibitors will promote the conversion of FeOOH into Fe₂O₃.Through X-ray diffraction technology,the main components of the passivation film have been further verified.4.In simulated carbonization solution,the passivation film of the steel bar incorporating the corrosion inhibitor is mainly FeOOH,Fe₂O₃,Fe²⁺,and Fe°,and a small amount of Fe element does not participate in the composition of the passivation film.The main components of the rebar passivation film in cement paste mixed with corrosion inhibitor under carbonization conditions are FeOOH,Fe₃O₄,FeO,Fe₂O₃.The density of the passivation film on the surface of the steel bar is related to the type of corrosion inhibitor.The better the corrosion inhibition effect,the higher the amount of FeOOH converted to iron oxide.5.Under carbonation,the corrosion inhibition effect of the test group with a water-cement ratio of 0.3 is better than that of the test group with 0.4.Among them,sodium molybdate can react with Fe²⁺to form a protective layer of FeMoO₄,and at the same time promote the conversion of FeOOH into denser oxides such as Fe₃O₄,FeO,etc,and play a role in corrosion prevention.In the cathodic corrosion inhibitor,the rebar passivation film mixed with BTA is denser than DMEA,BTA can complex with iron.In the composite rust inhibitor,the composition of the sodium molybdate+BTA passivation film is more abundant and dense,and the iron oxide content is high.