A Study On Corrosion Behavior Of Rebar In Reinforced Concrete Under Carbonation Condition

For decades researchers and relevant institutions have summarized different detection and monitoring methods with high efficiency and convenience basing on massive research results of rebar corrosion,through which standards with considerable reliability for the assessment of rebar corrosion condition and residual life for reinforced concrete structures were established.However,less studies were done on the mechanism of concrete carbonation,one of the other important factors which lead to rebar corrosion.In spite of the fact that a basic theory ofcarbonation-induced corrosion is generally accepted,there are still relatively fewer researches on effects of bicarbonate ion and carbonate ion introduced to pore solution on rebar corrosion,as well as the specific electrochemical reaction types and processes.Therefore,the corrosion behavior of rebar in reinforced concrete under carbonation condition is studied based onsimulated concrete pore solution under laboratory condition,using electrochemical method and surface analysis.The main work in this thesis can be concluded as below:?1?Linear polarization measurement was performed,where corrosion potential and linear polarization resistance results obtained,along with the macroscopic feature,are used to judge the corrosion condition of rebar,while the effect of bicarbonate ion and carbonate ion on rebar corrosion was studied.It is found that concrete carbonation may leads to rebar corrosionthrough not only the pH drop in pore solution,but also bicarbonate ion and carbonate ion's promotion effect on rebar corrosion.?2?Cyclic voltammetry behavior of rebar specimens in different electrolytes were studied to explain the types and processes of reactions during rebar corrosion from the electrochemical aspect.Meanwhile,phase analyses of corrosion products were carried out through X-raydiffraction technology to discuss the effect of Ca²⁺on rebar corrosion under carbonation condition.The results shows that rebar corrosion is a gradual oxidation process of Fe,after which iron oxides with higher valence state and structural complexity are produced.Ca²⁺can alter the reaction path of rebar corrosion which leads to the difference of corrosion products.?3?Electrochemical impedance spectrum of rebar specimens in solutions with different pH and compound methods were measured and fitted with different equivalent circuits.Electrochemical processes during measurement were briefly explained and the measurement and fitting results were used to judge the corrosion condition.The result infers that pHthresholds vary with the ionic environment of solutions and can be significantly different from each other.The reliability of corrosion condition judgment method through solution pH islimited.