Effect Of Calcined Hydrotalcite On Steel Bar Corrosion In Chloride Ion Environment

Corrosion of steel bars is an important cause of premature failure of building structures.In different environments,reinforced concrete structures will suffer from various forms of damage.Chloride ion erosion,as one of the main factors causing corrosion of steel bar.Because of its discrete distribution,the corrosion caused by it is more urgent and unpredictable.Eventually,the lack of durability of concrete structures will cause huge losses to actual projects.Therefore,early monitoring of steel bar corrosion is particularly important.Corrosion of steel bars is a process of electrochemical reaction,and electrochemical method is a common monitoring method for corrosion of steel bars in steel-concrete structures.Compared with the traditional physical method and analytical method,electrochemical method has the advantages of fast,non-destructive,sensitive and real-time,and has been widely used in engineering research.In order to deal with the corrosion of steel bars in concrete,scholars have conducted extensive research.Among them,adding corrosion inhibitor to concrete is a simple and economical method to prevent corrosion.With the development of research,hydrotalcite with anion adsorption and exchange ability has become the focus of researchers.The calcined products(CLDHs)produced by hydrotalcite after calcination can absorb chloride ions through interlayer exchange to inhibit corrosion reaction,which has a good protective effect on steel bars.In this paper,the corrosion inhibition effects of hydrotalcite on steel bars with two surface states in simulated concrete solution with different calcination temperatures and different contents are compared,and the protection mechanism of calcined hydrotalcite is discussed.In this paper,firstly,the desensitization critical value and corrosion tendency of steel bars with different surface conditions under chloride ion erosion were compared by self-corrosion potential electrochemical method.On this basis,the self-corrosion potential,polarization curve and polarization resistance method were used to study the reaction and action mechanism of steel bar specimens after adding calcined hydrotalcite at different temperatures and different amounts.The results show that:(1)The steel bars with two surface states are passivated when immersed in the simulation solution added with CLDHs.(2)With the addition of CLDHS,the resistance of reinforcement to chloride ion erosion is gradually stronger;When the chloride ion concentration in the simulated solution is increased,the corrosion inhibition effect of CLDHs is weakened,and the best effect is obtained when CLDHS is added at 500?,which significantly improves the electrochemical stability of steel bars.(3)The existence of oxide film makes the formation of passivation film on the surface of steel bar incomplete,and the anti-rust effect of CLDHs on steel bar with oxide film is slightly lower than that without oxide film.At the same time,the morphology and changes of hydrotalcite before and after calcination were analyzed by XRD and SEM,and the corrosion formation of steel bar surface was characterized by optical microscope.The risk parameters of steel bar corrosion were evaluated by measuring and calculating the p H value and Cl~-/OH~-molar ratio before and after adding CLDHs,and the protection mechanism of CLDHs on chloride ion corrosion process of steel bar under two surface conditions was discussed.The results showed that:(1)After calcination at 500?,the interlayer of hydrotalcite collapsed and the ions could be controlled.(2)After adding CLDHs,the p H value of the simulated solution increased significantly,and the Cl~-/OH~-molar ratio of steel bars without oxide film decreased from 11764 to 0.14,while steel bars with oxide film decreased from 6779 to 1.38.(3)With the increasing proportion of CLDHs,the corrosion products on the surface of steel bars decrease step by step,and the corrosion resistance of steel bars shows a rising trend.The corrosion inhibition mechanism of calcined hydrotalcite was preliminarily discussed,and the changes of electrochemical parameters of steel bars in two surface states were monitored.The corrosion inhibition effects of calcined hydrotalcite on steel bars without oxide film and steel bars with oxide film in simulated pore fluid were compared under different calcination temperatures and different dosage.The test results show that the addition of calcined hydrotalcite has a good corrosion inhibition effect on steel bars in chloride ion environment,which greatly enhances the corrosion resistance of steel bars.