Study On The Corrosion Mechanism Of The High-Strength Corrosion-Resistance Steel Reinforcement And Inhibitor In Marine Structures

The corrosion of steel reinforcement in marine environment is serious,leading to the premature damage of concrete and the decline of safety and durability of engineering structure.This paper focuses on the low alloy steel reinforcement,aiming to obtain the effect mechanism of alloy element(Cr)and chloride-sensitive inhibitor.Natural corrosion tests,modern physical technologies,electrochemical methods,simulation calculation based on first principles,and machine learning were performed,to study the corrosion electrochemical mechanism of Cr bearing low alloy and high strength steel in the micro solution,the long-term corrosion behavior of Cr bearing steel in marine field,the inhibition behavior and mechanism of chloride-sensitive inhibitor on the high strength steel,and the synergistic effect of Cr and chloride-sensitive inhibitor on the steel corrosion.The corrosion electrochemical behavior of Cr bearing steel reinforcement in the concrete pore solution is different from that in the conventional bulk electrolytic cell.The corrosion of 5Cr steel is significantly inhibited with the decrease of solution volume.When compared with that in the bulk solution,the pitting potential in the micro solution of 30 ?L moves forward by 250 mV,and the corrosion current density decreases by 3 times.What's more,there is a good linear relationship between the local corrosion rate and the logarithm of pore volume.The cathodic process of steel corrosion does not change a lot with the pore volume,while the anodic process is inhibited in the micro solution.The main reason of the suppressed anodic process is that the Fe2+ enrichment leads to the positive shift of equilibrium electrode potential,the increase of passive film resistance,and the enhancement of anodic polarization retardation.A good agreement exists between the actual corrosion behavior in reinforced concrete and that in the micro solution.However,the corrosion rates of steel reinforcement in the conventional electrolytic cell system have been over-evaluated.The Cr bearing steel reinforced concrete structure preforms fine corrosion resistance and durability in the actual marine splash zone.The corrosion area of 5Cr steel is 6 times lower than that of HRB400,and the local corrosion rate is 3 times lower.At the corrosion progress stage,Cr increases the Fe2+ and OH-content and decreases the ?-FeOOH content in the corrosion products,improving their buffer ability to corrosive ions.In addition,the water content of corrosion products is lower for the Cr bearing steel,increasing the film resistance and decreasing the electrochemical activity.What's more,the rusts formed on Cr bearing steel are more density with lower oxidation degree,inhibiting thier expansion effect on concrete.As a result,the corrosion rate of Cr bearing steel reinforcement reduces,and the concrete durability increases.According to the long-term and non-uniform reinforcement corrosion,a chloride sensitive corrosion inhibitor of Zn-Al-NO2 LDH with controlled release,long-term and targeted function is designed,which shows good corrosion inhibition performance in the polluted concrete environment.NO2-ions in the Zn-Al-NO2 LDH are easy to be replaced by Cl-and CO32-in the environment,which realized on-demand release of inhibitor in the concrete environment.The corrosion inhibition efficiency of 5 g/L Zn-Al-NO2 LDH is as high as 81%in the simulated concrete solution with 1 wt.%NaCl and pH 11.5,that is,the corrosion rate decreases by an order of magnitude.Zn-Al-NO2 LDH exhibits better long-term corrosion inhibition performance than traditional NaNO2,as the chloride ion threshold and critical[NO2-]/[Cl-]decrease by 1.7 times and 3 times,respectively.The long-term corrosion inhibition of Zn-Al-NO2 LDH is due to the on-demand release of nitrite ions and the timely repair of steel oxide film.In the chloride induced and/or carbonated concrete,Zn-Al-NO2 LDH spontaneously adsorbs Cl-,CO32-and releases NO2-through the ion exchange reaction.The stimulation of CO32-on Zn-Al-NO2 LDH is more significant,resulting in Zn-Al-CO3 LDH with thinner interlayer spacing,stronger interlayer interaction,and the more stable structural.The traditional corrosion inhibitor NaNO2 is consumed in the early passivation stage,in order to form a passivation film with higher polarization resistance,thicker space charge layer and fewer defects.Compared with the traditional NaNO2,Zn-Al-NO2 LDH prolonged the protection cycle by releasing inhibitor ions slowly and on-demand,repairing the metastable damage of oxide films and maintaining the thickness of space charge layer and density of oxide films.The synergistic usage of Cr-bearing steel and chloride-stimulated corrosion inhibitor had efficient protection efficiency to the reinforcement corrosion.The polarization resistance of steel reinforcement with different Cr content at different pH,chloride concentration and LDH dosage was obtained based on the support vector machine algorithm.The machine learning model provided quantitative guidance for the selection of alloy element and inhibitor in the carbonation and chloride induced concrete.