Steel Bar Corrosion In Reinforced Concrete Structures And Its Prevention Approach In Seawater

Currently,many researches foucus on the steel corrosion of reinforced concrete structures in the splash zone which may face dry/wet alternate environment with high salt concentration.Therefore,many efforts have been made on the corrosion process and protecting methods of reinforced steels in concrete structures in the splash zone.Unlike the splash zone,little attention was paid on the corrosion of reinforced steels in seawater,as the dissolved oxygen in seawater is deficient,and the corrosion is considered hard to occur in this area.However,some concrete reinforced structures in seawater were reported to be corrosive in some researches.The accumulation of corrosion products will lead to the expansion of concrete and even spalling.Then the corrosive ions will reach the steels through the cracks,which will result in more serious corrosion,consequently the strength of the steel will decrease.Eventually the marine structures are probably led to fail in design service life.Therefore,it is of great significance to study the corrosion process,the mornitoring and protecting methods of the steels under concrete layers in seawater to guarantee good performance and stability of marine reinforced concrete structures.The main works of this dissertation are as follows:A real sea test is carried out to confirm that the corrosion of steels under concrete layers in seawater will occur.Then the effect of the concrete layer thickness and water cement ratio on the steel corrosion are studied by comparing the corrosion area ration of the specimens.The general corrosion processes of pre-passive steels in simulated pore solution added chloride ions and sulfate ions are studied using the methods of open circuit potential(OCP),linear polarization resistance(LPR)and electrochemical impedance spectroscopy(EIS).Then the wire beam electrode(WBE)is employed to study the propagation of localized corrosion of steels in different solutions.And the coupling effect of sulfate ions and chloride ions on the localized corrosion is researched when the simulated pore solution contains these two kinds of ions at the same time.After investigating the traditional corrosion monitoring methods,an electrical resistance multi-electrodes sensor is introduced to in-situ monitor the localized corrosion of steels accurately and quantificationally.Furthermore,a test is set up to study the effect of sulfate ions on the localized corrosion of steels which have been corrosive in the choride ions contained simulated pore solution to simulate the real corrosion process in marine environment and verify the feasibility of the sensor.Based on a good understanding of the essential corrosion condition and the actual conditions of the seawater,a novel corrosion protecting method,called Electrochemical Dissolved Oxygen Removal(EDOR),is proposed.The factors that influence the corrosion processes,such as the pH value and the dissolved oxygen concentration,are monitored for 48 hours in this system.And the effects of the dissolved oxygen consumption under different output currents and flow rates are compared.Then the corrosion rate of the steels under EDOR protection is monitored.At last,a comparative analysis is conducted between the SEM images of two bare steel specimens immersed in the underwater zone for 30 days with and without EDOR protection.