Reinforced Concrete Electrochemical Monitoring Detection And Ph Affect The Mechanism Of Failure Process

Corrosion of reinforcing steel is the most significant deterioration process affecting reinforced concrete structures, therefore, the assessment of whole-life costing and residual service life prediction of structures is very important. The two most important causes of corrosion of reinforcing steel are carbonation and chloride contamination of the concrete. Carbonation is a problem that mainly affects buildings, while chloride contamination affects structures that exposed to de-icing salts or marine environments. Normally the reinforcing steel is chemically protected from corrosion by the alkaline (pH>13.5) nature of the concrete. If the alkalinity is lost through carbonation or if chlorides are present, the protective film is destroyed and the reinforcing steel is depassivated, then corrosion occurs. The objective of this present work is to investigate the different stages of corrosion process and the effect of the acidity for reinforcing steel in concrete mainly by electrochemical technology, especially EN technique.(1) Reinforced concrete specimens subjected to full-immersion test and wet-dry test have been investigated in this work. The corrosion behavior of reinforcing steel in concrete has been studied by electrochemical techniques, especially by electrochemical noise (EN). Scanning electron microscope (SEM) examination and optical observation have also been employed in this work. The experimental results show that the general corrosion rates of the reinforcing steel from wet-dry group are higher than that from the full-immersion group. Electrochemical impedance spectroscopy (EIS) and SEM images are in good agreement with the results obtained from the EN analysis.(2) The corrosion behavior of reinforcing steel in concrete under dry-wet cycle condition has been studied by EN compared with EIS. The statistical method has been employed to analyze the EN data of reinforcing steel in concrete, which revealed three different corrosion stages of reinforcing steel in concrete, including the dissolution of the passive film, the active corrosion and the cumulation of corrosion product. The wavelet transform has also been employed, which indicated steel in concrete with pH=1 is associated with uniform corrosion, while steel in concrete with pH=3 and pH=7 are associated with localized corrosion, such as pitting corrosion. From the analysis of the shot noise theory, it was found that pitting corrosion is enhanced in pH=1 solution. Electrochemical impedance spectroscopy (EIS) also indicated that there were three corrosion stages of reinforcing steel in concrete. During the first stage, the spectrum consists of two capacitive loops, indicating that the reinforced concrete system contained two time constants. The first loop in the high-frequency region was related to the capacitance and resistance of the concrete, while the second capacitive loop in the low frequency corresponding to the steel-concrete interface; during the second stage, there are three capacitive loops in the spectrum, the second capacitive loop in the intermediate frequency region should be ascribed to the rust layer of the steel; during the third stage, due to the diffusion of the corrosion product, the diameter of the semi-circles in the intermediate frequency region begin to decrease, especially in pH=1 system, it drops to very low value.(3) The pH values of the simulated concrete pore solutions have a great influence on the electronic band structure and components of passive film by which obtained from the Mott-Schottky plot. Electrochemical noise (EN) indicated that the passive film on steel surface is imperfect, and there are competitive between activation and deactivation during the immersion test. Contrast experiments indicated that HCO3-benefit the film forming on the steel and specific adsorption of the SO42- facilitate the corrosion of the steel.