Study On Electrochemical Corrosion Behavior Of Stray Current In Mortar In Coastal Environment

Stray Current refers to the flow of current outside design or regulation loop. It is also known as "vagabond flow". The most common source is city subway which used direct current pulled. Reinforced concrete main structure of the subway will be affected by the threat of stray current corrosion. For coastal chlorine areas, the durability of reinforced concre te structure suffered with superposition effect of stray current corrosion and chloride ion erosion facing a more serious problem, and the corrosion degradation mechanism under the action of both factors mentioned above is more complex than single factor effect.Stray current laboratory simulation system was designed in this paper, studied the reinforcement corrosion and degradation mechanism suffered with stray current and chloride ions in concrete. In this paper, it also compared the difference between direct current and stray current. The main results obtained are as follows:1) Stray current laboratory simulation system, which is different from DC stray current simulation method, based on measured subway stray signal characteristics, is designed innovative. The system can achieve with the measured signal frequency and the equivalent simulation of dual polarity. The system can also exactly reflect the real characteristics of stray current, and the stability and reliability of the simulation system is verified by experiment.2) Based on discrete data of Fourier transform method, frequency-domain analysis was proceeded using MATLAB preparation of spurious signal spectrum characteristics analysis. It is found the stray current dominated by DC component and AC components are mainly concentrated in 0-0.1 Hz. By frequency statistics analysis also found that the stray current size is normally distributed, the greater the disturbance amplitude stray, the role of the shorter the time, and the statistical mean there is a non-zero offset.3) The stray current and direct current corrosion experiment was carried on using bare metal specimen dipping in simulated concrete pore solution and the reinforced mortar specimens as the research object. The results show that the DC analog stray current overestimated the harm of stray current corrosion, at the same time, no matter what DC or SC and chloride ion significant all effect on steel corrosion. In addition, unlike DC corrosion, stray current corrosion behavior of reinforced mortar and stray current average non- zero offset direction is closely related, are offset direction acceleration steel corrosion, while negative deviation direction of cathodic protection for steel bar.4) By means of linear polarization(LPR), scanning electron microscopy(SEM) and energy spectrometer(SEM/EDS) and X-ray diffraction(XRD), and other testing methods, this paper expounds the common under the action of stray current and chloride ion corrosion mechanism of reinforced mortar: when there is c hloride ion, the stray current dual polarity make power on both ends of the steel surface passivation membrane are rapid destruction of the non- zero average is offset direction(A), mainly the anodic dissolution reaction of the metal, and hydroxyl and enrichment of chloride ion in steel- mortar interface area, and in nonzero mean negative deviation direction(B), mainly cathode oxygen or hydrogen evolution reaction, and as a result of hydrogen ions in steel- mortar interface zone of enrichment and neutralization of interfacial area.