Electrochemical noise analysis of carbon steel in simulated concrete pore solution affected by CO2 and SO2 using wavelet transform

Purpose - The aim of this paper is to show that the use of energy distribution plot (EDP), usually employed by researchers to characterize the behavior of electrochemical signals in the framework of wavelet transform, could provide better understanding of the electrochemical behavior of a corroding surface if used along with the plot that is obtained from the standard deviation (SD) of partial signals (SDPS). A partial signal (PS) is obtained by limiting the inverse discrete wavelet transform to one crystal, and hence an SDPS is obtained by computing the SD of the corresponding PS. Design/methodology/approach - The electrochemical current signals, obtained from two identical working electrodes (carbon steel electrodes) exposed to simulated concrete pore solution, sparged simultaneously with SO2 and CO2 were studied using wavelet transforms. Findings - The results show two steps of passive oxide layer formation: formation of defective passive oxide layer, and strengthening of the passive oxide layer. The passive oxide layer breakdown where CO2 as well as SO2 are involved occurred at a pH of approximately 11. Both the EDP and SDPS plots should be used, simultaneously, to characterize the processes occurring on the surfaces of the exposed electrodes. Practical implications - The results that were obtained can be regarded as the basis for better understanding and improvement of the noise analysis method. Originality/value - This paper studies the corrosion behavior of carbon steel rebar before and after the simultaneous introduction Of CO2 and SO2 gases in simulated pore solution, using EDP and SDPS plots obtained from the electrochemical current signals at different pH values.