Abstract
This study compares corrosion activities of carbon steel B450C and SS 430 (Mn in low content) exposed for 30 days in cement extract solution. Iron oxide and hydroxide were formed as corrosion products, in addition to CaCO3, in the presence of Cr2O3 on SS 430. Because of the decrease in pH, B450C lost the passive state when OCP shifted to negative values, while SS 430 showed positive OCP values, maintaining its passive state. The SEM images confirmed that the corrosion attack on the surface was less aggressive for SS 430. The Nyquist plots of EIS initially showed capacitive behavior and later changed to semi-linear diffusion impedance, which SS 430 maintained firmly. The phase angle Bode diagrams confirmed these changes. Two equivalent circuits were applied. The calculated values of Rp for SS 430 increased over time (protective passive layer mainly of Cr2O3 oxide), while for carbon steel, Rp reached maximum value after 168 h and then decreased, maintaining minimum values approximately five orders lower than those of the stainless steel.
Highlights
Concrete is one of the most widely used materials in the construction industry because of low cost and mechanical performance [1]
A variety of alkaline solutions simulating the electrolytic environments of concrete pores have been used in order to evaluate the electrochemical behavior of steel-reinforced concrete over a short period of time, the proposed models differ in the results obtained [24,25,26]
Electrochemical Impedance Spectroscopy (EIS) measurements were performed at the open circuit potential (OCP), applying an AC signal of ± 10 mV amplitude, in a frequency range from 100 kHz to 10 mHz, and with a sampling size of 10 data points/decade
Summary
Concrete is one of the most widely used materials in the construction industry because of low cost and mechanical performance [1]. A variety of alkaline solutions simulating the electrolytic environments of concrete pores have been used in order to evaluate the electrochemical behavior of steel-reinforced concrete over a short period of time, the proposed models differ in the results obtained [24,25,26]. This research compares the corrosion activity of commercial Italian carbon steel to that of low chromium ferritic Finnish stainless steel, exposed for 30 days in cement extract unbuffered solution in order to simulate the concrete environment at the steel-concretepore interface. Both steels have been proposed as reinforcement in a lower pH of concrete than the traditional pH of Portland cement-concrete, in the presence of binders. No other research on this topic has been previously undertaken
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