Combined effect of marine environment and pH on the impedance of reinforced concrete studied by electrochemical impedance spectroscopy

Abstract

In the present investigation, behavior of OPC and fly ash based concretes were assessed by electrochemical impedance spectroscopy (EIS) technique after exposing the samples to the marine environment in combination with five pH levels (1, 4, 7, 10, and 13). Three different dosages of fly ash (15, 25, and 35%) were used to produce fly ash based concretes. After 90 days of exposure to the aggressive environment, the OPC and fly ash based concretes were tested for impedance analysis and corrosion resistance by electrochemical studies. For the equivalent electrical circuit in EIS study, a total of four electrical circuits were tried for the possible best fit of obtained Nyquist plots. The equivalent electrical circuits proposed by previous researchers failed to provide the best fit for the obtained Nyquist plots. A new equivalent electrical circuit is being proposed in this study which will provide the possible best fit of Nyquist plots when the concrete is being exposed to acidic and alkaline marine environment. It is observed that the pH of the marine environment has a decisive influence on the impedance of reinforced concrete. As the acidity of marine environment reduces to pH 1, the impedance of OPC and fly ash based concrete reduced significantly due to the severe deterioration of concrete composites especially because of acid attack and Cl− ions migration. However, in the case of alkaline nature of the marine environment (pH 13), there was comparably less deterioration of concrete composites which reflected in higher impedance values. The higher dosage of fly ash addition has led to substantial improvement in concrete impedance and also lower corrosion rate.