EIS Investigation on the Influence of Natural Releasing of Inhibitor from Coral Aggregate on the Steel Corrosion in Coral Aggregate Concrete

Abstract Steel corrosion in coral aggregate concrete (CAC) mixed with different inhibitors was investigated using electrochemical impedance spectroscopy (EIS) technique in this paper. Considering the porosity characteristic of coral aggregate, a novel method of premixing inhibitor into coral aggregate was proposed and compared with the conventional mixing method for inhibitor. Three equivalent circuits were proposed and validated for the interpretation of EIS data of CAC. Finally, the influences of inhibitor type (calcium nitrite [CN] and amino-alcohol [AA] inhibitor), inhibitor content, and mixing method on the steel corrosion in CAC were analyzed and discussed through the EIS results. Results indicated that there were good fitting effects for the proposed circuits fitting the EIS data of steel in CAC mixed with different inhibitors. The anticorrosion effect of 3 % CN inhibitor is better than that of 2 % AA inhibitor in early phase (0–180 days), whereas the effect of the latter is more pronounced than the former in late period (180~270 days). In addition, according to the evolution of passive film resistance of steel in CAC, the premixing method is proven to be more effective than the direct-mixing method in long-term anticorrosion work. Finally, a unified equivalent circuit was established to interpret the EIS data of CAC, which has a promising significance in the further investigation of steel corrosion in CAC.