The application of electrochemical impedance spectroscopy to determine the long-term effectiveness of corrosion inhibitors for steel in concrete

The excellent corrosion resistance of steel in reinforced concrete is decreased in the presence of chloride ingress the carbonation of this cover.
The use of inhibitors is one of several possible methods to protect rebar from corrosion. The most common practice is their addition together with the mixing water of concrete.
In this work, we have studied the effect of two “commercial” inhibitors: calcium nitrate and alkanolamine on the corrosion resistance of reinforcing steel, as function of time.
The concrete tested was made with 400 kg m−3 Portland cement, which has a high resistance to sulphate, and the water–cement ratio was equal to 0.4. Inhibitors were introduced in fresh concrete mix at different contents. Tests were conducted with reinforced concrete specimens.
Specimens were immersed in salt solution (0.5 M of NaCl) for three years. During this period, the condition of steel was monitored each year, with measuring zero-current potential and electrochemical impedance spectroscopy (EIS).
It appears that alkanolamine based inhibitor has not a negative effect on the bulk concrete cover. However, calcium nitrate inhibitor does not improve the concrete properties. These “commercial” inhibitors are not effective, when chloride is present on the steel–concrete interface.