Effect of a Nitrate-Based Corrosion Inhibitor on Carbonation-Induced Corrosion

Corrosion inhibitors are additives that can work both as a preventative technique to delay the onset of corrosion or as a protection system to reduce corrosion rate, once corrosion is initiated. Several substances have been evaluated as possible candidates, both organic and inorganic in nature. Recently, a nitrate-based compound has been proposed as a corrosion inhibitor, as nitrates are still used in concrete as set accelerators. Nitrates inhibiting mechanism is similar to nitrites, the latter being the most efficient compound nowadays available. This work evaluates the effect of a nitrate-based corrosion inhibitor on carbonated-induced corrosion in concrete. Results show that the addition of calcium nitrate (4% vs. cement weight) can delay the carbonation penetration rate: the carbonation coefficient is reduced by about 30% with respect to the noninhibited specimens. Once corrosion is initiated, nitrate-based inhibitor, even at a high dosage (4% vs. cement weight), is not effective in reducing the corrosion rate: values as high as 10 μm/y were measured after about 2 y of external exposure.