Nitrite Binding in Cement and the Influence of Chloride Ions

If reinforced concrete contains chloride ions, e.g. due to the use of deicing salts, the reinforcement is no longer protected against corrosion. Nitrite salts are in use as corrosion inhibitors. As only nitrite ions dissolved in the pore solution of the cement matrix and not the ions bound in cement can inhibit, it is of great practical relevance to study the degree of nitrite binding in cement and the influence of chloride ions on it. Results show that nitrite ions are bound in cement to a certain degree, however to a lesser extent than chloride. In case of the simultaneous presence of both, chloride and nitrite ions, nitrite binding is further reduced. This is proven by pore solution analysis of cement paste samples prepared with the addition of nitrate or chloride and of both (NaCl and/or NaNO2). The nitrite concentration in pore solutions of the samples containing both salts is demonstrated to be higher than in comparable samples prepared with the addition of nitrite only.