Nitrite binding in cement

Abstract

Pore solution has been pressed out of hardened cement pastes prepared with the addition of nitrite-containing corrosion inhibitors. The binding of nitrite was assessed by comparing the concentration in the mixing water with that in the pore solution in both the presence and absence of chlorides. The results indicate that a major controlling mechanism is the adsorption of nitrite and chloride ions on the surface of hydration products. However, there is clear competition between adsorption of nitrite and chloride on cement and as a result at the presence of chloride there is more free nitrite available to inhibit steel corrosion. Using calcium nitrite results in lower free nitrite and hydroxyl ion concentrations than when sodium nitrite is used because precipitation of calcium hydroxide is enhanced and therefore higher dosage rates are needed. All this information enables guidance for the satisfactory use of nitrite inhibitors to be produced.