Calcium nitrite corrosion inhibitor in portland cement: Influence of nitrite on chloride binding and mineralogy: Fid-Bau Portal

Calcium nitrite corrosion inhibitor in portland cement: Influence of nitrite on chloride binding and mineralogy

Balonis, Magdalena / Glasser, Fredrik P.

'Smart' behavior of cements containing nitrite corrosion inhibitor has been observed. Nitrite can be stored within the AFm phase. Sequestered nitrite is released in response to chloride ingress. Entering chloride displaces nitrite from the AFm and is bound by forming Friedel's salt. Released nitrite ions are liberated to an aqueous phase and result in increased [NO2(-)]/[Cl(-)] ratios, which are important to assure corrosion inhibition of embedded steel. The storage capacity of cement systems for nitrite is influenced by design of the cement system. Alumina and sulfate contents, which affect the balance between AFm and AFt phases and accordingly, total AFm, are important variables with which to optimize the first instance nitrite storage and subsequently, the 'smart' release mechanisms triggered by chloride ion penetration. Cements, with low SO3/Al2O3 ratio, will have initially more AFm formed and therefore higher capacity for nitrite storage and, subsequently, for chloride binding to solids. That is, the capacity of the cement to behave as 'smart' material with respect to corrosion control is itself a function of cement composition. However, maximizing sequestered nitrite is not the only factor for optimization. In general, the corrosion protection afforded by nitrite is not believed to be much affected by calcite additions or the presence of soluble alkalis at low concentrations and form the basis of a robust system for protection of embedded steel.