Critical ratio, inhibitor/chloride

Laboratory studies of steel in mortar showed that by applying several intense flushings before the ingress of chlorides [6], the onset of corrosion during the test duration of 90 days could be prevented even at chloride concentrations as high as 2 % by mass of cement. A critical concentration ratio MFP/chloride greater than 1 had to be achieved, otherwise the reduction in corrosion rate was not significant [6]. MFP acts as a corrosion inhibitor in carbonated concrete as well. 

E7.5. Corrosion of passive metals occurs by pitting in chloride solutions. This pitting can be prevented by the addition of anionic inhibitors. At a critical ratio of adsorbed chloride ions to adsorbed anion, the passive film is displaced by chlorides, allowing a pit to initiate. 

The efficiency of calcium and sodium nitrite as inhibitors in concrete has been reported by several authors (Gaidis and Rosenberg, 1987 El-Jazairi and Berke, 1990) since the early 1970s. The investigations, conducted using different experimental techniques in solutions, mortar and concrete, revealed a critical inhibitor (nitrite) to chloride concentration ratio of about 0.6. This implies fairly high nitrite concentrations in the pore water of concrete. Nitrite acts as a passivator due to its oxidizing properties and stabilizes the passive film accord-... 

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