A mechanistic study of corrosion inhibiting admixtures

Abstract

PurposeThis research aims to unravel the role of salt contamination and corrosion inhibiting admixtures in the processes of cement hydration and rebar corrosion.Design/methodology/approachMortar samples were prepared with NaCl and one of three corrosion inhibitors, sodium nitrite, disodium β‐glycerophosphate, or N,N′‐dimethylethanolamine, admixed. After 28 days curing, all steel‐mortar samples were ponded with 3 percent NaCl solution and electrochemical impedance spectroscopy (EIS) measurements were conducted periodically during the first 48 days. After 60 days of ponding by 3 percent NaCl solution, field‐emission scanning electron microscopy (FESEM) analyses were conducted on the fracture surface of the steel‐mortar sample.FindingsThe FESEM results revealed that admixing chlorides and inhibitors in fresh mortar changed the morphology and cement hydration product of hardener mortar at the steel‐mortar interface. The EIS data indicated that all inhibitors increased the polarization resistance of steel, implying reduced corrosion rate of the steel over 48‐day exposures to salt ponding. 0.05 M N,N′‐dimethylethanolamine was the most effective corrosion inhibitor, followed by 0.5 M sodium nitrite; whereas 0.05 M disodium β‐glycerophosphate was a slower and less capable corrosion inhibitor. The admixing of inhibitors in fresh mortar consistently increased the capacitance and decreased the electrical resistance of hardened mortar. The effect of sodium nitrite inhibitor on the resistance of steel mortar interfacial film compensated that of corrosive NaCl by participating to the formation of a protective ferric oxide film.Originality/valueThe results reported shed light on the complex role of admixed salt and corrosion inhibitors in cement hydration and their implications on the durability of steel‐reinforced concrete.