Effect of sodium nitrite on chloride-induced corrosion of steel in concrete

Abstract

Corrosion attack on reinforcement steel in concrete causes cracking, loss of bond strength, reduction in steel cross-section, and decrement of serviceability. Among the various measures applied to protect corrosion of steel, the use of inhibitors is one of them. The present work evaluates the effectiveness of sodium nitrite as corrosion inhibitor in inhibiting chloride induced corrosion attack on reinforcement steel in concrete. Electrochemical tests included half-cell potential and linear polarization resistance were carried out on steel in concrete specimens. For electrochemical tests, reinforced concrete prisms with a steel bar placed centrally were made from concrete mixes using 53 grade Portland cement at w/c ratio of 0.50 and admixed with different dosages of sodium chloride and sodium nitrite. The dosages of sodium chloride used were 3% and 6% (by cement mass) and the dosages of sodium nitrite were 0%, 1.5%, 3%, and 4.5% (by cement mass). At the end of 28 days of curing, the prisms were dried for 10 days in laboratory exposure condition and then exposed to chloride solution containing 3% sodium chloride with alternating wet-dry process. The electrochemical tests were conducted on the prisms at different intervals. At the end of exposure period to chloride environment, free chlorides of the prisms at different depth intervals were determined. In addition, concrete cubes were also prepared from the same concrete mixes to obtain the 28-day compressive strength. The obtained results indicated that addition of nitrite in concrete admixed with chloride reduces the compressive strength of concrete. Further, corrosion of steel in concrete increased with increment in the dosage of admixed chloride salts. The addition of nitrite minimized the corrosion attack on steel bar in concrete and its effectiveness against corrosion was enhanced at higher dosages. With an increment in dosages of admixed sodium chloride, the free chlorides increased at all depth intervals from concrete surface. However, there was no noticeable variation in free chlorides with admixed sodium nitrite dosages at different depth intervals from the concrete surface.