Passivation of Galvanized Reinforcement by Inhibitor Anions

Abstract

Concrete reinforced by galvanized reinforcing bars requires the addition of inhibitor anions to passivate the zinc; otherwise evolution of hydrogen reduces the bond strength. In the present study, zinc in saturated calcium hydroxide solution, which is the principal electrolyte formed on initial hydration of cement, was found to passivate in the presence of either sodium chromate or chromic oxide. In both cases chromate ions were reduced instead of water so that there was no evolution of hydrogen. The passive film consisted of zinc chromate and chromic oxide, but calcium hydroxo-zincate was also produced, which assisted in passivating the zinc surface. In the case of chromic oxide a smaller concentration of chromate ions was present and passivated the zinc to a lesser extent. While 70 ppm of sodium chromate was sufficient to passivate the zinc, at least 300 ppm of chromic oxide was necessary to achieve the same degree of passivation. Chloride ions in the presence of chromate ions compete for the zinc surface and a critical concentration of chromate is necessary. This observation has been correlated with the passivation of galvanized reinforcing bars in concrete and it is considered that passivation is best achieved by the addition of 70-ppm sodium chromate to the concrete mix.

The Influence of Graded Amount of Potassium Permanganate on Corrosion of Hot-Dip Galvanized Steel in Simulated Concrete Pore Solutions

“…Since the natural amount of CrO 4 2− in current cement production is very low (<10 ppm), the concentration needs to be increased [ 41 ]. While the positive effect of chromate anions on RDHE reduction has been proven [ 42 , 43 , 44 ], it is no longer feasible due to legislative limitations ([ 31 , 32 ]).…”

Electrochemical Corrosion Behavior of Carbon Steel and Hot Dip Galvanized Steel in Simulated Concrete Solution with Different pH Values

“…The electrochemical measurements were made at room temperature using a EG&G-PAR263A electrochemical workstation. The OCP data was recorded for 3600 s at a rate of 10 s after working electrode samples were immersed in SCP solutions of pH 10, 11, 12, 12.5, and 13 successively [15]. A three-electrode system was used with SCE as the reference electrode, a platinum electrode as the auxiliary electrode, and samples with exposed areas of 1 cm 2 as the working electrode.…”

Effect of Addition of Chromate to Concrete on the Bond Strength of Hot-Dip Galvanized Ribbed Rebar at Ambient Temperature

“…In this regard, addition of chromate anions (CrO4 2-) were discussed previously [7,8]. Formerly produced cements could contain higher amount of chromate anions (> 100 ppm) and in this case, the effect of chromates on hydrogen evolution was discussed [9] as well as the prevention of bond strength reduction between such concrete and rebar. Also, other, inorganic [10] and organic compouns [4] were tested.…”