The Effect of Sodium Chloride on the Corrosion of Concrete Reinforcing Steel and on the pH of Calcium Hydroxide Solution.

摘要

The electrical half-cell potential measurement is a valid technique for detecting the existence of corrosion in the steel reinforcement of chloride-containing concrete. The voltage which it measures is not directly affected by the presence of sodium chloride. The only effect of the salt on the voltage is an indirect one,caused by the tendency of sodium chloride to initiate the corrosion process in steel. Corrosion in saturated calcium hydroxide solution exposed to air occurred at a sodium chloride concentration al low as 0.03 M. This threshold concentration was raised to 1.0 M when oxygen was excluded. To determine whether pH change might contribute to the cause of corrosion,measurements were made in a carbon dioxide-free atmosphere on the change in pH produced by the addition of sodium chloride to saturated calcium hydroxide solution. The results indicate that pH reduction may be a contributing factor in steel corrosion in concrete,but do not conclusively prove that it is. (Modified author abstract)