SODIUM CHLORIDE, CORROSION OF REINFORCING STEEL, AND THE PH OF CALCIUM HYDROXIDE SOLUTION

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 measured is not directly affected by the presence of sodium chloride. The salt affects the voltage only indirectly by its tendency to initiate steel corrosion. Corrosion in saturated calcium hydroxide solution exposed to air occurred in these tests at a sodium chloride concentration as low as 0.03 molar. This threshold concentration was raised to 1.0 molar when oxygen was excluded. To determine whether pH change might be a factor in corrosion, measurements were made in a carbon dixoide- free atmosphere on the pH change produced by addition of sodium chloride to saturated calcium hydroxide solution. The pH of saturated calcium hydroxide decreased with increasing NaCl concentration and increased with decreasing NaCl concentration. Small additions of NaCl up to a concentration of 0.008 molar actually produced a pH increase. The results indicate that pH reduction may contribute to steel corrosion in concrete, but do not conclusively prove that it does. Nevertheless, they suggest the desirability of investigating the addition of alkaline materials to concrete containing, or exposed to, chloride ions above the critical concentration, as a means of restoring a suitable pH and thereby preventing steel corrosion. /Author/

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  • Accession Number: 00096133
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jul 2 1975 12:00AM