THE EFFECT OF SODIUM CHLORIDE ON THE CORROSION OF CONCRETE REINFORCING STEEL AND ON THE PH OF CALCIUM HYDROXIDE SOLUTION

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 OCCURED AT A SODIUM CHLORIDE CONCENTRATION AS 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 PH OF SATURATED CALCIUM HYDROXIDE DECREASED WITH INCREASING NAC1 CONCENTRATION UP TO 2.4 M NAC1, THE HIGHEST CONCENTRATION STUDIED, AND INCREASED WITH DECREASING NAC1 CONCENTRATION. SMALL ADDITIONS OF NAC1 TO CHLORIDE-FREE SATURATED CALCIUM HYDROXIDE UP TO A CONCENTRATION OF 0.008 M ACTUALLY PRODUCED AN INCREASE IN PH. THE RESULTS INDICATE THAT PH REDUCTION MAY BE A CONTRIBUTIN FACTOR IN STEEL CARROSION IN CONCRETE, BUT DO NOT CONCLUSIVELY PROVE THAT IT IS. NEVERTHELESS, THEY SUGGEST THE DESIRABILITY OF INVESTIGATING THE ADDITION OF ALKALINE MATERIALS TO CONCRETE AS MEANS OF RESTORING A SUITABLE PH AND THEREBY PREVENTING STEEL CORROSION. /FHWA/

• Corporate Authors:

  Federal Highway Administration

  Chemistry and Coatings Group, Materials Division, 1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Berman, H A
• Publication Date: 1974-1

Media Info

• Pagination: 24 p.

Subject/Index Terms

• TRT Terms: Bridge decks; Calcium hydroxide; Chlorides; Corrosion; pH value; Reinforced concrete; Reinforcing steel; Resistivity method; Salts; Sodium chloride
• Subject Areas: Bridges and other structures; Geotechnology; Highways; Materials;

Filing Info

• Accession Number: 00216007
• Record Type: Publication
• Report/Paper Numbers: FHWA-RD-74- 1 Intrm Rpt., FCP 24B1-032
• Files: TRIS, USDOT
• Created Date: May 7 1976 12:00AM