CAUSES AND REPAIR OF DETERIORATION TO A CALIFORNIA BRIDGE DUE TO CORROSION OF REINFORCING STEEL IN A MARINE ENVIRONMENT. PART II: FUNDAMENTAL FACTORS CAUSING CORROSION

AVAILABLE CONSTRUCTION RECORDS SHOW THAT, JUDGED BY PRESENT DAY STANDARDS, THE WATER-CEMENT RATIO OF THE CONCRETE IN THE SAN MATEO-HAYWARD BRIDGE WAS HIGH FOR THE CONDITIONS OF EXPOSURE. IT IS EVIDENT THAT THE CONCRETE HAS SUFFERED FROM SULFATE ATTACK TO A MODERATE, BUT NOT YET CRITICAL, DEGREE. THE CONCRETE HAS RELATIVELY HIGH ABSORPTION AND PERMEABILITY. HOWEVER, THE CONCRETE SHOWS LITTLE OUTWARD INDICATION OF DISTRESS OTHER THAN SEVERE CRACKING IN THE PLANE OF MAIN REINFORCING MEMBERS, ACCOMPANIED BY SEVERE SPALLING AT SOME LOCATIONS. IT IS EVIDENT THAT RUPTURE AND SPALLING ARE PRIMARILY THE RESULT OF PRESSURE CAUSED BY CORROSION PRODUCTS OF THE REINFORCING STEEL WHICH HAVE CHARACTERISTICS DIFFERING FROM THOSE FOUND ON STEEL SUBJECTED TO ATMOSPHERIC CORROSION. NO EVIDENCE COULD BE FOUND THAT STRAY CURRENTS HAD PRODUCED ELECTROLYSIS. CHLORIDES IN SAMPLES OF THE CONCRETE INDICATE THAT SUBSTANTIAL QUANTITIES OF SEA SALT HAVE BEEN ABSORBED. CHARACTERISTICALLY THE CONCENTRATION OF SALT VARIES FROM POINT TO POINT AND FOR THIS REASON MACRO GALVANIC CORROSION CELLS OF THE DIFFERENTIAL CONCENTRATION TYPE HAVE BEEN ESTABLISHED. ELECTRICAL POTENTIALS APPROACHING 0.5 HAVE BEEN MEASURED BETWEEN POINTS 2 TO 10 FT APART. POTENTIAL MEASUREMENTS OVER A SYSTEMATIC GRID ON THE SURFACE OF MEMBERS INDICATE THE EXISTENCE OF NUMEROUS, DISTINCT ANODIC AND CATHODIC AREAS. THE RATE OF CORROSION IS DETERMINED BY THE ACTIVITY OF THE CELL. VARIATIONS IN AVERAGE ATMOSPHERIC HUMIDITY AT DIFFERENT PARTS OF THE BRIDGE ARE BELIEVED TO EXPLAIN VARIATIONS IN THE RATE OF CORROSION. WHEN AFFECTED CONCRETE IS REMOVED AND REPLACED WITH NEW SHOTCRETE, THE PATTERN OF CATHODIC AND ANODIC AREAS IS CHANGED. LABORATORY TESTS HAVE CONFIRMED THE ROLE OF SALTS AND MOISTURE IN PROMOTING CORROSION. BOTH LABORATORY AND FIELD STUDIES ARE BEING CONTINUED. WORK ON TWO EXPERIMENTAL METHODS OF ELIMINATING OR RETARDING FUTURE CORROSION IS UNDER WAY AT THE BRIDGE SITE. THIS CONSISTS OF (1) CATHODIC PROTECTION AND (2) THE APPLICATION OF A COATING IMPERVIOUS TO OXYGEN TO THE SURFACE OF CATHODIC AREAS OF THE DECK UNITS. /AUTHOR/

• Record URL:
  • http://onlinepubs.trb.org/Onlinepubs/hrbbulletin/182/182-002.pdf
• Supplemental Notes:
  • No 182, pp 18-41, 28 FIG, 10 TAB, 27 REF Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Authors:
  • Tremper, Bailey
  • Beaton, John L
  • Stratfull, R F
• Publication Date: 1958

Media Info

• Monograph Title: Corrosion of reinforcing steel and repair of concrete in a marine environment
• Serial:
  • Highway Research Board Bulletin
  • Issue Number: 182
  • Publisher: Highway Research Board

Subject/Index Terms

• TRT Terms: Absorption; Anodes; Cathodes; Concrete; Concrete bridges; Corrosion; Cracking; Deterioration; Electric potential; Galvanic corrosion; Humidity; Laboratory tests; Permeability; Reinforcing steel; Seas; Shotcrete; Sodium chloride; Sodium chloride; Spalling; Sulfates; Water cement ratio
• Uncontrolled Terms: Concrete cracking; Corrosive environments
• Old TRIS Terms: Concrete bridge structures; Marine atmospheres
• Subject Areas: Bridges and other structures; Highways;

Filing Info

• Accession Number: 00208825
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: Sep 16 1994 12:00AM