PROTECTION OF STEEL IN PRESTRESSED CONCRETE BRIDGES

STUDIES WERE MADE OF FACTORS AFFECTING THE CORROSION OF STEEL IN PRESTRESSED CONCRETE BRIDGES AND OF POSSIBLE METHODS OF MINIMIZING THE CORROSION DANGERS. THE INVESTIGATION WAS DIVIDED INTO THE FOLLOWING PHASES: (1) A SURVEY OF DOMESTIC AND FOREIGN DATA ON CORROSION AND PREVENTION OF CORROSION ON PRESTRESSING STEEL IN BRIDGES AND OTHER STRUCTURES, INCLUDING CIRCULATION OF A QUESTIONNAIRE TO DETERMINE THE EXPERIENCE OF BRIDGE ENGINEERS WITH THE CORROSION OF BRIDGE TENDONS, (2) A REVIEW OF PRACTICES IN CURRENT USE FOR PREVENTING CORROSION OF TENDONS, (3) FIELD INSPECTIONS OF BRIDGES AND RELATED STRUCTURES TO ASCERTAIN THE EXTENT OF ANY DAMAGE TO TENDONS, (4) EXPERIMENTS TO IDENTIFY MORE CLEARLY THE CORROSION MECHANISMS AS AN AID IN DETERMINING THE DIRECTION NEEDED IN THE DEVELOPMENT OF PROTECTIVE COATINGS, (6) TESTS TO DETERMINE THE EFFECTIVENESS OF GROUTING METHODS, AND (8) PREPARATION OF RECOMMENDED SPECIFICATIONS FOR PROTECTIVE SYSTEMS, HANDLING, SHIPPING AND STORING OF TENDONS, METHODS OF PRESTRESSING, METHODS OF GROUTING, AND THICKNESS OF CONCRETE COVER. THE TESTS SHOWED THAT NEITHOR HYDROGEN EMBRITTLEMENT CRACKING NOT STRESS CORROSION CRACKING OCCUR WHEN THE PRESTRESSING STEEL IS IN A CHLORIDE-BEARING BEAMS EXPOSED TO 3.5% SODIUM CHLORIDE SOLUTIONS SHOWED CAN OCCUR AND IS CONSIDERED TO BE A POTENTIALLY SERIOUS PROBLEM IF CONCRETE COVER IS INADEQUATE OR IF THE PH OF THE CONCRETE IS LOWERED BY CARBONATION. PROTECTIVE COATINGS SHOWING THE GREATEST PROMISE WERE HOT-DIPPED GALVANIZED AND EPOXY. GALVANIZING LOWERED THE STEEL STRENGTH AND INCREASED RELAXATION. EPOXY COATINGS PROVIDED EXCELLENT CORROSION PROTECTION BUT WERE LACKING IN WEAR RESISTANCE AND EASE OF APPLICATION AS WELL AS IN COST. TESTS WITH PRETENSIONED BEAMSBEAMS EXPOSED TO 3.5% SODIUM CHLORIDE SOLUTIONS SHOWED THAT CONCRETE COVERS OF GREATER THAN 3/4 IN. ARE REQUIRED TO PROVIDE PROTECTION FOR THE STEEL, EVEN IN SHORT-TIME TESTING. LABORATORY STUDIES OF THE FLOW BEHAVIOR OF GROUTS PROVIDE INFORMATION ON SUCH VARIABLES AS WATER-CEMENT RATIO TYPE AND AMOUNT OF ADDITIVE, AND MIXING TIMES. A THEORETICAL EXPRESSION WAS DERIVED FOR COMPUTING PRESSURE DROPS, FLOW RATES, AND MAXIMUM PUMPING DISTANCE FOR GROUTS PUMPED INTO DUCTS WITH VARYING STEEL-TO-DUCT AREA RATIOS. EXAMINATION OF STEEL FROM FRAGMENTS OF PRESTRESSED BRIDGES AND PILES THAT HAD BEEN EXPOSED IN SEVERE ENVIRONMENTS FOR EXTENDED PERIODS SHOWED VIRTUALLY NO CORROSION OR LOSS IN PROPERTIES OF THE STEEL. IT WAS CONCLUDED THAT CONCRETE WHEN PROPERLY USED CAN PROVIDE SATISFACTORY LONG-TIME CORROSION PROTECTION FOR PRESTRESSING STEEL.

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    • 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. Originally published as NCHRP Research Results Digest, No. 5, March 1969, which was superseded by this report.
  • Authors:
    • Moore, D G
    • Klodt, D T
    • Hensen, Ronald D
  • Publication Date: 1970

Media Info

  • Media Type: Digital/other
  • Pagination: 86 p.
  • Serial:
    • NCHRP Report
    • Issue Number: 90
    • Publisher: Transportation Research Board
    • ISSN: 0077-5614
  • Publication flags:

    Open Access (libre)

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Filing Info

  • Accession Number: 00216975
  • Record Type: Publication
  • Files: TRIS, ATRI
  • Created Date: Aug 3 1970 12:00AM