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PROTECTIVE COATINGS FOR HIGHWAY STRUCTURAL STEEL

A CURRENT STATE-OF-THE-ART SURVEY IS PRESENTED WITH REGARD TO PAINTING OF HIGHWAY STRUCTURAL STEEL. A THOROUGH LITERATURE REVIEW WAS CONDUCTED AND AN INSPECTION AND EVALUATION MADE OF MORE THAN 4,000 PAINT EXPOSURE TESTS. PAINT FILM THICKNESS MEASUREMENT STUDIES WERE MADE. SPECIFIC RECOMMENDATIONS ARE GIVEN FOR SELECTING TYPICAL PAINT SYSTEMS ON THE BASIS OF SIX ENVIRONMENTAL ZONES, WHICH REPRESENT THE RANGE OF SEVERITY OF ENVIRONMENT IN WHICH HIGHWAY STEEL STRUCTURES ARE LOCATED IN THE UNITED STATES. MODEL SPECIFICATIONS ARE SUGGESTED FOR SURFACE PREPARATION, APPLICATION, MATERIAL PROCUREMENT, AND PAINT SYSTEM. ALTERNATE PAINT SYSTEMS WERE PROVEN FOR USE IN PLACE OF PRIMARY SYSTEMS IN EACH ZONE. THESE INCLUDE EPOXIES, CHLORINATED RUBBER, COAL TAR EPOXIES, SILICONE-ALKYD FINISH COATS, AND HIGH-BUILD COATINGS, AS PROVEN BY STEEL-PAINTING EXPERIENCE OF HIGHWAY DEPARTMENTS AND OTHER USERS. CRITERIA INFLUENCING THE CHOICE ARE DISCUSSED, INCLUDING COST, APPEARANCE, DESIGN, AVAILABLE MATERIALS, AND APPLICATION EXPERIENCE. COATINGS DISCUSSED WHICH DESERVE SPECIAL ATTENTION FOR HIGHWAY USE INCLUDE: WATER-BASE PAINTS, SOLVENT-FREE MATERIALS, COLORED ALUMINUM PAINTS, NON-LEAFING ALUMINUM INTERMEDIATE COAT, COLORED FINISH COATS, AND REFORMULATIONS MEETING AIR POLLUTION CONTROL REQUIREMENTS. CONDITIONS ARE ALSO INDICATED UNDER WHICH PAINTING MIGHT BE ELIMINATED IN FAVOR OF METALLIZING, GALVANIZING, GREASE-COATING, OR USE OF UNPAINTED STEEL. A RESUME IS PRESENTED OF THE BEST CURRENT PRACTICES OF THE HIGHWAY AND STEEL-PAINTING INDUSTRIES. ABOUT ONE-FIFTH OF THE STATES REQUIRE BLAST CLEANING, AND ANOTHER FIFTH ARE CONSIDERING IT. AIRLESS SPRAY, HOT SPRAY, AND ROLLER APPLICATION ARE PROVING EFFECTIVE, BUT MANY STATES REQUIRE BRUSHING OF PRIMER, PARTICULARLY OVER HAND-CLEANED STEEL. NEW PAINTS IN USE INCLUDE BASIC LEAD SILICO CHROMATE PIGMENTATION IN CONVENTIONAL VEHICLES, ZINC-RICH PAINTS (BOTH ORGANIC AND INORGANIC) WITH SUITABLE TOPCOATS, AND VINYL SYSTEMS FOR OTHER SEVERE EXPOSURES. THE MOST PRESSING PROBLEMS SEEM TO BE FILM THICKNESS, INSPECTION, PAINTING EDGES, POOR SPECIFICATIONS, DE-ICING SALTS, PAINTING BOLTED JOINTS, AND LACK OF OBJECTIVE TEST INFORMATION. THE STUDY SHOWED THAT SURFACE PREPARATION, PROPER APPLICATION, AND FILM THICKNESS ARE ALL MORE IMPORTANT THAN THE TYPE OF PAINT USED. THE PAINT THICKNESS MEASUREMENT SHOWED THAT: (1) A DIRECT CORRELATION EXISTS BETWEEN FILM THICKNESS AND PAINT LIFE, (2) SOME CURRENT PROCEDURES IN MEASURING DRY THICKNESS LEAD TO SERIOUS ERRORS, (3) THE USUAL METHOD OF MEASURING WET FILM THICKNESS IS MISLEADING, (4) THE HEIGHT OF BLAST-CLEANING PEAKS AND VALLEYS GREATLY AFFECTS THE AMOUNT OF PAINT NECESSARY TO ACHIEVE A GIVEN DRY FILM THICKNESS, AND (5) EACH OF THE SIX MOST COMMON THICKNESS GAGES HAS ITS OWN MERITS, BUT REQUIRES SPECIAL PRECAUTIONS IN USE.

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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. 8, July 1969, which was superseded by this report.
  • Authors:
    • Keane, J D
  • Publication Date: 1969

Media Info

  • Media Type: Digital/other
  • Pagination: 64 p.
  • Serial:
    • NCHRP Report
    • Issue Number: 74
    • Publisher: Transportation Research Board
    • ISSN: 0077-5614

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Filing Info

  • Accession Number: 00216923
  • Record Type: Publication
  • Files: TRIS, ATRI
  • Created Date: Mar 9 1970 12:00AM