EFFECT OF SURFACE CONTAMINANTS ON COATING LIFE. FINAL REPORT

This study investigated the influence of soluble salts on the performance and lifetime of protective coatings on steel bridges. Laboratory and field methods were established for measuring chloride ion, sulfate ion, ferrous ion, ammonium ion, conductivity and pH, and for extracting aqueous samples from blast cleaned steel. Aqueous samples were extracted from blast cleaned steel surfaces of 18 bridges and analyzed using the methods established. Comparisons were made among the level and type of salts (principally chloride and sulfate) and the type, structure, and environment of the bridges. Plates were blast cleaned with a variety of commonly used abrasives to determine the amount of salt transferred to the steel. The effect of those abrasives on the performance of several coatings was evaluated in a pressure immersion screening test. Several representative highway bridge coating systems were then applied over blast cleaned steel doped with various levels of chloride and sulfate in order to determine the effect of these salts on coating performance. These same coatings were also applied over steel blast cleaned with both highly contaminated and standard abrasives to evaluate the effect of the abrasivve contaminants. Coated specimens were placed in several accelerated exposure environments, including pressurized immersion in deionized water, exposure to salt spray, and exposure to an accelerated outdoor environment and a conventional exterior exposure. The coatings were evaluated for blistering, rusting, and undercutting at the scribe. On the basis of the observed degradation, and reputable work by other laboratories, a set of preliminary guidelines for allowable salt levels was prepared. Levels were given for two environments, "aggressive atmospheric" and "severe immersion-like." In addition, a users guide was prepared to assist the highway engineer in understanding and implementing the findings.

  • Corporate Authors:

    Steel Structures Painting Council

    4400 Fifth Avenue
    Pittsburgh, PA  United States  15213

    Federal Highway Administration

    Turner-Fairbank Highway Research Center, 6300 Georgetown Pike
    McLean, VA  United States  22101
  • Authors:
    • Appleman, B
    • Boocock, S
    • Weaver, R
    • Soltz, G
  • Publication Date: 1991-11

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 256 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00621614
  • Record Type: Publication
  • Report/Paper Numbers: FHWA-RD-91-011, SSPC 91-01, 3E4C0172
  • Contract Numbers: DTFH61-88-C-00027
  • Files: TRIS, USDOT
  • Created Date: Apr 30 1992 12:00AM