Invisible soluble salts present on steel highway structures can act to promote corrosion even after maintenance painting. Soluble salts include chloride, nitrate and sulfate ions. Soluble salts found on bridge decks and roadways are the result of usage of deicing salts (chlorides), and the deposition of atmospheric pollution (nitrates and sulfates) on exterior surfaces. Typical pollution-related sources of soluble salts are coal-fired power plants, refineries, farming operations, vehicle emissions, and chemical plants. Sites for soluble salt damage on bridges include:

  • Beam ends under open or leaking expansion joints,
  • Flanges and lower portions of webs of overpass structures,
  • Lower chords and connecting members (end posts, portals, vertical posts and diagonals), and guard rails of truss bridges near roadway level, and
  • Outside faces of fascia girders and other bridge elements constantly exposed to the environment.

Maximum acceptable concentrations of soluble salts are very low (e.g. 10 μg/cm2 for chlorides).

Report Date


Report Number

KTC-03-02/UI 4-02-1F

Digital Object Identifier



The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or the policies of the University of Kentucky, nor the Kentucky Transportation Cabinet. This report does not constitute a standard, specification, or regulation.