Protective coatings typically fail in localized areas of steel highway structures, such as bridges and tunnels. The failed areas normally comprise a relatively small percentage of the coated surface area. Detection and remediation of soluble salts (e.g., chlorides, sulfates, and nitrates) extends the service life of protective coatings by reducing such causes of premature coatings failure. Current test methods may not be effective in evaluating problematic soluble salt levels on or available to steel surfaces when the soluble salts are concentrated randomly (i.e., in pits). This may allow retention of high, localized concentrations that will promote premature failure in subsequently applied protective coatings. Another issue is the identification of practical, effective methods for surface preparation of existing steel surfaces to mitigate these localized “hot spots” prior to application of coatings. Investigations have shown that pressure washing, abrasive blasting, or a combination of the two are not always effective in removing soluble salt "hot spots". Effective detection and remediation of soluble salt contamination are essential to maximizing the life of structural steel protective coatings.
The objectives of this research were to (1) evaluate the effectiveness of existing and new methods for detecting the location, distribution, and concentration of soluble salts on or available to steel highway structures; (2) evaluate the effectiveness of existing and new remediation methods for soluble salts; (3) based on the outcomes of objectives 1 and 2, propose effective practices, specifications, or methods in AASHTO standard format for detection and remediation of soluble salts; and (4) develop training materials for the design, specification, and field application of the detection and remediation methods by steel structure owners.
A practical guide of means and methods for effective detection and remediation of soluble salt contamination on highway steel structures is presented in NCHRP Report 912. The technical report supporting the findings in Report 912 is available for download here.