An Evaluation of MoDOT's Current Coatings Programs Final ... - TSP2

The implementation of the findings of this Task Force will ensure better quality
coatings in the preservation of steel bridges on Missouri’s state highway system.
Introduction
The bridge design community has long recognized the capabilities of steel for
economical bridge construction. While the physical properties of steel make it
viable and desirable as a material of construction for bridges, steel is subject to
corrosion if it is not properly coated.
For decades, moisture and residual chlorides were prevented from attacking
steel by the use of lead-based coatings. When environmental and health issues
associated with the use of lead-chromium and other heavy metals-based
coatings came to the forefront, the coating industry responded by introduced new
technologies. Presently, the primary method or “Gold Standard” for coating bare
steel entails the use of an inorganic zinc-rich primer with topcoats to protect the
primer and provide for aesthetic considerations.
When some old paint is intact, adherent, and performing satisfactorily, it is
MoDOT’s policy to extend the service life of that coating by overcoating.
Overcoating is the term used to describe the practice of applying paint over some
or all of the old coating. This practice allows for the repair of the coating in some
areas. Usually, a coating that contains calcium sulfonate is applied. Primarily,
MoDOT uses the calcium sulfonate system for overcoating painted steel. These
surfaces usually contain lead paint.
MoDOT’s structural steel coatings program can be categorized into three areas.
The first category is MoDOT’s Internal Coatings Program. This program involves
the use of MoDOT forces to coat the steel. The second category is classified as
the Contract Maintenance coating program in which coatings contractors are
retained. The third category is classified as the New Construction Coating
Program. During this program, inspection in the shop is performed by the
MoDOT inspectors. Inspection of the intermediate coat and topcoat in the field at
the jobsite is performed by MoDOT construction inspectors or materials
inspectors, depending on the District policy.
The Bridge Coatings Task Force is comprised of Coating Contractors,
Fabricators, Bridge Engineers, Chemists, Consultants, Professionals from the
Coating Industry, and Field Personnel. (See Appendix A for the list of Task Force
Members.)
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