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

coating repairs. Based on those evaluations and needs, the regional bridge
crews schedule coating operations based on work priorities and available
resources (manpower, funding, etc.).
The current evaluation process is based on the inspector’s opinion. There is no
objective visual evaluation or in-depth analysis of the existing coating to identify
need and appropriate scope of work. Wholesale use of CSA overcoating is not
as cost effective as when using overcoating only as dictated by existing coating
condition.
Contract Maintenance Coating Program
The Contract Maintenance Coating Program utilizes CSA coatings for
overcoating. In addition, either System G or System H is used when recoating
bare steel. All structures selected for the Contract Maintenance Coating
Program are either recoated or overcoated. The selection of structures for the
Program is based on the visual inspection conducted by Central Office bridge
maintenance personnel, District Office bridge personnel, or District Office
resident engineers. The option to recoat or overcoat involves a careful
engineering judgment that depends in part on the amount of corrosion present
and / or the amount of steel section loss that has taken place.
At this time, District 6 is the only District that is conducting additional tests of the
coating during the selection / screening process. District 6 personnel evaluate
the thickness of the existing coating, its adhesion, and whether it contains lead
prior to recommending prospective coating maintenance actions.
Ultimately, however, funding issues, rather than technical engineering-type
coating condition parameters, will usually determine whether the bridge is
overcoated or whether the coating system is completely removed and replaced.
Overcoating Issues
The Missouri Standard Specifications for Highway Construction address the
methods used for surface preparation and coating application. One issue that
exists with the overcoating process is that the removal of chlorides from the
surface of the coating or the substrate is not addressed. The specifications
allow, as an option, the contractor to use power washing to clean the steel
surface prior to application of the new coating.
Note: According to definitions provided in SSPC-SP 12 “Surface Preparation and
Cleaning of Metals by Water Jetting Prior to Recoating,” there are four levels of
water cleaning / water jetting. They are:
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