Abstract
There are several thousand bridges that are scheduled for maintenance painting both in the State of Tennessee and Missouri. The Caruthersville Bridge (I-155 Mississippi River Bridge) is an on-going project, which is the northern-most bridge over the Lower Mississippi River, with the combined flow of the Upper Mississippi and the Ohio River. Although there is an increased risk of coating incompatibility (stress, premature failure, etc.), over-coating this unique asymmetrical structure with a Calcium Sulfonate system was a viable option spear headed by the Tennessee Department of Transportation (TDOT) and supported by the Missouri Department of Transportation (MoDOT). This option provided both DOT’s with an initial low cost as well as extended the coating life of the bridge thus providing corrosion protection.
Every generic coating system has its unique requirements in terms of surface preparation and application as well as advantages and disadvantages in terms of performance and life-expectancy. The advantages of using a Calcium Sulfonate Alkyd System as a corrosion inhibitor are as follows: Easy mixing, single package, easy to apply, can have a relatively low volatile organic compound (VOC), low cost, relatively good corrosion-resistance and surface tolerant of many SSPC/NACE surface preparation standards. This coating is typically used in mild service environments. Although alkyd systems are convertible coatings, flexible and cure by (oxidation) reaction with oxygen from the air, there are several drawbacks from this surface tolerant coating. Due to the curing mechanism, alkyds have a relatively slow-drying process (i.e. residual tack) without modification. The unique challenges in providing third-party inspection services on this project have provided invaluable experience and knowledge with the use of the Calcium Sulfonate Alkyd coating system. These project specific challenges have been evaluated, researched and successfully solved to the satisfaction of the respective DOT’s. The interaction between the DOT’s, Inspection Firm and the Painting Contractor are presented in order to assist in future contracts (design and construction) when using a Calcium Sulfonate Alkyd System. This paper discusses those unique requirements of a Calcium Sulfonate system as learned from its use on the Caruthersville Bridge located between the states of Tennessee and Missouri.
