Corrosion

Chapter 23





Corrosion Protection
of Steel Bridges


























Disclaimer


All data, specifications, suggested practices, and drawings presented herein, are based on the best available information and delineated in accordance with recognized professional engineering principles andpractices, and are published for general and procedural information only. Procedures and products, suggested or discussed, should not be used without first securing competent advice respecting their suitability for any given application.

Publication of the material herein is not to be construed as a warranty on the part of the National Steel Bridge Alliance - or that of any person named herein -that these data and suggested practices are suitable for any general or particular use, or of freedom from infringement on any patent or patents. Further, any use of these data or suggested practices can only be made with the understanding that the National Steel Bridge Alliance makes no warranty of any kind respecting such use and the user assumes all liability arising there from.Corrosion is a serious threat to the long term function and integrity of a steel bridge. Structural steel will corrode if left un protected or inadequately protected from the natural environment. This corrosion can take the form of general uniform thickness loss or concentrated pitting depending on exposure to the environment and the steeldesign detail in question. The designer should view corrosion as a long term threat to the integrity of the bridge structure – a critical design consideration that must be addressed in a rational manner during the design process. Corrosion is a time-based process that generally takes several years to develop deterioration significant enough to cause concern. For this reason, corrosion is oftenconsidered an ownership or maintenance issue. While this may be true in practical terms, corrosion is most appropriately addressed by specification of a proper corrosion protection system during the design phase. It has been shown that corrosion played a significant role in the catastrophic collapse of both the Silver Bridge (Point Pleasant, WV) in 1967 and the Mianus River Bridge (Connecticut) in1983 (1) (2). Therefore, corrosion is not an issue to be taken lightly by the designer. It is important to place the issue of corrosion in perspective. Corrosion is a concern beyond steel bridges alone. Because reinforced concrete and prestressed concrete bridges also employ steel components in their designs, these bridges are also susceptible to the effects of corrosion. It can be reasonablyargued that although steel bridges tend to show the outward effects of corrosion more readily than concrete structures, steel bridges are inherently easier to inspect and maintain than concrete bridges. While there are several proven strategies for corrosion protection of steel bridges, there is no universal solution. The proper system must be chosen to accommodate cost, fabrication and productivity,long term performance and maintenance. Additionally, each corrosion protection system must be selected based on the anticipated exposure of the structure to corrosive elements over its lifetime. The following chapter highlights the most common issues confronting the steel bridge designer regarding corrosion protection and provides some guidance in this area.


KEY ISSUES
There are four keyissues to consider in the design of a bridge corrosion protection system: Environment, Materials of Construction, Design Detailing, and Cost.

Environment
The local environment of a structure substantially influences the rate of corrosion of exposed steel and the deterioration of the protective coating. Traditionally, corrosion
engineers have classified the general (macro) environment...