Whether to use corrosion protection of steel bridges is one of the largest decisions that can be made during design because it will ultimately affect the life-cycle cost due to various maintenance actions throughout the life of the bridge. However, the various protection schemes of zinc coatings (i.e., galvanizing, metalizing, and zinc primers) all have variable lives, which are challenging to predict, based on the macro- and micro-environments of a bridge. In marine and heavy industrial locations, even the best 3-coat, zinc-rich paint, or galvanizing can break down and require maintenance every 25 to 30 years. With a push to increase service lives of bridges out to 100 years and beyond, in severe environments, between two and five substantial maintenance actions could be required to attain the design lives. Many attempts have been made through research to develop more corrosion resistant alloys (i.e., weathering steels) or coatings for bridge applications. However, historical performance has shown that despite these attempts, areas beneath joints and/or in severe environments still result in corrosion of the steel and require continual maintenance.
The only steel alloys that will actually remain corrosion-free for a 100-year service life in any macro- and micro-environment are stainless steels. While these alloys are typically four to six times the cost of A709 Grade 50W, the ability to remain truly maintenance-free for a lifetime makes the alloy competitive in a life-cycle cost analysis. In less severe environments, there may be an advantage to using just stainless alloys in targeted locations (i.e., near joints and abutments) and creating a hybrid girder of A709 and stainless steel. Besides the issue of first cost, the other major obstacle to using stainless steel for bridges is a general unfamiliarity with the material in design, fabrication, and construction that is not addressed in any AASHTO specification.
The objective of the research project was to develop guidelines and/or specifications to help designers and fabricators use stainless steel in the superstructure of highway bridges.
