Steel that was previously bare or painted, but is otherwise fit for purpose, can also be hot-dip galvanized for corrosion protection because the after-fabrication galvanizing process is the same for new and reused steel. To prepare the reused steel for the galvanizing process, existing coating must be removed by abrasive or chemical methods. Next, articles not originally designed for HDG may require minor fabrication steps to ensure proper galvanizing. These steps may include the addition of vent and drainage holes, and cropped corners to allow the flow of pretreatment chemicals and zinc, which ensure full coverage of the parts during immersion in the process tanks and molten zinc bath (refer to “The Design of Products to be Hot-dip Galvanized After Fabrication” by AGA). When galvanizing reused steel, it is important to note the impact on appearance for projects where aesthetics are of primary concern, such as architecturally exposed structural steel (AESS). The galvanized coating forms at a uniform rate across all surfaces, and will not fill in dimples, roughness, damages, or holes present on the reused steel members. While some architects may prefer the imperfect appearance, these visual aspects may not meet the requirements of all projects.
A rehabilitation project for the Indian Mill truss bridge in Wyandot County, Ohio, demonstrates the ability to easily expand and galvanize an existing painted steel structure (Figure 5). Originally constructed in 1913, this single-lane vehicular steel truss bridge was deemed functionally obsolete in 2010 and required significant repairs. To preserve the original bridge aesthetic and to expand it, a similar truss was designed to incorporate pieces of the original steel. These components were disassembled, galvanized, and reused in the new construction along with the new galvanized steel members. The result was a fully galvanized bridge that will provide the county and rural community with maintenance-free longevity for another 100 years.
On the other hand, sometimes the steel to be reused on a project has already been galvanized. For galvanized steel that has previously been in service, the components can be reused as is, regalvanized, or painted over. If inspection reveals suitable coating thickness, no further processing may be required prior to reuse. Regalvanizing requires steel to be disassembled, stripped of any remaining coating at the facility, galvanized, and then reassembled at the desired location. This process effectively restores the galvanized steel to its initial condition in a very short time. Painting over the existing galvanizing can be achieved in the field, and is most suitable for parts that cannot be removed from service or where a shorter extension in coating life is needed.
Regalvanizing was a successful choice for the reuse of guardrail panels, originally galvanized in 1955, for the M-102 Bridge Rail Reconstruction Project (Detroit, Michigan). For 50 years of Michigan weather, traffic mishaps, road grime, and salts, HDG provided maintenance-free protection from corrosion, but highway traffic over time damaged 20 percent of the panels. Under a ‘Keep It Green’ initiative supported by the Michigan Department of Transportation (MDOT), the old but undamaged guardrail was stripped of the remaining galvanizing, regalvanized, and returned to service. Since only 20 percent of the existing steel required replacement, MDOT saved more than half of the budget allocated for this project. In addition to freeing up funds for future projects, the reuse of HDG will provide the M-102 Bridge Rail reconstruction project maintenance-free longevity for over 50 years.
Although the above examples demonstrate the many ways steel can be reused efficiently and cost-effectively with minimal or no processing, additional opportunities may be revealed on further evaluation of existing steel projects. Additionally, different steel articles from a variety of industries are also well-suited for reuse, including balcony railings, security barriers, fencing, highway products, architectural panels, sculptures, and recreation equipment. As sustainability becomes a larger part of specifying and engineering, the use of materials like steel and zinc ensures designs stand the test of time while improving the quality of life for future generations. Reusing steel and specifying HDG for corrosion protection can provide additional opportunities to make any project more sustainable.