Conservation at Its Best: Reuse Galvanized Steel
During a reconstruction or rehabilitation project, there are often building materials that can be reused in a future project. Reclaiming material from an existing structure is a sustainable option that many specifiers are turning to recently. Steel is a material that can easily be reclaimed if it has not suffered from severe corrosion. Whether the steel has been painted or hot-dip galvanized in the past, the existing coating can be removed and replaced with a galvanized coating that will provide decades of maintenance free corrosion protection.
Removing an existing hot-dip galvanized coating from steel for recoating is often referred to as "strip and re-dip." Often times, it is performed if a galvanized structure has seen several decades of service and is in need of repair. The structure can be disassembled, cleaned and recoated at a galvanizing facility, and then reassembled at a desired location. Sometimes, due to the longevity of the coating, steel can be reused without the recoating procedure.
Hot-dip galvanized steel that has been in use for 60 or more years may begin to show signs of rusting and be in need of repair. The steel, which has been protected for many years by the coating, will still be usable at this point, but the coating will need repair to prevent any corrosion of the steel. One option, is to paint the surface of the steel for corrosion protection. This may seem like the best option because it appears to be less expensive and work-intensive to repair in place. However, maintaining a painted steel structure proves to be very costly and unsustainable over a long period of time. More sustainable and long term option would be to coat the used steel with hot-dip galvanizing. This option does require the structure to be disassembled and the steel shipped to a galvanizing facility where it is stripped of the old coating and re-galvanized. However, the longevity and sustainability of a hot-dip galvanized coating are unmatched. Once the initial work of re-galvanizing the steel is complete, the coating will provide decades of maintenance free protection. This option has been chosen several times in the past such as in the Port Security Barriers, Michigan/M-102 Bridge Rail Reconstruction Project, Commonwealth of Kentucky Guardrail, Knox County Bridge Rehab, Bridges of Stark County and Playlands Castaway Cove Ferris Wheel.
There are a few cases where re-galvanizing steel and putting it back into use is not an option. Bolts, for example, that must be tensioned to a specific torque, cannot be re-used after they have been brought to that tension and then taken out of service. This actually has very little to do with the bolt being galvanized and re-galvanized, but is more of a general rule in the fastener industry. The properties of the steel bolt (galvanized or not) prohibit its repeated use at specific torques; re-galvanizing the bolt will not make it new again. Specifiers should also be wary of re-galvanizing high strength steels (tensile strength > 150 ksi), as the steel may become embrittled if stripped or pickled in an acid bath. An old coating on these steels may be stripped using a sandblaster or similar process.
Reclaiming material from an existing structure is an excellent option for specifiers. When steel is reclaimed, hot-dip galvanizing will offer the steel a brand new coating that will provide several decades of maintenance free corrosion protection. Sustainability has become a large part of specifying and engineering, and hot-dip galvanizing provides the opportunity to make your next project a sustainable one.