According to the Federal Highway Research Institute, there are around 1,200 steel and steel composite bridges with a steel surface area of around 15 million square meters on federal trunk roads alone. In addition, there are several kilometers of steel used in railroad bridges. "Steel is a fascinating material that is truly versatile. But in the area of bridge construction in particular, it is exposed to great stress under certain circumstances," says Erdal Kara Osman, Managing Director of Rodopi Marine GmbH. This is not least due to the ever-increasing volume of traffic. It is therefore all the more important to protect all this installed material from corrosion - and to do so in a customized and long-term manner.
Corrosion protection in transition
Many of the steel bridges that were built in the 1960s, for example, have been showing increasing damage for around twenty years. However, it is not always an option to completely replace the bridge. In the case of historic bridges in particular, there are also cultural reasons for their preservation. The most common causes of defects include material fatigue and wear and tear. The latter is becoming more and more common due to the increasing stress caused by heavy traffic, for example. However, corrosion is also one of the fundamental causes of damage. Corrosion protection has been undergoing enormous change for some time now. Until the 1970s, most steel structures in Germany were painted with a red lead paint to protect them from corrosion. Over the years, wind and weather repeatedly released lead particles from the coating, posing a long-term danger to the environment. Large quantities of lead were also frequently released during repair work on the coating, as the necessary protective measures were rarely taken when sanding down the damaged areas. However, knowledge of the danger of the substance also changed the way it was handled, so that for some years now, corrosion protection has been handled in a completely different way.
Adapted to the conditions
Parameters such as environmental protection and occupational safety now play just as important a role as the economic aspect. The aim here is to achieve a solution as quickly as possible that also lasts longer. After all, a railroad line that is closed for a long time naturally represents a major economic factor, both due to angry passengers and the change in journey times. The same applies to trunk roads, where detour can lead to high capacity utilization in other areas. From an overall economic point of view, timely repair is therefore the more sensible option than postponing the application of new corrosion protection. "As every part rusts differently, it is important to pay attention to the specific conditions of the bridge," says Erdal Kara Osman. For example, corrosion occurs to a significant extent at a relative humidity of over 80 percent and a temperature of over 0°C. In combination with seawater or road salt, however, corrosion can occur even at much lower humidity levels. "Innovative products, such as zinc flake coatings, therefore provide lasting protection, even for bridges that are subject to particularly high levels of stress, and therefore also maintain their value," concludes Osman.
