Deterioration of reinforced concrete caused by corrosion of the carbon steel reinforcing bars (rebar) is a worldwide problem. The corrosion product, rust, occupies a greater volume than the original steel bar and this creates a pressure which causes cracking and subsequent spalling of the surrounding concrete.
The progression of corrosion on the Route 438 overpass over the NYS Thruway
Corrosion of carbon steel rebar is greatly accelerated when chlorides are present in the concrete. In some parts of the world, chlorides may be incorporated into the original mix due to their presence in the sand, aggregate or water. Most often, chlorides penetrate through the cover when the external surfaces of the concrete are exposed to seawater, marine atmospheres or de-icing salts.
Several methods are currently employed in an attempt to reduce the corrosion of carbon steel rebar. These include:
- Chloride Extraction – Chemical sprayed on bridge surface to extract chloride from the bridge deck. Requires lane closures and cannot stop the accumulation of chloride over time.
- Remove and replace the top 2-3 inches of concrete – Results in lengthy lane closures and does not address the chloride that is deeper in the concrete.
- Cathodic Protection
- Increase Concrete Cove
- Concrete Coatings/Sealers
None of these methods have been proven effective.
The use of reinforcing materials that have inherently good corrosion resistance, thus minimizing the need for maintenance and monitoring of the structure is becoming more and more essential. Stainless Steel rebar is such a material. It is being used as a long-term solution in concrete reinforcing across the USA, Europe, Canada, and Australia.