Steel will readily corrode, unless it is coated. However, when steel is placed in concrete it develops a ppassive oxide film, due to the high pH of the concrete. This passive film prevents further corrosion of the steel and there are many examples where common reinforcing steel in concrete has remained uncorroded for over 100 years. If steel corrodes in concrete it may cause cracking or spalling of the concrete.
Corrosion of reinforcing steel may occur if the pH of the concrete is decreased, either from chemical attack or from reaction of the concrete with CO2 in the atmosphere. It may also occur if sufficient chloride ions reach the bar. These are typically introduced by into the concrete, from either deicing salts or sea water.
There are many ways to reduce the risk of corrosion- related distress in concrete. The first layer of defense is the concrete, which should be dense and cracks should be minimized. Appropriate concrete cover should also be used.
Reinforcing bars with improved corrosion resistance over traditional carbon steel reinforcing bars are readily available. When selecting a particular type of corrosion resistant bar, issues such as level of corrosion resistance, cost, and availability should be considered. For publicly funded projects, FHWA and other agencies place restrictions on proprietary material and “Buy U.S.A” requirements may be in effect and should be carefully evaluated during the evaluation and purchasing process.
Types of Rebar with Improved Corrosion Resistance:
- Stainless Steel Bars
- Galvanized Steel Bars
- Epoxy-Coated Reinforced Bars
Bar Designations with Improved Corrosion Resistance over Uncoated Bars:
- ASTM A767/A767M: Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement
- ASTM A775/A775M: for Epoxy-Coated Reinforcing Steel Bars
- ASTM A934/A934M: Epoxy-Coated Prefabricated Steel Reinforcing Bars
- ASTM A955/A995M: Deformed and Plain Stainless-Steel Bars for Concrete Reinforcement
- ASTM A1035/A1035M: Deformed and Plain, Low-carbon, Chromium, Steel Bars for Concrete Reinforcement