In most cases, local building codes and engineering standards specify the minimum required concrete cover for various types of structures.
The carbon steel of rebars is protected from oxidation by atmospheric oxygen by the high pH of concrete interstitial water.
A high quality concrete made with a low water-to-cement (w/c) ratio will have a lower porosity and will be less permeable to water and to the ingress of corrosive species (dissolved oxygen, chloride, ...).
Concrete covers are frequently used in the construction of commercial developments, homes, bridges, municipalities, curb forming, and other locations or projects requiring long-lasting, durability.
[2] Concrete and steel reinforcement bars combine to create strong, resilient structures in the following ways: National codes also specify minimum cover requirements based on their respective local exposure conditions.