Steel reinforcement is generally placed inside concrete without any galvanization or corrosion protection coatings. The concrete itself acts as a strong shell which protects the steel reinforcement from the exposed elements and chemicals (such as roadway cleaning chemicals, or sulphates in the ground).
However, in order to guarantee a reliable amount of protection, we have to provide adequate
How is Concrete Cover Defined?
The following illustration explains the basic definition of cover.
As you can see from the above image, the concrete cover is defined from the surface of the concrete until the first instance of steel reinforcement (in this case, the stirrups).
Why do we need a Minimum Concrete Cover?
In the absence of adequate cover, water and chlorides could penetrate the concrete and make contact with the embedded steel reinforcement (which is usually not protected). The water and chlorides may cause a large volume of rust material to form on the bars, leading to spalling of the concrete as the concrete breaks away to make room for the rust material, and finally wearing of the RC member.
Minimum Cover for Various RC Members
The the minimum cover requirements for various types of reinforced concrete members depend on the code provisions. You can examples of various requirements for different codes at the link below:
※ Minimum Concrete Cover Requirements? Specific RC Members. Differences between Codes
What is the Design Cover?
The minimum concrete cover is specified in most codes, but most mandate that a design cover is followed. The design cover is typically defined as:
This design cover helps to accommodate any tolerance issues (for example, tolerance in steel reinforcement placement, steel size, actual concrete cover) so it allows some more room for human error which is inevitable on a busy construction site.