Why Clear cover is provided in RCC ? and How much clear cover is provided ?

 Why Clear cover is provided in RCC :

The result is going to be something like this. In order to protect the reinforcement from this phenomenon called corrosion and to provide fire resistance to bars embedded in concrete, nominal cover is provided for Reinforced Concrete Structures.

Concrete cover is the least distance between the surface of embedded reinforcement and the outer surface of the concrete.

Why do we provide cover then?

1. To protect the reinforcement steel from environment in order to prevent the corrosion
2. To give reinforcing bars sufficient embedding to enable them to be stressed without slipping
3. And to provided insulation from fire or heat.

However each national code suggests different cover depths like American code suggest for 40-50 mm cover where as UK code suggest for 25-50 mm.

You may think now like this " the more cover is the safer the reinforcement is". However this is not true, because as the cover depth increase it leads to increased crack width in flexural RCC members and crack width greater than 0.3 mm permit ingress of moisture and chemical attack to the concrete, resulting in possible corrosion of reinforcement and deterioration of concrete. Therefore, thick covers defeat the very purpose for which it is provided. There is a need for judicious balance of cover depth and crack width requirements

Item-wise clear cover provided in RCC as Below :

sr no                 Item                                                                  Cover Provided.
  1                   Raft foundation Bottom and side                   75 mm
  2                   Raft Foundation top                                         50 mm
  3                   Footings                                                              50mm
 4                    Beam                                                                   25 mm
 5                    Column                                                               40 mm
 6                    Slab                                                                     15-20mm
 7                    Staircase                                                             15 mm
 8                    Retaining wall                                                  20-25 mm

Note : In Order to protect R/f from this phenomenon called corrosion and provide fire resistance to bar embeded in concrete