Correct Answer - Option 3 : 50 mm
Explanation:
Cover requirements as per IS 456:2000:
-
In order to prevent the reinforcement from corrosion, a layer of concrete should be there in reinforced concrete structures.
- In actual construction practices, the specified minimum cover is very difficult to maintain. Thus IS 456:2000 specifies tolerance levels ranging from 0 mm to +10 mm i.e. no reduction in clear cover is permitted but the nominal cover can be increased up to 10 mm.
Exposure Conditions |
Minimum concrete grade |
Nominal cover |
Mild |
M20 |
20 mm |
Moderate |
M25 |
30 mm |
Severe |
M30 |
45 mm |
Very severe |
M35 |
50 mm |
Extreme |
M40 |
75 mm |
- Nominal cover can be decreased by 5 mm for main reinforcing bars of less than 12 mm diameter.
- Nominal cover can be decreased by 5 mm if the concrete grade is M35 or higher.