Question

A certain RC structure has to be constructed along a sea coast. The minimum grade of concrete to be used as per IS 456-2000 is 
1. More than M 20
2. More than M 20 and less than M 30
3. Not less than M 30
4. Less than M 45 and more than M 30

Answer 1

Correct Answer - Option 3 : Not less than M 30

Concrete in Sea-water (as per IS 456: 2000)

Concrete in sea-water or exposed directly along the sea-coast shall be at least M 20 Grade in the case of plain concrete and M 30 in case of reinforced concrete. The use of slag or pozzolana cement is advantageous under such conditions.

Exposure class	Environmental condition	Minimum grade required for reinforced concrete
Mild	Concrete surface protected against aggressive conditions.	M20
Moderate	Concrete surface sheltered from severe rain or continuously underwater	M25
Severe	Concrete surface: 1. Exposed to severe rain and alternate wetting and drying 2. Completely immersed in sea water 3. Exposed to coastal environment	M30
Very severe	Concrete surface exposed to sea water spray	M35
Extreme	Surface members in tidal zone	M40