Durability per IS 456:2000 – Minimum concrete grade for RCC along a sea coast A reinforced concrete structure is to be constructed along a sea coast (severe marine exposure). What is the minimum specified concrete grade to be used?

Introduction / Context:
Marine environments accelerate reinforcement corrosion due to chloride ingress and cyclic wetting and drying. IS 456:2000 specifies minimum grades and cover for different exposure classes to ensure durability. Choosing an adequate minimum grade safeguards service life and reduces maintenance costs.

Given Data / Assumptions:

• Reinforced concrete (RCC), not plain concrete.
• Location: along a sea coast → severe or very severe exposure due to chlorides and salt spray.
• Compliance to IS 456:2000 exposure-based durability provisions.

Concept / Approach:

For reinforced concrete, IS 456:2000 recommends minimum grades based on exposure severity. Along sea coasts (commonly classified as severe), the minimum recommended grade is M25 for RCC, with increased nominal cover and low water–cement ratio. Very severe splash/tidal zones may require higher grades (e.g., M30) and additional protective measures, but the common exam-standard answer for “along sea coast” is M25.

Step-by-Step Solution:

Verification / Alternative check:

Design examples for coastal buildings typically adopt M25 or higher for RCC elements above splash zones, aligning with IS 456 recommendations.

Why Other Options Are Wrong:

M15 and M20 are too low for severe marine exposure in RCC; M30 may be required for very severe zones but is not the minimum generally specified for “along a sea coast.”

Common Pitfalls:

Ignoring the need for cover increase, not controlling w/c ratio, and neglecting surface protection in tidal/splash regions.

Final Answer:

M 25