For reinforced concrete members immersed in sea water or exposed to heavy sea spray (adverse marine conditions), what is the maximum permissible nominal cover to reinforcement?

Introduction / Context:
Nominal cover ensures steel reinforcement is protected from corrosion and provides fire resistance. Marine exposure accelerates chloride-induced corrosion, so codes increase the required cover. In adverse conditions such as immersion and severe sea spray, the largest standard nominal cover category is typically invoked.

Given Data / Assumptions:

• Environment: sea water immersion or severe spray.
• Member type: reinforced concrete (RC).
• We seek the maximum nominal cover commonly prescribed for such exposure.

Concept / Approach:

As exposure severity increases from moderate to extreme, nominal cover rises stepwise (e.g., ≈20–50 mm for normal conditions; up to ≈75 mm in extreme/marine). The intent is to slow chloride ingress and delay corrosion onset in reinforcement.

Step-by-Step Solution:

Verification / Alternative check:

Marine projects often pair 75 mm cover with dense concrete (e.g., M 30+ for RC), low w/c ratio, and supplementary cementitious materials (fly ash/slag) to enhance durability.

Why Other Options Are Wrong:

• 40–70 mm: Typical for lower exposure classes; may be insufficient for harsh marine conditions.

Common Pitfalls:

• Using nominal cover values meant for moderate exposure in aggressive chloride environments.
• Neglecting construction tolerances; inadequate cover on site defeats the design intent.

Final Answer:

75 mm