Durability of Concrete MCQ with answer and solution

Concept

Corrosion of reinforcement in concrete is mitigated by maintaining an alkaline environment and preventing the ingress of moisture, oxygen, and harmful ions like chlorides.

Step-by-step solution

1. Understand the causes of corrosion in reinforced concrete: ingress of moisture, oxygen, and chloride ions. 2. Evaluate option (A): Sufficient curing time ensures proper hydration and reduces permeability, aiding corrosion protection. 3. Evaluate option (B): Dense concrete has lower porosity, preventing the entry of aggressive agents. 4. Evaluate option (C): Proper concrete cover provides a physical barrier and increases the diffusion time for harmful chemicals to reach the rebar. 5. Evaluate option (D): Chloride-containing admixtures actively promote steel corrosion and pitting, making this option incorrect for corrosion protection.

Explanation

Chloride-containing admixtures (such as calcium chloride) accelerate the corrosion of reinforcing steel in concrete by breaking down the passive oxide film on the steel surface. Therefore, using chlorides is detrimental to corrosion protection, while dense concrete, sufficient curing, and proper clear cover protect against corrosion.

Why the other options are wrong

A: Sufficient curing reduces permeability and protects against corrosion. B: Dense concrete acts as a barrier against moisture and aggressive agents. C: Proper cover increases the path length for corrosive agents to reach the steel reinforcement.

Shortcut

Remember that chlorides and sulphates are enemies of reinforced concrete durability.

Common mistake

Confusing accelerating admixtures (which often contain chlorides and cause corrosion) with corrosion-inhibiting admixtures.