Durability of Concrete MCQ with answer and solution

Concept

Corrosion of reinforcing steel in concrete is an expansive process that causes internal pressure, resulting in cracking, delamination, and spalling of the concrete cover.

Step-by-step solution

1. Understand that steel corrosion creates rust products with a much larger volume than parent steel. 2. The volumetric expansion generates heavy radial pressures around the rebar. 3. Initially, this causes longitudinal tensile cracks along the reinforcement. 4. Continued corrosion leads to delamination between concrete layers and subsequent spalling of the cover concrete. 5. Therefore, all listed damages are typical manifestations of reinforcement corrosion.

Explanation

When reinforcement steel corrodes, it forms rust which occupies a volume significantly larger (up to 6 times) than the original steel. This expansion exerts high internal tensile stresses on the surrounding concrete, leading successively to cracking, delamination (separation of concrete layers), and eventually spalling (breaking off of the outer concrete cover).

Why the other options are wrong

A: Cracking is only one part of the damage sequence; delamination and spalling also occur. B: Delamination is a valid damage symptom, but cracking and spalling also happen. C: Spalling is correct, but cracking and delamination are equally valid outcomes of the same process.

Shortcut

Remember the sequence of corrosion damage: Rusting -> Volume Expansion -> Cracking -> Delamination -> Spalling.

Common mistake

Thinking corrosion only causes surface staining (rust streaks) without structural damage like cracking or spalling.