What is the role of corrosion inhibitors in concrete durability?

• A. They reduce the rate of reinforcing steel corrosion by mitigating chloride ingress.
• B. They increase the strength of concrete.
• C. They replace the need for concrete cover.
• D. They are only used in asphalt pavements.

Answer: (A)

Corrosion inhibitors in concrete are about durability of reinforced concrete in aggressive environments. Chloride ions from salt sources can penetrate the concrete, reach the reinforcing steel, and disrupt the protective oxide film on steel, initiating corrosion that leads to cracking and spalling. Inhibitors help mainly by slowing how fast chlorides diffuse into the concrete or by strengthening the steel’s passivity at the steel–concrete interface. Admixtures like calcium nitrite are common examples; they act to keep the steel in a passive state and, in some formulations, reduce the local aggressive conditions around the rebar. Because of this, their primary role is to reduce the rate of reinforcing steel corrosion, not to increase concrete strength, not to replace cover, and they are used for concrete—not asphalt pavements.