What is concrete cover and why is it specified?

Concrete cover is the minimum distance between the surface of reinforcement and the outer concrete surface. It protects steel from corrosion by providing an alkaline barrier against moisture, chlorides, and carbonation. Cover requirements vary: 25-40mm for interior members, 40-50mm for exterior exposure, 50-75mm for marine or aggressive environments. Inadequate cover leads to premature corrosion, spalling, and structural deterioration.