In most building construction, concrete effectively protects reinforcement from damage caused by environmental factors or exposure to fire. In severe environments found in some industrial plants, marine structures, bridge decks and parking structures, destructive effects of reinforcement corrosion have been a problem. With proper design, mix selection, and construction practices, reinforced concrete structures can perform well in corrosive environments. Concrete cover makes an important contribution to this performance.
In most cases, reinforcement corrodes when chloride ions, often supplied by deicer chemicals or marine spray, penetrate to the steel in a sufficient amount, called the "corrosion threshold."
Although concrete is not impermeable, conventional concrete with low permeability can be successfully produced and placed. For corrosion protection, use concrete made with good-quality materials and the lowest water-cementitious material ratio possible to meet placing requirements. If chlorides are present in the concrete mix, fewer chlorides have to penetrate the cover to reach the corrosion threshold. Also follow proper consolidation, finishing, and curing practices.