Chlorides
Salts, most often from deicing chemicals or seawater, that penetrate concrete and destroy the passive film protecting embedded steel, initiating corrosion.
What does chlorides mean?
Chloride ingress is the leading durability threat to reinforced concrete in the United States, driving deterioration in bridges, parking structures, and coastal buildings. The defenses are low permeability, adequate cover, crack control, and in severe cases coated or non-metallic reinforcement, corrosion inhibitors, or sealers. Chlorides can also enter from mix ingredients, which is why admixture and water chemistry are controlled.
In practice
Every winter of salt application on a parking deck is a deposit toward a repair bill that arrives fifteen years later.