How does chloride-induced corrosion affect reinforced concrete?

Chloride ions from marine environments, deicing salts, or contaminated materials penetrate concrete and accumulate at reinforcement level. When chloride concentration exceeds threshold (0.2-0.4% by cement weight), it breaks down the passive oxide layer on steel, initiating corrosion. Corrosion products occupy 2-6 times original steel volume, causing concrete cracking and spalling. Prevention includes adequate cover, low permeability concrete, corrosion-resistant reinforcement, and cathodic protection for severe exposures.