Since the 1970s, the number of pre-tensioned and post-tensioned (PT) concrete bridge structures utilizing high-strength seven-wire strands has increased steadily. For bonded PT tendons, the grout functions as the last layer of corrosion protection for the highly stressed seven-wire strands by providing a high pH environment to form a protective oxide film on the strand surface and also acting as a physical barrier to water, oxygen, and chloride ions. Corrosion of strands initiates when the protective oxide film is compromised due to chloride attack or carbonation of the surrounding grout upon exposure to water and air. Once corrosion starts, it propagates at a certain rate controlled by many factors such as oxygen availability, moisture content, electrical resistance, grout pH, and chloride concentration. In this TechBrief, a prestressed seven-wire strand will be simply referred to as a “PT strand.”