What does chloride ion do in relation to steel?

Chloride ions are known to have a detrimental effect on steel, particularly in reinforced concrete structures. When chloride ions are present, they can penetrate the protective oxide film on the surface of steel, which normally helps to prevent corrosion. Once this film is compromised, the steel becomes susceptible to corrosion processes, leading to rust formation. This corrosion expansion can cause cracking and spalling in concrete, ultimately affecting the structural integrity and lifespan of the concrete element.

In contrast, the other options do not accurately describe the role of chloride ions in relation to steel. For example, they do not prevent corrosion, nor do they enhance bonding or directly strengthen concrete. Instead, chloride ions are primarily associated with promoting corrosion in steel reinforcement, highlighting the importance of managing chloride exposure in concrete structures to ensure durability and performance.