Case 2 – Chloride Ion Attack

Cause of Defects

In marine locations:

Accumulation of salt spray on reinforcement and formwork ahead of concreting, and be incorporated into concrete during placement.

In coastal and near coastal areas:

Deposition of salt spray onto hardened concrete surface and the salt can permeate into the concrete.

For architectural purposes:

Surface of concrete may been etched with hydrochloric acid to expose the aggregate or cleaned to receive architectural finishes.

Mechanism:

• Soluble chlorides to combine with water in the “pores” of concrete to form hydrochloric acid
• Hydrochloric acid reacts with reinforcement to form ferrous chlorides
• This ferrous chlorides subsequently breaks down into form of ferrous hydroxide and hydrochloric acid for further cyclic reaction

Consequences

The results of chloride attacks are:

• reduction of passivity of the concrete conditions, promotion of corrosion of steel reinforcement in concrete
• resultant rust formation occupies a volume that is several times that of the reinforcement bar, causing cracking and eventually spalling of concrete.

Risk of reinforcement corrosion as a result of chloride contamination depends on:

• concentration of chloride
• alkalinity of concrete
• type of cement
• whether chloride was present at time of mixing
• whether chloride has penetrated the hardened concrete