Chlorides can be present in concrete either due to addition / contamination during construction or from contamination post construction.
Calcium Chloride was sometimes added to accelerate the setting times of concrete epically in the colder months or for early stripping in precast units up until 1977. Chlorides can also be present as a contaminant of the aggregate. Any concrete structure pre 1977 can be affected but after that date an amendment to the code of practice effectively stopped the use of calcium chloride as an accelerant or stripping agent.
Post construction contamination can be due to de-icing salts on structures close to roads, motorways & car parks or because of a marine environment.
Excessive levels of chloride present in the concrete can accelerate the electro chemical corrosion of the steel reinforcement creating up to 2.2 times volume increase, this can then cause spalling and cracking of the concrete around it.
The chloride testing to determine the chloride content of concrete can be carried out from a small drilling sample then testing it in our laboratories with strict reference to the methods outlined in BS 1881 and BS 4551.