Chloride ion concentration
In chloride-contaminated concrete, it is necessary to determine the concentration of chloride ions at various depths in order to determine the likelihood of corrosion of the reinforcing steel. To do this dust samples (see separate entry) are taken from increments of depth (say 5 to 25 mm, 25 to 50 mm, 50 to 75 mm etc). Note that the first 5 mm drillings are normally discarded as being non-representative. The sample should consist of a minimum of 25 g of dust at each depth to be representative. Care must be taken to ensure that all the drilling dust is collected as studies have shown that more chloride is contained in the finer component of the dust.
The chloride content must be determined by an experienced laboratory, preferably having accreditation such as UKAS (the United Kingdom Accreditation Service). It is important that the laboratory work is carried out to the appropriate national standards. This is covered by BS EN 14629, Products and systems for the protection and repair of concrete structures. Test methods. determination of chloride content in hardened concrete.