Determination of free chlorides in aggregates and concrete

Chlorides exist as either "bound" or "free" chloride in concrete. It is well recognised that it is the free chloride that contributes to steel depassivation and subsequent corrosion in concrete. In measuring the amount of chlorides in aggregates and concrete, both "water-soluble" and "acid-soluble (total) chloride" test methods have been used. The aggressiveness of the extractive techniques determines the type and amount of chlorides. This was investigated in terms of the type of extracting agent and degree of fractured surface of the materials. It was found that the use of boiling water on materials passing 850-micron sieve offered a well balanced measure of the free chloride contents in aggregate. The findings were also confirmed valid in testing hardened concrete.