ABSTRACT
Chlorides exist in concrete in two forms: free and bound. It is the general understanding that only free chloride ions in the pore solution in concrete are movable. However, in practice it is diffi cult to separate the free chlorides from the total chlorides (free plus bound). Both the free and the total chlorides are often determined using classical chemical analysis. The amount of chloride ions in concrete may, therefore, be expressed in a number of ways. Nilsson et al. (1996) have summarised the most frequently used expressions, as follows:
cI (kg Cl/m 3 of solution) (2.1:1)
cII (kg Cl/m 3 of pore solution) (2.1:2)
cIII (kg Cl/m 3 of material) (2.1:3)
cIV (kg Cl/m 3 of solid material) (2.1:4)
cV (kg Cl/kg of cement or binder) (2.1:5)
cVI (kg Cl/kg of gel (‘gel’ = hydrated cement + bound water)) (2.1:6)
cVII (kg Cl/kg of concrete) (2.1:7)
cVIII (kg Cl/kg of sample) (2.1:8)
Consequently, giving the quantity of chlorides in only kg/m3, kg/kg or % might cause confusion and large errors when trying to use the data. The unit of kilogram (kg) for mass is sometimes replaced by moles (mol). It does not change the relations and the relation between kg Cl and mol Cl is obvious. Concentrations in g/l are identical to concentrations in kg/m3 of solution, but it should be clearly stated whether the mass is that of chloride ions or salt (NaCl); for instance, g Cl per litre or g NaCl per litre. The difference in quantity between chloride ions and NaCl is greater than 50%, due to the different molar weights (35.45 g Cl and 58.45 g NaCl).
