Two methods were used to determine the 'free' and 'water soluble' chlo
ride ions concentration in four differing strength grade concretes. Ea
ch grade of concrete had varying concentration of Cl- admired as NaCl.
In all 24 different batches of concretes were made with admired Cl- c
oncentration varying from 0.2 to 2%, by weight of cement. The first me
thod was the analysis of the pore solution expressed from specimens an
d the second by the analysis of the decanted solution of pulverised sp
ecimens. The results suggest that the concentration of Cl- and OH- ion
s as measured in the expressed pore solution represent their true free
ion concentrations. Furthermore, the Cl- concentration of both the ex
pressed and decanted solutions were found to depend on the (i) concent
ration of the admired Cl- ions; (ii) strength of the concrete; (iii) p
resence or absence of fly ash and (iv) presence or absence of a superp
lasticiser. Accordingly, there is no simple relationship between the C
l- concentration as found in decanted and pore solutions. Whereas the
presence of fly ash improves the chloride binding capacity of a concre
te, the presence of superplasticisers tends to lower it. The paper con
cludes that in order to limit the damage caused by Cl- in the concrete
, an upper limit on the total Cl- contents of the admired chloride rat
her than the percentage of Cl- by the weight of cement should be presc
ribed.