CHLORIDE BINDING IN CEMENT

This article describes an investigation into the various methods used to determine the chloride concentration in hardened cement. The methods include the following: (a) chloride extraction with (i) water and water solutions or (II) ethyl alcohol; (b) analysis of pressed-out pore water. These methods are then evaluated to ascertain which gave the most accurate results, by testing cement paste samples with a known concentration of chloride in pore water. These results show that only the pressing-out method gives a correct determination. Up to the highest pressure exerted of approx 3500 bar, the expression force hardly has any influence on the chloride and hydroxide concentration of the pore solution. Crushing of samples prior to expression should be avoided as even brief contacts of the pulverised samples with ambient air result in a decrease in hydroxide and an increase in the chloride concentration of the pore solution due to co2 uptake.(a)