AN INVESTIGATION OF EXPERIMENTAL METHODS USED TO DETERMINE FREE AND TOTAL CHLORIDE CONTENTS

The free chloride content in cement pastes may be assessed by analysin g the pore solution expressed under pressure using a pore press, or ac hieving an equilibrium between a known external solution and the pore solution, while the total chloride content is commonly determined usin g acid soluble extraction. A comparison of these techniques indicates that loosely bound chloride is released during pore solution expressio n under pressure and this may result in a significant overestimation o f the free chloride content. Chloride binding relationships determined in this manner may produce errors when used in modelling chloride tra nsport as the expressed pore solution concentration can be significant ly greater than that in the contaminating solution. Furthermore acid s oluble extraction may underestimate the total chloride content. The us e of ultrasonic treatment to accelerate the achievement of equilibrium also results in the release of loosely bound chloride which in turn l imits the chloride taken up by such samples.