Effects of metakaolin and the interfacial transition zone on the diffusion of chloride ions through cement mortars

The effects of metakaolin and variations in aggregate volume content on the diffusion kinetics of chloride ions in hydrated Portland cement model mortars were studied. Chloride diffusion was monitored under both steady- and non-steady-state conditions, and capillary porosity data were obtained for the specimens under investigation. The observed variations in chloride diffusivity were interpreted in terms of the pozzolanic effect of metakaolin and the influence of an increasing proportion of paste-aggregate interfacial transition zone (ITZ) material as aggregate volumes increase. Metakaolin reduced the rate of chloride diffusion through the hydrated cement matrix and also tended to enhance the resistance to chloride transport of the ITZ material within the mortars. (C) 2001 Elsevier Science Ltd. All rights reserved.