Long-term testing of the chloride-penetration resistance of concrete containing high-reactivity metakaolin

This paper presents the long-term results of a study investigating the chloride penetration resistance of concrete containing high-reactivity metakaolin (HRM). The metakaolin evaluated in this study is a highly processed kaolinite clay that has been heat-treated under controlled conditions to produce high pozzolanic activity. Six concrete mixtures were cast with 0%, 8%, or 12% by mass replacement of portland cement with HRM at water-to-cementitious materials ratios (w/cm) of 0.30 or 0.40. The early age test results are summarized and include (1) strength, (2) 28-day and 90-day bulk diffusion, (3) rapid chloride permeability, and (4) resistivity. The long-term tests performed include bulk diffusion testing at 140 days, 1 year, and 3 years and chloride migration testing. It was found that strength increased at all ages with decreasing w/cm and increasing content of HRM. The results from all of the early age experimental work showed that higher metakaolin content and lower w/cm decreased diffusion, permeability, and conductivity and increased resistivity. Resistance to chloride migration increased with increasing metakaolin content and decreasing w/cm. The long-term bulk diffusion testing showed a continued improvement in chloride resistance for all of the mixtures. (C) 2001 Elsevier Science Ltd. All rights reserved.