Co-addition of metakaolin and silica fume in mortar: effects and advantages

Metakaolin (MK), ground to finer than cement, is an emerging pozzolanic material for concrete production. Silica fume (SF), which is even finer than MK, has been proven to be effective in improving the strength of concrete. Both are being added separately, but in theory, they can also be added together. To explore the possible co-addition of MK and SF and evaluate their combined effects, mortar mixes with varying water, MK and SF contents were tested for their fresh and hardened properties. From the experimental results, it was found that regarding workability, MK has positive effect, SF has negative effect, and co-addition of MK and SF can mitigate the negative effect of SF. Regarding strength, both MK and SF have positive effects, but co-addition of MK and SF has the synergistic effect that the increase in strength due to co-addition of MK and SF is larger than the increase in strength due to sole addition of MK or sole addition of SF. Such synergistic effect should be particularly useful for production of high-performance concrete. (C) 2018 Elsevier Ltd. All rights reserved.