Performance and Properties of Concrete made with Calcined Clays

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Title: Performance and Properties of Concrete made with Calcined Clays

Author(s): Nancy Beuntner and Karl-Christian Thienel

Publication: Special Publication

Volume: 320

Issue:

Appears on pages(s): 7.1-7.12

Keywords: calcined clay; metakaolin; porosity; reactivity; supplementary cementitious materials; shrinkage; solubility

Date: 8/1/2017

Abstract:
Improving the ecological and economical properties of concrete requires efficient supplementary cementitious materials (SCM) in future, which can even be used in significantly higher substitution rates than common today. Such potential is ascribed to calcined clays. Thus tests were conducted in order to investigate various substitution rates of differently reactive calcined clays. The suitability and efficiency of low-grade kaolinitic calcined clays were compared to an industrial by-product rich in metakaolin and a commercial metakaolin. The pozzolanic reaction kinetics and the formation of hydrate phases were affected by the calcined clays’ specific surface, their high water demand and did depend in addition on the aluminum content. These factors influenced the fresh and hardened mortar and concrete properties as well. Other than for metakaolin rich SCM the application of low-grade kaolinitic calcined clays in concrete and mortar is especially interesting even for high substitution levels of 20 to 30 % by mass due to their lower and retarded reactivity.