Supplementary cementitious materials (SCM) are required to improve the technical and environmental characteristics of high-performance concrete. They will substitute conventional binders to a greater extent than previously common. Calcined clays are considered to provide huge potential in this regard. Besides the well-known, highly reactive but relatively expensive metakaolin, which can be used in concrete only to a limited extent, calcined mixed layer clays are an alternative solution that appears to be very promising both in environmental and economic terms. In this study, the suitability and efficiency of a calcined mixed layer clay as SCM is compared to a metakaolin and a silica fume. The latter served as reference since it is the most common SCM used in high-performance concrete. The pozzolanic reaction kinetics and the formation of hydrate phases were specifically affected by the calcined clays' specific surface, their high water demand and did depend in addition on their aluminum content. These factors influence fresh and hardened concrete properties as well. The study investigates the impact of different calcined clays on microstructure and on strength, young's modulus of high performance concrete. The pozzolanic efficiency of calcined clay in blended pastes for highperformance concrete with low water-binder ratio was also determined by thermogravimetrical analyses. Other than for metakaolin and silica fume the application of low-grade calcined mixed layer clays in concrete and mortar is especially interesting even for high substitution levels of up to 30 wt.{%} of cement due to their lower and retarding reactivity.    «

Supplementary cementitious materials (SCM) are required to improve the technical and environmental characteristics of high-performance concrete. They will substitute conventional binders to a greater extent than previously common. Calcined clays are considered to provide huge potential in this regard. Besides the well-known, highly reactive but relatively expensive metakaolin, which can be used in concrete only to a limited extent, calcined mixed layer clays are an alternative solution that appe...    »