Cement Replacement Materials

Metakaolin (MK), commercially available since the mid-1990s, is one of the recently developed supplementary cementing materials (SCM) that conforms to ASTM C 618, Class N pozzolan Specifications. Metakaolin differs from other supplementary cementitious materials (SCMs), like fly ash, silica fume, and slag, in that it is not a by-product of an industrial process; it is manufactured for a specific purpose under carefully controlled conditions [1, 2]. This allows manufacturing process of metakaolin to be optimized, ensuring the production of a consistent pozzolanic material. Metakaolin is produced by heating kaolin, one of the most abundant natural clay minerals, to temperatures of 650–900 °C. The Meta prefix in the term is used to denote change. The scientific use of the prefix is used for a combining form denoting the least hydrated of a series. In the case of metakaolin, the change that is taking place is dehydroxylization, brought on by the application of heat over a defined period of time. This heat treatment, or calcinations, serves to break down the structure of kaolin. Bound hydroxyl ions are removed and resulting disorder among alumina and silica layers yields a highly reactive, amorphous material with pozzolanic and latent hydraulic reactivity, suitable for use in cementing applications [3, 4]. The first documented use of MK was in 1962, when it was incorporated in the concrete used in the Jupia Dam in Brazil [5].