Metakaolin is the anhydrous calcined form of the clay mineral kaolinite. Minerals that are rich in kaolinite are known as china clay or kaolin, traditionally used in the manufacture of porcelain. The particle size of metakaolin is smaller than cement particles, but not as fine as silica fume.

Metakaolin is used to Increased compressive and flexural strengths and Reduced permeability (including chloride permeability). Metakaolin is also Reduced potential for efflorescence, which occurs when calcium is transported by water to the surface where it combines with carbon dioxide from the atmosphere to make calcium carbonate, which precipitates on the surface as a white residue. Metakaolin is mostly used in Precast and poured-mold concrete, Fibercement and ferrocement products, Glass fiber reinforced concrete, Mortar and stucco etc.

Metakaolin is a porcelain, probably the most effective pozzolanic material for use in concrete. It is a product that is manufactured for use rather than a by-product and is formed when china clay, the mineral kaolin, is heated to a temperature between 600 and 800ºC.

Metakaolin (MTK) is a metastable reaction product of dehydroxylation of kaolin at the temperature of 650 – 850 ºC. The research on the influence of additives on the properties of MTK cement compositions was initiated in the middle of the twentieth century, but until now various issues on its application are still unclear. Disagreement among researchers relates to the formation of various compositions of hydrate neoplasms.

Metakaolin (MTK) without 5% super plasticizer increases frost concrete brand (F 300) in comparison with non-additive composition (F 200), which is associated with accelerated cement hydration process and therefore a seal structure. Developed complex additives - modifiers can significantly improve the frost resistance of concrete. Since the introduction of additives have U-YF hardiness increases by three times (F 600) for cement compared with non-additive composition.