Term: Metakaolin

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Kaolinite Sources:
– Quality and reactivity of metakaolin depend on raw material characteristics
– Metakaolin is dehydrated kaolinite, a type of clay mineral
– Sources of kaolinite for metakaolin production include high purity deposits
– Other sources include tropical soils with kaolinite, paper sludge waste, and oil sand tailings
– Metakaolin grain size is smaller than cement particles but larger than silica fume

Forming Metakaolin:
– Dehydroxylation temperature varies based on kaolinite structure
– Kaolinite transforms into metakaolin above dehydroxylation temperature
– Aluminum in kaolinite layer changes coordination upon dehydroxylation
– Optimum activation temperature for metakaolin production ranges from 550-850°C
– Kaolinite’s broad temperature interval favors metakaolin formation

High-Reactivity Metakaolin:
– Highly processed reactive aluminosilicate pozzolan
– Reacts with slaked lime to form strong cement
– Produced by calcining purified kaolinite at 650-700°C
– Accelerates hydration of ordinary portland cement
– Reduces deterioration of concrete by Alkali Silica Reaction

Adsorption Properties:
– Metakaolin’s adsorption surface properties analyzed by inverse gas chromatography
– Characterization helps understand metakaolin’s interaction with other substances

Concrete Admixture:
– Metakaolin has double the reactivity of most pozzolans
– Adding 8-20% metakaolin to concrete improves engineering properties
– Effects include filler effect, OPC hydration acceleration, and pozzolanic reaction
– Filler effect is immediate, while pozzolanic reaction occurs within 3-14 days

– Increased compressive and flexural strengths in concrete
– Reduced permeability and efflorescence
– Improved resistance to chemical attack and ASR
– Enhanced workability and finishing of concrete
– Higher thermal resistance and reduced shrinkage in concrete

– Metakaolin used in high performance, high strength, and lightweight concrete applications

Metakaolin (Wikipedia)

Metakaolin is the anhydrous calcined form of the clay mineral kaolinite. Rocks 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.

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