Term: Metakaolin
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
Advantages:
– 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
Uses:
– Metakaolin used in high performance, high strength, and lightweight concrete applications