Structural and physical changes of re-calcined metakaolin regarding its reactivity

[Display omitted] •The re-calcination of metakaolin at 800°C for 4h increased substantially its reactivity.•SAXS showed nanoparticles of a new (spinel/mullite) phase starting at ⩾800°C.•Mullite phase growth at 900°C caused decrease in specific surface area and reactivity. The re-calcination of comme...

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Bibliographic Details
Published in:Construction & building materials 2015-04, Vol.80, p.98-104
Main Authors: Kovářík, T., Bělský, P., Novotný, P., Říha, J., Savková, J., Medlín, R., Rieger, D., Holba, P.
Format: Article
Language:English
Subjects:
Analysis
Annealing
Clay minerals
Mechanical properties
Metakaolin
Pozzolanic reactivity
Raw materials
Re-calcination
SAXS
SEM/TEM
XRD
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Summary:[Display omitted] •The re-calcination of metakaolin at 800°C for 4h increased substantially its reactivity.•SAXS showed nanoparticles of a new (spinel/mullite) phase starting at ⩾800°C.•Mullite phase growth at 900°C caused decrease in specific surface area and reactivity. The re-calcination of commercial metakaolin was carried out and structural changes were observed in relation to pozzolanic activity and specific surface area in temperature range 500–1000°C. The re-calcined metakaolins were characterized by XRD, SAXS, SEM, TEM in relation to structure state and reactivity variation based on Chapelle test. The re-calcination led to ∼40% rise of reactivity in the range of 650–800°C. Considering the structural changes the mullite phase crystallization and partial sintering of the particles caused rapid decreasing of reactivity. SAXS spectrum revealed the formation of new phase already at annealing temperature 800°C.
ISSN:0950-0618
1879-0526
DOI:10.1016/j.conbuildmat.2014.12.062