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Figure: Ahmed Yahia in a kaolin cave. |
Kaolin is composed mainly of the kaolinite mineral (Al2O3.2SiO2.2H2O). It can be thermally or mechanically activated into metakaolin with pozzolanic characteristics, i.e., reacts with calcium hydroxide released from the cement hydration to form compounds with cementing properties. The advantage of metakaolin on the other supplementary cementitious materials, such as slag, fly ash and limestone, that it has a better pozzolanic reactivity in addition to its higher purity.
Thermal/calcination and mechanical/grinding methods could be applied to activate the raw kaolin into pozzolanic metakaolin. The pozzolanic activity of the metakaolin depends mainly on the de-hydroxylation degree of kaolin, i.e., amorphization, and the available surface area for the reaction between the reactive alumina and silica provided by the metakaolin. Impurities of iron- and titanium-oxides, quartz, feldspar and calcite may influence the activity of the kaolin activation into metakaolin.
