Study on the Activity of Metakaolin Produced by Traditional Rotary Kiln in China

Abstract

This paper analyzed the activity of coal‐based metakaolin and non‐coal‐based metakaolin (ordinary metakaolin) commonly used in the Chinese market. The content of kaolin was detected by XPF. The phases of kaolin, metakaolin and corresponding alkali‐excited reactants were detected by XRD. The contents of Al (IV), Al (V) and Al (VI) in kaolin and metakaolin were analyzed by27Al NMR. The micromorphology of kaolin and metakaolin were observed by SEM. The water‐resistance of alkali‐activated metakaolin was tested by immersion experiment. The results showed that a lot of corundum and quartz were present in the coal‐based metakaolin, which was caused by over cal-cination. Furthermore, large amounts of sillimanite, quartz and cristobalite existed in ordinary me-takaolin with a low content of amorphous aluminum silicate, which was caused by excessive impu-rities in the raw materials and over calcination. These crystalline substances could not react in an alkali solution, and their existence reduced the activity of the two metakaolins. Both of the two me-takaolin production methods need to be improved to increase the activity.