Effects of Temperature on the Pozzolanic Characteristics of Metakaolin-Concrete

This paper focused on the thermal technique of activating pozzolanic activity of natural pozzolans, specifically calcined kaolinite clay in the form of metakaolin. The effect of heating temperatures over the range 450ºC-1050ºC in steps of 150ºC on the dehydroxylation of the kaolin and the pozzolanic activity of the resulting amorphous material were determined. The compressive strengths of metakaolin-concrete samples with 10%, 20% and 30% replacement of cement, calcined at different temperatures 450ºC, 600ºC, 750ºC, 900ºC and 1050ºC comparable to the control samples were analysed to determine the optimum temperature. Also, mixtures of mortar containing variable amounts of kaolin in the ration 5% to 30% in steps of 5% were calcined at the optimum temperature of 750ºC and investigated.

The results showed the optimum heating temperature for the kaolin to be 750ºC and the proportion of metakaolin in concrete should be 10% of the cement weight. For 10% metakaolin at temperature of 750ºC, the strengths were about 109% and 107% of normal mortar cubes at 28 days and 90 days respectively, while those of concrete cubes were 99% and 97% of normal concrete cubes. Also, with replacement proportion range of 15-25% of metakaolin (MK) in concrete, a relative concrete strength of 22.23MPa and 23.15MPa for 28 and 60 days curing ages respectively can be achieved.