POZZOLANIC PROPERTIES OF FLASH-CALCINED KAOLINITE - A COMPARATIVE-STUDY WITH SOAK-CALCINED PRODUCTS

Flash-calcination enables the dehydroxylation of powdered kaolinite clay within several tenths of a second, when traditional soak-calcinations require minutes at least. The pozzolanic properties of the metakolin produced from two different kaolinites, using two different flash calciners, are shown to increase with the dehydroxylation rate, and rapidly to decrease at the occurence of recrystallisation for temperatures above 900 degrees C. Flash-calcined products also revealed structural properties different from soak-calcined products. Two different lime reactivity tests were thus necessary to asses the pozzolanic properties of products: the compressive strengths of minicylinders of metakaolin+lime+water after solidification, and the Chapelle test. Processing flash-calcination in a temperature range that was determined, with a sufficient residence time, lead to metakaolins with lime reactivities similar or better than reactivities of standard metakaolin obtained by soak-calcination.