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

Flash-calcination enables the dehydroxylation of powdered kaolinite cl ay within several tenths of a second, when traditional soak-calcinatio ns require minutes at least. The pozzolanic properties of the metakoli n produced from two different kaolinites, using two different flash ca lciners, are shown to increase with the dehydroxylation rate, and rapi dly 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 propertie s of products: the compressive strengths of minicylinders of metakaoli n+lime+water after solidification, and the Chapelle test. Processing f lash-calcination in a temperature range that was determined, with a su fficient residence time, lead to metakaolins with lime reactivities si milar or better than reactivities of standard metakaolin obtained by s oak-calcination.