Pozzolanic activation of metakaolin

Abstract

Metakaolin may be calcined without grinding and suitably activated by Ca(OH)2, Na2SO4, CaSO4 (beta anhydrite) and/or NaOH. The best strengths, 50 MPa from mortar cubes at 18 months, were obtained using Ca(OH)2 and CaSO4 activators. The handling and set properties are similar to those of Portland cement; aluminous C-S-H gel is the best binder. All compositions contain K+ derived from mineral impurities in kaolin, thus the performance and activation of kaolins may depend partly on their alkali content. The microstructures of the cured products are described, and the importance of good space filling by the hydrates is emphasized. Since the precursor minerals are widely distributed, kaolin deserves more investigation as the principal component of low-energy binder systems.