High Strength Geopolymers Produced from Coal Combustion Fly Ash

High strength geopolymers were produced from coal combustion fly ashes. These matrices
reached compressive strength values over 100 MPa, much stronger and denser than
obtained by using Portland Cement binders. Size fractions were obtained by size separation
techniques and the relationship between strength and particle size was investigated. The
differences in compressive strength measured in the geopolymers made from fine fractions,
the original fly ash and a coarse fraction of the same ash, were not significantly higher than
the variation found for a reference geopolymer material. Therefore, a direct size-strength
relationship could not be proven. Moreover, the chemistry and the pH of the fractions also
varied, and this might as well has played a role in the strength development.