Effect of composition of fly ash on compressive strength of fly ash based geopolymer mortar

This paper discusses the changes in compressive strength of fly ash (FA) based geopolymers due to variation of chemical composition, activator modulus (AM) and particle size distribution. Mortar specimens were prepared using Class F fly ash obtained from five different power stations in Australia. To optimize the best mix ratio for each type of FA based geopolymer, AM was varied between 0.625 and 1.75 by fixing Na2O dosage to 15. A variation in compressive strength for the five FA based geopolymers was observed between 21.2MPa and 60.6MPa. In addition to the specific chemical composition of the individual FA this variation also attributed to the carbon content and fineness ratio of FA, both of which enhance the activator solution demand well beyond that needed to merely activate the source material.