Beneficiation of Collie fly ash for synthesis of geopolymer Part 2 – Geopolymers

This paper follows on from Beneficiation of Collie fly ash for synthesis of geopolymer: Part 1 – Beneficiation [1]. In Part 1 beneficiation of fly ash was conducted in a three stage procedure using sieving, milling and magnetic separation to improve fly ash homogeneity and reactivity. At each stage of beneficiation the proportion of reactive amorphous material increases resulting in increased reactivity. This increase in reactivity necessitated changes in solids:liquids ratio to maintain a workable geopolymer mixture. The outcomes from this research clearly identifies that different levels of fly ash beneficiation lead to different geopolymer properties which in turn extends the range of applications for which geopolymers can be used. Compressive strength of all samples were 100 MPa or more with sieving producing a 32% increase in strength. The microstructure of geopolymers changed considerably with beneficiation leading to a very unusual interlocked structure for the sample made from non-magnetic, sieved and milled ash. Although one specific fly ash was used the results presented here are applicable to many other fly ashes.