Strategies to control thermally induced shrinkage in fly ash based geopolymers are investigated. The use of low (<2) Si:Al ratios in the geopolymer provides superior thermal properties and the addition of fillers delivered additional improvements resulting in impressive thermal resistance. Two thermally stable inorganic fillers, a-alumina and wollastonite, were used because of their high melting points and relatively low thermal expansion. Shrinkage events at elevated temperatures revealed that samples containing filler exhibited 30-35% less volume shrinkage than the control at 1000 degrees C. Initial compressive strength was moderate (similar to 30 MPa), but increased markedly when samples were fired in excess of 600 degrees C (>100 MPa). Wollastonite addition also improved the flexural strength of the samples which was attributed to its acicular shape imparting fibre-like qualities. Microstructural investigations showed that unfired samples predominantly consisted of spherical particles coated with reaction product. Firing to 1000 degrees C converted the morphology to a more compact phase with increased pore size. (C) 2014 Elsevier B.V. All rights reserved.