This paper describes research into the use of granulated blast furnace slag as an active filler in the making of geopolymers. During this work it was found that geopolymer setting time correlates well with temperature, potassium hydroxide concentration, metakaolinite and sodium silicate addition. The physical and mechanical properties of the geopolymer also correlated well with the concentration of alkaline solution and the amount of metakaolinite that is added. The highest compressive strength achieved was 79 MPa. For fire resistance tests, a 10 mm thick geopolymer panel was exposed to a 1100degreesC flame, with the measured reverse-side temperatures reaching less than 350 degreesC after 35 min. The products can be fabricated for construction purposes and have great potential for engineering applications. (C) 2003 Elsevier Science Ltd. All rights reserved.