The amount of fused slag generated is continuously increasing and is expected to reach 50,000 tons per year as coal gasification facilities and waste treatment systems producing fused slag have been actively adopted recently in Korea. One of the prospective solutions is to make geopolymers with the slags because geopolymers are a cement substitute that can reduce the generation of carbon dioxide and have thus attracted increasing interest from recycling and eco-friendly construction industries because they provide sufficient mechanical strength for application in construction materials. There has not yet been a comprehensive microscopic investigation of geopolymers or diffraction pattern analysis of the crystallites produced by geopolymerization. Geopolymers made of fused slags with an alkali activator exhibited very high compressive strength compared with those of ordinary geopolymers, and their microscopic structures were analyzed by transmission rlectron microscopy (TEM) to confirm the formation of crystallites during the geopolymerization and to explain the relationship between the microstructure and mechanical property of the geopolymers. At least two types of phases, C-S-H and Ca(OH)2, have been identified by selected area diffraction (SAD) pattern analyses on the crystallites in the geopolymer matrix.

Keywords: Fused slag, Geopolymer, Microstructure, Si/Al ratio, TEM.