In this study, lightweight foamed geopolymers based on metakaolin were synthesized and characterized. By considering the compressive strength, density, and crystal phase of the specimens according to the type and amount of forming agent, the possibility of replacing Al powder, a foaming agent, with Si sludge in lightweight foamed geopolymers was analyzed. The specimens foamed with Al powder had lower density than those with Si sludge. However, the compressive strength of the former was higher than that of the specimens foamed with Si sludge, owing to a more uniform pore distribution and microstructure. Through this study, lightweight foamed geopolymers having density of 0.36~1.05 g/cm³ and compressive strength of 0.7~4.7 MPa can be prepared by controlling the process conditions such as the amount of Si sludge added, alkali activator concentration, L/S ratio, etc. The possibility of Si sludge replacing Al powder as a foaming agent thus has been demonstrated. The lightweight foamed geopolymer fabricated in this study can be applied to various fields as it can meet the required physical properties according to the application.

Keywords: Geopolymer, Light Weight, Si Sludge, Metakaolin