Integrated gasification combined cycle (IGCC) slags and Si sludges were used as the raw material and bloating material for obtaining lightweight geopolymers, respectively. When Si sludge was used for the bloating reaction to obtain ultra-lightweight geopolymers, the specimens have large pores an inhomogeneous pore distribution, resulting in adverse effects on the mechanical properties of lightweight geopolymers. Three curing temperatures and two different curing methods were investigated for the control of the microstructure and pore distribution of lightweight geopolymers. Compressive strengths, pH changes, FT-IR spectra, microstructure observations, and ICP results before and after immersion were compared for the specimens obtained with different curing temperatures and methods. The highest compressive strength after immersion was obtained for the specimen cured at 123 ^oC in an autoclave because the degree of geopolymerization of this specimen was higher than for any other specimens as found from the analysis of the pH changes, FT-IR spectra, microstructure observation, and ICP results. In conclusion, curing at high temperature (123 ^oC) with an autoclave is the optimal curing for maintaining stable mechanical properties in a wet service environment

Keywords: Geopolymer, IGCC slag, Si sludge, Curing temperature and method