황산나트륨 첨가제에 따른 플라이애시 기반 지오폴리머의 미세구조 및 강도 특성

Abstract

This paper presents an investigation of the mechanical and microstructural properties of Class F fly ash based geopolymer containing sodium sulfate as an additive. Sodium sulfate was used as an chemical additive at the dosage levels of 0, 2, 4, and 6wt% of fly ash. Sodium hydroxide and sodium silicate solutions were used to activate fly ash. The compressive strengths of geopolymer pastes were measured at the age of 28 days. The microstructures of the geopolymer pastes were examined using XRD, MIP and SEM tests. The additions of 2wt% and 4wt% sodium sulfate produced geopolymers with high strength, while increasing the dosage of levels to 6% resulted in almost no changes in strength, comparing with the control geopolymer. The optimum increase in strength was obtained with the addition of 4wt% sodium sulfate. As the amount of sodium sulfate is increased, no additional crystalline phase was detected and no change of amorphous phase indicated despite the change in the strength development. The increase in the strength was due to the change of pore size distribution in samples. As addition of sodium sulfate altered the morphologies of reactive productions and Si/Al ratios of the reaction products, the strengths were thus affected. It was found that the strengths of geopolymer were larger for lower Si/Al ratios of reaction products formed in samples. The optimal amount of sodium sulfate in the fly ash based geopolymer helps to improve mechanical properties of the geopolymer, on the other hand, the high percentage of sodium sulfate could exist as an impurity in the geopolymer and hinder the geopolymer reaction.