Cleaner one-part geopolymer prepared by introducing fly ash sinking spherical beads: Properties and geopolymerization mechanism

摘要

One-part geopolymeric binders which are considered as cleaner non-Portland cementitious materials are prepared by first mixing the aluminosilicate materials with the solid alkaline activators before adding water, which makes the mixing method of the geopolymer being the same as Portland cement. In this paper, sinking spherical beads (SSB) is introduced into the raw materials containing fly ash (CFA) and ground granulated blast furnace slag (GGBS) to synthesize a ternary one-part geopolymer. A systematic investigation of the effect of SSB on the geopolymer pastes and mortars is performed through measuring the fluidity, final setting time, compressive strength and flexural strength. It is found that SSB can significantly improve the fluidity and mechanical properties of geopolymer due to its high reactive effect and remarkable morphological effect. The action mechanism of SSB for improving the performance of the geopolymer was also dissected. It is interesting to note that SSB has little influence on the initial heat flow and increases the cumulative heat relating to the strength development. The changes in the formation of C-A-S-H and N-A-S-H gels after the introduction of SSB are well captured by the XRD and EDX analysis. It clearly appears that the N-A-S-H gel with the optimal Na/Si ratio of 0.5 can be generated by optimizing the rational proportion of raw materials and alkaline activators. This study not only demonstrates the superiority of SSB in synthesizing a ternary one-part geopolymer, but also develops a method to design the novel non-Portland cement only by using industrial wastes. (C) 2019 Elsevier Ltd. All rights reserved.