Assessing the viability of a high performance one-part geopolymer made from fly ash and GGBS at ambient temperature

This study aims to investigate the feasibility of preparing a one-part geopolymer using fly ash (FA) and ground granulated blast furnace slag (GGBS) as the main raw materials and solid sodium hydroxide and sodium silicate as activation conditions under ambient conditions. Orthogonal tests were conducted to study effects of FA on the GGBS mass ratio (F:G), solid alkali content, sodium hydroxide–to–sodium silicate mass ratio (SH:SS), and water-to-solid ratio on the unconfined compressive strength (UCS), setting time, and fluidity of the one-part geopolymers. The microstructure, composition, and pore distribution characteristics of the geopolymers were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), and mercury intrusion porosimetry (MIP). The findings revealed that (1) the mechanical characteristics of the geopolymer were most severely influenced by F:G, and the compressive strength of the geopolymer considerably decreased with an increase in F:G. (2) The influences of the alkali content and water-to-solid ratio on the setting time of the geopolymer were essentially the same and significantly larger than those of the F:G and SH:SS variables. (3) The most important element affecting the fluidity of the geopolymer was the water-to-solid ratio. Microscopic analysis verified the results of the macroscopic experiments. The XRD and SEM-EDS tests indicated that the reaction system produced a mixed gel by activating some of the Ca in the GGBS was activated with FA, which filled the pores of the geopolymer and increased its strength. The MIP test also revealed that specimen S7 exhibited the smallest pore space among the selected specimens. The microscopic experiments revealed that the reaction system produced a mixture of calcium silicate hydrate (C-S-H) gels and hydrated sodium silicate N(C)-A-S-H gels.