Mechanical properties and microstructure of circulating fluidized bed fly ash and red mud-based geopolymer

Circulating fluidized bed fly ash (CFA) and red mud (RM)-based geopolymers were characterized in terms of setting time, mechanical properties, microstructure, chemical and mineral compositions by considering the effects of curing duration, curing temperature, and RM/CFA mass ratio. X-ray diffraction, X-ray fluorescence, scanning electron microscopy, Fourier transform infrared spectroscopy, low-field nuclear magnetic resonance, flexural and compressive testing, and Vicat apparatus were applied to investigate the pore structure, amorphous phase content, and strength development of final geopolymer products and their mutual effects. The strength and amorphous phase content to porosity ratios were comparatively studied to investigate the relationship among these three properties. Based on the results and discussions, longer curing time and higher curing temperature increase strength, while a lower RM/CFA ratio causes the reduction of mechanical properties of geopolymer paste. The results show that the change in the strength is excellently correlated to the varied porosity and amorphous phase content. In addition, it is concluded that, under ambient curing conditions, RM/CFA ratio of 39% is the critical upper limit to produce the CFA-RM based geopolymers considering the mechanical properties and microstructure.

Automated summary

Circulating fluidized bed fly ash (CFA) and red mud (RM)-based geopolymers were characterized in terms of setting time, mechanical properties, microstructure, chemical and mineral compositions. The effects of curing duration, curing temperature, and RM/CFA mass ratio were considered. The study found that longer curing time and higher curing temperature increase strength, while a lower RM/CFA ratio causes a reduction in mechanical properties. The results show a strong correlation between strength, porosity, and amorphous phase content. Under ambient curing conditions, an RM/CFA ratio of 39% is identified as the critical upper limit for producing geopolymers with desired mechanical properties and microstructure.