To analyze the impact of mix proportions on the performance of geopolymer concrete (GC)

the effects of the ratio of fly ash (FA) to granulated blast furnace slag (GGBS)

the sodium silicate modulus

and the content (mass fraction) of sodium silicate on the mechanical properties of geopolymer concrete were studied. Further

the microstructure of geopolymer concrete was investigated by means of scanning electron microscope (SEM)

energy dispersive spectroscopy (EDS)

X-ray diffraction (XRD)

Fourier transform infrared spectroscopy (FT-IR)

and mercury intrusion porosimetry (MIP) tests. Results show that with the increase in curing age

the degree of polymerization was higher

the amount and types of gel observed in SEM images increased

and the macroscopic strength of geopolymer concrete was higher. The decrease in the modulus of sodium silicate resulted in the decrease in Si/Al ratio and increase in Na+

which promoted the formation of gel and made the geopolymer concrete exhibit higher mechanical properties. A decrement in the ratio of fly ash to slag

i.e. the increase in the amount of Ca in the system

promoted the generation of gel. When the content of sodium silicate increased from 20% to 25%

Si/Al ratio increased from 1.31 to 3.37

and the microstructure density and macroscopic strength of geopolymer concrete samples were improved. However

when the content of sodium silicate was excessive

Si/Al ratio decreased from 3.37 to 2.00

and the formation of gel was difficult

showing a lower strength of the geopolymer concrete samples. Reducing the modulus of sodium silicate and increasing the proportion of slag can both promote the polymerization

which is helpful to the improvement of the mechanical properties and the compactness of the microstructure of geopolymer concrete.