Quantitative study of the reactivity of fly ash in geopolymerization by FTIR

Fourier transform infrared (FTIR) spectroscopy has been applied to analyse the environments of Al–O and Si–O bonds in fly ash, which are used as raw materials of geopolymer synthesis. It is noted that the relative intensities of the bands at around 1000, 910 and 700 cm−1 are much higher in fly ash with higher reactivity, as reflected by the compressive strength of geopolymer. Deconvolution analysis of the band from 400 to 1400 cm−1 shows that the cumulative area of these three resolved bands, together with the band at ∼1090 cm−1, which is assigned to the asymmetric stretching of Si(Al)–O–Si, is proportional to the reactivity of fly ash. If it is assumed that the area of the resolved bands is proportional to the concentration of the corresponding bonds, a general indication is therefore that fly ash containing more reactive bonds will exhibit higher reactivity in geopolymerisation. FTIR spectroscopy in combination with particle size analysis provides a fast approach to predict the reactivity of fly ash, from the perspective of aluminosilicate glass chemistry.