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 similar to 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.