Co-existence of aluminosilicate and calcium silicate gel characterized through selective dissolution and FTIR spectral subtraction

Alkali activation of a fly ash and slag mixture supposedly forms a combination of aluminosilicate and calcium silicate hydrate gel as reaction products. Fourier transform infrared spectroscopy (FTIR) is often used to characterize the complex nature of the reaction products. However, interpretation of FTIR results is difficult as the Si–O–T (T = Al, Si) vibrations from the initial ash, geopolymer product, unreacted slag, and calcium silicate hydrate yield an overlapping spectrum. This paper reports how the issue can be resolved by selectively dissolving calcium silicate hydrate and geopolymer product, and subtracting FTIR spectra of the insoluble residue from the original material to determine IR spectrum of the material dissolved.