title: Attenuated total reflectance fourier transform infrared analysis of fly ash geopolymer gel aging.
abstract: Structural changes in fly ash geopolymers activated with different sodium hydroxide and silicate concentrations are investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy over a period of 200 days. A strong correlation is found between the concentration of silicate monomer in the activating solution and the position of the main Si-O-T stretching band in the FTIR spectrum, which gives an indication of the relative changes in the gel Si/Al ratio. The FTIR spectra of geopolymer samples with activating solution concentrations of up to 1.2 M SiO2 indicate that an Al-rich gel forms before the final gel composition is reached. The time required for the system to reach a steady gel composition depends on the silicate activating solution concentration and speciation. Geopolymers activated with solutions containing predominantly high-order silicate species rapidly reach a steady gel composition without first forming an Al-rich gel. A minimum silicate monomer concentration of approximately 0.6 M is required to shift the geopolymer synthesis mechanism from hydroxide activation to silicate activation. Silicate speciation in the activating solutions also affects zeolite formation and geopolymer microstructures, with a more homogeneous microstructure and less zeolite formation observed at a higher SiO2 content.
authors.affiliation: Department of Chemical and Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia.
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Rees
authors.forename: John L
authors.initials: JL
authors.lastname: Provis
authors.forename: Grant C
authors.initials: GC
authors.lastname: Lukey
authors.forename: Jannie S J
authors.initials: JS
authors.lastname: van Deventer