Spectroscopic studies of fly ash-based geopolymers

Piotr Rożek; Magdalena Król; Włodzimierz Mozgawa

doi:10.1016/j.saa.2018.03.034

Spectroscopic studies of fly ash-based geopolymers

Spectrochim Acta A Mol Biomol Spectrosc. 2018 Jun 5:198:283-289. doi: 10.1016/j.saa.2018.03.034. Epub 2018 Mar 13.

Authors

Piotr Rożek¹, Magdalena Król², Włodzimierz Mozgawa²

Affiliations

¹ AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Al. Mickiewicza 30, 30-059 Krakow, Poland. Electronic address: prozek@agh.edu.pl.
² AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Al. Mickiewicza 30, 30-059 Krakow, Poland.

PMID: 29558727
DOI: 10.1016/j.saa.2018.03.034

Abstract

In the present work fly-ash based geopolymers with different contents of alkali-activator and water were prepared. Alkali-activation was conducted with sodium hydroxide (NaOH) at the SiO₂/Na₂O molar ratio of 3, 4, and 5. Water content was at the ratio of 30, 40, and 50wt% in respect to the weight of the fly ash. Structural and microstructural characterization (FT-IR spectroscopy, ²⁹Si and ²⁷Al MAS NMR, X-ray diffraction, SEM) of the specimens as well as compressive strength and apparent density measurements were carried out. The obtained geopolymers are mainly amorphous due to the presence of disordered aluminosilicate phases. However, hydroxysodalite have been identified as a crystalline product of geopolymerization. The major band in the mid-infrared spectra (at about 1000cm^-1) is related to SiO(Si,Al) asymmetric stretching vibrations and is an indicator of the geopolymeric network formation. Several component bands in this region can be noticed after the decomposition process. Decomposition of band at 1450cm^-1 (vibrations of CO bonds in bicarbonate group) has been also conducted. Higher NaOH content favors carbonation, inasmuch as the intensity of the band then increases. Both water and alkaline activator contents have an influence on compressive strength and microstructure of the obtained fly-ash based geopolymers.

Keywords: Alkali-activation; Carbonation; Fly ash; Geopolymer; Geopolymerization; IR spectra.