Material structure

The FT-IR spectra of the fly ash with different fineness is shown in Figure 5. Based on the IR spectra of raw and mechanically activated fly ash it can be seen that when the fly ash had a specific surface area of 2016-3600 cm²/g, the band referring to T-O-Si (T = Si, Al) bonds signed with double peak (1101 and 1009 cm^-1), which has shown a wide band at higher fly ash fineness. Furthermore at 678 and 598 cm^-1 can be assigned to Si–O–Si and Al–O–Si bonds symmetric stretching vibration, while double peaks at 796 and 778 cm^-1 refer to O-Si-O bond (Criado et al. 2005).

FIGURE 5 FT-IR SPECTRA OF FLY ASHES WITH DIFFERENT FINENESS

Figure 6 shows IR spectra of GF with different fly ash fineness. Based on Swanepoel and Strydom (2002) peaks at 3370 cm^-1 and 1644 cm^-1 have been assigned to the vibrations of weakly bound molecules of H2O which are adsorbed on the surface or trapped in the large cavities. The broad band at about 1413 cm^-1 which is attributed to stretching vibrations of O-C-O bond is a result of the presence of Na2CO3. This may be due

to a large concentration of Na carried to the surface where it carbonates. Peak observed between 1009 and 1101 cm^-1 in the case of fly ash shifted lower wavenumber (960 cm^-1) in the FT-IR spectra of GF, indicating the formation of a new product (the amorphous aluminosilicate gel phase) (Swanepoel and Strydom, 2002, Criado et al. 2005). Furthermore, the absorption bands in the IR spectrum of the fly (678; 598; 796 and 778 cm^-1) disappeared after geopolymerization.

FIGURE 6 FT-IR SPECTRA OF GEOPOLYMER FOAMS

4. Conclusion

Based on the experimental results presented above the following conclusions can be drawn:

– The rheology of geopolymer paste changed by decrease of particle size (increase of specific surface area) of fly ash by keeping constant liquid/solid ratio (L/S).

– Changing rheology of geopolymer paste modified the compressive strength, density and porosity of geopolymer foam.

– Increasing specific surface area of fly ash the density and strength of geopolymer foams also increased.

– Grinding caused significant change on the structure of fly ash detected by FTIR.

– Based on the IR spectra of GF it can be stated that the fly ash fineness did not cause a significant change in their structure.

5. Acknowledgement

The described work was carried out as a part of the „Sustainable Raw Material Management Thematic Network – RING 2017”, EFOP-3.6.2-16-2017-00010 project in the framework of the Széchenyi2020 Program. The realization of this project is supported by the European Union, co-financed by the European Social Fund.

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III. RING – Sustainable Raw Material Management Thematic Network 2019 October 10-11 - Sopron