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TECHNICAL PAPER

3.5 Fourier transform infrared spectroscopy The deduction in the peak formations in the samples exposed
(FTIR) at higher temperatures represents the lack of water and thus
indirectly indicates the extend of degradation.
Figure 6 shows the FTIR spectra of the four different geopolymer
mixes before exposure (BE), and exposed at elevated Under this elevated temperature exposure, the mixes with clay
temperatures-300, 600 and 900°C. In all cases, the significant in either calcined clay or metakaolin form have demonstrated
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peak at 1000 cm indicates the asymmetric stretching vibrations an increase in intensity of transmittance at 560 cm that
of Si-O-Si or Si-O-Al bonds, which is common in any kind of corresponds to the stretching of tetrahedral aluminium bonds.
geopolymers. Similarly, the peaks at around 1600 cm are The increase in intensity of crystalline phases represents the
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because of the (OH) bending vibration of the absorbed H 2 O [24] . reduction in amorphous content in geopolymer cement matrix
The occurrence of broad peaks around 3200 and 3600 cm and hence, the strength reduction at elevated temperature
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represents the stretching vibrations of the hydroxyl group (OH) could be attributed to that [27] . For metakaolin mixes, the
of physically free water at higher frequencies, and at lower differences in the peaks of the samples at various temperature
frequencies, they represent the chemically bounded water from exposures are the highest among all the mixes, which represents
the inorganic polymer having hydrogen bonds [26-27] . These peaks the highest deterioration of metakaolin geopolymers at elevated
around 3200-3400 cm disappeared at temperature higher than temperatures. The best performance of fly ash geopolymers at
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600°C that can be corroborated with the non-availability of elevated temperatures can be deduced clearly from Figure 6 (a),
hydroxyl groups due to decomposition of any available Ca(OH) 2 . which are followed by FACC and CC mixes. The FTIR results

120 120
FA CC
100 100
Transmittance (%) 80 Transmittance (%) 80

60
60
40
BE
300 0 40 BE 0
300
20 600 0 20 600 0
900 0 900 0
0 0
0 1000 2000 3000 4000 0 1000 2000 3000 4000
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Wave number (cm ) Wave number (cm )
(a) FA mix (b) CC mix

120 120
FACC MK
100 100
Transmittance (%) 60 Transmittance (%) 80
80

60

40
BE
300 0 40 BE 0
300
20 600 0 20 600 0
900 0 900 0
0 0
0 1000 2000 3000 4000 0 1000 2000 3000 4000
Wave number (cm ) Wave number (cm )
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(c) FACC mix (d) MK mix
Figure 6: FTIR spectra of the different geopolymer mixes which were exposed to different temperatures

24 THE INDIAN CONCRETE JOURNAL | MAY 2022