# Formulation of Alkali-Activated Slag Binder Destined for Use in Developing Countries
## 3 Results
### FTIR Analysis of Pastes  
Figure 8 shows the FTIR spectra of the pastes cured at 7, 28 and 90 days at ambient temperature. Table 4 presents the main assignations of the vibrations on the FTIR curves. The assignment was based on some research works by different authors [35; 36; 37; 38].  
The unreacted BFS presented various peaks: (a) at around 1477 cm\({}^{-1}\), the peak was identified as the asymmetric stretching mode of O-C-O in CO\({}_{3}\)\({}^{-2}\) due to the presence of calcite; (b) the broadband centered at 933 cm\({}^{-1}\) corresponded to the asymmetric stretching vibration mode of Si-O-T (T: Si or Al); (c) the shoulder at 875 cm\({}^{-1}\) was attributed to the asymmetric stretching of the AlO\({}_{4}\) groups; (d) the peak at 663 cm\({}^{-1}\) corresponded to vibration modes of sulfate, (e) finally at around 445 cm\({}^{-1}\) the band assigned to the Si-O-Si bending vibrations appeared.  
When analyzing the peaks in the bands near 1400 cm\({}^{-1}\), which are affected by asymmetric stretching bond C-O (CO\({}_{3}\)\({}^{-2}\)), we can conclude that these bands were strong in pastes SC and SHC, derived by the presence of calcium or sodium carbonates. The presence of carbonates of different natures was corroborated by the DTG analysis. The formation of the hydrotalcite phase was identified by the presence of the stretching vibration mode of Al-O and Mg-O at around 1050 cm\({}^{-1}\), and this peak was identified in all the pastes for all three curing ages.  
Figure 7: DTG curves of the pastes cured for: (a) 7 days; (b) 28 days; (c) 90 days.  
The band within the 933-954 cm\({}^{-1}\) range was attributed to the asymmetric stretching vibration of the Si-O-T units (T: Si or A, tetrahedral) of CSH and CASH. This band was found in all the FTIR of the pastes. The bands at 875 and 711 cm\({}^{-1}\) were visible only in pastes SC and SHC, and these bands were attributed to the carbonated phases. The bands located within the lowest wavenumber range were attributed to the bending bands associated with products such as CSH, CASH or NASH. The FTIR of pastes SC and SHC were similar and only differed slightly from paste SH, especially in the vibration bands corresponding to the carbonated phases.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Wavenumber (cm\({}^{-1}\))** & **Affected** & **Present in the Specters of** \\ \hline
1398–1477 & \(v\) O-C-O (CO\({}_{3}\)\({}^{-2}\)) & BFS, SH, SC and SHC \\
1041–1058 & \(v\) Mg–O/Al-O (hydrotalcite) & SH, SC and SHC \\
933–954 & \(v\) Si-O-T (T: Al or Si) (CSH and CASH) & BFS, SH, SC and SHC \\
873–875 & \(v\) C-O (CO\({}_{3}\)\({}^{-2}\)) & BFS, SC and SHC \\
700–713 & \(v\) C-O (CO\({}_{3}\)\({}^{-2}\)) & SC and SHC \\
655–671 & \(\delta\) Si–O–Si (CASH) & BFS, SH, SC and SHC \\
590–594 & \(\delta\) Si–O–Si/Si–O–Al (NASH) & SH \\
470–486 & \(\delta\) Si–O–Si & SH, SC and SHC \\
420–447 & \(\delta\) Si–O (SiO\({}_{4}\) Td) & BFS, SH, SC and SHC \\ \hline \hline \end{tabular} The v stretching bands and the \(\delta\) bending bands.  
\end{table}
Table 4: Assignment of the bands of the FTIR spectra.  
Figure 8: FTIR spectra of the pastes cured for: (a) 7 days; (b) 28 days; (c) 90 days.