# Alkali-Activated Binders Using Bottom Ash from Waste-to-Energy Plants and Aluminium Recycling Waste
## 3 Results and Discussion
### Physicochemical Characterization  
The crystalline phases found in the AA-WBA/PV binders are summarized in Table 4. The presence of calcite, cristobalite, corundum, dolomite, gibbsite, and quartz was due to the unreacted WBA and PV. Calcium silicate hydrate as the main C-S-H phase and gismondine [44] and gehlenite [45] as the C-A-S-H phases were detected in all the AA-WBA/PV formulations. The presence of anorthite in the W98 PV2 formulations and albite in all the formulations indicated the formation of (C,N)-A-S-H [46] and N-A-S-H [47] gels, respectively. Sodalite, which is associated with a zeolitic product [48; 49], was also detected in all the XRD patterns. Kanemite, another typical phase of alkali-silica reaction products [50; 51], was identified in the formulations activated with 6 M NaOH. The XRD results are consistent with the SAM and HCl extraction results (Section 3.2) in demonstrating the formation of new reaction products (C-S-H, C-A-S-H, and (C,N)-A-S-H gels). Figure 4: AA-WBA/PV specimens (**a**) before and (**b**) after the boiling test. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Samples** & **Mass Dissolved by SAM (wt. \%)** & **Mass Dissolved by HCl (wt. \%)** \\ \hline OPC paste & 89.8 & - \\ WBA powder & 5.5 & 27.1 \\ PV powder & 6.5 & 30.4 \\ \hline W98-PV2-4M & 20.5 & 38.5 \\ W95-PV5-4M & 20.2 & 37.9 \\ W90-PV10-4M & 20.4 & 38.1 \\ \hline W98-PV2-6M & 22.8 & 39.1 \\ W95-PV5-6M & 23.3 & 39.6 \\ W90-PV10-6M & 23.1 & 39.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Selective chemical extraction results. Figure 5 shows the results of the FT-IR analysis of the WBA and AA-WBA/PV formulations in the range of 1650-600 cm\({}^{-1}\). There is a broad band (1200-900 cm\({}^{-1}\)) in all the spectra that is associated with the asymmetric T-O (T = Si or Al) stretching mode [41]. The change in the position and shape of this broad band in the AA-WBA/PV spectra regarding that of the WBA indicates alkali activation and the formation of new phases. The displacement of the broad band to higher frequencies in the AA-WBA/PV spectra, when compared to the WBA spectrum, demonstrates the formation of the C-S-H and C-A-S-H phases [52]. The broad band shifts to lower frequencies with increasing NaOH concentration and aluminium in the AA-WBA/PV spectra. This is probably due to the formation of the N-A-S-H phases [53] and the inclusion of aluminium in the C-S-H gel [54]. This agrees with the results from the selective chemical extractions (Section 3.2) and XRD analysis. There is a band at 785 cm\({}^{-1}\) in all the spectra corresponding to the quartz contained in the WBA [53]. The other observed peaks are attributed to the stretching vibrations (1405, 1436, and 1483 cm\({}^{-1}\)) and bending vibrations (875 and 713 cm\({}^{-1}\)) of calcium carbonates [55]. The deconvoluted FT-IR spectra in the range of 1200-800 cm\({}^{-1}\) are shown in Figure 6. The W98 PV2-4M and W90 PV10-6M samples were selected as they had the lowest and highest NaOH concentration and aluminium content, respectively. The spectra present the same peaks that have slightly displaced to lower frequencies due to increases in the NaOH concentration and PV content. The main narrow band at 1016-1013 cm\({}^{-1}\) and the band at 1144-1153 cm\({}^{-1}\) are ascribed to the v\({}_{3}\)(Si-O) bridging bond stretching vibrations [56]. The displacement of these bands to lower frequencies for the W90 PV10-6M sample indicates a lower degree of polymerization of the silicate chains [41]. The two bands at \(\approx\) 900 and \(\approx\) 866 cm\({}^{-1}\) correspond to Si-O terminal bonds, indicating an incomplete polymerization of the gel [56]. Finally, the narrow peak at 875 cm\({}^{-1}\) corresponds to calcium carbonate stretching vibrations (C-O).