# Alkali-Activated Binders Using Bottom Ash from Waste-to-Energy Plants and Aluminium Recycling Waste
## 4 Conclusions  
The use of WBA and PV in the formulation of AABs can lead to a low-carbon and zero-waste manufacturing of cement. This study demonstrated the potential of the coarse fraction of WBA and PV as silica-rich and alumina-rich precursors, respectively. The AA-WBA/PV binders remain stable after immersion in boiling water due to the formation of new phases. Selective chemical extractions, XRD analysis, and FT-IR analysis revealed the presence of C-S-H, C-A-S-H, and/or (N,C)-A-S-H gels as the main reaction products formed in the AA-WBA/PV binders. The NaOH concentration and PV content influenced the mechanical and physical properties of the binders. Increasing the NaOH concentration and the PV content increased the formation of the reaction products as well as porosity. Increasing the PV content, however, reduced the compressive strength of the binders. These results reflect the versatility of PV when applied to enhance mechanical properties or used as an aerating agent to improve thermal conductivity. Finally, the environmental impact of the binders was assessed with leaching tests, which revealed that a high pH of the alkaline activator solution increased the leaching of metalloids from AA-WBA/PV. Considering that the main goal of this study was to obtain AABs with good mechanical properties, W98 PV2-4M is the optimal formulation, with the lowest metalloid leaching potential.  
A.M.-A.: conceptualization, formal analysis, investigation, writing--original draft, review and editing; J.M.: formal analysis, investigation, writing--review and editing; J.G.-P.: conceptualization, supervision, validation, writing--review and editing; J.F.: funding acquisition, validation, writing--review and editing; J.M.C.: conceptualization, supervision, validation, funding acquisition. All authors have read and agreed to the published version of the manuscript.  
This research was partially funded by the Spanish Government (BIA2017-83912-C2-1-R).  
[PERSON] and [PERSON] are grateful to the Catalan Government for their research Grants, FI-DGR 2017 and FI-2020, respectively.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Sample** & **As** & **Ba** & **Cd** & **Cr** & **Cu** & **Hg** & **Mo** & **Ni** & **Pb** & **Sb** & **Zn** & **pH** \\ \hline WBA & 0.02 & 0.25 & \textless{}0.01 & 0.17 & 0.69 & 0.01 & 0.33 & 0.11 & 0.01 & 0.27 & 0.12 & 9.54 \\ PV & 0.10 & 0.06 & \textless{}0.01 & 0.01 & 0.15 & \textless{}0.01 & 2.90 & \textless{}0.20 & 0.01 & 1.38 & 0.10 & 10.03 \\ \hline W98-PV2-4M & 2.44 & 0.14 & \textless{}0.01 & 0.12 & 0.54 & 0.04 & 0.42 & \textless{}0.20 & 0.44 & 2.82 & 0.76 & 11.61 \\ W95-PV5-4M & 2.45 & 0.16 & \textless{}0.01 & 0.14 & 0.50 & 0.02 & 0.50 & \textless{}0.20 & 0.54 & 2.86 & 0.71 & 11.59 \\ W90-PV10-4M & 2.34 & 0.31 & \textless{}0.01 & 0.14 & 0.55 & 0.01 & 0.72 & \textless{}0.20 & 0.49 & 2.86 & 0.51 & 11.48 \\ \hline W98-PV2-6M & 2.78 & 0.15 & \textless{}0.01 & 0.05 & 0.53 & 0.01 & 0.52 & \textless{}0.20 & 0.55 & 3.15 & 0.54 & 11.63 \\ W95-PV5-6M & 2.77 & 0.19 & \textless{}0.01 & 0.18 & 0.81 & 0.06 & 0.50 & \textless{}0.20 & 0.52 & 3.22 & 0.68 & 11.57 \\ W90-PV10-6M & 2.68 & 0.22 & \textless{}0.01 & 0.24 & 0.34 & 0.02 & 0.70 & \textless{}0.20 & 0.50 & 3.18 & 0.80 & 11.57 \\ \hline \hline \end{tabular} \({}^{1}\) Inert waste (mg:kg\({}^{-1}\))  
\({}^{1}\) Non-hazardous waste (mg:kg\({}^{-1}\))  
\({}^{2}\) & 100 & 1 & 10 & 50 & 0.2 & 10 & 10 & 10 & 0.7 & 50 \\ \({}^{1}\) Hazardous waste (mg:kg\({}^{-1}\))  
\({}^{3}\) & 5 & 70 & 100 & 2 & 30 & 40 & 50 & 5 & 200 \\ \hline \hline \end{tabular} \({}^{1}\) limit for acceptance in landfills [59].  
\end{table}
Table 5: Leaching concentrations (mg:kg\({}^{-1}\)) in WBA, PV, and AA-WBA/PV binders after leaching tests (EN 12457-2) and limits for acceptance at landfills.