# Alkali-Activated Binders Using Bottom Ash from Waste-to-Energy Plants and Aluminium Recycling Waste
## 2 Materials and Methods  
### Materials  
WBA and PV were used as precursors to prepare the AA-WBA/PV formulations. The WBA was supplied by the VECSA company and collected from a WtE plant located in Tarragona (Spain), which produces 32 kt\(\cdot\)y\({}^{-1}\). PV was provided by the BEFESA company from its salt slag treatment plant located in Valladolid (Spain), which generates around 90 kt y\({}^{-1}\) of this aluminium salt slag [35]. Na\({}_{2}\)SiO\({}_{3}\) was supplied by Scharlab, S.L. (Barcelona, Spain),while the NaOH solutions were prepared by dissolving NaOH pearls (Labbox Labware S.L. (Barcelona, Spain); purity > 98%) in deionized water. The WBA and PV were first dried for 24 h in a stove at 105 \({}^{\circ}\)C. Both materials were then sieved through standard sieves to determine the particle size distribution (PSD) (shown in Figure 1). The shaded area of the WBA in Figure 1 shows the least polluted fraction (8 to 30 mm), which was used to formulate the AA-WBA/PV binders. Finally, the WBA and PV were crushed and milled separately until a particle size below 80 \(\upmu\)m was obtained. Table 1 shows the chemical compositions of the WBA and PV determined by X-ray fluorescence (XRF) using the Panalytical Philips PW2400 Sequential X-ray spectrophotometer (Malvern Panalytical, Malvern, United Kingdom) equipped with the UniQuant(r) version 5.0 software. The main oxide compounds identified in the WBA were SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and CaO from the high levels of glass cullet and fired ceramics in the least polluted fraction [31]. The main oxides found in PV were SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\). Therefore, the WBA and PV were considered potential AABs precursors due to their calcium aluminosilicate-rich nature. Furthermore, these elemental oxides have reactive phases (amorphous SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\)) to form AABs, as well as unreactive or less reactive phases (SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) crystalline phases) that probably remain inert in the alkali-activation process. The availability of the reactive phases of the WBA and PV was assessed using different concentrations of NaOH solution (4, 6, or 8 M) [17; 37]. These experimental trials consisted of mixing 1 g of WBA and PV with 100 mL of the NaOH solution in a Teflon beaker and stirring for 5 h at 80 \({}^{\circ}\)C. Afterwards, the leached Si and Al concentrations were determined by analyzing the resulting filtered solution with inductively coupled plasma optical emission spectrometry (ICP-OES) using the PerkinElmer Optima 3200 RL spectrometer (PerkinElmer Inc., Waltham, MA, USA). The percentages of available SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) in both the WBA and PV are plotted in Figure 2. Around 20% of SiO\({}_{2}\) and 3% of Al\({}_{2}\)O\({}_{3}\) were available in the WBA, while approximately 2.5-5% of SiO\({}_{2}\) and 3% of Al\({}_{2}\)O\({}_{3}\) were available in PV. These \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & & & & & & & \\ \hline \multicolumn{1}{c}{**SiO\({}_{2}\)**} & **CaO** & **Al\({}_{2}\)O\({}_{3}\)** & **Na\({}_{2}\)O** & **K\({}_{2}\)O** & **Fe\({}_{2}\)O\({}_{3}\)** & **MgO** & **TiO\({}_{2}\)** & **LOI 1** ** \\
52.08 & 20.72 & 6.35 & 3.38 & 2.09 & 4.12 & 2.43 & 0.65 & 6.1 \\ \hline \hline \multicolumn{1}{c}{} & & & **PV (wt. \%)** & & & & \\ \hline \multicolumn{1}{c}{**SiO\({}_{2}\)**} & **CaO** & **Al\({}_{2}\)O\({}_{3}\)** & **Na\({}_{2}\)O** & **K\({}_{2}\)O** & **Fe\({}_{2}\)O\({}_{3}\)** & **MgO** & **TiO\({}_{2}\)** & **LOI 1** ** \\
7.93 & 2.24 & 61.02 & 3.22 & 0.68 & 2.65 & 4.73 & 0.80 & 15.71 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Major and minor elements composition of weathered bottom ash (WBA) and PAVAL® (PV) powders. Figure 1: **Particle size distribution** (PSD) of weathered bottom ash (WBA) and PAVAL® (PV). results indicate that the WBA and PV have the potential to be secondary silica-rich and alumina-rich sources, respectively.