# Alkali-Activated Binders Using Bottom Ash from Waste-to-Energy Plants and Aluminium Recycling Waste
## 2 Materials and Methods
### Test Methods  
The hydrolytic stability of AA-WBA/PV was evaluated by using the boiling water test [18], which evaluates the resistance of the binders to degradation in water. One specimen for each formulation was first dried in a desiccator with silica gel to constant weight. The specimen was then placed in boiling water for 20 min, before being dried again in a desiccator to constant weight. Later, visual analysis was conducted to verify the cohesion of the sample. Finally, the sample was weighed to calculate the weight loss percentage. A selective chemical extraction was carried out to determine the main reaction products formed. The formation of calcium silicate hydrate (C-S-H), calcium aluminosilicate hydrate (C-A-S-H), and sodium aluminosilicate hydrate (N-A-S-H) gels after the alkali activation can be estimated from the calcium and aluminium contents of the precursors [39]. Salicylic acid/methanol (SAM) extraction can be used to determine the formation of the C-S-H and C-A-S-H phases [40]. SAM extraction consisted of mixing 1 g of the binder sample with salicylic acid (6 g) and methanol (40 mL) for 1 h. The resulting solution was then filtered (Whatman filter paper with a 20-um pore size), and the residual fraction (RF) was washed and dried to constant weight in a desiccator with silica gel. The RF was weighed to calculate the mass dissolved percentage. Another selective chemical extraction test with HCl was performed to determine the formation of the C-S-H, C-A-S-H, and N-A-S-H \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Reference**} & \multicolumn{2}{c}{**S**} & \multicolumn{2}{c}{**L**} & \multirow{2}{*}{**Na\({}_{2}\)SiO\({}_{3}\)**} & \multirow{2}{*}{**SiO\({}_{2}\)/Na\({}_{2}\)O 3**} \\ \cline{3-4} \cline{6-7}  & & & & **NaOH 2** & & \\ \cline{3-4} \cline{6-7}  & **WBA 1** & & & **4 M** & **6 M** & \\ \hline W98-PV2-4M & 98 & 2 & 20 & & 80 & 5.2 & 2.5 \\ W95-PV5-4M & 95 & 5 & 20 & & 80 & 5.2 & 2.5 \\ W90-PV10-4M & 90 & 10 & 20 & & 80 & 5.2 & 2.5 \\ \hline W98-PV2-6M & 98 & 2 & 20 & 80 & 5.8 & 2.3 \\ W95-PV5-6M & 95 & 5 & 20 & 80 & 5.8 & 2.3 \\ W90-PV10-6M & 90 & 10 & 20 & 80 & 5.8 & 2.3 \\ \hline \hline \end{tabular}  
* wt. % respect to the total solid; 2 wt. % respect to the total liquid; 3 Ms of alkali-activator solution (molar ratio).  
\end{table} 
Table 2: AA-WBA/PV mix proportion. gels [39]. The extraction process consisted of stirring 1 g of the binder sample with 250 mL of the HCl solution (1:20) for 3 h. Afterwards, the solution was filtered (Whatman filter paper with a 20-um pore size), and the weight loss percentage of the washed and dried RF was determined. XRD analysis of the AA-WBA/PV formulations was performed using a Bragg-Brentano Siemens D-500 powder diffractometer (Siemens, Munich, Germany) with CuK\(\alpha\) radiation to identify the main crystalline phases. Fourier transform infrared spectroscopy (FT-IR) spectra of the AA-WBA/PV binders in the attenuated total reflectance (ATR) mode were obtained with a Spectrum Two\({}^{\text{TM}}\) FT-IR spectrometer from PerkinElmer (PerkinElmer Inc., Waltham, MA, USA). Measurements were performed in the 4000-400 cm\({}^{-1}\) range with a 32-scan average and a 4-cm\({}^{-1}\) resolution. FT-IR spectra deconvolution of the most representative samples in the 1200-800 cm\({}^{-1}\) range was also performed. This range is associated with the symmetric and asymmetric stretching vibrations of the Si-O bonds [41]. The computer software Origin Pro 9 (OriginLab Corporation, Northampton, MA, USA) was used to fit and adjust the shape of the spectra with Gaussian functions, following some of the criteria from the literature [41]. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) was used to evaluate the microstructure of the samples using an ESEM FEI Quanta 200 equipment (Thermo Fisher Scientific, Waltham, MA, USA). The samples were cut with a diamond disc cutter and coated with graphite. Bulk density and open porosity tests were performed following the EN 1936:2006 standard.