## 2 Materials and Methods  
### Raw Materials  
Raw materials used in this study were obtained from different sources of the same region (Cantabria, Spain), most of them from waste flows. Low calcium fly ash (ASTM class F) were supplied by Reciclados De Cabezon S.l. - (Cabezon de la Sal, Cantabria, Spain) and was used as the main silicoaluminate agent. Quarry clay was collected from an industrial brickwork and was used as secondary silicoaluminate source. EAFD were produced by a steel production company, which uses scrap in an electric arc furnace to produce steel of different qualities and supplied by FCC Ambito S.A. (Guarnizo, Cantabria, Spain) a waste treatment company.  
The composition of FA, clay, and EAFD were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) and X-ray fluorescence (XRF) in Activations Laboratories (Ancaster, ON, Canada). The elemental major and minor oxides and trace element concentrations in raw materials are given in Table 1. Both precursors, FA and clay, are mainly constituted by SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) while, the EAFD show a predominant presence of Fe and Zn, and to a lesser extent Pb and Cr, with similar values to those reported by other authors [17; 37; 46].  
Figure 1 shows the FA and clay mineralogical results obtained by XRD Bruker D8 advance equipment fitted with a Cu tube with a wavelength of 1.5418 10\({}^{-10}\) m. The X-ray powder diffraction pattern have been fitted using the pattern matching routine in the DIFFRACplus EVA program supplied by Bruker. A halo is observed between 20\({}^{\circ}\) and 35\({}^{\circ}\) due to the vitreous nature of FA sample. However, this halo is not observed in the clay sample, which means that the amount of amorphous silica that can react is very small due to the mineralogy of its components is mainly crystalline.  
Fly ash and quarry clay was activated by an alkaline solution prepared by mixing Na\({}_{2}\)SiO\({}_{3}\) and NaOH solutions. Sodium silicate solution (Na\({}_{2}\)O = 8.5%, SiO\({}_{2}\) = 28.5%, and density of 1.4 g/cm\({}^{3}\)) was a commercial water glass supplied by Panreac AppliChem, Santander, Spain, and sodium hydroxide solution was obtained by dissolving solid NaOH pellets (99% purity) in deionized water.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Raw Materials** & **FA** & **Clay** & **EAFD** \\ \hline \multicolumn{4}{c}{**Composition (wt \%)**} \\ \hline SiO\({}_{2}\) & 52.38 & 64.22 & 4.18 \\ Al\({}_{2}\)O\({}_{3}\) & 21.32 & 16.93 & 0.98 \\ Fe\({}_{2}\)O\({}_{3}\) & 6.88 & 5.94 & 33.36 \\ K\({}_{2}\)O & 2.50 & 3.03 & 1.40 \\ CaO & 6.23 & 0.52 & 6.71 \\ MgO & 2.48 & 0.89 & 2.38 \\ Na\({}_{2}\)O & 2.02 & 0.58 & 1.88 \\ TiO\({}_{2}\) & 0.92 & 0.86 & 0.09 \\ MnO & 0.07 & 0.06 & 2.42 \\ P\({}_{2}\)O\({}_{5}\) & 0.82 & 0.08 & 0.97 \\ LOI & 5.39 & 5.78 & 11.33 \\ \hline \multicolumn{4}{c}{**Composition (mg/kg)**} \\ \hline As & 44 & 30 & 39.50 \\ Ba & 2662.25 & 483 & 477 \\ Cd & 1.10 & 0.50 & 260 \\ Cr & 76.25 & 46 & 2040 \\ Cu & 85.75 & 27 & 2030 \\ Hg & n.d. & n.d. & n.d. \\ Mo & 18 & 2 & 35.10 \\ Ni & 129 & 29 & 150 \\ Pb & 52.50 & 28 & 23,000 \\ Sb & 7.80 & 2.5 & 136 \\ Se & 0.55 & 0.02 & 38.70 \\ Zn & 291.25 & 139 & 259,000 \\ \hline \hline \end{tabular} n.d. not determined.  
\end{table}
Table 1: Major, minor oxides and trace elements in Fa, clay, and EAFD.