## 2 Materials and Methods  
### Materials  
The copper slag used in this study was Koranel(r) from Aurubis Beerse nv in Beerse, Belgium, with 2600 cm\({}^{2}\)/g Blaine surface. The Blaine was measured with an air permeability apparatus as described in EN 196-6:2018 [24]. The particle size distributions of the Koranel slag, metakaolinite and OPC were determined by a laser particle size analyzer (BeckmanCoulter LS 13320, Pasadena, CA, USA) (Figure 1a). X-ray powder diffraction (XRD) spectra of the slag were taken by a Bruker D2 Phaser, Karlsruhe, Germany, in the 6-70\({}^{\circ}\) 20 range using Cu K\(\alpha\) radiation (voltage 40 kV and current 40 mA), a step size of 0.02\({}^{\circ}\) and scan speed of 0.5 s/step. The XRD pattern shows that the material is mainly amorphous (Figure 1b), with few crystalline features ascribed to Fayalite, Fe\({}_{2}\)SiO\({}_{4}\) (PDF 34-0178), Ankerite, Ca (Fe, Mg)(CO\({}_{3}\))\({}_{2}\) (PDF 33-0282), and Fe-rich spinel, (Al,Fe)\({}_{2}\)O\({}_{4}\) (PDF 21-0540) (see also [25]). The metakaolinite (MK) used in this study is Argical(tm)-M 1000 from IMAPS Fused Minerals, Paris, France. The ordinary Portland cement used was of CEM I 52.5 R from CBS Heidelberg cement group, Heidelberg, Germany. The chemical composition of Koranel, OPC and metakaolinite, as determined by X-ray fluorescence (PW 2400 Philips) on powder, is presented in Table 1. The d10, d50 and d90 of Koranel were respectively 2.51 \(\upmu\)m, 13.22 \(\upmu\)m and 27.87 \(\upmu\)m. These values were, respectively, 0.87 \(\upmu\)m, 7.88 \(\upmu\)m and 30.40 \(\upmu\)m for OPC and 1.31 \(\upmu\)m, 16.01 \(\upmu\)m and 80.57 \(\upmu\)m for the metakaolinite. The 2-Methyl 2,4-Pentanediol and the Polyethylene Glycol 600 (PEG 600) used as surfactant were from Sigma Aldrich, Overjise, Belgium. The potassium hydroxide (Sigma Aldrich; 85 wt.% purity) and potassium silicate solution (Silmaco, Lanaken, Belgium) were used for the preparation of the activating solution. The potassium silicate solution was made of 27.22 wt.% SiO\({}_{2}\), 15.01 wt.% K\({}_{2}\)O and 57.3 wt.% H\({}_{2}\)O, with a molar ratio (R = SiO\({}_{2}\)/K\({}_{2}\)O) of 2.84 and density of 1.424 g/cm\({}^{3}\) at 20 \({}^{\circ}\)C. The potassium hydroxide was used to adjust the ratio in the solution. For instance, for 100 g of the potassium silicate solution, the amounts of KOH added to achieve the SiO\({}_{2}\)/K\({}_{2}\)O molar ratios of 1, 1.5, 2 and 2.25 were, respectively, about 38.7 g, 18.8 g, 8.9 g and 5.5 g. This corresponded to an addition of 32.9 g of pure KOH for the solution with R = 1, 15.9 g for R = 1.5, 7.5g for R = 2 and 4.7 g for R = 2.25; one hundred (100) g of these solutions contained a total mass of water (including water from dissolved KOH) of 44.4 g, 50.2 g, 53.9 g and 55.3 g, respectively. The properties of the 200 g/m\({}^{2}\) carbon fabric used (Fibermax Composite, London, UK) are presented in Table 2. Carbon fiber was chosen due to its high specific strength and its relatively chemical and thermal stability [26]. This allows the composite properties to be relatively stable over time, since no fiber degradation is expected due to the alkaline nature of the alkali-activated matrix. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Samples** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **CaO** & **MgO** & **Cr\({}_{2}\)O\({}_{3}\)** & **K\({}_{2}\)O** & **TiO\({}_{2}\)** & **P\({}_{2}\)O\({}_{5}\)** & **SO\({}_{3}\)** & **Others *** & **LOI ** \\ \hline K & 26.6 & 9.5 & 57.4 & 2.8 & 0.9 & 0.7 & 0.2 & 0.2 & 0.8 & 0.9 & 0.0 & - \\ \hline MK & 51.9 & 40.9 & 1.7 & 0.1 & 0.1 & 0 & 1 & 2.1 & 0 & 0 & 0.3 & 1.9 \\ \hline OPC & 19.7 & 5.2 & 3.0 & 64.2 & 1.7 & 0 & 0 & 0.3 & 0 & 2.7 & 1.6 & 1.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Normalized chemical composition in wt.% by XRF analyses for Koranel (K), metakaolinite (MK) and OPC.