## 2 Materials and Methods
### Sample Preparation  
To select the appropriate activating solution with low reactivity at ambient temperature and relatively high reactivity at 50-100 \({}^{\circ}\)C, a series of experiments with different potassium silicate solutions were performed. Different silica to potassium moduli (R = SiO\({}_{2}\)/K\({}_{2}\)O molar ratio), ranging from 1 to 2.75, with 0.25 intervals, were investigated with an L/S of 0.55, with L being the silicate solution. The prepared solutions were stored for 1 day in the laboratory environment for further equilibration. The dry components (Koranel (K) + metkaolinite (MK) + Portland cement (OPC)) and liquid components (prepared potassium silicate solution and 2-methyl 2,4-pentanediol (\"m\") or polyethylene glycol (\"p\") were first mixed separately; then, both liquid and solid components were mixed using an electric laboratory stirrer at a speed of 1000 rpm for 5 min to obtain a homogeneous slurry. The details on the formulated matrices for the preparation of the composite materials are presented in Table 3.  
For the composite preparation, a thin layer of about 0.5 mm of alkali-activated matrix was spread on a plastic PET film placed on a wooden mold in a pre-drawn square of 15 \(\times\) 15 cm\({}^{2}\). The first layer of carbon-woven fabric (15 \(\times\) 15 cm\({}^{2}\)) was placed on top of the matrix layer. Thereafter, the carbon fabric was manually wet out (impregnated) with alkali-activated matrix using a roller (1; Figure 2). The process was repeated for 4 layers of the woven fabric and finally, a layer of geopolymer matrix was added; hence, we obtained a composite made of 5 matrix layers and 4 fiber layers (2; Figure 2). Caution was taken to use a minimum amount of matrix to ensure sufficient fiber impregnation with a high fiber volume fraction. Four weights of 5 kg each (3; Figure 2), equivalent of a total force of 196 N, were equally distributed on top of the laminate composites, and cured at 80 \({}^{\circ}\)C for 24 h in a conventional oven (4; Figure 2). After the curing period, the samples were cut in composite beams of 2.5 cm width and 14 cm length, then kept for 3 days in a laboratory environment before testing.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Area Density** & **Tensile Strength** & \begin{tabular}{c} **Tensile** \\ **(MPa)** \\ \end{tabular} & \
\begin{tabular}{c} **Tensile** \\ **Modulus/E-Modulus** \\ **(GPa)** \\ \end{tabular} &
\begin{tabular}{c} **Elongation at** \\ **Break (\%)** \\ \end{tabular} \\ \hline Carbon & 200 & 4410 & 235 & 1.9 \\ (Plain woven) & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Properties of individual carbon fiber from Fibermax Composite.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & \multirow{2}{*}{**Koranel (g)**} & \multicolumn{2}{c}{**Potassium Silicate**} & \multirow{2}{*}{**Metakao-Linite (g)**} & \multirow{2}{*}{**OPC (g)**} & \multicolumn{2}{c}{**2-Methyl**} \\
**Codes** & & & & & **2,4-Pentanediol (g)** & \\ \hline K & 100 & 55 & - & - & - & - \\ \hline Kp & 100 & 55 & - & - & - & 2 \\ \hline Km & 100 & 55 & - & - & 2 & - \\ \hline
90K10 MK & 90 & 55 & 10 & - & - & - \\ \hline
80K20 MK & 80 & 55 & 20 & - & - & - \\ \hline
80K20 MKm & 80 & 55 & 20 & - & 2 & - \\ \hline
80K20 MKp & 80 & 55 & 20 & - & - & 2 \\ \hline
95K5 OPC & 95 & 55 & - & 5 & - & - \\ \hline
90K10 OPC * & 90 & 55 & - & 10 & - & - \\ \hline \hline \end{tabular}
\end{table}
Table 3: Composition of the different matrices used for the preparation of the laminates with Koranel (K), metkaolinite (MK), Portland cement (OPC), 2-methyl 2,4-pentanediol (m) or polyethylene glycol (p). Sample names are composed of the letters mentioned between brackets and corresponding number of wt.% of the solid. * Discarded due to short setting time.  
For comparative purposes, selected matrices were cast as paste in 4 \(\times\) 4 \(\times\) 16 cm\({}^{3}\) molds at once without vibrating and cured at 80 \({}^{\circ}\)C for 24 h.