## 2 Materials and Methods  
### Materials and Samples Preparation  
The basic material for geopolymer samples was fly ash obtained from CEZ Skawina CHP Plant (Skawina, Poland) and river sand (Swietochlowice, Poland). Table 3 shows the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Properties** & **Basalt Fiber** & **Carbon Fiber** &
\begin{tabular}{c} **Glass Fiber** \\ **(E-Type)** \\ \end{tabular} \\ \hline Fiber Diameter (\(\upmu\)m) & 6–21 & 5–15 & 6–21 \\ \hline Density (g/cm\({}^{3}\)) & 2.7 & 1.6–2.0 & 2.54 \\ \hline Breaking Strength (GPa) & 3.0–4.8 & 3.5–6.0 & 3.1–3.8 \\ \hline Breaking Extension (\%) & 3.1 & 1.5–2.0 & 4.7 \\ \hline Modulus of Elasticity (GPa) & 90–100 & 72.5–75.5 & 83–86 \\ \hline Temperature Withstand (\({}^{\circ}\)C) & \(-\)260–750 & \(-\)50–700 & \(-\)50–380 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of selected properties of basalt, glass, and carbon fibers (based on [59; 60; 61; 62; 63; 64]). chemical composition of fly ash, which is used as one of the components of the geopolymers. This fly ash has a chemical composition typical for class F [70]. Figure 1 shows the particle size distribution of river sand, which was one of the precursors of the geopolymer materials investigated. One of the geopolymer batches contained Portland cement \"Gorazdze Cement Premium 42.5R\" (Chorula, Poland) in addition to fly ash and river sand. A mixture of metakaolin and sand was also used in the study as one of the variants of geopolymer matrices. The following materials were used to reinforce the geopolymers. (1) Glass fiber of type E (2400 TEX), in roving form as shown in Figure 2a and chopped form (4.5 mm, 12 mm)--Figure 2b,c. 2. Carbon fiber--\"Carbon 1600 TEX\" (Havel Composites, Cieszyn, Poland) in the form of roving as shown in Figure 3a and chopped fibers, 5 mm in length--see Figure 3b. (3) Basal grid--Deutsche Basalt Faser GmbH, (Sangerhausen Germany) shown in Figure 4, 10 mm \(\times\) 15 mm mesh; one or two layers of reinforcement in geopolymer. The alkaline activator was a solution of 5 M and 10 M sodium hydroxide and R-145 sodium hydroxide with a molar modulus of 2.5 and density of about 1.45 g/cm\({}^{3}\). The solutions were prepared according to the scheme: flakes of technical hydroxide were dissolved in water, and then, an aqueous solution of sodium silicate was added. The ratio of sodium hydroxide solution to sodium water glass was 1:2.5 by weight in each case. The ingredients were mixed and allowed to reach a constant concentration. To prepare the geopolymer mass, the precursors were mixed with the activator for about 10 min. Subsequently, different matrix-reinforcement bonding methods were used depending on the reinforcement form (short or long fibers):  
Figure 4: Basalt grid—mesh size 10 mm \(\times\) 15 mm. Figure 3: Carbon fiber: (**a**) in continuous form; (**b**) cut into 5 mm lengths. For short fibers (up to 12 mm), the fibers are added to the geopolymer paste and then mixed. A schematic of how this works is shown in Figure 5.  
For long fibers (roving)--pour part of the geopolymer mass into the mold, placing the reinforcement and then covering the rest of the geopolymer mass with the reinforcement. The operating schematic is shown in Figure 6.  
The fibers were directly bonded to the geopolymer matrix, without any pretreatment to prevent the action of the alkaline activator. The molds filled with geopolymer mass were placed on a vibrating table to remove air bubbles. After preparing the molds, the samples were covered with foil and placed in a laboratory dryer (SLW 750 STD, Pol-Eko-Aparatura, Wodzislaw Slaski, Poland) for 24 h at 75 \({}^{\circ}\)C. Then, the samples were unmolded and assigned to seasoning in laboratory conditions (temperature about 20 \({}^{\circ}\)C, relative humidity about 50%) for 28 days. After this period, strength tests were carried out. Tables 4-6 give the names of the samples for better systematization, the mixing ratios of the products, and the form of reinforcement.