## 3 Results
### Designing the Composition and Properties of Geopolymer Binders Based on Fly Ash
In this regard, aqueous solutions of NaOH have a consistently strong alkaline reaction for a long time, providing conditions for the dissolution of the aluminosilicate component and the further occurrence of structure-forming processes. At the second stage of the experiment, an assessment was made of the effect of the NaOH concentration and the HT regime on the strength characteristics of concrete based on GB. The plan of the second stage of experimental studies is presented in Table 9. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Composition** & **Series No.** & **Compressive Strength of a** & **Average Compressive** & **Tensile Strength in** & **Average Tensile Strength** \\
**Marking** & & **Series of Samples, MPa** & **Strength, MPa** & **Bending, MPa** & **in Bending, MPa** \\ \hline
1N & 1 & 29.2 & 28.5 & 3.2 & 3.4 \\
2 & 2 & 27.8 & 3.6 & 3.4 \\
2K & 1 & 4.4 & 0.7 & 0.6 \\
2 & 2 & 5.2 & 4.8 & 0.5 & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Strength characteristics of control compositions of geopolymer binders. As output parameters, similarly as in the first stage of experimental studies, the compressive strength and tensile strength in bending of specimen beams based on fly ash were evaluated. Again, the strength indicators of experimental samples were determined at 28 days. The results of the obtained data are presented in Table 10 and in Figures 7 and 8. From Table 10 and Figures 7 and 8, it can be seen that the maximum values of ultimate compressive strength and tensile strength in bending were recorded for specimens of composition type 11N and are respectively equal to 51.5 MPa and 6.2 MPa, which correspond to a processing temperature of 75 \({}^{\circ}\)C and NaOH concentration equal to 14 mol. Thus, the heat treatment temperature, equal to 75 \({}^{\circ}\)C, is the most optimal for the obtained GB based on fly ash. Analyzing the effect of sodium hydroxide concentration on the strength characteristics of GB, it can be seen that in the range of sodium hydroxide concentration from 8 to 14 mol/L, an intensive increase in the strength characteristics of GB samples is observed. However, as the concentration of NaOH increases to 16 mol/L, the values of strength characteristics begin to decrease. Thus, the concentration of sodium hydroxide solution, equal to 14 mol/L, is the most effective for the obtained GB based on fly ash. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Composition Marking** & **Compressive Strength, MPa** & **Tensile Strength in Bending, MPa** \\ \hline
1N & 28.5 & 3.4 \\
2N & 37.8 & 4.5 \\
3N & 36.5 & 4.0 \\
4N & 37.5 & 4.5 \\
5N & 41.8 & 5.5 \\
6N & 40.8 & 4.9 \\
7N & 40.7 & 4.9 \\
8N & 44.4 & 5.3 \\
9N & 43.5 & 5.2 \\
10N & 45.7 & 5.5 \\
11N & 51.5 & 6.2 \\
12N & 48.9 & 5.9 \\
13N & 46.9 & 5.5 \\
14N & 48.7 & 5.7 \\
15N & 47.8 & 5.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Results of determining the compressive strength and tensile strength in bending of concrete based on GB. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Composition Marking** & **Type of Alkaline Activator** & **Hydroxide Concentration, mol/L** & **Heat Treatment Temperature, \({}^{\circ}\)C** \\ \hline
1N & & & 65 \\
2N & & 8 & 75 \\
3N & & & 85 \\
4N & & & 65 \\
5N & & 10 & 75 \\
6N & & & 85 \\
7N & & & 65 \\
8N & Na\({}_{2}\)SiO\({}_{3}\):NaOH\(\div\)(1:1) & 12 & 75 \\
9N & & & 85 \\
10N & & & 65 \\
11N & & 14 & 75 \\
12N & & & 85 \\
13N & & & 65 \\
14N & & 16 & 75 \\
15N & & & 85 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Experimental plan for evaluating the effectiveness of the effect of NaOH concentration and the HT regime on the strength characteristics of concrete based on GB. Development of the Composition of Fine-Grained Concrete (FGC) Based on Fly Ash and Evaluation of its Corrosion Resistance  
Within the framework of this work, studies were carried out to study the corrosion resistance of FGC based on the optimal compositions of GB. A 2% mixture of a solution of lactic, acetic, and oxalic acids was chosen as an aggressive medium for the experiment.