## 3 Results
### Designing the Composition and Properties of Geopolymer Binders Based on Fly Ash
This choice of a mixture of acids is justified by the organogenic nature of corrosion resulting from the vital activity of microorganisms on the surface of concrete structures, which in the process of metabolism release organic acids that form complex compounds with the components of silicates and aluminosilicates, as well as easily soluble calcium salts. For the test, samples-beams of mortar mixtures were molded based on the optimal compositions of GB as well as a cement-sand mortar in the ratio of binder/sand--\(1/3\). The experimental samples were kept in the above-mentioned aggressive environment for 90 days with a control measurement of the weight loss and strength of the samples every 30 days. As the main indicators of the corrosion resistance of the developed FGC compositions, the following were chosen: the change in the compressive strength and the change in the mass of experimental samples over time (Figure 9 and Table 11). Figure 8: Dependence of the tensile strength in bending of GB samples on the concentration of NaOH and the mode of HT. Figure 7: Dependence of the compressive strength of GB samples on the concentration of NaOH and the mode of HT. Under conditions of aggressive action, for all FGC compositions, there is a tendency of a decrease in compressive strength within 10-16% (Table 11). The nature of the change in the strength of experimental samples is ambiguous and tends both to increase with an increase in the time of aggressive action of the medium and decline. The loss of compressive strength under conditions of exposure to a 2% acid solution at the age of 90 days for fine-grained geopolymer concrete based on fly ash is less than 5% in comparison with the loss of strength of samples made from the cement-sand mortar. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \multirow{2}{*}{**Indicator**} & \multirow{2}{*}{**Type of Binder**} & \multicolumn{6}{c}{**Exposure Time in an Aggressive Environment, Days**} \\  & & **10** & **20** & **30** & **40** & **50** & **60** & **70** & **80** & **90** \\ \hline Loss of compressive & On a geopolymer binder & 0.8 & 2.1 & 3.4 & 4.5 & 5.8 & 7.1 & 7.9 & 8.9 & 10.5 \\ strength, \% & On a cement binder & 1.9 & 3.8 & 6.1 & 7.4 & 8.8 & 10.5 & 12.2 & 13.9 & 15.7 \\ Mass loss, \% & On a geopolymer binder & 0.2 & 0.7 & 1.1 & 1.6 & 2.0 & 2.4 & 3.1 & 3.6 & 4.0 \\ On a cement binder & 1.3 & 2.9 & 5.0 & 6.3 & 7.8 & 9.5 & 10.7 & 12.2 & 13.2 \\ \hline \end{tabular}
\end{table} 
Table 11: Main indicators of corrosion resistance of the developed FGC compositions in 2% acid solution. Figure 9: Kinetics of changes in the parameters of experimental FGC compositions over time under conditions of exposure to a 2% mixture of a solution of lactic, acetic, and oxalic acids (CB—samples on a cement binder; GB—samples on a geopolymer binder): (**a**) masses; (**b**) compressive strength. As for the weight loss of the FGC samples under the aggressive action of a 2% acid solution, the same trend is observed here as in the analysis of the loss of strength characteristics. For FGC samples on HPV, the weight loss did not exceed 4%, and the weight loss for FGC samples on CV was about 14% (Table 11). Thus, the value of the coefficient of chemical resistance for FGC on HPV was 0.9, and the value of the coefficient of chemical resistance for FGC on CV was 0.86. It should be noted that the developed FGC compositions based on HPV in terms of controlled indicators of compressive strength loss and weight loss, in comparison with samples of cement-sand mortar, demonstrate higher corrosion resistance.