## 3 Results  
### Designing the Composition and Properties of Geopolymer Binders Based on Fly Ash  
Geopolymer binder (GB) is an inorganic polymer synthesized as a result of the reaction between a solution of an alkali or alkaline earth metal and an aluminosilicate component in the temperature range of 25-120 \({}^{\circ}\)C. The low-temperature process leads to a rapid setting of the material, which exhibits sufficiently high hardness and strength, indicating that geopolymers have similar properties to cement. When choosing raw materials for the production of geopolymer binders, it is necessary to take into account such features as the origin of the aluminosilicate component: starting  
Figure 6: Testing samples-half beams for compressive strength: (**a**) before testing; (**b**) after testing. material, methods, and temperature of combustion, methods for removing ash from filters, etc., and chemical properties of the alkaline component in terms of its activating ability. These factors have a significant impact on the kinetics and nature of structure formation, as well as geopolymerization products, and, ultimately, on the main performance characteristics of the finished binder. According to literature sources [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 28; 30; 31; 46], Na\({}_{2}\)SiO\({}_{3}\), NaOH, and KOH are used as the most common alkaline components to obtain geopolymers. The choice of alkaline activators data is explained by the highest reactivity of the aluminosilicate component with respect to the glass phase and athermicity during their production. So, to evaluate the effectiveness of the alkaline component, two control compositions of GB were made. In the first case, a solution based on sodium silicate and sodium hydroxide in a ratio of 1:1 was used as an activator of the hardening process. The concentration of the sodium hydroxide solution was 8 mol/L. In the second case, a solution based on sodium silicate and potassium hydroxide in a ratio of 1:1 was used as an activator of the hardening process. The concentration of the potassium hydroxide solution, as in the first case, was 8 mol/L. In order to select the most effective alkaline component of the GB systems under study, beam samples were molded (three beams in a series, two series in total for each case). Freshly molded products were placed in an environment with a temperature of 20 \(\pm\) 5 \({}^{\circ}\)C; relative humidity of 45-50%, and kept for 24 h, after which the samples were subjected to heat treatment (HT) according to the following regime:  
* Rise in temperature--4 h;
* Isothermal exposure--16 h;
* Temperature drop--4 h.  
The isothermal holding temperature was 65 \({}^{\circ}\)C. In this case, the pre-exposure time before HT was chosen as a universal value sufficient for aluminosilicate components of varying degrees of activity and to ensure equality of experimental conditions. The test results of these compositions are presented in Table 8.  
Analyzing the results of the test, it should be noted that the binder samples using the Na\({}_{2}\)SiO\({}_{3}\):KOH combination as an alkaline activator have very low strength properties. Based on this, KOH is an ineffective activator for the studied fly ash. From a chemical point of view, it can be assumed that this phenomenon is probably associated with a large atomic radius of potassium, which leads to loosening of the structure of aluminosilicates and prevents the binding and structuring of the system. The most reactive alkaline activator is the Na\({}_{2}\)SiO\({}_{3}\):NaOH combination; this activator provides the highest compressive strength of geopolymer concrete. The greatest reactivity of NaOH is explained by the fact that sodium ions have a large radius of the electron shell (an indicator of the degree of electrochemical activity). Therefore, when interacting with water, the substance wholly and quickly dislocates in water, easily giving up Na + ions.