## 3 Results
Figure 5: Dependence of the change in the structural quality coefficients of vibro-centrifuged concretes on the pH level of activated water (see Figure 3; C is the control composition; \(\Delta\) is the value of the change in the coefficients of the strength variatropic efficiency). \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Concrete Characteristic**} & \multicolumn{2}{c}{**Control Composition (Heavy Concrete**} & \multicolumn{6}{c}{**Lightweight Concrete**} \\ \cline{3-13}  & **on Non-Activated Water, pH = 6.7)** & \multicolumn{2}{c}{**pH = 7.3**} & \multicolumn{2}{c}{**pH = 8.5**} & \multicolumn{2}{c}{**pH = 9.9**} \\ \cline{2-13}  & **VC\({}_{\text{1}}\)** & **VC\({}  
Table 7 shows that in lightweight vibro-centrifuged concrete made on activated water, with an increase in the pH level from 7.3 to 8.5, an increase in strength is observed. This fact is due to an increase in the degree of cement hydration and an increase in the homogeneity of the concrete structure. When the pH level rises from 8.5 to 9.9, the strength characteristics of concrete decrease. The maximum changes in strength and deformation characteristics were recorded at pH = 8.5. Differential strength and strain characteristics of prototypes of vibro-centrifuged concrete are shown in Table 8.  
After analyzing the obtained graphical dependences of changes in the coefficients of strength and deformative variatropic efficiency, it was found that the values of these coefficients in lightweight vibro-centrifuged concretes are an order of magnitude higher in comparison with heavy vibro-centrifuged concrete. Additionally, with an increase in  
Figure 6: Dependence of the difference between the strength characteristics of layers of variatropic sections of vibro-centrifuged concrete on the pH level of activated water (1—the difference between the inner and middle layer; 2—the difference between the inner and outer; 3—the difference between the middle and outer; C is the control composition; \(\Delta\) is the value of the change in the coefficients of the strength variatropic efficiency). Figure 7: Dependence of the difference between the elastic moduli of different layers of variatropic Figure 6. (C is the control composition; \(\Delta\) is the value of the change in the coefficients of the strength variatropic efficiency). the pH of activated water, there is a clear tendency to increase the coefficients of strength and deformation efficiency in lightweight vibro-centrifuged concretes, and their maximum values were recorded when using activated water with a pH of 8.5. As for the coefficients of constructive quality, it can be seen from Figure 5 that the values of these coefficients for both heavy and lightweight vibro-centrifuged concrete differ insignificantly. A slight increase in the values of the coefficients of constructive quality was recorded for lightweight vibro-centrifuged concretes made on activated water with a pH = 8.5. It is known from the normative and technical documents [39] that the maximum permissible pH value for water for concrete is 12.5. After analyzing the theoretical basis of the question, a hypothesis was put forward that the real efficiency of the mixing water used is limited by the pH value equal to 10, due to the further transformation of the medium into a highly alkaline one, and the achievement of values above 12.5 is completely unacceptable. In this regard, when drawing up the program of experimental studies, we determined the assumed range of pH values, varying from 7 to 10. The midpoint was taken to be the assumed optimal pH equal to 8.5. During the practical leaching of water, the values of pH = 7.3, pH = 8.5, pH = 9.9 were obtained. A study has been carried out in this range. Based on the results of the experimental study, our hypothesis on the effectiveness of water with pH = 8.5 was confirmed. This value was recorded as rational and recommended for to prepare vibrated lightweight concrete with the best physical, mechanical, and structural characteristics.