## 3 Results and Discussion
### Changes in the Composition and Structure of Bentonite during Experiments  
The long-term interaction of bentonite with the synthetic water solutions after leaching of concrete led to an increase in the specific surface area by almost 1.5 times; at the same time, the pore volume practically did not change. The displacement of the pore distribution to the side of a lower pore width as well as a reduction in the macropore quantity (>50 nm), leading to a decrease in the average pore size from 6 to 4 nm, was observed after the analysis of pore distribution (Figure 6). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Phase (Ideal Formula)** & **Concrete before Leaching** & **Concrete after Leaching** \\ \hline Quartz (SiO\({}_{2}\)) & 3.1 & 5.7 \\ Dolomite (CaMg(CO\({}_{3}\))\({}_{2}\)) & 1.4 & - \\ Calcite (CaCO\({}_{3}\)) & 12.9 & 15.5 \\ Vaterite (CaCO\({}_{3}\)) & 20.0 & 2.8 \\ Magnetite (MgCO\({}_{3}\)) & 1.4 & 0.2 \\ Afwilleite (Ca\({}_{3}\)(SiO\({}_{4}\))\({}_{2}\)H\({}_{2}\)O) & - & 8.5 \\ Oldhamite ((Ca\({}_{3}\)Mg)S) & 0.9 & 1.3 \\ Chabazite ((K\({}_{2}\)C\({}_{3}\)La\({}_{3}\)Zn\({}_{2}\)Sr,Mg)\({}_{2}\)[Al\({}_{2}\)Si\({}_{4}\)O\({}_{12}\)]\({}_{2}\)\(\cdot\)12H\({}_{2}\)O) & 3.7 & 4.1 \\ Gismondine (CaAl\({}_{2}\)Si\({}_{2}\)O\({}_{8}\) 4H\({}_{2}\)O) & 9.4 & 10.1 \\ Wairakite (Ca\({}_{4}\)(Al\({}_{2}\)Si\({}_{4}\)O\({}_{12}\)) 2H\({}_{2}\)O) & 1.4 & 1.0 \\ Alite (Ca\({}_{3}\)SiO\({}_{5}\)) & 3.9 & 6.8 \\ Belite (Ca\({}_{2}\)SiO\({}_{4}\)) & 4.0 & 6.3 \\ \(\alpha\)-C2 SH (Ca\({}_{2}\)[SiO\({}_{3}\)OH](OH)) & 5.4 & 14.9 \\ Portlandite (Ca(OH)\({}_{2}\)) & 13.0 & 7.8 \\ Alunite (KAl\({}_{3}\)(SO\({}_{4}\))\({}_{2}\)(OH)\({}_{6}\)) & \textless{}0.5 \({}^{*}\) & 2.3 \\ Nordstrandite (Al(OH)\({}_{3}\)) & - & 0.9 \\ Hydrocalumite (Ca\({}_{4}\)Al\({}_{2}\)(OH)\({}_{12}\)(Cl,CO\({}_{3}\)OH)\({}_{2}\) 4H\({}_{2}\)O) & 1.5 & 2.1 \\ Larnite (Ca\({}_{2}\)SiO\({}_{4}\)) & 6.5 & 6.3 \\ Magnetite (Fe\({}^{2+}\)Fe\({}^{2+}\)\({}_{2}\)O\({}_{3}\)) & 1.2 & 1.4 \\ Wuestite (FeO) & 3.5 & 2.0 \\ Gypsum (CaSO\({}_{4}\)-2H\({}_{2}\)O) & 6.5 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Phase composition of concrete. Figure 5: SEM images of concrete sample (before leaching—unchanged central zone, after leaching—altered marginal zone). Arrows mark vaterite. In the region of (001) reflections, a slight shift was observed from 14.9 A in the natural bentonite to 13.1 A after treatment for 3 months (Figure 7a). Moreover, after prolonged exposure, the half-width and the intensity of the reflections changed. According to the data of chemical analysis (Table 5), the contents of calcium, potassium, and sodium in the bentonite in the course of the experiments increased, which may indicate, among other things, a change in the composition of the exchange cations. Probably, the substitution of predominantly divalent exchangeable cations (Mg) for monovalent (Na, K) took place simultaneously with a change in the nature of the interaction of particles with each other as a result of prolonged contact with highly alkaline solutions. The latter led to a decrease in the ordering in the smectite structure and to a change in the profile of the 001 line. Figure 6: The change in the pore distribution of bentonite as a result of its exposure, for 1 and 3 months, to the synthetic water solution after concrete leaching. Figure 7: **(a)** X-ray diffraction patterns of the samples; **(b)** IR spectra of the samples. During the experiments, the bentonite was exposed to high temperatures and a highly alkaline medium (the pH of the solution at the time of the experiment was 12.1). High pH values affected the colloidal properties of the smectites, which manifested in the degree of orientation of the clay particles in the plane of the substrate of the preparation for X-ray photography and in the degree of order in the superposition of montmorillonite layers in the composition of the particles. Both the pH of the medium and the duration of exposure affected the solubility of various components of the bentonite.