## 3 Research Results--Analysis and Discussion
### pH Value  
The optimal stabiliser content refers to the percentage of a stabiliser in the soil mixture that provides the most effective stabilisation of soil of weak properties in its natural conditions. Furthermore, the optimal content of stabiliser contributes to the increase in load-bearing capacity, i.e., reduced plasticity, of the soil. Some of the studies have shown that in the case of applying lime as a stabiliser, the most effective outcome of the stabiliser is achieved at a soil pH value of 12.4 [39; 40; 41]. With suitable external conditions, a pozzolanic reaction develops between the stabiliser and the soil, in which the stabiliser causes a high pH value of the environment and thus dissolves silicon and aluminium compounds of the clayey soil.  
The changes in the pH value of the treated soil over time for each of the considered stabilisers and for the corresponding percentage share of the stabiliser in the mixture with clayey soil are given in Table 3. **Conventional stabilisers** and **stabilisers based on waste materials** used in this research showed the ability to increase the pH value of clayey soil, which initiates pozzolanic reactions. In the first 24 h after mixing with the stabiliser, an increase in pH values was noted, after which the values remained constant or slightly decreased. These results clearly indicate the potential of stabilisers to cause permanent chemical changes in soil. High pH values are associated with the dissolution of primary minerals, in particular, clay minerals, which further leads to the formation of secondary minerals. It is also noticeable that the suggested optimal pH value of 12.4, which results in the strongest effect of the stabiliser, except in the case of lime, was also achieved in the case of cement (thus, in the case of conventional stabilisers), whereas in the case of stabilisers based on waste materials, it was still somewhat lower.  
On the other hand, adding a **chloride-based stabiliser** reduced the pH value of the treated soil compared to the natural state of the soil. This result is due to the fact that only  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{pH Value} \\ \cline{3-5}
**Soil Conditions** & & **After 24 h** & **After 3 Days** & **After 28 Days** \\ \hline Soil in natural conditions & & 9.5 & 9.5 & 9.5 \\ \hline \multirow{3}{*}{Lime} & 3\% & 12.1 & 12.0 & 12.0 \\  & 5\% & 12.5 & 12.5 & 12.4 \\  & 7\% & 12.8 & 12.8 & 12.7 \\ \hline \multirow{3}{*}{Cement} & 5\% & 11.6 & 11.6 & 11.6 \\  & 10\% & 12.0 & 12.0 & 12.0 \\  & 15\% & 12.4 & 12.4 & 12.4 \\ \hline \multirow{3}{*}{Fly ash} & 10\% & 11.2 & 11.2 & 11.0 \\  & 15\% & 11.6 & 11.3 & 11.3 \\  & 20\% & 12.0 & 11.8 & 11.6 \\ \hline \multirow{3}{*}{Soil after chemical stabilisation} & 5\% & 10.5 & 10.5 & 10.2 \\  & 10\% & 10.9 & 10.8 & 10.5 \\  & 15\% & 11.1 & 11.1 & 10.6 \\ \hline \multirow{3}{*}{Ferric chloride} & 1\% & 9.5 & 9.5 & 9.2 \\  & 2\% & 9.4 & 9.4 & 9.2 \\  & 3\% & 9.4 & 9.3 & 9.0 \\ \hline \multirow{3}{*}{Calcium chloride} & 1\% & 9.2 & 9.2 & 9.2 \\  & 2\% & 9.0 & 9.0 & 9.0 \\  & 3\% & 9.0 & 9.0 & 9.0 \\ \hline \multirow{3}{*}{Potassium chloride} & 1\% & 9.5 & 9.5 & 9.5 \\  & 2\% & 9.5 & 9.5 & 9.5 \\ \cline{1-1}  & 3\% & 9.4 & 9.4 & 9.4 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Change in the soil pH value after the treatment with the analysed stabilisers.  
the solution of calcium chloride in water is alkaline (pH \(\approx\) 8.5), whereas the solutions of ferric chloride and potassium chloride are acidic (pH < 7.0).