## 2 Materials and Methods
### Materials
#### 2.1.2 Chitosan  
Chitosan is biocompatible, biodegradable and non-toxic cationic polymer obtained by deacetylation of chitin [46]. Chemical structure of chitin is made up of 1-4 linked 2-acetamido-2-deoxy-\(\beta\)-D-glucopyranoside. Chitosan, a deacetylated form of chitin to at least 50% of the free amine form, has a heterogeneous chemical structure made up of both 1-4 linked 2-acetamido-2-deoxy-\(\beta\)-D-glucopyranoside as well as 2-amino-2-deoxy-\(\beta\)-D-glucopyranose [47]. Chemical structure of chitosan is presented in Figure 3, and chitosan powder particles are shown in magnification in Figure 4.  
Figure 1: Grains of “silica sand 1” in magnification.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Soil Type** & \(G_{a}\) [-] & \(d_{50}\) [mm] & \(d_{60}\) [mm] & \(d_{10}\) [mm] & \(C_{ll}\) [-] & \(e_{max}\) [-] & \(e_{min}\) [-] & \(\rho_{dmax}\) [g/cm\({}^{3}\)] & **w** \\ \hline Silica sand 1 & 2.65 & 0.33 & 0.35 & 0.22 & 1.6 & 0.68 & 0.41 & 1.68 & 3.30 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Parameters of the tested soil (“silica sand 1”) *.  
Figure 2: Determination of maximum dry density (g/cm\({}^{3}\)) and optimum moisture content (%) for “silica sand 1”.  
The physical parameters of the chitosan powder that was used in this study are presented in Table 3. Additionally, in Figure 5 particle size distribution of both materials (sand and chitosan) is compared.  
Figure 4: Grains of chitosan in magnification.  
Figure 3: Chemical structure of chitosan [47].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \(G_{s}\) [-] & \(d_{50}\) [mm] & \(d_{60}\) [mm] & \(d_{10}\) [mm] & \(C_{U}\) [-] & \(e_{max}\) [-] & \(e_{min}\) [-] \\ \hline
1.47 & 0.11 & 0.13 & 0.044 & 2.85 & 3.29 & 1.73 \\ \hline \hline \end{tabular} \({}^{t}\)\(d_{50}\), \(d_{60}\), \(d_{10}\)—the values of the particle diameter at 50%, 60% and 10% in the cumulative distribution; \(e\)—void ratio, C\({}_{U}\)—uniformity coefficient, \(G_{s}\)—specific gravity.  
\end{table}
Table 3: Parameters of the tested chitosan \({}^{*}\).  
It can be noted (Figure 5) that the particle size distributions make it possible to create a uniform particle mixture of both materials even when mixing dry ingredients. This aspect can be beneficial for further physical-chemical processing.  
Commercial chitosan is usually a fine powder of white to slightly yellow color (Figure 6a). It is insoluble in water, but it is easy to dissolve in solutions of weak acids, e.g., in 10% acetic acid CH\({}_{3}\)COOH (Figure 6b,c). Chitosan solutions in acetic acid are viscous fluids. The viscosity increases with the increase in chitosan concentration (in this study 4% solution in 10% acetic acid and 7% solution in 10% acetic acid were used. The increase in the liquid's viscosity was easily noticeable but has not been quantitatively measured).  
Laboratory tests were performed on cylindrical specimens of oven-dry \"silica sand 1\" and two types of mixtures of \"silica sand 1\" and chitosan-water-acetic acid solutions. Specimens were compacted with respect to the ASTM standard [48]. In Table 4 the composition of prepared specimens is presented.  
Figure 5: Particle size distribution of used materials.  
Figure 6: Chitosan (**a**) powder, (**b**) 4% solution in 10% acetic acid, (**c**) 7% solution in 10% acetic acid.