## 3 Results  
### Moisture Retention Tests  
#### 3.1.1 Medium-Grained Sand  
Results of the moisture retention tests are shown in Figure 5 (exact values are appended in Table 2). Four days (96 h) after treatment, the control sample, which was treated with water, contained 6.9% (SD = 1.2) of the initially applied 20.3 g water. In the following, results of the polysaccharide and protein applications on the medium-grained sand are presented and compared.  
Figure 4: Process of removing the crust from the sample. (**a**) Loosening of the crust with a spatula from the mould rim, (**b**) removal of the crust with a spatula, (**c**) weighing of the sample without the crust.  
_P polysaccharidesachrides._ Compared to the control, the 1 wt% (XG = 0.25 wt%) treatments either increased or decreased the samples' moisture retention. A slight reduction in moisture retention was observed for samples treated with CMC, POS, WS, and XG, whereas it increased for samples treated with CS, NLS, and PES. Relative to the 1 wt% treatment, the application of 2 wt% resulted in the samples' moisture retention either decreasing, increasing, or changing negligibly. It decreased slightly for CMC and CS and significantly for PES, while no change was observed for POS. By contrast, it moderately increased for NLS and XG and even doubled for WS-amended samples.  
_Proteins._ Protein applications at 1 wt% concentration reduced the moisture retention for samples amended with PP and WPC relative to the control group, while a negligible effect was observed for HG. Doubling the concentration decreased moisture retention for HG- and PP-treated samples, increased it for FBPC-, TG-, and WP-amended samples and had a negligible effect on applications with HEA and WP.  
_Comparison of polysaccharide and protein treatments._ At the 1 wt% concentration, the polysaccharide-treated samples had, on average, higher moisture retention than the protein-amended samples. Doubling the concentration resulted in a slight increase in the average moisture retention of polysaccharide and protein-treated substrate. A direct comparison of the polysaccharide and protein amendments that resulted in the highest moisture retention shows that the material treated with proteins achieved higher moisture retention regardless of the concentration tested.  
_Statistical analysis._ Results of the two-way ANOVA (Table 3) show that the types of polysaccharide (\(p<.001\)) and protein (\(p<.001\)) have a significant effect on moisture retention, whereby no general trend could be identified: whether the treatments increase or decrease moisture retention. Doubling the concentration has no significant effect on moisture retention among polysaccharide- (\(p=.596\)) and protein-amended samples (\(p=.470\)), and there is no general trend, whether doubling the concentration results in the moisture retention to increase or decrease.  
Figure 5: Mean moisture retention of medium-grained sand samples 4 days (96 h) after treatment at 1.6 L/m\({}^{2}\) and biopolymer concentrations of 1 and 2 wt% (XG = 0.25 and 0.50 wt%). Biopolymers are grouped into polysaccharides and proteins with water as control. Tests were performed in triplicates (\(n=3\)), and error bars indicate the standard deviation (SD). Note. The exact values of experimental results are appended in Table 2.  
_Conclusions_. On medium-grained sand, the type of biopolymers has a significant effect on the samples' moisture retention, whereby some biopolymers significantly increased moisture retention. In contrast, others have a negligible effect or even decrease moisture retention relative to the control sample treated with water. The biopolymer's concentration does not have a significant effect on the moisture retention of the treated samples.