## 3 Results
### Crust Thickness Measurements  
#### 3.3.1 Medium-Grained Sand  
The results of the crust thickness measurements are shown in Figure 9 (exact values are appended in Table 10). Figures 10 and 11 show exemplary pictures of upside-down-facing crusts formed by the tested biopolymer amendments (visual classification appended in Table 11). While the control group, treated with water, formed no recoverable crust, all tested biopolymers formed crusts of varying thicknesses. _Polysacchardie._ Treatments at 1 wt% (XG = 0.25 wt%) produced crusts ranging from 2 to 7.2 mm in thickness. While amendments with NLS and POS formed relatively thin to medium-thick crusts, the remaining polysaccharide applications yielded thick crusts on medium-grained sand. Compared to the 1 wt% treatment, doubling the concentration decreased the crust thickness for substrate treated with XG, CS, and WS, while crusts resulting from amendments with CMC and PES displayed a slight, and NLS and POS a significant, increase in thickness, respectively. Figure 8: Mean maximum penetration resistance of crusts from fine-grained silica sand samples measured by penetrometer tests. Biopolymers are grouped into polysaccharides and proteins with water as control. Tests were performed in triplicates (\(n=3\)), with error bars indicating the standard deviation (SD). Note. The exact values of experimental results are appended in Table 12.  
ProteinsProtein applications at 1 wt% concentration produced crusts of varying thickness. While treatments with HEA and HG formed fragile, brittle, and barely recoverable crusts, TG already formed slightly thicker crusts. Thick crusts formed on medium-grained sand amended with PP, WP, WPC, and FBPC, with the latter resulting in the thickest crusts of all biopolymers tested at 1 wt%. At the higher tested concentration, the crust thicknesses of all treatments increased, whereby HEA, TG, and HG displayed the most significant increases. Comparison of polysaccharide and protein treatmentsAt treatments with 1 wt% (XG = 0.25 wt%) biopolymer concentration, medium-grained sand amended with polysaccharides, on average, formed slightly thicker crusts than applications with proteins. Doubling the concentration to 2 wt% (XG = 0.50 wt%) resulted in the thickness of polysaccharide-induced crusts to increase slightly, while protein-induced crusts displayed significant increases. ConclusionsOn medium-grained sand, all biopolymer treatments formed crusts, with the resulting crust thickness varying significantly among the biopolymers tested. For most polysaccharides, doubling the concentration only slightly increased the crust thickness, whereas most protein treatments exhibited significant increases in crust thickness. Statistical analysisResults of the two-way ANOVA (Table 5) show that the types of polysaccharide (\(p<.001\)) and protein (\(p<.001\)) have a significant effect on the crust thickness, with some biopolymers forming only very thin crusts and others thick crusts. Increasing the concentration only had a significant effect on the crust thickness of protein amendments (\(p<.001\)), whereby increasing the concentration caused the crust thickness of all protein-treated samples to increase. Figure 9: Mean thickness of crust formed on medium-grained sand samples. Biopolymers are grouped into polysaccharides and proteins with water as control. Tests were performed with six replicas (\(n=3\)), with error bars indicating the standard deviation (SD). Note. The exact values of experimental results are appended in Table 5.  
Figure 10: Examples of polysaccharide-induced crusts recovered from the samples (cf. Table A6 for classification). Figure 11: Examples of protein-induced crusts recovered from the samples (cf. Table A6 for classification). Polysaccharides.Polsaccharide applications at 1 wt% (XG = 0.25 wt%) formed crusts of varying thickness. WS formed only very thin and rather ductile crusts, while the remainder of the tested polysaccharide applications yielded significantly thicker crusts.