# Compaction Characteristics and Mechanical Response of Gravel-Glass-Rubber Mixtures +
## 4 Experimental Results and Discussions  
### Compaction Characteristics of GGRM  
The results of compaction tests are reported in Figure 4a and Table 1 for all tested materials. Test results for GRM reported by [PERSON] et al. [38], who used the same gravel and rubber materials used in this study, are also reported for the sake of comparison. It is observed that the dry density (\(\rho_{\rm dry}\)) of GGRM decreases linearly with increasing \(G_{\rm L}\) from 1310 kg/m\({}^{3}\) to 1167 kg/m\({}^{3}\) for \(R_{\rm B}\) = 0.4 and from 1141 kg/m\({}^{3}\) to 1058 kg/m\({}^{3}\) for \(R_{\rm B}\) = 0.55. This is mainly due to the slightly different specific gravity of the gravel (\(G_{\rm S}\) = 2.66) and of the green glass (\(G_{\rm S}\) = 2.50). The lower values of \(\rho_{\rm dry}\) obtained for GGRM (with \(R_{\rm B}\) = 0.4 and 0.55), as compared with the glass (\(\rho_{\rm dry}\) = 1526 kg/m\({}^{3}\)) and the gravel (\(\rho_{\rm dry}\)) = 1749 kg/m\({}^{3}\)) alone, are the results of the presence of lightweight rubber inclusions (\(G_{\rm S}\) = 1.15; \(\rho_{\rm dry}\) = 652 kg/m\({}^{3}\)) in the mixtures. Figure 3: A typical loading pathway used in the 1D compression tests. The duration of the creep loading stage varied depending on the stress applied. As reported in Figure 4b, test results from [PERSON] et al. [38] show that \(\rho_{\rm dry}\) of GRM (i.e., \(G_{\rm L}=0\)) decreases linearly with increasing \(R_{\rm B}\); this was confirmed in this study. Moreover, this study indicates that the \(\rho_{\rm dry}\) of glass-rubber mixes (i.e., \(G_{\rm R}=0\)) also decreases linearly with increasing \(R_{\rm B}\). The linear trends shown in Figure 4b were attained by using Equation (4), which is valid for GGRM. Specific equations for gravel-glass mixtures (\(R_{\rm B}=0\)), GRM (\(G_{\rm L}=0\)), and glass-rubber mixtures (\(G_{\rm R}=0\)) are reported in Table 2 for completeness. Interestingly, as shown in Figure 4c, the data points for GGRM with \(R_{\rm B}=0.4\) and \(0.55\) can be connected by linear trends that are parallel to those of the gravel-glass mixtures. Similarly, as shown in Figure 4d, the data points for GGRM with varying \(G_{\rm R}=0\)-\(0.6\) are aligned with linear trends that are parallel to those of the glass-rubber mixtures. Sieve analyses were carried out before and after each compaction test (Figure 5a) to evaluate the amount of glass breakage/crushing induced by compaction (calculated with respect to the mass of glass in the mixture); for instance, for the green glass alone (\(G_{\rm L}=1\)), the amount of crushed material passing through the 3.35 mm sieve was about 6.9% (i.e., before compaction, the amount of glass retained at the 3.35 mm sieve was zero). In the case of GGRM (\(G_{\rm L}=0.15\)-\(0.6\)), an increase in glass breakage with increasing \(G_{\rm L}\) was observed (Figure 5b), with the maximum amount of breakage (2.24%) obtained for \(R_{\rm B}=0.4\) (\(G_{\rm L}=0.6\)). This is associated with the higher amount of glass in the mixtures. In contrast, the glass breakage seems to decrease with increasing \(R_{\rm B}\) in the mixture; that is, because soft rubber inclusions in the GGRM act as a cushion that absorbs part of the impact energy delivered  
Figure 4: Results of standard Proctor compaction tests carried out on GGRM: (**a**) experimental data from this study; (**b**) comparison with GRM experimental results from [PERSON] et al. [38]; (**c**) prediction using Equation (4) for various volumetric rubber content; and (**d**) predictions using Equation (4) for various volumetric gravel content. to the specimen, the higher amount of rubber in the mixture helps reduce glass breakage during compaction.