# Mechanical Behavior of Sand Mixed with Rubber Aggregates
## 3 Results and Discussion  
### Effect of Aggregate Rubber Content on Shear Strength of Sand  
Figures 7 and 8 represent an example of material response as a function of relative horizontal strain for the different procedures, namely Hostun sand-Rubber and Dune sand-Rubber. These direct shear tests were performed for different aggregate rubber contents ranging from 0% to 30% under an applied normal stress of 100 kPa. It is found that the presence of aggregate rubber significantly affects the shear stress where a maximum shear stress is observed for both sands. The shear stress of the sand-rubber mixtures in both cases still tends to increase slightly up to 20% crushed rubber content. The mixtures exhibit a typical behavior of a medium dense sand (\(D_{r}=55\%\)), with no drop-in strength after maximum for the Hostun sand, but for the Dune sand there is a remarkable drop-in strength. It clearly shows that the presence of additional crushed rubber in both sands leads to an improvement in the strength of the sand. Therefore, it can be concluded that the addition of aggregate rubber can significantly improve the shear strength of the mixtures. The increase in the shear strength of the mixtures with the increase in the aggregate rubber content can be attributed to the redistribution of the samples. Thus, the grains of sand are pushed towards the grains of rubber which deform and increase the contact surface between the particles of sand and the grains of rubber. An additional aggregate rubber 30% content increased the shear strength of pure sands, but it decreased compared to 20%. This is because in the shear zone the rubber grains surround the sand grains and tends to roll and slide over them to create more voids. While higher normal stresses cause shrinkage rather than swelling and therefore the mixture becomes more and more compact. It is also showing that for Dune sand mixed with aggregate rubber, after the initial shear at low horizontal strain, less significant dilation occur as the mobilized shear stress approaches its maximum value. In contrast, for Hostun sand mixed with rubber aggregates, when the horizontal deformation is less than 0.25%, the shear stress increases quickly. Additional shear induces a significant expansion but a relatively small change in shear stress, resulting in a \"plateau\" on the stress-horizontal strain curves. As a comparison between Hostun sand and Dune sand, it is observed that Hostun sand/rubber mixture requires larger horizontal deformations to mobilize the maximum shear strength than Dune sand of the same relative density, but the post-maximum strain softening after is gentler than that of Dune sand-rubber mixture. Regarding vertical deformation as a function of the horizontal deformation (Figures 9 and 10), it is noted that the dilatant character of the mixtures increases with the increase in the rubber content. All lightly compacted sand-rubber mixtures expand under the effect of shear stress. It is also noted that, for pure sand and the 10% aggregate rubber mixture, the expansion phase appears from low horizontal deformation, while for samples with rubber content of 20% to 30% the dilatancy is delayed and appears from a relatively high horizontal strain. This result is in accordance with the results obtained for the sands which showed that the presence of rubbers amplifies the dilatant character of the sand-rubber mixture. \begin{table}
\begin{tabular}{c c} \hline \hline
**Designations** & **Sand-Rubber** \\ \hline _RC0_ & 100\% Sand + 0\% Rubber \\ \hline _RC10_ & 90\% Sand + 10\% Rubber \\ \hline _RC20_ & 80\% Sand + 20\% Rubber \\ \hline _RC30_ & 70\% Sand + 30\% Rubber \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Designations for the differents mixtures; Hostun or Dune sand-Rubber. Figure 8: Shear stress variation curves for different rubber contents under a normal stress of 100 kPa. Figure 7: Shear stress variation curves for different rubber contents under a normal stress of 100 kPa.