## 3 Results and Discussions
### Determination of Optimal Material Combinations and Comparison of Results  
Once the physical and mechanical properties of the different families of bituminous mixtures with increasing binder percentages had been determined, the optimum bitumen percentage was chosen. This percentage was selected on the basis of the results of the Marshall test, choosing the percentage of bitumen that developed the greatest resistance. The choice of this test to obtain the optimum combination of materials is mainly based on the fact that this is the test that most conditions the quality of the bituminous mix, since the high percentages of bitumen in the mixes are prone to the formation of plastic deformations. However, the choice of the percentage of bitumen for each family as the maximum of the Marshall stability was decided as long as the other properties of the conformed mixtures were acceptable. As discussed, Table 11 shows the results of the optimum bitumen percentages for each family, as well as the physical and mechanical properties obtained for each combination. These properties were obtained after conforming and testing various samples with the optimum combination of materials for each family. The percentages of optimum bitumen for the three families of bituminous mixtures are very similar; however, the percentage is slightly higher for the SS family. This is due to the greater specific surface area of the ladle furnace slag which allows a higher percentage of bitumen to be absorbed, as mixtures conformed with electric furnace slag and hornfels aggregate obtain similar percentages. The bulk density and maximum density are higher for mixtures conformed with electric arc furnace slag due to the higher density of this \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test** & **Standard** & **HC** & **SC** & **SS** \\ \hline \% bitumen in & & & & \\ volume & - & 15.79 & 15.75 & 15.87 \\ Bulk density, & UNE-EN 12697-6 & 2342 \(\pm\) 60 & 2842 \(\pm\) 87 & 2846 \(\pm\) 92 \\ kg/m\({}^{3}\) & UNE-EN 12697-5 & 2460 \(\pm\) 63 & 2983 \(\pm\) 97 & 2986 \(\pm\) 78 \\ density, kg/m\({}^{3}\) & UNE-EN 12697-8 & 4.81 \(\pm\) 0.17 & 4.74 \(\pm\) 0.15 & 4.70 \(\pm\) 0.16 \\ Stability & UNE-EN & & & & \\ Marshall, N & 12697-14 & 14,444 \(\pm\) 370 & 15,084 \(\pm\) 471 & 17,290 \(\pm\) 516 \\ Marshall & UNE-EN & & & & \\ Deformation, m & 12697-14 & 0.0030 \(\pm\) 0.0001 & 0.0027 \(\pm\) 0.0001 & 0.0025 \(\pm\) 0.0001 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Results of the tests for the optimum combination of materials from the HC, SC, and SS families of bituminous mixtures. Figure 10: Marshall deformation of the HC, SC, and SS families of bituminous mixtures according to the percentage of bitumen. material; however, the void content is similar in all three families and acceptable according to the regulations. It can be seen how the Marshall stability is far superior in the mix conformed with electric arc furnace and ladle furnace slags, demonstrating the excellent properties of ladle furnace slags as fillers in hot mix asphalt. This fact is corroborated with a lower Marshall deformation, showing a material of high rigidity and resistance. In turn, the Marshall stability of the samples conformed with electric arc furnace slag is superior to that of hornfels aggregate, as it reflects higher values and lower deformations. The goodness of electric arc furnace slag and ladle furnace slag in hot mix asphalt is therefore demonstrated. Finally, and with the aim of corroborating the durability of the families of bituminous mixtures over time, the wheel-tracking test was carried out. This test measures the deformation produced in the bituminous mix by the continuous passage of a standardized wheel with load during thousands of cycles. The results of this test are shown in Figure 11.  
The wheel-tracking test reflects how the bituminous mix conformed with electric arc furnace slag and ladle furnace slag has less deformation after the test, demonstrating the rigidity, strength, and durability previously determined by the Marshall test.