## 5 Results and Discussion  
### Results of Image Analysis  
The compaction behavior of asphalt mixtures can be represented by the vector magnitudes (\(\Delta\)) as a parameter of aggregate orientation. Aggregate orientation is well-known as a good representative to reflect the shear resistance and stiffness of asphalt mixtures against compaction. Thus, aggregate behavior primarily affects the compactibility of an asphalt mixture, resulting in a preferred aggregate orientation that can reduce compaction resistance. For studying the preferred aggregate behavior, the changes in vector magnitudes were evaluated as a function of the compaction temperature. Figure 9 shows the vector magnitude variations from three images for each mixture at a compaction temperature. The average vector magnitudes increased with an increase in the compaction temperature from 90 \({}^{\circ}\)C to 115 \({}^{\circ}\)C for the PG64-28 mixture. A similar result is shown for the PG58-28 mixture from 80 \({}^{\circ}\)C to 110 \({}^{\circ}\)C, which is a high-viscosity period. In this compaction temperature period, a \(t\)-test was applied to the data to examine the significance of the change in the vector magnitudes. For the PG64-28 mixture, the computed \(t\) value of 2.33 shows a statistically significant change in the vector magnitude with the rejection probability of 2.22%. A similar \(t\)-test result is obtained with the \(t\) value of 1.77 for the PG58-28 mixture. On the other hand, on the lower asphalt binder viscosities (at compaction temperatures higher than 115 \({}^{\circ}\)C for the PG64-28 mixture and 110 \({}^{\circ}\)C for the PG58-28 mixture), the aggregates are not sufficiently constrained to achieve their preferred orientation, which exists at 115 \({}^{\circ}\)C for the PG64-28 mixture and 110 \({}^{\circ}\)C for the PG58-28 mixture. These results are in good agreement with the findings of [PERSON] et al. [28]. The most preferred orientation in both mixtures is achieved after increasing the compaction temperature up to a certain asphalt binder viscosity, and then decreasing it with increases in the compaction temperature. This can be because the asphalt binder viscosity mainly governs the compaction at a low compaction temperature, and the high viscosity of the asphalt binder makes it difficult to move and pack the aggregates. However, at high temperatures, the low viscosity of the asphalt binder appears to reduce the preferred orientation of the aggregates because of the greater shear resistance of the aggregate resulting from the higher interaction of the aggregate compared with the binder's resistance to compaction.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Aggregate Source**} & **Gradation \&** & **Asphalt Binder** & **Compaction** & **Number of** \\  & **NMAS** & **Grade** & **Temperature (\({}^{\circ}\)C)** & **Specimens** \\ \hline \multirow{4}{*}{Crushed Gravel} & \multirow{4}{*}{Fine (19 mm)} & \multirow{4}{*}{PG64-28} & 90 & 2 \\  & & & 115 & 2 \\ \cline{1-1}  & & & 140 & 2 \\ \cline{1-1} \cline{3-5}  & & & 80 & 2 \\ \cline{1-1}  & & & 110 & 2 \\ \cline{1-1}  & & & 140 & 2 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Compaction matrix. (NMAS: Nominal maximum aggregate size).