# Assessing the Compaction Quality of Dolomitic Asphalt Pavements Using Ground Penetrating Radar
## 6 Results
### The RD of Asphalt Layers  
Standardized at-a-point nuclear gauge measurements provide only a limited number of data and a low spatial resolution of the potential air void content of asphalt layers. Based on the systematic tests made during the compaction process and the equations determined, detailed maps were generated on the RD of the different asphalt layers to visualize the parameter's spatial homogeneity. RD maps can be important in predicting the pavement's long-term performance, supporting maintenance strategies, and facilitating the detection of different defects. In general, we found that the RD values showed significant differences across the pavement's depth and along the roadway section. Across the depth of the pavement, the lowest RD values were experienced regarding the wearing course (Table 3 and Figure 8). Based on the relationships in Figure 7, this result occurred because the AC 11 mixture can incorporate more air voids, which simultaneously decreases its density and \(\varepsilon\) compared to the applied AC 22 mixture. In the case of both sections, the RD of the base course was higher than the RD of the binding course, even though both layers were constructed from the same mixture, and the same number of roller passes were applied during their construction. This suggests that the compaction of the binding and wearing courses led to the additional compaction of the base course, even though the base course had cooled down by the time of the construction of the overlying layers. Consequently, the RD of the base course was found to be the highest of the investigated layers. However, the base course had the highest variability, or standard deviation (SD) of RD values (Table 3 and Figure 8), referring to a less uniform compaction, probably due to the uneven sub-base layer. The most uniform compaction was achieved in the case of the binding course. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Number of Compaction Passes**} & \multicolumn{2}{c}{**Sub-Base Course**} & \multicolumn{2}{c}{**Base Course**} & \multicolumn{2}{c}{**Binder Course**} & \multicolumn{2}{c}{**Wearing Course**} \\ \cline{2-9}  & \(\mathbf{G_{mb}}\) & \(\varepsilon\) & \(\mathbf{G_{mb}}\) & \(\varepsilon\) & \(\mathbf{G_{mb}}\) & \(\varepsilon\) & \(\mathbf{G_{mb}}\) & \(\varepsilon\) \\ \hline
1 & 2.6 & 8.77 & 2.31 & 5.11 & 2.3 & 5.11 & 2.11 & 3.77 \\ \hline
2 & 2.65 & 9.5 & 2.34 & 5.49 & 2.33 & 5.49 & 2.15 & 4.31 \\ \hline
3 & 2.69 & 9.99 & 2.39 & 5.88 & 2.41 & 5.88 & 2.19 & 4.36 \\ \hline
4 & 2.72 & 10.05 & 2.42 & 5.99 & 2.44 & 5.99 & 2.22 & 4.41 \\ \hline
5 & 2.78 & 10.55 & 2.46 & 6.33 & 2.49 & 6.33 & 2.27 & 4.50 \\ \hline
6 & 2.8 & 10.88 & 2.52 & 6.44 & 2.56 & 6.44 & 2.29 & 4.70 \\ \hline
7 & 2.8 & 10.88 & 2.52 & 6.44 & 2.56 & 6.44 & 2.29 & 4.70 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The \(\mathrm{G_{mb}}\) and \(\varepsilon\) values during the compaction process for each pavement layer. Figure 8: Horizontal variation of RD in terms of investigated layers: (**a**) Section I; (**b**) Section II. In addition to the layer-to-layer differences in the RD values, a significant within-layer inhomogeneity was also apparent in the investigated courses (Table 3). This is most striking when the right and left lanes, compacted separately, are compared to each other (Figure 7). The greatest difference in the compaction of separate lanes can be seen in terms of the wearing course; for example, at Section II., a 3.6% difference was identified between the average RD of the two lanes (Figure 8b). The density variation was significant along the same lane as well (Figure 8a,b), suggesting that the temperature of the asphalt mixture was changing during the construction process. Based on the results, additional roller passes should have been made during the construction of the wearing course, especially on the left lane at Section II. (Figure 8b).