## 4 Conclusions  
Aiming towards the problem of over 100% compactness in practical engineering, the mechanical properties of cement stabilized macadam specimens molded by static pressure and vibration compaction  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**The Type of** & **The Type of** & **Minimum** & **Maximum** & **Average** & **Median** &
\begin{tabular}{c} **Coefficient** \\ **of Variation** \\ \end{tabular} \\ \hline \multirow{3}{*}{XM} & SPC & 1.7404 & 1.7548 & 1.7427 & 1.7468 & 0.3926 \\  & VC & 1.7237 & 1.7389 & 1.7272 & 1.7259 & 0.2719 \\  & OS & 1.7208 & 1.7250 & 1.7282 & 1.7272 & 0.2127 \\ \hline \multirow{3}{*}{GM} & SPC & 1.7353 & 1.7567 & 1.7450 & 1.7400 & 0.3552 \\  & VC & 1.7271 & 1.7317 & 1.7287 & 1.7281 & 0.1248 \\ \cline{1-1}  & OS & 1.7185 & 1.7313 & 1.7273 & 1.7280 & 0.2418 \\ \hline \hline \end{tabular}
\end{table}
Table 11: Fractal dimension of void image of cement stabilized macadam mixture.  
Figure 8: Fractal dimension of void cement stabilized macadam mixture.  
were studied, and related to on-site samples in practical engineering. In addition, the characteristics of the molding method were explained by the mesoscopic structure. The following conclusions are drawn:  
1. The test results showed that the maximum dry density of the mixture under vibration compaction were larger, and the optimal moisture content was smaller than that of heavy compaction, which indicates that vibration compaction method has incomparable advantages in rolling mechanism and field compaction simulation;
2. After a 7 days health period, the on-site sample was complete and close with a good skeleton structure, having compressive strength and splitting strength indexes that were much higher than those of indoor static pressure specimens but close to those of vibration compaction specimens, which verifies the reliability and accuracy of the vibration compaction test;
3. X-ray CT, VG Studio, MATLAB, and IPP software were used to collect the internal void information of the mixture. Then the reconstructed void ratio, the number of cross-sectional void, average diameters, shape parameters, and fractal dimension were calculated and counted, and the internal void distribution characteristics of the mixture under different molding methods were analyzed. The results showed that the void distribution of vibration compacted specimens was much more similar to the on-site sample than that of static pressure specimens, and the uniformity of the void distribution was: on-site sample \(>\) vibration specimens \(>\) static pressure specimens;
4. Mechanical test and mesoscopic analysis results showed that the indexes of vibration compaction specimens were close with those of the on-site sample. Thus the vibration compaction test method is validated for its reliability and accuracy to simulate the actual mechanical properties and guide the actual construction.  
Conceptualization, F.W. and Y.J.; methodology, F.W., Y.F. and W.P.; software, Y.L. and W.P.; validation, L.H., F.W. and W.P.; formal analysis, L.H. and Y.L.; resources, F.W. and Y.L.; data curation, Y.L., L.H. and W.P.; writing--original draft preparation, F.W., Y.F. and W.P.; writing--review and editing, F.W., Y.J., W.P. and L.H.; project administration, F.W.; funding acquisition, F.W. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Transportation Technology Program of Jilin province of China, grant number 2017 ZDGC-7.  
The authors express their appreciation for the financial support of the Transportation Technology Program of Jilin province of China, grant number 2017 ZDGC-7. Thanks to editors and reviewers for their efficient work.  
The authors declare no conflict of interest.