## 4 Results and Discussion
### Gradual Change Behaviour of Mesoscopic Evaluation Indices for the Main Skeleton  
#### 4.2.1 Gradual Trend of Coarse Aggregate Coordination Number  
The distribution characteristics of the coordination number in the three types of asphalt mixtures at different loading stages are summarised in Table 9; the bold italic numbers represent the peak positions. The data listed in Table 9 indicate the following:  
(1) The maximum and minimum coordination numbers of coarse aggregates are 5 and 0 respectively. The particles with coordination numbers of 4 and 5 are mainly coarse aggregates with particle sizes larger than 4.75 mm; the number of these particles is relatively small. There are more coarse aggregates with coordination number of 0 in the three types of asphalt mixture; this indicates that there are more coarse aggregates that do not come into contact with other coarse aggregates and can be regarded as 'free' coarse aggregates. (2) With the increase in loading time, the quantity of coarse aggregates with coordination numbers of 0 and 1 decreases gradually, whereas the quantity of coarse aggregates with coordination numbers larger than 2 increases continuously. Before loading, the proportion of coarse aggregates with a coordination number of 0 to the total coarse aggregates decreases from 30% to approximately 7%. At the end of the loading stage, the proportion of coarse aggregates with a coordination number larger than 3 to the total coarse aggregates increase gradually from 11% to 36% and from 7% to 24% in SMA-13 and AC-13C, respectively. (3) With the asphalt mixture being continuously compacted under the load action, the peak position of the coordination number gradually moves to the direction of increase. The peak value of coordination number in the three types of asphalt mixtures before loading and after 1-h loading is 1. The peak value at the end of the loading stage is 2; at this point, the amount of coarse aggregates with the peak coordination number is approximately 35% of the coarse aggregate amount. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & \multicolumn{6}{c}{**Coordination Number**} \\ \cline{3-8}
**9** & **Loading Time (h)** & **0** & **1** & **2** & **3** & **4** & **5** \\ \cline{3-8}  & & & \multicolumn{6}{c}{**Corresponding quantity of coarse aggregates with**} \\  & & & \multicolumn{6}{c}{**coordination number: total quantity and (percentage)**} \\ \hline \multirow{3}{*}{70\# asphalt} & Before loading & 87(30) & _108(37)_ & 79(27) & 15(5) & 3(1) & 2(1) \\  & After 1-h loading & 61(21) & _102(35)_ & 92(31) & 31(11) & 5(2) & 3(1) \\ \cline{1-1}  & After 2-h loading & 37(13) & 91(31) & 106(36) & 46(16) & 10(3) & 4(1) \\ \cline{1-1}  & After 3-h loading & 22(7) & 87(30) & 112(38) & 55(19) & 12(4) & 6(2) \\ \hline \multirow{3}{*}{Rock asphalt} & Before loading & 68(24) & _105(38)_ & 86(30) & 21(7) & 2(1) & 1(0) \\ \cline{1-1}  & After 1-h loading & 45(16) & _102(35)_ & 96(33) & 37(13) & 6(2) & 2(1) \\ \cline{1-1}  & After 2-h loading & 30(10) & 99(34) & _102(35)_ & 45(16) & 8(3) & 4(1) \\ \cline{1-1}  & After 3-h loading & 21(7) & 95(33) & _108(38)_ & 49(17) & 9(3) & 6(2) \\ \hline \multirow{3}{*}{SMA-13} & Before loading & 63(28) & _91(40)_ & 46(20) & 18(8) & 5(2) & 2(1) \\ \cline{1-1}  & After 1-h loading & 33(15) & _76(34)_ & 63(28) & 37(16) & 12(5) & 4(2) \\ \cline{1-1}  & After 2-h loading & 18(8) & 65(29) & _70(31)_ & 48(21) & 18(8) & 6(3) \\ \cline{1-1}  & After 3-h loading & 11(5) & 60(27) & _72(32)_ & 55(24) & 20(9) & 7(3) \\ \hline \end{tabular}
\end{table} 
Table 9: Coordination number distribution at different loading stages.