# Dynamic Response of Reinforced Recycled Aggregate Concrete Pavement under Impact Loading
## 3 Experimental Results and Discussion
### Damage Characteristics and Crack Patterns  
Prior to the test, the surfaces of the PCP specimen were painted white and then meshed with spacing of 100 mm grids in order to observe damage characteristics and crack patterns. The \"E/S/W/N\" symbols were marked at top, bottom and side surfaces of the RCP specimen, and the RCP specimen was divided into four regions according to direction. The cracks that developed after each test were marked, and the crack widths were measured manually by HC-CK101 Concrete Crack Width Meter. For impacting at the mid-point, the sketched cracks profiles of the RCP specimen are shown in Figure 9.  
Figure 8: Peak impact load and peak inertial force. Figure 9: _Cont._  
Figure 9: Cont. The type of damage and crack development mode on the bottom surface of all RCP specimens are similar. The crack patterns mainly appeared as the radial crack and diagonal crack, indicating that the deformation of the specimen was a global flexural deformation. The major radial crossing cracks and the failure took place simultaneously. The concrete scabbing was quite limited and mainly centralized in the region of 200 mm \(\times\) 200 mm beneath the impacting point. The maximum residual width of the crack was also found in this region, which reached up to 1.46 mm-1.8 mm. For all RCP specimens, the widths of radial cracks were larger than those of diagonal cracks. This is because the radial crack developed prior to the diagonal crack, and the radial crack could dissipate more impact energy, thus reducing the crack width [27]. There were two different crack patterns on the top surface of the RCP specimen: one was the radial crack propagating from the bottom surface towards the top surface, and the other was the circumferential crack with the impact point as the center. No obvious penetration was observed on the surface of the RCP specimen that was found in References [47; 48]. The final crack properties of all tested specimens are presented in Table 7.  
The final damage status of the 7 MR specimen is similar to that of the 7 MN specimen. In the E-W direction, radial cracks were fully developed, and their widths were in the range of 1.2-1.4 mm for both 7 MR and 7 MN. While, in the N-S direction, the cracks generated in 7 MR are slightly more than those in 7 MN, this could be attributed to the character of RCA, whose adhesive mortar and cracks caused by procession have an adverse effect on the behavior of the concrete matrix. Furthermore, due to the high brittleness of RAC, the radial crack propagation was normally unstable [49]. As shown in Figure 10, the radial cracks extending from the bottom to the top run along the W-E direction toward the impact point, simultaneously with the crack widths being gradually reduced. The radial crack \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**RCP Specim**} & \multicolumn{3}{c}{**Bottom Surface**} & \multicolumn{3}{c}{**Top Surface**} \\ \cline{2-7}  & **Crack Pattern** & **Num of Crack** & **Maximum Crack** & **Crack Pattern** & **Num of Crack** & **Maximum Crack** \\  & & & **Widths** & & **Widths** & **Widths** \\ \hline
6 MR & radial crack, diagonal crack & 21 & 1.60 & radial crack & 1 & 0.08 \\
7 MR & radial crack, diagonal crack & 9 & 1.80 & radial crack & 1 & 0.12 \\
8 MR & radial crack, diagonal crack & 7 & 1.80 & circumferential crack & 2 & 0.08 \\
7 MN & radial crack, diagonal crack & 8 & 1.46 & radial crack & 2 & 0.06 \\
7 MiR & radial crack, diagonal crack & 14 & 1.50 & circumferential crack & 2 & 0.04 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Final crack properties of all RCP specimens. Figure 9: Sketched cracks profiles of the (**a**) 6 MR specimen, (**b**) 7 MR specimen, (**c**) 8 MR specimen, (**d**) 7 MN specimen, and (**e**) 7 MiR specimen. widths of 7 MR on the top surface were larger than those of 7 MN. Furthermore, the radial crack of 7 MR extended to the impact point, while the radial crack of 7 MN extended only a quarter of the slab span.