# Dynamic Response of Reinforced Recycled Aggregate Concrete Pavement under Impact Loading
## 3 Experimental Results and Discussion
### Displacement Response
The 8 MR specimen always maintained a large displacement value at D1 and D2, indicating that when the drop-weight impacted against the 8 MR specimen, almost all the impact energy was dissipated through global deformations. As described in Section 3.2, the 8 MR specimen had the fewest number of radial cracks on the bottom surface among all RCP specimens. At the same time, as the velocity of drop-weight progressively slowed down with the increase of displacement, the circumferential cracks were formed on the top surface near the impact area. As can be seen from Figure 11, under first impact, the RCP specimen reached the peak downward displacement and then rebounded upward. The amplitude of D1 and D2 rebound displacement changed differently between specimens. For 7 MR, 6 MR, and 7 MN, the peak upward displacement at D2 point were \(-\)2.53 mm, \(-\)1.79 mm, and \(-\)1.49 mm respectively (downward is positive), while the peak upward displacement at D1 point remained positive. The specimen showed a trend of reverse bending deformation, and the \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**RCP** & \multicolumn{3}{c}{**D1**} & \multicolumn{3}{c}{**D2**} \\ \cline{2-7}
**Specimen** & \(\omega_{\text{p1}}\) & \(\omega_{\text{r1}}\) & \(\omega_{\text{fr1}}\) & \(\omega_{\text{p2}}\) & \(\omega_{\text{r2}}\) & \(\omega_{\text{r2}}\) \\ \hline
6 MR & 15.87 & 7.46 & 9.24 & 9.80 & 5.04 & 6.83 \\
7 MR & 16.40 & 7.54 & 9.67 & 9.75 & 4.67 & 5.83 \\
8 MR & 17.10 & 8.47 & 10.42 & 11.61 & 5.91 & 7.89 \\
7 MN & 14.60 & 6.84 & 8.50 & 10.55 & 5.27 & 6.23 \\
7 MIR & 15.25 & 6.63 & 8.16 & 11.53 & 5.34 & 6.66 \\ \hline \hline \end{tabular} \(\omega_{\text{p1}}\) and \(\omega_{\text{p2}}\): the peak displacement at D1 point and D2 point, respectively; \(\omega_{\text{r1}}\) and \(\omega_{\text{r2}}\): the residual displacement under first impact at D1 point and D2 point, respectively; \(\omega_{\text{r1}}\) and \(\omega_{\text{r2}}\): the final cumulated residual displacement at D1 point and D2 point, respectively.  
\end{table} 
Table 8: Displacement response of all tested specimens. stress wave bounced back from the base to the surface to form tensile stress, which could further explain the radial cracks which appeared on the top surface of these specimens. For 8 MR and 7M1R specimens, the upward displacements of D2 point were relatively small, and the radial crack development was limited due to the higher stiffness. The 8 MR specimen with the minimum reinforcement ratio had the maximum final cumulative residual displacement, while the 7M1R specimen with the maximum reinforcement ratio had the minimum final cumulative residual displacement. The final cumulative residual displacement of the RCP specimen was found to correlate with the reinforcement ratio more than with other factors. Research addressing the displacement shapes of the RCP specimens could provide more information regarding the impact response, which was difficult to directly observe in the displacement analysis at D1 and D2 points. Therefore, the displacement shapes of the RCP specimens were addressed in this paper, which provides a quantitative index for comparing the global impact responses of the RCP specimens. Accelerometers A1 and A2 were arranged along the same axis as displacement sensors D1 and D2, which were 50 mm away from the left and right sides of D1 and D2, respectively, as shown in Figure 4. As described in Section 3.1, the acceleration-time history \(a\)(t) at A1 point and A2 point of the RCP specimens were recorded by A1 and A2 accelerometers, respectively.