# Dynamic Response of Reinforced Recycled Aggregate Concrete Pavement under Impact Loading
## 3 Experimental Results and Discussion
### Displacement Response  
The displacement-time histories of D1 and D2 are shown in Figure 11, and it is found that the displacement-time history shapes of all RCP specimens are similar in terms of magnitude, time response, and residual displacement. With each impact event performed, the RCP specimen exhibited progressively increasing peak displacements, and  
Figure 10: Radial cracks extending from the bottom to the top. then decreased to a stable residual displacement, followed by few small displacements due to rebounding of the drop-weight after impacting the RCP specimen. It should be recalled that the magnitude of first impact was very high compared with other subsequent peaks; therefore, the peak displacement and residual displacement due to the first impact were recorded in Table 8. The final cumulated residual displacement would affect the performance of the RCP specimen; it was also recorded in Table 8. It can be seen that the displacement at D1 point was larger than that at D2 point for all RCP specimens from Figure 11. This is because when the drop-weight impacted the top surface, due to the limited impact area, sufficient impulse should be provided in this area to prevent the drop-weight from falling until it stopped. Therefore, compared with other areas, the stress around the impact area was greater, the damage was more serious, and the deformation was more obvious. Figure 11: Displacement -time histories of the (**a**) 6 MR specimen, (**b**) 7 MR specimen, (**c**) 8 MR specimen, (**d**) 7 MN specimen, and (**e**) 7M1R specimen. As can be seen from Table 8, the peak and residual displacements at D1 point of 7 MN specimen were lower than that of 7 MR specimen, reduced by 11.0% and 5.3%, respectively. According to the literature [51; 52], the elasticity modulus of concrete decreased with the increase in RCA replacement ratio. In addition, the micro cracks in adhesive mortar of RCA had a detrimental effect on crack development, which would reduce the stiffness of the specimen. With increased distance from the impact area, both the peak displacement and the residual displacement showed an opposite trend to that of before. The peak and residual displacements at D2 point of 7 MN specimen were higher than that of 7 MR specimen, increased by 8.2% and 12.9%, respectively. This meant that the difference between D1 and D2 was decreasing, indicating that the deformation on the front surface of 7 MN specimen became gentle, and showed more flexural response. The reinforcement ratio plays an important role in peak deflection and residual displacement [47]. As the reinforcement ratio was increased from 0.48% to 0.72%, the peak and residual displacements at D1 point decreased by 7.0% and 12.2%, respectively. The reason for such behavior may be attributed to the fact that more steel bars could effectively arrest the propagation of cracks inside the concrete, thus improving the stiffness of RCP specimens. Compared with the 7 MR specimen, the 7 MIR specimen exhibited smaller displacement amplitudes under same impacts and was expected to be able to undergo larger displacement amplitudes before failure. The variation trend of the displacement at D2 point of 7 MIR specimen was similar to that of 7 MN specimen, and the peak value and residual displacement at D2 point of 7 MIR specimen are 18.3% and 12.1% higher than that of 7 MR specimen, respectively. At D1 point, compared with the peak and residual displacements of the 7 MR specimen, those of the 6 MR specimen had undergone approximately 3.2% and 1.11% decrease, respectively, while those of the 8 MR specimen had undergone approximately 4.3% and 12.3% increase, respectively. The peak and residual displacements of 6 MR specimen and 7 MR specimen at D2 point were not significantly different. In this case, it is thought that before the overall deformation occurred, the impact energy of 6 MR specimen would have been dissipated through the development of the dense radial cracks on the bottom surface.