Macro-mesoscopic investigation of cushioning mechanism of recycled concrete aggregate under successive rockfall impacts

Cushion materials can effectively reduce the impact load acting on the rigid protective structures such as shed tunnel and improve the impact resistance of the structures. In order to investigate the variation of cushioning performance of recycled concrete aggregate (RCA) under successive impacts, drop weight impact tests and discrete element simulations are carried out. Test results show that compared with the quartz sand cushion, the transmitted load at the center of concrete shed for RCA under the first impact reduces by 83%, and it is distributed more uniformly. With the increase in the number of impacts, the cushioning performances of both the RCA and quartz sand deteriorate. For the sixth impact, the maximum transmitted loads at the center of concrete shed for RCA and quartz sand are 11.2 times and 1.4 times those of the first impact, respectively. Furthermore, the cushioning performance is strongly influenced by particle shape. The numerical simulation results show that when the proportion of strip particles increases from 0% to 100%, the rotation angle and translation distance of the particles decrease by 40% and 20%, respectively, and the maximum drop weight impact load increases by 37%. The inter-locking effect between particles increases with the irregularity of particle shape, which limits the rotation and translation of the particles, and increases the drop weight impact load and the transmitted load on the concrete slab. The research results may provide theoretical basis and engineering guidance for RCA as a new type of eco-friendly cushion.