High-quality coarse aggregate recycling from waste concrete by impact crushing

This study presents a liberation process for recycling high-quality coarse aggregates from waste concrete by impacting with steel grits. Considering the mortar liberation ratio and specific energy for the liberation process as well as the water absorption and apparent density of the recycled coarse aggregates (RCA), the effects of impact velocity, impact time, and concrete strength on the quality of the RCA are investigated. The results show that larger impact velocity or longer impact time of the steel grits is advantageous for improving the mortar liberation ratio and the apparent density of the RCA, as well as reducing its water absorption. A high-velocity short-time impact is an efficient way to reduce the specific energy. With regard to the concrete strength, the influence mechanism of mortar liberation is relatively complex, and proper impact velocity and impact time should be chosen to obtain the high-quality RCA under lower specific energy. These results suggest that liberating the mortar by particle impacting can recycle high-quality coarse aggregates from waste concrete.