An experimental study on the recovery of the hardened cement from crushed end of life concrete

In the C2CA concrete recycling process, autogenous milling of the crushed End of Life (EOL) concrete is a mechanical method to remove cement paste from the surface of aggregates. During autogenous milling, the combination of shearing and compression forces, promotes selective attrition and delivers a better liberation. In order to investigate the effects of shear and compression on the cement recovery and specify the importance of them, a new set-up is designed and constructed. This set-up permits aforesaid forces to be determined and controlled. For experimental design, the MINITAB 16 software was used and 13 different experimental runs based on varying shear and compression forces were conducted. After each experiment, the amount of cement recovery using XRF analysis, water absorption of the recycled aggregates and energy consumption during the process were measured. Results show that both shear and compression forces have in?uence on improving the cement recovery. With simple changes in the setting of an autogenous mill like bed height or residence time the need for high-cost secondary crushing during concrete recycling could be eliminated.