Recovery and activation of recycled concrete powder using thermo-mechanical process

Abstract

The use of recycled concrete powder (RCP) from concrete recycling as a cement replacement is an important area to reduce the environmental impact of concrete. Although the performance and benefits of RCP have been demonstrated in previous studies, much less is known about the separation and recovery method of RCP, and its effect on the rehydration potential (i.e., activation) of recovered RCP. Thus, we investigate a thermo-mechanical recovery (TMR) process for the recovery and activation of RCP from industrial concrete waste. We found that the TMR process results in an RCP recovery rate of 8.5 % whereas a conventional jaw crushing method could only recover 1.1 % of RCP. In addition, the TMR process effectively recovers and activates cementitious phases in the recovered RCP, resulting in approximately 29 % reactive phases, primarily comprising dehydrated phases (belite and brownmillerite) and residual unhydrated cement phases, together with about 34 % amorphous phases, based on the total mass of the RCP. This leads to the significant rehydration effect of TMR-RCP with comparable strength at 3 and 7 days for 10–40 % cement replacement levels while 28-day strength at 40 % replacement level reaches 77 % of the cement control sample. The findings demonstrate that the TMR process is a promising approach to recover and activate RCP from concrete waste for cement replacement.