Enhancing quality and strength of recycled coarse and fine aggregates through high-temperature and ball milling treatments: mechanisms and cost-effective solutions

The effects of high-temperature treatment and ball-mill treatment on recycled coarse aggregates (RCA) and recycled fine aggregates (RFA) were investigated in this study by comparing the physical properties such as water absorption, void ratio, density, crushing index and residual paste content of recycled aggregates before and after treatments and the flexural and compressive strengths of concrete/mortar made from 100% RCA/RFA. The results show that the combination of high temperature and ball milling significantly enhanced the physical properties of the recycled aggregates (RA), and improved the mechanical properties of the recycled aggregate concrete/mortar. The mechanism of thermal treatment to RA is that the aggregate and attached mortar show different thermal expansion at high temperature, and the connection between aggregate and residual mortar will be weakened, which makes it easier to separate during grinding. Through the ball milling, frictional collisions between different aggregate particles as well as between aggregate and grinding balls can strip and separate the attached surface mortar. In addition, ball milling improves the appearance and shape of the aggregate, resulting in smoother edges and smoother corners, and breaks up and removes light materials such as mortar adhering to the RA. Besides, the cost calculation shows that the treatment cost of RCA and RFA could be lower than the direct usage cost of natural aggregates. From the perspective of considering the actual ecological benefits and resource utilization, more low-cost treatment methods such as ball milling could be a good option to optimize the RA.