Minimizing environmental impact and maximizing performance in concrete recycling

The sheer amount of concrete in use and in stock compared with other building materials throws up environmental issues such as the huge amount of CO₂ emitted when cement and concrete are produced and transported and the enormous amount of waste generated when concrete is disposed of. In addition, we are beginning to deplete aggregate resources at a fast rate. Concrete has conventionally been regarded as being difficult to recycle. The construction industry has addressed these problems and carried out research and development regarding the recycling of concrete since the 1970s. Recycling technology has been shifting from simple crushing into scrubbing with some preparations to produce high-quality recycled aggregate for structural concrete, and recycling of concrete in a completely closed loop has now become technically feasible. This paper reviews the development history of recycling technologies in Japan from the viewpoint of the properties of recycled aggregate and recycled aggregate concrete as well as the environmental impact such as CO₂ emissions and waste generation in recycling. The paper also presents the outline of completely recyclable concrete, with which closed-loop circulation of component materials is realized.