OVERVIEW OF RESOURCE CONSERVATION AND CLOSED-LOOP RECYCLING IN CONCRETE TOWARD SUSTAINABILITY

Providing excellent performance as a structural material, concrete has long been deemed essential for modern civilization and recognized as a material that will continue to maintain and support the development of human society. The sheer amount of concrete in use and in stock compared with other building materials brings up the issue of the enormous amount of waste generated when concrete is disposed of. Besides, resources for good quality aggregate are beginning to be depleted at a high speed. 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. The development history of concrete recycling is summarized in a paper from the viewpoints of the properties and the application of recycled concrete aggregate. The paper categorizes recycling technologies according to the quality of recycled concrete aggregate into several types. Advanced techniques avoid down cycling and recover recycled concrete aggregate, having the same quality as natural aggregate from waste concrete, forming a closed-loop in terms of the resource circulation of concrete materials. However the problems are remained in the energy-induced environmental impact and cost increase. The time has come when establishment of a new design concept for complete recycling of concrete is definitely necessary. The principle of complete recycling is that the concrete is subject to material design to reduce waste generation and facilitate resource circulation in a closed-loop system. Development technology based on such material design is regarded as proactive technology. The materials of concrete should be used as parts of concrete during the service life of concrete and remain usable after demolition as parts of similar or other products without quality deterioration, continuing circulation in various products as the media. The paper introduces a history of development of completely recyclable concrete, with which closed-loop circulation of component materials is realized like steel and aluminum.