The realization of dematerialization and decarbonization is an important goal towards sustainable society. In recent times, OECD countries have initiated some measures to decrease environmental impacts and increase resource efficiency. In Japan, in order to pursue a “sound material-cycle society”, the government has been actively advancing the improvement of resource productivity and recycling rates of the country. In particular, wastes of construction minerals, which accounts for more than 30% of demolition, have reached high recycling rates of 97%. However, the spatial evaluation of recycling and material balance is not yet clarified, especially in terms of regional symbiosis and cyclical use, which debilitates the efficient usage of recycled material. This research evaluates the optimal size of regional recycle zones for cyclical material usage of construction minerals in Japan, from 2010 to 2050. Two major models were created for this objective. The first is a construction demand model to estimate building floor area and road area to be constructed, accounting for population distribution changes. The second model is an aggregate transportation model that provides the transport paths of recycled materials in a self-organized process. By integrating these two models, the optimal sizes of regional recycle zones were estimated. Additionally, scenarios of building lifespan were chosen for future analysis: a business-as-usual scenario which keeps Japan’s current average building lifespan of 38 years, and a second scenario which assumes gradual changes to the parameters of demolition curves to double building lifespans by 2050. These reveal that concrete mass demolished from the building sector will be in surplus to the input demand of road construction, especially in urban areas. It is also indicated that the optimal size for regional recycle zones should be within 40 km in radius, as a result of longer lifespans of buildings in the future.
Prof. Hiroki Tanikawa