The estimation of stock and flow material in a city as a first step to evaluate the recycling potential and future needs for aggregate. Case study in France
Résumé
Urban areas have accumulated and accumulate in their buildings and infrastructures enormous quantities of material. These stocks, made from the extraction and processing of raw materials, are locked there for a variable period of time (a few decades for some buildings, "eternity" for historical monuments). These materials will one day be "liberated" during development, rehabilitation, deconstruction or demolition works, with often very low traceability in terms of destination and recycling ratio. There is no quantitative or qualitative composition of the stock and building and infrastructures life cycle is often unknown. Stakeholders do not have a global vision of the recycling potential in their city and consequently the organisation of recycling structures and platforms is very difficult. In order to evaluate the potential material stock in a city, regarding to French context, a methodology is proposed based on expert/observed ratios (material compositor indicators), as it was done for example in Germany (Ortlepp et al. 2015). Individual characterization of each building is not adapted because no database containing all necessary information really exists. Built-up areas of the cities have been characterized by use-types (dwelling, commercial, industrial, and public services), construction age and structural type as for example old constructive techniques as unreinforced stone masonry or newer techniques as reinforced concrete. Building geometry (floor area, height) is taken from national GIS databases (IGN). Other elements as roads and street surfaces and underground lifelines are also considered. For each combination of building types, material ratios are proposed (for example tons of concrete per super built-up area). Combining ratios with the estimated super built-up area in the city (in this case Orléans city, in France) a total tonnage is calculated, divided into main materials groups (inert, metal, wood, plastics, gypsum). Moreover, looking at main construction and demolition works in Orléans city from 2004 to 2006, material inflows and outflows were estimated. During this period the stock was increased, meaning that the city was growing and cumulating stock.