In the last issue of LINEAR AKTUELL, the article "Sustainable construction with Cradle to Cradle" (short: C2C) dealt with the topic of how buildings and the materials used can be designed in advance to be recyclable in accordance with the C2C concept, so that at best they can be seamlessly returned to the cycle of re-usability after their utilization phase. In line with the guiding principle of "storing" raw materials for future use in the form of buildings or goods and building them in such a way that the deconstruction of these valuable materials does not pose any difficulty. In this way, buildings would be interpreted as raw material deposits for future generations. However, to enable this transformation to a circular economy, a transitional state is needed that prepares the construction industry for the challenges of a circular economy and brings it closer, step by step.
Urban mining is a principle that closes precisely this gap, explains Dirk Hebel, architect and professor of design and sustainable building at KIT (Karlsruhe Institute of Technology). According to this principle, existing "raw material mines" are to be used, for example in the form of buildings. These "urban mines" can be exhausted in order to reprocess and use secondary raw materials for new buildings. The term secondary raw material refers to those materials that are recovered from recycled material, such as steel. This is in contrast to primary raw materials, which are taken directly from the source, such as sand or wood from forestry.
For construction to get one step closer to a true circular economy, the design concept of buildings must incorporate the end-of-life and materials have to be installed in a recyclable manner to ensure that the value chain is maintained. Currently, the concept of urban mining is proving to be challenging, as existing buildings and goods are not designed to be returned to the recycling loop at the end of their useful life. The currently prevailing straightforward economic model that proclaims, "take, make & waste" rather contrasts with the idea of recycling. Thus, irreversible compounds are created by bonding or mixing in the material flow, which are thus inseparable or can only be recycled at great expense. On this basis, the extraction of resources from anthropogenic space is an energy- and time-consuming undertaking.
Nevertheless, it is worthwhile. The president of the Federal Environment Agency, Maria Krautzberger states, that the material assets in Germany amount to around 50 billion tons. And this value increases by 10 tons per inhabitant every year. Thus, raw materials have been tied up in buildings, infrastructures, industrial structures and durable consumer and fixed goods over many years. These potentially represent immense benefit for future generations. Particularly for a country like Germany, which primarily imports raw materials due to a lack of resources, taking existing materials into account is a real gold mine in view of the scarcity of resources.
To ensure sustainable access to these resources, meticulous cataloging of the materials used in buildings is required. After all, not every building has the same suitability for recycling-oriented deconstruction.