Surveying the building stock of Graz with regard to a circular economy in the construction sector

Construction consumes about 40% of resources globally. The switch to a circular economy model in the building industry can contribute to the reduction of use of resources, and lower the environmental impact by extending the life cycle of building components and materials. However, circular economy principles in building industry are not yet established, while at the same time the complexity and consequences of such a transition require further research. The objective of the exploratory study “City Remixed”, whose first results are discussed in this paper, is to identify re-use and recycling potentials of Graz's building stock for the city of Graz, in order to initiate the transformation of the building sector of the city towards the circular economy. Considering the city of Graz and its surroundings in a reasonably short transport distance as a closed system, we started by quantifying the existing building stock in form of a digital 3D model as shown in this paper. In addition to the recording of the materials or construction elements present in buildings and infrastructure (networks) and quasi bound in them with regard to type of building material, quantity, condition and position in a geoinformation system ("urban cadastre"), the expected future time of availability of the material or construction element is also to be recorded digitally. In the future we will enrich the model with metadata, in order to enable the investigation of re-use and recycling potential of the components and materials as well as to determine companies, manufacturers testing and certification institutes that are necessary for these processes. Finally, we will develop renewal scenarios based on the existing building stock, as a result of possible component and material flows. From this process, we identify the fields of action, we settle decision-making bases and provide recommendations with regard to the transformation to a circular economy for different stakeholders, including the citizens. In this context digital technologies allow the storage, retrieve, management and update of large amounts of information, support the development of circular economy scenarios, which in turn offer a simple way towards the re-use and recycle of materials in the building industry.