Georg Schiller

Material stocks in Germany's non-domestic buildings: a new quantification method

The building sector consumes large quantities of resources and generates high levels of construction and demolition (C&D) waste. From an ‘urban mining’ perspective, the building stock can be seen as a repository of natural resources. In order to manage this repository, evidence is needed on its quantity and dynamics. Although data exist for domestic buildings, little evidence exists for non-domestic buildings. A new method is presented to quantify the material stock of non-domestic buildings – based on the German building stock. The quantification process involves three steps: (1) material composition indicators (MCIs) are calculated with respect to various building types; (2) the countrys total floor space is estimated and disaggregated; and (3) the total material stock is calculated. The main results are MCIs and the floor space for both domestic and non-domestic stocks, as well as the material mass in total. In Germany the total material mass of non-domestic buildings is approximately 6.8 billion tonnes, accounting for 44% of the entire building stock. The method can be adapted and validated for use in other countries. These results will assist both policy-makers and the construction industry to understand the potential for moving toward a more circular economy.

Materials in Germany’s domestic building stock: calculation model and uncertainties

ABSTRACT Building stocks are the dominant consumers of resources within national economies. Correspondingly, there is high demand for improved knowledge of material stocks and flows in the built environment. Material flow analysis is well suited to meet this demand. Although numerous studies have been conducted on this topic over recent years, these frequently lack applicability and transferability due to insufficient documentation or treatment of uncertainties. A new approach is presented here to calculate material stocks and flows for domestic buildings using the example of multi-family housing (MFH) in Germany. The approach is critically examined to determine its validity. The calculation process involves four steps: (1) building types are classified according to building age; (2) highly specific material composition indicators (MCIs) are calculated for the respective building types; (3) the total material stock as well as inflows and outflows are derived from the total floor space of Germany’s MFH; and (4) validity tests are performed to quantify uncertainties. The main results are age-based MCIs for MFH, the total material mass as well as quantitative information on parameter- and model-related uncertainties. Conclusions are drawn on the validity of results, the scalability and applicability of the model and its implementation, along with potential model refinements.

Continuous Material Flow Analysis Approach for Bulk Nonmetallic Mineral Building Materials Applied to the German Building Sector

Summary Material flow analysis (MFA) is a helpful tool to understand and develop the circular economy. There exist a number of MFA models to depict inflows and outflows of bulk nonmetallic mineral building materials, which are, in fact, the largest flows in terms of tonnes. However, until now such models have not attempted to directly link inflows and outflows. In order to achieve such closed loops, it is necessary to consider the qualitative aspects of inflows and outflows as well as quantities. The technical possibilities of recycling are, in fact, determined by both the quality and quantity of materials. This requires the integration of knowledge on process engineering, the technology of waste management, and indeed the structure of buildings. The article integrates these aspects within a continuous MFA approach (C-MFA), which is able to analyze and quantify the entire material cycle of bulk nonmetallic mineral building materials by considering the use of recycled aggregates in concrete building elements. This is achieved by methodological expansions that take into account qualitative aspects with regard to outflows and inflows. The approach is applied to questions of high-quality recycling within the German building stock. The continuity of construction and demolition waste output and secondary material input is realized by integrating the process steps required to capture high-quality waste in the course of building demolition, material processing of the material to produce recycled aggregates, and admixing of the aggregates to produce new concrete used in buildings. This can be extended by considering the inflows and outflows of other sectors, for example, the infrastructure sector. The main outcome is an extended C-MFA approach that enables quantification of sectoral as well as, in principle, intersectoral material loops of bulk nonmetallic mineral building materials while uncovering potentials to save natural resources as well to better exploit anthropogenic resources.

Quantification of anthropogenic metabolism using spatially differentiated continuous MFA

Abstract Coefficient-based, bottom-up material flow analysis is a suitable tool to quantify inflows, outflows and stock dynamics of materials used by societies, and thus can deliver strategic knowledge needed to develop circular economy policies. Anthropogenic stocks and flows are mostly of bulk nonmetallic mineral materials related to the construction, operation and demolition of buildings and infrastructures. Consequently, it is important to be able to quantify circulating construction materials to help estimate the mass of secondary materials which can be recovered such as recycled aggregates (RA) for fresh concrete in new buildings. Yet as such bulk materials are high volume but of low unit value, they are generally produced and consumed within a region. Loops are thus bounded not only by qualitative and technical restrictions but also spatially to within regions. This paper presents a regionalized continuous MFA (C-MFA) approach taking account of these restrictions of local consumption, quality standards and technical limitations, illustrated using the example of Germany. Outflows and inflows of stocks are quantified at county level and generalized by regional type, considering demand and supply for recycled materials. Qualitative and technical potentials of recycling loops are operationalized by defining coefficients to reflect waste management technologies and engineering standards. Results show that 48% of outflows of concrete and bricks are suitable for high-quality recycling, while 52% of outflows do not fulfill the quality requirement and must be recovered or disposed of elsewhere. The achievable inflow to RA is limited by the building activity as well as the requirements of the construction industry, e.g. the RA fraction of fresh concrete must not exceed 32%. In addition, there exist spatial disparities in construction across the country. In Germany, such disparities mean that there will be a shortfall in RA of 6.3 Gt by the year 2020, while the technically available but unusable RA (due to a regional mismatch of potential supply and demand) will total 3.2 Gt. Comprehensive recycling strategies have to combine high-quality recycling with other lower-grade applications for secondary raw materials. Particularly in the case of building materials, essential constraints are not only technical but also local conditions of construction and demolition. These interrelations should be identified and integrated into a comprehensive system to manage the social metabolism of materials in support of circular economy policies.