sustainability Article Matching Demolition and Construction Material Flows, an Urban Mining Case Study Teun Johannes Verhagen 1, * , Marijn Louise Sauer 2 , Ester van der Voet 1 and Benjamin Sprecher 1   Citation: Verhagen, T.J.; Sauer, M.L.; van der Voet, E.; Sprecher, B. Matching Demolition and Construction Material Flows, an Urban Mining Case Study. Sustainability 2021, 13, 653. https:// doi.org/10.3390/su13020653 Received: 11 December 2020 Accepted: 8 January 2021 Published: 12 January 2021 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional clai- ms in published maps and institutio- nal affiliations. Copyright: © 2021 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Institute of Environmental Sciences, Leiden University, 2333 CC Leiden, The Netherlands; voet@cml.leidenuniv.nl (E.v.d.V.); sprecher@cml.leidenuniv.nl (B.S.) 2 Leiden Municipality, 2333 CW Leiden, The Netherlands; m.sauer@leiden.nl * Correspondence: t.j.verhagen@cml.leidenuniv.nl Abstract: The recycling of demolition waste is essential to lower the construction sectors primary material demand, responsible for 50% of the global primary material consumption. Almost all demolition waste is used as filler material for the construction of roads, preventing further reuse or recycling after this application. The built environment generates considerable annual material in-and outflows. However, there has been little discussion on the availability and further application of this potential supply of secondary materials as a replacement for primary materials. In this study, we quantify the percentage of demolition waste that can be repurposed as secondary materials in the Dutch construction sector. We analyzed the yearly building material flows for the municipality of Leiden using municipal data on demolition and construction to explore the viability of the Dutch government’s policy goal to reduce primary materials consumption by 50% before 2030. From this analysis, we find that the recycling of demolition waste has a sizable potential but just falls short of the stated policy goal. Even in a situation with more construction than demolition, there will remain a considerable mismatch in the yearly construction material demand and available supply of demolition waste for our municipal-wide case study. More importantly, the current processing of demolition waste in the Netherlands will require significant improvements to achieve this goal. New governmental policies are required to focus on maintaining material quality and allowing further use of recycled materials as buildings materials. Keywords: urban mining; circular economy policy; GIS 1. Introduction The worldwide extraction of materials has tripled over the past 40 years. Driven by the urbanization of the developing world and an ever-growing population, the global demand for materials is expected to triple again before 2050 [1]. The construction sector is currently responsible for a significant share (50%) of this material demand [2]. In Western Europe, the construction sector accounts for 40% of primary material use [3]. At the same time a substantial percentage of the built environment is demolished each year, especially in already developed urban regions, which generates large volumes of waste that could be reused as secondary construction material. Currently, construction and demolition waste (C&DW) is most commonly reused as aggregates as road foundation [4]. The materials are downcycled, and further reuse is not possible. To prevent this wasteful form of reuse, one can look at urban mining as a concept for reclaiming and high-level recycling materials from the built environment [5,6]. Based on the European Commission’s Circular Economy Action Plan, the Dutch government formulated its circular economy policy to reduce the country-wide use of primary materials (minerals, metals, and fossil fuels) by 50% before 2030, including the construction sector [7,8]. In this paper, we quantify to what extent secondary materials generated through urban mining could replace the primary material demand in the Dutch construction sector. Sustainability 2021, 13, 653. https://doi.org/10.3390/su13020653 https://www.mdpi.com/journal/sustainability