Socio-economic metabolism of urban construction materials: A case study of the Taipei metropolitan area

Material stock is an urban issue related to urban mining. In recent years, urban metabolism issues, i.e., the determination of urban stability, have also emerged as important. The manifestation of dynamic materials in a city involves processes of importing, supply, transformation, consumption, and exporting and other activities involved in the flow of materials. Socioeconomic factors must be considered to transform study results into useful policies. This study examines cement and gravel flows in Taipei and New Taipei City to explore such concepts. Our results show that more than 80% of the construction material use in Taipei and New Taipei City is mainly dedicated to the construction of buildings and secondarily to road improvements and road maintenance. Approximately 447 t of waste concrete is generated each year, and the consumption of cement and gravel in Taipei and New Taipei City has grown over the last decade. Factors that have heavily affected urban metabolism patterns include the slowdown of economic activities after the financial crisis of 2007–2008 and the emergence of new urban zoning laws. We find that roadwork has intensified dramatically due to road-smoothing and short-term urban construction projects, which may have been influenced by elections. This study measures flows in an urban metabolic system and examines socioeconomic factors that have led to an increase in the consumption of cement and gravel.