The Urban Metabolism of Cement and Gravel

Urban metabolism is the manifestation of dynamic materials of city, including the processes of import, supply, transformation, consumption, export, and other activities involving the flow of materials. Different processes are required to sustain a city. One-third of Taiwan population live in the Taipei metropolis. Since Taipei and New Taipei City have expanded dramatically, especially, the construction activities have consumed massive materials that were imported from other areas. Cities are also accumulating massive stock of materials which will turn into waste or secondary resource. An analytical framework of urban metabolism is essential for the sustainable development of cities. This research aims to measure the flows in an urban metabolic system and analyze the social-economic factors which led to the increase of consumption of cement, sand and gravels. This understanding is the basis to formulate the strategies to alleviate the pressure of resource consumption, waste generation and CO2 emission, in terms of long term urban sustainability. In my study, the material flow analysis were implemented to investigate the metabolism of Taipei city and New Taipei city. Cement, sand and gravel are chosen for the focus of the analysis because they are the major material in construction industry. The material flow system is composed of two subsystems that are infrastructure (such as road, bridge, flood prevention projects, MRT, piping,) and construction of buildings. The data collected for Taipei metropolis ranges from 2004 to 2013. To understand the factors which drives the urban metabolic activities, this research examined urban development policies and several socioeconomic factors for their possible influences on the variation of urban metabolism. Several indicator are calculated to measure carbon footprint, generation of demolition waste and intensity of material consumption. The results show that the top consumption of construction material in the Taipei metropolis is dominated by the construction of buildings, the second one is road improvement and road maintenance. Every year, about 447 metric tons waste concrete were generated in the last decade. The factors of major influence on the metabolism includes the financial crisis in 2007 to 2008, Eurozone debt crisis and emergence of new urban zoning. It was found that the road work increased dramatically due to Road-smoothing project and short term urban construction which might be influenced by the election. The manufacture of cement accounts for the most of CO2 emission, the main driver of CO2 emission is the need for construction new buildings in both cities. An issue is how to face current material stock after the demolition as waste in the future. For the solutions of sustainable urban metabolism, the cities should transition the construction of buildings toward the structure types of less environmental pressure of build. Also, current unoccupied indoor spaces should be used more efficiently. Auditing on the necessity and frequency of road maintenance should be implemented, build common duct, deal with waste concrete disposal for urban metabolism efficiency rises.