The Urban Metabolism of Cement and Gravel

都市代謝是指因都市各式產業活動，以及居民居住、工作、飲食育樂等活動，所帶動的各種物質以不同貨物的型式流動，其中流通量最大量也造成對應環境負荷的是營建材料，係用於居住、工商服務、與公共建設，有需要系統性的視野來，分析這些物質如果經過生產、消費、轉換後再從都市釋出的過程。台灣已近1/3人口居住於大台北地區，都市代謝隨著都市成長的脈動而變化，隨著都市建設與人口成長需求，更加倚賴從外地供應的資源，亦累積大量的物質，未來將成為廢棄物或新的資源。都市代謝分析需要一個系統性的框架，以量測和解析資源投入的趨勢，對於都市消費、廢棄物處置、與都市社會經濟的永續發展有何關聯性。 本研究以台北市及新北市十年間之水泥與砂石相關之物質流的變化描繪動態的都市代謝現象，並探討與相關都市社會經濟活動的關係，代謝標的物質為水泥及砂石兩種物質，調查的系統範圍含蓋各式營建工程，包括公共工程（包含道路、橋樑、防洪、管線、捷運工程）及建築工程兩個子系統，盤查各系統程序的物質流，並解析都市代謝趨勢與過去都市政策、社會經濟因子的關係。另外，運用指標比較兩都市，兩物質的代謝密集度，並計算水泥、砂石在都市建設的二氧化碳排放當量。 結果顯示兩市之水泥砂石代謝，以建築工程為主要驅動力，其次為道路改善維護工程，另一方面平均每年產生447噸之營建混凝土廢棄物。回顧過去的發展政策與社會經濟趨勢，建築工程建案會受到如全球金融風暴、歐債危機及政府都市政策影響，而道路工程會因建設、選舉前夕及路平專案計畫等，使工程數量增多。在環境面，都市水泥砂石代謝所導致的材料製程碳排放以建築工程為大宗，主要來自水泥生產過程。未來營建廢棄物處置將是一個問題。建議政府針對改變建築結構、提高閒置空間再利用率、檢討道路政策、共同管道設置、營建廢棄物處置問題等，以提升都市代謝效率的永續性。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