鋪面整修工程之節費與減碳對策

Abstract

為找出適用我國環境的鋪面整修節費減碳策略、了解鋪面整修時之成本與二氧化碳排放量之關聯性，進而評估鋪面整修減碳對於國家減碳目標的貢獻潛力，本研究以鋪面工程之整修為標的，透過文獻回顧、專家訪談與模式推導等方式，發現對於節費減碳最重要之關鍵在於「降低單次施工所需之天然資源使用量」以及「減少分析年限內所需之施工次數」，可分由材料、施工和設計三方面加以著手研擬適用之節費減碳方案，可能之方向包含：使用再生瀝青混凝土、提升施工品質(降低初始IRI)、增加密級配結構厚度以及改使用SMA進行刨除回鋪等四類。 研究以生命週期觀點量化評估各種策略在節費與減碳之適用性，將分析年限長度設定為40年，使用美國AASHTO 最新版本之MEPDG鋪面設計法軟體，搭配符合國內國道之基本環境條件進行交通量及鋪面結構設定，進行每次刨除重鋪之服務壽年預測，進而對各方案於分析年限內之財務成本花費與二氧化碳排放量進行盤查。評估結果顯示，提升施工品質(降低初始IRI)之策略均既節費又減碳，於財務永續和環境永續方面均有最佳的成效。效率次之則為使用再生瀝青混凝土，在節費和減碳上均有正面效益。加厚密級配厚度於中交通量時對節費及減碳兩項指標均無正面效益，財務成本上造成的負面效應較環保的影響要大，僅有在高交通量時，若不過度加厚密級配結構，則略有減碳效果但花費之成本仍高於0方案。使用SMA混凝土取代刨除回鋪時之一般瀝青混凝土能夠節費也能減碳，財務節省效果相當好，比使用再生瀝青混凝土表現更佳，但減碳效果不明顯，其生命週期內之排碳量幾乎與0方案相同。短期內，我國主管機關若欲追求節費與減碳，應先從兩方面績效均最佳，且最容易推動達成之提升施工品質做起。 溫室氣體減量與管理法之通過後，未來行政院各部會均配有各自之減碳責任，且碳排放將會被量化以配額方式管制。我國目前尚未開始對二氧化碳排放徵收排放費或碳稅，但若未來各項施工活動必須被課徵碳稅或購買碳排放權時，使用添加刨除料之再生瀝青混凝土可負荷每公斤1.70元至8.37元之碳價，已較我國一般減碳成本每公噸750元(約每公斤0.75元)明顯要高，而降低初始IRI則可提供更高之排碳成本容忍度，故未來交通部可考慮使用減碳效果較佳的整修策略來換取更多排放權。 鋪面整修之節能減碳迄今並未被納入交通部之節能減碳行動方案中。以現況而言環保署建議交通部應分配每年約79.2萬公噸二氧碳之減量責任。依據本就之估算結果，鋪面整修時若將初始IRI降低至100 in./mi. (約1.57m/km)，平均每年可以減碳10,831噸，佔運輸部門一年需減碳79.2萬公噸之1.37%。對於我國現況而言，提升鋪面刨除除鋪施工品質、延長每次整修的服務壽命實為首要工作。

The aim of the study is to find out feasible strategies for cost-saving and carbon reducing of pavement rehabilitation (milling and overlay) and estimate the potential of CO2 reduction of pavement rehabilitation strategies by lifecycle cost inventory and CO2 emission inventory. According to literature review, expert interview, and model derivation, it was found that the most important factors for cost saving and CO2 reduction are lower expense of natural material and longer service life of each milling and overlay. Alternatives evaluated in this study are designed based on change of material (by reclaimed asphalt mixture and stone matrix asphalt mixture, improve construction quality (providing lower initial roughness), and thicker dense grade layer of the pavement structure. The length of the analysis period in this study is 40 years of operation and maintenance of pavement that set based on the characteristic of the National Freeway in Taiwan. The software of AASHTO (American Association of State Highway and Transportation Officials) latest design guide, MEPDG (Mechanistic-Empirical Pavement Design Guide) is used to predict the length of service life that every milling and overlay provides of each alternative. All factors that used in the simulation, like amount of daily truck traffic, basic structure, and climate are set as close as possible to the real situation in Taiwan. The analysis shows that lower initial IRI (International Roughness Index) leads to the least CO2 emission and rehabilitation cost. Improving the construction quality provides the best performance for financial and environmental sustainability. Secondly, using reclaimed asphalt mixture also shows good performance in the two phases. Thicker dense grade layer does not benefit to neither economical nor environmental phases. Using SMA mixture as replacement of part of dense grade layer has benefits on cost saving, but does not make significant contribution to CO2 reduction. For the short term, improving construction quality is what Taiwanese highway agencies should do first to save maintenance cost and reduce CO2 emission. Although Taiwanese government does not levy a tax on CO2 emission so far, with the trend of CO2 reduction across the world, it is possible that all of the emission must pay for carbon rights. Since some of the alternatives evaluated in this study shows good performance on reducing CO2 emission, like lower initial IRI and use reclaimed asphalt mixture, those methods should be applied to exchange more carbon rights for road rehabilitation. Those alternatives also provide good potential on CO2 reduction. For example, it is suggest that the authority must reduce 7.92 million tons of CO2 every year to meet the national emission reduction targets. According to the inventory in this study, if the initial IRI of highway pavement has been lower to 100 in./mi. (1.57 m/km), the amount of CO2 emission would decease 10,831 tons, about 1.37% of the reduction target (7.92 million tons). Improving the construction quality is undoubtedly the most urgent task for Taiwanese road agencies.