Environmental life cycle assessment of bridge deck pavement and case studies of two bridges in China

Abstract

The durability of deck pavement material has great impact on deck performance and carbon emission. This paper aims to analyze the durability of different deck pavement materials and structures by taking two bridges across the Yangtze River in China as examples, and establish the carbon emission model of the bridge deck pavement during the whole life cycle. The carbon emissions of the two bridges during twenty years of service are then calculated based on the model. It can provide reference for future bridge deck pavement schemes and measures to reduce carbon emissions. In this paper, two typical representative bridges in Jiangsu Province in East China are selected for case analysis, namely the Jiangyin Yangtze River Highway Bridge and the Second Nanjing Yangtze River Bridge. Firstly, this paper introduces the specific forms of various bridge deck pavement schemes since the construction of the two bridges. After many years of experiments, the pavement of the Jiangyin Yangtze River Highway Bridge has changed from mastic asphalt mixture to double-layer hot mix epoxy asphalt concrete, and that of the Second Nanjing Yangtze River Bridge has changed from warm mix epoxy asphalt to hot mix epoxy asphalt. Focusing on the carbon emission of bridge deck pavement, the carbon emission model of different asphalt mixture pavements based on life cycle assessment (LCA) is established. The assessment can be divided into five stages: material production, transportation, construction, maintenance and demolishment. This paper takes extra traffic congestion during repair and maintenance into consideration. In this paper, two bridges were taken as cases to calculate the carbon emission. In initial construction, the deck of the Jiangyin Yangtze River Highway Bridge was paved with mastic asphalt mixture; while the deck of the Second Nanjing Yangtze River Bridge was paved with epoxy asphalt concrete. The paving material of the Jiangyin Yangtze River Highway Bridge was changed into epoxy asphalt concrete gradually in repair and maintenance. The analysis results show that in the initial 20 years of life, considering the initial construction and major maintenance of deck pavement, the total carbon emission of the Jiangyin Yangtze River Highway Bridge and the Second Nanjing Yangtze River Bridge is 179,195 kg CO2e and 101,577 kg CO2e respectively. The unit carbon emission of the Jiangyin Yangtze River Highway Bridge after 20 years of opening to traffic is 5.079 kg/m2 CO2e. The proportions of the five stages were 76.4 %, 2.7 %, 2.5 %, 16.8 % and 1.6 %, respectively. The unit carbon emission of the Second Nanjing Yangtze River Bridge after 20 years of opening to traffic is 3.352 kg/m2 CO2e. The proportions of the five stages were 66.3 %, 2.4 %, 2.6 %, 28.2 % and 0.6 %, respectively. The results show that epoxy asphalt material has better durability and can reduce carbon emission of bridge deck pavement.