Bridge life cycle assessment with data uncertainty

PURPOSE: Although life cycle assessment (LCA) has been employed to analyze the environmental impacts of bridges, the uncertainties associated to LCA have not been studied, which have a profound effect on the LCA results. This paper is intended to provide a comprehensive environmental impact assessment of bridge with data uncertainty, by assigning probability distributions on the considered parameters, assessing the variability in the acquisition of inventory and identifying the key parameters with significant environmental impacts. METHODS: A life cycle assessment of a bridge in Shanxi Province of China was conducted in a cradle-to-grave manner, by considering the source of the uncertainty of LCA. A statistical method was applied to quantify the uncertainty of measured inventory data and to calculate the probability distribution of the data. The uncertainty propagation was conducted through using a Monte Carlo simulation. Finally, the factor which is of vital importance to the assessment result was identified by sensitivity analysis. RESULTS AND DISCUSSION: For the case of bridge, normal distribution can be adopted to fit environmental substances and environmental impact in steel production. The distributions of the weighted value of human health damage, ecological system damage, and resource and energy consumption can be represented by an approximate similar normal distribution function. The coefficient of variance (COV) of each weighted value is about 40, 30 to 40, and about 6 %, respectively. The COV for the total environmental impact is about 10 % in all stages of the bridge’s life cycle, except the operation stage, which is up to 22.67 %. By conducting sensitivity analysis, PM₁₀, NOₓ, and oil consumption was found to have a great influence on the result of human health damage, ecological system damage, and resource and energy consumption, respectively. CONCLUSIONS: The COV for the total environmental impact is 22.67 % in the bridge’s operation stage; it is important to establish a reasonable maintenance strategy to decrease the uncertainty of the bridge’s environmental impact. The COVs of the weighted value for human health damage and resource and energy consumption have a quite modest difference among the four stages of the bridge’s life cycle. However, The COV of the weighted value for ecological system damage shows large difference among the four stages of the bridge’s life cycle; construction stage has the greatest uncertainty.