Life cycle environmental impact assessment of a bridge with different strengthening schemes

A large number of highway bridges have been constructed in China since 1980s. Most of the aging bridges are in need of strengthening, which will lead to consuming big amounts of material and energy resources, producing air emissions and solid waste. This paper made a life cycle assessment for a highway bridge with four different strengthening plans by using Eco-indicator 99 to figure a total environmental impact score of the bridge.

Based on analyzing the life cycle assessment (LCA) investigations of bridges, the adopted LCA method for the highway bridge tracks materials and energy resources through the various stages of the bridge life cycle including production, transportation, construction, strengthening, and demolition, considering the impact of vehicle detours during strengthening construction, to calculate environmental impact for ecosystem quality, human health, energy, and resources. This is done for four strengthening schemes, which are traditionally compared based only on the basis of economic cost. In order to account for the variability of critical input variables, a Monte Carlo simulation was performed to estimate the variability of environmental scores associated with the transportation distance, the average fuel consumption for each vehicle, detouring distance, the structure closure period, and maintenance times. Ten thousand iterations were conducted based on previous studies.

The analysis shows that the maintenance phase alone contributes about 66 % of the total environmental impact (including detouring stage 50 %, repaving bridge deck 12 %, strengthening 4 %), followed by material production stage (approximately 40 %). Of the four strengthening plans, plan 1 and plan 3 have relatively greater contributions in terms of environmental damage while the cost budgets are much lower. On the contrary, plan 2 and plan 4 have lower environmental burdens but cost much more. Sensitivity analysis shows that the damage to resources and ecosystem quality are more sensitive to the variation of parameters.

A life cycle assessment for a highway bridge in China with four different strengthening plans is conducted by using Eco-indicator 99 to figure a total environmental impact score of the bridge. It determines that the maintenance phase contributes the most to the environment deterioration. This study also shows that the energy consumptions and pollutant emissions related to traffic disruption during maintenance operations should not be excluded. Regarding the strengthening plans, it can be concluded that the environmental impact of bonding carbon fiber-reinforced polymer is fewer than that of bonding steel plates.