Abstract
A cradle-to-grave life cycle assessment is done to identify the environmental impacts of chromated copper arsenate (CCA)-treated timber used for highway guard rail posts, to understand the processes that contribute to the total impacts, and to determine how the impacts compare to the primary alternative product, galvanized steel posts. Guard rail posts are the supporting structures for highway guard rails. Transportation engineers, as well as public and regulatory interests, have increasing need to understand the environmental implications of guard rail post selection, in addition to factors such as costs and service performance. This study uses a life cycle inventory (LCI) to catalogue the input and output data from guard rail post manufacture, service life, and disposition, and a life cycle impact assessment (LCIA) to assess anthropogenic and net greenhouse gas (GHG), acidification, smog, ecotoxicity, and eutrophication potentially resulting from life cycle air emissions. Other indicators of interest also are tracked, such as fossil fuel and water use. Comparisons of guard rail post products are made at a functional unit of one post per year of service. This life cycle assessment (LCA) finds that the manufacture, use, and disposition of CCA-treated wood guard rails offers lower fossil fuel use and lower anthropogenic and net GHG emissions, acidification, smog potential, and ecotoxicity environmental impacts than impact indicator values for galvanized steel posts. Water use and eutrophication impact indicator values for CCA-treated guard rail posts are greater than impact indicator values for galvanized steel guard rail posts.
Highlights
A highway department’s selection of a guard rail system and its materials primarily is based on safety; factors such as cost, aesthetics, and environmental acceptance play a role in decisions made
A cradle-to-grave life cycle assessment is done to identify the environmental impacts of chromated copper arsenate (CCA)-treated timber used for highway guard rail posts, to understand the processes that contribute to the total impacts, and to determine how the impacts compare to the primary alternative product, galvanized steel posts
This study provides a basis for understanding the environmental impacts associated with the production, use, and final disposition of CCA-treated guard rail posts with comparison to galvanized steel posts
Summary
A highway department’s selection of a guard rail system and its materials primarily is based on safety; factors such as cost, aesthetics, and environmental acceptance play a role in decisions made. While most highway guard rails are made of W-beam galvanized steel, the supporting posts are mostly either preserved wood or galvanized steel; The feasibility of composite materials as guard rail posts, has been studied [1], but the current use does not represent a significant portion of the guard rail post market. While alternative copper-based water-borne preservatives such as alkaline copper quaternary (ACQ) and copper azoles became popular in the early 2000s, CCA is approved for industrial uses [4] and remains the waterborne preservative of choice for many demanding, commercial applications, including guard rail systems. Wood post products fulfill the same function as galvanized steel posts and both products have advantages and disadvantages
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