Life-Cycle Greenhouse Gas Emissions of Materials Used in Road Construction

This paper provides a comprehensive summary of greenhouse gas (GHG) emissions factors for producing asphalt concrete (referred to as “asphalt”) and portland cement concrete (referred to as “concrete”) pavements. Life-cycle emissions factors are provided for the key components of upstream emissions. GHG components included carbon dioxide (CO 2 ), methane, and nitrous oxide, as well as the oxidation of nonmethane, nonethane volatile organic compounds and carbon monoxide to CO 2 . The approach described in this paper enabled the evaluation of emissions from hot-mix, warm-mix, and cold-mix asphalts with assumptions on heating requirements for each. The sources used for the emissions factors were derived from existing sources and models, and a key contribution was the synthesis of these factors for ready use by transportation agencies. Results of the comparison of hot-mix asphalt, warm-mix asphalt, and concrete revealed that warm-mix asphalt might have had as little as 34% of the life-cycle GHG emissions of concrete and 76% of those of hot-mix asphalt. Substitution of fly ash for 25% of the cement in concrete reduced global warming potential by 22%.