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 (CO2), methane, and nitrous oxide, as well as the oxidation of nonmethane, nonmethane volatile organic compounds, and carbon monoxide to CO2. 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%.