Life Cycle Assessment of Asphalt Binder, Warm Mix Asphalt Additives, and Bonded Concrete Overlay of Asphalt for California Conditions

The UCPRC is updating and expanding the life cycle inventories (LCIs) that are available for materials, pavements, and practices being used in or introduced to California for use in the project-level design software, eLCAP, and in the Caltrans pavement management system,PaveM. This report presents the results of developing LCI for use in life cycle assessment (LCA) for three types of materials or pavement structures being used in California: (1) asphalt binder regionalized to California from a national average, (2) warm mix asphalt (WMA) technologies, and (3) bonded concrete overlay of asphalt (BCOA). These LCIs fill important gaps because asphalt binder environmental product declarations (EPDs) will not be available for several years and very few WMA EPDs are available. The results of the binder LCI showed that California has a typical asphalt binder global warming (GW) of 0.456 kgCO2 eq/kg of binder compared to Petroleum Administration for Defense District (PADD) 5 (western states) at 0.487 and the US/Canada average from the Asphalt Institute (AI) LCA study, which was 0.637. This difference is due to the percentage of heavy Canadian oil sands in the crude oil slates in the AI LCA study compared to PADD 5 and California. In the AI study, the heavy oil imported from Canada is 53% of crude input, 18% in PADD 5, and 3% in California. The results of the main study and of the sensitivity analysis suggest that asphalt binder GW should be considered to be a distribution of values rather than a single value, or, if a single value is used, it should be understood that there can be considerable variability around it. WMA is considered a potential means for reducing energy consumption and emissions during the material and construction stages of asphalt concrete by allowing for the lowering of mixing temperatures in the asphalt plant. WMA can also be used with the same mixing temperatures to allow for compaction at lower temperatures at the construction site, which does not reduce energy and emissions from mixing but can result in better compaction and longer pavement life. When WMA is used to reduce the mixing temperature to the lowest recommended temperature, the net reductions in GW range between approximately 2% and 5%, except for one WMA additive where the reduction in mixing temperature resulted in a net GW increase of 14%. It was found that the material stage can be considered the hot spot due to high environmental impacts and high energy consumption compared with the transportation and construction stages, as expected.