Environmental Impacts of Producing Asphalt Mixtures with Varying Degrees of Recycled Asphalt Materials

The environmental impacts of producing asphalt mixtures with different percentages of asphalt binder replacement (ABR) are assessed using the technique of life cycle assessment (LCA). In this paper, only the material production phase of the pavement life cycle is considered. To improve the quality of the LCA, a regionalized life cycle inventory (LCI) database for the Northern Illinois region is compiled for the production of various materials used in flexible pavement construction. Data from local questionnaires, published literature, and commercial LCI databases are used to validate and model unit processes with a LCA software. The environmental impacts modeled include energy consumption and greenhouse gas (GHG) emissions from producing asphalt binder, recycled asphalt materials, and aggregates as well as from operating hot-mix asphalt plants. Using the regionalized LCI database, a partial LCA is used to investigate the environmental effects of producing asphalt mixtures with increasing ABR contents. Eleven mixes containing varying percentages of recycled asphalt pavement and recycled asphalt shingles are analyzed. When compared to a mix with 0% ABR content, 25% ABR mixes show an average decrease of 6.3% in energy and 6.5% in GHGs while a 60% ABR mix shows savings of 20.9% and 21.8%, respectively. In addition, conducting the same case study using asphalt binder LCI data from different sources reveals differences of up to 135 GJ and 9.9 tonnes of CO2e per 3-inch-lane-mile in environmental savings for using the 60% ABR mix, emphasizing the importance of using the most relevant LCI data when performing environmental analyses.