Development of a Consumption-Weighted Benchmarking Methodology for Asphalt Cradle-to-Gate Global Warming Potential in Colorado

Abstract

Green public procurement policies in the United States are beginning to require benchmarking of construction materials’ global warming potential (GWP) values for government environmental policies and programs. At the state level, Buy Clean legislation requires state transportation departments to measure and reduce the greenhouse gas emissions of construction materials. This study proposes a cradle-to-gate (A1 to A3 life cycle phases) GWP benchmarking methodology for hot-mix asphalt mixtures in Colorado. Statistical analysis of GWP results and a review of Colorado Department of Transportation (DOT) asphalt mixture types indicate that Colorado GWP asphalt benchmarks should be subdivided into five primary mixture types. For each of the five mixture types, a limit value benchmark data set was generated from published Environmental Product Declarations (EPD) data, and a reference value benchmark data set was generated from job mix formulas submitted to Colorado DOT projects. The reference value benchmarks were consumption weighted by the quantity of the mix placed on Colorado DOT projects. The limit value data set and reference value data set were divided into percentiles (or quantiles) to compare with industry averages and national benchmarks. For the five primary mixture types, the average Colorado DOT consumption-weighted reference value was 5% to 29% higher than the average GSA national benchmark value as a result of the required inclusion of a minimum of 1% hydrated lime in Colorado DOT mixtures, which highlights the need for regional data when calculating local or state benchmarks. The reference value benchmark results indicate that consumption weighting yielded slightly different GWP values than an unweighted analysis, but with meaningfully different procurement implications.