Balanced Mix Design as an Equalizer to Assess the Environmental Performance of Asphalt Mixtures

Abstract

This study assesses the environmental impacts of asphalt mixtures with high reclaimed asphalt pavement (RAP) content through a comparative life cycle assessment (LCA), using a balanced mix design (BMD) framework to ensure equivalent performance. The study examined 11 different mix designs from four asphalt producers. The asphalt mixes contained a RAP content of either 30% or 40%. The increase to 40% RAP content was achieved using two strategies: 1) employing a softer binder; and 2) incorporating a recycling agent while maintaining the same binder grade. Performance tests on the mix designs provided by the producers indicated that not all met the Virginia Department of Transportation (DOT) benchmarking thresholds for the Indirect Tensile Asphalt Cracking Test (IDT-CT), Asphalt Pavement Analyzer rut depth test (APA), and Cantabro Mass Loss test. Performance test results at various binder contents were, therefore, used in a method referred to as the equivalently balanced mixtures method to estimate the binder contents that would meet Virginia DOT’s BMD benchmarking thresholds. A comparative LCA was then conducted using OpenLCA for these mixes after they were balanced according to Virginia DOT’s selected performance criteria. A reduction in global warming potential (GWP) of 4% to 11% was observed when using 40% RAP compared with 30% RAP in asphalt mixtures. A similar trend was observed for other impact indicators as well, except for eutrophication potential for mixes with recycling agents. The strategy of using a softer binder resulted in greater reductions in GWP compared with the use of a recycling agent.