Balanced Mix Design for Surface Mixtures: 2021 and 2022 Plant Mix Schedule Pilots
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2023-06-01
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Edition:Final Report
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Abstract:Many state highway agencies are currently exploring a new approach for designing and accepting asphalt mixtures, known as the balanced mix design (BMD) method (hereinafter “BMD”). The Virginia Department of Transportation (VDOT) has made a commitment to adopt BMD to enhance the performance of asphalt mixtures. Since 2018, VDOT has taken incremental steps to phase in the use of BMD in production while addressing concerns expressed by VDOT and the industry. The use of BMD line items in selected 2021 and 2022 contracts has been an important learning opportunity for VDOT and the industry along the path to implementation. This study documented and assessed the 2021 and 2022 maintenance plant mix schedule pilots. The objectives of the study were to provide information on quality control, acceptance testing, and independent assurance testing; analyze the performance properties of reheated mixtures and extracted and recovered binders; and document lessons learned from the process. The analysis addressed several topics, including variability in production and testing and binder characterization and implications for performance. The pilot projects were developed by the VDOT districts using maintenance plant mix schedule contracts. In 2021, approximately 72,000 tons of BMD mixtures were paved on selected routes in 10 maintenance schedules across five districts. In 2022, approximately 222,000 tons of BMD mixtures were paved in 13 maintenance schedules distributed across all nine VDOT districts, with at least one BMD contract executed per district. The Cantabro mass loss test, the indirect tensile cracking test (IDT-CT), the Asphalt Pavement Analyzer rut test, and the indirect tensile test at high temperature (IDT-HT) were performed on laboratory-produced design specimens and non-reheated and reheated plant-produced, laboratory-compacted specimens. Basic and advanced binder testing and analysis were conducted on extracted and recovered binders from selected samples of the mixtures.
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