Developing a Balanced Mix Design (BMD) Framework for SBS Modified Dense-Graded Asphalt Surface Mixtures – Phase I

Project No: 124333

Target Completion Date: July 31, 2026 Pavements

About the project:

The Virginia Department of Transportation (VDOT) has established a balanced mix design (BMD) framework for its 9.5 mm and 12.5 mm nominal maximum aggregate size (NMAS) dense-graded asphalt surface mixtures with unmodified binders (commonly referred with A and D designations) and is in the process of full-scale implementation. VDOT desires to further explore the implementation of BMD for other mixtures, such as dense-graded surface mixtures with E designation (denoted “E mixtures”), gap-graded mixtures, base mixtures, and intermediate mixtures.

The next phase of BMD implementation will focus on VDOT’s E mixtures, containing polymer modified binders (PMBs) typically modified with styrene-butadiene-styrene (SBS) polymer. However, findings from the work assessing high polymer modified asphalt mixtures suggest that the tests within VDOT’s BMD framework for “A” and “D” mixtures, particularly the cracking resistance test, may not adequately capture the performance improvement resulting from the use of polymer modified binders (PMBs). Given the central role of performance tests in the BMD methodology, it is of paramount importance to identify test methods and associated indices capable of accurately capturing the performance of SBS-polymer-modified mixtures. This crucial first step holds significant implications for the decision-making process regarding the establishment and implementation of a BMD framework for such mixtures within VDOT.

The primary objective of this study is to develop a BMD framework(s) specifically designed for VDOT’s SBS-polymer-modified dense-graded asphalt surface mixtures (i.e., E mixtures). Accordingly, the research will thoroughly evaluate test methods that can accurately reflect the performance enhancements of mixtures achieved by polymer modification. Subsequently, the research will offer a roadmap for BMD methodology adoption for these mixtures. 

Project Team

Principal Investigators

  • Ilker Boz, Ph.D.

Co-Principal Investigators

Last updated: April 1, 2024

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