Balanced Mix Design (BMD) is defined as “asphalt mix design using performance tests on appropriately conditioned specimens that address multiple modes of distress taking into consideration mix aging, traffic, climate and location within the pavement structure” per AASHTO PP 105-20. This definition was initially established by the former Federal Highway Administration (FHWA) Expert Task Group (ETG) Balanced Mix Design Task Force in 2015.
Why is Balanced Mix Design Needed?
ENSURE PERFORMANCE
Concerns with durability and cracking issues of asphalt pavements along with the growing awareness of the shortcomings of volumetric mix design systems have driven many SHAs and the asphalt pavement industry to explore the use of BMD as a better approach to evaluate a mixture resistance to common distresses for asphalt mix design approval and production acceptance.
ENABLE INNOVATION
BMD offers a better way to evaluate the impact of mix design variables such as recycled materials, recycling agents, and other innovative additives by testing the composite mixture for resistance to cracking, rutting, and moisture damage. As the industry puts more emphasis on sustainability and decarbonization, BMD will be the foundation to ensure that new paving mixtures will provide equal or better field performance.
ECONOMIC OPTIMIZATION
BMD allows for the optimization of mixes in terms of cost-effective material use (e.g., binders, aggregates, recycled materials, additives, etc.) and performance. Mix designers will be able to take a fresh look at local materials, binders, and additives and assess what combinations of materials provide the expected resistance to distresses at the lowest cost. Mix designers will have the means to truly evaluate how changing mix components and percentages will affect costs and performance.
NCAT provides stakeholders with a variety of useful resources, including:
The BMD Implementation Guide from the National Cooperative Highway Research Program (NCHRP)
BMD Training Classes and Workshops
NCAT also offers ongoing research efforts:
Round Robin programs for BMD tests: A second round was conducted in 2021 to include several mixture performance tests evaluated for BMD implementation and quality assurance during production in order to help participating labs compare their results to other labs and generate data to develop within-lab and between-lab variability estimates for the different test procedures. Learn more about Round Robin programs for BMD Tests.
Lag & Dwell Time Study: The issue is currently being investigated by NCAT in an ongoing survey.
Test Track experiments:
Top-down cracking group experiment: NCAT report 21-03, Chapter 2
Low-temperature cracking group experiment: NCAT report 23-03
Cargill Anova Recycling Agent N3A/N3B: NCAT report 21-03, Chapter 5
Oklahoma BMD criteria validation N9 & S1: NCAT report 21-03, Chapter 13
Texas BMD vs volumetric mix design S10 & S11: NCAT report 21-03, Chapter 16
Useful references from state DOTs:
Case Studies on the Implementation of BMD and Performance Tests for Asphalt Mixtures: CalTrans
Case Studies on the Implementation of BMD and Performance Tests for Asphalt Mixtures: Illinois DOT
Case Studies on the Implementation of BMD and Performance Tests for Asphalt Mixtures: Louisiana DOTD
Case Studies on the Implementation of BMD and Performance Tests for Asphalt Mixtures: Maine DOT
Case Studies on the Implementation of BMD and Performance Tests for Asphalt Mixtures: New Jersey DOT
Case Studies on the Implementation of BMD and Performance Tests for Asphalt Mixtures: Texas DOT
Case Studies on the Implementation of BMD and Performance Tests for Asphalt Mixtures: Virginia DOT