What is Balanced Mix Design?
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?
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 new approach to asphalt mix design and production acceptance.
Establishing the state of performance of commonly used mixes (i.e., cataloging mixes) and optimizing those mixes to achieve performance will allow companies to help move asphalt related specifications forward to better ensure the needed field performance can be obtained.
Balanced Mix Design allows for the optimization of mixes in terms of cost-effective material use (e.g., asphalt binder, aggregate, recycled material, additive, etc.) and performance. Without knowing the true performance of mixes, decisions on material use will likely be made based on assumptions, past experience (which may not hold true currently), raw cost alone or current specification limits and constraints. A total picture concept of materials plus performance provides the most benefit in terms of managing risk and increasing margin opportunity.
The National Asphalt Pavement Association would like to acknowledge and thank the National Center for Asphalt Technology for their contributions in compiling this information and their continued work to keep this information up-to-date.