Greener Roads Ahead
Driving More Sustainable Practices with Balanced Mix Design in Asphalt Pavement.
By Brett Williams
Senior Director, Engineering & Technical Services
AS THE WORLD GRAPPLES with the pressing need to adopt more sustainable practices, the asphalt pavement industry is paving the way towards greener roads.
The 2022 construction season recycled materials and warm mix survey reveals a significant shift towards sustainability, with asphalt mixture producers increasingly utilizing recycled materials and decreasing production temperature through the use of Warm-Mix Asphalt (WMA) technologies. These practices not only conserve natural resources and reduce greenhouse gas emissions but also offer economic benefits by lowering material costs and extending the lifespan of pavements.
In addition to these strides in sustainability, the industry is also working on implementing Balanced Mix Design (BMD) as a new approach to asphalt mix design. BMD focuses on performance-based criteria, addressing the limitations of traditional volumetric mix design systems and ensuring that asphalt mixtures meet the durability and cracking resistance requirements specific to project needs. By freeing asphalt mixtures from prescriptive material limits, BMD allows for more sustainable solutions, optimizing material use and enhancing pavement performance and economic efficiency.
RECLAIMED ASPHALT PAVEMENT (RAP)
In 2022, the asphalt pavement industry continued its sustainability progress through widespread use of reclaimed asphalt pavement (RAP). Utilizing 98.1 million tons of RAP represents a 75.2 percent increase since 2009, conserving 4.9 million of tons of asphalt binder and more than 93 million tons of aggregate annually 3while reducing greenhouse gas emissions by 2.7 million metric tons CO2e which is equivalent to removing around 600,000 passenger vehicles from the road each year.
WARM-MIX ASPHALT (WMA)
Warm-Mix Asphalt technologies were employed in 175 million tons of asphalt mixtures in 2022, comprising 39.6 percent of the market. These technologies allow for the reduction of mix production temperatures, thereby cutting energy consumption and emissions. During the 2022 construction season reducing production temperature resulted in an estimated reduction of 0.18 million metric tons of CO2e, equivalent to the annual emissions of 40,000 passenger vehicles.Opens in modal lightbox
SR-229 AGENCIES & CONTRACTORS SURVEYS ON BARRIERS TO HIGHER RAP USAGE IN ASPHALT MIXTURES
NAPA’s report on barriers to higher RAP usage in asphalt mixes identified barriers to increasing RAP usage, highlighting agency concerns about durability, cracking resistance, and mix consistency in high RAP mixes.
AGENCIES’ CONCERNS ON PERFORMANCE AND THE ROLE OF BALANCED MIX DESIGN (BMD)
Despite the increases in RAP use, recent data indicates that use has plateaued just above 20% RAP in a new asphalt mix.
To advance sustainability efforts, the long-term performance of pavements will play a critical role in reducing our transportation infrastructure’s carbon footprint, making it essential to address these performance concerns.
BMD focuses on performance-based criteria, allowing engineers to tailor asphalt mix designs that incorporate recycled materials like RAP to meet specific project requirements. By integrating tests that correlate with field performance, such as cracking and rutting resistance, BMD helps ensure sustainable and resilient pavements. This approach supports flexibility in binder selection, the use of additives like Warm Mix Asphalt (WMA), and recycling agents, which are essential for optimizing higher RAP mixes. As agencies refine specifications and practices, BMD emerges as a crucial tool to enhance pavement performance while maximizing the benefits of recycled materials.
Understanding the importance of shifting the focus of mix design to the performance of the mix and removing barriers to optimal incorporation of recycled and innovative materials is a crucial aspect to selecting the BMD approach to implement.
Learn more about agency efforts in BMD implementation by visiting the NAPA BMD Resource Guide.
The FHWA’s Low-Carbon Transportation Materials (LCTM) Program, established under the Inflation Reduction Act (IRA), offers $2 billion to promote construction materials with significantly reduced greenhouse gas emissions. This initiative supports State Departments of Transportation in integrating low carbon materials, including asphalt mixes, through funding for technical specifications and innovative practices. By incentivizing the adoption of materials with lower embodied carbon, such as those evaluated under the LCTM Program, transportation agencies can advance their efforts toward sustainable infrastructure, including the implementation of Balanced Mix Design (BMD) for enhanced pavement performance and reduced environmental impact.
CONCLUSION: MAPPING THE ROUTE TO A MORE SUSTAINABLE FUTURE
Through the widespread use of RAP and WMA technologies, the industry is significantly reducing greenhouse gas emissions, conserving natural resources, and lowering production costs. However, to further advance these efforts, the long-term performance of the mixtures and, ultimately, the pavements is crucial to achieve success.Opens in modal lightbox
For further guidance, refer to NAPA’s report, SR-228 GUIDANCE ON PROGRESSING THROUGH BMD APPROACHES.Opens in modal lightbox
BMD offers a promising solution by focusing on performance-based criteria, allowing for the effective incorporation of recycled materials while meeting durability and cracking resistance requirements. The FHWA’s Low-Carbon Transportation Materials (LCTM) Program further supports these efforts by providing significant funding to promote low-carbon construction materials, aiding in the transition towards more sustainable infrastructure.
Central to these efforts is The Road Forward, the asphalt industry’s initiative to produce and construct net zero carbon emission asphalt pavements by 2050. By continuing to refine specifications, invest in new technologies, and prioritize performance-based design, the asphalt pavement industry can map the route to more sustainable asphalt roads. The journey is ongoing, but with collaborative efforts and innovative practices, the industry is well-positioned to meet the challenges ahead, achieve net zero carbon emissions, and drive meaningful environmental change.
13TH ANNUAL ASPHALT PAVEMENT INDUSTRY SURVEY ON RECYCLED MATERIALS AND WARM-MIX ASPHALT USAGE
The objective of this annual survey is to quantify the use of recycled materials, primarily RAP and RAS, as well as the use of WMA technologies by the asphalt pavement industry. Download the latest report.
