Are warm mix asphalts fulfilling their environmental promises, or do energy savings come at the expense of long-term performance?

Warm mix asphalt technologies were introduced to reduce mixing and compaction temperatures, cutting fuel consumption and emissions during production. Over two decades later, their widespread use raises new questions about long-term durability and performance consistency

Mohammad Sadeghi NCAT Ph.D.Student

Lower production temperatures have largely fulfilled Warm Mix Asphalt’s (WMA) environmental promise. Studies typically report 15–30 % reductions in burner fuel consumption, leading to near proportionally lower CO₂ and pollutant emissions. For example, one study documented 8 % and 19 % fuel savings when production temperatures were reduced by 40 °F (20 °C) and 65 °F (36 °C), respectively using chemical additives [1]. While these percentages may seem modest, a 19 % reduction across the U.S. asphalt industry would, given reasonable assumptions, save roughly 154 million gallons of fuel annually— about $538 million—and prevent 1.3 million metric tons of CO₂e, equivalent to removing 283 000 cars from roads each year, given reasonable assumptions. This highlights the potential environmental impact achievable through greener production technologies. On a per-ton basis, the energy savings (≈ $1.2 per ton) can offset or surpass the added cost of producing WMA.

Performance outcomes, however, are more nuanced. Laboratory studies often show WMA mixtures to be softer at high temperatures, indicating reduced rutting resistance, but also more flexible at low temperatures, suggesting improved cracking resistance [1]. Given that many current volumetric mix designs yield relatively “dry” mixtures, this trade-off can end up beneficial: non-significant reductions in rutting resistance are unlikely to compromise pavement performance and functionality, while enhanced flexibility may improve long-term durability. Field evaluations, including NCHRP Report 843 [2], generally confirm comparable rutting and cracking performance between WMA and traditional Hot Mix Asphalt (HMA).

In summary, WMA offers similar performance and cost efficiency while providing substantial sustainability advantages. As confidence in its field performance continues to grow, adopting lower production temperatures could further amplify these benefits—removing even more “imaginary cars” from our atmosphere.

[1] Sadeghi, M., et al. "Effects of Reducing Asphalt Production Temperatures Using Warm Mix Technologies on Burner Fuel Consumption and Mixture Performance" Transportation Research Record (2025).

[2] Shen, S., et al. "Long-term field performance of warm mix asphalt technologies." NCHRP Report 843 (2017).

Carolina Rodezno, Ph.D. Associate Research Professor, NCAT.

From its initial introduction in the United States in the early 2000s, WMA quickly transitioned from research to mainstream use due to its multiple benefits, including lower energy demand during production and construction, as well as reduced emissions. However, one of the obstacles to implementation was the uncertainty about how WMA would affect the long-term field performance.

One of the most significant research efforts that provided more definitive data on the long-term performance of WMA was NCHRP Project 9-49A, "Long-Term Field Performance of Warm Mix Asphalt Technologies" (NCHRP Report 843). The project was conducted to compare the long-term field performance of 28 projects built across the United States that included single- or multiple-WMA technology pavement sections and an HMA control section. Overall, the performance of the WMA and HMA sections in all projects was practically identical, with no reduction in long-term performance that occurred from replacing HMA with WMA on these projects.

In addition, NCHRP Project 20-44 (01), “Increasing WMA Implementation by Leveraging the State-of-the-Knowledge, “reported that out of 50 agencies, 94 percent reported no differences in performance between WMA and HMA pavements. Since this project was conducted in 2017, the observations by state agencies are based on the performance of pavements with several years of field service.

Over the past 20+ years, significant research and current practices by state DOT have shown that WMA can be designed and produced with few or no changes when compared to conventional hot mixes without having a detrimental effect on their long-term performance.

It is essential to note that energy savings with the use of WMA are directly proportional to the temperature reduction achieved during production. Therefore, when WMA technologies are used solely to improve workability and aid in compaction, the environmental benefits may not be fully accomplished.

Jenna Bowers, P.E. Recycling and Stabilization Innovation Manager, Ingevity.

Interesting question – actually, I think it’s quite the opposite. Energy savings and long-term performance of low temperature warm mix asphalt (WMA) are not mutually exclusive. In fact, these qualities go hand in hand. When asphalt mixtures are produced at lower temperatures (<275°F), not only is it possible for a plant to save up to 20% in fuel consumption and reduced emissions, but the lower temperatures limit the binder oxidation that occurs during production. This reduced oxidation preserves the binder’s flexibility and fatigue resistance, resulting in greater long-term durability and extended pavement life.

Numerous studies and field trials have confirmed that WMA can deliver equivalent or improved compaction compared to hot mix asphalt (HMA), even at lower temperatures. Long-term performance data accumulated over more than a decade—including FHWA demonstration projects, NCAT Test Track sections, and state DOT experience – generally show that properly designed and produced WMAs perform as good or better than HMAs in terms of rutting, cracking, and moisture resistance.

Although chemical warm mix additives, like Evotherm, were originally developed with environmental factors in mind, the widespread use of these additives have shifted over the past 20 years for the many other benefits that they provide, like anti-stripping properties and compaction aids for example. However, after understanding the role that production temperatures play on the life of an asphalt pavement – and our ability to control that factor – it’s more important than ever for contractors to turn down the burner and take full advantage of this technology. Hopefully, as agencies begin to incentivize contractors to do this, like MNDOT has started to do, not only will there be environmental rewards, but our pavements will last longer because of it.

Graham Hurley, P.E. Assistant Research Engineer, NCAT

Warm Mix Asphalt (WMA) technologies were introduced to reduce the high energy demands and emissions associated with traditional Hot Mix Asphalt (HMA) production. By lowering mixing and compaction temperatures by 25-50 °F, WMA offered immediate environmental benefits—cutting fuel consumption, reducing greenhouse gas emissions, improving working conditions for paving crews, and expanding the construction season. These advantages helped WMA gain rapid acceptance worldwide as agencies sought more sustainable infrastructure solutions.

After more than two decades of use, the focus has started to shift from short-term environmental gains to long-term pavement performance. Early concerns suggested that lower production temperatures might lead to incomplete aggregate drying, insufficient binder coating, or reduced binder aging—factors that could increase moisture susceptibility and rutting potential. However, extensive research from the National Center for Asphalt Technology (NCAT), the Federal Highway Administration (FHWA), and European field studies indicate that most WMA mixtures perform comparably to HMA when properly designed and produced. In some cases, WMA even improves compaction and reduces aging-related cracking due to its cooler production process.

That said, not all WMA technologies behave identically. The performance of WMA can vary depending on the type of additive, plant configuration, aggregate moisture content, and quality control during production. Poor implementation of WMA may negate both the environmental and performance advantages.

Overall, warm mix asphalt has largely fulfilled its environmental promises without sacrificing long-term durability. It represents a successful step toward greener pavement construction, providing meaningful reductions in energy use and emissions. Still, continued field monitoring is necessary as pavements age and climate conditions evolve. Ensuring that environmental savings do not compromise performance will require ongoing research, consistent mix design standards, and adherence to best practices. With proper implementation, I fully believe WMA can deliver both sustainability and durability—an essential balance for future infrastructure development.

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