Are recycled plastics in asphalt mixtures an environmental solution or just creating ‘plastic pavement’ problems?

Recycled plastics are increasingly promoted as a sustainable solution in asphalt pavements. Yet, concerns remain about long-term performance. In your view, do the potential environmental benefits outweigh the risks of poor performance? Or do you see a niche where plastics can truly add value to asphalt technology?

Amir Jafarmilajerdi NCAT Student

Recycled plastics in asphalt are often promoted as a two-way benefit solution: tackling plastic waste while improving pavement performance and sustainability. From what I have seen in the research, the reality is more nuanced, but at the same time, the opportunities are worth exploring further.

There are still significant challenges that need to be addressed, including binder and mixture characterization in plastic-modified systems, plant operations, standardized methods for plastic incorporation, compatibility between different plastic sources and binders, and the recyclability of pavements containing plastic. If these issues are not addressed through comprehensive research and field validation, poor performance could lead to more frequent maintenance and undermine the very benefits this technology is intended to deliver. Another concern is environmental fate. Recent studies have raised questions about microplastic release and chemical leaching resulting from the weathering of in-service asphalt pavements, and long-term monitoring will be necessary to fully understand these risks.

Despite these challenges, there is room for optimism. Many studies have reported positive performance outcomes and potential environmental benefits when using plastics in asphalt pavements. Early findings suggest that, with the right processing and controls, plastics could complement the tools we already use to enhance both performance and sustainability of asphalt mixtures.

That said, I see potential niches where recycled plastics could add value. Real progress, however, will require patience. Building a solid foundation of laboratory and field data, developing transparent life-cycle assessments, and fostering collaboration between industry, agencies, and academia are all essential steps for advancing the technology toward safe and effective use.

Finally, I believe recycled plastics are very likely to become part of asphalt pavement engineering practice in the future, but only if we approach them with rigor and caution. Otherwise, we risk trading the “plastic waste” problem for a “plastic pavement” problem.

Randy West, Ph.D.,P.E. NCAT Director

First of all, this is a great question. The short answer is, we don’t know yet, but we're getting closer to answering that big picture question.

Often in engineering, we jump straight into working on a technical solution without thinking about the big picture. Specifically, in pavement materials research, we often explore whether another industry's waste material can be used in asphalt pavements. In my career, I've evaluated recycled glass, ground tire rubber, recycled asphalt shingles, cellulose from recycled paper, sulfur removed from crude oil, waste carpet fibers, incinerator bottom ash, and the list goes on.

When someone proposes to use a recycled material in asphalt pavements, we should ask six questions:

1. What is the impact of adding the recycled material on pavement performance, or as you stated, does it add value to asphalt technology?
2. If there is a performance benefit to adding the recycled material, does the economic benefit exceed the cost of the material and the cost of adding it to a paving mixture during production?
3. Will there be a sufficient supply of the recycled material to meet the demand of the asphalt paving industry if the answer to question number 1 is very positive?
4. Will there be negative environmental or health consequences due to using the recycled materials in pavements?
5. After the recycled material is added to an asphalt pavement, can that pavement be recycled at the end of its life?
6. If the recycled material adds value (Q1), is economically feasible (Q2), there is sufficient supply (Q3), it causes no harm to humans or the environment (Q4), and does not disrupt the circular economy of asphalt pavements(Q5), does using it in pavements solve the waste issue, or at least have a substantial impact on it?

If the answer to any of these questions is negative, then it’s game over. There’s no need to proceed to the other questions.

With regard to recycled plastics, NCAT and other research teams are actively trying to answer many of these questions. The best answer to the first question will come from well-controlled and documented test sections built in a handful of locations across the USA. Although the lab test results for most mixtures containing recycled plastics are not particularly compelling from the cracking resistance indicators, the field performance data for the test sections to date are generally neutral compared to control mixtures. It will take more time to know if the mixtures containing recycled plastics provide a benefit.

We do know that waste plastic is an enormous environmental problem, with 389 million tons of plastic waste generated globally each year, and the quantity is growing fast. Of that total, roughly 30 percent are polyethylenes, which past research indicates is the most suitable for use in asphalt pavements because of their melting points. However, even if we take an optimistic projection of the potential use of recycled plastics in asphalt, the asphalt pavement industry would only consume about 2.4% of the waste polyethylene generated in the US each year.

So, the bottom line is that using recycled plastic in pavements will not solve the plastic waste issue. For that reason, I believe that society needs to work on other solutions, and foremost, we must reduce the amount of plastic being used and thrown away each day.

Jhony Habbouche, Ph.D., P.E. Western Regional Engineer, Asphalt Institute

The idea of paving roads with recycled plastics sparks both excitement and skepticism. During my time at the Virginia Transportation Research Council (VTRC) as a Senior Research Scientist, I led two projects that explored whether plastics can truly add value in asphalt mixture.

Our findings show that incorporating recycled plastics into asphalt mixtures is promising but nuanced. From a construction standpoint, recycled plastic-modified mixtures can generally be produced and placed using routine paving practices, though warmer weather is preferred. Performance testing indicated that “engineered” recycled plastics may improve cracking resistance compared with unmodified mixtures, but results varied depending on incorporation method (wet vs. dry), dosage, and aging conditions. In comparison to conventional polymer (SBS)-modified binders, recycled plastics provided benefits over base binders but did not consistently match SBS performance.

Field sections constructed in Virginia between 2021 and 2023 remain in very good condition, with no negative impacts observed on rutting, roughness, or texture, though it is still too early for definitive long-term conclusions. Environmental monitoring showed consistently low emissions of polycyclic aromatic hydrocarbons (PAHs), asphalt fumes (AF), and volatile organic compounds (VOC) during paving, often below reporting limits. The potential release of microplastics remains an open research question, requiring more field data.

In my view, recycled plastics are not a silver bullet for sustainability, but neither are they merely “plastic pavement problems.” Their value lies in niche applications where performance is validated through binder and mixture testing, and where lifecycle monitoring confirms both engineering and environmental benefits. Long-term data will ultimately determine whether the environmental promise outweighs performance risks.

References:

UPC Project 120030: Evaluation of Recycled Plastic Modified Asphalt Mixtures and Pavements: Phase I – A Case Study in Virginia

FHWA/VTRC Report 25-R11, https://vtrc.virginia.gov/media/vtrc/vtrc-pdf/vtrc-pdf/25-R11.pdf​

UPC Project 122604: Sustainable Surface Mixtures Incorporating Recycled Plastic Waste and High RAP Contents

​https://vtrc.virginia.gov/projects/all-projects/122604/​

Maede Mottaghi, Ph.D. Senior Engineer - Asphalt Mixtures ArrMaz Products Inc.

The idea of using recycled plastics in asphalt pavements has generated tremendous interest in recent years, and for good reason. Plastics are one of the most persistent waste streams in our environment, and the notion of turning them into roads seems like a win–win: cleaner communities and more sustainable pavements. But the evidence so far shows that this story is not that straightforward.

Findings from the NCHRP 9-66 project and several national demonstration projects confirm that performance outcomes vary widely depending on the type of plastic, how it is processed, and how it is introduced into the mixture. In some cases, we see improvements in rutting resistance; in others, there are real concerns about cracking performance, consistency, and long-term durability. The variability makes it difficult to establish broad design guidelines or specifications at this stage.

From an environmental perspective, there is clear potential to divert plastic waste from landfills and create value in transportation infrastructure. But these benefits quickly diminish if pavements underperform and require earlier rehabilitation. There are also unanswered questions about what happens during milling or long-term weathering, including the possible release of microplastics.

That said, I don’t believe the idea should be dismissed. Plastics may find value in specific applications, for example, in certain binder modifications through the wet process, or as aggregate substitutes in applications where structural performance demands are lower. But we need rigorous, transparent testing and continued monitoring of current field projects before making recycled plastics a mainstream solution.

In short, plastics in asphalt are not yet a proven environmental solution on a broad scale. They remain an emerging technology with potential, but one that must be pursued carefully to ensure the sustainability promise matches real-world performance