According to Klein-Seetharaman, there have not been sufficient studies of the long-term effects of asphalt-related toxins on the body.

“To give justice to the complexity of the problem, we need a systems-level view of the interactions between asphalt fume components and their biological targets,” Klein-Seetharaman said. "There are thousands of molecules present in asphalt, as well as thousands of biomolecular targets inside the human body that can bind to these molecules and respond to their presence with downstream biological effects, some of which can lead to adverse health outcomes.”

Fini has conducted ongoing research to investigate alternative asphalt binders, including a study on how iron-rich biochar absorbs volatile organic compounds from asphalt surfaces, and how it is both an eco-friendly and cost-effective alternative to bitumen components.

“When we use algae to make AirDuo, as we did from last year’s November harvest from ASU’s Center for Algae Technology and Innovation (AzCATI), it can be carbon negative,” said Fini, who collaborated on the algal components of the project with Peter Lammers, a research professor in SSEBE; Taylor Weiss, a Polytechnic School assistant professor; and Shuguang Deng, a professor in the School for Engineering of Matter, Transport and Energy (SEMTE).

“The use of algae in the AirDuo binder provides a critically important environmental benefit,” Lammers said. “As algal photosynthesis removes carbon dioxide from the air, the AirDuo manufacturing process retains that carbon in an improved asphalt product relative to petroleum-derived binders.” 

“We plan to scale up the process by growing algae on wastewater, thus providing an additional ecosystem service," he said of future plans for substituting algae for petroleum products in other roadway projects.

Other bio-based materials the team has used include biochar from fire-reduction efforts in California and northern Arizona. Process sustainability depends on the feedstock sourcing and, in the case of AirDuo, the use of biomass waste from forest residue, according to Fini.

“This promotes resource conservation and waste valorization, as well as enhances public health and safety — all while providing a more sustainable pavement material.”

SSEBE Professor Mahour Parast oversaw sourcing and supply chain to enable scale-up for AirDuo. DPE Materials, the team’s partner based in Yuma, brought 10, 40-pound bags of AP1 (AirDuo Paving) for the patch at Gammage.

“AirDuo represents a complete sustainability package,” Fini explained. “We are using biomass as our feedstock — it has already pulled CO2 from the air prior to harvesting. The AP1 helps create a sustainable built environment and provides reduced health risks to both asphalt workers and those using asphalt-surfaced areas.”

Fini’s lab studies showed a nearly 70% reduction in emission when AirDuo was used. While not a one-to-one translation to the field, according to Fini, it clearly illustrates toxic fume reduction. The mix also had notably less smell than any other mix made in the plant. 

The research on bitumen asphalt binder alternatives began with a 2019 grant from the National Science Foundation on algae-derived products. A grant from the U.S. Department of Agriculture with a focus on emission reduction and environmental health supported the research and also helped with the lab-to-market transition.

“Our next steps are larger projects on the ASU campus, and then perhaps in Flagstaff and Tucson. Our team invites other states and institutions to join the AP1 (AirDuo Paving) campaign and test it on their sites, too,” Fini said.

But Fini and her team are delighted ASU is leading the effort. 

“It is an Arizona-born technology inspired by Arizona’s sun and heat,” Fini said. “Arizona is ideal for growing our feedstock algae, and also a great testbed for AirDuo. With 320 days of sun in the Valley, the smell of asphalt-surfaced areas never stops.

“You can verify this the next time you get out of your car in an open parking lot in summer.”

SSEBE students and postdocs engaged with AirDuo research include Sand A A Aldagari, Abdullah Aloraini, Mohammadjavad Kazemi, Anna Melis, Masoumeh Mousavi, Albert Hung and Farideh Pahlavan.

Top photo: ASU’s Ellie Fini surveys the ASU Gammage Auditorium parking lot site where the first trial of AirDuo, a low-carbon asphalt binder, was used for a recent patch. AirDuo has the potential to be used for many asphalt paving processes, not just patches. Photo by Bobbi Ramirez/ASU