For most drivers, a road is just a means to an end. But for civil engineering senior Chase Plager, it’s become something much more: a path to new solutions for building better roads.
In Cal Poly’s Pavement Advanced Materials Lab, Plager starts each Friday morning at 5 a.m., heating aggregates and mixing asphalt so he can begin compacting samples by noon. The work is messy and demanding, but for Plager, it’s a chance to turn raw materials into meaningful discoveries.
“Now, I look at roads in a completely new way,” Plager said. “You don’t realize just how much engineering and planning goes into them until you see it firsthand.”
The samples Plager prepares form the foundation of a research project led by civil engineering Professor Ashraf Rahim, who has spent decades advancing sustainable practices in road construction and maintenance.
Together, they are exploring how to improve the performance of Reclaimed Asphalt Pavement (RAP), made from old roads that would otherwise go to waste. RAP helps reduce landfill material and offers an environmentally friendly alternative to mining new resources. However, at higher percentages, RAP can lead to durability challenges such as cracking and wear.
The addition of polymer fibers to the asphalt mix, Rahim and Plager hope, will bridge those gaps — literally and figuratively.
“If we can make asphalt with higher amounts of recycled material from old roads perform just as well, we can keep that waste out of landfills and reduce the need to quarry new materials,” Rahim said.
Rahim, who has taught at Cal Poly for 21 years, was drawn to asphalt research early in his academic career in Egypt. For him, the importance of pavement goes far beyond its surface.
“We can’t get from Point A to Point B without driving on pavement,” Rahim said. “It affects how we drive and our comfort during the drive,” Rahim said. “But beyond that, it’s all about helping society by ensuring safer, more reliable roads for everyone.”
With 95% of roads in the U.S. made from asphalt and stretching across 4 to 5 million miles, Rahim emphasizes that the stakes are high. “It’s a huge investment, and if we don’t keep up with maintenance, it costs a lot of money,” he explained. “That’s why we have to design it better from the beginning.”
The opportunity for sustainability is equally significant. Asphalt is the most recycled material in America, with 70 million tons of pavements reused every year. This makes RAP a key component in creating more sustainable roadways.
Building on prior work along California’s Highway 1 near Hearst Castle, Rahim is exploring whether polymer fibers can further enhance the performance of high-RAP asphalt mixes. While Caltrans permits up to 25% RAP in surface layers and 40% in lower layers, using 25% RAP in surface mixes is still uncommon. Rahim’s team is working to push these limits by testing whether fibers can enable even higher RAP content without compromising performance.
Funded with a $75,000 grant from the Mineta Transportation Institute at San Jose State University, the project began in June 2024 and will run through May 2025. To date, the team has prepared and tested over 200 samples, evaluating two types of asphalt mixes: one with 15% RAP and another with 25%. Three fiber dosages — small, medium and high — are being tested to find the ideal balance for improving durability and reducing wear.
At Cal Poly, samples are tested for rutting, the type of wear caused by repeated vehicle pressure, and moisture sensitivity, which measures resistance to water damage. However, cracking resistance requires specialized equipment not available at Cal Poly, so samples are sent to Cal State Long Beach, where their team conducts tests to evaluate how the fibers strengthen the asphalt under stress.
“If we can make high-RAP mixes perform reliably, it’s not just about recycling — it’s about creating a more sustainable approach to building roads,” Rahim said.
Plager weighs a newly made asphalt puck, jotting its weight on a whiteboard. The lab is coated with a fine layer of dust and smells faintly of hot asphalt, but Plager is in his element.
After growing up in Pacific Palisades, Plager chose to study civil engineering at Cal Poly, drawn to a field that combined his love of math with the chance to make a difference. As a student assistant at Caltrans, he gained hands-on experience in both the field and the materials lab, earning certifications in nine test methods — skills that proved invaluable when he joined Rahim’s project.
The experience has transformed his perspective, giving him a deeper appreciation for the engineering and innovation needed to build better roads.
“There’s so much more to pavement than people realize,” Plager said. “Every detail, every material choice, affects how long a road will last and how well it will perform.”
His work in the lab has also made him hopeful about what’s possible. “If this project can help the field adopt greener practices, that would be huge,” he said.
By Emily Slater
