Did you know recycled human hair has many industry uses? As you might expect, beauty trends have fueled growth in the global hair business.
But could those clippings — the ones often found on the floor of a hair salon — help repair dilapidated bridges and buildings across Kentucky and beyond?
A research team in the College of Engineering at the University of Kentucky is leading the charge to answer that very question.
Identifying the Problem
Bridges are a crucial component of Kentucky's infrastructure — providing access between regions and cities and linking workers to jobs. But as traffic continues to increase, bridges across the state are aging at an accelerated pace.
According to the American Road & Transportation Builders Association, 7% of the state’s bridges are classified as "structurally deficient."
What exactly does that mean? Well, more than 1,100 of them are in poor condition.
When a repair is needed — that's where Issam Harik and Abheetha Peiris come in. Harik, a professor in the Department of Civil Engineering and Peiris, a researcher at the Kentucky Transportation Center, offer much more than advice.
Since 1994, Harik has been at the helm of a group of students — dubbed CatStrong — researching the deployment of fiber reinforced polymer (FRP) composites in bridges and buildings.
“Sustainability has recently become a ‘buzzword’ seen on many products and websites,” he said. “But, for engineers, it has been and remains integral to optimizing material, energy and time, while minimizing cost and environmental impact.”
Concrete is one of three major materials used for construction. While it’s relatively sustainable, it’s also important to maximize the use of renewable materials — rather than depleting Earth’s limited resources.
Working Toward a Solution
The CatStrong team — comprising undergraduate, graduate and even Fayette County high school students — is investigating how to make the concrete construction process more sustainable.
And they believe human hair is one of the answers.
“We are constantly searching for new materials. While fiber producing plants and trees only grow in specific geographical regions, human hair grows in any region humans live in,” Harik said. “Since human hair, when trimmed, is generally discarded, it became a perfect candidate for our study.”
“The project involves analyzing, designing and deploying concrete construction forms fabricated with human hair (fiber reinforcement),” Peiris explained. “First, it’s cleaned with water and acidic liquid (lemon juice). Then, the hairs are mixed with a binder (water and grain flour). Lastly, it’s pressed into thin sheets to produce the concrete construction forms.”
Harik admits, the process of using human hair may sound strange. But the benefits are undeniable.
In fact, the average strength of human hair is 30,000 pounds per square inch.
“Human hair has an average strength of 30 kilopounds per square inch (KSI),” Harik further explained. “That’s compared to 20 KSI for sheep wool, 60 KSI for steel rebars and 70 KSI for silkworm fibers.”
Students Remain Key to Solving Structural Challenges
Harik, who is quick to give credit where credit is due, admits he doesn't physically create the materials.
Instead, that's the work of dedicated students — who he lovingly refers to as "minions." On any given day, you will find them working busily in the Structures Lab on campus.
“This experience has been invaluable in determining my outlook on civil engineering. I have been afforded the opportunity to work on projects that almost nobody else has ever investigated,” Trent Woolard, a civil engineering student, said. “This has allowed me to look at problems differently and be okay with approaching solutions in alternative ways. This change in mindset will allow me to become a better problem-solver.”
From design to development, students are involved in every aspect of CatStrong. Over the years, more than 70 undergraduates have been, and remain, an integral part of the research.
Woolard, along with fellow students, is currently experimenting with different ingredients for natural binders to determine the ideal mix and molding process.
“This experience has opened my eyes to the exciting world of research,” Eric Williams added. “I’ve been able to get hands-on experience in labs and with equipment I never would’ve gotten to had I done only what my degree required. I’m very fortunate and grateful for this opportunity.”
Additionally, over the last two decades, more than 25 high school students have joined the team for a year or two at a time — a partnership between UK and Fayette County Public Schools (FCPS) that serves as an invaluable experience.
“Lab work with classmates has been thrilling, especially the hands-on testing of hair samples,” Arnav Palle, a STEAM Academy student and a START apprentice, said. “The experience has sharpened my communication and teamwork skills and has taught me persistence in problem-solving.”
“It has been very exciting to have the ability to work in the lab. I've experienced so much I wouldn't have been able to in the classroom,” Huston Mountjoy, a STEAM Academystudent and a START apprentice, added. “Seeing how the undergrads respond to errors is something I will carry with me.”
CatStrong’s History, Impact
This latest project builds upon the unprecedented work completed by CatStrong — with human hair becoming part of a family of fiber reinforced products for structural repair.
Using remarkably resilient carbon fiber fabrics, panels and wraps, the group has successfully restored more than 40 Kentucky bridges by strengthening beams, columns, piles and walls.
As part of an experimental study, in 2019, the team repaired one of the piles on the KY 32 bridge over Blaine Creek in Lawrence County using hemp — marking the first time the natural fiber has been used as a construction material for bridge repair.
“This undergrad research has allowed me to experience first-hand the importance of sustainability in structural engineering,” Grabrielle Dice, a civil engineering student, said. “It showcases a growing interest, need and opportunity in the field to utilize natural materials that produce structural benefits at lower costs and increased environmental consciousness.”
Despite extraordinary success, CatStrong has been on a quest to find even more reliable resources.
The next phase of the current project includes additional testing and product development, followed by field application.
The goal is for the human hair-based materials to be replicated in any and all communities — a successful outcome that would continue to show the world what can be done right here at UK.
“None of this success would be achieved without the students,” Harik said. “And the pride they experience to have been part of the development, testing and deployment is precious.”