Pavement Made From Algae Could Cut Toxic Asphalt Fumes By 100 Times And Make Roads Last Longer
Source: ZME Science (MSN), Tibi Puiu
Photo: Unsplash © ZME Science
Step outside in any major city on a blistering summer afternoon, and you will smell it. It is the distinct, heavy scent of hot asphalt.
We pave our modern world with it. If you gathered all the pavement in Phoenix, Arizona, and piled it into one place, it would blanket San Francisco four times over. Roads and parking lots cover roughly 40% of the Arizona capital.
They absorb the sun’s heat by day and radiate it by night. And that’s a problem because this urban heat island effect drives up energy use and makes cities swelter.
But scientists now warn that the real threat lies hidden in the fumes.
As petroleum-based roads age and bake in the sun, they release toxic, microscopic vapors that infiltrate our lungs and bloodstreams.
Now, an international coalition of engineers and biologists has proposed a radical, green solution. They want to replace the crude oil in our roads with fast-growing algae.
This bio-bitumen should cut carbon emissions, but, most importantly, it captures the worst toxic fumes, heals its own cracks in freezing weather, and could completely transform how we build the arteries of our civilization.
The Hidden Cost of the Open Road
Historically, sustainable road and pavement design mostly focused on the carbon footprint. Elham Fini wants us to look closer to home.
Fini serves as a senior scientist at Arizona State University’s Global Futures Laboratory. For her, the health impacts of our built environment demand urgent attention.
“To make something truly sustainable,” she said, “you cannot ignore the human side of it.”
Fini spent years investigating why asphalt crumbles. Asphalt consists mostly of crushed rock and sand. To hold it all together, builders use bitumen — a black, sticky sludge left over from refining crude oil.
When bitumen breaks down, it releases volatile organic compounds. These carbon-based vapors escape continuously. On hot, bright days, they spike.
In the short term, breathing them leaves people dizzy and gasping for air. Over time, construction workers who inhale these fumes face a sharply elevated risk of lung cancer.
Worse, the danger grows as the road ages. Recent studies show that ultraviolet sunlight and heat change the chemical profile of bitumen. The aging pavement starts emitting smaller, more toxic, and often completely odorless compounds.
These tiny molecules easily breach our body’s defenses. They slip into arteries and travel directly to vital organs. Tests and models link these specific emissions to significant neurological damage, especially in women and elderly people.
“Heat is worsening the situation,” Fini said. “It’s exacerbating the emissions from asphalt.”
So, how do we fix a material that covers millions of miles of the Earth’s surface?
The answer might surprisingly lie in the nearest puddle.
Algae grow with terrifying speed. Some species double their entire mass in a single day.
They act as nature’s ultimate carbon sponges. Through photosynthesis, they suck carbon dioxide out of the atmosphere and trap it in organic matter. A single acre of cultivated algae yields up to ten times more biomass than a field of corn or soybeans.
But how does a green, watery plant become thick, black road tar? Some experimental studies have used a process called hydrothermal liquefaction. They essentially put harvested algae into a high-tech pressure cooker.
This mimics the immense heat and pressure the Earth uses to turn ancient organic matter into crude oil over millions of years. But instead of waiting epochs, scientists produce a rich bio-oil in mere hours.
They refine this bio-oil into bio-bitumen, just like the traditional variety is made from fossil fuel. Even better, we do not need pristine drinking water or fertile farmland to grow the raw material.
Fini teamed up with Peter Lammers, a chief scientist at the Arizona Center for Algae Technology and Innovation, to cultivate specific algae strains. They feed the algae using wastewater straight from a Phoenix treatment plant.
“It’s a great setup,” Lammers said, “because we use water that’s far too high in nitrogen and phosphorus to be released anywhere. And instead, we reuse it to grow more algae.”
Fini then bakes this algae in a low-oxygen oven. She creates a sticky binder that road crews can easily fold into standard asphalt mixes.
Freezing Winters and Self-Healing Streets
You might wonder if roads made from algae can survive a harsh winter. It turns out they handle the cold far better than traditional petroleum.
In a recent study led by researchers from the Pacific Northwest National Laboratory and ASU, scientists tested how algae-infused pavement handles subzero temperatures.
Adding just a 6% blend of bio-binder derived from wild-type Ulva (a common macroalgae) radically changes the physical properties of the pavement.
Petroleum asphalt turns brittle in the cold. It snaps and forms dangerous thermal cracks. But the algae bio-binder seems to make the material flexible. It absorbs the stress of heavy traffic without breaking too much.
Even more incredibly, the algae give the road a self-healing quality. It resists the deep fatigue cracking that destroys highway infrastructure.
When researchers tested a bio-oil made from another species, Haematococcus pluvialis, they watched the asphalt’s elastic recovery under heavy loads jump from a dismal 0.1% to a staggering 71%.
Moreover, every time you replace 1% of the petroleum binder with algae bio-binder, net carbon emissions drop by 3%.
Pumping, refining, and heating crude oil spews massive amounts of ancient, trapped carbon dioxide into the air. Algae do the exact opposite. As they grow, these tiny plants act like microscopic trees. They breathe in and suck carbon dioxide directly out of the atmosphere to build their cells. When engineers bake those harvested algae into a bio-binder, they permanently lock that captured carbon inside the sticky black material.
Theoretically, if a city paves a road using a 33% bio-binder blend, that road achieves total carbon neutrality. Push the blend higher, and the highway actively removes more carbon from the environment than it creates.
Turning Down the Toxicity
But what about the deadly fumes? Does adding green algae solve the neurological and respiratory threats posed by black tar?
Fini and her colleagues at the Mayo Clinic are working hard to answer that exact question. They want strict protections for communities and construction crews. And they believe the algae binder provides an immediate shield.
Lab tests on algae-infused asphalt have been promising. While it does not entirely stop the road from releasing vapors, it traps the most dangerous ones.
The algae binder locks in the highly toxic compounds that penetrate human arteries. Tests show that incorporating the algae drops the overall toxicity of the asphalt emissions by roughly 100-fold.
Furthermore, the algae slow down the natural degradation of the pavement. The road stays intact longer and releases fewer fumes, requires less maintenance, and costs cash-strapped cities far less money over its lifespan.
Fini is already looking beyond algae. She is experimenting with binders made from the crushed branches of forest-thinning projects.
Currently, she is collaborating with the city of Phoenix to pave an actual test section of road with the algae-infused asphalt.
Air quality experts frequently ignore the volatile organic compounds bleeding out of our sidewalks and streets. Testing these bio-roads in the intense Arizona sun will provide undeniable data.
The Long Road to Commercial Reality
For over a century, our infrastructure relied almost entirely on fossil fuels. Moving toward a bio-based economy forces us to rethink everything from the ground up.
However, challenges loom on the horizon.
Right now, producing bio-bitumen costs significantly more than pumping crude oil. Scaling up production to meet global demand requires massive investment in biorefineries.
We also need years of rigorous traffic testing to ensure these bio-roads do not fail unexpectedly under the weight of millions of commercial trucks. Real-world, practical infrastructure often behaves differently than in lab tests, no matter how well researchers design their experiments.
But the global push has already begun.
In France, the Algoroute project has successfully placed bio-bitumen on test tracks, proving that the material slashes carbon emissions by up to 70%. In the United Kingdom, construction giant Tarmac is running similar pilot projects.
Governments and private industries recognize the urgent need to divest from petroleum. And as Fini points out, the sheer scale of the opportunity demands action.
“We have 4 million miles of roads in America,” Fini said. “We should make those 4 million miles do more for us than just get from A to B.”
This story originally appeared on ZME Science. Want to get smarter every day? Subscribe to our newsletter and stay ahead with the latest science news.