Heat, precipitation, freeze-thaw cycles mean worse roads unless innovation can outpace disrepair.
Whether you’re driving a car, riding a bike or just enjoying a sidewalk stroll, potholes are annoying, dangerous and expensive. So be prepared — as the spring thaw begins in much of Ontario, so too does pothole season.
Over the years, CBC stations have told hundreds of stories about problems with potholes in areas of Ontario and across Canada. Rapidly deteriorating roads already cost Canadians an extra $3 billion in vehicle upkeep every year, according to the Canadian Automobile Association.
So we should all be concerned about the havoc climate change could wreak on our streets, with cities already preparing for more potholes, bumps, cracks and ruts.
Fortunately, engineers have been working to develop better, longer-lasting and more sustainable materials, with innovations like self-healing asphalt and roads connected to artificial intelligence (AI) technology that can help predict where cracks and potholes will develop.
The Great Lakes Climate Change Project is a joint initiative between CBC’s Ontario stations to explore climate change from a provincial lens. You can read some of the recent stories from the project here:
Canadian climates perfect for potholes
Canada encompasses many different climates, but it just so happens that many of them already provide perfect conditions for potholes in the spring.
“Any time [temperatures] start fluctuating back and forth between above zero and below zero, especially if those shifts are large, that’s basically pothole season,” said Scott Berry, operations manager of roads and traffic for the City of Kitchener.
“Whether that’s happening in January as a short little week instead of being cold, or whether it’s happening in the traditional pothole season of March and April and May — that’s what is contributing significantly to potholes on roadways.”
How potholes are created
Pothole season is well under way. This is how potholes are created, and why they feel worse some years than others.
This is known as a freeze-thaw cycle, and such cycles are common across Canada, said Ali Nazemi, an associate professor of building, civil and environmental engineering at Concordia University in Montreal.
The problem for roads comes when water infiltrates the subbase beneath the top layer of asphalt and undergoes freeze-thaw cycles. Water is the only known non-metallic substance that expands when frozen, and it exerts a lot of power when it does.
“When [water] expands, it starts putting pressure on the soil and infrastructure … it cracks the infrastructure,” said Nazemi. “Then when it’s getting thawed, the water droplets start to move toward those cracks that it previously made, and then another cycle of freezing happens and the pore expands.”
The more freeze-thaw cycles occur, the more of these expanding, ice-filled voids form beneath the top layer of asphalt and the larger they grow.
“If this cycle carries on, that basically increases the speed of deterioration of the infrastructure quite significantly,” Nazemi said.
When it warms and the ice melts, the top layer of asphalt is unsupported. As a truck or other heavy vehicle drives over that spot, the asphalt can give way, revealing the void underneath.
And so a pothole is born.
Could potholes become year-round issue?
Using novel modelling techniques and data from remote-sensing satellites, Nazemi was senior author on a 2021 Journal of Hydrology paper and a 2022 Nature Scientific Reports paper that highlight some previously overlooked key impacts of climate change in Quebec. He is currently applying those techniques to a pan-Canadian model.
His research suggests the transitional seasons before and after winter will grow longer, meaning more temperatures around zero and more freeze-thaw cycles, threatening infrastructure across the country.
That’s an issue for cities and those using the roads, said Scott Berry, the city operations manager in Kitchener, Ont.
“If that happens, then we will have a longer pothole season. It won’t be just contained to March, April and May. You might see pothole season creeping its way into all of February at some point.”
There are many other ways climate change will affect our roads, said Hassan Baaj, a professor of civil engineering at the University of Waterloo and director of its Centre for Pavement and Transportation Technology.
Extreme heat in the summers means an increase in rutting, where depressions in the asphalt are worn by the tire tracks of heavy vehicles. Increased precipitation can result in flooding and damage roads, and more sun exposure degrades the asphalt and forms more cracks that water can infiltrate.
Of course, the best way to prevent additional damage to our roads is to reduce emissions. But since we have already committed to several decades of warming, researchers are looking at ways to mitigate the damage.
There’s actually ‘self-healing’ asphalt
Researchers have long found ways to produce “better” asphalt, said Baaj, including changing the mix to make the asphalt more resilient, easier to produce, require less maintenance or even be self-salting.
“We’re working on developing high-performance asphalt mixes that have high resistance to the different modes of deterioration of pavements.”
In recent years, sustainable engineering has been the name of the game. That means the innovations that engineers are exploring are expected to be long lasting and environmentally friendly.
As one example, Baaj cited “self-healing” asphalt, which is inspired by the biology of the human body.
There are numerous ways to do this. One involves injecting bacteria into the asphalt. When exposed to water, the bacteria produce calcium carbonate, sealing up any cracks with limestone.
There’s also smart asphalt — roads powered by artificial intelligence that helps predict and detect cracks well before they can be detected at the surface, making repairs cheaper, easier, quicker and more effective.
“We have different instruments that are embedded within the different layers of the pavement [and] transmitters that will collect the data and send it to our team at the University of Waterloo to be analyzed, using algorithms that we will be creating using artificial intelligence,” said Baaj.
“When we see patterns, when we see like things happening like high stresses, etcetera, we would be able to connect those events that are happening in the pavement and future events that will happen later, like cracks that will appear.”
Research is also underway to find more environmentally and climate-friendly alternatives to traditional asphalt, which uses the crude oil product bitumen as a binder and is known to release harmful air pollutants for years after being laid down.
In Thunder Bay in northwestern Ontario and a couple of other Canadian cities, a pilot project is underway to investigate partially substituting an alternative binder called lignin, a plant polymer and abundant waste product from paper mills.
Baaj is also working on recycling old pavement to create new, more resilient asphalt while keeping the old materials from going to waste. He said it’s more complex than you may think, but well worth it.
“If we use recycled materials in a good way, we will build resilient roads that will be as good or better than the ones that are not using the recycled material. So I’m not creating a problem for future generations to deal with … my successors will have to deal with that. My kids will have to deal with that.”
ABOUT THE AUTHOR
Darius Mahdavi is a CBC science specialist covering the impacts of climate change on the people and ecosystems of Ontario. He’s worked as a researcher and graduated from the University of Toronto, where he earned a degree in conservation biology and immunology with a minor in environmental biology. If you have a science or climate question, reach out at firstname.lastname@example.org.
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