Asphalt Science and the Holey Roads

We heart Edmonton.

We hate potholes.

We hate the molar-loosening, coffee spilling, compound-curse- word-inspiring experience of driving — ba-BAM! — over an unseen Edmonton pothole.

Potholes mar our collective psyche as much as our public roads. But I was curious: Is Edmonton really the centre of the pothole universe?

Well, the City of Edmonton is the only municipality in Canada to fund serious asphalt science. Asphalt alchemy and research is practiced each day at the City’s materials testing lab, under the supervision of engineer Hugh Donovan.

Donovan and his team use high-tech equipment to manipulate — shake, bake, drench, freeze, thaw, vibrate, stretch, twist — and beat the bejeebers out of various asphalt recipes to evaluate the best mix of oil, sand-and-gravel aggregate and filler.

And they endure our carping and complaining. Donovan suggests, however, that this isn’t some localized plague. Potholes, in fact, are a global pandemic.

Sure enough, a bit of Google research reveals that one in three drivers in England claims vehicle damage from potholes. Brisbane Australia is swimming in hard rains and potholes. Even the paved paradise of Honolulu is grumpy about potholes.

So Edmonton’s chronic road pox isn’t unique, though we live in a climate seemingly designed to grow bumper pothole crops.

On average, Edmonton experiences 122 freeze-thaw cycles per year. Water seeps into cracks during the thaw. The sub-surface water then freezes and expands, creating a kind-of road zit. Then it thaws again and along come vehicles to pop those zits. Or at least, that’s one way to describe it. But you get the point — freeze-thaw cycles are to asphalt what tortilla chips and banana splits are to your skin.

So far this year, Edmonton has already recorded 125 freeze- thaw cycles. And there’s a lot of fall and winter left in the calendar year. Those numbers inspire Donovan to work even harder.

The science suggests climate change will only bring more extreme weather and more freeze-thaw cycles to our roads.

Donovan is a welcoming, congenial and obsessed with his work. He’s an asphalt nerd, so to speak. He’ll happily talk your ear off about oil viscosity and aggregate shape, sizes and varieties.

But it’s a complex art, getting asphalt right. The variables are numerous: soil type; oil viscosity; aggregate size; ratio of fill or recycled asphalt; construction and compaction techniques. Not to mention, the weather and season in which the asphalt was applied, the type of sealer… It just goes on and on.

Donovan says innovations in testing methods are improving asphalt mixes and construction techniques all the time. The team has high-tech testing in the labs, but also a number of test pads on roads throughout the city to test the durability of materials and paving techniques through our full year of vehicle and weather impact.

Nonetheless, Donovan isn’t predicting a pothole-free world anytime soon.

“We don’t want our roads to not perform,” says Donovan. “I personally wish I could fix it all in one day. But even if I had a magic elixir, I couldn’t do it all in one day.”

Still, Donovan and the City transportation department are dancing as fast as they can to stop the pothole plague. They filled 453,600 potholes in 2012 and did as much road maintenance and replacement as their budget allowed.

This year, they’ve already topped 263,000 pothole repairs.

But all this work is like the proverbial thumb in the dike. Much of Edmonton’s vast road system isn’t in great shape. Asphalt left too long without proper rehabilitation will heave, crack and erupt in road acne.

In the early 1990s, the city councils of the day passed several budgets with no tax increase. Infrastructure maintenance was cut to the bone. No problem back then. But we’re now paying for the sins of those city fathers. Our roads suffer from neglect. City Council recently bumped up the arterial road rehabilitation budget another $9 million per year, and they are considering options for establishing long-term sustainable funding for arterial roadways.

That is a lot of money. And City Council must weigh those demands against myriad other civic challenges and aspirations.

At the same time, paying for “softer” programs such as for arts and recreation opportunities are crucial to attract and keep families and businesses in Edmonton, who will pay taxes… so we can keep maintaining our roads.

Cities function best when citizens are engaged with City Hall. When they talk to their city councillor, read news stories and better understand the true cost and benefits of civic services, facilities and infrastructure.

Not to mention, the true costs of cutting budgets. Saving a few dollars on your tax bill today might cost you serious money down the road.

Civic budgets are complex, challenging and frustrating. At best, they are a subtle and nuanced balancing act.

Then along comes a pothole.


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About the Author
Scott McKeen
The City of Edmonton's first-ever blogger in residence is long-time city writer and journalist Scott McKeen. McKeen is best known for his stint as The Edmonton Journal's civic affairs columnist, a position he held from 2002 - 2010. He won a number of awards during his 24 years at The Journal, including an international writing prize for his investigative work on a growing Edmonton cult. McKeen left the paper in 2010 for a shot at politics. He came out of that experience, he says, with much greater humility and respect for those who run for public office. McKeen is now a freelance writer and communications consultant. His hobbies include guitar, photography and napping.
  1. carrie thuesen
    7 years ago

    Good information thank you.

  2. Lisa Hennigar
    7 years ago

    This is really well written.

  3. David
    6 years ago

    Do you know if Donovan is aware of what the government of Norway is doing in asphalt research? There was a TEDtalk given by their lead scientist that put some hope into this “global pandemic”.

    See video link:
    Scott share this link with Donovan if he isn’t aware of it.

  4. Laura McNabb
    6 years ago

    Thank you for your post, David. Yes, our Engineering Services staff is aware of the technology to which you referred. Porous pavements that were the focus of this presentation are predominantly used in coastal regions of Europe, the Eastern and Western United states and some of the coastal areas of Canada. In areas where roadways are subject to freeze-thaw, however, porous pavements do not hold up.

  5. Andrew Anderson
    6 years ago

    This is really interesting – shows how important ongoing research into pavements is going to be in the future. Although the research discussed in the Netherlands was for very porous asphalt structures, there has been research in using induction heating for dense asphalt structures as well. The main challenge is getting an even heat into a placed pavement. In the video, he is able to put a chunk of the road in a microwave, which is not possible in the real world. Large heating devices have been tested to try to heat the road evenly but it is tough to do, if asphalt gets too hot then it starts to evaporate some of its chemical components that make it flexible. The idea of steel fibres is something that is currently being researched more for use in cold climates, the downside is that it makes road surfaces more expensive.

    The City currently does something similar to healing the surface of the road in what is called “microsurfacing”. The idea is to add a small amount of material and a emulsifying chemical to repair the surface and avoid development of deep cracks. The trick is you need to do it regularly, if you let a road go to long it can’t be fixed without some serious repair work and then the potholes are way worse. I guess there are no ‘magic bullets’ other than a good program of preventative maintenance.


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