Pothole archeologist alarmed by decaying roads

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Most of us see a pothole as something to dodge. Douglas Fisher studies it like a pavement archeologist. He examines the gritty texture of the aggregate around the edges of a hole, and it speaks to him about why it crumbled. He’s like a pothole whisperer.

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Opinion

Most of us see a pothole as something to dodge. Douglas Fisher studies it like a pavement archeologist. He examines the gritty texture of the aggregate around the edges of a hole, and it speaks to him about why it crumbled. He’s like a pothole whisperer.

In our conversation this week, Fisher came across as understated, a man who is cautious about his opinions — until the topic turned to the dismal condition of Winnipeg roads.

“I know asphalt. I studied asphalt. There are ways to design a mix that’s better for the roads in this climate,” he said.

Douglas Fisher says coarse asphalt mixes are much more susceptible to aggregate loss in freeze/thaw conditions than finer mixes. (Ruth Bonneville / Winnipeg Free Press files)

Fisher’s career included 37 years with the Manitoba highways department, helping develop the best possible mix of pavement aggregate. He retired as the manager of engineering audit and quality assurance. When he offers an informed suspicion about why roads in Winnipeg are decaying faster than ever, he has street cred (please excuse the pun).

“I have never seen new asphalt pavement in Winnipeg perform as poorly as in the last few years,” he said.

He sent a letter saying as much to Mayor Brian Bowman this week. The mayor undoubtedly gets many letters complaining about the roads, but Fisher’s letter offers a novel reason why new pavement is crumbling in only three to five years when it should be lasting four times as long.

He started by explaining a pavement problem that is familiar even to those of us who are not experts in road construction. Potholes form in pavement due to the freeze-thaw action, where water enters the structure and the asphalt loses its ability to hold the mix together. Nothing new there. The freeze-thaw problem has long been known as a Winnipeg challenge that results from extreme weather.

That usually happens in old pavement, though, as aged asphalt becomes brittle. Potholes in relatively new pavement are caused by something else, and Fisher has an informed suspicion.

He says a major factor contributing to the rapid failure of new pavement could be a shift towards coarser asphalt mixes. He keeps an eye on tenders for asphalt mix, and he notes provincial specifications have recently shifted to reduce the amount of fine sand and increase the amount of coarse aggregate.

He explained that coarse asphalt mixes are much more susceptible to aggregate loss in freeze/thaw conditions than finer mixes.

The consequence is that new pavements that should last 15 to 25 years, depending on wear and tear, are failing prematurely. That’s why Winnipeg drivers who encounter road construction often comment: “Didn’t they just do this stretch of road a few years ago?”

So why would Manitoba road engineers invite problems by choosing a coarser asphalt mix? Fisher wonders whether they’re following a a U.S. industry trend towards a coarser mix, which is better suited to more temperate climates in that country. Fisher said mixes with higher fine-sand content are better suited to Winnipeg’s freeze-thaw climate.

“Manitoba has an abundance of fine sand. It’s by far the cheapest ingredient in an asphalt mix.”

To put it bluntly, using coarse asphalt mixes instead of less-expensive sand mixes may mean Winnipeg is paying more and getting less durable road covers.

Given the high costs of road reconstruction, the city and the province should be eager to extend longer life to the crumbling pavement and the average of 170,000 potholes that typically pit Winnipeg streets from March to November.

The province announced in May grants totalling $15 million to fix roads. That announcement was also memorable for a coffee spill that was unfortunate but also serendipitously apt; Premier Heather Stefanson was en route to the press conference on potholes when her vehicle hit a pothole and she spilled coffee on herself.

Manitobans feel the premier’s pain, not necessarily from hot coffee, but many of us know the financial pain of slamming into potholes that damage our tires and the front end of our vehicles’ suspension. Manitoba Public Insurance says claims for pothole damage to vehicles was up about five times this spring.

We don’t need experts to tell us that driving on disintegrating pavement is costly and dangerous. But we should welcome experts who can knowledgeably discuss ways to make Winnipeg road surfaces last longer.

What seems to be needed is a deep dive by the city into its pavement content and paving processes. That should include an investigation into whether Fisher is correct in his supposition that the coarser gradation of asphalt mix that is becoming popular in the U.S. is not suitable for the city.

The goal should be to learn why new pavement in Winnipeg is failing before its time. The answer might lie below the surface.

carl.degurse@freepress.mb.ca

Carl DeGurse is a member of the Free Press editorial board.

Carl DeGurse

Carl DeGurse
Senior copy editor

Carl DeGurse’s role at the Free Press is a matter of opinion. A lot of opinions.

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