Is there a better way to fix potholes so the repairs last longer?

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There are so many potholes this year, but for the most part they look like old ones where the stuff used to fill the holes has just come out. Is there not a better material or way to fill potholes so city staff don’t have to keep redoing the same job over and over again? – Jordy, Toronto

When it comes to potholes, there might be better Band-Aids, but aging roads are the real problem, pavement experts said.

“When you’re repairing potholes, you’re near the end of the life of the road, really,” said Simon Hesp, a professor of chemistry at Queen’s University in Kingston, Ont. “Roads should last 15-20 years without cracking.”

Potholes happen after water seeps through cracks in the road. As it freezes, it expands, weakening the pavement, which collapses under traffic.

Most cities, including Toronto, use two types of asphalt for pothole repairs: cold mix and hot mix.

Cold mix – also called a cold patch – is pre-mixed asphalt that doesn’t need heating or specialized equipment. It’s meant to be temporary and city crews carry it with them.

“[Cold mix] is used to address immediate safety concerns, mainly during the winter and early spring when hot asphalt is not always available,” Myles Currie, director of winter and seasonal services with the city of Toronto, said in an email.

A cold patch might only last a few months, “or in some cases, much shorter,” Pejoohan Tavassoti, an assistant professor of pavement engineering at the University of Waterloo, said in an email.

For longer-lasting repairs, crews use hot mix asphalt. It’s produced at industrial asphalt plants that typically don’t operate during the winter.

But even hot mix has limits – it typically lasts three to five years, but might fail within a year or two if the underlying road is already in rough shape, Tavassoti said.

However, Currie said the city considers all repairs – whether cold or hot mix – to be “permanent.” We asked exactly what that means and didn’t get an immediate answer.

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Rough patch?

So far this year, Toronto has repaired nearly 76,000 potholes and counting – nearly 10,000 fewer than this time last year. About 25 per cent of those were cold mix repairs and the rest were hot mix, Currie said. We asked the city how many had been repaired before and whether it keeps track of how long repairs typically last. It didn’t answer.

Asphalt – a mix of sand, gravel and stone bound together with bitumen left over from refining petroleum – is more complex than it looks.

According to a 2019 report by the Transportation Association of Canada, there are hundreds of pothole repair products available, but the best patch is hot mix applied in warm, dry conditions.

Right now, a standard pothole repair costs Toronto about $25, Currie said.

There are newer techniques that may last longer, but they tend to cost more and be slower to apply, Waterloo’s Tavassoti said.

One is spray injection, which has been used in a few U.S. states, including Minnesota – but it requires special trucks.

Going to pot?

Many Canadian cities, including Edmonton and Montreal, are struggling with potholes this year. That’s often partly because of more temperature swings from above freezing to below freezing – so roads freeze, thaw and freeze again more often than they were designed to handle, Tavassoti said.

“Climate patterns have been shifting over the past two decades, moving away from relatively stable trends toward more variable and, at times, extreme conditions,” he said. “This means accelerated material degradation ... beyond what was expected to happen.”

Hotter summers and heavier precipitation aren’t helping either, he said.

Roads built in the 1980s typically lasted 30-40 years before needing resurfacing – now many last half that long, Hesp said.

Hesp blames that on some contractors using more recycled pavement – old roads that have been ground up – to save costs without testing it to make sure it’s durable enough.

But Tavassoti said recycled pavement can work well if done properly – and the U.S. and Europe use more of it than we do.

While there have been news stories about cities testing artificial intelligence to catch potholes sooner and trials of pavement that repairs itself, the bigger problem is that many cities can’t afford to properly maintain the roads they have, Tavassoti said.

Potholes are often a sign that a road needs resurfacing, he said.

“Especially during winter, pothole repairs are best viewed as semi-permanent solutions until more comprehensive rehabilitation can be carried out.”

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