The road to better roads
Local engineer paves way to pothole-free future
By: Kevin Ma
| Posted: Saturday, Aug 24, 2013 06:00 am
There’s an old joke about Alberta having just two seasons: winter and construction.
And that’s certainly been true of St. Albert this summer. St. Albert Trail, Mission Ave., Campbell, Hebert, Veness … it seems you can’t drive two blocks without running into one of those orange construction signs.
About 90 per cent of Canada’s goods and services are transported by roads, says Susan Tighe, the Canada Research Chair in sustainable pavement and infrastructure management at the University of Waterloo. “We complain about the amount of construction, but it’s really critical to our livelihood.”
But why can’t we build ones that don’t break every summer?
Hugh Donovan is working on it. The long-time St. Albert resident and engineer is the head of the City of Edmonton’s materials testing and quality assurance lab, and it’s his job to figure out why roads break – and how to stop that from happening.
Donovan, 57, is a construction services engineer who has spent about 34 years in the road-building industry. He was actually a student in the Edmonton materials lab a few decades before he became its head in 2000, he notes. “I jokingly said it took me 25 years to get my old job back,” he chuckles.
He strides into the lab, which is like an industrial kitchen for rocks. Much of this experimentation happens in the materials lab, like a well-equipped kitchen for the master chef. The faint smell of asphalt mingles with the rush of gravel and roar of fans as overall-clad scientists burn, crush, sieve, wash, pour and mix bricks of blacktop to figure out what’s in and what’s wrong with each.
The guys here call him the “Big Enchilada,” he says, with a laugh.
Donovan points out a row of foot-long core samples of asphalt taken from the Yellowhead Trail. There’s a strange bump on the road, he explains, and they’ve taken these samples to try and discover the cause.
Asphalt has three components, he explains: gravel, oil (bitumen) and air. The air pockets let water flow through the road, the oil gives it flexibility, and the gravel gives it strength. You use crushed rock with lots of surfaces (and therefore friction) for heavy, Yellowhead-Trail-level loads, and bigger, rounder rock for lighter residential ones.
Most roads will have 10 to 30 centimetres of asphalt atop 30 to 60 centimetres of gravel, Donovan reports. The gravel drains water away from the road so it doesn’t build up, freeze and cause cracks. The hard top prevents ruts and mud, making for a smoother drive.
Why do they break?
Roads usually break due to weather. “We live in a very harsh environment,” says Bob Dunford, Edmonton’s road maintenance director, one where the temperature swings 70 degrees in a year. “It’s a huge change, and it’s tough on roads.”
Asphalt in roads has a temperature range, Donovan says, of 58 C to -28 C for most of Edmonton. If it’s too warm, it melts, which causes ruts. Too cold, and it becomes brittle and cracks. Water can enter those cracks and weaken them by freezing and thawing. Pound those weakened cracks with car tires, and they widen into potholes.
Climate change worsens weather problems, Donovan notes, as it prompts more frequent and bigger temperature swings, more precipitation, and more extreme weather.
Road collapses are usually due to water. Poor drainage can give a gravel bed the consistency of peanut butter, for example, making it so weak that a street sweeper’s tires will punch through it – something that actually happened this spring, Donovan notes.
Leaky pipes can wash away gravel bases and create sinkholes. The Yellowhead recently had one that was four metres deep and swallowed one of the crew’s jackhammers, Donovan says.
And some roads are just old – Jasper Avenue’s base dates back to the 1940s, for example. Edmonton has the cash to fix maybe five per cent of its roads a year, Donovan says, so it would take 20 years to do them all. And since the average road lasts about 15 years, by that point you’re starting over again.
Edmonton crews use many tools to figure out why a road fails and how to fix it, Donovan says, including ground penetrating radar, thermal cameras and a falling weight reflectometer (which smacks a road with a weight and measures the road’s rebound to determine carrying capacity).
In the lab, crews will take core samples of a broken road and bash, sift and burn it to determine its original contents. They can then reconstruct the original asphalt mix, test it, and come up with a superior one.
Test samples get cooked, chilled and crushed to make sure they meet requirements, Donovan explains. Some samples get thrown on the asphalt pavement analyzer as well, which runs a tiny wheel across the sample about 8,000 times to simulate 50 years of traffic.
Building better roads
Canadians spend about $12 billion a year on roads, Tighe says. If we could even shave one per cent off that through better roads, the savings would be huge.
Savings start with proper maintenance. “When we see a problem,” Tighe says, “we need to be able to get out and fix it quickly.”
Edmonton uses a gadget-filled van called an automatic road analyzer to scan roads at up to 100 km/h, Dunford says, letting crews figure out what needs to be repaired where.
In addition to crack-sealing and pothole repairs, Dunford says Edmonton has started doing micro-surfacing on its roads. Much like repainting a deck before the wood rots, this involves adding a fresh half-centimetre-thick coat of material to a road’s surface before the entire road goes to pot.
Better materials can also help. Tighe’s lab has been adding synthetic fibres to concrete to give it more flexibility, and has had good results with recycled asphalt – which, when mixed with new asphalt, can cut costs and boost strength.
Donovan’s lab recently developed a mix with fine, crushed gravel, lots of oil and special additives that tests suggest is super-tough and pothole-resistant. “Ultimately,” he says, while holing a core sample of it, “(the roads) should perform better.” Crews are now using this mix in select neighbourhoods and should enter full production next year.
You can design your roads in new ways.
Ontario is now testing “perpetual pavements,” Donovan notes, which feature three layers: a flexible, crack-resistant bottom, a weight-bearing middle and a rut-proof top. The top can be scraped off and replaced several times, making for a long-lived road. It’s pretty expensive, though, so it’s not very common.
Japan has started using porous roads, Tighe notes, which are super-permeable and use water for evaporative cooling. Others are working on “cool pavements” which generate less heat by being a different colour (e.g. lighter black).
“We’re also working on a solar road concept,” she says of her own team. By building solar panels into a road’s surface, her team hopes to turn highways into power generators.
Donovan is the kind of guy who would gladly talk about roads all day. “You’re constantly dealing with materials that are not perfectly homogeneous,” he says, as well as shifting weather, soil and traffic conditions – the kind of challenging “fuzzy engineering” he loves.
“I think I have the best job in the city,” he says, with a hearty laugh. “I get to play with different materials. I get to evaluate different processes … Hopefully, I get to make a difference in the performance of the roads.”
He says he has no plans to stop any time soon. “I’m having too much fun.”