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By Debbie Waldman

Hugh Donovan (Civil ’78) has no trouble remembering his introduction to asphalt rubber. It was 1976, and he was testing the then-new road surface for the City of Edmonton.

He wasn’t impressed. “It did not perform well,” he recalls. “The surface deteriorated, and the rocks started coming out of the mix.”And yet, when the Tire Recycling Manufacturers Association (TRMA) approached him in late 2000 to reconsider the technology, Donovan, didn’t hesitate. Now director of engineering services for the City of Edmonton, he’d read enough to know the process had been modified and worked well in other jurisdictions. “I went in with an open mind,” he says.

And, you might say, open roads: in the project’s second year, 23,000 tonnes of asphalt rubber were laid on test sections on Edmonton and Sherwood Park streets, up from 3,500 tonnes in 2002. It’s also being tested in Calgary and Lethbridge, and on a few sections of highway in the province.

The engineers who served on the steering committee have been uniformly impressed with the latest incarnation of the material. It has proven to be quieter, less likely to rut, and more skid resistant than traditional asphalt.

“Everybody seems pleased so far,” says Lyle Treleaven (Civil ’97), the project manager/
coordinator for EBA Engineering Consultants, Ltd. in Edmonton, which was hired by the TRMA and Alberta Transportation in early 2001 to research asphalt rubber and provide the department with recommendations on ideal applications in Alberta. “It’s not a miracle material, but it is better than conventional asphalt for several reasons.”

For one thing, it’s considerably quieter. According to Treleaven, asphalt rubber reduces the ambient sound level by up to eight decibels—a significant difference not only for drivers but for those living nearby.

In the City of Edmonton and in Strathcona County, residents and officials have been vocal and enthusiastic about the noise reduction. Some have gone so far as to request asphalt rubber be used to pave more roads.

“There was an article in the local paper about asphalt rubber, and people in general just noticed the difference,” says Bob Horton (Civil ’80), county engineer and manager of engineering and environmental planning for Strathcona County. “We’ve had people calling in and there have been letters submitted.”

Because asphalt rubber is still in the evaluation stage, no decisions have yet been made as to its future in the province. But no one is ruling out the possibility that it will become a permanent fixture in at least some jurisdictions.

“We have a number of locations within the City of Edmonton that require noise attenuation structures,” Donovan says. “If we can reduce the noise by using an asphalt rubber mix, it may preclude us from having to build very expensive noise attenuation devices to get a similar result.”

Asphalt rubber’s reintroduction in Alberta came about through the efforts of the TRMA, which was founded in 1993 after then-Minister of the Environment, Ralph Klein, decided the province needed to recycle tires instead of letting the old ones pile up and become potential hazards.

“Eliminating stockpiles prevents or avoids threat of tire fires, which have significant impact on groundwater contamination,” explains Al Schulz (Chemical ’68, MEng Mechanical ’74), who was assistant deputy minister of environmental regulatory service under Klein and is now the APEGGA representative to the TRMA. Because abandoned tires are an ideal place for water to collect, getting rid of them also minimizes the threat of West Nile by
eliminating potential breeding grounds.

The TRMA began recycling tires in earnest in the mid-1990s. By the early part of this decade, the stockpiles were gone, Schulz says. Recycled tires are shredded into
one- and two-inch chips, or shred, which are used in civil engineering projects including road stabilization and leachate for landfills. Some of that shred is further processed into rubber crumb.

Since 2001, when the TRMA asphalt rubber steering committee got off the ground, rubber crumb has been used primarily as an alternative surface for playgrounds and riding arenas, and to make molded products and dairy mattresses.

“Fundamentally, the challenge for the Tire Recycling Management Association and for an effective recycling program, is to encourage the development of markets for the product,” Schulz says. “That is why we’re getting involved in asphalt rubber—to see if it works in this climate. Once we have tested and evaluated the technology, the industry can develop those markets and run on its own.”

In North America, asphalt rubber has been used the longest and with the greatest success in warm climates, mostly in Arizona and California. In fact, Alberta engineers spent some time studying the roads in Arizona and meeting with transportation experts there to learn more about asphalt-rubber’s benefits and drawbacks.

In 2002 and 2003, the TRMA brought in an asphalt-blending company from Arizona to make asphalt rubber for Alberta roads. The company used locally recycled tires, Alberta asphalt oil, and gravel. But bringing the experienced workers and their equipment here, even for very short periods, drove costs up significantly. Also, by importing the equipment and technology, Alberta municipalities had to fit their schedules around American projects.
 
This year, the TRMA opted to find an Alberta-based contractor willing to invest in the equipment and expertise. Fath Industries of Edmonton won the contract, bought the equipment, and sent a plant operator to Arizona for training.

“Everybody seems to be fairly confident that Fath will have success with this equipment,” Treleaven says. “They have their own paving plant, and they have been guaranteed a certain amount of tonnage or production days for the next three years to make the purchase feasible for them.”

Asphalt rubber is made from rubber crumb, aggregate, and asphalt oil binder. Back in the 1970s, the crumb was blended into the aggregate and the oil was added afterwards in what was known as a “dry” process. In the new, “wet” process, developed in Arizona, the asphalt oil binder is heated to approximately 195 C. The rubber crumb is added and the mixture is agitated and cooked simultaneously for approximately 45 minutes. After the rubber crumb reaches a gel-like consistency, the asphalt rubber binder gets pumped into the asphalt mixing plant with the aggregate or gravel. The two are mixed together and used immediately.

The latest technology has been more successful than its predecessor. But while the California and Arizona engineers’ claims of noise reduction have certainly proven to be true, Albertans aren’t yet reaping other benefits touted by those south of the border.
In California, engineers have been able to reduce the asphalt rubber overlay thickness on the road surface by 50 per cent and still retain good performance. Alberta engineers aren’t convinced that will work here.

“We’ve tried in a couple of locations, but the thinner stuff isn’t performing as well as we would like,” Treleaven says. “It’s cracking more than the thicker layers. We’re thinking more along the lines of being able to reduce it by closer to a third, but that’s not proven yet. It’s something that’s going to take some time to evaluate.”

Arizona’s asphalt rubber roads have had no reflective cracking (where a crack “reflects” through an overlay), but that hasn’t been the case in Alberta. Almost all asphalt will develop some cracks, but Alberta’s cold temperatures mean it’s bound to happen sooner and more extensively.

 “We looked at Flagstaff, Arizona. They do have a low temperature value of -30 in the winter, but I suspect that’s for about 30 seconds,” Donovan says. “They get snow, but their high-end temperatures are much hotter than ours, and their low-end temperatures don’t last for as long as ours.”

Donovan isn’t convinced that asphalt rubber prevents low-temperature cracking. “I haven’t seen an asphalt that does that, and that we can use in our environment,” he says. To accomplish that, the asphalt would require an oil binder two-to-three grades softer than what’s currently used here. The result: “We would find there would be phenomenal
rutting of our roadways, because the material would shove and push under tire traffic.”

Low-temperature, or thermal cracking, is inevitable in Alberta’s climate regardless of the surfacing material used, but asphalt rubber seems less likely to sustain permanent damage from fatigue cracking—which occurs from repeated use and aging. “Any fatigue cracking that’s reflecting through does knead back together with traffic on it,” Horton says. “That doesn’t happen with other kinds of road surfaces.”

 Asphalt rubber’s ability to mend itself is one reason that Allan Kwan (Civil ’78) feels it has such promise. As the executive director of technical standards for Alberta Transportation, Kwan searches for state-of-the-art practices and new engineering solutions for the province. He believes he’s found a good one in asphalt rubber.

“Rubber can stretch. So by that logic, if you can integrate it into the pavement, the material is more flexible,” he says. “The more flexible the pavement, the less cracking there will be. But of course, we don’t want it to be so flexible that it can’t handle the traffic flow, so we’re looking for that perfect balance.”

The key word there is we. “It’s a team effort,” Treleaven says. His employer, EBA, was honoured earlier this year for its work with asphalt rubber—winning an Award of Excellence in Transportation Infrastructure from the Consulting Engineers of Alberta. But Treleaven stresses the importance of input from the TRMA, Alberta Transportation; the Cities of Calgary, Edmonton, and Lethbridge; Strathcona County; Husky Energy; the Alberta Roadbuilders and Construction Association; and the U of A’s Faculty of Engineering, where Dr. Hamid Soleymani is studying the performance of asphalt rubber.

Al Schulz, who has chaired the steering committee since its inception, also credits teamwork for the project’s success. “The strong engineering component and the years of paving experience represented on the steering committee provided an excellent project sounding board for the program development and has provided technical direction and
critical evaluation of the project,” he says.

The TRMA and the key road owners have committed to continue testing asphalt rubber through 2006. “By that time we will have had it on the roads for five years and we’ll have a much better idea of whether it’s going to perform in our climate,” Treleaven says. “We’re experimenting with different mix designs and using different grades of asphalt cement to see if we can get the performance level we are seeking.”
Alberta is currently the only province
in Canada using asphalt rubber, although
the technology has been tested in Ontario
and will be tested in British Columbia this year. It’s more expensive than conventional asphalt; the rubber crumb and higher-than-normal oil binder content add to the cost, as does the blending process itself. But if Alberta engineers can fine-tune the recipe to make it work here, the benefits in terms of longevity may outweigh the initial cost.
Whether it will ever be cost-effective enough for widespread use is unclear. That has to be evaluated over the life-cycle of roadways, generally 10–15 years, and has to include repair and maintenance. Other performance benefits such as noise reduction, may be quantified in terms of avoiding more costly and unsightly alternatives.

“For the foreseeable future, let’s say for the next five years, due to the high initial cost, it’s probably only going to be feasible for large rural highway paving projects, large communities that have large paving projects, or smaller communities located in proximity to a larger one,” Treleaven says.

That’s not to say that smaller communities may never have a chance to experience
the benefits of asphalt rubber. Kwan argues that the entire province is already benefiting, even those who have never had the experience of driving on a smooth and quiet asphalt
rubber road.

“If you look at our department’s business plan, we are also charged with being
environmentally responsible,” he says. “Noise is an environmental issue. And even though asphalt rubber is more expensive, if you use half the thickness in the long run, over its life it may be cheaper than the conventional asphalt, so that’s why I’m so optimistic.”

Asphalt rubber may have had a wobbly beginning, but don’t be surprised if it bounces back for a strong future.

Fall 2004
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	Dean Lynch is Markin' a Milestone
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	Taking Control Systems Out of the Box
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	When the rubber hits the road
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Home > Fall 2004 > When the rubber hits the road