Doing Asphalt Right

Are we ensuring that our clients are getting the best surface and subgrade paving structures possible?

Supported by new engineering and the experience of other paving contractors in Canada and the U.S., some say no.

 Canadian paving contractors can do a better job of building paved structures with the requisite strength, flexibility, durability and frictional properties clients want by taking another look at underused technologies, according to some in the industry. Better still, they can do it without breaking the bank or undermining their project schedule.

STABLE SOIL

It’s a major concern for Lewis O’Toole, vice president of Technical Services for AMEC’S Earth and Environmental division. Canadian paving contractors have been slow to understand – and apply – chemical or cement stabilization techniques to their paving substructures, he says, despite their obvious importance to paved surfaces in Canada.

“We didn’t invent it in Canada, but we’ve adapted it to Canada,” he notes. “We have some of the most challenging soil and weather conditions anywhere in the free world.” Soil stabilization involves intermixing lime or cement with unstable, wet soils to create chemical reactions that remove standing water – transforming wet soil into workable material. It’s particularly useful in areas where aggregate is scarce or has to be trucked in over long distances, on projects subject to rain delays under tight deadlines. Instead of waiting around for the soils to dry, lime or cement work quickly to dry and harden the surrounding clay. “It’s just very sound technology,” O’Toole asserts, citing a large expressway project in the U.S. which AMEC just completed, using extensive soils stabilization to put some backbone into the surrounding abundance of very soft clay.

Here in Canada, soils stabilization finds its greatest use in northern Alberta, southern Ontario, New Brunswick and Quebec – places where weak clays abound. But O’Toole believes strongly that other parts of Canada might benefit by using lime- or cement-based soil stabilization, too. One example is the muddy Lower Mainland’s Delta basin or the Fraser River. Or consider the mudflats associated with the Bay of Fundy and along the shores of Nova Scotia. It’s “an ideal solution for new construction there,” O’Toole maintains.

The benefits of lime and cement are not confined to stabilizing weak clays, as some believe. Cement stabilization is particularly good at strengthening “soils that are sandier in nature,” says O’Toole. But once again, “not everyone is aware of these technologies.” It is a tough sell to some in the industry, despite the proven benefits. “If you talk to a hot-in-place recycling paving contractor, he’ll say it’s hocus-pocus because that’s not what his experience is or where his interests are from an economic perspective. It takes time to educate people,” says O’Toole.

A good example of the potential benefits can be seen in a recent project in southern Ontario. Soils scientist Dr. Christopher Holt, P.Eng, is a global expert in soils stabilization. He prepared the specs for lime and cement soil stabilization on new access roads built during expansion of the Chatham Energy Windfarm in 2010.

“It was really the first time it was used in Ontario. It was based on an economic argument in terms of reducing the amounts of crush to develop these access roads to each of the 44 new turbines. The aggregate coming in from the US was a little more costeffective, but nonetheless it was still very expensive,” says Holt.

Instead of a remove-and-replace approach – importing a 350 – 400 mm depth of granular to cover plastic clay and topsoil – the existing clay was mixed with a combination of lime and cement kiln dust. “As a result, we reduced the gravel import by a good 12 inches,” says Holt.

In fact, three things were achieved, according to Holt’s subsequent report:

• Minimal soil removal (100 mm) to ensure that the access roads were below the existing grade of the surrounding agricultural land;
• Expedited construction of haul roads with less disruption because of bad weather and minimized soil movement;
• Reduced carbon footprint because less quarried material was required.

Why is it so hard to convince builders to use soils stabilization?

The answer varies, says Holt. Many areas of BC and the Atlantic provinces are made up almost entirely of hard rock, so that supplies of aggregate are readily available. In other areas, roadbuilding and aggregates alliances do all they can to lock out or discourage soils stabilization companies from gaining access to their customer base.

“If you come in with an alternative, you pretty much get crushed – excuse the pun. But they have been trying to use it more in Saskatchewan and Alberta, particularly where they have the silty tills and clay soils.”

Adolf Friesen can attest to that. The general manager at Alberta Paving Ltd. in Calgary says that in rainy weather on clay-based job sites, “You can sit there forever and wait for it to dry.” Instead, he notes, you can use the lime to dry it out and harden it up to get the densities you need. Reduced shrinkage and swell, increased compressive strength (by as much as 40 times), better beam strength and load-bearing values – it’s all there in the lime, says Friesen.

There is not much clay at the Port of Vancouver, Imperial Paving project manager Robin Smith says. However, the silt soils under the access roads leading to the Port’s storage containers are very weak. They are subject to stresses from huge forklifts unloading container ships and high traffic volumes. “It needs a good base, but those old silts aren’t the best structures for that,” says Smith.

Cement powder mixed with gravel and water are, “forming almost a kind of soil cement.” We asked Smith how useful lime is for asphalt projects. “They used to build asphalt curbs nine inches high, and they used to fall over all the time because asphalt couldn’t support until it hardened,” he points out. “You put lime in it and it holds everything together.”

MICRO-SURFACING

Another underused technology, like soils stabilization, is micro-surfacing for new roads and general asphalt maintenance. Like lime and cement stabilization, micro-surfacing to fill ruts, repair longitudinal and transverse cracking has also been slow to take off in Canada. “It’s like anything,” says Andrew Arnill, operations manager for West-can Sealcoating Inc. in Didsbury, Alta. “It’s changing people’s perceptions. ‘Shave and pave’ – all most people know – is 50 mm.”

In Alberta, perceptions about micro-surfacing just might change. A year ago when it was awash in oil money, Alberta road contractors and governments thought nothing of spreading thick asphalt on major roads and highways. Now, with a recession looming and budgets tightening, says Arnill, “You’re really going to see people gearing more to preservation strategies. For long term spending strategies, it can’t be just a ‘worst first’ road-maintenance approach.”

Micro-surfacing is a mixture of polymer modified asphalt emulsion, aggregate, Portland cement, water, and liquid additives. Depending on the weather, it sets quickly, allows traffic timely access, provides good skid resistance and does a decent job extending a roadway’s life cycle. “We’re also able to minimize how long we’re on a section of road,” says Arnill. “We’ve got the ability to do 10-
plus lane kilometers of road on an average day, which is a fast-moving operation.”

Micro-surfacing is popular in urban areas, Arnill adds, because it eliminates utility adjustments and “ties right into curbs, so you don’t have to mill out in advance. And you have the skid resistance, of course. So there’s a lot of pros to using the product.”

Results vary. “We don’t do any of that (in BC),” says Smith. When asked why not, he cites a job he’s currently working on to pave a section of road on a hill in Mission, B.C. It was micro-surfaced a year and a half ago. “About 60 to 70 per cent of it is now missing. We don’t find good results with it,” he says. Assuming micro-surfacing has worked elsewhere, Smith’s other concern is getting rid of the product once it has served its purpose. “Does it meet all the standards of recyclable liquid asphalt? I doubt it.”

However, Trevor Moore, corporate technical director at The Miller Group, says that it does. Miller Group has micro-surfaced across the country, and Moore says it has gained particular traction on important road projects in BC in the past few years, including the Sea-to-Sky highway and work in the Sunshine Coast, Prince George and the Okanagan Valley. “It’s gaining more and more acceptance in BC,” according to Moore.

“Once the emulsified asphalt has fully cured, the water evaporates and you’re left with asphalt cement and aggregate. The small portion of micro-surfacing material that may be left on a roadway when its recycled doesn’t have a big impact on the quality of recycled asphalt pavement or the environment,” says Moore.

Like soils stabilization, micro-surfacing has the potential to reduce the number of trucks needed to carry aggregate to the jobsite. In the case of micro-surfacing, new specialized equipment could see a boost in sales as the technique is used more and more across the country. This includes continuous paving equipment as well as truck-mounted machines which carry emulsion, aggregate, cement and water to the site on a tri-axle unit.

“In some areas of Canada… micro-surfacing is being used in record quantities. Manitoba, for example, probably has the biggest micro-surfacing program in North America. And I think we’re only going to see that spread across the other provinces.”

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David Godkin is a B.C.-based freelance writer and editor. Send comments to editor@on-sitemag.com