In The Wizard of Oz, Dorothy and her companions travelled down the yellow brick road of fantasy. In the real world, when it comes to building streets and highways, gold isn't practical or economical. But construction crews are finding considerable value in recycled materials as diverse as rubber, wood, steel, concrete and slag, a waste byproduct from steel production.

"There was a time, 25 years ago or more, when people simply dumped things," says Michael O'Connor, executive director of the Ontario Hot Mix Producers Association (OHMPA). "If you were rebuilding a road you would take the old asphalt and concrete and dump it someplace, whether in a landfill or in the back of some property, and use new aggregates."

The OHMPA promotes the use of recycled materials as ingredients in hot-mix asphalt pavements and O'Connor says a prime material for recycling back into a road is the road itself. Crews can take broken concrete, crush it and reuse it as an aggregate beneath the driving surface. Reclaimed asphalt is also fully recyclable back into new pavement.

"You can send in a milling machine that actually grinds off the surface. Those grindings are perfect to recycle back into the same hot-mix that will go back down in the same project," he says.

Photo courtesy of Saskatchewan Highways and Transportation
Saskatchewan highway workers apply rubber from recycled tires to a stretch of pavement.

O'Connor says asphalt is the most recycled material in North America. "On average, 80 per cent of all asphalt pavement is now recycled. That's taken a great deal of weight off landfills."

Old pavement is not the only recycled material used in road construction. O'Connor says rubber has been proven to work in a hot-mix and, while it can be a relatively expensive additive, it has the benefit of reducing vehicle noise.

He also praises slag. "There's hundreds of thousands of tonnes of it in Hamilton from companies such as Stelco and Dofasco. It needs to be cured first, but it's a strong aggregate and has very good frictional properties."

Not all recycled materials are equally suitable for building roads, however. O'Connor says old asphalt roofing shingles contain high-quality asphalt cement, which is perfect for hot mixes. But the nails can be difficult to remove, so shingle recycling is often limited to cut-offs left over from the manufacturing process.

And, while glass has been looked at experimentally, it generally doesn't bind well with other compounds. Broken glass can also damage tires and it costs more than many better-quality aggregates.

"We don't want to use our pavements as a linear landfill, just to get rid of things," O'Connor says. "Some things simply shouldn't be in there."

In Saskatchewan, the provincial government is considering crumb rubber, made from shredded scrap tires, as an ingredient in asphalt concrete.

Rubber isn't an entirely new additive in pavement mixes - Saskatchewan used it briefly two decades ago - and the material has been catching on for many years in jurisdictions ranging from Alberta to Arizona.

However, new equipment and methods for producing the right blend, coupled with heightened environmental awareness, have led Saskatchewan to test it along a 20-kilometre stretch of Highway 11 near Chamberlain. The rubber, from recycled tires, is being used in the northbound and southbound driving lanes, while the passing lanes and shoulders are being built with conventional unadulterated asphalt.

Allan Widger, executive director of engineering standards with Saskatchewan Highways and Transportation, describes the project, undertaken in July 2005, as a "demonstration test" designed to give the province's contractors experience with the modern mix. It will also allow them to see how it fares in a harsh winter climate.

Stephen Damp

"There were problems back in the '80s with the equipment, the blending portions and the handling of it," Widger says.

As part of the project, the National Research Council embedded gauges to measure any undue pressure or strain beneath the surface. "Initial indications are there hasn't been the cracking that happens with conventional roads," Widger says.

Widger also says that similar rubber-asphalt mixes reduce pavement thickness and vehicle noise, and prolong pavement life compared with conventional asphalt, while there are no differences in road construction operations. "Rubber gives better resistance to rutting, and it has give to help prevent cracking. With normal concrete you have to go thicker. This is more durable."

In British Columbia's Lower Mainland, road builders have found a novel use for wood waste. Colloquially known as hog fuel, the tree bark and outside layers of wood junked at local saw mills are encapsulated in plastic and placed beneath the water table in low-lying, swampy areas to support roads.

The province first used hog fuel 19 years ago beneath a section of Highway 91, a major, full-volume route near Delta.

"It's standing up quite well," says Rob Buchanan, the B.C. transportation ministry's acting chief engineer for geotechnical materials and pavements.

He adds that the highly anaerobic environment beneath the water surface is unfriendly to bacteria and thus keeps rot at bay. "It would have taken a long time to get all the settlement out for the road bed. This essentially creates a raft, and you float your highway construction on it."

The province has done smaller hog-fuel projects in recent years, including overpass approaches in similar soil conditions. Buchanan says the pavement above is completely normal and there are no weight restrictions. "You wouldn't know it's any different from a normal highway."

Of course, the use of any recycled material depends on economic factors such as supply, demand and cost. Buchanan says wood waste is generated nearby, in the Fraser Valley, which minimizes transportation costs.

Stephen Damp, a senior vice-president with Miller Paving in Markham, Ont., and president of the Maryland-based Asphalt Recycling and Reclaiming Association, says the success of using old materials ultimately depends on quality and price - and the factors that contribute to quality and price.

Recycled asphalt leads the way in road construction because it performs well, is readily available and costs less than virgin aggregates, Damp says, adding that construction companies gain a commodity while avoiding costly trips to the landfill to dispose of something they don't need.

"Dumping fees can be used to offset the end product, therefore making it cost-effective," Damp says. He extends this principle to other materials such as rubber and glass, but adds that the availability and proximity of materials must also be considered.

"Do the supply and demand in any one area work so that the materials can be recycled and incorporated cost-effectively in the local geography? This needs to happen before anyone spends big money on transportation to move it," he says.

Ironically, Damp says, trucking is not only costly but it's also environmentally harmful.

"It burns a ton of fossil fuels. There's a limit to how far you can start trucking materials before you lose both the economic and environmental benefits."

Damp says he is optimistic Canadians will increasingly be driving over recycled roads. "We're seeing continual growth in recycling every year and we're seeing a lot more research and development into more cost-effective ways of processing old materials.

"I firmly believe we will see the percentages and the volumes of recycled materials incorporated into road construction continue to grow," he says.

(Saul Chernos can be reached at chernos@businessedge.ca)