February 26, 2010

MTO

A strip of perpetual pavement along Highway 406 is being tested. It costs a little more but pays back the investment over the lifetime because maintenance is easier, officials say.

FEATURE | Roadbuilding

Highway 406 a perpetual paving testing ground

IAN HARVEY

correspondent

When it comes to designing pavement and engineering road building specifications, there’s nothing like a real world test lab to prove out ideas — the highway itself.

The Ministry of Transportation Ontario is always testing and evaluating design, mixes and materials to see which is best suited for a given application, says Chris Raymond, PhD, PEng, the acting Acting Head, Bituminous Section Materials Engineering and Research Office at MTO.

“What we’re looking for is sustainable pavement,” says Raymond, repeating the MTO mantra, which has gain traction over last couple of years.

Still, he says, there’s always a going to be relationship between the design and the cost of the pavement that has to be kept in mind.

While he heads up the bituminous section, other materials also fall within his mandate. One of the intriguing developments now being tested, he says, is the use of pre-cast concrete sections to repair concrete pavement. A section is manufactured under controlled factory conditions that allow for optimum curing and is then trucked to the road location where a section of damaged pavement has been cut out to exact proportions.

The road bed is prepared and the new section dropped in place like a giant piece of Lego.

“It’s a little more expensive but the advantage is that we can get the road repaired overnight in most cases and not have to wait a couple of days for it to cure and set up enough to be able to handle traffic from transport trucks,” says Raymond. “The next step is to see whether we can do longer sections.”

Pervious concrete is also getting a test run on Highway 427 while there are also some Portland cement texturing trial along Highway 401 which involves trying different rakes or combs on the surface to add texture and see how it affects traction and road noise.

On the asphalt side, the MTO is also warming to warm mix asphalt, a modified mix that can be rolled at temperatures up to 50C degrees less than conventional hot mix, reducing energy consumption, greenhouse gas emissions, and fumes.

Warm mix asphalt can also be used to extend the paving season and lengthen haul distances.

MTO

There are still questions about pervious pavement’s long term viability and safety, issues which are being investigated in testing.

Meanwhile, perpetual pavement is also creating a buzz . There are three major test projects — one single kilometre over a four lane stretch along Highway 406 near Thorold, 44 lane kilometres on Highway 7 near Ottawa which will be finished later this year and two other test sections on Highway 401 near Woodstock, six lanes wide and two kilometres long, also due for completion this year.

While perpetual pavement costs more, its 50-year life span and ease of resurfacing will balance the cost and the evaluation underway now seeks to prove that theory out.

On the flip side, ‘quiet’ pavement sounds great – figuratively and literally — but is proving to have a shorter life span, which is prompting engineers to tweak its composition and look for applications where it might the cost might justify its application.

“It’s good to take something from the lab and theory and test it out,” says Raymond. “Even if the test fails to meet expectation we end up with a lot of really great data.”

Rubber crumb additives to asphalt mix are a case in point. The concept has been around since the 1980s as a way to turn scrap tires into a useable and valuable commodity.

There are three main methods to create the mix — dry, wet and semi-wet —which describes the stage and size of the crumb.

The problem has always been that the dry process hasn’t produced a pavement that performs well enough under high traffic volumes, while the other processes involve fine crumb that is expensive to produce without marked improvement in performance.

However, in 2008, two semi-wet trials on Highway 15 near Smith Falls using cryogenically processed crumb – the rubber is frozen at extremely low temperature and then shattered to separate it from the steel belts of the tire — produced more promising results.

None of the data goes to waste. Performance data from all Ontario roads and highways — not just those in the test and evaluation programs — is dumped into the MTO database where it can be analyzed through a process known as data mining.

In this way, says Raymond, a fairly predictive model of how materials and engineering might react can be pulled out.

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