January 4, 2012

Shift to warm mix paving in road construction continues

DAN O’REILLY

correspondent

An international, provincial, and local perspective on the growing use of warm mix asphalt (WMA) in road construction was presented to the members of the Ontario Hot Mix Producers Association at the their recent annual conference.

“Warm mix paving has been used very successfully in the United States and around the world,” said Mike O’Leary, co-chair of the Asphalt Pavement Alliance, an American industry group which promotes the benefits of asphalt.

Its use has been steadily increasing south of the border and regulatory agencies ranging from the Federal Highway Administration to several state and local transportation agencies are major proponents, he said.

“Why are we shifting?,” asked O’Leary, one of three panellists who provided an overview of warm mixing paving which allows producers to mix and lay asphalt at temperatures as low as 20 C to 30 C.

O’Leary explained there are several reasons including the need to complete paving before the onslaught of winter and the fact warm mix paving generates less greenhouse emissions.

Another reason is the evolution of new technologies which make the production and installation of warm mix paving more practical and economical.

“There are now 20 warm mix technologies in the country compared to about three or four, seven or eight years ago.”

A somewhat more cautious note on those technologies, however, was subtly voiced by Chris Raymond, head of the bituminous section of Ontario’s Ministry of Transportation.

“Not all the technologies are the same,” said Raymond, who cited other WMA challenges including ensuring long-term performance and moisture susceptibility, plus the mix design procedures and the restrictions and adjustments required at asphalt plants.

Still, the production and installation of warm mix asphalt reduces energy consumption and plant emissions and those are some of the reasons the ministry is promoting it as part of its overall mission to deliver the “greenest roads in North America”.

In 2010 the ministry created a WMA task force in partnership with the Ontario Hot Mix Producers Association and the Ontario Good Roads Association with a broad range of objectives.

Since 2008 approximately 320,000 tonnes of warm mix asphalt have been paved in Ontario, of which more than 250,000 tonnes was applied in 2011.

The high tonnage stemmed from a ministry decision to target 10 per cent WMA on projects where a number of challenges were expected such as late season work and operational constraints preventing echelon paving, he explained.

The audience learned the ministry had some conclusive findings to support that decision.

An analysis of warm mix asphalt paving contacts completed in 2010, at temperatures ranging from 10 C to 30 C lower than hot mix asphalt, concluded there was no “adverse effect on mix.”

Other findings show that rutting depths were comparable with hot mix asphalt projects and that the ERS (End Result Specification) results were “either equal or better” than hot mix asphalt, said Raymond.

Six different warm mix asphalt projects involving five different contractors have been completed in Hamilton, Ont. said Gary Moore, director of emergency services for the city’s public works department.

“Warm mix asphalt may be a solution,” said Moore in a reference to the special challenges municipalities face on road construction.

In an earlier seminar, specifically dealing with late season paving, Moore explained that municipal employees are often under pressure from elected officials and the public to complete projects before winter and not hold them over to the spring.

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