The first asphalt paving steamroller hit roadbuilding equipment markets in Europe circa 1860. While the cab design and method of propulsion have changed over the years, the basic design featuring two heavy metal rollers has not.
That’s unfortunate, says Abd El Halim, a professor in Carleton University’s Faculty of Engineering and Design and director of its Centre for Advanced Asphalt Research and Technology. His research indicates the design of heavy steel rollers has not been the salvation of roads, but the cause of premature cracking in asphalt pavement for well over a century.
Enter the Asphalt Multi-Integrated Roller (AMIR), a different type of asphalt compactor Halim believes will revolutionize road paving and result in roads with a much longer design life.
As a student completing his PhD at the University of Waterloo, Halim’s thesis involved the use of polymer grids to reinforce asphalt pavement. A field test on Highway 5 was designed to prove that the design could prevent cracks from appearing for as many as 20 years.
“In 20 minutes there were cracks all over the place,” says Halim. “I was in shock.”
While the polymer material was initially blamed for the failure, Halim examined photos of the site and compared them to photos of asphalt using no grids. The cracks looked identical.
“I was watching my wife roll out dough using a rolling pin and I saw the same phenomenon,” he says. “The dough was cracking because the roller pulled up on the dough after it passed over it. The same cracking happens with asphalt with the roller first pushing the asphalt ahead and then pulling it up in behind as it passes.”
Conventional wisdom suggests that cracks begin deep in the roadbed and gradually migrate upward, eventually breaking out on the asphalt surface. Not so, claims Halim. The cracks have already been created by the rollers, regardless of the temperature and asphalt mixture used.
“Friction on the road surface caused by traffic opens the existing cracks so that we can see them,” he says.
While traditional paving uses a heavy roller that passes over the asphalt quickly, the lighter AMIR compactor applies less pressure over a greater surface area using a rubber track.
“Compaction is not about weight,” says Halim. “It’s about how long the rollers are in contact with the asphalt.”
However, Halim notes that patience is a virtue for revolutionary paving technology — the development of AMIR has spanned decades. Ontario’s Ministry of Transportation (MTO) took an interest in the idea in 1983 and the first prototype, AMIR I, was built in the early 1990s by Lovat Tunnel Equipment Inc., with support from the National Research Council.
While Canadian funding temporarily dried up, Australia’s Pioneer Road Services developed a production-ready version of the AMIR roller in 1998 under the name Hot Iron Process Asphalt Compaction. Fast forward to 2010 when the MTO, Carleton University and infrastructure firm R.W. Tomlinson Limited revived the concept and upgraded the AMIR prototype.
AMIR II has since been used in a number of MTO field test projects in eastern Ontario, including locations on Highways 15, 17 and 28.
The MTO had also expressed interest in the use of AMIR to compact asphalt on bridge decks, where cracks are more likely to allow chlorides to attack concrete and metal underneath the pavement.
In 2014, the unit was used to compact asphalt on the Highway 417 underpass bridge at Highway 34, at a temperature of -2 C. Halim says that all field test projects have demonstrated surfaces of continuing quality.
“Especially on the bridge,” he says. “MTO loves it and the asphalt hasn’t required maintenance after three years.”
The AMIR has undergone significant upgrades in the interim. AMIR IV features four smaller rollers replacing the original, allowing for greater manoeuverability. Halim says he expects the unit to go into commercial production next year.
“We also decided not to go with a full unit,” he says. “We produced a kit that can allow contractors to adapt their own machinery for about half the price of a new build.”