Preventing cracks in asphalt pavement has been an issue troubling the construction industry for more than 100 years. However, as a two year research study between Carleton University and the Ministry of Transportation of Ontario (MTO) draws to a close, it appears the ultimate solution may be in sight.
The joint study has been testing the performance of an innovative asphalt compactor known as the Asphalt Multi-Integrated Roller (AMIR), conceived and developed by Abd El Halim, a professor of civil and environmental engineering in Carleton’s research-intensive Faculty of Engineering and Design. The unique design aims to improve the longevity and resilience of pavement by preventing cracking at its source.
Now the director of Carleton’s Centre for Advanced Asphalt Research and Technology, Halim’s initial inspiration for AMIR occurred as he was nearing the completion of his PhD at the University of Waterloo.
“My thesis was to use polymer grids to reinforce asphalt pavements,” he recalls. “Research in the lab suggested that using these grids would prevent certain cracks from forming for 15 to 20 years. However, our first field trial resulted in pavement that began cracking after only 20 minutes.”
While initially disheartened by the setback, Halim recognized that the cracks he observed were actually being caused by the conventional steel drum rollers used in pavement compaction.
“As the roller travels along the pavement, the asphalt in front of the roller is pushed ahead, causing a pulling force in the asphalt behind the drum,” he explains. “This pushing and pulling action causes the asphalt to crack.”
It was this realization that sparked the idea that would ultimately lead to the development of AMIR. Halim’s alternative design forgoes the use of traditional steel drums and replaces them with a track made of specially designed rubber.
One only has to reflect upon the abundance of potholes that appear every spring to appreciate how AMIR’s innovative design could potentially revolutionize our roadways. Halim strongly believes that AMIR can help to make these perennial hazards a thing of the past.
“Once AMIR’s technology is integrated into regular pavement construction in Ontario, we will see a vast reduction in the emergence and severity of potholes, even in northernmost climates,” he says. “As a result we will have safer roads that are long lasting and require less maintenance, leading to significant cost savings.
AMIR first garnered support from MTO in 1983. A full-scale prototype was then produced in the early 1990s by Lovat Inc., a Canadian manufacturer specializing in tunnel-boring machines.
Interest in the technology began to shift in 1998 when an Australian civil engineering company known as Pioneer Road Services Pty. Limited developed a production-ready version of the AMIR roller, known as HIPAC (Hot Iron Process Asphalt Compaction). Soon after, development of AMIR within Canada was put on hold due to lack of funds.
After the project sat dormant for more than a decade, MTO renewed its interest AMIR in 2010, leading to an agreement between the ministry, Carleton University and Ottawa-based transportation infrastructure firm R.W. Tomlinson Limited, to upgrade the Canadian prototype. Heavy Civil Manager at Tomlinson, Russ Perry, believes that AMIR’s new prototype holds immeasurable potential for the industry.
“It will improve the lifespan of asphalts around the globe by establishing a higher standard,” he says. “Setting the bar higher will ultimately lead to the phasing out of substandard compaction techniques.”
In October 2014, MTO entered into a bi-lateral research project with Carleton in which the newly updated AMIR would be tested under numerous real-world scenarios. During the study, AMIR was deployed in the paving of four bridge decks on MTO highways in eastern, central and northeast Ontario. The study assessed AMIR’s effectiveness with various asphalt mixtures and thicknesses compared to conventional compaction technology, along with its versatility in different construction seasons.
“Roads compacted with the newest AMIR prototype are holding well,” notes Halim. “Our monitoring has also shown them to be resilient to thermal cracking, which can result from repeated freeze/thaw cycles.”
Perry is also impressed with the results of the study to date, stressing the importance of producing pavement that is resilient to harsh Canadian winters.
“We have many paving projects that fail prematurely due to cracking and the effects of freeze/thaw cycles,” he explains. “By eliminating these cracks and improving pavement permeability, we can extend the lifespan of our highways and reduce the amount tax dollars that are spent on maintaining our roads.”
While the newest iteration of the technology has been outfitted with refined mechanics and features a streamlined design, the main principles behind AMIR’s original concept remain unchanged.
“We’ve adjusted the design to solve technical problems that were encountered over the years, but the original idea behind AMIR has always defined the project as it evolved,” says Halim. “We’re also taking advantage of new technologies and enhancements that have been developed since AMIR’s first prototype was created in the 1990s.”
While MTO cannot integrate the updated AMIR into commercial projects until the results of the study are finalized and several more units of the roller become available, the ministry has expressed ongoing support for the new technology, continuing to identify specific projects for its implementation on an experimental basis.
“We’re very interested in the potential of this unique Canadian technology to improve the performance and longevity of asphalt pavements, ultimately reducing maintenance and construction costs for MTO and the taxpayers of Ontario,” said Frank Pinder, area contracts engineer at MTO, Eastern Region Operations Office. “In general, if an asphalt pavement could last even one year longer, that would translate into an average savings of around $50 million per year for MTO provincially.”