Moves to increase recycled asphalt in road surfacing has gained pace in Canada, thanks to research conducted by Dr Susan Tighe and her colleagues. She was in New Zealand recently to share her experiences. By CAMERON OFFICER.
In her role as director of the Centre for Pavement and Transportation Technology (CPATT), Dr. Tighe presented her team’s findings and predictions on sustainable pavement engineering practices.
A professor of Civil and Environmental Engineering at the University of Waterloo in Ontario, Tighe is also the author of over 400 technical publications in pavements and infrastructure and is involved in a number of research projects, both nationally and internationally. In 2006 she was named one of Canada’s Top 40 Under 40 for her leadership and vision with respect to the Canadian transportation community.
So does she know her stuff? In a word, yes.
Tighe and her research group have been testing recycled materials in Canada in order to ensure the building of “green roads” becomes best practice; a target of 10 to 15 percent substitution of virgin aggregate for recycled material is something she believes can be adopted by contractors and road agencies in many regions, New Zealand included.
“We recognised as early as 1992 that there is a much greater need to handle natural resources in a more sustainable manner,” she told conference goers.
“We need to reduce the impact on the environment by minimising consumption of energy and virgin materials. In our minds, sustainable pavement is a subset of sustainable transport.”
The increased resources required for agencies and operators to source high quality aggregates further afield has also seen an increase in focus on the potential applications of recycled materials in Canada’s roading network.
“New quarrying licences simply aren’t being granted as readily in the Toronto area anymore, so for transit agencies the choices are, go further afield – and with two-thirds of aggregate costs being their transportation, suffer higher knock-on costs – or investigate ways of sustainably recycling existing pavements,” she says.
“Underlying this are a few simple calculations around the levels of remaining aggregate. Estimates suggest there is approximately 3.4 billion tons of aggregate left in the Greater Toronto area, so in as little as 10 years distinct shortages could be notable.
“Aggregate demand will stay the same, but a gradual increase in the use of recycled materials would benefit operators, transit agencies and urban planners.”
Tighe’s team has been using recycled material in new hot mix asphalt for sub-bases and applying test methods designed to better predict aggregate performance.
“Naturally any recycled material used needs to meet the same technical specifications as what it is being used in conjunction with. In other words, if you’re utilising premium virgin product you need to use premium recycled asphalt pavement too.”
Thanks to CPATT research, Recycled Asphalt Pavement – or RAP – is already being used in higher percentages in lower coarse binder pavement. In a New Zealand context, Tighe suggested that a RAP product might not be suitable for State Highway One, but could be satisfactory for local roads.
She adds that, due to Toronto’s proximity to the Canada-US border, heavy duty pavement is required due to equally heavy traffic flow.
“Ninety percent of goods transferred between Canada and the US are moved by truck. With the Ontario region hosting one of the three busiest border crossings between the US and its neighbouring nations, we need an extremely robust road network to stand up to traffic demands.
“One contractor in the Toronto area is already stockpiling pavement from the Trans-Canada Highway because it was premium product when first laid. It will be interesting to see how that contractor benefits over the next few years as acceptance of recycled material increases.”
Additional to research on what’s going on at ground level, Tighe says CPATT actively supports multidisciplinary and interdisciplinary research by second and third tier entities such as road builders and machinery manufacturers.
“We’re very focused on climate change for example, and how warmer temperatures impact on infrastructure. Being able to incorporate sustainable designs into existing road networks is ideal. Using existing roading infrastructure we’re researching the idea of a solar road.This is an idea which we hope will take flight in the near future,” says Tighe.
“For now though, greener roads which divert large quantities of material from overloaded landfills back into the road surface is something that municipalities should be encouraged to engage in.
“We would love to see at some point in the future a transit agency not necessarily opting for the lowest bid price for a contract, but instead awarding the contract to a more expensive bid, but one that contains ‘green’ pavement material.”