A Kingston-based researcher says our potholes could be prevented by changing the way asphalt is made. The issue is a lot more controversial that you'd think.
Simon Hesp says too many Ontario roads are paved with asphalt made of cheap, subpar ingredients. And, says the Queen’s University chemistry professor, it’s causing our streets and highways to degrade and crack far faster than they should.
Asphalt concrete, the road-paving material most of us refer to simply as asphalt, is made up of about 95 per cent aggregate, like gravel, stones, and sand; and five per cent asphalt cement—petroleum product that binds the aggregate together.
What pavement producers have started to do, particularly since oil prices began to skyrocket, is cut their asphalt cement with small amounts of different oily substances. Hesp’s asphalt research lab at Queen’s has found recycled motor oil residue (what the industry refers to as Recycled Engine Oil Bottoms) in about half of Ontario’s roads. Hesp says vegetable oil, used roof shingles, and oil from pulp and paper mills have been tried by some producers, too.
The problem, Hesp told Torontoist, is that these additives make the finished paving product more prone to moisture damage, and less able to withstand low temperatures. Local governments must do a better job of testing the materials they use to ensure they last, he added.
Toronto is well acquainted with potholes and road cracks caused by the cold and damp. The City budgeted $6 million for pothole maintenance this year alone. In March, municipal road crews were filling holes at a rate of 4,000 per day.
In May 2014, city council voted for municipal transportation and construction staff to “undertake a review of the City’s current testing procedures to ensure asphalt laid in the City of Toronto meets strength and longevity requirements.”
The City of Toronto has specifications for roadwork materials, and these standards must be adhered to by contractors bidding for municipal construction projects. The specifications call for “an asphalt-based cement that is produced from petroleum residue either with or without the addition of non-particulate organic modifiers.”
The asphalt cement must come from an Ontario Ministry of Transportation–approved producer. And contractors must provide the City with quality-control testing results, and samples, for the asphalt cement it intends to use at least 10 working days before paving begins.
But what may happen, said Robert Klimas, a senior engineer at the City’s construction standards office, is that the City accepts substitutes that seem as good as pure asphalt, but produce different outcomes over time.
“We say, ‘We want this [type of] asphalt,’ and they say, ‘Oh we have an equivalent one here which meets the specs,’ but then, maybe longer term, it doesn’t meet the specs,” said Klimas. “It’s cheaper for them.”
Motivated in part by Hesp’s work, the states of Maine and New Hampshire have banned the use of Recycled Engine Oil Bottoms in asphalt. And associations in the North American asphalt production industry are re-examining the efficacy of additives with projects like the Asphalt Institute’s Re-refined Engine Oil Bottom Residue task force. The institute has said publicly that it supports the “responsible modification of asphalt materials for improved performance and better life cycle costs, but does not endorse any specific or proprietary form of modification.”
The Ontario Hot Mix Producers Association, representing this province’s asphalt industry, has Pothole 101 Facts & Fiction Sheet that, despite not referring to Hesp by name, appear to specifically refute his findings. The backgrounder says it is a “fiction” that Toronto potholes are caused by asphalt failures or by subpar material in the asphalt cement.
And as for the City of Toronto? “We’re looking into it…” said Klimas. “I’ve heard it causes problems, but then some people say it doesn’t cause problems.”