February 12, 2014, Toronto, Ont. – Thanks to the “polar
vortex”, pothole season arrived a little early this year. As a result, this
winter there has been a lot of talk about potholes and whether there could be a
cure for what ails the roadways.
February 12, 2014, Toronto, Ont. – Thanks to the “polar
vortex”, pothole season arrived a little early this year. As a result, this
winter there has been a lot of talk about potholes and whether there could be a
cure for what ails the roadways.
The reality is that there is no panacea for potholes, which
are caused by water that gets into the pavement base. When the ground freezes,
so does the water at the base of the pavement, causing expansion. Repeated
freezing and thawing of this water weakens the pavement, softening it to the
point where the weight of passing vehicles begins to break up the pavement
matrix and a pothole is born.
According to Sandy Brown, technical director of the Ontario
Hot Mix Producers Association (OHMPA), the key to pothole prevention is to
build a durable road with good drainage, adequate pavement thickness and tight
longitudinal joints.
“You also want to properly maintain road by sealing cracks,”
explained Mr. Brown. “If water doesn’t get to the pavement base in the first
place, the pothole problem is resolved.”
The quality of the asphalt cement used also plays a part in
how well a road performs. All asphalt cement used in Ontario meets OPSS.MUNI 1101
specifications.
“There is no ‘garbage asphalt’ in Ontario,” said Mr. Brown.
In the 1970s, polymer modification was introduced in North America to help
pavements perform better within a wide range of climate conditions and heavy
traffic. “It’s not the amount of polymer but rather the method of incorporation
that is important.”
Currently Ontario does not have a test procedure that
identifies proper polymer modification. Ontario’s Ministry of Transportation
(MTO) and the industry are examining the Double Edge Notched Tension (DENT)
test and a new procedure developed in the U.S. called the Percent Recovery
portion of the Multiple Stress Creep Recovery (MSCR) procedure. These tests
help to determine the quality of the polymer and how well it binds with the asphalt
cement. Both tests are being evaluated on 33 contracts in an industry/MTO
partnership through the MTO-OHMPA Binder Task Group, testing asphalt cement
grades ranging from PG 52-40 to PG 70-34 all across Ontario. These test
sections are full MTO reconstruction projects. Some of the contracts are three
years old and will be inspected this year. All of the trials will be completed
in five years.
One modifier that may be used in some grades of asphalt
cement is derived from recycled and re-refined engine oil. High Vacuum
Distillate Oil (HVDO) is a product that comes from a refinery, which is used to
produce recycled engine oil for your car.
“It is not the sludge collected from the local garage,” said
Mr. Brown. “Using recycled/refined engine oil is a sound environmental
practice, instead of burning or landfilling the material.” The controlled use
of HVDO in asphalt cement not only improves the quality, according to papers
presented in the last two years at the Canadian Technical Asphalt Association
(CTAA), but also fits with MTO’s initiatives to have the greenest roads in
North America.
“The industry agrees that there is a continual need for better
performing roads and for improved tests to evaluate asphalt cement and that is
what OHMPA and the industry is striving for,” said Mr. Brown. “However, the
asphalt cement plays a very small part in the development of potholes.”
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