By Doug Duke
The pothole blues - Searching for a cure for Canada’s potholes
By Doug Duke
Thanks to the polar vortex that engulfed most of North America this past
winter, pothole season arrived a little early this year, making the
roadway ailment appear as quickly as the springtime dandelions.
Thanks to the polar vortex that engulfed most of North America this past winter, pothole season arrived a little early this year, making the roadway ailment appear as quickly as the springtime dandelions. There has been a lot of talk about potholes and whether there could be a cure for what some might call the pothole blues.
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.
The key to pothole prevention is to build a durable road with good drainage, adequate pavement thickness and tight longitudinal joints. Additionally, roads must be properly maintained and any cracks must be sealed. The fact is, if water doesn’t get into the pavement base in the first place, no pothole will develop.
During OHMPA’s provincial Road Tour Seminars this spring, OHMPA Technical Director Sandy Brown demonstrated how pavement thickness directly impacts the quality of the pavement. Taking a two-by-four plank of plywood, he first laid the piece of wood flat and showed that he could easily bend the wood. He then simply turned the wood on its side to make it thicker. Mr. Brown was unable to bend the wood. This simple demonstration visibly pointed out that thickness matters.
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, which guarantees that there is no garbage asphalt in Ontario’s pavements. 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.
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. 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 and OHMPA agrees that there is a continual need for better-performing roads and for improved tests to evaluate asphalt cement. However, despite the exceptional winter Ontario and its roadways have endured this year, Ontario is still home to the smoothest, most sustainable and long-lasting roads in North America. That fact along with the much-improved weather that is upon us should help somewhat to cure the “pothole blues.”
For more information on potholes, download OHMPA’s newly release Potholes 101 – Fact & Fiction and the ABC’s of Potholes available on OHMPA’s website www.ohmpa.org.
The Toronto problem
The majority of roads in Toronto have a concrete base with 80mm of asphalt overlay to improve ride comfort and provide adequate skid resistance on wet pavement and during winter conditions. The concrete base is jointed at 3m intervals to control the cracking of the concrete. The joints cause cracking of the asphalt overlay within one to two years of placement. If these cracks are not sealed and maintained, potholes will form at the reflection cracks in the asphalt overlay.
The key to pothole prevention is to build a durable road with good drainage, adequate pavement thickness and tight longitudinal joints and to maintain that pavement over its 15 to 20 year life.
DOUG duke, OHMPA Executive Director