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 roads by sealing cracks,” explained 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,” says 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 that is used to produce recycled engine oil for your car. “It is not the sludge collected from the local garage,” explains 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,” concludes Brown. “However, the asphalt cement plays a very small part in the development of potholes.
