ASPHALTopics | Spring 2014 | VOL 27 | NO 1

TECHNICALLY
SPEAKING
by Sandy Brown
OHMPA Technical Director
Potholes – fact and fiction
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 in the media about potholes and whether there
could be a cure for what ails the roadways.
The reality is that there is no panacea for potholes.
Potholes typically occur five to seven years after the
road is paved and are the result of water that gets into
the pavement. When the ground freezes, so does the water,
causing expansion. Repeated freezing and thawing of the
water in the pavement structure weakens the surfacing 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. You also need to properly
maintain the road by sealing the cracks and the longitudinal
joints. If water doesn’t get to the pavement in the
first place, the pothole problem is resolved.
There has also been a lot of talk about the quality of the
asphalt cement in Ontario with references in the media to
“garbage asphalt”. Nothing could be further from the truth.
All asphalt cement used by Ontario municipalities meets
OPSS.MUNI 1101 specifications and this specification is
under constant development. MTO and industry formed
a Binder Task Group in 2006 to look at improving the
performance of asphalt cement used in Ontario. Initially
the group looked at low temperature performance, but
the scope has broadened to include other aspects.
The municipal specification is revised regularly and the
latest revision, issued in November of 2013, is based on
work by the Task Group. The specification incorporates
two new test procedures. The first limits the use of
polyphosphoric acid (PPA) and the second limits the use
Re-refined Heavy Vacuum Distillate Oil (RHVDO) residue.
However, there is no municipal specification in Ontario
for the use of polymers, and in particular elastomeric
polymers, in asphalt cement. Polymer modification
was introduced in North America in the 1970s, but it
wasn’t until we started to specify asphalt cement using
Superpave Performance Grading (PGAC) in the late
1990s that polymer use became more prevalent. PGAC
grading requires the asphalt cement to perform over
a wider range of temperature reflecting different traffic
and environmental conditions.
There is no “new asphalt” as has been referenced in the
media. Higher performance asphalt cements have been
available in Ontario for municipal use since the adoption
of the Superpave specification, but they are seldom asked
for because there is an increase in cost. These materials
are available and specified in OPSS.MUNI 1101 under
what is called grade bumping. While typically only used
on higher traffic roads, products such as PGAC 70-28 have
been available for over 10 years and can be specified on
any project.
The MTO and Industry Binder Task Group have been
studying new test procedures for asphalt cement for the
last seven years. Two different test procedures have been
reviewed: The Double Edge Notched Tension (DENT)
test (using equipment originally introduced in 1910), and
a newer procedure developed in the United States called ››
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