ASPHALTopics | Summer 2014 | VOL 27 | NO3

The MSCR test uses the creep and recovery testing
method and is carried out in the Dynamic Shear
Rheometer (DSR), which is the same equipment used
for the existing PG specification. Unlike the PG system,
however, the MSCR test measures higher levels of stress
and strain through 10 cycles of creep/recovery. The test
better represents what occurs in actual pavements, and
captures both the stiffening effects and the delayed
elastic effects of the polymer.
To accommodate heavy traffic, the MSCR method
tests binders at the environmental temperature that
the pavement is expected to experience, and requires
higher stiffness unlike the current high temperature grade
bumping PG practice. Because polymers soften at high
temperatures, the results can be misleading. Under the
MSCR grading, the specification values for standard,
heavy, very heavy or extreme traffic are changed, and
the temperature remains the same at 58°C or 52°C for
Ontario. The test identifies the rut resistance of both
modified and non-modified binders, and verifies the
presence of a polymer and the characteristics of the
polymer in the binder. As such, it is no longer necessary
to run additional tests, such as elastic recovery, toughness
and tenacity, and/or force ductility to ascertain polymer
modification of asphalt binders.
“We produced several materials that had a lot of different
properties, and then tested them in the lab,” D’Angelo
says. “We then added them to aggregate mixtures to
validate that the properties were
evident in the mix. The material was
applied on multiple test sections to
test the asphalt binders in real road
conditions, and to make sure that the
results correlated back to the binder
testing. The biggest challenge was
identifying the true properties of the
material. We found that the mixture
test was not capturing the same
properties as the binder test, which
required further testing. You need
to duplicate the results in order to
validate your findings.”
At the FHWA’s Accelerated Loading
Facility (ALF), test sections were
constructed using unmodified, airblown,
SBS-modified, crumb rubbermodified
and Elvaloy-modified binders.
The rutting of the high temperature parameters for both
PG and MSCR were compared after heating the sections
to 64°C and trafficking the sections with a super-single
tire loaded to 10,000 lb (4,535 kg). The study showed
that the MSCR parameter did a better job correlating with
rutting and could identify the rutting performance of both
the modified and non-modified binders. Further testing
on test sections on I-55 in Mississippi confirmed a better
correlation between the MSCR parameter and rutting,
when compared to the PG parameter.
“MSCR testing gets you a better
product in the end,” D’Angelo says.
“In the U.S., there are approximately
10 to 12 state highway agencies that
are making the test standard. Some
have used it for two to three years and
others are just starting. I expect that
MSCR testing will roll out and become
more mainstream next year.”
ENBRIDGE GAS DISTRIBUTION INC. has a more than 165-year history and is
Canada’s largest natural gas distribution company. Enbridge Gas Distribution delivers
safe, reliable natural gas in more than 100 communities across Ontario and is a leader
in delivering energy efficiency programs. Our free services are available to drive
energy-related solutions that can help you save money and improve your bottom line.
We also offer financial incentives that can help reduce your cost of implementation.
Call 1-888-427-8888 to find out how you can reduce your energy consumption.
FIND OUT MORE
enbridgegas.com/industrial
30 OHMPA | ASPHALTOPICS
In Ontario, the Ministry of
Transportation (MTO) has specified
the MSCR test to be performed on
all MTO contracts since 2011. The
acceptance criteria for the MSCR
in these contracts was only for
standard traffic, and MTO still uses
high temperature grade bump-ups
based on the traffic levels on a given
highway. MSCR has not yet been
used on any MTO contracts in place
of high temperature bump-ups for