ASPHALTopics | Summer 2014 | VOL 27 | NO3

The MSCR test is superior to an Elastic Recovery type test
because it puts the AC to test at very high stress levels.
of the AC when exposed for extended times to a constant low
temperature. The reasoning for the development of this test
is because in our climate the regular BBR test (part of the PG
Specification) is claimed to not entirely capture the thermal
stresses that accumulate in a pavement during our long and
cold winters. The ExBBR test consists of conditioning beams
of aged AC in a freezer for three days and measuring how
much the AC stiffens over this time.
The DENT test is targeting the fatigue properties of the
AC in a ductile state (around room temperature). The test
attempts to quantify the work required to fracture the AC in
a ductile state, which is typical of fatigue failure. The testing
protocol consists of several ductility-type specimens with
progressively larger notches, which are tested to failure. By
extrapolating the specimen cross-section to a dimension of
zero, the essential and plastic works of fracture are calculated,
as well as a parameter that estimates the strain tolerance of
the AC (CTOD).
A number of years ago, U.S. researchers developed a quick
and simple test that combines the measurement of the asphalt
cement stiffness and its elastic response using the DSR. This
test was developed as an attempt to reduce specification
proliferation and, at the same time, capture the benefits of
polymer modification of the binder. The test is called Multiple
Stress Creep and Recovery and has become known as the
MSCR (read “massacre”) test.
The MSCR test is superior to an Elastic Recovery type test
because it puts the AC to test at very high stress levels. It
measures more than just elasticity; it measures if the elastic
response of an AC breaks down under high loads. In terms of
stiffness, validation of the MSCR test has proven that it currently
correlates to field rutting better than any previous AC test. In
terms of polymer modification, the test was validated during
the two Inter-laboratory Studies (ILS) carried out in the US.
The MSCR test has since evolved into the AASHTO M332
specification aimed at replacing the PG grading as it is ››
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