Performance Testing of Hot-Mix Asphalt Aggregates
VINCENT C. JANOO AND CHARLES KORHONEN
INTRODUCTION
cleanliness, toughness/hardness, durability sound-
ness, surface texture, particle shape, absorption,
When one thinks of hot-mix asphalt (HMA)
and affinity for asphalt. These tests however, do
pavement distresses, the following come to mind:
not give any clear indication of the performance
thermal cracking, rutting, fatigue cracking, ravel-
of the aggregates in HMA with respect to the dis-
ing, and moisture-induced damage (stripping).
tresses mentioned above. SHRP realized the im-
Some of these, such as low temperature and
portance of aggregate properties on the perfor-
fatigue cracking, are more directly related to the
mance of HMA pavements, but due to a lack of
properties of the asphalt cement. The aggregates
funds and time, the selection of aggregate proper-
play a minor role in crack retardation once a crack
ties for the SUPERPAVE mixes was based on
has formed. Rutting and moisture-induced dam-
"expert consensus." SHRP retained some previ-
age are not only dependent on the asphalt content
ously used aggregate tests, such as determining
but on the characteristics of the aggregates in the
the proportion of flat and elongated particles,
mixture as well, and thus a proper selection of
sand equivalent tests for determining the amount
aggregates can reduce rutting and moisture-
of plastic fines and dust in the fine aggregates,
induced damage to HMA. For example, rutting
and the shape and angularity of both the coarse
can be reduced by the use of large aggregates,
and fine aggregates. No tests were recommended
and/or angular rough coarse and fine aggre-
for skid resistance.
gates. Raveling is more of a mixture-proportion-
Realizing this shortfall, the National Coopera-
ing problem, i.e., the amount of asphalt cement in
tive Highway Research Program (NCHRP) con-
the mixture is critical. Low asphalt content can
ducted a study on the relationship between exist-
accelerate the raveling of an HMA
mixture. Another distress, not
Table 1. Recommended aggregate tests (Kandhal and Parker 1998).
usually mentioned, is the amount
of change in skid resistance. Here
Aggregate
Fatigue
Permanent
Moisture-induced
again, a proper choice of aggre-
properties
cracking deformation Raveling damage (stripping)
gate surface characteristics and
shape qualities can significantly Gradation and size
x
x
enhance skid resistance.
Uncompacted void content
Although aggregates consti- of coarse aggregates
x
x
tute approximately 90% of an Uncompacted void content
HMA mixture, there is no perfor- of fine aggregates
x
mance grading of aggregates Methylene blue tests of
similar to the Strategic Highway fine aggregates
x
Research Program (SHRP) PG Methylene blue test of
system for asphalt cement. P200 materials
x
Many ASTM and AASHTO index Micro-Deval tests
x
tests attempt to characterize the Magnesium sulfate
qualities of aggregates needed soundness tests
x
for HMA mixtures; they measure Particle size analysis of
size and gradation, aggregate P200 material
x
x
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