Guideline for the Design and Use of Asphalt Pavements for ...

SUPERPAVE GYRATORY COMPACTOR
In addition to a new and improved specification system for asphalt binders
(Performance Grade - PG binders) and enhanced aggregate requirements, the
Superpave mixtures design system is based on volumetric properties and utilizes
a gyratory compactor (Superpave Gyratory Compactor - SGC) as the method of
compaction. In contrast to the Marshall hammer, the Superpave Gyratory
Compactor uses a kneading-type action to compact specimens in a way that is
more consistent with in-place roadway compaction.
The number of gyrations (i.e. 68, 76, 86, 96, and 109 - Asphalt Institute’s mix
design procedure) is used to specify mixtures similar to the Marshall method of
50 Blow or 75 Blow design. The number of design gyrations (Ndesign or gyration
level) is dependent on the traffic volume of the roadway. The higher the traffic
volume, the higher the mix design gyration level (Ndesign). Table 2-6 identifies the
Ndesign level vs. traffic levels that have been established by MGPEC in the Denver area for Superpave design
mixes.
Table 2-6
MGPEC Superpave Mix Design Guidelines
Lift Thickness - in. Aggregate Gradation Designation
< 2 SX
2 to 3 S
4 to 4 SG
Traffic Level Traffic Loadings - ESALs Gyration Level - Ndesign Asphalt Binder Grade - PG
1 < 0.3 x 10 6
2 0.3 x 10 6 to < 1.0 x 10 6
3 1.0 x 10 6 to < 3.0 x 10 6
4 3.0 x 10 6 to < 1.0 x 10 7
5 1.0 x 10 7 to < 3.0 x 10 7
68 58-28
76 58-28
86 58-28, 64-22, 76-28
96 64-22, 76-28
109 64-22, 76-28
Table 2-6 differs from the number of gyrations (Ndesign) shown in Table 2-1. The Metropolitan Government
Pavement Engineers Council (MGPEC) specifications for 2001 are following the Asphalt Institute’s mix
design procedures. In 2002 they are adopting the gyration levels shown in Table 2-1. Agencies can use the
gyration levels shown in Table 2-1 prior to 2002 and are encouraged to do so. The gyration levels shown in
Table 2-1 are a result of a comparison of HMA mix properties at the various gyration levels to see the
difference between each level mixture. The results of the comparison shown very little difference for the
gyration ranges in mixture properties. The reduced number of gyration levels will result in lower cost mix
designs in the future.
SPECIFYING A SUPERPAVE TYPE MIX
To specify a Superpave mixture design, three parameters are needed, namely:
· Mix type (SX, S, or SG, see Table 2-2)
· Gyration level (Ndesign - 68, 76, 86, 96 or 109) or (Ndesign - 50, 75, 100)