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WSDOT uses the following standard HMA mixes:
- Superpave.
Dense-graded HMA conforming to
Superpave mix design
requirements. WSDOT uses Superpave mixes with the following
nominal maximum aggregate sizes:
25 mm (1 inch), 19 mm (0.75 inch), 12.5 mm (0.5 inch) and 9.5 mm (0.375 inch).
12.5 mm (0.5 inch) Superpave has the same nominal maximum aggregate size as
WSDOT Class A and B mixes and is considered, along with Class A, as WSDOT's
"standard" surface course mix. Minimum lift thicknesses are as
follows:
| Mix Type |
Minimum
Lift Thickness |
| 25 mm (1 inch
Superpave) |
75 mm (0.25 ft) |
| 19 mm (0.75 inch Superpave) |
60 mm (0.20 ft) |
| 12.5 mm (0.5 inch Superpave) |
36 mm (0.12 ft) |
| 9.5 mm (0.375 inch Superpave) |
25 mm (0.08 ft) |
- Class A.
Dense-graded HMA with at least 90 percent of the
coarse aggregate having at least one
fractured
face. Its primary use is as a
surface
course for locations with high traffic levels or when the potential for
rutting
within the HMA layer exists. This is considered, along with 12.5 mm
Superpave, WSDOT's "standard" surface course paving
mix. Minimum lift thickness is 36 mm (0.12 ft).
- Class B.
Dense-graded HMA with at least 75 percent of the
coarse aggregate having at least one
fractured
face. Its primary use is as a
leveling course
or
surface course. Minimum lift thickness is 36 mm (0.12 ft).
- Class D. An
open-graded HMA. Class D HMA overlays are used primarily to seal and
maintain aged, but otherwise structurally sound flexible pavements.
Class D HMA (known previously as “open-graded asphalt seal coat”) is basically
a
bituminous surface treatment (BST) aggregate mixed hot in a plant with a
relatively high percentage of asphalt binder. Class D overlays are placed with
an asphalt
paver at a compacted depth of 18 mm (0.06 ft.). WSDOT's targeted
service life for a Class D overlay is eight years, although performance of
these mixes has varied on the state route system because Class D HMA is susceptible to
studded tire
wear. Thus, this mix is seldom used on high ADT routes or where high
studded tire use is expected. Minimum lift thickness is 18 mm (0.06 ft).
- Class E.
Dense-graded HMA primarily intended for use as a
base
course. This is WSDOT's "standard" base course paving mix for both
flexible and rigid pavements. Minimum lift thickness is 60 mm (0.20 ft).
- Class F.
Dense-graded HMA similar to Class B but a bit coarser. This is used
in lieu of Class B where aggregate sources cannot meet Class B grading
requirements. Thus, it has a higher
performance risk. Minimum lift thickness is 36 mm (0.12 ft).
- Class G.
Dense-graded HMA for thin lifts (25 mm (1 inch) or less). The
nominal maximum aggregate size is about 9.5 mm (0.375 inches). This
small size allows for its use as a thin, hot maintenance seal. Minimum
lift thickness is 18 mm (0.06 ft).
- Asphalt Treated Base (ATB).
Dense-graded HMA with a wide gradation band and lower asphalt content (2.5
- 4.5 percent by weight of aggregate) intended for use as a
base
course.
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