Standard Washington Mixes

This section lists the standard HMA  mixes used in Washington State.  A WSDOT HMA mix type gradation specification animation at the end shows these mixes on a standard gradation chart.

WSDOT Standard Superpave Mixes

• Superpave.  Dense-graded HMA conforming to Superpave mix design requirements.  WSDOT uses Superpave mixes with the following nominal maximum aggregate sizes: 1 inch, 0.75 inch, 0.5 inch and 0.375 inch.  0.5 inch Superpave has the same nominal maximum aggregate size as WSDOT Class A and B mixes. 

WSDOT Standard Hveem Mixes

• 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.
• 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 because its nominal maximum aggregate size provides a good compromise between offering a smooth surface texture and low rut potential.  This is WSDOT's "standard" surface course paving mix.
• Class D.  An open-graded HMA.  Typically, Class D mixes are placed as 0.70 inch thick wearing courses (essentially, an OGFC).  Proper maintenance requires a fog seal about every 5 years.  The performance of these mixes has varied on the state route system.  There is clear evidence that this type of wearing course is susceptible to studded tire wear.
• Class E.  Dense-graded HMA primarily intended for use as a base course.  This is WSDOT's "standard" base course paving mix.  Can also be used as a heavy duty mix.
• Class F.  Dense-graded HMA similar to Class B but with a wider gradation specification.  This is used in lieu of Class A/B where aggregate sources properties cannot meet Class A/B requirements (generally limited to some areas of Eastern Washington).  Thus, it has a higher performance risk.
• Class G.  Dense-graded HMA for thin lifts (usually 1 inch or less).  The nominal maximum aggregate size is about 0.375 inches.  This small size allows for use as thin, hot maintenance seals and for playground, bicycle path and athletic facility pavements.

Other WSDOT Standard Mixes

• 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.  ATB will serve most paving structure applications and is advantageous in many situations.

Other Standard Mixes

• Modified Class B (sometimes called Commercial Mix).  Similar to Class B in nature but with a finer gradation.  Most of the above mix classes have specific purposes, however it is not uncommon for finer gradation versions of these mixes to be used for commercial and city/county purposes because they can provide a smoother surface texture than a Class A or Class B mix without sacrificing much strength.  Modified Class B (Commercial) mixes are more pedestrian friendly due to the smooth surface texture, are less likely to segregate, easier for handwork and easier to use in small quantities.  A few agencies, such as the City of Everett, have Modified Class B (Commercial) gradation specifications.  The "Typical Modified Class B (Commercial Mix)" gradation plot shown below is from the City of Everett's specification.  Although this gradation is typical, Modified Class B (Commercial Mix) gradations can and will vary throughout the State.

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