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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.

Similar to Class B in nature but with a finer gradation.

Modified Class B or Modified Class 1/2 inch HMA (sometimes called Commercial Mix).

In applications with highway or arterial traffic volumes, the use of Class 3/8 inch HMA Superpave mix is highly encouraged as it can be tested for stability at the mix design stage. This small size allows for use as a thin surface overlay, in pre-leveling applications, as a hot maintenance seal and for playground, bicycle path and athletic facility pavements. The nominal maximum aggregate size is about 0.375 inches. Dense-graded HMA for thin lifts (usually 1 inch thickness or less). Class E was supplanted by the current Class 1 inch HMA Superpave mix design. This was WSDOT’s “standard” base course paving mix that could also be used as a heavy duty surface mix. Dense-graded 1-1/4 inch HMA primarily intended for use as a base course. There is clear evidence that this type of wearing course is susceptible to studded tire wear and therefore it is a rarely used mix. The performance of these mixes has varied on the state route system. Proper maintenance requires a fog seal about every 5 years. Typically, Class D mixes are placed as 0.70 inch thick wearing courses (essentially, an Open Graded Friction Course for surface applications). It was supplanted by the Class 1/2 inch HMA Superpave design. This was WSDOT’s “standard” surface course paving mix for lower volume roads. 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.

Dense-graded 5/8 inch HMA with at least 75 percent of the coarse aggregate having at least one fractured face. WSDOT current Superpave replacement equals Class 1/2 inch HMA. 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. Dense-graded 5/8 inch minus HMA with at least 90 percent of the coarse aggregate having at least one fractured face. In most applications, using a current WSDOT mix design of the same nominal maximum aggregate size is preferrable to using the out-of-date specifications. WSDOT Retired Hveem Mix DesignationsĪlthough WSDOT does not use these mixture classifications any more, they may still exist in local city/county specifications using legacy mix design references. The ATB specification is a local agency specification that can be found in the Local Agency specification section on the WSDOT website. ATB will serve many paving structure applications and is advantageous in many situations, especially when used in staged construction where the ATB can provide protection of the subgrade and serve as a construction staging surface during construction. Asphalt Treated Base (ATB)Īsphalt Treated Base (ATB) is dense-graded HMA with a wide gradation band and lower asphalt content intended for use as a base course. These HMA design specifications are listed in the current edition of the WSDOT Standard Specifications in section 9-03.8. The Class 1/2 inch HMA is the most commonly used design but the Class 3/8 inch mixes are gaining popularity since the advent of the Hamburg Wheel-Track Testing device (AASHTO Test Method T 324) as a reliable predictive test for pavement stability and stripping susceptibility. WSDOT uses Superpave mixes with the following nominal maximum aggregate sizes: Class 1 inch, Class 3/4 inch, Class 1/2 inch and Class 3/8 inch. Superpave is dense-graded HMA conforming to Superpave mix design requirements.

Most modern HMAs are listed to designate both the nominate maximum aggregate size of the mix and the PG (Preformance Grade) of binder used in the mix (e.g. This section lists the standard HMA mixes used in Washington State both today and prior to changing from the Hveem mix design method.