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Hot Mix Asphalt (HMA) For Local Agency Applications

Unlocking the Benefit of Superpave for Local Agencies in Washington

The Superpave system allows for mixes to be designed in the laboratory at four different levels (50, 75, 100, and 125 gyrations) simulating four different 20-year traffic levels in the field. 

The majority of WSDOT highway mixes are designed at the 100 gyration level. While appropriate for WSDOT highways, this system is not likely to be appropriate for facilities with lower traffic volume, such as the majority of city streets and county roads in the State of Washington.

Extracting the benefit of Superpave is not automatic.  Public works departments must “unlock” the benefit of lower-gyration Superpave mixes by making a few adjustments to the way that HMA mixes are designed, specified, and accepted on their projects.

Aggregate and PG Binder alone will not improve bad roads. To effectively utilize HMA, local agencies need to do four things:

  1. Design the correct pavement section for the roadway needs
  2. Select the correct gyration level mix during pavement design
  3. Ask for the correct mix in the contract documents
  4. Incorporate appropriate specification changes to implement the process you want during construction