Modified Class D HMA (Hot Mix Asphalt), a ¾ inch nominal maximum aggregate size open graded friction course used by The Washington State Department of Transportation (WSDOT), is evaluated as an alternative to dense graded HMA. Modified Class D HMA was found to perform better than dense graded HMA at resisting fatigue cracking, but is susceptible to failure by raveling or stripping. When compared to dense graded HMA in eastern Washington, Modified Class D HMA was found to have a shorter service life. Much of the reduction in service life was due to two early-failing Modified Class D HMA projects on I-90.
Modified Class D HMA was not recommended as an alternative to dense graded HMA because of a shorter service life, the risk of early failure and higher cost.