Restricted zone

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Eliminated from Superpave specifications in late 2002. A particular area of the FHWA’s 0.45 power gradation graph associated with Superpave mix designs. It was observed that mixes closely following the 0.45 power maximum density line sometimes had unacceptably low VMA. Therefore, Superpave introduced a restricted zone through which a typical gradation should not pass. By avoiding the restricted zone, mixes should have sufficient VMA to allow enough asphalt for adequate durability.