Determining N-Design Values Using Relative Performance Approach For North Carolina Surface Mixes

摘要

The Superpave? design method requires that asphalt concrete mixtures satisfy various volumetricrequirements at specific levels of compactive effort in the Superpave gyratory compactor. These levels area function of climate and total traffic during the pavement service life, expressed in Equivalent SingleAxle Loads (ESALs). Asphalt concrete mixtures for higher traffic levels are compacted to a highernumber of design gyrations (N_(design)) as a mix that resists further compaction also resists rutting moreeffectively. This often negatively impacts the fatigue performance due to lower asphalt content in the mix.Therefore, a performance-oriented approach to determine N_(design) was developed that optimizes mixtureperformance with respect to both rutting and fatigue cracking.Asphalt concrete mixes were designed at N_(design) levels of 50, 75, 100 and 125 gyrations for surface mixeswith 9.5 mm nominal maximum aggregate size. Dynamic modulus (E~*) was measured for specimensprepared at optimum asphalt content. Rutting and fatigue performance was predicted usingDARWin-ME? software, and relative performance indicators were developed based on the number ofESALs to failure. Relative performance was plotted against the asphalt content to determine optimumnumber of design gyrations. An N_(design) value of 65 gyrations was recommended for a design traffic levelup to 3 million ESALs.