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 volumetric requirements at specific levels of compactive effort in the Superpave gyratory compactor. These levels are a function of climate and total traffic during the pavement service life, expressed in Equivalent Single Axle Loads (ESALs). Asphalt concrete mixtures for higher traffic levels are compacted to a higher number of design gyrations (N_(design)) as a mix that resists further compaction also resists rutting more effectively. 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 mixture performance 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 mixes with 9.5 mm nominal maximum aggregate size. Dynamic modulus (E~*) was measured for specimens prepared at optimum asphalt content. Rutting and fatigue performance was predicted using DARWin-ME? software, and relative performance indicators were developed based on the number of ESALs to failure. Relative performance was plotted against the asphalt content to determine optimum number of design gyrations. An N_(design) value of 65 gyrations was recommended for a design traffic level up to 3 million ESALs.