Effect of Superpave Defined Restricted Zone on Hot-Mix Asphalt Performance

Abstract

The effect of the Superpaver defined restricted zone on hot-mix asphalt rutting performance was evaluated. One gradation that violated the restricted zone (TRZ) and two gradations that did not violate the restricted zone (BRZ and ARZ) were evaluated. Evaluated mixes represented a range of maximum aggregate sizes (MASs), design traffic levels, and aggregate types. Three laboratory tests—asphalt pavement analyzer, rotary-loaded wheel tester, and Marshall test—were used to evaluate the rutting performance. From the analysis, it was found that mixes with gradations violating the restricted zone performed similarly to or better than the mixes with gradations passing outside the restricted zone with respect to laboratory rutting tests. This conclusion was drawn from the results of experiments with 12.5-, 19.0-, and 25.0-mm MAS gradations at Ndesign (design number of gyrations) values of 100, 75, and 50 gyrations. This conclusion is confirmed and supported by the recently completed NCHRP Project 9-14: The Restricted Zone in the Superpave Aggregate Gradation Specification. The results also showed that rutting performance of mixes having gradations below the restricted zone, which was commonly recognized to be rut resistant, appeared to be more sensitive to aggregate properties than mixes having gradations above or through the restricted zone.