Warm-mix asphalt (WMA) mixes produced by an emulsion process were evaluated under accelerated loading in three total sections of the National Center for Asphalt Technology Test Track and used as the surface mix for two of the sections. Evotherm was incorporated into the same mixes used previously on the track. In-place densities of the WMA surface layers were equal to or better than the hot-mix asphalt (HMA) surface layers, even when compaction temperatures were reduced by 8°C to 42°C (15°F to 75°F). Laboratory rutting-susceptibility tests conducted in the asphalt pavement analyzer indicated similar performance for the WMA and HMA surface mixes with the PG 67-22 base asphalt. However, laboratory tests indicated an increased potential for moisture damage with the WMA mixes. The two WMA sections and the HMA section showed excellent rutting performance in the field after the application of 515,333 equivalent single-axle loads in a 43-day period. One of the WMA sections was also evaluated for quick turnover to traffic and showed good performance.
In 1990, members of FHWA participated with other industry and highway agencies in a European asphalt study tour to examine pavement technology. One of the technologies brought back from this tour was laboratory wheel-tracking devices. However, the ability of these devices to predict or rank field performance has been questioned. WesTrack provides a unique opportunity for comparing accelerated laboratory wheeltracking devices with full-scale pavement performance under controlled conditions. The three devices examined here are the asphalt pavement analyzer (APA), the French pavement rutting tester (FPRT), and the Hamburg wheel-tracking device (HWTD). WesTrack is a 2.9-km oval test track with each tangent consisting of 13- to 70-m sections. Samples for laboratory evaluation using three wheel-tracking devices were taken from the 5-m sampling segments of the rehabilitated sections: 10 sections placed in the summer of 1997. Based on the data and analyses in this study, the three laboratory devices examined satisfactorily correlate with the permanent deformation of the WesTrack sections studied. The correlations are 89.9, 83.4, and 90.4 percent for the APA, FPRT, and HWTD, respectively. The devices, although not perfect in predicting or ranking section performance, did exhibit increased variability with poorer performance. This increased variability with mean permanent deformation or creep rate allows for a rational method to establish mixture design specifications for all three devices. The procedure exhibited here is flexible, allowing an agency to select the level of performance desired. The selection of an appropriate test temperature that reflects the in-service temperature at which the pavement will be expected to perform was found to be necessary as well.
A pavement quality indicator device developed through an NCHRP project, the Corelok device, and laboratory and field permeability index devices were evaluated for their potential to improve the Virginia Department of Transportation’s density specification or to be designated for use in a replacement specification. Fifteen samples were taken from six projects representing three nominal maximum aggregate sizes. Densities measured by a nuclear gauge correlated well with core densities measured in accordance with AASHTO T166 and by the Corelok device. Pavement quality indicator readings appeared to be repeatable but did not correlate with the densities measured in accordance with AASHTO T166 or with the Corelok device. A fair correlation was obtained for two projects. Laboratory permeability and field permeability indices were correlated with pavement density. A good correlation was found between the laboratory permeability and field permeability indices. The relationship appears to be linear in the range agencies typically specify.
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