Estimating Results of a Proposed Simple Performance Test for Hot-Mix Asphalt from Superpave Gyratory Compactor Results (05-0891)**
Ahmed Fatin Faheem, Temple University
Hussain U. Bahia, University of Wisconsin, Madison
Hossein Ajideh, County of Orange

Several approaches were introduced lately to characterize the performance related properties of asphalt mixtures. The majority of the efforts are focused on developing special equipment to test at conditions similar to those acting on the pavements due to moving traffic. Because the Superpave gyratory compactor (SGC) is used routinely for compaction, and because it has components to measure load and densification, this study was intended to use it as a basis for estimating the stability of asphalt mixtures as a surrogate or an estimate for results of the proposed method for the simple performance test. Several asphalt mixtures were produced using four different sources, different asphalt contents, and different gradations. Every mixture was compacted using the SGC. To evaluate if the results from the SGC can be related to rutting of mixtures as measured by the new repeated compression test procedure for rutting measurements recommended by the National Cooperative Highway Research Program project 9-19 and used in the AASHTO 2002 pavement design manual. Densification curves produced by the SGC were used to determine volumetric properties of the mix as well as the calculation of the traffic densification index (TDI), which is the value of the area under the densification curve from 92% density to 98% density, represents the densification experienced by the traffic loading during pavement service life. One more index is calculated, traffic force index (TFI). The TFI is the amount of work done to change the density of the mix from 92% to 98% measured using a special accessory added to the SGC while compaction is taking place called the pressure distributor analyzer (PDA). The results from the mixture rutting tests were used to estimate the rutting rate and the flow number (FN), which is the point at which the mixture starts to exhibit tertiary flow. The flow number, which is considered an important mixture property, is shown to have a strong correlation to the TFI derived from the mixtures resistance behavior measured in the SGC and the PDA. The TFI was found to be strongly correlated to the TDI, giving the opportunity to estimate the mixture resistance to compaction forces using its volumetric behavior. The main finding of the study is that SGC appears to give information that can be used to characterize the stability of the mixtures. Such information could be used as an initial screening criterion to select mixture for various traffic levels.