Using the Superpave Gyratory Compactor to Estimate Rutting Resistance of Hot-Mix Asphalt

Several approaches have been introduced lately to characterize the performance-related properties of asphalt mixtures. The majority of these efforts are focused on developing special equipment to test mixtures at conditions similar to those acting on 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 investigated its use 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 aggregate sources, different asphalt contents, and different gradations. Each mixture was compacted using the SGC. To evaluate if the results from the SGC can be related to rutting, mixtures were also tested using the new repeated compression test procedure recommended by the NCHRP Project 9-19 and used in the "Mechanistic–Empirical Pavement Design Guide." Densification curves produced by the SGC were used to determine volumetric properties of the mix and to calculate the traffic densification index (TDI), which is the value of the area under the densification curve from 92% density to 98% density and which represents the densification experienced due to traffic loading during the pavement service life. One more index, the traffic force index (TFI), is calculated. 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 called the pressure distribution 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 FN, 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 the SGC gives information that can be used to characterize the stability of asphalt mixtures. Such information could be used as an initial screening criterion to select mixtures for various traffic levels.