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Achieving proper compaction of asphalt pavement is crucial to its longevity and acceptable performance. Laboratory compaction is an essential part of mix design. In order for the mix design process to be effective, laboratory compaction must adequately simulate field compaction. This study used mechanical properties measured with the Superpave shear tester to evaluate field compaction and laboratory compaction. The field compaction consisted of three test sections with different compaction patterns. The laboratory compaction used the Superpave gyratory compactor with adjustments to several parameters. Results of this study indicate that current gyratory protocol produces specimens with significantly different mechanical properties than field cores produced with the same material and compacted to the same air voids. Results also show that adjustments to certain parameters of the gyratory can produce specimens that better simulate the mechanical properties of pavement cores. [ABSTRACT FROM AUTHOR]

Most modified asphalt binders show pseudoplastic characteristics and their viscosity values depend on shear rate. The calculation of compaction temperatures for Superpave gyratory compactors (SGCs) depends on viscosity measurements. Therefore, for modified asphalt binders, it is not possible to calculate the compaction temperatures without including the effect of shear rate in the SGC during viscosity measurements. Prior to this study, no experimental study on the calculation of shear rate in the SGC had been performed. The calculation of the shear rate in the SGC will make it possible to include the effect of shear rate during viscosity measurements. In this study, the shear rate inside the SGC was approximately 490 1/s. Standard error (SE) values of the estimates of shear rate values were calculated by the propagation of error method. The average value for SE was approximately 53 1/s. [ABSTRACT FROM AUTHOR]

Due to increasing traffic levels and vehicle wheel loads, it has become necessary to improve the effectiveness and efficiency of the design of hot mix asphalt (HMA). The Superior Performing Asphalt Pavement (Superpave) mix design and analysis system was introduced for this purpose. The Superpave Gyratory Compactor (SGC) is a vital part of this new mixture design and analysis system. The SGC makes use of a 150-mm- (6-in.) diameter cylindrical mold to produce specimens for design and evaluation under the Superpave system. The objective of this study was to explore the potential for using a 100-mm-(4-in.) diameter mold to produce test specimens in the laboratory. Loose HMA was collected from over 40 paving projects throughout the state of Tennessee. The mixes were tested in the laboratory, and the relative density (%G[sub mm]) of the 150-mm-diameter specimens was statistically compared with that of the 100-mm-diameter specimens. The results of paired t-tests conducted on the data indicate that the difference in %G[sub mm] is statistically significant. However, further analysis of the data demonstrates that the observed difference in %G[sub mm] is smaller than the documented precision of the currently available laboratory test methods used. Thus, it is concluded that the observed difference has no “engineering” significance. Based on these findings, it has been recommended to the Tennessee Department of Transportation (TDOT) that it is feasible to use 100-mm-diameter specimens in lieu of the 150-mm-diameter specimens for quality assessment/quality control (QA/QC) acceptance and verification testing of HMA. It should be noted that this recommendation is limited to mixes with a maximum aggregate size of 25.4 mm (1 in.) or less. [ABSTRACT FROM AUTHOR]