100-mm-Diameter Mold Used with Superpave Gyratory Compactor

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 $(\%G_{\mathrm{mm}})$ 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 $\%G_{\mathrm{mm}}$ is statistically significant. However, further analysis of the data demonstrates that the observed difference in $\%G_{\mathrm{mm}}$ 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.