Effect of Compaction Mode on the Mechanical Performance and Variability of Asphalt Mixtures

This paper investigates the relationship between mode of asphalt mixture compaction and resulting mechanical performance in terms of stiffness modulus, permanent deformation and fatigue resistance. Four modes, comprising three laboratory methods of gyratory, vibratory, and roller compaction together with site compaction were included in the study. An interlaboratory program was undertaken using these compaction methods and three asphalt mixture designs. The results showed that mold based compaction methods, such as gyratory and vibratory, generally produce stiffer specimens with higher resistance to permanent deformation when compared to roller compacted or field specimens of comparable air voids. However, the results also showed significant variability within a particular compaction method between different laboratories. The statistical two-sample t -confidence test was used to compare the sample means of air voids content and stiffness modulus between the different compaction methods. The statistical analysis showed that producing volumetrically identical asphalt mixture specimens using different compaction methods does not produce materials with identical mechanical properties. Statistical analysis was also undertaken on stiffness and permanent deformation results to provide engineers with the number of tests required to obtain a mean value within a certain accuracy of the “true” value, for a given confidence level. Stiffness modulus was found to have a far higher repeatability than permanent strain with the mode of compaction not affecting the variability of the results.