Determining Gyratory Compaction Characteristics Using Servopac Gyratory Compactor

Investigations are reported on that were carried out by Transport SA initially into the effects of the major parameters (gyratory angle, vertical stress, and gyratory speed) on the density of specimens compacted using the new Australian gyratory compactor, the Servopac. More recent investigations were carried out into the benefits of measuring shear resistance during the compaction process. Australian Standard AS 1289.2.2 for asphalt gyratory compaction was formulated as a result of investigations during the early 1990s using the first Australian gyratory compactor, the Gyropac, and this standard is now part of asphalt contract specifications for a number of state road authorities. The more versatile and accurate Servopac is seen as a technological advance on the Gyropac, and its ability to quickly modify critical gyratory parameters has enabled these studies to be carried out more efficiently. The voids and cycle precision and how tolerances affect these parameters were evaluated over a wide range of angles, vertical pressures, and rotation, with findings indicating that gyratory angle and vertical pressure settings are critical. Rotation speed was found to be a noncritical parameter. Subsequent investigations into shear resistance measurements, however, have indicated the potential for new windows to be opened for their use in characterization of asphalt mixes. This new approach hinges around maximum shear resistance and the rate of change of voids at the maximum shear stress position and the probability that gyratory settings may not be so critical when looked at in this way.