RELATIONSHIP OF SUPERPAVE GYRATORY COMPACTION PROPERTIES TO HMA RUTTING BEHAVIOR
This report presents the findings of a research project to examine whether there is a relationship between any property of hot mix asphalt (HMA) measurable with the Superpave gyratory compactor and the rutting behavior of HMA pavements in service. Its main finding is that the parameter N-SRmax, the number of gyrations at maximum stress ratio, may be used within certain limits to identify mix designs likely to show gross instability under the shear stresses produced by traffic in HMA pavements. The report will be of particular interest to materials engineers in state highway agencies, as well as to materials suppliers and paving contractor personnel responsible for HMA design and quality control.
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.
Stress Conditions in NGI Simple Shear Test
This technical note describes the results of the three-dimensional analysis in the elastic range of deformations for an undrained test and presents answers to two questions: What is the state of stress in the sample; and how extensive are the zones in which the shear differs from the average value?