Norwegian experiences and conclusions regarding Gyratory Compactors

The Norwegian research project PROKAS was conducted in 19982004. One of the goals of the project has been to evaluate the suitability of the gyratory compactor for mix design of asphalt in stead of using the Marshall method. Another goal has been to establish a method for using the gyratory compactor for preparing specimens for further testing. The results are showing a variation between different gyratory compactors for thesame asphalt mixture that is not satisfactory regarding the compaction curves. Although the gyratory angle is set according to the description from the manufacturer, there is a significant deviation of internal angles in the mould during compaction between different compactors (and also between the top and bottom plate in the same compactor). There are also results indicating that the compaction curves are very sensitive to small changes in the gradation curve of the stone material. By testing different mix compositions of the same asphaltmixtures that have performed well under traffic, recommendations have been made regarding how the compaction curves for an asphalt mixture should look like to perform well in the field. The Finnish compactors (ICT) used in Norway have the ability to measure the shear force applied to the specimen during compaction. The equipment used for measuring the internal angle have proven to be useful also for adjusting the levels of shear curves from different Gyratory compactors for comparing purposes. Based on an investigation for voidsdistribution in the different parts of the specimens a method for preparing specimens for further testing has been chosen. This has been done despite of the fact that tests on specimen taken from the road show different levels of results.