Design Gyrations Research Articles

Comparison of Superpave and Marshall Mix Performance in Alabama

The Alabama Department of Transportation specifies the Superpave® design system for most of its dense-graded HMA mixes. However, there is concern that the number of design gyrations (NDesign) may be too high for specified traffic levels. Mixes designed with an NDesign level that is too high would be rut resistant but may be difficult to compact in the field and may suffer from durability problems such as premature cracking and raveling. The objective of this project is to evaluate the performance of Alabama's mixes designed according to Superpave criteria and compare them to the performance of Alabama's Marshall-designed mixes to determine whether current NDesign levels should be adjusted. The following conclusions are based on an evaluation of 25 Marshall and Superpave projects placed about the same time and serving under approximately the same traffic conditions: (a) Generally, both Marshall and Superpave mixtures are performing quite well with little rutting and cracking after a period of about 4 years...

Implementing the Gyratory Mix Design System for Local Agency Projects in Iowa

A team of county, Iowa Department of Transportation, and asphalt paving contractors developed an implementation plan for the successful application of Superpave® by Iowa’s local public agencies. The plan is intended for use by engineers, technicians, and researchers interested in the implementation program and technical process used to develop the gyratory hot-mix asphalt design criteria for local agencies in Iowa. The plan identified seven activities. The mixture analysis activity is the focus and is the core of the implementation effort. The analysis studied the gyratory properties of mixtures prepared by use of the existing Marshall design (Marshall mixtures) with proven performance. The local agencies selected Marshall mixtures with good performance histories for the analysis. The mixtures were sampled directly behind the paving screed and were analyzed for gradation, compaction characteristics, and volumetric properties. The database contained data for mixtures from 92 local agencies from the 1999 and 2000 construction seasons. The first step in the compaction analysis was to normalize the data for comparison of groups of mixes. This step shifted the gyratory compaction envelopes to meet a specific set of criteria for the number of design gyrations. The next step in the analysis was to define the critical mixture properties. The critical mixture properties were founded on sound engineering principles with the recognition that routes with very low volumes should be designed for durability with a minor risk of fatigue or rutting failure. The final step weighed the impact of the selected criteria on maintenance of the material proportions of the currently acceptable mixtures.