Use of Georgia Loaded Wheel Tester to Evaluate Rutting of Asphalt Samples Prepared by Superpave Gyratory Compactor

Abstract

The Georgia loaded wheel tester (LWT) developed by the Georgia Department of Transportation has been used since 1985 in the laboratory during the design stage to evaluate rutting susceptibility of asphalt concrete mixtures. In the LWT testing, asphaltic concrete is subjected to an elevated temperature in a loaded wheel system under repetitive loading conditions, and the permanent deformation induced under the wheelpath is measured. This approach to assess rutting susceptibility was thought to be much more representative than the current test methods and can provide a fast and more accurate means of assessing rutting susceptibility of asphalt concrete under actual field conditions. The asphaltic beam samples used for the LWT testing are prepared by a rolling compaction machine. The new LWT developed in 1992 is described. To promote the concept of using Georgia LWT as a supplement to the Superpave Level 1 design procedure for evaluating permanent deformation of hot-mix asphalt (HMA), a test method utilizing Superpave gyratory compactor-prepared samples to evaluate the rutting resistance of HMA by the LWT was developed. The gyratory samples placed in a specially designed mold can be tested in the LWT identical to that for performing the LWT testing on the beam samples. A test program was conducted to evaluate the applicability of the testing procedure and to develop correlations between the rut depth of asphalt mixes using the beam samples and the gyratory samples. The test program used three asphalt mixes of different degrees of rutting resistance ranging from high to low rut susceptibility. Both types of samples were tested at 40°C, 50°C, and 60°C temperatures for 8,000 cycles under the standard LWT testing procedure. The rut depth results from the beam samples and the gyratory samples showed good correlations for all three mixes tested. The test results also showed a strong relationship between the rut depth values and the air void content in the mixes.