RESULTS OF ROUND-ROBIN TEST PROGRAM TO EVALUATE RUTTING OF ASPHALT MIXES USING LOADED WHEEL TESTER

The results of a round-robin test program to evaluate the loaded wheel tester (LWT) procedure developed by the Georgia Department of Transportation (DOT) are presented. The procedure is used for determining rutting susceptibility of asphalt mixes using an LWT. This program was sponsored by FHWA and had the participation of six state DOT laboratories. In the test program, the asphalt mix ingredients necessary for fabrication of the asphalt beam samples were prepared by Georgia DOT and shipped to each participating laboratory. Each laboratory used the same procedure to fabricate the beam samples and perform the LWT testing. Results from this test program indicated the following. On the beam sample fabrication, the within-laboratory beam density repeatability was excellent with a standard deviation of 8.1 kg/cu m (0.5 pcf), whereas the between-laboratory beam density variability was high, primarily because of variations in the sample fabrication procedures used by each laboratory. On the LWT rutting test results, the within-laboratory rut depth repeatability was very good with a standard deviation of 0.04 cm (0.016 in.) over the mean rut depth value of 0.34 cm (0.133 in.), whereas the between-laboratory rut depth variability was quite high, primarily because of the high between-laboratory variability in beam density. On the basis of these findings, recommendations are offered for improving the LWT machine and the sample fabrication and testing procedure.