1.1 This test method describes two procedures for testing the rutting and moisture-susceptibility of Hot Mix Asphalt (HMA) specimens using the Rotary Asphalt Wheel Tester (RAWT). 1.2 The test method describes the testing of submerged, compacted HMA cylindrical sample confined between three metal wheels in continuous synchronized rotation, each wheel applying a fixed load around the periphery of the specimen. In addition to the number of load cycles, the deformation of the specimen (rut depth) is recorded and based upon the changed in diameter of the specimen (in the roller path), averaged over each full rotation of the specimen. The system provides an intense loading of the specimen by having three roller passes each rotation allowing the measurement of the structural and stripping characteristics of the HMA. Because of the high loading intensity, tests are completed in a short time frame as compared to other tests. 1.3 The test method is used to determine the premature rutting susceptibility of HMA due to weakness in the aggregate structure, inadequate binder stiffness, or moisture damage. The method measures the rut depth as a function of number of rotations throughout the test. 1.4 This test method also measures the potential for moisture damage effects because the specimens are submerged in temperature-controlled water during loading. 1.5 The RAWT test uses a standard Superpave Gyratory Compactor (SGC) specimen (Test Method D6925). After a specimen is compacted, it is cooled for at least 12 hours to ambient temperature. The sample is then wrapped in polyethylene stretch warp and conditioned in water at the test temperature. 1.6 Two test methods are described in this standard; Method A follows the City of LA procedure (XXXXXXX) where the test sample is prepared at 3% 1% air voids and cooled to room temperature for 12 hours before conditioned after wrapping in water at 60C for 2 hrs 10 min. The test in Method A is terminated at 6,900 cycles or 6.0 mm rut depth, whichever is achieved first. In Method B, the test sample voids content is similar to the Hamburg Wheel-Tracking (HWT) Test (AASHTO T324) in which the test sample is prepared at 7% 1% air voids. The sample in Method B is also cooled to room temperature for 12 hours before wrapping and conditioning in water at the test temperature for 30 min. The test in Method B is terminated after 20,000 passes or when the rut depth reaches a preselected limit. 1.7 The test method describes the testing apparatus, instrumentation, specimen fabrication, and analysis procedures required to determine the rutting and moisture-susceptibility of HMA. 1.8 The standard unit of measurement for rut depth is mm [in]. 1.9 The text of this test method references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the test method. 1.10 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. 1.11 This standard does not purport to address all the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
In recent years the measurements of rutting of asphalt mixtures have become a requirement for acceptance of mixtures designs in specifications of road and airport pavement. One of the most widely used testing method is the Hamburg Wheel-Tracking (HWT) Test as described in the AASHTO T324 standard. The procedure requires cutting and assembling two sections of a cylindrical sample, and is shown to be affected by the details of the loading wheel speed variation, and the interference of outside mold holding the samples, as well and the accuracy of the sample cuts (NCHRP Project 20-07). The test is also very long and takes more 6 hours to complete. A simpler, more repeatable test, and faster test is needed. The proposed standard requires no cutting of samples, utilizes a much simpler wheel loading arrangement, and allows faster application of wheel passes. It has also been shown to have less variability due to the concentric loading of the sample. The test has been used by the City of LA for more than 10 years and is applied in practice. Recent study has shown that it achieves same objectives as the HWT test and could be a better substitute to the HWT test used today.
KeywordsAsphalt concrete; rutting; moisture-susceptibility; Rotary Asphalt Wheel Tester; Angle ; Creep Slope; Stripping Slope, Stripping Infection Point
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Draft Under Development