1.1 This test method describes a procedure for testing the rutting and moisture susceptibility of asphalt specimens using the rotary wheel tester (RWT). Superpave gyratory compactor (SGC) specimens (Test Method D6925) are wrapped, conditioned, submerged in water, and confined between three metal wheels in continuous synchronized rotation with each wheel applying a fixed load around the periphery of the specimen. The system records the number of load cycles applied to the specimen, the deformation of the specimen (rut depth), the loading rate, the temperature of the water, and Sigma, which is an indication of specimen roundness. 1.2 This test method is used to determine the premature rutting susceptibility of asphalt mixtures by measuring rut depth as a function of number of load cycles throughout the test. 1.3 This test method also measures the potential for moisture damage effects because the specimens are submerged in temperature-controlled water during preconditioning and for the duration of the test. Note 1-This test uses a typical specimen produced by a SGC. Note 2-The ruggedness study identified air void content as the most influential factor evaluated and recommended a tolerance of 0.25 % to minimize the effect of air void content on the test results. The precision study evaluated three asphalt mixtures with specimen air void contents ranging from 2.87 to 3.23 %, 4.28 to 4.64%, and 5.77 to 6.19%. Lemke and Bahia found that asphalt mixture with 7 % air void content was more susceptible to rutting than mixture with 3 % air void content and that the test results for the 7 % AV mixture did not differentiate between control factors such as test temperature and mixture source like mixture with 3 % air void content did. Note 3-60C is the test temperature used by City of LA for testing all of its asphalt mixtures. University of Wisconsin at Madison Modified Asphalt Research Center reported that City of LA selected 60C because (1) it approximates the observed high average temperature of most pavements, (2) it is close to the high temperature performance grade classification of the asphalt binder used in most local applications, (3) it allows a test to be performed in an accelerated timeframe (about 2 hours excluding preconditioning time, and (4) research on rut testing has shown [that] the asphalt binder seems to have the most control over the test results at lower test temperatures. The Ruggedness Study was completed at 60C using PG 64-10 with 50 % RAC asphalt mixture. The precision study was completed at 60C using PG 64-10 with 50 % RAC asphalt mixture for two of the mixtures evaluated and using PG 76-22 for the third mixture considered. One may wish to consider lower test temperatures because Lemke and Bahia reported reducing the test temperature from 60 to 52C when testing PG 58S-28 and PG 58H-28 asphalt because of premature failure. Note 4-City of LA uses 6900 load cycles as the maximum load cycles. University of Wisconsin at Madison Modified Asphalt Research Center reported that City of LA selected 6,900 Load Cycles as the Maximum Load Cycles because initial observations from tests showed that most samples tested showed their performance well before these values (6900 load cycles and 6.0 mm) were attained while those that exhibited low rut depth in the field and no moisture susceptibility showed test result curves that behaved as asymptotes to their initial creep slope until the maximum number of cycles (30 000 cycles) of the machine was attained. The value, 6900 load cycles, was used in both the ruggedness and precision work as well. The machine has an allowable range of 300 to 30 000 load cycles. Note 5-City of LA uses 6.0 mm as the maximum rut depth. University of Wisconsin at Madison Modified Asphalt Research Center reported that City of LA selected 6.0 mm as the maximum rut depth because initial observations from tests showed that most samples tested showed their performance well before these values [6,900 Load Cycles and 6.0 mm] were attained ... while those that exhibited low rut depth in the field and no moisture susceptibility showed test result curves that behaved as asymptotes to their initial creep slope until the maximum number of cycles (30 000 cycles) of the machine was attained. 6.0 mm was used in both the ruggedness and precision work as well. Note 6-City of LA uses a loading rate of 70 CPM for all of its testing. University of Wisconsin at Madison Modified Asphalt Research Center reported that City of LA selected 70 CPM because that is what its RWT was set at by the factory. 70 CPM was used in both the ruggedness and precision work as well. The machine has an allowable range of 60 to 90 CPM. Note 7-City of LA uses an applied load of 75 lb for all of its testing. University of Wisconsin at Madison Modified Asphalt Research Center reported that City of LA selected 75 lb because that is what its RWT was set at by the factory. The value,75 lb, was used in both the ruggedness and precision work as well. The machine has an allowable range of 75 to 110 lb in 5 lb increments. City of LA advises against applied loads of greater than 75 lbs based on their experience. 1.5 Criteria for the evaluation and interpretation of test results shall be developed for local conditions and materials characteristics. 1.6 The text of this test method references notes and footnotes that provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the test method. 1.7 Units--The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard. 1.8 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.
Keywordsasphalt concrete; rutting; moisture-susceptibility; rotary asphalt wheel tester; angle; creep slope; stripping slope; stripping infection point
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 h to complete. A simpler, more repeatable, and faster test is needed. The proposed standard requires no cutting of samples, uses a much simpler wheel loading arrangement, and allows faster application of wheel passes. It has also been shown to have less variability because of the concentric loading of the sample. The test has been used by the City of LA for more than ten 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.
The title and scope are in draft form and are under development within this ASTM Committee.Back to Top
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