United States Department of Transportation
i
Validation of Asphalt Binder and Mixture Tests that Measure Rutting
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2000-11-01
[PDF-3.57 MB]
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Abstract:The Accelerated Loading Facility (ALF) was used to validate the Superpave asphalt binder parameter for rutting, namely, G*/sin(delta), and several laboratory mixture tests that have been developed to predict or compare rutting performance. The ALF is a full-scale, pavement testing machine that applies one half of a single rear truck axle load. The asphalt binders used in this study were AC-5 AC-IO, AC-20, Novophalt, and Styrelf I-D, having Superpave high-temperature continuous Performance Grades (PG’s) of 59,65, 70, 77, and 88, respectively. This is the temperature at 2.20 kPa after rolling thin-film oven aging. A dynamic shear rheometer was used to obtain these data. All five binders were used with an aggregate gradation having a nominal maximum aggregate size of 19.0 mm. The PG 59 and 70 binders were also used with a gradation having a nominal maximum aggregate size of 37.5 mm. Pavements with these materials were tested by the ALF. The relationship between G*/sin(delta) and ALF pavement rutting performance at temperatures ranging from 46 to 76 C was poor. However, the trend was correct for the unmodified binders, and the 2.20-kPa criterion used by the Superpave binder specification appeared to be valid. The main discrepancy was provided by the two modified binders, which were both highly resistant to rutting. The G*/sin(delta) for Styrelf was higher than for Novophalt, but the pavement with Novophalt was more resistant to rutting. This discrepancy was not resolved, although tests performed on mastics indicated that the relative rutting performances of the modified binders may have to be based on mastic properties. The ALF, French Pavement Rutting Tester, Hamburg Wheel-Tracking Device, Georgia Loaded-Wheel Tester, an unconfined repeated load compression test, and six Superpave Shear Tester measurements ranked the five 19.0-mm mixtures the same as ALF based on the average test data. The rankings based on statistics were generally different, but they were similar to ALF. Therefore, any of these tests can be used to estimate the effects of various asphalt binders on rutting. Four mixtures, consisting of the two gradations with the PG 59 and PG 70 binders, were used to determine the effect of increased nominal maximum aggregate size and the associated 0.85-percent decrease in optimum binder content on rutting performance. None of the laboratory mixture tests matched the ALF pavement rutting performances of the four mixtures. The tests listed above were sensitive to binder grade but not to aggregate gradation. The PURWheel was sensitive to gradation but did not distinguish the PG 59 binder from the PG 70 binder. The sensitivities of these tests to other key mixture variables need to be determined in future studies.
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