Evaluation of the internal angle of gyration of Superpave gyratory compactors in Alabama
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Evaluation of the internal angle of gyration of Superpave gyratory compactors in Alabama

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      The application of a compaction effort that will produce similar densities from one Superpave Gyratory Compactor (SGC) to another is crucial to the proper design, production control, and acceptance of HMA mixes. Currently in Alabama, differences in air voids for the average of 3 compacted samples of up to 0.8 percent may be expected between samples compacted in different brands of SGCs. The difference could be as high as 2.3 percent air voids between any two compactors. The angle of gyration is an important factor affecting the compaction effort. This study evaluated the relationship between the internal angle of gyration measured by the Dynamic Angle Validation Kit (DAVK) versus the resulting compacted sample density for a wide range of SGC?s. The DAVK device was used to measure the angle of gyration of all of the SGCs used in Alabama. Each of the compactors should have been set at an angle of gyration within the specification values (1.23 to 1.27 degrees) provided in AASHTO T312. AASHTO T312 measures an angle of gyration that is external to the mold while the DAVK measures an internal angle of gyration. Following the measurements with the DAVK, three replicate samples of a standard mix were compacted to evaluate the sample density produced by the compactor. Based on the data collected, there is an evident trend between internal angle of gyration and SGC type (Brand and Model). There is also an evident trend between internal angle of gyration and sample density. Precision analysis indicates a target dynamic internal angle of gyration of 1.16 1 0.03 degrees should reduce the bias between SGCs but only slightly improves the precision of compacted sample densities. Based on the density data collected during the study, the difference in the Gmb of three properly compacted samples by two different laboratories would not be expected to exceed 0.032 (approximately 1.26 percent air voids) 95 percent of the time. If a target DIA of 1.16 1 0.03 degrees were adopted, these differences would be expected to be 0.026 Gmb (1.02 percent air voids). Ref, 2 append., 19 fig., 14 tables, 58 p.
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