Control of Superpave Gyratory Compactor’s Internal Angle of Gyration: Experience of the Utah Department of Transportation (05-2472)**
Pedro Romero, University of Utah
Murari Man Pradhan, Arizona Department of Transportation

The State of Utah Department of Transportation (UDOT) started a program to use the Dynamic Angle Validator (DAV) to measure the internal angle of all Superpave gyratory compactors (SGCs) used in construction of hot-mix asphalt in the State. The results show that differences in internal angle exist unless the compactors are calibrated regularly and technicians are trained in laboratory procedures. Once the program was in place, the internal angle of 36 out of 46 SGCs tested was within the limits of 1.16  0.03º. However, seven SGCs, all of one model, had angles between 0.860 and 1.212 degrees with an average angle of 1.026 degrees even after calibration. If the limits are narrowed to 1.16 ± 0.02º, then only 28 out of 46 SGCs (60%) of the SGCs will be within these range The results also show that it is possible to obtain acceptable density values on specimens compacted using machines that have internal angles outside the proposed range. It was concluded that the internal angle limits of 1.16  0.03º are too restrictive for the machines and types of mixes used in the State of Utah. It was recommended that the equipment be calibrated often, that molds be checked for cleanliness and dents, and that temperature measuring devices be verified. In those cases where there are large differences in measured properties of compacted samples even after repeated calibration, the internal angle should be verified since it was noted that external calibration did not always correct the internal angle. This will help reduce conflict between State Labs and consultants.