Control of Superpave Gyratory Compactor's Internal Angle of Gyration

Abstract

The State of Utah Department of Transportation started a program to use the dynamic angle validator (DAV) to measure the internal angle of all Superpave^® gyratory compactors (SGCs) used in the construction of hot-mix asphalt in the state. 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 of the 46 SGCs tested was within the limits of 1.16° ± 0.03°. However, seven SGCs, all of one model, had angles between 0.860° and 1.212°, with an average angle of 1.026° even after calibration. If the limits are narrowed to 1.16° ± 0.02°, then only 28 of 46 (60%) of the SGCs will be within the range. 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° ± 0.03° were 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. When large differences in measured properties of compacted samples remain even after repeated calibration, the internal angle should be verified because it was noted that external calibration did not always correct the internal angle. That will help reduce conflict between state labs and consultants.