Field evaluation of a portable gyratory compactor.

PDFTech ReportFHWA-OR-RD-02-18SPR 375EvaluationCompactorsAsphalt pavementsPavement performanceAsphalt concreteTestingOregonOregon. Dept. of Transportation. Research GroupLeahy, RitaGilchrist, William D.Oregon. Dept. of Transportation. Research GroupUnited States. Federal Highway AdministrationUS Transportation CollectionApplication of quality management concepts to asphalt paving evolved because recipe specifications frequently proved inadequate for ensuring pavement performance. Quality management of asphalt concrete is founded on the premise that the producer controls the end-quality of the product, including the in-place void content on which pavement performance is highly dependent. In its quality management program the Oregon Department of Transportation (ODOT) originally used the Marshall hammer, since neither the Hveem (kneading) nor Superpave prototype compactor was suitable for field quality control/assurance (QC/QA). Post-SHRP research led to the development of truly portable gyratory compactors, ie, those of 70 kg to 140 kg mass. Although selecting and proportioning materials as well as compaction are integral parts of the Superpave technology, there is some apprehension given the fact that no strength test is required at low traffic levels.Given ODOT\ue2\u20ac\u2122s long and successful use of the Hveem method of mix design, the primary objective of this research was to assess the effectiveness of a portable gyratory compactor for field quality control purposes. A secondary objective was to determine the quality of Superpave mixes as measured by Hveem stability. To achieve these objectives plant-produced material was sampled during construction and compacted with both portable and prototype gyratory compactors. Shortly after construction, cores were extracted. All samples (gyratory compacted and field cores) were subsequently tested in the Hveem stabilometer.The following conclusions are noteworthy: Overall, the operational characteristics of the portable gyratory, including calibration and maintenance, were satisfactory. There was essentially no difference between the portable and prototype gyratory compactors as measured by air void content of 150 mm samples. In no case was the difference in air void content greater than 0.5 percent. Comparison of 100 mm and 150 mm samples compacted in the prototype gyratory was instructive in that the latter were consistently lower in air void content, typically by 0.5 to 1.5 percent. The air void content of plant mix samples compacted to Ndesign gyrations was consistently lower than that of the field cores, generally by at least 2 percent. The range in air void content of plant mix samples compacted to Ndesign gyrations was 3.0 to 8.8 percent, whereas the range in air void content of the field cores was 6.8 to 9.1 percent. The data indicate that there is virtually no difference in air void content between 100 mm and 150 mm field cores. Field cores generally had lower stabilities than did gyratory- or kneading-compacted samples. However, there was virtually no difference in the stability of lab compacted samples, regardless of gyratory type or specimen diameter. None of the field cores, regardless of project, met ODOT\ue2\u20ac\u2122s minimum Hveem stability criterion of 35.The data gathered in this research indicate that there is virtually no difference between the prototype (Pine) and portable (Test Quip) gyratory compactors as measured by air void content and Hveem stability. Accordingly, it is recommended that ODOT consider the use of the portable gyratory for QC/QA purposes, assuming that the more fundamental issues of Superpave mix design are resolved. Since Hveem stability of field cores did not meet ODOT\ue2\u20ac\u2122s minimum criterion of 35, early and continuous monitoring of the field performance is imperative. As part of the performance monitoring, it is recommended that wheel-path air void content be periodically measured to confirm/refute the Ndesign concept