Gyratory Samples Research Articles

More Practical Wheel Tracking Test for Rutting Resistance of Asphalt Mixtures

Wheel tracking tests have seen a vast increase in usage among various state department of transportations for measuring rutting resistance of mixtures that already meet volumetric property requirements. With the increase in using recycled materials and warm mix additives, it is clear that using volumetric properties alone to approve asphalt mixture designs is a risky approach. Wheel tracking tests are among the most widely used methods for evaluating rutting resistance, and the AASHTO T324 (Hamburg Wheel-Tracking [HWT]) is the most widely accepted and followed procedure used today in the U.S. However, there are challenges using the HWT, among which the most difficult are the poor repeatability, time required to complete the test, and the sample preparation details. This study reports on an alternative wheel tracking method called the Rotary Asphalt Wheel Tester (RWT) that can successfully address the challenges currently faced with using the HWT. The method requires no cutting of the gyratory samples, significantly reduces time to complete a sample, and appears to offer acceptable repeatability of the results. The method has existed for more than 15 years, available commercially, but used only in a few labs, and one acceptance criterion is already developed by one agency. The study includes evaluating an expanded set of mixtures tested at two temperatures, and two air voids. The results of the RWT are compared with the results of the HWT for numerous mixtures and they show that similar qualitative ranking can be achieved.

Effect of compaction procedure on air void structure of asphalt concrete

Past studies found a significant difference of strength between laboratory and field compacted asphalt concrete (AC). This study evaluated the pore structure of AC compacted by gyratory compactor, linear kneading compactor (LKC) and field cores. The different components of pores were determined and compared for different compaction procedures. The variation of permeability as well as moisture damage of samples prepared by different compaction procedures was also compared. It was observed that the pore structure of field samples is totally different from linear kneading compacted and gyratory compacted samples. Permeability of field samples does not depend on the level of compaction as much as for laboratory compacted samples. The indirect tensile strength (IDT) of field samples is always less than gyratory samples and more than linear kneading compacted samples. Field samples and linear kneading compacted samples are more susceptible to moisture than the gyratory compacted samples.

Evaluation of moisture susceptibility tests for warm mix asphalts

Moisture sensitivity has been identified as an area of concern for warm mix asphalt (WMA) mixtures. To evaluate WMA’s influence on moisture damage, three field-produced mixes were selected for evaluation. All WMA mixes studied used the same chemical WMA additive. The objectives are to compare hot-mix and WMA performance in moisture susceptibility tests, compare indirect tensile strength and Hamburg performance of pavement-cores and laboratory compacted samples, investigate reheating effect of WMA compared to hot-mix asphalt for quality-control purposes, and understand the sensitivity of WMA’s stripping inflection point to oven-aging time and temperatures. Tests indicate pavement-cores performed better than gyratory samples in the Hamburg. Trends indicate Hamburg results are dependent upon temperature and higher temperatures correlate with better performance.

Coefficients of Thermal Contraction and Expansion of Asphalt Concrete in the Laboratory

AbstractThe research reported in this paper investigates the coefficient of thermal contraction (CTE) and coefficient of thermal expansion (CTE) of asphalt concrete (AC) under different conditions in the laboratory. As a first step, the CTC and the CTE of AC at different temperatures ranging between −20 and 55°C were measured using field samples to examine the temperature effect. Then, the difference in the CTC and the CTE values in the vertical and horizontal directions (cross anisotropy) were evaluated using field samples. The influences of air void (AV), aggregate type, and aggregate gradation on the CTC and the CTE values were also investigated using laboratory prepared SuperPave gyratory samples. The deformation measuring devices, LVDTs, were calibrated using a zerodur to eliminate the temperature effect on the LVDTs. Results show that the CTC and the CTE values of AC are nonlinear with temperature and vary with aggregate type. However, gradation of aggregate and AV of sample do not affect the CTC an...

Verification of Superpave Number of Design Gyration Compaction Levels for Georgia

The objective of this project was to evaluate the performance of Georgia's mixes designed by using the Superpave® gyratory compactor. Mixes designed with numbers of design gyrations that are too high would be rut resistant but may be difficult to compact adequately in the field and may lack sufficient durability because of reduced asphalt binder content. The following conclusions were made on the basis of an evaluation of field projects and from laboratory volumetric and performance testing with various aggregate sources and gyration levels: (a) It is unlikely that Superpave mixtures will reach the design air voids of 4.0% during the life of the pavement. After nearly 5 years, the average air voids measured in the wheelpaths were 5.7% for Superpave projects and 3.8% for Marshall projects. On the basis of volumetric comparisons, 66 gyrations with the laboratory-produced mix gave approximately the same density achieved on the Superpave projects in the field. (b) The difference between 4-in.-diameter Marshall samples and 6-in.-diameter gyratory samples for moisture susceptibility was not statistically significant enough to assign a relationship between the tensile strength ratio (TSR) for samples with a diameter of 4 in. and the TSR for samples with a diameter of 6 in. (c) Although the asphalt binder content was an important factor in extending fatigue life, aggregate source and strain level were the most significant variables affecting fatigue results.

Effect of Mix Gradation on Rutting Potential of Dense-Graded Asphalt Mixtures

A study was conducted to evaluate the effect of mix gradations, both complying with and violating the Superpave restricted zone, on rutting potential of hot-mix asphalt. Superpave gyratory samples of mixes with granite, limestone, and gravel aggregates were used. The following gradations were used: gradation above the restricted zone, gradation through the restricted zone in close proximity to the maximum density line, and gradation below the restricted zone. Rut tests were conducted at 64°C with the asphalt pavement analyzer under 689-kPa contact pressure and 45.2-kg wheel load. Rut depths were measured at the end of 8,000 cycles. Repeated shear tests at a constant height were also conducted with the Superpave shear tester. Statistical analysis of rut data generally indicates a significant difference between rut depths obtained in mixes using different aggregate types and gradations. The gradations violating the restricted zone did not necessarily give relatively higher rut depths compared with the gradations in compliance with the zone.

Suitability of Asphalt Pavement Analyzer for Predicting Pavement Rutting

Findings are summarized from an investigation performed to evaluate the suitability of a wheel-tracking device known as the asphalt pavement analyzer (APA) for assessing the rutting potential of asphalt mixes. The evaluation process consisted of correlating the APA’s predicted rutting with known field measurements. The correlation between beam and gyratory samples and the testing variability were also investigated. In addition, the APA test results were compared with those obtained using the Georgia loaded-wheel tester. The findings of this investigation indicated that the APA may be an effective tool to rank asphalt mixtures in terms of their respective rut performance. However, for each mixture type, the APA testing variability was significant between tests and between the three testing locations within each test. Differences in rut measurements of up to 4.7 and 6.3 mm were recorded for beam and gyratory samples, respectively. Therefore, using the APA as a clear pass-or-fail criterion for performance prediction purposes of asphalt mixtures may not be appropriate at this time. It should be noted that these findings are based on data collected on three mixes. Therefore, it is suggested that the APA testing variability (testing and testing locations within the device) be further assessed with a wider range of mixtures. The intent of such an assessment should not only be to correlate the APA results with field data but also to develop potential pass-or-fail limits and procedures.

Use of Georgia Loaded Wheel Tester to Evaluate Rutting of Asphalt Samples Prepared by Superpave Gyratory Compactor

The Georgia loaded wheel tester (LWT) developed by the Georgia Department of Transportation has been used since 1985 in the laboratory during the design stage to evaluate rutting susceptibility of asphalt concrete mixtures. In the LWT testing, asphaltic concrete is subjected to an elevated temperature in a loaded wheel system under repetitive loading conditions, and the permanent deformation induced under the wheelpath is measured. This approach to assess rutting susceptibility was thought to be much more representative than the current test methods and can provide a fast and more accurate means of assessing rutting susceptibility of asphalt concrete under actual field conditions. The asphaltic beam samples used for the LWT testing are prepared by a rolling compaction machine. The new LWT developed in 1992 is described. To promote the concept of using Georgia LWT as a supplement to the Superpave Level 1 design procedure for evaluating permanent deformation of hot-mix asphalt (HMA), a test method utilizing Superpave gyratory compactor-prepared samples to evaluate the rutting resistance of HMA by the LWT was developed. The gyratory samples placed in a specially designed mold can be tested in the LWT identical to that for performing the LWT testing on the beam samples. A test program was conducted to evaluate the applicability of the testing procedure and to develop correlations between the rut depth of asphalt mixes using the beam samples and the gyratory samples. The test program used three asphalt mixes of different degrees of rutting resistance ranging from high to low rut susceptibility. Both types of samples were tested at 40°C, 50°C, and 60°C temperatures for 8,000 cycles under the standard LWT testing procedure. The rut depth results from the beam samples and the gyratory samples showed good correlations for all three mixes tested. The test results also showed a strong relationship between the rut depth values and the air void content in the mixes.