In 1988, the Florida legislature passed a bill directing the Florida Department of Transportation (FDOT) to investigate the feasibility and potential use of ground tire rubber (GTR) in asphalt-concrete mixtures. To address this legislative mandate, the FDOT planned and constructed three test projects to define performance that would allow for rational decisions about the use of GTR in Florida. A major finding of a 10-year performance evaluation of these test sites is that the wet process addition of rubber improved the crack resistance of surface mixtures. State Road 16 test sections with wet process rubberized mixes showed about 1 to 6 percent cracked areas, depending on the amount of rubber, whereas those with virgin asphalt or dry-mixed asphalt rubber showed about 30 percent cracked areas. In addition, the cracking data collected during this evaluation appear to suggest that an effective optimum rubber content is within the 10 to 15 percent range. The long-term performance evaluation program of the three test projects is described here and its findings are discussed.
The Florida Department of Transportation (FDOT) initiated monitoring of its first Superpave section on I-75 in Columbia County for stripping potential using AASHTO T 283, which specifies that all conditioned test samples be saturated to between 55 and 80 percent based on 7 ± 1 percent air voids. A fairly large saturation range is allowed because it was thought that mixtures may have different percentages of permeable air voids. However, the potential interaction between air void content and the level of saturation has not been fully investigated. It is also not clear whether test results from samples saturated to 55 percent are comparable with those of the same mixture saturated to 80 percent for a similar air void content. Therefore, although FDOT adopted AASHTO T 283, it also initiated a parallel study on the effects of different degrees of saturation on moisture damage. Findings are reported of both the ongoing monitoring of the I-75 project for potential stripping and the investigation of the effects of different levels of saturation on moisture susceptibility test results as determined using AASHTO T 283.
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.
An important concern that limits the RAP content in asphalt mixtures is the fact that the aged binder that is present in the RAP can cause premature cracking. Rejuvenators are frequently added to high RAP mixtures to enhance the properties of the binder. There is no existing method to predict the longevity of a rejuvenated asphalt. This study investigated the aging of rejuvenated binders and compared their durability with that of virgin asphalt. Various samples with different types and proportions of RAP, virgin binder, and rejuvenator were aged by RTFO and three cycles of PAV. DSR and BBR tests were conducted to examine the high-temperature and low-temperature rheological properties of binders. Results indicated that the type and dosage of the rejuvenator have a great influence on the aging rate and durability of the binder. Some rejuvenators make the binder age slower, while others accelerate aging. These observations confirm the importance of evaluating the long-term aging of recycled binders. For this purpose, critical PAV time was proposed as a measure of binder’s longevity.
Presented are the findings of an investigation performed to identify possible correlations between nuclear density gauge readings and core density results. The nuclear density data were collected on a Superpave section of I-95 in Brevard County, Florida. Core samples also were obtained from this section for laboratory density determination. Five gauge units [Troxler models 3401, 3440 (two units), 3450, and 4640] and three core density methods (Florida test method FM 1-T 166, ASTM D1188, and dimensional analysis) were considered. The relationships among the core density results were analyzed, then an investigation of the correlation among the different gauges used in this study was evaluated. Finally, the performance of each of the units with respect to the core density results was assessed. The findings indicated that the five nuclear gauge density units did not always produce similar results and did not consistently correlate with the core densities. In addition, the nuclear density testing variability differed not only from gauge to gauge but also from location to location within each gauge.
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