In December 2007, a portion of State Route 11 in Deland, Florida, was milled and repaved with 45% reclaimed asphalt pavement (RAP). These high RAP mixes were produced at lower than normal hot-mix temperatures and with foamed warm-mix asphalt (WMA) technology. This project was the first large production in which the Florida Department of Transportation (DOT) allowed the use of high RAP in combination with WMA. FHWA, in cooperation with Florida DOT and the National Center for Asphalt Technology, was on site for production and placement of the high RAP-WMA. Plant-produced mix was collected by FHWA for performance testing evaluation. Two mixes were produced: a high RAP–hot-mix asphalt (HMA) control mix and a high RAP-WMA mix. Performance tests conducted by FHWA included performance grade (PG) determination of binders, dynamic modulus, and flow number. PG results of the binders indicate that the high RAP-WMA mix is softer than the high RAP-HMA control mix. This is further confirmed by flow number results, where the high RAP-WMA mix had a lower flow number than the high RAP-HMA control mix did. Dynamic modulus results indicate that the high RAP-WMA mix is slightly softer than the high RAP-HMA control mix, especially at intermediate temperatures. Comparison of measured dynamic modulus results with those predicted using the Hirsch and Witczak models confirm that complete blending occurred in the high RAP-HMA control mix. However, incomplete mixing of RAP and virgin binders may have occurred in the high RAP-WMA mix.
Flow number determined with the repeated-load test is used as a criterion to characterize the rut resistance of hot-mix asphalt. The repeated-load test is performed with the asphalt mixture performance tester (AMPT). The algorithm currently used in the AMPT to determine flow number was found to be extremely sensitive to noise in the data and identifies erroneous flow number results, especially for modified mixes. A new algorithm that uses the Francken model to fit the flow number data is considered for implementation. The robustness of the Francken model is verified in this study by fitting flow number data obtained from field projects. The flow number test is time-consuming, especially for high-stiffness binders and, in many cases, can take as long as 6 h. In this study, other parameters are examined to determine whether the test can be terminated early without loss of information on rut resistance. Steady-state slope and slope at 2% strain are found to correlate well with flow number; the correlation indicates that they may be robust indicators of rut resistance. The flow number test can be terminated once steady-state slope or slope at 2% strain is reached; this substantially reduces test time. This paper discusses the findings from analysis of flow number data from the Francken model and the development of a refined, more expedient method for determining flow number.
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