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.

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.

Reclaimed asphalt pavement (RAP) mixtures have shown good resistance to rutting for hot-mix asphalt (HMA) pavement. Mixtures with polymer-modified binders such as styrene-butadiene-styrene (SBS) have also shown good performance against rutting and cracking. This paper presents the laboratory evaluations used to determine the rutting and cracking performance of the RAP mixtures with SBS polymer-modified binders as virgin binders. The asphalt pavement analyzer (APA) test and indirect tensile (IDT) test were conducted for the laboratory evaluation. The properties of SBS polymer-modified binders blended with recovered RAP binders were also investigated. The binder tests included G*/sinδ as the rutting parameter and G*sinδ as the cracking parameter of the Super-pave® PG grade system. The multiple stress creep and recovery test, which has recently received attention as an indicator of the rutting potential of polymer-modified asphalt binders, was also performed. RAP mixtures with SBS polymer-modified binders were fabricated containing different amounts of RAP materials: 0%, 15%, 25%, and 35%. From the APA and Superpave IDT tests, RAP mixtures with modified binders showed good performance regardless of the amounts of RAP materials in HMA. Even though the parameters, G*/sinδ and G*sinδ, and the percentage of recovery indicated the different amounts of RAP binders in polymer-modified binders, the relationship between these parameters and mixture performance was not clearly identified.

The new 2002 AASHTO guide for the design of pavement structures is based on mechanistic principles and requires the dynamic modulus as input to compute stress, strain, and rutting and cracking damage in flexible pavements. The 2002 AASHTO guide has three different levels of analysis; the level used depends on the importance of the pavement structure in question. Dynamic modulus testing is required for Level 1 pavement analysis, whereas no laboratory test data are required for Level 2 and Level 3 pavement analysis. Instead, a predictive dynamic modulus equation is used to generate input values. It is of significant importance to state agencies to understand how well the dynamic modulus for locally available materials compares with the predicted dynamic modulus. This paper presents the results of a study by the Florida Department of Transportation and the University of Florida that focused on the evaluation of the dynamic modulus predictive equation used in the new AASHTO 2002 guide for mixtures typical to Florida. The resulting research program consisted of dynamic modulus testing of 28 mixtures common to Florida. Results showed that on average the predictive modulus equation used in the new AASHTO 2002 flexible pavement design guide appeared to work well for Florida mixtures when used with a multiplier to account for the uniqueness of local mixtures. Results of the study also identified optimal viscosity–temperature relationships that result in the closest correspondence between measured and predicted dynamic modulus values.

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