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Pages 5-27

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From page 5...
... 5 Introduction The economic and environmental advantages of using reclaimed asphalt pavement (RAP) in asphalt mixes have been recognized for decades.
From page 6...
... 6• Mix design for mixtures containing RAP, • Mechanical properties of mixtures containing RAP, and • Field performance of mixes containing high RAP contents. Field Management of RAP Materials RAP management practices vary greatly among HMA producers and from state to state.
From page 7...
... 7 respondents combine all RAP sources into a single stockpile while the other half keep separate stockpiles for each RAP source. Contractors who maintain multiple stockpiles often do so because either the state specifications allow only DOT RAP to be used in mixes for DOT projects, or they do so to better control fines by separating millings from other RAP material, or to improve consistency.
From page 8...
... 8yield 70 to 80 percent passing the ½-inch screen. The report notes that most contractors were doing a good job of processing, managing, and testing RAP, but some operations were observed digging into multiple source piles at one location during processing.
From page 9...
... 9 recover and test aggregates from RAP and how to recover and characterize RAP binder. Prowell and Carter conducted a study in Virginia to evaluate how aggregate properties were affected by testing materials in an ignition furnace (14)
From page 10...
... 10 Another basic property that must be determined for RAP materials is the binder content. The common methods for determining asphalt contents of asphalt paving mixtures, AASHTO T 164 and AASHTO T 308, commonly known as solvent extraction methods and the ignition method, respectively, may be used for RAP.
From page 11...
... 11 bining properties of the RAP binder and the virgin binder. NCHRP Project 9-12 evaluated the RAP-virgin binder blending issue with an experiment that considered three scenarios of blending.
From page 12...
... 12 specimens, the predicted shear moduli, |G* |, of the effective binder in the specimens were calculated.
From page 13...
... 13 charts for estimating the properties of virgin and RAP binder blends at any proportion. Additional work was done to determine if the same shifting procedure could be applied to testing low-temperature fracture energy properties using the single-edge notched beam (SENB)
From page 14...
... 14 grade of the blended binder, as illustrated in Figure 1-3. Tensile strengths at 3°C were used to estimate low PG temperatures, and tensile strengths at 38°C were used to estimate the effective high performance grades of the blended binder.
From page 15...
... 15 designing mixes containing RAP. In general, it recommends that standard Superpave mix design procedures should be followed with a few added details: • In laboratory mix designs, it is common to fractionate virgin aggregate to individual sieve sizes down to about the No.
From page 16...
... 16 after 1 hour of storage. The results indicated that the virgin aggregate preheating temperatures needed to be increased when RAP preheating temperatures were decreased to allow for proper mixing and compaction.
From page 17...
... 17 to adjusting the grade of the virgin binder based on the RAP content. NCHRP Project 9-12 also included an experiment to assess differences between plant- and laboratory-produced mixes.
From page 18...
... 18 sample variability due to inconsistent RAP gradations since it was not fractionated. Uniaxial creep flow testing was conducted at 45°C with a stress of 600 kPa.
From page 19...
... 19 30 percent RAP (43)
From page 20...
... 20 This study was a continuation of a previous, unpublished study and contained the results of that work as well. The goal of this research was to use the high- and low-temperature properties of plant-produced RAP to determine if the current tiered guidelines for RAP usage are valid.
From page 21...
... 21 dissipated creep strain energy (DCSEf) from the IDT creep test and the dissipated creep strain energy threshold from the IDT strength test were used to calculate the energy ratio for each mix.
From page 22...
... 22 to determine their continuous grade temperatures and PG grades according to AASHTO M 320. Compacted mix specimens were subjected to either 0, 1, or 3 freeze-thaw cycles and then tested to determine their resistance to moisture damage using the tensile strength ratio (TSR)
From page 23...
... 23 the modified Overlay Tester procedure, and resistance to thermal cracking using the IDT creep compliance and strength tests. The results of the mix tests showed that the rejuvenator reduced the mix stiffness, improved all four fracture properties included in the energy ratio computation, and improved the low-temperature critical cracking temperature.
From page 24...
... 24 RAP had a higher amount of cracking, less rutting, and similar roughness change over time. The overall evaluation revealed that a well-designed mix with 35 percent RAP could perform as satisfactorily as that produced with virgin materials.
From page 25...
... 25 rutting and 61 feet of low-severity cracking. That was slightly better than the performance of the polymer-modified, 15 percent RAP mix sponsored by the Mississippi DOT in the previous cycle of the NCAT Test Track.
From page 26...
... 26 commonly used for convenience, and they may tend to help shed precipitation, but they are more prone to segregation. Covering stockpiles and placing them on a sloped surface to drain water away from the side used to feed the plant can help reduce moisture contents.
From page 27...
... 27 In-Service Performance Numerous studies of in-service pavements containing up to 50 percent RAP have shown that high RAP content mixtures can provide performance similar to virgin mixes. Good performance with high RAP content mixes has been reported in projects with diverse climates and traffic.

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