Fundamental evaluation of the interaction between RAS/RAP and virgin asphalt binders.
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Fundamental evaluation of the interaction between RAS/RAP and virgin asphalt binders.

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    A comprehensive laboratory testing program was conducted in this research project to examine the blending between reclaimed asphalt pavement (RAP)/recycled asphalt shingles (RAS) and virgin asphalt binders and to evaluate the factors that may affect fatigue and low temperature cracking as well as moisture-induced damage in asphalt mixtures prepared using these materials. This project included two parts: a binder study and a mixture study. In the binder study, atomic force microscopy (AFM) was utilized to characterize the micromechanical properties of the interfacial zone that develops between the RAP/RAS binders and the virgin asphalt binders. Three virgin asphalt binders with different performance grades (PG 58-28, PG 64-28, and PG 64-22), three RAP sources, as well as manufacturing waste and tear-off RAS were used in this project. A new sample-preparation procedure was developed to simulate the blending between the RAS/RAP and the virgin asphalt binders that occurs during asphalt mixture production. The micro-structure, stiffness and the adhesive properties along the blending zone were evaluated for different combinations of RAP/RAS binders and virgin binders. In the mixture study, several asphalt mixtures were used to evaluate the effect of the incorporation of RAP and/or RAS on the mix performance, including a control mixture (no RAP or RAS), a mixture containing 30% RAP, a mixture containing 5% tear-off RAS, and a mixture containing 20% RAP and 3% tear-off RAS. All mixtures were designed to meet ODOT specifications for Item 442 (Superpave) Type A for heavy traffic intermediate course asphalt mixes. The resistance of the asphalt mixtures to fatigue cracking was evaluated using the semi-circular bend (SCB) and the indirect tensile strength (IDT) tests. The SCB test was performed using the Illinois Method and the Louisiana Method. In addition the potential for low-temperature cracking was evaluated using the asphalt concrete cracking device (ACCD), and the susceptibility of the asphalt mixtures to moisture-induced damage was evaluated using the AASHTO T 283 (modified Lottman) test. The AFM test results indicated that blending occurred to a varying degree between the RAP binders and the virgin binders for all RAP-virgin binder combinations. The average modulus of the blending zone depended on the properties of the RAP and the virgin binders. For all binders, a reduction in the adhesive bonding energy was also observed in the blending zone due to the presence of RAP. However, the adhesive properties of the blending zone were significantly higher than those in the RAP binders. Statistical analysis also indicated that the stiffness of the interface blending zone is affected by the properties of the RAP and virgin asphalt binders, while the adhesive properties of the interface blending zone is primarily affected by those of virgin binder used. A linear regression model was developed to predict the modulus and adhesive bonding energy of the blending zone in terms of RAP and virgin binder properties. The validation of the regression models suggested that these models can serve as a viable tool in selecting the virgin binder to be used in a RAP mixture based on the properties of the RAP binder. Finally, the AFM imaging and force spectroscopy experiments revealed very limited to no blending between manufacturing waste or tear-off RAS materials and the virgin binders considered. The asphalt mixture test results also showed that the use of tear-off RAS in intermediate asphalt mixes significantly reduced their resistance to low-temperature and fatigue cracking as well as moisture damage, which can be attributed to the limited blending observed in the AFM experiments between the RAS and the virgin asphalt binders
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