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Oxidative Aging of Binders with High Recycled Asphalt Materials
AdvisorHajj, Elie Y.
Civil and Environmental Engineering
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The objectives of this research effort focused on the oxidative aging of binders with high recycled asphalt materials. A coordinated program of forced-draft oven aging experiments was conducted on eleven sorts of binder blends including three different types of base binders from TX, NH, and NV, two different types of recycled material (RAP/RAS), and two different types of recycling agents (RA). Implementing the Fourier-Transform Infrared Spectroscopy (FT-IR) and Dynamic Shear Rheometer (DSR) isothermal frequency sweep tests, the oxidation kinetics and rheological performance were determined for the evaluation materials. Results indicated that the oxidative aging rates were influenced by the aging temperature, duration, base binder type, as well as the utilized asphalt modifier, i.e. recycled materials and RAs. It was also noted that the RAs reduced the overall stiffness in the investigated stages of oxidation. However, differential aging rates and hardening susceptibilities were observed between the RA and RAP/RAS additions to each of the three bases, noting that these differences were not consistent with the type of RAS, i.e. MWAS or TOAS. Additionally, the base binder aging properties due to the addition of the recycled material was highly influenced by the RA dosages within each blend.Furthermore, the binder blend oxidative aging predictions at binder specific geographical location indicated that using the recycled materials along with the RAs at the optimum dosage, according to the proposed methodology, was able to restore the binder blend properties to the virgin binder. The influences of the recycled material and RAs on the PG 64-28P base binder were also investigated through the binder PG grading and mortar testing. Consistent directions for the influence of the evaluation materials were observed within both procedures, suggesting the capability of the mortar procedure in characterizing the effects of RAP and RA materials on virgin binder without the use of chemical extraction. The Uniaxial Thermal Stress and Strain Test (UTSST) was also conducted on the PMFC and RPMLC specimens of the NV field project to investigate the influence of the high recycled material and RAs on the asphalt mixtures. Through consideration of the thermo-viscoelastic properties, marked differences in the binder oxidation were noted between the experimental factors. Typically, decreases in the viscous response of the mixtures as well as increases in both the stiffness and brittle behavior were observed with aging and also inclusion of the recycled material. Although the addition of the RAs to the recycled mixtures indicated some extent of properties restoration, crack initiation and fracture were observed to occur in significantly warmer temperatures compared to the virgin mixture.