Interaction between New and Age-hardened Binders in Asphalt Mixes Containing High Quantities of Reclaimed Asphalt Pavement and Reclaimed Asphalt Shingles

As virgin pavement material sources become scarcer and costlier the use of higher quantities of reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in the production of new asphalt mixes becomes increasingly desirable. RAP/RAS binder in the mix has different levels of aging. Through oxidation, the binder becomes stiffer and more rigid than virgin binder, and thus results in a pavement material that is more brittle and susceptible to fatigue and thermal cracking. The purpose of this dissertation study was to investigate the interactions between new and age binders and evaluate asphalt mixes performance.;A major concern associated with the use of high percentages of RAP and/or RAS is the level of blending between virgin and age-hardened binders, because the performance of the mix can be highly influenced by the properties of the composite binder. The blending between new binder and age-hardened RAP binder can be explained through diffusion mechanisms. This research used asphalt binder testing and diffusion and aging theory to investigate the evolution of blending between virgin and RAP binders during asphalt mix production, storage, and placement. The rheological properties of a two-layer asphalt binder sample composed of virgin and simulated RAP binder were measured using a dynamic shear rheometer (DSR) after conditioning following hot mix asphalt (HMA) and warm mix asphalt (WMA) time-temperature paths during mixing and placement. The diffusion and aging coefficients for the composite binder were estimated by comparing measured shear stiffness values with those predicted using a diffusion model and considering asphalt binder aging over time. The diffusion model is solved numerically based on the finite control volume approach. Results show that the HMA results in nearly full blending of the new and aged binders following the time-temperature paths used in this study; while the WMA results in only partial blending.;Traditionally, the properties of blended binders in asphalt mixes containing RAP and RAS are evaluated through rheological testing of the binder extracted and recovered from a mix. However, this approach has long been criticized for being labor intensive, for potentially altering the chemistry of the binder and consequently changing the binder rheology, for forcing blending of binders that may not have been present in the mix, and for creating hazardous material disposal issues. The research presented in this dissertation proposes an alternative approach for characterizing blended binders by testing the linear viscoelastic properties of a fine aggregate matrix (FAM) asphalt mix using a torsion bar fixture in a DSR. A procedure has been developed for preparation and testing of small FAM cylindrical FAM specimens. The results demonstrated that this testing is sensitive to FAM mixes made of different virgin binders, RAP/RAS contents, with and without rejuvenating agent. More importantly, FAM mix testing shows similar results as that from DSR binder testing and full mix testing in terms of rankings of master curves and Black diagrams. Statistical analysis (ANOVA) on stiffness values from FAM testing also provides the same conclusion to that at binder and mix levels. Therefore, FAM approach has the potential to be used as a substitute to stiffness testing for mix comparison purposes. It is also a less expensive and more efficient testing approach than the full mix testing.