Rheological and nanomechanical characterization of aging in polymer modified asphalt

In this study, change in rheological and nanomechanical properties of asphalt due to aging is determined in the laboratory. Asphalt binders are aged using Rolling Thin Film Oven (RTFO), Pressure Aging Vessel (PAV), and draft ovens. Asphalt binder includes an unmodified base binder, Styrene-Butadiene (SB) and Styrene-Butadiene-Styrene (SBS) polymer modified binders. Rheological properties such as viscosity, phase angle, shear modulus, creep compliance, stiffness, etc. are determined using Dynamic Shear Rheometer (DSR) test, Multiple Stress Creep Recovery (MSCR) test, Bending Beam Rheometer (BBR) test, Rotational Viscosity (RV) test and the Direct Tension (DT) test. Nanomechanical properties such as hardness and reduced elastic modulus are determined using a nanoindenter. Laboratory test results are expressed in terms of Aging Index (AI) defined by relative change in specific rheological or nanomechanical property of aged and unaged binder. As it was expected, binder rheological properties such as stiffness increases and phase angle and creep compliance decrease due to aging. Based on aging index defined by complex shear modulus (G*), increase in percentage of polymer results in decrease in the AI value for both SB and SBS modified binder. It means percent increase of polymer is not good for long term stability but may be good for fatigue. When comparing AI defined by G* of SB and SBS, it is shown that SBS has higher AI than SB. Aging index of RTFO condition binder does not vary as significantly as it varies in PAV conditioned sample. When comparing AI defined by G*, elastic modulus (G'), viscous modulus (G″), of oven aged sample, base binder ages more than modified binder and G' changes exponentially compared to the linear change of G″. At low temperature, the difference in creep compliance of unaged and aged binder is small compared to that at high temperature. This confirms that temperature significantly affects aging. Based on AI defined by BBR stiffness, original binder shows AI value similar to the modified binder. Again, SBS has higher AI defined BBR stiffness than SB. Based on ductility measured in DT test, it can be said as sample ages its ductility reduces. Nanoindentation is conducted on thin asphalt binder film deposited on glass slides. For both unmodified and modified binders, hardness and reduce modulus increase exponentially due to aging. Nanoindentation results show similar trend obtained by rheological test. Aging decreases the creep compliance defined by indentation depth, similar trend is observed in MSCR test by DSR.Civil EngineeringMastersUniversity of New Mexico. Dept. of Civil EngineeringTarefder, RafiqulMaji, ArupNg, Perc