Non-linear viscoelastic and fatigue properties of asphalt binders

A study was conducted to relate linear visco-elastic properties of asphalt binders of the same PG-Grade to rheological properties of asphalt mixtures of same aggregates source, gradation, and volumetric proportions. The only variable was the type of modifier used in production of the binder. Results indicated that linear properties are not good indicators of mixture response. The study was expanded to evaluate the role of non-linear viscoelastic properties in mixture response. The results collected indicate that modified and un-modified asphalt binders vary significantly in their non-linear behavior. The non-linear study was expanded to include fatigue performance of binders at varies strain levels in the linear and non-linear range. This paper is written to discuss the need for using large-strain nonlinear shear testing to evaluate binder contributions to mixture behavior. It provides numerical analyses showing that strain domains within binders are much higher than mixture bulk strain. It also suggests that because binders exist as thin films, they can be performing in the non-linear region due to the significant difference between modulus of mineral aggregates and modulus of binders, and because of the boundary conditions. The paper presents a parametric study showing factors that influence strain dependency of asphalt binders of a wide variety of chemical composition and modification techniques. The results of fatigue testing of the binders are also presented to show factors that influence fatigue behavior. It is found that both strain dependency and fatigue are highly sensitive to composition of binders, type of additive, temperature, heating rate, aging and interaction of these factors. It is also found that binders can recover from damage caused by large strains or by fatigue. The recovery trends clearly indicate that the healing of binders is a time dependant phenomenon that is sensitive to chemical composition of binders and other factors. This paper is intended to stimulate the research on the non-linear behavior of binders and to suggest that non-linear properties are essential for effective estimation of role of binders in mixture behavior.