Estimation of Glassy Modulus and Differences Between Analysis Methods with Consideration of Aging

Abstract

As a binder is aged in laboratory procedures such as Rolling Thin Film Oven (RTFOT) and Pressure Aging Vessel (PAV) the stiffness characteristics change. In a series of studies, an extended PAV condition of 40 h, standard PAV, RTFOT and Orginal conditions have been tested with binders used in Africa, Asia and the USA including those graded by Penetration, Viscosity and Performance Graded (PG) specifications. In all conditions of aging Bending Beam Rheometer (BBR) tests have been conducted to carefully define the low temperature rheology whereas isotherms of stiffness collected with a Dynamic Shear Rheometer (DSR) has been used to define the intermediate and high stiffness properties. The parameters calculated from the BBR data include the glassy modulus and the shape parameters of the master curve including the delta Tc. The BBR data is combined, via an interconversion process, with the DSR and the complete master curve is obtained. Various parameters have been determined such as the R-value (rheological index), glassy modulus, Glover-Rowe parameter and the cross over modulus. The changes observed in Glassy Modulus also correlates to the R-value which supports the view that this characteristic changes with aging. Glassy Modulus has been calculated using six different methods and is compared to other methods developed over the past 50-years. In all cases the value determined relies upon some extrapolation. This suggests that the oxidation products effect the value of glassy modulus as well as the overall shape of the master curve. The choice of analysis method will affect other binder parameters that are dependent of the Glassy Modulus and the consequence of this is discussed.