Modeling of the linear viscoelastic response of polymer modified asphalt binders at intermediate and high temperatures
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An experimental study was conducted to characterize the dynamic mechanical properties of polymer modified asphalt binders at intermediate and high service temperatures. A typical paving grade asphalt and seven different elastomeric modifiers were used. The modifiers, representing a wide variety of random copolymers and thermoplastic block copolymers, were blended with asphalt at three concentration levels to yield a total of twenty one mixes. The effect of short term aging was simulated by the rolling thin film oven test (RTFOT) procedure. A dynamic shear rheometer with parallel plate configuration was used to conduct the dynamic mechanical tests at frequencies between 0.06 to 188.5 rad/s and temperatures ranging from 5 to 75° C. After establishing the linear viscoelastic range of response through performing stress sweeps, a series of frequency sweeps was carried out. Investigation of the resulting isothermal response curves indicated that simple time-temperature superposition is applicable, and dynamic master curves can be constructed by empirical superposition. Effects of polymer type, polymer content, and aging treatment on the behavior of dynamic master curves and relaxation spectra were studied. Feasibility of using the current mathematical models of frequency dependence to characterize the experimental dynamic master curves of modified binders was investigated. These models were generally found inadequate in representing the behavioral complexities of modified binders. To address this inadequacy, two new analytical expressions were developed to represent the dynamic storage shear modulus and dynamic loss shear modulus of polymer modified asphalts. The predictive capability of the developed equation for storage modulus is high for moduli below 108 Pa. The developed model for loss modulus was found to be accurate over the entire range of measured moduli. A procedure for application of these models to practical engineering problems was presented. The measured shift factor data was used to study the dependency of the viscoelastic response on temperature variations. It was observed that this dependency is dominated by the asphalt phase. Within the studied range of temperatures, the WLF equation with universal constants was found to be adequate in describing the temperature dependence of response.
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