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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