Interconversion of dynamic modulus to creep compliance and relaxation modulus : numerical modeling and laboratory validation - final report.
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2016-09-01
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Edition:Final report
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Abstract:Viscoelastic material functions such as time domain functions, such as, relaxation modulus and creep compliance,
or frequency domain function, such as, complex modulus can be used to characterize the linear viscoelastic behavior
of asphalt concrete in modeling and analysis of pavement structure. Among these, the complex modulus has been
adopted in the recent pavement Mechanistic-Empirical (M-E) design software AASHTOWare-ME. However, for
advanced analysis of pavement, such as, use of finite element method requires that the complex modulus function
to be converted into relaxation modulus or creep compliance functions. There are a number of exact or approximate
methods available in the literature to convert complex modulus function to relaxation modulus or creep compliance
functions. All these methods (i.e. exact or approximate methods) are applicable for any linear viscoelastic material
up to a certain level of accuracy. However, the applicability and accuracy of these interconversion methods for
asphalt concrete material were not studied very much in the past and thus question arises if these methods are even
applicable in case of asphalt concrete, and if so, what is the precision level of the interconversion method being used.
Therefore, to investigate these facts, this study undertaken an effort to validate a numerical interconversion technique
by conducting representative laboratory tests. Cylindrical specimens of asphalt concrete were prepared in the
laboratory for conducting complex modulus, relaxation modulus, and creep compliance tests at different test
temperatures and loading rates. The time-temperature superposition principle was applied to develop broadband
linear viscoelastic material functions. A numerical interconversion technique was used to convert complex modulus
function to relaxation modulus and creep compliance functions, and hence, the converted relaxation modulus and
creep compliance are compared to the laboratory tested relaxation modulus and creep compliance functions. The
comparison showed good agreement with the laboratory test data. Toward the end, a statistical evaluation was
conducted to determine if the interconverted material functions are similar to the laboratory tested material functions.
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