Measured versus Interconverted Viscoelastic Material Functions of Asphalt Concrete

Author(s):  
A. S. M. Asifur Rahman ◽  
Hasan M. Faisal ◽  
Rafiqul A. Tarefder
Author(s):  
A. S. M. Asifur Rahman ◽  
Hasan M. Faisal ◽  
Rafiqul A. Tarefder

In this study, field collected loose asphalt-aggregate mixtures were used to prepare cylindrical asphalt concrete specimen using a Superpave gyratory compactor and samples were subjected to four levels of aging. Unaged and aged samples were then tested for complex modulus, relaxation modulus, and creep compliance in the laboratory at different temperatures and loading conditions. To determine broadband characteristics, mastercurves of related viscoelastic material functions were determined by applying time-temperature superposition principle. A comparison study showed that increasing levels of aging have significant effect on viscoelastic functions of asphalt concrete. In addition, liquid asphalt binder corresponding to the asphalt-aggregate mixture was tested for complex shear modulus at various levels of aged conditions, using a dynamic shear rheometer. Results showed that even though the binder shear modulus increases significantly with aging, asphalt concrete modulus does not necessarily show similar increment.


Author(s):  
A. S. M. Asifur Rahman ◽  
Rafiqul A. Tarefder

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.


2012 ◽  
Vol 17 (1) ◽  
pp. 53-82 ◽  
Author(s):  
Jacques Luk-Cyr ◽  
Thibaut Crochon ◽  
Chun Li ◽  
Martin Lévesque

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