Abstract
This paper studies the applicability of an automated non-destructive testing method to monitor the stiffness of asphalt concrete at low temperatures. A loudspeaker is used as a source of non-contact excitation of the axially symmetric fundamental resonant frequencies of a disc-shaped asphalt concrete specimen positioned inside an environmental chamber. Measured resonant frequencies are used to calculate the dynamic moduli of the specimen at different temperatures. The repeatability of the method as well as the effect of loudspeaker height above the sample are studied. Results show that the main advantage of the non-contact excitation method, compared to manually applied impact hammer excitation, is that repeatable automated measurements can be performed while the specimen is placed inside an environmental temperature chamber. This methodology enables to study the effect of only low temperature conditioning on the dynamic modulus of asphalt concrete without interference from mechanical loading.
Highlights
The application of impact resonance and modal testing has been proven successful in determining the complex dynamic modulus of asphalt concrete samples [1,2,3,4,5]
Resonant frequency tests performed on cylindrical samples of asphalt concrete using an impact method were successfully used to obtain a low-strain complex modulus at different frequencies and temperatures [7,8,9]
Agreements with conventional test methods have been obtained for the dynamic modulus of asphalt concrete within a wide range of mixture types [8, 9]
Summary
The application of impact resonance and modal testing has been proven successful in determining the complex dynamic modulus of asphalt concrete samples [1,2,3,4,5]. The technique is based on excitation of samples and measurement of their corresponding resonant frequencies of different modes of vibration. This process leads to the determination of the viscoelastic properties of the samples. Since the resonant frequency of any material is dependent on its geometry, density, boundary conditions, and viscoelastic material properties, one can back-calculate its viscoelastic properties from the measured resonant frequency This technique enables the study of a higher range of loading frequencies and small magnitudes of strains. Resonant frequency tests performed on cylindrical samples of asphalt concrete using an impact method were successfully used to obtain a low-strain complex modulus at different frequencies and temperatures [7,8,9]. Agreements with conventional test methods have been obtained for the dynamic modulus of asphalt concrete within a wide range of mixture types [8, 9]
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