Anders Gudmarsson

Characterizing the low strain complex modulus of asphalt concrete specimens through optimization of frequency response functions

Measured and finite element simulated frequency response functions are used to characterize the low strain (~10(-7)) complex moduli of an asphalt concrete specimen. The frequency response functions of the specimen are measured at different temperatures by using an instrumented hammer to apply a load and an accelerometer to measure the dynamic response. Theoretical frequency response functions are determined by modeling the specimen as a three-dimensional (3D) linear isotropic viscoelastic material in a finite element program. The complex moduli are characterized by optimizing the theoretical frequency response functions against the measured ones. The method is shown to provide a good fit between the frequency response functions, giving an estimation of the complex modulus between minimum 500 Hz and maximum 18|000 Hz depending on the temperature. Furthermore, the optimization method is shown to give a good estimation of the complex modulus master curve.

Non-contact excitation of fundamental resonance frequencies of an asphalt concrete specimen

Impact hammer and non-contact speaker excitation were applied to an asphalt concrete, a PVC-U and a concrete specimen to measure the fundamental longitudinal resonance frequency at different strain levels. The impact and the noncontact excitation methods resulted in similar resonance frequencies for the undamaged asphalt concrete and for the PVC-U specimen. However, the two excitation approaches gave different results for the concrete specimen, which was shown to have a nonlinear response to increasing strain levels. A reduction and a following recovery of the resonance frequency of the asphalt concrete were shown after the specimen was exposed to a small amount of damage. However, no fast nonlinear dynamics were observed for the asphalt concrete through the speaker measurements.

Nondestructive evaluation of the complex modulus master curve of asphalt concrete specimens

The dynamic Young’s modulus of asphalt concrete is directly related to pavement quality and is used in thickness design of pavements. There is a need for a nondestructive laboratory method to evaluate the complex modulus, which can be linked to nondestructive field measurements. This study applies seismic measurements to an asphalt concrete beam where resonant acoustic spectroscopy and optimization of frequency response functions are used to estimate the complex moduli. A good estimation of the master curve is obtained.

Slow dynamic diagnosis of asphalt concrete specimen to determine level of damage caused by static low temperature conditioning

The phenomenon of slow dynamics has been observed in a variety of materials which are considered as relatively homogeneous that exhibit nonlinearity due to the presence of defects or cracks within ...

Determination of the Frequency Dependent Dynamic Modulus for Asphalt Concrete Beams Using Resonant Acoustic Spectroscopy

The objective of this paper is to study the application of resonant acoustic spectroscopy (RAS) to beam shaped asphalt concrete samples. Natural modes of vibration are generated by a small load impulse at different temperatures and an accelerometer measures the resulting acceleration through the specimen. By using the Fast Fourier Transform the obtained information is transformed to frequency domain from which the solid’s damped natural frequencies can be determined. For each frequency and temperature the corresponding complex modulus is calculated using the approach of RAS. Results of the dynamic modulus from RAS are presented and compared with results of the dynamic modulus calculated according to ASTM E 1876-99 [1]. By using ASTM E 1876-99 only the fundamental frequency of each type of vibrational mode can be used. However, using RAS several resonance frequencies from the same temperature can be used in the evaluation. This opens the possibility of determining the high frequency (or the low temperature) part of the dynamic modulus mastercurve directly from RAS.

Application of resonant acoustic spectroscopy to beam shaped asphalt concrete samples.

The dynamic modulus of asphalt concrete is a key parameter needed in modern pavement design and management. Traditional laboratory tests based on cyclic loading (0.1–25 Hz) at different testing temperatures are time consuming and require expensive equipment. There is therefore a need for more efficient non‐destructive methods to determine the dynamic modulus of asphalt concrete. This study applies resonant acoustic spectroscopy (RAS) to beam shaped asphalt concrete samples. Multiple modes of vibration are measured at each testing temperature using a miniature accelerometer and a small steel sphere as impact source. The complex modulus from each resonant frequency is calculated using the Rayleigh–Ritz method. The heterogeneous and viscoelastic nature of asphalt concrete presents challenges to the application of conventional RAS. The number of measurable modes decreases with increasing test temperature. In an attempt to extend the usable frequency and temperature range measured, transfer functions are inverted using the finite element method along with a frequency dependent complex modulus. Initial results indicate that RAS can be an efficient method for the prediction of the high‐frequency part of the asphalt concrete dynamic modulus mastercurve.