Characterizing the Complex Modulus of Asphalt Concrete Using a Scanning Laser Doppler Vibrometer

Abstract

Asphalt mixtures are the most common types of pavement material used in the world. Characterizing the mechanical behavior of these complex materials is essential in durable, cost-effective, and sustainable pavement design. One of the important properties of asphalt mixtures is the complex modulus of elasticity. This parameter can be determined using different standardized methods, which are often expensive, complex to perform, and sensitive to the experimental setup. Therefore, recently, there has been considerable interest in developing new, easier, and more comprehensive techniques to investigate the mechanical properties of asphalt. The main objective of this research is to develop an alternative method based on an optical measurement technique (laser Doppler vibrometry). To do this, a frequency domain system identification technique based on analytical formulas (Timoshenko’s beam theory) is used to determine the complex modulus of asphalt concrete at its natural frequencies and to form their master curve. The master curve plotted by this method is compared with the master curve obtained from the standard four-point bending test, and it is concluded that the proposed method is able to produce a master curve similar to the master curve of the standard method. Therefore, the proposed method has the potential to replace the standard stiffness tests. Furthermore, the standard stiffness methods usually conduct experiments up to the maximum frequency of 30 Hz. However, the proposed method can provide accurate complex modulus at high frequencies. This makes an accurate comparison between the properties of the asphalt mixtures in high frequencies and the development of more accurate theoretical models for simulation of specimens possible.

Identification of the viscoelastic properties of an asphalt mixture using a scanning laser Doppler vibrometer

“…In this research, a back-calculation procedure is proposed that can provide the master curve of the complex modulus and phase angle of asphalt mixtures from modal analysis experiments performed at different temperatures. Then, these E * and phase angle master curves are compared with the master curves of the same asphalt mixture estimated using a forward-calculation method [8], and the standard Four-Point Bending test on Prismatic specimens (4PB-PR) [2]. For more information on these two methods, refer to [8].…”

“…Then, these E * and phase angle master curves are compared with the master curves of the same asphalt mixture estimated using a forward-calculation method [8], and the standard Four-Point Bending test on Prismatic specimens (4PB-PR) [2]. For more information on these two methods, refer to [8].…”

“…The asphalt mixture used in this research previously has been used in [8] to develop a forward-calculation methodology to compute the master curve of E * . This mixture is a typical base layer developed in the EMIB research group of University of Antwerp as a reference for common tests.…”

“…The first approach, called the forward-calculation method, relies on some analytical formulas to compute the complex modulus of elasticity from modal parameters. Based on the analytical formulas used, the complex modulus of elasticity can be determined for the fundamental natural frequency [7] or multiple natural frequencies [8]. The second approach is called the backcalculation or inverse method.…”

“…Having the full field vibration allows for the comparison of the mode shapes acquired from the experiments and FEM, and therefore the computation of the Modal Assurance Criteria (MAC). Since this method is based on FEM simulations and not any geometry dependent theory (e.g., Timoshenko's beam theory [8]), it can be applied to specimens with different or even random geometries. Furthermore, this method uses all measured modal parameters of the specimens as opposed to some previous methods that only use the fundamental resonance frequency [12,13] or only the flexural mode shapes [8] of the specimens.…”