Towards Rapid Estimation of Complex Modulus Master Curve for Bituminous Materials

Abstract: This study presents a novel approach for the rapid estimation of the master curve of complex modulus in bituminous mortar, using laser Doppler vibrometry, infrared thermography, and high-power ultrasonic excitation. Conventional methods for evaluating the viscoelastic properties of bituminous materials involve extensive mechanical testing across various temperatures and frequencies within a climate-controlled chamber, making the process both time-consuming and resource-intensive. Our proposed technique significantly reduces characterization time, achieving master curve estimation in less than one minute. This is accomplished by using a high-power ultrasonic transducer and optical measurement systems that collect non-contact data at multiple points under varying conditions, thus eliminating the need for traditional load cells, strain gauges, and multiple tests across different conditions. We have previously developed and validated this methodology for other viscoelastic materials, such as polymers, and in this study explore its applicability to bituminous mortar, which is more viscous at room temperature and therefore presents unique challenges for testing with this setup. In these tests, bituminous mortar samples are excited near their first longitudinal natural frequency using a high-power ultrasonic transducer, generating a controlled, non-uniform strain rate and temperature gradient along the sample length. The temperature of the material increases at the center while remaining stable at the edges. Additionally, the strain rate reaches its maximum at the center and remains near zero at the free edges. Vibrational data captured by a laser Doppler vibrometer are processed to extract stress and strain values, which are then used to compute complex modulus values across the sample over time, with local temperature variations recorded via infrared thermography. The resulting data are synthesized to construct the complex modulus master curve, which is then compared to the master curve obtained through a traditional dynamic shear rheometer. If successful, this approach has the potential to make bituminous mortar characterization more efficient, allowing for rapid testing on a greater number of samples and ultimately enabling improvements in mixture design.