Improving the Modulus Master Curve of Bituminous Mixes Using Ultrasonic Measurements

The stiffness of bituminous mixtures varies with temperature and frequency of load due to its viscoelastic nature, and this behavior is represented by the modulus master curve. This curve can be constructed using laboratory test results and models based on known material properties. This approach uses material specifications to provide a good estimation of the modulus over a range of frequencies. This estimated curve should be corrected with respect to a measured reference value; which can be obtained by non-destructive ultrasonic methods. Once the dynamic modulus at high loading frequencies is measured with the ultrasonic test, the predictive master curves can be calibrated as to represent the materials properties in the linear viscoelastic domain. In this study, Ultrasonic Waves Velocity (UWV) tests are conducted on specimens of two laboratory prepared mixes to correct the conventional modulus master curves. Moreover, the variability introduced by ultrasonic receiver type and coupling in the UWV measurements are examined, and a practical testing configuration is proposed. The measured dynamic moduli are found consistently higher than the conventional master curves; which underestimate the modulus of bituminous mixture. Finally, the method is verified by shifting the moduli measured at different frequencies and temperatures to the reduced frequencies at the reference temperature of 20 °C.