An efficient quality control and acceptance (QA/QC) procedure for constructing hot mix asphalt (HMA) pavements requires the complimentary use of traditional destructive test methods and innovative non-destructive testing (NDT) methods. Current wave-based NDT methods are efficient and economical for the evaluation of material properties. For instance, the ultrasonic pulse velocity (UPV) method is one of the most common NDT methods used for material characterization. However, its isolated use for predicting material strength is limited because of the different variables that affect the strength-velocity relationship. Wave velocity alone does not provide complete information of the materials strength. Thus, additional wave characteristics such as wave attenuation as a function of frequency should be also considered to complement the wave velocity information. In this study, three signal processing techniques: Fourier transform, short-time Fourier transform, and the wavelet transform are used to analyze wave attenuation and frequency content to develop a suitable condition index for HMA mixtures based on wave characteristics. The relative condition of HMA mixtures is evaluated by considering three wave attenuation parameters: peak-to-peak amplitude, spectral area, maximum spectral amplitude. The results of UPV tests are compared to the standard dynamic modulus test for selecting the most suitable condition index. The results indicate that the condition index based on the amplitude measurement has the potential to provide a reliable assessment of the quality of HMA mixtures.
