Nondestructive ultrasonic testing methodology for condition assessment of hot mix asphalt specimens

The ultrasonic pulse velocity (UPV) test is widely used for material characterization for engineering applications. However, wave velocity alone does not provide a complete picture of material conditions because different variables affect wave velocity and material strength. Additional wave characteristics such as wave attenuation should be also considered in nondestructive evaluation of materials. Six cylindrical hot mix asphalt (HMA) specimens were prepared each compacted with different numbers of gyrations to generate a wide range of stiffness moduli. The UPV method and standard dynamic modulus testing were used to evaluate the condition of the HMA specimens. Wave characteristics were measured in the time domain and the frequency domain. The relative condition of HMA mixtures was evaluated in terms of five wave characteristics: wave velocity, peak-to-peak (PTP) amplitude, maximum Fourier spectrum magnitude, spectrum area, and dominant frequency. The correlations between these characteristics and the dynamic modulus were examined to select suitable wave-based quality condition indices. The results showed that the complementary use of wave velocity and three amplitude-related wave characteristics enables a reliable assessment of the quality of HMA mixtures. This result was verified by repeating the experiments on three sets of polymer-modified asphalt concrete specimens.