Effect of loading rate on failure characteristics of asphalt mixtures using acoustic emission technique

Uniaxial compression tests of asphalt mixtures with six loading rates were conducted to investigate the failure characteristics and failure modes of asphalt mixtures. The whole failure process was monitored combined with acoustic emission (AE) technology. The typical AE characteristic parameters including amplitude, hits, and energy were analyzed using correlation analysis. In addition, the dominant frequency of AE signal was obtained by the Fast Fourier Transform (FFT) to characterize failure modes of asphalt mixture under different loading rates. Results show that the failure load and compressive strength of the asphalt mixtures increase significantly with the increase of the loading rate. The amplitude-hits and amplitude-energy of asphalt mixtures at the loading rates of 0.2-5 mm/min have favorable correlation and obvious regularity. By contrast, there is no obvious regularity at the loading rate of 0.05 mm/min. The dominant frequency of AE signals is concentrated in 50-350 kHz, from asphalt mixtures loading to the whole failure process. It can be divided into six frequency bands, and the f-2 band (100-125 kHz) runs through the whole test process. The loading rate of 0.05mm/min has a smaller number of frequency bands than other loading rates, and the AE signal in the high frequency band is less. The failure mode of asphalt mixtures under different loading rates can be identified according to the correlation difference of AE parameters and the difference in dominant frequency evolution distribution.