Cracking Process Analysis and Fracture Pattern Recognition of Asphalt Mixture Based on Acoustic Emission Characteristics

Abstract

Acoustic emission (AE) technology has advantages in characterizing the damage of asphalt mixture and its microcrack formation and development. In this study, AE characteristic parameters and high-speed camera recording results were combined to explore the cracking process, fracture propagation characteristics, and fracture modes of asphalt mixtures with different gradations under different loading rates. The test results show that the crack propagation process of an asphalt mixture can be divided into four stages: elastic deformation, damage accumulation, crack propagation, and failure. After the crack propagation stage, the crack path of the asphalt mixture changes from the interface between coarse aggregate and asphalt mortar to the pass-through coarse aggregate. The peak load, AE count, density of peak frequency points, and proportion of peak frequency in a higher frequency range for an asphalt mixture increase with the increase of loading rate and the decrease of nominal maximum size of aggregate. The change of loading rate affects the number of peak frequency bands, but the nominal maximum size of aggregate has no effect on the number of peak frequency bands. The peak frequency mainly distributes in low and mid-low frequency. Under semicircular bending (SCB), tensile fracture is the main failure mode and shear failure is the secondary failure mode for an asphalt mixture with prefabricated cracks. With the increase of loading rate and nominal maximum size of aggregate, the number of tensile cracks decreases and the number of shear cracks increases in an asphalt mixture.