Investigation of fracture behaviors of asphalt mixtures with different loading rates based on acoustic emission

Abstract

This study investigated the fracture behaviors of AC10 asphalt mixture under four loading rates (0.2, 0.5, 2, and 5 mm/min) at 25 °C using semi-circular bending (SCB) tests combined with acoustic emission (AE) technology. Mechanical response − including load–displacement curves, fracture energy, elastic energy, and plastic energy − were analyzed, and damage development was evaluated through these energy parameters. AE parameters such as amplitude, count, energy, b-value, and RA-AF characteristics were utilized to characterize crack initiation, propagation, and failure modes. Results demonstrate that fracture energy exhibits a non-linear relationship with increasing loading rate, peaking at 0.5 mm/min, with post-peak fracture energy declining sharply at higher rates, indicative of enhanced brittleness. As the loading rate increased from 0.2 mm/min to 2 mm/min, damage progression accelerated based on the correlation between damage level and normalized displacement. AE amplitude distributions revealed a higher proportion of high-amplitude events (≥55 dB) at faster loading rates, reflecting intensified energy release. Cumulative count and energy curves were classified into three stages: microcrack closure, dynamic crack propagation, and failure stabilization. These trends inversely correlated with b-value dynamics: low b-values signaled macro-crack nucleation or accelerated growth, while high b-values corresponded to microcrack-dominated behavior. Both cumulative counts and energy increased significantly with loading rate. Gaussian mixture modeling (GMM) of RA-AF data identified a transition from shear to tensile cracking at higher loading rates, attributed to reduced viscoelastic deformation and accelerated brittle fracture mechanisms.