Acoustic emission characterization of mode I fracture in asphalt mixtures at intermediate temperatures

This study investigated the Mode I fracture behavior of AC10 and AC16 asphalt mixtures at intermediate temperatures (10 °C and 25 °C) utilizing semi-circular bending (SCB) tests coupled with acoustic emission (AE) monitoring. Analysis of key parameters—fracture energy, equivalent stress intensity factor (K_IC*), and AE-derived cumulative energy/count—revealed that AC10 exhibited significantly higher K_IC* and fracture energy than AC16, indicating superior resistance to both pre- and post-region cracking. Concomitantly, cumulative AE energy and count delineated three distinct damage stages: Stage I involves micro/meso-crack development and void closure; Stage II features alternating plateaus and sharp growth points with rapid parameter increases, reflecting accelerated damage; Stage III marks rapid failure with inapparent growth of the cumulative count and energy. Load ratio analysis further demonstrated AC10's higher initiation load-to-peak load ratio and lower failure load-to-peak load ratio versus AC16, signifying slower damage propagation and better fracture resistance. Crack classification via a Gaussian mixture model (GMM) applied to RA-AF data confirmed that tensile cracks are dominant, with AC10 exhibiting a greater proportion of tensile cracks than AC16 at equivalent temperatures. Collectively, these results underscore the significant influence of mixture composition on fracture mechanics and AE response, providing critical insights for optimizing asphalt design to enhance intermediate-temperature cracking resistance.