Integrated ultrasonic and acoustic emission techniques for spatiotemporal damage analysis in concrete.

This study presents a multi-method ultrasonic investigation of progressive damage in a concrete specimen subjected to quasi-static uniaxial compression. We integrate three complementary approaches using a shared transducer array: linear ultrasonic testing (P-wave velocity and energy), coda wave interferometry (CWI), and passive acoustic emission (AE) monitoring, from which we also derive the acoustoelastic nonlinearity parameter β∗ using stress-dependent velocity changes. Joint analysis of these measurements captures heterogeneous changes in material properties at both macroscopic and microscopic scales during damage progression. The evolution of microcracking was spatially heterogeneous, initiating in the upper region of the specimen and spreading toward the lower region, while the central part remained largely intact until the later loading stages. Decreasing P-wave velocity and energy indicated irreversible stiffness degradation, coinciding with clusters of high-energy AE events. CWI-based velocity changes reflected the applied stress protocol and provided early indicators of microcrack accumulation. The nonlinearity parameter β∗, marking transitions from microscopic to macroscopic crack formation, together with the AE-derived NE ratio (cumulative hits divided by cumulative energy), effectively distinguished distributed microcracking from localized cracks. Our findings highlight the complementarity of these methods for capturing the full complexity of damage progression. By integrating wave velocity, β∗, and spatiotemporal AE evolution, this study provides a comprehensive framework for understanding concrete degradation across multiple damage length scales. The proposed approach holds promise for structural health monitoring and non-destructive evaluation of critical infrastructure.