Characterization of Surface-Breaking Cracks in Concrete Using Ultrasonic Imaging

Surface-breaking cracks in concrete structures can accelerate deterioration by facilitating the ingress of moisture, chlorides, and other aggressive agents. Reliable characterization of crack depth is therefore essential for structural health monitoring and maintenance of concrete infrastructure. This study presents an ultrasonic common midpoint (CMP)-based approach for crack-tip localization and crack-depth characterization in concrete. Ultrasonic measurements were acquired using a pitch-catch configuration in which the transmitter and receiver were positioned symmetrically on both sides of surface crack while maintaining a fixed midpoint. Measurements obtained at multiple transmitter–receiver separations were processed to extract the time-of-arrival (ToA) associated with crack-tip diffraction. The measured ToAs were subsequently used within a travel-time-based localization framework to generate crack-tip images and estimate crack-tip coordinates. The proposed methodology was evaluated on concrete slabs containing vertical and inclined surface-breaking cracks of varying depths. In addition, the approach was applied to a reinforced concrete beam specimen containing thin cracks caused by flexural loading. The localized crack-tip positions from ultrasonic imaging are in good agreement with the observed crack depths and geometries. The proposed method offers a non-destructive approach for crack-tip localization and crack-depth characterization in concrete and may support condition assessment of concrete infrastructure.