Ultrasonic characterization of distributed cracking damage in concrete using multiply scattered wave fields

This paper reports work to detect, visualize, and characterize alkali–silica reactivity cracking damage in concrete using multiply scattered ultrasonic wave fields. Numerical simulations and laboratory-scale experiments are performed to understand ultrasonic surface wave scattering caused by distributed cracks in concrete, distinguishing that caused by the internal aggregate network. The simulations and experimental results reveal that incident ultrasonic surface waves undergo complicated multiple scattering set up by distributed cracks. To extract the crack-induced multiply scattered ultrasonic wave fields, a frequency-wavenumber (f-k) domain signal filtering approach is proposed. The feasibility of the signal analysis approach is then established by a series of experiments on large steel reinforced concrete blocks with known and controlled cracking damage. The experimental results demonstrate that distributed cracks can be detected and visualized using the proposed ultrasonic signal analysis approach, even at very early stages of the damage process. In addition, we demonstrate that the progress of damage over time can be monitored, where the cracking damage extent is closely related to the extracted multiply scattered wave field energy.