Damage detection on a 3D printed beam with an induced microcrack with a surface waves-based methodology for concrete applications

Accurate evaluation of the depth of damaged in concrete structures is key for the condition assessment of infrastructure and the optimal use of condition-based maintenance. Previous studies show that the environmental effects and even radiation in concrete is reflected as microcracks which are generated by different mechanisms such as alkali-silica reaction, heat, loss of interlayer water, separation of chemically bonded water and change in the microstructure of the cement paste. Ultrasonic surface waves methodologies can be used to determine the depth of damaged concrete as the ultrasonic parameters (.i.e. wave velocity and attenuation) are affected by the presence of microcracks in a material. Since damaged concrete samples are difficult to mimic, this work present the results of a new methodology tested first on 3D printed specimens. Thus, ultrasonic surface waves are used on a 3D printed beams with the inclusion of a microcrack under the top surface at its middle section. Ultrasonic pulses are sent using compressional and shear wave transducers and the induced ultrasonic displacements are measured with a high-frequency laser vibrometer at different locations evenly separated. The measurements are analyzed in the time and frequency domain, the dispersion curves are computed using the 2D Fourier transform. Results shown a significant energy decrease (of approximately 40%) of the surface waves amplitude due to the presence of a single microcrack. In comparison, the reduction of the phase velocity is less than 15%. Hence, attenuation measurements of surface waves are more sensitive for detection of damage due to microcracks than the traditional wave velocity methods.