Nondestructive evaluation of surface crack depth in concrete

Subsurface damages in concrete may cause considerable durability loss in the structure since they are not visible from the surface and let water and other chemicals to penetrate into the structure and cause reinforcement corrosion. Ultrasonic methods have been widely applied for defect detection in concrete, however, there are not many applications of the method found in literature for subsurface damage identification. Specifically, when the damage is deeper considering the distance from the top surface. Therefore, in this study concrete blocks including subsurface cracks with different depths as well as a sound concrete block were tested by applying ultrasound. Wave parameters such as velocity and attenuation for each case were evaluated. Rayleigh wave and longitudinal wave velocities do not change for different subsurface crack depths. Even though, wave energy attenuates more in case of a shallower crack, it is difficult to correlate the attenuation rate with crack depth. Still, attenuation rate is an indicative parameter for subsurface damage identification. Numerical results obtained by Boundary Element Method (BEM) analysis are in good agreement with experimental ones. Stack imaging procedure applied to ultrasonic echo data is used as a complementary technique for subsurface crack depth identification. Reflection at the crack depth can be clearly identified.