NDT approach for characterization of subsurface cracks in concrete

A combination of nondestructive testing techniques is applied in this paper for the detection and characterization of subsurface damage in concrete. Thermography is initially used to locate the defects, in the form of vertical cracks beneath the surface, due to the variation of the temperature field as monitored by an infrared camera. Additionally, cooling down curves enhance the characterization by the different rate of heat exchange between cracked and sound areas. Consequently ultrasound propagation is used to estimate the depth, by the firm correlation between wave transmission and damage characteristics. The complementary use of the two techniques is discussed as a potential robust methodology for evaluation of difficult damage in concrete before it is visible.