CLOSED CRACK DETECTION IN CONCRETE WITH CODA WAVE NON-LINEAR MODULATION

An ultrasonic method, based on nonlinear acoustic mixing of coda waves by lower-frequency swept pump waves, providing for an efficient global detection of small cracks in concrete is presented in this paper. By simultaneous comparison, for uncracked and cracked mortars, of ultrasonic velocity variations and decorrelation coefficient between the unperturbed and the perturbed signals with pump amplitude, the method allows to accurately detect cracks with a width of around 20 µm correlated with velocity variations of approximately 0.01%