Crack Depth Measurement in Concrete Using Surface Wave Transmission

A technique to estimate the depth of surface-breaking cracks in concrete is presented. The surface wave transmission coefficient across the crack plane is determined and used to estimate the depth. A self-compensating testing scheme is applied to eliminate experimental difficulties. Here the self-compensating testing scheme is introduced, and the approach used to estimate crack depth from the measured surface wave transmission coefficient is described. Experimental results obtained from concrete specimens with pre-placed surface-breaking notches are then presented. BACKGROUND Techniques that non-destructively detect defects, measure the mechanical properties, or monitor the state of deterioration in concrete structures are of considerable interest to civil engineers [1,2]. A distinct single surface-breaking crack is a common and significant defect that can eventually lead to failure of a concrete structure. Thus it is important to monitor in a non-destructive fashion the distance that the crack extends into the concrete. Several studies on the time-of-flight technique to predict surface-breaking crack depth in concrete have been reported. The time-of-flight method however is not effective when realistic concrete cracks are tested, that is when the crack tip is ill defined and the crack is tightly closed [3]. Wave transmission or attenuation measurements do show high sensitivity to realistic cracking in concrete under laboratory conditions [4]. Practical one-sided surface wave transmission coefficient measurements in relatively homogeneous materials such as metals have been achieved through the use of a self-compensating testing scheme. In this paper, the surface wave transmission coefficient obtained using a self-compensating scheme is used to predict the depth of surface-breaking notches in concrete. SELF-COMPENSATING THEORY In the frequency domain, we can represent the surface wave signal sent at point i and received at point j (Vy) as a simple product of terms CP657, Review of Quantitative Nondestructive Evaluation Vol. 22, ed. by D. O. Thompson and D. E. Chimenti © 2003 American Institute of Physics 0-7354-0117-9/03/S20.0