Laboratory Evaluation of Ultrasonics for Crack Detection in Concrete


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Title: Laboratory Evaluation of Ultrasonics for Crack Detection in Concrete

Author(s): L. I. Knab, G. V. Blessing, and J. R. Clifton

Publication: Journal Proceedings

Volume: 80

Issue: 1

Appears on pages(s): 17-27

Keywords: amplitude; concretes; cracking (fracturing); evaluation; nondestructive tests; ultrasonic tests; velocity.

Date: 1/1/1983

A laboratory study was performed to quantify the capabilities of ultrasonic through-transmission methods to detect cracks in concrete. Pulse velocity and amplitude measurements were taken perpendicular to the crack plane (in cracked concrete) and compared with measurements parallel to the crack plane (in untracked concrete). The direct path length was 152 mm (6 in.). Parallel crack surfaces, approximately 0.05 mm (0.002 in.) apart and having depths of 19, 38, and 57 mm (0.75, 1.50, and 2.25 in.) and widths of 152 mm (6 in.), were fabricated in the specimens. Transducer frequencies of 150 and 54 kHz were used. Concrete specimens with a 28 day compressive strength of about 36 MPa (5.2 ksi) were tested at several ages. A sensitivity ratio was used to determine if the cracks could be detected. The numerator of the sensitivity ratio was the difference between velocity or amplitude values in the cracked as compared to uncracked concrete, while the denominator represented the variablity of the velocity or amplitude values in both the cracked and uncracked concrete. With the 57 and 38 mm (2.25 and 1.5 in.) deep cracks, nearly all the sensitivity values for velocity and amplitude indicated that these crack depths could be detected under the test conditions. The velocity and amplitude sensitivity values with the 19 mm (0.75 in.) crack depth were lower, indicating that the 19 mm (0.75 in.) crack depth could not be clearly detected. In this study, it was concluded that both velocity and amplitude values were meaningful parameters in crack dection. Based on the sensitvity values, howver, velocity appeared to be the more meaningful parameter.