Acoustic evaluation of concrete delaminations using ball-chain impact excitation

Abstract

This letter presents an automated acoustic sensing device for rapid detection of delamination in concrete. The device consists of ball-chains for continual impact excitation and multi-channel microphones for acoustic sensing. A ball-chain is formed by multiple metal balls connected by flexible ropes and is dragged on concrete surface to excite vibration of delaminations. Compared to the conventional chain drag test, the ball-chain generates acoustic signals with higher signal-to-noise ratio (S/N) because the balls give isolated but continual impacts on concrete surface during dragging. The proposed method was validated on a concrete specimen with artificial delaminations.

Sounding of subsurface concrete defects using frequency response of flexural vibration

“…Infrared thermography can rapidly assess the condition of large areas of concrete, and is capable of detecting subsurface defects but not estimating their depth. Some of these methods like chain drag as presently standardized are operator dependent [16], but newer techniques that record acoustic signals and process them for frequency content to remove subjectivity have been demonstrated [17]. A laser Doppler vibrometer can be coupled with a method of excitation, a long-range acoustic device for example, to detect subsurface concrete defects [18].…”

“…Similarly, larger lateral size to depth ratios on the slabs imaged correspond to sharper edges between the defective and non-defective areas. [39], steel spheres [40], hammers [41], and steel chain [17] has been shown to be capable of detecting defect locations.…”

“…The chain used was a hot dipped galvanized proof coil chain with link diameter 3/8 inch (9.5 mm) and total link length 2 1/8 in (54 mm). However, it has been reported that multiple chain links used during the standard test can sometimes produce unwanted noise and false positives in part due to the added noise of chain links bumping into each other [17]. With self-noise due to chain links colliding with each other in mind, a single-link chain drag was also performed, in addition to the three link drag.…”

“…A percussion test is an alternative that uses the flexural frequency of the vibration response caused by a surface impact to estimate the depth of a subsurface defect [17].…”

“…A hammer percussion test may be said to be a type of coin tap test that uses a hammer as the impactor[1].To remove the subjectivity of operator variance from the tests, the sound of the impact can be recorded by a microphone and the frequency content of the acoustic recording is used to identify defects. Sun, Zhu, and Ham[17] used a microphone to record the response of the concrete for a chain drag test[17]. A hammer percussion test using a microphone to record the sound of the impact has been shown by Wu and Siegel[41] to be roughly…”