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Newmark Structural Engineering Laboratory >
Newmark Structural Laboratory Report Series (NSEL Report Series ISSN 1940-9826) >
Please use this identifier to cite this item:
http://hdl.handle.net/2142/5320
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| Title: |
Non-contact NDT of Concrete Structures Using Air Coupled Sensors |
| Authors: |
Zhu, Jinying |
| Keywords: |
air-coupled sensing
concrete
imaging
impact-echo
Lamb's problem |
| Issue Date: |
2008-May |
| Publisher: |
Newmark Structural Engineering Laboratory. University of Illinois at Urbana-Champaign. |
| Series Name / Report no.: |
Newmark Structural Engineering Laboratory Report Series 010 |
| Abstract / Summary: |
Elastic wave-based non-destructive test (NDT) methods are effective for detecting flaws
in concrete structures. With the recent developments in computing hardware and software,
imaging techniques have become very popular in NDT applications. However the
application of elastic wave-based imaging methods for concrete structures is severely limited
by the physical coupling between sensors and concrete surface, which reduces testing
efficiency. In this report, the air-coupled sensing technique is proposed as a solution to
improve the efficiency of elastic wave-based test methods for concrete structures.
Theoretical analyses are first conducted to study the propagation of leaky Rayleigh
waves in fluid-solid half spaces. Closed-form solutions of the Green’s function are derived
for pressure and displacement in both the fluid and solid. This analysis provides theoretical
background necessary for practical air-coupled sensing of leaky Rayleigh waves
in concrete. The theory is also extended to underwater NDT applications.
Two applications of air-coupled sensing are considered. One is air-coupled leaky
surface wave sensing in concrete. A laboratory study and field tests demonstrate that
air-coupled sensors are very effective for sensing leaky surface waves in concrete. The
sensitivity and accuracy of air-coupled sensors are comparable to contact sensors. Aircoupled
sensors are suitable replacement for contact sensors in SASW and MASW tests
and moreover help improve test efficiency. In addition, the contact-less nature of aircoupled
sensing enables the study of the effect of defects on wave attenuation. The experimental
results show leaky Rayleigh waves are sensitive to the existence of cracks in
concrete when waves propagate across cracks; the crack positions are clearly located in a
2-D scanning test image.
The second application is air-coupled impact-echo. Two reinforced concrete slabs
containing different types of defects were inspected using an air-coupled impact test testing
scheme. 2-D scanning impact-echo tests were conducted over the slab containing
voids and delaminations. The 2-D scanning image clearly shows the location of embedded
defects, and their depths are also determined. Air-coupled impact-echo is also applied
to examine the grouting condition of embedded ducts. The poorly-grouted and ungrouted
sections are identified within the metal duct. |
| URI: |
http://hdl.handle.net/2142/5320 |
| ISSN: |
1940-9826 |
| Type of Resource: |
text |
| Genre of Resource: |
technical report |
| Publication Status: |
published or submitted for publication |
| Appears in Collections: |
Newmark Structural Laboratory Report Series (NSEL Report Series ISSN 1940-9826)
|
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NSEL Report 010 |
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