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Air-coupled microphone measurements of guided waves in concrete plates
KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.ORCID iD: 0000-0002-5665-8288
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Quality control and quality assurance of pavements is today primarily based on core samples. Air void content and pavement thickness are parameters that are evaluated. However, no parameter connected to the stiffness is evaluated. There is a need for fast and reliable test methods that are truly non-destructive in order to achieve an effective quality control and quality assurance of pavements. This licentiate thesis presents surface wave testing using air-coupled microphones as receivers. The measurements presented in this work are performed in order to move towards non-contact measurements of material stiffness. The non-contact measurements are compared to conventional accelerometer measurements in order to compare the noncontact measurements to a “reference test”. The two appended papers are focused on evaluating one parameter in each paper. In the first paper all equipment needed to perform non-contact measurements are mounted on a trolley in order to enable measurements while rolling the trolley forward. It is shown that rolling measurements can provide rapid and reliable measurements of the Rayleigh wave velocity over large areas. However, the measurements are shown to be sensitive to misalignments between the microphone array and the measured surface. An uneven surface can thus cause major errors in the calculated results. The second paper presents an alternative method to evaluate the thickness resonance frequency of a concrete plate. It is demonstrated how the established Impact Echo method can give erroneous results when aircoupled microphones are used as receivers. Instead a method based on backward wave propagation is introduced. It is demonstrated how waves with negative phase velocities can be identified in a narrow frequency span close to the thickness resonance.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , ix, 32 p.
Series
TRITA-TSC-LIC, ISSN 1653-445X ; 14-004
Keyword [en]
Non-destructive testing, Lamb waves, surface waves, air-coupled microphones, non-contact measurements
National Category
Infrastructure Engineering
Identifiers
URN: urn:nbn:se:kth:diva-155912ISBN: 978-91-87353-51-2 (print)OAI: oai:DiVA.org:kth-155912DiVA: diva2:763348
Presentation
2014-12-08, B25, Brinellvägen 23, Stockholm, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20141128

Available from: 2014-11-28 Created: 2014-11-14 Last updated: 2014-11-28Bibliographically approved
List of papers
1. Non-contact surface wave testing of pavements: comparing a rolling microphone array with accelerometer measurements
Open this publication in new window or tab >>Non-contact surface wave testing of pavements: comparing a rolling microphone array with accelerometer measurements
2016 (English)In: Smart Structures and Systems, ISSN 1738-1584, E-ISSN 1738-1991, Vol. 17, no 1, 1-15 p.Article in journal (Refereed) Published
Abstract [en]

Rayleigh wave velocity along a straight survey line on a concrete plate is measured in order to compare different non-destructive data acquisition techniques. Results from a rolling non-contact data acquisition system using air-coupled microphones are compared to conventional stationary accelerometer results. The results show a good match between the two acquisition techniques. Rolling measurements were found to provide a fast and reliable alternative to stationary system for stiffness determination. However, the non-contact approach is shown to be sensitive to unevenness of the measured surface. Measures to overcome this disadvantage are discussed and demonstrated using both forward and reverse rolling measurements.

Keyword
Non-destructive testing, seismic testing, Lamb waves, surface waves, material characterization
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-155908 (URN)10.12989/sss.2016.17.1.001 (DOI)000373916400002 ()2-s2.0-84957577517 (Scopus ID)
Note

QC 20160412

Available from: 2014-11-14 Created: 2014-11-14 Last updated: 2017-12-05Bibliographically approved
2. Detecting the thickness mode frequency in a concrete plate using backward wave propagation
Open this publication in new window or tab >>Detecting the thickness mode frequency in a concrete plate using backward wave propagation
2016 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 139, no 2, 649-657 p.Article in journal (Refereed) Published
Abstract [en]

Material stiffness and plate thickness are the two key parameters when performing quality assurance/quality control on pavement structures. In order to estimate the plate thickness non-destructively, theImpact Echo (IE) method can be utilized to extract the thickness resonance frequency. An alternativeto IE for estimating the thickness resonance frequency of a concrete plate, and to subsequently enablethickness determination, is presented in this paper. The thickness resonance is often revealed as asharp peak in the frequency spectrum when contact receivers are used in seismic testing. Due to a lowsignal-to-noise ratio, IE is not ideal when using non-contact microphone receivers. In studying thecomplex Lamb wave dispersion curves at a frequency infinitesimally higher than the thickness frequency,it is seen that two counter-directed waves occur at the same frequency but with phase velocitiesin opposite directions. Results show that it is possible to detect the wave traveling with anegative phase velocity using both accelerometers and air-coupled microphones as receivers. Thisalternative technique can possibly be used in non-contact scanning measurements based on aircoupled microphones.

Place, publisher, year, edition, pages
Acoustical Society of America (ASA), 2016
Keyword
Thickness frequency, zero group velocity, backward wave propagation
National Category
Infrastructure Engineering Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-155909 (URN)10.1121/1.4941250 (DOI)000373705300014 ()2-s2.0-84957576596 (Scopus ID)
Funder
Swedish Transport Administration
Note

QC 20160412

Available from: 2014-11-14 Created: 2014-11-14 Last updated: 2017-12-05Bibliographically approved

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Licentiate Thesis(925 kB)418 downloads
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Bjurström, Henrik

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