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Effect of Surface Unevenness on In Situ Measurements and Theoretical Simulation in Non-Contact Surface Wave Measurements Using a Rolling Microphone Array
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.ORCID iD: 0000-0002-5665-8288
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
2015 (English)In: NDT-CE2015 proceedings, Berlin: NDT , 2015Conference paper, Published paper (Refereed)
Abstract [en]

Non-destructive seismic testing using air-coupled microphones is today an attractive alternative to the more conventional stationary accelerometer testing, in order to perform fast and reliable material characterization on pavement structures. A multichannel microphone array enables fast mobile data collection using a rolling trolley. It is essential that the microphone array and the material surface are perfectly aligned to receive a correct result. This study presents estimations of the calculation errors due to misalignments between the microphone array and the material surface. It is shown that even small misalignments can cause large errors. A realistic pavement roughness is simulated in order to quantify the errors in different situations and for different materials (stiffness). A simple solution to correct the errors under certain circumstances is also presented.

Place, publisher, year, edition, pages
Berlin: NDT , 2015.
Keyword [en]
Surface waves, surface unevenness, non-contact measurements, air-coupled measurements
National Category
Geotechnical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-185950OAI: oai:DiVA.org:kth-185950DiVA: diva2:924912
Conference
International Symposium Non-Destructive Testing in Civil Engineering, September 15-17,2015 Berlin, Germany
Note

QC 20160503

Available from: 2016-04-29 Created: 2016-04-29 Last updated: 2017-02-09Bibliographically approved
In thesis
1. Non-contact surface wave measurements on pavements
Open this publication in new window or tab >>Non-contact surface wave measurements on pavements
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, nondestructive surface wave measurements are presented for characterization of dynamic modulus and layer thickness on different pavements and cement concrete slabs. Air-coupled microphones enable rapid data acquisition without physical contact with the pavement surface.

Quality control of asphalt concrete pavements is crucial to verify the specified properties and to prevent premature failure. Testing today is primarily based on destructive testing and the evaluation of core samples to verify the degree of compaction through determination of density and air void content. However, mechanical properties are generally not evaluated since conventional testing is time-consuming, expensive, and complicated to perform. Recent developments demonstrate the ability to accurately determine the complex modulus as a function of loading time (frequency) and temperature using seismic laboratory testing. Therefore, there is an increasing interest for faster, continuous field data evaluation methods that can be linked to the results obtained in the laboratory, for future quality control of pavements based on mechanical properties.

Surface wave data acquisition using accelerometers has successfully been used to determine dynamic modulus and thickness of the top asphalt concrete layer in the field. However, accelerometers require a new setup for each individual measurement and are therefore slow when testing is performed in multiple positions. Non-contact sensors, such as air-coupled microphones, are in this thesis established to enable faster surface wave testing performed on-the-fly.

For this project, a new data acquisition system is designed and built to enable rapid surface wave measurements while rolling a data acquisition trolley. A series of 48 air-coupled micro-electro-mechanical sensor (MEMS) microphones are mounted on a straight array to realize instant collection of multichannel data records from a single impact. The data acquisition and evaluation is shown to provide robust, high resolution results comparable to conventional accelerometer measurements. The importance of a perfect alignment between the tested structure’s surface and the microphone array is investigated by numerical analyses.

Evaluated multichannel measurements collected in the field are compared to resonance testing on core specimens extracted from the same positions, indicating small differences. Rolling surface wave measurements obtained in the field at different temperatures also demonstrate the strong temperature dependency of asphalt concrete.

A new innovative method is also presented to determine the thickness of plate like structures. The Impact Echo (IE) method, commonly applied to determine thickness of cement concrete slabs using an accelerometer, is not ideal when air-coupled microphones are employed due to low signal-to-noise ratio. Instead, it is established how non-contact receivers are able to identify the frequency of propagating waves with counter-directed phase velocity and group velocity, directly linked to the IE thickness resonance frequency.

The presented non-contact surface wave testing indicates good potential for future rolling quality control of asphalt concrete pavements.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 70 p.
Series
TRITA-JOB PHD, ISSN 1650-9501 ; 1025
Keyword
seismic testing, asphalt concrete, dynamic modulus, non-contact measurements, rolling measurements, surface waves, Lamb waves, MEMS microphones
National Category
Geotechnical Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-201147 (URN)978-91-7729-263-0 (ISBN)
Public defence
2017-03-08, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20170209

Available from: 2017-02-09 Created: 2017-02-09 Last updated: 2017-02-13Bibliographically approved

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fulltext(691 kB)95 downloads
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