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Highway IDEA Program Vehicle-Mounted Bridge Deck Scanner Final Report for Highway IDEA Project 132 Prepared by: Yajai Tinkey, Larry D. Olson, Olson Engineering, Inc. August 2010
Highway IDEA Program
Vehicle-Mounted Bridge Deck Scanner
Final Report for Highway IDEA Project 132 Prepared by: Yajai Tinkey, Larry D. Olson, Olson Engineering, Inc. August 2010
INNOVATIONS DESERVING EXPLORATORY ANALYSIS (IDEA) PROGRAMS MANAGED BY THE TRANSPORTATION RESEARCH BOARD (TRB) This NCHRP-IDEA investigation was by Research & Technology Corp. completed as part of the National Cooperative Highway Research Program (NCHRP). The NCHRP-IDEA program is one of the three IDEA programs managed by the Transportation Research Board (TRB) to foster innovations in highway and intermodal surface transportation systems. The other two IDEA program areas are TRANSIT-IDEA, which focuses on products and results for transit practice, in support of the Transit Cooperative Research Program (TCRP), and ITS-IDEA, which focuses on products and results for the development and deployment of intelligent transportation systems (ITS), in support of the U.S. Department of Transportation’s national ITS program plan. The three IDEA program areas are integrated to achieve the development and testing of nontraditional and innovative concepts, methods, and technologies, including conversion technologies from the defense, aerospace, computer, and communication sectors that are new to highway, transit, intelligent, and intermodal surface transportation systems. For information on the IDEA Program contact IDEA Program, Transportation Research Board, 500 5th Street, N.W., Washington, D.C. 20001 (phone: 202/334-1461, fax: 202/334-3471, http://www.nationalacademies.org/trb/idea).
The project that is the subject of this contractor-authored report was a part of the Innovations Deserving Exploratory Analysis (IDEA) Programs, which are managed by the Transportation Research Board (TRB) with the approval of the Governing Board of the National Research Council. The members of the oversight committee that monitored the project and reviewed the report were chosen for their special competencies and with regard for appropriate balance. The views expressed in this report are those of the contractor who conducted the investigation documented in this report and do not necessarily reflect those of the Transportation Research Board, the National Research Council, or the sponsors of the IDEA Programs. This document has not been edited by TRB. The Transportation Research Board of the National Academies, the National Research Council, and the organizations that sponsor the IDEA Programs do not endorse products or manufacturers. Trade or manufacturers' names appear herein solely because they are considered essential to the object of the investigation.
VEHICLE-MOUNTED BRIDGE DECK SCANNER
IDEA Program Final Report
Sponsored by NCHRP – 132
Prepared for the IDEA Program Transportation Research Board
The National Academies
Prepared By
Principal Investigator Yajai Tinkey, Ph.D., P .E.
Associate Engineer Olson Engineering, Inc.
Co-Principal Investigator
Larry D. Olson, P .E. President
Olson Engineering, Inc.
A report from Olson Engineering
12401 W 49th Ave. Wheat Ridge, CO Phone: 303-423-1212 Fax: 303-423-6071
www.olsonengineering.com
August 2010
Table of Contents
1.0 EXECUTIVE SUMMARY ................................................................................................. 1 2.0 PROBLEM STATEMENT.................................................................................................. 4 3.0 CONCEPT AND INNOVATION........................................................................................ 6 4.0 LITERATURE REVIEWS.................................................................................................. 8
4.1 Non-Contact Transducers Used In Nondestructive Evaluation ......................................... 8 4.1.1 Microphones............................................................................................................ 8 4.1.2 Laser Vibrometers................................................................................................... 9 4.1.3 Microwave Sensors................................................................................................ 10
4.2 Background of Nondestructive Evaluation Methods Applicable for Bridge Decks ......... 11 4.2.1 Sounding................................................................................................................ 11 4.2.2 Impact Echo........................................................................................................... 11 4.2.3 Spectral Analysis of Surface Waves........................................................................ 13 4.2.4 Slab Impulse Response........................................................................................... 14
4.3 Rolling Contact Transducers Used In Nondestructive Evaluation................................... 14 5.0 INVESTIGATION APPROACH....................................................................................... 16
5.1 Introduction................................................................................................................... 16 5.2 Preliminary Investigation of Non-Contact Transducers .................................................. 16
5.2.1 Preliminary Investigation of Non-Contact Microphones ........................................ 17 5.2.2 Preliminary Investigation of Laser Vibrometer...................................................... 24 5.2.3 Preliminary Investigation of Microwave Transducer.............................................. 31
5.3 Development of the Bridge Deck Scanner Prototype...................................................... 36 5.4 Description of Test Structures and Test Procedures ....................................................... 43
5.4.1 Douglas Bridge in Douglas, WY ............................................................................ 43 5.4.2 1st Street Bridge in Casper , WY.............................................................................. 45
6.0 BRIDGE DECK SCANNER HARDW ARE AND SOFTW ARE IMPROVEMENTS........ 48 6.1 Hardware....................................................................................................................... 48
6.1.1 Original Hardware Design.................................................................................... 48 6.1.2 First Iteration BDS Improvements ......................................................................... 48 6.1.3 Second Iteration BDS Improvements (Current Design) .......................................... 51
6.2 Software........................................................................................................................ 53 7.0 TEST SETUP AND RESULTS FROM 1st STREET BRIDGE (CASPER, WY)................ 54
7.1 Test Setups and Results from Traditional NDE Test Methods........................................ 54 7.1.1 Test Setup and Results from Sounding Using Chain Drags..................................... 54 7.1.2 Test Setup and Results from Ground Penetrating Radar (GPR) Tests..................... 57 7.1.3 Test Setup and Results from Point by Point Impact Echo Tests............................... 62 7.1.4 Test Setup and Results from Infrared Thermography.............................................. 64
7.2 Test Setups and Results from the Bridge Deck Scanner Prototype ................................. 65 7.2.1 Test Setup Using the BDS Prototype...................................................................... 65 7.2.2 Findings from Impact Echo Scanning Tests from the BDS Prototype...................... 67 7.2.3 Findings from Spectral Analysis of Surface Waves Tests from the BDS Prototype.. 70 7.2.4 Findings from Automated Acoustic Sounding with the BDS Prototype.................... 72 7.2.5 Findings from Slab Impulse Response Tests from the BDS Prototype..................... 75
7.3 Comparison of Test Results ........................................................................................... 81 8.0 CONCLUSIONS AND RECOMMENDATIONS ............................................................. 82 9.0 INVESTIGATOR PROFILES........................................................................................... 84 10.0 REFERENCES.................................................................................................................. 86
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1.0 EXECUTIVE SUMMARY The objective of the research project was to develop a Bridge Deck Scanner (BDS) that can be mounted behind a vehicle for comprehensive condition evaluation of concrete bridge decks with nondestructive evaluation methods (Impact Echo-IE, Slab Impulse Response-SIR, Spectral Analysis of Surface Waves-SASW and Acoustic Sounding-AS). In addition, the research explored and compared ground contact transducers to non-contact transducers for a vehicle mounted scanning system. The non-contact transducers explored in this research project include microphone, laser vibrometer and microwave transducer. The results from this research are to provide information on top/bottom delamination, internal cracks, vertical crack depths, thickness profile, and the stiffness of the bridge deck. Contacting vs. Non-Contacting Transducers. Such non-contacting transducers as a laser displacement vibrometer, microwave velocity transducer, directional and non-directional microphones were compared with contacting displacement, velocity (geophone) and accelerometer transducers for the above nondestructive test methods. The non-directional microphones were found to have the most potential application for leaky Lamb surface waves and impact echo and for acoustic sounding. However, at this time, the contacting transducers were determined to be more robust for use in the IE, SASW and SIR tests. Problems with rolling noise limited the use of the laser displacement vibrometer for IE tests and sensitivity of the microwave velocity transducer was found to be poor for SIR tests. Prototype BDS Unit. A prototype BDS unit was developed for this research project as shown in Photos 1 and 2 below. The prototype BDS is composed of one unit with two transducer wheels connected by an axle and an automatic nail gun impulse hammer. Each transducer wheel is identical and has six built-in displacement transducers and six automatic solenoid impactors. The Impact Echo test can be performed from either of the two transducer wheels. The Spectral Analysis of Surface Waves test uses both transducer wheels in a synchronized fashion. The non-contact microphone mounted near the transducer wheel (the one with the active impactor) is used to “listen” to shallow delaminations. Note that all three tests (Impact Echo, Spectral Analysis of Surface Waves and Automated Acoustic Sounding) are performed simultaneously (see Photo 1). The Slab Impulse Response test is performed using an automatic nail gun to drive a 3lb impulse hammer mounted on a separate frame and a non-contact geophone mounted to the axle between the two transducer wheels (see Photo 2). Overview of Field BDS Bridge Deck Test Program. The first BDS prototype was used on the Douglas bridge located in Douglas, Wyoming. The bridge deck of the Douglas Bridge was a silica fume overlay on a concrete deck. It was not the objective to perform a full investigation of this concrete bridge deck, but rather to initially test the prototype bridge deck scanner system. BDS performance feedback from the experiment on the Douglas Bridge were used to improve both the hardware and software of the BDS prototype. After the hardware modifications were completed, the BDS prototype was used on the concrete deck of the 1 st Street Bridge in Caster, Wyoming at slow rolling speeds of 1 to 1.5 mph maximum. The 1st Street Bridge Investigation was conducted as a full investigation of the two east-bound lanes of the bridge. Test runs for IE, SASW and AS were performed the full length of the bridge every 0.5 ft along the bridge length at 1 foot transverse
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spacings to provide for these tests every 0.5 sq ft of the bridge. The SIR tests were conducted every 3 ft along the length of the bridge at 1 ft transverse spacings to provide a test every 3 sq ft. This extensive day of real world field testing again led to several hardware improvements and a better understanding of the BDS system. Discussion of Bridge Deck Scanner Results from 1st Street Bridge. The results from the Impact Echo tests every 0.5 ft showed areas with top and bottom delaminations with excellent precision. The BDS IE results showed good agreement with the previous results from acoustic sounding by chain dragging and Ground Penetrating Radar methods with less correlation with Infrared Thermography tests for shallow delaminations by the University of Wyoming. In addition, the results from the IE tests were able to determine thinner sections and bottom delaminations of the bridge deck versus AS or GPR. The test results from the SASW tests indicated concrete quality was good, but were not so applicable to the 1st Street Bridge since the bridge deck is a one layer system with no significant freeze thaw cracking damage. The data obtained from the Slab Impulse Response tests with the BDS unit were poor due to deck coupling/vibration problems between the impulse hammer deck impact and geophone (on the axle), and vibrations as a result of rolling. The Acoustic Sounding tests did detect delaminations with the microphone as well, but the Impact Echo tests also provided more information on the deeper concrete deck conditions. In comparing nondestructive testing results from all methods used on the 1st street deck, the BDS Impact Echo tests provided the most detail on bridge deck concrete conditions in terms of top/bottom delaminations in comparison to Ground Penetrating Radar, point by point Impact Echo, chain drag Acoustic Sounding and Infrared Thermography test results as presented in Section 7 herein. In addition, BDS Surface Wave and Acoustic Sounding tests were found to provide useful information on the bridge deck conditions. Bridge Deck Scanner (BDS) Status. As the research team wrapped up the project, the hardware and software of the BDS system has continued to be improved; in particular the Slab Impulse Response components have been improved. The BDS unit has been used for a project demonstration for the SHRP II R06 research project on detection of debonded hot mix asphalt pavement layers being conducted by Dr. Michael Heitzman of the National Center for Asphalt Technology in Auburn, Alabama. Consulting projects are also being discussed and proposed for evaluation of bridge and parking deck conditions.
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Photo 1: Bridge Deck Scanner (BDS) Test Setup for Impact Echo (IE), Spectral Analysis of Surface Waves (SASW) and Automated Acoustic Sounding (AS) on the 1st Street Bridge over the North
Platte River in Casper, Wyoming
Photo 2: Bridge Deck Scanner Test Setup for Slab Impulse Response Tests on the 1st Street
Bridge over the North Platte River in Casper, Wyoming
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2.0 PROBLEM STATEMENT Most of the reinforced concrete bridges in the nation were built between 1955 and 1970
(Concrete Society 1996). After 1970, the proportion of prestressed concrete bridges has been
increasing steadily (Concrete Society 1996). As traffic flow increases and heavier truckloads are
permitted, older bridges can become deficient. In addition, environmental attacks including freeze-
thaw degradation and intrusion of chloride ions from deicing salts can cause active corrosion of
reinforcing. Cracks which can be caused by shrinkage, poor curing, moisture and temperature
changes and loading, provide numerous open pathways for water and deicing salt to infiltrate the
concrete bridge deck (Woodward et al 1988). Further, the porous microstructure of the cement and
aggregate provides additional avenues through which water and chemicals migrate into uncracked
concrete initiating the cracking process, typically due to reinforcing steel corrosion and/or freeze-
thaw cracking damage. Although current concrete mix designs and components are much more
resistant to the forces of deterioration than older concrete, there are still problems with older bridges
(Woodward et al 1988). Chase and Washer showed that there were more than 19,000 structurally
deficient concrete bridges in the US in 1997 and the most serious types of deterioration include
decks, superstructure or substructure (Concrete Society 1996). Corrosion of reinforcement leading
to concrete deck delaminations is a major maintenance repair/replacement cost for state DOT’s and
accurate mapping of top and bottom delaminations is needed for repair/replacement decisions.
The Federal Highway Administration (FHW A) requires all bridges to be inspected at least
every two years (Woodward et al 1988). The inspection of concrete bridge decks typically includes
a delamination survey (with chain dragging for acoustic sounding that detects top rebar
delaminations only – not deck bottom delaminations), chloride sampling and core sampling. The
drilled cores can be used to determine the “soundness”, strength and thickness of existing deck
concrete. This research focused on the development of technologies for rapid inspection that can
provide the following information about the bridge deck:
1. Top delamination mapping
2. Internal conditions; including cracks, crack depth, concrete deterioration and bottom deck
delamination mapping
3. Thickness profiling
4. Stiffness/structural integrity of the deck
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Although the proposed techniques do not provide information about the chloride content in a
bridge deck, they do provide critical structural integrity data such as information on both top and
bottom delaminations as well as cracks and crack depth/severity. For example, the Automated
Sounding (Acoustic) and Impact Echo tests provide information on top delamination. The Impact
Echo test also provides additional information on the existence of cracks parallel to the testing
surface, bottom delamination and the thickness profile. Cracks perpendicular to the testing surface
can be detected and the depth can be measured with the Spectral Analysis of Surface Waves
technique. Last, the Slab Impulse Response test provides the stiffness of the deck. The current
practice (using acoustic sounding, visual inspection or Ground Penetrating Radar) is not able to
provide information on bottom delaminations and the internal condition of the bridge deck without
destructive coring of the concrete deck. The prototype BDS system will save time and cost by
minimizing the need for coring and accurately map deck areas in need of repair/replacement, thus
improving safety for the public.
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3.0 CONCEPT AND INNOVATION
This research project proposed to develop an effective and reliable system using non-
destructive evaluation methods (stress waves and acoustic) to quickly and simultaneously determine
the concrete bridge deck thickness profile, stiffness, and internal condition of the deck including top
and bottom delamination, crack locations, crack depths and deterioration of the concrete deck. This
device is attached behind a vehicle so a controlled rapid survey can be undertaken in a continuously
rolling fashion. In addition to microphone based acoustic sounding, the stress wave techniques
include Impact Echo (IE), Spectral Analysis of Surface Waves (SASW) and Slab Impulse Response
(SIR - sometimes called Impulse Response). Multiple channels of non-contact transducers are also
used as receivers for the NDE tests. The non-contact transducers used in this prototype include
airborne microphones.
The Ground Penetrating Radar (GPR) method has been extensively researched and
developed for pavement or bridge deck thickness surveys (Maser et al 1990, Azevedo et al 1996,
Davidson et al, 1998, and Mast 1993). GPR systems are commercially available that can be used to
determine pavement layer thickness and base and sub-base evaluations. The GPR surveys can
determine the top delamination of the concrete bridge deck (Romero et al 2009 and Parrillo et al
2009) and GPR surveys were done for comparison purposes in this research as reported herein
However, the GPR test is heavily dependent on a pre-select threshold to determine the areas with
shallow delamination which can be subjective. Recent research has shown that the use of both GPR
and IE methods can be complementary for condition assessment of bridge decks (Gucunski et al
2009).
The result of the research project is the first product that provides a complete scanning of
bridge decks including mapping the thickness profile, evaluation of the stiffness and the internal
condition of the bridge deck (top and bottom delaminations, internal cracks and general concrete
deterioration). This is the first time that all four NDE techniques have been combined in the same
system and performed simultaneously. Results from the IE test provide a thickness profile of the
bridge deck (Sansalone et al 1997). In addition, the IE test can detect top and bottom
delaminations, location of cracks and general deterioration of concrete (Sansalone et al 1997).
Results from the SASW test provide surface wave velocity that can be used to theoretically
7
calculate the compressional wave velocity used to calibrate the Impact Echo test. The SASW test
can also detect cracks perpendicular to the surface of the bridge deck and evaluate the crack depth
(Kalinski 2004). Most importantly, results from the SASW test provide the depth of concrete
deterioration in the bridge deck (Kalinski 2004). The Slab Impulse Response (SIR) test can be used
in the evaluation of concrete conditions to provide secondary information from the IE and SASW
tests (Davis et al 2003). In addition, information from the SIR test can be used to determine the
dynamic stiffness of the bridge deck (Davis et al 2003). Non-contact microphones are used to
“listen” to the hollow sound for shallow delamination detection. Data from all the three NDE tests
plus information from the automated sounding with a microphone will not only compliment each
other but also still provide redundancy to increase the confidence level of the data interpretation.
Excluding the information on the chloride content of the bridge deck, the results from the proposed
technologies provide comprehensive information that typical routine bridge inspections acquire on a
bridge deck.
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4.0 LITERATURE REVIEWS
4.1 Non-Contact Transducers Used In Nondestructive Evaluation Several types of non-contact transducers were studied throughout the research presented
herein. Non-contact transducers are of significant interest because they may allow the test methods
to be performed more rapidly, which would allow greater speeds of a vehicle mounted bridge deck
scanner. Non-contact transducers may also eliminate noise sources associated with rolling wheels
and other contact points. Based upon the research team’s experience and extensive knowledge of
the test methods and governing wave mechanics, as well as knowledge gained from discussions
with other researchers, it was determined that the most promising non-contact transducers to pursue
were microphones, laser vibrometers, and microwave transducers. Below is a review of the current
literature available discussing the implementation of these non-contact transducers in measuring
vibrations similar to those inherent in the proposed test methods.
4.1.1 Microphones
The physical basis of utilizing non-contact microphones to measure surface waves is a
phenomenon known as Leaky Lamb Waves (LLW). This phenomenon is essentially the coupling of
wave energy from the surface of the excited medium (in our case concrete) into the fluid in contact
with that surface (in our case air). A detailed discussion of the LLW phenomenon as well as
information regarding the development of the method can be found in Bar-Cohen et al (2001) and in
Holland and Chimenti (2003). Since the method’s development for use on thin composite materials
with high frequency excitation and response, several researchers have applied the same principles in
performing both the Surface Wave and similarly the Impact Echo test methods on concrete slabs
using non-contacting microphone receivers. It is these recent studies pertaining to Surface Wave
and Impact Echo testing that are most pertinent to our research investigation. Note that non-
contacting excitation of the concrete surface has been unsuccessful in past studies (Cetrangolo and
Popovics 2006) but is of little concern due to the relative ease of employing contacting solenoid
impacts for excitation.
In 2001 Zhu and Popovics implemented air-coupled surface wave testing using directional
microphone receivers to detect the LLW from the concrete surface. This study was supported by
additional studies by Zhu (2005), Zhu and Popovics (2005), as well as a study by Ryden et al (2006)
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in which non-directional audio microphones, which are much less expensive than directional
microphones, were utilized in surface wave testing. Ryden et al (2006) mentions external noise
sources such as wind noise but reports good results. There is also concern of interference from the
direct air wave arrival from the impact source, however for surface wave testing the distance
between the impact source and receiver can be made large enough that the two arrivals occur at
significantly different times due to the differences in velocities of the air born p-wave and LLW on
the concrete surface (Zhu and Popovics 2007). Digital signal processing techniques such as
windowing the wave arrivals with exponential decay or Hanning windows are often performed
during data analysis to eliminate any effects of unwanted wave arrivals. Because of the need for
separation of the LLW and direct air wave arrivals it is advantageous for the microphone receiver to
be located as near the concrete test surface as possible.
Multiple studies have also been conducted in which non-contacting microphones were used
to perform impact echo testing. Non-contact impact echo testing has proved to be more difficult
than non-contact surface wave testing (Zhu and Popovics 2007) because the separation of the
impact source and microphone receiver is much less than in surface wave testing, which leads to
interference from the direct air wave. The spacing between the receiver and impact source is
critical in impact echo testing because the excitability of the S1 Lamb wave mode, which is the
impact echo resonance in a slab type structure (Gibson and Popovics 2005), decreases drastically as
the source-receiver spacing increases (Gibson 2005). An additional complication is the need for a
longer time signal in the impact echo test to determine the resonance, whereas often times in surface
wave testing only the first arrival (1 wave cycle) is considered, thus enabling sharp windowing
functions to remove unwanted direct air wave arrivals. Zhu and Popovics (2007) demonstrated that
sound insulation material can be used for shielding purposes to encapsulate (open on one end) the
microphone receiver and reduce the direct air wave energy detected by it.
4.1.2 Laser Vibrometers
Another important emerging technology in the field of non-contacting vibration
measurements is the laser vibrometer. Laser vibrometers are used extensively in the automotive,
aerospace and other manufacturing fields. The laser vibrometer measures vibration using the
Doppler shift effect. Laser vibrometers generally have a wide frequency range, excellent vibration
resolution and are well suited to indoor laboratory testing. The ability of the laser vibrometer to
10
measure high frequencies (> 100 MHz) has made it the ideal receiver to measure surface waves in
thin ceramic and metal materials (Somekh et al 1995). This testing is often conducted to determine
material strength and locate defects or anomalies within the material, very similar to testing at lower
frequencies on concrete specimens. Some models have been ruggedized and made more portable to
allow for field testing situations. The primary drawback of laser vibrometers is the cost, which
typically ranges from $10,000 – $50,000 for a single receiver. Due to the cost, few studies have
been conducted to date in which a laser vibrometer was implemented for surface wave testing on
concrete. Abraham et al 2009 performed a successful study in which an extreme number of
repetitive surface wave tests were performed on a variety of concrete samples using a laser
vibrometer receiver mounted to a semiautonomous robot.
The laser vibrometer has also been successfully implemented as a receiver for impact echo
testing on concrete structures (Abe et al 2001; Algernon et al 2008). The laser vibrometer has been
shown to produce high quality impact echo data and is fairly easy to implement. Because the
device relies on the Doppler shift effect of the vibrating surface and not an air coupled wave,
proximity to the impact source and shielding of direct air waves are not of concern.
4.1.3 Microwave Sensors
The microwave transducer has also been pursued as a possible non-contacting receiver for
structural vibrations. Based upon our understanding of the sensor as well as discussions with other
researchers, the sensor is not applicable to the relatively high frequency vibrations found in Impact
Echo and Surface Wave testing. However, it is possible that the microwave transducer may be
implemented in Slab Impulse Response (SIR) testing in which the frequency range of interest is
primarily less than 500 Hz. The current SIR method involves holding a geophone in contact with
the concrete structure while the structure is impacted with an instrumented hammer. The geophone
measures the transient vibration induced in the concrete slab. Recently multiple research studies
have used microwave interferometers to measure movements of large scale structures such as
bridges and buildings (Bernardini et al 2007; Farrar et al). These systems, which are commercially
available, have typical maximum sampling frequencies from static to 100 Hz (Bernardini et al 2007)
to 200 Hz. A separate research study also showed that microwave transducers can be used to
measure transient seismic vibrations of the ground (Wijk et al 2005). In the Wijk et al (2005) study,
a sledge hammer impacting a steel plate was used to excite the seismic vibrations in the ground
11
while a microwave transducer was suspended nearby to receive the vibration signals. The research
study involved averaging 32 separate impacts at a single test location to improve the signal to noise
ratio.
4.2 Background of Nondestructive Evaluation Methods Applicable for Bridge Decks
4.2.1 Sounding
Chain dragging or hammer sounding, where either a heavy chain(s) is literally dragged
across a bare concrete deck, or a rock-hammer or similarly designed hammer is used to repeatedly
strike its surface, are two common acoustic sounding methods widely used to determine areas with
shallow surface delamination in bare concrete bridge decks. Common chain configurations consist
of four or five segments of 1 in. links of chain that are approximately 18 in. long (ASTM D 4580-
03). Distinctive hollow sounds produced by the chain drags or hammer impacts are indicative of
shallow delaminations. Other investigators have connected the chain drag apparatus to a
microphone in an attempt to standardize and automate the evaluation (Henderson et al, 1999).
Although chain drags or hammer sounding are simple to perform, most of the damage mapping is at
the discretion of the operator due to different levels of experience and hearing among operators. In
addition, delamination located deeper than 3 to 4 inches from the surface is hard to determine by
acoustic sounds (hollow and drummy due to flexural resonant vibrations of the shallow,
horizontally cracked concrete due to steel rebar expansion as a result of corrosion).
4.2.2 Impact Echo
The IE method involves hitting the concrete surface with a small impactor (or impulse
hammer) and identifying the reflected wave energy with a displacement (or accelerometer) receiver
mounted on the surface near the impact point (ASTM C 1383-04). A simplified diagram of the
method is presented in Figure 1.
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Flaw
Olson Instruments, Inc. handheldtest head for Impact Echo tests
*Reflection from backside occurs at a lower frequency than thatfrom the shallower concrete/flaw interface
Reflection from concrete/flawinterface
Reflection from backside oftest member
Receiver Impact
Figure 1 – Schematic of Impact Echo (IE) method.
Following the impact, the resulting displacement or acceleration response of the receiver is
recorded. The resonant echoes are usually not apparent in the time domain. The resonant echoes
are more easily identified in the frequency domain (linear displacement spectrum). Consequently,
the time domain test data are processed with a Fast Fourier Transform (FFT) which allows
identification of frequency peaks (echoes). The displacement spectrum of the receiver or the
transfer function (receiver displacement output/hammer force input vs. frequency) are used to
determine the resonant peaks. If the thickness of a slab is known, the compression wave velocity
(Vp) can be determined by the following equation:
Vp = 2*d*f/β (1)
where d = slab thickness, f = resonant frequency peak. The above equation is modified by a β
(Beta) factor of 0.96 for concrete walls and slabs (Sansalone et al 1997 and per the ASTM
standard).
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4.2.3 Spectral Analysis of Surface Waves
The SASW method uses the dispersive characteristics of surface waves to determine the
variation of the surface wave velocity (stiffness) of layered systems with depth (M.F. Aouad 1993).
The SASW testing is applied from the surface which makes the method nondestructive and
nonintrusive. Shear wave velocity profiles can be determined from the experimental dispersion
curves (surface wave velocity versus wavelength) obtained from SASW measurements through a
process called forward modeling (an iterative inversion process to match experimental and
theoretical results). The SASW method can be performed on any material provided an accessible
surface is available for receiver mounting and impacting. Materials that can be tested with the
SASW method include concrete, asphalt, soil, rock, masonry, and wood.
Applications of the SASW method include, but are not limited to:
1) determination of pavement system profiles including the surface layer, base and subgrade
materials,
2) determination of seismic velocity profiles needed for dynamic loading analysis,
3) determination of abutment depths of bridge substructure, and
4) condition assessment of structural concrete.
For bridge decks, the SASW method can be used to check for deteriorated zones in concrete
such as cracking from freeze-thaw, alkali-silica/aggregate reactions (ASR/AAR) and fire damage.
SASW can also measure crack depths (for cracks perpendicular to the surface) in bridge decks. The
SASW method uses the dispersive characteristics of surface waves to evaluate concrete integrity
with increasing wavelength (depth). High frequency or short wavelength waves penetrate through
shallow depths, and low frequency or long wavelength waves penetrate through deeper depths.
Open, unfilled cracks will result in slower surface wave velocities. Weak, fire damaged and poor
quality concrete also produce slower surface wave velocities.
It should be understood that if a crack is in tight grain-to-grain contact then the SASW
dispersion curve will show minimal effect from the crack. This is because the surface wave energy
will propagate across a tight crack that is under stress.
14
4.2.4 Slab Impulse Response
Slab Impulse Response (Slab IR) investigations are performed primarily to identify subgrade
voids below slabs-on-grade. The method is applicable for evaluating the repair of slab subgrade
support conditions by comparing the support conditions before and after repairs. The elements that
can be tested include concrete slabs, pavements, runways, spillways, pond and pool bottoms, and
tunnel liners. The Slab IR method is often used in conjunction with Ground Penetrating Radar for
subgrade void detection and mapping. In addition, the Slab IR test method can be used on other
concrete structures to quickly locate areas of delamination or void in the concrete, if the damage is
relatively shallow. Slab IR can be performed on reinforced and non-reinforced concrete slabs as
well as asphalt or asphalt-overlaid slabs.
4.3 Rolling Contact Transducers Used In Nondestructive Evaluation The only rolling contact transducers used commercially in non-destructive evaluation is the
rolling displacement transducer for Impact Echo Scanning. The rolling Impact Echo Scanner (IES)
was first conceived by Mr. Larry Olson and researched and developed as a part of a US Bureau of
Reclamation prestressed concrete cylinder pipe integrity research project (Sack and Olson, 1995).
This technique is based on the impact-echo method (Sansalone and Streett, 1997; ASTM
C1338(2004)). In general, the purpose of the impact-echo test is usually to either locate
delaminations, honeycombing or cracks parallel to the surface or to measure the thickness of the
structures (concrete beams, floors or walls). To expedite the impact-echo testing process, an
impact-echo scanning device has been developed with a rolling transducer assembly incorporating
multiple sensors, attached underneath the test unit. When the test unit is rolled across the testing
surface, an optocoupler on the central wheel keeps track of the distance traveled. This unit is
calibrated to impact and record data at intervals of nominally 25 mm (1 in.). If the concrete surface
is smooth, a coupling agent between the rolling transducer and test specimen is not required.
However, if the concrete surface is rough, water can be used as a liquid couplant.
A comparison of the impact-echo scanner and the point by point impact-echo unit is shown
in Figure 2. Typical scanning time for a line of 157 in (4 m), approximately 150 points, is 60 s. In
an impact-echo scanning line, the resolution of the scanning is about 1 inch (25.4 mm) between
impact points. Data analysis and visualization is achieved using impact-echo scanning software
15
developed by Dr. Yajai Tinkey for a National Cooperative Highway Research Program Innovations
Deserving Exploratory Analysis (NCHRP-IDEA) grant for stress wave scanning of post-tensioned
bridges (Tinkey and Olson, 2007). Raw data in the frequency domain were first filtered using a
Butterworth filter with a high-pass frequency range of 1-5 kHz and a low-pass frequency of
typically 20 kHz depending on the range of frequencies (inversely related to thickness echo depth)
of interest. Automatic and manual picks of dominant frequency are performed on each data
spectrum and an impact-echo thickness is calculated based on the selected dominant frequency. A
thickness surface plot (skewed 3-D view of X-Y distance and thickness echo depths) of the
condition of the scanned element is then generated by combining the calculated impact-echo
thicknesses from each scanning line.
Figure 2 – Impact Echo Scanning Unit and Point by Point Impact Echo Unit
16
5.0 INVESTIGATION APPROACH
5.1 Introduction The objective of the research was to develop an effective and reliable system using non-
destructive evaluation methods (stress waves and acoustic) to quickly and simultaneously determine
the concrete bridge deck thickness profile, stiffness, and internal condition of the deck including top
and bottom delamination, crack locations, crack depths and deterioration of concrete bridge decks.
The product(s) from this research is to be used as a tool for inspection and non-destructive
evaluation (NDE) of concrete bridge decks. The first stage of the research project included a
comprehensive study of potential non-contact transducers and rolling contact transducers. The
second stage of the research project entailed research and development of the BDS prototype
hardware and software.
Field experiments using the prototype BDS were conducted on two bridge decks in
Wyoming. The tested bridges are referred to herein as the Douglas Bridge in Douglas, WY and the
1st Street Bridge in Casper, WY. Feedback from the first BDS field experiments on the Douglas
Bridge were used to improve the hardware and software. Then the BDS prototype was used on the
second tested bridge, the 1st Street Bridge, for a thorough inspection of the concrete bridge deck.
Note that other traditional NDE tests were also conducted on the 1 st Street Bridge. These NDE tests
were conducted as part of a Wyoming DOT bridge deck NDE assessment conducted by Dr. Jennifer
Tanner of the University of Wyoming and included the following organizations and methods: 1.
ground penetrating radar (GPR) with contact and airborne horn antenna performed by the Olson
Engineering research team, 2. traditional chain drag by the Wyoming DOT, and 3. Infrared
Thermography (IR) and point-by-point Impact Echo tests (3 ft x 3 ft grid) performed by a research
team from the University of Wyoming under the direction of Dr. Jennifer Tanner. The results from
the traditional NDE tests and the results from the BDS prototype are presented and compared in
Section 7.0 herein.
5.2 Preliminary Investigation of Non-Contact Transducers The first stage of the research began with studies of different types of non-contact
transducers with potential applications for acoustic sounding (AS), IE, SASW and SIR tests. These
17
transducers include microphone, laser vibrometer and microwave transducers. The results and
summary of the findings from the non-contact transducers are presented in this section
5.2.1 Preliminary Investigation of Non-Contact Microphones
The initial part of this study consisted in part of the exploration of non-contact Directional
Microphones to be used as receivers for the AS, IE, SASW and SIR tests. This task extends the
previous work of the research team at Olson Engineering in the development of the Impact Echo
Scanner with a non-contact directional microphone and also followed on the recent research work
from many researchers [Holland et al 2003, Gibson 2005, and Ryden et al 2006]. Between 2002 -
2003, as part of in-house research and development, the research team at Olson Engineering added a
non-contact directional microphone in addition to a rolling displacement transducer for Impact Echo
Scanning tests. The bottom view of the scanner (in 2003) with non-contact microphone and rolling
displacement transducer for Impact Echo tests is shown in Figure 3.
Figure 3 - Bottom View of the Impact Echo Scanner with non-contact microphone and
ground contact rolling displacement transducer and automated solenoid impactor for Impact Echo
Scanning Tests
5.2.1.1 Microphone for IE Tests
Detailed studies were performed of non-contact microphones as compared with contacting
displacement and accelerometer transducers in Impact Echo tests. The studies included looking at
the effects of the separation distance between the source and receiver so that the direct interference
airborne wave can be excluded, applying a shielding mechanism to protect the microphone
Non-contact directional microphone Impactor
Rolling ground contacted displacement transducer
18
receivers from acoustic airborne noise, and assessing the best filters to be applied to minimize the
effects of ambient or traffic noise [Gibson 2005 and Zhu et al 2007]. One typical laboratory setup
of the preliminary experiments is shown in Figure 4.
Figure 4 – Test Setup to Compare the Non-contacted and Ground-contacted Sensors for Impact Echo Tests
A non-contact microphone (ADK SC-1 Small Capsule Condenser Microphone with an
external 48V Phantom Power supply) and a small, high frequency accelerometer were used in the
comparison study. The tests were performed on a nominally 4” thick concrete slab. The
microphone was mounted at various heights above the slab surface directly above the
accelerometer. The studies included looking at the effects of the separation distance between the
source and receiver so that the direct interference airborne wave could be excluded [after Gibson
2005]. An automatic solenoid impactor was applied on the slab in line with both sensors starting at
4” and performed every 1” away until it was located 24” away from the sensors. Time domain
Impact Echo (IE) data and the spectrum (converted to depth scales) from the accelerometer and
microphone (mounted 3 inches above the concrete slab) with the impactors located 4” and 12” away
from the transducers are presented in Figures 5 and 6. Note that the time domain data presented in
Figures 5 and 6 are filtered with a digital bandpass Butterworth filter with a range of 3– 20 KHz.
Accelerometer
Non-contact microphone (non-directional)
Impactor
Accelerometer
Non-contact microphone (non-directional)
Impactor
19
Figure 5a – IE Data from an Accelerometer Figure 5b – IE Data from the Microphone
Figure 5 - Comparison of IE Data from Accelerometer and Microphone with the Source 4” away
Review of Figure 5a indicates that the spectrum of the time domain IE data taken from the ground-
contact accelerometer had a dominant resonant echo peak corresponding to a slab thickness of 4”.
However, the spectrum of the time domain IE data taken from a non-contacted microphone showed
multiple peaks in Figure 5b. This is because two wave modes (actual Lamb waves and airborne
waves) blended together.
Figure 6a – IE Data from an Accelerometer Figure 6b – IE Data from the Microphone
Figure 6 - Comparison of IE Data from Accelerometer and Microphone with the Source 12” away
Depth (in) Depth (in)
Time (us)0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000
-4
-2
0
2
4
Depth
0 2 4 6 8 10 12 14 16 18 20
10
20
30
40
50
Time (us)0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000
-10
0
10
Depth
0 2 4 6 8 10 12 14 16 18 20
500
1000
Main peak at 4”Multiple peaks due to several wave modes
Depth (in) Depth (in)
Time (us)0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000
-4
-2
0
2
4
Depth
0 2 4 6 8 10 12 14 16 18 20
10
20
30
40
50
Time (us)0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000
-10
0
10
Depth
0 2 4 6 8 10 12 14 16 18 20
500
1000
Main peak at 4”Multiple peaks due to several wave modes
Time (us)0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000
-2
-1
0
1
2
Depth
Depth (ft)0 2 4 6 8 10 12 14 16 18 20
5
10
15
Time (us)0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000
-4
-2
0
2
Depth
Depth (ft)0 2 4 6 8 10 12 14 16 18 20
5
10
15
Depth (in) Depth (in)
Multiple peaks Multiple peaks
Time (us)0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000
-2
-1
0
1
2
Depth
Depth (ft)0 2 4 6 8 10 12 14 16 18 20
5
10
15
Time (us)0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000
-4
-2
0
2
Depth
Depth (ft)0 2 4 6 8 10 12 14 16 18 20
5
10
15
Depth (in) Depth (in)
Multiple peaks Multiple peaks
20
Review of Figure 6a indicates that multiple peaks are present in the spectrum of the time
domain IE data from the accelerometer. This is mainly because the source was too far from the
accelerometer [Sansalone et al 1997]. Multiple peaks were also observed in the spectrum from
Figure 6b due to the fact that the spectrum was calculated from both Lamb waves and airborne
waves. To eliminate the erroneous response, the airborne wave should be excluded from the
analyzed data. The speed of the sound or airborne compressional wave is approximately 1,100
ft/sec and is significantly slower than the speed of Lamb waves in concrete. Consequently, further
distances between the microphone and the source can separate the two wave modes. Figure 7
presents an unfiltered time domain data record which shows the time separation of the two wave
modes. Therefore, if the airborne waves are excluded from the calculation of the spectrum, the
erroneous response can be eliminated. The time domain IE data with the airborne waves excluded
and its spectrum (in depth scales) are presented in Figure 8. Reviews of Figure 8 show a dominant
response corresponding to a slab thickness resonant echo of 4”.
Figure 7 – Unfiltered Time Domain IE Data from the Microphone with the Source 12” Away
Figure 8 – Microphone Time Domain IE Data with the Airborne Waves Excluded and the Spectrum
21
5.2.1.2 Microphone for SASW Tests
For non-contact SASW tests, two non-contact microphones (ADK SC-1 Small Capsule
Condenser Microphones with external 48V Phantom Power) were used in this study. The distance
between the two microphones is 4 inches and a solenoid impactor was used as an impact source.
The tests were performed on a 4” thick concrete slab. The microphones were mounted 3 inches
above the concrete slab and the source was located between 8 and 18 inches away from the closest
microphone. Figure 9 shows the un-filtered and un-windowed time domain data from the two
microphones when the source was located 8 inches away. The two traces of Figure 10 present the
time domain data from the two microphones with an exponential window (decay of 1000), the
middle trace of Figure 10 presents the coherence of the data and the last trace of Figure 10 is a plot
of the phase difference for the passage of the surface (Rayleigh) wave by the two receivers versus
frequency SASW data. The surface wave velocity is calculated from the phase plot as a function of
wavelength (velocity = frequency x wavelength). Figure 11 shows a uniform surface wave velocity
of approximately 7,000 ft/sec from wavelengths of 0.2 to 0.4 ft and this plot is referred to as a
dispersion curve.
Figure 9 – Time Domain SASW Data from a pair of Microphones 4 inches apart
Am
plit
ude
(V
olt)
Am
plit
ude
(V
olt)
22
Figure 10 – SASW Data Processing of Figure 9 Microphone data
23
Figure 11 – SASW Surface Wave Velocity vs. Wavelength Plot (Dispersion Curve)
24
5.2.2 Preliminary Investigation of Laser Vibrometer
5.2.2.1 Laser Vibrometer for Stationary Impact Echo Tests
A Laser Vibrometer continuously transmits and receives the signal and uses a Doppler shift
of the laser to measure surface displacement vibrations. In this study, the unit was rented from
Polytec, Inc. The maximum Doppler frequency that the unit can acquire is 22 kHz. In this
experiment, both a Laser Vibrometer and an accelerometer transducer were used as receivers. The
Laser Vibrometer was attached to a tripod 40 inches above the tested concrete slab. A small Allen
wrench was used as an impact source. In this case, a normal concrete velocity of 12,000 ft/sec was
used to calculate the IE thickness. Figure 12 shows the Impact Echo data from the Laser
Vibrometer on a 4.5 inch thick concrete slab. Figure 13 shows the Impact Echo data from the
accelerometer on a nearby location. The top trace of Figures 12 and 13 is the time domain IE data
and the bottom trace is the linear displacement spectrum of the time domain data. Review of
Figures 12 and 13 shows that the results from both Laser Vibrometer and accelerometer are of very
good quality.
Figure 12 – IE Results from a Non-Contact Laser Displacement Vibrometer
25
Figure 13 – IE Results from a Ground Contact Accelerometer at the same locations as the Figure 12 test
26
5.2.2.2 Laser Vibrometer for Moving Impact Echo Tests
Next, a test configuration was set up for movable IE tests (scanning fashion) which included
the non-contact Laser Vibrometer mounted on a moving tripod (a tripod with wheels). In this setup,
a Laser Vibrometer and the automated solenoid impactor from the handheld Impact Echo Scanner
(see Figure 2) were used on a smooth four inch thick concrete slab. Figure 14 shows the Laser
Vibrometer attached to a movable tripod (with 3 wheels) and the automated impactor (in the IE
scanner) attached to the bottom frame of the tripod for the IE test. The IE scanner was attached to
the frame of the tripod, therefore the IE scanner rolled at the same speed as the tripod moved. As it
was rolled, the automatic solenoid impactor tapped the concrete slab ~ every inch along the scan
line distance and the Laser Vibrometer constantly measured the Doppler shift that corresponded to
vibration induced displacements in the slab. The IE results from the slowly and very smoothly
moving Laser Vibrometer (over 2.3 ft in distance) are presented in Figure 15. Review of Figure 15
shows good quality IE data with the corresponding IE thickness of approximately 4.3 inches.
Figure 14 – Test Setup for Impact Echo Scanning Test using Moving Laser Vibrometer
Laser Vibrometer
Movable Tripod
An automatic solenoid impactor (within the Impact Echo Scanner) attached to the frame of the tripod
Laser Vibrometer
Movable Tripod
An automatic solenoid impactor (within the Impact Echo Scanner) attached to the frame of the tripod
27
Figure 15 – IE Results from a Slowly Moving Displacement Laser Vibrometer on a smooth
concrete slab
Time Domain IE Data from Moving Laser Vibrometer
Spectrum
Time Domain IE Data from Moving Laser Vibrometer
Spectrum
28
5.2.2.3 Laser Vibrometer for Stationary Slab Impulse Response (SIR) Test
In this study, the Laser Vibrometer was used in the SIR tests. Figure 16 shows the Slab IR
test setup using a non-contact Laser Vibrometer mounted 40 inches from the slab and slab contact
velocity transducer (vertical 4.5 Hz geophone) for comparison purposes. A 3 lb instrumented
impulse hammer was used as a source and calibrated to measure the impact force. The Slab IR
results from the Laser Displacement Vibrometer and the velocity transducer are presented in
Figures 17 and 18. A comparison of data between the non-contact Laser Vibrometer in Figure 17
and the velocity transducer in Figure 18 shows good coherence of the data from the Laser
Vibrometer from near zero frequency to a frequency of approximately 500 Hz. However, low
frequencies from ground motion (from the impact) had an influence on the Laser Vibrometer
attached to a tripod. The high amplitude of the low frequency showed that the tripod was not able
to shield the vibrometer from the ground motion generated by the 3 lb impulse hammer with a hard
plastic tip.
Figure 16 – Slab IR Test Setup Using Non-Contact Laser Vibrometer and Ground Contact Velocity Transducer
3 lb Instrumented HammerVelocity Transducer
Laser Vibrometer(mounted on a Tripod)
Focused Red dot from Laser Vibrometer
Velocity Transducer
3 lb instrumented Hammer
3 lb Instrumented HammerVelocity Transducer
Laser Vibrometer(mounted on a Tripod)
Focused Red dot from Laser Vibrometer
Velocity Transducer
3 lb instrumented Hammer
29
Figure 17 – Slab IR Test Result Using Non-Contact Laser Vibrometer
Figure 18 – Slab IR Test Result Using Ground-Contact Velocity Transducer
Due to ground movingDue to ground moving
Good coherence up to ~500 Hz
Due to ground movingDue to ground moving
Good coherence up to ~500 Hz
High coherence up to ~1000 HzHigh coherence up to ~1000 HzHigh coherence up to ~1000 Hz
30
5.2.2.4 Laser Vibrometer for Moving Slab Impulse Response (SIR) Test
A moving tripod is not practical for the SIR preliminary tests using a Laser Vibrometer as
illustrated in Section 5.2.2.2. Thus, a pulley system was attached to roof concrete twin-tee girders
to provide an even smoother moving mechanism (see Figure 20). The Laser Vibrometer was
attached to an aluminum rod hanging from a roof frame. While the Laser Vibrometer was slowly
moved along the frame, hammer impacts were performed manually on the ground along the test line
(along the roof frame). An example result from one of the SIR tests from the scan line is presented
in Figure 19. Review of Figure 19 shows that the time domain data is noisy with the low frequency
moving noise and some spike noises from the small jerking effect of the relatively smooth pulling.
Note that the coherence of the data is 1 because there is only one SIR record at each location
(scanning fashion). A better moving mechanism was thus found to be required to carry the Laser
Vibrometer as the low frequency moving noise has significant impact of the SIR data quality. Figure 19 - Slab IR Test Result Using Laser Vibrometer Moving using a Pulley System
31
5.2.3 Preliminary Investigation of Microwave Transducer
5.2.3.1 Microwave Transducer for Stationary Slab Impulse Response (SIR) Test
A microwave transceiver continuously transmits and receives the signal. It uses a Doppler
shift concept to measure surface vibration in velocity units. The Ka band microwave transceiver
used in this study has a rectangle waveguide of 28 and a frequency range between 26.5 – 40 GHz.
Figure 20 shows the Slab Impulse Response (Slab IR) test setup using the non-contact microwave
transceiver. The microwave transceiver was attached to an aluminum rod connecting to the wooden
frame from the ceiling to minimize the effect of the slab movement due to the impulse hammer
impact on the microwave transceiver as was similarly done for the laser vibrometer. The study
included variation of the height of the non-contact microwave transceiver above the testing surface.
Figure 21 presents the data from Slab IR tests using the microwave transceiver attached to the frame
with a height of 0.25 inches above ground. The top trace of Figure 21 presents time domain Slab
IR data of the transceiver vibration response to the 3 lb instrumented impulse hammer impact. The
middle trace of Figure 21 presents a coherence plot (related to signal to noise ratio, a coherence
value near 1 indicates good quality data and that the response is due to the impact). The bottom
trace of Figure 21 presents a plot of mobility (vibration velocity amplitude per pound force) as a
function of frequency measured in cycles per second or Hertz (Hz). Figure 22 shows the data from
the Slab IR test using the traditional ground contact velocity transducer (vertical 4.5 Hz geophone).
The comparison of data between the non-contact microwave transducer in Figure 21 and the
velocity transducer in Figure 22 reveals poor coherence of the data for the microwave transceiver.
The Doppler shifts from the microwave transceiver were low frequency and not adequate to acquire
good quality Slab IR data. Figure 23 presents the data from a Slab IR test using the microwave
transceiver attached to the frame with a height of 2 inches above ground. Review of Figure 23
shows that the quality of the time domain data and coherence drop drastically with a 1.5 inch
increase of the height above ground for the transceiver.
32
Figure 20 – Slab IR Test Setup Using Non-Contact Microwave Transceiver with Roof Frame
Frame
Aluminum Rod
Microwave Transceiver
Pulley SystemFrame
Aluminum Rod
Microwave Transceiver
Pulley System
33
Figure 21 – Slab IR Test Result from the Microwave Transceiver Positioned 0.25 inch above the Slab
34
Figure 22 – Slab IR Test Result from the Slab Contact Velocity Transducer
35
Figure 23 – Slab IR Test Result from the Microwave Transceiver Positioned 2 inches above the Slab
36
5.3 Development of the Bridge Deck Scanner Prototype The design and development of the Bridge Deck Scanner prototype involved the fusion of
knowledge gained from our literature review, discussions with other researchers, our extensive prior
experience with the test methods and equipment, preliminary investigations with non-contact
transducers as well as significant mechanical and electrical research and development. Because of
our mixed results with the non-contacting transducers, it was considered critical that our early
prototype incorporate both contacting transducers as well as non-contacting transducers where
applicable. Olson Instruments has had excellent success with the Impact Echo Scanner, which was
designed to perform impact echo testing at 1 inch intervals while rolling across a formed or smooth
concrete surface. The IE Scanner was designed for high resolution testing on finished concrete
surfaces such as concrete floors, walls, girders, etc. The major limitations of the IE scanner are the
scan rate (maximum of 1 ft/sec) and the poor results on rough surfaces due to poor contact of the
transducer, impactor, or both. Therefore the central idea at the beginning of development was to
create a large scale IE scanner that could achieve greater scan rates, perform well on relatively
rough surfaces (typical of concrete bridge decks), incorporate additional test methods such as
SASW (by synchronizing multiple rolling transducer wheels) and SIR (by automating a 3-lb
instrumented hammer impact and measuring the induced lower frequency vibration) and be easily
towed and maneuvered by a van or truck.
The Bridge Deck Scanner (BDS) wheel is shown in Figure 24 and was designed to include
six impact echo piezocermaic displacement transducers at 6 inch spacings, resulting in a wheel
circumference of 3 feet or a diameter of approximately 11.5 inches. The 6 inch transducer spacing
was considered to provide relatively close measurement intervals consistent with a high data
resolution bridge deck survey. Six transducer elements from the Olson Instruments IE-1 head were
incorporated into the wheel. The 6 transducers were spring mounted with rubber isolators and
captured with a thin (1/16”) urethane tire approximately 2.5” wide that is replaceable. The thin
urethane tire was added as a dust cover to prevent dirt from entering the sensor housing and more
importantly to increase sensor contact area and coupling. The Bridge Deck Scanner wheel design
uses a slightly larger solenoid impactor than is typical in our other IE products. The larger solenoid
imparts more energy into the concrete creating higher amplitude signals which are more easily
measured. The larger solenoid also performs better on rough surfaces than a smaller solenoid
because it is less affected by the immediate surface condition such as loose material, roughness,
37
paint coatings, etc. The urethane tire, larger impacting solenoids, and overall sensor weight
(approximately 25 lbs), which effects contact pressure, are the primary changes that improved the
rough surface performance over the handheld Impact Echo Scanner. Six solenoids per wheel were
used in the design. The solenoids were mounted to the side of the rolling transducer wheel in line
with the sensor element, instead of suspending a single solenoid from the Bridge Deck Scanner
frame, thus ensuring the solenoid height (distance between bridge surface and solenoid) remained
constant to improve test consistency. This style mounting also reduced the wear and tear on the
solenoids by avoiding slippage and spreading the impacts out among six solenoids rather than
relying on a single solenoid. A similar approach was taken with the electronics to power and
acquire data from the sensors; instead of having a single very complex system housed independent
of the rolling wheel, 6 small circuits were designed and incorporated into the wheel itself (Figure
26). This system has many advantages: first it reduces the number of “wires” which must be passed
through the spinning hub assembly; second it makes the system more modular and robust where a
single small component can easily be replaced if broken or damaged; and, third it makes the system
more economical and simpler to produce six identical circuit boards than one large complex board.
Figure 24 - Bridge Deck Scanner Transducer Wheel, hub assembly side (outside).
Slip-Ring Hub
Assembly
Embedded IE Test Head
Sensors
IE and SW Impact
Solenoids
38
Figure 25 - Bridge Deck Scanner Transducer Wheel, axle side (inside) with dust cover removed.
To incorporate SASW we chose to use multiple Bridge Deck Scanner transducer wheels,
described above, oriented, synchronized and timed in a transverse (across the bridge lane) line. As
can be seen in Figure 26, the transducer wheels were mechanically connected using two u-joint slip
couplers that would allow the wheels to move up and down independently and remain rotationally
aligned such that one transducer from each wheel was in contact with the bridge deck surface at the
same time. A mechanical adjustment was designed into the system so that either wheel could be
delayed slightly if this was later deemed necessary due to the speed of travel in the forward
direction. For SASW testing, the 2nd wheel’s solenoids would be turned off so that only one
solenoid was firing at a time. The 2nd wheel would become a SASW measurement only wheel. The
wheels could also be offset 30 degrees apart in rotation and the solenoids on both wheels turned on
to allow IE only testing on both wheels simultaneously.
IE Sensor Retaining
Screw
On-board Electronics
Thin Urethane Tire
39
Figure 26: Bridge Deck Scanner Sister Transducer Wheels with two u-joint slip couplers for rotational synchronization in SASW tests or offset 30 degrees for IE tests.
To incorporate Slab Impulse Response (SIR), a rolling or sliding geophone receiver was
designed as well as an automated 3-lb instrumented impulse hammer. The rolling SIR system
incorporated a geophone receiver into the axle of the Bridge Deck Scanner wheel. Therefore the
geophone itself would not be rotating with the wheel but it would be continuously coupled to the
concrete surface through the wheel. This type of contact has the potential to be able to transfer the
relatively high amplitude and low frequency signals typical of SIR testing. Several designs of an
automated impulse hammer were considered which included the following approaches: hydraulic
driven, gravity driven, pneumatic driven, electrically driven, and coil-spring driven. Ultimately it
was decided to purchase and adapt a pneumatic framing nailer to drive the automated instrumented
impulse hammer. The nail magazine, contact mechanism, and other unnecessary parts were
removed from the nailer. Several new parts were designed and machined to support the added
weight of an impulse head load cell (Dytran Model 1060V) and rubber/plastic impact tip, including:
a stronger piston rod and bolt assembly/piston retainer. Two springs were added to the exterior of
the piston to help return the piston and hold it in the neutral position. A large solenoid was installed
to trigger the framing nailer once per revolution of the Bridge Deck Scanner instrument wheel or
every 3 ft. The nailer was then mounted to a frame as shown in Figure 27 which had two rubber
U-joints Couplers
Inside Dust Cover and
Axle Mount
Microphone Microphone
40
wheels for stability and was positioned next to the bridge deck scanner transducer wheel. The
pneumatic framing nailer was air driven from a small gas powered air compressor mounted in the
back of the vehicle. The hammer system was independently mounted to the towing frame to travel
alongside the bridge deck scanner instrument wheel which housed the geophone sensing element at
its axle as shown in Figure 28
Figure 27 - Bridge Deck Scanner SIR Impulse hammer System, side view.
Air Hose Fitting
Nailer plus Solenoid for
Triggering Impact Hammer
41
Figure 28: Bridge Deck Scanner Impulse Hammer System, rear view.
Microphone transducers were incorporated into the Bridge Deck Scanner prototype design
in order to perform real world field testing of their applicability to Acoustic Sounding (AS), Impact
Echo and Surface Wave testing. The microphones were shielded by inserting them into a short
section of rubber tubing. This helped block unwanted direct air wave arrivals and exterior noise due
to the wind, vehicle or rolling apparatus. The original design included two microphones, one
mounted on the outsides of each of the two mirrored instrument wheels. The microphones were
vertically oriented near the solenoid impact points to perform AS and IE testing (see Figure 29).
Two additional microphones were added to allow SW testing in later iterations of the prototype
design.
Transducer Wheel Axle with Embedded Geophone
Plastic Impact Tip
Load Cell
Return and Hold
Springs
New Bolt Assembly /
Piston Retainer
42
Figure 29: Bridge Deck Scanner System showing Microphone Placement.
Concerning the overall prototype system, multiple mechanical and electrical adjustments
were incorporated into the design to facilitate solenoid/sensor timing, wheel #1/wheel #2 timing,
trigger/acquisition timing, and multiple test method timing. The original prototype with one pair of
transducer wheels and a instrumented impulse hammer could theoretically perform IE and SASW at
6 inch spacings with the contacting transducers, IE and AS at 6 inch spacings with non-contacting
microphone transducers and SIR with the impulse hammer and axle mounted geophone at 3 foot
spacings.
The transducer wheels and impulse hammer system were attached to a towing apparatus as
shown in Figure 30. The apparatus consisted of a triangular frame with a ball hitch coupler at the
apex. The corners of the frame were designed to be supported on the concrete surface with small
rubber dolly wheels. This design allowed the axle-mounting-bar, attached to the transducer wheel,
to maintain a consistent angle regardless of variation of the height of the truck hitch, which is
Microphone Hung from
Frame Next to Impactor
43
critical in the solenoid firing and acquisition timing of the system. The impact hammer system was
also attached to this towing apparatus for simplicity. The apparatus was mounted to the vehicle via
a standard ball hitch. Because the two transducer wheels were rotationally synchronized for SW
testing, the system cannot make sharp corners without one of the wheels skidding on the concrete
surface. The prototype system also did not easily allow for traveling in the reverse direction.
Figure 30: Bridge Deck Scanner System Original Design.
5.4 Description of Test Structures and Test Procedures
5.4.1 Douglas Bridge in Douglas, WY
The Douglas Bridge located near Douglas, WY is composed of two sister bridges, each
supporting two lanes of traffic on Interstate 25. Only the south-bound bridge was evaluated during
the investigation. The bridge consists of four spans and is supported by wide flange concrete
girders. The bridge was 38 feet wide (curb to curb) and approximately 179 feet long. The bridge
Dolly Wheels
To Put on Ball Hitch on Vehicle
Transducer Wheels
Pneumatic Impulse Hammer
44
was mostly straight however both ends were skewed. The bridge deck consisted of silica fume
overlay concrete with a nominal thickness of 8 ¼ inches and it was reinforced in both directions.
Figure 31: Douglas Bridge, Douglas, WY, Bridge Deck Scanner Testing 8/6/2009.
The testing on the Douglas Bridge was the first field testing performed with the bridge deck
scanner (see Figure 31). It was not the objective to perform a full investigation of the concrete
bridge deck, but rather to test the bridge deck scanner system. Therefore all testing was performed
on approximately the same test line in the right hand lane of the bridge. Test runs were conducted
45
the full length of the bridge deck. Multiple test runs were conducted with different test methods
(e.g. IE, SW, SIR, AS) active for each test run (see Figure 32). Once a run was completed, the
Bridge Deck Scanner was disconnected from the towing vehicle and manually rolled back to the
beginning of the bridge. The vehicle was also returned to the north end of the bridge and the Bridge
Deck Scanner (BDS) was reconnected and another test run was performed.
Figure 32: Douglas Bridge, Douglas, WY, Bridge Deck Scanner (BDS) Test Run 8/6/2009.
5.4.2 1st Street Bridge in Casper , WY
The 1st Street Bridge in Casper, WY is a four lane concrete structure over the North Platte
River on 1st Street. Only the two east-bound lanes were evaluated during our field investigation.
The bridge is curved and skewed at both ends, with a centerline distance of approximately 357 feet
and a deck width of ~ 36 ft (curb to curb). The deck is bare concrete with a nominal thickness of 7
inches. Note that the areas on top of girders are a couple of inches thicker than the nominal
thickness since the slab was thickened to bear on the steel girders. Figure 33 shows the BDS on the
concrete deck of the 1st Street Bridge. Figure 34 shows the steel girders underneath the deck. A
plan drawing of the Casper Bridge is included in Appendix A.
Freedom Data PC - Data Acquisition
System
Gas Powered Air
Compressor
46
Figure 33: 1st Street Bridge, Casper, WY, Bridge Deck Scanner Testing 8/19/2009.
Figure 34: The Underneath View of the 1st Street Bridge, Casper, WY which crosses over the North Platte River
47
The testing on the 1st Street Bridge was performed as a full investigation of the concrete
bridge deck conditions with the BDS. Testing was performed in test runs the full length of the
bridge deck with approximately 1 foot transverse spacings. Improvements to the towing apparatus
to permit moving the scanner in 1 foot increments across the width of a 12 foot lane were made
after initial testing (see Section 6.1.2) which allowed test runs to be performed near the edges of the
bridge deck as shown in Figure 35 below. Once a run was completed, the Bridge Deck Scanner was
disconnected from the towing vehicle and manually rolled back to the beginning of the bridge. The
vehicle was also returned to the west end of the bridge, then the Bridge Deck Scanner was
reconnected and another test run was performed. In some areas of the bridge, significant gravel was
present on the roadway and brooms were used to sweep the surface so that it was free of debris.
Figure 35: 1st Street Bridge, Casper, WY, Bridge Deck Scanner Test Run 8/19/2009.
48
6.0 BRIDGE DECK SCANNER HARDWARE AND SOFTWARE IMPROVEMENTS
6.1 Hardware
6.1.1 Original Hardware Design
The original hardware design is described in Section 5.3. The original prototype of the
Bridge Deck Scanner (BDS) was used for all testing on the Douglas Bridge in Douglas, WY as
described in Section 5.4.1.
6.1.2 First Iteration BDS Improvements
After initial testing on the Douglas Bridge in Douglas, WY several changes were made to
the Bridge Deck Scanner to address issues with the system. In general, the IE and AS testing
worked extremely well with good reliability and excellent data quality. The SW testing resulted in
some locations having good data and some with poor data. The SIR testing provided only poor
quality data.
One significant limitation of the original prototype was the fact that it attached directly to
the ball hitch on the towing vehicle; therefore the Bridge Deck Scanner system was always directly
behind the center of the truck, making it impossible to perform test runs near the edges of the bridge
deck. To address this problem, a 10 foot steel beam was attached to the towing hitch of the vehicle
in the transverse direction as shown in Figure 36. The beam had trailer ball hitches at 1 foot
spacings and would allow test runs to be performed at any location within a lane width while
driving in the center of that lane.
49
Figure 36: Bridge Deck Scanner 10 foot steel beam addition.
It was determined that the major issue in the collection of SW testing data was the
synchronization of the two transducer wheels. It was discovered that the two slip u-joints
connecting the two transducer wheels had sufficient play to allow the wheels to become
unsynchronized. To address this issue, it was decided to replace the slip u-joints with a solid axle
between the transducer wheels. The original design employed slip u-joints to allow the two
transducer wheels to independently move up and down following the contour of the road. After
testing on the Douglas Bridge, it was determined that the contour differences within a one foot
transverse spacing were minimal and would not effect the data acquisition, thus a solid axle was
deemed appropriate.
Due to the promising results of other researchers in performing surface wave testing with
audio microphones, two additional microphones (resulting in a total of 4) were added to the frame
10 Foot Steel Beam Holes for
Ball Hitch Mounting
Bridge Deck Scanner offset from Vehicle
Center
50
of the transducer wheels as shown in Figure 37. This allowed several configurations of
microphones with regards to spacing between transducers as well as the spacing from the point of
impact to the transducers for experimentation purposes.
Figure 37: Bridge Deck Scanner Additional Microphones and Rigid Axle Updates.
There were several apparent issues when employing the SIR testing. The geophone (28 Hz
resonant frequency) that was originally designed to attach to the transducer wheel axle did not have
adequate response at low frequencies; therefore the original geophone was replaced with a 4.5 Hz
resonant frequency geophone. The geophone also showed that the vibration from the firing of the
impulse hammer was traveling through the frame and affecting the measured vibration readings,
thus more isolation was required. Taking advantage of the new towing apparatus, which consisted
of the 10 foot long beam with ball hitches at 1 foot spacings, the impulse hammer was reconfigured
to have an independent frame and connect to a separate ball hitch, thus providing more isolation.
The final obvious issue with SIR testing was the instability of the impulse hammer. Although the
impulse hammer system weighed approximately 25 lbs, it still bounced significantly from the force
of the impact on the bridge deck. To quickly address this issue in the short-term, three additional 25
lbs bags of lead shot were attached to the impulse hammer system (see Figure 38).
Microphone
Rigid
51
Figure 38: Bridge Deck Scanner Design After First Iteration of Modifications, Highlighting SIR Improvements.
6.1.3 Second Iteration BDS Improvements (Current Design)
The Bridge Deck Scanner with the first iteration of improvements (as described above in
Section 6.1.2) was used to perform testing on the 1st Street Bridge in Casper, WY (described above
in Section 5.4.2). The 1st Street Bridge Investigation was conducted as a full investigation of the 2
east-bound lanes of the bridge. Test runs were performed the full length of the bridge at 1 foot
transverse spacings. This extensive day of real world field testing again led to several hardware
improvements and a better understanding of the system.
Separate Mounting for Impact Hammer and Geophone Receiver
4.5 Hz Geophone
Additional Weight for
Impact Hammer
52
One of the evident differences in the data quality after the first iteration improvements was
notably more vibration noise in the sister transducer during surface wave testing. It is believed that
the major contributing change was the addition of a fixed axle between the transducer wheels to
provided exact and fixed rotational alignment. The original design with the two u-joint slip
couplers did not transfer notable vibrations, but it also did not provide reliable rotational alignment
needed for surface waves (SW) testing. The second design provided excellent alignment but also
transferred vibrations through the fixed axle and distorted the surface wave data. To address this
problem, a third design was implemented using a solid axle with a rubber high frequency isolator
inserted in the middle of the axle.
The Slab Impulse Response (SIR) testing again proved to be problematic on the 1st Street
Bridge. The added weight to the impulse hammer system significantly improved the consistency of
the hammer impulse force applied to the deck. The adjustments to the frame which isolated the
impulse hammer system, by mounting it to a separate ball hitch, eliminated most of the direct
vibration noise traveling through the frame. However, the 4.5 Hz geophone, which is much more
sensitive and linear in its response to low frequency vibrations than the original 28 Hz geophone,
was sensitive to the so-called rolling noise. This vibration noise is generated by the rolling wheel
following the contours of the roadway and is at the frequencies important for SIR data analysis. Dr.
Kenneth H. Stokoe, II and his students at the University of Texas at Austin have done similar
testing with Rolling Dynamic Deflectometers (RDD). The RDD’s have overcome rolling noise
issues with geophone measurements by using extremely large input forces (10,000 pounds peak-
peak is typical and therefore the vibration of interest is much greater than the rolling noise), forced
frequency vibrations (the vibration of interest is at a single frequency between 25 – 35 Hz instead of
a wide frequency range), and have coupled the rolling geophone transducer mounted on a 2-wheel
platform with an air piston spring to hold it down (Lee et al 2009). Based upon our results thus far
from testing in our research lab and on both the Douglas and 1st Street bridges, we believe a rolling
geophone approach may be unsuitable for the SIR vibration measurement if implementing some of
the RDD approaches do not resolve the problem in the future. The research team is currently
exploring other possibilities that include a “walking” geophone design in which the geophone
would be placed on a discrete location while the testing is performed and picked-up and moved
ahead to the next test location as the vehicle proceeds forward.
53
The primary changes made in the second iteration were to the towing apparatus. To
simplify the design, the dolly wheels were moved from the intermediate frame to the ends of the 10
foot long steel beam (square tube). The beam was then outfitted with a rotating slider system that
allowed it to move up and down and twist in order to follow the contour of the road yet still be
attached to the truck. The dolly wheels were also changed from small rubber wheels to larger, air-
filled rubber wheels. The 10 foot long beam was spliced in two locations to allow a more compact
shipping package. The two transducer wheels were attached to one another with a u-shaped yoke to
make them easier to pick up together. The yoke was designed with rubber isolation joints to
dampen any vibration between the two wheels. A handle was also attached to the yoke that enables
the transducer wheels to be easily lifted and provides support to the rubber isolation joints.
Previous versions of the system also had multiple cable connections to the power source and
data acquisition system. In this iteration, significant re-wiring and design refinement was
performed to concentrate all cables from the sister transducer wheel system into a single connection.
This makes a much more user friendly and less complex system that is also quicker and easier to set
up.
Near the end of testing, one of the transducer wheel hub bearings seized and all transducer
and solenoid cables were broken (due to twisting). Upon disassembly, it was discovered that a
granular particle (either gravel or metal) had become embedded in the smooth plastic bushing
causing the bushing to wear and eventually seize. The design was altered to utilize a more durable
brass bushing and to increase clearances within this portion of the hub assembly so that particles
will not wear on surfaces. It is believed that this particle was a metallic shaving from our
manufacturing shop and was not picked up in the field during deck testing.
6.2 Software The Bridge Deck Scanner prototype was developed to run under Microsoft Windows XP on
the Olson Instruments Freedom Data PC data acquisition system (1.1 GHz Intel Pentium M with 1
GB of RAM) which utilizes a 16 channel, 16-bit A/D data acquisition card by National Instruments.
To support the new hardware prototype, software improvements were added to the original Impact
Echo Scanner software. Multi-channel data acquisition capability was added to acquire data from
the second rolling transducer, and two additional microphones. Relevant data analysis concerning
microphone and SASW analysis was also added to the existing software.
54
7.0 TEST SETUP AND RESULTS FROM 1st STREET BRIDGE (CASPER, WY)
The internal condition study of the bridge deck of the 1st Street Bridge was a collaboration
effort between the research team at Olson Engineering, Inc and the University of Wyoming under
the supervision of Dr. Jennifer E. Tanner of the Department of Civil Engineering along with the
support of the Wyoming DOT. The title of the research project conducted by the University of
Wyoming is “Bridge Deck Evaluation using Non-destructive Test Methods” and their project is
funded by the Wyoming Department of Transportation (WYDOT).
The scope of work of the University of Wyoming research included the studies of traditional
Impact Echo method (point by point testing with an Olson Instruments Concrete Thickness Gauge)
and Infrared Thermography to delineate the areas with top delamination. In addition, personnel
from WYDOT performed a traditional chain drag on the bridge deck to locate areas with hollow
sounds indicative of shallow delamination on the bridge deck.
The scope of work of Olson Engineering, Inc. included the studies of the newly developed
Bridge Deck Scanner prototype as part of this research, and radar surveys with ground-coupled and
non-contact air horn antennae for Ground Penetrating Radar (GPR) based deck condition
assessments in support of the University of Wyoming research.
7.1 Test Setups and Results from Traditional NDE Test Methods This section includes test setups and results from traditional nondestructive evaluation
(NDE) test methods including Ground Penetrating Radar (GPR), Impact Echo (point by point),
Infrared Thermography and chain drag acoustic sounding (AS) methods.
7.1.1 Test Setup and Results from Sounding Using Chain Drags
This section is a summary of the test setup and results using traditional chain dragging for
acoustic sounding (AS) to locate areas with hollow, drummy sounds indicative of shallow
delamination. The chain drag testing was performed by WYDOT personal. The test setup and
results presented herein were summarized from the quarterly report written by Tanner and Robinson
submitted to WYDOT in August 09 [Tanner et al 2009].
55
The chain dragging was performed using a row of chains that is attached to a handle and is
brushed back and forth across the bridge deck (Figure 39). Common chain configurations will
consist of four or five segments of 1 in. links of chain that are approximately 18 in. long (ASTM D
4580-03 standard). A 3x3 ft grid was previously laid out on the deck to assist in documenting
delaminations. The operator must have a trained ear to hear the lower frequency, hollow, drummy
tones that correspond to delaminated sections of the deck which flexurally resonate when excited by
the dragging of the chains and are typically audible for the top 3-4 inches of a deck. Sound concrete
has a sharper, higher frequency ringing sound by comparison.
The hollow, drummy sounds denote a delamination and are marked directly on the bridge
deck using paint. After the entire deck has been sounded, the operator then marks the delamination
locations and develops a map of the bridge deck indicating the location of the delaminations.
However, most of the damage mapping is at the discretion of the operator due to different levels of
experience and hearing among operators. The results from the chain drag tests, which were
performed by the WYDOT bridge crew, are presented as shaded areas in Figure 40 on a 3 ft square
grid.
Figure 39: Chain Dragging Evaluation by Wyoming DOT (photo courtesy of the University
of Wyoming).
56
Figu
re 4
0: T
op D
elam
inat
ion
Map
from
Tra
ditio
nal S
ound
ing
Usi
ng C
hain
Dra
gs (c
ourte
sy o
f Uni
vers
ity o
f Wyo
min
g)
N
57
7.1.2 Test Setup and Results from Ground Penetrating Radar (GPR) Tests
The GPR tests were performed by the Olson Engineering research team using a Geophysical
Survey Systems, Inc. (GSSI), 1500MHz ground coupled antenna as well as a 1GHz (1000MHz) air
horn antenna along the length of the concrete bridge deck using a cart as shown in Figure 41. The
tests were performed on the top of the deck per drawings provided by the Wyoming Department of
Transportation (WYDOT). Traffic control for the testing was provided by WYDOT. The deck was
scanned using a grid spacing of 1.5 feet along the N-S direction (width of the bridge) and 0.25 inch
along the W-E direction (along a scan line). GPR data files were recorded in the eastbound
direction, in one and a half foot transverse intervals from the centerline of the bridge to the south
curb edge. The 1GHz air horn antenna data was collected from 4.5 feet inside the centerline to 4.5
feet from the curb due to the width of the truck the radar was mounted on. The objective of the
GPR tests was to determine areas of the bridge deck with potential corrosion or delamination
(cracks) at the top layer of steel reinforcement.
Figure 41 - GPR testing with the 1500MHz ground-coupled antenna over the North Platte River in Casper, Wyoming.
Data collected with the 1500MHz antenna contained clear reflections from each individual
rebar in the deck. The raw data even shows evidence of some variance in signal attenuation within
the concrete. The areas undergoing corrosion show up as weaker, attenuated signals than areas in
58
good condition (Figure 42). The data from the 1500MHz antenna was of good quality as shown in
the figures below.
Data from the 1GHz air horn was accurate but lacked the resolution (due to the wavelength
of the signal) to pick out individual rebar. Figures 43 and 44 show data collected over the same
location with the 1,500MHz antenna and the 1GHz air horn, respectively. Both plots show the
depth and amplitude of the signal, but only the 1500MHz data allows for precise location of the
reinforcement.
Figure 42: 1500MHz GPR Scan 6 feet offset from the bridge centerline. Note the variance of the signal strength as the radar passed areas of suspected corrosion.
Weak Good
59
Figure 43: 1500MHz ground coupled antenna GPR Scan 4.5 feet offset from the South curb. The West joint is located at the far left of the plot.
Figure 44: 1GHz air horn antenna GPR Scan – note the rebar reflections are not distinct - 4.5 feet offset from South curb. The West joint is located at the far left of the plot.
Rebar denoted by hyperbolic reflectors
Surface Reflecti
Rebar
60
The GPR data from the deck was processed using GSSI RADAN 6.5 software to measure
the reflection amplitudes (dB) in each GPR data file of the individual transverse reinforcing bars
within the top reinforcement mat as well as the depth of concrete cover over the rebar. Signal losses
in the reinforcing bar reflection amplitudes vary according to the bar size and the relative abundance
of moisture and chloride in the concrete cover and concrete above the top reinforcing bar mat. The
signal losses have been correlated in previous studies (Gucunski et al 2008) with the location and
extent of corrosion and corrosion-induced damage of the surface cover layer.
The reflection amplitude data was corrected for geometric losses due to reinforcing bar
depth using a statistical regression approach fit to the 90th percentile amplitude (dB) versus the two-
way travel time of the GPR signal. Predictions of the location and quantities of probable
delamination and probable active corrosion were evaluated using proprietary thresholds calibrated
for use on exposed-surface reinforced concrete bridge decks developed in research by Dr.
Christopher Barnes at Dalhousie University, Halifax, Nova Scotia, Canada (Barnes et al 2008).
This approach assumes that the 90th percentile strongest reflection amplitudes correspond to
undamaged regions of the deck containing low quantities of moisture and chlorides. Areas with
significantly more attenuated data below the thresholds correspond to upper reinforcement mat
corrosion and/or corrosion induced-cracking of the concrete cover layer. Please note that the GPR
investigation for delamination survey is most accurate for bridge deck areas with no previous
repairs.
The GPR results presented in Figure 45 show the deck surface in plan view and indicate
probable delaminations in red and probable active corrosion areas in red and yellow. The quantity
of probable delaminations was estimated to be 1,167 sq ft, or 10.8 percent of the deck surface area.
The quantity of probable active corrosion was estimated to be 1,798 sq ft, or 16.7 percent of the
deck surface area. Depth-corrected GPR amplitudes that were outside the damage thresholds are
shown in grayscale to indicate the predicted relative variation in moisture and chlorides over the
undamaged deck surface. Darker regions may indicate areas where moisture and chloride ingress is
approaching levels sufficient to initiate corrosion. The chain drag AS results are presented in the
top of Figure 45 for comparison purposes.
61
N
Figu
re 4
5: G
PR E
valu
atio
n of
Del
amin
ated
(red
), C
orro
ded
(yel
low
) and
Dar
ker G
ray
(pos
sibl
y be
ginn
ing
to c
orro
de) A
reas
on
1st S
treet
B
ridge
Dec
k w
ith C
hain
Dra
g A
cous
tic S
ound
ing
Res
ults
at t
op fo
r com
paris
on
62
7.1.3 Test Setup and Results from Point by Point Impact Echo Tests
The traditional point by point Impact Echo (IE) tests were performed by graduate students
from the University of Wyoming (Dr. Jennifer Tanner’s team). The IE tests were performed using a
Concrete Thickness Gauge (CTG-1TF) manufactured by Olson Instruments. The tests were
performed on a 3 ft x 3 ft grid fashion. The test results from the point by point IE tests are
presented in Figure 46. Note that an interpolation technique was used to estimate the data between
the grid lines.
The test results summarized in this section were obtained from the quarterly report written
by Tanner and Robinson submitted to WYDOT in August 09 [Tanner et al 2009]. In Figure 46, the
darker blue areas represent shallow readings and darker red areas represent thicker readings from
the CTG. Shallow regions represent potential areas of delamination and thicker regions correspond
to sound concrete. The dark blue regions on either side of the contour map represent the skewed
ends of the deck. Figure 47 is a simplified version of Figure 46 and only presents outlined damaged
and delaminated zones. In all grid figures, the top section is the north portion of the bridge and the
bottom section is the south section. The chain drag AS results are presented at the top of Figure 47
for comparison purposes with the point by point IE results.
63
Figu
re 4
6: T
est R
esul
ts fr
om th
e Po
int b
y Po
int I
mpa
ct E
cho
Tes
ts (3
ft x
3 ft
Grid
) (co
urte
sy o
f Uni
vers
ity o
f Wyo
min
g)
Figu
re 4
7: S
hallo
w D
elam
inat
ion
Map
from
the
Poin
t by
Poin
t Im
pact
Ech
o T
ests
- 3
ft x
3 ft
Grid
(cou
rtesy
of
Uni
vers
ity o
f Wyo
min
g) w
ith C
hain
Dra
g A
cous
tic S
ound
ing
Res
ults
at t
op fo
r com
paris
on
N
64
7.1.4 Test Setup and Results from Infrared Thermography
The Infrared Thermography tests were performed by the researchers from the University of
Wyoming. The test results in this section are a summary from the quarterly report written by
Tanner and Robinson submitted to WYDOT in August 09 [Tanner et al 2009]. Bridge deck
delaminations are indicated by hotter temperatures as a deck warms up and comparatively cooler
temperatures as a deck cools down from solar radiation. Approximately 900 images were overlaid
to produce the thermal image of the bridge deck as presented in Figure 48. Figure 49 presents the
outline of the shallow delamination damages from the results in Figure 48,
Figure 48: Temperature Images of the Bridge Deck from Infrared Thermography Tests (courtesy of University of Wyoming)
Figure 49: Shallow Delamination Map of the Bridge Deck from Infrared Thermography (courtesy of University of Wyoming)
65
7.2 Test Setups and Results from the Bridge Deck Scanner Prototype This section presents test results from all tests performed using the BDS prototype and
discussions of current limitations from each test and future modifications planned for the BDS
prototype.
7.2.1 Test Setup Using the BDS Prototype
The BDS prototype was used on the 1 st Street Bridge to determine the damage conditions
and damage locations of the concrete bridge deck. The BDS unit was mounted to a hitch behind a
truck and the data acquisition system (controller) was placed on the tailgate of the truck. A
maximum speed of 1 to 1.5 mph was achieved for the testing in order to maintain good data quality
which degenerated at higher speeds. The BDS prototype performed Impact Echo tests using one
transducer/impactor wheel in a line and Spectral Analysis of Surface Waves (SASW) tests were
conducted using both transducer/impactor wheels simultaneously with the IE tests. Automated
Sounding (AS) using microphones was also done simultaneously in the same test line as the IE test
line. The BDS test setup for the IE, SASW and AS is presented in Figure 50.
The BDS unit was then driven again on the same test line using the automated pneumatic
nail gun impulse hammer and a geophone attached to the axle to perform the Slab Impulse
Response (SIR) tests. The BDS test setup for the SIR tests is presented in Figure 51. IE, SASW
and AS tests were performed every 1 ft along the entire width of the deck and 0.5 ft along each scan
line over the length of the deck. SIR tests were performed on a separate run and only performed on
one line. The SIR tests were performed every 3 ft along the scan line.
66
Figure 50: BDS Test Setup for IE, SASW and Automated Sounding on the 1st Street Bridge
Figure 51: Bridge Deck Scanner Test Setup for SIR Tests on the 1st Street Bridge
67
7.2.2 Findings from Impact Echo Scanning Tests from the BDS Prototype
The graphical IES test results from the Bridge Deck Scanner are presented in Figure 52.
The plot is a surface thickness tomogram presented in a 3D thickness tomogram to elaborate the
general condition of the tested concrete deck. The color thickness/echo depth scales are all in
inches in Figure 52. The majority of the indicated anomalies are predominantly top delaminations
based on the IES results. The green color represents areas where the thickness results ranged from
7.5 to 9 inches indicative of “sound concrete”, normal thickness deck areas. Dark green and light
blue represent areas with greater thickness echo results of approximately 9-10 inches or areas with
thickened slabs over the steel girders underneath the deck. Purple, Gray, and black colors represent
areas with top delaminations. Yellow and red colors represent areas with thinner thickness results
or more likely areas with either bottom delamination or internal cracks. Figure 53 presents a
shallow delamination map of the bridge deck by the BDS IE system and the delamination map from
chain drag AS in the top of Figure 53 for comparison purposes. The quantity of probable
delaminations detected from the BDS was estimated to be 1,004 sq ft, or 11.1 percent of the tested
deck surface area which compares well with the GPR results.
There is a decent correlation of the Bridge Deck Scanner IE top delamination results with
the chain drag AS results shown in Figure 53. However, review of Figure 52 shows a much more
precise delineation of deck damage conditions with both top and bottom delamination and other
deck integrity information from the BDS IE tests. The IE echoes indicative of the thickened slab
over girder areas are evident as the 5 linear features in Figures 52 and 53 along the length of the
deck. This further validates the accuracy of the Impact Echo scanning data obtained by the BDS
prototype.
68
Figu
re 5
2: IE
Tes
t Res
ults
from
the
BD
S Pr
otot
ype
from
the
1st S
treet
Brid
ge D
eck
69
Figu
re 5
3: IE
Tes
t Res
ults
from
the
BD
S Pr
otot
ype
from
the
1st S
treet
Brid
ge D
eck
Show
ing
Top
Del
amin
atio
n M
appi
ng w
ith C
hain
D
rag
AS
resu
lts sh
own
at to
p fo
r com
paris
on p
urpo
ses
(Pro
babl
e D
elam
inat
ion
Are
a =
1,00
4 sq
ft o
r 11.
1%)
70
7.2.3 Findings from Spectral Analysis of Surface Waves Tests from the BDS Prototype
Full analysis of the SASW data was not performed for the 1st Street Bridge as the bridge
deck had not suffered extensive freeze-thaw damage where the cracking damage depths (from the
top surface) and extent are of interest. This section presents example BDS SASW data from sound
and delaminated concrete in Figures 54 and 55, respectively, with the following information:
1) Windowed data in time domain from the transducer near the impact (see Trace 1)
2) Windowed data in time domain from the transducer located 1 foot from the impact
(see Trace 2)
3) Frequency spectrum representing thickness (or condition) of concrete deck from the
transducer near the impact (see Trace 3)
4) Surface wave velocity between the two transducers (see Trace 4)
5) Phase plot calculated from data from both transducers (see Trace 5).
Review of Figure 54 reveals an average surface wave velocity of 7,000 ft/sec which is
indicative of normal, good quality concrete. This surface wave velocity predicts a compressional
wave velocity of 12,500 ft/sec which is indicative of sound concrete. Review of Figure 55 reveals
an average surface wave velocity of 3,000 ft/sec. This surface wave velocity predicts a
compressional wave velocity of 5,357 ft/sec which is indicative of deteriorated concrete, in this case
a delamination.
71
Figure 54: BDS SASW Data Obtained from Sound Concrete
Figure 55: SASW Data Obtained from Concrete with Surface Delamination
Trace 1 Trace 2
Trace 3 Trace 4
Trace 5
Trace 3
Trace 1 Trace 2
Trace 3 Trace 4
Trace 5
Trace 1 Trace 2
Trace 3 Trace 4
Trace 5
Trace 3
Trace 1 Trace 2
Trace 4
Trace 5
Trace 3
Trace 1 Trace 2
Trace 4
Trace 5
Trace 3
72
7.2.4 Findings from Automated Acoustic Sounding with the BDS Prototype
This section presents example data from sound concrete and delaminated concrete. In this
case, a microphone was placed 1 inch away from the impact and 0.7 inch off the ground. A
simplified diagram in Figure 56 shows the location of ground contacted displacement transducer (on
the transducer wheel), impactor and microphone.
Figure 56: Locations of Microphone, Impact and Displacement Transducer on the BDS Wheel
Figure 57a shows the time domain data from the displacement transducer and Figure 57b
shows the time domain data from the adjacent microphone. The first arrival time of the data from
the displacement transducer is 3,560 us and the first arrival time of the data from the adjacent
microphone is 3,620 us with a phase change at 3,680 us. The following paragraph shows
calculations for the impact time.
An average compressional wave velocity of concrete is 12,000 ft/sec. Therefore the speed
of the Rayleigh wave is 6,720 ft/sec from elastic wave equations. The impact time can be
calculated in Eq. 2 as follows:
r
disp
VD
tt −= 10 ……………………………………..(2)
where t0 is the impact time, Ddisp is the distance between the impact and displacement transducer, t1
is the first arrival time of the displacement transducer and Vr is the Rayleigh wave velocity. In this
case, t1 is 3,560 us, Ddisp is 1.685 inches and Vr is 6,720 ft/sec. Therefore t0 is calculated to be 3551
us. The paragraph below shows the calculation for the first arrival of the airborne wave (direct
acoustic wave).
0.7”
1”
Microphone
Displacement Transducer (inside the transducer wheel)
1.685”
Impactor
0.7”
1”
Microphone
Displacement Transducer (inside the transducer wheel)
1.685”
Impactor
73
The speed of air (Vair) is ~1,100 ft/sec and the distance between the microphone and the
impact is 1.7 inches (1 inch + 0.7 inch). The travel time for the airborne wave from the impact to
the microphone is calculated to be 129 us. The impact time (from the above paragraph) is
calculated to be 3551 us. Therefore, based on the speed of air of 1,100 ft/sec, the first arrival time
of the airborne wave is 3680 us (3551 + 129 us). This agrees well with the change in phase at 3680
us shown in Figure 57b.
Figure 57a: Time Domain Data from Displacement Transducer
Figure 57b: Time Domain Data from Adjacent Microphone
Figure 57: Time Domain Data from Displacement Transducer and Microphone
3560 us3560 us
3620 us
Change of phase at 3680 us
3620 us
Change of phase at 3680 us
74
Figure 57b shows that the time domain data obtained from the microphone adjacent to the
impact is a combination of energy from the leaky Lamb wave and direct airborne wave. However,
findings from the automatic sounding using microphone adjacent to the impact also showed that the
microphone can be used to determine severe surface delamination when the leaky Lamb wave is a
dominant portion within the time domain data.
The top trace of Figure 58 shows the unfiltered time domain data from the displacement
transducer located on areas with severe surface delamination and the bottom trace is the frequency
spectrum of the top time domain data which has a high amplitude resonance indicative of flexure of
a near-surface delamination. The top trace of Figure 59 shows the time domain data from the
adjacent microphone and the bottom trace is the frequency spectrum of the top time domain data
and has a similar high amplitude resonant frequency peak around 2000 Hz as identified with the IE
displacement transducer in Figure 58.
Figure 58: Time Domain and Spectrum of Data from Displacement Transducer from an Area with Severe Top Delamination
High amplitude of low frequency(typically an indication of surface delamination)
High amplitude of low frequency(typically an indication of surface delamination)
75
.
Figure 59: Time Domain and Spectrum of Data from Non-contact Microphone from an Area with Severe Top Delamination
7.2.5 Findings from Slab Impulse Response Tests from the BDS Prototype
The Slab Impulse Response (SIR) component in the BDS prototype unfortunately did not
result in a fully successful field experiment in this research. An example of typical Slab IR time
domain data is shown in Figure 60. The left trace in Figure 60 shows the time domain data from the
geophone attached to the axle and the right trace in Figure 60 shows the time domain data of force
from the automated nail gun. Review of Figure 60 Reveals that the geophone on the axle was
unable to sense the movement of the concrete deck due to rolling noise. In addition, interference
from rolling results in low frequency rolling noise also adversely affected the SIR data. This
section also presents the results of a laboratory experiment with the SIR test using the geophone
attached to the axle of the BDS prototype and the automated nail gun.
This is from the IE dataThis is from the IE data
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Figure 60 – Time Domain SIR Data from the Geophone and Automated Nail Gun
Laboratory SIR Testing with the Bridge Deck Scanner Prototype Once the Bridge Deck Scanner original prototype design was complete, extensive testing
was performed with the system in the laboratory on the shop floor. Of particular interest was the
performance of the axle mounted geophone (at the time of laboratory testing, the 28 Hz natural
frequency geophone was installed in the prototype) for SIR testing. One of the primary concerns
was if the resonant frequency of the transducer wheel itself would interfere with the SIR data. This
issue is not a problem in IE and SASW testing because the frequency ranges of interest are much
higher.
SIR testing is typically performed by impacting the concrete slab with an instrumented 3-lb
impulse hammer while holding a geophone (4.5 Hz resonant frequency) in contact with the floor
near the impact (within 4-6 inches) in order to measure the resulting vibration. In order to test the
response of the geophone mounted to the axle of the bridge deck scanner, stationary tests were
performed by using a 3-lb instrumented hammer to impact a 5 inch thick concrete slab within 6
inches of both the transducer wheel and a 4.5 Hz geophone held in contact with the floor. This
allowed the results of both geophones to be directly compared for the same test location and the
same impact. Figures 61 (a-d) and 62(a-d) below show the test results from a sound and voided test
location (the voided location shows signs of significant loss of subgrade support beneath the slab).
In both Figures 61 and 62, plot (a) shows the time domain vibration signal from the axle
mounted geophone, plot (b) shows the transfer function (mobility = velocity/force vs. frequency)
between the input force and axle mounted geophone measured vibration, plot (c) shows the time
domain vibration signal from the geophone held in contact with the concrete slab, and plot (d)
shows the corresponding mobility transfer function for the geophone on the slab.
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Ch 5: T ime Domain SlabIR Data - No Filter
0 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000
-10
0
10
20
Avg. Mob - F1 = 100 to F2 = 500 : 2.03505e-002, Ratio = 0.61
Frequency (Hz)0 50 100 150 200 250 300 350 400 450 500
0
0.02
0.04
0.06
0.08
0.1
Ch 6: T ime Domain SlabIR Data - No Filter
0 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000-8
-6
-4
-2
0
2
4
6
8
Avg. Mob - F1 = 100 to F2 = 500 : 1.91448e-003, Ratio = 0.48
Frequency (Hz)0 50 100 150 200 250 300 350 400 450 500
0
0.002
0.004
0.006
0.008
0.01
Figure 61: Axle mounted 28 Hz geophone (a-b) and hand coupled 4.5 Hz geophone (c-d) response
to 3-lb instrumented hammer impact for SIR testing at a “Sound” location.
A)
B)
C)
D)
Transducer Wheel Resonant
Frequency
Sound Support Conditions
78
Ch 5: T ime Domain SlabIR Data - No Filter
0 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000
-20
-10
0
10
20
Avg. Mob - F1 = 100 to F2 = 500 : 1.71309e-002, Ratio = 2.1
Frequency (Hz)0 50 100 150 200 250 300 350 400 450 500
0
0.02
0.04
0.06
0.08
0.1
Ch 6: T ime Domain SlabIR Data - No Filter
0 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000
-8
-6
-4
-2
0
2
4
6
Avg. Mob - F1 = 100 to F2 = 500 : 2.44573e-003, Ratio = 1.5
Frequency (Hz)0 50 100 150 200 250 300 350 400 450 500
0
0.002
0.004
0.006
0.008
0.01
Figure 62: Axle mounted 28 Hz geophone (a-b) and hand coupled 4.5 Hz geophone (c-d) response
to 3-lb instrumented hammer impact for SIR testing at a “Voided” location.
A)
B)
C)
D)
Voided Support Conditions Transducer Wheel
Resonant Frequency
Voided Support Conditions
79
The difference between the signals in both the time domain (plots a and c) and the frequency
domain transfer function (plots b and d) are obvious. The time domain signal from the axle
mounted geophone shows much less high frequency content. The transducer wheel is apparently
acting has a filter of the high frequency energy. However, this is not of major concern because the
data analysis of SIR testing involves frequency values typically from 10 – 500 Hz. The other
predominant difference is in the transfer function plot (plot b) of the axle mounted geophone which
shows a predominant system resonance near 220 Hz, which is in the range of interest. Therefore,
the axle mounted geophone response is only reliable up to approximately 150 Hz. The axle
mounted SIR mobility result is also ~ 10 x higher than the slab mounted geophone SIR mobility.
A voided test result is often identified by the amplitude and shape of the transfer function at
low frequencies (10 – 100 Hz) relative to higher frequencies (100 – 500 Hz). If the hand-coupled
geophone transfer function from both the sound and voided test locations (both plot d’s) are
compared, the voided condition is indicated by the much higher mobility at frequencies from 10 –
50 Hz. The data from the axle mounted geophone shows a similar change in the mobility shape and
amplitude at these frequencies (as seen in both plot b’s); however the resonant frequency of the
transducer wheel is apparent in both records. The limitation of the 28 Hz geophone at low
frequencies can also be observed in the transfer function where little or no vibration is apparent at
less than 20 Hz.
These laboratory results indicate that, while the response of the axle mounted geophone is
significantly different from the hand-coupled geophone, the indications of changes in slab support
may still be evident. Therefore the axle mounted geophone may be a viable solution of SIR
vibration measurement if the design is further improved to minimize the effects of the wheel frame
and rolling noise on the results as discussed below.
The other factor of concern in the implementation of SIR testing with the bridge deck
scanner is the low frequency noise associated with rolling wheels. This rolling noise may be much
higher amplitude than the signal that we are trying to measure and is likely in the range of
frequencies of interest. Therefore, it may be difficult to remove the rolling noise using digital signal
processing techniques. To study the effects of rolling noise in the laboratory environment with as
few variables as possible, some basic experiments were performed. The Bridge Deck Scanner
transducer wheel was hand rolled along the concrete floor while a 3-lb impulse hammer was used to
hit the slab next to the wheel. This test set-up eliminated multiple complicating factors including:
80
the pneumatic automated impulse hammer driven by the gas powered air compressor, the vehicle
attachments, coupling noise directly from the impulse hammer through the towing apparatus into
the receiver, traffic vibration and deck roughness by testing a very smooth (finished concrete floor)
test surface. The data was recorded and a typical response recorded by the axle mounted geophone
is presented below in Figure 63.
Ch 5: Time Domain SlabIR Data - No Filter
0 50000 100000 150000 200000 250000 300000 350000 400000 450000-6
-4
-2
0
2
4
6
Figure 63: Axle mounted 28 Hz geophone response while rolling on finished concrete laboratory
floor, “Sound” location. The response signal from the 3-lb hammer impact is clearly evident near the beginning of
the record. Rolling noise from the transducer wheel rolling across the smooth concrete surface is
apparent throughout the record and at times is as high in amplitude as the signal of interest. The
concrete laboratory floor is significantly smoother, and therefore less noisy, than a typical concrete
bridge deck. The data shown above could easily be processed using digital filtering techniques such
as windowing and filtering, however the rolling noise may become more of an issue when field
testing.
Response to Impact Force
Significant Rolling Noise
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7.3 Comparison of Test Results
Table 1 presents the calculated areas of top concrete delamination damage from the 1st Street
Bridge broken down by each NDE method performed on the bridge deck. The percent of damaged
area ranged from 11 to 17% in the 1st Street Bridge. Reviews of Table I show that the test results
from GPR, IE (point by point) and IE Scanning correlate well with the test results from traditional
sounding using chain drag.
Table I – Percentage of Areas with Top Concrete Delaminations Test Method Percentage
(%) Note
Acoustic Sounding with Chain Drag
12
Tests performed by personnel from Wyoming Department of Transportation and test results plotted by a graduate student from University of Wyoming – See Figure 40.
Ground Penetrating Radar
10.8
Note that combined top delamination and probable active corrosive areas are calculated to be 16.7% - See Figure 45
Impact Echo using Point by Point Grid of 3 ft by 3ft or 9 ft2 resolution
13
Tests performed by graduate students from University of Wyoming – See Figures 46 and 47
Impact Echo Scanning using the Prototype Bridge Deck Scanner with a 0.5 ft2 test resolution
11.1
Scanning with resolutions of 0.5 ft along a scan line and 1 ft between each scan line – See Figures 52 and 53
Infrared Thermography
17
Tests performed by graduate students from University of Wyoming – See Figures 48 and 49
82
8.0 CONCLUSIONS AND RECOMMENDATIONS
The research project fulfilled its proposed objectives by developing an instrument system
(the prototype Bridge Deck Scanner, BDS) that can determine the internal conditions of concrete
bridge decks in a quick scanning fashion with a high degree of accuracy on an automated basis.
This BDS can employ three non-destructive evaluation methods simultaneously depending on the
nature of defects encountered in the bridge deck. These methods include the Impact Echo, Spectral
Analysis of Surface Waves and Acoustic Sounding methods (IE, SASW and AS). Note that the test
results from the IE component is the only test method experimentally verified on a control specimen
(concrete bridge deck of 1st Street Bridge). The Impact Echo test results from the BDS indicated
both top and bottom concrete delaminations with a test resolution of 0.5 sq ft while chain dragging
can only locate top delaminations. Note that the bottom concrete delamination predicted by the BDS
IE testing could not be verified in this structure.
Although the current speed of the scanning is approximately 1 – 1.5 mph, several tests can
be performed simultaneously to accelerate the testing process. The prototype BDS researched and
developed to nondestructively evaluate many deck condition features including thickness, stiffness
and internal condition (such as top/bottom concrete delamination, cracks, depth of cracks and
concrete deterioration) using the IE, SASW and SIR test methods. The SIR component of the BDS
is currently not capable of performing the testing in a scanning fashion due to rolling vibration
problems that adversely affect this lower frequency test. The IE and SASW components for the
BDS performed well in laboratory testing and in comparison with traditional IE and SASW testing.
In this phase of research, only top concrete delamination defects found using the Impact Echo
component of the prototype BDS could be verified. The concrete top delamination map from the IE
component of the BDS system compared well with the delamination map from the acoustic
sounding using chain drag. In addition, the test results from the BDS are not subjective to the
operator and the testing (using the BDS) can be performed faster than the chain drag.
Possible Phase II future research includes the following items:
1. Adding more transducer wheels to further accelerate data collection and to
span the 12 ft lane width (6 to 12 wheels for 2 or 1 ft line spacings)
83
2. Testing additional bridges (with bare concrete an asphalt overlays) where
various damage types can be identified so that other types of internal damage
can be tested with the BDS
3. Implement pneumatic hold-down for Slab IR tests to minimize wheel
vibrations
4. Refine Acoustic Sounding/Microphones for improved top delamination
sensing and “leaky Lamb” wave surface waves testing.
84
9.0 INVESTIGATOR PROFILES Key investigators for the research project include Dr. Yajai Tinkey as a Principal
Investigator, Larry D. Olson as a CO-PI and Mr. Patrick Miller as a Research Project Engineer.
Dr. Yajai Tinkey, P .E., has a computer engineering and structural engineering background.
She is currently an Associate Engineer and Vice President with Olson Engineering and has been
with the company for 10 years. She has intensive experience with non-destructive evaluation
methods applied to structures and infrastructure. These NDE methods include Impact Echo,
Spectral Analysis of Surface Waves and Slab Impulse Response tests. Dr. Tinkey has developed a
number of non-destructive testing analysis software programs available for in-house and
commercial uses. Prior to this research project, she was a Principal Investigator for a research
project titled “Non-destructive Evaluation Methods for Determination of Internal Grout Conditions
inside Bridge Post-tensioning Ducts using Rolling Stress Waves for Continuous Scanning” funded
by the NCHRP-IDEAS program.
Mr. Larry D. Olson, P .E., is President and Principal Engineer of Olson Engineering, Inc.
Mr. Olson has a background in geotechnical, materials and pavement engineering and has over 25
years of non-destructive evaluation and structural condition assessment experience. Mr. Olson
previously served as a PI for a number of research projects funded by different government
organizations totaling over $1.8 million in funded research including the NCHRP 21-5 and 21-5(2)
studies on nondestructively determining unknown bridge foundation depths and conditions for scour
safety evaluation studies. He has been a member of TRB Committee AFF40 for Field Testing and
NDE of Transportation Structures for over six years. Mr. Olson also teaches ASCE Seminars on
Structural Condition Assessment of Existing Structures and Bridge Condition Assessment and
Performance Monitoring and is on ACI Committees 228 – Nondestructive Testing and 309 –
Consolidation. He developed shear and compressional wave sensors and sources for an offshore
bottom-hole seismic device in his Master’s research and continues to be actively involved in
development of sensor/source hardware systems. He is the primary US patent holder and inventor
of the Impact Echo Scanner technology.
85
Mr. Miller has worked as a Project Engineer for Olson Engineering since March 2007. At
Olson Engineering Mr. Miller has been involved in numerous nondestructive evaluation (NDE)
investigations to determine the conditions of such facilities as concrete bridges (including post-
tensioned girders), various concrete slabs (including spillways and dams), various structural
elements of buildings, concrete retaining walls, deep foundations as well as geophysical
investigations to determine in-situ soil properties. These investigations were performed with a
variety of methods, including: ground penetrating radar (GPR), impact echo (IE), spectral analysis
of surface waves (SASW), multi-channel analysis of surface waves (MASW), slab impulse
response (Slab IR), ultrasonic pulse velocity (UPV), sonic echo/ impulse response (SE/IR), parallel
seismic (PS), cross-hole sonic logging (CSL), and cross-hole and down-hole seismic (CS/DS)
methods to evaluate existing conditions for quality assurance and forensic investigations. At Olson
Engineering, Mr. Miller has also been involved in development of new products, including the RT-1
Resonance Tester and multiple research studies, including a comparison of surface wave test
methods for the determination of soil properties immediately below concrete pavements.
Dr. Yajai Tinkey ([email protected]), Mr. Larry Olson
([email protected]) and Mr. Patrick Miller ([email protected]) can be
contacted at the Olson Engineering, Inc. main office located at 12401 W. 49th Ave, Wheat Ridge,
Colorado (phone: 303-423-1212).
86
10.0 REFERENCES “ASTM C 1383-04 Standard Test Method for Measuring the P-Wave Speed and Thickness of
Concrete Plates Using the Impact-Echo Method."
"ASTM D 4580-03 Standard Practice for Measuring Delaminations in Concrete Bridge Decks by Sounding."
Abe, M., Fujino, Y ., and Kaito, K., (2001). “Damage detection of civil concrete structures by laser doppler vibrometry.” Proc. of the International Modal Analysis Conference – IMAC, v1, p 704-709. Abraham, O., Villain, G., Lu, L., Cottineau, L.M., Durand, O., (2009). “A laser interferometer robot for the study of surface wave sensitivity to various concrete mixes.” Non-destructive Testing in Civil Engineering, Nantes, France, 2009. Algernon, D., Grafe, B., Mielentz, F., Kohler, B., and Schubert, F. (2008). “Imaging of the elastic wave propagation in concrete using scanning techniques: application for impact-echo and ultrasonic echo methods.” J. of Nondestructive Evaluation, v27, n 1-3, p83-97. Azevedo, S.A, Mast, J.R., Nelson, S.D., Rosenbury, E.T., Jones, H.E., McEwan, T.E., Mullenhoff,
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Using GPR by Accounting for Signal Depth-Amplitude Effects", NDT & E International, Vol. 41, No. 6, September.
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Impulse Response”, International Symposium (NDT-CE 2003) Non-Destructive Davidson, N.C. and Chase, S.B., "Radar Tomography of Bridge Decks," in Structural Materials
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Gibson, A. “Advances in Non-Contact Impact Echo Scanning.” Civil Engineer Layne Christenson Co. – Colog Division, Lakewood, CO. Gibson, A. (2005). “Advances in nondestructive testing of concrete pavements.” Ph.D. dissertation, Univ. of Illinois at Urbana-Champaign, Urbana, IL. Gibson, A., and Popovics, J.S. (2005). “Lamb wave basis for impact-echo method analysis.” J. Eng. Mech., 131(4), 438 – 443. Gucunski, N., Rascoe, C., Parillo, R., and Roberts, R. (2009). “Complementary Condition
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SPIE--The International Society for Optical Engineering, v 3587, n, 219-227. Holland, S.D., and Chimenti, D.E., “Air-coupled acoustic imaging with zero-group-velocity Lamb modes.” Applied Physics Letters, Volume 83 Number 13, September 2003. Kalinsi, M.E., 1994. Measurements of intact and cracked concrete structural elements by the SASW method. Masters Thesis, Civil Engineering Department, University of Texas at Austin. Maser K.R, Kim Roddis, W.M., “Principles of Thermography and Radar for Bridge Deck
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Structures," PhD Thesis, University of Illinois at Urbana-Champaign, 1993. Ryden, N., Lowe, M., Cawley, P ., and Park, C. (2006). “Non-contact surface wave measurements using a microphone.” Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP 2006), Seattle, W A. Sansalone, M. J. and Streett, W. B., Impact-Echo Nondestructive Evaluation of Concrete and Masonry. ISBN: 0-9612610-6-4, Bullbrier Press, Ithaca, N. Y, 1997 339 pp Sack, D., and Olson, L.D., “Impact Echo Scanning of Concrete Slabs and Pipes”, International
Conference on Advances on Concrete Technology, Las Vegas, NV, June 1995. Somekh, M.G., Liu, M., Ho, H.P., and See, C.W., (1995). “An accurate non-contacting laser based system for surface wave velocity measurement.” Meas. Sci. Technol. 6 (1995) 1329 – 1337.
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Impact-Echo Scanning Method”, Journal of Transportation Research Board, Washington, DC, 2007. Van Wijk, K., Scales, J.A., Mikesell, T.D., Peacock, J.R., (2005). “Toward noncontacting seismology.” Geophysical Research Letters, vol. 32, L01308. Woodward, R.J. and Williams, F.W., “Collapse of the Ynys-y-Gwas Bridge, West Glamorgan,”
Proceeding of The Institution of Civil Engineers, Part 1, Vol. 84, August 1988, pp. 635-669. Zhu, J. (2005). “Non-contact NDT of concrete structures using air-coupled sensors.” Ph.D. dissertation, Univ. of Illinois at Urbana-Champaign, Urbana, IL. Zhu, J., and Popovics, J.S. (2007). “Imaging concrete structures using air-coupled impact echo.” J. Eng. Mech., 133(6), 628-640. Zhu, J., and Popovics. J.S. (2001). “Non-contact detection of surface waves in concrete using an air- coupled sensor.” Review of progess in quantitative nondestructive evaluation, Vol. 20B, D. O. Thompson, and D.E. Chimenti, eds., American Institute of Physics, Melville, N.Y ., 1261 – 1268. Zhu, J., and Popovics, J.S. (2005). “Non-contact imaging for surface-opening cracks in concrete with air-coupled sensors.” Mater, Struct., 38(283), 801-806.
