Nondestructive Evaluation of Concrete Dams · 2020-06-17 · NDE of Concrete Dams Case Histories...
Transcript of Nondestructive Evaluation of Concrete Dams · 2020-06-17 · NDE of Concrete Dams Case Histories...
Nondestructive Evaluation of
Concrete Dams
16 June 2020
Larry D. Olson, P.E.President and Chief Engineer
NDT Methods for Estimating In-Place Concrete Strength
Rebound (Schmidt or Swiss) Hammer
Windsor Probe Penetration
Pin Penetration Resistance
Pull-out or Capo Tests
Ultrasonic Pulse Velocity
Maturity (hydration temperatures and time vs. strength)
American Concrete Institute Manual of Concrete Practice - ACI 228.1R-19 –
Report on Methods for Estimating In-Place Concrete Strength
NDT Methods for Evaluation of Concrete in Structures
Stress Waves for Structures and Pavements
◦ Ultrasonic Pulse Velocity
◦ Impact Echo
◦ Pulse Echo
◦ Spectral Analysis of Surface Waves
Stress Waves for Deep Foundations
◦ Sonic Echo
◦ Impulse Response
◦ Crosshole Sonic Logging
◦ Parallel Seismic
American Concrete Institute Manual of Concrete Practice ACI 228.2R-13 –
Report on Nondestructive Test Methods for Evaluation of Concrete in Structures
Magnetic Methods
Electrical Methods
Nuclear Methods
Penetrability Methods
Infrared Thermography
Ground Penetrating Radar
Sonic/Ultrasonic Velocity Tomography
Physics – Elastic Wave Propagation
(3 most used Wave Modes of Primary-compressional, Secondary-shear and Rayleigh-surface)
Stress Wave Basics - Primary Compressional Waves
The particle motion associated with compressional waves can be described as vibration parallel
to the direction of wave travel.
Stress Wave Basics – Secondary Shear Waves
The particle motion associated with shear waves can be described as vibration perpendicular to the
direction of wave travel.
Stress Wave Basics – Rayleigh Surface Wave
A Rayleigh wave moves across a surface. As it passes, a surface particle moves in a circle or
ellipse in the direction of propagation.
Stress Wave Basics Wave Velocity for Concrete at Poisson’s Ratio of 0.2
NDE of Concrete Dams Case Histories Outline
Impact Echo for Cracking, Thickness and Integrity
Spectral Analysis of Surface Waves for Freeze-thaw Cracking and Alkali-Silica Reaction Cracking and Concrete/Masonry Quality
Sonic Cross Dam Tomography for Imaging Internal Conditions of Concrete and Masonry Dams
Slab Impulse Response for Void/Subgrade Support Evaluation of Spillways and Conduits
Ground Penetrating Radar for Void/Subgrade Support Evaluation of Spillways and Conduits and Steel Reinforcement Mapping
Infrared Thermography for Shallow Delamination Mapping
Impact Echo Test
(ASTM C1338 and ACI 228.2R)
D = bVp/(2*f)
b= Shape Factor (0.96 for
slab/wall shape)
D = Thickness Echo Depth
Vp = Compressional
Wave Velocity
f = Resonant Echo Frequency
Impact Echo IE-1 Test Head
Displacement Transducer with
Automated Impactor for thickness
echoes from 8 to 60 cm – use
hammer for greater thickness
echoes to 180 cm
Waterproof Version for Underwater
Testing (with a Diver) has been used
on canal linings and bridge piers
Impact Echo Testing was done
on Grid on the Downstream
Face to Determine Extent of
Freeze-Thaw Cracking Damage
Impact Echo Testing of a Thin-Arch Concrete Dam
Impact Echo Testing on Face
Example Impact Echo Result Indicative of Cracking
IE Velocity Check and Cracking Confirmed by Coring
NDE can evaluate thicknesses & corrosion conditions of
concrete, steel, composite outflow works and pipes (any size)
Impact Echo and Ultrasonic Pulse Echo
NDE Evaluation of Dam Conduit Steel Lining and Concrete Conditions
IE Testing on Steel-Lined (Bonded) Concrete Dam Conduit
Testing on steel-lined
(bonded) concrete dam
conduit to check
thickness and integrity
IE Test Result
Result indicating
25.7 inch thick
sound concrete
behind steel-lined
dam conduit
Impact Echo Result through Steel Liner
Ch 3: Time Domain IE Data
Time (us)
0 5000 10000 15000 20000 25000 30000 35000 40000
-2
-1
0
1
Avg Frequency Spectrum, T = 68.6 in V = 144000 in/sec
Frequency (Hz)
0 5000 10000 15000 20000 25000
0
0.005
0.01
0.015
0.02
0.025
Result shows ringing void
Ultrasonic Thickness/Pulse Echo Testing
Testing found steel lining
thicknesses of ~0.4 inch
(ranged from 0.34 to 0.52
inch)
Spectral Analysis of Surface Waves (ACI 228.2R)
Velocity = Frequency x Wavelength
NDE Data Acquisition Platforms and SASW Systems
Freedom Data PC Platform
Windows 10 Field Ruggedized
NDE-360 Platform
Touch Screen w/ Compact Flash
SASW-S Bar for 6 to 80 cm spacings
SASW-S Accelerometers for variable
spacings
Example Test Results SASW
Typical Time Domain
Records for the Two
Receivers used in SASW
Testing, R1-R2 = 30 cm
for 2.62ft SASW Bar spacing = 1 wavelength (-360o phase), Velocity=frequency x wavelength=2.62 x 2628Hz=6900 ft/s
SASW Phase Plot from Sound Area
2628 Hz at -360o
+180o
Wrapped Phase
0o
-180o
Signal 1Coherence
0
0 Frequency (Hz) 13000
V =6900 ft/s Surface Wave Velocity for Sound Concrete
0 Wavelength (ft) 5
Surface Wave Velocity vs. Wavelength
1.0
Signal Coherence
0
8,000Surface Wave Velocity (ft/s)
0
SASW on Outflow Pipe Wall for:
SASW Testing on Steel-Lined (Bonded) Concrete Dam
Voids behind steel pipe wall
Concrete thickness and
integrity from IE and concrete
quality from SASW as it
shows velocity vs. depth
SASW Results
Sound concrete
behind steel lining
with velocity of
~7,300 ft/s
SASW Result from Void/Intermittent Location
Note slow Surface Wave Velocities of 3000 to 5000 ft/s
SASW Data Collection – Concrete Dams
SASW Testing on a Concrete Dam:
Investigating interior degradation
due to freeze/thaw cycles
Cracking due to alkali-silica or
alkali-aggregate reaction (ASR
or AAR)
Typical SASW Data on a Dam Face – Freeze/Thaw Cracking
Location with Freeze/Thaw Cracking to about 3 ft
deep behind Surface Patch where surface wave
velocity increases (Visually LOOKS Sound…)
Sound Concrete to 4 feet deep – surface wae
velocity ~6,500 ft/s
SASW Crack Damage Depth Plot
This plot shows the depth of damage (scale on the right) from freeze-thaw versus location on the downstream face of a thin-arch concrete dam
Evaluation of freeze-thaw cracking damage depth behind 3 year old failed,
debonded shotcrete repair at Rogers Dam in Big Rapids, Michigan – ICRI
Award Winner in 1996
Debonded Shotcrete on Pier by Tainter Gate
Debonded Shotcrete
SASW test with
Accelerometers
SASW Dispersion Curve From East Abutment Wall
SASW Velocity Plot From East Abutment Wall
Cracked & Sound Impact Echo Results
Ultrasonic/Sonic Pulse Velocity Tests for Tomography
UPV Applications
ASTM Standard C597-16 Standard Test Method for Pulse Velocity Through Concrete
Used to locate voids, honeycomb, cracks, discontinuities or poor quality concrete
Best used on structures with 2 accessible sides◦ Beams◦ Columns◦ Elevated Slabs
Sonic Pulse Velocity (SPV) used on large structures like bridge piers and dams UPV Testing on a Column
Below 7,000 (2,100)Very Poor
7,000-10,000 (2,100 – 3,000)Poor
10,000-12,000 (3,000 – 3,600)Questionable
12,000-15,000 (3,600 – 4,500)Good
Above 15,000 (4,500)Excellent
Ultrasonic Pulse Velocity
ft/s (m/s)
General Concrete
Condition
Concrete Compressional Wave Pulse Velocity and Quality
Note: Surface Wave Velocity is 0.56 of Compressional
Pulse Velocity for Concrete with a Poisson’s ratio of 0.2 (After Leslie and Cheeseman, 1949)
UPV/SPV Test
Using 2 transducers - source and receiver
Measure signal time and signal amplitude between the source and receiver (transmission test)
Calculate concrete compression wave velocity (Vp)
SPV uses an impact source rather than piezotransducer
Pulse Velocity = Vp = Distance/Wave Travel Time
Strength Correlations per ACI 228.1R-89f’c ~ E2 ~ V4 – must calibrate with cores or cylinders
UPV Test Procedure: Calibration on Standard Test Bar
SPV (Sonic Pulse Velocity) Testing
SPV is a low-frequency/high energy version of UPV.
Requires an instrumented hammer or a steel hammer and sensor
as a source
Can be done using two UPV transducers and a hammer
Example Sonic Pulse Velocity Data
tDVelocity /=
Sonic Pulse Velocity = Distance/Travel Time = 8 ft / (2566 ms – 1990 ms) = 13,889 ft/s
Figure 5: Example SPV results for the North Pier – File NL7 at height = 15 feet, Path 2 to 6. Sound Concrete
Condtion Rating with SPV = 13,455 ft/s Receiver Response at 8 ft from impact point Impulse Hammer impact response
Acoustic Sonic Dam Velocity Tomography
Acoustic method – measures the compression (or shear) wave velocity
of sonic waves traveling on a mesh of paths through the dam interior
Allows 2-D slices and 3-D images of the velocity profile of the dam to be
created
Velocity of concrete is related to strength and condition – low velocity
zones are areas of weak, cracked, or degraded concrete
The testing is EASIEST done on dams with a full pool to allow
hydrophones to be used on the upstream face
Wave source can be from climbers or remote operated impactor
Sonic Dam Tomography: Fieldwork
Small or Large Concrete Dams
Remote Access for Source Impacts
Instrumented Electrical Solenoid Impact Source on smooth concrete
Sonic Dam Tomography Testing by Climber
3-lb Impulse Hammer
impacts on downstream
face for testing on rough
surfaces and thick dams
Crossing Velocity Tomography Ray Paths: Straight vs. Curved
Rays - Infinitesimally narrow path perpendicular to the spherically spreading seismic wave front.
Straight Rays
◦ “Travel” from Source Location to the Receiver Location in the most direct path.
Curved Rays (AKA Bending Rays)
◦ Seismic Waves and therefore their associated rays can bend within a volume if there are changes in the material properties (I.e. density)
◦ These rays are initially estimated as Straight Rays and then iteratively perturbed until the residuals are minimized.
◦ More appropriate for mediums containing strong velocity contrasts.
Raypath Diagram
Note Hydrophone
Receivers are typically 3
ft apart underwater on
upstream and automated
impacts or 3 lb impulse
hammer impacts with
climber downstream
Sonic Dam Tomography - Method
Sonic Cross Dam Tomography
Sonic Cross Dam
Tomography conducted
for safety evaluation on
24 2-D cross-sections
over 480 ft dam length in
5 field days
Velocity Tomography Remotely Operated Impact Source
Solenoid Source in use on Dam Downstream Face
Hydrophone Receiver String and Solenoid Impactor Source
Freedom PC Data Acquisition Equipment and
Solenoid Driver
These plots show the typical raypath mesh
resulting from tomographic data collection of
sonic pulse veloctity travel times along the
test paths (scales in ft) R denotes a
hydrophone receiver upstream and S denotes
downstream solenoid source impact point
Raypath Density Plots
Example Sonic Pulse Velocity Result for CDT
Velocity Tomogram with Anomalous Areas and Debonded Joint
Imaged DebondedJoint – confirmed by Divers that the small green band at 38 feet is a degraded copper waterstop embedded in the concrete
(scales in ft on dam cross-
section and kilo ft/s) and
Hydrophones (R) upstream-
Source (S) Impacts downstream
Impact Source Options
Tomography on Rough Concrete: Direct Impacting Using Climber
Above Velocities in 1000’s of ft/s
Low velocity zones at downstream face
(left side) correspond to degraded,
cracked concrete due to freeze-thaw
Velocity Tomography Test Results
Note blue colors indicate slower
velocity concrete due to freeze-
thaw cracking damage
Sonic Dam Velocity Tomography:
Multiple 2D Results
Sonic Cross Dam Tomography Advantages & Disadvantages
Image internal flaws in 2-D and now 3-D fashion with angled and direct tests
A picture is worth a thousand words and velocity tomograms provide an image of internal void, cracking and honeycomb and other concrete damage/defect conditions
Slab Impulse Response (SIR) & Ground Penetrating
Radar for Spillway Subgrade Support Evaluation
Used to Locate and Define Voids Under
Spillways, Roadways, Building Slabs, Tunnel
Liners, Pipe Walls, and Rigid Concrete
Pavements
Slab Impulse (SIR) Response Method
ASTM C1740 - 16 Standard
Practice for Evaluating the
Condition of Concrete Plates
Using the Impulse-Response
Method
Slab Impulse Response Method & Equipment
Detects thin voids less than 1/16 inch
Compliments GPR and improves accuracy of void detection greatly
Test slab thicknesses up to ~18-24 inches
Olson Instruments Freedom Data PC with Slab IR system (SIR-1)
3-lb instrumented hammer impacts and geophone records time domain data◦ Wilcoxson velocity transducer for non-flat
structural elements such as conduits, tunnel liners, walls and other structural elements
Data converted to frequency domain via FFT
Measure velocity response of slabTime domain and Velocity Spectrum of Geophone
Time Domain Velocity
Receiver
Spectral Domain
Velocity as a function
of frequency
FF
T
Measure Impulse Hammer force in time and spectra
2
ms
3000 lbf
Time of
Impact
Delay ~
10% of Total
Time
Total Time =
20.48 ms
2000 Hz
FF
T
Transfer Function: Mobility (Velocity/Force Spectra)
=
Δf
𝐹(𝑓) ∗𝑉(𝑓)
𝐹(𝑓)= 𝑉(𝑓)
Flexibility Transfer Function Flexibility (inches/lbf) which is inverse of Stiffness - lbf/inch)
)()(
)(*)( fD
fF
fDfF =
MEASURED
OUTPUT
MEASURED
INPUTFLEXIBILITY
TRANSFER
FUNCTION
Dam Spillway Case History
NDE methods of Slab Impulse
Response, Ground Penetrating Radar
and Video Borescope
Field Project background
Survey design and data collection
procedures
Example results
Combined NDE results - data
presentation and interpretation for
subgrade void evaluation
Corehole Ground-truthing
and conclusion
Spillway Project Background
Spillway Characteristics
◦ Alpine reservoir dam concrete spillway in
Colorado at 3000 m above sea level
◦ Reservoir capacity ~ 800 acre-ft serves as
water source for nearby town
◦ Dimensions are 45.7 m long x 15.8m wide
at top, tapering to 9.7m wide at bottom
◦ 180-350mm (7-14 inches) thick concrete,
reinforced with one mat at nominally
304mm (12 inches)
Reasons for NDT&E
◦ Observed water seepage at joints and
concrete spalling
◦ Prior hammer sounding was hollow
◦ Drilling investigation showed subgrade void
NDE Methods
Ground Penetrating Radar (GPR)
◦ Electromagnetic wave reflection
– 400 MHz Antenna
Slab Impulse Response (Slab IR)
◦ Acoustic modal vibration method
– 3 lb impulse hammer and
geophone (velocity transducer)
Complementary tools for
determining areas of poor
subgrade support or voids
Slab IR Field Survey
Data collected at a 4 x 4 ft grid
3 hammer impact (records) collected at each point and averaged
428 data points total
Centerline of the spillway, running longitudinally for more than
47mdownstream named ‘C’
Longitudinal lines designated at 4 ft intervals from right of center
eastward as R1 through R6 and at 4 ft intervals from left of center
westward as L1 through L6 looking downstream from the spillway crest
Survey began 2 ft downstream of the reservoir shore edge through line
40 at 4 ft intervals
Slab IR Data Processing Time domain data of hammer input and receiver output shown below that are converted
to frequency domain by FFT operations on 2-3 hammer blows
Transfer function normalizes receiver spectrum in velocity units by hammer spectrum in
force units (Mobility = M = V(f)/F(f) on next slide
Ch 1: Time Domain SlabIR Data
Time (us)
0 50000 100000 150000 200000 250000 300000
-6
-4
-2
0
2
4
6
Ch 2: Time Domain SlabIR Data
Time (us)
0 50000 100000 150000 200000 250000 300000
0
2000
4000
6000
Hammer Signal (lbf)
Receiver Signal (in/s)
Slab IR Results
Subgrade support condition
evaluation parameters
◦ Mean mobility (in/sec/lbf)
◦ Shape of the mobility plot
◦ Initial slope of the mobility plot
gives the low-strain flexibility
(in/lbf)
Interpretation Pitfalls
◦ Slab thickness
◦ Local reinforcement
◦ Local joints/seams
Avg. Coherence
Frequency (Hz)
0 100 200 300 400 500 600 700 800 900 1000
0
0.2
0.4
0.6
0.8
1
Avg. Mobility from F1 = 100 to F2 = 800 : 1.23748e-004
Frequency (Hz)
0 100 200 300 400 500 600 700 800 900 1000
0
0.0005
0.001
0.0015
M
ob
ilit
y (
in /
s /
lb
f)
Avg. Coherence
Frequency (Hz)
0 100 200 300 400 500 600 700 800 900 1000
0
0.2
0.4
0.6
0.8
1
Avg. Mobility from F1 = 100 to F2 = 800 : 7.21102e-004
Frequency (Hz)
0 100 200 300 400 500 600 700 800 900 1000
0
0.0005
0.001
0.0015
Mo
bil
ity
(in
/ s
/ l
bf)
Good subgrade
support – low,
smooth mobility in
bottom plot and
good data
coherence in top
plot
Poor subgrade
support – high,
irregular mobility
in bottom plot –
much more
flexible/less stiff
slab
Ground Penetrating Radar (GPR) Method
EM (radio) wave reflection
Reflection occurs when
encountering a change in
electrical impedance or
material relative dielectric,
termed e
Concrete to steel, concrete to
air (void), concrete to soil
Amplitude of reflection, R,
defined by:
R = (erU0.5 – erL
0.5 ) /(erU0.5 + erL
0.5 )
Tim
e (n
s)
Ground Penetrating Radar: Physics & Theory for a Signal
The collected raw data is in the form of echo amplitude versus time.
By inputting the dielectric constant, which defines the material velocity, and by estimating the signal zero point, the echo time data can be converted to echo depth.
VEM = c / er0.5 Equation 1
D = (VEM * T) / 2 Equation 2
Where
◦ VEM = material electromagnetic wave velocity
◦ c = speed of light (in air)
◦ er= material relative dielectric constant to air (1.0 in air at speed of light
◦ D = depth of GPR reflection
◦ T = the two-way radar pulse travel time (shown for slab top and bottom)
◦ Typical concrete dielectric constant - er = 6
The round-trip transit time of the pulse emitted by the GPR and its reflection
provide range information on the target
GPR Working Principle
GPR Physical Principle – Corroded vs. Non-Corroded Rebar
GPR Test and Relative Dielectric Constants
Locations with dielectric contrast
between the two materials (see table)
Large concrete cracks/voids (air filled)
Smaller gap/void filled with water very
well – larger dialectic contrast
Smaller amplitude of the
reinforcement reflector indicates
possible reinforcement corrosion due
to diffraction by rust byproducts
Typical Spillway GPR Field Survey - Sloping Spillway
400 MHz antenna, 106 pulses
per meter
Survey wheel records distance
Data collected in 3-D fashion
with unidirectional parallel lines
at 1.2m intervals
Spillway scanned in lines from
top to bottom or side to side
GPR Field Survey
400 MHz antenna, 106 pulses per meter
Survey wheel records distance
Data collected in 3-D fashion with unidirectional
parallel lines at 1.2m intervals
Spillway split into upper and lower portions
Scanning from spillway crest to bottom for each
portion
Treacherous footing because of moss. Felt-
bottom shoes worn
Nor
thin
g, D
owns
tream
(ft)
10 20 30 40 50
Easting (ft)
Upp
er S
pillw
ay
Low
er
Spill
way
GPR Example Results Slab bottom/subsurface amplitude reflection = bright spot analysis
R = (erU0.5 – erL
0.5 ) /(erU0.5 + erL
0.5 )
Material er R
Concrete 9.8 ---
Void (air) 1.0 0.52
Soil 4.0 0.22
Concrete/soil Concrete/void
Combined NDE Results
Ground-Truthing
Coring locations recommendations based on NDE results
Video borescope probe for motion and still pictures
Excellent correlation – extensive subgrade voids found in all coreholes
Corehole 9L1 - East - File 030821AXCorehole 9L1 - East - File 030821AX
GPR Applications
GPR Field Survey: Routine Spillway Inspection & Dam LinersLocating void below concrete spillways and soil-cement liners
400 MHz antenna on soil cement liner checking for void over 2.5 miles of liner
4 scans per inch (48 scans/ft)
Survey wheel to record distance
Can record with GPS
Data collected along lines (top to bottom or side to side, or both)
Fig. 2 GPR Testing with the 400 MHz Antenna on the Reservoir LinerFig. 2 GPR Testing with the 400 MHz Antenna on the Reservoir Liner
Core # 9 Location
Void Area
Small Void
Slab Top
GPR Results: Voids beneath Soil – Cement Embankment Liner
Verify Visual and Destructive Test Results with NDT Extend details beyond the known conditions*
Coring
Drilling
Chipping
Borescope
Visual Inspection
Standard Methods:
Ground-Truthing Results
Coring locations recommendations were based on NDE results
Cores Confirm Large Cavities with high GPR accuracy
Infrared Thermography
for Shallow Delaminations
ASTM D4788 - 03(2013) Standard Test Method for Detecting
Delaminations in Bridge Decks Using Infrared Thermography
Physical Principle of Infrared Thermography
Infrared Thermography of Cyclopean Masonry Dam Spillway
Infrared Thermography (IRT) Delaminations Spillway Crest
Picture 1. Captured at: Spillway Crest Sections 11-7
Date & Time: 11/7/2012 10:38:53 AM
46.2
57.7 °F
50
55
Comment:
Although the hottest areas are the most delaminated of the crest patch, the yellow-
orange areas are also debonded patches from the underlying concrete.
Recommendation:
IRT Delaminations Outlined in Black on SpillwayPicture 1. Captured at: DSF Sections 11-7
Date & Time: 11/7/2012 10:59:59 AM
48.3
60.6 °F
50
55
60
Comment:
Recommendation:
Summary for the Infrared Thermography Technique
Simple and easy to train
Good to detect shallow anomalies of 2 to 3 inches deep
Difficult to detect deeper anomalies
Both actual photograph accompanied by the thermographic image of the
same location are required in the interpretation
The test results are dependent on the weather condition and the time of the
day of the testing – solar heating generally required
NDE of Dam Facilities - General Application Guide Stress Wave Methods for Material Integrity and Deterioration of Concrete,
Masonry and Steel Materials
◦ Impact Echo
◦ Spectral Analysis of Surface Waves
◦ Ultrasonic and Sonic Pulse Velocity
◦ Sonic Velocity Cross Dam Tomography
◦ Ultrasonic Pulse Echo/Impact Echo for corrosion and bolt integrity/length
Electromagnetic and Modal Vibration Methods for steel mapping and Spillway/Conduit Subgrade Support
◦ Ground Penetrating Radar for subgrade void ¼+ inch and steel mapping
◦ Slab Impulse Response for even thinner voids and soft subgrade evaluation
Infrared Thermography (IRT) for shallow concrete delamination mapping
Thank You