ML12157A308
| ML12157A308 | |
| Person / Time | |
|---|---|
| Issue date: | 06/05/2012 |
| From: | Office of the Chief Human Capital Officer |
| To: | |
| References | |
| Download: ML12157A308 (176) | |
Text
s Codes Codes InIn--Place Evaluation Place Evaluation M
h d M
h d gy and gy and Methods Methods hnolog hnolog te Tech te Tech Concret Concret C
Evaluation of Concrete Evaluation of Concrete Evaluation of Concrete Evaluation of Concrete Visible features Visible features Cracking, deterioration, deflections In-place strength p
g Internal conditions Corrosion of reinforcement Voids Honeycombing Voids in tendon ducts Delaminations Member thickness Member thickness
Tools Tools Tools Tools Visual inspection Visual inspection Removal of samples Core compressive strength Core compressive strength Petrographic analysis Tests for in-place uniformity p
y In-place strength methods Stress-wave methods Ground penetrating radar Corrosion evaluation methods
References References References References
Outline Outline Outline Outline Tests for uniformity Tests for in-place strength Methods to locate internal defects Evaluation of corrosion
Tests for Uniformity Tests for Uniformity Tests for Uniformity Tests for Uniformity Determine which portions of structure are Determine which portions of structure are similar Identify areas for further investigation by other Identify areas for further investigation by other means Methods Methods Rebound number (hammer)ASTM C805 Ultrasonic pulse velocityASTM C597
p y
Rebound Number (Hammer)
Rebound Number (Hammer)
(
)
(
)
ASTM C805 ASTM C805 Measure the rebound of spring-driven mass (hammer) after impact with rod in contact with concrete.
Push down Lock/release button Push down Rod Rod
Rebound Hammer Rebound Hammer Rebound Hammer Rebound Hammer
Operation Operation Push Body Body Hammer Released Rebound Latch Slider Released Latch S
i Hammer Spring d
Rod
Slider Rebound number = 41 Rebound number = 41
Near Near--surface Effects surface Effects Result = average of 10 readings Result = average of 10 readings Discard reading > 6 units from average Aggregate Rough Dry or Carbonation Air void
Factors Affecting Rebound Factors Affecting Rebound g
Number Number Strength and elastic modulus of near surface concrete concrete Layer of carbonation Surface texture Surface texture Surface moisture condition
To Estimate Strength To Estimate Strength To Estimate Strength To Estimate Strength The only reliable approach is to correlate rebound number with strength of cores Need at least 6 strength levels (ACI 228.1R)
Thus at least 12 cores to establish a correlation
Example Example p
7000 7000 5000 6000 h, psi 5000 6000 h, psi 4000 5000 Strength 4000 5000 Strength 2000 3000 Core Strength, psi Upper 95 % CL Lower 95 % CL Core S 2000 3000 Core Strength, psi Upper 95 % CL Lower 95 % CL Core S 1000 25 30 35 40 Rebound Number 1000 25 30 35 40 Rebound Number Ward, M.A. and Langan, B.W., Cement Concrete and Aggregates, 16(2), Dec. 1994, 181-185 Rebound Number Rebound Number
Ultrasonic Pulse Velocity Ultrasonic Pulse Velocityy ASTM C597 ASTM C597 Measure travel time of ultrasonic pulse Measure travel time of ultrasonic pulse (compressional stress wave) over known path length.
path length.
Stress Wave Stress Wave Stress Wave Stress Wave A disturbance that transfers energy progressively gy p g
y from point to point in a medium WebFiles\\waves-intro.html Speed of compression stress wave in concrete:
E 1.05 p
E C
For good concrete: Cp 4000 m/s http://www.kettering.edu/~drussell/Demos/waves-intro/waves-intro.html
UPV UPV Principle of Operation Principle of Operation UPV UPVPrinciple of Operation Principle of Operation Transmitter Couplant L
L C
Pulser L
t C p
=
Ti t Timer Receiver t
Couplant Receiver
Example Example Pulser/Timer Display Transmitter Display R
i Receiver t
Threshold level Transmitter Receiver Courtesy of CNS Farnell
Measurement Paths Measurement Paths Measurement Paths Measurement Paths Direct path Semi-direct path p
Courtesy of James Instruments Inc.
Effects of Effects of Internal Internal Defects Defects T
R Solid Defects Defects Presence of "defects" Honeycomb increases travel time, and results in lower computed speed.
Honeycomb speed.
Crack L
Assessment of Uniformity Assessment of Uniformity Assessment of Uniformity Assessment of Uniformity Draw grid on the surface of test object Draw grid on the surface of test object Perform tests at grid points Test at same points to assess age related Test at same points to assess age related deterioration Plot UPV contours 1
2 3
4 5
6 7
8 9
10 11 12 A
B C
D
Assessment of Uniformity Assessment of Uniformity Assessment of Uniformity Assessment of Uniformity Draw grid on the surface of test object Draw grid on the surface of test object Perform tests at grid points Test at same points to assess age related Test at same points to assess age related deterioration Plot UPV contours 4000 3900 3800 4010
Depth of Surface Damage Depth of Surface Damage p
g p
g UPV Method can be used to estimate depth of damaged concrete (such as by fire) damaged concrete (such as by fire)
Requires distinct boundary between sound and damaged concrete g
Multiple travel time measurements along surface Damaged concrete C C < C T
d
?
R R
R R
Damaged concrete Cd Cd< Cs d = ?
Sound concrete Cs
Depth of Surface Damage Depth of Surface Damage There are two ray paths Depth of Surface Damage Depth of Surface Damage Path 1: through damage concrete Path 2: through damaged concrete and sound concrete For certain separation, Xo, transit times are equal Transmitter Receiver X
d = ?
Path 2 Path 2 Path 1 Path 1
Determination of Determination of d Determination of Determination of d 1
Transit Time 1
Cs Xo 2
o s
d s
d X
C C
d C
C
=
+
1 s
d Cd Distance, X Chung and Law, Cement Concrete and Aggregates, 7(2), 1985, 84-88
Tests of Uniformity Tests of Uniformity Tests of Uniformity Tests of Uniformity R b d
b Rebound number Fast and simple to use Assesses surface condition Assesses surface condition Pulse velocity R l ti l
i l t Relatively simple to use Assess concrete between transducers Advanced application depth of surface Advanced applicationdepth of surface damage (fire)
InIn Place Strength Place Strength InIn-Place Strength Place Strength Common method: drill cores according to Common method: drill cores according to ASTM C42/C42M and test according to ASTM C39/C39M
/
Requires at least 3.7 in. diameter and length No reinforcing steel in core g
Post-installed pullout test (CAPO)
Estimate compressive strength based on p
g correlation Pull-off test Direct tensile strength
Pullout Test Pullout Test ASTM C900 ASTM C900 Measure force to pullout an insert h
d i anchored in concrete.
Cast-in-place (CIP): attached to formwork or inserted into top surface of freshly cast slab (during construction)
Post-installed (PI); placed into drilled hole with undercut slot (existing construction) construction)
CIP CIP Pullout Test Pullout Test CIP CIP-Pullout Test Pullout Test 25 mm Insert Insert 25 mm Formwork
CIP CIP Pullout Test Pullout Test CIP CIP-Pullout Test Pullout Test Insert Reaction Pullout Force Reaction Ring Force
CIP CIP Pullout Test Pullout Test CIP CIP-Pullout Test Pullout Test Insert Reaction Pullout Force Reaction Ring Force
Pullout Test Pullout Test LOK Test LOK Test Pullout Test Pullout Test-LOK Test LOK Test Conical Fragment Pull Machine g
Results of 16 Correlations Results of 16 Correlations Results of 16 Correlations Results of 16 Correlations Manufacturers Curve
Post Post Installed Tests Installed Tests Post Post-Installed Tests Installed Tests Does not require pre-planning test locations Can perform test at any accessible location Permits testing of existing structures
Post Post--Installed Pullout Test Installed Pullout Test CAPO Test CAPO Test
Prepare Concrete Prepare Concrete Prepare Concrete Prepare Concrete Grind surface Drill hole 18 mm 25 mm 25 mm C t slot Cut slot 25 mm
Drill Hole Drill Hole Drill Hole Drill Hole
Surface Surface Planing Planing
Cut Slot Cut Slot Cut Slot Cut Slot
Cut Slot Cut Slot Cut Slot Cut Slot
Cut Slot Cut Slot Cut Slot Cut Slot
Insert Expansion Cone Insert Expansion Cone p
and Coiled Ring and Coiled Ring Coiled ring Cone Cone
Ring Expansion Hardware Ring Expansion Hardware Nut Coiled ring Cone
Expand Ring Expand Ring Expand Ring Expand Ring Nut Nut
Expand Expand Expand Expand Ring Ring
Pullout the Expanded Ring Pullout the Expanded Ring Pullout the Expanded Ring Pullout the Expanded Ring
Apply Apply pp y pp y Pullout Pullout Force Force Force Force
CAPO CAPO Test Test vs vs LOK LOK Test Test CAPO CAPO-Test Test vs vs LOK LOK-Test Test 70 50 60 N
Line of Equality 30 40 50
-Test, k 20 30 CAPO-0 10 0
10 20 30 40 50 60 70 0
10 20 30 40 50 60 70 LOK -Test, kN
Pull Pull--off Test off Test ASTM C1583 ASTM C1583 Measure force required to pull off a metal di b
d d f
disc bonded to concrete surface.
Pull Pull off Test off Test Pull Pull-off Test off Test Direct tensile strength test Evaluate condition of concrete surface before application of overlay or repair material Measure bond strength of overlay or surface repair materials
Pull Pull off Test off Test Pull Pull-off Test off Test B
d t l di t
f Bond metal disc to surface Drill partial core A
l il f Apply tensile force Overlay 50 or 75 mm (2 or 3 in.)
10 mm (0.5 in.)
Pull Pull off Test off Test Pull Pull-off Test off Test B
d l di f
Bond metal disc to surface Drill partial core Apply tensile force Fu F
Fu fpo =
Fu A
Schematic of Apparatus Schematic of Apparatus pp pp ASTM C1583 ASTM C1583 Tensile loading device Steel disc Swivel joint Diameter: D Thickness: 0.5 D j
Pull Pull off Test Apparatus off Test Apparatus Pull Pull-off Test Apparatus off Test Apparatus Proceq Germann Instruments
Pull Pull off Test Failure Locations off Test Failure Locations Pull Pull-off Test Failure Locations off Test Failure Locations Interfacial bond failure (bond strength)
Pull Pull off Test Failure Locations off Test Failure Locations Pull Pull-off Test Failure Locations off Test Failure Locations Cohesive failure in the existing concrete (substrate strength)
Pull Pull off Test Failure Locations off Test Failure Locations Pull Pull-off Test Failure Locations off Test Failure Locations Cohesive failure in the repair material
- Can not predict failure location
- Can not predict failure location
- Average the results for same failure locations
Pull Pull off Test Failure Locations off Test Failure Locations Pull Pull-off Test Failure Locations off Test Failure Locations Bond failure at the adhesive Inconclusive testbond strength is at least failure stress
Evaluation of Surface Evaluation of Surface Preparation Methods Preparation Methods Surfaces to receive overlay or repair material are usually prepared to ensure good bonding Some repair methods can damage concrete and reduce the apparent bond strength
Evaluation of Surface Evaluation of Surface Preparation Methods Preparation Methods Test substrate before applying overlay ACI 503R (Use of Epoxy Compounds with Concrete) recommends substrate pull-off strength > 175 psi (1.2 MPa)
Stretch Break Stretch Break Stretch Break Stretch Break
Flaw Detection Flaw Detection Flaw Detection Flaw Detection Voids (e.g., in tendon ducts)
Honeycombing (poor consolidation)
Delaminations Thickness of members Corrosion of reinforcement
Stress Stress Wave Methods Wave Methods Stress Stress-Wave Methods Wave Methods A stress wave (sound) is easy to generate Mechanical impact Transducers Travel speed affected by elastic constants and density of concrete Stress wave traveling through a solid (such as concrete) is reflected at an air interface Monitoring the arrival of reflected stress wave allows us to look into concrete D f Defects Thickness
Outline Outline Outline Outline Basic principles of stress wave propagation Wave types Reflection Ultrasonic pulse velocity Sounding (chain drag)
Impact-echo method Impulse-response Ultrasonic-echo method
Stress Waves due to Impact Stress Waves due to Impact Stress Waves due to Impact Stress Waves due to Impact R-wave Impact 65 %
S 25 %
S-wave P wave 10 %
P-wave
Wave Modes Wave Modes Wave Modes Wave Modes P-waveassociated with normal stress S-waveassociated with shear stress R-wavecombination of normal stress and shear stress WebFiles\\wavemotion.html www.kettering.edu/~drussell/Demos/waves/wavemotion.html
Summary of Wave Modes Summary of Wave Modes Summary of Wave Modes Summary of Wave Modes Particle Motion Wave Speed P-Wave (1
)
(1
)(1 2 )
P E
C
=
(1
)(1 2 )
P
+
G S-Wave S
G C
=
R-Wave 0.87 1.2 1
R S
C C
+
=
+
Wave Propagation Direction 1
+
Relative Wave Speeds Relative Wave Speeds Relative Wave Speeds Relative Wave Speeds
( = 0 2)
P-Wave C
= 1
( = 0.2)
P Wave Cp
= 1 S Wave C
= 0 62 C S-Wave Cs
= 0.62 Cp R-Wave CR
= 0.56 Cp
Reflection and Refraction Reflection and Refraction Reflection and Refraction Reflection and Refraction appliedgeophysics.berkeley.edu:7057/seismic/seismic_21.pdf
P--wave Reflection wave Reflection Coefficients (R)
Coefficients (R)
Interface R
Concrete-Air Concrete-Water
-1.00
-0.71 Concrete-Steel 0.68 A negative value indicates that the stress changes sign when reflected: e.g., a compressive stress wave is reflected as a tensile stress wave.
Outline Outline Outline Outline Basic principles Wave types Reflection Ultrasonic pulse velocity Sounding (chain drag)
Impact-echo method p
Impulse-response method Ultrasonic-echo method U
aso c ec o e
od
ASTM D4580 Practice ASTM D4580 Practice for Measuring Delaminations for Measuring Delaminations High Frequency Ringing Low Frequency Rattle Ringing Rattle
Sounding Methods Sounding Methods g
Chain drag Automated Rotary percussion Automated chain drag www.acoustics.org/press/146th/Costley.htm www.soundingtech.com
Limitations Limitations Limitations Limitations D t ti i diffi lt h
Detection is difficult when:
Deep Defect O
l Overlay Results are operator-dependent and may be affected by ambient noise
Impact Methods Impact Methods Impact Methods Impact Methods Impact-echo method Depth of reflecting interface Impulse-response method Comparative indication of mobility Spectral analysis of surface waves Elastic constants of layered system
Impact Impact--Echo Method Echo Method p
Displacement e
Time Force Time Signal Analysis Amplitude Di l
t Contact time Time A
Frequency fTfT Displacement transducer d
Flaw Flaw
Field Testing System Field Testing System Impactor
Multiple Reflections of P Multiple Reflections of P--wave wave p
in a Plate in a Plate Compression wave T
i Tension wave
Multiple Reflections of P Multiple Reflections of P--wave wave p
in a Plate in a Plate Reflection from bottom Compression wave T
i Tension wave
Multiple Reflections of P Multiple Reflections of P--wave wave p
in a Plate in a Plate First arrival Compression wave T
i Tension wave
Multiple Reflections of P Multiple Reflections of P--wave wave p
in a Plate in a Plate Reflection from top and back to bottom p
Compression wave T
i Tension wave
Multiple Reflections of P Multiple Reflections of P--wave wave p
in a Plate in a Plate 2nd reflection from bottom Compression wave T
i Tension wave
Multiple Reflections of P Multiple Reflections of P--wave wave Reflected wave arrives at top surface in a periodic p
in a Plate in a Plate 2nd arrival at top Reflected wave arrives at top surface in a periodic fashion p
Compression wave T
i Tension wave
Surface Displacement Surface Displacement p
Waveform Waveform ent 1st 2nd 3rd 4th aceme P
Displa P-wave Periodic waveform R-wave Time
Frequency Analysis Frequency Analysis Frequency Analysis Frequency Analysis V
t T
T 2
1 C
Time p
C T
t 2
=
t f
= 1 f
C T
p 2
=
How do we determine f ?
Amplitude Spectrum Amplitude Spectrum Amplitude Spectrum Amplitude Spectrum By signal processing (FFT), waveform is converted into frequency domain to obtain lit d t
amplitude spectrum Amplitude spectrum represents the amplitudes of the frequency components in amplitudes of the frequency components in the signal For a plate the thickness frequency is the For a plate, the thickness frequency is the predominant peak in the spectrum
Examples Examples Solid Slab Void in Slab Examples Examples 0.5 m 0.25 m 3.42 kHz 0 8 1.0 1.2 de 7.32 kHz 0 8 1.0 1.2 de 0.4 0.6 0.8 mplitud 0.4 0.6 0.8 Amplitud 30 25 20 15 10 5
0 0.0 0.2 Am 30 25 20 15 10 5
0 0.0 0.2 A
30 25 20 15 10 5
0 Frequency (kHz) 30 25 20 15 10 5
0 Frequency (kHz)
Applications Applications Applications Applications Voids or honeycombing Delaminations (at reinforcement, h l /
i f
l i )
asphalt/concrete interface, overlay, repair)
Voids in grouted tendon ducts Bond quality -porosity at interface Thickness of plate-like structures (ASTM C1383)
ASTM C1383 ASTM C1383 ASTM C1383 ASTM C1383 Procedure A:
Procedure A:
Determine wave speed Procedure B:
Thickness frequency
Procedure A: Determine C Procedure A: Determine C Procedure A: Determine C Procedure A: Determine Cp Perform impact-echo test and measure thickness at corresponding point Surface measurement of P-wave: Cp s
Travel time between two transducers
Hole Drilling Method Hole Drilling Method Hole Drilling Method Hole Drilling Method mplitude Am Frequency fT T
2 C
f T q
y fT 2
p T
C f T
=
Surface Measurement of Surface Measurement of P--Wave Speed Wave Speed Impact L
Impact
Surface Measurement of Surface Measurement of P Wave Speed Wave Speed P-Wave Speed Wave Speed L
appliedgeophysics.berkeley.edu:7057/seismic/seismic_21.pdf
Surface Measurement Surface Measurement Surface Measurement Surface Measurement DA and Analysis System 300 mm 150 +/-10 mm Impact Transducer 1 Transducer 2 Spacer device Impact Transducer 1 Transducer 2
Impactor
Procedure B: Thickness Procedure B: Thickness Frequency Frequency 0.96 s
p C
T DA and Analysis System Amplitude 2
p T
T f
=
I
< 0.4 T A
Frequency fTfT Impact Transducer T
P-wave P-wave T
Impact Impact Echo Limitations Echo Limitations Impact Impact-Echo Limitations Echo Limitations Complexity Point-to-point testing Takes time to evaluate test surface Closely spaced testing required for visualization methods New multi-sensor system based on ultrasonic-echo technique overcomes f th li it ti some of these limitations
Impulse Impulse Response Method Response Method Impulse Impulse-Response Method Response Method Originated as method to test deep foundations Requires measurement of impact force Signal processing examines the impact response per unit of applied force as a function of frequency Lower frequency than impact-echo
Impulse Impulse-Response for Shafts Response for Shafts Impulse Impulse Response for Shafts Response for Shafts Computer p
v(t) f(t) f(t)
Response
function H()
Frequency
Impulse Impulse--Response Test Response Test System System System System
Transfer Functions Transfer Functions Transfer Functions Transfer Functions Measured
Response
Transfer Function Units l
/
Displacement Dynamic Compliance L/F Velocity Mobility (L/s)/F Velocity Mobility (L/s)/F Acceleration Accelerance (L/s2)/F
Idealized Mobility Plot of Idealized Mobility Plot of y
Pile Pile Mobility L
f f
(m/s)/N L
1 p
M C A
=
1 C
p
1 Stiffness 2
p C
L f
=
Frequency (Hz)
Application to Plates Application to Plates Application to Plates Application to Plates Impulse-response testing has its origin in the testing of drilled shafts and piles Recent work has demonstrated that it can also be used successfully to assess plate-l k like structures Comparative test to assess differences in t i t f response to impact force Locate anomalous regions
Hammer and Geophone Position Hammer and Geophone Position Geophone Rubber-tipped hammer
Impulse Impulse-Response Testing of Response Testing of Impulse Impulse Response Testing of Response Testing of Plate Plate--like Structures like Structures Permits rapid screening of suspect structures Various features of mobility plot are used as indicators of conditions Dynamic stiffness (initial slope 0 to 50 Hz) bili (100 800
)
Average mobility (100 to 800 Hz)
Slope of mobility vs. frequency Ratio of low frequency peak mobility to mean Ratio of low frequency peak mobility to mean mobility ASTM Standard under development p
Example of I Example of I--R Test of Slab R Test of Slab p
D i
Dynamic Stiffness AAverage Mobility
Average Mobility of Slab Average Mobility of Slab Average Mobility of Slab Average Mobility of Slab I-R test causes flexural vibration of slab within vicinity of impact A
bili i
ff d b Average mobility is affected by Quality of the concrete (Cp)
P f i t l
id Presence of internal voids Plate thickness S
t diti Support conditions
Void Below Slab Void Below Slab Void Below Slab Void Below Slab v(t) f(t)
Void Below Slab Void Below Slab Void Below Slab Void Below Slab L
f fl l ib i
Low frequency flexural vibration
Void Below Slab:
Void Below Slab:
High Peak at Low Frequency High Peak at Low Frequency V id b th l b Void beneath slab Supported Slab
Mobility Slope Mobility Slope Mobility Slope Mobility Slope Slope of best-fit line to mobility spectrum between 100 and 800 Hz A high mobility slope has been found to be indicative of poorly consolidated concrete
Mobility Slope Mobility Slope Mobility Slope Mobility Slope 1 10
-5 1 10
-5 8 10-6 1 10
)/N 8 10-6 1 10
)/N Hi h bilit l
4 10
-6 6 10
-6 ity, (m/s) 4 10
-6 6 10
-6 ity, (m/s)
High mobility slope 2 10-6 Mobil 2 10-6 Mobil Normal mobility slope 0
0 100 200 300 400 500 600 700 800 Frequency, Hz 0
0 100 200 300 400 500 600 700 800 Frequency, Hz Normal mobility slope
Applications Applications Applications Applications D t ti id b th l b d
Detecting voids beneath slabs-on-ground Detecting delaminations and honeycombing Detecting slab c rling Detecting slab curling Evaluation of anchorage of exterior wall panels panels Location of areas of distributed cracking (F-T, ASR)
Evaluation of load transfer at construction joints
Example Example Example Example Contour plot of average mobility Contour plot of average mobility
Ultrasonic Echo Methods Ultrasonic Echo Methods Ultrasonic Echo Methods Ultrasonic Echo Methods Pulse Echo Pitch Catch Pulse-Echo Pitch-Catch t
V t
V V
V Time Time 2
t T
C
=
T
Ultrasonic Ultrasonic Echo Methods Echo Methods Ultrasonic Ultrasonic-Echo Methods Echo Methods Limited success before the 1990s Developments since the 1990s Low frequency (50 to 100 kHz), broadband, dry coupled, point transducers Compressional and shear waves Compressional and shear waves Availability of computing power Use of transducer arrays Use of transducer arrays Digital signal processing Visualization methods
Pulse Shapes Pulse Shapes Pulse Shapes Pulse Shapes Lightly damped or narrow Lightly damped or narrow band transducer (UPV)
Impact (I-E) p
(
)
Damped or broadband transducer (U-E)
Shear Shear Wave Phased Arrays Wave Phased Arrays Shear Shear-Wave Phased Arrays Wave Phased Arrays EyeCon 4
6 4 x 6 MIRA 4 x 10
MIRA MIRA MIRA MIRA
Transducer Array System Transducer Array System Transducer Array System Transducer Array System Multiple pitch-catch tests
Transducer Array System Transducer Array System Transducer Array System Transducer Array System Transducers function as transmitters and receivers; results in multiple ray paths
Detection Range Detection Range Detection Range Detection Range Detection Range Detection Range Aperture
Depth Correction Depth Correction Depth Correction Depth Correction Depth of reflector based on measured travel time 1
2 3
4 5
2X Depth of reflector based on measured travel time d
2 d
2 2
2 X
t C
d
=
2
C = wave speed C = wave speed t = total travel time
Transducer Array System Transducer Array System Transducer Array System Transducer Array System Presence of large reflecting interface results in g
g detection by multiple sensors
MIRA Antenna MIRA Antenna MIRA Antenna MIRA Antenna 4 x 10 transducer arrayy 45 x 4 = 180 ray paths per scan Scan time = 0.35 s PZT Elements
Scanning Scanning Scanning Scanning
2--D Scan D Scan X
Y Z
Synthetic Aperture Focusing Synthetic Aperture Focusing y
p g
y p
g Technique (SAFT)
Technique (SAFT)
Times of flight obtained from 2-D scan with transducer array are used to reconstruct transducer array are used to reconstruct location of reflecting interfaces The result is a 3-D image of the internal The result is a 3 D image of the internal reflectors View in three image planes g p
Image Planes Image Planes g
X Y
Z
13 mm hole 55 mm deep Example Example 30 h l 0.8 m x 0.4 m x 0.4 m Cs= 2385 m/s 55 mm deep 13 h l p
30 mm hole 130 mm deep Cs 2385 m/s 13 mm hole 160 mm deep 55 mm B-Scan X
130 mm 160 mm Z
Higher sensitivity 400 mm g
y
Grouted Tendon Duct Grouted Tendon Duct Duct diameter: 60 mm Cover depth: 80 mm Slab thickness: 300 mm Slab thickness: 300 mm
D Scan Elevation Scan Elevation D-Scan Elevation Scan Elevation Voids in duct Fully grouted duct Backwall reflection Fully grouted duct
Stress Stress Wave Methods Wave Methods Stress Stress-Wave Methods Wave Methods Ultrasonic pulse velocity Sounding (chain drag)
Impact-echo method Impulse-response method p
p Ultrasonic-echo method
Assessment of Reinforcement Assessment of Reinforcement Assessment of Reinforcement Assessment of Reinforcement Location and size Location and size Covermeters Radar (location)
Radar (location)
Corrosion condition Half-cell potential (likelihood of corrosion)
Half cell potential (likelihood of corrosion)
Polarization resistance (corrosion rate)
Concrete resistivity Concrete resistivity Depth of carbonation Chloride ion concentration
Reinforcement Corrosion Reinforcement Corrosion Reinforcement Corrosion Reinforcement Corrosion Anodic and cathodic sites exist on bar Iron goes into solution at active sites (anode)
Electrons travel through bar and iron ions travel through concrete Rust forms rust at cathode Anodic Reaction:
2 2
Fe Fe e
+
+
H20 O2 Rust Rust Fe Fe2+
2+
Cathodic Reaction:
2 Fe Fe e
+
Anode Cathode e-2 2
2 4
2
(
)
Fe H O O
e Fe OH
+
+
+
+
2 2
2 2
2 4
2
(
)
Fe H O O
e Fe OH
+
+
+
Half Half-Cell Potential Method Cell Potential Method Half Half Cell Potential Method Cell Potential Method ASTM C876 ASTM C876 When bar is corroding, charge flow through concrete is associated with an electrical field Measure the electrical potential (voltage) of Measure the electrical potential (voltage) of the field at the concrete surface Magnitude of the measured voltage, relative Magnitude of the measured voltage, relative to a standard half-cell, is indicative of corrosion activity Higher voltage indicates higher likelihood of active corrosion
Potential Field Potential Field Potential Field Potential Field Potential contours
-400
-300
-300
-200
-200 Current Current
-500 Elsner and Bohni, ASTM STP 1065, 1990
Half Half--Cell Potential Method Cell Potential Method ASTM C876 ASTM C876 Cu/CuSO half cell
-0.28 Cu/CuSO4 half cell Voltmeter CuSO4 solution
+
Copper rod Porous plug Sponge Open-circuit potential
Example Example Example Example Proceq Proceq SA SA
Half Half--Cell Potential Cell Potential Contour Plot Contour Plot J. Woodhouse, Quantifying the Invisible, Concrete Repair Bulletin, July/August 1996
Considerations Considerations Considerations Considerations Concrete must be sufficiently moist ASTM C876 provides criterion Provides only indication of likelihood of active corrosion M
iti th 200 V
i lik l More positive than -200 mV: corrosion unlikely More negative than -350 mV: corrosion likely 200 t 350 V ???????
-200 to -350 mV: ???????
Other factors have to be considered (see ASTM C876)
C876)
Polarization Resistance Polarization Resistance Polarization Resistance Polarization Resistance Half-cell potential provides information on likelihood that corrosion is occurring Polarization resistance provides indication of corrosion current (or corrosion rate)
At the time of testing Rate affected by in-place conditions
(
i t t
t
)
(moisture, oxygen, temperature)
Polarization Polarization Polarization Polarization Change from the open-circuit potential as a result of passage of current A bar that is actively corroding will have small change in potential when l
l d h b external current is applied to the bar
Polarization Resistance Polarization Resistance Apparatus Apparatus W
ki l
t d
th i f i
b Working electrode - the reinforcing bar Counter electrode - provides current flow to bar R f l
d h
i Reference electrode - measure change in potential P l i
ti t
Polarization system Current supply V lt t
Voltmeter Ammeter Hardware and software to acquire and analyze Hardware and software to acquire and analyze data
Polarization Resistance Polarization Resistance 3LP 3LP 3LP 3LP
- Measure open circuit potential, Eo p
p o
Voltmeter Eo Switch D.C.
Reference cell Ammeter Switch Reference cell Counter electrode Working electrode Working electrode
- Close switch and apply small current, Ip M
h i
lt
- Measure change in voltage
- Increase current, and repeat measurement
- Di id t b f b th t i l
i d i
- Divide current by area of bar that is polarized, ip
- Plot voltage vs. current density Eo + E Ip
Polarization Resistance Polarization Resistance R Polarization Resistance, Polarization Resistance, Rp Voltage Rp = E E
g p
ip ip Current/(Area of Bar), ip, (µA/cm2)
Corrosion Rate Corrosion Rate Corrosion Rate Corrosion Rate Stern-Geary corrosion rate relationship:
i
=
B
(µA/cm2)
B = 25 to 50 mV icorr Rp
(µA/cm )
(active less active)
Faraday law can be sued to convert icorr to uniform metal loss:
1 µA/cm2 = 0.012 mm/y
Guard Electrode Guard Electrode Guard Electrode Guard Electrode Current density is based on area of bar that is Current density is based on area of bar that is polarized by applied current Area of steel that is polarized is not well Area of steel that is polarized is not well known in 3LP method Use of outer (guard) electrode confines Use of outer (guard) electrode confines current to portion of bar below guard ring Results in more accurate measure of current density
Guard Guard--Electrode Method Electrode Method Confines current so that polarized area of bar is well defined Voltmeter V lt Ip Voltage Follower Guard Electrode Ammeter
Example of Guard Example of Guard-Electrode Electrode Example of Guard Example of Guard Electrode Electrode G
d El t
d Guard Electrode Counter Electrode Resistivity Probe Computer James Instruments
Static vs Pulse Methods Static vs Pulse Methods Static vs. Pulse Methods Static vs. Pulse Methods The polarization resistance technique that has been discussed is time consuming; 3 to 5 min at each point at each point Voltage (or current) is increased in several steps steps Equilibrium conditions need to be established at each step Pulsed methods allow faster measurement
Galvanic Pulse Method Galvanic Pulse Method Galvanic Pulse Method Galvanic Pulse Method Apply constant current pulse ( 10 s)
Apply constant current pulse ( 10 s)
Guard electrode is used Monitor potential change of working Monitor potential change of working electrode (bar)
From recorded voltage history evaluate From recorded voltage history, evaluate polarization resistance, Rp, by regression analysis y
Assumes Randles equivalent circuit to represent corrosion activity
Randles Randles Equivalent Circuit Equivalent Circuit Randles Randles Equivalent Circuit Equivalent Circuit Computer Ip R
Rp Cdl E
Voltage Voltage-Time Curve Time Curve 300 Voltage Voltage Time Curve Time Curve 200 V
E = IpRP 100 age, mV IpR 3
1 2
t C
V C
C e
=
-100 0
Volta p
-200 100 0
1 2
3 4
5 6
7 Time, s
Instrumentation Instrumentation Instrumentation Instrumentation Several commercial instruments are based on the pulsed method GalvaPulse RapidCor Do not give the same readings, but will give same relative order of corrosion activity
GalvaPulse GalvaPulse GalvaPulse GalvaPulse Based on galvanic-pulse method Based on galvanic-pulse method Integrates into one unit:
Half cell potential Half-cell potential Resistance (not resistivity)
Polarization resistance Polarization resistance Software for data analysis and 3-D displays
GalvaPulse GalvaPulse Computer Computer Sensor Sensor
icorr = 0.43 A/cm2 corr
or 0.005 mm/year
33 i
15 9 A/
2 icorr = 15.9 A/cm2 or 0.2 mm/year
RapiCor RapiCor RapiCor RapiCor G l i
l th d Galvanic pulse method Rectangular probe with guard electrode M d l l
i i
b d
Modulates polarization current based on corrosion activity Higher current needed for higher corrosion Higher current needed for higher corrosion rate Calculates concrete resistivity Calculates concrete resistivity Requires knowing cover thickness
RapiCor RapiCor Counter electrode Reference electrode Ag/AgCl Guard electrode
Cover:
Bar size:
Thi k l
Thickness loss:
Half-cell potential:
Resistivity:
Summary Summary Summary Summary I t d
ti t t l f i
l l
ti Introduction to tools for in-place evaluation of concrete and steel reinforcement Uniformity Uniformity Strength Internal defects Internal defects Corrosion assessment Principles of methods have been stressed Principles of methods have been stressed Not a training course on proper use of instruments instruments
Tests for Uniformity Tests for Uniformity Tests for Uniformity Tests for Uniformity Locate anomalous areas for closer examination Locate anomalous areas for closer examination Rebound hammer Indicator of surface condition Indicator of surface condition Affected by texture, moisture content, carbonation carbonation Pulse velocity Overall condition of concrete between Overall condition of concrete between transducers Does not provide depth information
InIn Place Strength Place Strength InIn-Place Strength Place Strength St th f d ill d i
f th d Strength of drilled cores is reference method Pullout test S
l i t ith t
i d
Sample more points without excessive damage Good correlation with compressive strength E al ates o ter 25 mm Evaluates outer 25 mm Pull-off test E
l t
b t t
ti b f i
Evaluate substrate preparation before repair Evaluate bond strength of repair Failure location depends on weakest link Failure location depends on weakest link
Internal Defects Internal Defects Internal Defects Internal Defects Stress wave methods are inherently powerful Stress wave methods are inherently powerful because of complete reflection at air interface Impact-echo method Impact echo method Point method; simple data processing Impulse-response method Impulse response method Measures flexural response; comparative Ultrasonic-echo Ultrasonic echo Computer intensive; rapid; 3-D imaging
Corrosion Assessment Corrosion Assessment Corrosion Assessment Corrosion Assessment H lf ll t
ti l Half-cell potential Likelihood of active corrosion P l i
ti i t Polarization resistance Indicator of corrosion rate at time of testing testing Assumptions made to arrive at corrosion current density
Training Training Training Training Different levels of expertise are required Rebound hammer impact-echo Training is essential for proper use of these methods No national programs Manufacturers and on the job Flaw detection methods require experience for proper interpretation Verification with invasive probing Corrosion assessment requires a corrosion expert