ML12157A308
| ML12157A308 | |
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| Issue date: | 06/05/2012 |
| From: | Office of the Chief Human Capital Officer |
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| Download: ML12157A308 (176) | |
Text
Concrette Tech C hnolog gy and Codes s
In--Place Evaluation In Methods M h d
Evaluation of Concrete Visible features Cracking, deterioration, deflections In-place p strength g
Internal conditions Corrosion of reinforcement Voids Honeycombing Voids in tendon ducts Delaminations Member thickness
Tools Visual inspection Removal of samples Core compressive strength Petrographic analysis Tests for in-place p uniformityy In-place strength methods Stress-wave methods Ground penetrating radar Corrosion evaluation methods
References ACI 349.3R ACI 364.1R Outline Tests for uniformity Tests for in-place strength Methods to locate internal defects Evaluation of corrosion
Tests for Uniformity Determine which portions of structure are similar Identify areas for further investigation by other means Methods Rebound number (hammer)ASTM C805 Ultrasonic p pulse velocityASTM y C597
Rebound Number ((Hammer))
ASTM C805 Measure the rebound of spring-driven mass (hammer) after impact with rod in contact with concrete.
Lock/release button Push down Rod
Rebound Hammer Operation Push Body Body Hammer Rebound Latch Released Slider Hammer S i Spring Rodd
Slider Rebound number = 41
Near--surface Effects Near Result = average of 10 readings Discard reading > 6 units from average Aggregate Air void Rough Dry or Carbonation
Factors Affectingg Rebound Number Strength and elastic modulus of near surface concrete Layer of carbonation Surface texture Surface moisture condition
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 p
7000 6000 Core S Strength h, psi 5000 4000 3000 Core Strength, psi Upper 95 % CL Lower 95 % CL 2000 1000 25 30 35 40 Rebound Number Ward, M.A. and Langan, B.W., Cement Concrete and Aggregates, 16(2), Dec. 1994, 181-185
Ultrasonic Pulse Velocityy ASTM C597 Measure travel time of ultrasonic pulse (compressional stress wave) over known path length.
Stress Wave A disturbance that transfers energy gy progressively p g y from point to point in a medium WebFiles\waves-intro.html Speed of compression stress wave in concrete:
E C p 1.05 For good concrete: Cp 4000 m/s http://www.kettering.edu/~drussell/Demos/waves-intro/waves-intro.html
UPV UPV Principle of Operation Couplant Transmitter Pulser L
L Cp =
t Timer Ti t Couplant Receiver
Example Pulser/Timer Transmitter Display R
Receiveri t
Threshold level Transmitter Receiver Courtesy of CNS Farnell
Measurement Paths Direct path Semi-direct path p
Courtesy of James Instruments Inc.
Effects of Internal T R Solid Defects Presence of "defects" Honeycomb increases travel time, and results in lower computed speed.
Crack L
Assessment of Uniformity Draw grid on the surface of test object Perform tests at grid points 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 Draw grid on the surface of test object Perform tests at grid points Test at same points to assess age related deterioration Plot UPV contours 3900 3800 4000 4010
Depth p of Surface Damage g UPV Method can be used to estimate depth of damaged concrete (such as by fire)
Requires distinct boundary between sound and damaged g concrete Multiple travel time measurements along surface T R R R R d=? Cd< Cs Damaged concrete Cd Sound concrete Cs
Depth of Surface Damage There are two ray paths Path 1: through damage concrete Path 2: through damaged concrete and sound concrete For certain separation, Xo, transit times are equal X
Transmitter Receiver d=? Path 1 Path 2
Determination of d 1
Transit Xo Time Cs Xo C s Cd d=
1 2 C s + Cd Cd Distance, X Chung and Law, Cement Concrete and Aggregates , 7(2), 1985, 84-88
Tests of Uniformity R b Rebound d number b
Fast and simple to use Assesses surface condition Pulse velocity Relatively R l ti l simple i l tto use Assess concrete between transducers Advanced application applicationdepth depth of surface damage (fire)
In--Place Strength In 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 reinforcingg steel in core Post-installed pullout test (CAPO)
Estimate compressive p strength g based on correlation Pull-off test Direct tensile strength
Pullout Test ASTM C900 Measure force to pullout an insert anchored h d iin 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)
CIP--Pullout Test CIP 25 mm Insert Insert 25 mm Formwork
CIP--Pullout Test CIP Insert Pullout Reaction Force Ring
CIP--Pullout Test CIP Insert Pullout Reaction Force Ring
Pullout Test Test--LOK Test Conical Fragment g
Pull Machine
Results of 16 Correlations Manufacturers Curve
Post--Installed Tests Post Does not require pre-planning test locations Can perform test at any accessible location Permits testing of existing structures
Post--Installed Pullout Test Post CAPO Test
Prepare Concrete Grind surface Drill hole 25 mm 18 mm C t slot Cut 25 mm
Drill Hole Surface Planing
Cut Slot Cut Slot Cut Slot Insert Expansion p Cone and Coiled Ring Coiled ring Cone
Ring Expansion Hardware Nut Coiled ring Cone
Expand Ring Nut
Expand Ring
Pullout the Expanded Ring Apply pp y Pullout Force
CAPO--Test vs LOK CAPO LOK--Test 70 60 Line of Equality CAPO--Test, kN 50 40 30 20 10 0
0 10 20 30 40 50 60 70 LOK -Test, kN
Pull-off Test Pull-ASTM C1583 Measure force required to pull off a metal di b disc bonded d d to concrete surface.
f
Pull--off Test Pull 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--off Test Pull Bond B d metal t l di disc tto surface f
Drill partial core A l tensile Apply il fforce Overlay 50 or 75 mm (2 or 3 in.)
10 mm (0.5 in.)
Pull--off Test Pull Bond B d metall di disc to surface f
Drill partial core Apply tensile force Fu Fu fpo =
A
Schematic of Apparatus pp ASTM C1583 Tensile loading device Swivel jjoint Steel disc Diameter: D Thickness: 0.5 D
Pull--off Test Apparatus Pull Proceq Germann Instruments
Pull--off Test Failure Locations Pull Interfacial bond failure (bond strength)
Pull--off Test Failure Locations Pull Cohesive failure in the existing concrete (substrate strength)
Pull--off Test Failure Locations Pull Cohesive failure in the repair material
- Can not predict failure location
- Average the results for same failure locations
Pull--off Test Failure Locations Pull Bond failure at the adhesive Inconclusive testbond strength is at least failure stress
Evaluation of Surface 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 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 Flaw Detection Voids (e.g., in tendon ducts)
Honeycombing (poor consolidation)
Delaminations Thickness of members Corrosion of reinforcement
Stress--Wave Methods Stress 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 Defects D f Thickness
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 Impact 65 %
R-wave 25 %
S S-wave 10 %
P wave P-wave
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 Particle Motion Wave Speed E (1 )
P-Wave CP =
(1 + )(1 2 )
G S-Wave CS =
0.87 + 1.2 R-Wave C R = CS 1 +
Wave Propagation Direction
Relative Wave Speeds
( = 0 0.2) 2)
P-Wave P Wave Cp = 1 S Wave S-Wave Cs = 0.62 0 62 Cp R-Wave CR = 0.56 Cp
Reflection and Refraction appliedgeophysics.berkeley.edu:7057/seismic/seismic_21.pdf
P-wave Reflection Coefficients (R)
Interface R Concrete-Air -1.00 Concrete-Water -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 Basic principles Wave types Reflection Ultrasonic pulse velocity Sounding (chain drag)
Impact-echo p method Impulse-response method Ultrasonic-echo U aso c ec o method e od
ASTM D4580 Practice for Measuring Delaminations High Frequency Low Frequency Ringing Rattle
Soundingg Methods Chain drag Rotary percussion Automated chain drag www.soundingtech.com www.acoustics.org/press/146th/Costley.htm
Limitations Detection D t ti isi diffi difficult lt when:
h Deep Defect O
Overlay l
Results are operator-dependent and may be affected by ambient noise
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 p -Echo Method Displacement Force e
Time Time A
Amplitude Contact time Signal Analysis Displacement Di l t transducer fT Frequency d
Flaw
Field Testing System Impactor
Multiple p Reflections of P- P-wave in a Plate Compression wave T i wave Tension
Multiple p Reflections of P- P-wave in a Plate Reflection from bottom Compression wave T i wave Tension
Multiple p Reflections of P- P-wave in a Plate First arrival Compression wave T i wave Tension
Multiple p Reflections of P- P-wave in a Plate Reflection from topp and back to bottom Compression wave T i wave Tension
Multiple p Reflections of P- P-wave in a Plate 2nd reflection from bottom Compression wave T i wave Tension
Multiple p Reflections of P- P-wave in a Plate Reflected wave arrives at top surface in a periodic fashion 2nd arrival at top p Compression wave T i wave Tension
Surface Displacement p
Waveform 1st 2nd 3rd 4th Displa aceme ent P-wave P
Periodic waveform R-wave Time
Frequency Analysis t
V T
Time 2T 1 Cp t = f = T=
Cp t 2f How do we determine f ?
Amplitude Spectrum By signal processing (FFT), waveform is converted into frequency domain to obtain amplitude lit d spectrum t
Amplitude spectrum represents the amplitudes of the frequency components in the signal For a plate plate, the thickness frequency is the predominant peak in the spectrum
Examples Solid Slab Void in Slab 0.25 m 0.5 m 1.2 1.2 1.0 3.42 kHz 1.0 7.32 kHz Am mplitud de Amplitud A de 08 0.8 08 0.8 0.6 0.6 0.4 0.4 0.2 0.2 0.0 0.0 0 5 10 15 20 25 30 0 5 10 15 20 25 30 Frequency (kHz) Frequency (kHz)
Applications Voids or honeycombing Delaminations (at reinforcement, asphalt/concrete h l/ iinterface, f overlay, l repair) i)
Voids in grouted tendon ducts Bond quality -porosity at interface Thickness of plate-like structures (ASTM C1383)
ASTM C1383 Procedure A:
Determine wave speed Procedure B:
Thickness frequency
Procedure A: Determine Cp Perform impact-echo test and measure thickness at corresponding point Surface measurement of P-wave: Cps Travel time between two transducers
Hole Drilling Method Am mplitude T
fT Frequency q y C p = 2 fT T
Surface Measurement of P-Wave Speed L
Impact
Surface Measurement of P-Wave L Speed appliedgeophysics.berkeley.edu:7057/seismic/seismic_21.pdf
Surface Measurement DA and Analysis System 300 mm 150 +/-10 mm Spacer device Impact Transducer 1 Transducer 2
Impactor Procedure B: Thickness Frequency A
Amplitude DA and Analysis s
0.96 C p System T=
2 fT < 0.4 T fT Frequency I
Impact Transducer T P-wave P-wave
Impact--Echo Limitations Impact 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 some off these th limitations li it ti
Impulse--Response Method Impulse 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--Response for Shafts Impulse Computer p
v(t) f(t)
Response H()
function Frequency
Impulse-Response Test Impulse-System
Transfer Functions Measured Transfer Function Units
Response
Displacement l Dynamic L/F
/
Compliance Velocity Mobility (L/s)/F Acceleration Accelerance (L/s2)/F
Idealized Mobilityy Plot of Pile f f Mobility L (m/s)/N 1
M=
1 Cp A Cp L=
Stiffness 2 f Frequency (Hz)
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 structures like Comparative test to assess differences in response to t impact i t fforce Locate anomalous regions
Hammer and Geophone Position Geophone Rubber-tipped hammer
Impulse--Response Testing of Impulse Plate--like Structures Plate 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)
Average mobility bili (100 to 800 Hz))
Slope of mobility vs. frequency Ratio of low frequency peak mobility to mean mobility ASTM Standard under development p
Example p of I-I-R Test of Slab Dynamic D i Stiffness Average Mobility
Average Mobility of Slab I-R test causes flexural vibration of slab within vicinity of impact A
Average mobility bili iis affected ff db by Quality of the concrete (Cp)
Presence P off internal i t l voids id Plate thickness Support S t conditions diti
Void Below Slab v(t) f(t)
Void Below Slab L
Low ffrequency flexural fl l vibration ib i
Void Below Slab:
High Peak at Low Frequency V id beneath Void b th slab l b Supported Slab
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
-5 1 10
-6 8 10 Mobility, (m/s))/N
-6 Hi h mobility High bilit slope l
6 10
-6 4 10
-6 2 10 Normal Normal mobility slope 0
0 100 200 300 400 500 600 700 800 Frequency, Hz
Applications Detecting D t ti voidsid b beneathth slabs-on-ground l b d Detecting delaminations and honeycombing Detecting slab curling c rling Evaluation of anchorage of exterior wall panels Location of areas of distributed cracking (F-T, ASR)
Evaluation of load transfer at construction joints
Example Contour plot of average mobility
Ultrasonic Echo Methods Pulse Echo Pulse-Echo Pitch Catch Pitch-Catch t t V V Time t Time T =C 2
T
Ultrasonic--Echo Methods Ultrasonic Limited success before the 1990s Developments since the 1990s Low frequency (50 to 100 kHz), broadband, dry coupled, point transducers Compressional and shear waves Availability of computing power Use of transducer arrays Digital signal processing Visualization methods
Pulse Shapes Lightly damped or narrow band transducer (UPV)
Impact p ((I-E))
Damped or broadband transducer (U-E)
Shear--Wave Phased Arrays Shear EyeCon 4x6 MIRA 4 x 10
MIRA Transducer Array System Multiple pitch-catch tests
Transducer Array System Transducers function as transmitters and receivers; results in multiple ray paths
Detection Range Detection Range Aperture
Depth Correction Depth of reflector based on measured travel time 1 2 3 4 5 2X d 2 t
d = C X 2 2
C = wave speed t = total travel time
Transducer Array System Presence of large g reflectingg interface results in detection by multiple sensors
MIRA Antenna 4 x 10 transducer arrayy PZT 45 x 4 = 180 ray paths per scan Elements Scan time = 0.35 s
Scanning 2-D Scan X
Y Z
Synthetic y Aperture p Focusingg Technique (SAFT)
Times of flight obtained from 2-D scan with transducer array are used to reconstruct location of reflecting interfaces The result is a 3-D 3 D image of the internal reflectors View in three image g planes p
Image g Planes X
Y Z
Example p 13 mm hole 55 mm deep 0.8 m x 0.4 m x 0.4 m Cs= 2385 m/s 30 mm hhole l 13 mm h hole l
130 mm deep 160 mm deep B-Scan X 55 mm Z 130 mm 160 mm Higher g sensitivity y
400 mm
Grouted Tendon Duct Duct diameter: 60 mm Cover depth: 80 mm Slab thickness: 300 mm
D-Scan Elevation Voids in duct Fully grouted duct Fully grouted duct Backwall reflection
Stress--Wave Methods Stress Ultrasonic pulse velocity Sounding (chain drag)
Impact-echo method Impulse-response p p method Ultrasonic-echo method
Assessment of Reinforcement Location and size Covermeters Radar (location)
Corrosion condition Half cell potential (likelihood of corrosion)
Half-cell Polarization resistance (corrosion rate)
Concrete resistivity Depth of carbonation Chloride ion concentration
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 H20 O2 Anodic Reaction:
Fe2+
Fe Fe +2 + 2e Rust Cathode Anode Cathodic Reaction: e-2 Fe +2 + 2 H 2O + O2 + 4e 2 Fe(OH ) 2
Half--Cell Potential Method Half ASTM C876 When bar is corroding, charge flow through concrete is associated with an electrical field Measure the electrical potential (voltage) of the field at the concrete surface 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 contours
-200 -300 -300 -200
-400
-500 Current Elsner and Bohni, ASTM STP 1065, 1990
Half--Cell Potential Method Half ASTM C876 Cu/CuSO4 half cell
-0.28 Voltmeter Copper rod
+ _
CuSO4 solution Open-circuit potential Sponge Porous plug
Example Proceq SA
Half-Cell Potential Half-Contour Plot J. Woodhouse, Quantifying the Invisible, Concrete Repair Bulletin, July/August 1996
Considerations Concrete must be sufficiently moist ASTM C876 provides criterion Provides only indication of likelihood of active corrosion More positive M iti th than -200 200 mV:
V corrosion i unlikely lik l More negative than -350 mV: corrosion likely
-200 200 to t -350 350 mV:
V ???????
Other factors have to be considered (see ASTM C876)
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
( it (moisture, oxygen, ttemperature) t )
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 externall current is applied l d to the h bbar
Polarization Resistance Apparatus Working W ki electrode l t d - theth reinforcing i f i b bar Counter electrode - provides current flow to bar R f Reference electrode l d - measure change h iin potential P l i ti system Polarization t Current supply Voltmeter V lt t Ammeter Hardware and software to acquire and analyze data
Polarization Resistance 3LP
- Measure open p circuit p potential, Eo Voltmeter Eo Switch D.C. Reference cell Counter electrode Ammeter Working electrode
- Close switch and apply small current, Ip
- M Measure h change iin voltage lt
- Increase current, and repeat measurement
- Divide Di id currentt b by area off b bar th thatt iis polarized, l i d ip
- Plot voltage vs. current density Eo + E Ip
Polarization Resistance Resistance, Rp Voltage g Rp = E ip E
ip Current/(Area of Bar), ip, (µA/cm2)
Corrosion Rate Stern-Geary corrosion rate relationship:
icorr = B (µA/cm2) B = 25 to 50 mV Rp (active less active)
Faraday law can be sued to convert icorr to uniform metal loss:
1 µA/cm2 = 0.012 mm/y
Guard Electrode Current density is based on area of bar that is polarized by applied current Area of steel that is polarized is not well known in 3LP method Use of outer (guard) electrode confines current to portion of bar below guard ring Results in more accurate measure of current density
Guard--Electrode Method Guard Confines current so that polarized area of bar is well defined Voltmeter Voltage V lt Follower Ip Ammeter Guard Electrode
Example of Guard- Guard-Electrode G
Guardd Electrode El t d Counter Electrode Computer Resistivity Probe James Instruments
Static vs vs. Pulse Methods The polarization resistance technique that has been discussed is time consuming; 3 to 5 min at each point Voltage (or current) is increased in several steps Equilibrium conditions need to be established at each step Pulsed methods allow faster measurement
Galvanic Pulse Method Apply constant current pulse ( 10 s)
Guard electrode is used Monitor potential change of working electrode (bar)
From recorded voltage history, history evaluate polarization resistance, Rp, by regression analysis y
Assumes Randles equivalent circuit to represent corrosion activity
Randles Equivalent Circuit Computer Ip R
Rp E Cdl
Voltage--Time Curve Voltage 300 200 E = IpRP Volta age, mV V
t 100 V = C1 C2 e C3 IpR 0
-100 100
-200 0 1 2 3 4 5 6 7 Time, s
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 Based on galvanic-pulse method Integrates into one unit:
Half-cell Half cell potential Resistance (not resistivity)
Polarization resistance Software for data analysis and 3-D displays
GalvaPulse Computer Sensor Sensor
icorr = 0.43 A/cm2 or 0.005 mm/year
3 15 9 A/cm icorr = 15.9 A/ 2 or 0.2 mm/year
RapiCor Galvanic G l i pulsel method th d Rectangular probe with guard electrode M d l Modulates polarization l i i current b basedd on corrosion activity Higher current needed for higher corrosion rate Calculates concrete resistivity Requires knowing cover thickness
RapiCor Counter electrode Reference electrode Ag/AgCl Guard electrode
Cover:
Bar size:
Thickness Thi k lloss:
Half-cell potential:
Resistivity:
Summary IIntroduction t d ti tto ttools l ffor iin-place l evaluation l ti of concrete and steel reinforcement Uniformity Strength Internal defects Corrosion assessment Principles of methods have been stressed Not a training course on proper use of instruments
Tests for Uniformity Locate anomalous areas for closer examination Rebound hammer Indicator of surface condition Affected by texture, moisture content, carbonation Pulse velocity Overall condition of concrete between transducers Does not provide depth information
In--Place Strength In Strength St th off d drilled ill d cores iis reference f method th d Pullout test SSamplel more pointsi t without ith t excessivei ddamage Good correlation with compressive strength Evaluates E al ates o outer ter 25 mm Pull-off test EEvaluate l t substrate b t t preparationti bbefore f repair i
Evaluate bond strength of repair Failure location depends on weakest link
Internal Defects Stress wave methods are inherently powerful because of complete reflection at air interface Impact-echo Impact echo method Point method; simple data processing Impulse-response Impulse response method Measures flexural response; comparative Ultrasonic-echo Ultrasonic echo Computer intensive; rapid; 3-D imaging
Corrosion Assessment H lf ll potential Half-cell t ti l Likelihood of active corrosion P l i ti resistance Polarization it Indicator of corrosion rate at time of testing Assumptions made to arrive at corrosion current densityy
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