2. BACKGROUND INFORMATION
WHY DO WE NEED NDT ?
• Regular condition evaluation of concrete structures is based mostly
on visual inspection according to which we choose locations for a
small amount of destructive testing (DT) and sample taking.
Problems:
Lack of info what is happing deeper in the concrete str.
Pre-stressed structures tendon ducts are left non-evaluated
Opening of the deck surface structures is done quite blindly.
What is the depth of cracks?
DT and samples target only points of the structure.
Do they give a true picture of the investigated structure condition ?
Guy Rapaport
3. MAIN BENEFITS OF NDT
• Optimizing the sample taking process by pinpointing logical
locations for invasive testing
• Enables to evaluate the inside of the concrete structure –
to discover what is hidden from the eye.
• Typical disadvantages of NDT:
High cost (systems, training process)
Useful as “advanced inspection tool for experienced inspectors”.
Experienced inspectors are rare and costly.
Difficult to use correctly (NOT BLACK BOXES!).
=> Active concrete structures NDT experts in Europe are very
scarce, not more than some dozens.
Guy Rapaport
4. NDT – THE GENERAL PRINCIPLE
• In order to know what is happening inside the concrete we need
an “agent” that will penetrate into the object and will return us a
message if there is something wrong.
• Suitable “agents” = mechanical waves which we can generate in
a controllable manner by an impact or an ultrasonic pulse.
• No further introduction regarding the physics of waves will be
given here due to time limit.
Guy Rapaport
5. SHORT INTRODUCTION : THE MAIN NDT SYSTEMS USUALLY USED
The Ultrasound 3D tomographer system (commercial name: MIRA)
• A state-of-the-art instrument for creating a 3-D representation of
internal interfaces (defects, steel…) that may be present in a
concrete structure.
• The detection (scanning and interpretation) is done almost
in real time (3 sec. delay) and in situ.
• Scanning: only from one side of the object surface.
• Effective scanning depth: up to 1 m in heavily reinforced
structures (bridge decks, girders)
Guy Rapaport
6. The 3D Tomographer System Components:
1. Antenna composed of 40 dry point transducers arranged in an
array and a control unit operating the trasducers.
2. Laptop with the MIRA software – responsible for data processing and
graphical presentation (reflected interfaces within the object)
3. Antenna power unit with wireless net transmitter.
DPC transducers
Guy Rapaport
ANTENNA
ANTENNAPOWER UNIT
7. Principle
• Based on the ultrasonic echo method using transmitting and
receiving transducers in a "Pitch-Catch" configuration,
i.e. one row of transducers send out short duration ultrasonic
pulses of stress-waves (S- waves) and the other transducers
receive the reflected pulses.
Guy Rapaport
DEFECT BACK WALL
RECEIVING TRANSDUSERSDetection of a defect:
8. DATA PRESENTATION- THE VISUALIZATION SOFTWARE:
B- SCAN
B- SCAN (ZOOM)
C- SCAN IN DEPTH OF 170 mm
D- SCAN
3D
IMAGE
1 st.
SCAN
POINT
2 nd.
SCAN
POINT
PLAN VIEW
LAST
SCAN
POINT
DEPTH
DEPTH
DIRECTION OF SCANNING
CONCRETE
SURFACE
Colour scale: more red => the more intensive wave reflections
=> different material interfaces (such as steel, air…)
C- SCAN
DUCT
DUCT
SIDE VIEW
ZOOM OF
SIDE VIEW
DUCT
LONGITUDINAL VIEW
Guy Rapaport
9. SHORT INTRODUCTION : THE MAIN NDT SYSTEMS USUALLY USED
The Impact-Echo system (commercial name: DOCter)
• Allows to obtain information on the depth of internal reflecting
interfaces (defects) or thickness of a solid member.
• As with the MIRA- tomographer, the detection is done almost
in real time, in situ and from one side of the object surface.
• Effective detection depth: up to about 1 m.
Guy Rapaport
10. The Impact-Echo System Components:
1. Mechanical spherical impactor source – generating short
duration pulses
2. High fidelity displacement transducer responsible to measure
the surface displacement
3. Laptop with the Impact - Echo software data acquisition, data
storage and signal analysis.
Guy Rapaport
IMPACTORS
TRANSDUCER
LAPTOP+SOFTWARE
11. Principle
• By mechanical impact we generate a short-duration P- wave
which penetrates into the test object and is reflected from the
back side of a solid object / from a defect inside the object.
• The P-wave undergoes multiple reflections between the object
surfaces => recorded by the Impact-Echo system as the
“Wave-Form Domain” => mathematically transformed (FFT-
algorithm) into the “Frequency Domain” => signal amplitude
(“Amplitude Spectrum”).
Guy Rapaport
• In the “Amplitude Spectrum” we
look for dominant frequencies
(signal peaks) which possibly
indicate of reflecting interface
(defect / back side).
12. Guy Rapaport
DATA PRESENTATION OF A TEST POINT:
Wave-Form Domain
Frequency
Domain:
The Amplitude
Spectrum
Dominant peak
Test-points data
(dominant frequencies)
13. The main applications of the Tomographer and the
Impact-Echo are:
- Locating of casting defects
- Internal cracking (delaminations)
- Grout injection evaluation in pre-stressed str.
Often used at same the task to back-up each other
and to increase credibility of testing results.
Guy Rapaport
14. SHORT INTRODUCTION OF THE MAIN NDT SYSTEMS USUALLY USED:
The Impulse-Response system (commercial name: s’MASH)
• A different principle than the Tomographer and the Impact-Echo!
Measuring the behavior (vibration) of the structure due to an
impact not detecting the wave reflections due to an impact.
• The Impulse-Response enables to perform rapid screening of
plate-like structures => searching for flaws and identifying
suspicious areas for further investigation (Impact-Echo, core
drilling…).
• Detection is done almost in real time, in situ
and from one side of the object surface.
• Effective testing depth: up to 0,3…0,5 m.
Guy Rapaport
15. The Impulse-Response System Components:
1. A low-strain impactor - hard rubber tipped hammer (~1 kg)
with a built-in load cell capable of measuring dynamic forces
2. Velocity transducer for 360o testing (geophone) that responds
to normal surface motion
3. Laptop with the s’MASH software (+Excel®) connected to an
amplifier data acquisition, data storage, signal analysis and
graphical presentation
Guy Rapaport
AMPLIFIER
GEOPHONE
LAPTOP+SOFTWARE
RUBBER TIPPED HAMMER
16. Principle
• With the hammer impact we send a P- wave through the tested
object which causes the object to vibrate in a bending mode.
The geophone measures the amplitude of the response (the
object vibration).
• The data is processed by the computer (FFT- algorithm) to a
frequency domain where the amplitude of the signals is
presented in Mobility.
• Mobility = velocity (from the geophone) / force (from the hammer).
• The Mobility describes the resistance of a plate-like object to
vibrate due to an impact.
The higher mobility => the smaller resistance to vibrate
Guy Rapaport
17. DATA PRESENTATION:
• Processed data is presented in graphics and contour plots
• According the analysis of the frequency domain and other
parameters, we can estimate locations of delaminations,
debondings, deterioration (F-T, ASR) and casting defects.
• Very useful for mapping the condition of bridge deck surface
structures – done from the surface of the asphalt.
Guy Rapaport
Frequency domain
M
O
B
I
L
I
T
Y
18. TEST CASES –
Usage of the NDT systems in inspection and quality control tasks
TEST CASE 1
AIM: ESTIMATION OF TENDON
DUCTS GROUT INJECTION.
BRIDGE INSPECTION TASK.
OBJECT: PRESTRESSED
CONCRETE BOX-GIRDER
BRIDGE.
OVERALL LENGTH: 102 m
USED NDT- SYSTEMS:
MIRA TOMOGRAPHER AND
IMPACT-ECHO
Guy Rapaport
21. LOCATION 3 (MID SPAN)
OK
(CONFIRMED)
-E UPPER DUCT
124 mm =>
SUSPICIOUS
I-E LOWER DUCT
NON-SUSPICIOUS
Guy Rapaport
IMPACT-ECHO
MIRA
22. TEST CASES –
Usage of the NDT systems in inspection and quality control tasks
TEST CASE 2
AIM: ESTIMATION OF TENDON
DUCTS GROUT INJECTION.
CONSTRUCTION QUALITY
CONTROL.
OBJECT: STEEL ARCHED
BRIDGE, PRESTRESSED
CONCRETE DECK.
OVERALL LENGTH: 163 m
USED NDT- SYSTEMS:
MIRA TOMOGRAPHER AND
IMPACT-ECHOGuy Rapaport
24. TEST CASES –
Usage of the NDT systems in inspection and quality control tasks
TEST CASE 3
AIM: ESTIMATION OF CASTING
DEFECTS AND PREVIOUS
DEFECTS PATCHING.
BRIDGE INSPECTION TASK.
OBJECT: PRESTRESSED
CONCRETE GIRDER BRIDGE.
OVERALL LENGTH: 59 m
USED NDT- SYSTEMS:
IMPULSE-RESPONSE AND
IMPACT-ECHO
Guy Rapaport
26. TEST CASES –
Usage of the NDT systems in inspection and quality control tasks
TEST CASE 4
AIM: INTEGRITY ESTIMATION
OF CONCRETE SLABS.
INSPECTION TASK.
OBJECT: GROUND SUPPORTED
AIRPLANES PARKING
CONCRETE SLABS.
USED NDT- SYSTEMS:
IMPULSE-RESPONSE AND
IMPACT-ECHO
Guy Rapaport
27. PEAK ~220 mm = THICKNESS OF
SLAB => OK
Guy Rapaport
LOCATION 1
IMPULSE-RESPONSE
IMPACT-ECHO
28. PEAK ~220 mm = THICKNESS OF
SLAB => OK
PEAK ~165 mm =>
SUSPICIOUS
Guy Rapaport
LOCATION 2
IMPULSE-RESPONSE
IMPACT-ECHO
29. TEST CASES –
Usage of the NDT systems in inspection and quality control tasks
TEST CASE 5
AIM: CONDITION EVALUATION
OF BRIDGE DECK SURFACE
STRUCTURES (AC SURFACE)
BRIDGE INSPECTION TASK.
OBJECT: CONTINUOS
CONCRETE SLAB BRIDGE.
OVERALL LENGTH: 92 m
USED NDT- SYSTEMS:
IMPULSE-RESPONSE AND
IMPACT-ECHO
Guy Rapaport
30. OK - CONFIRMED
LOOSED WATERPROOFING AND
CONCRETE DETERIORATION
CONFIRMED
Guy Rapaport
IMPULSE-RESPONSE
31. TEST CASES –
Usage of the NDT systems in inspection and quality control tasks
TEST CASE 6
AIM: INVESTIGATION OF
CRACKS - MEASURING THE
DEPTH AND WIDTH OF CRACKS
BRIDGE INSPECTION TASK.
OBJECT: CONTINUOS
CONCRETE GIRDER BRIDGE.
OVERALL LENGTH: ~200 m
USED NDT- SYSTEMS:
IMPACT-ECHO, SURFER,
CRACK WIDTH GAUGE
Guy Rapaport
32. DEPTH OF CRACK, BY IMPACT-ECHO
DEPTH OF CRACK, BY SURFER
Guy Rapaport
34. THANK YOU
CONTACT DETAILS:
Guy Rapaport
Senior Consultant , Civil Eng. (Tech. University)
Ramboll Finland Oy
Asset Management, Bridges and Structures
M +358 40 824 5622
guy.rapaport@ramboll.fi
www.ramboll.fi
Guy Rapaport
