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NON-DESTRUCTIVE TESTING IN PRACTICE Eng. Guy Rapaport Asset Management, Bridges and Structures NVF ANNUAL BRIDGE CONFERENCE 2013

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NON-DESTRUCTIVETESTING IN PRACTICE

Eng. Guy Rapaport

Asset Management, Bridges and Structures

NVF ANNUAL BRIDGE CONFERENCE 2013

BACKGROUND INFORMATIONWHY 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-evaluatedOpening 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

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

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

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

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 transducersGuy Rapaport

ANTENNA

ANTENNAPOWER UNIT

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 RapaportDEFECT BACK WALL

RECEIVING TRANSDUSERSDetection of a defect:

DATA PRESENTATION- THE VISUALIZATION SOFTWARE:

B- SCAN

B- SCAN (ZOOM)

C- SCAN IN DEPTH OF 170 mm

D- SCAN

3D IMAGE

1 st.SCANPOINT

2 nd.SCANPOINT

PLAN VIEW

LASTSCANPOINT

DEPTH

DEPTH

DIRECTION OF SCANNING

CONCRETE SURFACE

Colour scale: more red => the more intensive wave reflections => different material interfaces (such as steel, air…)

C- SCANDUCT

DUCT

SIDE VIEW

ZOOM OF SIDE VIEW

DUCT

LONGITUDINAL VIEW

Guy Rapaport

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

The Impact-Echo System Components:1. Mechanical spherical impactor source – generating short

duration pulses2. High fidelity displacement transducer responsible to measure

the surface displacement3. Laptop with the Impact - Echo software data acquisition, data

storage and signal analysis.

Guy Rapaport

IMPACTORS

TRANSDUCER

LAPTOP+SOFTWARE

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).

Guy Rapaport

DATA PRESENTATION OF A TEST POINT:

Wave-Form Domain

Frequency Domain:The Amplitude Spectrum

Dominant peak

Test-points data (dominant frequencies)

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

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

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 motion3. 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

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

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

MOBI LI TY

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

LOCATION 1

Guy Rapaport

UPPER DUCT

LOWER DUCT

LOCATION 2

UPPER DUCT

LOWER DUCT

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LOCATION 3 (MID SPAN)

OK(CONFIRMED)

-E UPPER DUCT124 mm => SUSPICIOUS

I-E LOWER DUCTNON-SUSPICIOUS

Guy Rapaport

IMPACT-ECHO

MIRA

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

DUCT 1

DUCT 2DUCT 5

DUCT 6

DUCT 1 DUCT 2

DUCT 5 DUCT 6

MIRA

IMPACT-ECHO

Guy Rapaport

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

Guy Rapaport

IMPACT-ECHO

IMPULSE-RESPONSE

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

PEAK ~220 mm = THICKNESS OF SLAB => OK

Guy Rapaport

LOCATION 1

IMPULSE-RESPONSE

IMPACT-ECHO

PEAK ~220 mm = THICKNESS OF SLAB => OK

PEAK ~165 mm => SUSPICIOUS

Guy Rapaport

LOCATION 2IMPULSE-RESPONSE

IMPACT-ECHO

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

OK - CONFIRMED

LOOSED WATERPROOFING AND CONCRETE DETERIORATION CONFIRMED

Guy Rapaport

IMPULSE-RESPONSE

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

DEPTH OF CRACK, BY IMPACT-ECHO

DEPTH OF CRACK, BY SURFER

Guy Rapaport

WIDTH OF CRACKS :

Guy Rapaport

THANK YOUCONTACT DETAILS:

Guy Rapaport

Senior Consultant , Civil Eng. (Tech. University)Ramboll Finland OyAsset Management, Bridges and Structures

M +358 40 824 [email protected]

www.ramboll.fi

Guy Rapaport