Non-destructive testing methods are used to analyze the internal condition of concrete structures without damaging them. Key methods include infrared thermography, ground penetrating radar, ultrasonic pulse velocity testing, rebound hammer testing, and radiography. These methods can locate rebar, cracks, voids, and other defects through different techniques including measuring surface temperature differences, transmitting and receiving radio waves, measuring ultrasonic pulse speeds, analyzing rebound from an impact hammer, and producing x-ray images. Together they provide important information about the internal condition and quality of concrete.

1. Non-Destructive Testing
Prepared by
Salahuddin
Khalil Ur Rehman

2. Non-Destructive Testing
Non- Destructive testing is the testing of material,
used for the Analysis of internally embedded objects
or flaws and defect inside it, without disturbing its
suitability for the service

3. Non-destructive Testing (NDT)
of concrete in Structures
In Concrete structures the NDT Purposes
locate objects embedded Condition and quality
in Concrete of concrete.
e.g Steel Reinforcement
location and development
of cracks and voids.
While the concrete Structure remains Undestroyed

4. Methods of NDT
Following are some important methods used for
NDT:
. Infrared Thermography
. Ground Penetrating Radar (GPR)
. UltraSonic Pulse Velocity (UPV)
. Rebound Hammer Testing
. Radiography

5. INFRARED THERMOGRAPHY
The Thermographic images of Material (concrete) are taken that give an internal
view showing the voids and flaws.
Basic Principle
The presence of flaws within the concrete affects the heat conduction properties. Which
creates difference in surface temperature. That give an indication of defects.

6. INFRARED THERMOGRAPHY
> The presence and location of hidden defects (such as delaminations or voids) is indicated by
the difference in surface temperature between sound and unsound concrete.
> The technique is considered suitable.
For Providing assessment of Flaws in concrete. i-e In Bridge Decks.
For Locating steel reinforcement,cableducts etc in Concrete.

7. Thermographic Process

8. Thermographic image

9. Drawbacks:
. Testing is not viable during periods of adverse weather (rain or wind).
. Testing can be adversely affected by several surface conditions such as:
Water
Wearing
Discolouration
Crack sealant
Strong wind, etc

10. GROUND PENETRATING RADAR (GPR)
Ground penetrating radar (GPR) provides subsurface reflection images of
structures, By transmitting and recieving Ultra High Frequency Radio wave.

11. Operation:
> GPR operates by transmitting pulses of ultra high frequency radio waves (microwave
electromagnetic energy) into the subsurface object through an antenna.
> The transmitting antenna is excited by repetitive high voltage pulses with repetition rates typically
of the order of 10,000 Hertz.
> A part of the penetrating wave is reflected by interfaces or objects with dielectric properties
different from that of the general medium.
> These reflections are detected by the receiving antenna and converted into electrical signals.
> The recorded reflections can be analysed in terms of shape, travel time and signal amplitude to
provide information about the size, depth and properties in relation to the material object.

12. Contd……
Enables
Identification: reinforcing bars, prestressing cables, cable ducts, zones of varying moisture
content and thickness of slabs, different concrete, asphalt-concrete overlay interface, plastic
spacers.
Assessment of delaminations and large voids in concrete.

13. ULTRASONIC PULSE VELOCITY (UPV)
Ultrasonic Pulse velocity (UPV) testing is the Relative Strength assessment of concrete, that
involves measuring the speed of travel of an ultrasonic pulse through concrete.
The speed of the pulse is influenced by the density and elastic modulus of the concrete.

14. Operation
• Low frequency ultrasonic pulses (about 30 kHz) are sent by the transmitting transducer and
received by the second transducer with the time taken for the ultrasonic pulse to travel
recorded by a timer.

15. • The pulse velocity is determined by dividing the path length between the two transducers by
the pulse travel time.
• The pulse velocity can be affected by concrete mix composition, concrete density and
compaction, moisture condition and age of concrete.
• The method is most effective when sound is transmitted directly between transducers placed
on opposite faces.
• The method is less effective but possible when transducers are positioned at right angles
over a corner or on the same surface.

16. Generally higher pulse velocity is associated with higher strength, and thus relative
assessment is obtained.

17. REBOUND HAMMER TESTING
The rebound hammer (such as the Schmidt Hammer) is a simple device
that is used to measure the hardness and predict the strength of the
concrete.

18. REBOUND HAMMER
Rebound hammer can be placed vertically, horizontally and inclined to the concrete
surface

19. Rebound Hammer Testing
• The surface of the concrete is cleaned to remove laitance and shutter
board marks.
• A series of twelve readings are taken with hammer in a diamond pattern
at the test point.
• The hammer is pressed against the surface, loading the sprung mass, and
releasing this at the end of the stroke.
• There is a slide indicator on the outside of the unit that records the
distance traveled during the rebound. This indication is known as the
rebound number.

20. REBOUND HAMMER

21. The strength value can be obtain from Rebound No through a calibration chart given by the
manufacturer

22. Factor Affecting the Results
 Surface Smoothness
 Concrete Age
 Moisture Content
 Aggregate, air void, Steel Reinforcement
 Temperature
 Surface Carbonation

23. RADIOGRAPHIC METHODS
Radiographic methods for concrete inspection include gamma-ray radiography,
X-ray radiography, and X-ray radioscopy .
A radiographic image is taken through a concrete component to reveal a picture
of the interior.
The Most commonly used is X-ray Radiograghy

24. Radiography
The concrete part is placed between the
radiation source and a piece of film.
Some of Radiation will absorb by the material
and some will pass through it,
Making an image of its internal Features.
It provides a fair assessment of flaws
and defects in concrete.
Locating cables and cable ducts, reinforcing
bars and cover thickness.

25. Advantage: The most important advantage of radiography over other NDT
techniques is that it is highly reliable and shows a “see-through” picture of the
inspected area.
Disadvantage: The Rays are Hazardous for health and required Properly
trained operator.