Non Destructive Testing for concrete -NDT

1. Non Destructive Testing(NDT)

2. NDT-Need & Importance.
• To test concrete structure after concrete has
hardened.
• To test structure without damaging.
• To determine whether the structure is suitable for
design use.
• It can be applied on both old and new structure.
• Cost effective.
Test available ranges from
• SDT(semi destructive test)-causes negligible
repairable damages on surface.
• NDT(non destructive test)-do not cause any damage

3. Where to use NDT
• Determining parameters- density, elastic
modulus, strength, surface adsorption.
• Location of Cracks/Joints/Honeycombing
• Determining position of reinforcement
• Quality control of Construction , in situ
• Confirming Workmanship

4. METHODS
• VISUAL TESTING
• SCHMIDTS REBOUND HAMMER TEST-surface hardness.
• ULTRASONIC PULSE VELOCITY TEST-compressive
strength.
• PERMEABILITY TEST-flow of water.
• HALF CELL ELECTRIC POTENCIAL METHOD-
corrosion potential.
• COVERMETER TESTING-dia and distance of bars from
surface.
• RADIO GRAPHIC TESTING-detects voids.
• CARBONATION DEPTH MEASUREMENT-detects
corrosion.
• IMPACT ECO-TESTING.
• GROUND PENETRATION RADAR TESTING.

5. Qualification/Certification
• A person / Organization should have
Certification From - ISO – 9712
• IS 1311 -Non Destructive Testing
• IS 13311 (PART 1) : 1992-Ultrasonic
Pulse Velocity
• IS 13311 (PART 2) : 1992-Rebound
Hammer Test

6. REBOUND
HAMMER TEST

7. INTRODUCTION
 The rebound hammer test is one of the non-destructive
tests used to check the compressive strength of concrete.
 The rebound hammer is designed to carryout instant
nondestructive test on concrete structure without damage
and gives an immediate indication of the compressive
strength of the concrete using the calibration curve
applied each instrument.
 Principle of the rebound hammer test is: The rebound of
an elastic mass depends on the hardness of the surface
against which its mass strikes.

9. Components of Hammer
• Schmidt’s rebound hammer
consist of a spring-controlled
mass that slides on a plunger
within a tubular housing.
• When plunger is pressed
against the surface of
the concrete ,the spring-
controlled mass
rebounds .
• The extent of such rebound
depends upon the surface
hardness of concrete.
• The rebound is read on a
scale which is designated as
rebound number or rebound
index

10. PROCEDURE
 Should be tested against the test anvil.
 Apply light pressure on the plunger and allow it to extend to the
ready position for the test.
 Apply a gradual increase in pressure until the hammer impacts.
 Take the average of about 15 readings.

11. cube compressive strength isN/sq.mm plotted against
rebound number
• This is used for measuring surface
hardness of existing concrete mass
which in turn is correlated with the
grade of concrete.
• calibration curves are available to
relate the rebound number with
the grade of concrete for the
hammer held either horizontal or
vertical (down or up) for both dry
and wet condition of surface.
• Result depends upon– Type and
nature of aggregate used, Surface
and internal moisture condition,
presence of void, Smoothness of
surface

12. • It can be best used to compare strength of one concrete against
another but usually not reliable in determining absolute strength.
• Moreover, each hammer varies considerably in performance
and require individual calibration
1. Original Schmidt Hammer-Impact direction perpendicular to
the surface, Used for concrete/mortar testing,900 g.
2. Silver Schmidt Hammer-Independent of impact
direction,Suitable for testing a wide variety of concrete,
mortar and rock,600 g.
• Quick, simple and in expensive method.

13. The rebound reading on the indicator scale has been
calibrated by the manufacturer of the rebound
hammer for horizontal impact.
Interpretation of Results:

14. ADVANTAGES
 Simple to use. No special experience is needed to conduct
the test. Establishes uniformity of properties.
 Equipment is inexpensive and is readily available.
 A wide variety of concrete test hammers is available
withan operational range of M10 to M70.
 For rehabilitation of old Monuments..

15. DISADVANTAGES
 Evaluates only the local point and layer of masonry to
which it is applied.
 No direct relationship to strength or deformation
properties.
 Unreliable for the detection of flaws.
 Cleaning maintenance of probe and spring mechanism
 Accuracy is 25% only
 Results effects by-angle of test, surface smoothness, mix
proportions
 Rebound hammer have to be calibrated frequently

17. ULTRASONIC PULSE
VELOCITY

18. INTRODUCTION
 Ultrasonic Pulse Velocity (UPV) testing of concrete is based on
the pulse velocity method to provide information on the
uniformity of concrete, cavities, cracks and defects. Presence of
voids, honeycombing or other discontinuities.
 The pulse velocity in a material depends on its density and its
elastic properties which in turn are related to the quality and the
compressive strength of the concrete.
 This test method is applicable to assess the uniformity and relative
quality of concrete, to indicate the presence of voids and cracks,
and to evaluate the effectiveness of crack repairs.
 It is also applicable to indicate changes in the properties of
concrete, and in the survey of structures, to estimate the severity of
deterioration or cracking

19. WORKING
 The equipment consists of two transducers, usually in the
form of metal cylindrical heads, one of which is used to
transmit an ultrasonic pulse and the other is a receiver.
 They are brought into contact with the concrete surface
(‘coupled’) using a gel or grease.
 They are connected by cable to a control box which
contains a pulse generator,timing circuit and digital display.
 The digital display indicates the time for the ultrasonic
pulse to travel between the transmitting and receiving
transducers.
 The path length b/w transducer divided by time of travel
gives avg velocity , Pulse velocity =
(Path length)
(Travel time)

22. METHODS
 There are two methods used for this test
1. Direct method
2. Semi _Direct
3. Indirect method
 Direct transmission is the most sensitive, and indirect
transmission the least sensitive.
 Indirect transmission should be used when only one face of the
concrete is accessible, when the depth of a surface defect or
crack is to be determined or when the quality of the surface
concrete relative to the overall quality is of interest.
Direct transmission
Indirect or surface transmission
Semi - Direct
transmission

23. USED IN
 Measurement of concrete uniformity.
 Detection of cracking and honeycombing.
 Strength estimation.
 Measurement of layer thickness
 Measurement of elastic modulus.
 Strength development monitoring.

24. Factors affecting
1. Smoothness of contact surface under test
2. Influence of path length on pulse velocity
3. Temperature of concrete
4. Moisture condition of concrete
5. Presence of reinforcing steel

25. • Determine quality of concrete.
> 4500 m/s à Excellent
3500-4500 m/s à Good
3000-3500 m/s à Doubtful
2000-3000 m/s à Poor
<2000 m/s à Very poor
• Determine the setting characteristic.
• Durability study-freeze thaw, acid attack..
• Detects cracks
• Measures detoration of concrete due to fire
• exposure.
Applications

26. ADVANTAGES & LIMITATIONS
 Ultrasonic pulse velocity measurement has been
found to be a valuable and reliable method of
examining the interior of a body of concrete in a truly
non-destructive manner.
 Modern equipment is robust, reasonably cheap and
easy to operate, and reliable even under site
conditions.
 However, it should be taken proper care that operators
must be well trained and aware of the factors
affecting the readings.