NDT (NON DESTRUCTIVE TESTING) OF CONCRETE STRUCTURE ANSHUL

Under guidance-
Prof. V. K. Gupta
HOD CIVIL DEPT.
2/13/2015 1

• Nondestructive testing in the broad sense
refers to methods whereby internal
characteristics of solid structures can be
examined without permanently affecting the
structure. Thus, parts that prove to be
satisfactory under specified test conditions are
not degraded by the test procedures
2/13/2015 2

Nondestructive testing (NDT) is the process of
inspecting, testing, or evaluating materials,
components or assemblies for discontinuities, or
differences in characteristics without destroying the
serviceability of the part or system. In other words,
when the inspection or test is completed the part
can still be used
2/13/2015 3

1)-Assessment of Existing Structures in the
Absence of Drawings.
2)-Quick assessment of the structure.
2/13/2015 4

1. Access to hidden items – “see through walls”
2. Better investigations with NDT
3. Rapid accumulation of data
4. Generally less expensive than destructive
testing.
2/13/2015 5

1. More than one test method may be required
2. Environmental conditions may effect or
distort results
3. Construction details & building components
may effect results
4. Some conditions cannot be determined with
a reasonable degree of accuracy without
destructive testing
2/13/2015 6

1-Rebound Hammer
2-Ultrasonic Pulse Velocity Meter
3-Pull Out
4.Core cutter
5-Covermeter
6- X ray computed tomography
7. Electric resistivity test
2/13/2015 7

• The rebound hammer can provide a fairly
accurate estimate of concrete compressive
strength.
• The concrete should be 14 to 56 days old.
• Surface Condition:
• The surface of the concrete at the point tested
must be smooth, dry, and free of honeycombing.
Otherwise, rebound readings will be low
Indicating a weaker concrete than is actually the
case. The rubbing stone provided can be used to
grind the surface smooth, if necessary.
2/13/2015 8

The concrete to be tested must be at least four
inches thick: It is also recommended that
readings be taken only where the concrete has
been in contact with the form. These conditions
are most easily satisfied if the readings are taken
along the edge of the tank on the sides and ends
where the adjoining concrete face (i.e., wall,
top, or bottom) can support the point of
contact.
2/13/2015 9

• A). Remove hammer from case and press the
plunger end against a hard surface to release the
plunger from the locked position. (Do not press
lock button while doing this.)
• B). Position hammer horizontally with plunger
end against wall at a point.
• C). Slowly apply pressure until hammer fires. This
will occur when only approximately 1/2 inch of
the plunger is still visible. Do not press the lock
button during this step.
2/13/2015 11

• With the hammer still pressed against the
wall, read the rebound number off the scale
provided on the hammer. If it is necessary to
move the hammer before reading, press the
lock button. The rebound number should be
read to two significant figures.
• Repeat the above procedure at different
points around the wall until a total of ten
readings has been taken
2/13/2015 12

• This is based on the principle that the velocity of an
ultrasonic pulse through any material depends
upon the density. Comparatively higher velocity is
obtained when concrete quality is good in terms of
density, uniformity etc.
• Pulse Velocity measurements can be used to assess
the presence of cracks, voids etc., quality of
concrete relative to standards requirements.
2/13/2015 14

There are three possible ways of measuring
pulse velocity.
i) Direct transmission
ii) Semi direct transmission
iii) Indirect transmission (surface probing)
Out of the three methods, the direct
transmission method is considered to be the best.
2/13/2015 15

condition of concrete based on pulse
velocity are given below:
S.No. Pulse Velocity Condition of concrete
I in(Km/Sec.)
• 1. Above 4.5 Excellent
• 2. 3.5 to 4.5 Good
• 3. 3.0 to 3.5 Medium
• 4. Below 3.0 Poor
2/13/2015 17

• The fundamental principle behind pull out testing
with LOK-test and CAPO test is that the test
equipment designed to a specific geometry will
produce results (pull-out forces) that closely
correlate to the compressive strength of concrete.
The first method ,using the cast steel disc is called LOK
test. The second method shown in fig.2 using
expandable ring is called CAPO test (i.e. Cut and Pull
out Test). The diameter of both the disc and ring is
25mm. the distance to the concrete surface is also
25mm. the inner diameter of the counter-pressure is
55mm.2/13/2015 18

The relationship between the pullout
force Fu in kN and compressive
strength Fc in MPa is given in fig
2/13/2015 20

• Determine in-situ compressive strength of the
concrete
• Ascertain the strength of concrete for carrying
out post tensioning operations.
• Determine the time of removal of forms and
shores based on actual in-situ strength of the
structure.
• Terminate curing based on in-situ strength of
the structure.
2/13/2015 21

The test should be taken at points where
minimum strength and maximum stress are likely to
coincide. But, at the same time, the core cutting
causes some damage to the member and may impair
the future performance of the member. Therefore, in
slender members, the core should be taken away
from the critical section. For compression testing, the
diameter of the core should be at least three times
the nominal maximum aggregate size.
2/13/2015 22

Core Cutter is used to cut the core from the
existing concrete structure for testing the
physical properties of the concrete like
compressive strength, density, water absorption,
crack depth and chemical test like depth of
carbonation and chloride content etc. It can also
be used to inspect the interior region of the
structural members.
2/13/2015 23

Cover meters are electromagnetic in operation.
Electric currents in a coil winding in the search
head generate a magnetic field which
propagates through the concrete and will
interact with any buried metal present, such as
reinforcing steel.It is the generic term for
equipment used to locate steel reinforcing bar in
concrete and to estimate the thickness of the
concrete cover over the reinforcement.

Tomography means imaging an object by taking
measurements from “slices” of its cross-section.
2/13/2015 27

In computed tomography, the image of an
object is reconstructed from projections of the
object.
• Most commonly the projections are obtained
by using penetrating x-rays, although other
modalities for measuring projection data are
also available.
2/13/2015 28

This test is carried out to assess the quality / uniformity
of concrete at various depths. The instrument consists of
a four probe device. Electrical current is passed through
the outer probes & the potential drop is measured by the
inner probes. From the current & voltage drop
measurements, the resistivity of concrete can be
measured.
Electrical resistivity = 2(pi)aE/i (in kilo-ohm cm)
where a = distance between probes
= 5 cm in the 1st set of readings
= 10 cm in the 2nd set of readings
E = potential difference between inner two probes in mV
Most useful test in tunnel structure.
2/13/2015 31

NDT (NON DESTRUCTIVE TESTING) OF CONCRETE STRUCTURE ANSHUL

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