Monday, December 8, 2014
NON DESTRUCTIVE TESTING
Non destructive test in CIVIL ENGINEERING Construction from Saurabh Gupta
•NDT
•After this seminar you will able to answer the
following
üNon- destructive
testing
üRebound hammer
testing
üUltrasonic pulse
velocity test
üCover test
methods including principle, advantages and point of action |
| NDT (NON DESTRUCTIVE TESTING |
•NDT
1.Technique to
test new or old concrete structure with respect to its strength and durability
,without or partial damage to a small part of concrete.
2.It doesn’t
estimate ultimate or yield strength of concrete.
3.It is easy
mechanized method, and is very cost effective , many test can be performed at
the same cost of single destructive test.
4.No sample is
required to collect for the laboratory testing as compare to some methods
destructive testing
OUTPUT OF NDT
•ELASTIC MODULUS
•REINFORCEMENT LOCTAION
•QUALITY OF WORKMANSHIP
•CRACKS AND VOIDS
•SURFACE HARDNESS
•DENSITY
•STRENGTH
•SURFACE ABSORPTION
•LIFE PERIOD
Sno.
|
TEST
|
1
|
Rebound Hammer Test
|
2
|
Windsore Probe Testing
|
3
|
Ultrasonic Pulse
Velocity Test
|
4
|
Acoustic Emission
Method
|
5
|
Pulse
Echo Method
|
6
|
Initial
Surface Absorption Test
|
7
|
Radar
Technique
|
8
|
Infrared Thermography
|
9
|
Quantab Test
|
10
|
Carbonation test
|
11
|
Profometer / Rebar
locator
|
NDT methods
Commonly used
•REBOUND HAMMER TEST (IS 13311 II)
Determination of
strength and hardness of concrete.
•ULTRASONIC PULSE VELOCITY TEST (IS 13311
I)
To determine the
homogeneity, compatibility and cracks or
void if present .
•PROFOMETER / REBAR LOCATOR
Location of bar and
diameter of bar
•CARBONATION TEST
To estimate the
amount of carbon and corrosion estimation.
REBOUND HAMMER TEST
•To assess the likely compressive strength
of concrete with help of with suitable co-relations
between rebound index and
compressive strength.
•To assess the uniformity of concrete.
•To assess the quality of concrete in
relation to standard requirements.
•To assess the quality of one element of
concrete in relation to another
•This method can be used with greater confidence for
differentiating between the
questionable and acceptable part of a structure or
for relative comparison between two
different structure.
When the plunger of rebound hammer is
pressed against the surface of concrete, the spring
control mass rebounds and
the extent of such rebound depend upon the surface hardness
of concrete, the
rebound is thus related with compressive strength of concrete and the
graduated
scale is designated as rebound number
It Consists of spring controlled mass that slides on a plunger within a
tubular housing.
The impact energy
required for rebound hammer for different application is different .
Rebound hammer is
used to check –
1 Compressive
strength of concrete
2 Uniformity of
concrete
3 Quality of element
of concrete
Limitation –
1 Accuracy ± 25%
2 Only suitable for
closed textured conc.
3 Partially compacted
concrete has no relation with rebound index
4 Result affected by
angle of test, surface smoothness and mix proportion.
AVG REBOUND NO.
|
QUALITY OF CONCRETE
|
>40
|
Very
good hard layer
|
30-40
|
Good
layer
|
20-30
|
Fair
|
<20
|
Poor
concrete
|
0
|
Delaminated
|
Ultrasonic pulse
velocity test
•To assess the uniformity and homogeneity
of concrete.
•To assess the quality of concrete in
relation of standard requirement.
•Detection of presence of voids, cracks
& imperfection of concrete.
•Measurement of changes occurring with time
in the properties of concrete.
•To compare quality of two different
concrete element.
Pulse velocity tests
measure the transit time of an ultrasonic pulse between two transducers,
a
transmitter and a receiver. The velocity of the pulse can be determined from
the transit
time and the distance between the transmitter and the receiver.
The pulse velocity measurement set consists of a pulse
generator, a transmitter, a
receiver,an amplifier, a circuit that measures the
elapsed time, a time display unit, and
connecting cables. Note that the pulse
generator, receiver, amplifier, timing circuit, and time
display unit are all
incorporated in the velocity meter shown in the schematic diagram of the
pulse
velocity measurement set
There are three ways in which the transducers may be
arranged, as shown in Figure :
(a) direct transmission through opposite faces
(b) semi-direct transmission through adjacent faces
(c) indirect transmission at the same face.
Factor affecting test results
•Smoothness of contact surface under test
•Influence of path line of pulse velocity
•Temperature of concrete
•Moisture content of concrete
•Presence of reinforcement steel
Stress level in concrete
Profometer /
REBAR LOCATOR
•To determine
1.Diameter of
reinforcement
2.Location of
R/F
3.Cover
The instrument is
based upon measurement of change of an electromagnetic field caused
by steel
embedded in the concrete.
Adequate cover to reinforcement is required in any reinforced concrete
structure to prevent corrosion and to improve durability of structure. To
calculate actual strength of concrete structures, the number of reinforcing
bars, their condition of corrosion, cover to reinforcement, and grade of
concrete is required. In the case of old structures, when the detailed drawings
are not available, it becomes very difficult to compute the strength of the
structure which is required for the strengthening scheme of the structure.
Sometimes, the strength of concrete structures are to be checked to permit
higher load and in absence of reinforcement details it becomes very difficult
to take a decision.
To overcome all these problems, the
methods have been developed for investigation and
evaluation of concrete
structures. Profometer is a small versatile instrument for
detecting
location, size of reinforcement and concrete cover. This instrument
is also known as rebar
locator. This is a portable
and handy instrument which is normally used to locate the
reinforcement on LCD
display. This instrument is available with sufficient memory to store
measured
data. Integrated software is loaded in the equipment for carrying out and printing
statistical values.
The equipment is quite handy and weighing
less than two kgs. It works on normal batteries
and thus
does not require any electrical connection.
Advantages
This is a purely non-destructive test for
evaluation of concrete structures particularly old
structures. The methods is
very fast and gives quite accurate results if the reinforcement is
not heavily
congested. The equipment is very light and even one person can perform the
test
without any assistance.
Factor affecting test methods
•Cover measurement may be affected by
neighboring bars parallel to the bras
being
measured.
•Magnetic effects from the aggregate
and matrix of the concrete.
•Variation in the properties of steel.
•Cross sectional shape of bars.
•Roughness of surface .
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