Ultrasonic Pulse Velocity (IS 13311
(PART 1) : 1992) 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.
Based on this
technique, the velocity of sound in a concrete is related to the concrete
modulus of elasticity.
V=√E/ρ
where,
E = modulus of
elasticity,
Ρ =density of the concrete
- Ultrasonic waves are very similar to light waves in
that they can be reflected, refracted, and focused.
- Reflection and refraction occurs when sound waves
interact with interfaces of differing acoustic properties.
- An ultrasonic reflection from the presence of
discontinuities or geometric features enables detection and location.
- 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.
- The UPV equipment includes a transducer, a
receiver and an indicator for showing the time of travel from the transducer to
the receivers.
- Ultrasonic
pulse uses fast potential changes to create vibration that leads to its basic
frequency.
- The transducer is firmly attached to concrete
surface to vibrate the concrete. The pulses go through the concrete and reach
the receiver. The pulse velocity can be determined from the following equation.
V=L/T
V= wave velocity.
L= length of specimen
T= time taken to travel through length
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| UPV equipment PUNDIT Manual 1992 |
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.
It is
possible to develop an empirical relationship between pulse velocity and
strength but this relationship is influenced by type of cement, type and size
of aggregate, presence of reinforcement, moisture condition, compaction and age
of concrete.
S.No
|
Pulse velocity in cross probing (km/sec)
|
Concrete Quality Grading
|
1.
|
Above 4.5
|
Excellent
|
2.
|
3.5 to 4.5
|
Good
|
3.
|
3.0 to 3.5
|
Medium
|
4.
|
Below 3.0
|
Doubtful
|
S.No
|
Pulse velocity in cross probing (km/sec)
|
Concrete Quality Grading
|
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