Concrete testing by Ultrasonic Pulse Velocity (UPV)

How many times as a civil
engineer, you have to test a concrete? Hunh! So many Times! But most of the
time you find concrete cubes and cylinders being crushed by Compression Testing
Machine (CTM) in the laboratory. Now that broken cylinder or cube is useless
for you, although you can recycle it but even then a recycled material can
never meet the standard of first class material. Think about hundreds of cubes
and hundreds of cylinders being tested, broken and then the crew throw them
away.

Concrete testing by Ultrasonic Pulse Velocity (UPV)
Performing UPV test by direct method

And then the Non-destructive
Testing (NTD) comes to rescue;
“Non Destructive Testing are non
invasive techniques to determine the integrity of a material, component or
structure or quantitavely measure some characteristic of an object”
Non-destructive Testing is an
easy way to detect or inspect the defects on the surface of the concrete or
structure, It is a fast techniques and need not any sort of huge calculation or
waiting, Mostly this technique is used in specialist high risk areas such as
nuclear and Sea shore structures, gas and oil pipelines.
There are a lot of method
involved in non-destructive testing like rebound test, ultrasonic pulse
velocity test; Here we are focusing on Ultrasonic Pulse Velocity Test (UPV)
We know that velocity of
ultrasonic waves is directly proportional to the density or in other words the
modulus of elasticity of the material; and as far as the concrete is concerned
we have a direct empirical relations between Modulus of Elasticity of Concrete
(E) and compressive strength of the concrete (fc’). Thus if we can measure the
velocity of ultrasonic waves through concrete we might easily get the
compressive strength of the concrete.
Concrete testing by Ultrasonic Pulse Velocity (UPV)
Idea of Receiver and Transmitter 

Methods of testing:

There are three methods of
testing the concrete depending upon the placement of the transducers;
Direct Method:
If the two transducers are placed
in such a way that one is placed at one end and other at the other end
throughout the member it is direct method
Indirect method
In this method both transducers
are place on the same surface of concrete and the receiver receives the pulse coming
after striking the concrete molecules
Semi-direct method
It is mostly used for corners of
concrete members
Concrete testing by Ultrasonic Pulse Velocity (UPV)
Methods of UPV tests

Apparatus Required:

Electrical Pulse Generator –
Transducer – Amplifier Electronic Timing Device

Designation:

ASTM C597 – 09

How it is performed?

By using the calibration
cylinder, first of all the calibration of the instrument was check, the default
ultrasonic pulse velocity through the calibration cylinder was 57.8 micro
seconds.
After calibration testing, on the
two surface of the concrete some sort of vasline or any similar material is
applied so that the two transducers might be leveled;
The travel time of velocity is
read from instrument in microseconds; this travel time is converted to velocity
by using the relation s=vt; or v=s/t; if we are testing two different ends of
cylinder; the distance between transducer will be 1 feet thus velocity will be
1/t where t is converted to seconds from microseconds;
This velocity in ft/sec is then
related to fc’ by using a graph between pulse velocity (ft/sec) on x-axis and
fc’ (psi) on y-axis
Concrete testing by Ultrasonic Pulse Velocity (UPV)
Graph Between Pulse Velocity and Fc’
To compare the results between destructive
compression testing of cylinder with this non-destructive compression testing;
the cylinder is then tested with compression testing machine.
At the end the percentage
difference between two fc’s is reported.

Discussion

The curves between fc’ and ft/sec
velocity is different for dry concrete and we concrete; the reason being if the
concrete is dry the voids will be filled with air; velocity of pulse through
air being lesser then that in water the pulse velocity reading will be smaller
in case of dry material then that of wet material.
The transducers must not touch
the reinforcement bars in the concrete; as the assumption of this method is
that the material must be homogeneous, isotropic and elastic;  
Determining the Quality of
Concrete Grading by using pulse velocity
Above 4.5 km/sec                            Excellent
3.5 to 4.5 km/sec                              Good
3.0 to 3.5 km/sec                              Medium
Below 3.0                                            Doubtful
Concrete testing by Ultrasonic Pulse Velocity (UPV)
performing UPV test indirectly

Advantages and Disadvantages of the Ultrasonic Pulse
Velocity Test:

As far as the advantage of the
ultrasonic pulse velocity is concerned; it has high penetrating power which
ensure very easy measurement even for the very deep concrete members; it is
highly sensitive thus giving accurate results; easy to use for estimating the
size, shape and nature of flaws in the concrete member;
But this method also have some limitations
like; manual operation of the instrument requires careful attention by
experienced technicians; if the surface is irregular it is difficult to
estimate accurately the pulse velocity; test objects must be water resistant.

Saad Iqbal
Hi there, I am Saad Iqbal from Pakistan. I am an enthusiastic blogger, passionate content creator, construction geek, and a creative graphic designer. Connect with me at my social channels.