satyace

Apprentice
Concrete is a very popular material in Indian construction, which we see in large scale projects like that of bridges, tunnels and dams. As time goes by it is important to see to the durability and integrity of the concrete which in some cases may not be amenable to direct testing (like coring). That is when we see the value of Ultrasonic Pulse Velocity (UPV) testing which is a non destructive method that gives us information about the inner quality of the concrete without in any way damaging the structure.

What is the Ultrasonic Pulse Velocity (UPV) Test?
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Ultrasonic Pulse Velocity UPV is an also a non destructive method (NDT) we use to check the homogeneity and integrity of concrete which is done by the means of measuring the speed of ultrasonic pulses as they travel through the material. Also it does not damage the concrete and is able to identify internal defects, cracks, or voids which are not present at the surface.

This test is also used in present structures which do not allow for or do not have resources for destructive tests.

Principle of Ultrasonic Pulse Velocity (UPV) Test

Ultrasonic Pulse Velocity (UPV) test is founded on the fact that in dense and homogeneous concrete ultrasonic waves travel faster which in turn passes through weak, porous or cracked sections.
  • A transducer on one side of the concrete emits a pulse of ultrasonic wave.
  • It passes through the concrete and is detected by another transducer which is at a known distance.
  • The duration of travel from sender to receiver is measured.
  • Velocity = Distance / Time
This issue we see is that velocity is a indicator of concrete quality. We see high velocity in good quality dense concrete, low values may indicate defects or low strength.

Applications of Ultrasonic Pulse Velocity UPV Testing

Ultrasonic Pulse Velocity UPV in India is a practice which is very much into in many sectors:
  • Bridges : For the evaluation of concrete uniformity and soundness in piers, decks, and bearings. Also for periodic inspections.
  • Tunnels : Used for inspection of lining concrete, to detect delamination, or honeycombing without the use of excavation or coring.
  • Dams : In terms of the assessment of aging infrastructure, identification of internal cracks, and evaluation of repair work.
  • Other Uses :
  1. Precast concrete quality control
  2. Post-fire damage assessment
  3. Strength of association (when using correlation methods).
  4. Reviewing uniformity in large columns or slabs.

Equipment Used in Ultrasonic Pulse Velocity Testing
To do the Ultrasonic Pulse Velocity UPV test you will need :

Pulse which generates :
Produces high energy electrical pulses (typically of 1000 volts or less) which are then turned into mechanical pulses (ultrasonic waves).

Transformers (Probes) :
  • One transducer produces the ultrasonic wave.
  • Another at the other end of the spectrum.
  • Frequencies range between 20 kHz to 150 kHz.
Time Circuit :
Measures the time of travel for the wave between sender and receiver.

Coupling agent :
A paste which also includes a grease for the best contact between the transducer and concrete surface, which in turn minimizes signal loss.

Display Module/Data Collector :
  • Shows time, reports velocity, and at times we present real time graphs and digital records.
  • Modern Ultrasonic Pulse Velocity (UPV) tools are digital and have portability which also includes the feature of data storage for analysis and reporting.

IS Code for Ultrasonic Pulse Velocity Test: IS 14800 Part 1
In 1992 published “Non Destructive Testing of Concrete Methods of Test Part 1: Ultrasonic Pulse Velocity.

Key Issues from IS 13311 Part 1:
  • Minimum concrete thickness should be over 100 mm for valid results.
  • Surface should be polished and clean for transducer contact.
  • Couplant (gel/grease) must be used.
  • Calibration of the instrument prior to the test is a must.
  • Transducer arrangements: Transducer configurations.
  • Direct Transmission (best accuracy).
  • Semi-Direct Transmission.
  • Indirect/SURFACE Transmission (which is for when only one side is accessible).

Ultrasonic Pulse Velocity (UPV) Test Results

Pulse Velocity (km/s) Concrete Quality
> 4.5
Excellent
3.5 – 4.5 Good
3.0 – 3.5 Medium
< 3.0 Doubtful

Note:
o UPV values are a function of moisture, temperature, age, and type of concrete.
o It doesn't produce compressive strength by itself.
o Doubtful areas require further testing (which may include core extraction or rebound hammer).

Best Practices While Using Ultrasonic Pulse Velocity (UPV) Instrument
o Always calibrate the UPV instrument before each use.
o For improved accuracy, use direct transmission. (transducers on opposite sides).
o Stay away from rough and cracked surfaces they give false results.
o Use a combination of methods (like UPV and Rebound Hammer) for better results.

What is the importance of Ultrasonic Pulse Velocity (UPV) in Indian Infrastructure Projects.
In the wake of India’s large scale infrastructure which includes highways, smart cities, metro systems, and aging bridges we see that non destructive testing methods are key to cost effective and timely inspections.

In India the Ultrasonic Pulse Velocity (UPV) test for concrete is a growing trend of which:
  • It is fast, easy to transport, and doesn’t require structural damage.
  • It provides real time feedback on quality of work.
  • It meets the standards of IS 13311 which is a great asset for tender and compliance audits.

Ultrasonic Pulse Velocity (UPV) is a very effective, quick, and non-invasive tool for the assessment of concrete integrity. But as with any method it has drawbacks. It is best used in association with other tests and engineering judgment for critical decisions.
If in bridge construction, tunnel work, or dam maintenance you are the project manager the UPV test is what you should use for inspection.