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Explain in detail the ultrasonic pulse velocity method of non destructive test of concrete ?
NON DESTRUCTIVE TEST:
The Test which is carried out on the site on the existing structural member of concrete. In this test no structural member is affected so this is called non destructive test.
Why we use non destructive test over cube compression test
The main reason of non destructive test is to check the actual strength of concrete other than cube compression. Because many site supervisor fill the cube purely and impose bad material in actual concrete casting.
Objective of Ultrasonic Pulse Velocity Test
- Check the homogeneous properties of concrete
- Check the crack, segregation or voids in concrete
- Check the elastic modulus of concrete
- Check the actual quality of concrete
Apparatus require for testing
- V- Meter
- Electrical pulse generator
- Electronic timing device
ULTRASONIC pulse is generated by transducer, which undergoes in whole concrete and detected by receiver.
The velocity of pulse is directly depends on the material and its homogeneity.
If material is poor and have voids or crack, gives the low pulse velocity otherwise it gives high velocity.
- Check the apparatus and connect properly
- place transducer on the concrete member, which we want to check
- Make sure the transmitter and receiver transducer should have opposite direction if possible, otherwise the test result may affected.
- The ultrasonic pulse is produced by the transducer. After a length (L) the pulse of vibrations is converted into an electrical signal by the second transducer, the timing circuit enables the transit time ( T ) of the pulse to be measured. The pulse velocity (V) is given by:
V = L/T
Effect of Reinforcing Bars
- The pulse velocity in steel is 1.2 to 1.9 times the velocity in plain concrete so velocity is higher in RCC
Effect of Moist concrete
- Make smooth surface of concrete
- The moisture concrete usually 2 percent higher pulse velocity than dry concrete
Effect of Length, Shape and Size of concrete member
- The transducer of 50 to 60 KHz is suitable mostly on all path length
|Path Length||Natural Frequency of Troasducer||Minimum Transverse Dimensions of member|
Effect of Temperature
- No effect of temperature on concrete having temperature 0 to 30 degree
- Pulse velocity reduced to 5 percent on temperature 30 to 60 degree
- Pulse velocity increased to 7 percent on temperature below freezing point
The result is depend upon the pulse velocity
|PULSE VELOCITY||CONCRETE QUALITY|
|>4.0 km/s||Excellent Quality Work|
|3.5 – 4.0 km/s||Good Quality|
|3.0 – 3.5 km/s||Medium|
|<3.0 km/s||Poor quality so recheck|