Ultra Sonic Pulse Velocity Test

• Widely used.
• Good reliability ;  truly NDT.
• Portable equipment ; easy to use.
• Developed in 1940s .
• Based upon propagation of ultrasonic waves in elastic medium.
• Measures velocity of propagation of ultrasonic waves.
• Velocity related to the density of the medium  V=(E/p)^1/2 .
• Strength is deduced from the density of the medium.
• Frequency of waves used - 20 - 150 khz.

 Procedure

• Good coupling between concrete and transducers (no gap, void).
• Select a suitable transmitting station.
• Select receiving stations.
• Take readings (time for travel of pulse).
• Calculate velocity (pulse velocity).
• From calibration, find concrete strength.

Types of testing method

• Direct transmission
• Semi direct transmission
• Surface transmission
• Direct transmission method is the best but it requires access to two opposite sides of concrete member

        

Velocity	Concrete quality
> 4.0 km/s 3.5 to 4.0 km/s 3.0 to 3.5 km/s < 3.0 km/s	Very good to excellent Good to very good, slight porosity may exist Satisfactory but loss of integrity is suspected Poor and loss of integrity exists

Semi Direct Transmission

Direct Transmission

Surface Transmission