Ultrasonic pulse velocity tester or UPV as it is referred is one of the few methods utilised for in situ testing of quality of concrete and strength.As the name suggests, an ultrasonic pulse velocity tester is based on the principle of energized pulses generated and transmitted through a crystal transmitter of an ultrasonic transducer and received by a crystal receiver of an ultrasonic transducer. The frequencies utilized by industry recognized UPV concrete testers such as the Ultracon 170 from MKC Korea are generally commercially utilised low frequencies standardized at 54kHz.The time taken for the signal to be transmitted and received allows analysis of the quality of concrete.
Test Method utilised for Insitu Ultrasonic pulse velocity testing of concrete:
The UPV tester is utilised on a concrete structure greater than 30 cms in width. An ultrasonic couplant (gel/paste) is applied on the ultrasonic transducers to allow a strong contact between the transducers and the concrete to ensure a good signal transmission through the concrete. If both the transmitter and receiver transducers are applied in line with each other, the method is referred to as a direct method of concrete testing with an ultrasonic instrument. If the transmitter and receiver transducers are aligned perpendicular to each other, the method is referred to as an indirect method. Care must be taken to avoid rebar in the path of the ultrasonic waves to avoid influence from the same.
Yardstick to be followed while interpreting results from a concrete ultrasonic pulse velocity tester :
|Pulse Velocity ft/sec||Interpretation of measured values in relation to quality of concrete|
|12000 to 15000||Good|
|10000 to 12000||Questionable|
|7000 to 10000||Poor|
|< 7000||Very Poor|
Application of UPV concrete testing in relation to building structures and building construction :
Firstly, as suggested initially, the ultrasonic pulse velocity method is suggested as a standard method for establishing whether the quality of the concrete is uniform or not. The test is applicable to both new structures under construction and existing building with concrete that has already aged. The basic fundamental to follow as indicated in the table referred, is that if the pulse velocity readings are low, there should be good reason to believe that the concrete is defective, not uniform or deteriorated.
If the readings are fluctuating i.e of if one reading is lower than the others, there should be good reason to presume the presence of defects such as cavities, cracks or voids in the concrete under test.
The Ultrasonic concrete test is highly suggested to be utilized on load bearing structures of bridges, high rise buildings, industrial plants etc to determine the quality and uniformity of concrete and the effects of elements such as acidic rain, sulphatic attacks , freeze thaw effects .