What is Ultrasonic velocity transmission (UVT) testing of concrete?
Ultrasonic velocity transmission testing of concrete is a non-destructive method to characterize the mechanical properties of concrete and detect internal defects such as cracks or voids.
By measuring the transmission time of ultrasonic waves through concrete structures variations in concrete density, elasticity, heterogeneity and compressive strength can be identified and mapped.
How does Ultrasonic velocity transmission (UVT) testing work?
The principle behind ultrasonic velocity transmission testing involves sending ultrasonic compression waves through concrete. The speed at which these waves travel is influenced by the concrete's density, elasticity, and internal structure.
By analysing wave velocity and attenuation, one can infer the material's mechanical properties and detect flaws or heterogeneities within the structure.
What is Ultrasonic velocity transmission (UVT) testing used for?
Deterioration process | Defects | Control of repairs |
Applicable to processes leading loss | To detect zones with different concrete strengths Surface crack depth | In-situ quality control |
How do I carry out Ultrasonic velocity transmission (UVT) testing?
BS EN 12504-4:2021 and ASTM C597 dictate a best practice procedure for UVT testing in the UK and US respectively.
Both outline a similar process that progresses through the following steps:
Select the most suitable test equipment to produce and receive the wave frequencies most suited to the test objectives.
Ensure the ultrasonic test device, including pulse generator, transducers, amplifier, and timing device, is ready and calibrated.
Smooth and clean the concrete surface, removing any loose particles, dust, or debris. In some cases, a grease or gel coupling agent is applied to improve signal transmission.
Position the transducers in one of three arrangements (direct, semi-direct, or indirect (surface) transmission) depending on accessibility, element depth and the specific objectives of the inspection.
Turn on the equipment and send ultrasonic pulses from the transmitter to the receiver.
Record the time it takes for the waves to travel the known distance between the transducers.
Determine the velocity of transmission and asses concrete quality
Pulse velocity (km/s) | Concrete quality grading |
> 4.5 | Excellent |
3.5 – 4.5 | Good |
3.0 – 3.5 | Medium |
< 3.0 | Poor |
Repeat this process performing multiple measurements at different locations on the concrete structure to detect variation in concrete quality and structural defects.
Software packages for UVT test data allow visual representation of wave patterns, automatic velocity calculation, production of 3-dimensional condition and defect maps, and comparison of results to assess concrete integrity and changes over time. Commercially available software packages are widely available and most test equipment providers will have their own sauch as Proceq Pundit Lab+ or Olympus Ultrasonic TOFD.
What equipment and expertise are required for Ultrasonic velocity transmission (UVT) testing?
Ultrasonic Velocity Transmission (UVT) testing for concrete defect detection involves specialized equipment like ultrasonic pulse velocity testers and, for complex analyses, tomographic imaging software.
This process demands skilled operators familiar with ultrasonic testing principles and concrete properties. Training is typically provided by equipment manufacturers or specialized trainers.
Leading suppliers such as Olson Instruments or Proceq offer systems catering to both basic quality assurance and advanced analyses, including early-age concrete strength prediction and internal structure imaging.
Availability and ease of access to these systems can vary based on location, but most manufacturers provide global distribution and support. Additionally, the need for training and expertise can make the implementation of UVT testing more complex, requiring investment in both equipment and personnel development.
What are the advantages of Ultrasonic velocity transmission (UVT) testing?
Immediate results.
No blemishes left on concrete surface.
Ultrasonic waves can penetrate deep into the concrete, allowing for the assessment of thick sections.
Allows detection of defects such as cracks, voids, and inclusions deep within the structure.
The equipment used for UVT testing is portable, making it convenient to use in various locations and on different parts of a structure.
UVT testing can be applied to a wide range of concrete structures, including bridges, buildings, and tunnels.
UVT provides quantitative data that can be used for comparative studies over time to monitor changes in the concrete's condition.
Allows visual representation of concrete quality across an entire structure.
What are the disadvantages Ultrasonic velocity transmission (UVT) testing?
The accuracy of UVT testing results significantly depends on the skill and experience of the operator.
UVT Requires smooth, parallel surfaces for sensor placement.
Concrete surfaces may need preparation to if not sufficiently smooth.
Environmental heat and moisture can skew test results.
Significant expertise is required to interpret results.
UVT may not be effective on thin elements where transmission distance is too short for accurate measurement.
High cost and slow measurement.
How accurate is Ultrasonic velocity transmission (UVT) testing?
The accuracy of UVT testing is dependent on factors such as environmental conditions, concrete properties, reinforcement layout and the skill of those carrying out the test and interpreting the results. The type of equipment used and the quality of its calibration are also vital to achieving high accuracy.
UVT testing can map defects several meters deep within the concrete with mm precision. To penetrate more deeply into the concrete lower frequency waves (24-50Hz) are required but these waves provide lower resolution.
As such the resolution with which UVT can pin point defects is inversely proportional to the depth. For near surface defect detection high frequency (>50Hz) waves with shallow penetration are used for maximum accuracy.
Figure 8 compares the compressive strength of concrete predicted by UVT tests against that of crushed cubes illustrating the close correlation but also the fact that this test may not give accurate readings of concrete weaker than 15mpa.
What are the limits of Ultrasonic velocity transmission (UVT) testing?
UVT is an expensive test and its effectiveness hinges on highly skilled operators and interpreters of results which may not be readily available.
Detection of small defects deep within the concrete may be challenging due to the small effect they have on the wave propagation compared to large defects closer to the surface and wave source.
This test also requires a smooth, consistent, parallel concrete surface to attach the transducers effectively, with severely deteriorated concrete this may not be possible to achieve even after preparation works.
Ancillary information
Maturity of test: > 10 years
Qualification & interpretation : Inspector and specialist
Service disruption: No
Preliminary works: Yes
Time consumption Medium (one day)
Cost High
Access to element 1 face