Ultrasonic Testing of Concrete – How it works?
The concept behind the technology is measuring the travel time of acoustic waves in a medium, and correlating them to the elastic properties and density of the material. Travel time of ultrasonic waves reflects internal condition of test area. In general, for a given trajectory, higher travel time is correlated to low quality concrete with more anomalies and deficiencies, while lower travel time is correlated to high quality concrete with fewer anomalies. Once ultrasonic wave spreads within the test area, the wave is reflected in boundary of anomalies resulting in higher travel time. This results in higher transmission time (lower wave speeds) in poor quality concrete and lower transmission time (higher wave speed) in good quality concrete.
Different configurations of transducers can be used to perform a UPV test. This includes direct transmission, semi-direct transmission, and indirect (surface) transmission. Figure above shows different configurations of transducer based on the access to the surface of test area. The ultrasonic velocity is prone to signal travel trajectory that is defined by the transducer configurations. Figure below is a representation of the effect of concrete anomalies and deficiencies on the acoustic wave travel time and the corresponding velocity throughout a given trajectory (ACI 228.2R, 2013).
Couplant | Concrete-Transducer contact
The UPV transducers must be in full contact with the concrete surface; otherwise the air pocket between the transducer and concrete may result in measurement error (i.e. inacurate measurement of transit time). One reason is that only negligible amount of wave energy will be transmitted in a poor contact. Different couplants can be used to eliminate air pockets and to assure good contact (e.g. petroleum jelly, grease, liquid soap, and kaolin-glycerol paste). It is recommended to make the couplant layer as thin as possible.
Applications of UPV Testing for Concrete
Several researchers and engineers have studied the use of ultrasonic testing of concrete in different engineering projects:
1- Pulse Velocity Determination
2- Concrete Quality Assessment (learn more)
3- Establishing Homogenity and Uniformity of Concrete
4- Measurement of Surface Crack Depth (read more)
5- Prediction of Compressive Strength of Concrete (read more)
UPV – Influencing Parameters
In order to conduct a reliable ultrasonic testing of concrete, the surface of concrete should be clean, and free of dust. A suitable couplant is needed to establish an ideal connection between concrete and UPV transducers. Special attention should be given to rebar in concrete, since the wave travel speed in metal is much higher than in concrete. The interpretation of test results in heavily reinforced concrete is somewhat difficult. The direct configuration is the most ideal for getting reliable readings; however, the use of this configuration is mainly limited to laboratory. In summary, the following issues should be addressed before, during, and after performing the test:
1- Concrete Properties (aggregate size, type, and content)
2- Transducer Contact/couplant material
3- Presence of Rebar
4- Sensor Configuration
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V. Good but need more precious because rejection & approval of concrete required solid evidence.
Rejection and approval is normally done based on approved standard test procedure such as concrete cylinders and cores.
When taking such samples is not possible, NDT methods can be used to study these structure. such cases will be existing structures with defects. coring and damaging will put structure integrity at risk.
The concrete strength test is only good for determining the laboratory strength of concrete. UPV aids in:
1. how uniform is the concrete?
2. is the concrete damaged?
3. are there any voids?
A sample helps get quantitative results. It depends an what your are trying to do.
Many years ago I was asked if piles should be rejected on the basis of the laboratory concrete sample test. My question to the field was “were the piles damaged during driving”?
This is a very intreasting issue as NDT is very essential espcially for concrete repair, strengthening, and retrofitting, where the actual mechanical properties and residual strength is deeply needed. For concrete flaws, UPV is an excellent technique. But the UPV needs enhancements to get strong and higher confidence results espcially for strength values. Would you till us how to enhance the UPV results.
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It was great to read this testing method. Thanks for sharing this useful blog.
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A very well explained post, thanks for sharing.
I have one question; What about the effect of the signal when you have cold joints? (Cold joints are formed primarily between two batches of concrete where the delivery and placement of the second batch has been delayed and the initial placed and compacted concrete has started to set)
We know that Cold Joints perform poorly when transmitting the vibration energy generated by the machine.
Do you have data about that?
Thanks in advance.
Dear all. The question is for my thesis, I want to know, if I have a set of signals recorded from UPV testing with a 54 kHz P trasducers, How can I perform a VELOCITY MAP of the concrete prism?
To achieve velocity map you should use Area Scan (A-Scan) method utilising Ultrasonic Pulse-Echo.
I am an ultrasonic level II technician for steel and have 40 years + experience in the trade. I was, however, contacted by a company here to try and sort out their CONCRETE UT MACHINE!! I am honest if I say that I do not know anything about concrete testing but would really like to help them out as they do not have a clue how to operate the machine and the job was dumped on them. My company do the NDT on the pipe work and they must do the concrete testing. Is it possible somebody that is willing to guide me through the calibration process of the machine with some hints
Thanks a million in advance
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DOES ULTRASOUND PASSES THROUGH COCONUT SHELL?
What is the effect of particle size and particle size distribution on UT echoes obtained? Is it possible that not a single echo is obtained during testing?
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we are fabricated and erected precast concrete elements, But we are not witnessed at that time of fabrication,ND test (Ultrasonic pulse velocity) suitable for precast elements,Kindly explain.
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This is vineeth persuing bachelor of engineering from vasavi college of engineering from civil engineering stream.
” Sir we are trying to do project on health monitoring of structures so we need the equipment that you are shown here”
I used UPV for more than 4000 times. I encounter a problem from UPV now which is the word “overflow” instead giving us the transit time.
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I didn’t know that we can use ultrasonic testing for determining the quality of the concrete. My husband was talking to me about determining the strength and quality of the concrete walls. I will let him know that there’s something called ultrasonic testing that can help with quality assessments for concrete.
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The article is informative about the Ultrasonic Testing of Concrete Images, and the videos are helpful. Thanks for such valuable information.
Can this equipment for Ultrasonic Testing be used on different types of materials? Like ceramics, plastics, or metals?
Great to read this testing method! The images and the video are helpful. Thanks for this useful information.