Abstract
Recently developed new transducers for ultrasonic transmission, which can be embedded right into concrete, are now used for non-destructive permanent monitoring of concrete. They can be installed during construction or thereafter. Large volumes of concrete can be monitored for changes of material properties by a limited number of transducers. The transducer design, the main properties as well as installation procedures are presented. It is shown that compressional waves with a central frequency of 62 kHz are mainly generated around the transducer’s axis. The transducer can be used as a transmitter or receiver. Application examples demonstrate that the transducers can be used to monitor concrete conditions parameters (stress, temperature, …) as well as damages in an early state or the detection of acoustic events (e.g., crack opening). Besides application in civil engineering our setups can also be used for model studies in geosciences.
Highlights
An experiment conducted more than 35 years ago to monitor the hardening of concrete at a massive water dam in Saxony, Germany, by embedded ultrasonic transmitters and receivers recently gave us the opportunity to prove that this kind of sensors might survive in concrete for decades [5]
The acoustic emission (AE) technique monitors acoustic waves produced by newly developing micro cracks, opening and closure of existing cracks, friction, etc., all of which are caused by internal stress variations [30]
The ultrasonic transducers developed for embedment in concrete have shown to be valuable tools for various tasks in structural monitoring
Summary
Ultrasonic transducers with frequencies from 25 kHz to 400 kHz have been used for concrete since decades. They are used in the lab on samples (and sometimes on site) in transmission mode to measure elastic properties and to assess degradation. All transducers used in practice today are for surface mounting For monitoring this approach shows three strong disadvantages. We started to develop a novel transducer, which can be permanently embedded in concrete. An experiment conducted more than 35 years ago to monitor the hardening of concrete at a massive water dam in Saxony, Germany, by embedded ultrasonic transmitters and receivers recently gave us the opportunity to prove that this kind of sensors might survive in concrete for decades [5]
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