Abstract. This paper deals with the use of embedded piezoelectric transducers to monitor the ultrasonic P -wave velocity evolution during the setting and hardening phases of concrete since casting time. The main advantage of the technique is the possibility to overcome the limitations of traditional methods which do not allow to apply specific mechanical boundary conditions during the measurement. The embedded transducers are based on the "Smart Aggregates" concept previously developed at the University of Houston, Texas. Two piezoelectric transducers are embedded in a prismatic mold and the evolution of the P -wave velocity is recorded for the first 24 hours in concrete after casting time. The results are very promising and show a good agreement with classical ultrasonic tests using external transducers.Confidential: not for distribution.
Concrete is the material most produced by humanity. Its popularity is mainly based on the low production cost and the great structural design flexibility. The operational and the ambient loadings including the environmental effects have a great impact in the performance and overall cost of concrete structures. Thus, the quality control, the structural assessment, the maintenance and the reliable prolongation of the operational service life of the existing concrete structures are turned into a major issue. In the recent years, non-destructive testing (NDT) is becoming increasingly essential for reliable and affordable quality control and integrity assessment not only during the construction of new concrete structures, but also for the existing ones. Choosing the right inspection technique is always followed by a compromise between its performance and cost. In the present paper, the ultrasonic pulse velocity (UPV) method, which is the most well-known and widely-accepted ultrasonic concrete NDT method, is thoroughly reviewed and compared with other well-established NDT approaches. Their principles, inherent limitations and reliability are reviewed. In addition, while the majority of the current UPV techniques are based on the use of piezoelectric transducers held on the surface of the concrete, special attention is paid to the very promising technique using low-cost and aggregate-size piezoelectric transducers embedded in the material. That technique has been evaluated based on a series of parameters, such as the ease of use, cost, reliability and performance.
Abstract.On-line Damage Detection is of high interest in the field of concrete structures and more generally within the construction industry. The current economic requirements impose the reduction of the operating costs related to such inspection while the security and the reliability of structures must constantly be improved. In this paper, non destructive testing is applied using piezoelectric transducers embedded in concrete structures. These transducers are especially adapted for on-line ultrasonic monitoring, due to their low cost, small size and broad frequency band. These recent transducers are called Smart Aggregates (SMAGs). The technique of health monitoring developed in this study is based on a Ultrasonic Pulse Velocity (UPV) test with embedded ultrasonic emitter-receiver pair (pitch-catch). The damage indicator focuses on the early wave arrival. The Belgian company MS3 takes an interest in evaluating the quality of the concrete around the anchorage system of highway security barriers after important shocks. The failure mechanism can be viewed as a combination of a bending and the failure of the anchorages. Accordingly, the monitoring technique has been applied both on a three-points bending test and several pull-out tests. The results indicate a very high sensitivity of the method which is able to pick-up the crack initiation phase and follow the crack propagation over the whole duration of the test.
The autonomous healing performance of concrete is experimentally verified by applying a technique based on the ultrasonic pulse velocity method using embedded piezoelectric transducers. Crack opening which deteriorates the mechanical capacity of concrete infrastructure is traditionally studied by different monitoring techniques that adequately provide a direct estimation of damage. Conversely in this research, an ultrasonic pulse velocity method is applied in order to monitor the crack closure and sealing of small-scale concrete beam elements. Short glass capsules filled with healing adhesive break due to crack formation and release those healing additives which fill the crack void and reset the element continuity. The damage index based on the early part of the wave arrival observes any emitted signal shape differentiation indicating the crack formation and development under two-cycle three-point bending loading tests (in the first cycle, the crack forms and healing release takes place, and consequently, after few hours of curing and crack reset, the beam is reloaded leading to crack reopening).
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