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Estimation of the mechanical properties of concrete at early age using embedded ultrasonic piezoelectric transducers
   
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Arnaud DeraemaekerCédric Dumoulin, Grigorios Karaiskos

   
Keywords Piezoelectric transducer, ultrasonics, embedded in concrete, early-age, setting, hardening
   
Motivation In most concrete applications, setting and hardening of concrete are important parameters in assessing the period during which concrete is still workable and the time when the framework can be removed. Additionally, such information is also useful for a better understanding of the development of the microstructure and the effect of admixtures and mineral additions on the hydration of the cement. Conventional methods for measuring these parameters (i.e. Vicat needle test (EN 196-3) for cement paste and penetration resistance test (ASTM C403)) do not allow one to perform the test twice at the same location due to their destructive nature and the fact that they are not applicable to concrete due to the presence of aggregates.

An alternative consists in using ultrasonic testing of concrete to determine the P-wave (compressive wave) velocity of the propagating waves. This is done by computing the time of travel of a short pulse sent from the emitter to the receiver and dividing by the distance separating them.

The P-wave velocity can be used to determine the initial and final setting time of concrete, estimate its mechanical properties and can be related to parameters such as the percolation of solid particles and the degree of hydration. The interest of embedding the transducers is to offer the possibility to combine ultrasonic tests with mechanical and/or thermal tests
   
 P-wave velocity in early-age concrete

In order to demonstrate the possibility to estimate the P-wave velocity in concrete at very early age, we have embedded a pair of emitter-receiver in two short concrete beams (Figure 1). The pairs are interrogated alternatively thanks to the switching card programmed in the interrogation unit.

 

Fig 3

Figure 1: Prismatic molds with SMAGs before pouring the concrete

 

Concrete was then cast and monitoring of the P-wave velocity was performed during three days. Figure 2 shows the evolution of the P-Wave velocity as a function of the time. This evolution follows an S-curve from which the setting time can be deterimed as the inflection point of this curve. The Young's modulus can also be estimated from the velocity values knowing the density of the concrete.

 

Fig 4

Figure 2: Evolution of the P-wave velocity as a function of time

We have also demonstrated the possibility to monitor the P-wave velocity in a larger scale concrete element (Figure 3)

Figure 3: Evolution of the P-wave velocity after casting of a concrete slab

 

   
Support

2011-2013: FNRS-MIS: Automated damage localization systems for civil engineering structures : application to cracking in prestressed concrete

2012-2016 : FNRS-GRANT : C. Dumoulin : In situ monitoring of concrete behaviour based on embedded piezoelectric transducers

   

Selected publications

[1] Dumoulin C., Karaiskos G., Carette J., Staquet S. and Deraemaeker A.. Monitoring of the ultrasonic P-wave velocity in early-age concrete with embedded piezoelectric transducers. Smart Materials and Structures, 21(4), (2012).